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The structural dynamics of an iodide layer adsorbed on Au(111) were investigated using X-ray photon correlation spectroscopy (XPCS), electrochemical scanning tunneling microscopy (STM), and time-resolved X-ray diffraction. At the adsorption equilibrium of iodide at a constant electrode potential, the STM images captured at regular intervals show the migration of atomic vacancy sites in the ordered adsorbed iodide layer. The results indicate that reversible adsorption/desorption and site conversion continuously occur at the equilibrium state. Although the transitions occur at various time scales according to the STM images, the time decay of the autocorrelation function at the specular position is estimated to be 127 s according to the XPCS measurement. The dynamics observed using XPCS suggest that the vertical relaxation of the surface layers is associated with the adsorption of iodide.

The beamline for angle-resolved photoemission spectroscopy (ARPES) with a nano-focused beam (nano-ARPES) is planned as one of the public beamlines in NanoTerasu, the 3-GeV next-generation synchrotron radiation facility at Tohoku, Japan, which is scheduled to start operation in 2024. A 4 m long APPLE-II type undulator provides brilliant soft X-rays with various polarizations (linear horizontal and vertical, and left and right circular) in the energy range of 50-1,000 eV. A collimated plane grating monochromator is adopted as a soft X-ray monochromator because we can select the demagnification factor of grating cf f = cosα/cosβ between the high energy-resolution (HR) mode for HR-ARPES experiments and the low divergence mode for high-flux nano-ARPES measurements. This beamline aims to produce the high flux nano-focused beam by using ultrahigh precision reflective mirror optics, not a Fresnel zone plate used as a focusing optics in the previous nano-ARPES station at other synchrotron facilities.

A synchrotron radiation beamline in the soft- and tender-X ray energy range of 180-3000 eV with versatile polarization control has been designed for NanoTerasu, the 3-GeV next-generation synchrotron radiation facility at Tohoku, Japan. A series of four APPLE-II type undulators is adopted as a photon source to realize the required beam properties with high-speed polarization switching. The beamline optics is designed for a highly efficient and precise use of x-ray magnetic circular/linear dichroism (XMCD/XMLD) technique balancing high photon flux and energy resolution. The simulated performance of the segmented undulator together with the monochromator optics achieved the sufficiently high flux and energy resolution (E/ΔE) in whole target energy range. Two endstations with the different re-focus optics, one for marginal spot size with high flux and the other for ultimate focus down to ∼10 nm are also designed. The simulated performance of the beamline encourages the future researches of high-throughput and nm-focused spintronic measurements.

The optical design of the ultrahigh-resolution RIXS beamline, which is currently developed at NanoTerasu in Japan, is described. The main goal of this beamline is to perform ultrahigh-resolution RIXS measurements with a total energy resolution of E/ΔE>150,000 for both beamline and RIXS spectrometer. To achieve the ultra-high resolution, a 2D-RIXS spectrometer using energy-dispersive X-ray is employed to compensate for lower throughput at higher energy resolution, and the optics of the beamline is optimized for the 2D-RIXS spectrometer. A vertically dispersing in-focus variable-included-angle varied-line-spacing plane grating monochromator is employed for the beamline, with an entrance slit to ensure the ultrahigh resolution. First and second mirrors focus X-ray on entrance slits vertically and horizontally, respectively, and the divergent X-ray is irradiated onto the grating. For the 2D-RIXS spectrometer, there is no exit slit, and the vertically energy-dispersed X-ray is irradiated directly onto a sample. In front of the sample, X-ray is horizontally refocused by a Wolter type-I mirror. The expected horizontal focus size at the sample is ~0.7 μm. The expected photon flux is ~1×1011 photons/s at 500–1000 eV with a virtual slit width of 2 μm required for E/ΔE>150,000. The height of the dispersed X-ray available in the 2D-RIXS spectrometer is ~120 μm, which allows the use of a remarkably high flux of ~6×1012 photons/s, and the beamline will serve as an ultrahigh-resolution and high-efficiency RIXS facility.

