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9 Jan 2006

Volume 88, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 88, 023101 (2006); http://dx.doi.org/10.1063/1.2161942 (3 pages)

R. Daineche, A. Degiovanni, O. Grauby, and R. Morin
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Improved laser triggering and guiding of meqavolt discharges with dual fs-ns pulses

Guillaume Méjean, Roland Ackermann, Jérôme Kasparian, Estelle Salmon, Jin Yu, Jean-Pierre Wolf, Kay Rethmeier, Wilfried Kalkner, Philipp Rohwetter, Kamil Stelmaszczyk, and Ludger Wöste

Appl. Phys. Lett. 88, 021101 (2006); http://dx.doi.org/10.1063/1.2162430 (3 pages) | Cited 17 times

Online Publication Date: 9 January 2006

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We demonstrate that the capacity of ultrashort high-power laser pulses to trigger and guide high-voltage discharges can be significantly enhanced by a subsequent visible nanosecond laser pulse. The femtosecond pulse induces a bundle of filaments, which creates a conducting channel of low density and cold plasma connecting the electrodes. The subsequent laser pulse photodetaches electrons from O2− ions in the electrode leader. The resulting electrons allow efficient heating by Joule effect in a retroaction loop, resulting in a 5% reduction of the breakdown voltage.
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52.38.-r Laser-plasma interactions
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.-b Plasma properties
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Relative phase tuning of coupled defects in photonic crystal vertical-cavity surface-emitting lasers

Ann C. Lehman, James J. Raftery, Aaron J. Danner, Paul O. Leisher, and Kent D. Choquette

Appl. Phys. Lett. 88, 021102 (2006); http://dx.doi.org/10.1063/1.2164347 (2 pages) | Cited 8 times

Online Publication Date: 10 January 2006

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Evanescent coupling can be achieved by patterning the top facet of a vertical-cavity surface-emitting laser (VCSEL) with a multiple defect photonic crystal pattern. We show that for 2×1 coupled defect arrays, the phase between these emission sites changes as the current is varied. The phase variation is manifest in the far field pattern and may be determined using antenna array theory. It is found that the phase varies 81 deg between transversely coupled cavities as the current to the VCSEL is varied by 24 mA. This corresponds to a far field angular change of approximately 1.5 deg.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials

Terahertz dielectric properties of high-resistivity single-crystal ZnO

Abul K. Azad, Jiaguang Han, and Weili Zhang

Appl. Phys. Lett. 88, 021103 (2006); http://dx.doi.org/10.1063/1.2164903 (3 pages) | Cited 16 times

Online Publication Date: 11 January 2006

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We present experimental characterization of complex dielectric properties of high-resistivity single-crystal ZnO by terahertz time-domain spectroscopy in the frequency range extending from 0.3 to 3.5 THz. The measured refractive index, power absorption, and dielectric function are well fit by the pseudo-harmonic model of dielectric response. In addition, from the extrapolation of the experimental results, we show that the absorption is dominated by the transverse optical (TO) E1 phonon mode centered at frequency (ωTO/2π) 12.42 THz.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
72.80.Ey III-V and II-VI semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Microscopic analysis of optical gain in InGaN/GaN quantum wells

B. Witzigmann, V. Laino, M. Luisier, U. T. Schwarz, G. Feicht, W. Wegscheider, K. Engl, M. Furitsch, A. Leber, A. Lell, and V. Härle

Appl. Phys. Lett. 88, 021104 (2006); http://dx.doi.org/10.1063/1.2164907 (3 pages) | Cited 27 times

Online Publication Date: 11 January 2006

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A microscopic theory is used to analyze optical gain in InGaN/GaN quantum wells (QW). Experimental data are obtained from Hakki–Paoli measurements on edge-emitting lasers for different carrier densities. The simulations are based on the solution of the quantum kinetic Maxwell–Bloch equations, including many-body effects and a self-consistent treatment of piezoelectric fields. The results confirm the validity of a QW gain description for this material system with a substantial inhomogeneous broadening due to structural variation. They also give an estimate of the nonradiative recombination rate.
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42.55.Px Semiconductor lasers; laser diodes

Tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers

Li Fan, Mahmoud Fallahi, James T. Murray, Robert Bedford, Yushi Kaneda, Aramis R. Zakharian, Jörg Hader, Jerome V. Moloney, Wolfgang Stolz, and Stephan W. Koch

