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1 Oct 2001

Volume 90, Issue 7, pp. 3135-3665

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Linear phase demodulation in photorefractive crystals with nonlocal response

Kimmo Päiväsaari, Alexei A. Kamshilin, Victor V. Prokofiev, Boris Sturman, Gabriel F. Calvo, Mercedes Carrascosa, and Fernando Agullo-Lopez

J. Appl. Phys. 90, 3135 (2001); http://dx.doi.org/10.1063/1.1397280 (7 pages) | Cited 4 times

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On the basis of the vectorial theory of light diffraction in cubic photorefractive crystals, we derive analytical expressions to describe the output intensities and polarization states of two coherent beams coupled via a dynamic index grating and subjected at the input to a fast phase modulation. It is shown that the linear transformation of fast phase excursions into intensity modulation can be achieved in the case of a nonlocal ac response by means of proper polarization filtering. Theoretical results are supported by the data obtained in experiments with Bi12TiO20 crystals of different orientations. The polarization technique is used for the evaluation of the space-charge fields created in different crystals. © 2001 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Ja Polarization
42.25.Fx Diffraction and scattering

Photopolymer holographic recording material parameter estimation using a nonlocal diffusion based model

Justin R. Lawrence, Feidhlim T. O’Neill, and John T. Sheridan

J. Appl. Phys. 90, 3142 (2001); http://dx.doi.org/10.1063/1.1396824 (7 pages) | Cited 16 times

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It has recently been shown [Sheridan and Lawrence, J. Opt. Soc. Am. A 17, 1108 (2000)] that by introducing a nonlocal response function into the one-dimensional diffusion equation governing holographic grating formation in photopolymers, both high frequency and low frequency cutoffs in the spatial frequency response of photopolymer materials can be deduced. Starting with this result, analytic solutions to this equation are derived assuming a two harmonic expansion of the monomer concentration. These expressions are first compared to the more rigorous four harmonic numerical results, indicating the range of physical parameters for which they are accurate. They are then compared to the experimental diffraction intensity growth curves produced during the formation of sinusoidal gratings recorded with different spatial frequencies. Fitting these curves using the analytic expressions, various material parameters, including the monomer diffusion constant, D, and the nonlocal variance, σ, can be estimated. Trends in material behavior as the grating spatial frequency is changed are discussed. © 2001 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.70.Jk Polymers and organics
42.40.Eq Holographic optical elements; holographic gratings

Time dependent analysis of the formation of a half-period surface relief grating on amorphous azopolymer films

F. Lagugné Labarthet, T. Buffeteau, and C. Sourisseau

J. Appl. Phys. 90, 3149 (2001); http://dx.doi.org/10.1063/1.1399025 (10 pages) | Cited 18 times

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The formation of a surface relief grating (SRG) on amorphous copolymer films containing azobenzene chromophores in side chain positions is conducted using two linearly polarized interfering beams with orthogonal polarization directions (p+s). Time dependent analyses of the diffraction efficiency were carried out by measuring simultaneously the transmitted zero order (I(0)) as well as the first (I(±1)) and second (I(±2)) diffracted orders. Two main contributions to the diffraction efficiency are evidenced: an anisotropic (birefringence) part coming from the normal period grating plus another anisotropic and surface relief part (SRG) due to the half-period grating. The origin of the weak amplitude SRG stems from the interference of particular I(±1) diffracted orders, whose resulting polarization and angular Bragg’s conditions are in accordance with the existence of a double frequency modulation. Using the matricial products of Jones, theoretical expressions of transmitted and diffracted orders are thus derived. Extracted values of the phase shifts and, therefore, of the birefringence (Δn,Δn′) and surface relief amplitude (2Δd) are then compared to data from optical and topographic atomic force microscopy measurements. Time dependent calculations of these relevant parameters as well as analyses of the polarization states of transmitted and diffracted orders are in good agreement with the proposed model. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
78.66.Qn Polymers; organic compounds
42.79.Dj Gratings
68.55.-a Thin film structure and morphology

Laser performance of pyrromethene 567 dye in solid polymeric matrices with different cross-linking degrees

