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16 Oct 2006

Volume 89, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 164101 (2006); http://dx.doi.org/10.1063/1.2362602 (3 pages)

Yen-Wen Lu and Chang-Jin(CJ) Kim
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Organic diodes as monolithically integrated surface plasmon polariton detectors

H. Ditlbacher, F. R. Aussenegg, J. R. Krenn, B. Lamprecht, G. Jakopic, and G. Leising

Appl. Phys. Lett. 89, 161101 (2006); http://dx.doi.org/10.1063/1.2362975 (3 pages) | Cited 21 times

Online Publication Date: 16 October 2006

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The authors show that organic p/n heterojunction diodes enable the direct electric detection of surface plasmon polaritons (SPPs). The organic diodes are built from two organic semiconductor thin film layers with an area of 150×500 μm2 deposited on an extended silver thin film. Besides serving as the bottom electrode of the diode this silver thin film is as well a waveguide feeding SPPs to the diode area. The authors visualize the direct SPP detection by a spatially resolved induced current map.
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85.30.Kk Junction diodes
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.Gz Photodetectors (including infrared and CCD detectors)

Low threshold current density distributed feedback quantum cascade lasers with deep top gratings

Gangyi Xu, Aizhen Li, Yaoyao Li, Lin Wei, Yonggang Zhang, Chun Lin, and Hua Li

Appl. Phys. Lett. 89, 161102 (2006); http://dx.doi.org/10.1063/1.2362580 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2006

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The authors report on pulsed and continuous-wave operation of single mode tunable distributed feedback quantum cascade lasers at λ ∼ 7.7 μm. A deep top grating and a thin heavily doped InP layer beneath the grating are formed in the upper cladding to obtain simultaneously a strong feedback effect and a low waveguide loss. A “three-well vertical transition” active region is used with a low doped injector. In pulsed operation, a very low threshold current density of 970 A/cm2 and a peak power of 75 mW are achieved at 300 K. Reliable single mode emission with a side mode suppression ratio of ∼ 30 dB is achieved in a large temperature range (155–320 K) with a tuning range of 90 nm. The lasers operate in continuous-wave mode up to 130 K.
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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
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Conditions for designing single-mode air-core waveguides in three-dimensional photonic crystals

Virginie Lousse, Jonghwa Shin, and Shanhui Fan

Appl. Phys. Lett. 89, 161103 (2006); http://dx.doi.org/10.1063/1.2362983 (3 pages) | Cited 3 times

Online Publication Date: 17 October 2006

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The authors present a general procedure that allows the design of single-mode air-core waveguides in three-dimensional photonic crystals. The procedure involves analyzing the modal profile of the band edge mode in the perfect crystal, identifying the regions of maximal electric-field intensity, and placing the air defects to enclose these regions. As an illustration, they present a detailed design of air-core waveguides in a recently proposed silicon body-center-cubic crystal structure that possesses a 25% complete band gap.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

III/V ratio based selectivity between strained Stranski-Krastanov and strain-free GaSb quantum dots on GaAs

G. Balakrishnan, J. Tatebayashi, A. Khoshakhlagh, S. H. Huang, A. Jallipalli, L. R. Dawson, and D. L. Huffaker

Appl. Phys. Lett. 89, 161104 (2006); http://dx.doi.org/10.1063/1.2362999 (3 pages) | Cited 34 times

Online Publication Date: 17 October 2006

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The authors demonstrate and characterize type-II GaSb quantum dot (QD) formation on GaAs by either Stranski-Krastanov (SK) or interfacial misfit (IMF) growth mode. The growth mode selection is controlled by the gallium to antimony (III/V) ratio where a high III/V ratio produces IMF and a low ratio establishes the SK growth mode. The IMF growth mode produces strain-relaxed QDs, where the SK QDs remain highly strained. Both ensembles demonstrate strong room temperature photoluminescence (PL) with the SK QDs emitting at 1180 nm and the IMF QDs emitting at 1375 nm. Quantized energy levels along with a spectral blueshift are observed in 77 K PL. Transmission electron microscope images identify the IMF array and crystallographic shape for both types of QD formation. Atomic force microscope images characterize QD geometry and density.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots

Defect reduction and efficiency improvement of near-ultraviolet emitters via laterally overgrown GaN on a GaN/patterned sapphire template

