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6 Jun 2005

Volume 86, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 233104 (2005); http://dx.doi.org/10.1063/1.1941462 (3 pages)

Yongbing Tang, Hongtao Cong, Zhigang Chen, and Huiming Cheng
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Evidence of native oxides on the capping and substrate of Permalloy gratings by magneto-optical spectroscopy in the zeroth- and first-diffraction orders

Roman Antos, Jan Mistrik, Tomuo Yamaguchi, Stefan Visnovsky, Sergej O. Demokritov, and Burkard Hillebrands

Appl. Phys. Lett. 86, 231101 (2005); http://dx.doi.org/10.1063/1.1944904 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2005

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Magneto-optical Kerr effect (MOKE) spectroscopy in the zeroth- and first-diffraction orders at polar magnetization is applied to Permalloy wire gratings deposited on Si substrates and protected by Cr capping. The experimental MOKE data are compared with data simulated using the local modes method. The extensive simulations of the MOKE spectroscopic parameters exhibit significant sensitivity to t(Cr2O3) and t(SiO2), the thicknesses of native oxide layers developed on the capping and the substrate, respectively. The approach may be useful for monitoring the basic micromagnetic properties of small elements with nanometer-scale resolution, as well as for monitoring the deposition processes and aging of magnetic nanostructures in magnetic recording and magnetic random access memory technologies.
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81.05.Bx Metals, semimetals, and alloys
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
42.79.Dj Gratings

Efficient chemical oxygen-iodine laser powered by a centrifugal bubble singlet oxygen generator

V. D. Nikolaev, M. I. Svistun, M. V. Zagidullin, and G. D. Hager

Appl. Phys. Lett. 86, 231102 (2005); http://dx.doi.org/10.1063/1.1946911 (2 pages) | Cited 4 times

Online Publication Date: 1 June 2005

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Efficient production of singlet delta oxygen in a bubble singlet oxygen generator (BSOG) under the influence of centrifugal acceleration, 136 g, has been obtained. An output power of 770 W with chemical efficiency of 25.6% has been achieved in a small-scale, supersonic chemical oxygen-iodine laser supplied by the centrifugal BSOG. The ratio of the output power to the basic hydrogen peroxide volumetric flow rate was 4.3 KJ/liter. Efficient chemical oxygen-iodine laser (COIL) operation with the centrifugal BSOG demonstrates the potential for mobile COIL applications.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
82.40.-g Chemical kinetics and reactions: special regimes and techniques

Background-limited terahertz quantum-well photodetector

H. Luo, H. C. Liu, C. Y. Song, and Z. R. Wasilewski

Appl. Phys. Lett. 86, 231103 (2005); http://dx.doi.org/10.1063/1.1947377 (3 pages) | Cited 36 times

Online Publication Date: 3 June 2005

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We report terahertz quantum-well photodetectors with background-limited infrared performance (BLIP). The device dark current characteristics were improved by employing thick barriers to reduce interwell tunneling. BLIP operations were observed for all samples (three in total) designed for different wavelengths. BLIP temperatures of 17, 13, and 12 K were achieved for peak detection frequencies at 9.7 THz (31 μm), 5.4 THz (56 μm), and 3.2 THz (93 μm), respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
72.40.+w Photoconduction and photovoltaic effects

Dielectric heating effects of dual-frequency liquid crystals

Chien-Hui Wen and Shin-Tson Wu

Appl. Phys. Lett. 86, 231104 (2005); http://dx.doi.org/10.1063/1.1944889 (3 pages) | Cited 23 times

Online Publication Date: 3 June 2005

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A noncontact birefringence probing method is developed to monitor the temperature rise of dual-frequency liquid crystals (DFLCs) due to the dielectric heating effect. This method allows us to determine the temperature change accurately without using a thermocouple. The dielectric heating effects of three DFLC mixtures are investigated quantitatively. By properly choosing the molecular structures, the dielectric heating effect can be minimized while keeping other desirable physical properties uncompromised.
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61.30.-v Liquid crystals
78.20.Fm Birefringence

Difference frequency mixing of strongly focused Gaussian beams in periodically poled LiNbO3

Husam H. Abu-Safe

Appl. Phys. Lett. 86, 231105 (2005); http://dx.doi.org/10.1063/1.1947886 (3 pages) | Cited 13 times

