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1 Feb 2012

Volume 111, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 031301 (2012); http://dx.doi.org/10.1063/1.3679521 (50 pages)

Shujun Zhang and Fei Li
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High performance ferroelectric relaxor-PbTiO3 single crystals: Status and perspective

Shujun Zhang and Fei Li

J. Appl. Phys. 111, 031301 (2012); http://dx.doi.org/10.1063/1.3679521 (50 pages) | Cited 2 times

Online Publication Date: 7 February 2012

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Ferroelectrics are essential components in a wide range of applications, including ultrasonic transducers, sensors, and actuators. In the single crystal form, relaxor-PbTiO3 (PT) piezoelectric materials have been extensively studied due to their ultrahigh piezoelectric and electromechanical properties. In this article, a perspective and future development of relaxor-PT crystals are given. Initially, various techniques for the growth of relaxor-PT crystals are reviewed, with crystals up to 100 mm in diameter and 200 mm in length being readily achievable using the Bridgman technique. Second, the characterizations of dielectric and electromechanical properties are surveyed. Boundary conditions, including temperature, electric field, and stress, are discussed in relation to device limitations. Third, the physical origins of the high piezoelectric properties and unique loss characteristics in relaxor-PT crystals are discussed with respect to their crystal structure, phase, engineered domain configuration, macrosymmetry, and domain size. Finally, relaxor-PT single crystals are reviewed with respect to specific applications and contrasted to conventional piezoelectric ceramics.
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77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
81.10.Fq Growth from melts; zone melting and refining
77.80.Jk Relaxor ferroelectrics
61.66.Fn Inorganic compounds
77.22.Gm Dielectric loss and relaxation
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back to top Lasers, Optics, and Optoelectronics

1D/2D switchable grating based on field-induced polymer stabilized blue phase liquid crystal

Ji-Liang Zhu, Jian-Gang Lu, Jing Qiang, En-Wei Zhong, Zhi-Cheng Ye, Zhenghong He, Xiaojun Guo, Cheng-Yuan Dong, Yikai Su, and Han-Ping D. Shieh

J. Appl. Phys. 111, 033101 (2012); http://dx.doi.org/10.1063/1.3680875 (5 pages)

Online Publication Date: 2 February 2012

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We present a 1D/2D switchable grating based on field-induced polymer stabilized blue phase liquid crystal (PSBPLC). For 1D grating, the diffraction efficiency of the first order is 37.2% and the phase modulation depth of the 1D grating can achieve 2π. For 2D grating, more than 90% of light intensity is distributed to the surrounding orders of zero order and the phase modulation depth is about 3.67π. Furthermore it shows fast phase modulation and 1D/2D switching time.
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61.30.Vx Polymer liquid crystals

Organic light-emitting diodes for lighting: High color quality by controlling energy transfer processes in host-guest-systems

Caroline Weichsel, Sebastian Reineke, Mauro Furno, Björn Lüssem, and Karl Leo

J. Appl. Phys. 111, 033102 (2012); http://dx.doi.org/10.1063/1.3679549 (7 pages)

Online Publication Date: 3 February 2012

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Exciton generation and transfer processes in a multilayer organic light-emitting diode (OLED) are studied in order to realize OLEDs with warm white color coordinates and high color-rendering index (CRI). We investigate a host-guest-system containing four phosphorescent emitters and two matrix materials with different transport properties. We show, by time-resolved spectroscopy, that an energy back-transfer from the blue emitter to the matrix materials occurs, which can be used to transport excitons to the other emitter molecules. Furthermore, we investigate the excitonic and electronic transfer processes by designing suitable emission layer stacks. As a result, we obtain an OLED with Commission Internationale de lÉclairage (CIE) coordinates of (0.444;0.409), a CRI of 82, and a spectrum independent of the applied current. The OLED shows an external quantum efficiency of 10% and a luminous efficacy of 17.4 lm/W at 1000 cd/m2.
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85.60.Jb Light-emitting devices

Deep traps and enhanced photoluminescence efficiency in nonpolar a-GaN/InGaN quantum well structures

A. Y. Polyakov, Lee-Woon Jang, Dong-Seob Jo, In-Hwan Lee, N. B. Smirnov, A. V. Govorkov, E. A. Kozhukhova, Kwang Hyeon Baik, and Sung-Min Hwang

