Soft X-ray beamline BL1N2 at Aichi Synchrotron Radiation Center and its industrial use.

BL1N2 is a soft X-ray XAFS (X-ray absorption fine structure) beamline that is well suited for industrial use. User service started in 2015. The beamline is a grazing optical system with a pre-mirror, an inlet slit, two mirrors for three gratings, an outlet slit and a post-mirror. Light of 150 eV to 2000 eV is available, and K-edge measurements of elements from B to Si are covered. The O K-edge is most often measured; transition metals such as Ni and Cu at their L-edges and lanthanoids at their M-edges are also often measured. Here, basic information about BL1N2, the effect of ageing by synchrotron radiation to remove mirror contamination, and a compatible sample handling system and transfer vessels to allow a one-stop service at three soft X-ray beamlines at AichiSR are described.

Aberration corrected spin polarized low energy electron microscope.

Spin Polarized Low Energy Electron Microscopy (SPLEEM) is a powerful tool to reveal the magnetic structure of ferromagnetic surfaces on the atomic depth scale level[1-3]. With aberration corrected LEEM and a high brightness spin polarized electron gun, high spatial resolution will provide more details for ultra-thin ferromagnetic film studies. This study reports the first realization of aberration corrected SPLEEM (AC-SPLEEM). The performance of the setup was tested on ferromagnetic Fe nanoscale islands on a W(110) single crystal, with spatial resolution of 3.3 nm in spin asymmetry images.

Recovery of quantum efficiency in spin-polarized photocathodes by atomic hydrogen cleaning.

We demonstrate a new method of cleaning superlattice (SL) photocathodes using atomic hydrogen that allows an increased number of repeat activations. GaAs/GaAsP SL photocathodes were activated with either conventional heat cleaning or atomic hydrogen cleaning. Repeated heat cleaning was found to gradually lower the quantum efficiency (QE) of the photocathodes, while a relatively constant QE was maintained over repeated atomic hydrogen cleaning. These results show that atomic hydrogen cleaning allows a greater number of photocathode cleanings without a loss of performance. Analyses of SL photocathodes indicated that the degradation resulting from heat cleaning can likely be attributed to the build-up of residual Cs compounds as well as damage to the GaAs cap layer. The present study also determined the 1/e lifetime for a GaAs/GaAsP SL photocathode to be 7 h at an initial current of 2.2 µA.

Interaction of Nd dopants with broadband emission centers in Bi2O3-B2O3 glass: local energy balance and its influence on optical properties.

Chemical and energetic interactions between broadband infrared intrinsic emission centers (IECs) of bismuthates and extrinsic emission centers (EECs) of Nd2O3 dopants were optically and electronically investigated. Although no visible absorption from the IEC was found in untreated Bi2O3-B2O3 glass, it was clearly observed after a moderate thermal treatment of <200 °C, indicating chemical activity of O-deficient sites as the origin of IECs. On the other hand, Nd2O3 doping chemically stabilized the Bi2O3-B2O3 glass and suppressed IEC formation. By using a microwave measurement sensitive to electric dipoles, we found a 'switching' in local energy balance resulting from the Nd2O3 doping. This was explained by metallization of the O-deficient sites in the Bi2O3-B2O3 glass and multi-phonon excitation of IEC and EEC complexes in the Nd2O3-Bi2O3-B2O3 glass phosphor. Although the electric dipole observed by the microwave measurement was not necessarily caused by IEC, emission properties of the IEC and EEC complexes were consistent with energy balance switching; emissions from IECs after thermal treatment were quenched by EECs with multi-phonon excitation.

Phase-locking of oscillating images using laser-induced spin-polarized pulse TEM.

Pulse-mode operation was realized in spin-polarized transmission electron microscopy (SP-TEM) using a laser-driven electron gun with a GaAs-GaAsP strained-layer-superlattice photocathode. TEM images were acquired with a pulsed electron beam with a 5-µs pulse duration. Phase locking of wobbling TEM images was demonstrated using a pulsed beam with a 1-kHz repetition frequency, which matched the image wobbling frequency. It was found that in composite images formed by superimposing 2 × 10(4) separate single-pulse exposures, the amount of image blurring due to wobbling was a linear function of the pulse duration. These results suggest the possibility of pump-probe measurements in SP-TEM using the pulsed electron beam as a probe, allowing nanometer-scale time-resolved spin mapping.

Picosecond electron bunches from GaAs/GaAsP strained superlattice photocathode.

