Surface studies of supported model catalysts

Unencapsulated, exfoliated black phosphorus (BP) flakes are found to chemically degrade upon exposure to ambient conditions. Atomic force microscopy, electrostatic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are employed to characterize the structure and chemistry of the degradation process, suggesting that O2 saturated H2O irreversibly reacts with BP to form oxidized phosphorus species. This interpretation is further supported by the observation that BP degradation occurs more rapidly on hydrophobic octadecyltrichlorosilane self-assembled monolayers and on H-Si(111) versus hydrophilic SiO2. For unencapsulated BP field-effect transistors, the ambient degradation causes large increases in threshold voltage after 6 h in ambient, followed by a ∼103 decrease in FET current on/off ratio and mobility after 48 h. Atomic layer deposited AlOx overlayers effectively suppress ambient degradation, allowing encapsulated BP FETs to ma...

Effective Passivation of Exfoliated Black Phosphorus Transistors against Ambient Degradation

Angle-resolved XPS and AES: depth-resolution limits and a general comparison of properties of depth-profile reconstruction methods

The oxidation of single crystal gallium nitride in dry air has been investigated. X-ray photoelectron spectroscopy (XPS) revealed minimal oxide growth at 450 and 750 °C for up to 25 h. However, at 900 °C the growth of an oxide approximately 5000 A thick was observed after 25 h. This oxide was determined to be the monoclinic β-Ga2O3 using glancing angle x-ray diffraction. XPS spectra of the Ga 3d and Ga 2p core levels indicated peak shifts of 1.2 and 1.3 eV, respectively, from Ga–O to Ga–N bonding. The Ga L3M45M45 core level binding energy was also investigated and β-Ga2O3 and GaN each presented a characteristic peak shape.

X-ray photoelectron spectroscopy and x-ray diffraction study of the thermal oxide on gallium nitride

Raman and IR-measurements on the high- T c material series La 2 CuO 4 and YBa 2 Cu 3 O 7 are reviewed. This summary focuses on lattice vibrations in these superconducting systems, on impurity phases, the influence of oxygen stoichiometry and element substitution. The determination of the superconducting gap, the phonon renormalization in the superconducting state, and the isotope effect with its implications on the theory of superconductivity in these materials are discussed. In addition, the measured lattice vibrations are compared with the results of lattice dynamics calculations.

Lattice vibrations in high-Tc superconductors: Optical spectroscopy and lattice dynamics☆

The XPS method combined with argon-ion etching has been applied in order to study the chemical depth profile of surface thermal-oxide layers on GaP(). The influence of the ion etching process on the depth profile has been studied. The deviation of the measured profile from the true one was caused mainly by the fact that atoms are not removed layer by layer by ion etching. The thermal oxide formed on GaP has been identified as GaPO4. It has been found that the width of the transition region increases as the thickness of the surface oxide layers increases. For example, when GaP() is oxidized at 700°C for 15 min, a surface oxide layer of 340 A is formed, and the transition region has a width of 175±73 A.

An XPS Analysis of Thermally Grown Oxide Film on GaP

The room temperature oxidation upon exposure to atmospheric dry O2 and thermal oxidation in air of some AIII-BV compounds have been studied by analyzing XP spectra quantitatively. For GaAs and Gap, evidences of the formation of metastable surface complexes by room temperature oxidation are shown: the values of the ratio of the oxidized AIII element to the oxidized BV element is about 2 and 1 for GaAs and GaP, respectively. For InSb, it is shown that both elements are oxidized to comparable extents, giving rise to In2O3 and probably Sb2O3. The rate of oxidation decreases in the order InSb>GaP>GaAs. The behaviors of thermal oxidation of GaAs and GaP are shown to be different.The formation of a GaPOx network which leads to GaPO4 at elevated temperatures is discussed.

https://iopscience.iop.org/article/10.1143/JJAP.17.1925/pdf

X-Ray Photoemission Study of the Oxidation Process at Cleaved (110) Surfaces of GaAs, GaP and InSb

Early stages of gold‐film formation on graphite by gold vapor deposition have been studied by means of scanning tunneling microscope (STM). Several kinds of microclusters of about 2 nm in diameter, as nuclei for film formation, are resolved to an atomic scale. Fine particles of 5–10 nm in diameter grow at nucleation sites. These particles aggregate and coalesce with each other to form large islands. The growth pattern depends on the substrate temperature. Dendritic islands are observed at a substrate temperature of around 80 °C

Dendritic aggregation of gold particles on graphite surface

A computational method to deduce depth profiles of elements from the dependence of the spectral intensity on angle has been formulated. The method is formulated as the minimization of the sum of the squares of the differences between experimental and theoretically expected relative intensities at all data points subject to proper constraints for elemental concentrations. A system consisting of a Mo substrate with a Cs overlayer [W. A. Fraser et al.: Surface Sci. 36 (1973) 661] has been analyzed. Depth distributions depend very sensitively both on the absolute value of the spectral intensity and its angular dependence.

Ryusuke Nishitani

Papers

An XPS Analysis of Thermally Grown Oxide Film on GaP

X-Ray Photoemission Study of the Oxidation Process at Cleaved (110) Surfaces of GaAs, GaP and InSb

Dendritic aggregation of gold particles on graphite surface

Determination of Depth Profiles by Angular Dependent X-Ray Photoelectron Spectra

STM fluorescence of porphyrin enhanced by a strong plasmonic field and its nanoscale confinement in an STM cavity