-
Variational Inference Using a Differentiable Multigrid Linear Solver
Authors:
Andrés Ramírez,
Philipp Haim,
David Föger,
Torsten A. Enßlin,
Philipp Frank,
Philipp Gschwandtner,
Dominik Jüstel,
Philipp Mertsch,
Vo Hong Minh Phan,
Laurin Söding,
Hanieh Zandinejad,
Ralf Kissmann
Abstract:
Gradient-based Bayesian inference methods require efficient access to Jacobian and adjoint-Jacobian operators of high-dimensional forward models. While multigrid solvers provide near-optimal complexity for elliptic partial differential equations, they are rarely available in forms compatible with automatic differentiation (AD). We develop a differentiable multigrid solver for steady-state diffusio…
▽ More
Gradient-based Bayesian inference methods require efficient access to Jacobian and adjoint-Jacobian operators of high-dimensional forward models. While multigrid solvers provide near-optimal complexity for elliptic partial differential equations, they are rarely available in forms compatible with automatic differentiation (AD). We develop a differentiable multigrid solver for steady-state diffusion-absorption problems and derive its adjoint operations analytically through the full multigrid hierarchy. The resulting solver, DMGS, is implemented in C++ and interfaced with JAX to provide efficient Jacobian-vector and vector-Jacobian products for variational inference in the NIFTy framework. We validate the approach on a 3D inverse problem involving diffuse radiative transfer in tissue, reconstructing an effective radiative source from Monte Carlo-simulated data. The reconstruction reproduces the data at a reduced chi-squared of 1.1 and generalizes to 32 independent validation datasets. Benchmarks against a JAX-native multigrid implementation show comparable runtimes and consistently lower peak memory for the hand-derived adjoint, with modest reverse-mode overhead. These results establish differentiable multigrid solvers as practical building blocks for variational inference in PDE-constrained problems.
△ Less
Submitted 1 August, 2026;
originally announced August 2026.
-
Non-Hermitian corner skin effect in a two-dimensional photonic crystal
Authors:
Huyen Thanh Phan,
Katsunori Wakabayashi
Abstract:
We numerically study topological effects of electromagnetic (EM) waves
in a two-dimensional (2D) non-Hermitian photonic crystal (PhC) composed
of lossy magneto-optical materials. In this system, not only the EM
wavefunctions but also the complex eigenfrequencies exhibit nontrivial
topological properties. We demonstrate that the non-Hermitian skin
effect, protected by point gaps in the co…
▽ More
We numerically study topological effects of electromagnetic (EM) waves
in a two-dimensional (2D) non-Hermitian photonic crystal (PhC) composed
of lossy magneto-optical materials. In this system, not only the EM
wavefunctions but also the complex eigenfrequencies exhibit nontrivial
topological properties. We demonstrate that the non-Hermitian skin
effect, protected by point gaps in the complex eigenfrequency spectrum,
emerges at both the edges and corners of truncated structures. This
phenomenon has no counterpart in Hermitian systems. In addition, we identify non-Hermitian topological edge states
originating from the nontrivial topology of the bulk bands. While most
previous studies of non-Hermitian topology have focused on
tight-binding models, our work addresses a continuous photonic system,
providing a more realistic platform and offering a concrete route
toward experimental realization of non-Hermitian effects.
△ Less
Submitted 25 April, 2026;
originally announced April 2026.
-
Amides from the carbonaceous asteroid (162173) Ryugu: nanoscale spectral and isotopic characterizations
Authors:
L. G. Vacher,
V. T. H. Phan,
L. Bonal,
M. Iskakova,
O. Poch,
P. Beck,
E. Quirico,
R. C. Ogliore
Abstract:
C-type asteroids, such as asteroid (162173) Ryugu, may have played a key role in delivering light elements to early Earth. Nitrogen (N)-bearing molecules have been chemically identified in some Ryugu grains, and based on the faint 3.06 um absorption band observed by the hyperspectral microscope MicrOmega, NH-bearing compounds appear to be globally distributed. However, the chemical forms of these…
▽ More
C-type asteroids, such as asteroid (162173) Ryugu, may have played a key role in delivering light elements to early Earth. Nitrogen (N)-bearing molecules have been chemically identified in some Ryugu grains, and based on the faint 3.06 um absorption band observed by the hyperspectral microscope MicrOmega, NH-bearing compounds appear to be globally distributed. However, the chemical forms of these NH-bearing compounds - whether organic molecules, ammonium (NH4+) salts, NH4+- or NH-organic-bearing phyllosilicates, or other forms - remain to be clarified. We report the characterization of two Ryugu particles (C0050 and C0052) using infrared spectroscopy at millimeter, micrometer, and nanometer scales, combined with NanoSIMS to constrain the nature and origin of NH-bearing components. Ryugu's C0052 particle contains rare (~1 vol.%) micrometer-sized NH-rich organic compounds with peaks at 1660 cm-1 (C=O stretching, amide I) and 1550 cm-1 (N-H bending, amide II), indicative of amides, absent in C0050. N isotopic analysis shows these amides are depleted in 15N (d15N ~ -200 permil), confirming their indigenous origin. The amides may have formed by hydrothermal alteration of carboxylic acids and amines on Ryugu's parent body or by irradiation of 15N-depleted N-bearing ice in the outer Solar System or interstellar medium. Such amides delivered by primitive small bodies may have contributed to prebiotic chemistry on early Earth.
