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15 Sep 2003

Volume 94, Issue 6, pp. 3675-4231

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Early stage of plastic deformation in thin films undergoing electromigration

B. C. Valek, N. Tamura, R. Spolenak, W. A. Caldwell, A. A. MacDowell, R. S. Celestre, H. A. Padmore, J. C. Bravman, B. W. Batterman, W. D. Nix, and J. R. Patel

J. Appl. Phys. 94, 3757 (2003); http://dx.doi.org/10.1063/1.1600843 (5 pages) | Cited 12 times

Online Publication Date: 29 August 2003

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Electromigration occurs when a high current density drives atomic motion from the cathode to the anode end of a conductor, such as a metal interconnect line in an integrated circuit. While electromigration eventually causes macroscopic damage, in the form of voids and hillocks, the earliest stage of the process when the stress in individual micron-sized grains is still building up is largely unexplored. Using synchrotron-based x-ray microdiffraction during an in-situ electromigration experiment, we have discovered an early prefailure mode of plastic deformation involving preferential dislocation generation and motion and the formation of a subgrain structure within individual grains of a passivated Al (Cu) interconnect. This behavior occurs long before macroscopic damage (hillocks and voids) is observed. © 2003 American Institute of Physics.
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66.30.Qa Electromigration
62.20.F- Deformation and plasticity
85.40.Ls Metallization, contacts, interconnects; device isolation
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Random field models for two-phase microstructures

Mircea Grigoriu

J. Appl. Phys. 94, 3762 (2003); http://dx.doi.org/10.1063/1.1600827 (9 pages) | Cited 8 times

Online Publication Date: 29 August 2003

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Level-cut filtered Poisson fields are defined by cuts of filtered Poisson fields above prescribed levels and used to model two-phase microstructures. The filtered Poisson fields are sums of deterministic functions h scaled by random variables and centered at random points generated by a Poisson field N. The structure of the level-cut filtered Poisson fields depends on the functional form of h, the properties of the random variables scaling h, and the intensity of N. Level-cut Gaussian fields used extensively to represent two-phase microstructures are special cases of level-cut filtered Poisson fields. A Monte Carlo algorithm was developed for generating two-phase composites based on level-cut filtered Poisson fields. It is shown by examples that level-cut filtered Poisson fields can produce a broad range of two-phase microstructures. © 2003 American Institute of Physics.
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61.72.Bb Theories and models of crystal defects
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Uu Applications of Monte Carlo methods

Ultrasonic absorption in ultra-low carbon steel

S. Bolognini and A. Moreau

J. Appl. Phys. 94, 3771 (2003); http://dx.doi.org/10.1063/1.1593220 (10 pages) | Cited 4 times

Online Publication Date: 29 August 2003

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The laser-based reverberant technique is used to measure ultrasonic absorption spectra in the 2 to 45 MHz frequency range. This technique, being contactless, allows measurements at high temperature. The absorption spectra of ultra-low carbon steel samples are studied at room temperature in a magnetic field (in order to suppress the magnetoelastic contribution) and in a high temperature furnace (20–1200 °C) without magnetic field. Small steel samples (about 10×10×1 mm3) are used. At room temperature, two main contributions to the ultrasonic absorption are identified: microeddy currents (magnetoelastic contribution) and absorption caused by dislocations (deformation contribution). A typical microeddy current peak is observed and yields a reasonable estimate of the magnetic domain size. Above 10 MHz, the nonmagnetic contribution to the total absorption follows the classical vibrating string model. However, other phenomena also contribute to the absorption spectra. Below 10 MHz, an amplitude-independent damping background is observed. In addition, a small frequency-independent contribution to the absorption is observed at room temperature and is attributed to a thin surface layer. The absorption at high temperature is dominated below the Curie point by the magnetoelastic contribution. Two internal friction peaks are also detected. The first one, at 100 °C, is related to the dislocation kink motion. The second one, measured at 330 °C and 10 MHz, is attributed to the Snoek relaxation of carbon and/or nitrogen in α-iron. The Curie transition as well as the ferrite-austenite transition strongly affect the internal friction spectra.
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62.65.+k Acoustical properties of solids
75.50.Bb Fe and its alloys
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
75.80.+q Magnetomechanical effects, magnetostriction
75.60.-d Domain effects, magnetization curves, and hysteresis
75.60.Ch Domain walls and domain structure
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions

