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We developed [Lu.sub.0.4][Gd.sub.1.6]Si[O.sub.5] (LGSO) crystal as a new scintillator for medical imaging applications. The size of the LGSO ingot obtained for this investigation was approximately 60 mm in diameter and 170 mm in length. The as-grown crystal was yellow in color. To eliminate the tint, the crystal was annealed in pure [N.sub.2] atmosphere after the growth. As a result, the LGSO became colorless with uniform and large light output which is about 2.0 times that of GSO. Index Terms--Annealing, LGSO, scintillation properties.

The emission spectra for X-ray and UV excitation, decay curve for emission above 460 nm under [gamma]-ray excitation, and energy spectrum by using avalanche photodiode (APD) for excitation with [sup.137] Cs [gamma]-rays have been measured for [Lu.sub.0.4] [Gd.sub.1.6] Si[O.sub.5] having 2.0 mol% Ce. The emission spectrum under X-ray excitation showed two peaks around 430 and 495 nm. The excitation-emission spectrum under UV excitation also had two peaks at 425 and 510 nm for excitation wavelength of 285 and 385 nm, respectively. There was no significant difference in decay constants of emission between the longer and shorter wavelength components. Energy resolution by using an APD was 8.0% for [sup.137] Cs [gamma]-ray excitation. Index Terms--Emission wavelength, radiation detector, scintillator.

Plasma-enhanced chemical vapor deposition methods were used for carbon-doped SiO2:F films deposited by changing the CH4 flow rate.

A study was conducted to analyze structural changes of polycrystalline silicon films support different deposition temperature. The role of deposition temperature and surface structure of substrates on the growth mechanism and structural characteristics of the films were examined. Results indicated that crystalline at a lower deposition temperature correlated with the surface morphology of the substrates.

The structural and bonding characteristics of 200-nm-thick polycrystalline Si films deposited by altering the deposition temperature through plasma-enhanced chemical vapor deposition of monosilane-hydrogen mixtures were studied. Findings showed that except for deposition temperature at 150 and 650 deg C, crystallization of the films was observed. Two infrared absorption bands around 850 and 1000/cm and an increase in the density of Si dangling bonds were observed in deposition temperatures above 500 deg C.

Single crystal Ce-doped [Gd.sub.2]Si[O.sub.5] (GSO) has a good balance of scintillation properties such as high density, intense light output, and short decay time, and also has an excellent temperature response and excellent radiation hardness. We studied causes for cracks in single-crystal GSO which have been a major problem in GSO growth, and tried to optimize the growth conditions by using a two-zone furnace which reduced thermal gradient. We were thus able to grow a crack-free single-crystal of GSO that was 80 mm in diameter and 280 mm long. Specimens with 20 x 20 x 200 [mm.sup.3] sampled from the large GSO boules with 0.5 and 1.5 mol% Ce have been evaluated for high energy physics application.

Research was conducted to examine the structure, optical absorption and photoluminescence (PL) properties of SiO(sub x) films which were subjected to thermal annealing at 750-1100 degrees C. Results revealed that threshold energies in optical absorption of the Si nanocrystallites were higher than that for bulk Si. Findings also showed that the PL peak energy of the annealed films changes to higher energy with decreasing crystallite size. It is concluded from the results that a localized state contributes to the PL mechanism.

Undoped amorphous-Si (a-Si) films are deposited as a function of deposition temperature on fused quartz substrates by low pressure chemical vapor deposition using 100% disilane. The texture of these poly a-Si films is significantly influenced by the deposition temperature of the initial films which serve as the substrates. The films grown below a temperature of 530 degrees Celsius exhibit a dominant (100) texture and beyond this temperature, a (111) texture. A decrease in deposition temperature results in a reduction of the nucleation rate.

A plasma-enhanced chemical vapor deposition method facilitates the deposition of undoped polycrystalline Si (poly-Si) as a function of rf power and deposition temperature using disilane. A shift in the surface-diffusion coefficient of (SiH)n adsorbates and ion bombardment effects result in a change in texture. The x-ray relative intensity and crystallinity of the poly-Si films decreases with decrease in film thickness. Increase in rf power or thickness favor formation of a low-angle grain boundary rather than an amorphous-like structure.

SiH4-NH3-H2 mixtures facilitated plasma-enhanced chemical vapor deposition of amorphous SiNx:H (a-SiNx:H) films at 300 degrees centigrade. The amorphous films revealed low intrinsic stress, high break-down strength and low buffered HF (BHF) etch rate, when RH and rf power values increased. Such films were used as passivation layers and gate insulators in thin-film transistors. The relaxation of intrinsic stress is due Si-NH-Si bond formation.

The correlation between the stress and bonding characteristics of amorphous hydrogenated SiNx thin films deposited on single crystal Si was investigated using a modified random bonding model. The results showed that intrinsic stress was responsible for the measured tensile stress infilms with an N content higher than 1.0. The incorporated NH bonds induced the intrinsic stress to relax.

The effect of phosphorous and nitrogen doping of polycrystalline SiC films prepared by plasma-enhanced chemical vapor deposition was investigated. The results showed that phosphorous and nitrogen doping of the SiC films enhanced the crystallinity of the material. However, high doping conditions resulted in a deterioration in the crystallinity. In addition, resistivity and dangling-bond density decreased as the crystallinity was enhanced.

X-ray diffraction and x-ray photoelectron spectroscopy were used to investigate the bonding characteristics of glow-discharge polycrystalline and amorphous Si-C films. The results showed that crystallization accompanied some degree of segregation of carbon atoms in grain boundaries. Bonds were observed in high carbon films, and this resulted in a compressive strain.

Undoped polycrystalline films were deposited from a SiH4-H2 mixture by a plasma-enhanced chemical vapor deposition method. Changingpreparation conditions influence the preferential orientation to a random, (100) or (110) crystal axis. Electron spin resonance and the dependence of dark conductivity on measurement temperature have been examined to determine how the structure of the grain boundary depends on the preferential orientationand affects the electrical properties.

A Ce doped [Gd.sub.2]Si[O.sub.5] (GSO) single crystal is an excellent scintillator featuring a large light output, a short decay constant and a high absorption coefficient. It was shown in our previous studies that the surfaces of the scintillator should be polished to get scintillation light output efficiently especially for long and narrow scintillators. Therefore, we newly developed a chemical process to polish the GSO crystal. The surface of the GSO crystal was found to become smooth when it was etched using anhydrous orthophosphoric acid at 150-300 [degrees] C. The process was also proved to be applicable to large size crystal such as 20x20x200 [mm.sup.3] preventing thermal shock crack. An improvement in the scintillator efficiency was confirmed using the chemical polishing process.