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21 Jan 2002

Volume 80, Issue 3, pp. 341-531

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Blue light-emitting devices from new conjugated poly(N-substituted-2,7-carbazole) derivatives

Jean-François Morin, Serge Beaupré, Mario Leclerc, Isabelle Lévesque, and Marie D’Iorio

Appl. Phys. Lett. 80, 341 (2002); http://dx.doi.org/10.1063/1.1433917 (3 pages) | Cited 44 times

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Light-emitting diodes derived from a new class of conjugated polymers, well-defined poly(N-substituted-2,7-carbazole) derivatives, are reported. Excimer-free electroluminescence in the blue range (424–432 nm) was observed. Good luminance (372 cd/m2 at 10 V) was reached in a device containing poly[N-(2-ethylhexyl)-2,7-carbazole] as the emitting material with indium tin oxide and Al as the electrodes. This high luminance value was achieved by adding ultrathin LiF layers next to the electrodes, and by using hole and electron transport molecules such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

Growth-temperature dependence of Er-doped GaN luminescent thin films

D. S. Lee, J. Heikenfeld, and A. J. Steckl

Appl. Phys. Lett. 80, 344 (2002); http://dx.doi.org/10.1063/1.1434312 (3 pages) | Cited 6 times

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Visible photoluminescence (PL) and electroluminescence (EL) emission has been observed from Er-doped GaN thin films grown on (111) Si at various temperatures from 100 to 750 °C in a radio-frequency plasma molecular beam epitaxy system. PL and EL intensities of green emission at 537 nm from GaN:Er films exhibited strong dependence on the growth temperature, with a maximum at 600 °C. Scanning electron and atomic force microscopy showed smooth surfaces at 600 °C and rough surfaces at 100 and 750 °C. X-ray diffraction indicated that the GaN:Er film structure was oriented with the c axis perpendicular to the substrate for all growth temperatures. The crystalline quality initially improves with an increase in growth temperature, and saturates at ∼500 °C. Considering both the luminescence and structural properties of the film, ∼600 °C seems to be the optimal temperature for growth of Er-doped GaN luminescent films on Si substrates. © 2002 American Institute of Physics.
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78.60.Fi Electroluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors

Anisotropy in detectivity of GaN Schottky ultraviolet detectors: Comparing lateral and vertical geometry

O. Katz, V. Garber, B. Meyler, G. Bahir, and J. Salzman

Appl. Phys. Lett. 80, 347 (2002); http://dx.doi.org/10.1063/1.1433910 (3 pages) | Cited 26 times

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Vertical and lateral geometry GaN-based Schottky barrier photodetectors have been implemented, using similar quality material and the same fabrication process. The vertical detector exhibits two orders of magnitude higher responsivity. This is attributed to improved ohmic backcontacts, due to the highly doped buried layer. The vertical detectors exhibits also lower 1/f noise level, which is attributed to the reduced effect of dislocations on the carrier transport, resulting in lower mobility fluctuations. The vertical detector normalized detectivity is four orders of magnitude higher. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

High differential efficiency (>16%) quantum dot microcavity light emitting diode

H. Chen, Z. Zou, C. Cao, and D. G. Deppe

Appl. Phys. Lett. 80, 350 (2002); http://dx.doi.org/10.1063/1.1434310 (3 pages) | Cited 11 times

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Data are presented on high differential efficiency quantum dot microcavity light emitting diodes. The data show that differential efficiencies >16% can be achieved by the use of quantum dots to reduce carrier diffusion in small oxide-apertured microcavities. The measured efficiencies are sensitive to both microcavity tuning of the resonance peak to the quantum dot light emitters, and nonradiative recombination effects brought on by temperature, bias current, and edge effects. The peak efficiencies are obtained at a resonance temperature of ∼ 160 K. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.Hc Quantum dots
85.30.De Semiconductor-device characterization, design, and modeling

