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The deposition of uniform, low-stress, thick and thin films of ultrananocrystalline diamond (UNCD) is investigated. The process methods and apparatus that enable the uniform and smooth deposition of both thin and thick (> 50 μm) UNCD across 3 in. diameters are described. UNCD films are synthesized by microwave plasma-assisted CVD using Ar/H 2 /CH 4 input gas mixtures over a wide pressure range (60–240 Torr) and temperature range (400–850 °C). Films were grown on 3 in. diameter silicon substrates with thicknesses ranging from 58 nm to greater than 50 μm. Film surface roughness as low as 10 nm (AFM) was obtained. Film uniformities of 70 to over 95% were achieved on 3 in. diameter silicon substrates. The growth rate increased as pressure, percent hydrogen and percent methane in the gas mixture, and microwave power increased. The highest growth rate 1.12 μm/h was achieved at 180 Torr, H 2 /Ar/CH 4 = (4:100:2) sccm and 1.5 kW absorbed power. Overall, a robust, repeatable process has been demonstrated for the deposition of UNCD films.

Surface acoustic wave (SAW) devices based on polycrystalline diamond have recently achieved success as microwave filters. This is due in part to the large acoustic wavelength of diamond at microwave frequencies, a consequence of its high surface wave velocity, and the resulting ability to use photolithography for transducer fabrication. Since nanocrystalline diamond has a smooth surface and is elastically isotropic, it may offer considerable advantages over thick films of polycrystalline diamond. We have studied the propagation of surface waves on nanocrystalline diamond prepared by microwave plasma chemical vapor deposition (CVD) on silicon substrates. Films were synthesized on 75-mm Si wafers using input gas mixtures consisting of Ar with 1% CH4 and 0–4% H2. The deposition parameters studied included pressure, 2.45 GHz microwave power, and total gas flow rate. Film thicknesses up to 23 μm were produced. SAW transducers were fabricated by photolithography on as-grown nanocrystalline diamond surfaces covered with a 1–3 μm overlayer of oriented polycrystalline piezoelectric ZnO prepared by reactive dc sputtering. The device response was analyzed with frequency and time domain methods. The resonant frequencies of the devices agree with the results of numerical solutions for sound propagation in layered media. Several surface acoustic modes exist at frequencies between 0.5 and 1 GHz that exhibit appreciable dispersion. We have propagated surface waves in nanocrystalline diamond over distances varying from 0.1 to 3 mm with low attenuation. For a film with mean grain size of approximately 30 nm, the SAW velocity is similar to test devices on thick polycrystalline diamond. We conclude that nanocrystalline diamond is a highly attractive substrate material for SAW devices, possessing the high sound velocity of diamond but requiring less materials processing.

The influence of varying nitrogen concentrations (5–1000 ppm) on the conventional CH 4 /H 2 diamond film deposition process using a microwave plasma disk reactor is investigated. This reactor has important differences, such as reactor volume, power density, gas flow, from the common tubular microwave reactors. The experimental behavior indicates, that similar to the tubular reactors, the addition of small amounts of a nitrogen stabilizes the growth of high quality, {100} faceted films. However, the actual threshold nitrogen concentrations and the variation of these threshold concentrations versus other independent experimental variables differs considerably from tubular reactor performance. This suggests that reactor design has an important influence on the deposition process in the presence of impurities.

Optical absorption has been used to study polyaniline at various levels of oxidation and protonation. The conversion of leucoemeraldine base to its salt accounts for the blue shift of the π-π∗ absorption from 3.94 to 4.17 eV. The emeraldine base has an absorption peak at 2.1 eV due to the localized benzenoid HOMO (highest occupied molecular orbital) to quinoid LUMO (lowest unoccupied molecular orbital) excitation. Protonation of the emeraldine base causes a lattice distortion of polyaniline to form a polaronic lattice structure, which accounts for the shift of the 2.1 eV absorption to 1.5 eV. Further protonation of emeraldine salt causes the breakdown of the polaronic lattice to a confined bipolaron lattice. When the acid strength of the solution is very high (96% H2SO4), most of the amine nitrogens are protonated. Characteristic absorptions of isolated quinoid imine units (∼2.5 eV) and benzene units (∼4.8 eV) have been found. The evolution of band structure corresponding to the optical-absorption change during the protonation of polyaniline at each specific oxidation state is studied by gradually changing the acid strength of the solution to which the polymer is subjected. We have also studied the optical-absorption change at one fixed acid strength by slowly oxidizing leucoemeraldine to emeraldine then to pernigraniline by electrochemical and chemical means. Detailed information has been obtained on the band structure changes in relation to lattice structure interconversions during the transitions between various oxidation and protonation states.

Calorimetric measurements were made on a coprecipitation-synthesized GdBa 2 Cu 4 O 8 at temperatures between 0.5 and 13 K and in magnetic fields up to 7 T. The heat capacity data in zero field show an antiferromagnetic transition with T N ⋟ 2.2 K followed by a broad should below, which is identified from entropy consideration to be also associated with the Gd 3+ -ordering. Similar observations were made in a magnetic field of 2 T, except that T N was lowered to 1.6 K. At a higher field of 4 T the calorimetric signature of a long range ordering disappeared, leaving behind a Schottky-type anomaly with a peak near 1 K. This peak moved to 2.5 K at 7 T.