Alexander Kazimirov

Structure of pentacene thin films

Grazing incidence x-ray diffraction, x-ray reflectivity and atomic force microscopy have been performed to study the structure of pentacene thin films on oxidized Si substrates from submonolayer to multilayer coverages. The volume of the unit cell in the thin film phase is almost identical to that of the bulk phase, thus the molecular packing efficiency is effectively the same in both phases. The structure forming from the first monolayer remains the same for films at least 190A thick. The in-plane structure of the submonolayer islands also remains unchanged within a substrate temperature range of 0<Tsub<45°C while the island size changes by more than a factor of 4.

Experimental measurement of lattice strain pole figures using synchrotron x rays

This article describes a system for mechanically loading test specimens in situ for the determination of lattice strain pole figures and their evolution in multiphase alloys via powder diffraction. The data from these experiments provide insight into the three-dimensional mechanical response of a polycrystalline aggregate and represent an extremely powerful material model validation tool. Relatively thin (0.5mm) iron/copper specimens were axially strained using a mechanical loading frame beyond the macroscopic yield strength of the material. The loading was halted at multiple points during the deformation to conduct a diffraction experiment using a 0.5×0.5mm2 monochromatic (50keV) x ray beam. Entire Debye rings of data were collected for multiple lattice planes ({hkl}’s) in both copper and iron using an online image plate detector. Strain pole figures were constructed by rotating the loading frame about the specimen transverse direction. Ideal powder patterns were superimposed on each image for the purpos...

Atomic-scale structure of the SrTiO3(001)-c(6×2) reconstruction : Experiments and first-principles calculations

The c(6×2) is a reconstruction of the SrTiO3(001) surface that is formed between 1050 and 1100 °C in oxidizing annealing conditions. This work proposes a model for the atomic structure for the c(6×2) obtained through a combination of results from transmission electron diffraction, surface x-ray diffraction, direct methods analysis, computational combinational screening, and density functional theory. As it is formed at high temperatures, the surface is complex and can be described as a short-range-ordered phase featuring microscopic domains composed of four main structural motifs. Additionally, nonperiodic TiO2 units are present on the surface. Simulated scanning tunneling microscopy images based on the electronic structure calculations are consistent with experimental images.

Microbeam high-resolution x-ray diffraction in strained InGaAlAs-based multiple quantum well laser structures grown selectively on masked InP substrates

Structural and optical properties of the InGaAlAs-based multiple quantum well (MQW) 1.3μm laser structures produced on InP (001) substrates by metal organic vapor phase epitaxy (MOVPE) technique in the regime of selective area growth (SAG) have been studied. An x-ray beam of 10μm diameter generated by a microbeam high-resolution x-ray diffraction (μ-HRXRD) setup based on an imaging one-bounce capillary optic and a three-bounce channel cut Si(004) analyzer crystal has been utilized to measure the diffraction curves from MQW structures grown between oxide mask stripes. The high angular resolution achieved in our experiments allowed accurate measurements of θ–2θ scans over a broad range of angles that was necessary for utilization of fitting algorithms for quantitative analysis of the strain and thickness of individual layers in the MQW structures. The thickness and strain variations in the quantum well and the barrier layers of the MQW SAG structure have been analyzed as a function of the oxide mask width i...

High energy x-ray diffraction/x-ray fluorescence spectroscopy for high-throughput analysis of composition spread thin films

High-throughput crystallography is an important tool in materials research, particularly for the rapid assessment of structure-property relationships. We present a technique for simultaneous acquisition of diffraction images and fluorescence spectra on a continuous composition spread thin film using a 60 keV x-ray source. Subsequent noninteractive data processing provides maps of the diffraction profiles, thin film fiber texture, and composition. Even for highly textured films, our diffraction technique provides detection of diffraction from each family of Bragg reflections, which affords direct comparison of the measured profiles with powder patterns of known phases. These techniques are important for high throughput combinatorial studies as they provide structure and composition maps which may be correlated with performance trends within an inorganic library.

Structure of a pentacene monolayer deposited on SiO2: Role of trapped interfacial water

In situ synchrotron x-ray reflectivity is used to probe the early stages of pentacene growth in real time, under conditions relevant to the fabrication of organic thin film transistors. The results reveal that there is an interfacial water layer initially present on the SiO2 substrate and that this water layer is still present at the interface after the deposition of a pentacene thin film. The thickness of the trapped interfacial water layer does not significantly change subsequent to film deposition, even after exposure to atmospheric pressure or during vacuum annealing at 70°C. However, a water layer is observed to form on the free surface of pentacene after sufficient exposure to water vapor, and the thickness of this layer can be reduced by subsequent vacuum annealing. These observations are correlated with organic thin film transistor mobilities measured at atmospheric pressure versus under vacuum.

