Lev D. Pokrovsky

Morphology and structure of hexagonal MoO3 nanorods

We have prepared h-MoO3 nanocrystals in the form of well-faceted straight hexagonal rods with an aspect ratio of l/d ≃ 60. The nanocrystals have been characterized by x-ray diffraction, scanning and transmission electron microscopy, and IR/Raman spectroscopy. Their phase composition has been determined, and their morphology and spectroscopic properties have been studied in detail.

Enhanced optical constants of nanocrystalline yttrium oxide thin films

Yttrium oxide (Y2O3) films with an average crystallite-size (L) ranging from 5 to 40 nm were grown by sputter-deposition onto Si(100) substrates. The optical properties of grown Y2O3 films were evaluated using spectroscopic ellipsometry measurements. The size-effects were significant on the optical constants and their dispersion profiles of Y2O3 films. A significant enhancement in the index of refraction (n) is observed in well-defined Y2O3 nanocrystalline films compared to that of amorphous Y2O3. A direct, linear L-n relationship found for Y2O3 films suggests that tuning optical properties for desired applications can be achieved by controlling the size at the nanoscale dimensions.

Surface crystallography and electronic structure of potassium yttrium tungstate

Structural and electronic characteristics of KY(WO4)2 (KYW) (010) crystal surfaces have been studied using reflection high-energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). The results indicate that the crystal structure and chemical composition of the mechanically polished pristine surface is stoichiometrically well maintained as expected for KYW crystals. Combined measurements of RHEED and XPS as a function of 1.5 keV Ar+ ion irradiation of the KYW (010) surfaces indicate amorphization, partial loss of potassium atoms, and partial transformation of chemical valence state of tungsten from W6+ to a lower valence state, W0 state predominantly, which induces electronic states at the top of valence band.

Structure and chemical properties of molybdenum oxide thin films

Molybdenum oxide (MoO3) exhibits interesting structural, chemical, electrical, and optical properties, which are dependent on the growth conditions and the fabrication technique. In the present work, MoO3 films were produced by pulsed-laser deposition and dc magnetron sputtering under varying conditions of growth temperature (Ts) and oxygen pressure (pO2). The effect of growth conditions on the structure and chemical properties of MoO3 films was examined using x-ray diffraction, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopic measurements. The analyses indicate that the microstructure of Mo oxide films is sensitive to Ts and pO2. The growth conditions were optimized to produce stoichiometric and highly textured polycrystalline MoO3 films. A comparison of the microstructure of MoO3 films grown using pulsed-laser deposition and sputtering methods is also presented.

Superstructure formation and X-ray photoemission properties of the TlTiOPO4 surface

X-ray photoemission spectroscopy (XPS) measurements have been executed for TlTiOPO4 to elucidate the general features in the electronic structure of the KTiOPO4 family compounds. The peculiarities of the valence band structure have been discussed for the crystals. The persistence of core level binding energy differences O1s–P2p and O1s–Ti2p3/2 has been detected in TlTiOPO4 and KTiOPO4, which relates well with the constancy of averaged P–O and Ti–O chemical bond lengths in this crystal family. The superstructure ordering of the TlTiOPO4 surface subjected to polishing and annealing has been detected by reflectance high energy electron diffraction (RHEED). From comparison of surface crystallographic properties of TlTiOPO4 and KTiOPO4, the most typical superstructure indices have been revealed.

Restoration of KTiOPO4 surface by annealing

Abstract Superstructure ordering with a=a0, b=b0 and c=4c0 has been observed for KTiOPO4 surfaces annealed at the temperatures 200–800 °C by reflection high energy electron diffraction. The surface decomposition with the precipitation of TiO2 as anatase polycrystal modification has been revealed in the temperature range 800–900 °C.

Growth and microstructure of heterogeneous crystal GaSe:InS

An optical quality GaSe:InS single crystal has been grown by modified Bridgman technique using nonstationary temperature distribution for effective melt mixing. The phase composition of the crystal has been verified with XRD and TEM. The chemical composition variation along the crystal has been evaluated with electron probe microanalysis (EPMA), atomic-emission spectrometry with inductively-coupled plasma (ICP-AES) and atomic-absorption spectrometry (AAS). The joint solubility limits in the GaSe:InS system are measured as yIn = 0.28 at% and yS = 7 at%. The optical properties of GaSe:InS crystal have been obtained with spectroscopic ellipsometry (SE).

Amorphization and chemical modification of β-BaB2O4 surface by polishing

Abstract Structure and chemical composition of mechanically polished β-BaB2O4 surface have been studied by reflection high energy electron diffraction and X-ray photoelectron spectroscopy. It has been shown that the optical surface is covered by thick layer of amorphous phase closely related to BaB2O4 in Ba/O atomic ratio and electronic structure. The presence of BaCO3 has been detected in top surface regions.

Cesium accumulation at CsB3O5 optical surface

Abstract Structure and element composition of polished CsB 3 O 5 surface have been studied. It has been shown that crystal surface is covered by thick layer (>50 A) of amorphous phase. This surface compound contains Cs, B and O and contaminated by hydrocarbons adsorbed on the surface. Element depth profiling produced by ion sputtering reveals quick and monotonic drop of C signal accompanied by increases of B and O signals with stabilization at depths higher than ∼20 A. The distribution of Cs over depth is irregular, top surface cesium content is ∼30% higher then that achieved for higher sputtering times. Being removed by sputtering, this top surface layer enriched by Cs is restored by few hours keeping at 24 °C in vacuum or air.

Structure and Refractive Indices of Proton-Implanted LiNbO3

Structural damage is found in -c-cut LiNbO3 single-crystal surfaces in which 1×1017 cm-2 protons are implanted. The observed damage is accompanied by a large decrease in the ordinary-ray refractive index, no, which falls to the same level as the extraordinary-ray refractive index, ne. The mechanism of the phenomenon can be explained by disordering in the implanted layer.