Brillouin scattering in RbNbWO6

Mirosław Ma̧czka, Jae-Hyeon Ko, Seiji Kojima, Jerzy Hanuza, and Andrzej Majchrowski

J. Appl. Phys. 94, 3781 (2003); http://dx.doi.org/10.1063/1.1601683 (4 pages) | Cited 1 time

Online Publication Date: 29 August 2003

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Micro-Brillouin scattering measurements of RbNbWO6, a defect pyrochlore, that exhibits superionic conductivity and ferroelectric properties, have been performed in the 213–573 K temperature range. In this work the presence of quasielastic scattering (central peak) has been documented. The obtained results suggest that the main contribution to the observed central peak comes from Rb+ ion hopping. The temperature dependences of the central peak intensity and bandwidth exhibit broad anomalies around 360 K. This result clearly shows that ion hopping is related to the phase transitions at 361.6 and 356.5 K. © 2003 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
66.30.H- Self-diffusion and ionic conduction in nonmetals
64.70.K- Solid-solid transitions
77.80.-e Ferroelectricity and antiferroelectricity

Optical spectroscopy of localized electronic states in SrS:Cu

D. R. Evans and W. M. Dennis

J. Appl. Phys. 94, 3785 (2003); http://dx.doi.org/10.1063/1.1601682 (6 pages)

Online Publication Date: 29 August 2003

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A combination of optical spectroscopy and thermoluminescence measurements were used to determine the mechanisms that can influence the emission in SrS:Cu+ thin film structures and increase the electroluminescence brightness by a factor of 2. In particular, the interaction of the emitting center with the trap states and the conduction band is considered. Thermal quenching, thermoluminescence, and temperature-dependent fluorescence transient results are compared to appropriate population dynamics models in order to determine the position of the Cu excited state and the trap states with respect to the conduction band. © 2003 American Institute of Physics.
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71.55.Ht Other nonmetals
78.60.Kn Thermoluminescence
78.60.Fi Electroluminescence
78.55.Hx Other solid inorganic materials

Optical properties of CdxZn1−xTe epilayers grown by molecular-beam epitaxy

Y. T. Shih, W. C. Fan, C. S. Yang, M. C. Kuo, and W. C. Chou

J. Appl. Phys. 94, 3791 (2003); http://dx.doi.org/10.1063/1.1601685 (5 pages) | Cited 2 times

Online Publication Date: 29 August 2003

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CdxZn1−xTe epilayers were grown on GaAs(001) substrates by molecular-beam epitaxy. The optical properties of the epilayers were studied by taking reflectance (R) and photoluminescence (PL) measurements. From the R and PL spectra, the energy gaps of the epilayers were determined and shown to decrease as the Cd concentration increased. A quadratic equation that related the energy gap to Cd concentration was also derived. The dependence of the PL spectra on temperature was studied as well. A redshift of the PL peaks was observed as the temperature increased. The exciton activation energy of the epilayers was determined from the plots of integrated PL intensity versus temperature. It tends to decrease as the Cd content increased. The temperature dependence of the energy gaps, determined from the PL spectra, was fitted according to both Varshni’s and O’Donnell and Chen’s relations [Y. P. Varshni, Physica 34, 149 (1967); K. P. O’Donnell and X. Chen, Appl. Phys. Lett. 58, 2924 (1991)]. Good fits were obtained using both relations for the samples with small Cd concentration. However, the fitted O’Donnell’s curve for the Cd0.582Zn0.418Te epilayer shows a more reasonable trend as temperature increases. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.20.-e Optical properties of bulk materials and thin films
71.20.Nr Semiconductor compounds
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Electron paramagnetic resonance characterization of impurity Gd3+ ions in a PbWO4 single crystal