D. S. Wuu, W. K. Wang, K. S. Wen, S. C. Huang, S. H. Lin, S. Y. Huang, C. F. Lin, and R. H. Horng

Appl. Phys. Lett. 89, 161105 (2006); http://dx.doi.org/10.1063/1.2363148 (3 pages) | Cited 32 times

Online Publication Date: 17 October 2006

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An approach to improve the defect density and internal quantum efficiency of near-ultraviolet emitters was proposed using a combination of epitaxial lateral overgrowth (ELOG) and patterned sapphire substrate (PSS) techniques. Especially, a complementary dot array pattern corresponding to the underlying PSS was used for the ELOG-SiO2 mask design. Based on the transmission-electron-microscopy and etch-pit-density results, the ELOG/SiO2/GaN/PSS structure can reduce the defect density to a level of 105 cm−2. The internal quantum efficiency of the InGaN-based ELOG-PSS light-emitting diode (LED) sample showed three times in magnitude as compared with that of the conventional GaN/sapphire one. Under a 20 mA injection current, the output powers of ELOG-PSS, PSS, and conventional LED samples were measured to be 3.3, 2.9, and 2.5 mW, respectively. The enhanced output power could be due to a combination of the reduction in dislocation density (by ELOG) and improved light extraction efficiency (by PSS). Unlike the previous double ELOG approaches, the presented ELOG-PSS structure needs only one regrowth process and will have high potential in future high-quality ultraviolet emitters, even blue/green laser diode applications.
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78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
85.40.Hp Lithography, masks and pattern transfer
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Interband cascade laser operating cw to 257 K at λ = 3.7 μm

W. W. Bewley, J. A. Nolde, D. C. Larrabee, C. L. Canedy, C. S. Kim, M. Kim, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 89, 161106 (2006); http://dx.doi.org/10.1063/1.2363169 (3 pages) | Cited 12 times

Online Publication Date: 17 October 2006

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A five-stage interband cascade laser with 12 μm ridge width and Au electroplating for improved epitaxial-side-up heat sinking operates cw to a maximum temperature of 257 K, where the emission wavelength is 3.7 μm. The device emits 100 mW̸facet for cw operation at 80 K, 54 mW at 200 K, and 10 mW at 250 K. The beam quality is within twice the diffraction limit for injection currents up to 14 times the lasing threshold at 120 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Locating hexagonal and cubic phases in boron nitride using wavelength-selective optically detected x-ray absorption spectroscopy

D. A. Evans, A. R. Vearey-Roberts, and N. R. J. Poolton

Appl. Phys. Lett. 89, 161107 (2006); http://dx.doi.org/10.1063/1.2360910 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2006

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Cubic and hexagonal phases of boron nitride (c-BN and h-BN) have been identified and located using optically detected x-ray absorption spectroscopy (ODXAS). Each phase was identified by distinct resonance features in the B K-edge absorption spectra. In a mixed-phase sample of predominantly c-BN, combined ODXAS and electron yield measurements suggested near-surface localization of h-BN. Using x-ray excited luminescence, emission bands due to each phase were identified and applied in wavelength-selective ODXAS to locate surface and bulk h-BN phases. These combined techniques provide a method of correlating the local structure and optical emission in these wide-gap semiconductors.
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78.70.Dm X-ray absorption spectra
78.55.Cr III-V semiconductors

High intensity light propagation in InAs

Srinivasan Krishnamurthy, Zhi Gang Yu, Shekhar Guha, and Leo Gonzalez

Appl. Phys. Lett. 89, 161108 (2006); http://dx.doi.org/10.1063/1.2363970 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2006

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The authors present their experimental and theoretical results on nonlinear absorption of light in InAs. The nonlinear variation of output intensity as a function of input intensity and time are calculated by solving four coupled rate equations simultaneously. All required quantities, including two-photon absorption, free-carrier absorption, Auger and radiative recombination lifetimes, and intrinsic carrier densities, have been obtained from the underlying band structures. The calculated thickness and energy-dependent output intensities in InAs agree very well with the values measured in their pump-probe experiments.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.At Surface states, band structure, electron density of states

