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15 Aug 2010

Volume 108, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

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

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin
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Preface to Special Topic: Invited Papers from the International Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, Aveiro, Portugal, 2009

Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin

J. Appl. Phys. 108, 041901 (2010); doi:10.1063/1.3474648 (2 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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Abstract Unavailable
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77.80.Dj Domain structure; hysteresis
68.37.Ps Atomic force microscopy (AFM)
82.45.-h Electrochemistry and electrophoresis
77.80.Jk Relaxor ferroelectrics
77.65.-j Piezoelectricity and electromechanical effects

Correlation of electron backscatter diffraction and piezoresponse force microscopy for the nanoscale characterization of ferroelectric domains in polycrystalline lead zirconate titanate

T. L. Burnett, P. M. Weaver, J. F. Blackburn, M. Stewart, and M. G. Cain

J. Appl. Phys. 108, 042001 (2010); doi:10.1063/1.3474940 (7 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The functional properties of ferroelectric ceramic bulk or thin film materials are strongly influenced by their nanostructure, crystallographic orientation, and structural geometry. In this paper, we show how, by combining textural analysis, through electron backscattered diffraction, with piezoresponse force microscopy, quantitative measurements of the piezoelectric properties can be made at a scale of 25 nm, smaller than the domain size. The combined technique is used to obtain data on the domain-resolved effective single crystal piezoelectric response of individual crystallites in Pb(Zr0.4Ti0.6)O3 ceramics. The results offer insight into the science of domain engineering and provide a tool for the future development of new nanostructured ferroelectric materials for memory, nanoactuators, and sensors based on magnetoelectric multiferroics.
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77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
79.20.Kz Other electron-impact emission phenomena
68.49.Jk Electron scattering from surfaces
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.55.H- Piezoelectric and electrostrictive films

Lateral piezoelectric response across ferroelectric domain walls in thin films

J. Guyonnet, H. Béa, and P. Paruch

J. Appl. Phys. 108, 042002 (2010); doi:10.1063/1.3474953 (11 pages) | Cited 3 times

Online Publication Date: 31 August 2010

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In purely c-axis oriented PbZr0.2Ti0.8O3 ferroelectric thin films, a lateral piezoresponse force microscopy signal is observed at the position of 180° domain walls, where the out-of-plane oriented polarization is reversed. Using electric force microscopy measurements we exclude electrostatic effects as the origin of this signal. Moreover, our mechanical simulations of the tip/cantilever system show that the small tilt of the surface at the domain wall below the tip does not satisfactorily explain the observed signal either. We thus attribute this lateral piezoresponse at domain walls to their sideways motion (shear) under the applied electric field. From simple elastic considerations and the conservation of volume of the unit cell, we would expect a similar lateral signal more generally in other ferroelectric materials, and for all types of domain walls in which the out-of-plane component of the polarization is reversed through the domain wall. We show that in BiFeO3 thin films, with 180°, 109°, and 71° domain walls, this is indeed the case.
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77.55.fg Pb(Zr,Ti)O3-based films
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis

Drive frequency dependent phase imaging in piezoresponse force microscopy

Huifeng Bo, Yi Kan, Xiaomei Lu, Yunfei Liu, Song Peng, Xiaofei Wang, Wei Cai, Ruoshi Xue, and Jinsong Zhu

J. Appl. Phys. 108, 042003 (2010); doi:10.1063/1.3474956 (5 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The drive frequency dependent piezoresponse (PR) phase signal in near-stoichiometric lithium niobate crystals is studied by piezoresponse force microscopy. It is clearly shown that the local and nonlocal electrostatic forces have a great contribution to the PR phase signal. The significant PR phase difference of the antiparallel domains are observed at the contact resonances, which is related to the electrostatic dominated electromechanical interactions of the cantilever and tip-sample system. Moreover, the modulation voltage induced frequency shift at higher eigenmodes could be attributed to the change of indention force depending on the modulation amplitude with a piezoelectric origin. The PR phase of the silicon wafer is also measured for comparison. It is certificated that the electrostatic interactions are universal in voltage modulated scanning probe microscopy and could be extended to other phase imaging techniques.
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07.85.-m X- and γ-ray instruments
02.10.Ud Linear algebra