Appl. Phys. Lett. 88, 021105 (2006); http://dx.doi.org/10.1063/1.2164921 (3 pages) | Cited 7 times

Online Publication Date: 12 January 2006

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We report on the development and the demonstration of tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers (VECSELs). A V-shaped cavity, in which the antireflection-coated VECSEL chip (active mirror) is located at the fold, and a birefringent filter are employed to achieve a large wavelength tuning range. Multiwatt cw linearly polarized TEM00 output with a 20 nm tuning range and narrow linewidth is demonstrated at room temperature.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Determination of dc Kerr coefficients of polymer filmswith prism-optical waveguide configuration

Jianhong Zhou, Xiaoxu Deng, Zhuangqi Cao, Qishun Shen, Wei Wei, Zhijian Zhang, and Shixiang Xie

Appl. Phys. Lett. 88, 021106 (2006); http://dx.doi.org/10.1063/1.2164923 (3 pages) | Cited 3 times

Online Publication Date: 12 January 2006

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A prism-optical waveguide coupling system, which consists of a prism and a symmetrical metal-cladding polymer optical waveguide, is used to analyze the field-induced intensity variation due to the quadratic electro-optic (QEO) effect. As a result, not only the dc Kerr coefficient, but also the whole components of the QEO tensor of the polymer film are determined experimentally.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics
42.79.Gn Optical waveguides and couplers
78.20.Jq Electro-optical effects

Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles

X. H. Yang, F. Jaiser, S. Klinger, and D. Neher

Appl. Phys. Lett. 88, 021107 (2006); http://dx.doi.org/10.1063/1.2162693 (3 pages) | Cited 52 times

Online Publication Date: 13 January 2006

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We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at ∼ 40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd∕A and 8.8 lm∕W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Quantum key distribution at telecom wavelengths with noise-free detectors

Danna Rosenberg, Sae Woo Nam, Philip A. Hiskett, Charles G. Peterson, Richard J. Hughes, Jane E. Nordholt, Adriana E. Lita, and Aaron J. Miller

Appl. Phys. Lett. 88, 021108 (2006); http://dx.doi.org/10.1063/1.2164307 (3 pages)

Online Publication Date: 13 January 2006

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The length of a secure link over which a quantum key can be distributed depends on the efficiency and dark-count rate of the detectors used at the receiver. We report on the first demonstration of quantum key distribution using superconducting transition-edge sensors with high efficiency and negligible dark-count rates. Using two methods of synchronization, a bright optical pulse scheme and an electrical signal scheme, we have successfully distributed key material at 1550 nm over 50 km of optical fiber. We discuss how use of these detectors in a quantum key distribution system can dramatically increase range and performance.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
03.67.Dd Quantum cryptography and communication security
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.60.Gz Photodetectors (including infrared and CCD detectors)
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Transport of ionized metal atoms in high-power pulsed magnetron discharges assisted by inductively coupled plasma

S. Konstantinidis, J. P. Dauchot, M. Ganciu, and M. Hecq

Appl. Phys. Lett. 88, 021501 (2006); http://dx.doi.org/10.1063/1.2162671 (3 pages) | Cited 26 times

Online Publication Date: 9 January 2006

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Transporting metallic ions from the magnetron cathode to the substrate is essential for an efficient thin-film deposition process. This letter examines how inductively coupled plasma superimposed onto a high-power pulsed magnetron discharge can influence the mobility of titanium ions. To this effect, time-resolved optical emission and absorption spectrometry are conducted and the current at the substrate is measured. With this new hybrid technique, ions are found to reach the substrate in two successive waves. Metal ions, only present in the second wave, are found to accelerate proportionally to the power supplied to the inductively coupled plasma. All the measurements in this study are made at 10 and 30 mTorr, with 10 μs long pulses at the magnetron cathode.
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52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Microdischarge-assisted ignition of dielectric-barrier high-pressure glow discharges

Jichul Shin and Laxminarayan L. Raja

Appl. Phys. Lett. 88, 021502 (2006); http://dx.doi.org/10.1063/1.2162676 (3 pages) | Cited 4 times

