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15 Dec 2009

Volume 106, Issue 12, Articles (12xxxx)

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Influence of the temporal shape of femtosecond pulses on silicon micromachining

Tissa C. Gunaratne, Xin Zhu, Vadim V. Lozovoy, and Marcos Dantus

J. Appl. Phys. 106, 123101 (2009); http://dx.doi.org/10.1063/1.3253330 (5 pages) | Cited 2 times

Online Publication Date: 17 December 2009

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The influence of femtosecond laser pulse shaping on silicon wafer micromachining is explored. Surface second harmonic generation provides in situ pulse characterization of the laser pulses, and plasma and atomic emissions were identified as valuable indicators of the micromachining process. The ablation threshold was found to decrease as the bandwidth of the pulses increases, as well as for shorter pulses. Dependence of atomic and plasma emissions on temporal shape of the pulses confirmed that emission preceded ablation and has a threshold as well. The morphology of micromachined holes was observed to be dependent upon pulse duration.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Far-field observation of the radial profile of visible whispering-gallery modes in a single microdisk based on Si-nanocrystal/SiO2 superlattices

Se-Young Seo, Rong-Jun Zhang, Wolfgang Löffler, Heinz Kalt, Kyung Joong Kim, and Margit Zacharias

J. Appl. Phys. 106, 123102 (2009); http://dx.doi.org/10.1063/1.3273360 (6 pages)

Online Publication Date: 21 December 2009

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The radial profile of visible whispering gallery modes (WGM) from a single microdisk based on silicon nanocrystals (Si-nc) and SiO2 superlattices was observed. Using thermal evaporation, the active layer, which consists of 30 pairs of ∼ 3 nm thick Si-ncs and ∼ 4 nm thick SiO2 layer, was fabricated on Si substrate. Si-ncs with diameters of 3 nm, which are well defined by SiOx layer thickness, were formed by high temperature annealing at 1100 °C for 60 min under N2 environment. After standard photolithography and dry etching procedure, a microdisk with 8.8 μm diameter on a silicon pedestal was successfully obtained. We calculated the expected radial profiles of the WGMs by solving the Maxwell equations using appropriate boundary conditions. Comparison with finite-difference time-domain (FDTD) simulation depicts similar radial profiles of the WGMs. Using a confocal microphotoluminescence setup, light emission from the top of a single disk was analyzed depending on the detection position. Thanks to the birefringence of nature of Si-nc/SiO2 superlattices, well-isolated sharp TE mode WGMs could be detected from the top, without using polarizers. Irrelative to detection position, broad Si-nc background luminescence is consistently found. And as the detection point was moved from the center to the outside of the disk, WGMs fields were strongly decreased especially for the detection at the outside. Taking experimental circumstances into account, the radial profile of WGMs field was estimated and was then compared to the experimental WGM profile. The expectation was consistent with experimental results confirming the confinement of WGMs fields within a disk. Although FDTD simulation reveals that the geometrical Q factor can reach >105, the maximum Q factor we observed was 2.5×103. This implies that the scattering and absorption losses must be suppressed in order to enhance the microdisk performance. Simulations show significant WGM field at the top/bottom surface of the disk and visible imperfections of the disk surface was confirmed by scanning electron microscopy, and are expected to produce considerable surface scattering loss limiting the overall disk cavity Q factor. However, such nondirectional surface scattering allowed us to successfully detect WGMs from the top of the disk.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.-m Photoluminescence, properties and materials

Anomalous wear-out phenomena of europium-implanted light emitters based on a metal-oxide-semiconductor structure

L. Rebohle, J. Lehmann, S. Prucnal, A. Nazarov, I. Tyagulskii, S. Tyagulskii, A. Kanjilal, M. Voelskow, D. Grambole, W. Skorupa, and M. Helm

