Showing 1–13 of 13 results for author: Huff, T

Towards Atom-by-Atom Fabrication: Mechanosynthetic donation and abstraction

Authors: Brandon Blue, Mathieu Morin, Alex Inayeh, Rosemary Cranston, Cameron J. Mackie, Marc Savoie, Adam Bottomley, Christian J. Imperiale, Zehra Ahmed, Rafik Addou, Aly Asani, Eduardo Barrera-Ramirez, Jeremy Barton, Doreen Cheng, Megan Cowie, Chris Deimert, Tyler Enright, James Zhangming Fan, Robert A. Freitas Jr, Alan T. K. Godfrey, Ryan Groome, Si Yue Guo, Kareem A. Clarcia, Aru Hill, Taleana Huff , et al. (33 additional authors not shown)

Abstract: Enabled by inverted-mode scanning tunneling microscopy (IM-STM) and the use of functionalized molecular tools, we demonstrate positionally-controlled mechanosynthetic addition (donation) of carbon and subtraction (abstraction) of silicon atoms on a model build site: atomically clean and crystalline Si(100). The resulting structures represent the first demonstrations of an emerging ability to manip… ▽ More Enabled by inverted-mode scanning tunneling microscopy (IM-STM) and the use of functionalized molecular tools, we demonstrate positionally-controlled mechanosynthetic addition (donation) of carbon and subtraction (abstraction) of silicon atoms on a model build site: atomically clean and crystalline Si(100). The resulting structures represent the first demonstrations of an emerging ability to manipulate radical chemistry with positional control of specific atoms and moieties in 3D. Furthermore, by comparing the behavior of molecular tools designed for atomic donation versus abstraction, we highlight general principles governing molecular tool design for selective and reliable mechanosynthetic functionality. △ Less

Submitted 11 June, 2026; originally announced June 2026.

Comments: 17 pages, 5 figures. Supplementary Information is available upon request

Atomically precise mechanosynthesis of carbon structures on hydrogenated Si(100) by inverted-mode STM

Authors: Megan Cowie, Chris Deimert, Ryan Groome, Alex Inayeh, Robert J. Kirby, Cameron J. Mackie, Jonathan Myall, Sam Rohe, Luis Sandoval, Khalil Sayed-Akhmad, Bheeshmon Thanabalasingam, Reid Wotton, Rafik Addou, Aly Asani, Brandon Blue, Adam Bottomley, Kareem A. Clarcia, Tyler Enright, James Zhangming Fan, Robert A. Freitas Jr., Alan T. K. Godfrey, Si Yue Guo, Aru Hill, Taleana Huff, Mark Jobes , et al. (22 additional authors not shown)

Abstract: The ability to build atomically precise structures on surfaces with complete control over both atomic placement and chemical bonding remains a central challenge in nanoscale fabrication. Here, we demonstrate simultaneous spatial and chemical control over the mechanosynthetic fabrication of carbon structures. Using inverted-mode STM, C$_2$ units are donated from surface-deposited molecules to pre-p… ▽ More The ability to build atomically precise structures on surfaces with complete control over both atomic placement and chemical bonding remains a central challenge in nanoscale fabrication. Here, we demonstrate simultaneous spatial and chemical control over the mechanosynthetic fabrication of carbon structures. Using inverted-mode STM, C$_2$ units are donated from surface-deposited molecules to pre-patterned reactive sites on a hydrogen-passivated Si(100) surface. We demonstrate single-site C$_2$ donation, spatially patterned multi-site C$_2$ donation, and the stepwise assembly of polyyne structures through successive C-C bond formation. Together, these results establish controlled mechanosynthetic donation as a foundational capability for programmable atomically precise fabrication. △ Less

Submitted 26 May, 2026; originally announced May 2026.

