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Supercritical fluids (SF) have been used in a wide variety of applications:
in industrial processes, analytical, waste detoxification, etc. Recently,
its usefulness extends to the semiconductor industry. Researches have shown
that supercritical CO2 (SCCO2) can be used to remove
photoresists and significantly reduce the amount of waste from solvents in
comparison to conventional stripping techniques. SF will also find its
usefulness in cleaning high aspect ratio vias and deep trenches as
semiconductor features shrink to submicron levels. We will report here the
use of supercritical CO2 treatments in extraction of porogens
from a nanohybrid film fabricated via templated-porogen approach. Its use as
a medium to repair the damage in porous films from plasma ashing will also
be presented. The ability to tune the solvation and diffusion power of
SCCO2 and to swell the film matrix make it a good medium for
silylation to restore hydrophobicity and functionalize the film.
A vapor deposition technique has been used to prepare nano-size particles of Fe, Co and Ni using argon gas. The particles were passivated from further oxidation using a small volume of air. The range of particle size obtained in these systems was 47–200 Å. The saturation magnetization of Fe particles varied between 25–200 emu/g with the higher values corresponding to larger particles and the highest coercivity achieved at room temperature was 1050 Oe. In the case of Co and Ni, the magnetization varied in the range 35–100 emu/g and 14–45 emu/g, respectively. The highest room temperature coercivity was 1200 and 41 Oe for Co and Ni, respectively. A shell-type structure consisting of a metallic core surrounded by an oxide shell has been proposed for the particles.
Microwave excited electron cyclotron resonance (ECR) plasmas have been used to fabricate a-Si:H,Cl and a-SiC:H films. By varying the absorbed microwave power, highly photoconductive a-Si:H,Cl films were obtained. The a-SiC:H films do not have appreciable photoconductivity, but they show a bright, broad continuous wave (cw) photoluminescence (PL) in the visible region under near-uv excitation. We have measured the photoluminescence decay in the picosecond range and have resolved the spectra into four distinct components. The four luminescence components may correspond to various recombination mechanisms of photogenerated electron-hole pairs.
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.
We have modified our previous fast analog technique to determine the luminescence decay times of scintillators following an excitation with a Sr90 β3-source. In the original technique , the sample was excited with a nitrogen-pumped dye laser, and the fluorescence pulses (consisting of typically 50 to 1000 photons) were detected by a multi-channel plate photomultiplier tube (MCP-PMT). The output from the MCP-PMT was directed to a fast waveform digitizer triggered externally by the exciting laser. In the modified technique, the digitizer acquires the fluorescence decay in the internal trigger mode, as no corresponding external trigger pulse is available from the Sr90 source. For efficient light collection from scintillators, an ellipsoidal mirror assembly has been tested. The fluorescence decays are acquired as multi-photon pulses and are subsequently corrected for the temporal instrument response by using a deconvolution technique. The overall time resolution of the technique is about 100 ps. The fluorescence decay time obtained using this technique for a commercial scintillator (SCSN-81) agrees well with literature. We also discuss our results on new epoxy-polymer based scintillators prepared in our laboratory. The primary motivation for this work was development of new scintillators with shorter fluorescence decay times for high collision rate experiments.
Maximum undercooling results for the icosahedral phase (i-phase), polytetrahedral C14 Laves phase, and solid solution phases are presented as a function of composition in Ti-Zr-Ni liquids. Containerless processing was achieved using the electrostatic levitation facility located at NASA/Marshall Space Flight Center. The maximum reduced undercooling decreases with increasing icosahedral short-range order in the ordered phase. The first synchrotron x-ray diffraction data from aerodynamically levitated liquids of Ti-Zr-Ni alloys suggest an icosahedral short-range order in the liquids, supporting Frank's hypothesis, correlating icosahedral order in the liquid with the nucleation barrier to the crystal phase. The strong negative heats of mixing between Ti/Zr and Ni and their relative atomic sizes likely favor the formation of this local icosahedral order.
