Zirconia–alumina transformation-toughening nanolaminates were fabricated by reactive sputter deposition. The average crystallite size and volume fraction of each zirconia polymorph were determined by x-ray diffraction. The volume fraction of tetragonal zirconia, the phase necessary for transformation toughening, was found to strongly depend upon the zirconia layer thickness. An end-point thermodynamics model involving hemispherical cap zirconia crystallites was developed to explain this phenomenon. In excellent agreement with experimental results, the model predicts that unity volume fraction of tetragonal zirconia is produced in the nanolaminate when the zirconia layer thickness is less than the radius at which a growing zirconia crystallite spontaneously transforms to the monoclinic phase.

We report the formation of highly oriented rutile titanium dioxide films. Films of a primarily amorphous nature were grown on fused silica by rf reactive sputter deposition using a Ti target and rare gas (Ne or Ar)-O2 discharges. Post-deposition annealing was done at 350–1150 °C in air for 60 minute intervals, followed by an air cool. The phase mixture of the as-deposited films, determined by x-ray diffraction, was of two types: (I) amorphous + rutile + anatase, or (II) amorphous + rutile. All phases were highly oriented with (110) rutile planes and (101) anatase planes parallel to the substrate. Upon annealing, the amorphous component of films containing no anatase transformed entirely to rutile, even at temperatures where it is possible to form anatase, <800 °C, indicating that anatase requires ‘‘seeds’’ to form. The results of this study clearly demonstrate that the crystal structure of the as-deposited film determines the development of the rutile phase with post-deposition annealing.

Ultrashort pulses of microwave radiation have been produced in a dielectric-lined Cherenkov free-electron maser (FEM) amplifier. An intense initial seed pulse, due to coherent spontaneous emission (CSE), arises at the leading edge of the electron pulse. There is evidence to show that 3-4 cycle spikes are produced through the amplification of these seed pulses. A strong dependence of the start-up power on the rise time of the electron pulse has been found. The experimental results are verified by a theoretical analysis. Our study shows that amplification in a FEM amplifier is always initiated by CSE arising from the edge of the electron pulse when the rise time is comparable to the electromagnetic wave period.

Experimental measurements of coherent stimulated radiation from intense, subnanosecond electron bunches moving through a periodic waveguide and interacting with a backward propagating TM01 male are presented. The ultra-short microwave pulses in Ka, W, and G band were generated with repetition frequencies of up to 25 Hz, Observation of RF breakdown of ambient air, as well as direct measurements by hot-carrier germanium detectors, gives an estimate of the peak power up to 140 MW for the 300-400 ps pulses at 38 GHz. The initial observation of 75 GHz 10-15 MW radiation pulses with duration less than 150 ps, and of 150 GHz microwave spikes with a risetime of 75 ps are also reported

Clean Si(111) surfaces were thermally nitrided at various temperatures by exposure to low pressures (1×10−6 Torr) of NO in a UHV system. The nitridation process was monitored by multiple surface analytical techniques including AES, XPS, UPS, LEED, and thermal desorption. At substrate temperatures below 800°C a silicon oxynitride was formed in which the nitrogen to oxygen ratio increased with increasing reaction temperature. These oxynitride films were converted to nitride films by loss of O and SiO when heated to temperatures greater than 850°C in vacuum. Exposure of the clean Si to NO at temperatures greater than 1000°C produced an oxygen-free nitride film. The nitride films formed by either route gave the ’’doublet’’ LEED pattern which has previously been associated with the formation of a two domain epitaxial α-Si3N4 layer. Due to the high reactivity of NO, the presence of 20%–30% C on the Si surface was not necessary for nucleation sites as had been reported for nitridation by NH3.