Research activities on surface activated bonding (SAB) of dissimilar semiconductor materials for targeting advanced energy-harvesting and energy-saving devices are reviewed.The structural and electrical properties of interfaces fabricated using the SAB technologies are examined.The change in the interface characteristics due to annealing after bonding is highlighted.The characteristics of SAB-based hybrid multi-junction solar cells, SiC/Si junctions as prototypes of wide bandgap/narrow bandgap hetero structures, and single-crystal diamond/Si junctions for integrating diamond and Si devices in the future are discussed.
Kelvin-probe force microscopy (KPFM) is a surface potential mapping technique based on dynamic-mode atomic force microscopy (AFM).It is useful to visualize carrier injection barriers and trapped charges in operating organic thin-ˆlm transistors (OTFTs).Since it is desirable to perform KPFM experiments in vacuum conditions, frequency modulation (FM) technique is often used to operate AFM/KPFM.We review two operating modes of KPFM using FM-AFM in vacuum and demonstrate visualization of the carrier injection barriers and trapped charges in OTFTs.We also introduce a method to visualize the transient distribution of the trapped charges being evacuated from the channel of the operating OTFT.
Oxide-semiconductor based gas sensors have been intensively investigated in order to improve the sensitivity and selectivity of a certain gas. This article reviews the recent research progress of gas sensors having oxide semiconductor as an active layer, in particular detecting for H2 and volatile organic compounds. The semiconductor material for gas sensors reported in this article includes SnO2, WO3, ZnO, In2O3, and NiO. The sensitivity of gas sensors having diŠerent structures and semiconductors is compared.
Thermal spraying technique is often applied to inner parts used for vacuum equipment. Sprayed ˆlms have the property to prevent separation of ˆlms deposited over inner parts, which in turn prevents dust generation in vacuum equipment and ensures stable operations of vacuum equipment for longer period. Inner parts of vacuum equipment is also subject to a number of surface treatment processes other than thermal spraying before incorporated into vacuum equipment. This article describes surface treatment technologies used for the inner parts of vacuum equipment.
Infrared spectroscopy combined with the matrix isolation method, where samples are trapped by a cold and inert-molecular solid, has been used for the investigations of small water clusters. After the descriptions of the stable structures and vibrations of the clusters, the author explains experimental techniques of the matrix isolation and demonstrates recent works on the clusters isolated in the solids of rare gases, para-hydrogen, and methane as well as the hydrogen adsorption layer on a vapor deposited NaCl ˆlm. The relation between the frequency shift of the hydrogen-bonded OH stretch and the matrix critical-temperature is also shown.
We investigated the band-splitting of GaAs thin film by invoking broken inversion symmetry within the bulk region and the lost of 2D symmetry on the surface due to strain in first-principles calculations using density functional theory with spin-orbit interaction. The system is modeled by unreconstructed GaAs(001)-(1×1) slab, and by its strained counterpart arising from As dimerization. For the unstrained system, we found that the valence bands split while the conduction bands remain degenerate. This degeneracy is attributed to the sole contribution of p-state of As atoms found on the surface to this band, where 2D symmetry is preserved. When strain is imposed on this surface, the symmetry is broken and the conduction bands are split. These findings identify the changes in the band structure due to broken symmetry, suggesting their incorporation in the conventional degenerate theoretical description of the GaAs thin films done to date.
A single spin-rotational state-selected [(J,M)=(2,2)] O2 beam allows us to conduct a spinand alignment -controlled O2 chemisorption experiment. We have recently expanded its available translational energy range to 0.10.9 eV. In this study, the beam has been used for the analysis of O2 chemisorption on Pt(111). Although this system has been investigated intensively due to its technological importance, the origin of the low O2 sticking probability and its unusual energy dependence has remained unclear. The present results indicate that, at low translational energy (E0) conditions, direct activated chemisorption occurs only when the O2 axis is nearly parallel to the surface. At high energy conditions (E0>0.5 eV), however, the sticking probability for the parallel O2 decreases with E0 while that of the perpendicular O2 increases, accounting for the nearly energy-independent O2 sticking probability determined previously by a randomly oriented O2 beam.
