Showing 1–50 of 59 results for author: Marin, E

Enabling Quantitative Polarimetry for Keck/NIRC2: Preliminary Mueller Matrix Model Calibration

Authors: Manxuan Zhang, Briley L. Lewis, Maxwell A. Millar-Blanchaer, Eduardo Marin, Jayke S. Nguyen, William Melby, Carlos Alvarez, Jaren N. Ashcraft, Mahawa Cisse, Charles-Antoine Claveau, Jacques-Robert Delorme, Greg Doppmann, Michael P. Fitzgerald, Matthew Freeman, Percy Gomez, Trisha Hammen, Ryan Hersey, Nemanja Jovanovic, Marc Kassis, Scott Lilley, Jessica Lu, James E. Lyke, Keith Matthews, Dimitri Mawet, Thomas McIntosh , et al. (5 additional authors not shown)

Abstract: The Keck/NIRC2 infrared imager was upgraded in 2025 with dual-beam polarimetric observing modes spanning approximately 1.1--4.1 microns (JHKL' bands). We present a preliminary JHK calibration of NIRC2 Polarimetry using a wavelength-dependent Mueller matrix model of the Keck tertiary mirror (M3), half-wave plate (HWP), image rotator (IMR), downstream optics, and Wollaston prism. We constrain the mo… ▽ More The Keck/NIRC2 infrared imager was upgraded in 2025 with dual-beam polarimetric observing modes spanning approximately 1.1--4.1 microns (JHKL' bands). We present a preliminary JHK calibration of NIRC2 Polarimetry using a wavelength-dependent Mueller matrix model of the Keck tertiary mirror (M3), half-wave plate (HWP), image rotator (IMR), downstream optics, and Wollaston prism. We constrain the model downstream of M3 using dome flat sequences spanning ten HWP and nine IMR angles in each band. Although the model reproduces the dominant modulation, the residuals show structure dependent on HWP and IMR angle. Measurement matrix inversion of unpolarized standard star observations gives M3 diattenuations of 0.0119+/-0.0009, 0.0098+/-0.0004, and 0.0068+/-0.0005 in J, H, and Kp, substantially closer to Fresnel predictions for aluminum than the values derived from dome flats. The larger dome flat modulation may indicate polarization in the incident dome illumination or Mueller matrix model inaccuracies. These results establish an initial calibration framework while motivating improved input polarization constraints, fixed HWP parameters from previous laboratory measurements, model validation with polarized standard stars, and extension to L'. △ Less

Submitted 14 August, 2026; originally announced August 2026.

Comments: Submitted to SPIE Astronomical Telescopes + Instrumentation 2026

On-sky capabilities and performance of the Keck All Sky Precision Adaptive Optics system

Authors: Avinash Surendran, Maxwell Service, Jacques R. Delorme, Carlos M. Correia, Marcos A. Van Dam, Eduardo Marin, Antonin Bouchez, Peter Wizinowich, Jason Chin, Sylvain Cetre, Sam Ragland, Uriel Conod, Jacob Taylor, Scott Lilley, Luke Gers, Ed Wetherell, Jessica Lu, Noah Stiegler, Anna Pusack, Zoe Haggard, Will Gauvin, Julien T. Bernard, Dietrich Pescoller, Roberto Biasi

Abstract: The Keck All Sky Precision Adaptive optics (KAPA) project upgrades the Keck I adaptive optics system to enable laser tomography using a four laser guide star (LGS) asterism. KAPA is now in operation in both narrow field and wide field modes to optimize correction on-axis or over the science field of view of the camera. The use of four LGSs, in conjunction with a tomographic reconstructor and pseud… ▽ More The Keck All Sky Precision Adaptive optics (KAPA) project upgrades the Keck I adaptive optics system to enable laser tomography using a four laser guide star (LGS) asterism. KAPA is now in operation in both narrow field and wide field modes to optimize correction on-axis or over the science field of view of the camera. The use of four LGSs, in conjunction with a tomographic reconstructor and pseudo open-loop control, leads to a significant reduction in wavefront error. We describe the overall architecture, development of the tomographic algorithm, real-time implementation and preliminary on-sky results here. By comparing the on-sky image quality with that obtained using a single LGS (sLGS) we clearly demonstrate the benefits of laser tomography, a technology which is crucial to the success of the next generation of extremely large telescopes. △ Less

Submitted 7 August, 2026; originally announced August 2026.

Comments: Published in SPIE proceedings. 14 pages, 13 figures

Ground control to major time-lag: on-sky results of data-driven predictive wavefront control at Keck Observatory

Authors: Jules Fowler, Rebeca Jensen-Clem, Sylvain Cetre, Maaike A. M. van Kooten, Maissa Salama, Antonin Bouchez, Avinash Surendran, Charlotte Guthery, Eduardo Marin, Mahawa Cisse, Max Service, Charlotte Z. Bond, Emiel Por, Nour Skaf, Will Gauvin

Abstract: Directly imaging and characterizing exoplanets requires extreme adaptive optics (XAO), which achieves exquisite wavefront correction over a small (<5") field of view. Temporal errors, where the wavefront evolves faster than the lag between wavefront sensing and control, are often a leading term in the error budget for these XAO systems. Predictive control mitigates temporal errors by predicting wh… ▽ More Directly imaging and characterizing exoplanets requires extreme adaptive optics (XAO), which achieves exquisite wavefront correction over a small (<5") field of view. Temporal errors, where the wavefront evolves faster than the lag between wavefront sensing and control, are often a leading term in the error budget for these XAO systems. Predictive control mitigates temporal errors by predicting where the wavefront will be by the time the system correction is applied. In particular, empirical orthogonal functions (EOF) learn linear correlations in a wavefront using previous states in the wavefront sensor history. We present on-sky results of a new implementation of EOF built directly into the Keck-II real time controller. On-sky engineering tests at Keck Observatory of the predictive controller show a 20% performance improvement over a classic integrator according to wavefront residuals from the Shack-Hartmann Wavefront Sensor (SHWFS). Parameter optimization studies show that there is a clear improvement based on varying predictive filter hyper-parameters, but that within a reasonable regime, varying filter parameters does not degrade performance to notably worse than an integrator. NIRC2 imaging through the Brackett Gamma=2190nm filter shows comparable performance between an integrator and predictor, both comparing Strehl Ratio (SR) and coronagraph-free contrast. We also explore power in principal components, and find a modest improvement (on the order of 3% less area under the curve of component strength) from the predictor over the integrator. This work not only improves current observing for the Keck community, but also acts as a pathfinder for predictive control methods with extremely large telescopes. △ Less

Submitted 18 June, 2026; originally announced June 2026.

Comments: Submitted to SPIE Astronomical Telescopes + Instrumentation 2026, Adaptive Optics Systems X Conference

uGen: An Agentic Framework for Generating Microarchitectural Attack PoCs

Authors: Debopriya Roy Dipta, Thore Tiemann, Eduard Marin, Thomas Eisenbarth, Berk Gulmezoglu

Abstract: Microarchitectural attacks continue to evolve, uncovering new exploitation vectors in modern processors. From a defensive perspective, assessing a system's susceptibility to such attacks remains challenging. Developing functional attack implementations is labor-intensive, requires deep microarchitectural expertise, and is highly sensitive to execution environments. Consequently, existing attacks o… ▽ More Microarchitectural attacks continue to evolve, uncovering new exploitation vectors in modern processors. From a defensive perspective, assessing a system's susceptibility to such attacks remains challenging. Developing functional attack implementations is labor-intensive, requires deep microarchitectural expertise, and is highly sensitive to execution environments. Consequently, existing attacks often lack portability, limiting systematic and scalable vulnerability assessment. Recent advances in large language models (LLMs) suggest a potential avenue for lowering these barriers. However, it remains unclear whether LLMs can reliably generate functionally correct microarchitectural attack code suitable for rigorous vulnerability testing. In this work, we present uGen, the first LLM-driven framework for automated microarchitectural attack code generation. A key challenge we address is identifying attack-specific knowledge gaps in LLMs. Through a systematic study of state-of-the-art models (GPT, Claude, and Qwen3), we find that LLMs frequently misgenerate or misplace critical attack primitives. Guided by this analysis, uGen employs a retrieval-augmented, multi-agent design that injects missing domain knowledge to synthesize functionally correct microarchitectural attack PoCs tailored to defender requirements. We evaluate uGen on cache-based and speculative-execution attacks across diverse set of microarchitectures, vulnerable functions, and LLM platforms. In the deployment stage, uGen achieves up to 100% success rate for Spectre-v1 (Claude Sonnet-4) and 80% for Prime+Probe (Qwen3-Coder). Finally, we demonstrate that uGen can generate a successful PoC code with a cost of $1.25 in under four minutes. △ Less

Submitted 14 May, 2026; originally announced May 2026.

BEACON: Automatic Container Policy Generation using Environment-aware Dynamic Analysis

Authors: Haney Kang, Eduard Marin, Myoungsung You, Diego Perino, Seungwon Shin, Jinwoo Kim

Abstract: This paper introduces BeaCon, a novel tool for the automated generation of adjustable container security policies. Unlike prior approaches, BeaCon leverages dynamic analysis to simulate realistic environments, uncovering container execution paths that may remain hidden during the profiling phase. To address the challenge of exploring vast profiling spaces, we employ efficient heuristics to reveal… ▽ More This paper introduces BeaCon, a novel tool for the automated generation of adjustable container security policies. Unlike prior approaches, BeaCon leverages dynamic analysis to simulate realistic environments, uncovering container execution paths that may remain hidden during the profiling phase. To address the challenge of exploring vast profiling spaces, we employ efficient heuristics to reveal additional system events with minimal effort. In addition, BeaCon incorporates a security and functionality scoring mechanism to prioritize system calls and capabilities based on their impact on the host OS kernel's security and the functionality of containerized applications. By integrating these scores, BeaCon achieves a customized balance between security and functionality, enabling cloud providers to enforce security measures while maintaining tenant availability. We implemented a prototype of BeaCon using eBPF kernel technology and conducted extensive evaluations. Results from the top 15 containers, which revealed significant improvements, demonstrate that BeaCon identifies an average of 16.5% additional syscalls by applying diverse environments. Furthermore, we evaluated its effectiveness in mitigating risks associated with 45 known vulnerabilities (e.g., CVEs), showcasing its potential to significantly enhance container security. Additionally, we performed proof-of-concept demonstrations for two well-known security vulnerabilities, showing that BeaCon successfully reduces attack surface by blocking these exploits. △ Less

Submitted 29 November, 2025; originally announced December 2025.

