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3 Apr 2006

Volume 88, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 143508 (2006); http://dx.doi.org/10.1063/1.2191448 (3 pages)

R. Chan, M. Feng, N. Holonyak, A. James, and G. Walter
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Efficient pure-white organic light-emitting diodes with a solution-processed, binary-host employing single emission layer

Jwo-Huei Jou, Ming-Chen Sun, Hung-Hsing Chou, and Chien-Hung Li

Appl. Phys. Lett. 88, 141101 (2006); http://dx.doi.org/10.1063/1.2189011 (3 pages) | Cited 25 times

Online Publication Date: 3 April 2006

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Efficient white light-emitting diodes were fabricated with a solution-processed single emission layer composing a molecular and polymeric materials mixed binary host. The main host used was a molecule of 4,4′-bis-(carbazol-9-yl) biphenyl and the assisting host used was a blue light-emitting polyfluorene-derived copolymer of poly[(9,9-dioctylfluo-renyl-2,7-diyl)-alt-co-(9-hexyl-3,6-carbazole)]. The hosts were doped via solution-mixing a green dye of tris(2-phenylpyridine) iridium (III) and a red dye of bis[2-(2′-benzo-thienyl)-pyridi-nato-N,C3,](acetylacetonate) iridium (III). One resultant device having a pure white emission of Commission Internationale de l’Eclairage (0.33, 0.33) has a maximum power efficiency of 4.2 lm/W at 802 cd/m2 and a maximum brightness of 11 800 cd/m2. The better efficiency performance may be attributed to the addition of the assisting host, which halves the energy barrier for holes to inject into the light-emitting zone.
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85.60.Jb Light-emitting devices

Electrically switchable, two-color quantum cascade laser emitting at 1.39 and 2.3 THz

Giacomo Scalari, Christoph Walther, Jérôme Faist, Harvey Beere, and David Ritchie

Appl. Phys. Lett. 88, 141102 (2006); http://dx.doi.org/10.1063/1.2191407 (3 pages) | Cited 38 times

Online Publication Date: 3 April 2006

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A quantum cascade laser emitting at 1.39 and 2.3 THz is demonstrated. The structure is based on a large single quantum well and multiwavelength operation is obtained by selectively injecting carriers by resonant tunneling in the excited states of the well. A magnetic field applied perpendicularly to the layers increases the gain enabling laser action. Extremely low values of the threshold current density (below 30 A/cm2) are observed for both wavelengths. A study of the dependence of the laser emission intensity as a function of the applied magnetic field is also presented.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Scanning particle trapped optical microscopy based on two-photon-induced morphology-dependent resonance in a trapped microsphere

Dru Morrish, Xiaosong Gan, and Min Gu

Appl. Phys. Lett. 88, 141103 (2006); http://dx.doi.org/10.1063/1.2186076 (3 pages) | Cited 4 times

Online Publication Date: 3 April 2006

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We report on scanning particle trapped optical microscopy based on two-photon-induced morphology-dependent resonance (MDR) in a trapped microsphere. In this imaging mode, a femtosecond pulsed laser is adopted for simultaneous laser trapping and two-photon excitation. Due to the localized excitation, MDR is significantly enhanced. As a result, an image contrast enhancement of 9.3% is achieved by the spectral detection of a single on-resonance MDR mode compared with that obtained by the off-resonance MDR mode without compromise in transverse resolution.
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07.60.Pb Conventional optical microscopes
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Control of the nonlinear carrier response time of AlGaAs photonic crystal waveguides by sample design

P. Murzyn, A. Z. Garcia-Deniz, D. O. Kundys, A. M. Fox, J.-P. R. Wells, D. M. Whittaker, M. S. Skolnick, T. F. Krauss, and J. S. Roberts

Appl. Phys. Lett. 88, 141104 (2006); http://dx.doi.org/10.1063/1.2191955 (3 pages) | Cited 8 times

