Heteroepitaxial growth of Cu2O thin film on ZnO by metal organic chemical vapor deposition

Cuprous oxide (Cu₂O) thin films were grown epitaxially on c-axis-oriented polycrystalline zinc oxide (ZnO) thin films by low-pressure metal organic chemical vapor deposition (MOCVD) from Copper(II) hexafluoroacetylacetonate [Cu(C₅HF₆O₂)₂] at various substrate temperatures, between 250 and 400 °C, and pressures, between 0.6 and 2.1 Torr. Polycrystalline thin films of Cu₂O grow as single phase with [1 1 0] axis aligned perpendicular to the ZnO surface and with in-plane rotational alignment due to (2 2 0)_Cu2O(0 0 0 2)_ZnO; [0 0 1]_Cu2O[1 2¯ 1 0]_ZnO epitaxy. The resulting interface is rectifying and may be suitable for oxide-based p–n junction solar cells or diodes.     

A thin film perspective on quantum functional oxides

Transition metal oxides show remarkably diverse quantum functional properties such as high temperature superconductivity, colossal magnetoresistance, multiferroicity, two-dimensional electron gas, and topological insulators. This diversity manifests as a result of many energy scales of similar magnitude competing rather than any particular one dominating in the system. In this regard, growth of atomically controlled epitaxial thin films and heterostructures would allow to control relevant energy scales by imposing various stimuli, such as reduction of dimensionality, introduction of interfaces, modification of the interfacial octahedral tilts, and symmetry breaking; in turn, modified functional properties or completely new phenomena may emerge in epitaxial thin films and heterostructures. Also of exceeding importance is the fact that atomically controlled epitaxial thin films and heterostructures of the multifunctional oxides offer promising potentials for next generation oxide electronics. In this short review, we collect representative examples of quantum correlated phenomena arising in epitaxial films and heterostructures of transition metal oxides and highlight some of the progresses achieved in thin film research of various functional oxides in the last couple of decades.     

Structural and optical properties of CuGaSe2 layers grown by the hot wall epitaxy method

Copper gallium selenide (CuGaSe₂, CGS) layers were grown by the hot wall epitaxy method. The optimum temperatures of the substrate and source for growth turned out to be 450 and 610 °C, respectively. The CGS layers were epitaxially grown along the 1 1 0 direction and consisted of Ga-rich components indicating the slight stoichiometric deviations. Based on the absorption measurement, the band-gap variation of CGS was well interpreted by the Varshni's equation. The band-gap energies at low temperatures, however, had a higher value than those of other CGS. It suggests that the band-gap increase is influenced by the slightly Ga-rich composition. From the low-temperature photoluminescence experiment, sharp and intensive free- and bound-exciton peaks were observed. By analyzing these emissions, a band diagram of the observed optical transitions was obtained. From the solar cell measurement, an 11.17% efficiency on the n-CdS/p-CGS junction was achieved.     

Chemical states of GeTe thin-film during structural phase-change by annealing in ultra-high vacuum

The chemical states of GeTe thin film are investigated using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation, during amorphous to crystalline structural phase transition. As the temperature increases from 250 to 400 °C, we observe the rock-salt crystalline structure and phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spin-orbit splitting of the Ge 3d core-level spectrum clearly appears after annealing at 400 °C for 5 min. However, the binding energy of the Ge 3d_5/2 core-level peak of 29.8 eV does not change in the amorphous to crystalline structural phase transition. In the case of the Te 4d core-level, change in binding energy and peak shapes is also negligible. We assume that the Te atom is fixed at a site between the amorphous and crystalline phases. Although the structural environment of the Ge atoms changes during the structural phase transition, the chemical environment does not.     

Interchip link system using an optical wiring method

A chip-scale optical link system is presented with a transmitter/receiver and optical wire link. The interchip link system consists of a metal optical bench, a printed circuit board module, a driver/receiver integrated circuit, a vertical cavity surface-emitting laser/photodiode array, and an optical wire link composed of plastic optical fibers (POFs). We have developed a downsized POF and an optical wiring method that allows on-site installation with a simple annealing as optical wiring technologies for achieving high-density optical interchip interconnection within such devices. Successful data transfer measurements are presented.     

Memory-efficient iterative process on a two-dimensional first-order regular graph

We present a parallel and memory-efficient iterative algorithm based on 2D first-order regular graphs. For an M x N regular graph with L iterations, a carefully chosen computation order can reduce the memory resources from O(MN) to O(ML). This scheme can achieve a memory reduction of 4 to 27 times in typical computation-intensive problems such as stereo and motion.     

Area of paradoxical signal drop after the administration of superparamagnetic iron oxide on the T2-weighted image of a patient with lymphangitic metastasis of the liver

We report a geographic area of prominent hypointensity in T2-weighted images vs. normal adjacent liver parenchyma in a patient with cholangiocarcinoma and lymphangitic metastasis of the liver after superparamagnetic iron oxide (SPIO) administration. The area showing this prominent signal drop showed Kupffer cell proliferation and lymphangitic metastasis during a pathologic examination.     

Solution-processed ZnO nanoparticle-based semiconductor oxide thin-film transistors

We have prepared solution-processed oxide semiconductor thin-film transistors using ZnO nanoparticles with various particle shapes. Uniform, dense, thin films were produced by spin-coating ZnO nanoparticle dispersions containing either nanorods or nanospheres. The influence of annealing atmosphere on both nanoparticle-based TFT devices was investigated. XPS analysis revealed that the ZnO particles of the nanorod and nanosphere dispersions have distinct stoichiometries (i.e., molar ratios of Zn:O). The starting particles in turn predetermine the carrier concentration within the annealed ZnO films, which in turn determines whether the device is a semiconductor or metallic conductor, depending upon the annealing atmosphere. Grain structures of the channel layer also play an important role in determining the device performance of the nanoparticle derived ZnO TFTs.     

Polymer waveguide with integrated reflector mirrors for an inter-chip link system

A polymer waveguide with integrated reflector mirrors is presented for an inter-chip link system. The cost-effective and repeatable technology for the integration of a polymer multimode waveguide and out-of-plane 45° reflector mirrors was developed for optical coupling between the light-sources and the light-detectors. This method enabled us to fabricate the waveguides and 45° reflector mirrors using a one-shot embossing process for inexpensive mass production. The optical inter-chip link system consisted of a metal optical bench, a module printed circuit board (PCB), a driver/receiver IC, a vertical-cavity surface-emitting laser (VCSEL)/photo-detector (PD) array, and an optical waveguide composed of integrated reflector mirrors. The presented data transfer measurements of the optical inter-chip link system are shown to be successful at a data rate of 5 Gb/s.     

Out-of-plane free vibrations of curved beams with variable curvature

The differential equations governing out-of-plane free vibrations of the elastic, horizontally curved beams with variable curvature are derived and solved numerically to obtain natural frequencies and mode shapes for parabolic, sinusoidal and elliptic beams with hinged–hinged, hinged–clamped, and clamped–clamped end constraints, in which the effects of the rotatory and torsional inertias and shear deformation are included. Experimental measures of frequencies for several laboratory-scale parabolic models serve to validate the theoretical results.