Fiber Bragg grating microphone system

Lipi Mohanty, Liang Mong Koh, and Swee Chuan Tjin

Appl. Phys. Lett. 89, 161109 (2006); http://dx.doi.org/10.1063/1.2363977 (3 pages) | Cited 5 times

Online Publication Date: 17 October 2006

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A fiber Bragg grating microphone has been developed and tested in the audible frequency range. The fiber Bragg grating is longitudinally attached to a membrane that vibrates in response to acoustic vibrations and is prestrained. The frequency and amplitude of the sound are encoded in the wavelength shift. The microphone can also pick up voices dynamically from a distance of a few meters. The simplicity of principle and structure of this fiber grating sensor provides scope for commercialization as an optical microphone.
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42.81.Pa Sensors, gyros
42.79.Jq Acousto-optical devices
42.79.Dj Gratings
42.81.Wg Other fiber-optical devices
43.38.Zp
43.58.-e

Microdroplet deposition of copper film by femtosecond laser-induced forward transfer

Li Yang, Ching-yue Wang, Xiao-chang Ni, Zhi-jun Wang, Wei Jia, and Lu Chai

Appl. Phys. Lett. 89, 161110 (2006); http://dx.doi.org/10.1063/1.2364457 (3 pages) | Cited 9 times

Online Publication Date: 18 October 2006

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Copper microdroplets were deposited onto a quartz substrate by the laser-induced forward transfer (LIFT) using laser pulses of 148 fs at a center wavelength of 775 nm. The droplets with 2–3 μm diameters were transferred at a laser pulse energy slightly above the threshold at which the copper film could be removed completely. The droplet formation was a result of the blow-off of a molten film from the quartz substrate by a compressive stress of plasma when the free surface was melted and was different from the microdroplet formation by the LIFT technique using nanosecond laser pulse.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Highly efficient optical pumping of photonic crystal nanocavity lasers using cavity resonant excitation

Masahiro Nomura, Satoshi Iwamoto, Masao Nishioka, Satomi Ishida, and Yasuhiko Arakawa

Appl. Phys. Lett. 89, 161111 (2006); http://dx.doi.org/10.1063/1.2369543 (3 pages) | Cited 13 times

Online Publication Date: 18 October 2006

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The authors demonstrate highly efficient optical pumping of photonic crystal (PhC) nanocavity lasers with InGaAs single quantum wells (QWs) using cavity resonant excitation at 10 K. The laser threshold power is largely reduced when the central wavelength of the excitation pulse is resonant with a higher-order cavity mode. The localized excitation by the cavity resonant effect increases the effective absorption of the QW region in the nanocavity. The direct photocarrier generation in the QW also results in the highly efficient optical pumping. This cavity resonant excitation technique can lower the laser threshold of PhC nanocavity lasers and avoid detrimental device heating.
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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
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials

Highly sensitive organic ultraviolet optical sensor based on phosphorescent Cu (I) complex

Zhiguo Kong, Wenlian Li, Guangbo Che, Bei Chu, Defeng Bi, Liangliang Han, Lili Chen, Zhizhi Hu, and Zhiqiang Zhang

Appl. Phys. Lett. 89, 161112 (2006); http://dx.doi.org/10.1063/1.2364156 (3 pages) | Cited 6 times

Online Publication Date: 18 October 2006

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Ultraviolet light-sensitive organic optical sensor based on photovoltaic diode was demonstrated by using a phosphorescent Cu complex and a diamine derivative as electroacceptor and electrodonor, respectively. The Cu complex is Cu(DPEphos)((Bphen))BF4, in which DPEphos and Bphen denote 6,7-dicyanodipyrido [2,2-d:2′,3′-f] quinoxaline and bathophenanthroline. And the diamine derivative, m-MTDATA, is 4, 4′,4″-tris-(2-methylphenyl phenylamino) triphenylamine. The sensor is highly sensitive to UV light band from 300 to 420 nm while it has almost no response to the visible light, and under illumination of 365 nm light with power of 1.7 mW/cm2, the sensor exhibits an open circuit voltage of 1.86 V, a short circuit current of 105.3 μA/cm2, a fill factor of 0.246, and a power conversion efficiency of 2.83%. The dependences of ultraviolet responsive sensitivity on illumination intensity and working temperature were also discussed.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.Gz Photodetectors (including infrared and CCD detectors)