J. Appl. Phys. 106, 123103 (2009); http://dx.doi.org/10.1063/1.3272781 (10 pages) | Cited 6 times

Online Publication Date: 23 December 2009

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The anomalous wear-out phenomena of Eu-implanted metal-oxide-semiconductor devices were investigated. It will be shown that in contrast to other rare earth elements the electroluminescence (EL) intensity of Eu-implanted SiO2 layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances, this rise may amount up to two orders of magnitude. The EL behavior will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy and Rutherford backscattering spectroscopy were applied to trace the development of Eu/Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer. The hydrogen profile within the SiO2–SiON interface region was determined by nuclear reaction analysis. Current-voltage characteristics, EL decay times, and the progression of the voltage and the EL spectrum with increasing charge injection were measured to study charge and trapping phenomena in the oxide layer to reveal details of the EL excitation mechanism. A first qualitative model for the anomalous life time behavior is proposed.
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82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.60.Fi Electroluminescence

Limited-view photoacoustic imaging based on linear-array detection and filtered mean-backprojection-iterative reconstruction

Songbo Ma, Sihua Yang, and Hua Guo

J. Appl. Phys. 106, 123104 (2009); http://dx.doi.org/10.1063/1.3273322 (6 pages) | Cited 4 times

Online Publication Date: 28 December 2009

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Most existing photoacoustic tomography techniques require collecting complete projection data that are acquired on a defined circle surrounding the object. However, in clinical application, the object can only be approached from a limited angle mostly. Furthermore, with the incomplete projection data acquired in limited view, the general filtered backprojection algorithm will streak image artifacts nearby the reconstructed location of absorbers. In this paper, we present a limited-view-scanning photoacoustic imaging system with a linear transducer array and develop a filtered mean-backprojection-iteration (FMBPI) algorithm to reconstruct the absorbed optical deposit distribution. The FMBPI algorithm combines the terseness of the filtered backprojection algorithm with the accuracy of the iterative reconstruction algorithm. Numerical simulation and experimental results validate that the algorithm can effectively reconstruct high-quality image with limited-view data. It is also demonstrated that with the FMBPI algorithm, the limited-view-scanning multielement photoacoustic imaging system has a great potential to be applied in fast noninvasive clinic diagnosis of breast cancer at the early stage.
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87.57.nf Reconstruction
87.19.xj Cancer
42.30.Wb Image reconstruction; tomography
87.63.L- Visual imaging
43.35.Ud

High-temperature lasing characteristics of randomly assembled SnO2 backbone nanowires coated with ZnO nanofins

H. Y. Yang, S. F. Yu, H. K. Liang, Rakesh G. Mote, C. W. Cheng, H. J. Fan, T. Sun, and H. H. Hng

J. Appl. Phys. 106, 123105 (2009); http://dx.doi.org/10.1063/1.3273390 (5 pages) | Cited 4 times

Online Publication Date: 28 December 2009

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Lasing characteristics of randomly assembled SnO2 backbone nanowires coated with ZnO nanofins are investigated. It is shown that the hierarchical nanostructures can sustain ultraviolet random lasing action even at substrate temperature higher than 700 K and the corresponding characteristic temperature is found to be about 390 K. This is because the presence of ZnO nanofins improves heat transfer from the SnO2 backbone nanowires to the surrounding. Hence, some portion of the hierarchical nanostructures can be cooled down and the corresponding optical gain can be maintained even at high substrate temperature.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
78.67.Lt Quantum wires

Probing diagonal laser transitions in InGaAs/AlInAs/InP quantum cascade lasers

M. R. Soulby, D. G. Revin, J. P. Commin, A. B. Krysa, J. S. Roberts, and J. W. Cockburn

J. Appl. Phys. 106, 123106 (2009); http://dx.doi.org/10.1063/1.3273479 (4 pages)

Online Publication Date: 30 December 2009

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We report on the midinfrared broadband transmission spectroscopy measurements of a λ ∼ 4.3 μm strain compensated In0.64Ga0.36As/Al0.58In0.42As/InP quantum cascade laser. A detailed experimental analysis of the electronic distribution for bias values below the laser threshold is presented, highlighting the effects of the design with strongly diagonal laser transition. A marked voltage induced Stark shift is observed for the diagonal laser transition while the vertical intersubband transitions involved higher energy levels remained nearly bias independent. We also demonstrate the direct observation of intersubband transitions originating from the ground level of the injector miniband to the level confined above the AlInAs barriers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
78.20.Jq Electro-optical effects
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Stopping power of a buffer gas for laser plasma debris mitigation