Using in situ synchrotron X-ray reciprocal space mapping, this study investigates the evolution of lattice deformations in the InGaAs/GaAs(1 1 1)A structure with or without a thin InAs layer grown by molecular beam epitaxy. During the initial growth phase, InGaAs directly grown on GaAs(1 1 1)A showed an anomalous lattice shrinkage along the c-axis, with no change in the indium composition. Conversely, the InGaAs grown on InAs/GaAs(1 1 1)A showed no initial lattice distortion, but a variable indium composition. The evolution of the diffraction peak broadening was also monitored. The results confirmed that the thin InAs layer effectively improved the crystal quality during the initial growth of InGaAs.

In this study, we analyzed the influence of indium supply on the growth dynamics of gold-catalyzed InGaAs nanowires by in situ synchrotron X-ray diffraction. A high In/Ga supply ratio results in strong size inhomogeneity of Au particles and interrupts the nanowire growth at a certain point of time. Based on the experimental results, we discussed the state of Au catalysts with high indium content during the nanowire growth. We found that a growth temperature below the eutectic temperature is essential to avoid the growth interruption and maintain the nanowire growth. The high In/Ga ratio necessitates accurate size control of Au particles before growth for further improvement of the nanowire growth.

Strain relaxation of InxGa1−xAs/GaAs(001) with systematically changed In content between x=0.23 and x=0.80 has been studied using in situ synchrotron X-ray diffraction during molecular beam epitaxy growth. Correlation between the In composition and the degree of relaxation in the InGaAs films was derived from the reciprocal space maps. While InGaAs with a uniform composition was grown in the regime of the two-dimensional growth, a separation of the In composition was observed for the InGaAs films grown in the Stranski-Krastanov mode.

In this work, in situ synchrotron X-ray diffraction reciprocal space mapping (RSM) measurements were carried out for the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) growth of GaInN on GaN and InN layers, which were also grown by RF-MBE on commercialized GaN/c-sapphire templates. In situ XRD RSM measurements were performed using an MBE apparatus directly coupled to an X-ray diffractometer at the beamline of the synchrotron radiation facility SPring-8. It was observed in situ that both lattice relaxation and compositional pulling occurred during the initial growth stage, reducing the strain of GaInN on GaN and InN. Different initial growth behaviors of GaInN on GaN and InN were also observed from the results of the evolution of GaInN integrated peak intensities.

In situ synchrotron X-ray reciprocal space mapping was carried out to investigate the evolution of lattice strain and crystal structure of InGaN/GaN heterostructure nanowires grown by molecular beam epitaxy. At the beginning of the growth, the InGaN lattice was compressively strained to that of GaN, resulting in the pseudomorphic growth. This strain started to relax at a thickness of 3 nm and fully relaxed at 9 nm. Concomitantly, polytypes consisting of the zinc-blende and wurtzite phases were formed in InGaN., Compound Semiconductor Week 2019

The molecular beam epitaxial (MBE) growth of twenty-period InGaN/GaN multi-quantum-well (MQW) nanowires was investigated by in situ X-ray reciprocal space mapping (in situ RSM). The evolution of strain, composition, and their inhomogeneities during the growth significantly varied with increasing number of QWs. After the growth of the ninth QWs, InGaN was tensilely strained with poor crystalline quality as inferred from the diffraction peak position and shape. At the same time, another peak emerged at the higher indium composition, suggesting the segregation of InN in the MQW nanowires., Compound Semiconductor Week 2019

In recent years, graphene growth technology has been greatly progressed, and it is possible to grow graphene with millimeter-size single crystals using metal-catalysis CVD. However, the transfer process is unavoidably which largely deteriorates the graphene. We have proposed direct precipitation method of graphene using a W capping layer. The method does not only require a transfer process, but also the introduction of wrinkles will be suppressed by optimizing the cooling rate at the graphene precipitation. The growth conditions such as thickness of amorphous carbon, annealing temperature, cooling rate and crystallinity of Ni catalyst were systematically changed to study the mechanism of the precipitation method using the W cap layer. By the optimization of the conditions, wrinkle-free multilayer graphene with D/G ratio of less than 0.1 were successfully obtained directly on a sapphire substrate.

