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1 Nov 2010

Volume 97, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 183105 (2010); http://dx.doi.org/10.1063/1.3506485 (3 pages)

Z. H. Zhang, X. Q. Deng, X. Q. Tan, M. Qiu, and J. B. Pan
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Efficiency droop alleviation in InGaN/GaN light-emitting diodes by graded-thickness multiple quantum wells

C. H. Wang, S. P. Chang, W. T. Chang, J. C. Li, Y. S. Lu, Z. Y. Li, H. C. Yang, H. C. Kuo, T. C. Lu, and S. C. Wang

Appl. Phys. Lett. 97, 181101 (2010); http://dx.doi.org/10.1063/1.3507891 (3 pages) | Cited 1 time

Online Publication Date: 1 November 2010

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InGaN/GaN light-emitting diodes (LEDs) with graded-thickness multiple quantum wells (GQW) was designed and grown by metal-organic chemical vapor deposition. The GQW structure, in which the well-thickness increases along [0001] direction, was found to have superior hole distribution as well as radiative recombination distribution by performing simulation modeling. Accordingly, the experimental investigation of electroluminescence spectrum reveals additional emission from the narrower wells within GQWs. Consequently, the efficiency droop can be alleviated to be about 16% from maximum at current density of 30 to 200 A/cm2, which is much smaller than that for conventional LED (32%). Moreover, the light output power was enhanced from 18.0 to 24.3 mW at 20 A/cm2.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.St Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors

Role of strain in polarization switching in semipolar InGaN/GaN quantum wells

Qimin Yan, Patrick Rinke, Matthias Scheffler, and Chris G. Van de Walle

Appl. Phys. Lett. 97, 181102 (2010); http://dx.doi.org/10.1063/1.3507289 (3 pages) | Cited 4 times

Online Publication Date: 2 November 2010

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The effect of strain on the valence-band structure of (11math2) semipolar InGaN grown on GaN substrates is studied. A k⋅p analysis reveals that anisotropic strain in the c-plane and shear strain are crucial for deciding the ordering of the two topmost valence bands. The shear-strain deformation potential D6 is calculated for GaN and InN using density functional theory with the Heyd–Scuseria–Ernzerhof hybrid functional [ J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 124, 219906 (2006)] . Using our deformation potentials and assuming a pseudomorphically strained structure, no polarization switching is observed. We investigate the role of partial strain relaxation in the observed polarization switching.
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81.05.Ea III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Bias-dependent absorption coefficient of the absorber section in GaN-based multisection laser diodes

W. G. Scheibenzuber, U. T. Schwarz, L. Sulmoni, J.-F. Carlin, A. Castiglia, and N. Grandjean

Appl. Phys. Lett. 97, 181103 (2010); http://dx.doi.org/10.1063/1.3514232 (3 pages) | Cited 4 times

Online Publication Date: 2 November 2010

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We measure the modal absorption coefficient of the InGaN quantum wells (QWs) in the absorber section of (Al,In)GaN multisection laser diodes as a function of bias voltage and photon energy using optical gain-spectroscopy. In the examined laser diodes, the modal absorption at the laser wavelength of 430 nm has a maximum of 270 cm−1 at low negative bias and decreases with increasing negative bias. We explain this behavior by comparing the measurements to absorption coefficients calculated from a band-edge profile simulation. The decrease of the absorption at large negative bias is caused by a shift in the transition energies in the quantum wells due to the quantum confined Stark effect.
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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.)

Control of spontaneous emission from InP single quantum dots in GaInP photonic crystal nanocavities

I. J. Luxmoore, E. D. Ahmadi, N. A. Wasley, A. M. Fox, A. I. Tartakovskii, A. B. Krysa, and M. S. Skolnick

Appl. Phys. Lett. 97, 181104 (2010); http://dx.doi.org/10.1063/1.3510469 (3 pages)

Online Publication Date: 3 November 2010

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We demonstrate semiconductor quantum dots coupled to photonic crystal cavity modes operating in the visible spectrum. We present the design, fabrication, and characterization of two dimensional photonic crystal cavities in GaInP and measure quality factors in excess of 7500 at 680 nm. We demonstrate full control over the spontaneous emission rate of InP quantum dots and by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode we observe a Purcell enhancement of ∼ 8.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.40.Fy Semiconductors
73.21.La Quantum dots

