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Imaging and characterization of film coating using scanning acoustic microscopy
Classified abstracts 6779-6788
grain boundaries in the carbons, along with a multitude of defects on the center of each grain, will be illustrated. B Marehon et al, Thin Solid Films, 154, 1987, 65-73. 54 6779. Cross-sectional transmission electron microscopy characterization of the interface between plasma-sprayed TiC and lnconel Transmission electron microscopy was used to study the very first layer of TiC deposited by plasma spraying over Inconel. Various techniques to prepare cross-sectional specimens have been reviewed and adapted to suit plasma-sprayed material. The main aspects considered were the relatively large thickness of the coatings, the irregularity of the interface and the different sputtering yields of the two materials. The results show that the TiC at the interface can have either a very fine unidirectional solidification or a coarser structure. These observations are discussed in terms of thermal contact with the substrate. We have not observed a structural link between the TiC and the substrfite; the structure and the composition change abruptly at the interface. Hence it is believed that the adhesion of this plasma-sprayed coating is mainly mechanical. G Veilleux et al, Thin Solid Films, 154, 1987, 91-100. 54 6780. Imaging and characterization of film coating using scanning acoustic microscopy The qualities of thin and thick film coatings are closely related to their mechanical parameters such as mass density, acoustic velocity and film thickness, and the defects at the interface. Simultaneous measurement o f these three parameters was carried out using a wide-band acoustic microscope operating in reflection mode at the frequency range of 50~ 250 MHz. This simultaneous measurement was achieved by first identifying the resonant frequency at which the film thickness was equal to one-quarter of the acoustic wavelength and the subsequent determination of the amplitude and phase of the signal reflected from the specimen. Several film coatings have been characterized and the results agree well with both the published data and the data obtained by other techniques. The adhesion of the film coating is greatly affected by the voids and defects at the film substrate interface. The same acoustic microscope operating in transmission mode was used to detect these voids and defects. Specifically, it was employed to image an Au-Sn eutectic layer which was melted on a gold-coated alumina substrate, and a similar eutectic layer that was used to bond a GaAs chip and an alumina substrate. Voids and defects were clearly observed and identified. These experiments have demonstrated that the scanning acoustic microscope is a useful instrument for non-destructive characterization of film materials and detection of voids and defects that occur at the film-substrate interfaces. Chin C Lee et al, Thin Solid Films, 154, 1987, 207~16. 54 6781. Transmission electron microscopy for the determination of the microstructure of thin films and interfaces The optics and construction of a transmission electron microscope are reviewed, along with electron diffraction and its relation to image contrast. Three general areas of thin film analysis by transmission electron microscopy are discussed: geometric determinations, involving variations in the thickness of thin films, substrate dislocations and grain size; microstructure determination by electron diffraction, using ionized cluster beam deposited aluminum; analysis of an interfacial reaction by a combination of diffraction and X-ray fluorescence, using Inconel 718 and a lithia-silica glass ceramic. Future trends in the use of transmission electron microscopy for the analysis of thin films are discussed. Michael C Madden, Thin Solid Films, 154, 1987, 43-56. 54 6782. Crystal growth of Ge studied by reflection high-energy electron diffraction and photoemission We have combined the techniques of reflection high-energy electron diffraction and photoemission in order to study crystal growth of Ge by molecular-beam epitaxy. Intensity oscillations in the reflected electron beam for deposition on both (001) and (111) surfaces at 20°C indicate that the growth is essentially layer by layer. The evolution of valence bands and core levels as a function of deposition reveals that in the case of Ge(001) and Ge bulk band structure remains present, indicating crystalline growth. For Ge(111) the bulk band structure disappears and finally resembles the band structure of amorphous Ge, indicating a completely disordered film. At 200°C, however, the crystalline band structure remains present. J Aarts et al, J Vac Sci Technol, A6, 1988, 607-610.