GaAs/GaAsP strained superlattices are excellent candidates for use as spin-polarized electron sources. In the present study, picosecond electron bunches were successfully generated from such a superlattice photocathode. However, electron transport in the superlattice was much slower than in bulk GaAs. Transmission electron microscopy observations revealed that a small amount of variations in the uniformity of the layers was present in the superlattice. These variations lead to fluctuations in the superlattice mini-band structure and can affect electron transport. Thus, it is expected that if the periodicity of the superlattice can be improved, much faster electron bunches can be produced.

Initial stages of high-temperature CaF2/Si(001) epitaxial growth studied by surface X-ray diffraction.

Surface X-ray diffraction was applied to study structure of the fluorite-silicon interface forming upon epitaxial growth of CaF2 on Si(001) surface kept at 750 degrees C. Samples with CaF2 coverage of 1.5-4 (110)-monolayers were grown and in-situ characterized using synchrotron radiation. The 3 x 1-like surface reconstruction was observed in agreement with the previous studies by electron diffraction. Interestingly, a well pronounced splitting of the fractional x 1/3 reflections was revealed. This splitting was ascribed to the effect of antiphase domain boundaries in the row-like structure of the interface layer. The in-plane integrated intensities were used to reconstruct two-dimensional atomic structure of the high-temperature CaF2/Si(001) interface.

Ga and As composition profiles in InP/GaInAs/InP heterostructures--x-ray CTR scattering and cross-sectional STM measurements.

Changes of composition profiles in GaInAs layers sandwiched by InP, due to the layer thicknesses, were measured by the x-ray CTR scattering and cross-sectional STM techniques. Both techniques showed quite similar results, which indicates that the x-ray CTR scattering measurements and analyses give us correct composition profiles both for group-III and group-V atoms in the buried heterostructures non-destructively. Limits of the CTR analysis are discussed, especially on the spatial resolution and composition grading below the bottom interface.

Local concentration of gel phase domains in supported lipid bilayers under light irradiation in binary mixture of phospholipids doped with dyes for photoinduced activation.

Recently, lipid bilayers supported on solid substrates are considered to offer potential as biological devices utilizing biological membranes and membrane proteins. In particular, artificially patterned supported bilayers hold great promise for the development of biological devices. In this study, we show control of the formation and location of phase-separated domain structures by light irradiation for gel phase and liquid-crystalline phase separation structures in a DMPC-DOPC binary lipid bilayer tagged with dye molecules on SiO2/Si substrates. Upon light irradiation, the gel phase domain structures disappeared from the phase-separated bilayers. This disappearance indicates that the light irradiation causes a local increase in the temperature of the lipid bilayer. In this disappearance phenomenon, the photoinduced activation of dye lipids, e.g. fluorescent lipids, is considered to play an important role, since the same phenomenon does not occur in lipid bilayers that have a low concentration of dye lipids. Thus, the local increase in temperature is propagated by light absorption of the dye lipid and subsequent photoinduced activation of nonradiative molecular vibrations. Subsequent interruption of the photoinduced activation for molecular motion allowed the gel phase domain structures to precipitate and grow again. Moreover, the domain area fraction remaining after the photoinduced activation was higher than that before the photoinduced activation. This result indicates that the local increase in temperature propagated by dye-excitation enhances formation of the gel phase domains. By utilizing this phenomenon, we could preferentially induce formation of domain structures within the light-irradiated regions. This technique could be the basis for a new patterning technique based on domain structures. Moreover, these domain structure patterns can be eliminated by increasing the temperature, allowing rewritable patterning.

First observation of In(x)Ga(1-x)As quantum dots in GaP by spherical-aberration-corrected HRTEM in comparison with ADF-STEM and conventional HRTEM.

In(x)Ga(1-x)As quantum dots in GaP(100) crystals prepared by the OMVPE technique are observed along the [011] direction with a newly developed 200-kV spherical aberration(Cs)-corrected HRTEM, a 200-kV annular dark-field (ADF)-STEM, and a 200-kV conventional HRTEM equipped with a thermal field-emission gun. The dots are 6-10 nm in size and strongly strained due to the misfit of about 9% with the GaP substrate and GaP cap layer. All of the cross-sectional high-resolution electron micrographs show dumbbell images of Ga and P atomic columns separated by 0.136 nm in well-oriented and perfect GaP areas, but the interpretable images are limited to those taken with the Cs-corrected HRTEM and ADF-STEM with Fourier filtering of the images. The Cs-corrected HRTEM and ADF-STEM are comparable from the viewpoint of interpretable resolution. A detailed comparison between the Cs-corrected HRTEM images and the simulated ones with electron incidence tilted by 1 degree to 5 degrees from the [011] zone axis gives information on local lattice bending in the dots from the images around 0.1 nm resolution. This becomes one of the useful techniques newly available from electron microscopy with sub-angstrom resolution.