Online Publication Date: 3 June 2005

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Difference frequency mixing of strongly focused Gaussian beams in periodically poled LiNbO3 was investigated. The beams were focused inside the crystal without damage. Mixing of cw and pulsed laser systems was employed to minimize the thermal lensing effects inside this crystal. A low-power cw 1.064‐μm Nd:YAG laser beam was used as the pump, whereas the signal beam came from a picosecond optical parametric oscillator. The two independently focused beams were made to overlap inside the crystal. The focusing parameters of the two beams were about the same. The focusing function developed by Boyd and Kleinman for tightly focused beams was extended to periodically poled crystals in order to fit the temperature-tuning curve. A 0.66%/W efficiency was obtained for the difference frequency mixing process.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Mp Nonlinear optical crystals
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Kerr and four-wave mixing spectroscopy at the band edge of one-dimensional photonic crystals

Luca Razzari, Denis Träger, Magali Astic, Philippe Delaye, Robert Frey, Gérald Roosen, and Régis André

Appl. Phys. Lett. 86, 231106 (2005); http://dx.doi.org/10.1063/1.1944887 (3 pages) | Cited 19 times

Online Publication Date: 3 June 2005

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Kerr and four-wave mixing spectroscopy is shown to be a powerful technique to quantify the strong enhancement of the third-order optical nonlinear susceptibilities at the band edge of photonic crystals. Local field factors of about 5 are demonstrated for crossed Kerr effect and a narrow resonance peak observed for the conjugate reflectivity. Moreover, a reduction of the effective nonlinear susceptibility of the four-wave mixing process with increasing pump intensities is measured, which is due to different Kerr-induced blueshifts of the band edge for forward and backward pump beams and signal and conjugate beams. This observation definitely demonstrates the need for considering all the nonlinear processes for the optimization of nonlinear photonic crystals for a given application in optical signal processing.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Qs Photonic bandgap materials

Evaluation of the effect of polymer coating on the lateral pressure tuning of fiber Bragg gratings

J. Paul, L. P. Zhao, B. K. A. Ngoi, and Z. P. Fang

Appl. Phys. Lett. 86, 231107 (2005); http://dx.doi.org/10.1063/1.1946187 (3 pages)

Online Publication Date: 3 June 2005

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We report the analysis of the expected effect of polymeric coating on the lateral pressure tuning of fiber Bragg gratings (FBGs). The dependence of the coating thickness and the stiffness of the polymer on the peak wavelength shift sensitivity and birefringence were evaluated using finite element analysis. A suitable polymeric coating with an optimum value of thickness could reduce the birefringence to an insignificant near-zero value and the peak shift sensitivity could be enhanced to almost ten times as high as that of bare FBGs.
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42.79.Wc Optical coatings
42.70.Jk Polymers and organics
42.81.Wg Other fiber-optical devices
42.81.Gs Birefringence, polarization
78.66.Qn Polymers; organic compounds
68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
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Dipole radio-frequency power from laser plasmas with no dipole moment

F. S. Felber

Appl. Phys. Lett. 86, 231501 (2005); http://dx.doi.org/10.1063/1.1947911 (3 pages) | Cited 4 times

Online Publication Date: 3 June 2005

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The radio-frequency power radiated from laser-target plasmas in a vacuum can be orders of magnitude greater than expected from such sources that have a negligible electric dipole moment. A model combining the Tidman–Stamper circuit model of a laser-target plasma with the theory of radiation from currents immersed in plasmas, however, predicts scaling of electric-dipole power radiated from laser plasmas in agreement with experiments.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Fi Transport properties
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides

Efficient soft x-ray emission source at 13.5 nm by use of a femtosecond-laser-produced Li-based microplasma

Takeshi Higashiguchi, Chirag Rajyaguru, Shoichi Kubodera, Wataru Sasaki, Noboru Yugami, Takashi Kikuchi, Shigeo Kawata, and Alex Andreev

Appl. Phys. Lett. 86, 231502 (2005); http://dx.doi.org/10.1063/1.1947890 (3 pages) | Cited 5 times

Online Publication Date: 3 June 2005

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A proof-of-principle experiment was demonstrated to optimize a Li-based microjet target coupled to dual subpicosecond laser pulses as a 13.5 nm soft x-ray emission source. An optimum pulse duration of 450 fs to achieve a maximum emission at 13.5 nm was well explained by the resonant absorption process. Utilization of dual femtosecond pulses revealed that the optimum pulse separation around 500 ps was necessary to achieve a maximum soft x-ray conversion efficiency of 0.2%, where plasma hydrodynamics could not be neglected. A one-fluid two-temperature hydrodynamic simulation reproduced this optimum pulse separation behavior.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Ph X-ray, γ-ray, and particle generation
52.65.Kj Magnetohydrodynamic and fluid equation
52.30.-q Plasma dynamics and flow
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Experimental imaging of silicon nanotubes