Strain evaluation in AlInN/GaN Bragg mirrors by in situ curvature measurements and ex situ x-ray grazing incidence and transmission scattering

A. Krost, C. Berger, J. Bläsing, A. Franke, T. Hempel, A. Dadgar, and J. Christen

Appl. Phys. Lett. 97, 181105 (2010); http://dx.doi.org/10.1063/1.3514241 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2010

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Strain in lattice matched and mismatched AlInN/GaN Bragg mirror structures were studied by in situ curvature and various ex situ x-ray measurements. In the case of lattice mismatched structures considerable deviations of the in-plane lattice parameters were evidenced near the surface region as well as in depth using x-ray grazing incidence and x-ray transmission scattering in Laue geometry. The experimental findings are explained in terms of partial stress relaxation of the AlInN/GaN Bragg layer stack with respect to the underlying GaN buffer and a mutual tensioning of the GaN and AlInN layers with respect to each other.
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78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Optomechanics in an ultrahigh-Q two-dimensional photonic crystal cavity

Amir H. Safavi-Naeini, Thiago P. Mayer Alegre, Martin Winger, and Oskar Painter

Appl. Phys. Lett. 97, 181106 (2010); http://dx.doi.org/10.1063/1.3507288 (3 pages) | Cited 5 times

Online Publication Date: 4 November 2010

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We demonstrate an ultrahigh-Q slotted two-dimensional photonic crystal cavity capable of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The measured optical quality factor is Q = 1.2×106 for a cavity with an effective modal volume of Veff = 0.04(λ)3. Optical transduction of the thermal motion of the fundamental in-plane mechanical resonance of the structure (νm = 151 MHz) is performed, from which a zero-point motion optomechanical coupling rate of g∗/2π = 320 kHz is inferred. Dynamical back-action of the optical field on the mechanical motion, resulting in cooling and amplication of the mechanical motion, is also demonstrated.
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42.79.Gn Optical waveguides and couplers
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Strain influenced indium composition distribution in GaN/InGaN core-shell nanowires

Qiming Li and George T. Wang

Appl. Phys. Lett. 97, 181107 (2010); http://dx.doi.org/10.1063/1.3513345 (3 pages) | Cited 4 times

Online Publication Date: 4 November 2010

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The optical properties, indium concentration and distribution, defect morphology, and strain distribution of GaN/InGaN coaxial nanowires grown by metal organic chemical vapor deposition were investigated using spatially resolved cathodoluminescence, scanning transmission electron microscopy, and finite element analysis. The results indicate that InGaN layers with 40% or greater indium incorporation and low defect density can be achieved. The indium distribution in the InGaN shell layer was measured and qualitatively correlated with the calculated strain distribution. The three-dimensional compliance of the GaN nanowire leads to facile strain relaxation in the InGaN heteroepitaxial layer, enabling high indium incorporation and high crystalline quality.
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78.67.Lt Quantum wires
81.07.Gf Nanowires
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence

Effect of an asymmetry AlGaN barrier on efficiency droop in wide-well InGaN double-heterostructure light-emitting diodes

Ray-Ming Lin, Mu-Jen Lai, Liann-Be Chang, and Chou-Hsiung Huang

Appl. Phys. Lett. 97, 181108 (2010); http://dx.doi.org/10.1063/1.3513394 (3 pages) | Cited 1 time

Online Publication Date: 4 November 2010

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External-quantum-efficiency (EQE) and efficiency droop in wide-well InGaN double-heterostructure light-emitting diodes have been investigated. It was found that the insertion of an AlGaN barrier between the n-type GaN layer and the InGaN well resulted in higher peak EQE and reduced efficiency droop at a higher injection level. EQE was improved by 5.7% and 25.8% over that of a sample without an AlGaN barrier at a current density of 104.3 A/cm2 and 521 A/cm2, respectively. It is suggested that the mechanism is attributed to an electron decelerating effect that enlarges the effective active region.
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85.60.Jb Light-emitting devices

Reliability in room-temperature negative differential resistance characteristics of low-aluminum content AlGaN/GaN double-barrier resonant tunneling diodes

