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We analyzed a number of complicated X-ray diffraction patterns using feature patterns obtained through unsupervised machine learning. A crystalline SiGe film on a Si substrate with a spatial fluctuation in both composition and crystal orientation was tested as a model sample having complicated X-ray diffraction patterns with multipeaks. Non-negative matrix factorization (NMF), an unsupervised machine learning method, was performed on 961 patterns obtained by spatial mapping of micro-beam X-ray diffraction measurements. Among the tested number of the feature patterns from 1 to 10, four feature patterns were the most useful for extracting the information about the composition and crystal orientation because they correspond to the diffraction patterns of typical SiGe films with high and low Si fraction, and right- and left-tilted orientation. Reasonable spatial maps of composition and crystal orientation were visualized using coefficients of the four feature patterns. Furthermore, the spatial constraint was tested for NMF using 225 diffraction patterns which were down-sized from 33 × 33 to 16 × 16 pixels due to the high computational cost of simple implementation without techniques to reduce the cost. Four feature patterns similar to those of the simple NMF without the constraints and the more reasonable distribution reflecting the SiGe spatial domain structure were obtained. The feature pattern extraction by NMF and interpretation by experts demonstrated in this study will be useful for quick analysis of a number of X-ray diffraction patterns with large and complicated fluctuations.

The three-dimensional ordering of the gallium (Ga) adlayers on GaN(0001) and (000 $\bar{1}$ ) surfaces was probed using in situ X-ray scattering under MBE conditions. An ordered bilayer of Ga forms on GaN(0001) but the ordering decreases at substrate temperatures of

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.

Advanced synchrotron radiation (SR) has been recognized as a premier research tool for developments of science and technology as well as for core industrial applications. Large-scale SR facilities around the world are constantly evolving, providing super brilliant and super directive X-rays. Consequently, a new range of applications in the nano-disciplines has been created. Since 2012, we have been pursuing a low emittance 3 GeV synchrotron radiation facility project: SLiT-J (Synchrotron Light in Tohoku, Japan). After extended deliberations, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan decided to initiate construction of the new 3 GeV facility on the campus of Tohoku University. The construction and operation of the facility will be carried out by a new organization. It is a combined public-private regional partnership, in which the partners are the National Institute of Quantum Radiological Science & Technology (QST), Tohoku University, Miyagi Prefecture, Sendai-City; the Tohoku Economic Federation; and the Photon Science Innovation Center. Funding comes from private sector investments, local governments, and MEXT through QST. The primary target of the project is to drive innovation by pioneering nanometer scale visualization of materials' function as a "Super Light Source for Industrial Technology (SLIT-J)". A groundbreaking concept, utilizing an industry-academic alliance for SR applications, called the "Coalition Concept", is also arising out of the dialogue with industries and professors about the outlook for the research market of SLIT-J. [ABSTRACT FROM AUTHOR]

We report an anomalous lattice deformation of GaN layers grown on SiC(0001) by molecular beam epitaxy. The evolution of the lattice parameters during the growth of the GaN layers was measured by in situ synchrotron X-ray diffraction. The lattice parameters in the directions parallel and normal to the surface showed significant deviation from the elastic strains expected for lattice-mismatched films on substrates up to a thickness of 10 nm. The observed lattice deformation was well explained by the incorporation of hydrostatic strains due to point defects. The results indicate that the control of point defects in the initial stage of growth is important for fabricating GaN-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

The evolution of polytypism duringGaAs nanowire growth was investigatedby in situ X-ray diffraction. The growth of nanowires was found tostart with the formation of zincblende structure, followed by thegrowth of wurtzite structure. The growth process was well reproducedby a simulation based on a layer-by-layer nucleation model. The goodagreement between the measured and simulated results confirms thatnucleation costs higher energy for the stackings changing the crystalstructure than for those conserving the preceding structure. The transitionin prevalent structure can be accounted for by the change of localgrowth conditions related to the shape of a triple phase line ratherthan by the change in supersaturation level, which quickly reachessteady state after starting growth. [ABSTRACT FROM AUTHOR]

