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There are many investigations about thin film. However, these are limited to the surface layer thin film on substrates. It Is very important to know the characteristics of the extremely thin film itself such as surface layer thin film.
In the present paper, the first part deals with the thickness measurements of the surface layer film and substrate by means of x-ray method, and then the measurement method of their stress - strain curves and the procedure of the measurement are described. The results obtained are discussed on the basis of their stress — strain curves.
Prototypes of magnetic actions in producing and shedding the X-ray-emitting high temperature plasmas in various astrophysical objects are witnessed in the spatially-resolved form on the Sun by the Solar X-ray Satellite “Yohkoh”. The most prominent of those are arcade flarings seen as powerful arcade flares in active regions with strong magnetic field. Larger scale fainter X-ray arcade formation observed at high latitudes, shedding a large amount of mass and energy as CME's (coronal mass ejections) also belongs to this category. Since some features found by the new observation by Yohkoh are incompatible with the so-called “classical model of arcade flarings”, we advance an alternative model based on the quadruple magnetic sources in the photosphere.
In the present paper, we stress the importance of the magnetic field in the problem of acceleration and collimation of astrophysical jets, and discuss our proposed generic picture for such “central gravitator + jets + lobes” systems and inherent interpretations of the various observational characteristics of such systems: Mechanisms are proposed for (1) the enhanced liberation of gravitational energy at the central object, (2) the transfer of a part of the liberated energy along the large-scale magnetic field by large-amplitude, torsional Alfvén wave trains that form collimated jets (we call this a sweeping pinch process), (3) the dumping of the transferred energy at the end of the jets when they impinge on the denser region outside the border of the “cavity” from which the mass contracted to the central condensation (central gravitator + accretion disk, as well as the larger-scale condensation surrounding them), and (4) the formation of wiggled jets and lobes as helical kinks and the tucked-up magnetic field produced in the sweeping pinch process, respectively.
A unified model for outbursts of dwarf novae is proposed based on the disk instability model in cataclysmic variable stars. In this model, two different intrinsic instabilities (i.e., the thermal instability and the tidal instability) within accretion disks are considered in non-magnetic cataclysmic variable stars. It is suggested that all of three sub-classes of dwarf novae (i.e., U Gem-type, Z Cam-type and SU UMa-type dwarf novae) may be explained in terms of two model parameters of the orbital period of the binary and of the mass transfer rate within the framework of the disk instability model.
A magnetohydrodynamic simulation in a 2.5D approximation is performed for the quadrupole source model for arcade flares treated years ago by Uchida (1980), and recently supported by the observations from Yohkoh. It is shown that this model can explain several key characteristic features of arcade flares found by Yohkoh, and can avoid some of the paradoxes existing in the “classical model”.
The correlation of stress in Silicon Carbide (SiC) crystal and frequency shift in micro- Raman spectroscopy was determined by an experimental method. We applied uniaxial stress to 4H- and 6H-SiC single crystal square bar specimen shaped with (0001) and (11-20) faces by four point bending test, under measuring the frequency shift in micro-Raman spectroscopy. The results revealed that the linearity coefficients between stress and Raman shift were -1.96 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (0001) face, -2.08 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (11-20) face and -2.70 cm-1/GPa for FTO(2/6)E2 on 6H-SiC (0001) face. Determination of these coefficients has made it possible to evaluate the residual stress in SiC crystal quantitatively by micro-Raman spectroscopy. We evaluated the residual stress in SiC substrate that was grown in our laboratory by utilizing the results obtained in this study. The result of estimation indicated that the SiC substrate with a diameter of 6 inch remained residual stress as low as ±15 MPa.
We investigated electrical and structural properties of Ta-doped SnO2 (TTO) films on anatase TiO2 seed layers with various growth parameters of pulsed laser deposition. We found that anatase TiO2 seed layers induced pseudo-epitaxial (100) growth of TTO films with enhanced mobility (μ) in a wide range of growth parameters. The highest μ of 83 cm2V-1s-1 [resistivity (ρ) of 2.8 × 10-4 Ωcm] and the lowest ρ of 1.8 × 10-4 Ωcm (μ of 60 cm2V-1s-1) were obtained at a substrate temperature of 600 °C. Amorphization and (101)-preferred growth competed with (100) growth on the TiO2 seed layer at low temperatures. Introducing sufficient process oxygen suppressed such unwanted film growth, resulting in improved transport properties.
