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1 May 2012

Volume 111, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri
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back to top Lasers, Optics, and Optoelectronics

Surface enhanced fluorescence on three dimensional silver nanostructure substrate

Jun Dong, Shixian Qu, Zhenglong Zhang, Meicen Liu, Gaining Liu, Xiaoqing Yan, and Hairong Zheng

J. Appl. Phys. 111, 093101 (2012); http://dx.doi.org/10.1063/1.4709442 (4 pages) | Cited 5 times

Online Publication Date: 2 May 2012

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Multi-dimensional metallic nanostructures were fabricated by self-assembling silver nanoparticles on 3-aminopropyltrimethoxysilane-modified glass substrate and using p-aminothiophenol molecule as a linker. Surface enhanced fluorescence was investigated for Rhodamine 6G fluorophore molecules on the prepared 2D and 3D substrates. The experimental observation showed that the 3D nanostructured substrate presented stronger fluorescence enhancement, comparing with what was observed on the 2D nanoparticle arrays. Higher intensity of local electric field and stronger coupling of surface plasmon resonance in 3D silver nanostructure enhanced the excitation and emission of fluorophore molecules more effectively, leading to a stronger fluorescence enhancement on 3D nanostructured substrate. The result suggests that a metallic substrate with 3D nanostructures can produce better fluorescence enhancement, which is important for studying the mechanism and expanding the potential applications of enhanced fluorescence effect.
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78.55.Hx Other solid inorganic materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
81.16.Dn Self-assembly

High-aspect-ratio grooves fabricated in silicon by a single pass of femtosecond laser pulses

Yuncan Ma (马云灿), Haitao Shi (史海涛), Jinhai Si (司金海), Hai Ren (任海), Tao Chen (陈涛), Feng Chen (陈烽), and Xun Hou (侯洵)

J. Appl. Phys. 111, 093102 (2012); http://dx.doi.org/10.1063/1.4709726 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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High-aspect-ratio grooves have been fabricated in silicon by a single pass of femtosecond laser pulses in water and ambient air. Scanning electron microscopy and energy dispersive x-ray spectroscopy were employed to image for the morphology of the photoinduced grooves and analyze the chemical composition in the surrounding of the grooves. It was observed that the sidewall of the grooves fabricated in water was much smoother than that in ambient air, and there were homogeneous nano-scale protrusions on the sidewall of the grooves fabricated in water. Meanwhile, oxygen species, which was incorporated into the grooves fabricated in air, was not observed in those in water.
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81.16.-c Methods of micro- and nanofabrication and processing
82.53.Mj Femtosecond probing of semiconductor nanostructures
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces
79.20.Ds Laser-beam impact phenomena
FREE

Waveguide terahertz time-domain spectroscopy of ammonium nitrate polycrystalline films

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Online Publication Date: 3 May 2012

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We report temperature-dependent measurements of the terahertz (THz) vibrational spectrum of ammonium nitrate (AN) films and mixed potassium nitrate (KN)–ammonium nitrate films using waveguide THz time domain spectroscopy. The experiments were performed on polycrystalline films on the metal surface of a parallel plate waveguide. At cryogenic temperature and with frequency resolution as high as 7 GHz, our measurements produce a complex vibrational spectrum for AN, and show vibrational resonances not observed in previous far infrared and Raman measurements. We investigate potential interactions between AN and the metal surface by measuring THz spectra of films on aluminum, gold, and a gold surface coated with an organic self-assembled monolayer. Measurements are also performed on a deuterated AN film and indicate that the observed THz modes are due largely to the motion of the nitrate ions in the AN crystal. Finally, the effect of introducing small amounts of an impurity into the AN lattice is examined. We find that introduction of as little as 1%-2% by weight of potassium nitrate into the AN lattice causes line broadening of the THz modes, which is consistent with increased disorder introduced by the impurity.
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78.70.Gq Microwave and radio-frequency interactions
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics

Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics

R. Gaume, Y. He, A. Markosyan, and R. L. Byer

J. Appl. Phys. 111, 093104 (2012); http://dx.doi.org/10.1063/1.4709756 (5 pages)

Online Publication Date: 3 May 2012

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High sensitivity optical absorption at 1 µm was measured in 40 undoped and Nd-doped Y3Al5O12 (YAG) transparent ceramics and single crystals using photothermal common-path interferometry. Concurrently, chemical trace analysis was performed on those samples by glow discharge mass-spectroscopy. Silicon and calcium were found to be the major impurities with concentrations up to 250 wt. ppm. A univocal linear correlation between the Si content and the absorption loss at 1 µm is revealed and a possible mechanism for the formation of Si-induced color centers based on a bound polaron model is discussed. Solutions to reduce this optical absorption in ceramics are also proposed.
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42.70.Hj Laser materials
71.38.-k Polarons and electron-phonon interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.jn Color centers
78.20.nb Photothermal effects

Transfer printing and nanomanipulating luminescent photonic crystal membrane nanocavities

Bowen Wang, Timothy Siahaan, Mehmet A. Dündar, Richard Nötzel, Sailing He, and Rob W. van der Heijden

J. Appl. Phys. 111, 093105 (2012); http://dx.doi.org/10.1063/1.4712410 (5 pages)

Online Publication Date: 4 May 2012

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The release of photoluminescent InGaAsP photonic crystal nanocavity chiplets from the host chip for creating autonomous functional microparticles is demonstrated. A transfer printing method using a soft polymeric material as a stamp is used to transfer cavity arrays to other substrates. Alternatively, cavities are transferred individually by a nanomanipulation technique. The chiplets can be fully deterministically positioned on both the host chip and another substrate (glass) with the nanomanipulator. The chiplets have the striking property of spontaneously orienting themselves with their plane perpendicular to the receiving surface. At each stage of the process, the condition of the cavities as dependent on their immediate surroundings is monitored from their photoluminescence spectrum.
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42.70.Qs Photonic bandgap materials
78.55.-m Photoluminescence, properties and materials

Strong nonlinear growth of energy coupling during laser irradiation of transparent dielectrics and its significance for laser induced damage

Guillaume Duchateau, Michael D. Feit, and Stavros G. Demos

J. Appl. Phys. 111, 093106 (2012); http://dx.doi.org/10.1063/1.4707755 (12 pages) | Cited 4 times

Online Publication Date: 4 May 2012

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The interaction of high power nanosecond laser pulses with absorbing defects, located in the bulk of transparent dielectric materials and having a multilevel electronic structure, is addressed. The model assumes a moderate localized initial absorption that is strongly enhanced during the laser pulse via excited state absorption and thermally driven generation of new point defects in surrounding material. This model is applied to laser induced damage initiation in the bulk of potassium dihydrogen phosphate crystals (KH2PO4 or KDP) and addresses how during a fraction of the pulse duration the host material around the defect cluster is transformed into a strong absorber that leads to the sufficiently large energy coupling resulting in a damage event. This scenario is supported by time resolved imaging of material modification during the initial phases of laser induced damage in KDP and fused silica.
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79.20.Ds Laser-beam impact phenomena
68.35.Dv Composition, segregation; defects and impurities
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states

Nonreciprocal light transmission in silicon by Raman-induced asymmetry of the permittivity tensor

Michael Krause

J. Appl. Phys. 111, 093107 (2012); http://dx.doi.org/10.1063/1.4709622 (4 pages)

Online Publication Date: 4 May 2012

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We consider the effect of Raman-induced nonreciprocal light transmission in silicon and show that it can be understood as the consequence of the asymmetry of an effective permittivity tensor at the Stokes wavelength. This viewpoint enables the derivation of a necessary condition for this effect: the pumping electric field must have components along two different crystallographic axes which are oscillating out of phase with respect to each other.
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78.30.Am Elemental semiconductors and insulators

High efficient antireflective down-conversion Y2O3:Bi,Yb films with pyramid preferred oriented nano-structure