M. De Crescenzi, P. Castrucci, M. Scarselli, M. Diociaiuti, Prajakta S. Chaudhari, C. Balasubramanian, Tejashree M. Bhave, and S. V. Bhoraskar

Appl. Phys. Lett. 86, 231901 (2005); http://dx.doi.org/10.1063/1.1943497 (3 pages) | Cited 39 times

Online Publication Date: 31 May 2005

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Transmission electron microscopy (TEM), electron energy loss near edge structures (EELNES) and scanning tunneling microscopy (STM) were used to distinguish silicon nanotubes (SiNT) among the reaction products of a gas phase condensation synthesis. TEM images exhibit the tubular nature with a well-defined wall. The EELNES spectra performed on each single nanotube show that they are constituted by nonoxidized silicon atoms. STM images show that they have diameter ranging from 2 to 35 nm, have an atomic arrangement compatible with a puckered structure and different chiralities. Moreover, the I-V curves showed that SiNT can be semiconducting as well as metallic in character.
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81.07.De Nanotubes
81.05.Cy Elemental semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.47.Fg Semiconductor surfaces
61.46.-w Structure of nanoscale materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.49.Jk Electron scattering from surfaces
79.20.Uv Electron energy loss spectroscopy

Deconvoluting the influences of heat and plastic deformation on internal strains generated by friction stir processing

Wanchuck Woo, Hahn Choo, Donald W. Brown, Mark A. M. Bourke, Zhili Feng, Stan A. David, Camden R. Hubbard, and Peter K. Liaw

Appl. Phys. Lett. 86, 231902 (2005); http://dx.doi.org/10.1063/1.1944207 (3 pages) | Cited 8 times

Online Publication Date: 31 May 2005

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Internal-strain profiles in friction-stir processed aluminum-alloy plates were investigated using neutron diffraction. Three different specimens were prepared with a purpose of separating the effects of frictional heating and severe plastic deformation on the internal-strain distribution: (Case 1) a plate processed with both stirring pin and tool shoulder, (Case 2) a plate processed only with the tool shoulder, and (Case 3) a plate processed only with the pin. The comparison between Cases 1 and 2 shows distinctly different strain profiles revealing deconvoluted effects of the different sources (i.e., heat, deformation, or the combination) on the internal strains generated during the friction-stir processing.
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81.40.Lm Deformation, plasticity, and creep
81.40.Pq Friction, lubrication, and wear
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
81.20.Vj Joining; welding

Elastic behavior during early stage of β phase decomposition in a Cu–Al–Ni shape memory alloy

V. Recarte, J. I. Pérez-Landazábal, and V. Sánchez-Alarcos

Appl. Phys. Lett. 86, 231903 (2005); http://dx.doi.org/10.1063/1.1946918 (3 pages) | Cited 3 times

Online Publication Date: 31 May 2005

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The precipitation of γ1 phase modifies the characteristics of the martensitic transformation in Cu-based shape memory alloys. In the early stage of decomposition, the knowledge of elastic constants of γ1 phase is of special interest due to the elastic interaction between martensite interfaces and precipitates. In this letter, neutron powder diffraction, differential scanning calorimetry, and accurate resonant ultrasound spectroscopy allow us to determine two different stages at the beginning of the γ1 phase precipitation process in a texture-free Cu–Al–Ni shape memory alloy. The elastic constants and Debye temperature of the γ1 phase in Cu–Al–Ni have been determined.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
81.30.Mh Solid-phase precipitation
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Off-diagonal elastic constant and sp2-bonded graphitic grain boundary in nanocrystalline-diamond thin films

Hirotsugu Ogi, Nobutomo Nakamura, Hiroshi Tanei, Masahiko Hirao, Ryuji Ikeda, and Mikio Takemoto

Appl. Phys. Lett. 86, 231904 (2005); http://dx.doi.org/10.1063/1.1946920 (3 pages) | Cited 18 times