Comments: Supplementary Information is available upon request

Inverted-Mode Scanning Tunneling Microscopy for Atomically Precise Fabrication

Authors: Eduardo Barrera, Bheeshmon Thanabalasingam, Rafik Addou, Damian Allis, Aly Asani, Jeremy Barton, Tomass Bernots, Brandon Blue, Adam Bottomley, Doreen Cheng, Byoung Choi, Megan Cowie, Chris Deimert, Michael Drew, Mathieu Durand, Tyler Enright, Robert A. Freitas Jr., Alan Godfrey, Ryan Groome, Si Yue Guo, Sheldon Haird, Aru Hill, Taleana Huff, Christian Imperiale, Alex Inayeh , et al. (35 additional authors not shown)

Abstract: Scanning Tunneling Microscopy (STM) enables fabrication of atomically precise structures with unique properties and growing technological potential. However, reproducible manipulation of covalently bonded atoms requires control over the atomic configuration of both sample and probe - a longstanding challenge in STM. Here, we introduce inverted-mode STM, an approach that enables mechanically contro… ▽ More Scanning Tunneling Microscopy (STM) enables fabrication of atomically precise structures with unique properties and growing technological potential. However, reproducible manipulation of covalently bonded atoms requires control over the atomic configuration of both sample and probe - a longstanding challenge in STM. Here, we introduce inverted-mode STM, an approach that enables mechanically controlled chemical reactions for atomically precise fabrication. Tailored molecules on a Si(100) surface image the probe apex, and the usual challenge of understanding the probe structure is effectively solved. The molecules can also react with the probe, with the two sides of the tunnel junction acting as reagents positioned with sub-angstrom precision. This allows abstraction or donation of atoms from or to the probe apex. We demonstrate this by using a novel alkynyl-terminated molecule to reproducibly abstract hydrogen atoms from the probe. The approach is expected to extend to other elements and moieties, opening a new avenue for scalable atomically precise fabrication. △ Less

Submitted 30 December, 2025; originally announced December 2025.

Molecular Tools for Non-Planar Surface Chemistry

Authors: Taleana Huff, Brandon Blue, Terry McCallum, Mathieu Morin, Damian G. Allis, Rafik Addou, Jeremy Barton, Adam Bottomley, Doreen Cheng, Nina M. Ćulum, Michael Drew, Tyler Enright, Alan T. K. Godfrey, Ryan Groome, Aru J. Hill, Alex Inayeh, Matthew R. Kennedy, Robert J. Kirby, Mykhaylo Krykunov, Sam Lilak, Hadiya Ma, Cameron J. Mackie, Oliver MacLean, Jonathan Myall, Ryan Plumadore , et al. (8 additional authors not shown)

Abstract: Scanning probe microscopy (SPM) investigations of on-surface chemistry on passivated silicon have only shown in-plane chemical reactions, and studies on bare silicon are limited in facilitating additional reactions post-molecular-attachment. Here, we enable subsequent reactions on Si(100) through selectively adsorbing 3D, silicon-specific "molecular tools". Following an activation step, the molecu… ▽ More Scanning probe microscopy (SPM) investigations of on-surface chemistry on passivated silicon have only shown in-plane chemical reactions, and studies on bare silicon are limited in facilitating additional reactions post-molecular-attachment. Here, we enable subsequent reactions on Si(100) through selectively adsorbing 3D, silicon-specific "molecular tools". Following an activation step, the molecules present an out-of-plane radical that can function both to donate or accept molecular fragments, thereby enabling applications across multiple scales, e.g., macroscale customizable silicon-carbon coatings or nanoscale tip-mediated mechanosynthesis. Creation of many such molecular tools is enabled by broad molecular design criteria that facilitate reproducibility, surface specificity, and experimental verifiability. These criteria are demonstrated using a model molecular tool tetrakis(iodomethyl)germane ($Ge(CH_{2}I)_{4}$; TIMe-Ge), with experimental validation by SPM and X-ray photoelectron spectroscopy (XPS), and theoretical support by density functional theory (DFT) investigations. With this framework, a broad and diverse range of new molecular engineering capabilities are enabled on silicon. △ Less

Submitted 22 August, 2025; originally announced August 2025.

Comments: Manuscript is pages 1-37, 4 Figures. Supplementary Information is pages 38-86, with 24 Figures

Ionic Charge Distributions in Silicon Atomic Wires

Authors: Jeremiah Croshaw, Taleana Huff, Mohamad Rashidi, John Wood, Erika Lloyd, Jason Pitters, Robert Wolkow

Abstract: Using a non-contact atomic force microscope (nc-AFM), we examine continuous DB wire structures on the hydrogen-terminated silicon (100) 2x1 surface. By probing the DB structures at varying energies, we identify the formation of previously unobserved ionic charge distributions correlated to the net charge of DB wires and their predicted lattice distortion. Performing spectroscopic analysis, we iden… ▽ More Using a non-contact atomic force microscope (nc-AFM), we examine continuous DB wire structures on the hydrogen-terminated silicon (100) 2x1 surface. By probing the DB structures at varying energies, we identify the formation of previously unobserved ionic charge distributions correlated to the net charge of DB wires and their predicted lattice distortion. Performing spectroscopic analysis, we identify higher energy configurations corresponding to alternative lattice distortions as well as tip-induced charging effects. By varying the length and orientation of these DB structures, we further highlight key features in the formation of these ionic surface phases. △ Less

Submitted 16 November, 2020; originally announced November 2020.