Piezoresponse force microscopy investigations of Aurivillius phase thin films

Lynette Keeney, Panfeng F. Zhang, Claudia Groh, Martyn E. Pemble, and Roger W. Whatmore

J. Appl. Phys. 108, 042004 (2010); doi:10.1063/1.3474959 (9 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The sol-gel synthesis and characterization of n ≥ 3 Aurivillius phase thin films deposited on Pt/Ti/SiO2–Si substrates is described. The number of perovskite layers, n, was increased by inserting BiFeO3 into three layered Aurivillius phase Bi4Ti3O12 to form compounds such as Bi5FeTi3O15 (n = 4). 30% of the Fe3+ ions in Bi5FeTi3O15 were substituted with Mn3+ ions to form the structure Bi5Ti3Fe0.7Mn0.3O15. The electromechanical responses of the materials were investigated using piezoresponse force microscopy and the results are discussed in relation to the crystallinity of the films as measured by x-ray diffraction.
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68.55.A- Nucleation and growth
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.65.-j Piezoelectricity and electromechanical effects

Individual switching of film-based nanoscale epitaxial ferroelectric capacitors

Yunseok Kim, Hee Han, Brian J. Rodriguez, Ionela Vrejoiu, Woo Lee, Sunggi Baik, Dietrich Hesse, and Marin Alexe

J. Appl. Phys. 108, 042005 (2010); doi:10.1063/1.3474960 (4 pages) | Cited 5 times

Online Publication Date: 31 August 2010

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We have investigated the individual switching of nanoscale capacitors by piezoresponse force microscopy. Nanoscale epitaxial ferroelectric capacitors with terabyte per inch square equivalent density were fabricated by the deposition of top electrodes onto a pulsed laser deposited lead zirconate titanate thin film by electron beam evaporation through ultrathin anodic aluminum oxide membrane stencil masks. Using bias pulses, the nanoscale capacitors were uniformly switched and proved to be individually addressable. These film-based nanoscale capacitors might be a feasible alternative for high-density mass storage memory applications with near terabyte per inch square density due to the absence of any cross-talk effects.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors

Real space mapping of polarization dynamics and hysteresis loop formation in relaxor-ferroelectric PbMg1/3Nb2/3O3–PbTiO3 solid solutions

B. J. Rodriguez, S. Jesse, A. N. Morozovska, S. V. Svechnikov, D. A. Kiselev, A. L. Kholkin, A. A. Bokov, Z.-G. Ye, and S. V. Kalinin

J. Appl. Phys. 108, 042006 (2010); doi:10.1063/1.3474961 (11 pages) | Cited 4 times

Online Publication Date: 31 August 2010

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Polarization switching in ergodic relaxor and ferroelectric phases in the PbMg1/3Nb2/3O3–PbTiO3 (PMN-PT) system is studied using piezoresponse force microscopy, single point electromechanical relaxation measurements, and voltage spectroscopy mapping. The dependence of relaxation behavior on voltage pulse amplitude and time is found to follow a universal logarithmic behavior with a nearly constant slope. This behavior is indicative of the progressive population of slow relaxation states, as opposed to a linear relaxation in the presence of a broad relaxation time distribution. The role of relaxation behavior, ferroelectric nonlinearity, and the spatial inhomogeneity of the tip field on hysteresis loop behavior is analyzed in detail. The hysteresis loops for ergodic PMN-10%PT are shown to be kinetically limited, while in PMN with larger PT content, true ferroelectric hysteresis loops with low nucleation biases are observed.
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77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
77.22.Gm Dielectric loss and relaxation
77.80.Jk Relaxor ferroelectrics
77.80.Fm Switching phenomena

Investigation of the ferroelectric-relaxor transition in PbMg1/3Nb2/3O3–PbTiO3 ceramics by piezoresponse force microscopy

