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Search Publications by: Thomas Mitchell Wallis (Fed)

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Displaying 1 - 25 of 79

Looking Forward to IMS 2022 (Guest Editorial)

May 1, 2022
Author(s)
Thomas Mitchell (Mitch) Wallis
As guest editor, it's my pleasure to welcome you to this issue of IEEE Microwave Magazine. This issue focuses on the 2022 International Microwave Symposium (IMS), which will be held in Denver in June. As I sit down to write this column, it is a wintry

Nanoscale Photoexcited Carrier Dynamics in Perovskites

March 8, 2022
Author(s)
Samuel Berweger, Fei Zhang, Bryon Larson, Andrew Ferguson, Axel Palmstrom, Obadiah Reid, Thomas Mitchell (Mitch) Wallis, Kai Zhu, Joseph Berry, Pavel Kabos, Sanjini Nanayakkara
The excellent optoelectronic properties of lead-halide perovskite thin films are complemented by their tolerance to broad compositional variations and associated strain, which allows tuning of desired properties such as the optical bandgap. On the other

Imaging of Magnetic Excitations in Nanostructures with Microwave Near-Field Microscopy

November 25, 2021
Author(s)
Samuel Berweger, Robert Tyrrell-Ead, Houchen Chang, Mingzhong Wu, Hong Tang, Hans Nembach, Karl Stupic, Stephen E. Russek, Thomas Mitchell (Mitch) Wallis, Pavel Kabos
We present images of spin-wave excitations in a patterned yttrium iron garnet (YIG) thin film obtained by use of near-field microwave microscopy, which can achieve spatial resolution as high as 50 nm. Visualization of magnetic excitations is an enticing

Spatially Resolved Photoconductivity in WS2/MoS2 lateral heterostructures

April 27, 2021
Author(s)
Samuel Berweger, Hanyu Zhang, Prasana Sahoo, Benjamin Kupp, Jeffrey Blackburn, Elisa Miller, Thomas Mitchell (Mitch) Wallis, Dmitri Voronine, Pavel Kabos, Sanjini Nanayakkara
The optical and electronic properties of 2D semiconductors are intrinsically linked via the strong interactions between optically excited bound species and free carriers. Here we use near-field scanning microwave microscopy (SMM) to image spatial

Microscopic Origin of Inhomogeneous Transport in Four-Terminal Tellurene Devices

December 22, 2020
Author(s)
Benjamin Kupp, Gang Qiu, Yixiu Wang, Clayton Caspeer, Thomas Mitchell (Mitch) Wallis, Joanna Atkin, Wenzhuo Wu, Peide Ye, Pavel Kabos, Samuel Berweger
Tellurene—the 2D form of elemental tellurium—provides an attractive alternative to conventional 2D semiconductors due to its high bipolar mobilities, facile solution processing, and the possibility of dopant intercalation into its 1D van der Waals lattice

Microwaves and Microscopy (Guest Editorial)

September 16, 2020
Author(s)
Thomas M. Wallis, Marco Farina
Welcome to this special issue of IEEE Microwave Magazine, which is focused on the topic of “Microwaves and Microscopy.” As that title implies, this topic lies at the intersection of two technical disciplines, namely microwave engineering and measurements

Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors

February 12, 2020
Author(s)
Samuel Berweger, Gang Qiu, Yixiu Wang, Benjamin Pollard, Kristen Genter, Thomas Mitchell (Mitch) Wallis, Wenzhuo Wu, Peide Ye, Pavel Kabos
Bipolar transport underpins a wide range of semiconductor homojunction device functionalities such as pn junctions or transistors. The capability to image and understand spatial inhomogeneities un carrier type and the conductivity associated with each

Design of an intelligent PYTHON code to run coupled and license-free finite-element and statistical analysis software for calibration of near-field scanning microwave microscopes

October 2, 2019
Author(s)
Jeffrey T. Fong, N. Alan Heckert, James Filliben, Pedro V. Marcal, Samuel Berweger, Thomas Mitchell (Mitch) Wallis, Pavel Kabos
To calibrate near-field scanning microwave microscopes (NSMM) for defect detection and characterization in semiconductors, it is common to develop a parametric finite element analysis (FEA) code to guide the microscope user on how to optimize the settings