C. Bayram, Z. Vashaei, and M. Razeghi

Appl. Phys. Lett. 97, 181109 (2010); http://dx.doi.org/10.1063/1.3515418 (3 pages) | Cited 12 times

Online Publication Date: 5 November 2010

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AlGaN/GaN resonant tunneling diodes (RTDs), consisting of 20% (10%) aluminum-content in double-barrier (DB) active layer, were grown by metal-organic chemical vapor deposition on freestanding polar (c-plane) and nonpolar (m-plane) GaN substrates. RTDs were fabricated into 35-μm-diameter devices for electrical characterization. Lower aluminum content in the DB active layer and minimization of dislocations and polarization fields increased the reliability and reproducibility of room-temperature negative differential resistance (NDR). Polar RTDs showed decaying NDR behavior, whereas nonpolar ones did not significantly. Averaging over 50 measurements, nonpolar RTDs demonstrated a NDR of 67 Ω, a current-peak-to-valley ratio of 1.08, and an average oscillator output power of 0.52 mW.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Ultrasmooth microfabricated mirrors for quantum information

G. W. Biedermann, F. M. Benito, K. M. Fortier, D. L. Stick, T. K. Loyd, P. D. D. Schwindt, C. Y. Nakakura, R. L. Jarecki, Jr., and M. G. Blain

Appl. Phys. Lett. 97, 181110 (2010); http://dx.doi.org/10.1063/1.3511743 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2010

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In this paper, we realize a scalable micromirror suitable for atom chip based cavity quantum electrodynamics applications. A very low surface roughness of 2.2 Å rms on the silicon cavity mirrors is achieved using chemical dry etching along with plasma and oxidation smoothing. Our Fabry–Perot cavity comprised of these mirrors currently demonstrates the highest finesse, F = 64 000, using microfabricated mirrors. We compute a single atom cooperativity for our cavities of more than 200, making them promising candidates for detecting individual atoms and for quantum information applications on a chip.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.79.Bh Lenses, prisms and mirrors
42.86.+b Optical workshop techniques

Widely tunable quantum cascade lasers with coupled cavities for gas detection

Peter Fuchs, Jochen Seufert, Johannes Koeth, Julia Semmel, Sven Höfling, Lukas Worschech, and Alfred Forchel

Appl. Phys. Lett. 97, 181111 (2010); http://dx.doi.org/10.1063/1.3514247 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2010

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The authors report the fabrication of widely tunable monolithic quantum cascade lasers (QCLs) with coupled Fabry–Pérot (FP) cavities on indium phosphide. Quasicontinuous tuning of the single mode emission over a total spectral range of 242 nm was realized at two regions between 8.394 and 8.785 μm. An absorption experiment with ammonia shows principle feasibility of gas detection with multisegment QCL devices. Good agreement of the experimentally observed tuning behavior with the one expected from calculated FP mode-combs indicates that the change in the refractive index is mainly due to thermal heating as a result of current injection.
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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
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Terahertz band gap properties by using metal slits in tapered parallel-plate waveguides

Eui Su Lee, Young Bin Ji, and Tae-In Jeon

Appl. Phys. Lett. 97, 181112 (2010); http://dx.doi.org/10.1063/1.3514558 (3 pages) | Cited 4 times

Online Publication Date: 5 November 2010

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We present experimental and finite-difference time-domain simulation studies on the properties of Bragg and non-Bragg band gaps; the studies are carried out by using metal slit arrays positioned at the center of the air gaps in tapered parallel-plate waveguides. Two Bragg stop bands, with a dynamic power transmission range of about 26 dB, are observed for an air gap of 29 μm. Two non-Bragg stop bands are observed for an air gap of 94 μm. Using the Ey field distribution and Poynting vectors, we confirm that the Ey field leaking from the slit and the Ey field propagating from another input vanish because they are out of phase. The Bragg and non-Bragg stop bands determined in the simulations show excellent agreement with those observed experimentally.
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42.79.Gn Optical waveguides and couplers
85.60.-q Optoelectronic devices
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Dependence of glass forming ability on liquid fragility: Thermodynamics versus kinetics

Li-Min Wang, Yongjun Tian, and Riping Liu

Appl. Phys. Lett. 97, 181901 (2010); http://dx.doi.org/10.1063/1.3506900 (3 pages) | Cited 3 times