An advanced FSG film of k=3.4 was developed, which exhibited excellent resistance for moisture absorption. Physical and chemical properties of this advanced FSG film were compared by typical FSG films deposited in both high density plasma (HDP) and PE-CVD reactors, for the same k value.
The advanced FSG film appears to be superior to the HDP-FSG film by a wide margin in the following tests. The moisture absorption rate by TDS (after 4 days of air exposure) is about 5 times lower, the hardness was 1.8 times more, and the hygroscopicity (after 1 hr. boiling) was 2.6 times lower.
We conclude that these differences are mainly due to the unique film structure of the advanced FSG film.
Ion implantation and thermal processing have been used to synthesize compound semiconductor nanocrystals (SiGe, GaAs, and CdSe) in both SiO2 and (0001) Al2O3. Equal doses of each constituent are implanted sequentially at energies chosen to give an overlap of the profiles. Subsequent annealing results in precipitation and the formation of compound nanocrystals. In SiO2 substrates, nanocrystals are nearly spherical and randomly oriented. In Al2O3, nanocrystals exhibit strong orientation both in-plane and along the surface normal.
Recent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.
The mechanical stress induced in as-prepared porous silicon is generally compressive. Upon thermal annealing, the stress shows hysteresis. Isothermal annealing reveals second-order kinetic processes for both the stress and hydrogen effusion. The correlations between the changes in stress and porous silicon composition and structure are discussed.
The demonstration of photoluminescence (PL) and electroluminescence (EL) in nanostructures of Si or Ge, such as those found in porous silicon, has significantly improved the prospects of all Si based photonic devices. While the physical mechanisms at work are still a subject of much study, it is clear that the luminescence is associated with the formation of nanometer or “quantum” sized particles. Further, it is clear that prototype NanoCrystal Displays (NCDs) and communication devices are being fabricated in these material systems. We report here on the electroluminescent properties of nanometer sized particles in an SiO2 host matrix, which were fabricated by LPCVD techniques. The films have demonstrated reproducible emission from well below 400 nm to well above 800 nm. We believe that dispersion effects of the nanocrystals can account for "white" light emission. The films have been characterized using PL, Raman, XRD, TEM, and SIMS. The nanocrystals are primarily in the 2-7 nm range although larger crystal clusters are also observed. The development of stable and efficient Si or Ge nanocrystalline EL based devices could find applications in lamps/LEDs, photonic integrated circuits, and displays.
Photoluminescence from l–3μm thick porous Si layers prepared by anodization of p-type c-Si wafers and subsequent chemical etching exhibits an anomalous temperature dependence and light-induced degradation. The luminescence intensity is almost quenched at temperatures below 30K and recovered by laser irradiation at 48K. This quenching phenomenon is not observed for PS thicker than 10μm. The luminescence fatigue is partially recovered by annealing at 150°C for 5min during which no further oxidation takes place. These observations are interpreted in terms of the structural metastability of hydrogen-terminated porous Si.
Raman scattering results on porous silicon, and silicon and gallium arsenide nanocrystals show that almost all vibrational modes become Raman active and remarkably soft in these nanocrystal systems. The experimental results further demonstrate that the carrier-induced strain effects play an important role on the optical properties of such nanocrystal systems.