△ Less
Submitted 29 October, 2025; v1 submitted 14 March, 2025;
originally announced March 2025.
-
Wilson Loop and Topological Properties in 3D Woodpile Photonic Crystal
Authors:
Huyen Thanh Phan,
Shun Takahashi,
Satoshi Iwamoto,
Katsunori Wakabayashi
Abstract:
We numerically study the first and the second order topological states of electromagnetic (EM) wave in the three-dimensional (3D) woodpile photonic crystal (PhC). The recent studies on 3D PhCs have mainly focused on the observation of the topological states. Here, we not only focus on finding the topological states but also propose a numerical calculation method for topological invariants, which i…
▽ More
We numerically study the first and the second order topological states of electromagnetic (EM) wave in the three-dimensional (3D) woodpile photonic crystal (PhC). The recent studies on 3D PhCs have mainly focused on the observation of the topological states. Here, we not only focus on finding the topological states but also propose a numerical calculation method for topological invariants, which is based on the Wilson loop. For the 3D woodpile PhC, the topological states emerge due to the finite difference in the winding number or partial Chern number. The selection rule for the emergence of topological hinge states is also pointed out based on the topological invariants. Our numerical calculation results are essential and put a step toward the experimental realization of topological waveguide in 3D PhCs.
△ Less
Submitted 15 December, 2024;
originally announced December 2024.
-
Passive wing deployment and retraction in beetles and flapping microrobots
Authors:
Hoang-Vu Phan,
Hoon Cheol Park,
Dario Floreano
Abstract:
Birds, bats and many insects can tuck their wings against their bodies at rest and deploy them to power flight. Whereas birds and bats use well-developed pectoral and wing muscles and tendons, how insects control these movements remains unclear, as mechanisms of wing deployment and retraction vary among insect species. Beetles (Coleoptera) display one of the most complex wing mechanisms. For examp…
▽ More
Birds, bats and many insects can tuck their wings against their bodies at rest and deploy them to power flight. Whereas birds and bats use well-developed pectoral and wing muscles and tendons, how insects control these movements remains unclear, as mechanisms of wing deployment and retraction vary among insect species. Beetles (Coleoptera) display one of the most complex wing mechanisms. For example, in rhinoceros beetles, the wing deployment initiates by fully opening the elytra and partially releasing the hindwings from the abdomen. Subsequently, the beetle starts flapping, elevates the hindwings at the bases, and unfolds the wingtips in an origami-like fashion. Whilst the origami-like fold have been extensively explored, limited attention has been given to the hindwing base deployment and retraction, which are believed to be driven by thoracic muscles. Using high-speed cameras and robotic flapping-wing models, here we demonstrate that rhinoceros beetles can effortlessly elevate the hindwings to flight position without the need for muscular activity. We show that opening the elytra triggers a spring-like partial release of the hindwings from the body, allowing the clearance needed for subsequent flapping motion that brings the hindwings into flight position. The results also show that after flight, beetles can leverage the elytra to push the hindwings back into the resting position, further strengthening the hypothesis of a passive deployment mechanism. Finally, we validate the hypothesis with a flapping microrobot that passively deploys its wings for stable controlled flight and retracts them neatly upon landing, which offers a simple yet effective approach to the design of insect-like flying micromachines.
△ Less
Submitted 25 July, 2024;
originally announced July 2024.
