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15 Jun 2008

Volume 103, Issue 12, Articles (12xxxx)

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Pump-wavelength dependence of terahertz radiation via optical rectification in (110)-oriented ZnTe crystal

Dong Li and Guohong Ma

J. Appl. Phys. 103, 123101 (2008); http://dx.doi.org/10.1063/1.2938847 (4 pages)

Online Publication Date: 16 June 2008

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The optical pump-wavelength-dependent generation and detection of terahertz wave in (110)-oriented ZnTe crystal were demonstrated. By using femtosecond laser pulses, terahertz radiation was generated. Both simulations and experimental results show that the terahertz wave in the frequency range of about 4–1 THz can be obtained by tuning the pumping wavelength from 700 to 900 nm. The theoretical analysis shows that the matching between the optical group velocity and terahertz phase velocity plays an important role for terahertz frequency tuning. The present studies also demonstrate that both the terahertz generation and detection are applicable in a single nonlinear optical crystal.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Mp Nonlinear optical crystals
78.47.J- Ultrafast spectroscopy (<1 psec)

The effect of disorder on two-dimensional photonic crystal waveguides

Leonardo L. Lima, Márcio A. R. C. Alencar, Dilson P. Caetano, Daniel R. Solli, and Jandir M. Hickmann

J. Appl. Phys. 103, 123102 (2008); http://dx.doi.org/10.1063/1.2939240 (4 pages) | Cited 4 times

Online Publication Date: 16 June 2008

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We investigate the effect of positional disorder on two-dimensional photonic crystal waveguides created by removing a line of cells from a finite 11×11 square lattice. By using transverse magnetic and transverse electric waves, we have studied three different configurations: disorder throughout the whole crystal, disorder only in the waveguide border, and disorder in the whole crystal except the waveguide border. We found that the waveguide performance is quite robust against disorder in the case where the waveguide border is not affected by disorder. In the other cases, disorder changes the size of the waveguide channel, which has a detrimental effect on the performance of the waveguide.
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42.79.Gn Optical waveguides and couplers

White light emission on amplified spontaneous emission with dye content controlled polymer system

Dingke Zhang, Zhenyu Chen, and Dongge Ma

J. Appl. Phys. 103, 123103 (2008); http://dx.doi.org/10.1063/1.2939582 (4 pages) | Cited 2 times

Online Publication Date: 17 June 2008

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White light emission from amplified spontaneous emission (ASE) was realized by optically pumping fluorescent dye 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl−9-enyl)-4H-pyran (DCJTB) doped semiconducting poly(9,9-dioctylfluorene) (PFO) polymer thin films. Two individual ASE peaks originating from DCJTB and PFO were observed by carefully controlling the DCJTB concentration in PFO. The studies of the ASE characteristics of DCJTB:PFO thin films lead to the conclusion that the DCJTB:PFO system with 0.3% w/w DCJTB dopant concentration in PFO showed the best ASE performance. In the DCJTB:PFO system with 0.3% w/w DCJTB dopant concentration, the net gains, loss coefficients, and threshold reached 36.3 and 22.35 cm−1, 7.39 and 15.88 cm−1, and 0.072 and 0.035 mJ pulse−1, for DCJTB emission and PFO emission, respectively. Our results predict an approach to achieve white light emission through amplified spontaneous emission in host polymer systems via controlled dye content.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Spectrally narrow emissions at cutoff wavelength from edges of optically and electrically pumped anisotropic organic films

Daisuke Yokoyama, Masato Moriwake, and Chihaya Adachi

J. Appl. Phys. 103, 123104 (2008); http://dx.doi.org/10.1063/1.2942401 (13 pages) | Cited 15 times

Online Publication Date: 18 June 2008

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The authors investigated the characteristics of spectrally narrow emissions at the cutoff wavelength from the edges of optically and electrically pumped organic semiconductor films. They estimated the optical properties of 4,4′-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) films using variable angle spectroscopic ellipsometry, revealing that the BSB-Cz films have uniaxial anisotropy and that BSB-Cz molecules lie nearly parallel to substrate surfaces. The authors discuss here the spectral changes in the edge emissions from neat BSB-Cz and tris(8-hydroxyquinoline)aluminum (Alq3) films of 15 different thicknesses under continuous-wave (cw) optical excitation. The spectrally narrow emissions of transverse electric (TE) and transverse magnetic (TM) modes were observed. The authors showed that the peak wavelengths of these emissions varied according to the cutoff wavelengths of asymmetric slab waveguides and that their spectral widths changed depending on the angular dispersion of the Fabry–Pérot interferometer composed of the organic film and its interfaces. The edge emissions from the BSB-Cz films had narrower bands than those from the Alq3 films and increased with a superlinear dependence on the stripe length of the excitation area, indicating the occurrence of light amplification under cw optical excitation. Finally, the authors demonstrate spectrally narrow emissions from the edges of electrically pumped organic light-emitting diodes (OLEDs) having a fine line-shaped waveguide structure with a silver metal cladding layer. Narrow emissions of TE mode were observed, and the peak wavelengths of the emission spectra corresponded well to the cutoff wavelength of the waveguide with the silver cladding layer. In addition to the narrow emissions, the authors observed some intriguing phenomena suggestive of the occurrence of light amplification in OLEDs under electrical pumping.
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85.60.Jb Light-emitting devices