The X-ray standing wave technique : principles and applications

Part I: X-Ray Standing Waves in a Nutshell (Jorg Zegenhagen and Alexander Kazimirov) Dynamical Theory of X-Ray Standing Waves in Perfect Crystals (Andre Authier) X-Ray Standing Wave in Complex Crystal Structures (Victor Kohn) X-Ray Standing Wave in a Backscattering Geometry (D P Woodruff) X-Ray Standing Wave at the Total Reflection Condition (Michael J Bedzyk) X-Ray Standing Wave at Grazing Incidence and Exit (Osami Sakata and Terrence Jach) X-Ray Standing Wave in Multilayers (Michael J Bedzyk and Joseph A Libera) Kinematical X-Ray Standing Waves (Martin Tolkiehn and Dmitri V Novikov) X-Ray Waveguides (Ianna Bukreev, Alessia Cedola, Daniele Pellicia, Werner Jark and Stefano Lagomarsino) Compton Scattering from X-Ray Standing Wave Field (Vladimir Bushuev) Theory of Photoelectron Emission from an X-Ray Interference Field (Ivan A Vartanyants and Jorg Zegenhagen) Site-Specific X-Ray Photoelectron Spectroscopy Using X-Ray Standing Waves (Joseph C Woicik) Experimental Basics (Alexander Kazimirov and Jorg Zegenhagen) Part II: XSW Imaging (Michael J Bedzyk and Paul Fenter) X-Ray Standing Waves in Quasicrystals: Atomic Positions in an Aperiodic Lattice (Terrence Jach) X-Ray Standing Waves in Thin Crystals: Probing the Polarity of Thin Epitaxial Films (Alexander Kazimirov, Jorg Zegenhagen, Tien-Lin Lee and Michael Bedzyk) Isotopic Effect on the Lattice Constant of Germanium and Silicon (Alexander Kazimirov, Jorg Zegenhagen, Evgeny Sozontov, Victor Kohn and Manuel Cardona) Biomembrane Models and Organic Monolayers on Liquid and Solid Surfaces (S I Zheludeva, N N Novikova, M V Kovalchuk, N D Stepina, E A Yurieva, E YU Tereschenko and O V Konovalov) Applications of XSW in Interfacial Geochemistry (Paul Fenter) Complex Surface Phases of Sb on Si(113): Combining XSW and Density Functional Theory (M Siebert, Th Schmidt, J I Flege and J Falta) X-Ray Standing Wave Analysis of Non-Commensurate Adsorbate Structures Produced by Ga Adsorption on Ge(111) (Jorg Zegenhagen) Photon Stimulated Desorption (Jan Ingo Flege, Thomas Schmidt, Jens Falta, Alexander Hille and Gerhard Materlik) Depth-Profiling of Marker Layers Using X-Ray Waveguides (Ajay Gupta) Coherent Diffraction Imaging with Hard X-Ray Waveguides (Liberato de Caro and Cinzia Giannini, Daniele Pelliccia, Alessia Cedola and Stefano Lagomarsino) X-Ray Standing Wave for Chemical-State Specific Surface Structure Determination (D P Woodruff) Site-Specific X-Ray Photoelectron Spectra of Transition-Metal Oxides (Joseph C Woicik) Probing Multilayer Nanostructures with Photoelectron and X-Ray Emission Spectroscopies Excited by X-Ray Standing Waves (S-H Yang, B C Sell, B S Mun and C S Fadley).

Strain relaxation and surface migration effects in InGaAlAs and InGaAsP selective-area-grown ridge waveguides

Surface migration of the group-III precursors and strain relaxation at the ridge sidewalls are compared for 2.5μm wide waveguides based on InGaAsP and InGaAlAs multiple-quantum-well (MQW) structures. The cross-sectional thickness and strain variations have been measured using synchrotron radiation-based x-ray diffraction with an angular resolution of 2arcs and a beam size of (0.24×0.35)μm2. Indium-rich overgrowth has been observed for the InGaAsP-based waveguides, while InGaAlAs-based waveguides demonstrate thickness uniformity of the MQW active region with a strain relief of 0.4%∕μm at the sidewalls.

High-resolution x-ray study of thin GaN film on SiC

The x-ray standing wave method (XSW) and high-resolution x-ray diffraction were used to study the structural perfection and polarity of GaN epitaxial thin film grown by hydride vapor phase epitaxy on the Si-face SiC substrate. The x-ray standing wave was generated inside the 300 nm thin film under the condition of Bragg diffraction from the film. Excellent crystalline quality of the GaN film was revealed by both x-ray techniques. The XSW analysis of the angular dependencies of the Ga–K fluorescence yield measured while scanning through the GaN(0002) diffraction peak unambiguously showed the Ga polarity of the film. Correlation between the mosaic structure and the static Debye–Waller factor of the GaN lattice was also studied.

Microbeam high angular resolution x-ray diffraction in InGaN∕GaN selective-area-grown ridge structures

GaN-based 6-μm-wide ridge waveguides with InGaN∕GaN multiple-quantum-wells (MQWs) produced by metal organic vapor-phase epitaxy in the regime of selective-area growth have been studied with microbeam high angular resolution x-ray diffraction and reciprocal-space mapping. Variation of the strain from 0.9% to 1.05% and a factor of 3 for the thickness enhancement of the MQW period have been measured for different widths of the oxide mask surrounding the GaN-based ridges. Only when the trapezoidal shape of the ridge cross section is taken into account can the difference between the experimentally measured thickness enhancement and predictions of the long-range gas-phase diffusion model be reconciled.