T. H. Yeom, S. H. Lee, S. H. Choh, T. J. Han, T. H. Kim, and J. H. Ro

J. Appl. Phys. 94, 3796 (2003); http://dx.doi.org/10.1063/1.1599048 (4 pages) | Cited 2 times

Online Publication Date: 29 August 2003

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Lead tungstate single crystals doped with Gd2O3 were grown by the Czochralski method in Ar atmosphere. The electron paramagnetic resonance of the Gd3+ ion in a PbWO4 single crystal has been investigated at 9.4 GHz. The spectroscopic splitting tensor g and zero-field splitting parameters Bkq were determined using the effective spin Hamiltonian. The rotation patterns in the crystallographic planes together with spin Hamiltonian parameters of Gd3+ ion show that the local site symmetry of the Gd3+ ion in PbWO4 crystal is tetragonal and that the Gd3+ ion substitutes for the Pb2+ ion without local charge compensation at the nearby surroundings. © 2003 American Institute of Physics.
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76.30.Kg Rare-earth ions and impurities
71.70.Ch Crystal and ligand fields

Effects of dry etching processes on effective refractive index of ZnTe surface layers in terahertz region

S. Wu, Z. Q. Ren, W. Z. Shen, H. Ogawa, and Q. X. Guo

J. Appl. Phys. 94, 3800 (2003); http://dx.doi.org/10.1063/1.1602568 (5 pages) | Cited 4 times

Online Publication Date: 29 August 2003

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We report on the far-infrared (FIR) reflection spectra of high-quality ZnTe crystals exposed to CH4/H2 gases under different rf plasma powers. The effects of reactive ion etching on the effective refractive index of perturbed ZnTe surface layers have been investigated in the terahertz (THz) frequency range of 1.5–10.0 THz. The FIR refractive index has been found to decrease with the increase of plasma power, which has been well described by Sellmeier formulas. Furthermore, the obtained experimental data have been employed for THz electro-optic applications by predicting the effects of RIE on the second-order nonlinear susceptibility and the THz pulse intensity after dispersive propagation/absorption in the ZnTe surface layers. © 2003 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
78.68.+m Optical properties of surfaces
42.65.An Optical susceptibility, hyperpolarizability
78.20.Jq Electro-optical effects

Properties of Cu/Au Schottky contacts on InGaP layer

Day-Shan Liu, Ching-Ting Lee, and Ching-Wu Wang

J. Appl. Phys. 94, 3805 (2003); http://dx.doi.org/10.1063/1.1602574 (5 pages) | Cited 3 times

Online Publication Date: 29 August 2003

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We use Auger electron spectroscopy (AES) measurements to obtain elemental distributions for Cu/Au Schottky contacts to an InGaP layer in as-deposited and thermally annealed samples. The AES depth profile shows an obvious Cu layer with no apparent interdiffusion between the Cu and the InGaP layers in either the as-deposited samples or in the samples annealed at 450 °C. However, when the annealing temperature reached 500 °C, the metallic Cu layer was released, and a distinct interdiffusion between the Cu and the InGaP layers is observed. Metallic Cu and Au intermixed to form a stable intermetallic region. Below this intermetallic region, an interaction region, composed mainly of Cu and P, is observed. The formation of this region is attributable to the diffusion of Cu into the InGaP layer, and is responsible for the thermal degradation of Cu/Au Schottky contacts to the InGaP layer. In the deep-level transient spectroscopy spectra, we find an obvious trap at 150 K. This was determined to be a native trap that exists in the InGaP materials with activation energies of 0.35–0.42eV. After annealing at 500 °C, another trap appeared. According to a thermal degradation investigation, this trap at Ec−0.70 eV can be attributed to the diffusion of Cu into the InGaP layer. © 2003 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Structure of electroless deposited Co0.9W0.02P0.08 thin films and their evolution with thermal annealing