Davide Bleiner and Thomas Lippert

J. Appl. Phys. 106, 123301 (2009); http://dx.doi.org/10.1063/1.3271142 (5 pages) | Cited 3 times

Online Publication Date: 18 December 2009

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The stopping power of a buffer gas against laser-plasma debris is quantitatively assessed by means of visualization techniques. For ablation of planar tin targets in an Ar ambient, an expanding wavefront was visualized, whose translation energy was rapidly reduced within a few millimeters above the target surface. The fastest debris component was along the normal to the target with an initial kinetic energy of 1.1 keV. The buffer gas efficiency changed in a line-of-sight-dependent way, thermalizing more efficiently the on-axis components. The maximum stopping power of the gas buffer was determined as high as 0.4 keV/mm. Due to the reduction in stopping power, nonlinearly with the debris kinetic energy, a gas buffer thickness of 10 mm is required at the studied atmospheric pressure in order to mitigate high energy debris below a fiducial threshold of 0.1 keV.
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52.38.Mf Laser ablation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Eb Laser ablation

Heuristic modeling of spectral plasma emission for laser-induced breakdown spectroscopy

Rolf Wester and Reinhard Noll

J. Appl. Phys. 106, 123302 (2009); http://dx.doi.org/10.1063/1.3259402 (10 pages)

Online Publication Date: 30 December 2009

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A heuristic model was developed to describe the spectral emission of laser-induced plasmas generated for laser-induced breakdown spectroscopy under the assumption that the composition of the plasma and the plasma state is known. The plasma is described by a stationary spherical shell model surrounded by an ambient gas, which partially absorbs the emitted radiation. The radiation transport equation is used to calculate the spectrum emitted by the plasma. Simulations of a multiline iron spectrum and a self-reversed Al line are compared with experimental spectra. For the iron spectrum, the degree of congruence is moderate to good, which may be attributed to a lack of precise atomic and Stark broadening data as well as a simplified plasma model. The line profile of the Al resonance line with self reversal can be simulated with a high degree of agreement. Simulated spectra of a steel sample in the vacuum ultraviolet spectral range demonstrate the strong influence of the ambient atmosphere in the spectral range between 178 and 194 nm. The number of free parameters of the plasma model of 8 can be further reduced down to 3, taking into account the integral parameters of the plasma that are accessible experimentally.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Thermal strain measurement in sol-gel lead zirconate titanate thin films

T. A. Berfield, J. F. Carroll, III, D. A. Payne, and N. R. Sottos

J. Appl. Phys. 106, 123501 (2009); http://dx.doi.org/10.1063/1.3251420 (7 pages) | Cited 1 time

Online Publication Date: 16 December 2009

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A fluorescence-based digital image correlation (DIC) technique is used to characterize the in-plane strain development of blanket sol-gel derived lead zirconate titanate thin films deposited on platinized silicon substrates. The in-plane strain is also measured within film line features patterned via a mediated octadecyltrichlorosilane (ODS) monolayer. The results indicate that the selective film failure induced by the mediated ODS layer succeeds in slightly reducing the in-plane strain transverse to the line feature direction ( ∼ 25% lower), while remaining nearly the same as the blanket film case in the direction parallel to the line direction. Additional in-plane stress estimates from wafer curvature measurements for the two film configurations (blanket and ODS patterned) were consistent with the DIC measured strain results.
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68.60.Bs Mechanical and acoustical properties
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.aj Insulators