Optical cavity modes in gold shell colloids

J. J. Penninkhof, L. A. Sweatlock, A. Moroz, H. A. Atwater, A. van Blaaderen, and A. Polman

J. Appl. Phys. 103, 123105 (2008); http://dx.doi.org/10.1063/1.2939249 (7 pages) | Cited 10 times

Online Publication Date: 18 June 2008

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Core-shell colloids composed of a dielectric core surrounded by a metal shell show geometric cavity resonances with optical properties that are distinctly different than those of the collective plasmon modes of the metal shell. We use finite-difference time domain calculations on silica colloids with a core diameter of 456 nm, surrounded by a 38 nm thick Au shell, to study the temporal evolution of the mode field intensity inside the cavity upon pulsed excitation. Calculations using Mie theory and the T-matrix method are used to analytically determine the dipolar cavity resonance spectrum, which is found superimposed on the broad collective dipolar plasmonic resonance modes. We characterize resonance wavelength and linewidth in terms of a geometric mode confined inside the cavity. Cavity linewidth can be controlled by metal shell thickness and quality factors Q>150 are observed. Due to the small cavity mode volume V = 0.2(λ/n)3, a Purcell factor as high as P = 54 is calculated. Introducing shape anisotropy lifts the cavity mode degeneracy, yielding blue- and redshifted longitudinal and transverse resonant modes, respectively. The relatively large volume over which the field enhancement is observed in these spherical and anisotropic metal shell cavities, combined with cavity quality factors that are much higher than that of the collective plasmonic modes, makes them attractive for application in nanoscale light sources, sensors, or lasers.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.70.Dd Colloids

Arsenic doped zinc oxide

N. Volbers, S. Lautenschläger, T. Leichtweiss, A. Laufer, S. Graubner, B. K. Meyer, K. Potzger, and Shengqiang Zhou

J. Appl. Phys. 103, 123106 (2008); http://dx.doi.org/10.1063/1.2917403 (6 pages) | Cited 4 times

Online Publication Date: 19 June 2008

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As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering∕channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.U- Doping and impurity implantation
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.ag Semiconductors
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

SiO2 nanoparticles as scatterers for random organic laser action in red fluorescent dye 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran doped polystyrene films

Dingke Zhang, Yanping Wang, and Dongge Ma

J. Appl. Phys. 103, 123107 (2008); http://dx.doi.org/10.1063/1.2940730 (4 pages) | Cited 1 time

Online Publication Date: 19 June 2008

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Random multimode lasers are achieved in 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped polystyrene thin films by introducing silicon dioxide (SiO2) nanoparticles as scatterers. The devices emit a resonance multimode peak at a center wavelength of 640 nm with a mode linewidth less than 0.87 nm. The threshold excitation intensity is as low as 0.25 mJ pulse−1 cm−2. It can be seen that the microscopic random resonance cavities can be formed by multiple scattering of SiO2 nanoparticles. The transport mean free length is estimated to be about 156 μm. The demonstration of random organic lasers opens up the possibility of using scattering as an alternative source of coherent light emission.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.55.Sa Microcavity and microdisk lasers

Radiative recombination spectra of p-type δ-doped GaAs/AlAs multiple quantum wells near the Mott transition

J. Kundrotas, A. Čerškus, G. Valušis, M. Lachab, S. P. Khanna, P. Harrison, and E. H. Linfield

J. Appl. Phys. 103, 123108 (2008); http://dx.doi.org/10.1063/1.2943262 (6 pages) | Cited 8 times

Online Publication Date: 19 June 2008

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Photoluminescence (PL) spectra of beryllium δ-doped GaAs/AlAs multiple quantum wells are studied over a range of doping concentrations. Possible mechanisms for carrier recombination, both above and below the Mott metal-insulator transition, are discussed. In 15 nm width Be δ-doped GaAs/AlAs quantum wells, it is found that the Mott transition can be observed if the acceptor concentration (NBe) ≥ 3×1012 cm−2. At doping concentrations near the Mott transition band the PL spectra are dominated by excitons-bound-to-acceptor impurity recombinations. Above the Mott transition, the radiative recombination of free electrons with a two-dimensional hole gas is found to be the dominant recombination mechanism.
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73.63.Hs Quantum wells
78.67.De Quantum wells
73.21.Fg Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Analysis of S-rich CuIn(S,Se)2 layers for photovoltaic applications: Influence of the sulfurization temperature on the crystalline properties of electrodeposited and sulfurized CuInSe2 precursors

