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Identifying risk factors of individuals in a clinical-high-risk state for psychosis are vital to prevention and early intervention efforts. Among prodromal abnormalities, cognitive functioning has shown intermediate levels of impairment in CHR relative to first-episode psychosis and healthy controls, highlighting a potential role as a risk factor for transition to psychosis and other negative clinical outcomes. The current study used the AX-CPT, a brief 15-min computerized task, to determine whether cognitive control impairments in CHR at baseline could predict clinical status at 12-month follow-up.
Baseline AX-CPT data were obtained from 117 CHR individuals participating in two studies, the Early Detection, Intervention, and Prevention of Psychosis Program (EDIPPP) and the Understanding Early Psychosis Programs (EP) and used to predict clinical status at 12-month follow-up. At 12 months, 19 individuals converted to a first episode of psychosis (CHR-C), 52 remitted (CHR-R), and 46 had persistent sub-threshold symptoms (CHR-P). Binary logistic regression and multinomial logistic regression were used to test prediction models.
Baseline AX-CPT performance (d-prime context) was less impaired in CHR-R compared to CHR-P and CHR-C patient groups. AX-CPT predictive validity was robust (0.723) for discriminating converters v. non-converters, and even greater (0.771) when predicting CHR three subgroups.
These longitudinal outcome data indicate that cognitive control deficits as measured by AX-CPT d-prime context are a strong predictor of clinical outcome in CHR individuals. The AX-CPT is brief, easily implemented and cost-effective measure that may be valuable for large-scale prediction efforts.
The planarizing ability of sol-gel films was investigated on several as-rolled stainless steel substrates. The smoothing effect afforded by the films was evaluated, using optical techniques, following deposition of silver over the planarized substrates. The specular reflectance of various substrates, initially ranging from 0.36 to 0.90, could be improved to final reflectance values of -0.93 with sol-gel processing. This process is being used to prepare prototype foil mirrors for evaluation in the next generation of solar concentrators.
We have developed a new electrochemical passivation method to obtain a quite stable sulfide layer on GaAs surface. This layer is very thick and contains a mixture of Ga, As, S, O and H compounds. The photoluminescence (PL) spectrum of such anodic sulfurized GaAs surface shows big intensity enhancement as compared with that of as-etched GaAs samples; No visual intensity decay occurs under laser beam illumination, which maintains for more than seven months. The structure and composition of the passivation layers are investigated by the X-ray photoelectron spectroscopy and the mechanism of the layer formation is suggested.
In the present work structural and electrical properties of thin films, deposited by PECVD from He-diluted S1H4+NH3+N2O gas mixtures, have been studied. Film compositions have been analyzed by NRA, RBS and hydrogen content has been determinated by ERDA while Infrared spectroscopy has been used to evaluate the local bonding configurations. Electrical properties have been measured in metal-insulator-metal structures by I-V ramp. From the results obtained, the oxynitride films show suitable properties for application as gate insulator in amorphous silicon thin film transistor.
The tunnelling front model has been used to obtain the spatial distribution of high-voltage, stress generated traps inside of MOS capacitors. It was found that the number of traps created by high voltage stress was proportional to the cube root of the fluence through the oxide during the stress. Measurement of the trap generation rate indicated that fewer traps were being created as higher amounts of charge were passed through the oxide. Further tests indicated that there was a voltage dependence to the trap generation which was independent of stress polarity.
The asymmetric amorphous silicon thin film transistors are fabricated and exposed to various stress environments. A visible light illumination of 200,000 Ix and gate bias of 30 V are applied to both asymmetric and widely used symmetric a-Si TFT's. It is observed that the leakage current of asymmetric structure, where only one electrode is fully overlapped by gate electrode, is much less than that of symmetric one. The visible light illumination as well as gate bias stress do not degrade the leakage current of the asymmetric a-Si TFT's, while the leakage current in die symmetric TFT's are increased considerably due to the stress. Also, the degree of degradation in the threshold voltage, the field effect mobility and the subthreshold slope of asymmetric TFT's are relatively much less than that of conventional symmetric TFT's.
We have used a fast analog technique (100 ps resolution) to study photoluminescence (PL) decay in a-SiNx:H films in nanosecond (0.1–50 ns) range. Films prepared using RF glow discharge of NF3 and pure SiH4 were used for these measurements. The PL decays in the films were studied as a function of nitrogen content for 0≤x≤0.13. When the PL decay measured at 25 K is fitted with I (t) = ao +Σai exp (-t/Ti), where ao, ai and ti, are fitting parameters, we get three distinct lifetimes with t1 = 0.8 ± 0.2 ns, T2 = 3.5 ± 0.5 ns and T3 = 14.0 ± 3.0 ns. We find that these lifetimes do not change with nitrogen content but their relative contributions to the PL decay change with nitrogen content. We have also studied the effect of temperature and excitation energy on the PL decays at different emission energies. We suggest an excitonic origin to these three recombination processes.
In the PECVD SixNyHzOw the hydrogen is principally incorporated as N-H bonds. For O/(O+N) below 0.4, the %H is constant at 25%; from 0.4 to 1, it decreases to 4%. We show that a chemical ordered model is likely to describe the hydrogen incorporation in the amorphous network while a random bond model fails.
Conditions for depositing quasi-stoichiometric silicon nitride films by low-temperature, remote plasma-enhanced chemical-vapor deposition, RPECVD, have been identified using on-line Auger electron spectroscopy, AES, and off-line optical and infrared, IR, spectroscopies. Quasi-stoichiometric films, by the definition propose in this paper, do not display spectroscopic evidence for Si-Si bonds, but contain bonded-H in Si-H and Si-NH arrangements. Incorporation of RPECVD nitrides into transistor devices has demonstrated that electrical performance is optimized when the films are quasi-stoichiometric with relatively low Si-NH concentrations.
