Office: 114 Thurston
Phone: 607.255.7339
Email: ccu1@cornell.edu
Website: Umbach Group
I joined the MS&E faculty in 2002. Previously (1995-2002) I had been active as a Research Associate in the MS&E department investigating glass and semiconducting surfaces with primary support from the Cornell Center for Materials Research. I was also a Lecturer in MS&E (1992-1994) and conducted my post-doctoral research at Cornell (1991-1995). My Ph.D. in Applied and Engineering Physics (Cornell 1991) addressed the atomic structure of microfabricated Si surfaces using the first scanning tunneling microscope built at Cornell. My B.A. was in physics and philosophy (Yale, 1981, summa cum laude); subsequently I spent a year on a DAAD fellowship at the Max Planck Institute in Stuttgart, Germany. I am a member of the Materials Research Society and the American Ceramic Society. Please feel free to send me an email should you have any questions.
Nanoporous metals: thin-films and membranes In an industry-university collaboration, I and my students are studying nanoporous gold (NPG), which is made by dealloying a 30% Au/70% Ag alloy in acid, producing a tortuous porous network with an initial pore size of ~30 nm. We have produced NPG both from films ~500 nm thick deposited via sputtering an alloy target and from 200 micron thick rolled-sheet membranes. Controlling the pore size is important for practical applications: annealing at moderate temperatures increases the pore size to several microns in a few hours. We have focused on understanding the mechanisms that drive this increase in pore size. We have also been investigating electromagnetic enhancement effects associated with the nanoroughness of NPG and have observed surface-enhanced Raman scattering (SERS) from thin-film NPG adsorbed with dodecanethiol molecules. I am interested in developing NPM for energy and sensing applications. Catalysts can be plated onto NPG and remain catalytically active; hence thin-film NPM is promising for electrodes in microfabricated fuel cells. NPM also has potential as the electrode in photoelectrochemical devices where charge transfer to conductors must take place over nanoscale dimensions. Its demonstrated optical enhancement makes NPG suitable for biosensors based on fluorescence and Raman scattering. I am particularly interested in combining the filtration properties of NPG with SERS to develop a sensor for rapid detection of bacteria such as E. coli.
Glass surfaces Many of the properties of glasses are determined by the heterogeneity at the nanoscale of composition and structure. Investigating heterogeneities in composition and structure at surfaces allows the application of powerful surface-sensitive imaging and spectroscopy techniques, which, when combined with surface modification, have enormous potential for developing new functionality in glass. We have applied ultra-high vacuum (UHV) non-contact atomic force microscopy (NC-AFM) to glasses fractured in-situ, ion sputtered ex-situ, and electron beam irradiated in-situ. The fracture surfaces of silica, calcium aluminosilicates, and a commercial boroaluminosilicate display glass all exhibit globular features 5 to 10 nm in width and <1 nm in height. When ion sputtered or electron beam irradiated, the display glass exhibits similar globular features. We have also developed a method to image some of these glass surfaces using scanning tunneling microscopy (STM). After either electron bombardment or laser irradiation at elevated temperature, the fracture surfaces of the display glass are sufficiently conductive to allow imaging and spectroscopy at moderate tunneling currents (picoamperes). The topographic images acquired with NC-AFM and STM are identical, implying that the induced conductivity is spatially uniform, opening up the possibility of near-atomic resolution of structural and chemical features of glasses. The directional surface roughness caused by ion-beam sputtering illustrates how nanoscale variations in glass morphology can be exploited. We have used display glass roughened by sputter-erosion to align liquid crystal (LC) molecules. Conventional LC displays use a polymer layer to align the LC’s, but display or sensor structures that use LC’s for guiding light at higher temperatures or for bistable switching of LC orientations may benefit from glass substrates with useful alignment and anchoring properties.
