William Durrer

Aluminum nitride and alumina composite film fabricated by DC plasma processes

Abstract Composite films of aluminum nitride and alumina were fabricated on aluminum 6061 alloys in a DC plasma chamber. Samples were treated by three main processes. These were: (1) Ar plasma etching, (2) NH 3 /Ar plasma with low pressure and low current density, and (3) NH 3 plasma with high pressure and high current density. The oxygen-free Al surface was obtained after 10 min 2.8 keV Ar + sputtering in an ultrahigh vacuum analysis chamber after the sample was treated by processes 1 and 2. Composite films of aluminum nitride and alumina were obtained on samples treated by processes 1, 2 and 3. The surface compositions and bonding environments of the composite films were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy. the thicknesses of the films were determined by argon sputtering in the ultra-high vacuum chamber. The surface morphologies of samples after fabrication processing in DC plasma were investigated by scanning electron microscopy. Al with the composite film not only shows a much better corrosion resistance in 1N HCl solution but also exhibits six times higher hardness than that of untreated Al. A possible formation mechanism of the composite film is proposed.

Ion beam assisted deposition of diamond-like nanocomposite films in an acetylene atmosphere

Abstract In recent years, doped diamond-like carbon (DLC) coatings have been shown to solve some intrinsic application difficulties of DLC, esp. reducing internal stresses and improving thermal stability. Diamond-like nanocomposite (DLN), by incorporating an amorphous Si-O network into the DLC, is a special class of modified DLC coatings, which have many excellent properties and wide applications. In this paper, a diamond-like nanocomposite film was synthesized by an ion beam assisted deposition method in an acetylene atmosphere. The composition and microstructure of the DLN film were investigated by various spectroscopic analyses, including Fourier transform infrared absorption spectroscopy, Rutherford backscattering spectroscopy. Raman scattering spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible absorption spectroscopy.

Observation of a novel electron beam effect: electron-stimulated associative desorption

We observed diatomic hydrogen and nitrogen desorbing from Pt(111) surfaces covered with multilayer ammonia at 120 K during electron irradiation at 600 eV. Experiments were conducted to verify that the source of H2(g) and N2(g) species was indeed the electron-irradiated ammonia multilayer. This effect, which we describe as electron-stimulated associative desorption (ESAD), has not been previously reported.

Initial adsorption of trimethylsilane on Ge(100) surfaces

Trimethylsilane (TMSiH) was adsorbed onto a Ge(100) surface at a temperature of -150 ± 3°C and x-ray photoelectron spectroscopy (XPS) was used to study the resulting surface species as functions of the TMSiH exposure in Langmuir (L). The core-level C 1s, Si 2p and Ge 3d photoelectrons were monitored after each dosing. It was observed that the C-C bonds are the dominant species formed at the low doses of TMsiH. The second abundant species at the low coverage is the C-Ge bond. This indicated dissociative adsorption of TMSiH molecules onto a clean Ge(100) surface, which is similar to the adsorption of TMSiH molecules onto an Si(100) surface. As the dose increases, the Si-C species gradually increase due to physisorbed TMSiH on top of the C-C- and C-Gecovered surface. This study clearly reveals the growth processes of TMSiH on a Ge(100) surface. The electronegativities of C, Si and Ge and the bond strengths of C-C, C-Si and C-Ge were invoked to discuss the initial formation of C-C and C-Ge on the Ge(100) surface.

Temperature dependence of surface charging of NaCl under electron irradiation: role of secondary electron emission

Abstract In initial observations during Auger studies of NaCl, we have observed stable, clearly resolved Auger peaks. With time, however, some of the Auger spectra reveal the occurrence of strong negative charging. This charging appears to be a result of irradiation-induced accumulation of sodium metal on the sample surface. We report the dependence of the strong negatively charged state on temperature. The results are consistent with the above model; the strongly negatively charged surface cannot be maintained at temperatures sufficiently high that sodium metal evaporation occurs.

Surface carbon and its effects on hydrogen adsorption on Rh(100)

Abstract Hydrogen gas was used as a probe to investigate the distribution of adsorption sites and their blocking by a submonolayer of carbon on a Rh(100) surface in ultra-high vacuum. TDS and AES results are consistent with a model in which carbon atoms residing only in four-fold hollow sites block the adsorption of hydrogen there.

Raman Computational and Experimental Studies of Dopamine Detection

A combined theoretical and experimental analysis of dopamine (DA) is presented in this work with the objective of achieving more accurate detection and monitoring of this neurotransmitter at very low concentrations, specific to physiological levels. Surface-enhanced Raman spectroscopy on silver nanoparticles was employed for recording DA concentrations as low as 10−11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of different DA molecular forms, such as uncharged DA±, anionic DA−, and dopaminequinone. Disappearance of the strongest bands of dopamine around 750 cm−1 and 790 cm−1, which suggests its adsorption onto the metallic surface, is not only consistent with all of these DA configurations, but also provides additional information about the analyte’s redox process and voltammetric detection. On the other hand, occurrence of the abovementioned Raman lines could indicate the formation of multilayers of DA or its presence in a cationic DA+ form. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be achieved for a better understanding of its detection at physiological levels, which is crucial if further optovoltammetric medical device development is envisioned.

Detection and Monitoring of Neurotransmitters - a Spectroscopic Analysis

Objectives:  We demonstrate that confocal Raman mapping spectroscopy provides rapid, detailed, and accurate neurotransmitter analysis, enabling millisecond time resolution monitoring of biochemical dynamics. As a prototypical demonstration of the power of the method, we present real‐time in vitro serotonin, adenosine, and dopamine detection, and dopamine diffusion in an inhomogeneous organic gel, which was used as a substitute for neurologic tissue.

Raman microscopic analysis of internal stress in boron-doped diamond

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp2 type carbon impurities, besides that of the expected lattice mismatch between film and substrate.

Raman computational and experimental studies of dopamine molecules on silver nanocolloids

Combined theoretical and experimental analysis of dopamine is presented in this work to better understand phenomena related to this neurotransmitters detection and monitoring at very low concentrations specific to physiological levels. Surface-enhanced Raman spectroscopy (SERS) on silver nanoparticles was employed for recording dopamine concentrations as low as 10−11 molar. Quantum chemical density functional calculations were carried out using Gaussian-09 analytical suite software. Relatively good agreement between the simulated and experimentally determined results indicates the presence of all dopamine molecular forms, such as neutral DA0, ionic DA− and DA+, and of dopaminequinone as well. Disappearance of the strongest bands of dopamine at 750 cm−1 and 795 cm−1, which suggests its adsorption onto the metallic surface, is consistent with the appearance of the latter molecular configuration. Thus, through coordinated experiment and theory, valuable insights into changes observed in the vibrational signatures of this important neurotransmitter can be analyzed and comprehended.