J. Appl. Phys. 111, 033103 (2012); http://dx.doi.org/10.1063/1.3680877 (3 pages)

Online Publication Date: 3 February 2012

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Nonpolar (11-20) a-GaN/InGaN quantum well (QW) structures were grown by metalorganic chemical vapor deposition on r-plane (1-102) sapphire substrate using a two-stage growth procedure. Our studies demonstrate that, in contrast to polar QWs, these structures show the presence of deep electron traps with activation energy of 0.41 eV in admittance spectra and 1 eV electron traps in capacitance transient spectra. These traps are suspected to be nonradiative recombination centers, decreasing the nonpolar QW photoluminescence (PL) efficiency in our structures compared to polar structures. The PL efficiency of nonpolar QWs is shown to be greatly enhanced by coupling to localized surface plasmons formed by Ag nanoparticles.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

ZnO/Si arrays decorated by Au nanoparticles for surface-enhanced Raman scattering study

Yu Fei Chan, Hai Jun Xu, Lei Cao, Ying Tang, De Yao Li, and Xiao Ming Sun

J. Appl. Phys. 111, 033104 (2012); http://dx.doi.org/10.1063/1.3682462 (6 pages)

Online Publication Date: 7 February 2012

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Large scale and highly ordered flowerlike ZnO/Si nanostructures are successfully prepared by combining two common techniques, viz. hydrothermally etch fabrication of nanoporous Si pillar array (NSPA) and self-catalytic chemical vapor transport growth of ZnO nanowires. Au nanoparticles are decorated onto the ZnO/Si nanoflowers by the hydrothermal method. The formed Au/ZnO/NSPA array is evaluated as a surface-enhanced Raman scattering SERS-active substrate, which exhibits very high sensitivity and good stability and reproducibility. The excellent SERS enhancement is mainly attributed to the strong local electromagnetic effect which is associated with the unique flowerlike nanostructures of Au/ZnO/NSPA and the formed metal-induced gap states at the Au/ZnO interfaces. The results indicated that Au/ZnO/NSPA might be employed as a promising SERS substrate for the fast detection of low-concentration biomolecules.
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78.30.Hv Other nonmetallic inorganics
81.16.-c Methods of micro- and nanofabrication and processing
71.20.Ps Other inorganic compounds

Remote lasing in air by recombination and electron impact excitation of molecular nitrogen

Joseph Peñano, Phillip Sprangle, Bahman Hafizi, Daniel Gordon, Richard Fernsler, and Marlan Scully

J. Appl. Phys. 111, 033105 (2012); http://dx.doi.org/10.1063/1.3681282 (8 pages)

Online Publication Date: 8 February 2012

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We analyze and simulate the physical mechanisms for a remote atmospheric lasing configuration which utilizes a combination of an ultrashort pulse laser to form a plasma filament of seed electrons, and a heater beam to heat the seed electrons. Nitrogen molecules are excited by electron impact and recombination processes to induce lasing in the ultraviolet. Recombination excitation, thermal excitation, gain, and saturation are analyzed and simulated. The lasing gain is sufficiently high to reach saturation within the length of the plasma filament. A remotely generated ultraviolet source may have applications for standoff detection of biological and chemical agents.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.68.Kh Effects of air pollution
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
82.80.Gk Analytical methods involving vibrational spectroscopy
87.80.-y Biophysical techniques (research methods)
42.62.Be Biological and medical applications

Lowering the excitation threshold of a random laser using the dynamic scattering states of an organosiloxane smectic A liquid crystal

Stephen M. Morris, Damian J. Gardiner, Malik M. Qasim, Philip J. W. Hands, Timothy D. Wilkinson, and Harry J. Coles

J. Appl. Phys. 111, 033106 (2012); http://dx.doi.org/10.1063/1.3681898 (6 pages)

Online Publication Date: 10 February 2012

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Smectic A liquid crystals, based upon molecular structures that consist of combined siloxane and mesogenic moieties, exhibit strong multiple scattering of light with and without the presence of an electric field. This paper demonstrates that when one adds a laser dye to these compounds it is possible to observe random laser emission under optical excitation, and that the output can be varied depending upon the scattering state that is induced by the electric field. Results are presented to show that the excitation threshold of a dynamic scattering state, consisting of chaotic motion due to electro-hydrodynamic instabilities, exhibits lower lasing excitation thresholds than the scattering states that exist in the absence of an applied electric field. However, the lowest threshold is observed for a dynamic scattering state that does not have the largest scattering strength but which occurs when there is optimization of the combined light absorption and scattering properties.
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42.70.Df Liquid crystals
42.25.Fx Diffraction and scattering

