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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 041901 (2010); http://dx.doi.org/10.1063/1.3474648 (2 pages)

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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back to top Plasmas and Electrical Discharges

Pressure and arc voltage coupling in dc plasma torches: Identification and extraction of oscillation modes

V. Rat and J. F. Coudert

J. Appl. Phys. 108, 043304 (2010); http://dx.doi.org/10.1063/1.3466982 (8 pages) | Cited 4 times

Online Publication Date: 19 August 2010

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This work is devoted to the instabilities occurring in a plasma torch, such as those found in plasma spraying. These instabilities are responsible for a lack of reproducibility of coatings properties, especially in the case of suspension plasma spraying that is an innovative way to obtain thin coatings of submicron-sized particles. Strong Helmholtz oscillations are highlighted in the plasma flow and it is demonstrated that they overlap with different acoustic modes in addition with the more commonly admitted “restrike” mode, the later being due to rearcing events in the arc region. The instabilities occur in the arc voltage but it is experimentally shown in this paper that the pressure within the torch body presents the same kind of instabilities. Besides, a numerical filtering technique has been adapted to isolate the different instability components. The operating parameters of the plasma torch were varied in order to highlight their influence on the amplitude of the different modes, both for the arc voltage and the pressure.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.75.Hn Plasma torches
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.-q Plasma dynamics and flow
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.-b Plasma properties

Time-resolved investigation of dual high power impulse magnetron sputtering with closed magnetic field during deposition of Ti–Cu thin films

Vitezslav Stranak, Martin Cada, Zdenek Hubicka, Milan Tichy, and Rainer Hippler

J. Appl. Phys. 108, 043305 (2010); http://dx.doi.org/10.1063/1.3467001 (8 pages) | Cited 11 times

Online Publication Date: 19 August 2010

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Time-resolved comparative study of dual magnetron sputtering (dual-MS) and dual high power impulse magnetron sputtering (dual-HiPIMS) systems arranged with closed magnetic field is presented. The dual-MS system was operated with a repetition frequency 4.65 kHz (duty cycle ≈ 50%). The frequency during dual-HiPIMS is lower as well as its duty cycle (f = 100 Hz, duty 1%). Different metallic targets (Ti, Cu) and different cathode voltages were applied to get required stoichiometry of Ti–Cu thin films. The plasma parameters of the interspace between magnetrons in the substrate position were investigated by time-resolved optical emission spectroscopy, Langmuir probe technique, and measurement of ion fluxes to the substrate. It is shown that plasma density as well as ion flux is higher about two orders of magnitude in dual-HiPIMS system. This fact is partially caused by low diffusion of ionized sputtered particles (Ti+,Cu+) which creates a preionized medium.
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81.15.Cd Deposition by sputtering
68.55.at Other materials
52.77.Dq Plasma-based ion implantation and deposition
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties

Growth model of binary alloy nanopowders for thermal plasma synthesis

Masaya Shigeta and Takayuki Watanabe

J. Appl. Phys. 108, 043306 (2010); http://dx.doi.org/10.1063/1.3464228 (15 pages) | Cited 8 times

Online Publication Date: 23 August 2010

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A new model is developed for numerical analysis of the entire growth process of binary alloy nanopowders in thermal plasma synthesis. The model can express any nanopowder profile in the particle size-composition distribution (PSCD). Moreover, its numerical solution algorithm is arithmetic and straightforward so that the model is easy to use. By virtue of these features, the model effectively simulates the collective and simultaneous combined process of binary homogeneous nucleation, binary heterogeneous cocondensation, and coagulation among nanoparticles. The effect of the freezing point depression due to nanoscale particle diameters is also considered in the model. In this study, the metal–silicon systems are particularly chosen as representative binary systems involving cocondensation processes. In consequence, the numerical calculation with the present model reveals the growth mechanisms of the Mo–Si and Ti–Si nanopowders by exhibiting their PSCD evolutions. The difference of the materials’ saturation pressures strongly affects the growth behaviors and mature states of the binary alloy nanopowder.
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81.07.Wx Nanopowders
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
52.77.Dq Plasma-based ion implantation and deposition
82.70.-y Disperse systems; complex fluids
81.16.-c Methods of micro- and nanofabrication and processing

Stages in the interaction of deuterium atoms with amorphous hydrogenated carbon films: Isotope exchange, soft-layer formation, and steady-state erosion