Online Publication Date: 31 May 2005

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This letter studies the relationship between the off-diagonal elastic constant C12 and bond configuration in nanocrystalline-diamond (NCD) thin films deposited by the nitrogen-doped chemical vapor deposition method. The film thickness was varied between 2.4 and 11.3 μm. The elastic constants were measured by resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry. The diagonal elastic constants C11 and C44, and Young’s modulus in NCD films are smaller than those of the bulk polycrystalline diamond and microcrystalline-diamond (MCD) thin films, and they decrease as the film thickness decreases. However, the off-diagonal elastic constant of the NCD films is significantly larger than that of the bulk diamond, while that of the MCD films is smaller. Micromechanics calculations revealed that this exceptional enhancement of C12 occurs when the material includes randomly distributed thin graphitic plates in the isotropic diamond matrix. Thus, this result indicates that the NCD films consist of sp3-bonded diamond grains and sp2-bonded grain boundaries.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.72.Mm Grain and twin boundaries
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Intensity modulation and polarization rotation of visible light by dielectric planar chiral metamaterials

W. Zhang, A. Potts, A. Papakostas, and D. M. Bagnall

Appl. Phys. Lett. 86, 231905 (2005); http://dx.doi.org/10.1063/1.1944211 (3 pages) | Cited 12 times

Online Publication Date: 31 May 2005

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We have demonstrated how dielectric planar chiral surfaces can both modulate the intensity and change the polarization state of visible light diffracted from patterned surfaces. These effects are shown to be dependent on the sense of chirality of the surface and the input polarization state of the light. Individual diffracted beams can show variations of over 30% in their intensities for different input polarization states while opposite enantiomeric structures can exhibit differences of over 50%. The size of these effects could make these surfaces particularly promising candidates for the development of solid-state polarization-state detectors.
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42.70.-a Optical materials
42.79.Hp Optical processors, correlators, and modulators
78.66.Nk Insulators
42.79.Wc Optical coatings

Electromigration effects on compound growth at interfaces

H. T. Orchard and A. L. Greer

Appl. Phys. Lett. 86, 231906 (2005); http://dx.doi.org/10.1063/1.1935772 (3 pages) | Cited 18 times

Online Publication Date: 1 June 2005

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Interfacial reactions are important in microelectronic devices and can be accelerated or decelerated by imposing a direct electric current normal to the interface. These effects are analyzed by including electromigration-driven interchange of atomic species in a conventional analysis of reaction layer thickening in a binary system controlled by interdiffusion in the layer and by an interfacial reaction barrier. New types of behavior are predicted. When the electromigration augments interdiffusion, layer growth can accelerate as the layer thickens, in contrast to the usual deceleration. When the electromigration opposes interdiffusion, there is a limiting layer thickness, inversely proportional to the applied current.
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66.30.Qa Electromigration
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
85.40.Ls Metallization, contacts, interconnects; device isolation

Investigation of pore initiation in metal foams by synchrotron-radiation tomography

L. Helfen, T. Baumbach, P. Pernot, P. Cloetens, H. Stanzick, K. Schladitz, and J. Banhart

Appl. Phys. Lett. 86, 231907 (2005); http://dx.doi.org/10.1063/1.1941453 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2005

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Synchrotron-radiation tomography was used to investigate early foaming stages of aluminium alloys. Monochromatic radiation, high spatial resolution down to the micrometer scale, partial beam coherence, and holographic reconstruction techniques permit the distinction between different foam constituents which are not visible by other volume imaging techniques. In combination with three-dimensional image analysis, the differences in the pore initiation processes in two different aluminium alloys are shown. We find that, in powder compacts made from prealloyed AA6061 alloy powder, pores appear predominantly around the blowing agent particles whereas, in compacts made from a powder blend of Al and Si, pores tend to initiate around Si particles.
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61.43.Gt Powders, porous materials
82.70.Rr Aerosols and foams

Colorless transparent fluorescence material: Sintered porous glass containing rare-earth and transition-metal ions

Danping Chen, Hiroshi Miyoshi, Tomoko Akai, and Tetsuo Yazawa

Appl. Phys. Lett. 86, 231908 (2005); http://dx.doi.org/10.1063/1.1946897 (3 pages) | Cited 19 times

