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  • 1
    Electronic Resource
    Electronic Resource
    Microstructure of ultrananocrystalline diamond films grown by microwave Ar–CH4 plasma chemical vapor deposition with or without added H2 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 118-122 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrananocrystalline diamond (UNCD) films, grown using microwave plasma-enhanced chemical vapor deposition with gas mixtures of Ar–1%CH4 or Ar–1%CH4–5%H2, have been examined with transmission electron microscopy (TEM). The films consist of equiaxed nanograins (2–10 nm in diameter) and elongated twinned dendritic grains. The area occupied by dendritic grains increases with the addition of H2. High resolution electron microscopy shows no evidence of an amorphous phase at grain boundaries, which are typically one or two atomic layer thick (0.2–0.4 nm). Cross-section TEM reveals a noncolumnar structure of the films. The initial nucleation of diamond occurs directly on the Si substrate when H2 is present in the plasma. For the case of UNCD growth from a plasma without addition of H2, the initial nucleation occurs on an amorphous carbon layer about 10–15 nm thick directly grown on the Si substrate. This result indicates that hydrogen plays a critical role in determining the nucleation interface between the UNCD films and the Si substrate. The relation between diamond nuclei and Si is primarily random and occasionally epitaxial. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377301
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  • 2
    Electronic Resource
    Electronic Resource
    Electron-beam-induced crystallization of isolated amorphous regions in Si, Ge, GaP, and GaAs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 974-982 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An energetic electron beam has been used to stimulate crystallization of spatially isolated amorphous regions in Si, Ge, GaP, and GaAs at 30 and 300 K. In the four materials it was found that crystallization was induced even when the energy of the electron beam was less than that required to create point defects in the crystalline structure. The rate of crystallization depended on the material and on the electron energy. In all materials, the rate decreases as the electron energy increases from 50 keV (the lowest electron energy used), reaching a minimum value at an electron energy slightly below the displacement threshold voltage. Above the displacement threshold, the regrowth rate again increases with increasing electron energy. The possible role of electron-beam heating was studied both theoretically and experimentally. Calculations suggested heating effects were negligible and this was confirmed by in situ ion implantations and electron irradiations performed at 30 K, where subthreshold electrons stimulated crystallization. The subthreshold and low-temperature results are consistent with the model that the crystallization process is dependent on the creation of defects (dangling bonds and kinks) at the crystalline-amorphous (c-a) interface. The crystallization stimulated by the subthreshold electron beams suggests that electronic excitation of the bonds along the c-a interface can induce the amorphous to crystalline transition. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360764
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  • 3
    Electronic Resource
    Electronic Resource
    Ion implantation damage in Al0.6Ga0.4As/GaAs heterostructures (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 97-103 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The damage produced at the interfaces in a sample of GaAs/Al0.6Ga0.4As/GaAs that has been subjected to ion implantation at 77 and 293 K with 1 MeV Kr+ ions has been investigated using a combination of ion channeling and transmission electron microscopy (TEM) techniques. Low temperature ion-channeling spectra obtained from samples implanted at 77 K, to an ion dose of 1014 ions cm−2, were similar to the random spectrum, indicating that the GaAs and Al0.6Ga0.4As layers had sustained a considerable degree of damage. An asymmetric signal developed in the He+ ion-channeling spectrum as the sample warmed to room temperature. The backscattering yield corresponding to the bottom interface (i.e., Al0.6Ga0.4As grown on GaAs) resembled that of the random yield, whereas that from the top interface (GaAs grown on Al0.6Ga0.4As) decreased, shifting toward the unirradiated channeled spectrum. This observation suggests that the damage produced near the top of the Al0.6Ga0.4As layer is thermally unstable. Cross-sectional TEM images reveal a greater amount of damage in the form of extended defects and amorphous regions at the bottom interface than at the top one. This difference is sufficient to account for the observed asymmetry in the channeling spectra. Increasing the ion dose to 1015 ions cm−2 produced a damage state throughout the Al0.6Ga0.4As layer that was stable at both 77 and 293 K. TEM examination revealed that at this ion dose the GaAs and Al0.6Ga0.4As layers were both amorphous. Room-temperature implantation to a dose of 1×1016 ions cm−2 was also performed. Planar defects were observed at both interfaces, although their density appeared to be greater near the bottom interface.In addition, the bottom interface was rougher than the top. The difference in the damage states at the bottom and top interfaces can be attributed to a variation in the number of displacement cascade events as a function of depth through the Al0.6Ga0.4As layer. This variation in the number of cascades results in different amounts of ion mixing at the top and bottom interfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360586
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  • 4
    Electronic Resource
    Electronic Resource
    A comparison of the amorphization induced in AlxGa1−xAs and GaAs by heavy-ion irradiation (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1287-1293 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of AlxGa1−xAs/GaAs samples to bombardment with heavy ions (50 keV Kr+, 50 keV and 1.5 MeV Xe+) was studied as a function of ion dose at temperatures of 30 and 300 K using transmission electron microscopy. Samples with x=0.2 and 0.85 were used. Under all irradiation temperature and ion combinations, the AlGaAs was more resistant to amorphization than GaAs. The resistance increased with increasing Al content and decreased with decreasing irradiation temperature. This difference in the response may be attributed to differences either in the mechanisms by which a region is rendered amorphous (i.e., by direct impact amorphization or by the buildup of point defects) or to differences in the inherent stability (recrystallization temperature and rate) of individual amorphous zones in AlGaAs and GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347262
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  • 5
    Electronic Resource
    Electronic Resource
    Columnar defects in YBa2Cu3O7−δ induced by irradiation with high energy heavy ions (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1573-1575 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect microstructures in three YBa2Cu3O7−δ single crystals irradiated with different high energy heavy ions show dramatically different damage morphologies. For Sn and Au projectiles with total energies of 580 MeV and 1.0 GeV, respectively, highly aligned tracks are observed which extend for many microns in the crystals. However, irradiation with 1.4 GeV Br ions results in the formation of spherical damage regions widely separated along the ion path through the entire crystal. The continuity of damage along the ion path for the different projectiles varies with the magnitude of the electronic energy loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110753
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