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6 Jul 1998

Volume 73, Issue 1, pp. 1-131

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Phonon density of states of bulk gallium nitride

J. C. Nipko, C.-K. Loong, C. M. Balkas, and R. F. Davis

Appl. Phys. Lett. 73, 34 (1998); http://dx.doi.org/10.1063/1.121714 (3 pages) | Cited 55 times

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We report the measured phonon density of states of a bulk GaN powder by time-of-flight neutron spectroscopy. The observed one-phonon excitation spectrum consists of two broad bands centered at about 23 and 39 meV corresponding to the acoustic and the first group of optical phonons; two sharp bands of upper optic modes at about 75 and 86 meV; and a gap of 45–65 meV. The phonon dispersion curves, lattice specific heat, and Debye temperature are calculated from fitting the data with a rigid-ion model. © 1998 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Experimental evidence of the size effect in thin ferroelectric films

Orest G. Vendik, Svetlana P. Zubko, and Leon T. Ter-Martirosayn

Appl. Phys. Lett. 73, 37 (1998); http://dx.doi.org/10.1063/1.121715 (3 pages) | Cited 48 times

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The phenomenological model based on the Ginsburg–Devonshire equation has been applied to investigate the size effect in thin SrTiO3 and BaxSr1−xTiO3 films. The size effect is caused by two phenomena: spatial correlation of the polarization and boundary conditions for the ferroelectric polarization on electrodes. The experimental data obtained by different groups were used to investigate the boundary conditions. The most remarkable result was found for the SrRuO3/BaxSr1−xTiO3/SrRuO3 structure which is characterized by free boundary conditions for the ferroelectric polarization. Such boundary conditions provide the highest value of the effective dielectric constant of a dielectric layer in the sandwich structure. The strain dependence of the dielectric permittivity of SrTiO3 at finite temperatures was taken into account as well. © 1998 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Surface dynamics studied by perturbing the surface with the tip of a scanning tunneling microscope—Si(100) at 80 K

K. Hata, M. Ishida, K. Miyake, and H. Shigekawa

Appl. Phys. Lett. 73, 40 (1998); http://dx.doi.org/10.1063/1.121716 (3 pages) | Cited 10 times

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We have utilized the tip of a scanning tunneling microscope to perturb a specific local structure (the C defect) of Si(100) at 80 K, and observed the dynamical symmetric⇔buckled transition of the surrounding dimers. The observed large-scale transition implies that the configuration of the dimers is determined by a detailed balance among many elastic long-range forces generated by the surrounding C defects. © 1998 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
68.35.B- Structure of clean surfaces (and surface reconstruction)

Stress evolution in Mo/Si multilayers for high-reflectivity extreme ultraviolet mirrors

J. M. Freitag and B. M. Clemens

Appl. Phys. Lett. 73, 43 (1998); http://dx.doi.org/10.1063/1.121717 (3 pages) | Cited 20 times

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The stress evolution of sputter deposited Mo/Si multilayers of possible application as extreme ultraviolet light mirrors has been investigated by in situ substrate curvature measurements using a multiple parallel laser beam technique. Our preliminary results show well-defined stress modulation concurrent with the deposition of Mo and Si layers in the multilayer structure. Large changes in substrate curvature were measured during the early stages of deposition of the individual layers, with Mo exhibiting apparent tension and Si exhibiting apparent compression. The magnitudes of these curvature changes partially offset each other, resulting in an average compressive stress of −350 MPa in the multilayer. Possible stress generating mechanisms during growth of these multilayers as well as single layer films of Mo and Si will be discussed. © 1998 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.43.Dq Amorphous semiconductors, metals, and alloys
78.66.Jg Amorphous semiconductors; glasses
42.79.Bh Lenses, prisms and mirrors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Ion-induced electron emission from diamond

R. Kalish, V. Richter, E. Cheifetz, A. Zalman, and P. Yona

Appl. Phys. Lett. 73, 46 (1998); http://dx.doi.org/10.1063/1.121718 (3 pages) | Cited 10 times

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The electron emission yields (γ) from conductive (B doped) and undoped chemical vapor deposited diamond caused by light (protons) and heavy (argon) ion impact were measured as functions of ion dose and energy (40–300 keV). Very large values of γ are obtained for the case of B doped diamond for both ions. Whereas the emission due to Ar is found to decay very rapidly towards the low γ value measured for graphite, it remains persistently very high (γ ∼ 25) for the case of protons, indicating possible application of diamond as a sensitive detector for light ions. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
72.80.Cw Elemental semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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