Ming-Hao Qu, Ru-Zhi Wang, Ying Zhang, Kai-Yu Li, and Hui Yan

J. Appl. Phys. 111, 093108 (2012); http://dx.doi.org/10.1063/1.4712461 (5 pages) | Cited 2 times

Online Publication Date: 8 May 2012

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The high efficient antireflective down-conversion Y2O3:Bi,Yb films with nano-structure pyramids were grown successfully on Si (100) substrates using the pulsed laser deposition (PLD). The films microstructure can be controllably tuned only by changing the oxygen pressure in PLD process. With the increasing of the oxygen pressure, the surface morphology changes from smooth surface to pyramid nano-structure, and the preferential orientation of films changes from (222) to (400). Besides, the average reflectance of the films decreases first and then increases, giving a minimum value of 15.8% at 5 Pa as the oxygen pressure increases, which is comparable to that of uniform pyramidal micro-textured surfaces with an average reflectance of 13%–15% fabricated by the complicated chemical etching method. Moreover, upon excitation of ultraviolet photon varying from 300 to 400 nm, near infrared emission of Yb3+ due to transition of the 2F5/2→2F7/2 was observed for all samples, which can be efficiently absorbed by silicon solar cell. These pyramid nano-structure down-conversion Y2O3:Bi,Yb films possess promising applications in enhancement of energy efficiency for crystalline Si solar cells by light trapping and spectrum shifting.
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81.16.Mk Laser-assisted deposition
81.65.Cf Surface cleaning, etching, patterning
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Thickness dependence of the amplified spontaneous emission threshold and operational stability in poly(9,9-dioctylfluorene) active waveguides

M. Anni, A. Perulli, and G. Monti

J. Appl. Phys. 111, 093109 (2012); http://dx.doi.org/10.1063/1.4711993 (5 pages) | Cited 2 times

Online Publication Date: 9 May 2012

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We investigate the thickness dependence of the amplified spontaneous emission (ASE) threshold and operational lifetime in air-poly(9,9-dioctylfluorene)(PF8)-glass asymmetric active waveguides. We show that the ASE threshold decreases with the film thickness up to about 200 nm, and increases for higher thicknesses. The ASE operational lifetime increases with the thickness up to about 300 nm, and it is almost thickness independent for higher thickness. We show that the observed results are related to the guided mode confinement in the waveguide and to the spatial overlap between the guided modes and the excited region in the film.
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42.79.Gn Optical waveguides and couplers
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems

Efficiency degradation behaviors of current/thermal co-stressed GaN-based blue light emitting diodes with vertical-structure

Lilin Liu, Minjie Ling, Jianfu Yang, Wang Xiong, Weiqing Jia, and Gang Wang

J. Appl. Phys. 111, 093110 (2012); http://dx.doi.org/10.1063/1.4712030 (9 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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With this work, we demonstrate a three-stage degradation behavior of GaN based LED chips under current/thermal co-stressing. The three stages in sequence are the initial improvement stage, the platform stage, and the rapid degradation stage, indicating that current/thermal co-stressing activates positive effects and negative ones simultaneously, and the dominant degradation mechanisms evolve with aging time. Degradation mechanisms are discussed. Electric current stress has dual characters: damaging the active layers by generating defects and at the same time improving the p-type conductivity by activating the Mg-dopant. High temperature stresses will promote the effects from electric current stresses. The activation of the Mg-dopant will saturate, whereas the generation of defects is carried on in a progressive way. Other mechanisms, such as deterioration of ohmic contacts, also operate. These mechanisms compete/cooperate with each other and evolve with aging time, resulting in the observed three-stage degradation behavior. There exist risks to predict the lifetime of LEDs by a model with a constant accelerated factor.
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85.60.Jb Light-emitting devices

Visual and quantitative measurement of the temperature distribution of heat conduction process in glass based on digital holographic interferometry

Qian Wang, Jianlin Zhao, Xiangyang Jiao, Jianglei Di, and Hongzhen Jiang

J. Appl. Phys. 111, 093111 (2012); http://dx.doi.org/10.1063/1.4712318 (5 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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multimedia

Show Abstract
The temperature distribution of heat conduction process in transparent solid medium is visually and quantitatively measured based on digital holographic interferometry. A series of phase maps reflecting the temperature distribution of a glass sample during the heat conduction process are numerically reconstructed from the digital holograms. Then, based on the derived relationship between temperature variation and phase change, we obtained the full field temperature distribution of the glass sample by the method of sample point calibration. By seriating maps of the temperature distribution, a movie is produced to show the heat conduction phenomenon more vividly. What is more, based on the thermodynamic model of heat conduction, we numerically figured out the temperature distribution of the glass sample using the finite element algorithm. It turns out that the experimental results are consistent with the numerical simulation results very well.
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44.10.+i Heat conduction
05.70.-a Thermodynamics
42.40.Kw Holographic interferometry; other holographic techniques
02.70.Dh Finite-element and Galerkin methods

First-principle description for the high-harmonic generation in a diamond by intense short laser pulse