Online Publication Date: 1 November 2010

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The dependence of glass forming ability on liquid fragility is studied with thermodynamic and kinetic analyses. A general expression of the Gibbs free energy difference between an undercooled liquid and its equilibrium crystal is presented to address thermodynamically the fragility effect on glass formation. It is found that increasing fragility thermodynamically favors glass formation, remarkably contrasting with the fragility effect from the kinetic point of view. The dependences of glass forming ability on fragility in metallic alloys and molecular isomers are compared, and kinetics and thermodynamics of glass formation are, respectively, emphasized.
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64.70.pm Liquids
65.40.G- Other thermodynamical quantities

Experimental verification of negative refraction for a wedge-type negative index metamaterial operating at terahertz

Shengxiang Wang, Frédéric Garet, Karine Blary, Eric Lheurette, Jean Louis Coutaz, and Didier Lippens

Appl. Phys. Lett. 97, 181902 (2010); http://dx.doi.org/10.1063/1.3511540 (3 pages) | Cited 2 times

Online Publication Date: 1 November 2010

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We report on angle-resolved time domain spectroscopy (TDS) carried out on a prismlike negative index metamaterial operating around 0.5 THz. The wedge-type devices are constituted of hole arrays etched in gold thin films, which are stacked according to a sequential mask shift. By means of a goniometric TDS setup and subsequent analysis of the temporal waveforms, negative refraction is demonstrated with values close to n = −1 around 0.5 THz. The dispersion of refractive index retrieved from the Snell–Descartes law shows comparable trends in comparison with the dispersion deduced from complex transmission and reflection measurements on slab-type samples.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Retrieval of terahertz spectroscopic signatures in the presence of rough surface scattering using wavelet methods

M. H. Arbab, D. P. Winebrenner, E. I. Thorsos, and A. Chen

Appl. Phys. Lett. 97, 181903 (2010); http://dx.doi.org/10.1063/1.3507384 (3 pages) | Cited 2 times

Online Publication Date: 1 November 2010

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Scattering of terahertz waves by surface roughness can obscure spectral signatures of chemicals at these frequencies. We demonstrate this effect using controlled levels of surface scattering on α-lactose monohydrate pellets. Furthermore, we show an implementation of wavelet methods that can retrieve terahertz spectral information from rough surface targets. We use a multiresolution analysis of the rough-surface-scattered signal utilizing the maximal overlap discrete wavelet transform (MODWT) to extract the resonant signature of lactose. We present a periodic extension technique to circumvent the circular boundary conditions of MODWT, which can be robustly used in an automated terahertz stand-off detection device.
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78.70.Gq Microwave and radio-frequency interactions
68.35.B- Structure of clean surfaces (and surface reconstruction)
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Rashba and Dresselhaus spin-orbit coupling in GaN-based heterostructures probed by the circular photogalvanic effect under uniaxial strain

Chunming Yin, Bo Shen, Qi Zhang, Fujun Xu, Ning Tang, Longbin Cen, Xinqiang Wang, Yonghai Chen, and Jinling Yu

Appl. Phys. Lett. 97, 181904 (2010); http://dx.doi.org/10.1063/1.3511768 (3 pages) | Cited 1 time

Online Publication Date: 1 November 2010

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The spin splitting in GaN-based heterostructures has been investigated by means of circular photogalvanic effect experiments under uniaxial strain. The ratios of Rashba and Dresselhaus spin-orbit coupling coefficients (R/D ratios) have been measured in AlxGa1−xN/GaN heterostructures with various Al compositions. It is found that the R/D ratio increases from 4.1 to 19.8 with the Al composition of the AlxGa1−xN barrier varied from 15% to 36%. The Dresselhaus coefficient of bulk GaN is experimentally obtained to be 0.4 eV Å3. The results indicate that the spin splitting in GaN-based heterostructures can be modulated effectively by the polarization-induced electric fields.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.40.+w Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Blue-green light photochromism in europium doped BaMgSiO4

Morito Akiyama

Appl. Phys. Lett. 97, 181905 (2010); http://dx.doi.org/10.1063/1.3509417 (3 pages) | Cited 1 time