Polyfluorenes (PFs) have emerged as a promising family of blue polymer light-emitting diodes (PLED) due to their high electroluminescence quantum yield. Metal-insulator-semiconductor (MIS) diodes are the two terminal analogues of thin film transistors sharing the same basic layer structure. We have investigated two different structures based on poly [9,9'-(di 2-ethylhexyl)fluorene] (PF2/6), a MIS diode and a hole-only PLED. The MIS diodes were fabricated with the PF2/6 layer on p+ Si /Al2O3 substrates, and were characterized by means of capacitance-voltage (C-V) measurements as a function of frequency. From C-V measurements, the unintentional doping density is evaluated as ∼5.7×1017 cm−3 at frequencies above 20 kHz. The interface trap density is estimated as ∼7.2×1011 eV−1cm−2 at 10 kHz. Current-voltage measurements of PF2/6-based PLEDs shows a shallow trap space-charge-limited conduction from which the energy of the traps and hole mobilities are estimated.
A cleaning process resulting in atomically smooth, hydrogen-terminated, silicon surface that would inhibit formation of native silicon oxide is needed for high-k gate dielectric deposition. Various cleaning methods thus need to be tested in terms of resistance to native oxide formation. Native oxide re-growth is studied as a function of exposure time to atmospheric ambient using ellipsometry. Hafnium dioxide film (k ~23) is deposited on the as-cleaned substrates by electron beam evaporation and subsequently annealed in hydrogen. The difference in the effective oxide thickness re-grown on surfaces treated with the conventional RCA and modified Shiraki cleaning methods, after one-hour exposure, can be as large as 2 Å. This is significant in device applications demanding equivalent oxide thickness less than 20 Å. The degree of hydrogen passivation, surface micro-roughness and organic removal capability are considered to be the main factors that explain the differences between the cleaning methods. Data derived from capacitance-voltage analysis of test capacitors verified the trend observed in the native oxide thickness measurements. An increase of 10~15 % in accumulation capacitance is observed in the samples treated by the new cleaning method.
Brinjal (Solanum melongena L.) is an important solanaceous vegetable in many countries of Asia and Africa. It is a good source of minerals and vitamins in the tropical diets. Assessment of genetic resources is the starting point of any crop improvement programme. In India, the National Bureau of Plant Genetic Resources is the nodal institute for management of germplasm resources of crop plants and holds more than 2500 accessions of brinjal in its genebank. In the present study, morphological diversity in a set of 622 accessions, comprising 543 accessions from indigenous sources and 79 accessions of exotic origin, was assessed. Wide range of variations for 31 descriptors, 13 quantitative and 18 qualitative, were recorded. The wide regional variations for plant, flower and fruit descriptors revealed enough scope for improvement of yield characters by selection. The genetic differences among the landraces are potentially relevant to breeding programmes in that the variability created through hybridization of the contrasting forms could be exploited.
We present a supercritical CO2 (SCCO2) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO2 extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450 °C) and by a SCCO2 process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO2 process is effective in removing the porogen phase at relatively low temperatures (<200 °C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.
The position and dimensions of the jugular bulb and the venous dural sinuses vary considerably. While the anatomical variations of the jugular bulb have been extensively reported in the literature, that of the sigmoid sinus have been reported only rarely. We report a case of unusual anterior course of the vertical segment of the sigmoid sinus which was encountered during an attempted myringoplasty. Anomalies of the jugular bulb in general are also described.
Solitary fibrous tumour was first described as a pleural tumour. It has been reported in a number of extrapleural sites including the head and neck. We present the first case of solitary fibrous tumour of the infratemporal fossa described in the English literature. Complete excision was achieved using the orbitozygomatic infratemporal craniotomy approach.
Blast, caused by Pyricularia oryzae Cav., one of the major foliar diseases of rice, appears sometimes in a devastating form in the seedling stage. The angles subtended by leaves may affect the establishment of the pathogen. Ono (1965) observed that leaf angles of rice plants, among many other factors, influenced deposition of spores. Gangopadhyay & Chattopadhyay (1974) found that brown spot disease (Helminthosporium oryzae) incidence in rice increased with increase in leaf angles. The present study is intended to find out the role of leaf angles in rice on the incidence of blast disease at the seedling stage.
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