Online Publication Date: 4 April 2006

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We have used reflection geometry pump-probe spectroscopy to investigate the free carrier response time of AlGaAs high refractive index contrast one-dimensional photonic crystal waveguides. We have observed pump-induced shifts of photonic resonances in the near infrared spectral region, and have studied the dependence of the decay time on the sample parameters. We find that the response time can be varied from 8 to 33 ps by changing the structure period and etch depth. This, combined with the large changes observed in the reflectivity, demonstrates excellent potential for application as ultrafast photonic switches with a controllable recovery time.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.65.Cf Surface cleaning, etching, patterning
42.15.Eq Optical system design

High sensitivity surface plasmon resonance sensor based on phase interrogation at optimal incident wavelengths

Hai-Pang Chiang, Jing-Lun Lin, and Zhi-Wei Chen

Appl. Phys. Lett. 88, 141105 (2006); http://dx.doi.org/10.1063/1.2192622 (3 pages) | Cited 7 times

Online Publication Date: 4 April 2006

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It is demonstrated that ultrahigh sensitivity of glucose refractive index measurement can be achieved via surface plasmon resonance excitation in which the phase difference between p- and s-polarized reflected waves is monitored as a function of the incident angle. Sensitivity with values down to the order of 10−8 is obtained by performing the measurements at optimal incident wavelengths. This represents an order of magnitude improvement compared to the previously reported values in the literature.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis
07.60.Hv Refractometers and reflectometers

Spatial and temporal sensitivity variations in photorefractive electro-optic field sensors

A. Garzarella, S. B. Qadri, Terence J. Wieting, and Dong Ho Wu

Appl. Phys. Lett. 88, 141106 (2006); http://dx.doi.org/10.1063/1.2192980 (2 pages) | Cited 6 times

Online Publication Date: 5 April 2006

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Experimental studies of the spatial and temporal fluctuations in photorefractive electro-optic (EO) field sensors have revealed that their maximum intrinsic responsivity is limited by incoherence in the polarization of the probe beam. This incoherence is generated within the irradiated crystal itself. We describe a novel method to measure the incoherence directly while suppressing the temporal fluctuations. Our results indicate that optically induced distributions of birefringence (photorefractivity) generally impair the modulating ability of EO crystals.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Scanning near-field optical microscopy images of microradiographs stored in lithium fluoride films with an optical resolution of λ/12

Alessandro Ustione, Antonio Cricenti, Francesca Bonfigli, Francesco Flora, Antonella Lai, Tiziana Marolo, Rosa Maria Montereali, Giuseppe Baldacchini, Anatoly Faenov, Tatiana Pikuz, and Lucia Reale

Appl. Phys. Lett. 88, 141107 (2006); http://dx.doi.org/10.1063/1.2193654 (3 pages) | Cited 17 times

Online Publication Date: 6 April 2006

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Here we show a new, simple method to observe soft x-ray microradiographs of biological material. A thin film of lithium fluoride (LiF) works as image detector, storing the microradiograph obtained exposing biological samples to extreme ultraviolet and soft x-ray radiations. To read the stored image, collecting the optically stimulated visible luminescence emitted by the LiF active color centers locally produced by the x rays, a scanning near-field optical microscope is used with an optical aperture of 50 nm, i.e., λ/12, where λ is the wavelength of the collected photoluminescence.
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87.64.mt Near-field scanning
42.79.Pw Imaging detectors and sensors
61.72.J- Point defects and defect clusters
78.55.Hx Other solid inorganic materials

Localized excitation of InGaAs quantum dots by utilizing a photonic crystal nanocavity

Masahiro Nomura, Satoshi Iwamoto, Toshihiro Nakaoka, Satomi Ishida, and Yasuhiko Arakawa

Appl. Phys. Lett. 88, 141108 (2006); http://dx.doi.org/10.1063/1.2193811 (3 pages) | Cited 3 times

Online Publication Date: 6 April 2006

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We have studied excitation wavelength dependence of light emission from InGaAs quantum dots (QDs) embedded in high-quality-factor photonic crystal nanocavities. The light emission of the cavity mode around 1 μm was very weak with below-band-gap excitation in the InGaAs wetting layer. However, the emission of the lowest-order cavity mode was strongly enhanced when the excitation wavelength was resonant with higher-order cavity modes. This phenomenon can be attributed to the local intensity enhancement of the excitation light which couples with the cavity mode. The on-resonant excitation technique selectively and efficiently excites only the QDs in the cavity without undesirable background emission.
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78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.70.Qs Photonic bandgap materials

