The thermal reaction sequence of a synthetic hectorite (Laponite CP) was studied by X-ray diffraction, i.r. spectroscopy and thermal analysis. Although most of the interlayer water is removed at 200°C, a smally steady weight loss occurs until dehydroxylation is complete at about 700°C, indicating that an anhydrous intermediate phase is not formed prior to dehydroxylation. Immediately after dehydroxylation, enstatite and cristobalite can be identified, but lithium silicates are formed only from lithium-saturated hectorite. Around 1200°C a glass is formed by reaction of the alkalis with cristobalite, and removal of silica from the enstatite produces some forsterite. An inhomogeneous mechanism of dehydroxylation is postulated by analogy with that proposed for talc.

Solid-state nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, and X-ray powder diffraction data on the tubular, hydrous aluminosilicate imogolite were found to be fully consistent with a previously proposed crystal structure consisting of a rolled-up, 6-coordinate Al-O(OH) sheet, bonded to isolated orthosilicate groups. The calculated 29Si chemical shift of this structure agreed with the observed shift within 3 ppm. Thermal dehydroxylation of the Al-O(OH) sheet produced predominantly NMR-transparent 5-coordinate Al, but a few 4- and 6-coordinate sites and some residual hydroxyl groups may also have formed, as shown by NMR spectroscopy. Changes in the 29Si NMR spectrum on dehydroxylation suggest a condensation of the orthosilicate groups, but steric considerations rule out bonding between adjacent silicons. To account for these observations, an alternative mechanism to orthosilicate condensation has been proposed, involving the fracture and unrolling of the tubes, followed by the condensation of fragments to form a layer structure. The layer structure has a calculated 29Si chemical shift of -95.6 ppm, in good agreement with the observed value of -93 ppm.

Examination of two volcanic and two precipitated allophanes by solid-state NMR, thermal analysis and X-ray powder diffraction shows three of the samples to contain structural features similar to both tubular imogolite and defect layer-lattice aluminosilicates such as kaolinite. The fourth allophane, a precipitated sample from New Zealand, had no imogolite-like features and contained tetrahedral as well as octahedral aluminum. The imogolite-like units in allophane are less stable thermally than tubular imogolite. The NMR spectra and their changes on heating can be accounted for by a structural model in which a two-sheet, kaolinite-like structure containing defects (holes in the tetrahedral sheet) is curved into a sphere in which imogolite-like orthosilicate units are anchored into the octahedral sheet and fit into the tetrahedral defects. Computer simulation shows that the model is crystallographically sound, and accounts for all the known facts, including the spherical morphology, the solid-state NMR spectra and the thermal dehydroxylation behavior of all except the New Zealand allophane, which is of a different structural type.

Mossbauer spectroscopy was used to study the valence and bonding changes of iron in (a) lattice sites, and (b) cation exchange sites during thermal treatment of kaolinite and halloysite. Lattice iron which is initially in octahedral sites occurs in octahedral and tetrahedral sites at the completion of the thermal reactions. At temperatures below 650°C some divalent ions in cation exchange positions become trivalent and assume octahedral co-ordination, which they retain until the later stages of mullite formation. The implications of the work on the high temperature reaction mechanism and structural sequence are discussed.

The cause of coloration of Blue John fluorite from Castleton, Derbyshire, and blue banded fluorites from Ashover, Derbyshire, and Weardale, Co. Durham, has been investigated by a number of techniques, including mass spectrometry, optical spectroscopy, and paramagnetic resonance measurements on natural and irradiated samples. In all respects Blue John is indistinguishable from the other blue banded fluorites. Although traces of hydrocarbons were found in all the natural fluorites including Blue John, they are shown not to be the cause of the colouration. The optical spectra and bleaching behaviour are consistent with colouration by colloidal calcium rather than F-centres. The causes of colour banding are discussed.

Healthy multiparous women having elective interval (N = 69) or postpartum (N = 69) sterilization were interviewed pre-operatively and 6 weeks and 6 months post-operatively, using standardized instruments. They did not differ significantly from control samples of comparable non-sterilized women with respect to mental state (Present State Examination) or subjectively-assessed mental or physical health or abdominal pain. More sterilization subjects than control subjects reported subjectively experienced improvement in sexual satisfaction at the later follow-up. Reports of poor physical health and abdominal pain increased over time within both the sterilization and the control groups. Reports of adverse effects at follow-up were often associated with higher PSE scores initially. Regrets and wish for reversal were rare and were also associated with higher initial PSE scores. Since the adverse effects were more common among postpartum subjects, it is suggested that subjectively experienced sequelae of sterilization may sometimes be attributable to ‘normal’ postnatal events.

As part of a prospective controlled study of the psychosomatic effects of elective tubal sterilization, 138 women were questioned about their menstrual functioning before sterilization, and again 6 months and 12 months post-operatively, using standardized interviewing procedures. Adverse changes, including (subjectively assessed) increased menstrual loss, shorter menstrual cycles and greater use of pads or tampons were reported by sterilized subjects at both of the post-operative interviews. Control subjects reported several comparable effects, although adverse changes overall were reported more commonly by sterilized women than by control subjects. However, many of the reported changes appeared to be related to pre-operative contraceptive methods, although consistent increases in use of pads or tampons were found in women who had pre-operatively used neither the pill nor the IUD.