In situ X-ray diffraction measurement was performed to study the precipitation mechanism of graphene from Ni catalyst with and without Ti capping layer using X-ray beam from a synchrotron radiation facility. The graphene precipitated on the surface of the catalyst in the case without the Ti capping layer while it did at the interface between the catalyst and the sapphire substrate in the case with the Ti capping layer. Each process, such as graphene nucleation and precipitation was successfully monitored even though graphene precipitated under the metal catalyst. The detailed mechanisms for both cases were discussed using the experimental results. Consequently, the crystallization of the catalyst is found to effectively suppress the precipitation at low temperature, which is useful to improve the quality of the precipitated graphene. The adjustment of the amount of the carbons is another important factor to precisely control the precipitation because graphene also precipitates after the carbons saturate the catalyst.

In-situ X-ray diffraction was used to investigate initial stages of GaN growth on graphene-covered SiO2 substrates with or without AlN buffer layers by plasma-assisted molecular beam epitaxy. The in-plane lattice parameter of GaN remained almost constant during growth without AlN buffer layers, confirming weak interactions between GaN and graphene. On the substrate with AlN buffer layers, the GaN lattice parameter continuously changed from AlN value to GaN value, indicating that the AlN islands act as seeds for GaN growth. Besides, GaN has preferential orientations epitaxial to graphene. Graphene can be used as a template of GaN growth on amorphous substrates.

We carry out real-time in situ synchrotron X-ray diffraction on the growth of GaN and AlN on SiC(0001) substrate by molecular beam epitaxy. At the initial growth stage of GaN/SiC or AlN/SiC heterostructure, the epitaxial overlayer develops affected by defects with the strain interaction between SiC, eventually showing characteristic lattice deformations. GaN was almost relaxed at the initial stage, showing the transition of the growth mode from 3D to 2D at around 4 nm. In contrast, AlN coherently grow on SiC(0001) at the initial stage for 13 nm concomitantly showing lattice deformation with the beneath SiC, subsequently showing gradual lattice relaxation.

The evolution of polytypism during GaAs nanowire growth was investigated by in situ X-ray diffraction. The growth of nanowires was found to start with the formation of zincblende structure, followed by the growth of wurtzite structure. The growth process was well reproduced by a simulation based on a layer-by-layer nucleation model. The good agreement between the measured and simulated results confirms that nucleation costs higher energy for the stackings changing the crystal structure than for those conserving the preceding structure. The transition in prevalent structure can be accounted for by the change of local growth conditions related to the shape of a triple phase line rather than by the change in supersaturation level, which quickly reaches steady state after starting growth.

Synchrotron X-ray diffraction has been applied to the in situ monitoring of the molecular beam epitaxial growth of self-assembled InAs/GaAs(001) quantum dots (QDs). As well as the strain distribution inside QDs, the lateral and vertical size of QDs was determined as a function of growth time. In combination with post-growth atomic force microscopy, the evolution of the total volume of QDs was evaluated. It was found that the QD volume increases at a similar rate over the temperature range of 450–480 °C. A significant mass transport from the wetting layer and the substrate was confirmed.

In situ three-dimensional X-ray reciprocal space mapping ( in situ 3D-RSM) was employed for studying molecular beam epitaxial (MBE) growth of InGaAs multilayer structures on GaAs(0 0 1). Measuring the symmetric 004 diffraction allowed us to separately obtain film properties of individual layers and to track the real-time evolution of both residual strain and lattice tilting. In two-layer growth of InGaAs, significant plastic relaxation was observed during the upper layer growth, and its critical thickness was experimentally determined. At the same thickness, it was found that the direction of lattice tilting drastically changed. We discuss these features based on the Dunstan model and confirm that strain relaxation in the multilayer structure is induced by two kinds of dislocation motion (dislocation multiplication and the generation of dislocation half-loops).