G. S. Oehrlein, T. Schwarz-Selinger, K. Schmid, M. Schlüter, and W. Jacob

J. Appl. Phys. 108, 043307 (2010); http://dx.doi.org/10.1063/1.3474988 (13 pages) | Cited 5 times

Online Publication Date: 24 August 2010

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We report studies of the interactions of quantified deuterium (hydrogen) atom beams with hard amorphous hydrogenated carbon films at a substrate temperature of ∼ 330 K in an ultrahigh-vacuum chamber. The modification/erosion of a-C:H (a-C:D) films was monitored in situ by ellipsometry in real time. By interpreting the ellipsometric information and combining it with measurements of the absolute D areal density changes in the a-C:H (a-C:D) films by ion beam analysis as a function of D (H) atom fluence, we are able to distinguish three sequential stages of D interaction with hard a-C:H films. The first stage is replacement of bonded hydrogen by deuterium up to an areal density of ∼ 5×1015 D cm−2 to a depth of ∼ 1.4 nm from the surface. This phase is complete after a deuterium fluence of ≈ 2×1018 cm−2. The effective cross section for isotopic exchange of H with D atoms for the a-C:H layer is found to be σ = 2.0×10−18 cm2, and is close to the cross section for H abstraction from a carbon surface. This may indicate that H abstraction by D from the a-C:H surface is the rate limiting step for isotope exchange in this situation. Hydrogen replacement is followed by creation of additional C–D bonds in the near-surface region and increases the D areal density by about 2.5×1015 D cm−2. By ellipsometry this process can be observed as the formation of a soft a-C:D layer on top of the hard a-C:H bulk film, with the soft layer extending about 1.4 nm from the surface. This stage is complete after a deuterium fluence of about 2×1019 cm−2. Subsequently, steady-state erosion of the a-C:H film takes place. Here, a soft a-C:D layer with roughly constant thickness ( ∼ 1.4 nm) remains on the hard a-C:H substrate and is dynamically reformed as the underlying hard a-C:H film becomes thinner. A similar sequence of processes takes place at a substrate temperature of 650 K, albeit at a much faster rate.
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68.60.Wm Other nonelectronic physical properties
81.65.-b Surface treatments
68.55.-a Thin film structure and morphology
61.43.-j Disordered solids

Phase-shift effect in capacitively coupled plasmas with two radio frequency or very high frequency sources

Xiang Xu, Shu-Xia Zhao, Yu-Ru Zhang, and You-Nian Wang

J. Appl. Phys. 108, 043308 (2010); http://dx.doi.org/10.1063/1.3475376 (6 pages) | Cited 6 times

Online Publication Date: 25 August 2010

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A two-dimensional fluid model was built to study the argon discharge in a capacitively coupled plasma reactor and the full set of Maxwell equations is included in the model to understand the electromagnetic effect in the capacitive discharge. Two electrical sources are applied to the top and bottom electrodes in our simulations and the phase-shift effect is focused on. We distinguish the difference of the phase-shift effect on the plasma uniformity in the traditional radio frequency discharge and in the very high frequency discharge where the standing wave effect dominates. It is found that in the discharges with frequency 13.56 MHz, the control of phase difference can less the influence of the electrostatic edge effect, and it gets the best radial uniformity of plasma density at the phase difference π. But in the very high frequency discharges, the standing wave effect plays an important role. The standing wave effect can be counteracted at the phase difference 0, and be enhanced at the phase difference π. The standing wave effect and the edge effect are balanced at some phase-shift value between 0 and π, which is determined by discharge parameters.
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52.80.-s Electric discharges
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b Plasma properties
52.65.-y Plasma simulation