InGaN/GaN multiple-quantum-well light-emitting diodes grown on Si(111) substrates with ZrB2(0001) buffer layers

Adam H. Blake, Derek Caselli, Christopher Durot, Jason Mueller, Eduardo Parra, Joseph Gilgen, Allison Boley, David J. Smith, Ignatius S. T. Tsong, John C. Roberts, Edwin Piner, Kevin Linthicum, James W. Cook, Jr., Daniel D. Koleske, Mary H. Crawford, et al.

J. Appl. Phys. 111, 033107 (2012); http://dx.doi.org/10.1063/1.3684557 (7 pages)

Online Publication Date: 13 February 2012

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Multiple-quantum-well light-emitting diode (LED) structures of InGaN/GaN were grown by metalorganic chemical vapor deposition on Si(111) substrates via ZrB2(0001) buffer layers and a GaN template comprising composite AlxGa1-xN (where x lies in the range from 0 to 1) transition layers to minimize cracking due to thermal expansion mismatch between Si and GaN. Photoluminescence and electroluminescence results from the LED structures compared favorably with similar measurements obtained on identical LED structures grown on sapphire substrates. However, in spite of all the precautions taken, cracking was still present in the LED structures. Scanning electron microscopy and transmission electron microscopy in plan-view and cross-section geometries were conducted on the LED structures to examine the presence and the influence of various defects such as microvoids, micropipes, and threading dislocations on the mechanism of cracking. Our results suggest that the crack network propagates from microvoids on the surface of the LED structure. The formation of microvoids appears to originate from imperfections in the epitaxial ZrB2(0001) buffer layer.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors

Extraction of optical Bloch modes in a photonic-crystal waveguide

S. R. Huisman, G. Ctistis, S. Stobbe, J. L. Herek, P. Lodahl, W. L. Vos, and P. W. H. Pinkse

J. Appl. Phys. 111, 033108 (2012); http://dx.doi.org/10.1063/1.3682105 (5 pages)

Online Publication Date: 13 February 2012

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We perform phase-sensitive near-field scanning optical microscopy on photonic-crystal waveguides. The observed intricate field patterns are analyzed by spatial Fourier transformations, revealing several guided transverse electric (TE) and transverse magnetic (TM) like modes. Using the reconstruction algorithm proposed by Ha et al. [Opt. Lett. 34, 3776 (2009)], we decompose the measured two-dimensional field pattern in a superposition of propagating Bloch modes. This opens new possibilities to study specific modes in near-field measurements. We apply the method to study the transverse behavior of a guided TE-like mode, where the mode extends deeper in the surrounding photonic crystal when the band edge is approached.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.30.Kq Fourier optics
07.79.Fc Near-field scanning optical microscopes

Theoretical description of thermal lens spectrometry in micro space

Mingqiang Liu, Dorota Korte, and Mladen Franko

J. Appl. Phys. 111, 033109 (2012); http://dx.doi.org/10.1063/1.3682481 (12 pages)

Online Publication Date: 13 February 2012

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For thermal lens spectrometry in micro space, temperature distributions in the sample under continuous-wave modulated excitations of either laser or incoherent light source (ILS) are for the first time deduced with respective considerations of different experimental parameters, such as flow of the sample, excitation beam divergence, effects of top/bottom layers adjacent to the sample, and sidewall effects. On the basis of the temperature distributions, thermal lens (TL) models are built based on the Fresnel diffraction theory. Numerical simulations of the influence of the above factors on the TL signal are made for different detection schemes in search of higher detection sensitivity. We were able to predict the optimum probe beam offset as a function of the flow of the sample, the optimum detection scheme to minimize the effects of fluctuation of the flow velocity and/or excitation beam radius, the optimum excitation beam radius for a given sample length, and propose a three-layer system in an ILS-excited thermal lens microscope for sensitivity enhancement of up to 10 times.
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42.79.-e Optical elements, devices, and systems
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.72.-g Optical sources and standards

Interference effects on indium tin oxide enhanced Raman scattering

Yimin Yang, Teng Qiu, Fan Kong, Jiyang Fan, Huiling Ou, Qingyu Xu, and Paul K. Chu