A. Kohn, M. Eizenberg, and Y. Shacham-Diamand

J. Appl. Phys. 94, 3810 (2003); http://dx.doi.org/10.1063/1.1602572 (13 pages) | Cited 17 times

Online Publication Date: 29 August 2003

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Electroless deposited Co0.9W0.02P0.08 thin films have been proposed as diffusion barriers and encapsulation layers for Cu metallization in ultralarge-scale integrated microelectronic devices. In this article, we present a study of the structure of these films and their evolution with thermal anneal up to 700 °C. The as-deposited microstructure is comprised of an amorphous CoWP component and nanocrystallites of hexagonal-close-packed (hcp) Co, approximately 5 nm in size. The amorphous CoWP component crystallizes to hcp Co at approximately 290 °C with an apparent activation energy of 1.6±0.1 eV, according to the Kissinger analysis. Isothermal anneals show that the rate of nucleation with time of the hcp Co grains is constant, and grain growth is controlled by diffusion. This diffusion is most probably of the P and W elements, which enrich the grain boundaries. At approximately 420 °C, the orthorhombic (o-) Co2P phase nucleates. The apparent activation energy of this phase transformation is 4.6±0.1 eV, according to the Kissinger analysis. We suggest that the nucleation of the o-Co2P phase occurs when the grain boundaries are saturated with P. At higher temperatures, the main structural changes observed in the films are the grain growth of the predominately hcp Co grains and a delayed transformation to face-centered-cubic Co compared to bulk Co. The chemical binding state of P after high temperature anneals is covalent as in the o-Co2P phase. In the as-deposited film, the chemical binding state of P is significantly different, attributed to the amorphous CoWP component and the P in a solid solution in the hcp Co grains. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
81.15.Pq Electrodeposition, electroplating
61.72.Cc Kinetics of defect formation and annealing

Study on atomic coordination around Er doped into anatase– and rutile– TiO2: Er–O clustering dependent on the host crystal phase

Masashi Ishii, Shuji Komuro, and Takitaro Morikawa

J. Appl. Phys. 94, 3823 (2003); http://dx.doi.org/10.1063/1.1602567 (5 pages) | Cited 10 times

Online Publication Date: 29 August 2003

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Alternative Er doping into anatase (A–) or rutile (R−)TiO2 can be achieved by O2 pressure control during Er-doped TiO2 deposition using laser ablation. An x-ray absorption fine structure analysis of the atomic coordination around Er revealed the dynamics of Er–O clustering in A– and R−TiO2. The Er local structure in A−TiO2 can be determined by a Ti–O arrangement of the host crystal surrounding Er, while that in R−TiO2 can be decided by the Er–O chemical properties rather than the Ti–O arrangement. Moreover, a substitution of Er for Ti induced O deficit in A−TiO2 and induced Ti removal in R−TiO2. These differences can be explained by the ErO6 stabilization mechanism based on the spontaneous symmetry reduction (SSR) theory. The Ti–O arrangement in A−TiO2 prevents the SSR, resulting in ErO6 instability. However, ErO6 is stabilized in the host crystal because the SSR is smoothly induced in R−TiO2. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra

X-ray reciprocal space mapping of strain relaxation in GaAs1−xNx on GaAs [100] by molecular-beam epitaxy

W. K. Cheah, W. J. Fan, S. F. Yoon, S. Z. Wang, and W. K. Loke

J. Appl. Phys. 94, 3828 (2003); http://dx.doi.org/10.1063/1.1600844 (6 pages) | Cited 6 times

Online Publication Date: 29 August 2003

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The effect of strain on GaAs1−xNx grown on GaAs is observed using two-dimensional [115] high-resolution x-ray diffraction rocking curves. The instance when the epilayer changes from a highly strained to a relaxed state, is captured and a change in peak profile is observed. The increase of growth rate is found to have an effect of maintaining the crystal quality and surface reconstruction. Interstitial N complex lowers the tensile strain due to its compressive nature, thereby increasing the critical thickness at high N%. We demonstrated that GaAs0.952N0.048 can be coherently grown to 100 nm on GaAs, exceeding the critical thickness by 4.7 times after an optimization of III–V–N growth by means of higher rf power compensation under an increased growth rate. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Cu gettering in ion implanted and annealed silicon in regions before and beyond the mean projected ion range