Laser ablation of dielectrics with temporally shaped femtosecond pulses

R. Stoian, M. Boyle, A. Thoss, A. Rosenfeld, G. Korn, I. V. Hertel, and E. E. B. Campbell

Appl. Phys. Lett. 80, 353 (2002); http://dx.doi.org/10.1063/1.1432747 (3 pages) | Cited 51 times

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A significant improvement in the quality of ultrafast laser microstructuring of dielectrics is demonstrated by using temporally shaped pulse trains with subpicosecond separation. The sequential energy delivery induces a material softening during the initial steps of excitation changing the energy coupling for the subsequent steps. This leads to lower stress, cleaner structures, and provides a material-dependent optimization process. © 2002 American Institute of Physics.
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52.38.Mf Laser ablation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
79.20.Ds Laser-beam impact phenomena

Two-photon-excited green emission and its dichroic shift of oriented thin-film CdS on glass formed by laser deposition

B. Ullrich, R. Schroeder, H. Sakai, A. Zhang, and S. Z. D. Cheng

Appl. Phys. Lett. 80, 356 (2002); http://dx.doi.org/10.1063/1.1432756 (3 pages) | Cited 4 times

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The photoluminescence of oriented thin-film CdS on glass formed by laser deposition was investigated employing 200 fs, 1.54 eV laser pulses at room temperature. The ultrafast excitation caused a two-photon absorption process, which results in purely green emission at the band gap. The spectra are fitted very well by the application of the van Roosbroeck–Shockley relation, density of states, and Urbach’s rule demonstrating the intrinsic character of the radiative recombination. It is further shown that the energy position of the emission peak depends on the polarization of the impinging laser beam due to the dichroism of the highly oriented films. © 2002 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.20.Fm Birefringence

Photoinduced permanent gratings inside bulk azodye-doped polymers by the coherent field of a femtosecond laser

Jinhai Si, Jianrong Qiu, Jianfeng Zhai, Yuquan Shen, and Kazuyuki Hirao

Appl. Phys. Lett. 80, 359 (2002); http://dx.doi.org/10.1063/1.1435808 (3 pages) | Cited 35 times

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Permanent holographic gratings were fabricated in bulk azodye-doped polymethylmethacrylate by the coherent field of a femtosecond laser. Optical microscopy and atomic force microscopy observations revealed that the gratings consist of two parts, surface relief gratings on both surfaces and refractive index modulated volume gratings in the interior of the polymers. The diffraction efficiency of the first-order Bragg for the gratings was estimated to be 90%. © 2002 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics

Organic bistable light-emitting devices

Liping Ma, Jie Liu, Seungmoon Pyo, and Yang Yang

Appl. Phys. Lett. 80, 362 (2002); http://dx.doi.org/10.1063/1.1436274 (3 pages) | Cited 64 times

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An organic bistable device, with a unique trilayer structure consisting of organic/metal/organic sandwiched between two outmost metal electrodes, has been invented. [Y. Yang, L. P. Ma, and J. Liu, U.S. Patent Pending, U.S. 01/17206 (2001)]. When the device is biased with voltages beyond a critical value (for example 3 V), the device suddenly switches from a high-impedance state to a low-impedance state, with a difference in injection current of more than 6 orders of magnitude. When the device is switched to the low-impedance state, it remains in that state even when the power is off. (This is called “nonvolatile” phenomenon in memory devices.) The high-impedance state can be recovered by applying a reverse bias; therefore, this bistable device is ideal for memory applications. In order to increase the data read-out rate of this type of memory device, a regular polymer light-emitting diode has been integrated with the organic bistable device, such that it can be read out optically. These features make the organic bistable light-emitting device a promising candidate for several applications, such as digital memories, opto-electronic books, and recordable papers. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Vb Optical storage systems, optical disks
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Wall sheath and optimal bias in magnetic filters for vacuum arc plasma sources

T. Zhang, Y. C. Zhang, P. K. Chu, and I. G. Brown

Appl. Phys. Lett. 80, 365 (2002); http://dx.doi.org/10.1063/1.1431690 (3 pages) | Cited 13 times