J. Appl. Phys. 111, 033110 (2012); http://dx.doi.org/10.1063/1.3684965 (4 pages)

Online Publication Date: 14 February 2012

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Optical interference is known to alter the intensity of Raman scattering signals. Its effect on enhanced Raman scattering from embedded indium tin oxide (ITO) nano-island arrays prepared by pulsed laser deposition of ITO films with different thicknesses on Si templates with nano-scale roughness are studied. Optical self-interference of the incident, scattered, and emitted light is observed to modulate the intensity and shape of the Raman signals as well as fluorescence background. The fluctuations in the Raman signals and fluorescence background can be explained by a theoretical model considering multiple reflections at the surface and interface. This interference effect must be taken into account in the investigation of enhanced Raman scattering from ITO.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
78.30.Hv Other nonmetallic inorganics
78.68.+m Optical properties of surfaces
81.16.Mk Laser-assisted deposition

Formation of silver nanoparticles inside a soda-lime glass matrix in the presence of a high intensity Ar+ laser beam

M. D. Niry, J. Mostafavi-Amjad, H. R. Khalesifard, A. Ahangary, and Y. Azizian-Kalandaragh

J. Appl. Phys. 111, 033111 (2012); http://dx.doi.org/10.1063/1.3684552 (7 pages)

Online Publication Date: 15 February 2012

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Formation and motion of the silver nanoparticles inside an ion-exchanged soda-lime glass in the presence of a focused high intensity continuous wave Ar+ laser beam (intensity: 9.2 × 104 W/cm2) have been studied in here. One-dimensional diffusion equation has been used to model the diffusion of the silver ions into the glass matrix, and a two-dimensional reverse diffusion model has been introduced to explain the motion of the silver clusters and their migration toward the glass surface in the presence of the laser beam. The results of the mentioned models were in agreement with our measurements on thickness of the ion-exchange layer by means of optical microscopy and recorded morphology of the glass surface around the laser beam axis by using a Mirau interferometer. SEM micrographs were used to extract the size distribution of the migrated silver particles over the glass surface.
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81.16.-c Methods of micro- and nanofabrication and processing
66.30.J- Diffusion of impurities
61.82.Ms Insulators

Modeling of room temperature current-voltage measurements on homo-junction HgCdTe diodes exhibiting nonequilibrium effects

Vanya Srivastav, R. Pal, and V. Venkataraman

J. Appl. Phys. 111, 033112 (2012); http://dx.doi.org/10.1063/1.3682483 (7 pages)

Online Publication Date: 15 February 2012

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HgCdTe mid wave infrared (MWIR) n+/ν/p+ homo-junction photodiodes with planar architecture are designed, fabricated, and measured at room temperature. An improved analytical I-V model is reported by incorporating trap assisted tunneling and electric field enhanced Shockley-Read-Hall generation recombination process due to dislocations. Tunneling currents are fitted before and after the Auger suppression of carriers with energy level of trap (Et), trap density (Nt), and the doping concentrations of n+ and ν regions as fitting parameters. Values of Et and Nt are determined as 0.79 Eg and ∼9 × 1014 cm−3, respectively, in all cases. Doping concentration of ν region was found to exhibit nonequilibrium depletion from a value of 2 × 1016 to 4 × 1015 cm−3 for n+ doping of 2 × 1017 cm−3. Pronounced negative differential resistance is observed in the homo-junction HgCdTe diodes.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Kk Junction diodes
back to top Plasmas and Electrical Discharges

Excitation wavelength dependence of water-window line emissions from boron-nitride laser-produced plasmas

M. Crank, S. S. Harilal, S. M. Hassan, and A. Hassanein

J. Appl. Phys. 111, 033301 (2012); http://dx.doi.org/10.1063/1.3682087 (6 pages)

Online Publication Date: 9 February 2012

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We investigated the effects of laser excitation wavelength on water-window emission lines of laser-produced boron-nitride plasmas. Plasmas are produced by focusing 1064 nm and harmonically generated 532 and 266 nm radiation from a Nd:YAG laser on BN target in vacuum. Soft x-ray emission lines in the water-window region are recorded using a grazing-incidence spectrograph. Filtered photodiodes are used to obtain complementary data for water-window emission intensity and angular dependence. Spectral emission intensity changes in nitrogen Ly-α and He-α are used to show how laser wavelength affects emission. Our results show that the relative intensity of spectral lines is laser wavelength dependent, with the ratio of Ly-α to He-α emission intensity decreasing as laser wavelength is shortened. Filtered photodiode measurements of angular dependence showed that 266 and 532 nm laser wavelengths produce uniform emission.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.59.Mv High-voltage diodes