T. Otobe

J. Appl. Phys. 111, 093112 (2012); http://dx.doi.org/10.1063/1.4716192 (7 pages)

Online Publication Date: 14 May 2012

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We present a first-principles description for the electron excitation and the high-harmonic generation (HHG) in a diamond by intense laser pulse irradiation and their laser parameter dependence. Above band gap harmonics are generated after the peak of the incident laser pulse and have duration much shorter than the laser pulse. The intensity of individual harmonic peaks increases as laser intensity increases nonlinearly, and we find the blue shift of the HHG spectrum when the optical breakdown occurs.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.-v Laser optical systems: design and operation

Heating dynamics of CO2-laser irradiated silica particles with evaporative shrinking: Measurements and modeling

S. Elhadj, S. R. Qiu, A. M. Monterrosa, and C. J. Stolz

J. Appl. Phys. 111, 093113 (2012); http://dx.doi.org/10.1063/1.4716016 (5 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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The heating dynamics of CO2-laser heated micron-sized particles were determined for temperatures <3500 K measured using infrared imaging. A coupled mass and energy conservation model is derived to predict single particle temperatures and sizes, which were compared with data from particles deposited on non-absorbing substrates to assess the relevant heat transfer processes. Analysis reveals substrate conduction dominates all other heat losses, while laser absorption determined from Mie theory is strongly modulated by particle evaporative shrinking. This study provides insights into the light coupling and heating of particle arrays where the material optical properties are temperature-dependent and particle size changes are significant.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
back to top Plasmas and Electrical Discharges

Effect of adding small amount of inductive fields to O2, Ar/O2 capacitively coupled plasmas

Min-Hyong Lee, Hyo-Chang Lee, and Chin-Wook Chung

J. Appl. Phys. 111, 093301 (2012); http://dx.doi.org/10.1063/1.4705362 (4 pages)

Online Publication Date: 1 May 2012

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Electron energy distribution functions (EEDFs) of low pressure O2 plasma were measured by adding small amount of coil power in a capacitive discharge. When the plasma was generated by bias power only, the measured EEDF showed a bi-Maxwellian distribution. However, when a very small coil power (a few Watts) was added, the EEDF evolved abruptly into a Maxwellian distribution, while the electron density was decreased. In an Ar/O2 mixture discharge, this EEDF evolution to the Maxwellian was also observed at a relatively higher coil power. This abrupt change in EEDFs with a very small coil power appears to be attributed to a combined effect of collisionless heating by capacitive and induced electric fields.
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52.25.Fi Transport properties
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.70.Ds Electric and magnetic measurements
52.80.Pi High-frequency and RF discharges

Characteristics of argon plasma waveguide produced by alumina capillary discharge for short wavelength laser application

Takeshi Higashiguchi, Nadezhda Bobrova, Pavel Sasorov, Shohei Sakai, Yasuhiko Sentoku, Ryosuke Kodama, and Noboru Yugami

J. Appl. Phys. 111, 093302 (2012); http://dx.doi.org/10.1063/1.4712038 (7 pages)

Online Publication Date: 7 May 2012

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We have reported the argon (Ar) plasma waveguide produced in an alumina (Al2O3) capillary discharge and used to guide ultrashort laser pulses at intensities of the order of 1016 W/cm2. The electron density in the plasma waveguide was measured to be 1×1018 cm−3, in agreement with one-dimensional magnetrohydrodynamic (MHD) simulations. The MHD code was also used to evaluate the degree of ionization of argon (Ar) in the preformed plasma waveguide. The maximum ion charge state of Ar3+ in capillary discharge was measured and obtained in the MHD simulations. The spectrum of the propagated laser pulse in the Ar plasma waveguide was not modified and was well reproduced by a particle-in-cell simulations under initial ion charge state of Ar3+ in the preformed plasma waveguide. The optimum timing for the laser pulse injection was around 150 ns after initiation of a discharge with a peak current of 200 A.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.Kj Magnetohydrodynamic and fluid equation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Gn Optical waveguides and couplers
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Ion velocity and plasma potential measurements of a cylindrical cusped field thruster