V. V. Shvartsman and A. L. Kholkin

J. Appl. Phys. 108, 042007 (2010); doi:10.1063/1.3474962 (6 pages) | Cited 4 times

Online Publication Date: 31 August 2010

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The spontaneous transition between the ferroelectric and relaxor states was investigated in 0.86PbMg1/3Nb2/3O3–0.14PbTiO3 ceramics using piezoresponse force microscopy (PFM). Macroscopically, the transition from the ferroelectric to relaxor phases manifests itself by an anomaly in the temperature dependences of the dielectric permittivity and by a sharp decline of the remanent polarization. Alternatively, PFM reveals a decay of the ferroelectric micron-size domains at the macroscopic Curie temperature, TC. Simultaneously, smaller domains of submicron sizes are observed at temperatures appreciably above TC, being concentrated near grain boundaries. It is argued that the particular mechanical and electrical conditions at the grain boundaries promote nucleation of the ferroelectric phase.
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77.80.B- Phase transitions and Curie point
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Jk Relaxor ferroelectrics
77.22.Ch Permittivity (dielectric function)
61.72.Mm Grain and twin boundaries

Analysis of the degradation induced by focused ion Ga3+ beam for the realization of piezoelectric nanostructures

D. Rémiens, R. H. Liang, C. Soyer, D. Deresmes, D. Troadec, S. Quignon, A. Da Costa, and R. Desfeux

J. Appl. Phys. 108, 042008 (2010); doi:10.1063/1.3474963 (6 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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Piezoelectric nanostructures (islands of dimensions in the lateral size range 50–500 nm) have been fabricated by focused Ga3+ ion beam (FIB) etching on PbZr0.54Ti0.46O3 thin films obtained by magnetron sputtering. The degradation induced by the etching process is investigated through the evolution of electromechanical activity measured by means of local piezoelectric hysteresis loops produced by piezoresponse force microscopy. The analysis of surface potential is performed by kelvin force microscopy and the measurement of current-voltage curves is carried out by conducting atomic force microscopy. Two kinds of structures, namely one based on crystallized films and the other based on amorphous ones, were studied. In this latter case, the amorphous films are postannealed after etching to obtain crystallized structure. For the structures based on the crystallized and then etched films, no piezoelectric signal was registered that evidences a serious degradation of material induced by Ga3+ ion implantation. For the structures based on the films etched in amorphous state and then crystallized, the piezoresponse signal was near to that of the reference films (crystallized and not etched) whatever were the ion dose and the island dimensions. Even for very small lateral size (50 nm), no size effect was observed. The island shapes fabricated by Ga3+ FIB etching process (islands with less than 50 nm lateral size) show a limitation of FIB processing and electron beam lithography seems to be necessary.
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81.16.Nd Micro- and nanolithography
61.80.Jh Ion radiation effects
77.65.-j Piezoelectricity and electromechanical effects
61.46.-w Structure of nanoscale materials
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Pyroelectric response of ferroelectric nanowires: Size effect and electric energy harvesting

A. N. Morozovska, E. A. Eliseev, G. S. Svechnikov, and S. V. Kalinin

J. Appl. Phys. 108, 042009 (2010); doi:10.1063/1.3474964 (6 pages) | Cited 6 times

Online Publication Date: 31 August 2010

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The size effect on pyroelectric response of ferroelectric nanowires is analyzed. The pyroelectric coefficient strongly increases with the wire radius decrease and diverges at critical radius Rcr corresponding to the size-driven transition into paraelectric phase. Size-driven enhancement of pyroelectric coupling leads to the giant pyroelectric current and voltage generation by the polarized ferroelectric nanoparticles in response to the temperature fluctuation. The maximum efficiency of the pyroelectric energy harvesting and bolometric detection is derived, and is shown to approach the Carnot limit for low temperatures.
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77.70.+a Pyroelectric and electrocaloric effects
77.80.B- Phase transitions and Curie point
73.63.Nm Quantum wires

Ferroelectric microdomains and microdomain arrays recorded in strontium–barium niobate crystals in the field of atomic force microscope

Tatiana R. Volk, Liliya V. Simagina, Radmir V. Gainutdinov, Alla L. Tolstikhina, and Lyudmila I. Ivleva

