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Root surface demineralization is widely used as an adjunct to periodontal treatment. To clarify the influence of citric acid root conditioning on periodontal wound healing, the effects of citric acid and associated extracellular acidosis on the viability (MTT assay), attachment and protein synthesis ([3H]-proline incorporation into tirchloroacetic acid-precipitated proteins) of human gingival fibroblasts (GF) were investigated. A concentration of 47.6 mmolL of citric acid (pH 2.3) in water led to total cell death within three minutes of incubation. Media containing 23.8 mmolL and 47.6 mmolL of citric acid exerted strong cytotoxicity (47 to 90 per cent of cell death) and inhibited protein synthesis (IC500.28 per cent) of GF within three hours of incubation. Incubation of cells in a medium containing 11.9 mmolL of citric acid also suppressed the attachment and spreading of fibroblasts on culture plates and Type I collagen, with 58 per cent and 22 per cent of inhibition, respectively. Culture medium supplemented with 11.9, 23.8 and 47.6 mmolL of citric acid also led to extracellular acidosis by decreasing the pH value from 7.5 to 6.3, 5.2 and 3.8, respectively. In addition, it was confirmed that the toxic effect of media containing citric acid was due to their acidity rather than the citrate content. Most of the citric acid-induced cell death could be prevented by adjusting the pH value of the culture medium to pH 7.5. Sodium citrate, at a concentration of 47.6 mmolL, also exerted little cytotoxicity. The results suggested that toxicity of citric acid in specific stages of the healing process must be considered prior to its clinical application. Careful management of citric acid in order to avoid contact with tissue or the development of other demineralizing agents is important in enhancing periodontal wound healing.

The etching characteristics of ZnSe, ZnS0.07Se0.93, Zn0.88Cd0.12Se and Zn0.95Mg0.05S0.09Se0.91have been studied using 2CH4/9H2/2Ar and 9H2/2Ar as the reactive ion etching (RIE) etching gas. It was demonstrated that a smooth surface and a good anisotropic feature can be achieved when these samples are etched in 9H2/2Ar at 60 mTorr with a 150 W plasma power. Under this etching condition, the etching rates of ZnSe, ZnS0.07Se0.93, Zn0.88Cd0.12Se and Zn0.95Mg0.05S0.09Se0.91were 7.8 nm/min, 9.5 nm/min, 10.4 nm/min and 8.3 nm/min, respectively. Carbon-related needlelike features were observed when methane was added to the etching gas, and these needlelike features can be removed by a high plasma power. Photoluminescence (PL) measurement shows that 9H2/2Ar can induce a greater amount of surface damage than 2CH4/9H2/2Ar. However, these damages can be partially removed by post etching annealing. The optimal annealing temperature is 450°C for samples etched in 9H2/2Ar and 250°C for samples etched in 2CH4/9H2/2Ar.

Silicon oxide (SiOx) films deposited on a silicon wafer by the Hg-sensitized photochemical vapor deposition (photo-CVD) method using silane (SiH4) and nitrous oxide (N2O) under the illumination of low pressure mercury lamps were investigated. While increasing the partial pressure ratio of SiH4to N2O, an increasing-maximum-decreasing behavior of the deposition rate and an increasing shape behavior of the refractive index have been observed. Infrared (IR) spectra analysis showed that the films were SiO2-like in the low silane partial pressure region and were SiO-like in the high silane partial pressure region. The 450 cm-1absorption peak was good evidence for differentiating these two types of films. The infrared absorption peak due to Si-H stretching can also be eliminated after the N2annealing treatment.

P-channel InSb MOSFET is fabricated by anodic oxidation and SiO evaporation for the MOS gate structure and by Cd diffusion for the source and drain. A breakdown voltage exceeding 11 V is obtained in the drain junction, which renders the drain current saturation fully observable. An on-off ratio of 104in the drain current is also obtained, indicating that the present InSb MOSFET is useful for a good switching operation.

InSb gate-controlled diodes were fabricated to study breakdown behavior and surface effects. I-Vcharacteristics were measured as a function of gate voltage and temperature. The results indicated that a field-induced junction was formed as the negative bias exceeded -4 V. The field induced junction was found to have a breakdown voltage smaller than that of the metallurgical junction. Saturation of the breakdown current in the field-induced junction was also observed, which could be explained by the conducting channel effect similar to that in the metal oxide semiconductor field effect transistor (MOSFET). The reverse current was also measured as a function of temperature to study the leakage mechanism. The strong exponential temperature dependence suggested that the reverse current was dominated by the G-R mechanism.