N. A. MacDonald, C. V. Young, M. A. Cappelli, and W. A. Hargus, Jr.

J. Appl. Phys. 111, 093303 (2012); http://dx.doi.org/10.1063/1.4707953 (7 pages) | Cited 1 time

Online Publication Date: 7 May 2012

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Measurements of the most probable time-averaged axial ion velocities and plasma potential within the acceleration channel and in the plume of a straight-channeled cylindrical cusped field thruster operating on xenon are presented. Ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition centered at λ = 834.72nm. Plasma potential measurements are made using a floating emissive probe with a thoriated-tungsten filament. The thruster is operated in a power matched condition with 300 V applied anode potential for comparison to previous krypton plasma potential measurements, and a low power condition with 150 V applied anode potential. Correlations are seen between the plasma potential drop outside of the thruster and kinetic energy contours of the accelerating ions.
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52.75.Di Ion and plasma propulsion
52.70.Ds Electric and magnetic measurements

Removal of amorphous C and Sn on Mo:Si multilayer mirror surface in Hydrogen plasma and afterglow

O. V. Braginsky, A. S. Kovalev, D. V. Lopaev, E. M. Malykhin, T. V. Rakhimova, A. T. Rakhimov, A. N. Vasilieva, S. M. Zyryanov, K. N. Koshelev, V. M. Krivtsun, Maarten van Kaampen, and D. Glushkov

J. Appl. Phys. 111, 093304 (2012); http://dx.doi.org/10.1063/1.4709408 (4 pages) | Cited 2 times

Online Publication Date: 9 May 2012

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Removal of amorphous carbon and tin films from a Mo:Si multilayer mirror surface in a hydrogen plasma and its afterglow is investigated. In the afterglow, the mechanism of Sn and C films removal is solely driven by hydrogen atoms (radicals). Probabilities of Sn and C atoms removal by H atoms were measured. It was shown that the radical mechanism is also dominant for Sn atoms removal in the hydrogen plasma because of the low ion energy and flux. Unlike for Sn, the removal mechanism for C atoms in the plasma is ion-stimulated and provides a much higher removal rate.
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81.65.Cf Surface cleaning, etching, patterning
52.80.Hc Glow; corona
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Spectroscopic ellipsometry model for optical constant of NiSi formed on silicon-on-insulator substrates

A. Vellei, R. Fallica, D. Sangalli, and A. Lamperti

J. Appl. Phys. 111, 093501 (2012); http://dx.doi.org/10.1063/1.4706561 (6 pages)

Online Publication Date: 1 May 2012

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Nickel silicide is considered the best candidate material to achieve the lowest contact resistance in sub 45 nm CMOS devices. NiSi films with thickness 20–60 nm were prepared by rapid thermal annealing of Ni (temperature 230 °C–780 °C) on top of thin 230 nm silicon-on-insulator substrates, with a constant formation ratio. Based on film independent characterizations, a novel model for the interpretation of spectroscopic ellipsometry data, featuring a combination of two Lorentzian oscillators and one Drude dispersion model, is proposed, and its goodness is checked in comparison to other known models. This new approach is proved to deliver more accurate estimation of the film thickness and resistivity.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.jd Thickness
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential

Time-resolved mirage method: A three-dimensional theory and experiments

N. G. C. Astrath, L. C. Malacarne, H. S. Bernabe, M. L. Baesso, and C. Jacinto

J. Appl. Phys. 111, 093502 (2012); http://dx.doi.org/10.1063/1.4707940 (6 pages)

Online Publication Date: 1 May 2012

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A general time-resolved three-dimensional theory of the photothermal beam deflection for the measurement of thermal properties of opaque materials is presented. We derive the analytical solutions for the laser induced temperature profiles in the sample and in the fluid above the sample assuming flux discontinuity at the interface sample/fluid. We compare the analytical solutions with all numerical modeling using finite element analysis. The photothermal deflection signal is calculated and an expression is provided for the transverse photothermal signal at a position-sensing detector. We use the model and the experimental method to investigate opaque plastic and metals, and the results for the thermal properties of the samples are in an excellent agreement in the literature values.
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65.90.+i Other topics in thermal properties of condensed matter (restricted to new topics in section 65)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
02.60.-x Numerical approximation and analysis
42.62.-b Laser applications