Defect characterization in molecular beam epitaxial (MBE) compositionally-graded InxGa1-xAs layers on GaAs substrates consisting different thickness of overshooting (OS) layers was carried out using cathodoluminescence (CL) and transmission electron microscopy (TEM). We found that the thickness of the OS layer influences not only stress but also lattice defects generated in a top InGaAs layer. While the top InGaAs layer with a thin OS layer is under compression and has mainly threading dislocations, the top layer with a thick OS layer is under tension and exhibits inhomogeneous strain associating with phase separation. We will discuss the mechanisms of defect generation and their in-plane distribution based on strain relaxation at the top and OS layers. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Multilayer structures comprised of a central layer of the binary transition metal pnictide MnSb and outer layers of standard semiconductors have been grown using molecular beam epitaxy (MBE). The growth of the GaAs overlayers was characterized using a combination of reflection high energy electron diffraction (RHEED) and in situ surface x-ray diffraction (SXRD). It was found that a GaAs overlayer can be grown via MBE onto a MnSb(1 101)/GaAs(001) virtual substrate. For both GaAs(111)A and InGaAs(111)A starting substrates, it was found that the GaAs overlayer altered the final strain state of the central MnSb layer causing a change from tensile strain to compressive strain in the out of plane direction.

In situ synchrotron X-ray diffraction studies during the growth of arsenide and nitride semiconductors are presented. The large penetration depth of X-rays was exploited for revealing structural changes at buried interfaces as well as near the surface. Experiments were performed at a synchrotron beamline, BL11XU, SPring-8, using a molecular-beam epitaxy chamber integrated with a high-precision X-ray diffractometer. A high-speed X-ray reciprocal space mapping technique was applied to a variety of heteroepitaxial systems including InGaAs on GaAs(001), InGaAs on GaAs(111)A and GaN on SiC(0001). Results showed that even layers as thick as 200 nm were not necessarily stable even after being buried under an overlayer but could undergo significant structural changes during growth.

This paper describes the development of a high-speed three-dimensional reciprocal-space mapping method designed for the real-time monitoring of the strain relaxation process during the growth of heterostructure semiconductors. Each three-dimensional map is obtained by combining a set of consecutive images, which are captured during the continuous rotation of the sample, and calculating the reciprocal-space coordinates from the detector coordinate system. To demonstrate the feasibility of this rapid mapping technique, the 022 asymmetric diffraction of an InGaAs/GaAs(001) thin film grown by molecular beam epitaxy was measured and the procedure for data calibration was examined. Subsequently, the proposed method was applied to real-time monitoring of the strain relaxation process during the growth of a thin-film heterostructure consisting of In0.07Ga0.93As and In0.18Ga0.82As layers consecutively deposited on GaAs(001). The time resolution of the measurement was 10 s. It was revealed that additional relaxation of the first In0.07Ga0.93As layer was induced by the growth of the second In0.18Ga0.82As layer within a short period of time corresponding to the deposition of only two monolayers of InGaAs.

The InSb(111)A surface is prepared by molecular beam epitaxy and investigated by reflection high-energy electron diffraction (RHEED). The complete two dimensional diffraction pattern is mapped out by azimuthal RHEED (ARHEED). Two reconstructions are identified and additionally a set of new symmetries is observed. At low temperature a 2 3 × 2 3 pattern is observed which changes to the (2 × 2) pattern at high temperature. In contrast to the GaSb(111)A surface the observed 2 3 × 2 3 structure is not stabilized by configurational entropy.

The effects of In incorporation on anisotropies in the strain relaxation mechanisms of InGaAs on GaAs systems are investigated using a three-dimensional reciprocal space mapping (3D-RSM) technique. Relaxation processes are classified as belonging to one of the following four phases: no relaxation, gradual relaxation, rapid relaxation, and relaxation saturation. Anisotropies appear in the gradual relaxation phase and almost disappear in the rapid relaxation phase. These anisotropies are enhanced by In content. When In content is low, both α- and β-misfit dislocations (MDs) are observed at the same thickness; the density of α-MDs increases more rapidly than that of β-MDs. When In content is high, only α-MDs appear in the gradual relaxation phase. These results suggest that In atoms prevent nucleation and/or gliding of β-MDs.