The Hidden Dangers of Public Serverless Repositories: An Empirical Security Assessment

Authors: Eduard Marin, Jinwoo Kim, Alessio Pavoni, Mauro Conti, Roberto Di Pietro

Abstract: Serverless computing has rapidly emerged as a prominent cloud paradigm, enabling developers to focus solely on application logic without the burden of managing servers or underlying infrastructure. Public serverless repositories have become key to accelerating the development of serverless applications. However, their growing popularity makes them attractive targets for adversaries. Despite this,… ▽ More Serverless computing has rapidly emerged as a prominent cloud paradigm, enabling developers to focus solely on application logic without the burden of managing servers or underlying infrastructure. Public serverless repositories have become key to accelerating the development of serverless applications. However, their growing popularity makes them attractive targets for adversaries. Despite this, the security posture of these repositories remains largely unexplored, exposing developers and organizations to potential risks. In this paper, we present the first comprehensive analysis of the security landscape of serverless components hosted in public repositories. We analyse 2,758 serverless components from five widely used public repositories popular among developers and enterprises, and 125,936 Infrastructure as Code (IaC) templates across three widely used IaC frameworks. Our analysis reveals systemic vulnerabilities including outdated software packages, misuse of sensitive parameters, exploitable deployment configurations, susceptibility to typo-squatting attacks and opportunities to embed malicious behaviour within compressed serverless components. Finally, we provide practical recommendations to mitigate these threats. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: Accepted at ESORICS 2025

Heimdallr: Fingerprinting SD-WAN Control-Plane Architecture via Encrypted Control Traffic

Authors: Minjae Seo, Jaehan Kim, Eduard Marin, Myoungsung You, Taejune Park, Seungsoo Lee, Seungwon Shin, Jinwoo Kim

Abstract: Software-defined wide area network (SD-WAN) has emerged as a new paradigm for steering a large-scale network flexibly by adopting distributed software-defined network (SDN) controllers. The key to building a logically centralized but physically distributed control-plane is running diverse cluster management protocols to achieve consistency through an exchange of control traffic. Meanwhile, we obse… ▽ More Software-defined wide area network (SD-WAN) has emerged as a new paradigm for steering a large-scale network flexibly by adopting distributed software-defined network (SDN) controllers. The key to building a logically centralized but physically distributed control-plane is running diverse cluster management protocols to achieve consistency through an exchange of control traffic. Meanwhile, we observe that the control traffic exposes unique time-series patterns and directional relationships due to the operational structure even though the traffic is encrypted, and this pattern can disclose confidential information such as control-plane topology and protocol dependencies, which can be exploited for severe attacks. With this insight, we propose a new SD-WAN fingerprinting system, called Heimdallr. It analyzes periodical and operational patterns of SD-WAN cluster management protocols and the context of flow directions from the collected control traffic utilizing a deep learning-based approach, so that it can classify the cluster management protocols automatically from miscellaneous control traffic datasets. Our evaluation, which is performed in a realistic SD-WAN environment consisting of geographically distant three campus networks and one enterprise network shows that Heimdallr can classify SD-WAN control traffic with $\geq$ 93%, identify individual protocols with $\geq$ 80% macro F-1 scores, and finally can infer control-plane topology with $\geq$ 70% similarity. △ Less

Submitted 18 October, 2025; originally announced October 2025.

Comments: 14 pages, 14 figures

Journal ref: Proceedings of the 38th Annual Computer Security Applications Conference (ACSAC '22), Austin, TX, USA, December 5-9, 2022, pp. 949-963

Ambusher: Exploring the Security of Distributed SDN Controllers Through Protocol State Fuzzing

Authors: Jinwoo Kim, Minjae Seo, Eduard Marin, Seungsoo Lee, Jaehyun Nam, Seungwon Shin

Abstract: Distributed SDN (Software-Defined Networking) controllers have rapidly become an integral element of Wide Area Networks (WAN), particularly within SD-WAN, providing scalability and fault-tolerance for expansive network infrastructures. However, the architecture of these controllers introduces new potential attack surfaces that have thus far received inadequate attention. In response to these conce… ▽ More Distributed SDN (Software-Defined Networking) controllers have rapidly become an integral element of Wide Area Networks (WAN), particularly within SD-WAN, providing scalability and fault-tolerance for expansive network infrastructures. However, the architecture of these controllers introduces new potential attack surfaces that have thus far received inadequate attention. In response to these concerns, we introduce Ambusher, a testing tool designed to discover vulnerabilities within protocols used in distributed SDN controllers. Ambusher achieves this by leveraging protocol state fuzzing, which systematically finds attack scenarios based on an inferred state machine. Since learning states from a cluster is complicated, Ambusher proposes a novel methodology that extracts a single and relatively simple state machine, achieving efficient state-based fuzzing. Our evaluation of Ambusher, conducted on a real SD-WAN deployment spanning two campus networks and one enterprise network, illustrates its ability to uncover 6 potential vulnerabilities in the widely used distributed controller platform. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Comments: 17 pages, 16 figures

Journal ref: IEEE Transactions on Information Forensics and Security, Vol. 19, pp. 6264-6279, May 2024

Volatile and Nonvolatile Resistive Switching in Lateral 2D Molybdenum Disulfide-Based Memristive Devices

Authors: Sofía Cruces, Mohit D. Ganeriwala, Jimin Lee, Ke Ran, Janghyun Jo, Lukas Völkel, Dennis Braun, Bárbara Canto, Enrique G. Marín, Holger Kalisch, Michael Heuken, Andrei Vescan, Rafal Dunin-Borkowski, Joachim Mayer, Andrés Godoy, Alwin Daus, Max C. Lemme

Abstract: Developing electronic devices capable of emulating biological functions is essential for advancing brain-inspired computation paradigms such as neuromorphic computing. In recent years, two-dimensional materials have emerged as promising candidates for neuromorphic electronic devices. This work addresses the coexistence of volatile and nonvolatile resistive switching in lateral memristors based on… ▽ More Developing electronic devices capable of emulating biological functions is essential for advancing brain-inspired computation paradigms such as neuromorphic computing. In recent years, two-dimensional materials have emerged as promising candidates for neuromorphic electronic devices. This work addresses the coexistence of volatile and nonvolatile resistive switching in lateral memristors based on molybdenum disulfide with silver as the active electrode. The fabricated devices exhibited switching voltages of ~0.16 V and ~0.52 V for volatile and nonvolatile operation, respectively, under direct-current measurements. They also displayed the essential synaptic functions of paired-pulse facilitation and short- and long-term plasticity under pulse stimulation. The operation mechanism was investigated by in-situ transmission electron microscopy, which showed lateral migration of silver ions along the molybdenum disulfide between electrodes. Based on the experimental data, a macroscopic semi-classical electron transport model was used to reproduce the current-voltage characteristics and support the proposed underlying switching mechanisms. △ Less

Submitted 3 April, 2025; originally announced April 2025.

Comments: 36 pages

Journal ref: Nano Letters, 25, 12455-12462, 2025

Numerical study of synaptic behavior in amorphous HfO2-based ferroelectric-like FETs generated by voltage-driven ion migration

Authors: Juan Cuesta-Lopez, Mohit D. Ganeriwala, Enrique G. Marin, Alejandro Toral-Lopez, Francisco Pasadas, Francisco G. Ruiz, Andres Godoy

Abstract: The continuous effort in making artificial neural networks more alike to human brain calls for the hardware elements to implement biological synapse-like functionalities. The recent experimental demonstration of ferroelectric-like FETs promises low-power operation as compared to the conventional ferroelectric switching devices. This work presents an in-house numerical tool, which self-consistently… ▽ More The continuous effort in making artificial neural networks more alike to human brain calls for the hardware elements to implement biological synapse-like functionalities. The recent experimental demonstration of ferroelectric-like FETs promises low-power operation as compared to the conventional ferroelectric switching devices. This work presents an in-house numerical tool, which self-consistently solves the electrostatics and time-dependent electronic and ionic transport. The tool is exploited to analyze the effect that various physical parameters such as mobility and ion concentration could have on the design of the ferroelectric-like FETs. Their suitability in emulating different functions of the biological synapses is also demonstrated. △ Less

Submitted 24 February, 2025; originally announced February 2025.

Comments: 19 pages, 8 figures, 1 table, paper

Journal ref: J. Appl. Phys. 136, 124501 (2024)

Technical description and performance of the phase II version of the Keck Planet Imager and Characterizer

Authors: Nemanja Jovanovic, Daniel Echeverri, Jacques-Robert Delorme, Luke Finnerty, Tobias Schofield, Jason J. Wang, Yinzi Xin, Jerry Xuan, J. Kent Wallacee, Dimitri Mawet, Aniket Sanghi, Ashley Baker, Randall Bartos, Charlotte Z. Bond, Benjamin Calvin, Sylvain Cetre, Greg Doppmann, Michael P. Fitzgerald, Jason Fucik, Maodong Gao, Jinhao Ge, Charlotte Guthery, Katelyn Horstman, Chih-Chun Hsud, Joshua Liberman , et al. (24 additional authors not shown)

Abstract: The Keck Planet Imager and Characterizer (KPIC) is a series of upgrades for the Keck II Adaptive Optics (AO) system and the NIRSPEC spectrograph to enable diffraction limited, high resolution (R>30000) spectroscopy of exoplanets and low mass companions in the K and L bands. Phase I consisted of single mode fiber injection/extraction units (FIU/FEU) used in conjunction with a H band pyramid wavefro… ▽ More The Keck Planet Imager and Characterizer (KPIC) is a series of upgrades for the Keck II Adaptive Optics (AO) system and the NIRSPEC spectrograph to enable diffraction limited, high resolution (R>30000) spectroscopy of exoplanets and low mass companions in the K and L bands. Phase I consisted of single mode fiber injection/extraction units (FIU/FEU) used in conjunction with a H band pyramid wavefront sensor. The use of single mode fibers provides a gain in stellar rejection, a substantial reduction in sky background, and an extremely stable line spread function in the spectrograph. Phase II, deployed and commissioned in 2022, brought a 1000 actuator deformable mirror, beam shaping optics, a vortex mask, and other upgrades to the FIU/FEU. An additional service mission in 2024 extended operations down to y band, delivered an atmospheric dispersion corrector, and provided access to two laser frequency combs. KPIC phase II brings higher planet throughput, lower stellar leakage and many new observing modes which extend its ability to characterize exoplanets at high spectral resolution, building on the success of phase I. In this paper we present a description of the final phase II version of KPIC, along with results of system level laboratory testing and characterization showing the instrument's phase II throughput, stability, repeatability, and other key performance metrics prior to delivery and during installation at Keck. We outlined the capabilities of the various observing modes enabled by the new modules as well as efforts to compensate for static aberrations and non common path errors at Keck, which were issues that plagued phase I. Finally, we show results from commissioning. △ Less

Submitted 3 February, 2025; originally announced February 2025.