R. Kögler, A. Peeva, A. Lebedev, M. Posselt, W. Skorupa, G. Özelt, H. Hutter, and M. Behar

J. Appl. Phys. 94, 3834 (2003); http://dx.doi.org/10.1063/1.1602951 (6 pages) | Cited 4 times

Online Publication Date: 29 August 2003

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The strong gettering of Cu atoms in single-crystal Si implanted with 3.5 MeV P+ ions is studied after thermal treatment and Cu contamination. Cu decorates the remaining implantation damage. Three separate Cu gettering layers are detected by secondary ion mass spectrometry: at the main projected ion range RP below RP (RP/2 effect) and beyond RP (trans-RP effect). The defects acting as gettering centers at RP/2 and RP are implantation induced excess vacancies and excess interstitials, respectively. Cu profiles fit very well with depth distributions of excess vacancies and excess interstitials determined by binary collision simulations for random and channeled ion incidence. The RP/2 effect for P+ implantation is found to be significantly reduced in comparison with Si+ implantation. It disappears completely for higher P+ ion fluences. The trans-RP gettering layer is formed by thermal treatment. The Cu accumulation in the trans-RP region increases with increasing temperature and/or with increasing annealing time. These results are in qualitative agreement with the assumption that interstitials carried by P diffusion are the origin of Cu gettering in the trans-RP region. The P diffusion may inject interstitials into the bulk and also into the RP/2 region thus decreasing the RP/2 effect. © 2003 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
81.65.Tx Gettering
81.05.Cy Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.J- Point defects and defect clusters
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.47.Fg Semiconductor surfaces

Molecular dynamics study of structural, mechanical, and vibrational properties of crystalline and amorphous Ga1−xInxAs alloys

Paulo S. Branicio, Jose P. Rino, Fuyuki Shimojo, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

J. Appl. Phys. 94, 3840 (2003); http://dx.doi.org/10.1063/1.1601691 (9 pages) | Cited 18 times

Online Publication Date: 29 August 2003

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Using an interaction potential scheme, molecular dynamics (MD) simulations are performed to investigate structural, mechanical, and vibrational properties of Ga1−xInxAs alloys in the crystalline and amorphous phases. For the crystalline phase we find that: (i) Ga–As and In–As bond lengths vary only slightly for different compositions; (ii) the nearest-neighbor cation–cation distribution has a broad peak; and (iii) there are two nearest-neighbor As–As distances in the As (anion) sublattice. These MD results are in excellent agreement with extended x-ray absorption fine structure and high-energy x-ray diffraction data and also with ab initio MD simulation results. The calculated lattice constant deviates less than 0.18% from Vegard’s law. The calculated phonon density of states exhibits a two-mode behavior for high-frequency optical phonons with peaks close to those in binary alloys (GaAs and InAs), which agrees well with a recent Raman study. Calculated elastic constants show a significant nonlinear dependence on the composition. For the amorphous phase, MD results show that: (i) the nearest-neighbor cation–anion distribution splits into well-defined As–Ga and As–In peaks as in the crystal phase; (ii) the cation–cation distribution is similar to that in the crystal phase; and (iii) the As–As distribution is quite different from that in the crystal, having only one nearest-neighbor distance. © 2003 American Institute of Physics.
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61.66.Fn Inorganic compounds
02.70.Ns Molecular dynamics and particle methods
62.20.D- Elasticity
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.43.Dq Amorphous semiconductors, metals, and alloys
61.43.Bn Structural modeling: serial-addition models, computer simulation
63.50.-x Vibrational states in disordered systems