J. Appl. Phys. 108, 042010 (2010); doi:10.1063/1.3474965 (8 pages) | Cited 3 times

Online Publication Date: 31 August 2010

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Microdomains and various one-dimensional (1D)- and two-dimensional (2D)-microdomain arrays were formed under dc-voltages applied to the tip of an atomic force microscope (AFM) in ferroelectric SrxBa1−xNb2O6 crystals. Detailed studies of the characteristics of the AFM—recording and decay kinetics of the written arrays have shown that the crucial factors of the stability of a domain array are its dimensionality and discreteness (described by a distance Δ between the recorded point domains forming the array). The dependence of the stability on the discreteness of domain ensembles is analyzed. With decreasing Δ, the decay times of the domain ensembles increases. The stability of 2D arrays (domain squares, complex-shaped arrays composed of the domain ensembles of opposite polarity) by orders of magnitude exceeds that of 1D-arrays (domain chains and lines) provided all factors of recording being the same. As an illustration, the decay time of individual (spatially separated) domains and quasicontinuous domain lines are tens of minutes and about 20 h, respectively, whereas a quasicontionuous domain square persists within at least ten days. We assume the existence of cooperative interactions in microdomain ensembles, which reveal themselves even in arrays consisting of spatially separated point domain.
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77.84.Ek Niobates and tantalates
77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Piezoresponse force microscopy studies of the triglycine sulfate-based nanofibers

D. V. Isakov, E. de Matos Gomes, B. G. Almeida, I. K. Bdikin, A. M. Martins, and A. L. Kholkin

J. Appl. Phys. 108, 042011 (2010); doi:10.1063/1.3474966 (4 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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Local ferroelectric and piezoelectric properties of triglycine sulfate (TGS) nanocrystals embedded into poly(ethylene) oxide (PEO) electrospun fibers were examined by piezoresponse force microscopy (PFM). Piezoresponse contrast was found to be strongly dependent on the position being much stronger at the fiber periphery. A model of the distribution of TGS crystals inside the core-shell PEO-TGS fiber structure was proposed. TGS nanocrystals were unevenly distributed along the fiber axis and tend to grow near the surface of the fiber. The volume fraction distribution of the TGS crystals extracted from PFM measurements is in a good agreement with the data obtained from the dielectric constant measurements.
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77.80.-e Ferroelectricity and antiferroelectricity
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
77.22.Ch Permittivity (dielectric function)
77.65.-j Piezoelectricity and electromechanical effects
81.16.-c Methods of micro- and nanofabrication and processing

Local probing of magnetoelectric coupling in multiferroic composites of BaFe12O19–BaTiO3

D. V. Karpinsky, R. C. Pullar, Y. K. Fetisov, K. E. Kamentsev, and A. L. Kholkin

J. Appl. Phys. 108, 042012 (2010); doi:10.1063/1.3474967 (5 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The BaFe12O19–BaTiO3 composite ferroelectric/ferromagnetic ceramics were prepared by conventional solid-state sintering technique. The magnetic properties are consistent with the ratio of the magnetic phase present but ferroelectric properties are degraded due to a sufficiently high degree of conductivity in the ceramics. Magnetoelectric coupling was observed at a local level by means of the scanning probe microscopy (SPM). Piezoresponse and magnetic force modes of SPM were both utilized to assess strain-mediated magnetoelectric coupling between neighboring grains. The observed variation in the magnetic signal after the electrical poling with SPM was attested to the changes in the magnetic interactions and magnetic anisotropy leading to broadening of the magnetic domain wall.
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75.85.+t Magnetoelectric effects, multiferroics
77.84.Lf Composite materials
77.80.-e Ferroelectricity and antiferroelectricity
75.60.Ch Domain walls and domain structure
81.20.-n Methods of materials synthesis and materials processing
75.30.Gw Magnetic anisotropy
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Effects of distorted lattice and nonequal-valvence substitution on the long lasting phosphorescence of Eu2+ and Gd3+ doped RMg2(PO4)2 (R = Sr,Ba) phosphors