Comments: 36 pages, 16 figures

Report number: 015005

Journal ref: Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 11, Issue 1, 015005 (February 2025)

Understanding Memristive Behavior: An Atomistic Study of the Influence of Grain Boundaries on Surface and Out-of-Plane Diffusion of Metallic Atoms

Authors: Mohit D. Ganeriwala, Daniel Luque-Jarava, Francisco Pasadas, Juan J. Palacios, Francisco G. Ruiz, Andres Godoy, Enrique G. Marin

Abstract: Atomic migration from metallic contacts, and subsequent filament formation, is recognised as a prevailing mechanism leading to resistive switching in memristors based on two-dimensional materials (2DMs). This study presents a detailed atomistic examination of the migration of different metal atoms across the grain boundaries (GBs) of 2DMs, employing Density Functional Theory in conjunction with No… ▽ More Atomic migration from metallic contacts, and subsequent filament formation, is recognised as a prevailing mechanism leading to resistive switching in memristors based on two-dimensional materials (2DMs). This study presents a detailed atomistic examination of the migration of different metal atoms across the grain boundaries (GBs) of 2DMs, employing Density Functional Theory in conjunction with Non-Equilibrium Green's Function transport simulations. Various types of metallic atoms, Au, Cu, Al, Ni, and Ag, are examined, focusing on their migration both in the out-of-plane direction through a MoS\textsubscript{2} layer and along the surface of the MoS\textsubscript{2} layer, pertinent to filament formation in vertical and lateral memristors, respectively. Different types of GBs usually present in MoS\textsubscript{2} are considered to assess their influence on the diffusion of metal atoms. The findings are compared with structures based on pristine MoS\textsubscript{2} and those with mono-sulfur vacancies, aiming to understand the key elements that affect the switching performance of memristors. Furthermore, transport simulations are carried out to evaluate the effects of GBs on both out-of-plane and in-plane electron conductance, providing valuable insights into the resistive switching ratio. △ Less

Submitted 1 January, 2025; originally announced January 2025.

Stimulated Brillouin scattering in a non-suspended ultra-low-loss thick-SOI platform

Authors: Kaixuan Ye, Akshay Keloth, Yisbel E. Marin, Matteo Cherchi, Timo Aalto, David Marpaung

Abstract: Silicon photonics, with its CMOS compatibility and high integration density, has enabled a wide range of novel applications. Harnessing stimulated Brillouin scattering (SBS), an optomechanic interaction between optical and GHz acoustic waves, in silicon-on-insulator (SOI) platforms attracts great interests for its potential in narrow-linewidth lasers and microwave photonics. However, the poor opto… ▽ More Silicon photonics, with its CMOS compatibility and high integration density, has enabled a wide range of novel applications. Harnessing stimulated Brillouin scattering (SBS), an optomechanic interaction between optical and GHz acoustic waves, in silicon-on-insulator (SOI) platforms attracts great interests for its potential in narrow-linewidth lasers and microwave photonics. However, the poor optoacoustic overlap in silicon nanowires on conventional SOI platforms has previously restricted the observation of SBS signals to suspended silicon waveguide structures. In this work, we report, for the first time, the SBS response in a non-suspended ultra-low-loss thick-SOI waveguide platform. The SBS process in this 3~$μ$m thick SOI platform is enabled by a leaky acoustic mode that coexists with the optical mode in the waveguide core, resulting in enhanced optoacoustic overlap. We measured a Brillouin gain coefficient of 2.5 m$^{-1}$W$^{-1}$ and 1.9 m$^{-1}$W$^{-1}$ at 37.6 GHz for the rib and strip waveguide, respectively. This work paves the way for Brillouin-based applications in non-suspended ultra-low-loss silicon photonics systems. △ Less

Submitted 24 October, 2024; originally announced October 2024.

Volatile MoS${_2}$ Memristors with Lateral Silver Ion Migration for Artificial Neuron Applications

Authors: Sofia Cruces, Mohit D. Ganeriwala, Jimin Lee, Lukas Völkel, Dennis Braun, Annika Grundmann, Ke Ran, Enrique G. Marín, Holger Kalisch, Michael Heuken, Andrei Vescan, Joachim Mayer, Andrés Godoy, Alwin Daus, Max C. Lemme

Abstract: Layered two-dimensional (2D) semiconductors have shown enhanced ion migration capabilities along their van der Waals (vdW) gaps and on their surfaces. This effect can be employed for resistive switching (RS) in devices for emerging memories, selectors, and neuromorphic computing. To date, all lateral molybdenum disulfide (MoS${_2}$)-based volatile RS devices with silver (Ag) ion migration have bee… ▽ More Layered two-dimensional (2D) semiconductors have shown enhanced ion migration capabilities along their van der Waals (vdW) gaps and on their surfaces. This effect can be employed for resistive switching (RS) in devices for emerging memories, selectors, and neuromorphic computing. To date, all lateral molybdenum disulfide (MoS${_2}$)-based volatile RS devices with silver (Ag) ion migration have been demonstrated using exfoliated, single-crystal MoS${_2}$ flakes requiring a forming step to enable RS. Here, we present volatile RS with multilayer MoS${_2}$ grown by metal-organic chemical vapor deposition (MOCVD) with repeatable forming-free operation. The devices show highly reproducible volatile RS with low operating voltages of approximately 2 V and fast switching times down to 130 ns considering their micrometer scale dimensions. We investigate the switching mechanism based on Ag ion surface migration through transmission electron microscopy, electronic transport modeling, and density functional theory. Finally, we develop a physics-based compact model and explore the implementation of our volatile memristors as artificial neurons in neuromorphic systems. △ Less

Submitted 19 August, 2024; originally announced August 2024.

Comments: 43 pages

Journal ref: Small Science, 5(5), 2400523, 2025

Dynamic Frequency-Based Fingerprinting Attacks against Modern Sandbox Environments

Authors: Debopriya Roy Dipta, Thore Tiemann, Berk Gulmezoglu, Eduard Marin, Thomas Eisenbarth

Abstract: The cloud computing landscape has evolved significantly in recent years, embracing various sandboxes to meet the diverse demands of modern cloud applications. These sandboxes encompass container-based technologies like Docker and gVisor, microVM-based solutions like Firecracker, and security-centric sandboxes relying on Trusted Execution Environments (TEEs) such as Intel SGX and AMD SEV. However,… ▽ More The cloud computing landscape has evolved significantly in recent years, embracing various sandboxes to meet the diverse demands of modern cloud applications. These sandboxes encompass container-based technologies like Docker and gVisor, microVM-based solutions like Firecracker, and security-centric sandboxes relying on Trusted Execution Environments (TEEs) such as Intel SGX and AMD SEV. However, the practice of placing multiple tenants on shared physical hardware raises security and privacy concerns, most notably side-channel attacks. In this paper, we investigate the possibility of fingerprinting containers through CPU frequency reporting sensors in Intel and AMD CPUs. One key enabler of our attack is that the current CPU frequency information can be accessed by user-space attackers. We demonstrate that Docker images exhibit a unique frequency signature, enabling the distinction of different containers with up to 84.5% accuracy even when multiple containers are running simultaneously in different cores. Additionally, we assess the effectiveness of our attack when performed against several sandboxes deployed in cloud environments, including Google's gVisor, AWS' Firecracker, and TEE-based platforms like Gramine (utilizing Intel SGX) and AMD SEV. Our empirical results show that these attacks can also be carried out successfully against all of these sandboxes in less than 40 seconds, with an accuracy of over 70% in all cases. Finally, we propose a noise injection-based countermeasure to mitigate the proposed attack on cloud environments. △ Less

Submitted 23 May, 2024; v1 submitted 16 April, 2024; originally announced April 2024.

A Review of Deep Reinforcement Learning in Serverless Computing: Function Scheduling and Resource Auto-Scaling

Authors: Amjad Yousef Majid, Eduard Marin

Abstract: In the rapidly evolving field of serverless computing, efficient function scheduling and resource scaling are critical for optimizing performance and cost. This paper presents a comprehensive review of the application of Deep Reinforcement Learning (DRL) techniques in these areas. We begin by providing an overview of serverless computing, highlighting its benefits and challenges, with a particular… ▽ More In the rapidly evolving field of serverless computing, efficient function scheduling and resource scaling are critical for optimizing performance and cost. This paper presents a comprehensive review of the application of Deep Reinforcement Learning (DRL) techniques in these areas. We begin by providing an overview of serverless computing, highlighting its benefits and challenges, with a particular focus on function scheduling and resource scaling. We then delve into the principles of deep reinforcement learning (DRL) and its potential for addressing these challenges. A systematic review of recent studies applying DRL to serverless computing is presented, covering various algorithms, models, and performances. Our analysis reveals that DRL, with its ability to learn and adapt from an environment, shows promising results in improving the efficiency of function scheduling and resource scaling in serverless computing. However, several challenges remain, including the need for more realistic simulation environments, handling of cold starts, and the trade-off between learning time and scheduling performance. We conclude by discussing potential future directions for this research area, emphasizing the need for more robust DRL models, better benchmarking methods, and the exploration of multi-agent reinforcement learning for more complex serverless architectures. This review serves as a valuable resource for researchers and practitioners aiming to understand and advance the application of DRL in serverless computing. △ Less

Submitted 5 October, 2023; originally announced November 2023.

Non-Volatile Resistive Switching of Polymer Residues in 2D Material Memristors

Authors: Dennis Braun, Mohit D. Ganeriwala, Lukas Völkel, Ke Ran, Sebastian Lukas, Enrique G. Marín, Oliver Hartwig, Maximilian Prechtl, Thorsten Wahlbrink, Joachim Mayer, Georg S. Duesberg, Andrés Godoy, Alwin Daus, Max C. Lemme

Abstract: Two-dimensional (2D) materials are popular candidates for emerging nanoscale devices, including memristors. Resistive switching (RS) in such 2D material memristors has been attributed to the formation and dissolution of conductive filaments created by the diffusion of metal ions between the electrodes. However, the area-scalable fabrication of patterned devices involves polymers that are difficult… ▽ More Two-dimensional (2D) materials are popular candidates for emerging nanoscale devices, including memristors. Resistive switching (RS) in such 2D material memristors has been attributed to the formation and dissolution of conductive filaments created by the diffusion of metal ions between the electrodes. However, the area-scalable fabrication of patterned devices involves polymers that are difficult to remove from the 2D material interfaces without damage. Remaining polymer residues are often overlooked when interpreting the RS characteristics of 2D material memristors. Here, we demonstrate that the parasitic residues themselves can be the origin of RS. We emphasize the necessity to fabricate appropriate reference structures and employ atomic-scale material characterization techniques to properly evaluate the potential of 2D materials as the switching layer in vertical memristors. Our polymer-residue-based memristors exhibit RS typical for a filamentary mechanism with metal ion migration, and their performance parameters are strikingly similar to commonly reported 2D material memristors. This reveals that the exclusive consideration of electrical data without a thorough verification of material interfaces can easily lead to misinterpretations about the potential of 2D materials for memristor applications. △ Less

Submitted 25 September, 2023; originally announced September 2023.