New defects were revealed in PECVD SiOxNyHz thin layers upon VUV-illuminations with a deuterium (De) lamp. The ESR signal measured after a 8-hour illumination reached a saturated amplitude one or two decades higher than the dark ESR signal. The dark ESR signal level was recovered after a 3-hour anneal at 380°C. In addition to the silicon dangling bonds already identified in the dark ESR, the bridging nitrogen dangling bonds and over-coordinated nitrogen were identified after VUV-radiations. The relative densities of the various kinds of defect are given as a function of the O/O+N oxynitride composition.
The accelerated degradation phenomena in amorphous silicon thin film transistors due to both electrical stress and visible light illumination under the elevated temperature have been investigated systematically as a function of gate bias, light intensity, and stress time. It has been found that, in case of electrical stress, the threshold voltage shifts of a-Si TFT's may be attributed to the defect creation process at the early stage, while the charge trapping phenomena may be dominant when the illumination periods exceed about 2 hours. It has been also observed that the degradation in the device characteristics of a-Si TFT's is accelerated due to multiple stress effects, where the defect creation mechanism may be more responsible for the degradation rather than the charge trapping mechanism.
Investigations of plasma grown native oxides on indium phosphide carried out recently [1,2] have shown that these oxides exhibit properties which are promising to be used in MIS structures on InP, due to their stable composition which includes [InxPyOz]n polyphosphate phase mainly and due to reduced density of interface states (Nss<1011 eV−1 cm−2). It has been shown also that MIS structures with plasma native oxides exhibit C-V characteristics shifted towards positive values of voltage bias. The flat band shift is assigned to a negative charge injected into oxide film during plasma oxidation. The presence of this negative charge in plasma grown native oxides on InP may cause instability of electric properties of MIS structures .
The aim of this work was to make an attempt to influence upon negative effective oxide charge density by means of hydrogen plasma treatment.
Thin amorphous SiN films grown on Si are studied with Near Edge X-Ray Absorption Fine Structure (NEXAFS). The NEXAFS spectra of N-rich films are characterized by a strong resonance line (RL) at the onset of the N K- edge. The intensity of the RL in N-rich films increases with the N/Si ratio, while the same RL is detected in the NEXAFS spectra of stoichiometric SiN films subjected to damage with Ar+ ion bombardment. The RL is attributed to a N-related defect which is strongly localized in a pure 2p orbital. The RL, which is identified as a bulk nitride property, can be annealed out at temperatures higher than the growth temperature. It is proposed that the annealing process of the RL, which is characterized by an activation energy of 0.87eV, is due to Si-N bond formation, where the Si atoms are provided by the stressed SiN/Si interface.
Borophosphosilicate glass (BPSG) is an essential insulating material used to modify thecomplex topography of highly dense, next generation dynamic random access memory (DRAM)devices. The shallow junctions in 16 and 64 Meg DRAMs can only be maintained by severely restricting the time, temperature, and atmosphere of all thermal process steps following the junction implant.
In this paper we present the results of rapid thermal process (RTP) assisted reflow of BPSG over complex topographies and compare the results of RTP to furnace reflow in both dry and wet ambients. We also compare the out-diffusion of boron and phosphorous from BPSG films during the RTP and furnace reflow. We found an optimum RTP cycle that completely removes voids in the vicinity of overhang geometries and provides sufficient activation of the underlying dopants (as compared to a furnace reflow and activation cycle). In this study we used the results of boron and phosphorous profile redistribution, underlying dopant activation, and the amount of reflow to compare RTP and furnace processing techniques.
Electrically active traps were induced in the Si-SiO2 interfacial region by silicon ion bombardment. A Kaufman source was used to introduce 400 eV hydrogen ions into the oxide and the interface. The interaction of the hydrogen species with the traps was monitored by a comprehensive set of electrical measurements of the metal-oxide-silicon [MOS] structures.
Ellipsometry and XPS investigations of RF plasma grown native oxide and C-V measurements of its interface were performed.
Strong dependence of the composition of the plasma grown native oxides and electric properties of MIS structures on the time of plasma treatment has been observed. The greater the content of stable polyphosphate phase of [InxPyOz] is in the native oxide composition, the better parameters of its interface with InP (NS 11 cm−2 eV−1 and the hysteresis of C-V characteristics≤0.2 V) and the lesser C-V drift after treatment may be achieved. Plasma oxidation results in creating a negative effective oxide charge density.
We summarize various measurements of the thermal conductivity of thin ceramic films which show that the thermal conductivity of thin films with thickness in the micron and sub-micron range may be up to two orders of magnitude lower than the thermal conductivityof the corresponding bulk solid. The reduction in the thin film effective thermal conductivity is attributed to the interfacial thermal resistance across the film/substrate interface.
A combination of Electron Cyclotron Resonance (ECR) plasma, electrochemical, and chemical growth process were examined to synthesize dielectric surface passivation layers on InSb. The material properties of ECR-grown SiOx Ny on InSb at temperatures from 30°C to 250°C were investigated. Composition analysis was done using Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD). The electrical quality of the passivation layer was characterized with capacitance-voltage (C-V) measurements on metal-insulator-semiconductor structures over the frequency range from 1 kHz to 1 MHz. Sulfided layers, Si3ON2 on InSb, and sulfided layers capped with S3ON2 all exhibited good C-V properties consistent with interface state densities on the order of 1011/cm2-eV, and flatband voltages of magnitude less than 1 V. The difference in adhesion of Si3N4 on InSb and the adhesion of Si3ON2 on InSb was described in terms of the strength of the bonding at the dielectric-InSb interface. This work is the first to demonstrate passivation of an InSb surface with high-quality ECR silicon oxynitrides grown at room temperature.