Control parameters for the tunable refractive index of magnetic fluid films

Chin-Yih Hong, S. Y. Yang, H. E. Horng, and H. C. Yang

J. Appl. Phys. 94, 3849 (2003); http://dx.doi.org/10.1063/1.1597760 (4 pages) | Cited 9 times

Online Publication Date: 29 August 2003

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In this work, we systematically investigate the influence of control parameters, including the concentration of magnetic particles, film thickness, external field direction, and field sweep rate, on the magnetically tunable refractive index of magnetic fluid films. We find that the variation in the refractive index of the magnetic fluid film with rising field strength is enhanced by increasing either the concentration or the film thickness, or by applying the field along the film surface, whereas it is independent of the sweep rate of the field. The results clearly reveal how to control the tunable refractive index of magnetic fluid films. Furthermore, they provide valuable information that may assist in the development of magnetic-fluid-based index-tunable devices. © 2003 American Institute of Physics.
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75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Gg Ferrimagnetics

Molecular dynamics simulations of mechanical deformation of amorphous silicon dioxide during chemical–mechanical polishing

Evgueni Chagarov and James B. Adams

J. Appl. Phys. 94, 3853 (2003); http://dx.doi.org/10.1063/1.1602551 (9 pages) | Cited 7 times

Online Publication Date: 29 August 2003

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We present molecular dynamics simulations of the mechanical deformation which occurs during chemical–mechanical polishing (CMP) of amorphous silicon dioxide for different geometries and relative velocities. The simulations clarify asperity shape evolution during the process of shear and reveal temperature distributions as a function of time. It was found that the ratio of radii of a particle and asperity strongly affects the amount of the material removed whereas the relative velocity has a weaker affect on it. During shear, the local temperature inside the deformed asperity is raised to 700 K at 0.5 Å/ps and up to 2200 K at 5.0 Å/ps. This temperature increase lasts for only a short time, but it can have a major impact on the amount of material removed. It was found that there could be significant deposition of the material from the particle to the slab, which can fill surface trenches and thereby make the surface smoother. An analytic model was developed for describing the amount of material removed as a function of asperity and particle radii and relative velocity. It was fit to the simulated data, and used to predict the amount of material removed at typical CMP velocities (∼1 m/s). © 2003 American Institute of Physics.
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81.65.Ps Polishing, grinding, surface finishing
02.70.Ns Molecular dynamics and particle methods
62.20.F- Deformation and plasticity

Blue- and green-emitting SrS:Cu electroluminescent devices deposited by the atomic layer deposition technique

Jarkko Ihanus, Mikko Ritala, Markku Leskelä, Erkki Soininen, Wounjhang Park, Alain E. Kaloyeros, William Harris, Karl W. Barth, Anna W. Topol, Timo Sajavaara, and Juhani Keinonen

J. Appl. Phys. 94, 3862 (2003); http://dx.doi.org/10.1063/1.1603349 (7 pages) | Cited 6 times

Online Publication Date: 29 August 2003

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Observed structural, compositional, and optical differences between blue- and green-emitting SrS:Cu thin films deposited by the atomic layer deposition technique were studied. The use of hydrogen in the deposition process resulted in green-emitting electroluminescent devices. The green-emitting devices had also the highest potassium (K) content, but the exact role of K was not resolved. The green emission is thought to originate from copper pairs and isolated off-centered copper ions at octahedral sites, whereas blue emission is suggested to originate from copper ions at tetrahedral interstitial sites. The brightest blue-emitting device, measured at 60 Hz, emitted 17 cd/m2 at 40 V above the threshold voltage (L40) with x=0.17 and y=0.30 as the Commission Internationale de l’Eclairage color coordinates. Conversely, the brightest green-emitting device emitted 44 cd/m2 with x=0.33 and y=0.58. The blue- and green-emitting devices also showed different time-resolved electroluminescence behavior, which suggests reduced dynamic space charge within the green-emitting phosphors resulting in the higher emission intensity in the green-emitting devices. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
42.79.Wc Optical coatings
78.66.Li Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.47.-p Spectroscopy of solid state dynamics
71.55.Ht Other nonmetals

Room-temperature 1.54 μm photoluminescence from Er-doped Si-rich silica layers obtained by reactive magnetron sputtering

