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  • 1990-1994  (12)
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  • 1
    Electronic Resource
    Electronic Resource
    Adhesion and mechanical properties of amorphic diamond films prepared by a laser plasma discharge source (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1446-1453 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphic diamond films can be grown in an ultrahigh vacuum environment free from hydrogen with a laser plasma discharge source. This technique produces films that adhere more readily to materials for which there are important applications as protective coatings. In this work adhesion and mechanical properties of amorphic diamond films have been examined. A beam bending method has been used to measure the internal stress and a relatively low value of compressive stress was found. The dependence of stress on the laser intensities at the graphite ablation target has been studied. Analyses of these films on silicon, SiO2, ZnS, and TiAl6V4 by Rutherford backscattering spectrometry show significant interfacial layers with compositions of SiC, C0.5SiO2, C2.5ZnS, and C0.62Ti0.35Al0.05V0.02, respectively. Adhesion properties on ZnS and other substrates have also been examined for harsh environments. The mechanical properties of hardness, Young's modulus, and stiffness have been obtained with a nanoindentation technique. These results together with the minimal amount of hydrogen in our process, make amorphic diamond an excellent candidate for direct deposition on several substrates including ZnS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351267
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructure of amorphic diamond films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7862-7870 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been previously reported that layers of amorphic diamond can be grown in a UHV environment free from hydrogen with a laser plasma source. Some advantages are offered by this technique which produces films that adhere more readily to materials for which there are important applications. Theory has recently suggested a structure for amorphic diamond that comprises nodules of carbon atoms linked by sp3 bonds in a matrix of other polytypes and the purpose of this article is to communicate strong evidence in support of that hypothesis. Extensive examinations of a variety of films with a scanning tunneling microscope show a clearly prevalent structure composed of dense nodules. Grain size is about 1000 A(ring) and the diamond character is attested by the agreement of morphology, high density, optical properties, soft x-ray spectroscopy, hardness, and lack of appreciable hydrogen. Measurements agree in supporting a fraction of about 75% diamond contents. The principal conclusion is that this material prepared with a laser plasma source has the structure expected for amorphic diamond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347519
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructural analyses of amorphic diamond, i-C, and amorphous carbon (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 239-245 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments have identified the microstructure of amorphic diamond with a model of packed nodules of amorphous diamond expected theoretically. However, this success has left in doubt the relationship of amorphic diamond to other noncrystalline forms of carbon. This work reports the comparative examinations of the microstructures of samples of amorphic diamond, i-C, and amorphous carbon. Four distinct morphologies were found that correlated closely with the energy densities used in preparing the different materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352168
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The bonding of protective films of amorphic diamond to titanium (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3260-3265 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of amorphic diamond can be deposited from laser plasma ions without the use of catalysts such as hydrogen or fluorine. Prepared without columnar patterns of growth, the layers of this material have been reported to have "bulk'' values of mechanical properties that have suggested their usage as protective coatings for metals. Described here is a study of the bonding and properties realized in one such example, the deposition of amorphic diamond on titanium. Measurements with Rutherford backscattering spectrometry and transmission electron microscopy showed that the diamond coatings deposited from laser plasmas were chemically bonded to Ti substrates in 100–200-A(ring)-thick interfacial layers containing some crystalline precipitates of TiC. Resistance to wear was estimated with a modified sand blaster and in all cases the coating was worn away without any rupture or deterioration of the bonding layer. Such wear was greatly reduced and lifetimes of the coated samples were increased by a factor of better than 300 with only 2.7 μm of amorphic diamond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351390
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Amorphic diamond films produced by a laser plasma source (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2081-2087 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, attention has been focused upon laser plasma sources of thin-film diamond. These depend upon laser-ignited discharges in which intense pulsed currents flow through the small volume of carbon plasma ablated from graphite feedstock by a focused laser beam. The materials produced in this way generally resemble the hard amorphic films deposited by ion beams. This paper reports a detailed characterization of these films which we call amorphic diamond. The combination of an optical band gap of 1.0 eV with a grain size of 100–200 A(ring) places this material far outside the range of possibilities available to the model of graphitic islands. A structure of very fine grained diamond would more readily explain the hardness of 13 GPa determined in the absence of any measurable fraction of hydrogen. Such amorphic diamond films have been grown uniformly on 100-cm2 areas at ambient room temperatures with no seeding or abrasion of the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345566
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Compact flash x-ray source producing high average powers in nanosecond pulses (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2320-2325 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray diodes driven by repetitively pulsed Blumleins have been shown to be able to deliver high dose rates of x rays in pulses of nanosecond duration. Reported here is a study of the scaling of such devices conducted to isolate the primary factors limiting performance. Low residual gas pressure in the output diode together with the critical alignment of the electrodes were found essential for enhanced output. Optimizations served to increase the x-ray yield by an order of magnitude and the resulting performance is reported. At the output window, dose rates exceeding 1.4 kR min−1 were obtained in nanosecond pulses from the finished device of table top size at a charging voltage of 30 kV and a pulse repetition rate of 50 Hz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143928
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  • 7
    Electronic Resource
    Electronic Resource
    Absolute measurement of spatial and spectral characteristics of bremsstrahlung using the photoexcitation of nuclear isomers (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2298-2305 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method of obtaining absolute, direct measurements of the spatial and spectral characteristics of bremsstrahlung is discussed. This technique, called x-ray activation of nuclei (XAN) is based on the use of well-known photonuclear reactions which populate long-lived nuclear isomers. These populations sample incident photon continua at discrete excitation energies and effectively store this information for convenient retrieval following the irradiation of gram-sized targets. Recently a series of experiments has been conducted which has significantly expanded the available data for the photoexcitation of a wide range of isomers at higher energies. Thus it has become feasible to extend the use of XAN to energies approaching 4 MeV. The utility of this technique is demonstrated by the characterization of bremsstrahlung from the newly installed research linac at the University of Texas at Dallas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143925
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Low-energy conversion electron Mössbauer spectroscopy using a chevron microchannel plate detector (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2570-2573 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A detection system for conversion electron Mössbauer spectroscopy is described. A chevron microchannel plate assembly attached to a two-stage electrostatic lens is used to preferentially detect electrons with energies ≤15 eV. Mössbauer spectra collected with these electrons can provide information about a variety of solid-state surface phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143869
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Production of high-energy photons from flash x-ray sources powered by stacked Blumlein generators (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 1448-1456 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Described here is the design and construction of a pulse-power generator capable of discharging at high repetition rates. It consists of eight triaxial Blumleins stacked in series at one end. These lines are charged in parallel and synchronously commuted with a single thyratron at the other end to produce an open circuit voltage across a stack of six times the charging voltage. An x-ray diode has been constructed and matched to this pulse-power source making possible the emission of an average bremsstrahlung exposure rate of 17 R/S from a sequence of 40-ns pulses. When operated at 60-kV charging voltage, direct spectral measurements show the output to be a true continuum, peaking at intensities in excess of 5×108 photons/keV/shot and containing useful intensities of photons having energies of 300 keV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141150
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Mössbauer effect measurement of the recoil-free fraction for 57Fe implanted in a nanophase diamond film (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1221-1223 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mössbauer effect was used to investigate films of nanophase diamond (NPD) implanted with isotopically pure 57Fe at a dose of 5×1016 atoms/cm2 and an energy of 20 keV. When defects and voids created by the implantation were repaired with an overcoating layer of NPD, the recoil-free fraction at room temperature for these samples was found to be fdia=0.94±0.06 with a corresponding Debye temperature of 1140 K. This relatively high value for f makes NPD films a promising host matrix for microgram quantities of Mössbauer isotopes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110845
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