54 6783. Low energy electron diffraction analysis of the Si(111)7 x 7 structure We have used the dynamical theory of low-energy electron diffraction to analyze data of the Si(111)7 × 7 surface and determined the atomic structure. The method includes the use of symmetrized wave functions in real and reciprocal spaces. Individual atomic coordinates for the first five atomic planes (containing 200 atoms) are determined. The low-energy electron diffraction optimized structure shows an oscillatory relaxation: atomic planes with stretched bonds followed by planes with compressed bonds. Geometric displacements from the bulk d i m e ~ a d a t o m stacking fault model are presented. S Y Tong et al, J Vac Sci Technol, A6, 1988, 615~524. 54 6784. Scanning tunneling microscopy of cubic silicon carbide surfaces Surface topographies of n-type t-SiC single crystals epitaxially grown by chemical vapor deposition on Si(100) and Si substrates inclined at 4 ° off (100) toward (011) were imaged by a scanning tunneling microscope. The images suggest that smooth surfaces can be achieved by epitaxial growth on the 4°-off substrates. Oxidation of the E-SiC surfaces followed by chemical etching to remove the oxide layer also tend to produce smooth surfaces. N J Zheng et ai, J Vac Sci Technol, A6, 1988, 696~98. 54 6785. Studies of superconductors using a low-temperature, high-field scanning tunneling microscope We have developed a scanning tunneling microscope (STM) capable of operating at temperatures as low as 0.4 K and fields as high as 8 T. We have used this STM to study the energy gap o f the high-To superconductors L ~ S r q = u O and Y B a ~ u - O . We find that the reduced gap for these oxide superconductors falls in the range 3 < 2A/kBT,. < 7, for polycrystalline, single-crystal, and thin-film samples. We have also simultaneously imaged the surface topography and superconducting energy gap for thin films o f the granular superconductor NbN. We occasionally see regions with smaller best-fit gaps that correlate with surface topographical features, but have been unable so far to image flux vortices. J R Kirtley et al, J Vac Sci Technol, A6, 1988, 259 262. 54 6786. Theory of scanning tunneling spectroscopy A new three-dimensional tunneling theory is introduced for interpreting scanning tunneling spectroscopy (STS) images. By expanding the asymptotic wave function o f the acting atom in terms o f complete sets of eigenfunctions in spherical coordinates and parabolic coordinates, a derivative rule is derived, which can be applied to interpret scanning tunneling microscopy and STS images immediately. The relation between the observed dynamic conductance and the density of states of the sample is shown in conjunction with a linear bias-distortion correction. C Julian Chen, J Vac Sci Technol, A6, 1988, 319 322. 54 6787. Theory of the local tunneling spectrum of a vibrating adsorbate We present a model describing the essentials of tunneling between the tip of a scanning tunneling microscope (STM) and an electronic resonance on an isolated adsorbed molecule. Conditions for observing enhanced inelastic tunneling and its experimental manifestations are identified in terms of the energy and width of the resonance and of its coupling to a particular molecular vibration. For a broad resonance, this occurs if it is partially filled; we then predict a conductance decrease as large as 10% at the inelastic threshold for typical chemisorption systems. For a resonance weakly hybridized with the underlying electrode, strong multiphonon excitation is possible, although as a rule it will not be readily apparent. Relevant systems of interest for local spectroscopy with future STM's are discussed. A Baratoff and B N J Persson, J Vac Sci Technol, A6, 1988, 331-335. 54 6788. Detection of atomic surface structure on NbSe2 and NbSe 3 at 77 and 4.2 K using scanning tunneling microscopy Scanning tunneling microscopy (STM) studies have been performed on NbSe2 and NbSe 3 at 77 and 4.2 K. The surface atomic structure has been clearly resolved, but evidence of charge-density wave (CDW) modulation has only been observed at 4.2 K in NbSe3. CDW's exist in NbSe2 at 4.2 K and in NbSe3 at 77 K, but the C D W amplitude is either too small or is screened by the remaining conduction electrons. The linear chain 527