Online Publication Date: 9 January 2006

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The ignition characteristics of dielectric-barrier high-pressure glow (DB-HPG) discharges in the presence of dc microdischarges are studied for pure helium and pure nitrogen working gases. In the presence of an array of microdischarges integrated with one of the DB-HPG electrodes, a substantial reduction of DB-HPG ignition voltage is observed for both working gases. The discharge structure within the DB-HPG volume gap is localized near the microdischarge holes when the DB-HPG first turns on in the presence of microdischarges, but subsequently expands to cover the entire volume at higher voltages for the pressures studied. The helium discharge is generally more uniform than the nitrogen gas. Our studies indicate that the localized discharge has a glow-like character rather than a Townsend- or streamer-like one.
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52.80.Hc Glow; corona
52.50.Dg Plasma sources

Evidence of plasma-catalyst synergy in a low-pressure discharge

Antoine Rousseau, Alexander V. Meshchanov, and Jürgen Roepcke

Appl. Phys. Lett. 88, 021503 (2006); http://dx.doi.org/10.1063/1.2164915 (3 pages) | Cited 11 times

Online Publication Date: 10 January 2006

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A low-pressure pulsed dc discharge in air has been used to study the mechanisms of the activation of an oxidative catalyst by plasma irradiation. Porous alumina has been employed as the catalyst. The oxidation of acetylene (C2H2) has been monitored measuring simultaneously the concentrations of CO and CO2 by infrared laser absorption spectroscopy. It was found, that the oxidation efficiency and the CO2/CO selectivity are greatly enhanced by the presence of the catalyst inside the plasma region and increase with the duty cycle ratio of the pulsed plasma.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
92.60.Sz Air quality and air pollution
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H-induced platelet and crack formation in hydrogenated epitaxial Si/Si0.98B0.02/Si structures

Lin Shao, Yuan Lin, J. G. Swadener, J. K. Lee, Q. X. Jia, Y. Q. Wang, M. Nastasi, Phillip E. Thompson, N. David Theodore, T. L. Alford, J. W. Mayer, Peng Chen, and S. S. Lau

Appl. Phys. Lett. 88, 021901 (2006); http://dx.doi.org/10.1063/1.2163992 (3 pages) | Cited 7 times

Online Publication Date: 9 January 2006

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An approach to transfer a high-quality Si layer for the fabrication of silicon-on-insulator wafers has been proposed based on the investigation of platelet and crack formation in hydrogenated epitaxial Si/Si0.98B0.02/Si structures grown by molecular-beam epitaxy. H-related defect formation during hydrogenation was found to be very sensitive to the thickness of the buried Si0.98B0.02 layer. For hydrogenated Si containing a 130 nm thick Si0.98B0.02 layer, no platelets or cracking were observed in the B-doped region. Upon reducing the thickness of the buried Si0.98B0.02 layer to 3 nm, localized continuous cracking was observed along the interface between the Si and the B-doped layers. In the latter case, the strains at the interface are believed to facilitate the (100)-oriented platelet formation and (100)-oriented crack propagation.
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81.05.Cy Elemental semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Grain boundary sliding mechanisms in ZrN-Ag, ZrN-Au, and ZrN-Pd nanocomposite films

S. M. Aouadi, P. Basnyat, Y. Zhang, Q. Ge, and P. Filip

Appl. Phys. Lett. 88, 021902 (2006); http://dx.doi.org/10.1063/1.2164391 (3 pages) | Cited 7 times

Online Publication Date: 9 January 2006

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Nanocomposite films of ZrN-Me (Me = Ag, Au, or Pd) were produced by reactive unbalanced magnetron sputtering and were found to form a dense and homogeneous microstructure whereby nanocrystals of Me are distributed evenly throughout the ZrN matrix. Interestingly, the Young’s modulus was found to decrease much more dramatically with the increase in metal content for the ZrN-Ag system. A systematic ab initio study was undertaken to understand the mechanism of grain boundary sliding in these nanostructures. The maximum energy variation during the sliding was found to be the largest and the smallest for ZrN-Pd and ZrN-Ag, respectively.
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81.07.Bc Nanocrystalline materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.15.Cd Deposition by sputtering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Surface termination and roughness of Ge(100) cleaned by HF and HCl solutions