Dynamics of the plumes produced by ultrafast laser ablation of metals

T. Donnelly, J. G. Lunney, S. Amoruso, R. Bruzzese, X. Wang, and X. Ni

J. Appl. Phys. 108, 043309 (2010); http://dx.doi.org/10.1063/1.3475149 (13 pages) | Cited 10 times

Online Publication Date: 30 August 2010

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We have analyzed ultrafast laser ablation of a metallic target (Nickel) in high vacuum addressing both expansion dynamics of the various plume components (ionic and nanoparticle) and basic properties of the ultrafast laser ablation process. While the ion temporal profile and ion angular distribution were analyzed by means of Langmuir ion probe technique, the angular distribution of the nanoparticulate component was characterized by measuring the thickness map of deposition on a transparent substrate. The amount of ablated material per pulse was found by applying scanning white light interferometry to craters produced on a stationary target. We have also compared the angular distribution of both the ionic and nanoparticle components with the Anisimov model. While the agreement for the ion angular distribution is very good at any laser fluence (from ablation threshold up to ≈ 1 J/cm2), some discrepancies of nanoparticle plume angular distribution at fluencies above ≈ 0.4 J/cm2 are interpreted in terms of the influence of the pressure exerted by the nascent atomic plasma plume on the initial hydrodynamic evolution of the nanoparticle component. Finally, analyses of the fluence threshold and maximum ablation depth were also carried out, and compared to predictions of theoretical models. Our results indicate that the absorbed energy is spread over a length comparable with the electron diffusion depth Lc ( ≈ 30 nm) of Ni on the timescale of electron-phonon equilibration and that a logarithmic dependence is well-suited for the description of the variation in the ablation depth on laser fluence in the investigated range.
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52.38.Mf Laser ablation
52.70.Ds Electric and magnetic measurements
61.82.-d Radiation effects on specific materials
79.20.Eb Laser ablation
61.82.Bg Metals and alloys
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Growth kinetics of AlN and GaN films grown by molecular beam epitaxy on R-plane sapphire substrates

R. Chandrasekaran, T. D. Moustakas, A. S. Ozcan, K. F. Ludwig, L. Zhou, and David J. Smith

J. Appl. Phys. 108, 043501 (2010); http://dx.doi.org/10.1063/1.3475521 (4 pages) | Cited 4 times

Online Publication Date: 16 August 2010

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This paper reports the growth by molecular beam epitaxy of AlN and GaN thin films on R-plane sapphire substrates. Contrary to previous findings that GaN grows with its (11math0) A-plane parallel to the (1math02) R-plane of sapphire, our results indicate that the crystallographic orientation of the III-nitride films is strongly dependent on the kinetic conditions of growth for the GaN or AlN buffer layers. Thus, group III-rich conditions for growth of either GaN or AlN buffers result in nitride films having (11math0) planes parallel to the sapphire surface, and basal-plane stacking faults parallel to the growth direction. The growth of these buffers under N-rich conditions instead leads to nitride films with (11math6) planes parallel to the sapphire surface, with inclined c-plane stacking faults that often terminate threading dislocations. Moreover, electron microscope observations indicate that slight miscut ( ∼ 0.5°) of the R-plane sapphire substrate almost completely suppresses the formation of twinning defects in the (11math6) GaN films.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.J- Morphology of films
61.66.Fn Inorganic compounds
61.72.Nn Stacking faults and other planar or extended defects

Amorphous copper tungsten oxide with tunable band gaps

Le Chen, Sudhakar Shet, Houwen Tang, Kwang-soon Ahn, Heli Wang, Yanfa Yan, John Turner, and Mowafak Al-Jassim

J. Appl. Phys. 108, 043502 (2010); http://dx.doi.org/10.1063/1.3475714 (5 pages) | Cited 3 times

Online Publication Date: 16 August 2010

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We report on the synthesis of amorphous copper tungsten oxide thin films with tunable band gaps. The thin films are synthesized by the magnetron cosputtering method. We find that due to the amorphous nature, the Cu-to-W ratio in the films can be varied without the limit of the solubility (or phase separation) under appropriate conditions. As a result, the band gap and conductivity type of the films can be tuned by controlling the film composition. Unfortunately, the amorphous copper tungsten oxides are not stable in aqueous solution and are not suitable for the application of photoelectrochemical splitting of water. Nonetheless, it provides an alternative approach to search for transition metal oxides with tunable band gaps.
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81.05.Gc Amorphous semiconductors
81.15.Cd Deposition by sputtering
73.61.Jc Amorphous semiconductors; glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
68.55.ag Semiconductors

Nanoscale precipitation patterns in carbon–nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle

Gintautas Abrasonis, Thomas W. H. Oates, György J. Kovács, Jörg Grenzer, Per O. Å. Persson, Karl-Heinz H. Heinig, Andrius Martinavičius, Nicole Jeutter, Carsten Baehtz, Mark Tucker, Marcela M. M. Bilek, and Wolfhard Möller

J. Appl. Phys. 108, 043503 (2010); http://dx.doi.org/10.1063/1.3467521 (7 pages) | Cited 5 times

Online Publication Date: 16 August 2010

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Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed filtered cathodic vacuum arc. We reveal the role of the film composition, ion energy and incidence angle on the film morphology using transmission electron microscopy and grazing incidence small angle x-ray scattering. Under these growth conditions, phase separation occurs in a thin surface layer which has a high atomic mobility due to energetic ion impacts. This layer is an advancing reaction front, which switches to an oscillatory mode, producing periodic precipitation patterns. Our results show that the ion induced atomic mobility is not random, as it would be in the case of thermal diffusion but conserves to a large extent the initial direction of the incoming ions. This results in a tilted pattern under oblique ion incidence. A dependence of the nanopattern periodicity and tilt on the growth parameters is established and pattern morphology control via ion velocity is demonstrated.
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68.55.aj Insulators
64.75.Jk Phase separation and segregation in nanoscale systems
64.75.St Phase separation and segregation in thin films
81.16.Rf Micro- and nanoscale pattern formation
78.70.Ck X-ray scattering
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Structural, electrical, and optical properties of atomic layer deposition Al-doped ZnO films