Variable optical reflectance of a self-supported Si grating

Kazuhiro Hane, Takashi Kobayashi, Fang-Ren Hu, and Yoshiaki Kanamori

Appl. Phys. Lett. 88, 141109 (2006); http://dx.doi.org/10.1063/1.2193989 (3 pages) | Cited 14 times

Online Publication Date: 6 April 2006

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Variable reflectance of a self-supported Si grating mirror is reported. A grating suspended in air consisted of an array of 300 nm wide, 300 nm thick, and 20 μm long beams. The period of the grating was varied with an electrostatic microactuator from 600 to 720 nm. A broadband reflection in the wavelength longer than the grating period was observed, which was caused by a resonant interference of the light wave propagating along the grating similar to the guided-mode resonant gratings. Increasing the period of the grating with a microactuator, the reflection spectrum changed. The results were explained by the theoretical calculations based on rigorous coupled-wave analysis.
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42.79.Dj Gratings
42.82.Gw Other integrated-optical elements and systems
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Internal-friction mapping on solids by resonance ultrasound microscopy

H. Ogi, H. Niho, and M. Hirao

Appl. Phys. Lett. 88, 141110 (2006); http://dx.doi.org/10.1063/1.2194479 (3 pages) | Cited 7 times

Online Publication Date: 6 April 2006

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An internal-friction microscopy is developed for quantitatively determining material damping on a local surface area by measuring vibrational attenuation of an isolated langasite oscillator point contacting the material. Noncontacting measurement of the resonance frequency and attenuation coefficient of the longitudinal vibration of the oscillator has been achieved with a line antenna, providing high sensitivity to the modulus and damping in the local contacting area. Formulation of the relationship between a material’s local internal friction and attenuation of the resonator system is proposed using the generalized Hertzian-contact model. Results on a dual-phase stainless steel and a Cu/NbTi composite are shown.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D- Elasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.37.Tj Acoustic force microscopy

Laser trapping of ice crystals

Kazuki Taji, Maki Tachikawa, and Kazushige Nagashima

Appl. Phys. Lett. 88, 141111 (2006); http://dx.doi.org/10.1063/1.2190074 (3 pages) | Cited 7 times

Online Publication Date: 7 April 2006

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Toward application to crystal physics, we demonstrate optical trapping of ice crystals as well as supercooled water droplets using counterpropagating laser beams. Confinement of an ice crystal is evidenced by the angular distribution of laser light deflected from the crystal faces. The average trap time, limited by air currents, is 5 s for ice crystals and much longer for water drops.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
64.70.D- Solid-liquid transitions

Cesium vapor laser pumped by a volume-Bragg-grating coupled quasi-continuous-wave laser-diode array

You Wang, Tadashi Kasamatsu, Yujin Zheng, Hirofumi Miyajima, Hirotake Fukuoka, Shinichi Matsuoka, Minoru Niigaki, Hiroyuki Kubomura, Teruo Hiruma, and Hirofumi Kan

Appl. Phys. Lett. 88, 141112 (2006); http://dx.doi.org/10.1063/1.2192975 (3 pages) | Cited 22 times

Online Publication Date: 7 April 2006

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The experimental demonstration of a broad-area Quasi-continuous-wave (QCW) laser-diode array pumped cesium vapor laser is reported in this letter according to our experimental results. We used a volume-Bragg grating to narrow the spectral linewidth for acquirement of enough resonance transitions. A glass cylindrical cell filled with cesium/buffer gas was set in an end-pumped flat-concave cavity and the gas pressure was set lower than 1 atm. Using the QCW drive mode with the repetitive rate and pulse width of 1 kHz and 50 μs, respectively, 13.45 μJ pulse energy has been achieved with the slope efficiency of about ∼ 1.8%.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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Optimization of laser parameters for the maximum efficiency in the generation of water-window radiation using a liquid nitrogen jet