The characteristics of diamond-like carbon (DLC) films deposited by high power impulse magnetron sputtering (HiPIMS) with multipolar magnetic plasma confinement (MMPC) were investigated. DLC films were prepared on silicon (Si) by HiPIMS and HiPIMS-MMPC over varying substrate bias voltage. Depositions were performed from a graphite target (210 mm in diameter) under argon (Ar) gas atmosphere at chamber pressure of 0.5 Pa. The DLC films were analyzed by several methods. In HiPIMS-MMPC, the peak power density was approximately 690 W/cm2 at a duty cycle of 1% (frequency: 200 Hz). According to Raman spectroscopy, the structure of DLC film deposited by HiPIMS-MMPC could be changed from amorphous carbon (a-C) to tetrahedral amorphous carbon (ta-C). The deposition rate in HiPIMS-MMPC was approximately 50% (10 nm/min) lower than that in HiPIMS. However, HiPIMS-MMPC is considered as one of the effective methods to prepare hard and dense DLC films (20 GPa and 2.00 g/cm3 at the maximum).
Stability improvement of the output of a quartz-oscillator-based pressure sensor for outdoor use was attempted by maintaining a constant temperature of the preamp connected to the quartz oscillator; this is because the preamp output is affected by temperature, which results in fluctuation of the pressure sensor output. The preamp was located at a place where the temperature is constant, while the quartz oscillator was fixed outdoor where temperature fluctuates. However, the stability of the pressure sensor output was not significantly improved by this method as compared to the other previous procedures to reduce influences of preamp temperature on pressure sensor output, although the fluctuation of preamp temperature was drastically and sufficiently reduced. The results obtained in the present study depict that the fluctuations in pressure sensor output in outdoor use may be attributed to other reasons than the fluctuation of preamp temperature.
A stackable Knudsen pump consisting of multistage pump units driven by temperature difference between hot and cold water is fabricated. Each unit has a porous membrane of 64 cm2 area, through which thermal transpiration flow, the driving force of the Knudsen pump, is induced at atmospheric ambient pressure. This study demonstrates the present device facilitates the cascade or parallel connection of multiple pump units to improve performance. For example, a Knudsen pump consisting of 6-cascaded units provides a shut-off pressure of 9.2 kPa and a 300 sccm maximum flow rate at the temperature difference of 45 K. The feasibility of the pumping system driven by low-grade waste heats is also demonstrated.
Graphene: a monolayer sheet of graphite shows many attractive properties, which are expected to be applied to various devices. Development of a high throughput method has been required to realize the applications. Chemical exfoliation via graphene oxide (GO) has been considered one of the promising methods. However, the graphene reduced from GO showed poor crystallinity and mobility than that of mechanically exfoliated graphene. Many reduction methods have been investigated to obtain high mobility graphene from GO lately. In this review, we introduce a novel reduction method which we have developed to convert GO to graphene by explaining their advantages and some flaws to be solved.
Average surface hitting number per molecule Nh when it exits vacuum tube has a close relation to pumping delay time. Several Nh were calculated using Monte-Carlo simulation method and Clausing's integral equation method for a cylidrical tube that has a point gas emission source. The results from both methods are in good agreement and the dependence of Nh on the tube length L are explained almost exactly with Clausing's integral equation.
Gas permeation test equipment was developed to measure the gas permeability through O-ring shape elastomers under actual condition of semiconductor manufacturing such as high vacuum and high temperature. The temperature dependencies of gas permeability on three kinds of elastomers, silicone (VMQ), fluoroelastomer (FKM) and perfluoroelastomer (FFKM), were investigated. Permeation rate for all materials increased as temperature increased. O2 and N2 gas permeation rate through VMQ was much higher than that through the other materials, especially in lower temperature. Moreover, the temperature dependencies of gas permeability with VMQ were completely different from those of FKM and FFKM. This was coming from different polymer structure which caused difference of solubility and diffusivity between silicon and fluoroelastomers.
This is to review a novel approach stabilizing reactive mode at transition regime in reactive high-power impulse magnetron sputtering (R-HiPIMS). The proposed method is based on a real-time monitoring of peak discharge current. To stabilize the process conditions at a given set point, a feedback control system, which automatically regulates the pulse frequency, and thereby the average sputtering power, was implemented to maintain a constant maximum discharge current. As a representative result, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a R-HiPIMS of Hf in an Ar-N2 atmosphere illustrates that the discharge current waveform is an excellent indicator of the process conditions. Applicability of the proposed method was successfully demonstrated.