Ag/AgCl reaction at the Ag bilayer, which was underpotentially prepared on a Au(111) surface, was investigated using electrochemical quartz crystal microbalance (EQCM), scanning tunneling microscopy (STM), surface X-ray scattering (SXS), and electrochemical techniques. When the potential was scanned positively from -200 mV, the Cl^[-] ion was adsorbed on the Au(111) electrode surface around 0 mV, and then the phase transition of the adsorbed Cl^[-] ion layer from random orientation to (√3 x √3) structure took place at around +130 mV. The Ag bilayer and Cl^[-] ions were oxidatively reacted to form the AgCl monolayer with (√13 x √13)R13.9° structure around +200 mV, accompanied with the formation of AgCl monocrystalline clusters on the AgCl monolayer surface. The structure of the AgCl monolayer on the Au(111) surface was changed from (√13 x √13)R13.9° structure to (4 x 4) structure around +500 mV. When the potential was scanned back negatively, the AgCl monolayer was electrochemically reduced, and a Ag monolayer, not a bilayer, was formed on the Au(111) surface. In the subsequent potential cycles, the structural change between the Ag monolayer and the AgCl monolayer was reversibly observed. All oxidative structural changes were much slower than the reductive ones.

Growth temperature dependence of strain relaxation during In 0.12 Ga 0.88 As/GaAs(0 0 1) molecular beam epitaxy was studied by in situ X-ray reciprocal space mapping. Evolution of the residual strain and crystal quality for the InGaAs film was obtained as a function of film thickness at growth temperatures of 420, 445 and 477 °C. In the early stages of strain relaxation, it was found that evolution of the residual strain and crystal quality was dependent on the growth temperature. In order to discuss this observation quantitatively, the strain relaxation model was proposed based on the Dodson-Tsao kinetic model, and its validity was demonstrated by good agreement with the experimental residual strain. Additionally, rate coefficients reflecting dislocation motions during strain relaxation were obtained as a function of growth temperature and strain relaxation was discussed in terms of the thermally active dislocation motion.

The interfacial structures of Ag bilayer prepared by underpotential deposition on Au(111) (Ag(2ML)/Au(111)) were determined by ex situ scanning tunneling microscopy and in situ surface X-ray scattering measurements before and after oxidative adsorption and after reductive desorption of a self-assembled monolayer (SAM) of hexanethiol (C6SH) in alkaline ethanol solution. While no structural change was observed after oxidative formation of C6SH SAM on the Ag(2ML)/Au(111) in an ethanol solution containing 20 mM KOH and 0.1 mM C6SH, some of the Ag atoms in the bilayer were stripped when the SAM was reductively desorbed.

Surface x-ray diffraction was employed, in situ, to measure the GaSb(001)-(1 × 5) and (1 × 3) surface phases under technologically relevant growth conditions. We measured a large set of fractional-order in-plane diffraction peaks arising from the superstructure of the surface reconstruction. From the data we calculated two-dimensional (2D) Patterson functions, the peaks of which represent inter-atomic distances weighted by the number of electrons in the individual atoms. For the (1 × 3) phase we obtained good agreement between our data and the β(4 × 3) model proposed in recent experimental and theoretical work. Our measurements on the Sb-rich (1× 5) phase provide evidence that the structure under growth conditions is, in fact, different from that of the models previously suggested on the basis of scanning tunneling microscopy (STM). We discuss reasons for this discrepancy as well as the identified structural elements for these reconstructions, which include surface relaxations and subsurface rearrangement.

An Sb-adsorbed GaAs(0 0 1) substrate that serves as a template for high-density InAs quantum dot (QD) growth was investigated using in situ X-ray diffraction. The Sb distribution in the top eight layers from the surface was determined by crystal truncation rod scattering analysis. It was found that Sb atoms penetrated to the eighth layer when GaAs(0 0 1) came in contact with an Sb environment. The amounts of Sb in the first and second layers were, however, saturated at 1 3 atomic layer (AL) and 2 3 AL, respectively. A comparison between the X-ray results and atomic force microscopy observations of the QD density showed that the formation of high-density QDs is correlated with the total amount of Sb in the surface and subsurface layers.

