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Notes: Summary  Background. The objective of this study was to investigate the role of preoperative three dimensional short-range magnetic resonance angiography (3D-TOF MRA) in predicting the clinical outcomes following microvascular decompression for the treatment of hemifacial spasm.  Method. Preoperative magnetic resonance (MR) imaging was performed on all patients with hemifacial spasm (564 cases) between January 1992 and September 1998. Of the 564 patients, 440 patients were included in this retrospective study. The presence of vascular contact, offenders, and anomalies in the vertebro-basilar system, were determined by 3D-TOF MRA prior to microvascular decompression of the facial nerve. The preoperative findings were compared with the surgical findings and clinical outcomes.  Findings. A correlation was found between the clinical outcome (p〈0.01) and the presence of a vascular indentation at the root entry zone (REZ) of the facial nerve. A shift of the vertebrobasilar system to the symptomatic side was found in 214 (48.6%) patients with hemifacial spasm, compared to only 10 (13.5%) patients in the control group (p〈0.01). The unilateral vertebral artery was observed in 43 (9.8%) patients with hemifacial spasm and in 8 (10.8%) of the control patients. A hypoplasia of the artery was found in 8 (1.8%) patients with hemifacial spasm and in 1 (1.4%) control patient. The compressing offenders in the patients, discovered by MRI in conjunction with MRA, were as follows: 45.9% (202 patients) in the anterior inferior cerebellar artery (AICA), 34.8% (153 patients) in the posterior inferior cerebellar artery (PICA), 12.5% (55 patients) in the vertebral artery (VA) and 6.8% (30 patients) in multiple vessels. In contrast to the compressing offenders seen on the MRA, the offenders confirmed during surgery were as follows: 43% (189 patients) in the AICA, 36.4% (160 patients) in the PICA, 1.4% (6 patients) in the VA, 19% (84 patients) in multiple vessels, and 0.2% (1 patient) in the vein.  In our long-term follow-up series of the 440 patients with hemifacial spasm, an excellent surgical outcome was obtained in 86.3% of cases and a good outcome was achieved in 6.4% (mean follow-up duration, 45.5 months).  Interpretation. Preoperative 3D-TOF MRA can identify the relationship between the facial nerve and adjacent vessels in patients with a hemifacial spasm and assist in preoperative planning. This study suggests that 3D-TOF MRA is useful for selecting appropriate patients for surgical treatment and, to some extent, as an additional role for predicting the clinical outcome.

Notes: The amorphous Ir–Si layer of several nanometers thick on Si(100)2×1 deposited at room temperature has been characterized by using both low energy electron diffraction (LEED) and synchrotron photoemission techniques. The double domain Si(100)2×1 LEED pattern disappeared when the deposited Ir onto Si(100) was higher than 1 ML. The ultrathin amorphous Ir–Si layer consisted of three different IrxSiy alloys, rather than a single homogeneous IrxSiy alloy as predicted by the conventionally used Gibbs free energy calculation in the solid state amorphization. The growth of the amorphous Ir–Si layer on Si(100) strongly depended on the interaction between Ir and Si(100) at the initial stage of Ir deposition. Three types of Ir–Si bonding formed on Si(100) at 1 ML Ir coverage and gradually evolved to be three different amorphous IrxSiy alloys. The growth mode of the amorphous Ir–Si layer was proposed to be the modified Stranski–Krastanov growth. The transition from layer-by-layer-like to island growth occurred at Ir coverage of ∼3 ML. The major amorphous IrxSiy alloy switched from Si to Ir rich when Ir coverage is over ∼3 ML. © 2002 American Institute of Physics.

Notes: This work is a systematic study of carbon incorporation in Ta2O5 and its effect on the material and electrical properties of Ta2O5, a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta2O5 performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta2O5 films with carbon. In thick (70 nm) Ta2O5 films, an optimal amount (0.8–1.4 at. %) of carbon doping reduced the leakage current to 10−8 A/cm2 at +3 MV/cm, a four orders of magnitude reduction compared to a leakage current of 10−4 A/cm2 in an undoped Ta2O5 film grown in similar conditions without CO2 in the plasma. This finding suggests that carbon doping can further improve the dielectric leakage property at an optimal concentration. X-ray Photoemission Spectroscopy analysis showed the presence of carbonate (carbon bonded to three oxygen) in these electrically improved carbon-doped films. Analysis by high-resolution transmission electron microscopy and Nomarsky microscopy exhibited no morphological or structural changes in these carbon-doped thin films. Moreover, carbon doping showed no improvement in the leakage current in thin (10 nm) Ta2O5 films. This phenomenon is explained by a defect compensation mechanism in which the carbon-related defects remove carriers at low concentrations but form a hopping conduction path at high concentrations. © 2002 American Institute of Physics.

Notes: To elucidate the dynamics of static charge elimination, we measured charge decay and residual potential (balance or offset voltage) in gases with various ion mobilities. It was observed that surface charge decay, especially for positive charges, occurs much faster in nitrogen than in air. The residual potential on the probe is negative in pure nitrogen and increases toward positive values with the injection of small quantities of air in front of the ionizer. The fluctuations in the residual potential are generally less than 3 V peak-to-peak. For ionizer operations in nitrogen environments, the charge decay rate increases with superficial gas-flow rate. The results are consistent with a theory of the interaction between bipolar ions and a charged object. © 2002 American Institute of Physics.