Atomic defects of the hydrogen-terminated Silicon(100)-2x1 surface imaged with STM and nc-AFM

Authors: Jeremiah Croshaw, Thomas Dienel, Taleana Huff, Robert A. Wolkow

Abstract: The hydrogen-terminated Silicon(100)-2x1 surface (H-Si(100)-2x1) provides a promising platform for the development of atom scale devices, with recent work showing their creation through precise desorption of surface hydrogen atoms. While samples with relatively large areas of the hydrogen terminated 2x1 surface are routinely created using an in-situ methodology, surface defects are inevitably form… ▽ More The hydrogen-terminated Silicon(100)-2x1 surface (H-Si(100)-2x1) provides a promising platform for the development of atom scale devices, with recent work showing their creation through precise desorption of surface hydrogen atoms. While samples with relatively large areas of the hydrogen terminated 2x1 surface are routinely created using an in-situ methodology, surface defects are inevitably formed as well reducing the area available for patterning. Here, we present a catalog of several commonly found defects of the H-Si(100)-2x1 surface. By using a combination of scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM), we are able to extract useful information regarding the atomic and electronic structure of these defects. This allowed for the confirmation of literature assignments of several commonly found defects, as well as proposed classification of previously unreported and unassigned defects. By better understanding the structure and origin of these defects, we make the first steps toward enabling the creation of superior surfaces ultimately leading to more consistent and reliable fabrication of atom scale devices. △ Less

Submitted 21 February, 2020; originally announced February 2020.

Journal ref: Beilstein J. Nanotechnol. 2020, 11, 1346-1360

Detecting and Directing Single Molecule Binding Events on H-Si(100) with Application to Ultra-dense Data Storage

Authors: Roshan Achal, Mohammad Rashidi, Jeremiah Croshaw, Taleana Huff, Robert A. Wolkow

Abstract: Many new material systems are being explored to enable smaller, more capable and energy efficient devices. These bottom up approaches for atomic and molecular electronics, quantum computation, and data storage all rely on a well-developed understanding of materials at the atomic scale. Here, we report a versatile scanning tunneling microscope (STM) charge characterization technique, which reduces… ▽ More Many new material systems are being explored to enable smaller, more capable and energy efficient devices. These bottom up approaches for atomic and molecular electronics, quantum computation, and data storage all rely on a well-developed understanding of materials at the atomic scale. Here, we report a versatile scanning tunneling microscope (STM) charge characterization technique, which reduces the influence of the typically perturbative STM tip field, to develop this understanding even further. Using this technique, we can now observe single molecule binding events to atomically defined reactive sites (fabricated on a hydrogen-terminated silicon surface) through electronic detection. We then developed a new error correction tool for automated hydrogen lithography, directing molecular hydrogen binding events using these sites to precisely repassivate surface dangling bonds (without the use of a scanned probe). We additionally incorporated this molecular repassivation technique as the primary rewriting mechanism in new ultra-dense atomic data storage designs (0.88 petabits per in$^{2}$). △ Less

Submitted 5 September, 2019; v1 submitted 7 July, 2019; originally announced July 2019.

Electrostatic Landscape of a H-Silicon Surface Probed by a Moveable Quantum Dot

Authors: Taleana Huff, Thomas Dienel, Mohammad Rashidi, Roshan Achal, Lucian Livadaru, Jeremiah Croshaw, Robert A. Wolkow