Raman spectroscopic determination of electron concentration in n-type GaInAsSb

J. E. Maslar, W. S. Hurst, and C. A. Wang

J. Appl. Phys. 106, 123502 (2009); http://dx.doi.org/10.1063/1.3271351 (11 pages) | Cited 3 times

Online Publication Date: 16 December 2009

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Phonon-plasmon coupled mode Raman spectra of n-type GaInAsSb were measured at room temperature as a function of electron concentration. A relatively simple spectral model for the electronic contribution to the dielectric function was evaluated to determine the electron concentration from the bulk coupled mode spectra. The electron concentration was determined from a Raman spectrum by minimizing the sum of the squared residuals between a measured and a simulated spectrum. The only two fitting parameters were the Fermi energy and a plasmon damping parameter. The electron concentrations determined from the fits to the Raman spectra were compared to the electron concentrations determined from single magnetic field Hall effect measurements that were corrected to account for carriers in two conduction band minima. Compared to the results obtained from the Hall effect measurements, the electron concentrations obtained using Raman spectroscopy were as much as ≈ 19% lower at low doping levels but not more than ≈ 1% higher at higher doping levels. At lower carrier concentrations, the deviations are attributed to limitations of the spectral model. At higher carrier concentrations, the two methods were in good agreement. However, given the known limitations of this relatively simple spectral model, this agreement may be fortuitous; i.e., elements of the spectral model that tend to increase the apparent carrier concentration may be offset by elements that decrease the apparent carrier concentration.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Nr Semiconductor compounds

B-spline parametrization of the dielectric function applied to spectroscopic ellipsometry on amorphous carbon

J. W. Weber, T. A. R. Hansen, M. C. M. van de Sanden, and R. Engeln

J. Appl. Phys. 106, 123503 (2009); http://dx.doi.org/10.1063/1.3257237 (9 pages) | Cited 9 times

Online Publication Date: 16 December 2009

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The remote plasma deposition of hydrogenated amorphous carbon (a-C:H) thin films is investigated by in situ spectroscopic ellipsometry (SE). The dielectric function of the a-C:H film is in this paper parametrized by means of B-splines. In contrast with the commonly used Tauc–Lorentz oscillator, B-splines are a purely mathematical description of the dielectric function. We will show that the B-spline parametrization, which requires no prior knowledge about the film or its interaction with light, is a fast and simple-to-apply method that accurately determines thickness, surface roughness, and the dielectric constants of hydrogenated amorphous carbon thin films. Analysis of the deposition process provides us with information about the high deposition rate, the nucleation stage, and the homogeneity in depth of the deposited film. Finally, we show that the B-spline parametrization can serve as a stepping stone to physics-based models, such as the Tauc–Lorentz oscillator.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
61.43.-j Disordered solids
68.55.-a Thin film structure and morphology
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.35.bt Other materials

Palladium in cubic silicon carbide: Stability and kinetics

Guido Roma

J. Appl. Phys. 106, 123504 (2009); http://dx.doi.org/10.1063/1.3234392 (9 pages)

Online Publication Date: 17 December 2009

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Several technological applications of silicon carbide are concerned with the introduction of palladium impurities. Be it intentional or not, this may lead to the formation of silicides. Not only this process is not well understood, but the basic properties of palladium impurities in silicon carbide, such as solubility or diffusion mechanisms, are far from being known. Here the stability and kinetics of isolated Pd impurities in cubic silicon carbide are studied by first principles calculations in the framework of density functional theory. The preferential insertion sites, as well as the main migration mechanisms, are analyzed and presented here, together with the results for solution and migration energies. The early stages of nucleation are discussed based on the properties of isolated impurities and the smallest clusters.
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66.30.J- Diffusion of impurities
71.55.Ht Other nonmetals
64.75.Bc Solubility
61.72.S- Impurities in crystals