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A plasma diffusion model is established to determine the optimal bias and sheath patterns in a positively biased magnetic filter of a metal arc plasma source. We determine the equation for the optimal bias on the magnetic filter. According to our model, the optimal bias is related to the electron speed, ion speed, ion mass, ion charge state, and plasma density in the filter. The optimal bias increases as these variables are increased with the exception of the electron speed. Even though the magnetic field is taken into account, it is not a variable in the final equation. Our experimental results confirm that the magnetic field has almost no influence on the optimal bias. An alternate design approach is suggested that should lead to enhanced plasma transport through the filter. © 2002 American Institute of Physics.
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52.50.Dg Plasma sources
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.40.Kh Plasma sheaths

Characterization of a high-density plasma produced by electrothermal capillary discharge

J. U. Kim and H. Suk

Appl. Phys. Lett. 80, 368 (2002); http://dx.doi.org/10.1063/1.1435807 (3 pages) | Cited 9 times

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The characteristics of a pulsed plasma jet originating from an electrothermal capillary discharge are reported from optical emission spectroscopy as well as from laser-induced fluorescence (LIF) measurement. The results show that the plasma temperature and electron density jump across the Mach disk. Their values are approximately 25 000 and 14 000 K downstream and upstream of the Mach disk, and the corresponding electron densities are about 1018 and 1017 cm−3, respectively. By applying the LIF imaging method in the highly luminous underexpanded region of the plasma jet, a spatially well-resolved flow field was achieved. © 2002 American Institute of Physics.
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52.30.-q Plasma dynamics and flow
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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Why does an external electrical field stimulate formation of new phase nuclei in dielectrics?

V. S. Vorob’ev and S. P. Malyshenko

Appl. Phys. Lett. 80, 371 (2002); http://dx.doi.org/10.1063/1.1433907 (3 pages) | Cited 6 times

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Contrary to many previous theoretical considerations, we show that both uniform and nonuniform electrical fields facilitates formation of vapor bubbles in superheated liquid and liquid drop in supersaturated gas. In the latter case, the field must exceed some threshold value, which becomes smaller in nonuniform field. Such conclusions are based on adequate expression for nucleus work formation in the presence of electrical field which we use in our consideration and are in agreement with experimental observations. © 2002 American Institute of Physics.
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64.60.Q- Nucleation
82.60.Nh Thermodynamics of nucleation
64.70.F- Liquid-vapor transitions
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
65.20.-w Thermal properties of liquids
77.22.Ej Polarization and depolarization

Simple model for patterned bidirectional anchoring of nematic liquid crystal and its bistability

Makoto Yoneya, Jong-Hyun Kim, and Hiroshi Yokoyama

Appl. Phys. Lett. 80, 374 (2002); http://dx.doi.org/10.1063/1.1435070 (3 pages) | Cited 10 times

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An effective anchoring model for the patterned surface with bidirectional rubbing by atomic force microscope was proposed. The model was a simple additive function of two bidirectional anchoring contributions of the patterned surface, with consideration of higher-order terms of the anchoring function. The bistable switching behavior of the nematic liquid crystal cells with the patterned surface was investigated analytically and numerically using this anchoring model. © 2002 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Dk Continuum models and theories of liquid crystal structure
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions

Local stresses induced by nanoscale As–Sb clusters in GaAs matrix

V. V. Chaldyshev, N. A. Bert, A. E. Romanov, A. A. Suvorova, A. L. Kolesnikova, V. V. Preobrazhenskii, M. A. Putyato, B. R. Semyagin, P. Werner, N. D. Zakharov, and A. Claverie

Appl. Phys. Lett. 80, 377 (2002); http://dx.doi.org/10.1063/1.1426691 (3 pages) | Cited 12 times