Abstract: With nanoelectronics reaching the limit of atom-sized devices, it has become critical to examine how irregularities in the local environment can affect device functionality. Here, we characterize the influence of charged atomic species on the electrostatic potential of a semiconductor surface at the sub-nanometer scale. Using non-contact atomic force microscopy, two-dimensional maps of the contact… ▽ More With nanoelectronics reaching the limit of atom-sized devices, it has become critical to examine how irregularities in the local environment can affect device functionality. Here, we characterize the influence of charged atomic species on the electrostatic potential of a semiconductor surface at the sub-nanometer scale. Using non-contact atomic force microscopy, two-dimensional maps of the contact potential difference are used to show the spatially varying electrostatic potential on the (100) surface of hydrogen-terminated highly-doped silicon. Three types of charged species, one on the surface and two within the bulk, are examined. An electric field sensitive spectroscopic signature of a single probe atom reports on nearby charged species. The identity of one of the near-surface species has been uncertain. That species, suspected of being boron or perhaps a negatively charged donor species, we suggest is of a character more consistent with either a negatively charged interstitial hydrogen or a hydrogen vacancy complex. △ Less

Submitted 17 June, 2019; v1 submitted 28 February, 2019; originally announced February 2019.

Journal ref: ACS Nano 13(9), 10566-10575 (2019)

Resolving and Tuning Carrier Capture Rates at a Single Silicon Atom Gap State

Authors: Mohammad Rashidi, Erika Lloyd, Taleana R. Huff, Roshan Achal, Marco Taucer, Jeremiah J. Croshaw, Robert A. Wolkow

Abstract: We report on tuning the carrier capture events at a single dangling bond (DB) midgap state by varying the substrate temperature, doping type, and doping concentration. All-electronic time-resolved scanning tunneling microscopy (TR-STM) is employed to directly measure the carrier capture rates on the nanosecond time scale. A characteristic negative differential resistance (NDR) feature is evident i… ▽ More We report on tuning the carrier capture events at a single dangling bond (DB) midgap state by varying the substrate temperature, doping type, and doping concentration. All-electronic time-resolved scanning tunneling microscopy (TR-STM) is employed to directly measure the carrier capture rates on the nanosecond time scale. A characteristic negative differential resistance (NDR) feature is evident in the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of DBs on both n and p-type doped samples. It is found that a common model accounts for both observations. Atom-specific Kelvin probe force microscopy (KPFM) measurements confirm the energetic position of the DB's charge transition levels, corroborating STS studies. It is shown that under different tip-induced fields the DB can be supplied from two distinct reservoirs: the bulk conduction band and/or the valence band. We measure the filling and emptying rates of the DBs in the energy regime where electrons are supplied by the bulk valence band. By adding point charges in the vicinity of a DB, Coulombic interactions are shown to shift observed STS and NDR features. △ Less

Submitted 1 November, 2017; originally announced November 2017.

Initiating and monitoring the evolution of single electrons within atom-defined structures

Authors: Mohammad Rashidi, Wyatt Vine, Thomas Dienel, Lucian Livadaru, Jacob Retallick, Taleana Huff, Konrad Walus, Robert Wolkow

Abstract: Using a non-contact atomic force microscope we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds (DBs) on the hydrogen terminated silicon surface. By varying the probe-sample separation we mechanically manipulate the equilibrium position of individual surface silicon atoms and use this to directly switch the charge state of i… ▽ More Using a non-contact atomic force microscope we track and manipulate the position of single electrons confined to atomic structures engineered from silicon dangling bonds (DBs) on the hydrogen terminated silicon surface. By varying the probe-sample separation we mechanically manipulate the equilibrium position of individual surface silicon atoms and use this to directly switch the charge state of individual DBs. Because this mechanism is based on short range interactions and can be performed without applied bias voltage, we maintain both site-specific selectivity and single-electron control. We extract the short range forces involved with this mechanism by subtracting the long range forces acquired on a dimer vacancy site. As a result of relaxation of the silicon lattice to accommodate negatively charged DBs we observe charge configurations of DB structures that remain stable for many seconds at 4.5 K. Subsequently we use charge manipulation to directly prepare the ground state and metastable charge configurations of DB structures composed of up to six atoms. △ Less

Submitted 29 May, 2018; v1 submitted 28 September, 2017; originally announced September 2017.

