Surface and Interface Analysis : SIA

Interpretation of X-ray photoelectron spectroscopy (XPS) spectra of complex material surfaces, such as those obtained after surface plasma treatment of polymers, is confined by the available references. The limited understanding of the chemical surface composition may impact the ability to determine suitable coupling chemistries used for surface decoration or assess surface-related properties like biocompatibility. In this work, XPS is used to investigate the chemical composition of various ultra-high-molecular-weight polyethylene (UHMWPE) surfaces...

Secondary ion mass spectrometry using the argon cluster primary ion beam enables molecular compositional depth profiling of organic thin films with minimal loss of chemical information or changes in sputter rate. However, for depth profiles of thicker organic films (> 10 μm of sputtered depth) we have observed the rapid formation of micron-scale topography in the shape of pillars that significantly affect both the linearity of the sputter yield and depth resolution. To minimize distortions in the 3D reconstruction of the sample due to this topography, a step-wise, staggered sample rotation was employed...

David Briggs was a surface analysis pioneer. Starting in 1970 and continuing throughout his career, Dave used his expertise, vision and ability to quickly master new surface analysis methods and solve important industrial problems. It certainly helped that he was an outstanding fund raiser in both industrial and academic settings, which ensured he always had an impressive array of the latest, most advanced surface analysis instrumentation at his disposal. He insisted on doing surface analysis correctly and through his publications, databases and books he provided the community with the needed guidelines and methods to do so...

Surfaces and interfaces play a critical role in material performance in many applications including catalysis, biomaterials, microelectronics, tribology and adhesion. Characterizing the important surfaces and interfaces involved in each application may present different challenges, but the approach to investigating them often is rather similar. Specialized instrumentation is typically used to probe the surface region of a material and often times it is required to develop new instrumentation and data analysis methods to obtain the desired information...

We have calculated inelastic mean free paths (IMFPs) for 42 inorganic compounds (AgBr, AgCl, AgI, Al2 O3 , AlAs, AlN, AlSb, cubic BN, hexagonal BN, CdS, CdSe, CdTe, GaAs, GaN, GaP, GaSb, GaSe, InAs, InP, InSb, KBr, KCl, MgF2 , MgO, NaCl, NbC0.712 , NbC0.844 , NbC0.93 , PbS, PbSe, PbTe, SiC, SiO2 , SnTe, TiC0.7 , TiC0.95 , VC0.76 , VC0.86 , Y3 Al5 O12 , ZnS, ZnSe, and ZnTe) for electron energies from 50 eV to 200 keV. These calculations were made with energy-loss functions (ELFs) obtained from measured optical constants for 15 compounds while calculated ELFs were utilized for the other 27 compounds...

We discuss the problem of quantifying common sources of statistical uncertainties for analyses of trace levels of surface contamination using X-ray photoelectron spectroscopy. We examine the propagation of error for peak-area measurements using common forms of linear and polynomial background subtraction including the correlation of points used to determine both background and peak areas. This correlation has been neglected in previous analyses, but we show that it contributes significantly to the peak-area uncertainty near the detection limit...

An indirect, compositional depth profiling of an inorganic multilayer system using a helium low temperature plasma (LTP) containing 0.2% (v/v) SF6 was evaluated. A model multilayer system consisting of four 10 nm layers of silicon separated by four 50 nm layers of tungsten was plasma-etched for (10, 20, and 30) s at substrate temperatures of (50, 75, and 100) °C to obtain crater walls with exposed silicon layers that were then visualized using time-of-flight secondary ion mass spectrometry (ToF-SIMS) to determine plasma-etching conditions that produced optimum depth resolutions...

We calculated electron inelastic mean free paths (IMFPs) for liquid water from its optical energy-loss function (ELF) for electron energies from 50 eV to 30 keV. These calculations were made with the relativistic full Penn algorithm (FPA) that has been used for previous IMFP and electron stopping-power calculations for many elemental solids. We also calculated IMFPs of water with three additional algorithms: the relativistic single-pole approximation (SPA), the relativistic simplified SPA, and the relativistic extended Mermin method...

This paper extends a straightforward technique for the calculation of shell thicknesses in core-shell nanoparticles to the case of core-shell-shell nanoparticles using X-ray Photoelectron Spectroscopy (XPS) data. This method can be applied by XPS analysts and does not require any numerical simulation or advanced knowledge, although iteration is required in the case where both shell thicknesses are unknown. The standard deviation in the calculated thicknesses vs simulated values is typically less than 10%, which is the uncertainty of the electron attenuation lengths used in XPS analysis...

Surface analysis plays a key role in understanding the function of materials, particularly in biological environments. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) provides highly surface sensitive chemical information that can readily be acquired over large areas and has, thus, become an important surface analysis tool. However, the information-rich nature of ToF-SIMS complicates the interpretation and comparison of spectra, particularly in cases where multicomponent samples are being assessed...