Comments: 30 pages

Exploiting ambipolarity in graphene field-effect transistors for novel designs on high-frequency analog electronics

Authors: Francisco Pasadas, Alberto Medina-Rull, Francisco G. Ruiz, Javier Noe Ramos-Silva, Anibal Pacheco-Sanchez, Mari Carmen Pardo, Alejandro Toral-Lopez, Andrés Godoy, Eloy Ramírez-García, David Jiménez, Enrique G. Marin

Abstract: Exploiting ambipolar electrical conductivity based on graphene field-effect transistors has raised enormous interest for high-frequency (HF) analog electronics. Controlling the device polarity, by biasing the graphene transistor around the vertex of the V-shaped transfer curve, enables to redesign and highly simplify conventional analog circuits, and simultaneously to seek for multifunctionalities… ▽ More Exploiting ambipolar electrical conductivity based on graphene field-effect transistors has raised enormous interest for high-frequency (HF) analog electronics. Controlling the device polarity, by biasing the graphene transistor around the vertex of the V-shaped transfer curve, enables to redesign and highly simplify conventional analog circuits, and simultaneously to seek for multifunctionalities specially in the HF domain. We present, here, new insights for the design of different HF applications such as power amplifiers, mixers, frequency multipliers, phase shifters, and modulators that specifically leverage the inherent ambipolarity of graphene-based transistors. △ Less

Submitted 15 September, 2023; originally announced September 2023.

Comments: 31 pages, 7 figures

Investigation of W-SiC compositionally graded films as a divertor material

Authors: Zihan Lin, Carlos Monton, Stefan Bringuier, Gregory Sinclair, Guangming Cheng, Eduardo Marin, Zachary Bergstrom, Dmitry Rudakov, Žana Popović, Ulises Losada, Igor Bykov, Evan T. Ostrowski, Shota Abe, Nan Yao, Bruce E. Koel, Tyler Abrams

Abstract: W-SiC composite material is a promising plasma-facing material candidate alternative to pure W due to the low neutron activation, low impurity radiation, and low tritium diffusivity of SiC while leveraging the high erosion resistance of the W armor. Additionally, W and SiC have high thermomechanical compatibility given their similar thermal expansion rates. The present study addresses the synthesi… ▽ More W-SiC composite material is a promising plasma-facing material candidate alternative to pure W due to the low neutron activation, low impurity radiation, and low tritium diffusivity of SiC while leveraging the high erosion resistance of the W armor. Additionally, W and SiC have high thermomechanical compatibility given their similar thermal expansion rates. The present study addresses the synthesis and performance of compositionally graded W-SiC films fabricated by pulsed-DC magnetron sputtering. Compositional gradients were characterized using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS), and crystallographic information was obtained using electron diffraction and X-ray diffraction (XRD). Samples were exposed to L-mode deuterium plasma discharges in the DIII-D tokamak using the Divertor Material Evaluation System (DiMES). Post-mortem characterizations were performed using scanning electron microscopy (SEM) and XRD. Electron diffraction and XRD showed that the compositionally graded W-SiC films were composed of polycrystalline W and amorphous SiC with amorphous W+SiC interlayers. No macroscopic delamination or microstructural changes were observed under mild exposure conditions. This study serves as a preliminary examination of W-SiC compositionally graded composites as a potential candidate divertor material in future tokamak devices. △ Less

Submitted 15 February, 2024; v1 submitted 30 August, 2023; originally announced August 2023.

Comments: Published in Journal of Nuclear Materials

Journal ref: J. Nucl. Mater. 592 (2024) 154942

CVD Graphene Contacts for Lateral Heterostructure MoS${_2}$ Field Effect Transistors

Authors: Daniel S. Schneider, Leonardo Lucchesi, Eros Reato, Zhenyu Wang, Agata Piacentini, Jens Bolten, Damiano Marian, Enrique G. Marin, Aleksandra Radenovic, Zhenxing Wang, Gianluca Fiori, Andras Kis, Giuseppe Iannaccone, Daniel Neumaier, Max C. Lemme

Abstract: Intensive research is carried out on two-dimensional materials, in particular molybdenum disulfide, towards high-performance transistors for integrated circuits. Fabricating transistors with ohmic contacts is challenging due to the high Schottky barrier that severely limits the transistors' performance. Graphene-based heterostructures can be used in addition or as a substitute for unsuitable metal… ▽ More Intensive research is carried out on two-dimensional materials, in particular molybdenum disulfide, towards high-performance transistors for integrated circuits. Fabricating transistors with ohmic contacts is challenging due to the high Schottky barrier that severely limits the transistors' performance. Graphene-based heterostructures can be used in addition or as a substitute for unsuitable metals. We present lateral heterostructure transistors made of scalable chemical vapor-deposited molybdenum disulfide and chemical vapor-deposited graphene with low contact resistances of about 9 k$Ω$$μ$m and high on/off current ratios of 10${^8}$. We also present a theoretical model calibrated on our experiments showing further potential for scaling transistors and contact areas into the few nanometers range and the possibility of a strong performance enhancement by means of layer optimizations that would make transistors promising for use in future logic circuits. △ Less

Submitted 5 April, 2024; v1 submitted 3 April, 2023; originally announced April 2023.

Comments: 39 pages

Journal ref: npj 2D Materials and Applications, 8, 35, 2024

Gemini North Adaptive Optics (GNAO) facility overview and status updates

Authors: Gaetano Sivo, Julia Scharwächter, Manuel Lazo, Célia Blain, Stephen Goodsell, Marcos van Dam, Martin Tschimmel, Henry Roe, Jennifer Lotz, Kim Tomassino-Reed, William Rambold, Courtney Raich, Ricardo Cardenes, Angelic Ebbers, Tim Gaggstatter, Pedro Gigoux, Thomas Schneider, Charles Cavedoni, Stacy Kang, Stanislas Karewicz, Heather Carr, Jesse Ball, Paul Hirst, Emmanuel Chirre, John White , et al. (32 additional authors not shown)

Abstract: The Gemini North Adaptive Optics (GNAO) facility is the upcoming AO facility for Gemini North providing a state-of-the-art AO system for surveys and time domain science in the era of JWST and Rubin operations. GNAO will be optimized to feed the Gemini infrared Multi Object Spectrograph (GIRMOS). While GIRMOS is the primary science driver for defining the capabilities of GNAO, any instrument oper… ▽ More The Gemini North Adaptive Optics (GNAO) facility is the upcoming AO facility for Gemini North providing a state-of-the-art AO system for surveys and time domain science in the era of JWST and Rubin operations. GNAO will be optimized to feed the Gemini infrared Multi Object Spectrograph (GIRMOS). While GIRMOS is the primary science driver for defining the capabilities of GNAO, any instrument operating with an f/32 beam can be deployed using GNAO. The GNAO project includes the development of a new laser guide star facility which will consist of four side-launched laser beams supporting the two primary AO modes of GNAO: a wide-field mode providing an improved image quality over natural seeing for a 2-arcminute circular field-of-view and a narrow-field mode providing near diffraction-limited performance over a 20x20 arcsecond square field-of-view. The GNAO wide field mode will enable GIRMOS's multi-IFU configuration in which the science beam to each individual IFU will be additionally corrected using multi-object AO within GIRMOS. The GNAO narrow field mode will feed the GIRMOS tiled IFU configuration in which all IFUs are combined into a "super"-IFU in the center of the field. GNAO also includes the development of a new Real Time Controller, a new GNAO Facility System Controller and finally the development of a new AO Bench. We present in this paper an overview of the GNAO facility and provide a status update of each product. △ Less

Submitted 30 August, 2022; originally announced August 2022.

Comments: SPIE conference 2022 Montreal

Design of SCALES: A 2-5 Micron Coronagraphic Integral Field Spectrograph for Keck Observatory

Authors: Andrew Skemer, R. Deno Stelter, Stephanie Sallum, Nicholas MacDonald, Renate Kupke, Christopher Ratliffe, Ravinder Banyal, Amirul Hasan, Hari Mohan Varshney, Arun Surya, Ajin Prakash, Sivarani Thirupathi, Ramya Sethuraman, Govinda K. V., Michael P. Fitzgerald, Eric Wang, Marc Kassis, Olivier Absil, Carlos Alvarez, Natasha Batalha, Marc-Andre Boucher, Cyril Bourgenot, Timothy Brandt, Zackery Briesemeister, Katherine de Kleer , et al. (27 additional authors not shown)

Abstract: We present the design of SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. SCALES enables low-resolution (R~50) spectroscopy, as well as medium-resolution (R~4,000) spectroscopy with the goal of discovering and characterizing cold exoplanets that are brightest in the thermal… ▽ More We present the design of SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) a new 2-5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. SCALES enables low-resolution (R~50) spectroscopy, as well as medium-resolution (R~4,000) spectroscopy with the goal of discovering and characterizing cold exoplanets that are brightest in the thermal infrared. Additionally, SCALES has a 12x12" field-of-view imager that will be used for general adaptive optics science at Keck. We present SCALES's specifications, its science case, its overall design, and simulations of its expected performance. Additionally, we present progress on procuring, fabricating and testing long lead-time components. △ Less

Submitted 23 August, 2022; originally announced August 2022.

Comments: 19 pages, 12 Figures, SPIE Astronomical Telescopes + Instrumentation, (#12184-18), 2022, Montreal, Canada

Daytime calibration and testing of the Keck All sky Precision Adaptive Optics Tomography System

Authors: Avinash Surendran, Jacques R. Delorme, Carlos M. Correia, Steve Doyle, Sam Ragland, Paul Richards, Peter Wizinowich, Philip M. Hinz, Daren Dillon, Cesar Laguna, Sylvain Cetre, Scott Lilley, Ed Wetherell, Jason C. Y. Chin, Eduardo Marin

Abstract: The development of the Keck All sky Precision Adaptive optics (KAPA) project was initiated in September 2018 to upgrade the Keck I adaptive optics (AO) system to enable laser tomography adaptive optics (LTAO) with a four laser guide star (LGS) asterism. The project includes the replacement of the existing LMCT laser with a Toptica laser, the implementation of a new real-time controller (RTC) and w… ▽ More The development of the Keck All sky Precision Adaptive optics (KAPA) project was initiated in September 2018 to upgrade the Keck I adaptive optics (AO) system to enable laser tomography adaptive optics (LTAO) with a four laser guide star (LGS) asterism. The project includes the replacement of the existing LMCT laser with a Toptica laser, the implementation of a new real-time controller (RTC) and wavefront sensor optics and camera, and a new daytime calibration and test platform to provide the required infrastructure for laser tomography. The work presented here describes the new daytime calibration infrastructure to test the performance for the KAPA tomographic algorithms. This paper outlines the hardware infrastructure for daytime calibration and performance assessment of tomographic algorithms. This includes the implementation of an asterism simulator having fiber-coupled light sources simulating four Laser Guide Stars (LGS) and two Natural Guide Stars (NGS) at the AO bench focus, as well as the upgrade of the existing TelSim on the AO bench to simulate focal anisoplanatism and wind driven atmospheric turbulence. A phase screen, that can be adjusted in effective altitude, is used to simulate wind speeds up to 10 m/s for a duration of upto 3 s. △ Less

Submitted 28 July, 2022; originally announced July 2022.