A. Costela, I. García-Moreno, C. Gómez, O. Garcia, and R. Sastre

J. Appl. Phys. 90, 3159 (2001); http://dx.doi.org/10.1063/1.1398598 (8 pages) | Cited 21 times

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We report on the laser action of pyrromethene 567 (PM567) incorporated into copolymers of methyl methacrylate (MMA) with different methacrylic and acrylic cross-linking monomers: ethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, tetraethyleneglycol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate (PETRA). The vol/vol proportion of the different co-monomers in each copolymer formulation was systematically varied, and the effect of each composition on the lasing properties of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5 mJ/pulse from a frequency doubled Q-switched Nd:KGW laser. Lasing efficiencies of up 26% and good stability with a drop of the initial laser output of 30% after 100 000 pump pulses at 5 Hz in P(MMA:PETRA 95:5) were demonstrated. © 2001 American Institute of Physics.
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42.55.Mv Dye lasers
42.70.Hj Laser materials
42.70.Jk Polymers and organics
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Growth and holographic characterization of nonstoichiometric sillenite-type crystals

H. Vogt, K. Buse, H. Hesse, E. Krätzig, and R. R. García

J. Appl. Phys. 90, 3167 (2001); http://dx.doi.org/10.1063/1.1400095 (7 pages) | Cited 17 times

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We have grown Bi12GeO20 and Bi12SiO20 single crystals from melts with different GeO2 and SiO2 contents, respectively, to investigate the influence of an intrinsic defect, the antisite defect (Bi on Ge or Si site), on the light-induced charge transport. The optical absorption and the effective trap density of the crystals increase with decreasing GeO2 and SiO2 content in the melt. Furthermore, a variation of the photoconductivity is observed. Our results can be described by a one-center model with the antisite defect Bi3+/4+ on Ge or Si site as dominant photorefractive center. © 2001 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
42.70.Ln Holographic recording materials; optical storage media
78.20.-e Optical properties of bulk materials and thin films
72.40.+w Photoconduction and photovoltaic effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.72.J- Point defects and defect clusters
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Role of metallic neutrals and gaseous molecular ions in a copper cathodic arc operated with oxygen gas

A. Lepone, H. Kelly, and A. Márquez

J. Appl. Phys. 90, 3174 (2001); http://dx.doi.org/10.1063/1.1397290 (8 pages) | Cited 9 times

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The plasma-neutral gas structure generated in a copper cathodic arc operated with oxygen gas at a constant current level of 100 A has been investigated by employing a Langmuir spherical probe and a calorimetric technique. The plasma potential and electron temperature at several axial distances (between 10 and 25 cm) from the cathode surface and for different O2 pressure values (between 0.5 and 5 Pa) have been measured. A simplified one-dimensional model which incorporates the relevant atomic processes of the problem (charge-exchange, lateral diffusion loses, electron impact ionization, and dissociative recombination) is developed. This model allows calculating densities and drift velocities of the different species and, in particular, predicts the creation of a considerable number of metallic neutrals and gaseous ions. A comparison of the experimental ion saturation probe current and the heat source term derived from the calorimetric measurements with the corresponding quantities predicted by the model is performed. We found good agreement between theory and experiment, notwithstanding the fact that the physical quantities presented large variations, and the atomic reaction rates varied for several orders of magnitude, over the range of gas pressure and axial position values investigated. © 2001 American Institute of Physics.
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52.80.Vp Discharge in vacuum
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
52.25.Fi Transport properties
52.70.-m Plasma diagnostic techniques and instrumentation
52.20.-j Elementary processes in plasmas

Optical actinometry of Cl2, Cl, Cl+, and Ar+ densities in inductively coupled Cl2–Ar plasmas