grain boundaries in the carbons, along with a multitude of defects on the center of each grain, will be illustrated. B Marehon et al, Thin Solid Films, 154, 1987, 65-73. 54 6779. Cross-sectional transmission electron microscopy characterization of the interface between plasma-sprayed TiC and lnconel Transmission electron microscopy was used to study the very first layer of TiC deposited by plasma spraying over Inconel. Various techniques to prepare cross-sectional specimens have been reviewed and adapted to suit plasma-sprayed material. The main aspects considered were the relatively large thickness of the coatings, the irregularity of the interface and the different sputtering yields of the two materials. The results show that the TiC at the interface can have either a very fine unidirectional solidification or a coarser structure. These observations are discussed in terms of thermal contact with the substrate. We have not observed a structural link between the TiC and the substrfite; the structure and the composition change abruptly at the interface. Hence it is believed that the adhesion of this plasma-sprayed coating is mainly mechanical. G Veilleux et al, Thin Solid Films, 154, 1987, 91-100. 54 6780. Imaging and characterization of film coating using scanning acoustic microscopy The qualities of thin and thick film coatings are closely related to their mechanical parameters such as mass density, acoustic velocity and film thickness, and the defects at the interface. Simultaneous measurement o f these three parameters was carried out using a wide-band acoustic microscope operating in reflection mode at the frequency range of 50~ 250 MHz. This simultaneous measurement was achieved by first identifying the resonant frequency at which the film thickness was equal to one-quarter of the acoustic wavelength and the subsequent determination of the amplitude and phase of the signal reflected from the specimen. Several film coatings have been characterized and the results agree well with both the published data and the data obtained by other techniques. The adhesion of the film coating is greatly affected by the voids and defects at the film substrate interface. The same acoustic microscope operating in transmission mode was used to detect these voids and defects. Specifically, it was employed to image an Au-Sn eutectic layer which was melted on a gold-coated alumina substrate, and a similar eutectic layer that was used to bond a GaAs chip and an alumina substrate. Voids and defects were clearly observed and identified. These experiments have demonstrated that the scanning acoustic microscope is a useful instrument for non-destructive characterization of film materials and detection of voids and defects that occur at the film-substrate interfaces. Chin C Lee et al, Thin Solid Films, 154, 1987, 207~16. 54 6781. Transmission electron microscopy for the determination of the microstructure of thin films and interfaces The optics and construction of a transmission electron microscope are reviewed, along with electron diffraction and its relation to image contrast. Three general areas of thin film analysis by transmission electron microscopy are discussed: geometric determinations, involving variations in the thickness of thin films, substrate dislocations and grain size; microstructure determination by electron diffraction, using ionized cluster beam deposited aluminum; analysis of an interfacial reaction by a combination of diffraction and X-ray fluorescence, using Inconel 718 and a lithia-silica glass ceramic. Future trends in the use of transmission electron microscopy for the analysis of thin films are discussed. Michael C Madden, Thin Solid Films, 154, 1987, 43-56. 54 6782. Crystal growth of Ge studied by reflection high-energy electron diffraction and photoemission We have combined the techniques of reflection high-energy electron diffraction and photoemission in order to study crystal growth of Ge by molecular-beam epitaxy. Intensity oscillations in the reflected electron beam for deposition on both (001) and (111) surfaces at 20°C indicate that the growth is essentially layer by layer. The evolution of valence bands and core levels as a function of deposition reveals that in the case of Ge(001) and Ge bulk band structure remains present, indicating crystalline growth. For Ge(111) the bulk band structure disappears and finally resembles the band structure of amorphous Ge, indicating a completely disordered film. At 200°C, however, the crystalline band structure remains present. J Aarts et al, J Vac Sci Technol, A6, 1988, 607-610.
