The icosahedral phase has been produced by pulsed laser melting of thin films of Mn-implanted Al. With increasing laser intensity, we observe a mixture of icosahedral and fee phases followed by a single phase fee region. Grains as large as 1 μm in diameter have been observed in 0.1 μm thick films. Electron diffraction studies of individual icosahedral grains indicate that the rapid growth direction from the melt is along the threefold symmetry axis.

Electrohydrodynamic (EHD) atomization has been used to rapidly solidify micron and submicron size droplets of Al-14 at. % Mn to study nucleation behavior of icosahedral phase. Icosahedral grain size has been found to decrease continuously with decreasing droplet size. Based on this result, formation of the icosahedral phase is explained by homogeneous nucleation. Extremely low resistance to nucleation of icosahedral phase can be understood if possible topological similarities between liquid and icosahedral quasicrystal are considered. Formation of glass as configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that the reported Al-Mn glass probably has a microquasicrystalline structure.

The structure and thermal stability of rapidly solidified Al-Cr-Si, Al-Mn-Si, Al-Fe-Si, Al-Co-Si, and Al-Ni-Si alloys have been investigated using x-ray diffraction and thermal analysis measurements. Each series of alloys shows a region of stoichiometry that yields icosahedral symmetry and a region that yields an amorphous phase. Thermal and structural properties of these alloys are reported as a function of stoichiometry and quench rate.

Dielectric breakdown of gas mixtures can be used to deposit thin films by chemical vapor deposition with appropriate control of flow and pressure conditions to suppress gas-phase nucleation and particle formation. Using a pulsed CO2 laser operating at 10.6 μ where there is no significant resonant absorption in any of the source gases, homogeneous films from several gas-phase precursors have been sucessfully deposited by gas-phase laser pyrolysis. Nickel and molybdenum from the respective carbonyls representing decomposition chemistry and tungsten from the hexafluoride representing reduction chemistry have been demonstrated. In each case the gas precursor is buffered with argon to reduce the partial pressure of the reactants and to induce breakdown. Films have been characterized by Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, pull tests, and resistivity measurements. The highest quality films have resulted from the nickel depositions. Detailed x-ray diffraction analysis of these films yields a very small domain size consistent with the low temperature of the substrate and the formation of metastable nickel carbide. Transmission electron microscopy supports this analysis.

A buildup of radiation-induced lattice defects is proposed as the cause for lattice instability that can give rise to a crystalline-to-amorphous transition. An analysis of published experiments on intermetallic compounds suggests that, when amorphization takes place, no microstructural evolution based on the aggregation of like-point defects occurs. This observation leads us to suggest that buildup of a different type of defect, which will destabilize the crystal, should occur. We thus propose that an interstitial and a vacancy may form a complex, giving rise to a relaxed configuration exhibiting a sort of short-range order. Two mechanisms of complex formation are analyzed, one diffusionless (limited by the point defect production rate) and the other temperature dependent. The amorphization kinetics as a function of temperature, dose, and point defect sink strength are studied. Theoretical predictions on the amorphization dose as a function of temperature are made for the equiatomic TiNi alloy and compared with available experimental results.

We report the preparation and properties of higher nitrides of Hf, Zr, and Ti synthesized by dual ion beam deposition. For Hf and Zr, evidence is given for the existence of a metastable nitride phase with composition of approximately Hf3 N4 and Zr3 N4. These two materials are insulating and transparent straw colored, in contrast to the well-known mononitrides, which are shiny, gold colored, and highly conducting. For Ti-N we do not reach as high an N content and do not obtain an insulating, transparent phase. The higher nitrides of Hf and Zr are synthesized under energetic nitrogen ion bombardment (200 e V) of a growing film and do not form in the presence of molecular nitrogen gas alone. Several variations of the ion beam deposition process are used to obtain a wide range of film composition and to study the transition from the mononitride to the higher nitride phase. Transmission electron diffraction shows the structure of Hf3N4 and Zr3N4 to be very close to the Bl (NaCl) structure of the mononitrides, but with a slight rhombohedral distortion. Additional evidence from noble gas incorporation (Ne, Ar, and Xe) supports a model of these higher nitrides as containing a large number of vacancies on the metal atom sites.

With the increasing use of optical fibers in the telecommunication network, there is need for fiber geometry compatible optical devices such as optical amplifiers, switches, couplers, and isolators. These active devices are based on field-dependent material properties, such as electrooptic and magneto-optic effects, which are stronger in single crystal than in amorphous materials. Single crystal fibers can be grown by the laser heated pedestal growth (LHPG) technique. In this paper we report the growth of single crystal fibers of ferroelectric barium titanate from sintered ceramic rods of stoichiometric barium titanate. Barium titanate is one of the most extensively investigated ferroelectric materials. However, its growth from stoichiometric melt always results in its hexagonal nonferroelectric phase. Using LHPG, single crystal strontium titanate seed, and sintered ceramic barium titanate rods, we have succeeded in growing single crystal fibers (∼ 100 μ m diameter) of pure barium titanate with tetragonal (ferroelectric) crystal structure. This paper discusses growth and characterization of these fibers.