Potential-dependent surface structures of Au(111) and Au(100) single-crystal electrodes in a 50 mM H2SO4 solution were investigated at an atomic level using in situ surface X-ray scattering (SXS) techniques. It was confirmed that both the Au(111) and Au(100) surfaces were reconstructed with an attached submonolayer of an oxygen species, most probably water, at 0 V (vs Ag/AgCl). Results at +0.95 V supported a previously suggested model for both the Au(111) and the Au(100) electrodes that, based on infrared and scanning tunneling microscopy measurements, the surfaces were a (1 x 1) structure with the coadsorbed sulfate anion and hydronium cation (H3O+). At +1.05 V, where a small amount of an anodic current flowed, adsorption of a monolayer of oxygen species was observed on both surfaces. When the single-crystal gold electrodes were electrochemically oxidized at +1.40 V, the expansion of the gold surface by about one monolayer of Au atoms was observed, suggesting the penetration of oxygen into the surface gold layers (i.e., the formation of two layers of surface oxide). When the surface oxide was reduced at +0.65 V, the surface structure returned back to the structure observed at +0.95 V before the oxide formation (i.e., a (1 x 1) structure with coadsorbed sulfate anion and H3O+). When the potential was reduced to 0 V, the surfaces were reconstructed again but with slightly more random structures than those before the potential cycle.

Surface structures of GaAs(0 0 1) under molecular beam epitaxy conditions are described on the basis of in situ X-ray diffraction measurements. Exploiting the high-intensity, high angular resolution and element sensitivity of synchrotron X-rays, we revealed the details of the most frequently used surfaces including several phases of ( 2 × 4 ) and c ( 4 × 4 ) .

The structural modification of InAs/GaAs(0 0 1) quantum dots (QDs) grown with 2.0 or 2.7 monolayers (ML) of InAs during annealing was investigated by a combination of in situ X-ray diffraction (XRD), reflection high-energy electron-beam diffraction (RHEED) and ex situ atomic force microscopy (AFM). For 2.0 ML in coverage, QD size increased due to the incorporation of Ga atoms into the QDs, after which QD ripening occurred. For 2.7 ML in coverage, on the other hand, the change in the strain energy due to enhanced intermixing of In and Ga atoms induced a morphological transition from three dimension (3D) to two dimension (2D). These results yielded some useful information about control of the SK QD structure during growth interruption.

The structure of epitaxially grown Pr2O3 on Si(0?0?1) has been investigated by grazing incidence x-ray diffraction and x-ray reflectivity. We report experimental results from measurements made in situ, after growth, and during annealing to determine the stability of Pr2O3 at temperatures relevant for complementary metal oxide semiconductor (CMOS) processing. Pr6O11 is evaporated and converted to Pr2O3 using an effusion source operating at 1970 ?C. Two different phases of Pr2O3 have been identified in the as-grown films in addition to a silicate layer that forms upon nucleation at the Si interface. The cubic Pr2O3 nucleates as a single crystal and grows in greater proportion to the polycrystalline hexagonal Pr2O3. The crystal structure of the as-grown film is stable during annealing up to about 800 ?C at which point the Pr2O3 is consumed at the expense of the silicate phase.

The surface structure of GaAs(0 0 1)-c(4 × 4) was investigated by synchrotron surface X-ray diffraction which is sensitive to both in-plane and out-of-plane structures. The atomic coordinates and Debye–Waller factors for up to the sixth layer from the surface are given. The resultant atomic coordinates were compared with those given by a first-principles calculation. Among a variety of heterodimer models that were examined by theoretical calculation, our data fit best a three-heterodimer model where three Ga–As heterodimers are present in one unit cell. The preference for the formation of heterodimers is discussed in relationship to the transition process from the 2 × 4 to the c(4 × 4) structures.

Molecular-beam epitaxial growth of InAs/GaAs(0 0 1) quantum dots was investigated by grazing-incidence X-ray diffraction using a diffractometer directly coupled to an molecular-beam epitaxy (MBE) apparatus. The use of synchrotron radiation and a two-dimensional X-ray detector enabled reciprocal space mapping at a rate of 9.6 s per frame. The X-ray diffraction images revealed that the strain and shape of the quantum dots change significantly during the sequential growth process consisting of island formation, growth interruption and GaAs encapsulation.

The molecular-beam epitaxial growth processes of GaAs on Si(001) were investigated using in situ synchrotron X-ray diffraction. Three-dimensional X-ray intensity distributions around the Si and GaAs 022 Bragg points in reciprocal space were measured during growth using combination of an area detector and one-axis scans. During the initial stage of growth, the average radius of GaAs islands was found to follow a second power law function of the growth time, in accordance with the growth being limited by the binding of Ga with As at step edges. With increasing GaAs thickness, streaky scattering extending from the GaAs 022 peak in the 〈 111 〉 directions was observed, indicating the development of plane defects.