B. Kim, B. Ahn, D. Lee, J. Kim, and D. Kim

Appl. Phys. Lett. 88, 141501 (2006); http://dx.doi.org/10.1063/1.2192088 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2006

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A laser-produced plasma is a suitable compact x-ray source that can be of broad band or quasimonochromatic with a proper choice of material and filter. To address the maximum conversion efficiency for an efficient, quasimonochromatic source at 2.88 nm (N VI 1s2‐1s2p transition) using liquid nitrogen jet for soft x-ray microscopy, the radiation characteristics such as absolute intensity, spectra, and angular distribution have been investigated for different laser pulse durations (picosecond and femtosecond pulses) and laser energies The comparison of conversion efficiencies between picosecond [120 ps full width at half maximum (FWHM)] and femtosecond (40–500 fs FWHM) lasers indicates that the picosecond laser would provide better conversion efficiency, which is 1.6% at 2×1013 W/cm2. The investigation shows that the laser intensity for the maximum conversion efficiency scales as Im∝1/τα, where α = 0.9±0.15. This empirical formula is useful to choose the laser parameters properly for a given pulse width.
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52.38.Ph X-ray, γ-ray, and particle generation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements

External magnetic field influence on Hα line in abnormal glow discharge

B. M. Obradović, I. P. Dojčinović, M. M. Kuraica, and J. Purić

Appl. Phys. Lett. 88, 141502 (2006); http://dx.doi.org/10.1063/1.2193052 (3 pages) | Cited 3 times

Online Publication Date: 5 April 2006

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Influence of the external axial magnetic field on the hydrogen Hα line profiles in an abnormal glow discharge has been studied. It has been found that the applied magnetic field predominantly increases the intensity of central component of the characteristic excessively broadened Hα profile. Magnetic filed causes helical motion of electrons along the electric field lines and prolongs their trajectories increasing the number of collisions with matrix gas. This explains the increase of the central component of Hα profile and can be regarded as an experimental proof for the main contribution of electron excitation to that part of the profile.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.Hc Glow; corona
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Controlled particle generation in an inductively coupled plasma

M. Schulze, A. von Keudell, and P. Awakowicz

Appl. Phys. Lett. 88, 141503 (2006); http://dx.doi.org/10.1063/1.2193041 (3 pages) | Cited 7 times

Online Publication Date: 6 April 2006

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By injecting pulses of acetylene into an inductive argon/helium discharge, carbon clusters with diameters in the range of 10–50 nm are produced. These particles cause an instability of the plasma, which becomes visible as an oscillation of the emission intensity. The particles are analyzed ex situ using atomic force microscopy and scanning electron micrographs. A unique linear dependence between particle size and oscillation time period is found. Thereby the oscillation phenomenon can serve as monitor signal to control the size of plasma produced particles.
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52.50.Dg Plasma sources
52.80.-s Electric discharges
52.77.Dq Plasma-based ion implantation and deposition
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Tx Emission, absorption, and scattering of particles
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Defects in Cu2O studied by deep level transient spectroscopy

G. K. Paul, Y. Nawa, H. Sato, T. Sakurai, and K. Akimoto

Appl. Phys. Lett. 88, 141901 (2006); http://dx.doi.org/10.1063/1.2175492 (3 pages) | Cited 19 times

Online Publication Date: 3 April 2006

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Hole traps in p-type Cu2O were studied by means of deep level transient spectroscopy in the heterostructure of p-Cu2O/i-ZnO/n-ZnO. In addition to the trap level at about 0.45 eV from the valance band edge, which is already reported as being due to Cu vacancy, we found a new trap level at about 0.25 eV. The new trap is tentatively assigned as Cu-di-vacancy from the trap concentration dependence on oxygen flow rate and substrate temperature.
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71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.At Surface states, band structure, electron density of states
73.21.Ac Multilayers
61.72.J- Point defects and defect clusters

Translation-related domain boundaries form to relieve strain in a thin alumina film on NiAl (110)