Chapter 10. Measurement of active nanoelectronic devices

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
Many of the most promising applications of nanomaterials involve active, nanoelectronic devices. For example, the intrinsic transport properties of single-walled, carbon nanotubes (CNTs) enable field effect transistors (FETs) that allow higher current

Chapter 11. Dopant profiling in semiconductor nanoelectronics

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
As nanoelectronic device dimensions are scaled down to atomic sizes, device performance becomes more and more sensitive to the exact arrangement of atoms, including individual dopants and defects, within the device. Thus, there is ongoing demand for

Chapter 12 Depth profiling

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
Microwave tomography is an active, developing research area. The objective is to visualize hidden, subsurface features through application of microwave radiation. Applications include ground penetrating radars (GPR) [1], defect spectroscopy in materials

Chapter 13. Dynamics of nanoscale magnetic systems

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
The topic of nanoscale magnetic systems is broad and could easily provide enough material for an entire book on its own. In this chapter, as in previous ones, we will focus on the nanoscale magnetic systems for which near-field scanning microwave

Chapter 6. Characterization of nanofiber devices

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
Previous chapters have introduced and described a variety of measurement techniques for RF nanoelectronic devices. Here, our objective is to work through an illustrative example that highlights strategies and challenges related to implementing a specific

Chapter 7. Probe-based measurement systems

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
In the preceding chapters, we have focused on broadband, calibrated measurements of nanoelectronic devices. In particular, we have described measurement techniques for the measurement of calibrated, complex scattering parameters and the subsequent

Chapter 8. Instrumentation for near-field scanning microwave microscopy

September 17, 2017
Author(s)
Pavel Kabos, Thomas Mitchell (Mitch) Wallis
In the previous chapter, we discussed the underlying physics and theory of operation for near-field scanning microwave microscopes (NSMMs) and related probe-based measurement systems. Here, we consider the practical implementations of such scanning probe

Chapter 9. Radio frequency scanning probe measurements of materials

September 17, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
Preceding chapters have described the near field scanning microwave microscope (NSMM), while discussing both the underlying theory of operation and practical considerations for instrumentation. A primary application area for NSMMs and related microscopes

Chapter 1. An introduction to radio frequency nanoelectronics

September 15, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
The field of radio frequency (RF) nanoelectronics focuses on the fundamental study and engineering of devices that are enabled by nanotechnology and operate within a frequency range from about 100 MHz to about 100 GHz. This range includes frequencies

Chapter 2. Core concepts of microwave and RF measurements

September 15, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
In this chapter we will review the core concepts of microwave and radio frequency (RF) propagation in both guided-wave and on-wafer environments. Because most of these concepts are well-known, we will introduce only the terms and definitions that are

Chapter 3. Extreme Impedance Measurements

September 15, 2017
Author(s)
Pavel Kabos, Thomas Mitchell (Mitch) Wallis
Microwave measurements of RF nanoelectronic devices present numerous challenges. Among these, perhaps the most difficult measurement challenge arises from the inherent, often extreme impedance mismatch between nanolectronic systems and conventional

Chapter 4. On-wafer measurements of RF nanoelectronic devices

September 15, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
The preceding chapters have introduced the core concepts and techniques of microwave measurements, in general, and techniques for microwave measurements of extreme impedance devices, in particular. Here, we narrow the focus further to on-wafer, microwave

Chapter 5. Modeling and validation of RF nanoelectronic devices

September 15, 2017
Author(s)
Thomas M. Wallis, Pavel Kabos
The development and engineering of nanoelectronic devices has been characterized by several significant technological trends. In addition to the ongoing scaling of feature sizes down to nanoscale dimensions, the need for superior performance has driven the

Lithographic sonication patterning of large area nanopillar forests

July 27, 2017
Author(s)
Joel C. Weber, Matthew D. Brubaker, Thomas M. Wallis, Kristine A. Bertness
This paper demonstrates a highly-scalable, material-independent method for patterning nanopillar forests known as lithographic sonication patterning. Through contact lithography, patterns with dimensions down to 3 υm were written across a 3-inch silicon