Liyan Liu, Ran Pang, Chengyu Li, and Qiang Su

J. Appl. Phys. 108, 043101 (2010); doi:10.1063/1.3475989 (5 pages) | Cited 1 time

Online Publication Date: 16 August 2010

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The afterglow of Eu2+ activated SrMg2(PO4)2 can be greatly enhanced by the codoping of Gd3+, as well as an interesting phenomenon of the improvement of the efficiency of the excitation light. However, Eu2+ activated BaMg2(PO4)2 does not show the phosphorescence until the codoping of Gd3+. It is suggested that the codoping of Gd3+ improve the electron storage ability of material by acting as electron-trapping centers resulted from the nonequal-valence substitution of Gd3+ replacing Sr2+ and Ba3+. And the Gd3+-induced enhancement of the excitation efficiency of Eu and Gd codoped SrMg2(PO4)2 is due to the improvement of the energy transfer efficiency caused by the distortion of lattice of Gd3+ located at the sites of Sr2+.
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78.55.Hx Other solid inorganic materials
78.60.-b Other luminescence and radiative recombination
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Enhancement of photovoltaic cell response due to high-refractive-index encapsulants

Ming Ma, Frank W. Mont, David J. Poxson, Jaehee Cho, E. Fred Schubert, Roger E. Welser, and Ashok K. Sood

J. Appl. Phys. 108, 043102 (2010); doi:10.1063/1.3466980 (3 pages) | Cited 1 time

Online Publication Date: 18 August 2010

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This study compares the electrical output of photovoltaic (PV) cells encapsulated with silicones having different refractive indices to unencapsulated PV cells. It is demonstrated that the optical concentration ratio of dome-shaped concentrator PV systems can be increased by using a higher refractive-index encapsulant. The short-circuit photocurrent of the PV cell having high-refractive-index encapsulation (n = 1.57) is 71% higher than that of the PV cell having a low-refractive-index encapsulation (n = 1.41), and 316% higher than that of the unencapsulated PV cell. These experimental concentration-ratio enhancements are consistent with the theoretical estimates of concentration ratio dependence on the refractive index of the PV concentrator.
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85.60.-q Optoelectronic devices

ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method

N. Bano, S. Zaman, A. Zainelabdin, S. Hussain, I. Hussain, O. Nur, and M. Willander

J. Appl. Phys. 108, 043103 (2010); doi:10.1063/1.3475473 (5 pages) | Cited 7 times

Online Publication Date: 19 August 2010

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We demonstrate white light luminescence from ZnO-organic hybrid light emitting diodes grown at 90 °C on flexible plastic substrate by aqueous chemical growth. The configuration used for the ZnO-organic hybrid white light emitting diodes (WLEDs) consists of a layer of poly (9, 9-dioctylfluorene) (PFO) on poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) coated plastic with top ZnO nanorods. Structural, electrical, and optical properties of these WLEDs were measured and analyzed. Room temperature electroluminescence spectrum reveals a broad emission band covering the range from 420 to 750 nm. In order to distinguish the white light components and contribution of the PFO layer we used a Gaussian function to simulate the experimental data. Color coordinates measurement of the WLED reveals that the emitted light has a white impression. The color rendering index and correlated color temperature of the WLED were calculated to be 68 and 5800 K, respectively.
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85.60.Jb Light-emitting devices
81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
78.60.Fi Electroluminescence
68.55.ag Semiconductors
78.66.-w Optical properties of specific thin films

Modeling high power light-emitting diode spectra and their variation with junction temperature

