Edward N. Farabaugh

Growth defects in diamond films

Abstract : Growth defects in diamond films grown by plasma-assisted chemical vapor deposition (CVD) were studied by high resolution electron microscopy. Several features of the microstructure were resolved and their importance to the growth of the diamond film was evaluated. The observations included various twin boundaries of the type sigma=3 as well as sigma=9, sigma=27 and sigma=81, which form by an interaction of lower order twins. These higher order boundaries, are loci of intersection points of growing planes on two adjacent twins and can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes in many cases can be traced back to a quintuplet twin point. A twin quintuplet has five reentrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows.

X-ray photoelectron spectroscopy of O 1s and Si 2p lines in films of SiOx formed by electron beam evaporation

X-ray photoelectron spectroscopy measurements were made of the line shapes and binding energies of the O 1s and Si 2p lines in films of the SiOx system prepared by electron beam evaporation. Stoichiometries were in the range 0 < x < 2. The spectra contain principally two Si 2p peaks which change in amplitude and move to higher energies in a continuous manner as a function of x. The O 1s peak is a single line which shifts in a non-linear manner as a function of x. The results for films with 0.9 < x < 2 are consistent with a mixture of silicon clusters and silicon-centered tetrahedra deficient in oxygen, silicon-centered tetrahedra conforming to the random bond model (RBM), and forms of oxygen other than bridging oxygen such as peroxy bonding, molecular oxygen or OH. The films with x < 0.9 appear to be composed of silicon clusters and silicon-centered tetrahedra richer in oxygen than would be expected on the basis of the RBM. In these films the non-bridging oxygen content would be greatly diminished.

Fitting of transmission data for determining the optical constants and thicknesses of optical films

A multiparameter, nonlinear‐curve fitting method is used to determine the refractive indices, absorption coefficients, and thicknesses of mixed yttria‐silica films from transmittance spectra. Both homogeneous and inhomogeneous models of refractive index in the films are used for the data analysis. Results suggest that inhomogeneity in the films should be considered when investigating the optical properties of thin films. However, care must be taken when computing a refractive index gradient in an absorbing film as both absorption and index gradients can affect the optical transmittance in a similar manner.

Optical properties of mixed yttria–silica films

The refractive indices and absorption coefficients of a series of mixed yttria-silica films prepared by electron beam codeposition have been calculated from transmission spectra. The dependence of the refractive index and film densification on composition suggests that porosity inherent in pure yttria films deposited by electron beam evaporation can be reduced by admixture with silica; however, the films show increased absorption which is attributed to oxygen deficiency. These effects are similar to those observed previously in mixed zirconia-silica films.

Structure of vapor-deposited yttria and zirconia thin films

Abstract The structures of thin films of zirconia and yttria, deposited by electron beam evaporation, have been examined by X-ray absorption fine structure (XAFS) analysis. It was found that the structure of the yttria film was similar to that of bulk yttria, which is a cubic oxide phase. The zirconia film, however, possessed a structure different from that of the bulk material. An analysis of the zirconia film data indicated a structure with a predominant tetragonal phase. Although lower coordination numbers were found in the films than in the standard powder specimens, it was not clear from the extended fine structure whether this deficit was due to film porosity observed in prior work or to the disorder that is generally observed in films. An analysis of the near-edge structure, however, suggested that porosity, rather than disorder, was present in the films. In addition, the K-edge positions observed for both the zirconia and the yttria films were higher in energy by approximately 3 eV than the corresponding K-edge in the powder specimens, indicating that the films may be more insulating than the standard bulk materials.

Dislocations and Stacking Faults in Rutile Crystals Grown by Flame‐Fusion Methods

Single crystals of rutile, grown by the Verneuil method, have been chemically thinned and examined by electron transmission microscopy. The density and distribution of dislocations agree with that expected from etch pit data. This density is at least two orders of magnitude below that for rutile films formed by oxidizing titanium carbide. The etching of dislocations and stacking faults is described.Some preliminary results of high‐temperature studies in the microscope are reported. These include the discovery of a hitherto unknown slip system, {001} 〈100〉.

Bonding structure of silicon oxide films

X‐ray photoelectron spectroscopy measurements of the O 1s and Si 2p lines in films of the SiOx system have been interpreted on the basis of continuous random network models. Fitting of the spectra to five lines corresponding to five silicon centered tetrahedral configuration yields the relative proportion of each configuration as a function of x. The distributions agree neither with the random mixture model nor with the random bond model (RBM). The total oxygen in the films exceeds the amount of oxygen in the tetrahedral structures indicating the presence of molecular oxygen, water, peroxy bonding, or other forms of oxygen not bonded to silicon. The general features of the distributions can be explained on the basis of silicon clusters, nonbridging oxygen, and the RBM. This conclusion implies that reactive evaporation with oxygen may result in material that is not as fully oxidized as might be expected on the basis of the oxygen content of the film.X‐ray photoelectron spectroscopy measurements of the O 1s and Si 2p lines in films of the SiOx system have been interpreted on the basis of continuous random network models. Fitting of the spectra to five lines corresponding to five silicon centered tetrahedral configuration yields the relative proportion of each configuration as a function of x. The distributions agree neither with the random mixture model nor with the random bond model (RBM). The total oxygen in the films exceeds the amount of oxygen in the tetrahedral structures indicating the presence of molecular oxygen, water, peroxy bonding, or other forms of oxygen not bonded to silicon. The general features of the distributions can be explained on the basis of silicon clusters, nonbridging oxygen, and the RBM. This conclusion implies that reactive evaporation with oxygen may result in material that is not as fully oxidized as might be expected on the basis of the oxygen content of the film.

X‐ray microscopy of single‐crystal potassium dideuterium phosphate

Examination of solution‐grown KD*P single crystals by the Lang technique has shown that the crystals are free from growth veils, impurity segregation, and subgrain boundaries. The density of dislocations varies throughout the volume of the crystals, some areas being nearly dislocation free. One Burgers vector identified as being parallel to 〈100〉 is common to the similar KDP and ADP single crystals.

Photoluminescence excitation by band-gap optical absorption in chemical vapor deposition diamond films

Photoluminescence excitation (PLE) spectra at photon energies near the indirect band gap of diamond have been obtained for diamond films grown by the filament‐assisted chemical vapor deposition (CVD) method. The PLE intensity was observed to increase abruptly with photon energy above 5.5 eV. This increase coincides with the onset of phonon‐emission‐assisted interband absorption, which was observed independently by diffuse transmittance measurements. A lower‐energy PLE threshold at ∼5.25 eV, which coincides approximately with the onset of phonon‐absorption‐assisted interband absorption, was observed in the spectrum of a gem‐quality natural diamond, but not in the spectra of the CVD‐grown films. Emission spectra of the luminescence excited by above‐band‐gap photons have features similar to luminescence spectra of the same specimens excited by 20‐keV electrons. The spectrally integrated intensities of the luminescence excited by above‐band‐gap photons and by electrons were found to vary from specimen to spec...

Preparation of polished substrates of BaF2

The utilization of Pb1−xSnxTe epitaxial films in high‐density forward‐looking infrared (FLIR) arrays has been hampered thus far by cleavage steps in the substrates. We have developed a chemical‐mechanical polishing technique for the (111) surface of BaF2 which leaves this substrate material single crystal and almost damage free. X‐ray data on the polished BaF2 and the Pb0.8Sn0.2Te epitaxial film indicate single‐crystal surfaces with very little damage. Furthermore, the electrical properties of the Pb0.8Sn0.2Te epitaxial film are sufficient for FLIR applications.