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8 Dec 2003

Volume 83, Issue 23, pp. 4689-4874

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 4707 (2003); http://dx.doi.org/10.1063/1.1631746 (3 pages)

Jan-Hendrik Klein-Wiele and Peter Simon
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Electrically tunable ring resonators incorporating nematic liquid crystals as cladding layers

Brett Maune, Rhys Lawson, Cary Gunn, Axel Scherer, and Larry Dalton

Appl. Phys. Lett. 83, 4689 (2003); http://dx.doi.org/10.1063/1.1630370 (3 pages) | Cited 36 times

Online Publication Date: 2 December 2003

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We have demonstrated electrical tuning in ring resonators fabricated from silicon-on-insulator wafers by incorporating nematic liquid crystals (NLCs) as the waveguide top and side cladding material. Photolithographically defined electrodes aligned around the ring resonator were used to control the orientation of the NLCs to modulate the cladding refractive index and, hence, the resonant wavelengths of the ring resonator. © 2003 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing
42.82.Et Waveguides, couplers, and arrays
85.60.-q Optoelectronic devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Df Liquid crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Hybrid electro-optic polymer/sol–gel waveguide modulator fabricated by all-wet etching process

Y. Enami, G. Meredith, N. Peyghambarian, and A. K.-Y. Jen

Appl. Phys. Lett. 83, 4692 (2003); http://dx.doi.org/10.1063/1.1630850 (3 pages) | Cited 9 times

Online Publication Date: 2 December 2003

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A simple all-wet-etch process fabricates a hybrid electro-optic-polymer (EOP)/sol–gel waveguide modulator, confining the EOP laterally in the sol–gel overcladding. The structure enables an adiabatic transition between the passive sol–gel waveguides and the active EOP overlayers without lateral radiation. Intensity is confined well in a 0.9-μm-thick EOP overlayer, resulting in a low half-wave voltage (Vπ) due to the larger overlap integral. This lateral confinement technique allowed the reduction of Vπ (at 1550 nm) by a factor of 4. © 2003 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.86.+b Optical workshop techniques
42.79.Gn Optical waveguides and couplers

Ultrahigh efficiency green polymer light-emitting diodes by nanoscale interface modification

Qianfei Xu, Jianyong Ouyang, Yang Yang, Takayuki Ito, and Junji Kido

Appl. Phys. Lett. 83, 4695 (2003); http://dx.doi.org/10.1063/1.1630848 (3 pages) | Cited 56 times

Online Publication Date: 2 December 2003

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We report highly efficient green polymer light-emitting diodes (PLEDs) achieved by introducing a nanoscale interfacial layer, made of calcium (2) acetylacetonate [Ca(acac)2], between the aluminum cathode and the green polyfluorene polymer. Ca(acac)2 is solution processible, therefore it is ideal for the fabrication of PLEDs. It is believed that the Ca(acac)2 layer plays multiple roles in enhancing the device performance. Firstly, it enhances the injection of electrons, which are the minority carriers in our green polyfluorene PLEDs. Secondly, it provides a buffer layer, preventing the quenching of luminescence from the aluminum electrode. Thirdly, it behaves as a hole-blocking layer, and subsequently enhances exciton formation. Based on Ca(acac)2/aluminum cathode, we obtained device efficiency as high as 28 cd/A at 2650 cd/m2 brightness, which is an improvement by a more than a factor of 3 over devices using calcium/aluminum as the cathode. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Kz Solid organic materials

High-temperature performance of GaAs-based bound-to-continuum quantum-cascade lasers

C. Pflügl, W. Schrenk, S. Anders, G. Strasser, C. Becker, C. Sirtori, Y. Bonetti, and A. Muller

Appl. Phys. Lett. 83, 4698 (2003); http://dx.doi.org/10.1063/1.1633021 (3 pages) | Cited 49 times

Online Publication Date: 2 December 2003

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GaAs-based quantum-cascade lasers based on a bound-to-continuum transition have been realized and characterized. This band structure design combines the advantages of the well known three-well and superlattice active regions. We observed lasing of Fabry–Pérot lasers in pulsed mode up to a temperature of 100 °C. Multimode emission with a pulsed peak power of 340 mW is observed at room temperature and 42 mW at 80 °C. Further, from aging tests we expect a lifetime of over 60 years for these devices. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells

4.5 mW operation of AlGaN-based 267 nm deep-ultraviolet light-emitting diodes

A. Yasan, R. McClintock, K. Mayes, D. Shiell, L. Gautero, S. R. Darvish, P. Kung, and M. Razeghi

Appl. Phys. Lett. 83, 4701 (2003); http://dx.doi.org/10.1063/1.1633019 (3 pages) | Cited 51 times

Online Publication Date: 2 December 2003

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We demonstrate 4.5 mW output power from AlGaN-based single quantum well ultraviolet light-emitting diodes at a very short wavelength of 267 nm in pulsed operation mode. The output power in continuous-wave mode reaches a value of 165 μW at an injected current of 435 mA. The measurements were done on arrays of four devices flip chip bonded to AlN submounts for thermal management. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.67.De Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.72.Bj Visible and ultraviolet sources

Ferroelectric inverse opals with electrically tunable photonic band gap

Bo Li, Ji Zhou, Longtu Li, Xing Jun Wang, Xiao Han Liu, and Jian Zi

Appl. Phys. Lett. 83, 4704 (2003); http://dx.doi.org/10.1063/1.1631737 (3 pages) | Cited 33 times

Online Publication Date: 2 December 2003

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We present a scheme for tuning the photonic band gap (PBG) by an external electric field in a ferroelectric inverse opal structure. The inverse opals, consisting of ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) ceramics, were synthesized by a sol–gel process. Optical reflection spectra show that the PBG of the PLZT inverse opals shifts continuously with the change in the applied electric field. As the photonic crystals (PCs) consist of the high-refractive-index constituent and possess an “all-solid” structure, it should supply a more reliable mode to tune the PBG by the electric field for the superprism effect in PCs. It should be of high interest in device applications. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.20.Jq Electro-optical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Fabrication of periodic nanostructures by phase-controlled multiple-beam interference

Jan-Hendrik Klein-Wiele and Peter Simon

Appl. Phys. Lett. 83, 4707 (2003); http://dx.doi.org/10.1063/1.1631746 (3 pages) | Cited 21 times

Online Publication Date: 2 December 2003

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A special beam splitting scheme based on distributed beam splitting with diffractive elements is presented. Multiple beams are created, whose phase relations can be controlled with almost arbitrary precision by only changing the distance between the applied diffractive elements. Integration of this scheme into a reflective imaging system ensures temporal and spatial overlap of all selected beams in the target plane, and enables the use of femtosecond radiation. Manifold photonic structures can be fabricated in this way by phase-controlled multiple-beam interference. We demonstrate the capability of the method for femtosecond laser treatment of solids. Using subpicosecond laser pulses at 248 nm, submicron sized periodic structures with different shapes and feature sizes in the range of 100 nm are ablated on the surface of polycarbonate samples. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.62.-b Laser applications

1.3 μm lasers with AlInAs-capped self-assembled quantum dots

I. R. Sellers, H. Y. Liu, M. Hopkinson, D. J. Mowbray, and M. S. Skolnick

Appl. Phys. Lett. 83, 4710 (2003); http://dx.doi.org/10.1063/1.1632533 (3 pages) | Cited 13 times

Online Publication Date: 2 December 2003

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We report 1.3 μm room-temperature lasing for a self-assembled quantum dot (QD) laser in which the dots are capped by a thin AlInAs layer. The inclusion of the Al-containing layer is shown to improve the dot uniformity, and the larger carrier confinement increases the separation between the QD transitions. A RT threshold current density of 80 A cm−2 is obtained for a device containing three QD layers. The inclusion of the AlInAs layer allows the modification of the dot physical structure and electronic structure of the device, without any significant incorporation of nonradiative centers. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
81.07.Ta Quantum dots

Optical properties of ZnO/GaN heterostructure and its near-ultraviolet light-emitting diode

Qing-Xuan Yu, Bo Xu, Qi-Hong Wu, Yuan Liao, Guan-Zhong Wang, Rong-Chuan Fang, Hsin-Ying Lee, and Ching-Ting Lee

Appl. Phys. Lett. 83, 4713 (2003); http://dx.doi.org/10.1063/1.1632029 (3 pages) | Cited 48 times