Raman scattering study of zinc blende and wurtzite ZnS

Y. C. Cheng, C. Q. Jin, F. Gao, X. L. Wu, W. Zhong, S. H. Li, and Paul K. Chu

J. Appl. Phys. 106, 123505 (2009); http://dx.doi.org/10.1063/1.3270401 (5 pages) | Cited 15 times

Online Publication Date: 17 December 2009

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We have conducted an experimental and theoretical study on first- and second-order Raman scattering of zinc blende and wurtzite ZnS. Based on the calculated phonon band structure, phonon density of states, and symmetry selection rules, we have clearly identified for the first time the origins of these vibration modes in the second-order Raman spectra from these two polymorphs. For zinc blende ZnS, it is found that the previously estimated frequency of the LA mode at X point in the Brillouin-zone boundary is much smaller than the value obtained from other experiments and our calculation. Considering the involvement of LA phonon at X point, we reassign the second-order Raman active modes and some other modes which have not yet been understood so far. This work clarifies some of the controversial Raman mode assignments in zinc blende and wurtzite ZnS.
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78.30.Fs III-V and II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
71.20.Nr Semiconductor compounds

Optical models for ultrathin oxides on Si- and C-terminated faces of thermally oxidized SiC

Peter Petrik, Edit Szilágyi, Tivadar Lohner, Gabor Battistig, Miklos Fried, Gergely Dobrik, and László P. Biró

J. Appl. Phys. 106, 123506 (2009); http://dx.doi.org/10.1063/1.3270424 (5 pages) | Cited 2 times

Online Publication Date: 17 December 2009

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The thickness, refractive index, density, and interface properties of thin thermal oxides on both Si- and C-terminated 4H-SiC faces were investigated by ellipsometry using optical models of increasing complexity. We used different parametrizations of the dielectric function, a transition layer, and also investigated the multisample approach. The thickness of the transition layer increases with decreasing oxide thickness below the layer thickness of about 30 nm, it correlates with the surface roughness measured by atomic force microscopy, and it was found to be significantly larger for the C-terminated than that for the Si-terminated face. For oxide layer thicknesses larger than 30 nm, the refractive index of the bulk oxide layer is the same as that of thermal SiO2 on Si. We found an apparent decrease in mass density (as well as optical density) with decreasing oxide thickness using a combination of ellipsometry and backscattering spectrometry, which can be explained by the surface roughness, depending on the layer thickness revealed by atomic force microscopy.
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78.66.Li Other semiconductors
68.55.jd Thickness
68.37.Ps Atomic force microscopy (AFM)
81.65.Mq Oxidation
81.40.Tv Optical and dielectric properties related to treatment conditions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Thermal modeling and experimental study of infrared nanosecond laser ablation of silicon

Sha Tao, Benxin Wu, Yun Zhou, and Yibo Gao

J. Appl. Phys. 106, 123507 (2009); http://dx.doi.org/10.1063/1.3271413 (5 pages) | Cited 2 times

Online Publication Date: 17 December 2009

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Nanosecond (ns) laser ablation of silicon has important applications in electronics, photovoltaics, and many other areas. However, most of the previous work is mainly focused on ultraviolet (UV) or visible ns lasers, and the investigation is very limited for infrared lasers (e.g., at 1064 nm), which have the advantage of much lower cost and external energy consumption. In this paper, a thermal model has been developed and experimentally verified for ablation of silicon by 200 ns and 1064 nm laser pulses. This kind of work has been rarely reported in literature. The model predictions agree reasonably well with experimental measurements. The investigation indicates that surface evaporation should be the dominant physical mechanism of material removal for laser silicon ablation under the studied conditions. It has also been found that the physical processes of multipulse laser-silicon interaction at 1064 nm may strongly depend on laser pulse number and repetition rate (the pulse-to-pulse temporal distance).
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78.47.J- Ultrafast spectroscopy (<1 psec)

Microstructure and tribological properties of Ti-contained amorphous carbon film deposited by DC magnetron sputtering

