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We outline the recent developments in CCD imager technology aimed at producing the very large format (8192 × 8192 pixels and larger) detector mosaics required for existing 4-m class and new 8 to 10-m class telescopes. The key technology areas include buttable array design and buttable element packaging, and optimization schemes for QE and readout time. As an example, we highlight the University of Hawaii effort to develop an 8192 × 8192 15 μm pixel CCD mosaic.
An elongated ERO with R - K′ = 7.5 behind the cluster A851 at z=0.4 was found to lie at z = 1.5 both by the photometric redshift and by a cross correlation method of its H-band SED with local E/SO spectra. the luminosity profile is well represented by a seeing convolved exponential disk, and the lack of redshifted H-alpha emission indicates that it has a dynamically relaxed disk with an old stellar population. Gravitational lensing of the cluster is not strong enough to stretch the image and cannot convert the de Vaucouleurs law into an exponential law.
We searched the time lag between the intra-day variables (IDVs) of Sagittarius A* at 22, 43, and 86 GHz bands using the Korean VLBI Network (KVN). The time lags between the IDV flare peaks at 22 and 43 GHz are reported, and they suggest that the flare emissions come from adiabatically expanding plasma blobs, ejected close to the Galactic center black hole. We searched the time lags between light curves at 90 and 102 GHz using the Nobeyama Millimeter Array, but could not find significant time lags. In order to detect the diversity of the time lags of Sgr A* flares, we performed observations of Sgr A* in the 22, 43, and 86 GHz bands using the KVN in the winter of 2013. Because the receiver system of KVN can observe Sgr A* in these three bands simultaneously, the KVN is very useful to detect the time lags of Sgr A* flares.
We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3 and Al2O3 substrates by Pulsed Laser Deposition (PLD) technique at various deposition temperatures (Tdep = 300 °C – 600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K - 600 K). AZO/STO films present superior performance respect to AZO/Al2O3 films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, with electrical conductivity 310 S/cm, Seebeck coefficient -65 μV/K and power factor 0.13 × 10-3 Wm-1K-2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to × 10-3 Wm-1K-2 at 600 K, surpassing the best AZO film previously reported in literature.
We have fabricated a hybrid nanodots floating gate (FG) in which Si quantum dots (QDs) and silicide nanodots (NDs) are stacked with a very thin SiO2 interlayer in order to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality for optoelectronic application. In electron charging and discharging characteristics measured with application of pulsed gate biases to MOS capacitors with a hybrid NDs FG, stepwise changes in the rates for electron injection and emission were revealed with increasing pulse width at room temperature. Also, nMOSFETs with a hybrid NDs FG show unique hysteresis with stepwise changes in the drain current - gate voltage characteristics. The observed characteristics can be interpreted in terms that the electron injection and storage into silicide-NDs proceed through the discrete charged states of Si-QDs. For MOS capacitors with a triple-stacked hybrid NDs FG fabricated by adding another Si-QDs, by subgap light irradiation from the back side of the Si substrate, a distinct infrared optical response in C-V characteristics was detected at room temperature. The result is attributable to the shift of charge centroid in the hybrid NDs FG as a result of transfer of photoexcited electrons from silicide NDs to Si-QDs.
The Shozu Herpes Zoster (SHEZ) Study was designed to clarify the incidence of and predictive and immunological factors for herpes zoster in a defined community-based Japanese population. As part of this series, a total of 5683 residents aged ⩾50 years received a varicella-zoster virus (VZV) skin test with VZV antigen, and 48 h later, the erythema and oedema were assessed by measuring the longest diameter. The diameters of both the erythema and oedema decreased with the increasing age of the subject. Sixty-three subjects contracted herpes zoster within a year after receiving the VZV skin test. Analysis of the herpes zoster incidence rate vs. the skin test reaction revealed that the shorter the diameter of erythema or oedema, the greater the likelihood of herpes zoster. These results demonstrated that the VZV skin test is an excellent surrogate marker for predicting the risk of herpes zoster.
We synthesized amorphous semiconductor films composed of Mo-encapsulating Si clusters (MoSin : n∼10) on solid substrates. The MoSi10 films had Si networks similar to hydrogenated amorphous Si and an optical gap of 1.5 eV. Electron spin resonance signals were not observed in the films indicating that dangling bonds of Si were terminated by Mo atoms. We fabricated thin-film-transistors using the MoSi10 film as a channel material. The electric field effect of the film was clearly observed. This suggests that the density of mid-gap states in the film is low enough for the field effect to occur.