Reversible high-pressure phase transition in LaN

Sebastian B. Schneider, Dominik Baumann, Ashkan Salamat, and Wolfgang Schnick

J. Appl. Phys. 111, 093503 (2012); http://dx.doi.org/10.1063/1.4709392 (6 pages) | Cited 1 time

Online Publication Date: 1 May 2012

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In situ high-pressure X-ray powder diffraction experiments on LaN up to 60.1 GPa at ambient temperature in a diamond-anvil cell revealed a reversible, first-order structural phase transition starting at ∼22.8 GPa and completed at ∼26.5 GPa from the ambient cubic phase (Fmmathm, no. 225) to a tetragonal high-pressure phase (P4/nmm, no. 19, a = 4.1060(6), c = 3.0446(6) Å, Z = 2, wRp = 0.011), which has not been claimed in theoretical predictions. HP-LaN is isotypic with a high-pressure polymorph of BaO, which crystallizes in a tetragonally distorted CsCl-type structure. The phase transition is accompanied by a volume collapse of about 11% which corresponds well with the reported data on HP-BaO. A linear extrapolation of the c/a ratio of the tetragonally distorted CsCl-type sub-cell reaches a value c/a = 1 of cubic CsCl-type HP-LaN at 91(12) GPa. In addition, the compressibility of LaN was investigated and resulted in a bulk modulus for the ambient pressure phase of B0 = 135(3) GPa and B′ = 5.0(5) after fitting a third-order Birch-Murnaghan equation of state to the experimental p–V data. The corresponding extrapolated bulk modulus of HP-LaN is found to be B0 = 278(6) GPa and its pressure derivative B′ = 1.2(2). Both as-calculated bulk moduli are compared to the respective values obtained from an Eulerian strain versus normalized stress plot to be 143(2) GPa for ambient LaN and 293(7) GPa for HP-LaN. Compared to other binary nitrides such as δ-ZrN or δ-HfN having bulk moduli of 285 GPa and 306 GPa, respectively, the extrapolated bulk moduli of HP-LaN are in the same order of magnitude, ranking HP-LaN as a highly incompressible material.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
62.50.-p High-pressure effects in solids and liquids
64.70.kp Ionic crystals
61.66.Fn Inorganic compounds
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations

Buckled colloidal crystals with nonspherical bases for two-dimensional slab photonic band gaps

E. K. Riley, E. Y. Fung, and C. M. Liddell Watson

J. Appl. Phys. 111, 093504 (2012); http://dx.doi.org/10.1063/1.4706556 (9 pages)

Online Publication Date: 2 May 2012

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Theoretical modeling of the photonic band gap forming properties is reported for the buckled phase of anisotropic particles. These exist between the first and second particulate layers of confined colloidal suspensions. Inspired by the range of non-spherical mushroom-cap building blocks for self-assembly that have been synthesized using seeded emulsion-polymerization, we explore in particular the band structures as a function of toroid shape parameter. The parameter is adjusted to incrementally transform hemispheres to spheres. Additionally, corrugation heights that systematically modulate the slab photonic crystal unit cell from rectangular monolayer to square bilayer are investigated. Polarization independent gaps in the guided modes are determined for direct and inverted structures that exhibit bifurcation in the particle orientation perpendicular to the slab plane. Gaps in the guided modes are observed between the fourth and fifth, twelfth and thirteenth, as well as higher band locales as the particle morphology and lattice aspect ratio vary.
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82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
87.15.rp Polymerization
42.70.Qs Photonic bandgap materials
62.90.+k Other topics in mechanical and acoustical properties of condensed matter (restricted to new topics in section 62)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Designing interlayers to improve the mechanical reliability of transparent conductive oxide coatings on flexible substrates

Eun-Hye Kim, Chan-Woo Yang, and Jin-Woo Park

J. Appl. Phys. 111, 093505 (2012); http://dx.doi.org/10.1063/1.4709295 (8 pages)

Online Publication Date: 2 May 2012

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In this study, we investigate the effect of interlayers on the mechanical properties of transparent conductive oxide (TCO) on flexible polymer substrates. Indium tin oxide (ITO), which is the most widely used TCO film, and Ti, which is the most widely used adhesive interlayer, are selected as the coating and the interlayer, respectively. These films are deposited on the polymer substrates using dc-magnetron sputtering to achieve varying thicknesses. The changes in the following critical factors for film cracking and delamination are analyzed: the internal stress (σi) induced in the coatings during deposition using a white light interferometer, the crystallinity using a transmission electron microscope, and the surface roughness of ITO caused by the interlayer using an atomic force microscope. The resistances to the cracking and delamination of ITO are evaluated using a fragmentation test. Our tests and analyses reveal the important role of the interlayers, which significantly reduce the compressive σi that is induced in the ITO and increase the resistance to the buckling delamination of the ITO. However, the relaxation of σi is not beneficial to cracking because there is less compensation for the external tension as σi further decreases. Based on these results, the microstructural control is revealed as a more influential factor than σi for improving crack resistance.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
81.15.Cd Deposition by sputtering
62.20.mq Buckling
62.20.mt Cracks
68.35.B- Structure of clean surfaces (and surface reconstruction)

