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12 Apr 2010

Volume 96, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 153701 (2010); http://dx.doi.org/10.1063/1.3385388 (3 pages)

Sinan Keten and Markus J. Buehler
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Two-dimensional optics on silicon nitride multilayer: Refraction of Bloch surface waves

Tristan Sfez, Emiliano Descrovi, Libo Yu, Marzia Quaglio, Lorenzo Dominici, Wataru Nakagawa, Francesco Michelotti, Fabrizio Giorgis, and Hans Peter Herzig

Appl. Phys. Lett. 96, 151101 (2010); http://dx.doi.org/10.1063/1.3385729 (3 pages) | Cited 5 times

Online Publication Date: 12 April 2010

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When properly designed, a dielectric multilayer can sustain Bloch surface waves (BSWs). Using a multiheterodyne scanning near-field optical microscope that resolves phase and polarization, we will show that a thin dielectric structure deposited on the multilayer deflects the BSW propagation according to Snell’s law. Moreover, the mechanism involved in this process is a transfer of energy from the BSW state in the bare multilayer to the new BSW state generated by the presence of the thin dielectric structure. No relevant radiative counterpart occurs. This characteristic validates the treatment of BSWs at the surface of dielectric multilayers as a two-dimensional phenomenon.
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42.70.-a Optical materials
42.15.-i Geometrical optics
42.25.-p Wave optics

Quantum efficiency and oscillator strength of site-controlled InAs quantum dots

F. Albert, S. Stobbe, C. Schneider, T. Heindel, S. Reitzenstein, S. Höfling, P. Lodahl, L. Worschech, and A. Forchel

Appl. Phys. Lett. 96, 151102 (2010); http://dx.doi.org/10.1063/1.3393988 (3 pages) | Cited 5 times

Online Publication Date: 12 April 2010

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We report on time-resolved photoluminescence spectroscopy to determine the oscillator strength (OS) and the quantum efficiency (QE) of site-controlled InAs quantum dots nucleating on patterned nanoholes. These two quantities are determined by measurements on site-controlled quantum dot (SCQD) samples with varying thickness of the capping layer. We determine radiative and nonradiative decay rates, from which we calculate an OS of 10.1±2.6 and an encouragingly high QE of (47±14)% for the SCQDs. The nonideal QE is attributed to nonradiative recombination at the etched nanohole interface.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.47.jd Time resolved luminescence

Phase-locked ring-defect photonic crystal vertical-cavity surface-emitting laser

Anjin Liu, Wei Chen, Mingxin Xing, Wenjun Zhou, Hongwei Qu, and Wanhua Zheng

Appl. Phys. Lett. 96, 151103 (2010); http://dx.doi.org/10.1063/1.3394006 (3 pages) | Cited 6 times

Online Publication Date: 12 April 2010

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Phase-locked oxide-confined ring-defect photonic crystal vertical-cavity surface-emitting laser is presented. The coupled-mode theory is employed to illustrate the two supermodes of the device, in-phase and out-of-phase supermode. Experimental results verify the two supermodes by the characteristics of the spectra and the far field patterns. At the lower current, only the out-of-phase supermode is excited, whereas under the higher current, the in-phase supermode also appears at the shorter wavelength range. In addition, the measured spectral separation between the two supermodes agrees well with the theoretical result.
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42.55.Tv Photonic crystal lasers and coherent effects
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking

Temperature-dependent carrier tunneling for self-assembled InAs/GaAs quantum dots with a GaAsN quantum well injector

C. Y. Jin, S. Ohta, M. Hopkinson, O. Kojima, T. Kita, and O. Wada

Appl. Phys. Lett. 96, 151104 (2010); http://dx.doi.org/10.1063/1.3396187 (3 pages) | Cited 6 times

Online Publication Date: 13 April 2010

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We have investigated the carrier tunneling process in a quantum-dot (QD) tunnel injection structure, which employs a GaAs1−xNx quantum well (QW) as a carrier injector. The influence of the barrier thickness between the GaAs1−xNx well and InAs dot layer has been studied by temperature-dependent photoluminescence. Although the 2.5 nm barrier sample exhibits the best tunneling efficiency, a 3.0 nm thickness for the barrier is optimum to retain good optical properties. The carrier capture time from the GaAs1−xNx QW to QD ground states has been evaluated by time-resolved photoluminescence. The result indicates that efficient carrier tunneling occurs at temperatures above 150 K due to the temperature dependent nature of phonon-assisted processes.
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73.40.Gk Tunneling
73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.63.Hs Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors

X-shaped plasmonic antenna on a quantum cascade laser

D. Austin, N. Mullin, I. Luxmoore, I. C. Sandall, A. G. Cullis, A. Bismuto, J. Faist, J. K. Hobbs, and L. R. Wilson

Appl. Phys. Lett. 96, 151105 (2010); http://dx.doi.org/10.1063/1.3380660 (3 pages)

Online Publication Date: 13 April 2010

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We report an x-shaped plasmonic antenna design patterned onto the gold coated facet of a mid-infrared quantum cascade laser. Using apertureless scanning near-field optical microscopy we measure a single enhanced region in the optical near-field at the center of the x-antenna, with a full-width-at-half-maximum of ∼ 100 nm for the operating wavelength of ∼ 8.8 μm. This design provides complete suppression of near-field signal away from the center, with concomitant improvements in imaging contrast expected. Our experimental results are also in good agreement with finite difference time domain simulations, which show a full-width-at-half-maximum of ∼ 80 nm.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.Ba Antennas: theory, components and accessories

Efficient visible to infrared quantum cutting through downconversion with the Er3+–Yb3+ couple in Cs3Y2Br9

J. J. Eilers, D. Biner, J. T. van Wijngaarden, K. Krämer, H.-U. Güdel, and A. Meijerink

Appl. Phys. Lett. 96, 151106 (2010); http://dx.doi.org/10.1063/1.3377909 (3 pages) | Cited 33 times

Online Publication Date: 14 April 2010

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Downconversion of one visible photon to two near-infrared photons may increase the efficiency of c-Si solar cells by 30%. The lanthanide ion couple Er3+–Yb3+ is well known for efficient upconversion but for the reverse process, downconversion, fast multiphonon relaxation from the 4F7/2 level has been shown to compete with downconversion. Here we report efficient downconversion for the Er–Yb couple in Cs3Y2Br9. The low phonon energy in this bromide host suppresses multiphonon relaxation and efficient two step energy transfer from the 4F7/2 level of Er3+ is observed and results in strong 1000 nm emission from Yb3+. Based on emission spectra and luminescence life time measurements an intrinsic downconversion efficiency close to 200% is determined.
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88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells
78.55.Hx Other solid inorganic materials

Controlling blinking in multilayered quantum dots

Ruimin Wang, Yanpeng Zhang, Chenli Gan, Javed Muhammad, and Min Xiao

Appl. Phys. Lett. 96, 151107 (2010); http://dx.doi.org/10.1063/1.3396985 (3 pages) | Cited 3 times

Online Publication Date: 14 April 2010

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The fluorescence intermittency of multilayered quantum dots (QDs) is experimentally investigated. The measured blinking statistical probabilities for QDs of different shell structures and at different excitation powers are compared with the diffusion controlled electron transfer model. The results show that the power law statistics for the “on” and “off” events depend strongly on the structure and thicknesses of the shells. Strongly suppressed blinking behavior is observed in the CdSe/CdS/ZnCdS/ZnS QDs.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors

Rare frustration of optical supercontinuum generation

D. R. Solli, C. Ropers, and B. Jalali

Appl. Phys. Lett. 96, 151108 (2010); http://dx.doi.org/10.1063/1.3374860 (3 pages) | Cited 8 times

Online Publication Date: 14 April 2010

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Recent work has shown that optical rogue waves, large bandwidth fluctuations following heavy-tailed statistics, can arise during spectral broadening by stochastic enhancement of nonlinearity. Here, we report the observation of a different form of extreme fluctuations in supercontinuum pulse trains: Pulses of unusually small spectral bandwidth following left-skewed heavy-tailed statistics. Displaying a pulse evolution strongly varying from that of large extremes in supercontinuum, these rogue events appear when spectral broadening is frustrated by competition between presolitonic features within the modulation-instability band. This suppression effect can also be externally induced with a weak control pulse.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
02.50.Ey Stochastic processes