N. C. M. Fuller, Irving P. Herman, and Vincent M. Donnelly

J. Appl. Phys. 90, 3182 (2001); http://dx.doi.org/10.1063/1.1391222 (10 pages) | Cited 32 times

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Optical emission (OE) actinometry has been used to measure the absolute densities of Cl2, Cl, Cl+, and Ar+ in a high-density inductively coupled (ICP) Cl2–Ar plasma at 18 mTorr as a function of the 13.56 MHz radio frequency (rf) power and Ar fraction. The fractional dissociation of Cl2 to Cl increases with rf power, with the dissociated fraction increasing from 78% to 96% at 600 W (10.6 W cm−2) as the Ar fraction increases from 1% to 78% due to an increase in electron temperature. Emission from Cl+∗ and Ar+∗ originates primarily from electron excitation of Cl+ and Ar+ (and not excitation of Cl and Ar), making actinometric determination of Cl+ and Ar+ densities feasible. For powers exceeding 600 W, the neutral (Cl2 and Cl) to ion (Cl+ and Ar+) flux ratio is found to be strongly dependent on Ar fraction, decreasing by a factor of ∼3.0 as the latter is increased from 13% to 78%. This dependence can be attributed mostly to the decrease in Cl density and relatively little to the small decrease in the total positive ion density from 1.8×1011 to 1.4×1011 cm−3, over the same range. OE spectroscopy is also used to estimate the rate constant for the dissociative excitation of Cl2 to the Cl (4p2D0J′=3/2,5/2) excited state with emission at 822.2 nm, yielding ∼10−13 cm3 s−1. © 2001 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.80.Pi High-frequency and RF discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Pm Rate constants, reaction cross sections, and activation energies

Density and temperature sensitive line ratios in plasmas generated by laser ablation

E. Pérez-Tijerina, J. Bohigas, and R. Machorro

J. Appl. Phys. 90, 3192 (2001); http://dx.doi.org/10.1063/1.1397281 (8 pages) | Cited 6 times

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Solving the statistical equilibrium equations we find line intensity ratios of C III, N III, O III, Si III, and Al III in the visible and ultraviolet range, that are sensitive to electron density and/or temperature in the regime commonly found in pulsed laser deposition. For thin film deposition, the plasma density is between 1012 and 1018 cm−3 and the temperature is close to 104 K. Our results are consistent with experimental data on Al II and Al III, previously reported in the literature. These line intensity ratios are a promising tool to diagnose the physical state of plasmas generated through laser ablation in thin film deposition techniques. © 2001 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.-b Plasma properties

Relaxation effect of electron inertial delay in an ion-beam plasma system

C. B. Dwivedi and Ram Prakash

J. Appl. Phys. 90, 3200 (2001); http://dx.doi.org/10.1063/1.1397284 (5 pages) | Cited 8 times

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In this article an interesting result has been reported to highlight the physical implication of finite nonzero electron inertial delay in acoustic oscillations of an ion-beam plasma system. A simple fluid model has been used to demonstrate the excitation of relaxation type resonant instability on the electron inertial delay time scale. Physical arguments have been included to understand and explain the driving mechanism of the instability and its utility to comprehend the ion-beam driven oscillations in plasma sheath experiments. The physical nature and origin of the potential relaxation instability has been correlated to the electron inertial delay effect in the ion current carrying plasma system. © 2001 American Institute of Physics.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Kh Plasma sheaths

Effect of Ar addition to an O2 plasma in an inductively coupled, traveling wave driven, large area plasma source: O2/Ar mixture plasma modeling and photoresist etching

K. Takechi and M. A. Lieberman

J. Appl. Phys. 90, 3205 (2001); http://dx.doi.org/10.1063/1.1398600 (7 pages) | Cited 31 times

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We report on the effect of Ar addition to an O2 plasma on photoresist etching in an inductively coupled, traveling wave driven, large area plasma source (LAPS). We also develop a simplified spatially varying O2/Ar mixture discharge model corresponding to the LAPS in a two-dimensional geometry in order to account for the effect of Ar addition. A photoresist etch kinetics model and spatially varying O2/Ar mixture discharge model are used to explain the experimental data. We find that the addition of 50% Ar increases the plasma density and etch rate approximately by a factor of 2. From the simulation we find that argon metastables (Ar∗) play an important role in the mixture plasma. The simulation predicts an enhancement in O-atom density due to Ar addition, even in the presence of dilution of the feed gas. The experimental data and predicted etch rates from the simulation are generally in good agreement, indicating that the increase in the etch rate with Ar addition is due to both the increase in the plasma density and the enhancement in O-atom density attributable to the dissociation of O2 by Ar∗. © 2001 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
52.50.Dg Plasma sources
52.65.-y Plasma simulation
81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.20.Pm Rate constants, reaction cross sections, and activation energies
52.25.-b Plasma properties
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Wt Computational modeling; simulation
52.77.Bn Etching and cleaning