Comments: 15 pages, 13 figures. Publishd as part of SPIE Astronomical telescopes + Instrumentation 2022 proceedings

Graphene on Silicon Hybrid Field-Effect Transistors

Authors: Mykola Fomin, Francisco Pasadas, Enrique Marin, Alberto Medina Rull, Francisco Ruiz, Andres Godoy, Ihor Zadorozhnyi, Guillermo Beltramo, Fabian Brings, Svetlana Vitusevich, Andreas Offenhaeusser, Dmitry Kireev

Abstract: The combination of graphene with silicon in hybrid devices has attracted attention extensively over the last decade. Most of such devices were proposed for photonics and radiofrequency applications. In this work, we present a unique technology of graphene-on-silicon heterostructures and their properties as solution-gated transistors. The graphene-on-Silicon field-effect transistors (GoSFETs) were… ▽ More The combination of graphene with silicon in hybrid devices has attracted attention extensively over the last decade. Most of such devices were proposed for photonics and radiofrequency applications. In this work, we present a unique technology of graphene-on-silicon heterostructures and their properties as solution-gated transistors. The graphene-on-Silicon field-effect transistors (GoSFETs) were fabricated exploiting various conformations of drain-source regions doping and channel material dimensions. The fabricated devices were electrically characterized demonstrating hybrid behavior with features specific to both graphene and silicon. Although GoSFET's transconductance and carrier's mobility were found to be lower than in conventional silicon and graphene field-effect transistors (SiFETs and GFETs), it was demonstrated that the combination of both materials within the hybrid channel contribute uniquely to the charge carrier transport. A comprehensive physics-based compact modeling was specifically developed, showing excellent agreement with the experimental data. The model is employed to rationalize the observed hybrid behavior as the theoretical results from the electrostatics and the carrier transport under a drift-diffusion approach show that graphene acts as a shield for the silicon channel, giving rise to a non-uniform potential distribution along it, especially at the subthreshold region. This graphene screening effect is shown to strongly affect the device subthreshold swing when compared against a conventional SiFET due to a non-negligible diffusion current in this operation regime. △ Less

Submitted 20 April, 2022; originally announced April 2022.

Compact Modeling of pH-Sensitive FETs Based on Two-Dimensional Semiconductors

Authors: Tarek El Grour, Francisco Pasadas, Alberto Medina-Rull, Montassar Najari, Enrique G. Marin, Alejandro Toral-Lopez, Francisco G. Ruiz, Andrés Godoy, David Jiménez, Lassaad El-Mir

Abstract: We present a physics-based circuit-compatible model for pH-sensitive field-effect transistors based on two-dimensional (2D) materials. The electrostatics along the electrolyte-gated 2D-semiconductor stack is treated by solving the Poisson equation including the Site-Binding model and the Gouy-Chapman-Stern approach, while the carrier transport is described by the drift-diffusion theory. The propos… ▽ More We present a physics-based circuit-compatible model for pH-sensitive field-effect transistors based on two-dimensional (2D) materials. The electrostatics along the electrolyte-gated 2D-semiconductor stack is treated by solving the Poisson equation including the Site-Binding model and the Gouy-Chapman-Stern approach, while the carrier transport is described by the drift-diffusion theory. The proposed model is provided in an analytical form and then implemented in Verilog-A, making it compatible with standard technology computer-aided design tools employed for circuit simulation. The model is benchmarked against two experimental transition-metal-dichalcogenide (MoS2 and ReS2) based ion sensors, showing excellent agreement when predicting the drain current, threshold voltage shift, and current/voltage sensitivity measurements for different pH concentrations. △ Less

Submitted 14 September, 2021; originally announced September 2021.

Comments: 4 pages, 3 figures, 1 table

Journal ref: IEEE Transactions on Electron Devices, 68(11), 5916-5919, 2021

Serverless Computing: A Security Perspective

Authors: Eduard Marin, Diego Perino, Roberto Di Pietro

Abstract: Serverless Computing is a virtualisation-related paradigm that promises to simplify application management and to solve the last challenges in the field: scale down and easy to use. The implied cost reduction, coupled with a simplified management of underlying applications, are expected to further push the adoption of virtualisation-based solutions, including cloud-computing or telco-cloud solutio… ▽ More Serverless Computing is a virtualisation-related paradigm that promises to simplify application management and to solve the last challenges in the field: scale down and easy to use. The implied cost reduction, coupled with a simplified management of underlying applications, are expected to further push the adoption of virtualisation-based solutions, including cloud-computing or telco-cloud solutions. However, in this quest for efficiency, security is not ranked among the top priorities, also because of the (misleading) belief that current solutions developed for virtualised environments could be applied (as is) to this new paradigm. Unfortunately, this is not the case, due to the highlighted idiosyncratic features of serverless computing. In this paper, we review the current serverless architectures, abstract and categorise their founding principles, and provide an in depth analyse of them from the point of view of security, referring to principles and practices of the cybersecurity domain. In particular, we show the security shortcomings of the analysed serverless architectural paradigms, point to possible countermeasures, and highlight a few research directions. △ Less

Submitted 27 January, 2022; v1 submitted 8 July, 2021; originally announced July 2021.

Unveiling the impact of the bias-dependent charge neutrality point on graphene-based multi-transistor applications

Authors: Francisco Pasadas, Alberto Medina-Rull, Pedro Carlos Feijoo, Anibal Pacheco-Sanchez, Enrique G. Marin, Francisco G. Ruiz, Noel Rodriguez, Andrés Godoy, David Jiménez

Abstract: The Dirac voltage of a graphene field-effect transistor (GFET) stands for the gate bias that sets the charge neutrality condition in the channel, thus resulting in a minimum conductivity. Controlling its dependence on the terminal biases is crucial for the design and optimization of radio-frequency applications based on multiple GFETs. However, the previous analysis of such dependence carried out… ▽ More The Dirac voltage of a graphene field-effect transistor (GFET) stands for the gate bias that sets the charge neutrality condition in the channel, thus resulting in a minimum conductivity. Controlling its dependence on the terminal biases is crucial for the design and optimization of radio-frequency applications based on multiple GFETs. However, the previous analysis of such dependence carried out for a single device can lead to confusion and if not properly understood could result in circuit designs with poor performance. The control of the Dirac point shift (DPS) is particularly important for the deployment of graphene-based differential circuit topologies where keeping a strict symmetry between the electrical balanced branches is crucial for exploiting the advantages of such topologies. This note sheds light on the impact of terminal biases on the DPS in a real device and sets a rigorous methodology to control it so to eventually optimize and exploit the performance of radio-frequency applications based on GFETs. △ Less

Submitted 14 May, 2021; originally announced May 2021.

Comments: 7 pages, 3 figures, 1 table

Journal ref: Nano Express, vol. 2(3), 036001, 2021

PPFL: Privacy-preserving Federated Learning with Trusted Execution Environments

Authors: Fan Mo, Hamed Haddadi, Kleomenis Katevas, Eduard Marin, Diego Perino, Nicolas Kourtellis

Abstract: We propose and implement a Privacy-preserving Federated Learning ($PPFL$) framework for mobile systems to limit privacy leakages in federated learning. Leveraging the widespread presence of Trusted Execution Environments (TEEs) in high-end and mobile devices, we utilize TEEs on clients for local training, and on servers for secure aggregation, so that model/gradient updates are hidden from adversa… ▽ More We propose and implement a Privacy-preserving Federated Learning ($PPFL$) framework for mobile systems to limit privacy leakages in federated learning. Leveraging the widespread presence of Trusted Execution Environments (TEEs) in high-end and mobile devices, we utilize TEEs on clients for local training, and on servers for secure aggregation, so that model/gradient updates are hidden from adversaries. Challenged by the limited memory size of current TEEs, we leverage greedy layer-wise training to train each model's layer inside the trusted area until its convergence. The performance evaluation of our implementation shows that $PPFL$ can significantly improve privacy while incurring small system overheads at the client-side. In particular, $PPFL$ can successfully defend the trained model against data reconstruction, property inference, and membership inference attacks. Furthermore, it can achieve comparable model utility with fewer communication rounds (0.54$\times$) and a similar amount of network traffic (1.002$\times$) compared to the standard federated learning of a complete model. This is achieved while only introducing up to ~15% CPU time, ~18% memory usage, and ~21% energy consumption overhead in $PPFL$'s client-side. △ Less

Submitted 28 June, 2021; v1 submitted 29 April, 2021; originally announced April 2021.

Comments: 15 pages, 8 figures, accepted to MobiSys 2021

Multi-scale analysis of radio-frequency performance of 2D-material based field-effect transistors

Authors: A. Toral-Lopez, F. Pasadas, E. G. Marin, A. Medina-Rull, J. M. Gonzalez-Medina, F. G. Ruiz, D. Jiménez, A. Godoy

Abstract: Two-dimensional materials (2DMs) are a promising alternative to complement and upgrade high-frequency electronics. However, in order to boost their adoption, the availability of numerical tools and physically-based models able to support the experimental activities and to provide them with useful guidelines becomes essential. In this context, we propose a theoretical approach that combines numeric… ▽ More Two-dimensional materials (2DMs) are a promising alternative to complement and upgrade high-frequency electronics. However, in order to boost their adoption, the availability of numerical tools and physically-based models able to support the experimental activities and to provide them with useful guidelines becomes essential. In this context, we propose a theoretical approach that combines numerical simulations and small-signal modeling to analyze 2DM-based FETs for radio-frequency applications. This multi-scale scheme takes into account non-idealities, such as interface traps, carrier velocity saturation, or short channel effects, by means of self-consistent physics-based numerical calculations that later feed the circuit level via a small-signal model based on the dynamic intrinsic capacitances of the device. At the circuit stage, the possibilities range from the evaluation of the performance of a single device to the design of complex circuits combining multiple transistors. In this work, we validate our scheme against experimental results and exemplify its use and capability assessing the impact of the channel scaling on the performance of MoS2-based FETs targeting RF applications. △ Less

Submitted 16 March, 2021; v1 submitted 15 March, 2021; originally announced March 2021.

Comments: 6 pages, 6 figures

A Graphene Field-Effect Transistor Based Analogue Phase Shifter for High-Frequency Applications

Authors: A. Medina-Rull, F. Pasadas, E. G. Marin, A. Toral-Lopez, J. Cuesta, A. Godoy, D. Jiménez, F. G. Ruiz

Abstract: We present a graphene-based phase shifter for radio-frequency (RF) phase-array applications. The core of the designed phase-shifting system consists of a graphene field-effect transistor (GFET) used in a common source amplifier configuration. The phase of the RF signal is controlled by exploiting the quantum capacitance of graphene and its dependence on the terminal transistor biases. In particula… ▽ More We present a graphene-based phase shifter for radio-frequency (RF) phase-array applications. The core of the designed phase-shifting system consists of a graphene field-effect transistor (GFET) used in a common source amplifier configuration. The phase of the RF signal is controlled by exploiting the quantum capacitance of graphene and its dependence on the terminal transistor biases. In particular, by independently tuning the applied gate-to-source and drain-to-source biases, we observe that the phase of the signal, in the super-high frequency band, can be varied nearly 200 degrees with a constant gain of 2.5 dB. Additionally, if only the gate bias is used as control signal, and the drain is biased linearly dependent on the former (i.e., in a completely analogue operation), a phase shift of 85 degrees can be achieved making use of just one transistor and keeping a gain of 0 dB with a maximum variation of 1.3 dB. The latter design can be improved by applying a balanced branch-line configuration showing to be competitive against other state-of-the-art phase shifters. This work paves the way towards the exploitation of graphene technology to become the core of active analogue phase shifters for high-frequency operation. △ Less

Submitted 15 March, 2021; v1 submitted 10 March, 2021; originally announced March 2021.