Schlieren imaging in a dielectric barrier discharge actuator for airflow control

A. Cristofolini, G. Neretti, F. Roveda, and C. A. Borghi

J. Appl. Phys. 111, 033302 (2012); http://dx.doi.org/10.1063/1.3682488 (7 pages)

Online Publication Date: 10 February 2012

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The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.
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52.77.-j Plasma applications
52.80.Tn Other gas discharges
47.40.-x Compressible flows; shock waves
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.85.L- Flow control
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Optical visualization and electrical characterization of fast-rising pulsed dielectric barrier discharge for airflow control applications

Nicolas Benard, Nourredine Zouzou, Alain Claverie, Julien Sotton, and Eric Moreau

J. Appl. Phys. 111, 033303 (2012); http://dx.doi.org/10.1063/1.3682568 (13 pages)

Online Publication Date: 15 February 2012

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Flow control consists of manipulating flows in an effective and robust manner to improve the global performances of transport systems or industrial processes. Plasma technologies, and particularly surface dielectric barrier discharge (DBD), can be a good candidate for such purpose. The present experimental study focuses on optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry. Positive and negative polarities are compared in terms of current behavior, deposited energy, fast-imaging of the plasma propagation, and resulting modifications of the surrounding medium by using shadowgraphy acquisitions. Positive and negative pulses of voltage produce streamers and corona type plasma, respectively. Both of them result in the production of a localized pressure wave propagating in the air with a speed maintained at 343 m/s (measurements at room temperature of 20 °C). This suggests that the produced pressure wave can be considered as a propagating sound wave. The intensity of the pressure wave is directly connected to the dissipated energy at the dielectric wall with a linear increase with the applied voltage amplitude and a strong dependence toward the rising time. At constant voltage amplitude, the pressure wave is reinforced by using a positive pulse. The present investigation also reveals that rising and decaying periods of a single pulse of voltage result in two distinct pressure waves. As a result, superposition or successive pressure wave can be produced by adjusting the width of the pulse.
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52.77.-j Plasma applications
52.80.Hc Glow; corona
47.85.Gj Aerodynamics
47.85.L- Flow control
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Oxygen vacancy–induced ferromagnetism in un-doped ZnO thin films

Peng Zhan, Weipeng Wang, Can Liu, Yang Hu, Zhengcao Li, Zhengjun Zhang, Peng Zhang, Baoyi Wang, and Xingzhong Cao

J. Appl. Phys. 111, 033501 (2012); http://dx.doi.org/10.1063/1.3679560 (5 pages)

Online Publication Date: 1 February 2012

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ZnO films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.
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75.70.Ak Magnetic properties of monolayers and thin films
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.70.Bj Positron annihilation
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Composition dependence of elastic constants in wurtzite AlGaInN alloys

M. Łopuszyński and J. A. Majewski

J. Appl. Phys. 111, 033502 (2012); http://dx.doi.org/10.1063/1.3678002 (4 pages)

Online Publication Date: 2 February 2012

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In this paper, we analyze the dependence of elastic constants cij on composition for random wurtzite quaternary AlxGayIn1-x-yN alloy in the whole concentration range. The study takes as its starting point the cij parameters for zinc blende phase calculated earlier by the authors on the basis of valence force field model. To obtain the wurtzite constants from cubic material parameters the Martin transformation is used. The deviations from linear Vegard-like dependence of cij on composition are analyzed and accurate quadratic fits to calculated moduli are presented. The influence of nonlinear internal strain term in the Martin transformation is also investigated. Our general results for quaternary AlxGayIn1-x-yN alloys are compared with the recent ab initio calculations for ternaries GaxIn1-xN and AlxIn1-xN (Gorczyca and Łepkowski, Phys. Rev. B 83 203 201, 2011) and good qualitative agreement is found.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.dq Other elastic constants
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations

Enhanced indirect ferromagnetic p-d exchange coupling of Mn in oxygen rich ZnO:Mn nanoparticles synthesized by wet chemical method