Single-gap pseudospark discharge experiments

H. Yin, W. He, A. W. Cross, A. D. R. Phelps, and K. Ronald

J. Appl. Phys. 90, 3212 (2001); http://dx.doi.org/10.1063/1.1398065 (7 pages) | Cited 7 times

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An experimental investigation of a single-gap pseudospark was conducted using a flexible discharge chamber. The voltage breakdown characteristics were studied against a wide range of parameters such as gas pressure, gap separation, cathode cavity depth, cathode aperture size, external capacitance and applied voltage. An empirical formula, VB=(0.20±0.05) p−4.02±0.18 d−1.77±0.01, was obtained for the breakdown voltage VB in kV, given the gas pressure p in Torr and the gap separation d in mm. The electron beam extracted from this single gap was also studied and a current of up to 100 A was measured at 10 kV. © 2001 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
07.77.Ka Charged-particle beam sources and detectors
29.25.-t Particle sources and targets
41.75.Fr Electron and positron beams
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Onset of slip in silicon containing oxide precipitates

K. Jurkschat, S. Senkader, P. R. Wilshaw, D. Gambaro, and R. J. Falster

J. Appl. Phys. 90, 3219 (2001); http://dx.doi.org/10.1063/1.1398596 (7 pages) | Cited 15 times

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We report a study of the behavior of dislocations at oxide precipitates in (001) Czochralski silicon wafers for different oxide-precipitate sizes (100–600 nm), densities (108−1011 cm−3), and background oxygen concentrations (7.7×1017−10.35×1017 cm−3) using a bending technique with annular knife edges causing a biaxial stress distribution in the samples. The main advantage of the method we use is the possibility of detecting single slip events that may be caused by precipitates with special properties. We found that the stress level at which dislocation movement can be detected around precipitates depends mainly on the mean-precipitate diameter. The stress threshold at which dislocations begin to move can be increased by a thermal treatment prior to application of an external stress. This effect is due to the diffusion of oxygen to the dislocations causing a locking effect and shows that the dislocations are associated with the oxide precipitates prior to any external stress being applied. It has been shown that such heat treatments can lead to a mechanical strengthening of the wafers in certain circumstances. © 2001 American Institute of Physics.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.F- Deformation and plasticity
66.30.J- Diffusion of impurities
66.30.Lw Diffusion of other defects
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.40.Lm Deformation, plasticity, and creep
61.72.Cc Kinetics of defect formation and annealing

Surface smoothing by energetic cluster impact

Oliver Rattunde, Michael Moseler, Andreas Häfele, Jürgen Kraft, Daniel Rieser, and Hellmut Haberland

J. Appl. Phys. 90, 3226 (2001); http://dx.doi.org/10.1063/1.1398067 (6 pages) | Cited 19 times

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This article reports on experimental observations of surface smoothing by high energy cluster impact. Thin films have been produced by energetic cluster impact deposition (ECI), and the surface roughness and the power spectrum of the films have been measured by atomic force microscopy. By depositing large metal clusters onto an initially rough substrate, the surface roughness is significantly reduced. On the other hand, the roughness of initially smooth surfaces increases only logarithmically. Results for both surface roughness and power spectrum can be quantitatively explained by a recently developed mesoscopic model for the ECI process employing a stochastic differential equation. In this model the smoothing effect results from a downhill particle current (consisting of both cluster and surface atoms) transferring the higher lying parts of the surface profile into the valleys. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology

Elastic relaxation of truncated pyramidal quantum dots and quantum wires in a half space: An analytical calculation

Frank Glas

J. Appl. Phys. 90, 3232 (2001); http://dx.doi.org/10.1063/1.1394158 (10 pages) | Cited 25 times

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We give a fully analytical solution for the elastic displacement and strain fields of arbitrarily shaped truncated pyramidal quantum dots (QDs) and trapezoidal quantum wires buried in a half space, assuming linear isotropic elasticity. The half-space geometry pertains in particular to QD semiconductor structures both during and after growth. The calculations are illustrated by examples showing quantitatively that with respect to the case of the infinite matrix and depending on the depth of the QD under the free surface the strain relaxation afforded by this surface may significantly affect the magnitude and the distribution of the various strain components inside the QD as well as in the matrix. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity

Direct observation of structural changes in organic light emitting devices during degradation

Dmitry Kolosov, Douglas S. English, Vladimir Bulovic, Paul F. Barbara, Stephen R. Forrest, and Mark E. Thompson

