This CAREER project seeks to 1) understand and manipulate electrical conduction in nanostructures, and 2) attract under-represented groups to physics by exposing them to cutting edge nanoscience. Experiments will be performed on three materials - carbon nanotubes, Indium-Arsenic nanowires, and graphene. These have all demonstrated novel physics and are considered leading candidates for nanoscale electronics applications. The research will use innovative fabrication and measurement techniques, such as local electric fields and substrates that can be controllably strained, to understand what factors most influence electron transport in nanoscale materials. The proposed research will also lay the groundwork for novel electronic devices. Education and research are integrated through a focus on recruiting and involving women and minorities in research activities. Specific educational tasks include mentoring under-represented undergraduates in research projects, and organizing special nanoscience sessions at conferences targeting women and minorities. The project will train talented scientists and help improve the science knowledge base of our society.
The goals of this CAREER project are to 1) significantly improve the understanding and manipulation of transport properties in nanostructures, and 2) recruit under-represented groups to physics by exposing them to cutting-edge nanoscience. Experiments will be performed on three scientifically and technologically relevant materials; carbon nanotubes, InAs nanowires, and graphene. The research will utilize local probes and novel tuning parameters to answer basic questions about transport in nanostructures, particularly regarding the interplay between electron-electron interactions, band structure, spin and charge distributions, and disorder. Innovative measurement and fabrication tools - such as quantum point contacts to detect spins, tunneling probes to measure energy distributions, and electric fields and flexible substrates to tune conductance and band gaps - will be developed to allow for precise studies of fundamental properties and also to lay the groundwork for novel tunable devices. Education and research are integrated through a focus on recruiting and involving women and minorities in research. Specific educational tasks include mentoring under-represented undergraduates, and organizing nanoscience sessions at major conferences and meetings targeting women and minorities. The plan will thus help increase the future pool of talented scientists and help improve the scientific knowledge base of our society.
Intellectual Merit This CAREER award focused on electrical and mechanical measurements of carbon-based materials, particularly graphene and carbon nanotubes. Graphene is a sheet of carbon that is a single atomic layer thick; carbon nanotubes are sheets of graphene that have been rolled into tubes one billionth of a meter in diameter. The extreme nano-scale of these materials gives them superlative electrical and mechanical properties, and they are considered leading candidates for next-generation electronic elements. The results of this research should enable new types of nanotube and graphene devices. The two main thrusts of this research were (1) developing new techniques for making multi-probe carbon nanotube devices, and (2) determining the mechanical properties of graphene on patterned surfaces. Carbon nanotubes are typically damaged by materials put on their surfaces, which limits the types of electrical contact that can be made to them. We developed a technique for making multi-probe, non-invasive contacts to carbon nanotubes, by protecting the tubes with a thin insulating layer (deposited via atomic layer deposition). We used this technique to perform an energy-dependent "spectroscopic" measurement of a carbon nanotube that had single electrons passing through it; in this way, we could characterize a carbon nanotube "single-electron transistor". The results led to a greater understanding of nanotube single-electron transistors, and paved the way for new probes of carbon nanotubes and similar delicate nanostructures. A parallel thrust of this grant involved studies of how graphene interacted with a grooved substrate. We determined that thin, few-layer graphene conforms to a grooved substrate, whereas thick, many-layer graphene lies flat on top of the substrate. At a critical thickness the graphene changes from conforming to not-conforming, thereby undergoing a "snap-through" transition. This was the first demonstration of such a transition in graphene. In addition, by comparing our data to theory, we could put limits on the graphene adhesion properties. It is typically very difficult to obtain information about adhesion and elasticity in small samples, yet this work demonstrated an entirely new and simple method of obtaining this information. The elastic and adhesive properties of graphene are relevant to graphene-based electronic and mechanical devices. In addition, there has been growing excitement about the use of graphene in composite materials (e.g., flexible, electronically active, super-strong), although the interplay between graphene and other materials has not been well studied. We not only explored the behavior of graphene placed on elastic and patterned materials, but also used the behavior to extract fundamental and sample-dependent parameters that are relevant to designing composite materials. Broader Impact Technological: There has been much excitement about the possible use of nanotubes and graphene in the next generation of scaled-down electronic circuits. This research laid the groundwork for novel devices using these materials. The results of this research were published in three separate articles in leading journals, and have thus been widely disseminated in the research community. Educational: The integrated research and education plan focused on the training of students in nanotechnology techniques, and on the involvement of women and minorities in physics through research-related activities. Specific educational tasks included: 1) developing a new graduate course entitled "Mesoscopics and Nanoscience," which covered topics directly related to this research, 2) training undergraduates, graduate students, and postdoctoral researchers in advanced fabrication and measurement techniques (5 graduate students, 5 undergraduates, 1 postdoc, and 1 high school student were involved in various aspects of this research; I particularly focused on mentoring under-represented undergraduates), and 3) organizing the nanoscience sessions at the major conference targeting African-American physics students and professionals. In addition, I engaged in multiple activities designed to expose under-represented groups to cutting edge nanoscience and to recruit women and minorities to physics. The major goal was to increase the future pool of talented scientists and help improve the scientific knowledge base of our society.
