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  • 1
    Electronic Resource
    Electronic Resource
    Mechanics of laser-assisted debonding of films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1527-1536 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of GaN and ZnO can be separated from the substrates on which they are grown by the use of a laser-assisted debonding process in which a pulsed laser is shone through the substrate and absorbed in the film. Experience shows that the success in separating the films intact and damage free depends sensitively on the laser parameters used and the physical and geometric properties of the films. In this contribution, the mechanics of the laser-assisted debonding of GaN films are presented and used to construct process maps that delineate the conditions for damage-free film separation. The key variable is the nondimensional group ΩEp/(dp2τ), where Ω is a lumped material constant, Ep is the laser pulse energy, dp is the diameter of the illuminated area and τ is the laser pulse length. Experimental observations of UV/excimer laser assisted debonding of GaN films from sapphire substrates are used to illustrate the types of deformations and cracking modes on which the process maps are based. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1338519
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  • 2
    Electronic Resource
    Electronic Resource
    Cracking of GaN films (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1025-1034 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Cracking of thick GaN films grown on sapphire is reexamined on the basis of a combination of microstructural observations of cracking and established mechanics of fracture of films. It is argued that cracking is motivated by tensile growth stresses once a critical thickness is reached. Subsequent growth on the cracked films occurs, perpetuating the cracked structure until the crack surfaces approach one another and touch. Continued film growth buries the crack. Once the crack faces touch, there are conditions under which it is energetically favorable for the cracks to close and heal. Crack healing can be kinetically limited. Whether the crack healing is complete within the growth time depends on several factors including, it is suggested, whether impurities have adsorbed to the surface during growth. Conditions under which cracks that have extended into the sapphire substrate during film growth can act as critical flaws for fracture of the substrate on cooling are also presented. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330243
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  • 3
    Electronic Resource
    Electronic Resource
    Moisture diffusion along the TiN/SiO2 interface and in plasma-enhanced chemical vapor deposited SiO2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3695-3698 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusivity of moisture along the TiN/SiO2 interface has been determined by imaging the inward diffusion of 18O and 2D from isotopically labeled water using a secondary ion mass spectroscopy (SIMS) technique. The diffusivity, at room temperature, of the 18O and 2D labeled species along the interface are indistinguishable and have a value of 6.0±2.0×10−13 cm2/s, four orders of magnitude faster than bulk diffusivity of the same species in the plasma-enhanced chemical vapor deposition silica, also determined by SIMS. From 8 to 90 °C, the activation energies for interface and bulk diffusivities of the 2D labeled species are found to be 0.21 and 0.74 eV, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289481
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  • 4
    Electronic Resource
    Electronic Resource
    Dielectric cracking produced by electromigration in microelectronic interconnects (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6302-6312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The development of stress during electromigration along Al lines, constrained within a dielectric in a coplanar test configuration, is measured. It is shown that, above a certain threshold current density, cracking of the dielectric is induced in the vicinity of the anode. Cracking of the dielectric leads to loss of mechanical constraint on the aluminum conductor which, in turn, leads to increases in electrical resistance with continued current flow. The electromigration-induced stresses are determined from the measured frequency shifts induced in a novel ruby strain sensor embedded immediately beneath the interconnect line on a sapphire substrate. The transparency of the sapphire substrate also facilitated the observation of a hitherto unreported form of dielectric cracking, namely cracking from the interconnect along internal interfaces. The observations of dielectric cracking are in agreement with a recent fracture mechanics model. Analysis of the stress data, together with the results of finite element calculations of the strain energy release rate for crack extension, gives a quantitative estimate of the effective valence Z*(=1.3±0.2) for aluminum. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289044
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  • 5
    Electronic Resource
    Electronic Resource