J. Appl. Phys. 90, 3242 (2001); http://dx.doi.org/10.1063/1.1389760 (6 pages) | Cited 44 times

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A method for studying the degradation of organic light emitting devices (OLEDs) in real time is described. Transparent OLEDs allow for the spatial correlation of cathode topographic images with optical images (transmission, photoluminescence, and electroluminescence) of the devices throughout the degradation process. In this study we focused on the evolution of nonemissive, “dark” spots during device operation. We conclude that the electroluminescent dark spots originate as nonconductive regions at the cathode/organic interface and expand or grow as a result of exposure to atmosphere. We propose a mechanism of dark spot growth involving aerobic oxidation of the cathode/organic interfacial region, leading to a highly resistive, carrier blocking interface at the dark spot locations. No initial defects on the cathode surface, which might be responsible for the formation of dark spots, were detected by atomic force microscopy. Structural changes, such as degradation of organic materials and the cathode surface, occur well after the formation and growth of the dark spots. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.65.Mq Oxidation
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.66.Qn Polymers; organic compounds
78.55.-m Photoluminescence, properties and materials
78.60.Fi Electroluminescence
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Cubic boron nitride thin film heteroepitaxy

H. Feldermann, C. Ronning, H. Hofsäss, Y. L. Huang, and M. Seibt

J. Appl. Phys. 90, 3248 (2001); http://dx.doi.org/10.1063/1.1392957 (7 pages) | Cited 17 times

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In this study we investigate the possibility of nucleating nanocrystalline cubic boron nitride (c-BN) thin films directly onto suitable substrates without the soft turbostratic BN (t-BN) interlayer that is usually observed. This would open a path to the epitaxial growth of c-BN films which is essential particularly for practicable applications in electronic devices. Appropriate substrates are required to exhibit a lattice that matches the c-BN crystallite structure, survives the ion bombardment imperative for c-BN film formation, and is not disturbed by the development of a heterogeneous interface layer. In accordance with these criteria, monocrystalline AlN is selected and employed as a potential substrate for direct c-BN film growth using mass selected ion beam deposition. A detailed examination of the BN/AlN interface microstructure by cross-sectional high-resolution transmission electron microscopy reveals that the AlN crystallinity is indeed retained, with no amorphous layer next to the BN film as commonly observed on Si substrates. Nanocrystalline BN grains with the cubic, and, more frequently, with the wurtzitic structure are found in direct contact with certain regions of the rugged AlN substrate, covering about one-third of its entire surface with no mediating t-BN or other interface layer. The c-BN and w-BN growth areas are textured and exhibit definite preferential orientation relationships with the faceted AlN substrate surface. The consequences of these findings for the understanding of the role of the t-BN interlayer in c-BN film nucleation are discussed. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Jj Ion and electron beam-assisted deposition; ion plating

X-ray diffraction analysis of a selectively grown InGaAsP epitaxial layer

Kiichi Nakashima and Yoshihiro Kawaguchi

J. Appl. Phys. 90, 3255 (2001); http://dx.doi.org/10.1063/1.1396830 (8 pages) | Cited 3 times

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We analyzed compositional fluctuation with lattice relaxation in a selectively grown InGaAsP epilayer by x-ray diffraction measurement. A simple and deterministic analysis procedure is described for analyzing the distribution of lattice constants (Δa⊥,Δa∥). The method is based on the systematic analysis of hkl-dependence of x-ray peak profiles. The method makes the direct observation of the distribution of lattice constants easier and is suitable for analysis of selectively grown samples. The method is applicable to a selectively grown InGaAsP epilayer with a small strain under a dislocation-free condition. Clear lattice relaxation is experimentally confirmed in the epilayer and is identified as the elastic relaxation that is caused by the three-dimensional shape of the selectively grown region. This is a direct observation of elastic relaxation in a selectively grown dislocation-free structure by x-ray diffraction measurement. Distributions of both perpendicular and parallel lattice constants are estimated from the x-ray data. The result shows that both the composition and relaxation rate fluctuate in the sample. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Thin films of the spinel Cd1+xIn2−2xSnxO4 transparent conducting oxide solution