Online Publication Date: 2 June 2005

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Transparent fluorescence oxide glass with high emission yields has been prepared. Porous glass was impregnated with rare-earth and transition-metal ions and consequently sintered at 1100 °C into a compact nonporous glass. Reduction sintering is indispensable for obtaining fluorescence glass with high emission yield. Sintering of glass impregnated with Eu ions in a reducing atmosphere enhances the emission intensity by about 15 times than that sintered in air. The Eu2+ and Ce3+ ions and Sn2+ and Cu+ ions incorporated in SiO2 glass obtained by reduction sintering exhibit intense fluorescence in the near-ultraviolet and visible ranges, their emission yields are 97%, 70%, 100%, and 90%, respectively.
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81.05.Kf Glasses (including metallic glasses)
81.05.Rm Porous materials; granular materials
78.55.Mb Porous materials
78.55.Qr Amorphous materials; glasses and other disordered solids

Observation of low-temperature specific-heat anomaly in CuZrAl bulk metallic glasses

Yong Li, Peng Yu, and Hai Yang Bai

Appl. Phys. Lett. 86, 231909 (2005); http://dx.doi.org/10.1063/1.1946898 (3 pages) | Cited 7 times

Online Publication Date: 2 June 2005

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Low-temperature specific heat and ultrasonic experiments on CuZrAl bulk metallic glass (BMG) are performed. The low-temperature specific-heat anomaly arising from the low-frequency vibrations responsible for the boson peak, which is correlated with the nature and physical properties of the glasses, is clearly observed in the BMG. The ratio of the excess specific heat to the Debye contribution around the maximum is 1.93 for the BMG.
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81.05.Kf Glasses (including metallic glasses)
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Footprints of deformation mechanisms during in situ x-ray diffraction: Nanocrystalline and ultrafine grained Ni

Z. Budrovic, S. Van Petegem, P. M. Derlet, B. Schmitt, H. Van Swygenhoven, E. Schafler, and M. Zehetbauer

Appl. Phys. Lett. 86, 231910 (2005); http://dx.doi.org/10.1063/1.1947385 (3 pages) | Cited 9 times

Online Publication Date: 3 June 2005

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In situ x-ray diffraction demonstrates that in ultrafine grained Ni synthesized by high pressure torsion with a coherent scattering domain size of 80 nm, a dislocation network is still built up during tensile deformation whereas this is not the case for electrodeposited nanocrystalline metals with a coherent scattering domain size of 30 nm. Simultaneously, the technique shows for the first time important differences in macroscopic stress accommodation during plastic deformation between the nanocrystalline and ultrafine grained Ni, such as the origin of the reduction in flow stress.
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81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.40.Lm Deformation, plasticity, and creep
81.40.Vw Pressure treatment
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.50.-p High-pressure effects in solids and liquids
61.46.-w Structure of nanoscale materials

Buffer-enhanced room-temperature growth and characterization of epitaxial ZnO thin films

Atsushi Sasaki, Wakana Hara, Akifumi Matsuda, Norihiro Tateda, Sei Otaka, Shusaku Akiba, Keisuke Saito, Tokuo Yodo, and Mamoru Yoshimoto

Appl. Phys. Lett. 86, 231911 (2005); http://dx.doi.org/10.1063/1.1947378 (3 pages) | Cited 25 times

Online Publication Date: 3 June 2005

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The room-temperature epitaxial growth of ZnO thin films on NiO buffered sapphire (0001) substrate was achieved by using the laser molecular-beam-epitaxy method. The obtained ZnO films had the ultrasmooth surface reflecting the nanostepped structure of the sapphire substrate. The crystal structure at the surface was investigated in situ by means of coaxial impact-collision ion scattering spectroscopy. It was proved that the buffer-enhanced epitaxial ZnO thin films grown at room temperature had +c polarity, while the polarity of high-temperature grown ZnO thin films on the sapphire was −c. Photoluminescence spectra at room temperature were measured for the epitaxial ZnO films, showing only the strong ultraviolet emission near 380 nm.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.62.-b Laser applications
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Strong polaronic effects on rutile TiO2 electronic band edges

Clas Persson and Antonio Ferreira da Silva

Appl. Phys. Lett. 86, 231912 (2005); http://dx.doi.org/10.1063/1.1940739 (3 pages) | Cited 15 times