Online Publication Date: 2 December 2003

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We report on photoluminescence in a ZnO/GaN heterostructure, which showed a donor–acceptor pair emission band at 3.270 eV and the longitudinal optical phonon replicas at 12 K. In comparison with p-type GaN, the positions of the peaks are redshifted. This may be associated with the variation of the residual strain in the GaN layer of the heterostructure. Using this heterostructure, near-ultraviolet light-emitting diodes were fabricated and their electroluminescence properties were characterized. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

White-electrophosphorescence devices based on rhenium complexes

Feng Li, Gang Cheng, Yi Zhao, Jing Feng, Shiyong Liu, Ming Zhang, Yuguang Ma, and Jiacong Shen

Appl. Phys. Lett. 83, 4716 (2003); http://dx.doi.org/10.1063/1.1632545 (3 pages) | Cited 45 times

Online Publication Date: 2 December 2003

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Efficient white emission from the mixing of yellow emission from the Re-complexes, (4,4′-dimethyl-2,2′-bipyridine)Re(CO)3Cl (Dmbpy-Re), and blue emission from the N,N′-di-1-naphthyl-N, N′-diphenylbenzidine (NPB) is reported. NPB is used as the hole-transporting layer. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as the exciton-blocking as well as electron-transporting layer. Dmbpy-Re is doped into the host material (4,4′-N-N′-dicarbazole)biphenyl (CBP). The chromaticity of the white emission can be tuned by adjusting the thickness of Dmbpy-Re:CBP layer or the concentration of Dmbpy-Re in CBP. The maximum luminance, efficiency, and Commission Internationale De L’Eclairage coordinates at 9 V of the devices with 20-nm-thick and 30-nm-thick Dmbpy-Re:CBP layer at a fixed Dmbpy-Re doping concentration of 2 wt % in CBP are 1332 cd/m2, 2.9 cd/A, and (0.30,0.37), and 2410 cd/m2, 5.1 cd/A, and (0.36,0.43), respectively. The turn-on voltage of these devices is ∼4 V. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Fabrication and characterization of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates

Ya. I. Alivov, E. V. Kalinina, A. E. Cherenkov, D. C. Look, B. M. Ataev, A. K. Omaev, M. V. Chukichev, and D. M. Bagnall

Appl. Phys. Lett. 83, 4719 (2003); http://dx.doi.org/10.1063/1.1632537 (3 pages) | Cited 196 times

Online Publication Date: 2 December 2003

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We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I–V characteristics, with threshold voltage ∼3.2 V and low reverse leakage current ∼ 10−7 A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 nm is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500 K and shown to originate from recombination within the ZnO. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Hf II-VI semiconductors
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence
73.20.-r Electron states at surfaces and interfaces
42.72.Bj Visible and ultraviolet sources
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Enhancement of collimated low-energy broad-beam ion source with four-grid accelerator system

E. K. Wåhlin, M. Watanabe, J. Shimonek, D. Burtner, and D. Siegfried

Appl. Phys. Lett. 83, 4722 (2003); http://dx.doi.org/10.1063/1.1631745 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2003

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An application of a four-grid ion acceleration system for generating highly collimated low-energy (<1.5 keV) ion beams is presented. The four-grid system offers significantly reduced beam divergence angles for practical low-energy source designs compared to current two- and three-grid systems. Ion beam divergence of the entire beam envelope has been reduced to less than 2° at 250 and 750 eV. Results are also compared with a conventional three-grid system. © 2003 American Institute of Physics.
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29.25.Ni Ion sources: positive and negative
41.85.Ew Particle beam profile, beam intensity

Plasma frequency measurements for absolute plasma density by means of wave cutoff method

Jung-Hyung Kim, Dae-Jin Seong, Jong-Yeon Lim, and Kwang-Hwa Chung

Appl. Phys. Lett. 83, 4725 (2003); http://dx.doi.org/10.1063/1.1632026 (3 pages) | Cited 34 times

Online Publication Date: 2 December 2003

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A method for precise measurements of absolute electron density in the plasma using plasma frequency is developed. A microwave perturbation of a frequency is introduced to plasma from a network analyzer and transmits in the plasma. The transmitting wave at a distance from a radiating antenna is monitored using a spectrum analyzer to scan the perturbing frequency. The transmitting wave rapidly decays by a cutoff at the plasma frequency, which gives the absolute electron density. The transmitting waves of some frequency including plasma frequency are characterized. The measured plasma frequency by this method is coincident with that obtained by the plasma oscillation method. © 2003 American Institute of Physics.
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52.70.Gw Radio-frequency and microwave measurements
52.25.-b Plasma properties