Electronic and optical properties of free-standing and supported vanadium nanowires

Poorva Singh, Tashi Nautiyal, and Sushil Auluck

J. Appl. Phys. 111, 093506 (2012); http://dx.doi.org/10.1063/1.4709432 (9 pages) | Cited 2 times

Online Publication Date: 2 May 2012

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We have investigated theoretically the electronic and optical properties of free-standing and substrate-supported ultrathin nanowires (NWs) of the transition metal vanadium. Ground state of the structures studied, except free-standing zigzag geometry, is found to be magnetic in nature. We show that for some structures, study of the antiferromagnetic state necessitates considering various possible configurations. All the structures, except dimerized, show metallic behavior. Structure with helical geometry possesses decent value of magnetic moment and is exceptionally stable as well as most stiff of all the structures studied. The plasma frequency and dielectric function nicely exhibit the anisotropy due to one-dimensional nature of the nanowires. The latter is structure-dependent and markedly different from that of bulk. More realistic case of linear chains supported on a substrate shows fair impact of the substrate in comparison with free-standing case. There is substantial charge redistribution on relaxing the geometry. The d-states are in general shifted to lower energies and the peaks in the density of states are broadened, resulting in softening of the structures in the optical spectra.
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73.22.-f Electronic structure of nanoscale materials and related systems
78.67.Uh Nanowires
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Excitation power and temperature dependence of excitons in CuInSe2

F. Luckert, M. V. Yakushev, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin

J. Appl. Phys. 111, 093507 (2012); http://dx.doi.org/10.1063/1.4709448 (8 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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Excitonic recombination processes in high quality CuInSe2 single crystals have been studied by photoluminescence (PL) and reflectance spectroscopy as a function of excitation powers and temperature. Excitation power dependent measurements confirm the identification of well-resolved A and B free excitons in the PL spectra and analysis of the temperature quenching of these lines provides values for activation energies. These are found to vary from sample to sample, with values of 12.5 and 18.4 meV for the A and B excitons, respectively, in the one showing the highest quality spectra. Analysis of the temperature and power dependent PL spectra from the bound excitonic lines, labelled M1, M2, and M3 appearing in multiplets points to a likely assignment of the hole involved in each case. The M1 excitons appear to involve a conduction band electron and a hole from the B valence band hole. In contrast, an A valence band hole appears to be involved for the M2 and M3 excitons. In addition, the M1 exciton multiplet seems to be due to the radiative recombination of excitons bound to shallow hydrogenic defects, whereas the excitons involved in M2 and M3 are bound to more complex defects. In contrast to the M1 exciton multiplet, the excitonic lines of M2 and M3 saturate at high excitation powers suggesting that the concentration of the defects involved is low.
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71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials

Ultrahigh electromechanical response in (1−x)(Na0.5Bi0.5)TiO3-xBaTiO3 single-crystals via polarization extension

Wenwei Ge, Chengtao Luo, Qinhui Zhang, Chris P. Devreugd, Yang Ren, Jiefang Li, Haosu Luo, and D. Viehland

J. Appl. Phys. 111, 093508 (2012); http://dx.doi.org/10.1063/1.4709619 (8 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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The dielectric, ferroelectric, and electric field-induced strain response of [001]-and [101]-oriented 0.944Na0.5Bi0.5TiO3-0.056BaTiO3 (0.944NBT-0.056BT) single crystals were investigated as a function of temperature and dc bias (E). An ultrahigh electromechanical response with large amplitude longitudinal piezoelectric coefficients as high as d33 = 2500 pm/V was found in [001]PC oriented 0.944NBT-0.056BT single crystals near a depolarization temperature of Td = 130 °C. In-situ XRD revealed that the enhanced piezoelectric properties resulted from a polarization extension between a polar pseudocubic phase with a slight tetragonal (P4bm) distortion and a polar tetragonal one with a large tetragonal distortion of c/a = 1.02. Our findings indicate a potential approach to high performance lead-free piezoelectrics, via polarization extension.
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77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
77.80.-e Ferroelectricity and antiferroelectricity
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