Online Publication Date: 3 June 2005

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Thin TiO2 films are prepared by dc magnetron sputtering as well as by the sol-gel technique, and the optical band edge absorption α(ω) is obtained from transmission spectroscopy. The electronic structure and optical properties are studied employing a first-principle linearized augmented plane-wave method within the local density approximation (LDA), improved by an on-site Coulomb self-interaction potential (LDA+USIC). We show that the correction potential, the polaronic screening, and the spin-orbit interaction are crucial for determining the TiO2 effective electron and hole masses. The dielectric function ε(ω) = ε1(ω)+iε2(ω) and the high-frequency constantε(0⪡ω⪡Eg/ℏ) show pronounced anisotropy. The electron-optical phonon interaction affectsε(ω ≈ 0) strongly.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
71.38.-k Polarons and electron-phonon interactions
63.20.K- Phonon interactions
71.20.Ps Other inorganic compounds
78.66.Nk Insulators
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Observation of visible luminescence from indium nitride at room temperature

Q. X. Guo, T. Tanaka, M. Nishio, H. Ogawa, X. D. Pu, and W. Z. Shen

Appl. Phys. Lett. 86, 231913 (2005); http://dx.doi.org/10.1063/1.1947914 (3 pages) | Cited 28 times

Online Publication Date: 3 June 2005

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InN films were grown on sapphire substrates with AlN buffer layers by reactive sputtering. C-axis-oriented crystalline InN films with a wurtzite structure were confirmed by x-ray diffraction and Raman scattering. Strong photoluminescence (PL) at 1.87 eV, together with a clear absorption edge at 1.97 eV, was observed at room temperature, which clearly demonstrates that it is not accurate in the previous assignment of an ∼ 0.7 eV fundamental band gap for intrinsic InN simply from PL and absorption data. The possible origin of the present large band gap was discussed in terms of the effects of oxygen and the Burstein-Moss shift.
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78.55.Cr III-V semiconductors
78.40.Fy Semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
71.20.Nr Semiconductor compounds

Surface adsorption effects on the lattice expansion of copper nanocrystals

Yannick Champion, Frédéric Bernard, Nadine Millot, and Pascal Perriat

Appl. Phys. Lett. 86, 231914 (2005); http://dx.doi.org/10.1063/1.1947887 (3 pages) | Cited 7 times

Online Publication Date: 3 June 2005

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Lattice expansion in nanocrystalline copper due to size and surface effect is reported. The lattice parameter is measured by in situ x-ray diffraction at various temperatures from −173 °C to 150 °C. The experiments are carried out on nanocrystalline copper powders having an average particle size of 40 nm. The size effect on the lattice expansion is examined regarding a modified Laplace law, where a surface stress is considered instead of the usual scalar surface energy. The results are discussed taking into account oxidation state and the sorption of molecular species at the nanoparticles surface.
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81.07.Bc Nanocrystalline materials
81.07.Wx Nanopowders
81.05.Bx Metals, semimetals, and alloys
68.43.Mn Adsorption kinetics
61.46.-w Structure of nanoscale materials
81.65.Mq Oxidation
61.66.Bi Elemental solids
61.43.Gt Powders, porous materials

On observation of freeze-dried smectite plane views of nanolayers

S. Laribi, B. Jouffrey, and J.-M. Fleureau

Appl. Phys. Lett. 86, 231915 (2005); http://dx.doi.org/10.1063/1.1946917 (2 pages) | Cited 2 times

Online Publication Date: 3 June 2005

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Observations were carried out on a purified and deshydrated smectite using scanning and transmission electron microscopy. They show extremely thin layers in the planar orientation (thickness of the order of a few nanometers). An important part of them is also bent with variable radii of curvature, often of the order of a few hundreds of nanometers. Some of the samples are complicated in shape, and present a succession of folds. Samples mainly grow as layers and not as a pile-up of layers. Electron energy loss spectroscopy shows that the Si/Al local ratio is of the order of 2 as expected.
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91.60.-x Physical properties of rocks and minerals
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Better bottom contact properties in organic field-effect transistors with ultrathin layers

T. Muck, J. Fritz, and V. Wagner

Appl. Phys. Lett. 86, 232101 (2005); http://dx.doi.org/10.1063/1.1944224 (3 pages) | Cited 24 times

Online Publication Date: 31 May 2005

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Organic field-effect transistors (OFETs) are very promising to realize cheap electronics for mass production. Structuring the electrodes of OFETs directly onto organic semiconductors is often prohibited, while substrates with prepatterned electrodes disturb organic film growths at the electrodes resulting in low contact quality. We report on the observation that thiophene-based ultrathin organic layers, in the monolayer range, exhibit smoother and more uniform growth characteristics close to gold contacts when compared to thicker organic layers. As a result, these ultrathin layers in bottom contact configuration exhibit superior electrical contact properties.
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85.30.Tv Field effect devices
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