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1

Digitale Medien

Mechanics of laser-assisted debonding of films (2001)

Tavernier, P. R. ; Clarke, D. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 89 (2001), S. 1527-1536

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1338519

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2

Digitale Medien

Cracking of GaN films (2001)

Etzkorn, E. V. ; Clarke, D. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 89 (2001), S. 1025-1034

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1330243

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3

Digitale Medien

Moisture diffusion along the TiN/SiO2 interface and in plasma-enhanced chemical vapor deposited SiO2 (2000)

Xu, G. ; Clarke, D. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 3695-3698

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1289481

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4

Digitale Medien

Dielectric cracking produced by electromigration in microelectronic interconnects (2000)

Chiras, S. ; Clarke, D. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 88 (2000), S. 6302-6312

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1289044

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5

Digitale Medien

Piezoelectric contributions to the electrical behavior of ZnO varistors (2000)

Verghese, P. M. ; Clarke, D. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 87 (2000), S. 4430-4438

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.373088

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6

Digitale Medien

INTERACTION OF CATECHOLAMINE AND AMINO ACID METABOLISM IN BRAIN: EFFECT OF PARGYLINE AND l-DOPA (1974)

Nicklas, W. J. ; Berl, S. ; Clarke, D. D.

Oxford, UK : Blackwell Publishing Ltd

Journal of neurochemistry 23 (1974), S. 0

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ISSN: 1471-4159

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: Abstract— The combination of l-DOPA and pargyline caused a decrease in level of aspartate and an increase in that of glutamine in vivo in cerebral cortex, cerebellum, brain stem, hypothalamus, neostriatum and cervical cord of rat. There was also a decreased incorporation of radioactivity from [1-14C]acetate into amino acids in vivo, most notably in cerebellum and brain stem. The labelling of glutamine was especially affected. In addition, cortical slices were prepared from guinea pigs which had been pretreated with pargyline. These slices were incubated with and without 1 mm l-DOPA in media containing [1-14C]acetate. Pargyline alone caused a stimulation of the labelling of glutamate and aspartate but not glutamine and GABA; the levels of aspartate and GABA were greater than in control slices. The addition of l-DOPA to slices from pargylinized animals caused a severe decrease in glutamine labelling but not in that of glutamate or aspartate; the level of glutamine was increased while that of glutamate was decreased. The results are discussed in terms of the known biochemical and morphological compartmentation of amino acids in brain. It is suggested that catecholamines, in the process of functioning as transmitters, may also function as metabolic regulators of other transmitters, e.g. amino acids, as well as of the energy required for balanced neuronal function.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1471-4159.1974.tb06929.x

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7

Digitale Medien

COMPARTMENTATION OF CITRIC ACID CYCLE METABOLISM IN BRAIN: EFFECT OF AMINOOXYACETIC ACID, OUABAIN AND Ca2+ ON THE LABELLING OF GLUTAMATE, GLUTAMINE, ASPARTATE AND GABA BY [1-14C]ACETATE, [U-14C]GLUTAMATE AND [U-14C] ASPARTATE (1970)

Berl, S. ; Clarke, D. D. ; Nicklas, W. J.

Oxford, UK : Blackwell Publishing Ltd

Journal of neurochemistry 17 (1970), S. 0

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ISSN: 1471-4159

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: —(1) The effects of aminooxyacetic acid, ouabain and Ca2+ on the compartmentation of amino acid metabolism have been studied in slices of brain incubated with sodium-[1-14C]acetate, l-[U-14C]glutamate and l-[U-14C]aspartate as tracer metabolites.(2) Aminooxyacetic acid (10-3 m) inhibited the labelling of aspartate from [14C]acetate and [14C]glutamate, as well as the incorporation of label from [14C]aspartate into glutamate and glutamine. It also inhibited the labelling of GABA from all three radioactive precursors, as would be anticipated if there was inhibition of several transaminases as well as glutamate decarboxylase. The RSA of glutamine labelled from [1-14C]acetate was increased. This finding indicated that the glutamate pool which is utilized for glutamine formation is associated with glutamate dehydrogenase, and this enzyme appears to be related to the ‘synthetic tricarboxylic acid cycle’. AOAA exerted its major inhibitory effects on the citric acid‘energy cycle’with which transaminases are associated.(3) Ouabain (10-5 m) inhibited the labelling of glutamine to a much greater extent than the labelling of glutamate from [1-14C]acetate. It also caused leakage of amino acids from the tissue into the medium. Its effect on the glutamate–glutamine system was interpreted to be a selective inhibition of the 'synthetic’citric acid cycle.(4) The omission of Ca2+ from the incubation medium was associated with formation of glutamine with RSA less than 1·0 when labelled from [U-14C]glutamate, [U-14C]aspartate and lower than normal when labelled from [1-14C]acetate.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1471-4159.1970.tb02253.x

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8

Digitale Medien

COMPARTMENTATION OF CITRIC ACID CYCLE METABOLISM IN BRAIN: LABELLING OF GLUTAMATE, GLUTAMINE, ASPARTATE AND GABA BY SEVERAL RADIOACTIVE TRACER METABOLITES (1970)

Berl, S. ; Nicklas, W. J. ; Clarke, D. D.

Oxford, UK : Blackwell Publishing Ltd

Journal of neurochemistry 17 (1970), S. 0

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ISSN: 1471-4159

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Medizin

Notizen: —(1) Compartmentation of the metabolism of amino acids in brain has been studied in slices of cerebral cortex incubated with sodium [1-14C]acetate, sodium [1-14C]-bicarbonate, [1-14C]GABA or l-[1-14C]glutamate and in samples of brain after injection in vivo of [1-14C]- or [3H]acetate.(2) The method of treatment of the slices (a) maintained in ice-cold medium prior to incubation; (b) preincubation at 37°C and transfer to fresh medium affected the metabolism of the added, labelled substrate, particularly its labelling of glutamine.(3) The specific activity of glutamine labelled from the above metabolites was greater than that of glutamic acid in experiments of 10–30 minutes duration, whether or not subjected to pretreatment in the cold.(4) Incubation in medium containing 27 mm-K+ was associated with a decrease in the relative specific activity (RSA) of glutamine, except for the increase when l-[1-14C]glutamate was the precursor.(5) The data have been discussed in terms of metabolic compartmentation and their consistency with the concept of the presence in brain of more than one citric acid cycle, one containing the relatively smaller pools of intermediates and associated with synthetic processes; the other containing the relatively larger pools of intermediates and functioning as a homeostatic buffer for energy metabolism.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/j.1471-4159.1970.tb02254.x

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9

Digitale Medien

Defining and Integrating Sequences in Site Analysis: The Evidence from Hillforts and Other Sites (2001)

Clarke, D. V.

Oxford, UK and Boston, USA : Blackwell Publishers Ltd

Oxford journal of archaeology 20 (2001), S. 0

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ISSN: 1468-0092

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Klassische Archäologie

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1111/1468-0092.00136

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10

Digitale Medien

Two-step growth of high-quality GaN by hydride vapor-phase epitaxy (2000)

Tavernier, P. R. ; Etzkorn, E. V. ; Wang, Y. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 77 (2000), S. 1804-1806

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1311600

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