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Notes: Silicon dioxide layers of 250 A(ring) thick were grown on Si at 1000 °C in a dry O2/TCA ambient. Thermal nitridation of the samples was performed in a pure ammonia ambient at temperatures from 900 to 1100 °C with one hour time intervals up to a maximum of 4 h. The fixed charge state densities at the interface of the samples were determined from high frequency C-V measurements, and the breakdown fields from I-V curves. Secondary ion mass spectroscopy depth profiles show low levels of contaminants, and high levels of nitrogen at the interface for samples annealed at temperature greater than or equal to 1000 °C and for periods longer than 2 h. Post metal annealing of the nitrided samples appears to help in reducing the trapped charges. Better quality films with lower Qf and VFB shifts, and higher breakdown fields were achieved for samples annealed at 1100 °C. Metal-oxide-semiconductor device quality nitrided films with a Qf of 1010/cm2 were achieved by optimizing the process conditions at 1100 °C. The fixed charge build up for lower nitridation temperatures (〈1000 °C) and times (〈2 h)is due to the dissociation of Si—O bonds in the presence of hydrogen, and is in accordance with the earlier results in the literature. However, the reduction in the fixed charge buildup at 1100 °C, we believe, is due to the increased levels of nitrogen.

Notes: The hole mobility of Be-doped ( ∼ 2 × 1017 cm−3) AlxGa1−xAs, for x=0–1, is analyzed both theoretically and experimentally. Alloy scattering is very important, and in fact reduces the hole mobility from 150 to less than 90 cm2/V s at x=0.5. The main parameter in the alloy scattering formulation, the alloy potential Eal, is found to be about 0.5 eV for p-type AlxGa1−xAs.

Notes: The effects of in-plane lattice mismatch have been studied for Ga0.92In0.08As(p+)/GaAs(n)/GaAs(n+) diodes. Different in-plane mismatch at the p–n junction was introduced by a variation of the GaInAs layer thickness (h=0.1, 0.25, 0.5, and 1 μm). Capacitance-voltage (C-V) measurements with different frequencies show a higher-frequency dispersion for a greater lattice-mismatched sample. From the frequency dependence of the C-V curve, single-level charged interface-state density (Ns) was estimated using the effective parallel capacitance and conductance components. The average charged interface density Nss was also estimated using Voltage-intercept (Vint) method. Nss shows a linear dependence on the in-plane mismatch. The charged interface state density is approximately 2.7 Δa(parallel)/a30 for partially lattice-relaxed heterojunctions. For the 1 μm sample, the forward I-V characteristic shows quasi-Fermi level pinning effect. Admittance spectroscopy measurement gives an equilibrium Fermi energy at about Ev+0.36 eV with hole capture cross section cp=2.7×10−15 cm2 for the 1 μm sample and at Ev+0.21 eV and cp=2.4×10−16 cm2 for the 0.5 μm sample.

Notes: The effects of the lattice-mismatch-induced defects on deep level traps in Ga0.92In0.08As(n+)/GaAs(p) heterojunction diodes have been studied by means of various deep level transient spectroscopy techniques and the frequency-dependent capacitance-voltage (C-V-f) characteristics. Three hole traps at 0.58, 0.42, and 0.27 eV were observed. We attribute the 0.42 eV trap to Cu impurity, the 0.58 eV trap to VGa or Fe, and the 0.27 eV trap to a complex associated with the 0.42 and 0.58 eV traps. Depth profiles of these hole traps in the GaAs side were measured in different lattice-mismatched samples. The depth profile data near the interface and from deep inside the bulk show evidence of impurity gettering by the mismatched interface. We also found that the concentrations of these traps were reduced by rapid thermal annealing. A U-shaped energy distribution of the interface states was obtained from the C-V-f measurements. For an in-plane mismatch greater than 0.25%, the interface state density shows no obvious dependence on the in-plane lattice mismatch, while at smaller mismatch the interface state density increases with increasing mismatch. The interface state density was on the order of 1011 cm−2.