Parag Banerjee, Won-Jae Lee, Ki-Ryeol Bae, Sang Bok Lee, and Gary W. Rubloff

J. Appl. Phys. 108, 043504 (2010); http://dx.doi.org/10.1063/1.3466987 (7 pages) | Cited 43 times

Online Publication Date: 17 August 2010

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Al-doped ZnO (AZO) films of ∼ 100 nm thickness with various Al doping were prepared at 150 °C by atomic layer deposition on quartz substrates. At low Al doping, the films were strongly textured along the [100] direction, while at higher Al doping the films remained amorphous. Atomic force microscopy results showed that Al–O cycles when inserted in a ZnO film, corresponding to a few atomic percent Al, could remarkably reduce the surface roughness of the films. Hall measurements revealed a maximum mobility of 17.7 cm2/V s. Film resistivity reached a minima of 4.4×10−3 Ω cm whereas the carrier concentration reached a maxima of 1.7×1020 cm−3, at 3 at. % Al. The band gap of AZO films varied from 3.23 eV for undoped ZnO films to 3.73 eV for AZO films with 24.6 at. % Al. Optical transmittance over 80% was obtained in the visible region. The detrimental impact of increased Al resulting in decreased conductivity due to doping past 3.0 at. % is evident in the x-ray diffraction data, as an abrupt increase in the optical band gap and as a deviation from the Burstein–Moss effect.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Ps Atomic force microscopy (AFM)
61.72.U- Doping and impurity implantation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
72.80.Ey III-V and II-VI semiconductors

The influence of Pt redistribution on Ni1−xPtxSi growth properties

J. Demeulemeester, D. Smeets, C. M. Comrie, C. Van Bockstael, W. Knaepen, C. Detavernier, K. Temst, and A. Vantomme

J. Appl. Phys. 108, 043505 (2010); http://dx.doi.org/10.1063/1.3455873 (11 pages) | Cited 8 times

Online Publication Date: 18 August 2010

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We have studied the influence of Pt on the growth of Ni silicide thin films by examining the Pt redistribution during silicide growth. Three different initial Pt configurations were investigated, i.e., a Pt alloy (Ni+Pt/〈Si〉), a Pt capping layer (Pt/Ni/〈Si〉) and a Pt interlayer (Ni/Pt/〈Si〉), all containing 7 at. % Pt relative to the Ni content. The Pt redistribution was probed using in situ real-time Rutherford backscattering spectrometry (RBS) whereas the phase sequence was monitored during the solid phase reaction (SPR) using in situ real-time x-ray diffraction. We found that the capping layer and alloy exhibit a SPR comparable to the pure Ni/〈Si〉 system, whereas Pt added as an interlayer has a much more drastic influence on the Ni silicide phase sequence. Nevertheless, for all initial sample configurations, Pt redistributes in an erratic way. This phenomenon can be assigned to the low solubility of Pt in Ni2Si compared to NiSi and the high mobility of Pt in Ni2Si compared to pure Ni. Real-time RBS further revealed that the crucial issue determining the growth properties of each silicide phase is the Pt concentration at the Si interface during the initial stages of phase formation. The formation of areas rich in Pt reduce the Ni silicide growth kinetics which influences the phase sequence and properties of the silicides.
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68.55.aj Insulators
64.75.Bc Solubility
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Compositional dependent thin film stress states