Kevin F. McCarty, John P. Pierce, and C. Barry Carter

Appl. Phys. Lett. 88, 141902 (2006); http://dx.doi.org/10.1063/1.2191739 (3 pages) | Cited 8 times

Online Publication Date: 3 April 2006

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We examine how translation-related domains form in thin alumina films synthesized by oxidizing a NiAl (110) surface. Low-energy electron microscopy observations reveal that translation-related domains (sometimes called antiphase domains in the literature) are created within isolated alumina islands as they grow or are annealed. Thus, the domains do not originate when islands with displaced lattices impinge, as frequently assumed in models of film growth. Even though the planar defects that bound the translation-related domains cost energy, the misfit dislocations that terminate the domain boundaries lower the film’s strain energy.
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61.72.Mm Grain and twin boundaries
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Generating random surfaces with desired autocorrelation length

Yilei Zhang and Sriram Sundararajan

Appl. Phys. Lett. 88, 141903 (2006); http://dx.doi.org/10.1063/1.2191882 (3 pages) | Cited 4 times

Online Publication Date: 3 April 2006

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A versatile surface processing method based on electrostatic deposition of particles and subsequent dry etching is shown to be able to tailor the autocorrelation length of a random surface by varying particle size and coverage. An explicit relation between final autocorrelation length, surface coverage of the particles, particle size, and etch depth is built. The autocorrelation length of the final surface closely follows a power law decay with particle coverage, the most significant processing parameter. Experimental results on silicon substrates agree reasonably well with model predictions.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces

Effect of hafnium germanate formation on the interface of HfO2/germanium metal oxide semiconductor devices

S. Van Elshocht, M. Caymax, T. Conard, S. De Gendt, I. Hoflijk, M. Houssa, B. De Jaeger, J. Van Steenbergen, M. Heyns, and M. Meuris

Appl. Phys. Lett. 88, 141904 (2006); http://dx.doi.org/10.1063/1.2192576 (3 pages) | Cited 23 times

Online Publication Date: 4 April 2006

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We have studied the thermal stability of HfO2 thin layers on germanium and the substrate interface development. HfO2 was deposited on Ge substrates and annealed in O2 or N2 at 500 °C (substrate temperature). After O2 anneal, we observed the formation of hafnium germanate, which is stable at 500 °C in N2 as opposed to GeO2 that desorbs as GeO. We believe that this hafnium germanate is an oxygen barrier and as such is at the origin of the much thinner interface between HfO2 and germanium as compared to silicon. In addition, results suggest that the HfGeOx is related to the high interface state density frequently reported for germanium metal oxide semiconductor devices.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing

Raman scattering in InAs/(AlGa)As self-assembled quantum dots: Evidence of Al intermixing

J. Ibáñez, R. Cuscó, L. Artús, M. Henini, A. Patanè, and L. Eaves

Appl. Phys. Lett. 88, 141905 (2006); http://dx.doi.org/10.1063/1.2191414 (3 pages) | Cited 9 times

Online Publication Date: 4 April 2006

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We use Raman scattering to study the composition of InAs self-assembled quantum dots (QDs) embedded in an AlxGa1−xAs matrix. When Al is introduced into the matrix (0.15<x<0.4), the QD phonon frequency exhibits a downward frequency shift with respect to x = 0. This shift is attributed to the incorporation of Al into the QDs. For the samples with an Al-rich matrix (x≳0.6), the QD phonon frequency is higher than that for the samples with a Ga-rich matrix, which suggests that Al/In intermixing is weaker than Ga/In intermixing. These processes affect strongly the energy of the QD luminescence.
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78.67.Hc Quantum dots
78.30.Fs III-V and II-VI semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.55.Cr III-V semiconductors

Room-temperature terahertz emission from nanometer field-effect transistors

N. Dyakonova, A. El Fatimy, J. Łusakowski, W. Knap, M. I. Dyakonov, M.-A. Poisson, E. Morvan, S. Bollaert, A. Shchepetov, Y. Roelens, Ch. Gaquiere, D. Theron, and A. Cappy