Low loss contacts for organic semiconductor lasers

P. Görrn, T. Rabe, T. Riedl, W. Kowalsky, F. Galbrecht, and U. Scherf

Appl. Phys. Lett. 89, 161113 (2006); http://dx.doi.org/10.1063/1.2360936 (3 pages) | Cited 18 times

Online Publication Date: 19 October 2006

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For the realization of electrically driven organic semiconductor lasers low loss contacts for charge injection are essential. The authors show that the addition of thin, highly transparent conducting layers (thickness on the order of 10–20 nm) of aluminum doped zinc oxide to a planar waveguide structure formed by a 145 nm thick polymer active layer leaves the threshold for the onset of amplified spontaneous emission almost unchanged. This finding paves the way towards electrically driven organic lasers without the need for unrealistically thick organic spacers to keep the waveguide mode away from the contacts.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Gw Other integrated-optical elements and systems

Diffraction-aided laser-induced microstructuring of thin TiO2 films on glass

O. Van Overschelde and M. Wautelet

Appl. Phys. Lett. 89, 161114 (2006); http://dx.doi.org/10.1063/1.2364462 (3 pages) | Cited 4 times

Online Publication Date: 20 October 2006

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Thin films of TiO2 are deposited by magnetron sputtering on glass substrate and are irradiated by ultraviolet radiation using a KrF excimer laser. These thin films are patterned with a razor blade placed in the way of the radiation. When the fluence is in the 1250–1550 mJ/cm2 range, a regular structure appears, with controlled ablation of the films. It is shown that above a critical local fluence, the ablated depth varies linearly with the local fluence. The proportionality factor is shown to be equal to two photons per evaporated molecule.
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81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.38.Mf Laser ablation

Large electro-optic effect in tensile strained Ge-on-Si films

Samerkhae Jongthammanurak, Jifeng Liu, Kazumi Wada, Douglas D. Cannon, David T. Danielson, Dong Pan, Lionel C. Kimerling, and Jurgen Michel

Appl. Phys. Lett. 89, 161115 (2006); http://dx.doi.org/10.1063/1.2363948 (3 pages) | Cited 19 times

Online Publication Date: 20 October 2006

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The authors report the first observation of a large, strain-enhanced, electro-optic effect in the weakly absorbing regime for Ge epitaxial films grown directly on Si substrates. The field dependence of absorption in the Ge films was measured from spectral responsivity measurements of Ge-on-Si p-i-n diodes. The experimental data were analyzed using the generalized Franz-Keldysh formalism [ H. Shen and F. H. Pollak, Phys. Ref. B 42, 7097 (1990) ] and the valence band edge shifts of the light- and heavy-hole energy positions were in response to biaxial stress. With measured Δα/α ∼ 3 and derived Δn/F = 280 pm/V, the material has significant potential for field-induced phase or electroabsorption modulator devices.
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78.66.Db Elemental semiconductors and insulators
78.20.Jq Electro-optical effects
71.20.Mq Elemental semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
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Electron energy distribution function close to the mode transition region in an inductively coupled gaseous electronics conference reference cell

S. V. Singh, P. Kempkes, and H. Soltwisch

Appl. Phys. Lett. 89, 161501 (2006); http://dx.doi.org/10.1063/1.2362599 (3 pages) | Cited 13 times

Online Publication Date: 16 October 2006

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The electron energy distribution function (EEDF) in the E to H mode transition region of an inductively coupled argon discharge has been studied experimentally. The EEDF, which has a Maxwellian- or Druyvesteyn-like shape (depending on pressure) in both “pure” modes, shows a trend to a bi-Maxwellian shape in the vicinity of both the E to H and the H to E mode transitions. Moreover, the normalized electron energy probability functions closely before the E to H and the reverse H to E mode jumps are almost identical, indicating a similar power coupling at both transition points.
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52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources
52.70.Ds Electric and magnetic measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Characteristics of radio-frequency, atmospheric-pressure glow discharges with air using bare metal electrodes

Hua-Bo Wang, Wen-Ting Sun, He-Ping Li, Cheng-Yu Bao, and Xiao-Zhang Zhang

Appl. Phys. Lett. 89, 161502 (2006); http://dx.doi.org/10.1063/1.2363040 (3 pages) | Cited 5 times