-
Topological Edge and Corner States in Biphenylene Photonic Crystal
Authors:
Huyen Thanh Phan,
Keiki Koizumi,
Feng Liu,
Katsunori Wakabayashi
Abstract:
The biphenylene network (BPN) has a unique two-dimensional atomic structure, where hexagonal unit cells are arranged on a square lattice. Inspired by such a BPN structure, we design a counterpart in the fashion of photonic crystals (PhCs), which we refer to as the BPN PhC. We study the photonic band structure using the finite element method and characterize the topological properties of the BPN Ph…
▽ More
The biphenylene network (BPN) has a unique two-dimensional atomic structure, where hexagonal unit cells are arranged on a square lattice. Inspired by such a BPN structure, we design a counterpart in the fashion of photonic crystals (PhCs), which we refer to as the BPN PhC. We study the photonic band structure using the finite element method and characterize the topological properties of the BPN PhC through the use of the Wilson loop. Our findings reveal the emergence of topological edge states in the BPN PhC, specifically in the zigzag edge and the chiral edge, as a consequence of the nontrivial Zak phase in the corresponding directions. In addition, we find the localization of electromagnetic waves at the corners formed by the chiral edges, which can be considered as second-order topological states, i.e., topological corner states.
△ Less
Submitted 28 December, 2023;
originally announced December 2023.
-
Microwave hinge states in a simple-cubic-lattice photonic crystal insulator
Authors:
Shun Takahashi,
Yuya Ashida,
Huyen Thanh Phan,
Kenichi Yamashita,
Tetsuya Ueda,
Katsunori Wakabayashi,
Satoshi Iwamoto
Abstract:
We numerically and experimentally demonstrated a higher-order topological state in a three-dimensional (3D) photonic crystal (PhC) with a complete photonic bandgap. Two types of cubic lattices were designed with different topological invariants, which were theoretically and numerically confirmed by the finite difference of their Zak phases. Topological boundary states in the two-dimensional interf…
▽ More
We numerically and experimentally demonstrated a higher-order topological state in a three-dimensional (3D) photonic crystal (PhC) with a complete photonic bandgap. Two types of cubic lattices were designed with different topological invariants, which were theoretically and numerically confirmed by the finite difference of their Zak phases. Topological boundary states in the two-dimensional interfaces and hinge states in the one-dimensional corners were formed according to the higher-order of bulk-boundary correspondence. Microwave measurements of the fabricated 3D PhC containing two boundaries and one corner showed a localized intensity, which confirmed the boundary and hinge states.
△ Less
Submitted 23 June, 2023;
originally announced July 2023.
-
Making Atomic-Level Magnetism Tunable with Light at Room Temperature
Authors:
V. O. Jimenez,
Y. T. H. Pham,
D. Zhou,
M. Z. Liu,
F. A. Nugera,
V. Kalappattil,
T. Eggers,
K. Hoang,
D. L. Duong,
M. Terrones,
H. R. Gutierrez,
M. H. Phan
Abstract:
The capacity to manipulate magnetization in two-dimensional dilute magnetic semiconductors (2D-DMSs) using light, specifically in magnetically doped transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe, Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in spintronics, spin-caloritronics, valleytronics, and quantum computation. This Perspective paper explo…
▽ More
The capacity to manipulate magnetization in two-dimensional dilute magnetic semiconductors (2D-DMSs) using light, specifically in magnetically doped transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe, Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in spintronics, spin-caloritronics, valleytronics, and quantum computation. This Perspective paper explores the mediation of magnetization by light under ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC resonance (MLCR) experiments with density functional theory (DFT) calculations, we show that the magnetization can be enhanced using light in V-doped TMD monolayers (e.g., V-WS2, V-WSe2, V-MoS2). This phenomenon is attributed to excess holes in the conduction and valence bands, as well as carriers trapped in magnetic doping states, which together mediate the magnetization of the semiconducting layer. In 2D-TMD heterostructures such as VSe2/WS2 and VSe2/MoS2, we demonstrate the significance of proximity, charge-transfer, and confinement effects in amplifying light-mediated magnetism. This effect is attributed to photon absorption at the TMD layer (e.g., WS2, MoS2) that generates electron-hole pairs mediating the magnetization of the heterostructure. These findings will encourage further research in the field of 2D magnetism and establish a novel direction for designing 2D-TMDs and heterostructures with optically tunable magnetic functionalities, paving the way for next-generation magneto-optic nanodevices.
△ Less
Submitted 1 May, 2023;
originally announced May 2023.