Proper surface passivation is critical for achieving stable, efficient PL from light-emitting porous silicon (LEPSi). As-anodized LEPSi is passivated by hydrogen which desorbs at a temperature as low as 400 °C. For device purposes, it is necessary that porous Si can tolerate at least 450 °C for post anodization annealing/metallization steps. We have established that, if the hydrogen at the surface is substituted by oxygen, the resulting Si-Ox passivation is significantly more stable. One way of achieving this is to implant low energy/low dose oxygen to form a thin coating of SiO2 on the surface. Post implantation FTIR data report the absence of Si-H peaks. XPS data indicate the formation of nearly stoichiometric SiO2 at the surface. Similar results were achieved by implanting with nitrogen to form Si3N4. As an alternative to implantation, we have deposited thin capping layers of SiO2, Si3N4 and SiC by plasma-enhanced chemical vapor deposition (PECVD) which resulted in a similar degree of passivation. Wafers were pre-treated at 400 °C to remove hydrogen from the surface. Finally, we carried out a low-pressure CVD (LPCVD) oxide deposition on LEPSi. Post implantation/CVD annealing was done at temperatures up to 600 °C. In most cases, little or no change was observed in the resultant PL intensities.
Disordered thin layer GaAs/AlAs superlattices with various disorder periods have been grown using MBE. The disorder was introduced by varying the thickness of GaAs and AlAs layers in the growth direction in various specific but randomly generated finite disorder sequences. The photoluminescence spectra of these disordered superlattice samples showed a sharp peak at the high energy side and a broad peak at the low energy side. The temperature, excitation, and disorder sequence dependence of the photoluminescence spectra indicates that the sharp peak is due to the pseudo-direct exciton emission, and the broad peak is strongly related to the localized states induced by disorder. In addition, the results demonstrate that the luminescence intensity of disordered superlattices can be improved by up to two orders of magnitude over that of ordered short period superlattices. Finally, we propose a kinetic model for the state population and find that the photoluminescence spectra can be well described by this model.
Two types of amorphous silicon (a-Si:H)/silicon nitride (a-Si3 N4 :H) multilayers have been prepared either by turning-off the plasma at each step of individual layer growth (step by step deposition) or by quick gas switching without interrupting the plasma (continuous deposition). It is found that the continuous deposition causes a significant mixing of nitrogen into the a-Si:H well layers and deteriorates the compositional abruptness in the a-Si:H/a-Si3N4 :H interface. Also, undesirable incorporation of nitrogen into the a-Si:H well layers tends to induce nonradiative recombination centers near the interface.
Photodissociation of trimethylaluminum molecules with a UV lamp is shown to be an effective technique for predisposing the irradiated silicon surface prior to subsequent aluminum film growth via visible laser induced pyrolysis. The Al deposits thus obtained are carbon contamination free. The UV exposure time needed for the onset of Al nucleation and growth is deduced from an in situ laser reflectometry technique. Direct laser writing is obtained using this two-step process and a microscopic analysis of the lines is made in correlation with the experimental procedure.
Near-edge and extended x-ray absorption fine structure measurements from a wide variety of H-passivated porous Si samples and oxidized Si nanocrystals, combined with electron microscopy, ir-absorption, α-recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the luminescence observed in these systems. For luminescent porous Si samples peaking in the visible region, i. e., ≤700nm, their mass-weighted-average structures are determined here to be particles–not wires, whose short-range character is crystalline – not amorphous, and whose dimensions – typically <15 Å – are significantly smaller than previously reported or proposed. These results depend only on sample luminescence behavior, not on sample preparation details, and thus have general implications in describing the mechanism responsible for visible luminescence in porous silicon. New results are also presented which demonstrate that the observed luminescence is unrelated to either the photo-oxidized Si species in porous Si or the interfacial suboxide species in the Si nanocrystals.
In applying porous Si (PS) to color display technology, it is important to fabricate light emitting devices with three primary colors. However, there have been few reports on blue and green electroluminescence (EL), and its mechanism (even the relationship between PL and EL spectra) is unclear. To obtain blue and green EL and to investigate its mechanism, we have formed PS anodized under UV illumination (UV-PS) with green photoluminescence (PL) and porous SiC with blue PL. Consequently, green and blue light emitting devices were successfully fabricated by using these materials. The observed spectra are from 350 to 750 nm with a peak of, 520 nm for ITO / UV-PS junctions and from 300 to 600 nm with a peak of 470 nm for ITO / porous SiC junctions. The EL mechanism is also discussed by reference to experimental results of comparing PL and EL spectra and of investigating the dependence of EL intensity on current.