A. Keppens, W. R. Ryckaert, G. Deconinck, and P. Hanselaer

J. Appl. Phys. 108, 043104 (2010); doi:10.1063/1.3463411 (7 pages) | Cited 2 times

Online Publication Date: 20 August 2010

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Spectral radiant flux is the primary optical characteristic of a light source, determining the luminous flux and color. Much research is dedicated to the modeling of light-emitting diode (LED) spectra and their temperature dependence, allowing for the simulation of optical properties in various applications. Most of the spectral radiant flux models that have been published so far are purely mathematical. For this paper, spectral radiant fluxes of commercial single color LED packages have been measured in a custom made integrating sphere at several junction temperatures by active cooling and heating with a Peltier element. A spectrum model at 300 K is constructed where the Boltzmann free carrier distribution and carrier temperature are included. Subsequently, the model is extended with the carrier temperature variation, the band gap energy shift, and the nonradiative recombination rate decrease with junction temperature. As a result, the skewness variation, peak frequency shift, and peak value change in the spectrum with temperature can be predicted. The model has been validated by comparing flux and color coordinates of measured and simulated spectra at 340 K junction temperature. In practice, only two spectral flux measurements at different junction temperatures are needed to accurately simulate a single color spectrum at any temperature.
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85.60.Jb Light-emitting devices

Intense whole area electroluminescence from low pressure chemical vapor deposition-silicon-rich oxide based light emitting capacitors

A. A. González Fernández, M. Aceves Mijares, A. Morales Sánchez, and K. M. Leyva

J. Appl. Phys. 108, 043105 (2010); doi:10.1063/1.3465335 (4 pages)

Online Publication Date: 24 August 2010

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Light emitting capacitors (LECs) based on silicon-rich oxide (SRO) were fabricated and its electroluminescent (EL) characteristics studied. Thin SRO films with R0 = 30 were deposited by low pressure chemical vapor deposition and submitted to thermal treatment at 1100 °C for 180 min. Photoluminescence was observed in the SRO films and intense visible EL was obtained from fabricated LECs when stimulated with direct current. Strong intensity, naked eye visible, full area EL was obtained after the application of an electrical treatment. The EL was attributed to the presence of Si related defects and full area emission obtained was due to the optimization of carrier injection through the material by the annulations of preferential conductive paths.
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84.32.Tt Capacitors
85.60.Jb Light-emitting devices

Detection of concealed and buried chemicals by using multifrequency excitations

Yaohui Gao, Meng-Ku Chen, Chia-En Yang, Yun-Ching Chang, Jim Yao, Jiping Cheng, Stuart Yin, Rongqing Hui, Paul Ruffin, Christina Brantley, Eugene Edwards, and Claire Luo

J. Appl. Phys. 108, 043106 (2010); doi:10.1063/1.3474651 (6 pages)

Online Publication Date: 25 August 2010

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In this paper, we present a new type of concealed and buried chemical detection system by stimulating and enhancing spectroscopic signatures with multifrequency excitations, which includes a low frequency gradient dc electric field, a high frequency microwave field, and higher frequency infrared (IR) radiations. Each excitation frequency plays a unique role. The microwave, which can penetrate into the underground and/or pass through the dielectric covers with low attenuation, could effectively transform its energy into the concealed and buried chemicals and increases its evaporation rate from the sample source. Subsequently, a gradient dc electric field, generated by a Van De Graaff generator, not only serves as a vapor accelerator for efficiently expediting the transportation process of the vapor release from the concealed and buried chemicals but also acts as a vapor concentrator for increasing the chemical concentrations in the detection area, which enables the trace level chemical detection. Finally, the stimulated and enhanced vapors on the surface are detected by the IR spectroscopic fingerprints. Our theoretical and experimental results demonstrate that more than sixfold increase in detection signal can be achieved by using this proposed technology. The proposed technology can also be used for standoff detection of concealed and buried chemicals by adding the remote IR and/or thermal spectroscopic and imaging detection systems.
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29.20.Ba Electrostatic accelerators
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Multiphoton-absorption induced ultraviolet luminescence of ZnO nanorods using low-energy femtosecond pulses

Susanta Kumar Das, Mahua Biswas, Daragh Byrne, Martin Bock, Enda McGlynn, Markus Breusing, and Ruediger Grunwald