Online Publication Date: 1 November 2010

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BaMgSiO4 (BMS) can be sensed to blue light (wavelength λ = 405 nm) by doped europium (Eu). Eu doped BMS turns to bright pink, and is bleached by green light (λ = 475–532 nm) irradiation in several seconds. The coloration-decoloration process is repeatable and first. The colored state hardly changes for over 480 h (20 days), and is stable even at 100 °C. The blue-green light photochromism can be explained by electron transfers between doped Eu and oxygen defects. The doped Eu broadens the absorption band of BMS, and supplies excited electrons. The oxygen defects form electron traps, which catch excited electrons, and become F-like color centers.
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78.20.-e Optical properties of bulk materials and thin films
61.72.jn Color centers
71.55.Ht Other nonmetals
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Enhanced carbon nanotube fibers by polyimide

Chao Fang, Jingna Zhao, Jingjing Jia, Zuoguang Zhang, Xiaohua Zhang, and Qingwen Li

Appl. Phys. Lett. 97, 181906 (2010); http://dx.doi.org/10.1063/1.3511451 (3 pages)

Online Publication Date: 2 November 2010

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The performance of carbon nanotube (CNT) fibers is limited by the intertube characteristics. Here we report a direct method of curing to improve mechanical properties of poly(amic acid)-infiltrated fibers. After curing at 190 °C for 60 min the fibers composed of double- and triple-walled CNTs, their strength is stably improved by 30.3%, from 1.58 to 2.06 GPa. The enhancement arises from the increase in shear stress between tube surfaces, by measuring the static frictional force of CNT fibers. Due to the existence of CNTs, the imidization temperature of polyimide drops greatly from 218 to 157 °C.
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81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
82.35.-x Polymers: properties; reactions; polymerization

In situ Raman spectroscopy for characterization of the domain contributions to electrical and piezoelectric responses in Pb(Zr,Ti)O3 films

Mitsumasa Nakajima, Hiroshi Nakaki, Yoshitaka Ehara, Tomoaki Yamada, Ken Nishida, Takashi Yamamoto, Minoru Osada, and Hiroshi Funakubo

Appl. Phys. Lett. 97, 181907 (2010); http://dx.doi.org/10.1063/1.3502591 (3 pages) | Cited 2 times

Online Publication Date: 2 November 2010

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We employed in situ Raman spectroscopy under electric field for (100)/(001)-oriented tetragonal Pb(Ti0.61Zr0.39)O3 films with (001)-volume fraction (VC) of 35%. The increase in VC was revealed above 200 kV/cm, which resulted in the larger remanent polarization. In addition, the application of high enough field also brings a feature, i.e., large reversible change in VC with/without electric field that can quantitatively explain the enhanced piezoelectric response. These demonstrate the usefulness of in situ Raman observation to probe the domain contributions to the electrical and piezoelectric responses.
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77.55.hj PZT
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
78.30.Hv Other nonmetallic inorganics

In situ spectroscopic ellipsometry studies of trivalent chromium coating on aluminum

Sameh Dardona and Mark Jaworowski

Appl. Phys. Lett. 97, 181908 (2010); http://dx.doi.org/10.1063/1.3511472 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2010

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In situ spectroscopic ellipsometry in the spectral region of 1.3–4.3 eV has been employed to monitor, in real-time, the formation of trivalent Cr process (TCP) conversion coatings on polished Al substrates. The measured ellipsometry parameters (Ψ and Δ), as a function of immersion time, reveal that the initial stages of film formation include the chemical thinning of the native oxide layer, formation of a very thin initiation layer and the subsequent rapid formation of the TCP film. The film optical constant is modeled using Cauchy dispersion relation and its thickness was determined as a function of immersion time during growth.
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78.66.Bz Metals and metallic alloys
78.40.Kc Metals, semimetals, and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.A- Nucleation and growth
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Broadening of optical transitions in polycrystalline CdS and CdTe thin films

Jian Li, Jie Chen, and R. W. Collins

Appl. Phys. Lett. 97, 181909 (2010); http://dx.doi.org/10.1063/1.3511744 (3 pages) | Cited 3 times