D. R. Kammler, T. O. Mason, D. L. Young, and T. J. Coutts

J. Appl. Phys. 90, 3263 (2001); http://dx.doi.org/10.1063/1.1399027 (6 pages) | Cited 7 times

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Thin films of a transparent conducting oxide solid solution Cd1+xIn2−2xSnxO4 (x=0.15, 0.45, and 0.70) were deposited via rf magnetron sputtering. X-ray diffraction indicated the films consisted of a polycrystalline spinel phase. Atomic force microscopy measurements revealed a surface root mean square roughness between 1.3 and 6.0 nm. Optical absorption was 10% or less in the visible for x=0.15, 0.45, and 0.70. Optical gaps averaged near 3.5, 3.70, and 3.65 eV for films annealed in Ar/CdS of compositions corresponding to x=0.15, 0.45, and 0.70. Conductivity exceeded 2000 S/cm for x=0.15 and 4000 S/cm for x=0.45 and 0.70. Mobilities of 43, 50, and 56 cm2/V s were measured for films annealed in Ar/CdS of compositions corresponding to x=0.15, 0.45, and 0.70, respectively. Composition data obtained via electron probe microanalysis indicate the films are becoming Cd deficient during the annealing process. This suggests an excess of In+3 and/or Sn+4 on Cd+2 sites may play a role in carrier production in these films. The Cd volatilization may also inhibit crystallization and decrease mobility. © 2001 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
81.15.Cd Deposition by sputtering
68.35.Dv Composition, segregation; defects and impurities

Measurement and analysis of nonhydrostatic lattice strain component in niobium to 145 GPa under various fluid pressure-transmitting media

Anil K. Singh and Takemura Kenichi

J. Appl. Phys. 90, 3269 (2001); http://dx.doi.org/10.1063/1.1397283 (7 pages) | Cited 26 times

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The d spacings in niobium have been measured to 145 GPa with a diamond anvil cell using a fluid pressure-transmitting medium [methanol–ethanol–water (MEW) mixture, or helium]. The conventional geometry, wherein the primary x-ray beam passes parallel to the load axis with image plate, has been used to record the diffraction patterns. The analysis of the d spacings using the lattice strain equations indicates the presence of nonhydrostatic stress component (with both MEW and He pressure-transmitting media) in the pressure ranges that are well below the freezing pressure of the pressure-transmitting medium. A method to correct the measured d spacings for the nonhydrostatic pressure effect is suggested. This study clearly emphasizes the need to carefully analyze the data for the nonhydrostatic compression effects even if the experiments are performed with fluid pressure-transmitting medium. © 2001 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.-x Mechanical properties of solids

Measurement of the in-depth stress profile in hydrogenated microcrystalline silicon thin films using Raman spectrometry

V. Paillard, P. Puech, R. Sirvin, S. Hamma, and P. Roca i Cabarrocas

J. Appl. Phys. 90, 3276 (2001); http://dx.doi.org/10.1063/1.1396828 (4 pages) | Cited 18 times

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Raman spectrometry is used to measure stress in hydrogenated microcrystalline silicon thin films. Moreover, by the use of different excitation wavelengths, from red to near ultraviolet, we can probe different film depths and get information on the stress distribution along the growth direction. For films deposited by standard rf glow discharge at different substrate temperatures, on glass substrates, we found large stress gradients. Indeed, the high compressive stress (up to 1 GPa) in the bulk of the film, close to the glass substrate, reduces and becomes tensile as the film free surface is approached. Moreover, the higher the substrate temperature, the higher the stress gradient. © 2001 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Compressibility of nanostructured alumina phases determined from synchrotron x-ray diffraction studies at high pressure

J. Zhao, G. R. Hearne, M. Maaza, F. Laher-Lacour, M. J. Witcomb, T. Le Bihan, and M. Mezouar

J. Appl. Phys. 90, 3280 (2001); http://dx.doi.org/10.1063/1.1394915 (6 pages) | Cited 14 times

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Synchrotron x-ray diffraction studies up to pressures of 30 GPa have been performed on both nanostructured γ-Al2O3 and α-Al2O3. The P-V equation of state has been calculated from a fit to the diffraction data to obtain the compressibility for each of the compounds. The bulk modulus B0 of nanostructured γ-Al2O3 having grain-size diameters in the range 4 – 8 nm is B0 =152(8) GPa, appreciably lower than the value B0≈250 GPa of its bulk structural analog. The bulk-modulus of nanophase α-Al2O3 of 25 nm average crystallite diameter, which is difficult to stabilize at smaller dimensions because of thermodynamic considerations, is 252(9) GPa and therefore similar to that of bulk α-Al2O3. These studies suggest that only if the grain-size of alumina is below a critical value of several nanometers can substantial changes be expected in the isothermal bulk modulus compared to that of the isostructural bulk compound. © 2001 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Functionalization of silicon step arrays I: Au passivation of stepped Si(111) templates