Shiyu Sun, Yun Sun, Zhi Liu, Dong-Ick Lee, Samuel Peterson, and Piero Pianetta

Appl. Phys. Lett. 88, 021903 (2006); http://dx.doi.org/10.1063/1.2162699 (3 pages) | Cited 24 times

Online Publication Date: 10 January 2006

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Oxide removal from Ge(100) surfaces treated by HCl and HF solutions with different concentrations are systematically studied by synchrotron radiation photoelectron spectroscopy (SR-PES). SR-PES results show that clean surfaces without any oxide can be obtained after wet chemical cleaning followed by vacuum annealing with a residual carbon contamination of less than 0.02 monolayer. HF etching leads to a hydrogen-terminated Ge surface whose hydrogen coverage is a function of the HF concentration. In contrast, HCl etching yields a chlorine-terminated surface. Possible etching mechanisms are discussed. Surface roughness after HF and HCl treatments is also investigated by atomic force microscopy which shows that HF treatment leaves a rougher surface than HCl.
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68.47.Fg Semiconductor surfaces
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Cy Elemental semiconductors
68.37.Ps Atomic force microscopy (AFM)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing

Kinetics of strain relaxation in Si1−xGex thin films on Si(100) substrates: Modeling and comparison with experiments

Kedarnath Kolluri, Luis A. Zepeda-Ruiz, Cheruvu S. Murthy, and Dimitrios Maroudas

Appl. Phys. Lett. 88, 021904 (2006); http://dx.doi.org/10.1063/1.2162683 (3 pages) | Cited 3 times

Online Publication Date: 10 January 2006

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We report the results of a theoretical analysis for the kinetics of strain relaxation in Si1−xGex thin films grown epitaxially on Si(100) substrates. The analysis is based on a properly parametrized dislocation mean-field theoretical model describing plastic deformation dynamics due to threading dislocation propagation and addresses strain relaxation kinetics during both epitaxial growth and thermal annealing, including post-implantation annealing. Theoretical predictions for strain relaxation as a function of film thickness in Si0.80Ge0.20/Si(100) samples annealed after epitaxial growth either unimplanted or after He ion implantation are in excellent agreement with experimental measurements [ J. Cai et al., J. Appl. Phys. 95, 5347 (2004) ].
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68.55.A- Nucleation and growth
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.72.Bb Theories and models of crystal defects
61.72.Cc Kinetics of defect formation and annealing

Holographically generated twisted nematic liquid crystal gratings

Hyunhee Choi, J. W. Wu, Hye Jeong Chang, and Byoungchoo Park

Appl. Phys. Lett. 88, 021905 (2006); http://dx.doi.org/10.1063/1.2162672 (3 pages) | Cited 11 times

Online Publication Date: 10 January 2006

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A reflection holographic method is introduced to fabricate an electro-optically tunable twisted nematic (TN) liquid crystal (LC) grating, forgoing the geometrical drawing. The photoisomerization process occurring on the LC alignment layers of an LC cell in the reflection holographic configuration gives a control over the twist angle, and the grating spacing is determined by the slant angle of reflection holographic configuration. The resulting diffraction grating is in a structure of a reverse TN LC, permitting a polarization-independent diffraction efficiency. The electro-optic tunability of the diffraction efficiency is also demonstrated.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
42.40.Eq Holographic optical elements; holographic gratings
82.50.-m Photochemistry

Structure of Sc2O3 films epitaxially grown on α-Al2O3 (0001)

A. R. Kortan, N. Kopylov, J. Kwo, M. Hong, C. P. Chen, J. P. Mannaerts, and S. H. Liou

Appl. Phys. Lett. 88, 021906 (2006); http://dx.doi.org/10.1063/1.2163989 (3 pages) | Cited 1 time

Online Publication Date: 10 January 2006

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The crystal structure of scandium oxide films epitaxially grown on α-Al2O3 (0001) under an ultrahigh-vacuum is studied by single-crystal x-ray diffraction. The Sc2O3 film grows in bixbyite phase on the basal (0001) surface of the sapphire substrate with its ⟨111⟩ axis aligned parallel to the substrate normal. In-plane orientation of the film, however, exhibits two distinct growth directions that are defined by the two possible surface orientations of the stepped α-Al2O3 substrate. The atomic structure of the high-quality epitaxial film is fully relaxed and the film has unusual thickness uniformity.
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77.55.-g Dielectric thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth

Nitrogen incorporation characteristics on a 4H-SiC epitaxial layer

Kazutoshi Kojima, Satoshi Kuroda, Hajime Okumura, and Kazuo Arai

Appl. Phys. Lett. 88, 021907 (2006); http://dx.doi.org/10.1063/1.2164912 (3 pages) | Cited 1 time

Online Publication Date: 11 January 2006

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The N incorporation characteristics on a 4H-SiC epitaxial layer were reinvestigated. It was found that the desorption process and thermally activated process are aspects of the N incorporation mechanism of 4H-SiC to which attention should be paid. This mechanism depends on both the rate-limiting condition and lattice polarity. The N desorption process dominates the N incorporation of the Si-face under the C-supply-limiting condition and that of the C-face without recourse to the rate-limiting condition. On the other hand, the thermally activated process dominates only the N incorporation of the Si-face under the Si-supply-limiting condition. The site-competition phenomenon was also found to depend on the rate-limiting condition.
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61.72.up Other materials

Pyramidal structural defects in erbium silicide thin films

Eu Jin Tan, Mathieu Bouville, Dong Zhi Chi, Kin Leong Pey, Pooi See Lee, David J. Srolovitz, and Chih Hang Tung

Appl. Phys. Lett. 88, 021908 (2006); http://dx.doi.org/10.1063/1.2162862 (3 pages) | Cited 13 times

Online Publication Date: 11 January 2006

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Pyramidal structural defects, 5–8 μm wide, have been discovered in thin films of epitaxial ErSi2−x formed by annealing thin Er films on Si(001) substrates at temperatures of 500–800 °C. The formation of these defects is not due to oxidation. We propose that they form as a result of the separation of the silicide film from the substrate and its buckling in order to relieve the compressive, biaxial epitaxial stresses. Silicon can then diffuse through the silicide or along the interface to fully or partially fill the void between the buckled erbium disilicide film and the substrate.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Cc Kinetics of defect formation and annealing

High-pressure torsion-induced grain growth in electrodeposited nanocrystalline Ni

X. Z. Liao, A. R. Kilmametov, R. Z. Valiev, Hongsheng Gao, Xiaodong Li, A. K. Mukherjee, J. F. Bingert, and Y. T. Zhu

Appl. Phys. Lett. 88, 021909 (2006); http://dx.doi.org/10.1063/1.2159088 (3 pages) | Cited 53 times

Online Publication Date: 12 January 2006

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Deformation-induced grain growth has been reported in nanocrystalline (nc) materials under indentation and severe cyclic loading, but not under any other deformation mode. This raises an issue on critical conditions for grain growth in nc materials. This study investigates deformation-induced grain growth in electrodeposited nc Ni during high-pressure torsion (HPT). Our results indicate that high stress and severe plastic deformation are required for inducing grain growth, and the upper limit of grain size is determined by the deformation mode and parameters. Also, texture evolution suggests that grain-boundary-mediated mechanisms played a significant role in accommodating HPT strain.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment
61.72.Mm Grain and twin boundaries

Combinatorial investigation of the isolated nanoparticle to coalescent layer transition in a gradient sputtered gold nanoparticle layer on top of polystyrene

S. V. Roth, H. Walter, M. Burghammer, C. Riekel, B. Lengeler, C. Schroer, M. Kuhlmann, T. Walther, A. Sehrbrock, R. Domnick, and P. Müller-Buschbaum

Appl. Phys. Lett. 88, 021910 (2006); http://dx.doi.org/10.1063/1.2161926 (3 pages) | Cited 13 times

Online Publication Date: 12 January 2006

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Within a combinatorial investigation, a gradient sputtered gold layer on top of polystyrene on silicon substrate is addressed. Results from a real-space inspection by transmission electron microscopy are compared with surface-sensitive microbeam grazing incidence small-angle x-ray scattering. The combinatorial approach allows distinguishing different morphologies prepared under exactly the same environmental conditions on one single substrate. The transition of a coalescent layer to an isolated nanoparticle layer is determined as a function of sputter rate. Though optical spectra show only slight differences, the morphology and structure are distinctly different from evaporated layers prepared with same mass thickness.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.15.Cd Deposition by sputtering
78.70.Ck X-ray scattering