Electroluminescence observation of nanoscale phase separation in quaternary AlInGaN light-emitting diodes

X. A. Cao and Y. Yang

Appl. Phys. Lett. 96, 151109 (2010); http://dx.doi.org/10.1063/1.3397987 (3 pages) | Cited 6 times

Online Publication Date: 15 April 2010

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Anomalous temperature-dependent electroluminescence (EL) of Al0.06In0.02Ga0.92N/Al0.1Ga0.9N multiple-quantum-well light-emitting diodes was investigated. At low temperatures and low currents, the EL was dominated by narrow peaks arising from GaN band edge (3.47 eV) and AlGaN localized state emission (3.59 eV). At 150 K, as thermalized carriers surmounted a static nanobarrier surrounding In-rich nanoclusters, the EL shifted to low-energy emission at 3.39 eV. These EL anomalies are evidence that, contradictory to theoretical predictions, there remains a strong effect of compositional fluctuation toward nanoscale phase separation in low In/Al AlInGaN alloys. During the interphase transfer at 150 K, the majority of excitons underwent nonradiative decay, leading to a sharp decrease in quantum efficiency by over one order of magnitude.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling

Semiconductor saturable absorbers for ultrafast terahertz signals

Matthias C. Hoffmann and Dmitry Turchinovich

Appl. Phys. Lett. 96, 151110 (2010); http://dx.doi.org/10.1063/1.3386542 (3 pages) | Cited 10 times

Online Publication Date: 15 April 2010

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We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP, and Ge in the terahertz (THz) frequency range at room temperature using nonlinear THz spectroscopy. The saturation mechanism is based on a decrease in electron conductivity of semiconductors at high electron momentum states, due to conduction band nonparabolicity and scattering into satellite valleys in strong THz fields. Saturable absorber parameters, such as linear and nonsaturable transmission, and saturation fluence, are extracted by fits to a classic saturable absorber model. Further, we observe THz pulse shortening, and an increase in the group refractive index of the samples at higher THz pulse peak fields.
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78.47.J- Ultrafast spectroscopy (<1 psec)
73.61.Ey III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Polydimethylsiloxane-enclosed liquid crystal lasers for lab-on-chip applications

Jürgen Schmidtke and Eugene M. Terentjev

Appl. Phys. Lett. 96, 151111 (2010); http://dx.doi.org/10.1063/1.3399760 (3 pages) | Cited 4 times

Online Publication Date: 15 April 2010

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We demonstrate the operation of a self-organized cholesteric liquid crystal laser confined between optically clear and elastic polydimethylsiloxane (PDMS) substrates. The formation of a planar helical texture in the cholesteric was supported by microsctructuring of PDMS layer surface, using the nanoembossing technique with glass substrates coated with conventional alignment layers as a template. The potential of combining miniature cholesteric laser sources and microfluidic devices for lab-on-chip applications is discussed.
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87.80.Ek Mechanical and micromechanical techniques
47.85.Np Fluidics
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.70.Jk Polymers and organics
42.55.Mv Dye lasers

Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination

Maik Scheller, Kai Baaske, and Martin Koch

Appl. Phys. Lett. 96, 151112 (2010); http://dx.doi.org/10.1063/1.3402767 (3 pages) | Cited 8 times

Online Publication Date: 15 April 2010

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We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2π uncertainty known from conventional photomixing systems while preserving a high spatial resolution.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Microcavity enhanced silicon light emitting pn-diode

J. Potfajova, B. Schmidt, M. Helm, T. Gemming, M. Benyoucef, A. Rastelli, and O. G. Schmidt

Appl. Phys. Lett. 96, 151113 (2010); http://dx.doi.org/10.1063/1.3385153 (3 pages) | Cited 2 times

Online Publication Date: 15 April 2010

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An electrically driven silicon light emitting diode with two distributed Bragg reflectors is reported. The active material is a Si pn-junction fabricated by boron ion implantation into an n-type silicon-on-insulator wafer. The cavity with a thickness of a few wavelengths is formed by amorphous Si/SiO2 multilayer stacks. A strong narrowing and enhancement of the electroluminescence at a resonant wavelength of λ = 1146 nm is observed with a quality factor of Q = 143 and a finesse of F = 11.
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85.60.Jb Light-emitting devices
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics

Focusing of millijoule picosecond Kα radiation from 100 TW laser-solid interaction

A. Lévy, F. Dorchies, P. Audebert, J. Chalupský, V. Hájková, L. Juha, T. Kaempfer, H. Sinn, I. Uschmann, L. Vyšín, and J. Gaudin

Appl. Phys. Lett. 96, 151114 (2010); http://dx.doi.org/10.1063/1.3386534 (3 pages) | Cited 1 time

Online Publication Date: 16 April 2010

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A calibrated x-ray spectrometer was used to characterize an intense 4.5 keV Kα source. Generated from the interaction of 30 J-320 fs laser pulses focused on 25 μm thick Ti foils, the conversion efficiency into Ti Kα line is estimated to (9±6)×10−5. Highly efficient collection, monochromatization and focusing were achieved using an ellipsoidally bent highly oriented pyrolytic graphite crystal. The measured 700 μm full width half maximum (FWHM) focal spot leads to a fluence of (3.0±2.1) mJ/cm2 hence paving the way to the study of intense x-ray pulse interaction with matter as demonstrated by a first simple experiment.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys

Ultraviolet GaN-based microdisk laser with AlN/AlGaN distributed Bragg reflector

Cheng-Chang Chen, M. H. Shih, Yi-Chun Yang, and Hao-Chung Kuo

Appl. Phys. Lett. 96, 151115 (2010); http://dx.doi.org/10.1063/1.3399781 (3 pages) | Cited 6 times

Online Publication Date: 16 April 2010

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We demonstrated a 4.7 μm GaN-based microdisk laser with 25-pair AlN/AlGaN distributed Bragg reflector in ultraviolet range without undercut or deeply-etching procedures. The distributed Bragg reflector provides a high reflectivity of 85%, and selects lasing mode around 375 nm wavelength. Under optical pumping conditions, the lasing action was observed with a low threshold power density of 0.03 kW/cm2. We also characterized the whispering gallery mode profiles of the microdisk with finite-different time-domain simulation.
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42.55.Sa Microcavity and microdisk lasers
02.70.Bf Finite-difference methods
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Laser wavelength effects on ionic and atomic emission from tin plasmas

D. Campos, S. S. Harilal, and A. Hassanein

Appl. Phys. Lett. 96, 151501 (2010); http://dx.doi.org/10.1063/1.3386524 (3 pages) | Cited 15 times

Online Publication Date: 12 April 2010

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We investigated the effects of laser wavelength on atomic and ionic emission from Sn plasmas. Plasmas were produced using planar Sn targets excited with 10.6 μm carbon dioxide (CO2) and 1.06 μm neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. Two-dimensional spectral imaging of visible emission showed that continuum emission was significantly more intense in the CO2 laser produced plasma (LPP) whereas line emission was considerably more extensive in the Nd:YAG LPP. Faraday cup analysis showed that ion profiles were narrower with CO2 LPPs although they possessed higher kinetic energies.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Numerical modeling of a table-top tunable Smith–Purcell terahertz free-electron laser operating in the super-radiant regime

C. Prokop, P. Piot, M. C. Lin, and P. Stoltz

Appl. Phys. Lett. 96, 151502 (2010); http://dx.doi.org/10.1063/1.3386543 (3 pages) | Cited 11 times

Online Publication Date: 16 April 2010

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Terahertz (THz) radiation occupies a very large portion of the electromagnetic spectrum and has generated much recent interest due to its ability to penetrate deep into many organic materials without the damage associated with ionizing radiation such as x-rays. One path for generating copious amount of tunable narrow-band THz radiation is based on the Smith–Purcell free-electron laser (SPFEL) effect. In this paper we propose a simple concept for a compact two-stage tunable SPFEL operating in the super-radiant regime capable of radiating at the fundamental bunching frequency. We demonstrate its capabilities and performances using the conformal finite-difference time-domain electromagnetic solver VORPAL.
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41.60.Cr Free-electron lasers
42.60.Fc Modulation, tuning, and mode locking
02.70.Bf Finite-difference methods

Microwave resonances of a hairpin probe in a magnetized plasma

G. S. Gogna and S. K. Karkari

Appl. Phys. Lett. 96, 151503 (2010); http://dx.doi.org/10.1063/1.3400214 (3 pages) | Cited 2 times