J. Appl. Phys. 108, 043107 (2010); doi:10.1063/1.3468632 (6 pages) | Cited 3 times

Online Publication Date: 25 August 2010

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Multiphoton-absorption (MPA) induced ultraviolet (UV) luminescence of ZnO nanorods grown by vapor phase transport was demonstrated using ultrafast excitation at pulse energies in the few nanojoules range, directly generated by a Ti:sapphire laser oscillator at wavelengths around 800 nm. The dependence of the UV luminescence on the excitation density reveals a two-photon absorption process as the responsible excitation mechanism. The broad spectral bandwidth of the excitation pulses obviously promotes the feasibility of the observed two-photon channel. Theoretical estimates concerning the contribution of nonlinear absorbance strongly support the experimental findings. The essential conditions for proper utilization of this process are discussed.
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78.55.Et II-VI semiconductors
78.67.Qa Nanorods

The measured dependence of the lateral ambipolar diffusion length on carrier injection-level in Stranski-Krastanov quantum dot devices

D. Naidu, P. M. Smowton, and H. D. Summers

J. Appl. Phys. 108, 043108 (2010); doi:10.1063/1.3471812 (10 pages)

Online Publication Date: 26 August 2010

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Using the segmented contact method we separate and numerically evaluate the components making up the threshold current density dependence of quantum dot ridge waveguide lasers. An increasing internal optical mode loss and an increasing lateral out-diffusion current are the significant processes in ridges of widths between 4 and 10 μm, with no significant contribution from a deteriorating gain-mode overlap. By fitting a diffusion length model to the lateral out-diffusion process, we extract the ambipolar diffusion length, Ld, as a function of intrinsic carrier injection-level which covers carrier densities appropriate for functioning light-emitting diode and laser devices. The measured dependence fits a diffusion mechanism involving the thermal redistribution of carriers via the wetting-layer and most significantly leads to two regimes where Ld can be reduced in self-assembled quantum-dot systems. Only one of these is shown to be beneficial to the overall efficiency of the device, while the other is at the expense of undesired high-order nonradiative recombination processes at high injection-levels. Covering a peak modal gain range of approximately 5 to 11 cm−1 over injection-levels of 65 to 122 meV at 350 K, this dependence caused Ld to change from 0.75 to 1.50 μm, with the maximum occurring at 84 meV where the peak modal gain is 6 cm−1. Decreasing the temperature to 300 K reduced Ld to <0.75 μm over approximately the same injection-level range.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Influence of period and amplitude of microwaviness on KH2PO4 crystal’s laser damage threshold

Mingjun Chen, Mingquan Li, Wei Jiang, and Qiao Xu

J. Appl. Phys. 108, 043109 (2010); doi:10.1063/1.3462430 (6 pages) | Cited 1 time

Online Publication Date: 31 August 2010

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The laser induced damage threshold (LIDT) has become a technical bottleneck which restricts the application and development of the inertial confinement fusion. Using single point diamond turning method to process KH2PO4 (KDP) crystals, the periodic microwaviness will be left on the machined surface which has a significant impact on the LIDT. In this paper, after acquiring the frequency information of machined surface of KDP crystals with the power spectral density method, we analyze quantitatively the influence of microwaviness on the LIDT of KDP crystal with the Fourier modal theory. Research results indicate that: the surface morphology of KDP crystal is consisted of the subwaviness with different characteristic spatial frequencies; and the reduced amount of the LIDT of KDP crystal leaded by such subwaviness is different; the experimental results of the LIDT are consistent with the theoretical calculations basically; for the machine tool and the processing technology we used, the leading frequency of microwaviness which caused the LIDT decreasing is between (350 μm)−1 and (30 μm)−1, especially between (90 μm)−1 and (180 μm)−1.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
68.35.bt Other materials
79.20.Ds Laser-beam impact phenomena
back to top Plasmas and Electrical Discharges

Spherical and cylindrical imploding and exploding shock waves in plasma system dominated by pair production