Online Publication Date: 3 November 2010

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The dielectric functions ε of polycrystalline CdS and CdTe thin films sputter deposited onto Si wafers were measured from 0.75 to 6.5 eV by in situ spectroscopic ellipsometry. Differences in ε due to processing variations are well understood using an excited carrier scattering model. For each sample, a carrier mean free path λ is defined that is found to be inversely proportional to the broadening of each of the band structure critical points (CPs) deduced from ε. The rate at which broadening occurs with λ−1 is different for each CP, enabling a carrier group speed υg to be identified for the CP. With the database for υg, ε can be analyzed to evaluate the quality of materials used in CdS/CdTe photovoltaic heterojunctions.
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78.66.Hf II-VI semiconductors
68.55.ag Semiconductors
81.15.Cd Deposition by sputtering
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Graphene as intermediate phase in fullerene and carbon nanotube growth: A Young–Laplace surface-tension model

Vinay Gupta

Appl. Phys. Lett. 97, 181910 (2010); http://dx.doi.org/10.1063/1.3509403 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2010

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Growth mechanism of carbon nanotubes using arc-discharge are not fully understood up to now. Here, I show that the formation of carbon nanotubes and fullerene in a pure carbon arc in helium atmosphere may involve graphene bubbles. Electron microscopy shows the graphene bubbles formation at the anode surface. The growth of fullerene and nanotubes can occur from these bubbles due to a large pressure difference (103–104 bar) at the anode interface and can be understood in terms of Young–Laplace law of surface tension. This model can explain the helium pressure dependence of fullerene and carbon nanotube formation.
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81.05.ub Fullerenes and related materials
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.03.Cd Surface tension and related phenomena
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Thermodynamic study on metastable phase: From polycrystalline to nanocrystalline system

Wenwu Xu, Xiaoyan Song, and Zhexu Zhang

Appl. Phys. Lett. 97, 181911 (2010); http://dx.doi.org/10.1063/1.3509407 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2010

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First an approach based on the Debye model is developed to quantify the thermodynamic parameters of metastable phase in the conventional coarse-grained polycrystalline systems. Subsequently, by combining the experimental measurements on heat capacity with the nanothermodynamic calculations for nanocrystalline alloys, a method is established to determine the fundamental thermodynamic functions of the metastable phases in both polycrystalline and nanocrystalline alloy systems. Taking the typical metastable-phase SmCo7 alloy as an example, the thermodynamic properties of polycrystalline and nanocrystalline systems are studied, and good agreement between model calculations and experimental results is achieved.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Micellization and adsorption of surfactant in a nonpolar liquid in micrometer scale geometries

F. Beunis, F. Strubbe, M. Marescaux, K. Neyts, and A. R. M. Verschueren

Appl. Phys. Lett. 97, 181912 (2010); http://dx.doi.org/10.1063/1.3503968 (3 pages)

Online Publication Date: 3 November 2010

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Mixtures of nonpolar liquid and surfactant are used increasingly in applications with microscopic dimensions. However, most methods to characterize them are performed on bulk solutions. We measure electrical transient currents in thin layers of nonpolar liquid with surfactant and derive several properties from these measurements. This paper reports the results for different liquid layer thicknesses and surfactant concentrations. We observe a dependence on the layer thickness of the inverse micelle concentration, which cannot be explained by bulk micellization alone. A model including surface adsorption is proposed that describes surfactant behavior in microscale geometries.
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82.70.Dd Colloids
61.20.Gy Theory and models of liquid structure
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
68.43.Mn Adsorption kinetics

Density of Mn interstitials in (Ga,Mn)As epitaxial layers determined by anomalous x-ray diffraction

V. Holý, X. Martí, L. Horák, O. Caha, V. Novák, M. Cukr, and T. U. Schülli

Appl. Phys. Lett. 97, 181913 (2010); http://dx.doi.org/10.1063/1.3514240 (3 pages)

Online Publication Date: 3 November 2010

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Densities of Mn ions in epitaxial layers of (Ga,Mn)As were determined by anomalous x-ray diffraction, i.e., by a measurement of the dependence of the intensity of weak diffraction 002 on the photon energy around the Mn K absorption edge. From the measured data it was possible to determine the density of Mn ions in substitutional positions and the difference in the Mn densities in two possible interstitial positions in the GaAs lattice. The data demonstrate that the rate of the out-diffusion of the Mn interstitials from the Ga tetrahedrons significantly exceeds that from the As tetrahedrons.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.Lw Diffusion of other defects
61.72.jj Interstitials
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