Comments: 10 pages, 10 figures, 2 tables

Journal ref: IEEE Access, 2020, vol. 8, p. 209055-209063

Flexible One-Dimensional Metal-Insulator-Graphene Diode

Authors: Zhenxing Wang, Burkay Uzlu, Mehrdad Shaygan, Martin Otto, Mário Ribeiro, Enrique González Marín, Giuseppe Iannaccone, Gianluca Fiori, Mohamed Saeed Elsayed, Renato Negra, Daniel Neumaier

Abstract: In this work, a novel one-dimensional geometry for metal-insulator-graphene (1D-MIG) diode with low capacitance is demonstrated. The junction of the 1D-MIG diode is formed at the 1D edge of Al2O3-encapsulated graphene with TiO2 that acts as barrier material. The diodes demonstrate ultra-high current density since the transport in the graphene and through the barrier is in plane. The geometry deliv… ▽ More In this work, a novel one-dimensional geometry for metal-insulator-graphene (1D-MIG) diode with low capacitance is demonstrated. The junction of the 1D-MIG diode is formed at the 1D edge of Al2O3-encapsulated graphene with TiO2 that acts as barrier material. The diodes demonstrate ultra-high current density since the transport in the graphene and through the barrier is in plane. The geometry delivers very low capacitive coupling between the cathode and anode of the diode, which shows frequency response up to 100 GHz and ensures potential high frequency performance up to 2.4 THz. The 1D-MIG diodes are demonstrated to function uniformly and stable under bending conditions down to 6.4 mm bending radius on flexible substrate. △ Less

Submitted 18 March, 2020; originally announced March 2020.

Journal ref: ACS Applied Electronic Materials, 2019, 1, 945-950

Large-signal model of 2DFETs: compact modeling of terminal charges and intrinsic capacitances

Authors: Francisco Pasadas, Enrique G. Marin, Alejandro Toral-Lopez, Francisco G. Ruiz, Andrés Godoy, Saungeun Park, Deji Akinwande, David Jiménez

Abstract: We present a physics-based circuit-compatible model for double-gated two-dimensional semiconductor based field effect transistors, which provides explicit expressions for the drain current, terminal charges and intrinsic capacitances. The drain current model is based on the drift-diffusion mechanism for the carrier transport and considers Fermi-Dirac statistics coupled with an appropriate field-ef… ▽ More We present a physics-based circuit-compatible model for double-gated two-dimensional semiconductor based field effect transistors, which provides explicit expressions for the drain current, terminal charges and intrinsic capacitances. The drain current model is based on the drift-diffusion mechanism for the carrier transport and considers Fermi-Dirac statistics coupled with an appropriate field-effect approach. The terminal charge and intrinsic capacitance models are calculated adopting a Ward-Dutton linear charge partition scheme that guarantees charge-conservation. It has been implemented in Verilog-A to make it compatible with standard circuit simulators. In order to benchmark the proposed modeling framework we also present experimental DC and high-frequency measurements of a purposely fabricated monolayer MoS2 FET showing excellent agreement between the model and the experiment and thus demonstrating the capabilities of the combined approach to predict the performance of 2DFETs. △ Less

Submitted 4 February, 2020; originally announced February 2020.

Comments: 7 pages, 6 figures

Journal ref: npj 2D Materials and Applications, vol. 3(47), 2019

Lateral Heterostructure Field-Effect Transistors Based on 2D-Material Stacks With Varying Thickness and Energy Filtering Source

Authors: Enrique G. Marin, Damiano Marian, Marta Perucchini, Gianluca Fiori, Giuseppe Iannaccone

Abstract: The bandgap dependence on the number of atomic layers of some families of 2D-materials, can be exploited to engineer and use lateral heterostructures (LHs) as high-performance Field-Effect Transistors (FET). This option can provide very good lattice matching as well as high heterointerface quality. More importantly, this bandgap modulation with layer stacking can give rise to steep transitions in… ▽ More The bandgap dependence on the number of atomic layers of some families of 2D-materials, can be exploited to engineer and use lateral heterostructures (LHs) as high-performance Field-Effect Transistors (FET). This option can provide very good lattice matching as well as high heterointerface quality. More importantly, this bandgap modulation with layer stacking can give rise to steep transitions in the density of states (DOS) of the 2D material, that can eventually be used to achieve sub-60 mV/decade subthreshold swing in LH-FETs thanks to an energy-filtering source. We have observed this effect in the case of a PdS2 LH-FET due to the particular density of states of its bilayer configuration. Our results are based on ab initio and multiscale materials and device modeling, and incite the exploration of the 2D-material design space in order to find more abrupt DOS transitions and better suitable candidates. △ Less

Submitted 9 January, 2020; originally announced January 2020.

Comments: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in ACS Nano, copyright American Chemical Society after peer review. To access the final edited and published work see acsnano.org

GFET Asymmetric Transfer Response Analysis through Access Region Resistances

Authors: A. Toral-Lopez, E. G. Marin, F. Pasadas, J. M. Gonzalez-Medina, F. G. Ruiz, D. Jiménez, A. Godoy

Abstract: Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene {field-effect} transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, little attention has been paid, so far, to the ro… ▽ More Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene {field-effect} transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, little attention has been paid, so far, to the role of the access regions in these devices. \mbox{Here, we analyse} in detail, via numerical simulations, how the GFET transfer response is severely impacted by these regions, showing that they play a significant role in the asymmetric saturated behaviour commonly observed in GFETs. We also investigate how the modulation of the access region conductivity (i.e., by the influence of a back gate) and the presence of imperfections in the graphene layer (e.g., charge puddles) affects the transfer response. The analysis is extended to assess the application of GFETs for RF applications, by~evaluating their cut-off frequency. △ Less

Submitted 14 November, 2019; originally announced November 2019.

Comments: 12 pages, 8 figures

Journal ref: Nanomaterials 2019, 9, 1027

Entering into the Wide Field Adaptive Optics Era on Maunakea

Authors: Gaetano Sivo, John Blakeslee, Jennifer Lotz, Henry Roe, Morten Andersen, Julia Scharwachter, David Palmer, Scot Kleinman, Andy Adamson, Paul Hirst, Eduardo Marin, Laure Catala, Marcos van Dam, Stephen Goodsell, Natalie Provost, Ruben Diaz, Inger Jorgensen, Hwihyun Kim, Marie Lemoine-Busserole, Celia Blain, Mark Chun, Mark Ammons, Julian Christou, Charlotte Bond, Suresh Sivanandam , et al. (10 additional authors not shown)

Abstract: As part of the National Science Foundation funded "Gemini in the Era of MultiMessenger Astronomy" (GEMMA) program, Gemini Observatory is developing GNAO, a widefield adaptive optics (AO) facility for Gemini-North on Maunakea, the only 8m-class open-access telescope available to the US astronomers in the northern hemisphere. GNAO will provide the user community with a queue-operated Multi-Conjugate… ▽ More As part of the National Science Foundation funded "Gemini in the Era of MultiMessenger Astronomy" (GEMMA) program, Gemini Observatory is developing GNAO, a widefield adaptive optics (AO) facility for Gemini-North on Maunakea, the only 8m-class open-access telescope available to the US astronomers in the northern hemisphere. GNAO will provide the user community with a queue-operated Multi-Conjugate AO (MCAO) system, enabling a wide range of innovative solar system, Galactic, and extragalactic science with a particular focus on synergies with JWST in the area of time-domain astronomy. The GNAO effort builds on institutional investment and experience with the more limited block-scheduled Gemini Multi-Conjugate System (GeMS), commissioned at Gemini South in 2013. The project involves close partnerships with the community through the recently established Gemini AO Working Group and the GNAO Science Team, as well as external instrument teams. The modular design of GNAO will enable a planned upgrade to a Ground Layer AO (GLAO) mode when combined with an Adaptive Secondary Mirror (ASM). By enhancing the natural seeing by an expected factor of two, GLAO will vastly improve Gemini North's observing efficiency for seeing-limited instruments and strengthen its survey capabilities for multi-messenger astronomy. △ Less

Submitted 15 February, 2021; v1 submitted 18 July, 2019; originally announced July 2019.

Comments: 12 pages, 6 figures, ASTRO 2020 Decadal Survey

Physical insights into the operation of a 1-nm gate length transistor based on MoS2 with metallic carbon nanotube gate

Authors: Marta Perucchini, Enrique G. Marin, Damiano Marian, Giuseppe Iannaccone, Gianluca Fiori

Abstract: Low-dimensional materials such as layered semiconductors or carbon nanotubes (CNTs) have been attracting increasing attention in the last decades due to their inherent scaling properties, which become fundamental to sustain the scaling in electronic devices. Inspired by recent experimental results (S.B. Desai, S.R. Madhvapathy, A.B. Sachid, J.P. Llinas, Q. Wang, G.H. Ahn, G. Pitner, M.J. Kim, J. B… ▽ More Low-dimensional materials such as layered semiconductors or carbon nanotubes (CNTs) have been attracting increasing attention in the last decades due to their inherent scaling properties, which become fundamental to sustain the scaling in electronic devices. Inspired by recent experimental results (S.B. Desai, S.R. Madhvapathy, A.B. Sachid, J.P. Llinas, Q. Wang, G.H. Ahn, G. Pitner, M.J. Kim, J. Bokor, C. Hu, H.-S. P. Wong, and A. Javey, Science 354, 99 (2016)), in this work we examined the ultimate performance of of MoS$_2$-channel Field Effect Transistors with 1-nm gate length by means of quantum transport simulations based on Poisson equation and Non-equilibrium Green's function formalism. We considered uniformly scaled devices, with channel lengths ranging from 5 to 20 nm controlled by a cylindrical gate with a 1-nm diameter, as would be required in realistic integrated circuits. Moreover, we also evaluated the effect of the finite density of states of a carbon nanotube gate on the loss of device performance. We noticed that the sub-threshold swing for all short-channel structures was greater than the ideal limit of thermionic devices and we attributed this to the presence of tunneling currents and gate-drain interactions. We tailored the transistor architecture in order to improve the gate control. We concluded that the limited CNT-channel capacitive coupling poses severe limitations on the operation and thus exploitation of the device. △ Less

Submitted 20 April, 2019; originally announced April 2019.

Comments: 4 pages, 3 figures

Journal ref: Appl. Phys. Lett. 113, 183507 (2018)

Tunnel-Field-Effect Spin Filter from Two-Dimensional Antiferromagnetic Stanene

Authors: Enrique G. Marin, Damiano Marian, Giuseppe Iannaccone, Gianluca Fiori

Abstract: We propose a device concept, based on monolayer stanene, able to provide highly polarized spin currents (up to a $98\%$) with voltage-controlled spin polarization operating at room temperature and with small operating voltage ($0.3$ V). The concept exploits the presence of spin-polarized edge states in a stanene nanoribbon. The spin polarization of the total current can be modulated by a different… ▽ More We propose a device concept, based on monolayer stanene, able to provide highly polarized spin currents (up to a $98\%$) with voltage-controlled spin polarization operating at room temperature and with small operating voltage ($0.3$ V). The concept exploits the presence of spin-polarized edge states in a stanene nanoribbon. The spin polarization of the total current can be modulated by a differential tuning of the transmission properties, and of the occupation of edge states of different spin, via the application of an in-plane electric field. We demonstrate device operation using ab-initio and quantum transport simulations. △ Less

Submitted 19 April, 2019; originally announced April 2019.