F. Gourbilleau, C. Dufour, M. Levalois, J. Vicens, R. Rizk, C. Sada, F. Enrichi, and G. Battaglin

J. Appl. Phys. 94, 3869 (2003); http://dx.doi.org/10.1063/1.1604479 (6 pages) | Cited 33 times

Online Publication Date: 29 August 2003

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Er-doped Si-rich silica layers were obtained by reactive magnetron sputtering and both structural and room-temperature photoluminescence properties were investigated. The controlled introduction of hydrogen in the plasma was found to play a critical role in the microstructure and distribution of the Si nanograins formed after annealing. Concomitant density increase and size decrease of these nanograins mostly amorphous were noticed upon increasing the hydrogen partial pressure in the plasma. This was accompanied by a systematic enhancement of the Er emission indicating that both crystallized and amorphous silicon nanoparticles are similarly efficient sensitizers for Er emission. The lifetime of the latter was found as high as 5–6 ms. © 2003 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing

Persistent photoconductivity and optical quenching of photocurrent in GaN layers under dual excitation

V. V. Ursaki, I. M. Tiginyanu, P. C. Ricci, A. Anedda, S. Hubbard, and D. Pavlidis

J. Appl. Phys. 94, 3875 (2003); http://dx.doi.org/10.1063/1.1604950 (8 pages) | Cited 16 times

Online Publication Date: 29 August 2003

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Persistent photoconductivity (PPC) and optical quenching (OQ) of photoconductivity (PC) were investigated in a variety of n-GaN layers characterized by different carrier concentrations, luminescence characteristics, and strains. The relation between PPC and OQ of PC was studied by exciting the samples with two beams of monochromatic radiation of various wavelengths and intensities. The PPC was found to be excited by the first beam with a threshold at 2.0 eV, while the second beam induces OQ of PC in a wide range of photon energies with a threshold at 1.0 eV. The obtained results are explained on the basis of a model combining two previously put forward schemes with electron traps playing the main role in PPC and hole traps inducing OQ of PC. The possible nature of the defects responsible for optical metastability of GaN is discussed. © 2003 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Boron and phosphorus diffusion in strained and relaxed Si and SiGe

N. R. Zangenberg, J. Fage-Pedersen, J. Lundsgaard Hansen, and A. Nylandsted Larsen

J. Appl. Phys. 94, 3883 (2003); http://dx.doi.org/10.1063/1.1602564 (8 pages) | Cited 51 times

Online Publication Date: 29 August 2003

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The diffusion of boron and phosphorus has been investigated in SiGe grown by molecular beam epitaxy. The analysis was done in relaxed Si1−xGex for x=0, 0.01, 0.12, and 0.24 for B and x=0, 0.07, 0.12, 0.24, and 0.40 for P. B diffusion in relaxed samples shows little effect of changing the Ge content while for P diffusion, increasing Ge content increases the diffusion coefficient from Si up to Si0.76Ge0.24. This is explained by a pairing of B and Ge atoms retarding the diffusion. B diffusion in compressively strained Si0.88Ge0.12 and Si0.76Ge0.24 and tensile strained Si and Si0.88Ge0.12 was also investigated. Compressive strain was found to decrease the diffusion coefficient of B and tensile strain to increase it. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities

Lateral ion transport in nematic liquid-crystal devices

K. Neyts, S. Vermael, C. Desimpel, G. Stojmenovik, A. R. M. Verschueren, D. K. G. de Boer, D. K. G. de Boer, R. Snijkers, P. Machiels, and A. van Brandenburg

J. Appl. Phys. 94, 3891 (2003); http://dx.doi.org/10.1063/1.1604453 (6 pages) | Cited 15 times

Online Publication Date: 29 August 2003

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Liquid crystals used in electronic displays usually contain small amounts of ions that move under the influence of the varying applied electric field. It is well known that the motion of ions perpendicular to the substrates may lead to modified electric fields resulting in image sticking effects. During operation, the modulation in the director tilt angle can also lead to a net residual lateral component of the ion motion, parallel with the glass plates. A sustained ac driving voltage will accumulate the lateral ion motion and may result in image sticking effects near the pixel edge. Such effects have indeed been observed in supertwisted nematic cells. © 2003 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
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