Online Publication Date: 16 October 2006

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In this letter, an induced gas discharge approach is proposed and described in detail for obtaining a uniform atmospheric-pressure glow discharge with air in a γ mode using water-cooled, bare metal electrodes driven by radio-frequency (13.56 MHz) power supply. A preliminary study on the discharge characteristics of the air glow discharge is also presented in this study. With this induced gas discharge approach, radio-frequency, atmospheric-pressure glow discharges using bare metal electrodes with other gases which cannot be ignited directly as the plasma working gas, such as nitrogen, oxygen, etc., can also be obtained.
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52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources

Anomalous cross field electron transport in a Hall effect thruster

C. Boniface, L. Garrigues, G. J. M. Hagelaar, J. P. Boeuf, D. Gawron, and S. Mazouffre

Appl. Phys. Lett. 89, 161503 (2006); http://dx.doi.org/10.1063/1.2360182 (3 pages) | Cited 15 times

Online Publication Date: 19 October 2006

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The origin of anomalous electron transport across the magnetic field in the channel of a Hall effect thruster has been the subject of controversy, and the relative importance of electron-wall collisions and plasma turbulence on anomalous transport is not clear. From comparisons between Fabry-Pérot measurements and hybrid model calculations of the ion velocity profile in a 5 kW Hall effect thruster, we deduce that one and the same mechanism is responsible for anomalous electron transport inside and outside the Hall effect thruster channel. This suggests that the previous assumption that Bohm anomalous conductivity is dominant outside the thruster channel whereas electron-wall conductivity prevails inside the channel is not valid.
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52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Ra Plasma turbulence
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.65.Ww Hybrid methods

Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen

Hua-Bo Wang, Wen-Ting Sun, He-Ping Li, Cheng-Yu Bao, Xing Gao, and Hui-Ying Luo

Appl. Phys. Lett. 89, 161504 (2006); http://dx.doi.org/10.1063/1.2362631 (3 pages) | Cited 10 times

Online Publication Date: 19 October 2006

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In this letter, atmospheric-pressure glow discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56 MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.
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52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources

Submicrosecond pulsed atmospheric glow discharges sustained without dielectric barriers at kilohertz frequencies

J. L. Walsh, J. J. Shi, and M. G. Kong

Appl. Phys. Lett. 89, 161505 (2006); http://dx.doi.org/10.1063/1.2361274 (3 pages) | Cited 30 times

Online Publication Date: 19 October 2006

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In this letter, the authors report the experimental observation of a large-volume atmospheric glow discharge sustained without dielectric barriers at 1 kHz. This barrier-free mode of operation is made possible with a submicrosecond pulsed excitation instead of the usual sinusoidal excitation. Its current-voltage characteristics are shown to be very different from conventional atmospheric dielectric barrier discharges, and its generation mechanism is studied with nanosecond resolved optical emission spectroscopy. The pulsed barrier-free atmospheric plasma is shown to produce very intense atomic oxygen emission line at 777 nm, up to one magnitude more intensive than that of a comparable atmospheric dielectric barrier discharge.
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52.80.Hc Glow; corona
52.50.Dg Plasma sources
52.25.Fi Transport properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Driving frequency effect on the electron energy distribution function in capacitive discharge under constant discharge power condition

S. K. Ahn, S. J. You, and H. Y. Chang

Appl. Phys. Lett. 89, 161506 (2006); http://dx.doi.org/10.1063/1.2363945 (3 pages) | Cited 11 times

Online Publication Date: 20 October 2006

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A modern trend of VHF driven plasma sources in semiconductor processing stimulates a lot of studies concerning the driving frequency effect on plasma parameters in a capacitive discharge. In spite of abundant studies, the validation and application of these results in industrial plasma processing are still questionable because these studies were performed under a fixed rf voltage condition or an assumption of Maxwellian electron energy distribution, while the fixed discharge power condition and non-Maxwellian distribution are typical in industrial plasma processing. To resolve this problem, the authors investigated the driving frequency effect on plasma parameters (electron density and temperature) under the fixed discharge power condition by measuring the electron energy distribution functions, which are the most important factor in chemical reactions during the plasma processing. A remarkable result was observed—as the driving frequency increases, the electron temperature increases and the electron density remains almost constant or decreases, which is opposite to what previous studies have suggested. This result can be tentatively explained as a result of an enhancement of collisional heating in the bulk plasma with driving frequency under the fixed discharge power condition.
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52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources
52.25.Fi Transport properties
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
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Deformation around a nanosized elliptical hole with surface effect