Journal ref: Phys. Rev. Lett. 121, 166801 (2018)

Binary Atomic Silicon Logic

Authors: Taleana Huff, Hatem Labidi, Mohammad Rashidi, Roshan Achal, Lucian Livadaru, Thomas Dienel, Jason Pitters, Robert A. Wolkow

Abstract: It has long been anticipated that the ultimate in miniature circuitry will be crafted of single atoms. Despite many advances made in scanned probe microscopy studies of molecules and atoms on surfaces, challenges with patterning and limited thermal stability have remained. Here we make progress toward those challenges and demonstrate rudimentary circuit elements through the patterning of dangling… ▽ More It has long been anticipated that the ultimate in miniature circuitry will be crafted of single atoms. Despite many advances made in scanned probe microscopy studies of molecules and atoms on surfaces, challenges with patterning and limited thermal stability have remained. Here we make progress toward those challenges and demonstrate rudimentary circuit elements through the patterning of dangling bonds on a hydrogen terminated silicon surface. Dangling bonds sequester electrons both spatially and energetically in the bulk band gap, circumventing short circuiting by the substrate. We deploy paired dangling bonds occupied by one movable electron to form a binary electronic building block. Inspired by earlier quantum dot-based approaches, binary information is encoded in the electron position allowing demonstration of a binary wire and an OR gate. △ Less

Submitted 19 June, 2018; v1 submitted 22 June, 2017; originally announced June 2017.

Journal ref: Nature Electronics 1(12), 636-643 (2018)

Atomic White-Out: Enabling Atomic Circuitry Through Mechanically Induced Bonding of Single Hydrogen Atoms to a Silicon Surface

Authors: Taleana Huff, Hatem Labidi, Mohammad Rashidi, Mohammad Koleini, Roshan Achal, Mark Salomons, Robert A. Wolkow

Abstract: We report the mechanically induced formation of a silicon-hydrogen covalent bond and its application in engineering nanoelectronic devices. We show that using the tip of a non-contact atomic force microscope (NC-AFM), a single hydrogen atom could be vertically manipulated. When applying a localized electronic excitation, a single hydrogen atom is desorbed from the hydrogen passivated surface and c… ▽ More We report the mechanically induced formation of a silicon-hydrogen covalent bond and its application in engineering nanoelectronic devices. We show that using the tip of a non-contact atomic force microscope (NC-AFM), a single hydrogen atom could be vertically manipulated. When applying a localized electronic excitation, a single hydrogen atom is desorbed from the hydrogen passivated surface and can be transferred to the tip apex as evidenced from a unique signature in frequency shift curves. In the absence of tunnel electrons and electric field in the scanning probe microscope junction at 0 V, the hydrogen atom at the tip apex is brought very close to a silicon dangling bond, inducing the mechanical formation of a silicon-hydrogen covalent bond and the passivation of the dangling bond. The functionalized tip was used to characterize silicon dangling bonds on the hydrogen-silicon surface, was shown to enhance the scanning tunneling microscope (STM) contrast, and allowed NC-AFM imaging with atomic and chemical bond contrasts. Through examples, we show the importance of this atomic scale mechanical manipulation technique in the engineering of the emerging technology of on-surface dangling bond based nanoelectronic devices. △ Less

Submitted 19 June, 2017; v1 submitted 16 June, 2017; originally announced June 2017.

Comments: 9 pages (including references and Supplementary Section), 8 figures (5 in the main text, 3 in Supplementary)

New fabrication technique for highly sensitive qPlus sensor with well-defined spring constant

Authors: Hatem Labidi, Martin Kupsta, Taleana Huff, Mark Salomons, Douglas Vick, Marco Taucer, Jason Pitters, Robert A. Wolkow

Abstract: A new technique for the fabrication of highly sensitive qPlus sensor for atomic force microscopy (AFM) is described. Focused ion beam was used to cut then weld onto a bare quartz tuning fork a sharp micro-tip from an electrochemically etched tungsten wire. The resulting qPlus sensor exhibits high resonance frequency and quality factor allowing increased force gradient sensitivity. Its spring const… ▽ More A new technique for the fabrication of highly sensitive qPlus sensor for atomic force microscopy (AFM) is described. Focused ion beam was used to cut then weld onto a bare quartz tuning fork a sharp micro-tip from an electrochemically etched tungsten wire. The resulting qPlus sensor exhibits high resonance frequency and quality factor allowing increased force gradient sensitivity. Its spring constant can be determined precisely which allows accurate quantitative AFM measurements. The sensor is shown to be very stable and could undergo usual UHV tip cleaning including e-beam and field evaporation as well as in-situ STM tip treatment. Preliminary results with STM and AFM atomic resolution imaging at $4.5\,K$ of the silicon $Si(111)-7\times 7$ surface are presented. △ Less

Submitted 20 July, 2015; v1 submitted 11 June, 2015; originally announced June 2015.

Comments: 5 pages, 3 figures

Journal ref: Ultramicroscopy 158, 33-37 (2015)