B. Fu and G. B. Thompson

J. Appl. Phys. 108, 043506 (2010); http://dx.doi.org/10.1063/1.3462431 (6 pages) | Cited 3 times

Online Publication Date: 18 August 2010

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This paper addresses in situ stress evolution of two-component FexPt1−x, where x spanned 0 to 1, alloy thin films. The stresses of the high-temperature, quenched-in, solid solution phase was determined by in situ wafer curvature measurements during ambient temperature growth. The measured stresses were shown to be compositional dependent and spanned both compressive and tensile stress states. Under specific growth conditions, a “zero-stress” state could be achieved. The alloy stress states did not show any significant stress recovery upon ceasing the deposition, i.e. the stress state during growth was retained in the film. X-ray diffraction, transmission electron microscopy, and atom probe tomography were used to characterize the microstructures of each thin film. The evolution of the stress state with composition is described in terms of a chemical potential term for preferential segregation of one species in the alloy to the grain boundaries.
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68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
65.40.G- Other thermodynamical quantities
81.40.Lm Deformation, plasticity, and creep
68.55.at Other materials
68.55.J- Morphology of films
81.30.Mh Solid-phase precipitation
61.72.Mm Grain and twin boundaries

Thermoreflectance of metal transducers for time-domain thermoreflectance

Yuxin Wang, Ji Yong Park, Yee Kan Koh, and David G. Cahill

J. Appl. Phys. 108, 043507 (2010); http://dx.doi.org/10.1063/1.3457151 (4 pages) | Cited 5 times

Online Publication Date: 18 August 2010

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We report measurements of the temperature dependence of the optical reflectivity, i.e., the thermoreflectance dR/dT, of 18 metallic elements at two laser wavelengths commonly used in ultrafast pump-probe experiments, 1.55 μm and 785 nm. The thermoreflectance is determined using time-domain thermoreflectance combined with measurements of the laser power and spot size and comparisons between the data and quantitative modeling of the temperature evolution at the surface of the sample. At a laser wavelength of 1.55 μm, four elements within this set of samples, Nb, Re, Ta, and V, have dR/dT comparable to or larger than 0.6×10−4 K−1. At a laser wavelength of 785 nm, the highest thermoreflectance is found in Al and Ta, dR/dT ≈ 2.1×10−4 K−1 and 2.2×10−4 K−1, respectively. Alloying Au with 5% Pd increases the optical absorption by a factor of 3 and the thermoreflectance by a factor of 2.
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78.20.N- Thermo-optic effects
07.07.Mp Transducers
42.25.Bs Wave propagation, transmission and absorption
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Influence of the excitonic broadening on the strong light-matter coupling in bulk zinc oxide microcavities

F. Médard, D. Lagarde, J. Zúñiga-Pérez, P. Disseix, M. Mihailovic, J. Leymarie, E. Frayssinet, J. C. Moreno, F. Semond, M. Leroux, and S. Bouchoule

J. Appl. Phys. 108, 043508 (2010); http://dx.doi.org/10.1063/1.3476553 (5 pages) | Cited 1 time

Online Publication Date: 18 August 2010

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We present an experimental study of the influence of excitonic broadening on the strong-coupling regime in a bulk-ZnO microcavity. At room temperature, the strong coupling is highlighted using both angle-resolved reflectivity and photoluminescence measurements; a Rabi splitting value of 40 meV is determined. The polaritonic behavior is also evidenced at low temperature, even if a bulklike reflectivity signature is observed in the excitonic range. Using transfer-matrix calculations, this phenomenon is explained through the influence of the huge excitonic absorption whose contribution depends on the broadening value. Finally, we demonstrate that this effect should not prevent a lasing from the polaritons.
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71.35.-y Excitons and related phenomena
78.55.Et II-VI semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Optical properties of deformed few-layer graphenes with AB stacking

S. H. Lee, Y. H. Ho, C. W. Chiu, and M. F. Lin

J. Appl. Phys. 108, 043509 (2010); http://dx.doi.org/10.1063/1.3463390 (6 pages)

Online Publication Date: 18 August 2010

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Optical excitations of deformed AB-stacked graphenes are studied through the gradient approximation. The interlayer atomic interactions induce prominent peaks, shoulder structures, and transition gaps in the low-energy absorption spectra. The uniaxial stress changes the energy spacing at the band-edge states and the Fermi momenta, which reflects on the spectrum peak frequencies and the transition gaps, respectively. These optical characteristics are also influenced by the layer number. Besides, deformation shows some similar and different effects in comparison with electric and magnetic fields. These predicted optical properties can be verified by optical measurements.
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78.67.Wj Optical properties of graphene
81.05.ue Graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Surface preparation and homoepitaxial deposition of AlN on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition

A. Rice, R. Collazo, J. Tweedie, R. Dalmau, S. Mita, J. Xie, and Z. Sitar

J. Appl. Phys. 108, 043510 (2010); http://dx.doi.org/10.1063/1.3467522 (8 pages) | Cited 11 times

Online Publication Date: 19 August 2010

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Chemical surface treatments were conducted on mechanically polished (MP) and chemomechanically polished (CMP) (0001)-oriented single crystalline aluminum nitride (AlN) substrates to determine a surface preparation procedure for the homoepitaxial deposition of AlN epitaxial layers by metalorganic chemical vapor deposition. MP AlN substrates characterized by atomic force microscopy exhibited 0.5 nm rms roughness and polishing scratches, while CMP AlN substrates exhibited 0.1 nm rms roughness and were scratch-free. X-ray photoelectron spectroscopy analysis of MP and CMP AlN substrates indicated the presence of a surface hydroxide layer composed of mixed aluminum oxide hydroxide and aluminum trihydroxide. Wet etching with sulfuric and phosphoric acid mixtures reduced the amount of surface hydroxide. Ammonia annealing at 1250 °C converted the substrate hydroxide layer to AlN and increased the rms roughness of MP and CMP AlN substrates to 2.2 nm and 0.2 nm, respectively. AlN epitaxial layers were deposited at 1100–1250 °C under 20 Torr total pressure with a V/III ratio of 180–300 in either N2 or H2 diluent. High-resolution x-ray diffraction measurements revealed that AlN epitaxial layers deposited on MP substrates were strained due to nucleation and coalescence of AlN grains on the mechanically damaged surfaces. AlN deposited on CMP substrates was epitaxial and strain-free. Thermodynamic models for nitridation and AlN deposition were also proposed and evaluated.
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81.65.Ps Polishing, grinding, surface finishing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.35.bg Semiconductors
68.37.Ps Atomic force microscopy (AFM)

Equation of state of TiH2 up to 90 GPa: A synchrotron x-ray diffraction study and ab initio calculations

Patricia E. Kalita, Stanislav V. Sinogeikin, Kristina Lipinska-Kalita, Thomas Hartmann, Xuezhi Ke, Changfeng Chen, and Andrew Cornelius

J. Appl. Phys. 108, 043511 (2010); http://dx.doi.org/10.1063/1.3455858 (8 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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We performed high-pressure studies and ab initio calculations of titanium hydride (TiH2), an important compound in hydrogen storage research. In situ, synchrotron x-ray diffraction studies were carried out in two separate compression runs: the first up to 19 GPa in quasihydrostatic conditions and the second up to 90 GPa in nonhydrostatic conditions, and followed by the subsequent decompression to ambient conditions. The pressure evolution of the diffraction patterns revealed a cubic [face-centered-cubic (fcc), Fm-3m] to tetragonal (body-centered-tetragonal (bct), I4/mmm) phase transition in TiH2 occurring at or below 0.6 GPa. The high-pressure tetragonal phase persisted up to 90 GPa. Upon decompression to ambient conditions the observed phase transition appeared irreversible. A third order Birch–Murnaghan fit of the unit cell volume as a function of pressure for all experimental points, yielded a zero pressure bulk modulus K0 = 142(7) GPa, and its pressure derivative K0′ = 3.3(0.2) for the high-pressure tetragonal phase of TiH2 and with K0′ held at four, K0 = 130(5) GPa. The experimental value of bulk modulus confirmed our ab initio calculations where K0 = 139.9 GPa, and K0′ = 3.7 for the high-pressure tetragonal phase of TiH2.
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64.30.Jk Equations of state of nonmetals
88.30.R- Hydrogen storage
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

A kinetics model for Tb3+ recombinations in low doped Tb:Lu1.8Y0.2SiO5 crystals

P. C. Ricci, M. Salis, R. Corpino, C. M. Carbonaro, E. Fortin, and A. Anedda

J. Appl. Phys. 108, 043512 (2010); http://dx.doi.org/10.1063/1.3467788 (6 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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The detailed characterization of the terbium related optical properties of low doped oxyorthosilicates of lutetium and yttrium is reported. The introduction of terbium ions generates an ultraviolet absorption band peaked at about 242 nm and line shaped emissions in the 350–600 nm range. The transitions are related to the 5D3 and 5D4 levels and the analysis of the decay time measurements allows to individuate a cross relaxation mechanism among Terbium ions. We propose a three level kinetic model which is able to reproduce the experimental data allowing to discriminate among the radiative and nonradiative contributions to the transitions in the case of low content of Tb ions (nominal content 10 ppm). The reported study addresses two important goals, providing, from one side, a detailed characterization of possible inorganic phosphors, and from the other side, since traces of unwanted elements were identified in numerous commercial samples of cerium doped oxyorthosilicates, it can contribute to increase the performance of scintillator devices by revealing the optical features of one of the more diffuse and critical impurities.
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78.40.Ha Other nonmetallic inorganics
78.70.Ps Scintillation
71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials

Electron irradiation effects on electrical and optical properties of sol-gel prepared ZnO films

J. S. Bhat, A. S. Patil, N. Swami, B. G. Mulimani, B. R. Gayathri, N. G. Deshpande, G. H. Kim, M. S. Seo, and Y. P. Lee

J. Appl. Phys. 108, 043513 (2010); http://dx.doi.org/10.1063/1.3452333 (8 pages) | Cited 4 times

Online Publication Date: 23 August 2010

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The effects of electron beam irradiation on the electrical and the optical properties of zinc oxide (ZnO) and aluminum-doped zinc oxide (ZnO:Al) thin films, prepared by the sol-gel technique, were investigated. The grain size, surface morphology, sheet resistance, optical constants, absorption edge, and direct and indirect optical band gaps of these films were analyzed before and after exposure to electron beam. The decrease in the structural homogeneity and the crystallinity of the films after exposure to electron irradiation is observed. The irradiation causes increase in the sheet resistance and blueshift in the absorption edge for both ZnO and ZnO:Al films. The change in carrier concentration due to doping as well as the exposure to electron beam are responsible for the modified electrical and optical properties.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
73.61.Ga II-VI semiconductors
68.55.J- Morphology of films
61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects

Photonic crystal composites-based wide-band optical collimator

Jinjie Shi, Bala Krishna Juluri, Sz-Chin Steven Lin, Mengqian Lu, Tieyu Gao, and Tony Jun Huang

J. Appl. Phys. 108, 043514 (2010); http://dx.doi.org/10.1063/1.3468242 (6 pages) | Cited 3 times

Online Publication Date: 23 August 2010

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Photonic crystal (PC) composites are sequenced series of PCs that feature the same periods but different filling fractions. By properly tuning the filling fractions of the individual PCs and merging the working band of each PC into a continuous frequency range, wide-band self-collimation of optical signals can be realized. The band diagrams and the equal-frequency contours of the PC structures were calculated through the plane wave expansion method and the finite-difference time-domain method was employed to simulate the propagation of electromagnetic waves through the PC structures. Our results show that while a single PC can only collimate optical waves over a narrow frequency range, a PC composite exhibits a much wider collimation band. Such a wide-band optical collimation lens can be useful in applications that demand directional optical energy flow over a long distance, such as optical imaging and biosensing.
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42.79.Ag Apertures, collimators
42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors

Determination of thickness, refractive index, and spectral scattering of an inhomogeneous thin film with rough interfaces

J. Anto Pradeep and Pratima Agarwal

J. Appl. Phys. 108, 043515 (2010); http://dx.doi.org/10.1063/1.3478706 (9 pages) | Cited 1 time

Online Publication Date: 23 August 2010

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The magnitude of spectral transmittance and reflectance is affected by the presence of inhomogeneity and interfacial roughness. Therefore, the methods, based on the magnitude of spectral transmittance and reflectance, are not adequate for the determination of thickness and optical constants of films with inhomogeneity and interfacial roughness. The present article proposes a method for the determination of thickness and refractive index using only the positions of the interference fringes in spectral transmittance and reflectance at two different angles of incidence. The proposed method is verified through numerical simulations, which result in <1% error for the film thickness. The complete parametrical dependence of spectral transmittance and reflectance of inhomogeneous film with rough interfaces on a substrate have been worked out for the film on transparent and opaque substrates, respectively. The spectrum envelopes have been solved simultaneously and the mathematical formulae are given for the determination of spectral scattering due to inhomogeneity and interfacial roughness for both transmittance and reflectance cases.
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07.60.Hv Refractometers and reflectometers
68.55.jd Thickness
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Indium-doped ZnO nanowires: Optical properties and room-temperature ferromagnetism

K. W. Liu, M. Sakurai, and M. Aono

J. Appl. Phys. 108, 043516 (2010); http://dx.doi.org/10.1063/1.3464229 (5 pages) | Cited 11 times

Online Publication Date: 23 August 2010

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We report the optical and magnetic properties of ZnO, Zn0.97In0.03O, and Zn0.94In0.06O nanowires (NWs). All samples have similar wirelike shape with an average diameter of about 70 nm and a length of about 10 μm. The comparison of photoluminescence (PL) spectra at 10 K indicated that a new broad emission band appeared after indium doping, which is associated with donor-acceptor-pair recombination. Additionally, the intensity of oxygen-vacancies-induced visible emission increased with increasing In content, indicating that In doping can induce many oxygen vacancies. Furthermore, magnetic measurements revealed that pure ZnO NWs are diamagnetic, while indium-doped ZnO NWs exhibit intrinsic ferromagnetism at room temperature. With the increase in In content, the coercive field and the magnetic moment for indium-doped ZnO NWs increase largely. Ferromagnetic ordering can be interpreted as being due to O vacancies induced by In doping, which is in good agreement with PL results.
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81.07.Gf Nanowires
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.Uh Nanowires
75.50.Dd Nonmetallic ferromagnetic materials