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Microstructure of GaAs films grown by molecular-beam epitaxy at low temperature and delta doped with Sb was studied by transmission electron microscopy. The material contained 0.5 at. % excess of arsenic that precipitated during post growth anneals. The Sb δ doping was found to strongly affect the microstructure of precipitates (clusters) and their ripening rate upon annealing. Segregation of Sb impurity in the clusters was revealed. In contrast to the well known pure As clusters, the As–Sb clusters induced strong local deformations in the surrounding GaAs matrix. Until a threshold diameter of 7–8 nm the clusters and surrounding matrix were coherently strained. Larger clusters were associated with dislocation loops of interstitial type. The cluster-loop orientation relationships were determined. Relaxation of local strains by formation of the dislocation loops was studied both experimentally and theoretically. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.46.-w Structure of nanoscale materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties

Color mapping by scanning tunneling microscopy: Chemical analysis of metal surfaces

Andrew Downes, Philippe Guaino, and Philippe Dumas

Appl. Phys. Lett. 80, 380 (2002); http://dx.doi.org/10.1063/1.1433918 (3 pages) | Cited 8 times

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We present true color maps of a metal surface imaged by scanning tunneling microscopy (STM). Light emission spectra were acquired at each imaging pixel, and converted into a real color map. A rough gold film was shown to exhibit minimal color changes across the sample, so spectra are dependent on material and not sample geometry, due to a small radius tip. A larger tip was still able to distinguish between Ag and Cu clusters with ∼10 nm resolution, despite the onset of geometric effects. We conclude that color mapping represents an ideal way of identifying metals in STM on the nanometer scale. © 2002 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
82.80.-d Chemical analysis and related physical methods of analysis
07.79.Cz Scanning tunneling microscopes
61.46.-w Structure of nanoscale materials

Indentation-induced damage in GaN epilayers

J. E. Bradby, S. O. Kucheyev, J. S. Williams, J. Wong-Leung, M. V. Swain, P. Munroe, G. Li, and M. R. Phillips

Appl. Phys. Lett. 80, 383 (2002); http://dx.doi.org/10.1063/1.1436280 (3 pages) | Cited 41 times

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The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable “footprint” of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the samples studied for loads of up to 250 mN. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.F- Deformation and plasticity
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Lm Deformation, plasticity, and creep

Effect of Si lattice strain on the reliability characteristics of ultrathin SiO2 on a 4° tilted wafer

Hyo Sik Chang, Sangmu Choi, Hyundoek Yang, Kyung-youl Min, Dae Won Moon, Hyung-Ik Lee, and Hyunsang Hwang

Appl. Phys. Lett. 80, 386 (2002); http://dx.doi.org/10.1063/1.1435404 (3 pages) | Cited 8 times

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The electrical and structural characteristics of an ultrathin gate dielectric, thermally grown on 4° tilted wafer has been investigated. Compared with a control wafer, a relaxation of the Si lattice strain at the SiO2/Si(001) interface was observed for the 4° tilted wafer, which was confirmed by medium energy ion scattering spectroscopy. A significant improvement in the reliability characteristics of a metal–oxide–semiconductor (MOS) capacitor, with a 2.5-nm-thick gate oxide, grown on a tilt wafer was observed. This improvement in reliability can be explained by the relaxation of strain at the SiO2/Si interface. An ultrathin gate dielectric grown on a tilt wafer represents a promising alternative for gate dielectric applications in future MOS devices. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.35.Ct Interface structure and roughness
73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
84.32.Tt Capacitors
85.30.Tv Field effect devices

Polarity determination by atomic location by channeling-enhanced microanalysis

N. Jiang, T. J. Eustis, J. Cai, F. A. Ponce, J. C. H. Spence, and J. Silcox

Appl. Phys. Lett. 80, 389 (2002); http://dx.doi.org/10.1063/1.1433919 (3 pages) | Cited 8 times

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In this letter, an alternative approach to determine the polarity of GaN thin films based on the atomic location by channeling-enhanced microanalysis technique is described. Theoretical calculations provide a straightforward criterion for polarity determination that is a major advantage of this method. At the Bragg position, the thickness-averaged incident electron intensity, and hence, electron induced characteristic x-ray yield, is higher on the N plane than on the Ga if the g vector of the diffraction beam is parallel to the Ga–N bond direction, and vice versa. Experimental results support the theoretical predictions. The possible errors in the experiments are also discussed. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Effect of annealing of polythiophene derivative for polymer light-emitting diodes

