Cody V. Cushman

Microfabrication, separations, and detection by mass spectrometry on ultrathin-layer chromatography plates prepared via the low-pressure chemical vapor deposition of silicon nitride onto carbon nanotube templates

Microfabrication of ultrathin-layer chromatography (UTLC) plates via conformal deposition of silicon nitride by low-pressure chemical vapor deposition onto patterned carbon nanotube (CNT) scaffolds was demonstrated. After removal of the CNTs and hydroxylation, the resulting UTLC phase showed no expansion or distortion of their microfeatures and the absence/reduction of remaining nitrogenic species. Developing time of a mixture of lipophilic dyes on this UTLC plates was 86% shorter than on high-performance thin-layer chromatography (HPTLC) plates. A water-soluble food dye mixture was also separated resulting in low band broadening and reduced developing time compared to HPTLC. For the latter example, mobile phase optimization on a single UTLC plate consisted of 14 developments with different mobile phases, each preceded by a plate prewashing step. The same plate was again reused for additional 11 separations under varying conditions resulting in a development procedure with a mean separation efficiency of 233,000theoretical plates/m and a reduced mobile phase consumption of only 400μL. This repeated use proved the physical robustness of the ultrathin layer and its resistance to damage. The layer was highly suited for hyphenation to ambient mass spectrometry, including desorption electrospray ionization (DESI) mass spectrometry imaging and direct analysis in real time (DART) mass spectrometry.

Low energy ion scattering (LEIS). A practical introduction to its theory, instrumentation, and applications

Low energy ion scattering (LEIS) probes the elemental composition of the outermost atomic layer of a material and provides static depth profiles of the outer ca. 10 nm of surfaces. Its extreme surface sensitivity and quantitative nature make it a powerful tool for studying the relationships between surface chemistry and surface related phenomena such as wetting, adhesion, contamination, and thin film growth. The high depth resolution obtained in LEIS in its static and sputter depth profile modes are useful for studying the layer structures of thin films. LEIS instrumentation has improved significantly in recent years, showing dramatic increases in its sensitivity and further expanding its potential applications. In this article, we provide a practical introduction to the technique, including a discussion of the basic theory of LEIS, LEIS spectra, LEIS instrumentation, and LEIS applications, including catalysts, solid oxide fuel cells (SOFCs), and thin films in integrated circuits.

Eagle XG® glass, optical constants from 230 to 1690 nm (0.73 - 5.39 eV) by spectroscopic ellipsometry

Eagle XG® glass is widely used in the manufacture of electronic displays. Spectroscopic ellipsometry and transmission data for this material were obtained from 193 to 1690 nm. The optical constants of the material were then modeled from 230 to 1690 nm. The data were initially fit with a basis spline (B-spline), and these results were used as the starting point for either a two-Gaussian oscillator model or a Tauc-Lorentz (T-L) + Gaussian oscillator model. Both models gave good fits, with unweighted mean squared error values of ca. 1.1. Samples were provided by Corning Incorporated directly from their production facility.

Optical constants of SiO2 from 196 to 1688 nm (0.735–6.33 eV) from 20, 40, and 60 nm films of reactively sputtered SiO2 on Eagle XG® glass by spectroscopic ellipsometry

Three thicknesses of reactively sputtered SiO2, nominally 20, 40, and 60 nm, deposited on Corning Eagle XG® (EXG), an important display glass, were analyzed by spectroscopic ellipsometry. Reflection ellipsometry data from the samples were analyzed from 196 to 1688 nm at angles of 55°–60°, inclusive, in 1° increments. These angles were chosen because they bracket the Brewster angles of both EXG glass and SiO2. The backsides of the samples were roughened by sand blasting to suppress backside reflections from the substrates. A total of nine datasets were collected from nine different samples (three for each nominal thickness of SiO2), each at six different angles of incidence (54 spectra). The optical constants for each thickness of SiO2 was determined, as well as a set of constants for all the films (the material in general) via a multisample analysis (MSA). The optical constants of the SiO2 films were modeled using two poles with transparency assumed over the entire spectral range (a Sellmeier model). A Br...