    Piezoelectric contributions to the electrical behavior of ZnO varistors (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4430-4438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Internal stresses exist in ZnO varistors as a result of both crystallographic anisotropy in thermal expansion of the constituents and thermal expansion mismatch between phases. Due to the piezoelectric nature of ZnO, these stresses induce a net electric dipole moment that modifies the grain boundary Schottky barriers and causes an alteration of the varistor current–voltage response in the nonlinear regime. We report Raman piezospectroscopic measurements of residual strains in polycrystalline ZnO and develop a stochastic model for the distribution of potential barrier heights based on the distribution of internal stresses. The model provides a physical basis for barrier height distributions used in electrical network simulations of varistor transport behavior. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373088
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  • 6
    Electronic Resource
    Electronic Resource
    Additions and Corrections-Catalytic Behavior of 2-Amino-2-methyl-1-propanol Vapor over Alumina (1952)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 74 (1952), S. 6321-6321 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01144a675
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  • 7
    Electronic Resource
    Electronic Resource
    Defining and Integrating Sequences in Site Analysis: The Evidence from Hillforts and Other Sites (2001)
    Oxford, UK and Boston, USA : Blackwell Publishers Ltd
    Oxford journal of archaeology 20 (2001), S. 0 
    Details
    ISSN: 1468-0092
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Archaeology
    Notes: The author sets out at length his personal views on the problems of periodising occupation-sequences on sites of the Iron Age in Britain, with examples from Wheeler to the 1990s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/1468-0092.00136
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  • 8
    Electronic Resource
    Electronic Resource
    Two-step growth of high-quality GaN by hydride vapor-phase epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 1804-1806 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of a low-temperature layer of GaN formed by hydride vapor-phase epitaxy (HVPE) as a template to grow high-quality HVPE films is demonstrated. Using layers formed by reacting GaCl and NH3 at 550 °C and annealed at a growth temperature of 1050 °C, thick films of GaN can be grown by HVPE with fewer than 108 dislocations per cm2. Dislocation densities measured by high-resolution x-ray diffraction, atomic-force microscopy step termination density and plan-view transmission electron miscroscopy reveal that ∼23 μm films have dislocation densities of ∼6×107 cm−2. Obtaining high-quality single-crystal character films was found to be dependent on several factors, most importantly, the rate of temperature increase to growth temperature and the layer thickness. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1311600
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  • 9
    Electronic Resource
    Electronic Resource
    Grain Boundaries in Polycrystalline Ceramics (1987)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Materials Research 17 (1987), S. 57-74 
    Details
    ISSN: 0084-6600
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ms.17.080187.000421
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  • 10
    Electronic Resource
    Electronic Resource
    Host Corticostriatal Fibres Establish Synaptic Connections with Grafted Striatal Neurons in the Ibotenic Acid Lesioned Striatum (1989)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 1 (1989), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The connections between host corticostriatal afferents and neurons in intrastriatal grafts of foetal striatal tissue have been studied with electron microscopic immunocytochemistry using Phaseolus vulgaris leucoagglutinin (PHA-L) as a label of the host corticostriatal fibres. Adult rats with unilateral ibotenic acid lesions of the head of the caudate putamen received foetal cell suspension grafts from E14–15 rat embryos into the lesioned striatal area. Ten months after transplantation, multiple iontophoretic injections of PHA-L were made into the host frontal cortex. These injections labelled large numbers of corticostriatal fibres which extended across the graft - host border to form a rich axonal network mainly in the peripheral portions of the grafts. At the ultrastructural level a total of 134 PHA-L-labelled terminals were identified to form asymmetric synaptic contacts with neurons within the grafts. Of these contacts, 83% were in contact with dendritic spines, 12% with dendritic shafts, and 5% with small shafts or spines. The synaptic contacts were similar to those identified in intact regions of the host striatum that were spared by the lesion. However, the synapses in the host striatum were almost exclusively in contact with spines (98%). These results demonstrate that the corticostriatal projection, which constitutes a major source of afferent control in the normal striatum, not only extends axons into the intrastriatal striatal grafts, but also establishes synaptic connections with the implanted neuronal elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1989.tb00787.x
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