Argon excimer emission from high-pressure microdischarges in metal capillaries

R. Mohan Sankaran, Konstantinos P. Giapis, Mohamed Moselhy, and Karl H. Schoenbach

Appl. Phys. Lett. 83, 4728 (2003); http://dx.doi.org/10.1063/1.1632034 (3 pages) | Cited 17 times

Online Publication Date: 2 December 2003

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We report on argon excimer emission from high-pressure microdischarges formed inside metal capillaries with or without gas flow. Excimer emission intensity from a single tube increases linearly with gas pressure between 400 and 1000 Torr. Higher discharge current also results in initial intensity gains until gas heating causes saturation or intensity drop. Argon flow through the discharge intensifies emission perhaps by gas cooling. Emission intensity was found to be additive in prealigned dual microdischarges, suggesting that an array of microdischarges could produce a high-intensity excimer source. © 2003 American Institute of Physics.
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52.80.-s Electric discharges
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Surface-layer band gap widening in Cu(In,Ga)Se2 thin films

M. J. Romero, K. M. Jones, J. AbuShama, Y. Yan, M. M. Al-Jassim, and R. Noufi

Appl. Phys. Lett. 83, 4731 (2003); http://dx.doi.org/10.1063/1.1631396 (3 pages) | Cited 16 times

Online Publication Date: 2 December 2003

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Transmission electron microscopy observations, cathodoluminescence spectroscopy and spectrum imaging are combined to investigate the emission spectrum in Cu(In,Ga)Se2 (CIGS) thin films with improved spatial resolution. We report direct evidence for a surface layer of wider band gap, which forms spontaneously in CIGS films. The existence of such a surface layer is critical for attaining high efficiency in solar cells based on these chalcopyrite semiconductor compounds. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
78.60.Hk Cathodoluminescence, ionoluminescence
84.60.Jt Photoelectric conversion
78.66.Li Other semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Structural changes on supercooling liquid silicon

Noël Jakse, Louis Hennet, David L. Price, Shankar Krishnan, Thomas Key, Emilio Artacho, Benoit Glorieux, Alain Pasturel, and Marie-Louise Saboungi

Appl. Phys. Lett. 83, 4734 (2003); http://dx.doi.org/10.1063/1.1631388 (3 pages) | Cited 33 times

Online Publication Date: 2 December 2003

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X-ray diffraction experiments and ab initio molecular dynamics (AIMD) simulations have been performed to investigate the atomic structure of liquid silicon into the deeply supercooled region. The levitation technique used has made it possible to extend the measurements down to a temperature of 1458 K, 230 K below the equilibrium melting point. The x-ray and AIMD results, which are in reasonable agreement, show conclusively that the tetrahedral order is reinforced and that the coordination number decreases as the liquid is supercooled, with implications for the liquid–liquid phase transition. © 2003 American Institute of Physics.
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61.25.Mv Liquid metals and alloys
61.20.Ja Computer simulation of liquid structure
64.70.Ja Liquid-liquid transitions

Electrical properties of a highly oriented, textured thin film of the ionic conductor Gd:CeO2−δ on (001) MgO

L. Chen, C. L. Chen, X. Chen, W. Donner, S. W. Liu, Y. Lin, D. X. Huang, and A. J. Jacobson

Appl. Phys. Lett. 83, 4737 (2003); http://dx.doi.org/10.1063/1.1629378 (3 pages) | Cited 28 times

Online Publication Date: 2 December 2003

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Highly oriented ionic conductor gadolinium-doped CeO2−δ (Ce0.8Gd0.2O2−δ) thin films have been grown on single-crystal (001) MgO substrates by pulsed-laser ablation. The films are highly c-axis oriented with cube-on-cube epitaxy, as shown by x-ray diffraction and electron microscopy. The interface relationship is, surprisingly, found to be (001)film//(001)sub and [100]film//[100]sub with an extremely large lattice misfit of more than 28%. Ac impedance measurements in the temperature range of 500 to 800 °C reveal that electrical conductivity is predominantly ionic over a very broad oxygen partial pressure range from pO2 from 1×10−19 atm to 1 atm. The activation energy Ea for ionic conductivity measured on unannealed films is 0.86 eV, but after heat treatment, Ea decreases to 0.74 eV. © 2003 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
81.40.Gh Other heat and thermomechanical treatments

