U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Search Publications by: Thomas Mitchell Wallis (Fed)

Search Title, Abstract, Conference, Citation, Keyword or Author
Displaying 26 - 50 of 79

Vector-Network-Analyzer Calibration Using Line and Multiple Coplanar-Waveguide Offset Reflects

December 9, 2016
Author(s)
Arkadiusz C. Lewandowski, Wojciech Wiatr, Dazhen Gu, Nate Orloff, Thomas Mitchell (Mitch) Wallis, Pavel Kabos
We present the application of our newly developed multi-reflect-thru technique to vector-network-analyzer calibration in the on-wafer environment. This technique uses a set of highly-reflective one-port devices, referred to as offset-reflects, and a single

Near-field microwave microscopy of one-dimensional nanostructures

May 23, 2016
Author(s)
Samuel Berweger, Paul T. Blanchard, Rebecca C. Quardokus, Frank W. DelRio, Thomas Mitchell (Mitch) Wallis, Pavel Kabos, Sergiy Krylyuk, Albert Davydov
With the ability to measure sample conductivity with nanometer spatial resolution, scanning microwave microscopy (SMM) is a powerful tool to study nanoscale electronic systems and devices. Here we demonstrate the general capability to image electronic

Near-field control and imaging of free charge carrier variations in GaN nanowires

February 15, 2016
Author(s)
Samuel Berweger, Paul T. Blanchard, Matthew Brubaker, Kevin J. Coakley, Norman A. Sanford, Thomas Mitchell (Mitch) Wallis, Kris A. Bertness, Pavel Kabos
Despite their uniform crystallinity, the shape and faceting of semiconducting nanowires (NWs) can give rise to variations in structure and associated electronic properties. Here we investigate local variations in electronic structure across individual n

Microwave characterization of ink-jet printed CPW on PET substrates

December 3, 2015
Author(s)
Thomas M. Wallis
This paper describes microwave characterization of coplanar waveguide (CPW) lines formed by ink-jet printed technology on flexible polyethylene terephthalate (PET) substrates. The reel-to-reel printing process uses inkjet printing as a precursor for 2$\mu

Introduction to the Special Issue

May 1, 2015
Author(s)
Thomas M. Wallis, Goutam Chattopadhyay, Fabio Cocetti, Luca Pierantoni
In the inaugural editorial of these IEEE Transactions on Terahertz Science and Technology – September 2011, the editor-in-chief anticipated that the work published in this journal would push beyond topics that are familiar to the traditional RF and

Microwave Near-Field Imaging of Two-Dimensional Semiconductors

January 27, 2015
Author(s)
Samuel Berweger, Joel Weber, Jimmy J. Li, Jesus M. Velazquez, Adam Pieterick, Norman A. Sanford, Albert V. Davydov, Thomas Mitchell (Mitch) Wallis, Pavel Kabos
Optimizing new generations of 2D devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging

GaN nanowire coated with atomic layer deposition of tungsten: a probe for near-field scanning microwave microscopy

September 25, 2014
Author(s)
Joel Weber, Paul T. Blanchard, Aric Sanders, Jonas Gertsch, Steven George, Samuel Berweger, Atif A. Imtiaz, Thomas Mitchell (Mitch) Wallis, Kris A. Bertness, Pavel Kabos, Norman A. Sanford, victor bright
We report on the fabrication of a GaN nanowire probe for near-field scanning microwave microscopy. The probe has a capacitive resolution of 0.03 fF, surpassing that of a commercial Pt tip. Imaging of MoS2 sheets found the probe to be immune to surface

Imaging the p-n junction in a gallium nitride nanowire with a scanning microwave microscope

July 2, 2014
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Kevin J. Coakley, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We used a broadband, atomic-force-microscope-based, scanning microwave microscope (AFM-SMM) to probe the axial dependence of the depletion in a GaN nanowire (NW) p-n junction structure. The NWs were c-axis oriented and grown by molecular beam epitaxy. The

Measurement Techniques for RF Nanoelectronics

January 20, 2014
Author(s)
Thomas M. Wallis, Luca Pierantoni
In 1882, in a lecture at the University of Leiden, Nobel prize-winner Heike Kammerlingh Onnes coined the motto: “Through Measurement to Knowledge” [1]. In that same lecture, he gave many historical examples of how measurements have fostered insight

Gallium Nitride Nanowire Probe for Near-Field Scanning Microwave Microscopy

January 15, 2014
Author(s)
Joel C. Weber, Paul T. Blanchard, Aric W. Sanders, Atif A. Imtiaz, Thomas M. Wallis, Kevin J. Coakley, Kristine A. Bertness, Pavel Kabos, Norman A. Sanford, Victor M. Bright
We report on the fabrication of a GaN nanowire probe for near-field scanning microwave microscopy. A single nanowire was Pt-bonded to a commercial Si cantilever prior to evaporation of a Ti/Al coating to provide a microwave signal pathway. Testing over a

Radio-Frequency and DC Electrical Characterization on a Modular MEMS Mechanical Test Platform for Nanomaterials