Taekyung Ahn, Haiwon Lee, and Sien-Ho Han

Appl. Phys. Lett. 80, 392 (2002); http://dx.doi.org/10.1063/1.1429292 (3 pages) | Cited 20 times

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The nature of the interface between the light-emitting layer and the metal electrode is of importance in determining device performance. The heat treatment of the electroluminescence device can enhance the adhesion of the polymer on the electrode by reducing free volume or pores in the interface. The current–voltage–luminance characteristic of the device with heat treatment at various temperatures was investigated. The annealed device above glass transition temperature (Tg) showed the most efficient characteristics. The current density was increased about 20 times over that of the unannealed device. The light intensity was also increased dramatically by 40 times. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
81.40.Tv Optical and dielectric properties related to treatment conditions
68.35.Np Adhesion
78.55.Kz Solid organic materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Elastic properties of hexagonal columnar mesophase self-organized from amphiphilic supramolecular columns

Hee-Tae Jung, Sang Ouk Kim, S. D. Hudson, and V. Percec

Appl. Phys. Lett. 80, 395 (2002); http://dx.doi.org/10.1063/1.1432449 (3 pages) | Cited 12 times

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By direct imaging, we evaluate the relative stiffness of a hexagonal columnar mesophase induced by the self-organization of amphiphilic columnar supramolecules, both quantitatively and qualitatively, based on examination of the planar texture, and of defects contained therein. Quantitative measurement was performed by an analysis of distortions around edge dislocations. The elastic anisotropy varies significantly with the degree of molecular association. The columnar supramolecule containing rigid tapered molecules is stiffer than weakly associated self-assembled macromolecules by an order, resulting in different stability of the mesophase. In addition, defect characteristics are examined to further understand these supramolecular assemblies and their elastic properties. Highly resolved +1/2 disclinations have been observed in the flexible columnar supramolecules. © 2002 American Institute of Physics.
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61.30.Jf Defects in liquid crystals
62.10.+s Mechanical properties of liquids

Bonding nature of rare-earth-containing lead-free solders

Ainissa G. Ramirez, Hareesh Mavoori, and Sungho Jin

Appl. Phys. Lett. 80, 398 (2002); http://dx.doi.org/10.1063/1.1435075 (3 pages) | Cited 28 times

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The ability of rare-earth-containing lead-free solders to wet and bond to silica was investigated. Small additions of Lu (0.5–2 wt. %) added to eutectic Sn–Ag or Au–Sn solder render it directly solderable to a silicon oxide surface. The bonding is attributed to the migration of the rare-earth element to the solder–silica interface for chemical reaction and the creation of an interfacial layer that contains a rare-earth oxide. It was found that additions of rare-earth materials did not significantly modify the solidification microstructure or the melting point. Such oxide-bondable solders can be useful for assembly of various optical communication devices. © 2002 American Institute of Physics.
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42.81.Bm Fabrication, cladding, and splicing
81.20.Vj Joining; welding
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
64.70.D- Solid-liquid transitions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Large second harmonic response in ZnO thin films

Gang Wang, G. T. Kiehne, G. K. L. Wong, J. B. Ketterson, X. Liu, and R. P. H. Chang

Appl. Phys. Lett. 80, 401 (2002); http://dx.doi.org/10.1063/1.1435065 (3 pages) | Cited 37 times

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The second-order susceptibilities in the ZnO films have been studied systemically. In very thin films, we observe an enhancement of second-order susceptibilities, which is larger than that of single-crystal ZnO. It was also observed that the second-order susceptibilities for ZnO films depend on the thickness but not on the film growth technique used (reactive sputtering or plasma-enhanced chemical vapor deposition). We suggest a mechanism to explain the reduction in the second-order susceptibilities of the thicker films. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Hf II-VI semiconductors

