T. Tomimatsu

Effect of thermal exposure on stress distribution in TGO layer of EB-PVD TBC

Abstract The stress distributions in thermally grown oxide (TGO) layer of electron beam enhanced physical vapor deposited thermal barrier coating (EB-PVD TBC) before and after thermal exposure are measured by photo-stimulated luminescence spectrum. It is found that the stress in the TGO layer in original state is an order of ~3 GPa. It increases from 3.0–3.9 GPa with the increase of heat exposure time from 0–100 h. The stress distribution in the direction of thickness in the TGO layer is not uniform. The stress near ceramic top coat is smaller than that close to metal bond coat. The stress at thickness imperfections in the TGO near the bond coat is smaller than that in the regular TGO.

Distribution and structures of nanopores in YSZ-TBC deposited by EB-PVD

Abstract Distribution and arrangement of nanopores in an YSZ (7 wt% Y2O3–ZrO2)-thermal barrier coating (TBC) deposited by an electron beam-physical vapor deposition (EB-PVD) have been investigated by means of transmission electron microscopy. The YSZ-TBC deposited by the EB-PVD showed a typical columnar structure normal to the bond coat surface on the substrate. It has been generally believed that one column is a single crystal and grows continuously from the substrate. In the present study, however, it was found that each column consisted of a number of subcolumns with different misorientations and contained nanopores at the subcolumn boundaries. In addition to the nanopores at the subcolumn boundaries, nanopores with smaller size were observed within subcolumns, and were arranged periodically perpendicular to the growth direction of the subcolumns. Such arrangement and distribution of nanopores may be due to the misorientation of YSZ plate-like grains in the formation and coalescence processes of the YSZ subcolumns.

Fabrication of micromodel grid for various moiré methods by femtosecond laser exposure

The femtosecond laser exposure system was used to fabricate model grids for the charge-coupled device (CCD) moiré method, scanning laser moiré method, and electron moiré method for microstrain deformation measurements. The femtosecond laser exposure produces mesoscopic variation patterns on the surface. These variation patterns make the grid in the scanning laser microscope and CCD images darker and make the grid in the scanning electron microscope image brighter. The CCD moiré fringe, scanning laser moiré fringe, and electron moiré fringe consisting of bright and dark lines were generated. As a demonstration, microstrain distribution of the three-point bending tested specimen was measured.

Scanning nuclear electric resonance microscopy using quantum-Hall-effect breakdown

We present a scanning nuclear-spin resonance (NSR) method that incorporates resistive detection with electric-field induced NSR locally excited by a scanning metallic probe. In the quantum-Hall effect breakdown regime, NSR intensity mapping at both the fundamental NSR frequency f75As and twice the frequency 2f75As demonstrates the capability to probe the distribution of nuclear polarization, particularly in a semiconductor quantum well. We find that f75As NSR excitation drives not only local NSR but also spatially overlapped nonlocal NSR, which suppresses the maximum intensity of local NSR, while the 2f75As NSR yields purely local excitation conferring a larger intensity.

Comparison of nuclear electric resonance and nuclear magnetic resonance in integer and fractional quantum Hall states

Electric-field-induced nuclear resonance (NER: nuclear electric resonance) involving quantum Hall states (QHSs) was studied at various filling factors by exploiting changes in nuclear spins polarized at quantum Hall breakdown. Distinct from the magnetic dipole interaction in nuclear magnetic resonance, the interaction of the electric-field gradient with the electric quadrupole moment plays the dominant role in the NER mechanism. The magnitude of the NER signal strongly depends on whether electronic states are localized or extended. This indicates that NER is sensitive to the screening capability of the electric field associated with QHSs.

Pump-probe nuclear magnetic resonance measurement in quantum Hall effect breakdown regime

An electrically detected nuclear magnetic resonance (NMR) signal is studied with respect to source-drain current for current-induced nuclear-spin polarization in the quantum Hall breakdown regime. We perform pump-probe measurements to discern the effects of current pumping and probing sensitivity on the NMR signal. We find that both factors contribute to the NMR signal. Within the higher current region in particular, nuclear-spin probing sensitivity has the dominant influence on the NMR signal rather than the nuclear-spin pumping effect. The results are discussed using a model, taking the resistance change with the nuclear-spin polarization and current-induced heating into account.

Determination of the R-line luminescence spatial resolution of a near-field optical spectroscopy system for piezospectroscopy

The spatial resolution of a near-field optical spectroscopy system in the R-line photoluminescence mode has been evaluated to assess the resolution with which stress measurements can be made by piezospectroscopy. The effect of the probe tip–sample distance as well as the aperture size of the near-field probe on the luminescence R-line intensity was obtained. The luminescence intensity was found to increase linearly with the third power of the aperture size, whereas the lateral spatial resolution was proportional to the aperture size. These findings are consistent with a simple model for the electric dipole moment interaction between the tip and the sample. The minimum lateral spatial resolution was found to be 160nm using the smallest available aperture size of ∼100nm. Images of the stress distribution in a polycrystalline alumina are presented, showing variations at this scale.

Scanning nuclear resonance imaging of a hyperfine-coupled quantum Hall system

Nuclear resonance (NR) is widely used to detect and characterise nuclear spin polarisation and conduction electron spin polarisation coupled by a hyperfine interaction. While the macroscopic aspects of such hyperfine-coupled systems have been addressed in most relevant studies, the essential role of local variation in both types of spin polarisation has been indicated in 2D semiconductor systems. In this study, we apply a recently developed local and highly sensitive NR based on a scanning probe to a hyperfine-coupled quantum Hall (QH) system in a 2D electron gas subject to a strong magnetic field. We succeed in imaging the NR intensity and Knight shift, uncovering the spatial distribution of both the nuclear and electron spin polarisation. The results reveal the microscopic origin of the nonequilibrium QH phenomena, and highlight the potential use of our technique in microscopic studies on various electron spin systems as well as their correlations with nuclear spins.Exploring the hyperfine-coupled quantum Hall (QH) system facilitates the nuclear spintronic applications. Here the authors reveal the origin of the nonequilibrium QH phenomena by mapping the spatial distribution of nuclear and electron spin polarization in a GaAs quantum well with scanning probe incorporated nuclear resonance technique.

Photothermal imaging of skeletal muscle mitochondria

The morphology and topology of mitochondria provide useful information about the physiological function of skeletal muscle. Previous studies of skeletal muscle mitochondria are based on observation with transmission, scanning electron microscopy or fluorescence microscopy. In contrast, photothermal (PT) microscopy has advantages over the above commonly used microscopic techniques because of no requirement for complex sample preparation by fixation or fluorescent-dye staining. Here, we employed the PT technique using a simple diode laser to visualize skeletal muscle mitochondria in unstained and stained tissues. The fine mitochondrial network structures in muscle fibers could be imaged with the PT imaging system, even in unstained tissues. PT imaging of tissues stained with toluidine blue revealed the structures of subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria and the swelling behavior of mitochondria in damaged muscle fibers with sufficient image quality. PT image analyses based on fast Fourier transform (FFT) and Grey-level co-occurrence matrix (GLCM) were performed to derive the characteristic size of mitochondria and to discriminate the image patterns of normal and damaged fibers.