High-pressure phase transformation of silicon nitride

John Patten, Ronnie Fesperman, Satya Kumar, Sam McSpadden, Jun Qu, Michael Lance, Robert Nemanich, and Jennifer Huening

Appl. Phys. Lett. 83, 4740 (2003); http://dx.doi.org/10.1063/1.1632031 (3 pages) | Cited 6 times

Online Publication Date: 2 December 2003

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We provide evidence for a high-pressure phase transformation (HPPT) in the ceramic material silicon nitride. This HPPT is inferred by a high-pressure diamond anvil cell, Raman spectroscopy, scanning/transmission electron microscopy, and optical and acoustic microscope inspection. In the case of silicon nitride, the HPPT involves a ductile or metallike behavior that is observed in severe deformation processes, such as nanoindentation and micromachining. This pressure-induced plasticity is believed to be similar to that found in silicon and germanium with its origin in the high-pressure metallic β-Sn phase formation. © 2003 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Low-loss as-grown germanosilicate layers for optical waveguides

Feridun Ay, Atilla Aydinli, and Sedat Agan

Appl. Phys. Lett. 83, 4743 (2003); http://dx.doi.org/10.1063/1.1631753 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguide technology. The films were deposited by plasma-enhanced chemical vapor deposition technique using silane, germane, and nitrous oxide as precursor gases. Fourier transform infrared spectroscopy was used to monitor the compositional properties of the samples. It was found that addition of germane leads to decreasing of N–H- and O–H-related bonds. The propagation loss values of the planar waveguides were correlated with the decrease in the hydrogen-related bonds of the as-deposited waveguides and resulted in very low values, eliminating the need for high-temperature annealing as is usually done. © 2003 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
42.79.Gn Optical waveguides and couplers
61.43.Fs Glasses
78.66.Jg Amorphous semiconductors; glasses
42.82.Et Waveguides, couplers, and arrays
78.40.Pg Disordered solids

Electroluminescence from Tm-doped GaN deposited by radio-frequency planar magnetron sputtering

Joo Han Kim, M. R. Davidson, and Paul. H. Holloway

Appl. Phys. Lett. 83, 4746 (2003); http://dx.doi.org/10.1063/1.1627471 (3 pages) | Cited 20 times

Online Publication Date: 2 December 2003

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Room-temperature blue and near-infrared (NIR) electroluminescence ac (EL) has been demonstrated from Tm-doped GaN thin films prepared by rf planar magnetron sputter deposition. Blue and NIR EL emission peaks at ∼475 and ∼800 nm, respectively, were observed from the Tm3+ 4f intrashell transitions from the 1G4 and 3F4 excited states to the 3H6 ground state, respectively. The threshold voltage for the 475 nm blue emission was consistently 11 to 19 V higher than that for the 800 nm NIR emission. The EL intensity ratio of the 475 to 800 nm emission (I475/I800) was increased ∼900% with a 67% increase in the applied ac voltage from 120 to 200 V. These results indicate that the excitation process of EL from GaN:Tm ACTFEL devices is dominated by impact excitation of the Tm3+ luminescent centers by direct interaction between hot electrons and the ground state 4f electrons. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
81.15.Cd Deposition by sputtering
78.66.Fd III-V semiconductors

Atomic-to-mesoscopic scale structural transition in metal–carbon diamondlike composites probed by second-harmonic generation

T. V. Murzina, R. V. Kapra, O. A. Aktsipetrov, and V. F. Dorfman

Appl. Phys. Lett. 83, 4749 (2003); http://dx.doi.org/10.1063/1.1631386 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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Structural features of diamondlike metal-doped carbon films are studied by means of optical second-harmonic generation (SHG). A high interfacial sensitivity of the SHG probe and its significant enhancement in metal nanoparticles allows one to distinguish between clusterlike and amorphous atomic scale structure of carbon-metal composites. These films appear to retain a stable amorphous atomic-scale structure in a wide range of metal concentration above the percolation threshold. Atomic-to-mesoscopic scale structural transition in diamondlike metaldoped carbon films is observed, which takes place under the thermal annealing. © 2003 American Institute of Physics.
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64.70.Nd Structural transitions in nanoscale materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids

Surface kinetics: Step-facet barriers

Hanchen Huang and Jian Wang

Appl. Phys. Lett. 83, 4752 (2003); http://dx.doi.org/10.1063/1.1631389 (3 pages) | Cited 23 times