Two-photon absorption cross-section spectrum of a π-conjugated polymer obtained using the white-light continuum Z-scan technique

S. L. Oliveira, D. S. Corrêa, L. De Boni, L. Misoguti, S. C. Zilio, and C. R. Mendonça

Appl. Phys. Lett. 88, 021911 (2006); http://dx.doi.org/10.1063/1.2164914 (3 pages) | Cited 7 times

Online Publication Date: 13 January 2006

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We have used the white-light continuum (WLC) Z-scan technique to determine the degenerate two-photon absorption (2PA) cross-section spectrum of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene). The results obtained show good agreement with those employing a single-wavelength source, although much faster because of the wavelength multiplexing introduced by the use of a broadband source. The improved spectral resolution of the WLC Z-scan allowed the observation of a 2PA peak around 675 nm, a subtle feature in the nonlinear spectrum that could be fitted using a sum-over-states model. The WLC Z-scan technique has proved to be an important tool to determine the 2PA spectrum of polymers.
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42.70.Jk Polymers and organics
78.40.Me Organic compounds and polymers
42.65.-k Nonlinear optics

Formation of (111) nanotwin lamellae hillocks in polycrystalline silicon thin films caused by deposition of silicon dioxide layer

Shigeki Imai and Masayuki Fujimoto

Appl. Phys. Lett. 88, 021912 (2006); http://dx.doi.org/10.1063/1.2162681 (3 pages) | Cited 2 times

Online Publication Date: 13 January 2006

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Plasma-enhanced chemical vapor deposition was used to deposit layers of tetraethylorthosilicate at different temperatures. In the case of low-temperature deposition (300 °C), the deposited film surface was smooth and the major surface defects of the polycrystalline silicon (poly-silicon) film surface were grooves of grain boundaries. In contrast, in the case of high-temperature deposition (500 °C), the deposited silicon oxide surface exhibited hillocks, and these hillocks were derived from the top end of inclined silicon (111) where protruding nanotwin lamellae penetrated the poly-silicon thin film. The observed hillocks stemming from nanotwin lamellae could have been formed by compressive stress during high-temperature silicon dioxide deposition.
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81.05.Cy Elemental semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Single rolled-up SiGe/Si microtubes: Structure and thermal stability

R. Songmuang, N. Y. Jin-Phillipp, S. Mendach, and O. G. Schmidt

Appl. Phys. Lett. 88, 021913 (2006); http://dx.doi.org/10.1063/1.2159414 (3 pages) | Cited 14 times

Online Publication Date: 13 January 2006

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We investigate the structure and thermal stability of freestanding SiGe/Si rolled-up microtubes by secondary ion mass spectroscopy, scanning and transmission electron microscopy, as well as micro-Raman spectroscopy. The tube walls show good crystal quality but become thinner during tube fabrication, leading to smaller diameters than expected. Si–Si vibration modes from the wall are consistent with Raman shifts induced by the strain distribution in the structure. Furthermore, the Raman shifts are used to monitor the tube temperature during laser annealing. At high temperatures, the tube structure irreversibly changes due to Si and Ge interdiffusion and, most remarkably, by Ge condensation.
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61.46.Fg Nanotubes
78.30.Hv Other nonmetallic inorganics
61.72.Cc Kinetics of defect formation and annealing
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.35.Fx Diffusion; interface formation
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

On the elastic constants of the zeolite chlorosodalite

Jennifer J. Williams, Kenneth E. Evans, and Richard I. Walton

Appl. Phys. Lett. 88, 021914 (2006); http://dx.doi.org/10.1063/1.2162859 (3 pages) | Cited 3 times

Online Publication Date: 13 January 2006

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The use of force-field based molecular modeling to predict the elastic constants of the zeolite chlorosodalite is described. Theoretical predictions of the on-axis and off-axis elastic constants strongly suggest that an error exists in the published elastic constants of the material. When the previous experimental data are corrected by transposing the published directional ultrasound velocities, excellent agreement is observed between the off-axis plots of sodalite produced by experiment and modeling. Further confirmation of the prediction is supplied by considering the Zener ratios of other inorganic materials that possess cubic symmetry.
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62.20.D- Elasticity
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