June 16, 2013
Author(s)
J. J. Brown, Thomas Mitchell (Mitch) Wallis, Pavel Kabos, Kristine A. Bertness, Norman Sanford, Victor Bright
In order to enable radio frequency (RF) data collection from a micromechanical system designed to strain nanomaterials, a coplanar electrical waveguide has been integrated with an actuated microscale stage. RF (100 MHz to 20 GHz) admittance measurements

Spatially-Resolved Dopant Characterization with a Scanning Microwave Microscope

March 25, 2013
Author(s)
Thomas M. Wallis, Atif A. Imtiaz, Alexandra E. Curtin, Pavel Kabos, Matthew D. Brubaker, Norman A. Sanford, Kristine A. Bertness
The scanning microwave microscope (SMM) is a tool for spatially-resolved microwave characterization of nanoelectronic materials and devices. The microscope incorporates a sharp, near-field probe, which measures local changes in reflected microwave signals

Near-Field Scaning Microwave Microscope (NSMM)

December 31, 2012
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, Pavel Kabos
Electromagnetic waves in the microwave frequency range are an essential tool for the investigation of material and device properties across a broad range of applications. Examples of materials of interest include: ferroelectric materials, ferromagnetic

Microwave Measurements and Systematic Circuit-Model Extraction of Nanowire Metal Semiconductor Field Effect Transistors

August 24, 2012
Author(s)
Dazhen Gu, Thomas M. Wallis, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We present detailed on-wafer scattering parameter measurements and equivalent circuit modeling of metal semiconductor field effect transistor (MESFET) that incorporates a GaN nanowire (NW). A systematic procedure is established to extract intrinsic model

Microwave measurements and systematic circuit-model extraction of nanowire metal semiconductor field-effect transistors

August 24, 2012
Author(s)
Dazhen Gu, Thomas M. Wallis, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We present detailed on-wafer scattering parameter measurements and equivalent circuit modeling of metal semiconductor field effect transistor (MESFET) that incorporates a GaN nanowire (NW). A systematic procedure is established to extract intrinsic model

A near-field scanning microwave microscope for characterization of inhomogeneous photovoltaics

August 10, 2012
Author(s)
Joel C. Weber, Kristine A. Bertness, John B. Schlager, Norman A. Sanford, Atif A. Imtiaz, Thomas M. Wallis, Pavel Kabos, Kevin J. Coakley, Victor Bright, Lorelle M. Mansfield
We present a near field scanning microwave microscope (NSMM) optimized for imaging photovoltaic samples. Our system incorporates a cut Pt-Ir tip inserted into an open ended coaxial cable to form a weak resonator, allowing the microwave reflection S11

A Direct Comparison System for Power Calibration up to 67 GHz*

July 1, 2012
Author(s)
Thomas M. Wallis, Thomas P. Crowley, Denis X. LeGolvan, Ronald A. Ginley
A direct comparison system for calibration of power sensors with 1.85 mm precision coaxial connectors up to 67 GHz has been developed. The comparison is implemented in two frequency bands. Between 10 MHz and 50 GHz, power sensors with 2.4 mm coaxial

Calibration Techniques for Scanning Microwave Microscopy

July 1, 2012
Author(s)
Thomas M. Wallis, Atif A. Imtiaz, Alexandra Curtin, Pavel Kabos, H. P. Huber, Joseph J. Kopanski, F. Kienberger
Two techniques are described for calibrating a scanning microwave microscope (SMM). The first technique enables spatially-resolved absolute capacitance measurements on the attofarad-to-femtofarad scale. The second technique enables profiling or dopant

A thickness-shear MEMS resonator employing electromechanical transduction through a coplanar waveguide

May 21, 2012
Author(s)
Ward L. Johnson, Thomas M. Wallis, Pavel Kabos, Eduard Rocas, Juan C. Collado Gomez, Li-Anne Liew, Albert Davydov, Alivia Plankis, Paul R. Heyliger
The design, modeling, fabrication, and characterization of a vibrationally trapped thickness-shear MEMS resonator is presented. This device is intended to avoid various limitations of flexural MEMS resonators, including nonlinearity, clamping losses

Frequency-selective contrast on variably doped p-type silicon with a scanning microwave microscope

May 14, 2012
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, SangHyun S. Lim, H. Tanbakuchi, H-P Huber, A. Hornung, P. Hinterdorfer, J. Smoliner, F. Kienberger, Pavel Kabos
We report frequency dependent contrast in d(S11)/dV measurements of a variably doped p-type silicon sample in the frequency range from 2GHz to 18GHz. The measurements were conducted bys use of a scanning microwave microscope. The measurements were done at

Calibrated nanoscale dopant profiling using a scanning microwave microscope.

January 3, 2012
Author(s)
Pavel Kabos, Thomas M. Wallis, H P. Hubner, I. Humer, M. Hochleitner, M. Fenner, M. Moertelmaier, C. Rankl, Atif A. Imtiaz, H. Tanbakuchi, P. Hinterdorfer, J. Smoliner, Joseph J. Kopanski, F. Kienberger
The scanning microwave microscope (SMM) is used for calibrated capacitance spectroscopy and spatially resolved dopant profiling measurements. It consists of an atomic force microscope (AFM) combined with a vector network analyzer operating between 1-20 GHz