Usman Ilyas, R. S. Rawat, T. L. Tan, P. Lee, R. Chen, H. D. Sun, Li Fengji, and Sam Zhang

J. Appl. Phys. 111, 033503 (2012); http://dx.doi.org/10.1063/1.3679129 (7 pages)

Online Publication Date: 3 February 2012

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This paper investigates the ferromagnetism in ZnO:Mn powders and presents our findings about the role played by the doping concentration and the structural defects towards the ferromagnetic signal. The narrow-size-distributed ZnO:Mn nanoparticles based powders with oxygen rich stoichiometery were synthesized by wet chemical method using zinc acetate dihydrate and manganese acetate tetrahydrate as precursors. A consistent increase in the lattice cell volume, estimated from x-ray diffraction spectra and the presence of Mn 2p3/2 peak at ∼640.9 eV, in x-ray photoelectron spectroscopic spectra, confirmed a successful incorporation of manganese in its Mn2+ oxidation state in ZnO host matrix. Extended deep level emission spectra in Mn doped ZnO powders exhibited the signatures of oxygen interstitials and zinc vacancies except for the sample with 5 at. % Mn doping. The nanocrystalline powders with 2 and 5 at. % Mn doping concentration were ferromagnetic at room temperature while the 10 at. % Mn doped sample exhibited paramagnetic behavior. The maximum saturation magnetization of 0.05 emu/g in the nanocrystalline powder with 5 at. % Mn doping having minimum defects validated the ferromagnetic signal to be due to strong p-d hybridization of Mn ions.
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81.16.Be Chemical synthesis methods
61.72.uj III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Characteristics of thickness-shear modes excited by two-layer piezoelectric film in acoustic sensors

Hui Zhang, Shu-yi Zhang, Li Fan, and Yu-ran Wang

J. Appl. Phys. 111, 033504 (2012); http://dx.doi.org/10.1063/1.3681187 (8 pages)

Online Publication Date: 3 February 2012

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The thickness-shear mode (TSM) excited by two-layer, (11math0)-textured, hexagonal piezoelectric film is studied to improve the performances of the acoustic sensors. The corresponding theoretical model is presented by the acoustic wave propagation theory in multi-layer structure combined with the excitation of TSM in two-layer piezoelectric film with opposite polarization direction. The model considers the effects of the acoustic attenuations in the Akheiser regime and Landau-Rumer regime. The calculated results manifest that, when the phase variation of two-layer piezoelectric film with opposite polarization direction is the same and equals to π, an enhanced second TSM can be excited and the corresponding first TSM is suppressed. The enhanced second TSM has higher resonant frequency and higher quality factor than the first TSM excited by a single- or two-layer piezoelectric film with identical polarization direction, which can be used for improving the mass sensitivity and sensitive resolution of the acoustic sensors in a liquid medium.
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77.55.H- Piezoelectric and electrostrictive films
62.60.+v Acoustical properties of liquids
77.65.-j Piezoelectricity and electromechanical effects

Tuning upconversion emission by controlling particle shape in NaYF4:Yb3+/Er3+ nanocrystals

Dangli Gao, Xiangyu Zhang, and Wei Gao

J. Appl. Phys. 111, 033505 (2012); http://dx.doi.org/10.1063/1.3681293 (5 pages)

Online Publication Date: 3 February 2012

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Rod-shaped and plate-shaped NaYF4:Yb3+/Er3+ nanocrystals (NCs) have been synthesized via a facile oleic acid-assisted hydrothermal route. The intensity and color tunability by shape controlling of NCs is demonstrated by up and down frequency conversions in NaYF4:Yb3+/Er3+ NCs. The results obviously show that rod-shaped NCs present much stronger upconversion luminescence intensity and smaller ratio of green to red emission intensity than that of plate-shaped NCs. The underlying reason of luminescence enhancement by shape controlling is explored, and a mechanism of the enhancement based on the decrease of nonradiation relaxation probability and the increase of energy transfer efficiency from Yb3+ to Er3+ is proposed for nanorods.
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78.67.Qa Nanorods
78.55.Hx Other solid inorganic materials
81.16.Rf Micro- and nanoscale pattern formation

Dielectric function spectra and critical-point energies of Cu2ZnSnSe4 from 0.5 to 9.0 eV