G. F. Wang and T. J. Wang

Appl. Phys. Lett. 89, 161901 (2006); http://dx.doi.org/10.1063/1.2362988 (3 pages) | Cited 19 times

Online Publication Date: 16 October 2006

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In the present letter, the effect of surface energy on the deformation around an elliptical hole is analyzed, and the closed-form solution is obtained by the complex variable formulation. The results show that when the size of the hole reduces to the same order of the ratio of surface energy to applied stress, the contribution from surface becomes important, and the shape of the hole coupled with surface energy has significant effect on the elastic state around the hole.
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68.35.Md Surface thermodynamics, surface energies
68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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Ultrahigh damping in R-phase state of Ti–Ni–Fe alloy

Genlian Fan, Yumei Zhou, Kazuhiro Otsuka, and Xiaobing Ren

Appl. Phys. Lett. 89, 161902 (2006); http://dx.doi.org/10.1063/1.2363173 (3 pages) | Cited 12 times

Online Publication Date: 16 October 2006

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Developing high damping materials with high strength is of significant technological importance, and Ti–Ni-based alloys are attracting much attention in this respect. The high damping peak in martensite state has been shown to be related to the interaction between twin boundary and hydrogen according to recent studies. In this letter the authors studied damping capacity of R phase in Ti50Ni48Fe2 alloy, which has the lowest twinning shear among known martensites (R, B19, and B19′) in Ti–Ni-based alloys. They obtained a very high internal friction Q−1 = 0.2 for the relaxation-type peak in R phase, much higher than that for B19 martensite or B19′ martensite. Their results suggest that choosing martensite with smallest twinning shear (thus with the highest mobility) is an important guideline for developing very high damping materials. Furthermore, avoiding introducing precipitates and dislocations is also essential for obtaining high damping.
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62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Mm Grain and twin boundaries
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

Determination of polarization charge density on interface of AlGaN/GaN heterostructure by electroreflectance

Dong-Po Wang, Chi-Chang Wu, and Chia-Chun Wu

Appl. Phys. Lett. 89, 161903 (2006); http://dx.doi.org/10.1063/1.2360909 (3 pages) | Cited 1 time

Online Publication Date: 16 October 2006

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Electroreflectance spectra of AlGaN/GaN heterostructure were obtained at various bias voltages (Vdc). Franz-Keldysh oscillations (FKOs) were observed above band gap of AlGaN. The strength of electric field in AlGaN (FAlGaN) was evaluated from the periods of the FKOs, yielding the strength of FAlGaN as a function of Vdc. A positive fixed polarization charge σp arises as a result of the polarization discontinuity across the heterointerface. The neighboring electrons are then attracted by the established σp to form a two-dimensional electron gas (2DEG) at the interface. The experimental value of σp, as obtained by completely depleting the 2DEG using a negative Vdc, is found to be reasonably close to the theoretical value.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.Nr Semiconductor compounds
78.20.Jq Electro-optical effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
72.20.Fr Low-field transport and mobility; piezoresistance

Evidences of an intermediate rodlike defect during the transformation of {113} defects into dislocation loops

S. Boninelli, N. Cherkashin, A. Claverie, and F. Cristiano

Appl. Phys. Lett. 89, 161904 (2006); http://dx.doi.org/10.1063/1.2361178 (3 pages) | Cited 11 times

Online Publication Date: 16 October 2006

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A detailed study of the transformation of the {113} defects into dislocation loops has been carried out in Ge preamorphized silicon (30 keV, 1×1015 Ge+/cm2) and annealed at 800 °C for time ranging from 15 to 2700 s. The presence of a stable defect, along the ⟨110⟩ directions, formed during the transformation from {113}’s into Frank dislocation loops (FDLs), has been revealed and studied. Performing a detailed transmission electron microscopy analysis in nonconventional zone axes, a 1/3 [111]-type Burgers vector has been found. These defects are shown to be more stable than {113}’s but less than FDLs.
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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
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