R. L. Li, J. P. Tu, C. F. Hong, D. G. Liu, D. H. Zhou, and H. L. Sun

J. Appl. Phys. 106, 123508 (2009); http://dx.doi.org/10.1063/1.3272018 (6 pages) | Cited 10 times

Online Publication Date: 17 December 2009

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Pure amorphous carbon (a-C) film and that with a small amount of Ti were deposited on high speed steel (W18Cr4V) substrates by means of dc closed field unbalanced magnetron sputtering. The chemical composition and microstructure of the a-C films were performed using x-ray photoelectron spectroscopy, x-ray diffraction, Raman spectra, and transmission electron microscopy. The mechanical and tribological properties were evaluated using a nanoindentor, Rockwell and scratch tests, and a conventional ball-on-disk tribometer, respectively. The pure a-C film showed the high hardness (53 GPa), elastic modulus (289 GPa), but the poor adhesive strength. When adding a small amount of Ti to the a-C film, both the adhesive strength and the tribological properties were improved. The Ti contained a-C film had the low wear rate (1.9×10−17 m3 N−1 m−1) and friction coefficient in humid air.
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68.60.Bs Mechanical and acoustical properties
78.66.Nk Insulators
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Pq Friction, lubrication, and wear
81.15.Cd Deposition by sputtering

Controlling the Bi content, phase formation, and epitaxial nature of BiMnO3 thin films fabricated using conventional pulsed laser deposition, hybrid pulsed laser deposition, and solid state epitaxy

S. Havelia, S. Wang, M. Skowronski, and P. A. Salvador

J. Appl. Phys. 106, 123509 (2009); http://dx.doi.org/10.1063/1.3266142 (11 pages) | Cited 1 time

Online Publication Date: 17 December 2009

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Loss of Bi during thin film growth of bismuth-based compounds is a major challenge to obtaining stoichiometric films. Three approaches to BiMnO3 film growth were investigated to understand and to control the loss of Bi. First, a systematic study was carried out using a conventional pulsed laser deposition (PLD) approach, using targets of different Bi compositions. Conventional PLD was plagued with high re-evaporation and slow reaction kinetics, which led to Bi-deficient multiphase films. A phenomenological model was developed to describe Bi loss in conventional PLD and demonstrated that the film composition was dependent on both the rate of reaction between the constituent oxides and the rate of desorption of bismuth species from the substrate surface. To overcome the problems of conventional PLD, two different growth approaches were developed: a solid state epitaxy approach, in which stoichiometric but amorphous films deposited at low temperatures (T<500 °C) were annealed to generate crystalline films, and a hybrid PLD approach, in which conventional PLD is supplemented with an effusion cell to provide a background flux of Bi. Both of these approaches produced stoichiometric, epitaxial films of BiMnO3 in a straightforward fashion since the local composition was maintained to the overall stoichiometry during crystallization.
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77.55.Nv Multiferroic/magnetoelectric films
81.15.Np Solid phase epitaxy; growth from solid phases
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Fg Pulsed laser ablation deposition
68.55.Nq Composition and phase identification
68.55.aj Insulators
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Infrared study of the concentration of H introduced into Si by the postdeposition annealing of a SiNx coating

S. Kleekajai, L. Wen, C. Peng, M. Stavola, V. Yelundur, K. Nakayashiki, A. Rohatgi, and J. Kalejs

J. Appl. Phys. 106, 123510 (2009); http://dx.doi.org/10.1063/1.3267317 (5 pages) | Cited 1 time

Online Publication Date: 17 December 2009

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The postdeposition annealing of a SiNx antireflection coating is commonly used to introduce hydrogen into a multicrystalline Si solar cell to passivate defects in the Si bulk. A quantitative comparison has been made of the concentrations of H that are introduced into a Si model system from SiNx coatings with high and low density that have been characterized by infrared spectroscopy. Experiments have also been performed in which the processing of the SiNx/Si interface was modified to compare how the preparation of the interface and properties of the SiNx film itself affect the concentration of H that is introduced into the Si bulk.
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78.66.-w Optical properties of specific thin films
78.30.Hv Other nonmetallic inorganics
81.40.Gh Other heat and thermomechanical treatments
42.79.Wc Optical coatings
42.70.-a Optical materials

Effect of hydrogen on nanoindentation-induced phase transformations in amorphous silicon