To evaluate local atomic structures around Co in high temperature diluted ferromagnetic semiconductor Co-doped TiO2, x-ray fluorescence holography and x-ray absorption fine structure experiments were carried out on rutile paramagnetic Ti0.99Co0.01O2 and ferromagnetic Ti0.95Co0.05O2 films. The Co atoms in the Ti0.99Co0.01O2 simply substituted for Ti sites in the rutile structure, whereas a suboxidic arrangement of CoO2Ti4 formed around Co in the Ti0.95Co0.05O2 films. A theoretical investigation based on a series of first-principles calculations indicated the stability of the aggregated suboxidic clusters in the rutile TiO2, supporting our hypothesis for the formation of suboxidic coordination in the highly Co-doped sample. The suboxidic coordination may be the source of strong exchange interaction, resulting in the high Curie temperature in Co-doped TiO2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract  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. [ABSTRACT FROM AUTHOR]

The application of in situ synchrotron X-ray diffraction (XRD) to the molecular-beam epitaxial (MBE) growth of III–V semiconductors is overviewed along with backgrounds of the diffraction theory and instrumentation. X-rays are sensitive not only to the surface of growing films but also to buried interfacial structures because of their large penetration depth. Moreover, a spatial coherence length up to µm order makes X-rays widely applicable to the characterization of low-dimensional structures, such as quantum dots and wires. In situ XRD studies during growth were performed using an X-ray diffractometer, which was combined with an MBE chamber. X-ray reciprocal space mapping at a speed matching a typical growth rate was achieved using intense X-rays available from a synchrotron light source and an area detector. The importance of measuring the three-dimensional distribution of XRD intensity in a reciprocal space map is demonstrated for the MBE growth of two-, one-, and zero-dimensional structures. A large amount of information about the growth process of two-dimensional InGaAs/GaAs(001) epitaxial films has been provided by three-dimensional X-ray reciprocal mappings, including the anisotropic strain relaxation, the compositional inhomogeneity, and the evolution of surface and interfacial roughness. For one-dimensional GaAs nanowires grown in a Au-catalyzed vapor-liquid–solid mode, the relationship between the diameter of the nanowires and the formation of polytypes has been suggested on the basis of in situ XRD measurements. In situ three-dimensional X-ray reciprocal space mapping is also shown to be useful for determining the lateral and vertical sizes of self-assembled InAs/GaAs(001) quantum dots as well as their internal strain distributions during growth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A molecular beam epitaxy (MBE) chamber dedicated to nitride growth was developed at the synchrotron radiation facility SPring-8. This chamber has two beryllium windows for incident and outgoing X-rays, and is directly connected to an X-ray diffractometer, enabling in situ synchrotron X-ray measurements during the nitride growth. Experimental results on initial growth dynamics in GaN/SiC, AlN/SiC, and InN/GaN heteroepitaxy were presented. We achieved high-speed and high-sensitivity reciprocal space mapping with a thickness resolution of atomic-layer scale. This in situ measurement using the high-brilliance synchrotron light source will be useful for evaluating structural variations in the initial growth stage of nitride semiconductors. [ABSTRACT FROM AUTHOR]

The polytypism of GaAs nanowires was investigated by in situ X-ray diffraction under different growth conditions. The growth of nanowires was found to start with the formation of the zincblende structure, followed by the growth of the wurtzite structure. The observed growth process of nanowires was well reproduced by simulations based on a layer-by-layer nucleation model. At a low growth temperature and a high growth rate, stacking faults were found to be frequently introduced owing to the reduction in energy barrier. As a result, the zincblend and wurtzite segments in nanowires were highly fragmented and the wurtzite structure was formed in the early stage of growth. [ABSTRACT FROM AUTHOR]

The local structures around Nb and Pb in the prototypical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) were investigated by x-ray fluorescence holography. The separate atomic images of nearest Pb around Nb revealed acute and obtuse rhombohedral structures of the crystal unit cells. The Pb-Pb correlated images showed a local structure of body-center-like 2a0 × 2a0 × 2a0 superlattice, proving a rigid three-dimensional network structural model combining the two kinds of rhombohedrons. The Pb atoms in the networks are positionally stable, while the other Pb atoms are fluctuating. This superstructure and the fluctuating Pb and Nb atoms are believed to play an important role in the relaxor behavior of PMN at the atomic level. [ABSTRACT FROM AUTHOR]