Comments: 15 pages, 5 figures

Journal ref: Phys. Rev. Applied 10, 044063 (2018)

ABMS of social network based on affinity

Authors: Juan Camilo Ramírez de los Rios, Paula Alejandra Escudero Marín, María Camila Vásquez-Correa

Abstract: An agent-based model is proposed for analyzing the dynamics that arise from interactions within social networks, analyzing the individual behavior of each profile. Said model considers a simplified construction of a social network while satisfying properties attributed to this type of systems. For that matter, previously established studies on the matter are taken into account, while including eac… ▽ More An agent-based model is proposed for analyzing the dynamics that arise from interactions within social networks, analyzing the individual behavior of each profile. Said model considers a simplified construction of a social network while satisfying properties attributed to this type of systems. For that matter, previously established studies on the matter are taken into account, while including each profiles preferences, and how they evolve with time, for the system's dynamic behavior. Results are analyzed based on concepts like the emergence of clusters, the polarization of the network and the homogeneity of preferences between connected profiles; and how they may depend on the characteristics of the profiles and of the network. △ Less

Submitted 28 February, 2019; originally announced March 2019.

Paradigm shift in electron-based crystallography via machine learning

Authors: Kevin Kaufmann, Chaoyi Zhu, Alexander S. Rosengarten, Daniel Maryanovsky, Tyler J. Harrington, Eduardo Marin, Kenneth S. Vecchio

Abstract: Accurately determining the crystallographic structure of a material, organic or inorganic, is a critical primary step in material development and analysis. The most common practices involve analysis of diffraction patterns produced in laboratory XRD, TEM, and synchrotron X-ray sources. However, these techniques are slow, require careful sample preparation, can be difficult to access, and are prone… ▽ More Accurately determining the crystallographic structure of a material, organic or inorganic, is a critical primary step in material development and analysis. The most common practices involve analysis of diffraction patterns produced in laboratory XRD, TEM, and synchrotron X-ray sources. However, these techniques are slow, require careful sample preparation, can be difficult to access, and are prone to human error during analysis. This paper presents a newly developed methodology that represents a paradigm change in electron diffraction-based structure analysis techniques, with the potential to revolutionize multiple crystallography-related fields. A machine learning-based approach for rapid and autonomous identification of the crystal structure of metals and alloys, ceramics, and geological specimens, without any prior knowledge of the sample, is presented and demonstrated utilizing the electron backscatter diffraction (EBSD) technique. Electron backscatter diffraction patterns are collected from materials with well-known crystal structures, then a deep neural network model is constructed for classification to a specific Bravais lattice or point group. The applicability of this approach is evaluated on diffraction patterns from samples unknown to the computer without any human input or data filtering. This is in comparison to traditional Hough transform EBSD, which requires that you have already determined the phases present in your sample. The internal operations of the neural network are elucidated through visualizing the symmetry features learned by the convolutional neural network. It is determined that the model looks for the same features a crystallographer would use, even though it is not explicitly programmed to do so. This study opens the door to fully automated, high-throughput determination of crystal structures via several electron-based diffraction techniques. △ Less

Submitted 10 February, 2019; originally announced February 2019.

Comments: 35 pages, 17 figures with extended data included

Journal ref: Science 367 (2020) 564-568

A High-Entropy Silicide: (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2

Authors: Joshua Gild, Jeffrey Braun, Kevin Kaufmann, Eduardo Marin, Tyler Harrington, Patrick Hopkins, Kenneth Vecchio, Jian Luo

Abstract: A high-entropy metal disilicide, (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2, has been successfully synthesized. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and electron backscatter diffraction (EBSD) collectively show the formation of a single high-entropy silicide phase. This high-entropy (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2 possesses a hexagonal C40 crystal structure with ABC stacking seque… ▽ More A high-entropy metal disilicide, (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2, has been successfully synthesized. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and electron backscatter diffraction (EBSD) collectively show the formation of a single high-entropy silicide phase. This high-entropy (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2 possesses a hexagonal C40 crystal structure with ABC stacking sequence and a point group of P6222. This discovery expands the known families of high-entropy materials from metals, oxides, borides, carbides, and nitrides to a silicide, for the first time to our knowledge, as well as demonstrating that a new, non-cubic, crystal structure (with lower symmetry) can be made into high-entropy. This (Mo0.2Nb0.2Ta0.2Ti0.2W0.2)Si2 exhibits high nanohardness of 16.7 +- 1.9 GPa and Vickers hardness of 11.6 +- 0.5 GPa. Moreover, it has a low thermal conductivity of 6.9 +- 1.1 W m-1 K-1, which is approximately one order of magnitude lower than that of the widely-used tetragonal MoSi2 and ~1/3 of those reported values for the hexagonal NbSi2 and TaSi2 with the same crystal structure. △ Less

Submitted 16 March, 2019; v1 submitted 4 February, 2019; originally announced February 2019.

Comments: 18 pages; 5 + 1 figures

Journal ref: Journal of Materiomics 2019

DARKMENTION: A Deployed System to Predict Enterprise-Targeted External Cyberattacks

Authors: Mohammed Almukaynizi, Ericsson Marin, Eric Nunes, Paulo Shakarian, Gerardo I. Simari, Dipsy Kapoor, Timothy Siedlecki

Abstract: Recent incidents of data breaches call for organizations to proactively identify cyber attacks on their systems. Darkweb/Deepweb (D2web) forums and marketplaces provide environments where hackers anonymously discuss existing vulnerabilities and commercialize malicious software to exploit those vulnerabilities. These platforms offer security practitioners a threat intelligence environment that allo… ▽ More Recent incidents of data breaches call for organizations to proactively identify cyber attacks on their systems. Darkweb/Deepweb (D2web) forums and marketplaces provide environments where hackers anonymously discuss existing vulnerabilities and commercialize malicious software to exploit those vulnerabilities. These platforms offer security practitioners a threat intelligence environment that allows to mine for patterns related to organization-targeted cyber attacks. In this paper, we describe a system (called DARKMENTION) that learns association rules correlating indicators of attacks from D2web to real-world cyber incidents. Using the learned rules, DARKMENTION generates and submits warnings to a Security Operations Center (SOC) prior to attacks. Our goal was to design a system that automatically generates enterprise-targeted warnings that are timely, actionable, accurate, and transparent. We show that DARKMENTION meets our goal. In particular, we show that it outperforms baseline systems that attempt to generate warnings of cyber attacks related to two enterprises with an average increase in F1 score of about 45% and 57%. Additionally, DARKMENTION was deployed as part of a larger system that is built under a contract with the IARPA Cyber-attack Automated Unconventional Sensor Environment (CAUSE) program. It is actively producing warnings that precede attacks by an average of 3 days. △ Less

Submitted 29 October, 2018; originally announced October 2018.

Evidence of topological superconductivity in planar Josephson junctions

Authors: Antonio Fornieri, Alexander M. Whiticar, F. Setiawan, Elías Portolés Marín, Asbjørn C. C. Drachmann, Anna Keselman, Sergei Gronin, Candice Thomas, Tian Wang, Ray Kallaher, Geoffrey C. Gardner, Erez Berg, Michael J. Manfra, Ady Stern, Charles M. Marcus, Fabrizio Nichele

Abstract: Majorana zero modes are quasiparticle states localized at the boundaries of topological superconductors that are expected to be ideal building blocks for fault-tolerant quantum computing. Several observations of zero-bias conductance peaks measured in tunneling spectroscopy above a critical magnetic field have been reported as experimental indications of Majorana zero modes in superconductor/semic… ▽ More Majorana zero modes are quasiparticle states localized at the boundaries of topological superconductors that are expected to be ideal building blocks for fault-tolerant quantum computing. Several observations of zero-bias conductance peaks measured in tunneling spectroscopy above a critical magnetic field have been reported as experimental indications of Majorana zero modes in superconductor/semiconductor nanowires. On the other hand, two dimensional systems offer the alternative approach to confine Ma jorana channels within planar Josephson junctions, in which the phase difference φ between the superconducting leads represents an additional tuning knob predicted to drive the system into the topological phase at lower magnetic fields. Here, we report the observation of phase-dependent zero-bias conductance peaks measured by tunneling spectroscopy at the end of Josephson junctions realized on a InAs/Al heterostructure. Biasing the junction to φ ~ π significantly reduces the critical field at which the zero-bias peak appears, with respect to φ = 0. The phase and magnetic field dependence of the zero-energy states is consistent with a model of Majorana zero modes in finite-size Josephson junctions. Besides providing experimental evidence of phase-tuned topological superconductivity, our devices are compatible with superconducting quantum electrodynamics architectures and scalable to complex geometries needed for topological quantum computing. △ Less

Submitted 9 September, 2018; originally announced September 2018.

Comments: main text and extended data

Report number: NBI QDEV 2018

Journal ref: Nature 569, 89-92 (2019)

Laser-beam patterned topological insulating states on thin semiconducting MoS2

Authors: H. Mine, A. Kobayashi, T. Nakamura, T. Inoue, S. Pakdel, E. Z. Marin, D. Marian, E. Gonzalez-Marin, S. Maruyama, S. Katsumoto, A. Fortunelli, J. J. Palacios, J. Haruyama

Abstract: Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low power dissipation. Members of the 2D transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conductio… ▽ More Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low power dissipation. Members of the 2D transition metal dichalcogenides (TMDCs) have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conduction seems fragile and limited to the monolayer phase fabricated on specified substrates. Here, we realize the controlled patterning of the 1T'-phase embedded into the 2H-phase of thin semiconducting molybdenum-disulfide (MoS2) by laser beam irradiation. Integer fractions of the quantum of resistance, the dependence on laser-irradiation conditions, magnetic field, and temperature, as well as the bulk gap observation by scanning tunneling spectroscopy and theoretical calculations indicate the presence of the quantum spin Hall phase in our patterned 1T' phases. △ Less

Submitted 2 September, 2019; v1 submitted 13 July, 2018; originally announced July 2018.