-
Nanoscale mineralogy and organic structure in Orgueil (CI) and EET 92042 (CR) carbonaceous chondrites studied with AFM-IR spectroscopy
Authors:
Van T. H. Phan,
Rolando Rebois,
Pierre Beck,
Eric Quirico,
Lydie Bonal,
Takaaki Noguchi
Abstract:
Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-micron scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables to probe of vibrations at the molecule-atomic scale of organic and inorganic comp…
▽ More
Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-micron scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables to probe of vibrations at the molecule-atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-IR spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (Hydrogen Fluoride/Hydrochloric) extraction on the nature of refractory organics (Insoluble Organic Matter, IOM) and provide insights on the mineralogy of meteorites matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions.
△ Less
Submitted 20 June, 2022;
originally announced June 2022.
-
Emergence of Intergranular Tunneling Dominated Negative Magnetoresistance in Helimagnetic Manganese Phosphide Nanorod Thin Films
Authors:
B. Muchharla,
R. P. Madhogaria,
D. DeTellem,
C. M. Hung,
A. Chanda,
A. T. Duong,
P. T. Huy,
M. T. Trinh,
S. Cho,
S. Witanachchi,
M. H. Phan
Abstract:
Helical magnets are emerging as a novel class of materials for spintronics and sensor applications; however, research on their charge and spin transport properties in a thin film form is less explored. Herein, we report the temperature and magnetic field dependent charge transport properties of a highly crystalline MnP nanorod thin film over a wide temperature range (2-350 K). The MnP nanorod film…
▽ More
Helical magnets are emerging as a novel class of materials for spintronics and sensor applications; however, research on their charge and spin transport properties in a thin film form is less explored. Herein, we report the temperature and magnetic field dependent charge transport properties of a highly crystalline MnP nanorod thin film over a wide temperature range (2-350 K). The MnP nanorod films of 100 nm thickness were grown on Si substrates at 500 oC using molecular beam epitaxy. The temperature dependent resistivity data exhibits a metallic behavior over the entire measured temperature range. However, large negative magnetoresistance of up to 12% is observed below 50 K at which the system enters a stable helical (screw) magnetic state. In this temperature regime, the MR(H,T) dependence seems to show a magnetic field manipulated phase coexistence. The observed magnetoresistance is dominantly governed by the intergranular spin dependent tunneling mechanism. These findings pinpoint a correlation between the transport and magnetism in this helimagnetic system.
△ Less
Submitted 16 February, 2022;
originally announced February 2022.
-
Valley-dependent Corner States in Honeycomb Photonic Crystal without Inversion Symmetry
Authors:
Huyen Thanh Phan,
Feng Liu,
Katsunori Wakabayashi
Abstract:
We study topological states of honeycomb photonic crystals in absence of inversion symmetry using plane wave expansion and finite element methods. The breaking of inversion symmetry in honeycomb lattice leads to contrasting topological valley indices, i.e., the valley-dependent Chern numbers in momentum space. We find that the topological corner states appear for 60$^\circ$ degree corners, but abs…
▽ More
We study topological states of honeycomb photonic crystals in absence of inversion symmetry using plane wave expansion and finite element methods. The breaking of inversion symmetry in honeycomb lattice leads to contrasting topological valley indices, i.e., the valley-dependent Chern numbers in momentum space. We find that the topological corner states appear for 60$^\circ$ degree corners, but absent for other corners, which can be understood as the sign flip of valley Chern number at the corner. Our results provide an experimentally feasible platform for exploring valley-dependent higher-order topology in photonic systems.
△ Less
Submitted 27 May, 2021;
originally announced May 2021.
-
Table-like magnetocaloric effect and enhanced refrigerant capacity in EuO1-δ thin films
Authors:
P. Lampen,
R. Madhogaria,
N. S. Bingham,
M. H. Phan,
P. M. S. Monteiro,
N. -J. Steinke,
A. Ionescu,
C. H. W. Barnes,
H. Srikanth
Abstract:
An approach to adjusting the conduction band population for tuning the magnetic and magnetocaloric response of EuO1-δ thin films through control of oxygen vacancies (δ = 0, 0.025, and 0.09) is presented. The films each showed a paramagnetic to ferromagnetic transition around 65 K, with an additional magnetic ordering transition at higher temperatures in the oxygen deficient samples. All transition…
▽ More
An approach to adjusting the conduction band population for tuning the magnetic and magnetocaloric response of EuO1-δ thin films through control of oxygen vacancies (δ = 0, 0.025, and 0.09) is presented. The films each showed a paramagnetic to ferromagnetic transition around 65 K, with an additional magnetic ordering transition at higher temperatures in the oxygen deficient samples. All transitions are observed to be of second order. A maximum magnetic entropy change of 6.4 J/kg K over a field change of 2 T with a refrigerant capacity of 223 J/kg was found in the sample with δ = 0, and in all cases the refrigerant capacities of the thin films under study were found to exceed that reported for bulk EuO. Adjusting the oxygen content was shown to produce table-like magnetocaloric effects, desirable for ideal Ericsson-cycle magnetic refrigeration. These films are thus excellent candidates for small-scale magnetic cooling technology in the liquid nitrogen temperature range.