Hemispherical silicon quantum dots (QDs) have been self-assembled with an areal density as high as ~2−1011 cm−2 on SiO2/Si(100) and quartz substrates by controlling the early states of low pressure chemical vapor deposition (LPCVD) of pure silane. It is found that, for the thermally-oxidized Si QDs, when the mean Si dot height is decreased from 6.3 nm to 1~2 nm, the photoluminescence (PL) peak energy is increased from 1.2 to 1.4 eV at room temperature while the optical absorption edge determined by photothermal deflection spectroscopy is shifted from 1.9 to 2.5 eV. In addition to the observed Stokes shift as large as 0.7−1.1 eV, a weak temperature dependence of the broad luminescence band and non-exponential luminescence decay with a mean life time of sub-msec even at room temperature suggest that localized, radiative recombination centers existing presumably in the SiO2/Si dot interface are responsible for the efficient PL from the Si QDs. From the change in room temperature PL by SiO2 thinning and removal in a dilute HF solution, it is demonstrated that the surface passivation of Si QDs plays an important role for the efficient light emission at room temperature.
The dielectric breakdown behavior of poly-Si gate CMOSFETs with HfAlOx/SiON gate dielectric fabricated using mass production worthy 300 mm process was investigated. If SiO2 is used as an interfacial layer (IL), the IL reduction and the intermixing between the HfAlOx layer and the IL occurred, which causes extrinsic breakdown. By using the SiON of [N]=18% as an IL and setting the maximum temperature after the HfAlOx deposition to be 1000°C, the interfacial reaction was suppressed and the extrinsic breakdown component was eliminated. In the case of the n-capacitor accumulation, an abrupt increase of gate leakage was observed, which is believed to correspond to the IL breakdown. The mean time to failure (MTTF for 0.1cm2 at 125°C) is long enough. On the other hand, gate current initially decreases and then starts to increase in the case of p-capacitor accumulation. If we define the time to breakdown at the onset of current increase, the MTTF would be only 3.7 years if it obeys the V-plot (MTTF predicted by 1/V-plot was 1.6×107 years).
We present a first-principles lattice dynamics for the assembly of the transition-metal (M)-encapsulated Sin clusters in amorphous phase (a-MSin), which has been proposed as a potential candidate for the channel material of the next-generation thin-film transistors (TFTs) [N. Uchida et al., Appl. Phys. Express1, 121502 (2008)]. The shape of calculated vibrational density of states (VDOS) curve of a-MoSi10 is similar to the counterpart of the high pressure phase of a-Si (HPA-Si) although the present systems are obtained as a result of pressure relaxation. Its radial distribution function (RDF) among Si themselves is characterized by the absence of a gap between the first and second shells, which is also the case in . We further present the VDOS of a-WSi10, whose curve shape is again similar to that of HPA-Si. A difference between a-MoSi10 and a-WSi10 is that the W-atom displacement components extracted from the vibration eigenvectors are mainly distributed over a lower frequency range (< ~ 150 cm-1) than the Mo counterpart (~ 150 cm-1 to ~ 300 cm-1). This may be attributed to a larger atomic mass of W than Mo.
Study of the microstructure of electronic materials can be enhanced by using high resolution transmission electron microscopy (TEM) combined with the technique of digitized image analysis. We show here a practical image analysis method for the microstructures of acceptor graphite intercalation compounds (GICs) with CuCl2 and FeCl3 intercalates. The two dimensional fast Fourier transform (2D-FFT) was used for the frequency analysis of the TEM pictures. It is found that the lattice images of CuCl2-GICs consist of different frequency images corresponding to specific frequencies. The detailed features of the stage-1 structure of the FeCl3-GICs is extracted quantitatively by this method from a relatively indistinct TEM picture. The stage structure of the CuCl2- and FeCl3-GICs are further investigated by analyzing the reconstruction of the TEM images by means of the two dimensional inverse FFT (2D-IFFT).
Thermally oxidized porous silicon shows stable visible luminescence under laser irradiation. The photoluminescence decay has been measured in the temporal range from microsecond to millisecond. The decay curve is well fitted to a stretched exponential function. The mean lifetime of the luminescence increases with increasing the excitation pulse width. It is also found that the higher energy emission exhibits a faster decay compared with the lower energy emission at 293K, while at 18K it is reversed. The results are explained by a model in which photogenerated carriers are captured by localized radiative centers through a thermally assisted tunneling mechanism
Polysilane thin films have been grown by the rf glow discharge decomposition of SiH4 at substrate temperatures ranging from -84 to -110°C. The infrared absorption spectra have shown that polysilane chains (SiH2)n are predominantly incorporated in the matrix together with SiH3 which terminates the chain. Also, the infrared absorption band at 2120∼2140 cm-1 and a distinct Raman peak at ∼430 cm-1indicates that fairly long chains (SiH2)n with n>11 are produced. Polysilane prepared at -110°C has an optical bandgap of about 3.1 eV and exhibits a visible luminescence around 2.75 eV at 100 K.