Online Publication Date: 16 April 2010

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The effect due to the electron cyclotron frequency on the microwave resonances of a hairpin probe is investigated in a moderate to strongly magnetized plasma. The magnetic field is independently varied over a wide range from 0.01–0.13 T while maintaining the local plasma density constant. At strong magnetic fields the resonance frequency is found to be lower than that measured in vacuum implying that the relative plasma dielectric permittivity, εp>1. It is proposed that the experiments reported here are consistent with a permittivity model that includes magnetic field.
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52.70.Ds Electric and magnetic measurements
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Mq Dielectric properties
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Nonlinear electrophoretic motion of dielectric microparticles in nematic liquid crystals

A. V. Ryzhkova, F. V. Podgornov, and W. Haase

Appl. Phys. Lett. 96, 151901 (2010); http://dx.doi.org/10.1063/1.3386570 (3 pages) | Cited 5 times

Online Publication Date: 12 April 2010

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The motion of dielectric microparticles induced by external ac electric field, E, was investigated in the cell with in-plane stripe electrodes and filled with homeotropically aligned nematic liquid crystal. It was demonstrated that the average velocity of the microparticles depended on the third power of the electric field strength (v = μ(3)E3). The experimental results were explained by the induced charge electrophoresis.
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82.45.Un Dielectric materials in electrochemistry
82.45.Wx Polymers and organic materials in electrochemistry
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Nature of deep center emissions in GaN

A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 96, 151902 (2010); http://dx.doi.org/10.1063/1.3389497 (3 pages) | Cited 15 times

Online Publication Date: 12 April 2010

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Photoluminescence (PL) emission spectroscopy was employed to probe the nature of deep center emissions in GaN. The room temperature PL spectrum measured in the infrared (IR) region revealed an emission band centered around 1.23 eV. Based on detailed analysis of both the IR and visible emission spectra, we suggest that this emission band is a band-to-impurity transition involving a deep level complex consisting of a gallium vacancy and an oxygen atom sitting on one of the neighboring nitrogen sites; the (VGa–ON)2− charge state of (VGa–ON)2−/1−. Two electronic structures, which arise due to two different configurations of (VGa–ON)2−/1−, with ON either along the c-axis (axial configuration) or in one of the three equivalent tetrahedral positions (basal configuration), were observed. Our result also provides explicit evidence that both the yellow luminescence band and the 1.23 eV emission line in GaN are related to a common deep center, which is believed to be (VGa–ON)2−/1−.
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78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
78.40.Fy Semiconductors
61.72.jd Vacancies

Abnormal pressure-induced structural transformations of gallium nitride nanowires

Zhaohui Dong and Yang Song

Appl. Phys. Lett. 96, 151903 (2010); http://dx.doi.org/10.1063/1.3394009 (3 pages) | Cited 1 time

Online Publication Date: 12 April 2010

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One-dimensional nanostructured GaN was studied at pressures up to 65 GPa by in situ synchrotron x-ray diffraction. A wurtzite-to-rocksalt transformation was observed at ∼ 55 GPa, an onset pressure higher than that for bulk GaN, but lower than that for nanocrystalline GaN. Such transformation was found extremely incomplete even at the highest pressure but was facilitated by decompression. In addition, GaN nanowires exhibited drastically different volume responses to compression than did GaN in other forms. These unusual pressure behaviors of GaN nanowires are attributed to the interplay of several factors involving the intrinsic nanoproperties and the compression conditions.
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62.50.-p High-pressure effects in solids and liquids
64.70.kg Semiconductors
64.70.Nd Structural transitions in nanoscale materials
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

Photoluminescence spectroscopy and positron annihilation spectroscopy probe of alloying and annealing effects in nonpolar m-plane ZnMgO thin films

A. L. Yang (杨安丽), H. P. Song (宋华平), D. C. Liang (梁德春), H. Y. Wei (魏鸿源), X. L. Liu (刘祥林), P. Jin (金鹏), X. B. Qin (秦秀波), S. Y. Yang (杨少延), Q. S. Zhu (朱勤生), and Z. G. Wang (王占国)

Appl. Phys. Lett. 96, 151904 (2010); http://dx.doi.org/10.1063/1.3394012 (3 pages) | Cited 7 times