Structure of the (0001) basal twin boundary in Bi2Te3

D. L. Medlin, Q. M. Ramasse, C. D. Spataru, and N. Y. C. Yang

J. Appl. Phys. 108, 043517 (2010); http://dx.doi.org/10.1063/1.3457902 (6 pages) | Cited 6 times

Online Publication Date: 24 August 2010

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We investigate the structure of the (0001) basal twin boundary in Bi2Te3. Electron diffraction measurements show that this interface corresponds to a 180° rotation of the crystal about the [0001] axis, an alignment that reverses the stacking of the basal planes. The basal planes in the perfect Bi2Te3 structure are arranged in a repeating sequence of five-layer wide Te(1)–Bi–Te(2)–Bi–Te(1) packets. Thus, it is possible for the twin interface to be located at one of three distinct locations: at the Te(2) layer, the Bi layer, or the Te(1) layer. Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy, we show that the twin boundary is terminated at the Te(1) layer, where the stacking forms a double-layer of Te. Our observations are consistent with ab initio calculations, which predict this twin termination to have the lowest interfacial energy of the three configurations we considered. Our calculations and observations also find a small expansion in the interplanar spacing at the interface.
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61.72.Mm Grain and twin boundaries
61.66.Dk Alloys
68.35.Ct Interface structure and roughness
68.37.-d Microscopy of surfaces, interfaces, and thin films
65.40.gp Surface energy

Temperature-dependent photoconductivity in β-In2S3 single crystals

C. H. Ho, Y. P. Wang, C. H. Chan, Y. S. Huang, and C. H. Li

J. Appl. Phys. 108, 043518 (2010); http://dx.doi.org/10.1063/1.3478719 (4 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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The solar-energy absorption material β-In2S3 was characterized using temperature-dependent photoconductivity (PC) measurements in the temperature range between 30 and 340 K in this study, and thermoreflectance (TR) and photoluminescence (PL) measurements were carried out to identify near-band-edge transitions in the β-In2S3 tetragonal crystal. The experimental analyses of PL, PC, and TR confirmed that β-In2S3 is a direct semiconductor with a band gap of 2.073 eV at 30 K and 1.935 eV at 300 K. The PL and PC spectra manifest some defect-related features in the β-In2S3 single crystal. Two defect emissions and two band-edge luminescences were simultaneously detected in the PL spectrum at 30 K, and the temperature-dependent PC spectra of β-In2S3 from 160 to 300 K reveal an additional defectlike or band-to-band feature with an energy located above the conduction band edge (EC). The temperature dependences of the PC transition features in the β-In2S3 defect crystal were analyzed. The origin and mechanism of all defect states and band-edge transitions in the β-In2S3 single crystal are evaluated and discussed.
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81.05.Hd Other semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.56.-a Photoconduction and photovoltaic effects
78.20.N- Thermo-optic effects
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Light-induced point defect reactions of residual iron in crystalline silicon after aluminum gettering

D. Abdelbarey, V. Kveder, W. Schröter, and M. Seibt

J. Appl. Phys. 108, 043519 (2010); http://dx.doi.org/10.1063/1.3474658 (6 pages) | Cited 3 times

Online Publication Date: 25 August 2010

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Deep level transient spectroscopy is used to study light-induced reactions of residual iron impurities after aluminum gettering (AlG) in crystalline silicon. White-light illumination at room temperature leads to the formation of a defect which is associated with a donor level at 0.33 eV above the valence band. This defect is stable up to about 175 °C where it dissociates reversibly in case of small iron concentrations and irreversibly for high iron concentrations. Since marker experiments using gold and platinum diffusion show a high vacancy concentration after AlG a tentative identification of the new defect as the metastable iron-vacancy pair is proposed.
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71.55.Cn Elemental semiconductors
75.30.Hx Magnetic impurity interactions
61.72.jd Vacancies
82.30.-b Specific chemical reactions; reaction mechanisms
61.80.-x Physical radiation effects, radiation damage
61.82.Fk Semiconductors
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