△ Less
Submitted 13 April, 2021;
originally announced April 2021.
-
Optimization of the high-frequency magnetoimpedance response in melt-extracted Co-rich microwires through novel multiple-step Joule heating
Authors:
O. Thiabgoh,
T. Eggers,
C. Albrecht,
V. O. Jimenez,
H. Shen,
S. D. Jiang,
J. F. Sun,
D. S. Lam,
V. D. Lam,
M. H. Phan
Abstract:
The optimization of high frequency giant magnetoimpedance (GMI) effect and its magnetic field sensitivity in melt-extracted Co69.25Fe4.25Si13B12.5Nb1 amorphous microwires, through a multi-step Joule annealing (MSA) technique, was systematically studied. The surface morphology, microstructure, surface magnetic property, and high frequency GMI response of the Co-rich microwires were explored using s…
▽ More
The optimization of high frequency giant magnetoimpedance (GMI) effect and its magnetic field sensitivity in melt-extracted Co69.25Fe4.25Si13B12.5Nb1 amorphous microwires, through a multi-step Joule annealing (MSA) technique, was systematically studied. The surface morphology, microstructure, surface magnetic property, and high frequency GMI response of the Co-rich microwires were explored using scanning electron microscopy (SEM), magneto-optical Kerr effect (MOKE) magnetometry, transmission electron microscopy (TEM), and impedance analyzer, respectively. An initial dc current (idc) of 20 mA, which was then increased by 20 mA at every time-step (10 min) up to 300 mA, was applied to the microwires. The MSA of 20 mA to 100 mA remarkably improved the GMI ratio and its field sensitivity up to 760% (1.75 time of that of the as-prepared), and 925%/Oe (more than 17.92 times of that of the as-prepared) at an operating frequency of 20 MHz, respectively. Our study indicates that the MSA technique can enhance the microstructures and the surface magnetic domain structures of the Co-rich magnetic microwires, giving rise to the GMI enhancement. This technique is suitable for improving the GMI sensitivity at small magnetic fields, which is highly promising for biomedical sensing and healthcare monitoring.
△ Less
Submitted 2 February, 2021;
originally announced February 2021.
-
Giant Spin Seebeck Effect through an Interface Organic Semiconductor
Authors:
V. Kalappattil,
R. Geng,
R. Das,
H. Luong,
M. Pham,
T. Nguyen,
A. Popescu,
L. M. Woods,
M. Kläui,
H. Srikanth,
M. H. Phan
Abstract:
Interfacing an organic semiconductor C60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12: YIG) and a non-magnet…
▽ More
Interfacing an organic semiconductor C60 with a non-magnetic metallic thin film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at ambient temperature, while its interface with a magnetic metal (Fe or Co) can tune the anisotropic magnetic surface property of the material. Here, we demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12: YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient spin current transport via the thermally driven spin Seebeck effect (SSE). Experiments and first principles calculations consistently show that the presence of C60 reduces significantly the conductivity mismatch between YIG and Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to enhanced spin mixing conductance across YIG/C60/Pt interfaces. As a result, a 600% increase in the SSE voltage (VLSSE) has been realized in YIG/C60/Pt relative to YIG/Pt. Temperature-dependent SSE voltage measurements on YIG/C60/Pt with varying C60 layer thicknesses also show an exponential increase in VLSSE at low temperatures below 200 K, resembling the temperature evolution of spin diffusion length of C60. Our study emphasizes the important roles of the magnetic anisotropy and the spin diffusion length of the intermediate layer in the SSE in YIG/C60/Pt structures, providing a new pathway for developing novel spin-caloric materials.
△ Less
Submitted 11 May, 2019;
originally announced May 2019.