A. Kirakosian, J.-L. Lin, D. Y. Petrovykh, J. N. Crain, and F. J. Himpsel

J. Appl. Phys. 90, 3286 (2001); http://dx.doi.org/10.1063/1.1397288 (5 pages) | Cited 14 times

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The growth mode of Au on stepped Si(111)7×7 surfaces is determined by scanning tunneling microscopy, with the goal of providing a continuous gold layer that replicates the step morphology. Functionalization with gold allows attaching organic and biomolecules via thiol groups (e.g., alkanes and DNA). On clean Si(111), gold grows in the Stranski–Krastanov mode and produces islands with a size comparable to the step spacing. A Ti wetting layer produces smooth Au films that preserve the step topography down to a scale of a few nanometers. © 2001 American Institute of Physics.
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81.65.Rv Passivation
81.05.Cy Elemental semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Mn Adsorption kinetics
68.08.Bc Wetting

Functionalization of silicon step arrays II: Molecular orientation of alkanes and DNA

J. N. Crain, A. Kirakosian, J.-L. Lin, Yuedong Gu, Rahul R. Shah, Nicholas L. Abbott, and F. J. Himpsel

J. Appl. Phys. 90, 3291 (2001); http://dx.doi.org/10.1063/1.1397297 (5 pages) | Cited 14 times

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Alkanes and DNA are adsorbed via thiol groups on ultrathin gold films that have been templated on stepped Si(111)7×7 surfaces. The orientation of the adsorbed molecules is determined by polarization-dependent near edge x-ray absorption fine structure spectroscopy from the C 1s and N 1s core levels. An anisotropy in the polar distribution is found which is consistent with models in which the molecules have a preferred tilt angle with respect to normal but a random azimuthal distribution. In order to obtain maximum coverage and an oriented overlayer it is necessary to deposit more than 3 nm of Au (12 monolayers). © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
87.14.G- Nucleic acids
78.70.Dm X-ray absorption spectra
68.43.Fg Adsorbate structure (binding sites, geometry)
87.15.H- Dynamics of biomolecules

Thermal diffusivity measurements in liquids using signal common-mode-rejection demodulation in a thermal-wave cavity

J. A. Balderas-López and Andreas Mandelis

J. Appl. Phys. 90, 3296 (2001); http://dx.doi.org/10.1063/1.1402136 (5 pages) | Cited 6 times

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A recently developed signal common-mode rejection demodulation signal methodology [Mandelis et al., Rev. Sci. Instrum. 71, 2440 (2000)] has been used to make direct absolute thermal diffusivity measurements in liquids using a thermal-wave cavity. This methodology combines the precision of the thermal-wave cavity scan and the flexibility of modulation-frequency scan modes, along with baseline suppression, yielding a high-resolution technique for thermal diffusivity measurements in liquids. The thermal diffusivity of two pure liquids (distilled water and ethylene glycol) has been measured and good agreement has been obtained with values reported in the literature. © 2001 American Institute of Physics.  
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66.25.+g Thermal conduction in nonmetallic liquids
07.20.-n Thermal instruments and apparatus

Structural properties of ZnSe epilayers on (111) GaAs

A. G. Kontos, N. Chrysanthakopoulos, M. Calamiotou, T. Kehagias, P. Komninou, and U. W. Pohl

J. Appl. Phys. 90, 3301 (2001); http://dx.doi.org/10.1063/1.1398593 (7 pages) | Cited 3 times

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Structural and optical studies of ZnSe epilayers, which were grown on the B side of (111)-oriented GaAs substrates, indicate the presence of tensile in-plane strains in the epilayers at room temperature. Electron microscopy observations showed that the ZnSe epilayer forms a coherent sharp interface with the GaAs substrate and consists of crystallites which are grown in epitaxial or twin orientation with respect to the substrate, having the (111) planes oriented parallel to the interface. In addition, embedded twins are observed within the epilayer. The twin boundaries are, generally, terminated by Shockley partial dislocations, which are expected to relax the compressive lattice mismatch strain. Plastic or thermal relaxation cannot account for sign and magnitude of the observed strains. Evidence is found that the observed tensile strains are piezoelectrically induced in a depletion layer, due to Fermi level pinning at the ZnSe/GaAs interface. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
61.72.Mm Grain and twin boundaries
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
73.20.At Surface states, band structure, electron density of states
77.65.-j Piezoelectricity and electromechanical effects
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