Journal ref: Phys. Rev. Lett. 123, 146803 (2019)

Ultra Low Specific Contact Resistivity in Metal-Graphene Junctions via Atomic Orbital Engineering

Authors: Vikram Passi, Amit Gahoi, Enrique G. Marin, Teresa Cusati, Alessandro Fortunelli, Giuseppe Iannaccone, Gianluca Fiori, Max C. Lemme

Abstract: A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 Ωm for a device with surface contacts to 456 Ωm when contacts are patterned with holes. Electrostatic doping o… ▽ More A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 Ωm for a device with surface contacts to 456 Ωm when contacts are patterned with holes. Electrostatic doping of the graphene further reduces contact resistivity from 519 Ωm to 45 Ωm, a substantial decrease of 91%. The experimental results are supported and understood via a multi-scale numerical model, based on density-functional-theory calculations and transport simulations. The data is analyzed with regards to the edge perimeter and hole-to-graphene ratio, which provides insights into optimized contact geometries. The current work thus indicates a reliable and reproducible approach for fabricating low resistance contacts in graphene devices. We provide a simple guideline for contact design that can be exploited to guide graphene and 2D material contact engineering. △ Less

Submitted 12 July, 2018; originally announced July 2018.

Comments: 26 pages

Journal ref: Advanced Materials Interfaces, 6(1): 1801285, 2019

First principle investigation of Tunnel FET based on nanoribbons from topological two-dimensional material

Authors: Enrique G. Marin, Damiano Marian, Giuseppe Iannaccone, Gianluca Fiori

Abstract: We explore nanoribbons from topological two-dimensional stanene as channel material in tunnel field effect transistors. This novel technological option offers the possibility to build pure one-dimensional (1D) channel devices (comprised of a 1D chain of atoms) due to localized states in correspondence of the nanoribbon edges. The investigation is based on first-principle calculations and multi-sca… ▽ More We explore nanoribbons from topological two-dimensional stanene as channel material in tunnel field effect transistors. This novel technological option offers the possibility to build pure one-dimensional (1D) channel devices (comprised of a 1D chain of atoms) due to localized states in correspondence of the nanoribbon edges. The investigation is based on first-principle calculations and multi-scale transport simulations to assess devices performance against industry requirements and their robustness with respect to technological issues like line edge roughness, detrimental for nanoribbons. We will show that edges states are robust with respect to the presence of non-idealities (e.g., atoms vacancies at the edges), and that 1D-channel TFETs exhibit interesting potential for digital applications and room for optimization in order to improve the Ion/Ioff at the levels required by the ITRS, while opening a path for the exploration of new device concepts at the ultimate scaling limits. △ Less

Submitted 10 April, 2018; originally announced April 2018.

Comments: 22 pages, 9 figures

Journal ref: Nanoscale, 9, 19390 (2017)

Transistor concepts based on lateral heterostructures of metallic and semiconducting phases of MoS$_2$

Authors: Damiano Marian, Elias Dib, Teresa Cusati, Enrique G. Marin, Alessandro Fortunelli, Giuseppe Iannaccone, Gianluca Fiori

Abstract: In this paper we propose two transistor concepts based on lateral heterostructures of monolayer MoS$_2$, composed of adjacent regions of 1T (metallic) and 2H (semiconducting) phases, inspired by recent research showing the possibility to obtain such heterostructures by electron beam irradiation. The first concept, the lateral heterostructure field-effect transistor, exhibits potential of better pe… ▽ More In this paper we propose two transistor concepts based on lateral heterostructures of monolayer MoS$_2$, composed of adjacent regions of 1T (metallic) and 2H (semiconducting) phases, inspired by recent research showing the possibility to obtain such heterostructures by electron beam irradiation. The first concept, the lateral heterostructure field-effect transistor, exhibits potential of better performance with respect to the foreseen evolution of CMOS technology, both for high performance and low power applications. Performance potential has been evaluated by means of detailed multi-scale materials and device simulations. The second concept, the planar barristor, also exhibits potential competitive performance with CMOS, and an improvement of orders of magnitude in terms of the main figures of merit with respect to the recently proposed vertical barristor. △ Less

Submitted 31 March, 2018; originally announced April 2018.

Comments: 7 pages, 8 figures

Journal ref: Phys. Rev. Applied 8, 054047 (2017)

Individual, Model-Independent Masses of the Closest Known Brown Dwarf Binary to the Sun

Authors: E. Victor Garcia, S. Mark Ammons, Maissa Salama, Ian Crossfield, Eduardo Bendek, Jeffrey Chilcote, Vincent Garrel, James R. Graham, Paul Kalas, Quinn Konopacky, Jessica R. Lu, Bruce Macintosh, Eduardo Marin, Christian Marois, Eric Nielsen, Benoît Neichel, Don Pham, Robert J. De Rosa, Dominic M. Ryan, Maxwell Service, Gaetano Sivo

Abstract: At a distance of 2~pc, our nearest brown dwarf neighbor, Luhman 16 AB, has been extensively studied since its discovery 3 years ago, yet its most fundamental parameter -- the masses of the individual dwarfs -- has not been constrained with precision. In this work we present the full astrometric orbit and barycentric motion of Luhman 16 AB and the first precision measurements of the individual comp… ▽ More At a distance of 2~pc, our nearest brown dwarf neighbor, Luhman 16 AB, has been extensively studied since its discovery 3 years ago, yet its most fundamental parameter -- the masses of the individual dwarfs -- has not been constrained with precision. In this work we present the full astrometric orbit and barycentric motion of Luhman 16 AB and the first precision measurements of the individual component masses. We draw upon archival observations spanning 31 years from the European Southern Observatory (ESO) Schmidt Telescope, the Deep Near-Infrared Survey of the Southern Sky (DENIS), public FORS2 data on the Very Large Telescope (VLT), and new astrometry from the Gemini South Multiconjugate Adaptive Optics System (GeMS). Finally, we include three radial velocity measurements of the two components from VLT/CRIRES, spanning one year. With this new data sampling a full period of the orbit, we use a Markov Chain Monte Carlo algorithm to fit a 16-parameter model incorporating mutual orbit and barycentric motion parameters and constrain the individual masses to be~$27.9^{+1.1}_{-1.0}$~$M_{J}$ for the T dwarf and~$34.2^{+1.3}_{-1.1}$~$M_{J}$ for the L dwarf. Our measurements of Luhman 16 AB's mass ratio and barycentric motion parameters are consistent with previous estimates in the literature utilizing recent astrometry only. The GeMS-derived measurements of the Luhman 16 AB separation in 2014-2015 agree closely with Hubble Space Telescope (HST) measurements made during the same epoch Bedin et al. 2017, and the derived mutual orbit agrees with those measurements to within the HST uncertainties of $0.3 - 0.4$ milliarcseconds. △ Less

Submitted 12 August, 2017; v1 submitted 9 August, 2017; originally announced August 2017.

Comments: Accepted for publication in the Astrophysical Journal. 2nd version: Added a reference

Multi-conjugated adaptive optics imaging of distant galaxies -- A comparison of Gemini/GSAOI and VLT/HAWK-I data

Authors: Mischa Schirmer, Vincent Garrel, Gaetano Sivo, Eduardo Marin, Eleazar R. Carrasco

Abstract: Multi-conjugated adaptive optics (MCAO) yield nearly diffraction-limited images at 2$μ$m wavelengths. Currently, GeMS/GSAOI at Gemini South is the only MCAO facility instrument at an 8m telescope. Using real data and for the first time, we investigate the gain in depth and S/N when MCAO is employed for $K_{\rm s}$-band observations of distant galaxies. Our analysis is based on the Frontier Fields… ▽ More Multi-conjugated adaptive optics (MCAO) yield nearly diffraction-limited images at 2$μ$m wavelengths. Currently, GeMS/GSAOI at Gemini South is the only MCAO facility instrument at an 8m telescope. Using real data and for the first time, we investigate the gain in depth and S/N when MCAO is employed for $K_{\rm s}$-band observations of distant galaxies. Our analysis is based on the Frontier Fields cluster MACS J0416.1-2403, observed with GeMS/GSAOI (near diffraction-limited) and compared against VLT/HAWK-I (natural seeing) data. Using galaxy number counts, we show that the substantially increased thermal background and lower optical throughput of the MCAO unit are fully compensated for by the wavefront correction, because the galaxy images can be measured in smaller apertures with less sky noise. We also performed a direct comparison of the signal-to-noise ratios (S/N) of sources detected in both data sets. For objects with intrinsic angular sizes corresponding to half the HAWK-I image seeing, the gain in S/N is 40 per cent. Even smaller objects experience a boost in S/N by a up to a factor of 2.5 despite our suboptimal natural guide star configuration. The depth of the near diffraction limited images is more difficult to quantify than that of seeing limited images, due to a strong dependence on the intrinsic source profiles. Our results emphasize the importance of cooled MCAO systems for $K_{\rm s}$-band observations with future, extremely large telescopes. △ Less

Submitted 3 August, 2017; originally announced August 2017.

Comments: 7 pages, 7 figures. Accepted for publication in MNRAS

Journal ref: 2017 MNRAS, 472, 217

Temporal Analysis of Influence to Predict Users' Adoption in Online Social Networks

Authors: Ericsson Marin, Ruocheng Guo, Paulo Shakarian

Abstract: Different measures have been proposed to predict whether individuals will adopt a new behavior in online social networks, given the influence produced by their neighbors. In this paper, we show one can achieve significant improvement over these standard measures, extending them to consider a pair of time constraints. These constraints provide a better proxy for social influence, showing a stronger… ▽ More Different measures have been proposed to predict whether individuals will adopt a new behavior in online social networks, given the influence produced by their neighbors. In this paper, we show one can achieve significant improvement over these standard measures, extending them to consider a pair of time constraints. These constraints provide a better proxy for social influence, showing a stronger correlation to the probability of influence as well as the ability to predict influence. △ Less

Submitted 5 May, 2017; originally announced May 2017.

Comments: 6 pages, 2 figures, 2017 International Conference on Social Computing, Behavioral-Cultural Modeling & Prediction and Behavior Representation in Modeling and Simulation (SBP-BRiMS 2017). July 5 - 8, 2017

Electrostatic Performance of InSb, GaSb, Si and Ge p-channel Nanowires

Authors: Celso Martinez-Blanque, Enrique G. Marin, Alejandro Toral, Jose M. Gonzalez-Medina, Francisco G. Ruiz, Andres Godoy, Francisco Gamiz

Abstract: The electrostatic performance of p-type nanowires (NWs) made of InSb and GaSb, with special focus on their gate capacitance behavior, is analyzed and compared to that achieved by traditional semiconductors usually employed for p-MOS such as Si and Ge. To do so, a self-consistent kp simulator has been implemented to achieve an accurate description of the Valence Band and evaluate the charge behavio… ▽ More The electrostatic performance of p-type nanowires (NWs) made of InSb and GaSb, with special focus on their gate capacitance behavior, is analyzed and compared to that achieved by traditional semiconductors usually employed for p-MOS such as Si and Ge. To do so, a self-consistent kp simulator has been implemented to achieve an accurate description of the Valence Band and evaluate the charge behavior as a function of the applied gate bias. The contribution and role of the constituent capacitances, namely the insulator, centroid and quantum ones are assessed. It is demonstrated that the centroid and quantum capacitances are strongly dependent on the semiconductor material. We find a good inherent electrostatic performance of GaSb and InSb NWs, comparable to their Ge and Si counterparts making these III-Sb compounds good candidates for future technological nodes. △ Less

Submitted 25 April, 2017; originally announced April 2017.