54 6783. Low energy electron diffraction analysis of the Si(111)7 x 7 structure We have used the dynamical theory of low-energy electron diffraction to analyze data of the Si(111)7 × 7 surface and determined the atomic structure. The method includes the use of symmetrized wave functions in real and reciprocal spaces. Individual atomic coordinates for the first five atomic planes (containing 200 atoms) are determined. The low-energy electron diffraction optimized structure shows an oscillatory relaxation: atomic planes with stretched bonds followed by planes with compressed bonds. Geometric displacements from the bulk d i m e ~ a d a t o m stacking fault model are presented. S Y Tong et al, J Vac Sci Technol, A6, 1988, 615~524. 54 6784. Scanning tunneling microscopy of cubic silicon carbide surfaces Surface topographies of n-type t-SiC single crystals epitaxially grown by chemical vapor deposition on Si(100) and Si substrates inclined at 4 ° off (100) toward (011) were imaged by a scanning tunneling microscope. The images suggest that smooth surfaces can be achieved by epitaxial growth on the 4°-off substrates. Oxidation of the E-SiC surfaces followed by chemical etching to remove the oxide layer also tend to produce smooth surfaces. N J Zheng et ai, J Vac Sci Technol, A6, 1988, 696~98. 54 6785. Studies of superconductors using a low-temperature, high-field scanning tunneling microscope We have developed a scanning tunneling microscope (STM) capable of operating at temperatures as low as 0.4 K and fields as high as 8 T. We have used this STM to study the energy gap o f the high-To superconductors L ~ S r q = u O and Y B a ~ u - O . We find that the reduced gap for these oxide superconductors falls in the range 3 < 2A/kBT,. < 7, for polycrystalline, single-crystal, and thin-film samples. We have also simultaneously imaged the surface topography and superconducting energy gap for thin films o f the granular superconductor NbN. We occasionally see regions with smaller best-fit gaps that correlate with surface topographical features, but have been unable so far to image flux vortices. J R Kirtley et al, J Vac Sci Technol, A6, 1988, 259 262. 54 6786. Theory of scanning tunneling spectroscopy A new three-dimensional tunneling theory is introduced for interpreting scanning tunneling spectroscopy (STS) images. By expanding the asymptotic wave function o f the acting atom in terms o f complete sets of eigenfunctions in spherical coordinates and parabolic coordinates, a derivative rule is derived, which can be applied to interpret scanning tunneling microscopy and STS images immediately. The relation between the observed dynamic conductance and the density of states of the sample is shown in conjunction with a linear bias-distortion correction. C Julian Chen, J Vac Sci Technol, A6, 1988, 319 322. 54 6787. Theory of the local tunneling spectrum of a vibrating adsorbate We present a model describing the essentials of tunneling between the tip of a scanning tunneling microscope (STM) and an electronic resonance on an isolated adsorbed molecule. Conditions for observing enhanced inelastic tunneling and its experimental manifestations are identified in terms of the energy and width of the resonance and of its coupling to a particular molecular vibration. For a broad resonance, this occurs if it is partially filled; we then predict a conductance decrease as large as 10% at the inelastic threshold for typical chemisorption systems. For a resonance weakly hybridized with the underlying electrode, strong multiphonon excitation is possible, although as a rule it will not be readily apparent. Relevant systems of interest for local spectroscopy with future STM's are discussed. A Baratoff and B N J Persson, J Vac Sci Technol, A6, 1988, 331-335. 54 6788. Detection of atomic surface structure on NbSe2 and NbSe 3 at 77 and 4.2 K using scanning tunneling microscopy Scanning tunneling microscopy (STM) studies have been performed on NbSe2 and NbSe 3 at 77 and 4.2 K. The surface atomic structure has been clearly resolved, but evidence of charge-density wave (CDW) modulation has only been observed at 4.2 K in NbSe3. CDW's exist in NbSe2 at 4.2 K and in NbSe3 at 77 K, but the C D W amplitude is either too small or is screened by the remaining conduction electrons. The linear chain 527