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Notes: Comparative ab initio restricted Hartree–Fock (RHF) and density functional theory (DFT) calculations were performed to investigate the geometric and electronic structures of various neutral aniline oligomers. These oligomers were selected to model polyaniline (PANI) in different intrinsic oxidation states, with an aim to study the applicability and extendibility of the theoretical methods to conjugated polymers. In general, we found that DFT calculations produce results that are in good agreement with observations from x-ray diffraction, ultraviolet-visible absorption, ultraviolet photoelectron and x-ray photoelectron spectroscopy. The DFT method has reproduced well the ∼4.0 eV π–π* transition of leucoemeraldine base and the ∼2.0 eV Peierls gap transition of pernigraniline base. The valence band structure and the ∼1.2 eV energy separation of nitrogen core levels of emeraldine base are also correctly predicted. On the other hand, large discrepancies with experimental measurements are predicted by the RHF method. Single-point MP2 calculations show that the DFT-optimized structures are all at lower energy than the RHF-optimized ones. © 2000 American Institute of Physics.

Notes: Angle-resolved x-ray photoelectron spectroscopy (ARXPS) has been used to study the Ar incorporation and surface compositional changes in InP(100) after 1–5 keV Ar+ bombardment at various ion fluences. The ARXPS measurements showed that the incorporated Ar concentration achieved saturation at ion bombardment fluences of 〉1016 cm−2. The surface Ar concentration decreased with increasing bombardment energy. No Ar bubbles were observed by atomic force microscopy, suggesting that Ar bubble formation was not the main Ar trapping mechanism. The altered layers were, on average, In rich up to the sampling depth of the ARXPS technique. However, the altered layers were inhomogeneous as a function of depth and appeared more In rich at the surface than in the subsurface region. The results are compared with those obtained by other authors and discussed in the context of preferential sputtering, radiation-enhanced diffusion and segregation, and Ar incorporation. Although the altered layers were In rich, a P-rich phase induced by Ar+ bombardment was identified in the altered layers. © 1996 American Institute of Physics.

Notes: An investigation of the structural properties of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films prepared by the plasma-enhanced chemical vapor deposition of silane and acetylene has been undertaken using a combination of infrared (IR), Raman, and x-ray photoelectron spectroscopy (XPS) measurements. The compositions of the silicon, carbon, and hydrogen in the films were found to be dependent on the preparation conditions. From the IR results, it is found that the Si—H bond decreases and the C—H bond increases as the film's carbon increases. The Raman spectra showed that while the Si—Si and C—C bonds can be detected in silicon-rich and carbon-rich samples, respectively, the Si—C band can only be observed in a-Si0.7C0.3:H and a-Si0.5C0.5:H. The XPS results showed that the stoichiometry calculation from the flow rates of the reacting gases was good for a-Si0.7C0.3:H but not for a-Si0.3C0.7:H. Reactive ion etching of the a-Si1−xCx:H films showed that the etch rate was dependent on the films' carbon concentration and films prepared with acetylene as source gas were more resistive to etching compared to that prepared by butadiene. © 1995 American Institute of Physics.

Notes: The effects of the rf power (100 to 600 W) and the hydrogen partial pressure (PH=0.15 to 0.6 Pa.) on the deposition rate and the structural and electrical properties of rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films were investigated. The films were deposited in an argon plus hydrogen ambient. The deposition rate increased with increasing rf power, but decreased with increasing PH. The refractive index increases from 1.85–3.6 as the rf power increases from 100–600 W and from 2.8 to 3.5 as PH increases from 0.15–0.6 Pa. The optical gap increases from 1.5 to 2.15 eV as PH increases from 0.15–0.6 Pa, but decreases from 2.8–1.38 eV as the rf power increases from 100–600 W. The Si–C bond gave the most prominent absorption peak in the infrared spectra, and increased with increasing rf power but not affected by changes in PH. The Si–H bonds increases from 3.06×1021 to 1.64×1022 cm−3 as PH was increased from 0.15–0.6 Pa. The optical gap increases from 1.5–2.15 eV and the conductivity reduces from 7.3×10−9 to 1.9×10−11 Ω−1 cm−1 accordingly. No C–Hn stretching mode was detected in all the films and this was attributed to the low carbon content of the films. We conclude that rf sputtering technique is not effective in varying the carbon content in a-Si1−xCx:H films. © 1996 American Institute of Physics.

Notes: Argon incorporation and the formation of silicon carbide in Si(100) by low energy Ar+ ion bombardment have been studied by angle-resolved x-ray photoelectron spectroscopy (XPS). The bombardment was performed at ion energies of 1, 1.5, and 2 keV and various ion fluences in an ultrahigh vacuum chamber equipped with XPS. The XPS measurements showed that the incorporated Ar concentrations achieved saturation in the near-surface region at ion bombardment fluences (approximately-greater-than)1016 cm−2. The surface Ar concentrations decreased with increasing bombardment energy. No Ar bubbles on the surface of Ar+-bombarded samples were observed by atomic force microscopy under these experimental conditions suggesting that Ar bubble formation was not the main Ar trapping mechanism in our study. The SiC formation was confirmed by characteristic XPS peaks of Si 2p and C 1s for SiC. The carbide formed at lower ion fluence was of a metastable structure as inferred by XPS. Bombardment at higher ion fluence yielded a stable carbide phase through continuous ion beam mixing. No strong dependence of carbide depth distribution on bombardment energy was observed suggesting that the carbide phase is probably dispersed inside the bombarded layer and that carbon is bonded to silicon at localized defect sites. © 1996 American Institute of Physics.