S. Ruffell, J. Vedi, J. E. Bradby, and J. S. Williams

J. Appl. Phys. 106, 123511 (2009); http://dx.doi.org/10.1063/1.3267853 (6 pages) | Cited 3 times

Online Publication Date: 17 December 2009

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The effect of local hydrogen concentration on nanoindentation-induced phase transformations has been investigated in ion-implanted amorphous silicon (a-Si). Elevated concentrations of H ranging from 5×1018 to 5×1020 cm−3, over the depth of indentation-induced phase transformed zones have been formed in the a-Si by H ion-implantation. Indentation has been performed under conditions that result in phase transformed zones composed totally of Si-III/Si-XII in the “H-free” samples. Deformation during indentation and determination of phase transformation behavior has been examined by analysis of load/unload curves, Raman microspectroscopy, and cross-sectional transmission electron microscopy (XTEM). With increasing H content, the probability of forming Si-III/Si-XII and the volume fraction of Si-III/Si-XII decrease. XTEM shows that these reduced volumes are randomly distributed within the phase transformed zone and are surrounded by indentation-induced a-Si. For a H concentration of 5×1020 cm−3, the probability of forming Si-III/Si-XII is reduced to 0.5 compared to 1 in “H-free” material and for those indents that exhibit the Si-III/Si-XII end phase the volume fraction is approximately 60 %. We suggest that the monohydride bonding configuration of Si and H in a-Si reduces the formation of the high pressure crystalline phases by retarding growth of the crystallites through a similar mechanism to that of hydrogen-retarded solid phase crystallization of a-Si to diamond cubic crystalline Si-I phase.
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64.70.kg Semiconductors
61.72.sd Impurity concentration
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
78.30.Am Elemental semiconductors and insulators
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Enhanced tetragonality in lead-free piezoelectric (1−x)BaTiO3–xNa1/2Bi1/2TiO3 solid solutions where x = 0.05–0.40

K. Datta, K. Roleder, and P. A. Thomas

J. Appl. Phys. 106, 123512 (2009); http://dx.doi.org/10.1063/1.3268443 (5 pages) | Cited 9 times

Online Publication Date: 17 December 2009

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A structural investigation was carried out on a perovskite-based solid solution of xNa1/2Bi1/2TiO3–(1−x)BaTiO3, where x ⩽ 0.40. The crystal structure remains tetragonal, P4mm, for these compositions; however, enhancement of the tetragonality up to 0.9% of the unit cell was observed as a function of doping which is an unusual phenomenon in BaTiO3 based binary solid solutions. Crystallographic details of the structural changes that have occurred because of the doping were obtained by performing Rietveld refinement on neutron powder diffraction data collected at HRPD of the ISIS spallation neutron source. Temperature- and frequency-dependent dielectric data as a function of composition are presented to understand the structure-property relationships in this novel system.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
61.66.-f Structure of specific crystalline solids
61.72.U- Doping and impurity implantation

Rate and state variable friction laws: Estimation of model parameters for slip velocity dependence at coseismic slip rates

Vikas Prakash

J. Appl. Phys. 106, 123513 (2009); http://dx.doi.org/10.1063/1.3259395 (7 pages)

Online Publication Date: 18 December 2009

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In the present study plate-impact pressure-shear friction experiments are conducted to study dynamics of high-speed slip at metal-on-metal interfaces. By using a CH tool-steel/Ti–6Al–4V tribo-pair and appropriate selection of the flyer and target plate thicknesses, the experiment has been used to investigate the frictional resistance of sliding interfaces subjected to step changes in slip rates. In order to describe the frictional memory effects a model based on Ruina–Dieterich slip law has been utilized. It is noted that the model parameter a in the range of 0.01–0.25 with characteristic lengths of L = 5–7 μm provides a reasonably good fit to the experimental data.
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68.35.Af Atomic scale friction
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear

Enhance diamond coating adhesion by oriented interlayer microcracking

Haibo Guo, Xingcheng Xiao, Yue Qi, Zhi-Hui Xu, and Xiaodong Li

J. Appl. Phys. 106, 123514 (2009); http://dx.doi.org/10.1063/1.3267162 (6 pages)

Online Publication Date: 18 December 2009

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In this paper, we report a microcrack toughening mechanism for enhancing the adhesion of diamond coating. The oriented microcracks were formed within the TiC interlayer to dissipate strain energy and accommodate deformation via the crack opening-closing mechanism, thus enhancing the coating/substrate interfacial toughness. The delamination of diamond coating was effectively prevented when the parallel microcracks were confined within the interlayer and arrested at interfaces of coating/interlayer/substrate. Density functional theory calculations revealed that the highly anisotropic fracture strength of the TiC phase energetically favors crack initiation and propagation along (100) planes only, which are 54.7° away from the interface. These microcracks are constrained inside the interlayer by the two strong interfaces in the substrate/interlayer/coating system. The new microcrack toughening mechanism with these combined features has a wide application to enhance the adhesion of thin-film coatings.
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68.60.Bs Mechanical and acoustical properties
62.20.mt Cracks
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains

Micropipe absorption mechanism of pore growth at foreign polytype boundaries in SiC crystals

M. Yu. Gutkin, A. G. Sheinerman, M. A. Smirnov, T. S. Argunova, J. H. Je, S. S. Nagalyuk, and E. N. Mokhov

J. Appl. Phys. 106, 123515 (2009); http://dx.doi.org/10.1063/1.3266677 (7 pages) | Cited 2 times

Online Publication Date: 21 December 2009

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Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption by an elliptic pore nucleated at the boundary of a foreign polytype inclusion. It is shown that depending on the inclusion distortion, the pore can either be a separate micropipe, or grow up to a certain length, or occupy the whole facet of the inclusion.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.55.Mb Porous materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Lk Linear defects: dislocations, disclinations
61.72.Mm Grain and twin boundaries
61.72.Bb Theories and models of crystal defects

Structure of annealed nanoindentations in n- and p-doped (001)GaAs

E. Le Bourhis and G. Patriarche

J. Appl. Phys. 106, 123516 (2009); http://dx.doi.org/10.1063/1.3270420 (6 pages) | Cited 2 times

Online Publication Date: 22 December 2009

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We have studied the structure of annealed nanoindentations realized at room temperature (RT) on (001) GaAs having either n or p doping under a large range of loads Fm (between 0.5 and 50 mN). Transmission electron microscopy was used to observe systematically the nanoindentation structures. The lengths of the rosette arms were multiplied by a factor of two to three during the annealing process at 500 °C and were determined to vary with math, which could be modeled considering the two step thermomechanical history. While almost no anisotropy was observed before annealing (after indentation at RT), the [110] arms were observed to extend almost twice as long as the [math10] ones in n-doped specimens after annealing. This anisotropy was much reduced in p-doped specimens. Furthermore, almost no partial dislocations were observed whereas they were obvious in n-doped specimens before annealing.
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61.72.Cc Kinetics of defect formation and annealing
62.25.-g Mechanical properties of nanoscale systems
81.40.Gh Other heat and thermomechanical treatments
61.72.uj III-V and II-VI semiconductors

High pressure behavior of ZrGeO4: A Raman spectroscopic and photoluminescence study

Rekha Rao, T. Sakuntala, S. N. Achary, and A. K. Tyagi

J. Appl. Phys. 106, 123517 (2009); http://dx.doi.org/10.1063/1.3270433 (5 pages) | Cited 1 time

Online Publication Date: 22 December 2009

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High pressure behavior of ZrGeO4 has been investigated using Raman and photoluminescence (PL) spectroscopies up to 25 GPa in a diamond anvil cell. Under the application of pressure, the GeO4 librational mode exhibits softening, suggesting dynamical instability of the scheelite structure. Qualitative changes are noted in the Raman spectrum above 12 GPa, suggesting a possible transition around this pressure. High pressure PL behavior of Eu3+-related crystal field transitions indicates a clear change in the site symmetry of Eu3+ around 12 GPa, strongly supporting structural transition to a lower symmetry phase at this pressure.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
71.70.Ch Crystal and ligand fields
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
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