Online Publication Date: 12 April 2010

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Temperature-dependent photoluminescence characteristics of non-polar m-plane ZnO and ZnMgO alloy films grown by metal organic chemical vapor deposition have been studied. The enhancement in emission intensity caused by localized excitons in m-plane ZnMgO alloy films was directly observed and it can be further improved after annealing in nitrogen. The concentration of Zn vacancies in the films was increased by alloying with Mg, which was detected by positron annihilation spectroscopy. This result is very important to directly explain why undoped Zn1−xMgxO thin films can show p-type conduction by controlling Mg content, as discussed by Li et al. [Appl. Phys. Lett. 91, 232115 (2007)] .
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78.66.Hf II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.55.Et II-VI semiconductors
78.70.Bj Positron annihilation
61.72.jd Vacancies
71.35.-y Excitons and related phenomena

Applying uniform reversible strain to epitaxial oxide films

M. D. Biegalski, K. Dörr, D. H. Kim, and H. M. Christen

Appl. Phys. Lett. 96, 151905 (2010); http://dx.doi.org/10.1063/1.3374323 (3 pages) | Cited 20 times

Online Publication Date: 13 April 2010

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We demonstrate using four-circle x-ray diffraction that the piezoelectric substrate of Pb(Mg1/3Nb2/3)0.72Ti0.28O3(001) induces uniform reversible in-plane strain to epitaxially-grown oxide films and bilayers. The biaxial in-plane strain depends linearly on the applied electrical voltage. Utilizing the reversible strain, the strain-dependent lattice structure and the Poisson number characterizing the elastic response is determined for 200 nm thick SrTiO3, LaScO3, and BiFeO3 films. The uniformity and reversibility of the strain provides access to the direct quantitative measurement of strain-dependent properties of epitaxial oxide films.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
68.35.Gy Mechanical properties; surface strains
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Thermal conductivity and dynamic heat capacity across the metal-insulator transition in thin film VO2

Dong-Wook Oh, Changhyun Ko, Shriram Ramanathan, and David G. Cahill

Appl. Phys. Lett. 96, 151906 (2010); http://dx.doi.org/10.1063/1.3394016 (3 pages) | Cited 13 times

Online Publication Date: 13 April 2010

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The thermal properties of VO2 thin films, 90–440 nm thick, are measured by time-domain thermoreflectance (TDTR) across the metal-insulator transition (MIT). The thermal conductivity increases by as much as 60% in the metallic phase; this increase in conductivity is in good agreement with the expected electronic contribution to the thermal conductivity. For relatively thick layers, TDTR data are sensitive to the dynamic heat capacity and show a pronounced peak near the MIT temperature created by a contribution to the enthalpy from periodic transformations at the 10 MHz frequency of the thermal waves used in the experiment. The dynamic heat capacity increases as the amplitude ΔT of the thermal waves becomes comparable to the width of the MIT and reaches ≈30% of the bulk latent heat for ΔT ≈ 1.6 K.
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71.30.+h Metal-insulator transitions and other electronic transitions
05.70.Ce Thermodynamic functions and equations of state
65.40.Ba Heat capacity
78.20.N- Thermo-optic effects

Thermal stability comparison of TaN on HfO2 and Al2O3

Jinhee Kwon and Yves J. Chabal

Appl. Phys. Lett. 96, 151907 (2010); http://dx.doi.org/10.1063/1.3396189 (3 pages) | Cited 1 time

Online Publication Date: 14 April 2010

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Changes in gate stacks (TaN/high-κ/SiO2/Si) are investigated during thermal processing using in situ Fourier transform infrared spectroscopy. Ta–O bonds, present in the initial tantalum nitride films, are crystallized in contact with HfO2 at 700–800 °C and completely dissociate at 900 °C, resulting in a microcrystalline TaNx phase. The TaN remains amorphous, however, with Al2O3 as the underlying dielectric layer. A partial reduction into a metallic Ta occurs after dissociation of Ta–N and Ta–O bonds, and Al2O3 decomposes at 700 °C. Dissociated Al atoms diffuse into all the neighboring layers to form silicate and Ta- and N-bound Al.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions
78.30.-j Infrared and Raman spectra
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