HF-treated Si surfaces and the oxidation kinetics in pure water or in clean room air have systematically been studied by x-ray photoelectron spectroscopy (XPS). The oxidation of heavily-doped n-type Si appears to proceed parallel to the surface, resulting in the layer-by-layer oxidation. The oxide growth rate in pure water for heavily-doped n-type Si is significantly higher than that of heavily-doped ptype Si. This is explained by the electron tunneling from the Si conduction band to adsorbed O2 molecules to form the O2 state. O2 ions easily decompose and induce a surface electric field, enhancing the oxidation rate. The growth rate of native oxide on heavily-doped n-type Si is less sensitive to the crystallographic orientations than the case of lightly doped Si where the steric hindrance against oxygen molecules significantly lowers the oxidation rate of the (110) and (111) surfaces. We suggest that the decomposed oxygen can penetrate into Si without steric hindrance. It is also found that the oxidation of heavily-doped n-type Si in pure water is effectively suppressed by adding a small amount (10 ∼ 3600 ppm) of HCI.
High dielectric constant thin film capacitors for integrated circuits were fabricated with an LSI process. The capacitors comprized AI/TiN top electrode, Si3N4 interlayer insulator, SrTiO3 dielectric and Pt/barrier-metal/Si bottom electrode. Two types of capacitor structure were discussed on the basis of dielectric property and fabrication process. The TiN layer played an important role in suppressing degradation of insulating properties at elevated temperature, which was caused by a reaction between Al and SrTiO3. Breakdown strength larger than 6.6 MV/cm was obtained for 0.001 mm2 area capacitors. However, the strength decreased with increasing capacitor area. The area dependence may be due to surface defects which were introduced during the processes subsequent to SrTiO3 film deposition. The capacitance density of about 9 fF/μm2 was obtained for 150nm thick film. Recent activities of ferroelectric thin film research in Japan was given as well.
Chemical bonding features and suboxide compositions in native oxide grown on chemically-cleaned hydrogen-terminated Si(100) surfaces stored in pure water have been studied by using surface sensitive infrared spectroscopy and x-ray photoelectron spectroscopy. The LO phonon peak for the native oxide is located at 1210cm−1, which is shifted to a significantly lower wavenumber side than the ultrathin thermal oxide peak at 1250cm−1. This is because an appreciable amount of SiHx bonds are incorporated in the native oxide/Si interface and such hydrogen termination in the network dramatically reduces strained bonds in the interface. Very weak Si2+ suboxide signal from the oxide grown in pure water is also explained by the incorporated SiHx bonds which interrupt the Si2+ suboxide formation in the interface.
The surface microroughness of Si(100) wafers has been studied by FT-IR-ATR. The final wafer clean in an 0.1% HF + 1% H2O2 aqueous solution significantly improves the hydrogenterminated surface morphology as demonstrated by a sharp SiH2 stretching vibration peak accompanied with the weak SiH and SiH3 peaks. The ultra-thin gate oxide grown on such surface exhibits nearly ideal tunneling current transport. The cleaning in 4.5% HF reduces the SiH2 peak height and enhances SiH3, making the surface rough. Nevertheless, the tunneling characteristics are hardly influenced with such spectral change.
The structure of thin SiO2 films thermally grown on Si(100) and Si(111) surfaces has been characterized by using infrared internal reflection and x-ray photoelectron spectroscopy. It is found that the infrared absorption peak due to the LO phonon mode originating from the Si-O-Si stretching vibration shows a considerable red shift in the thickness range below 30A. This red shift is interpreted in terms of the compressive stress near the interface.
Growth kinetics of native oxide on HF-treated Si surfaces terminated with Si-H bonds has been studied by angle-resolved x-ray photoelectron spectroscopy. The oxide growth rate in pure water for an n+ Si(100) surface is significantly high compared to that of p+, and the n or p type Si oxidation rate is in between. This is explained by the formation of ions through electron transfer from Si to adsorbed O2 molecules and the resulting enhancement of the oxidation rate. The oxide growth on Si(100) is faster than (110) and (111) as interpreted in terms of the steric hindrance for molecular oxygen adsorption on the hydrogen terminated silicon 1×1 surface structures.
Ti-Ni thin films with three different types of compositions, titanium-rich Ti-Ni, near equiatomic TiNi and nickel-rich Ti-Ni were prepared by sputtering. The sputter-deposited films were annealed at various temperatures between 773 and 973K in order to crystallize. After the heat treatment, the shape memory behavior was examined with a thermomechanical tester. The shape memory behavior of the near equiatomic composition films was not affected by the heat treatment. On the other hand, the shape memory behavior of the other composition films strongly depended on the annealing temperature. As the annealing temperature increases, the martensitic and reverse martensitic transformation temperatures of the nickel-rich films decreased and those of the titanium-rich films increased. These opposite behaviors of the transformation temperatures can be explained by the opposite dependence of the precipitation of the second phase on the annealing temperature. All the nickel-rich films exhibited good shape memory effect over a wide range of stress, while all the titanium-rich films exhibited a small plastic strain only in the stress range where the shape changes associated with both the R-phase and the martensitic transformations were observed.