Notes: Surface and interface properties of CdTe/CdS/SnO2/glass heterojunction solar cells are studied by means of x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and optical reflectance (OR) techniques. First, n-type CdS layer was grown by solution growth technique on the SnO2 coated glass substrate and then the p-type CdTe was deposited on CdS by metal-organic chemical-vapor deposition. Despite many other efficiency limiting mechanisms in CdTe solar cells, this article shows that surfaces and interfaces play an important role in determining the cell efficiency. In an attempt to correlate the surface and interface properties to the cell performance, a series of CdTe/CdS solar cells with different conversion efficiencies were fabricated and analyzed. It was found that high efficiency cells possess Te-rich CdTe surface along with smooth interfaces, as revealed by XPS, SIMS, and OR measurements, while low efficiency cells display near stoichiometric or Cd-rich CdTe surface and abrupt interfaces. The impact and role of interface/surface properties on CdTe solar cell performance are discussed. © 1996 American Institute of Physics.

Notes: An investigation of the electrical and structural properties of rapid thermal annealed Czochralski silicon wafers has been carried out. The electrical properties examined here are the minority carrier lifetime, measured using the laser microwave photoconductance technique, and the donor concentration (Nd), determined by the four-point probe method. Thermal donors were intentionally introduced into the silicon and were found to be completely annihilated by the rapid thermal annealing (RTA) process. The minority carrier lifetime was found to increase significantly for wafers annealed at 900 and 1000 °C. It was concluded that due to the very short annealing time used in this work, a denuded zone was unlikely to form in silicon and be responsible for the increase in the lifetime. Infrared, x-ray photoelectron (XPS) and Auger electron spectroscopies were used for the structural analysis. Auger results showed that higher oxygen concentration could be found in a thicker layer of silicon in annealed wafers, as compared to the as-received, virgin sample. The XPS data showed that the SiO2:Si ratio increased from 0.28 for the virgin sample to 3.5 for wafers annealed at 1000 °C. It is suggested that the Auger and XPS data could be explained by considering oxygen outdiffused from the bulk of the silicon to the native oxide and the silicon next to the native oxide. We believe this is the first investigation of the effect of RTA on the behavior of oxygen and thermal donors, and its influence on the minority carrier lifetime of Czochralski silicon. © 1995 American Institute of Physics.

Notes: The structural and electrical properties of radio frequency (rf) sputtered hydrogenated amorphous silicon carbide films are presented in this paper. Films were prepared with sputtering pressure Ps varied from 0.8 to 3 Pa, or with substrate temperature Ts varied from 100 to 300 °C. For films deposited with an argon plus hydrogen ambient, the deposition rate was found to increase with increase in Ps and decrease with an increase in Ts. For films prepared with an argon ambient only, the deposition rate increased slightly with an increase in Ps or Ts. The deposition rate was also approximately two to eight times higher when sputtering was carried out in an argon plus hydrogen ambient than in argon only. Infrared (IR), x-ray photoelectron (XPS), and Raman spectroscopies were employed in the structural analysis. The IR results showed that the Si–C bond gave the most prominent absorption peak and was affected by changes in Ps. The Si–H and SiHn stretching modes were observed in all films, and the amount of Si–H bonds NSi–H were found to increase as Ps or Ts was increased. The C–Hn stretching mode was absent in all films, and this was attributed to the low carbon content in these films.The Si–N stretching mode was suggested to contribute to the extra features between 800 to 1100 cm−1 in the IR spectra for films prepared at a higher Ps (3 Pa) or Ts (300 °C). The stoichiometry of silicon carbide and the film composition were determined by the XPS method. The carbon content of silicon carbide was found to be similar to the target composition and varied only slightly with changes in Ps or Ts. The Raman spectra showed that only the C–C bond can be detected in all of the films. From the electrical measurements, the film's conductivity was found to reduce from 4.21×10−9 to 4.35×10−11 Ω−1 cm−1 as Ps was increased from 0.8 to 3 Pa; and decreased from 3.81×10−9 to 1.31×10−8 Ω−1 cm−1 when Ts was raised from 150 to 300 °C. The conductivity was found to be related to NSi–H, with higher NSi–H resulting in lower conductivity. A comparison with data published in the literature suggested that rf sputtering technique was not effective in varying the carbon content in amorphous silicon carbide film. This technique, however, can be used to vary NSi–H and thus change the structural and electrical properties of the sputtered films. © 1995 American Institute of Physics.

Notes: A case of abdominal pregnancy occurring on two consecutive occasions is reported; such an occurrence is unique. Apparently the abdominal pregnancy was a result of a rent in the uterine fundus, a most unusual route of escape from the uterine cavity.