Muhammad Noaman ul Haq, R. Saeed, and Asif Shah

J. Appl. Phys. 108, 043301 (2010); doi:10.1063/1.3475725 (5 pages) | Cited 3 times

Online Publication Date: 18 August 2010

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The propagation of ion acoustic shock waves in cylindrical and spherical geometries has been investigated. The plasma system consists of cold ions, Boltzmannian electrons and positrons. Spherical, cylindrical Korteweg–de Vries–Burger equations have been derived by reductive perturbation technique and their shock behavior is studied by employing finite difference method. Our main emphasis is on the behavior of shock as it moves toward and away from center of spherical and cylindrical geometries. It is noticed, that the shock wave strength and steepness accrues with time as it moves toward the center and shock enervates as it moves away from center. The strength of shock in spherical geometry is found to dominate over shock strength in cylindrical geometry. Positron concentration, kinematic viscosity are also found to have significant effect on the shock structure and propagation. The results may have relevance in the inertial confinement fusion plasmas.
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52.35.Tc Shock waves and discontinuities
52.50.Lp Plasma production and heating by shock waves and compression
52.58.-c Other confinement methods
52.80.Qj Explosions; exploding wires
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Optimization of La0.7Ba0.3MnO3−δ complex oxide laser ablation conditions by plume imaging and optical emission spectroscopy

S. Amoruso, C. Aruta, R. Bruzzese, D. Maccariello, L. Maritato, F. Miletto Granozio, P. Orgiani, U. Scotti di Uccio, and X. Wang

J. Appl. Phys. 108, 043302 (2010); doi:10.1063/1.3467770 (8 pages) | Cited 7 times

Online Publication Date: 18 August 2010

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The properties of thin films of complex oxides, such as La1−xDxMnO3−δ (D = Ba, Ca, Sr, etc.), produced by pulsed laser deposition depend critically on the experimental parameters in which laser ablation is carried out. Here, we report a comparative analysis of the pulsed laser ablation process of La0.7Ba0.3MnO3−δ, in oxygen background, in the ambient pressure range from 10−2 to 1 mbar, typically employed in pulsed laser deposition of manganites. The laser ablation plume was studied by using time-gated imaging and optical emission spectroscopy techniques. It was found that at a pressure of ≈ 10−2 mbar, the plume species arriving at the substrate are characterized by hyperthermal kinetic energy ( ≈ 10 eV), and high degree of excitation. On the contrary, at larger oxygen pressure (0.1–1 mbar), the velocity of plume species reaching the substrate, and their degree of excitation are much reduced by the confining effects of the background gas. These features explain why an appropriate choice of the experimental conditions in which the deposition process is carried out leads to better quality films, providing helpful indications to improve control over the growth process of both La1−xDxMnO3−δ and other perovskitic oxides.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
52.38.Mf Laser ablation

Low temperature plasma enhanced chemical vapor deposition of thin films combining mechanical stiffness, electrical insulation, and homogeneity in microcavities

S. Peter, M. Günther, D. Hauschild, and F. Richter

J. Appl. Phys. 108, 043303 (2010); doi:10.1063/1.3474989 (12 pages)

Online Publication Date: 19 August 2010

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The deposition of hydrogenated amorphous carbon (a-C:H) as well as hydrogenated amorphous silicon carbonitride (SiCN:H) films was investigated in view of a simultaneous realization of a minimum Young’s modulus (>70 GPa), a high electrical insulation ( ≥ 1 MV/cm), a low permittivity and the uniform coverage of microcavities with submillimeter dimensions. For the a-C:H deposition the precursors methane (CH4) and acetylene (C2H2) were used, while SiCN:H films were deposited from mixtures of trimethylsilane [SiH(CH3)3] with nitrogen and argon. To realize the deposition of micrometer thick films with the aforementioned complex requirements at substrate temperatures ≤ 200 °C, several plasma enhanced chemical vapor deposition methods were investigated: the capacitively coupled rf discharge and the microwave electron cyclotron resonance (ECR) plasma, combined with two types of pulsed substrate bias. SiCN:H films deposited at about 1 Pa from ECR plasmas with pulsed high-voltage bias best met the requirements. Pulsed biasing with pulse periods of about 1 μs and amplitudes of about −2 kV was found to be most advantageous for the conformal low temperature coating of the microtrenches, thereby ensuring the required mechanical and insulating film properties.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
62.20.de Elastic moduli
77.22.Ch Permittivity (dielectric function)
52.77.Dq Plasma-based ion implantation and deposition
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