The environmental toxin β-N-methylamino-L-alanine (BMAA) has been causatively linked to neurodegenerative disease pathology. In a rat model, neonatal BMAA exposure resulted in selective uptake in the hippocampal formation and caused learning and memory impairments in adult animals. Moreover, high dose neonatal BMAA exposure resulted in formation of protein inclusions in the CA1 region of the adult hippocampus. However the mechanism underlying BMAA induced neuropathology remains elusive. Imaging mass spectrometry is a powerful method for spatial interrogation of biochemical distribution in biological tissue with high chemical specificity...

We employed a method of electrostatic peak switching allowing for the quasi-simultaneous measurement of (16)O, (18)O, C2H, C2D,(12)C(14)N, (13)C(14)N, (12)C(15)N, P, and S with the NanoSIMS 50L instrument to derive ratios for D/H, (13)C/(12)C, (18)O/(16)O, and (15)N/(14)N from biological samples. This approach involves two steps: (i) derivation of the D/H ratio from measurements of C2D and C2H and (ii) switching of the voltage on deflection plates located in front of two detectors. The method is reliable and easy to set up compared with the magnetic peak-switching mode usually used to perform this type of analysis...

Molecular depth profiling of multilayer organic films is now an established protocol for cluster secondary ion mass spectrometry (SIMS). This unique capability is exploited here to study the ionization mechanism associated with matrix-enhanced SIMS and possibly matrix assisted laser desorption/ionization (MALDI). Successful depth profiling experiments were performed on model bi-layer systems using 2,5-dihydroxybenzoic acid (DHB) as the matrix with dipalmitoylphosphatidylcholine (DPPC) or phenylalanine (PHE)...

Despite the widely recognized importance of the several species of inositol polyphosphates in cell biology, inositol has not been successfully imaged and quantified inside cells using traditional spectrophotometry. Multi-isotope imaging mass spectrometry (MIMS) technology, however, has facilitated direct imaging and measurement of cellular inositol. After pulsing cells with inositol labeled with the stable isotope Carbon-13 ((13)C), the label was detected in subcellular volumes by MIMS. The tridimensional localization of (13)C within the cell illustrated cellular distribution and local accumulation of inositol...

Multi-isotope imaging mass spectrometry (MIMS) combines stable isotope tracers with the quantitative imaging of NanoSIMS ion microscopy. With extensive safety precedent, use of stable isotopes in MIMS applications opens the possibility of studying a wide array of biological questions in humans([1]). Here we describe a series of approaches to increase the effective analytical throughput for detecting rare nuclear labeling events with MIMS. At the level of sample preparation, cells in suspension were either smeared at high density or pelleted cells were embedded and sectioned to reach nuclear depth...

Cell division is commonly quantified by the administration of nucleotide labels that are incorporated by the nucleotide salvage pathway. A new approach uses precursors of the de novo nucleotide synthesis pathway, such as labeled water or glucose. Because such precursors are not specific for DNA synthesis, studies utilizing this approach have analyzed isolated genomic DNA to exclude nonspecific background labeling. We hypothesized that pulse-chase administration of stable isotope labeled water would result in sufficient nuclear labeling to enable discrimination of recently divided cells by quantitative ion microscopy...

The classical view of neuronal protein synthesis is that proteins are made in the cell body and then transported to their functional sites in the dendrites and the dendritic spines. Indirect evidence, however, suggests that protein synthesis can directly occur in the distal dendrites, far from the cell body. We are developing protocols for dual labeling of RNA and proteins using (15)N-uridine and (18)O- or (13)C-leucine pulse chase in cultured neurons to identify and localize both protein synthesis and fate of newly synthesized proteins...

Multi-isotope imaging mass spectrometry (MIMS) allows high resolution quantitative imaging of protein and nucleic acid synthesis at the level of a single cell using stable isotope labels. We employed MIMS to determine the compartmental localization of selenoproteins tagged with stable isotope selenium compounds in human aortic endothelial cells (HAEC), and to compare the efficiency of labeling (to determine the ideal selenium source) from these compounds: [(82)Se]-selenite, [(77)Se]-seleno-methionine, and [(76)Se]-methyl-selenocysteine...

We have developed a method that combines the use of stable isotopes, MIMS and antibody. We began with using well-established antibodies, anti-actin and anti-synaptophysin, in mouse intestinal cells. We extended the method to an immunogold assay to specifically localize Ribeye, a major protein component of retina synaptic ribbons, or to localize a synaptic vesicle-containing protein, synaptophysin. Both are localized in presynaptic nerve terminal of photoreceptors cells in retina. Our results show that by MIMS analysis of the Au signal we can directly identify antibodies tagged with non amplified 1...

Although antidepressants have been used in the treatment of affective disorders for over fifty years, the precise mechanism of their action remains unknown. Treatment regimens are based by and large on empirical parameters and characterized by a trial and error scheme. A better understanding of the mechanisms involved in antidepressant drug response is of fundamental importance for the development of new compounds that have a higher success rate and specificity. In order to elucidate the molecular pathways involved in the action of antidepressants, we wish to identify brain areas, cell types, and organelles that are targeted by antidepressant treatment in mice...