Appl. Phys. Lett. 88, 141906 (2006); http://dx.doi.org/10.1063/1.2191421 (3 pages) | Cited 40 times

Online Publication Date: 4 April 2006

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Room-temperature generation of terahertz radiation in nanometer gate length InAlAs/InGaAs and AlGaN/GaN high-mobility transistors is reported. A well-defined source-drain voltage threshold for the emission exists, which depends on the gate bias. Spectral analysis of the emitted radiation is presented. The highest emission power emitted from a single device reached 0.1 μW.
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85.30.Tv Field effect devices
84.40.-x Radiowave and microwave (including millimeter wave) technology

Coating thickness and elastic modulus measurement using ultrasonic bulk wave resonance

S. Dixon, B. Lanyon, and G. Rowlands

Appl. Phys. Lett. 88, 141907 (2006); http://dx.doi.org/10.1063/1.2192144 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2006

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Measurement of the resonant through thickness ultrasonic modes of a homogeneous plate using a fast Fourier transform of the temporal data can be used to calculate plate thickness very accurately. We describe an extension of this principle to two-layer systems, examining a thin coating on a substrate of known properties. The resonant behavior of these systems is predicted and we explain how this approach is used to measure coating thickness and elastic modulus. Noncontact electromagnetic acoustic transducers are used for ultrasonic measurement, as they do not significantly affect the resonant response of the system, unlike alternative contact transducers.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.10.-h Mechanical instruments and equipment
43.35.Yb
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Crossover in thermal transport mechanism in nanocrystalline silicon

Arun Bodapati, Pawel Keblinski, Patrick K. Schelling, and Simon R. Phillpot

Appl. Phys. Lett. 88, 141908 (2006); http://dx.doi.org/10.1063/1.2192145 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2006

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Using vibrational mode analysis, we demonstrate that lattice vibrations in small grain (≲3 nm) structurally inhomogeneous nanocrystalline silicon are almost identical to those in homogeneous amorphous structures with the majority of the vibrations delocalized and unpolarized. As a consequence the principal thermal conductivity mechanism in such a nanocrystalline material is the same as in the amorphous material. With increasing grain size the ability of vibrations to homogenize over the nanocrystalline structure is gradually lost and the phonon spectrum becomes progressively more like that of a crystalline material; this is reflected in a crossover in the mechanism of thermal transport.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials

Effect of high-temperature annealing on the residual strain and bending of freestanding GaN films grown by hydride vapor phase epitaxy

T. Paskova, D. Hommel, P. P. Paskov, V. Darakchieva, B. Monemar, M. Bockowski, T. Suski, I. Grzegory, F. Tuomisto, K. Saarinen, N. Ashkenov, and M. Schubert

Appl. Phys. Lett. 88, 141909 (2006); http://dx.doi.org/10.1063/1.2192149 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2006

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The effect of high-temperature high-pressure annealing on the residual strain, bending, and point defect redistribution of freestanding hydride vapor phase epitaxial GaN films was studied. The bending was found to be determined by the difference in the in-plane lattice parameters in the two faces of the films. The results showed a tendency of equalizing the lattice parameters in the two faces with increasing annealing temperature, leading to uniform strain distribution across the film thickness. A nonmonotonic behavior of structural parameters with increasing annealing temperature was revealed and related to the change in the point defect content under the high-temperature treatment.
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81.05.Ea III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.J- Point defects and defect clusters

Determination of electron-phonon interaction parameters from time-domain terahertz spectroscopy

M. A. Gilmore, Saeid Kamal, D. M. Broun, and J. S. Dodge

Appl. Phys. Lett. 88, 141910 (2006); http://dx.doi.org/10.1063/1.2192625 (3 pages) | Cited 2 times

Online Publication Date: 4 April 2006

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We present an analytical framework for determining metallic electron-phonon interaction parameters from time-domain terahertz spectroscopy measurements. We apply this analysis to the case of lead, where we obtain values that are consistent with existing estimates. We discuss the statistical and systematic errors that limit the uncertainty in the parameter estimates.
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71.38.-k Polarons and electron-phonon interactions
78.70.Gq Microwave and radio-frequency interactions
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