The GaAs(0 0 1)-( 2 × 4 ) reconstructed surface was investigated by in situ surface X-ray diffraction. X-ray diffraction patterns were measured with increasing substrate temperature within the β phase of GaAs(0 0 1)-( 2 × 4 ) in a constant As flux of 5 × 1 0 − 7 Torr. At relatively low temperatures up to 545 ∘C, the observed X-ray diffraction patterns agree well with the β 2( 2 × 4 ) surface. However, a different X-ray diffraction pattern was obtained at temperatures close to the α phase, while the 2 × 4 periodicity still persisted. This change is explained by partial As-dimer desorption which results in a mixture of the β 2( 2 × 4 ) and α 2( 2 × 4 ) structures.

The dynamics of the molecular-beam-epitaxy (MBE) of GaAs (0 0 1) was investigated with a surface X-ray diffractometer coupled to an MBE chamber. The diffracted intensity of X-rays was measured in real time during growth. The temporal oscillation of the intensity for the growth at 550°C was explained well by the distributed-growth model, while the intensity for the growth at 435°C showed a complicated behavior arising from the changes in the surface reconstruction and the morphology. A method for separating the dynamics of the morphology from that of the reconstruction is presented.

An X-ray diffractometer connected with a molecular-beam epitaxy (MBE) system has been constructed for in situ studies on the growing surfaces of III–V compound semiconductors. This diffractometer is based on the (4+2) type, which has four axes for orienting the sample and two axes for positioning the detector. In addition, it is equipped with an axis for rotating the receiving slit about the normal of the slit plane to align the resolution of the receiving slit properly for the surface X-ray diffraction measurement. For the alignment of the sample and the entire setup with respect to the X-ray beam, an XYZ-stage and an adjustable base plate are available. X-rays enter and leave the chamber through two Be windows welded directly to the MBE chamber. A graphite sheet which can be heated up to 250°C is placed along the inside of the Be windows to protect the Be windows from being coated with evaporated materials. Preliminary data are presented to demonstrate the feasibility of static and dynamic measurements of growing surfaces using this instrument.

A newly designed spectroelectrochemical cell was constructed for surface X-ray scattering (SXS) to study single crystal electrodes. Electrochemical characteristics of a specific face of a single crystal electrode can be investigated in the meniscus mode, and SXS measurement can be easily carried out using the spectroelectrochemical cell. The usefulness of the present cell was demonstrated by studying the electrochemical deposition of thin Pd layers on Au(111) and Au(100) that require precise amounts of Pd deposits.

The effect of substrate orientation on strain relaxation mechanisms of an InGaAs layer grown on vicinal GaAs substrates was investigated by in situ X-ray diffraction (XRD). The crystallographic tilt and indium segregation in the InGaAs layer were altered depending on the miscut direction and angle. In the case of the substrate tilted 6° toward the [110] direction, one type of misfit dislocations was formed preferentially rather than other types, especially in the rapid relaxation phase. While in the case of the substrate tilted 6° toward the direction, no anisotropies during relaxation were observed. The present finding indicates that the appropriate use of vicinal substrates may lead to a novel method of improving the crystal quality of heterolayers.

Organopalladium species ({Pd}) immobilized on an Sterminated GaAs substrate (S/GaAs) effectively catalyzes C-C bond formation in the Mizoroki-Heck reaction with cycle durability. However, the immobilizing mechanism of {Pd} is unknown. In this study, we deposited Pd(OCOCH3)2 on S/GaAs in two different methods, namely dry-physical vapor-deposition and wetchemical deposition, and compared the catalytic activities in the Mizoroki-Heck reaction. Also, S-termination and {Pd}-immobilization on GaAs grains were performed by the wet-chemical method to monitor the change in the surface chemical structure during the preparation process with diffuse reflectance Fourier transform infrared spectroscopy (FT-IR). FT-IR measurements implied that the immobilization of catalytic active {Pd} was related to the OH groups on the S-terminated surface. {Pd}-S/GaAs prepared dryphysically showed poor catalytic activity, because {Pd} was not immobilized under absence of OH groups. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)