High-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon nitride and silicon dioxide. In particular, inductively-coupled plasma chemical vapor deposition (ICPCVD) offers a great advantage for low temperature processing over plasma-enhanced chemical vapor deposition (PECVD) for a range of devices including compound semiconductors. In this paper, the development of low temperature (< 200°C) silicon nitride and silicon dioxide films utilizing ICP technology will be discussed. The material properties of these films have been investigated as a function of ICP source power, rf chuck power, chamber pressure, gas chemistry, and temperature. The ICPCVD films will be compared to PECVD films in terms of wet etch rate, stress, and other film characteristics. Two different gas chemistries, SiH4/N2/Ar and SiH4/NH3/He, were explored for the deposition of ICPCVD silicon nitride. The ICPCVD silicon dioxide films were prepared from SiH4/O2/Ar. The wet etch rates of both silicon nitride and silicon dioxide films are significantly lower than films prepared by conventional PECVD. This implies that ICPCVD films prepared at these low temperatures are of higher quality. The advanced ICPCVD technology can also be used for efficient void-free filling of high aspect ratio (3:1) sub-micron trenches.

Aluminosilicate precursors were prepared by mechanochemical treatment of gibbsitesilica gel mixtures. The effect of grinding on their structure and thermal behavior has been examined by 27Al and 29Si MAS NMR, x-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), and Fourier transform infrared (FTIR). After 8 h grinding, the hydrated alumina was completely changed to an amorphous phase which showed a new exothermic DTA peak at about 980 °C due to the formation of γ–Al2O3 or spinel phase. This behavior was related to changes in the Al and Si environments, as deduced from the MAS NMR spectra. With increased grinding time, some 4-coordinated Al appears, together with an Al resonance at about 30 ppm. Simultaneously, a new Si resonance appears at about −90 ppm, indicating a greater degree of homogeneity in the ground samples. Mullite crystallizes at 1200 °C from samples ground for 8–20 h, its XRD intensity increasing with increased milling times, in agreement with the NMR, DTA, and FTIR data. Changes in the Al and Si environments during heat treatment, as reflected by the NMR spectra, are also reported.

InN has been grown in a gas-source MBE system using an RF nitrogen plasma source and standard TMI, solution TMI and solid In. Both solid and solution TMI produce InN with electron and carbon concentrations ≥ 1020 cm−3. Solution TMI-derived material, however, contains significantly less oxygen (8 × 1018 cm−3 vs. ≥ 1020 cm−3 for solid TMI). While the amine used to liquefy the TMI helps to displace the ether believed to be responsible for the oxygen contamination, it also appears to interfere with the growth, resulting in poorer morphology than for standard TMI. While solid In produced the lowest carrier concentration (≤ mid-1018 cm−3), it also produced the worst morphology of the sources examined, presumably due to poor surface mobility. Based on this data, it appears that carbon can play a significant role in the electrical properties of InN, and that the In source is critical in determining the structural quality.

During gate mesa plasma etching of InN/InAlN field effect transistors the apparent conductivity in the channel can be either increased through three different mechanisms. If hydrogen is part of the plasma chemistry, hydrogen passivation of the shallow donors in the InAlN can occur, we find diffusion depths for 2H of ≥ 0.5 micron in 30 mins at 200°C. The hydrogen remains in the material until temperatures ≥ 700°C Energetic ion bombardment in SF6/O2 or BCl/Ar plasmas also compensates the doping in the InAlN by creation of deep acceptor states. Finally the conductivity of the immediate InAlN surface can be increased by preferential loss of N during BCl3 plasma etching, leading to poor rectifying contact characteristics when the gate metal is deposited on this etched surface. Careful control of plasma chemistry, ion energy and stoichiometry of the etched surface are necessary for acceptable pinch-off characteristics.

The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0.55Ga0.35N and InN was measured in the range -50 °C to 125 °C. The results were compared to theoretical values for different conduction mechanisms, to further elucidate the conduction mechanism in these contact structures. The data indicates the conduction mechanism is field emission for these contact schemes for all but as-deposited metal to InN where thermionic emission appears to be the dominant mechanism. The contacts were found to produce low specific resistance ohmic contacts to InGaN at room temperature, ϱc ∼ 10-7 Ω ·cm2 for W and ϱc of 4× 10-7 Ω ·cm for WSix. InN metallized with W produced ohmic contacts with ϱc ∼ 10-6 Ω ·cm and ϱc ∼ 10-6 Ω ·cm. for WSix at room temperature.

Bioactive ORMOSILS (Organically Modified Silicates) were synthesized by a sol-gel method, with tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS). Ca(II) ions were incorporated into the ormosil monoliths by addition of calcium nitrate. The synthesized samples were examined on the bioactivity by the use of a simulated body fluid (the Kokubo solution). The Ca(II) containing ormosils were bioactive that deposited apatite during soaking in the Kokubo solution. The dissolution of Ca(II) from the sample favored the formation of the hydrated silica, which gave nucleation sites for apatite, while the effect of dissolved Ca(II) ions to increase the degree of supersaturation in the fluid could not be neglected.

In order to maximize the performance of III-Nitride devices, it is necessary to develop thermally stable low resistance Ohmic contacts to III-N based electronic structures. This paper reports on the utility of InN as an aid to contact formation on widegap materials such as InAIN. For n-type materials, several questions relating to the growth conditions have been explored. Specifically, the impact of substrate type (GaAs vs. Sapphire), cap layer growth temperature and V/III ratio on contact resistance has been investigated. It was found that the use of sapphire substrates combined with high growth temperatures (575°C) and high V/III ratios produced acceptable contact resistances (∼10−6Ohm-cm2) to InAIN.

Atom-probe techniques have been used to characterise nanostructured metallic materials prepared by thermal evaporation and by sputtering. Multilayer samples of Fe-Cr have been prepared by sputter deposition and analysed using the Oxford position-sensitive atom probe. This has made it possible to observe the quality of interfaces in the material, and also accurately determine local compositions at each layer within the multilayer stack. Preliminary experiments aimed at producing dual phase nanocrystalline films by thermal evaporator deposition are also reported.