Notes: The optical properties and band alignment of ZnSe/ZnMgBeSe heterostructures are investigated. Two sets of ZnSe/ZnMgBeSe multi-quantum-well structures that consist of five or three wells with different well thicknesses and 100-nm-thick ZnMgBeSe barrier layers are grown on GaAs (100) substrates by molecular beam epitaxy. Low-temperature photoluminescence spectra show dominant sharp excitonic emission whose peak position systematically shifts to the higher energy side with decreasing the well thickness. Photoluminescence excitation spectra show optical transitions between excited quantum levels in addition to the ground levels. The standard analysis based on the effective-mass approximation gives the valence band offset of ΔEυ=(0.4±0.1)ΔEg. This is consistent with calculated values based on Harrison's linear combination of atomic orbitals theory. © 2002 American Institute of Physics.

Notes: The nature of the silicon oxide transition region in the vicinity of the Si/SiO2 interface is probed by infrared and x-ray photoelectron spectroscopies. The layer-by-layer composition of the interface is evaluated by uniformly thinning thermal oxide films from 31 Å down to 6 Å. We find that the thickness dependence of the frequencies of the transverse optical and longitudinal optical phonons of the oxide film cannot be reconciled by consideration of simple homogeneous processes such as image charge effects or stress near the interface. Rather, by applying the Bruggeman effective medium approximation, we show that film inhomogeneity in the form of substoichiometric silicon oxide species accounts for the observed spectral changes as the interface is approached. The presence of such substoichiometric oxide species is supported by the thickness dependence of the integrated Si suboxide signal in companion x-ray photoelectron spectra. © 2000 American Institute of Physics.

Notes: Angle-resolved x-ray photoelectron spectroscopy (AR–XPS) is utilized in this work to accurately and nondestructively determine the nitrogen concentration and profile in ultrathin SiOxNy films. With furnace growth at 800–850 °C using nitric oxide (NO) and oxygen, 1013–1015 cm−2 of nitrogen is incorporated in the ultrathin (≤4 nm) oxide films. Additional nitrogen can be incorporated by low energy ion (15N2) implantation. The nitrogen profile and nitrogen chemical bonding states are analyzed as a function of the depth to understand the distribution of nitrogen incorporation during the SiOxNy thermal growth process. AR–XPS is shown to yield accurate nitrogen profiles that agree well with both medium energy ion scattering and secondary ion mass spectrometry analysis. Preferential nitrogen accumulation near the SiOxNy/Si interface is observed with a NO annealing, and nitrogen is shown to bond to both silicon and oxygen in multiple distinct chemical states, whose thermal stability bears implications on the reliability of nitrogen containing SiO2. © 2000 American Institute of Physics.

Notes: The thermal stability of ZrO2/ZrSixOy and ZrO2/ZrSixOy/SiNx thin films on silicon was examined by synchrotron radiation ultraviolet photoemission spectroscopy. The ZrO2/ZrSixOy layer deposited by atomic-layer-controlled deposition is stoichiometric, uniform, amorphous, and has an equivalent oxide thickness of ∼1 nm and a dielectric constant of ∼18 with low leakage current. These ZrO2/ZrSixOy samples are thermally stable in vacuum up to 880 °C at which the film decomposed to form ZrSi2, the most thermodynamically stable metal silicide at a per zirconium atom basis, and the desorption of SiO(g) and ZrO(g) accounted for the greatly reduced oxygen and zirconium photoemission intensities. The thermal stability of ZrO2/ZrSixOy is improved to 950 °C when deposited on a 0.5–0.7 nm SiNx film. © 2001 American Institute of Physics.

Notes: Analytical electron microscopy has been employed to characterize the localized physical and electronic structure of a Co/AlOx/Co magnetic tunnel junction. The tunnel barrier is amorphous alumina with an extensive conduction band tail due to disorder. Both barrier edges are Al terminated and an Al-rich layer exists at the bottom Co/AlOx interface. sp-d hybridization between interfacial Co and Al atoms is observed and it is likely that the interfacial Al is metallic. All of these features are expected to be important to the magnetoresistance behavior of the junction. © 2001 American Institute of Physics.

Notes: N-type ZnTe layers with high electron concentration are grown by molecular-beam epitaxy using aluminum as the donor species. The ZnTe:Al layers show a high structural quality with a narrow x-ray diffraction linewidth (24 arcsec) and a high carrier concentration up to n=4×1018 cm−3 with low resistivity (ρ=0.017 Ω cm). The dependence of the electron mobility on the carrier concentration suggests that the dominant scattering mechanisms in the ZnTe:Al layers are ionized impurity scattering and polar optical phonon scattering. The photoluminescence spectrum of moderately doped ZnTe layers shows strong Al–donor-related bound exciton lines: I2 (2.378 eV) and donor–acceptor pair emission (zero phonon energy=2.324 eV) with a weak deep-level emission (2.19 eV). Highly Al-doped layers show an increase in the deep-level emission intensity and a decrease in carrier mobility, which are interpreted in terms of the increase in the carrier compensation. © 2001 American Institute of Physics.