Fluorescence imaging of surface plasmon fields

H. Ditlbacher, J. R. Krenn, N. Felidj, B. Lamprecht, G. Schider, M. Salerno, A. Leitner, and F. R. Aussenegg

Appl. Phys. Lett. 80, 404 (2002); http://dx.doi.org/10.1063/1.1435410 (3 pages) | Cited 88 times

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We demonstrate that surface plasmon fields can be imaged in real time by detecting the fluorescence of a molecular film close to the plasmon carrying metal surface. We use this method to image the field profile of surface plasmons launched at lithographically designed nanoscopic defects. © 2002 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.55.Hx Other solid inorganic materials

Nanostructure of sol–gel films by x-ray specular reflectivity

S. L. Morelhão, G. E. S. Brito, and E. Abramof

Appl. Phys. Lett. 80, 407 (2002); http://dx.doi.org/10.1063/1.1436271 (3 pages) | Cited 3 times

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Recently, several studies have been carried out on sol–gel films for optical applications, mostly motivated by the quickness and low cost of the film preparation process. In order to preserve the coherence properties of the light, improvements in the current quality of such films are necessary as well as appropriated techniques for structural characterization and quality control. X-ray specular reflectivity could be one of such techniques, but it is limited by the complexity of the internal nanostructure of the films. In this work, we have developed a procedure to extract the exact density profile of sol–gel films, and applied it to analyze a sol–gel derived Er2O3 film. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
61.05.cm X-ray reflectometry (surfaces, interfaces, films)
81.07.Bc Nanocrystalline materials
68.60.Wm Other nonelectronic physical properties

The level position of a deep intrinsic defect in 4H-SiC studied by photoinduced electron paramagnetic resonance

M. E. Zvanut and V. V. Konovalov

Appl. Phys. Lett. 80, 410 (2002); http://dx.doi.org/10.1063/1.1432444 (3 pages) | Cited 25 times

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Photoinduced electron paramagnetic resonance studies performed on nominally semi-insulating, high purity 4H-SiC have revealed charge transfer from an intrinsic defect (ID) to both the shallow boron acceptor and nitrogen donor. At 4 K, incident photon energy between 1.0 and 1.7 eV produces an increase in paramagnetic boron of approximately the same magnitude as the decrease in the paramagnetic defect concentration. For T<80 K, both spectra remain unchanged after removing the light. Illumination with energy greater than 1.8 eV at 4 K increases the nitrogen, boron, and ID spectra simultaneously, but after blocking the light all three signals return to the pre-illumination level. A model based on excitation to and from the bandedges places the defect level 1.1±0.2 eV above the valence bandedge. © 2002 American Institute of Physics.
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71.55.Ht Other nonmetals
76.30.Mi Color centers and other defects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Polarization-dependent spectroscopic study of M-plane GaN on γ-LiAlO2

Sandip Ghosh, P. Waltereit, O. Brandt, H. T. Grahn, and K. H. Ploog

Appl. Phys. Lett. 80, 413 (2002); http://dx.doi.org/10.1063/1.1434306 (3 pages) | Cited 26 times

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We investigate the polarization dependence of the absorption, reflectance, and photoreflectance spectra of a compressively strained, M-plane, wurtzite GaN(1math00) film grown by molecular-beam epitaxy on a γ-LiAlO2(100) substrate. The measurements are done with the electric-field vector (E) of the probe light being parallel (∥) and perpendicular (⊥) to the c axis of GaN, which lies in the growth plane. We observe a significant increase in the effective optical band gap of the M-plane GaN film for E∥c compared to its value for E⊥c. This result is explained by including the effect of the M-plane biaxial compressive strain on the electronic band structure of GaN. We also determine the extraordinary refractive index of GaN at energies below its band gap from the reflectance measurements. © 2002 American Institute of Physics.
Show PACS
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
78.20.-e Optical properties of bulk materials and thin films
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