The reliability of microfocus x radiography for detecting internal voids in structural ceramic test specimens was statistically evaluated. The microfocus system was operated in the projection mode using low x-ray photon energies (<20 keV) and a 10 μm focal spot. The statistics were developed for implanted internal voids in green and sintered silicon carbide and silicon nitride test specimens. These statistics were compared with previously obtained statistics for implanted surface voids in similar specimens. Problems associated with void implantation and characterization are discussed. Statistical results are given as probability-of-detection curves at a 95% confidence level for voids ranging in size from 20–528 μm in diameter.

Raman spectroscopy (RS) and low-angle x-ray diffraction (LAXRD) have been used to characterize semiconductor multilayer interfaces. In the present study a model for Raman spectra of multilayers is developed and applied to the specific case of the interfaces of a-Si/a-Ge multilayers. Quantification of the “blurring” of interfaces is possible because peak heights in the Raman spectra of thin films are proportional to the number of scatterers, thus RS is capable of directly “counting” the total number of chemical bonds of a given type in the film. Multilayers, prepared by various deposition techniques, are compared. The relative roles of LAXRD and RS in investigating interfaces are contrasted. Several a-Si/a-Ge multilayers deposited by ultra-high vacuum (UHV) evaporation (MBD) are found to exhibit very regular periodicities and exceptionally sharp interfaces (<1.0 Å intermixing).

High concentrations of self-interstitials are trapped by dopant atoms during ion implantation into Si. For group V dopants, these complexes are sufficiently stable to survive solid-phase-epitaxial (SPE) growth but break up on subsequent thermal processing and cause a transientenhanced diffusion. Dopant diffusion coefficients are enhanced by up to five orders of magnitude over tracer values and are characterized by an activation energy of approximately one half of the tracer values. In the case of group III dopants, any complexes formed during implantation do not survive SPE growth but a second source of self-interstitials becomes significant and leads to similar transient effects. This is the damaged layer underlying the original amorphous/crystalline interface. These observations provide direct evidence for longrange self-interstitial migration in Si, and we believe these are the first observations of the interstitialcy diffusion mechanism with no vacancy contribution. We propose that the complexes are simply interstitial dopant atoms (in a split <100> interstitialcy configuration) that are particularly stable in the case of group V dopants. As they decay self-interstitials are released and cause the transient-enhanced diffusion.

Molybdenum disilicide thin films having the tetragonal crystal structure were prepared by furnace reaction of ion-beam-sputtered molybdenum layers with silicon substrates. The room temperature intrinsic resistivity is ∼20 μΩ cm. The Hall effect indicates predominantly hole conduction. Geometrical magnetoresistance measurements provide a carrier mobility estimate of 90 cm2 /V.s at room temperature. The Hall mobility is much less than this; the large difference between the two mobility values suggests multiband conduction. An isotropic, degenerate, twoband model may be fitted to the data with a comparatively low majority carrier concentration (holes) of ∼ 1.5 × 1021 cm−3 Regarding the effects of microstructure on transport, the residual resistivity for films formed on 1-0-0 silicon wafers is much greater than for those formed on an (LPCVD) polysilicon layer: 92 vs 29 μΩ cm, respectively. A correlation with average grain size for the two sample types suggests that grain boundary scattering is the principal cause of the residual resistivity. electronic materials; electrical properties; thin film

The removal of defects in diamond by light-ion bombardment has been studied by means of Rutherford backscattering spectroscopy (RBS) channeling techniques. The damage produced by 1 × 1014 Sb ions cm−2 at 300 keV (below the critical dose for graphitization) was observed to diminish by as much as 50% under bombardment with H and He ions. The ion-beam-induced annealing has been studied as a function of ion dose and incident angle (channeling and random). Although the data sets differ markedly, they nearly coincide when the dose is normalized to the energy deposited by elastic collisions in the damaged region. This may indicate that nuclear and not electronic collisions contribute primarily to the in situ annealing in a reasonably good insulator such as diamond.

Electrical conductivity for polyethylene-carbon black, polycarbonate-carbon black composites was measured for conducting compositions well above the percolation limit. Three conductivity methods were employed in our studies: sputtering coated metal electrodes, painted metal electrodes, and the four-point method. Results suggest that while the two latter methods do not modify substantially the material surface, the former method introduces a low conductivity region at the surface. The effect of contact resistance developed during metal coating is discussed in the light of both fluctuation-induced tunneling predictions and “hopping” transport mechanisms. Experimental results favor the tunneling alternative across the evaporated metalcomposite interphase.