Notes: A thin, undoped, molecular beam epitaxial (MBE) GaAs cap layer grown on top of an n-type conductive layer significantly reduces the free-electron depletion from the latter. By analyzing electron transfer to surface, interface, and bulk acceptor states in the cap, as a function of cap thickness, we show that either (1) the usual EC−0.7 eV surface states are absent, (2) a dense donor near EC−0.4 eV exists or (3) a high donor interface charge (∼5×1012 cm−2) is present. Any of these conclusions constitutes an important new aspect of low-temperature MBE GaAs.

Notes: O, Sr and C isotopes from east-central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross-layer fluid fluxes of 104−106 moles m−2; absolute values depend on the Sr fluid-rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ13C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO2 and CH4-bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO2 released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.

Notes: Reaction progress exhibited by multivariant assemblages in micaceous limestones can provide an excellent record of metamorphic fluid flow. However, it is necessary to understand the sensitivity of these assemblages to bulk-composition parameters. Here, analysis of bulk composition on different scales and pseudosection construction are used to draw conclusions on relationships between bulk composition, fluid flow and reaction progress. Issues addressed include the effects of bulk composition on the mineralogical evolution of micaceous carbonates, the sensitivity of bulk composition to bulk-composition sampling methods, the magnitude of cross-layer fluid-composition gradients, the potential for metasomatism to drive reaction progress, and the relative timing of reaction in adjacent layers. Pseudosections successfully represent observed mineral assemblages, constrain the position of reactions in T–X(CO2) space, and allow assessment of the sensitivity of reaction position, inferred reaction progress and calculated fluid fluxes to uncertainties in bulk composition. The scale of bulk-composition sampling affects bulk compositions, calculated modes, predicted mineral assemblages and calculated fluid compositions. Larger samples record an average of different lithological subdomains, while point-count-derived bulk compositions are subject to uncertainties related to the small number of sample points. The optimum bulk composition for pseudosection purposes probably lies between measured bulk compositions. Results suggest that reaction progress in some extensively reacted layers was driven by infiltration of H2O-rich fluid which flowed or diffused parallel to layering, perpendicular to layering in response to fluid-composition gradients, and out of veins. Small variations in fluid composition across layering (ΔX(CO2) 〈 0.02) were maintained by internal buffering by the mineral assemblages. Internal buffering must also have driven samples up a sequence of narrow low-variance fields in T–X(CO2) space, and so reaction in adjacent layers must have close to simultaneous. Metasomatic effects on reaction progress are likely to have been small, so long as the porosity was low.

Notes: An analysis of factors influencing the time of booking at seven hospital antenatal clinics in one Health Authority Area showed that only 52.5 per cent of patients booked before 16 weeks gestation and 78.9 per cent before 19 weeks gestation. The principle reasons for late booking were delay in the patient seeking medical advice and delay in referral to hospital the general practitioner (GP) after pregnancy was confirmed. Possibilities for improving early attendance and hence implementing an effective screening programme for the detection of neural tube defects are discussed.

Notes: Two oestrogens, stilboestrol and quinestrol, were used to inhibit lactation and their effects upon coagulation and fibrinolysis were compared with control patients before delivery, during the puerperium and six weeks after delivery. During the first week of the puerperium, stilboestrol therapy was associated with rises of factors IX and X and quinestrol therapy with rises of factors IX and 11. Six weeks after delivery, the clotting factors were similar to the control values in those who had received stilboestrol but factor II was still raised in the quinestrol treated patients. Additionally, a significant rise of factor X in the quinestrol group was noted at this time. Plasma antithrombin levels rose during the first week of the puerperium in all three groups but, six weeks after delivery, they were lower in those who had received oestrogens. Stilboestrol and quinestrol were also associated with a rise of plasminogen and antiplasmin concentration during the first week of the puerperium. Six weeks after delivery, quinestrol treated patients still had raised levels of plasminogen and antiplasmin while the stilboestrol treated patients only had raised levels of antiplasmin. These changes in coagulation and fibrinolysis are similar to those reported during oral contraceptive therapy. The persisting changes six weeks after delivery in women who had taken quinestrol might indicate an increased thrombogenic risk when long acting oestrogen preparations are used to inhibit lactation.