Online Publication Date: 2 December 2003

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This letter presents a concept of surface kinetic barrier: The step–facet barrier. This concept is demonstrated for two face-centered-cubic metals, aluminum and copper, through molecular statics calculations. Our numerical results show that the step–facet barrier is substantially larger than step–step or diffusion barriers on flat surfaces; true for both metals. Based on the relative magnitudes of kinetic barriers, we discuss implications of the step–facet barrier on surface processing, particularly the step flow. This discussion shows that the kinetic barrier potentially may enable us to pattern nanowires on a metal surface. © 2003 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
81.07.Lk Nanocontacts
81.65.Cf Surface cleaning, etching, patterning
68.47.De Metallic surfaces

Anisotropy in thermo-optic coefficients of polyimide films formed on Si substrates

Yoshiharu Terui and Shinji Ando

Appl. Phys. Lett. 83, 4755 (2003); http://dx.doi.org/10.1063/1.1631744 (3 pages) | Cited 20 times

Online Publication Date: 2 December 2003

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The temperature dependence of in-plane and out-of-plane refractive indices (i.e., thermo-optic coefficients dn/dT) was measured for seven kinds of aromatic polyimide (PI) films formed on silicon substrates. The absolute values of dnTE/dT (polarization parallel to the film plane) are significantly larger than dnTM/dT (perpendicular to the film plane). The dn/dT for average refractive indices (nav) are −94 to −58 ppm/K, independent of film thickness. The anisotropies (dnTE/dT−dnTM/dT) are −9 to −39 ppm/K. Although the values of nav are independent of film thickness, the anisotropies slightly increase as the film thickness decreases for flexible PI films. As expected from the temperature derivative of the Lorentz–Lorenz (LL) equation, the amorphous PI films exhibiting high nav show large dnav/dT, however, significant anisotropies are observed even for the PI films exhibiting very small birefringence. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology
78.20.Fm Birefringence

Thermal stability of epitaxial Pt films on Y2O3 in a metal-oxide–Si structure

M.-H. Cho, D. W. Moon, K. H. Min, R. Sinclair, S. A. Park, Y. K. Kim, K. Jeong, S. K. Kang, and D.-H. Ko

Appl. Phys. Lett. 83, 4758 (2003); http://dx.doi.org/10.1063/1.1632541 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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High-quality epitaxial Pt films were grown by a sputtering deposition method using epitaxial Y2O3 as a dielectric buffer layer. A high degree of crystallinity was achieved with an ion-beam minimum channeling yield (χmin) of ∼11%, and a high degree of coherence between the film surface and interface was obtained for the Pt(111)/Y2O3(111)/Si, with a large lattice mismatch. High-resolution transmission electron microscopy results showed that the atomic arrangement at the interface between the Pt and the oxide was well ordered, and no perceptible interdiffusion was observed, even at an annealing temperature of up to 700 °C under an oxygen atmosphere. The atomic arrangement at the Pt/Y2O3 interface was drastically degraded after a high-temperature annealing at 900 °C due to the deformation of Y2O3. © 2003 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation

Raman study of the A1(LO) phonon in relaxed and pseudomorphic InGaN epilayers

M. R. Correia, S. Pereira, E. Pereira, J. Frandon, and E. Alves

Appl. Phys. Lett. 83, 4761 (2003); http://dx.doi.org/10.1063/1.1627941 (3 pages) | Cited 18 times

Online Publication Date: 2 December 2003

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The behavior of the A1(LO) phonon mode of relaxed and pseudomorphic InxGa1−xN epilayers, at the surface, is investigated by Raman spectroscopy. This study involves relaxed and pseudomorphic samples, with a compositional range of 0.12 ⩽ x<0.30 and 0.04<x ⩽ 0.20, respectively. Raman measurements were performed under excitation at 3.71 eV. Due to the low depth penetration of the incident light (40 nm), the major contribution to Raman scattering comes from the surface, where strain and composition have been independently determined. For relaxed samples, a linear dependence of the A1(LO) phonon frequency is obtained, as theoretically expected for an one-mode behavior alloy: Ω0(x) = (736±1)-(149±2)x. In the case of pseudomorphic samples, the phonon frequency is almost composition independent up to x = 0.11, probably due to the opposite effects of strain and alloying. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.35.Ja Surface and interface dynamics and vibrations
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