Alex H. Weiss

Bio: Alex H. Weiss is an academic researcher from University of Texas at Arlington. The author has contributed to research in topics: Positron & Auger electron spectroscopy. The author has an hindex of 20, co-authored 152 publications receiving 1771 citations. Previous affiliations of Alex H. Weiss include Harvard University & Brandeis University.

Surface roughness of water measured by X-ray reflectivity

Abstract: The roughness of the liquid-vapor interface for pure water was measured by a technique of x-ray reflectivity. With synchrotron radiation ($\ensuremath{\lambda}\ensuremath{\sim}1.5$ \AA{}A), the angular dependence of the x-ray reflectivity was measured from grazing incidence (\ensuremath{\sim}0.0021 rad), where the reflectivity was greater than 0.96, to an incident angle of \ensuremath{\sim}0.05 rad, where the reflectivity was \ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. A fit to the data by a theory with only one adjustable parameter obtains 3.2 \AA{}A for the root-mean-square roughness of the water surface.

Auger-electron emission resulting from the annihilation of core electrons with low-energy positrons.

Abstract: We report the first demonstration of positron-induced Auger-electron spectroscopy. A beam of low-energy (${10}^{1}$ eV) positrons was used to create core holes at the surface of Ni and Cu by matterantimatter annihilation. Estimates are developed for the probability of positrons annihilating with a $3p$ electron found to be as high as 3.7(7)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ in Ni. The implications of the extremely high signal to background are discussed and several important advantages of this process for surface analysis are suggested.

Electrodeposition and Characterization of SnS Thin Films

Abstract: A new room‐temperature electrodeposition technique was devised to synthesize thin films on indium tin oxidecoated glass slides. This technique is based on a nonaqueous ethylene glycol bath containing anhydrous and elemental sulfur. Three types of electrosyntheses, namely, potentiostatic, galvanostatic, and pulse modes, are discussed and their relative merits compared. A wide variety of characterization techniques were employed to develop a self‐consistent and complementary picture of the morphology, composition, and photoactivity of the thin films. These included scanning electron microscopy, x‐ray diffractometry, electron probe microanalyses, Auger electron spectroscopy, x‐ray photoelectron spectroscopy, optical analyses, and voltammetry. The photoactivity of these films was evaluated using photoelectrochemical techniques. Finally, the dark and photocorrosion behavior of these films are discussed with the aid of Pourbaix diagrams.

Low-Energy Positron Diffraction from a Cu(111) Surface

Abstract: The first observation of low-energy positron diffraction from a solid surface is reported. Slow (20-400-eV) monochromatic positron beams were focused onto a Cu(111) surface and their elastically scattered distributions detected with a channel electron multiplier. Measurements of the scattered intensity versus angle as a function of incident energy show peaks at the predicted ($0\overline{1}$) and ($0\overline{2}$) diffraction angles. Profiles of intensity versus energy at fixed angles exhibit maxima corresponding to the primary Bragg peaks.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Highly active oxide photocathode for photoelectrochemical water reduction

Abstract: A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.

Surface effects and anchoring in liquid crystals

Abstract: As their name indicates, liquid crystals simultaneously exhibit some characteristics common to both ordinary isotropic liquids and solid crystals. This ambivalence is also found in the effects of surfaces on these systems which lead to a great diversity of phenomena. These phenomena are reviewed focusing on nematic liquid crystals which have the simplest structure among the many existing types and which have been the most extensively studied. Three main kinds of effects can be distinguished. The first concerns the perturbation of the liquid crystalline structure close to the surface. Beyond this transition region, the bulk liquid crystalline structure is recovered with an orientation which is fixed by the surface: this phenomenon of orientation of liquid crystals by surfaces is the so-called anchoring. Finally, close to bulk phase transitions, critical adsorption or wetting can occur at surfaces as is also seen in isotropic systems.