S. G. Choi, H. Y. Zhao, C. Persson, C. L. Perkins, A. L. Donohue, B. To, A. G. Norman, J. Li, and I. L. Repins

J. Appl. Phys. 111, 033506 (2012); http://dx.doi.org/10.1063/1.3681814 (6 pages)

Online Publication Date: 3 February 2012

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We present dielectric function ɛ = ɛ1 + iɛ2 spectra and critical-point energies of Cu2ZnSnSe4 determined by spectroscopic ellipsometry from 0.5 to 9.0 eV. We reduce artifacts from surface overlayers to the maximum extent possible by performing chemical-mechanical polishing and wet-chemical etching of the surface of a Cu2ZnSnSe4 thin film. Ellipsometric data are analyzed by the multilayer model and the ɛ spectra are extracted. The data exhibit numerous spectral features associated with critical points, whose energies are obtained by fitting standard lineshapes to second energy derivatives of the data. The experimental results are in good agreement with the ɛ spectra calculated within the GW quasi-particle approximation, and possible origins of the pronounced critical-point structures are identified.
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78.66.Li Other semiconductors
68.35.bt Other materials
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Ps Polishing, grinding, surface finishing

Interfaces between nonpolar and semipolar III-nitride semiconductor orientations: Structure and defects

J. Kioseoglou, A. Lotsari, E. Kalesaki, and G. P. Dimitrakopulos

J. Appl. Phys. 111, 033507 (2012); http://dx.doi.org/10.1063/1.3680876 (10 pages)

Online Publication Date: 6 February 2012

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Observations of easy transition between nonpolar and semipolar orientations during III-Nitride heteroepitaxy identify the 90o 〈math2math0〉 rotation relationship as being very important in defining this coexistence. A rigorous analysis of this relationship using the topological theory of interfaces showed that it leads to a high order of coincident symmetry and makes energetically favorable the appearance of the intergranular boundaries. Principal low-energy boundaries, that could also be technologically exploited, have been identified by high-resolution transmission electron microscopy (HRTEM) observations and have been studied energetically using empirical potential calculations. It is also shown that these boundaries can change their average orientation by incorporating disconnections. The pertinent strain relaxation mechanisms can cause such boundaries to act as sources of threading dislocations and stacking faults. The energetically favorable (10math0) || (0001) boundary was frequently observed to delimit m-plane crystallites in (math2math2) semipolar growth.
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68.35.Ct Interface structure and roughness
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects

In situ crystallization kinetics studies of plasma-deposited, hydrogenated amorphous silicon layers

K. Sharma, M. A. Verheijen, M. C. M. van de Sanden, and M. Creatore

J. Appl. Phys. 111, 033508 (2012); http://dx.doi.org/10.1063/1.3681185 (6 pages) | Cited 2 times

Online Publication Date: 6 February 2012

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The impact of the amorphous silicon properties, i.e., the microstructure parameter R* and the medium range order (MRO), on the crystallization process is highlighted and discussed. In agreement with literature, the development of large grains extending through the thickness of the poly-Si layer is found to be promoted by an increase in the amorphous silicon microstructure parameter, R*. Furthermore, while the role of the MRO in controlling the incubation time and, therefore, the onset in crystallization is generally acknowledged, it is also concluded that the presence of nano-sized voids plays an essential role in the crystallization kinetics.
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52.77.Dq Plasma-based ion implantation and deposition
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

The study of pressure induced structural phase transition in spin-frustrated Yb2Ti2O7 pyrochlore

A. K. Mishra, H. K. Poswal, Surinder M. Sharma, Surajit Saha, D. V. S. Muthu, Surjeet Singh, R. Suryanarayanan, A. Revcolevschi, and A. K. Sood

J. Appl. Phys. 111, 033509 (2012); http://dx.doi.org/10.1063/1.3681300 (6 pages)

Online Publication Date: 6 February 2012

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Our in situ x-ray diffraction and Raman measurements of Yb2Ti2O7 pyrochlore show that it undergoes a reversible structural phase transition from cubic pyrochlore to a monoclinic phase at ∼28.6 GPa. Analysis of the x-ray data shows the transition to be thermodynamically first order and the high pressure phase to be substitutionally disordered. These experimental results are supported by our first principles calculations.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
78.30.Hv Other nonmetallic inorganics
62.50.Ef Shock wave effects in solids and liquids
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