-
Strain effect in highly-doped n-type 3C-SiC-on-glass substrate for mechanical sensors and mobility enhancement
Authors:
Hoan-Phuong Phan,
Tuan-Khoa Nguyen,
Toan Dinh,
Han-Hao Cheng,
Fengwen Mu,
Alan Iacopi,
Leonie Hold,
Tadatomo Suga,
Dzung Viet Dao,
Debbie G. Senesky,
Nam-Trung Nguyen
Abstract:
This work reports the strain effect on the electrical properties of highly doped n-type single crystalline cubic silicon carbide (3C-SiC) transferred onto a 6-inch glass substrate employing an anodic bonding technique. The experimental data shows high gauge factors of -8.6 in longitudinal direction and 10.5 in transverse direction along the [100] orientation. The piezoresistive effect in the highl…
▽ More
This work reports the strain effect on the electrical properties of highly doped n-type single crystalline cubic silicon carbide (3C-SiC) transferred onto a 6-inch glass substrate employing an anodic bonding technique. The experimental data shows high gauge factors of -8.6 in longitudinal direction and 10.5 in transverse direction along the [100] orientation. The piezoresistive effect in the highly doped 3C-SiC film also exhibits an excellent linearity and consistent reproducibility after several bending cycles. The experimental result was in good agreement with the theoretical analysis based on the phenomenon of electron transfer between many valleys in the conduction band of n-type 3C-SiC. Our finding for the large gauge factor in n-type 3C- SiC coupled with the elimination of the current leak to the insulated substrate could pave the way for the development of single crystal SiC-on-glass based MEMS applications.
△ Less
Submitted 22 February, 2018;
originally announced February 2018.
-
Nano strain-amplifier: making ultra-sensitive piezoresistance in nanowires possible without the need of quantum and surface charge effects
Authors:
Hoang-Phuong Phan,
Toan Dinh,
Takahiro Kozeki,
Tuan-Khoa Nguyen,
Afzaal Qamar,
Takahiro Namazu,
Nam-Trung Nguyen,
Dzung Viet Dao
Abstract:
This paper presents an innovative nano strain-amplifier employed to significantly enhance the sensitivity of piezoresistive strain sensors. Inspired from the dogbone structure, the nano strain-amplifier consists of a nano thin frame released from the substrate, where nanowires were formed at the centre of the frame. Analytical and numerical results indicated that a nano strain-amplifier significan…
▽ More
This paper presents an innovative nano strain-amplifier employed to significantly enhance the sensitivity of piezoresistive strain sensors. Inspired from the dogbone structure, the nano strain-amplifier consists of a nano thin frame released from the substrate, where nanowires were formed at the centre of the frame. Analytical and numerical results indicated that a nano strain-amplifier significantly increases the strain induced into a free standing nanowire, resulting in a large change in their electrical conductance. The proposed structure was demonstrated in p-type cubic silicon carbide nanowires fabricated using a top down process. The experimental data showed that the nano strain-amplifier can enhance the sensitivity of SiC strain sensors at least 5.4 times larger than that of the conventional structures. This result indicates the potential of the proposed strain-amplifier for ultra-sensitive mechanical sensing applications.
△ Less
Submitted 15 July, 2016;
originally announced July 2016.
-
Flow boiling of water on nanocoated surfaces in a microchannel
Authors:
Hai Trieu Phan,
Nadia Caney,
Philippe Marty,
Stéphane Colasson,
Jérôme Gavillet
Abstract:
Experiments were performed to study the effects of surface wettability on flow boiling of water at atmospheric pressure. The test channel is a single rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was set at 100 kg/m2 s and the base heat flux varied from 30 to 80 kW/m2. Water enters the test channel under subcooled conditions. The samples are silicone oxide (SiOx), titan…
▽ More
Experiments were performed to study the effects of surface wettability on flow boiling of water at atmospheric pressure. The test channel is a single rectangular channel 0.5 mm high, 5 mm wide and 180 mm long. The mass flux was set at 100 kg/m2 s and the base heat flux varied from 30 to 80 kW/m2. Water enters the test channel under subcooled conditions. The samples are silicone oxide (SiOx), titanium (Ti), diamond-like carbon (DLC) and carbon-doped silicon oxide (SiOC) surfaces with static contact angles of 26°, 49°, 63° and 103°, respectively. The results show significant impacts of surface wettability on heat transfer coefficient.
△ Less
Submitted 27 August, 2010;
originally announced August 2010.