V. Izquierdo-Roca, A. Pérez-Rodríguez, J. R. Morante, J. Álvarez-García, L. Calvo-Barrio, V. Bermudez, P. P. Grand, L. Parissi, C. Broussillon, and O. Kerrec

J. Appl. Phys. 103, 123109 (2008); http://dx.doi.org/10.1063/1.2939833 (7 pages) | Cited 10 times

Online Publication Date: 23 June 2008

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This paper reports the microstructural analysis of S-rich CuIn(S,Se)2 layers produced by electrodeposition of CuInSe2 precursors and annealing under sulfurizing conditions as a function of the temperature of sulfurization. The characterization of the layers by Raman scattering, scanning electron microscopy, Auger electron spectroscopy, and XRD techniques has allowed observation of the strong dependence of the crystalline quality of these layers on the sulfurization temperature: Higher sulfurization temperatures lead to films with improved crystallinity, larger average grain size, and lower density of structural defects. However, it also favors the formation of a thicker MoS2 interphase layer between the CuInS2 absorber layer and the Mo back contact. Decreasing the temperature of sulfurization leads to a significant decrease in the thickness of this intermediate layer and is also accompanied by significant changes in the composition of the interface region between the absorber and the MoS2 layer, which becomes Cu rich. The characterization of devices fabricated with these absorbers corroborates the significant impact of all these features on device parameters as the open circuit voltage and fill factor that determine the efficiency of the solar cells.
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84.60.Jt Photoelectric conversion
61.72.Cc Kinetics of defect formation and annealing
78.30.Hv Other nonmetallic inorganics
79.20.Fv Electron impact: Auger emission
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Li Other semiconductors

Analysis of asymmetric Bragg–coupler based optical add-drop multiplexer operating on certain phase-matching conditions

A. Muldarisnur, A. Soehianie, A. Iskandar, and M. O. Tjia

J. Appl. Phys. 103, 123110 (2008); http://dx.doi.org/10.1063/1.2939634 (11 pages) | Cited 1 time

Online Publication Date: 24 June 2008

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The operational characteristics of a two-dimensional optical add-drop multiplexer were investigated for coupled planar waveguides with embedded grating structure in one of them. The analytical formulation of the wave propagation property was carried out on the basis of coupled mode theory derived from the Lorentz reciprocity theorem. Simplified mathematical formulation and analytical solution for the device modeling were attained by means of well-defined phase-matching conditions. Further numerical analysis was performed to study the effects of various geometrical and material parameters on the device performance in terms of the drop reflectance, input insertion loss, the transmission bandwidth, and the midgap separation. The optimal performance characterized by 99% drop reflectance, 1% input insertion loss, and 0.2 nm full width at half maximum at λ = 1.55 μm was achieved with realistically chosen device parameters consisting of refractive indices of the materials and geometrical parameters of the system. This result has demonstrated in principle the feasibility of developing the model for dense wavelength division multiplexing application.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.65.-k Nonlinear optics
42.79.Dj Gratings

Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

Patricia Forcén, Luis Oriol, Carlos Sánchez, Rafael Alcalá, Katja Jankova, and Søren Hvilsted

J. Appl. Phys. 103, 123111 (2008); http://dx.doi.org/10.1063/1.2943260 (8 pages) | Cited 2 times

Online Publication Date: 24 June 2008

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Recording of anisotropy and holographic polarization gratings using 532 nm, 4 ns light pulses has been carried out in thin films of polymers with the same azobenzene content (20 wt %) and different molecular architectures. Random and block copolymers comprising azobenzene and methylmethacrylate (MMA) moieties as well as statistical terpolymers with azobenzene, biphenyl, and MMA units have been compared in terms of recording sensitivity and stability upon pulsed excitation. Photoinduced anisotropy just after the pulse was significantly higher in the case of the block copolymers than in the two statistical copolymers. The stability of the recorded anisotropy has also been studied. While a stationary value of the photoinduced anisotropy (approximately 50% of the initial photoinduced value) is reached for the block copolymer, photoinduced anisotropy almost vanished after a few hours in the statistical copolymers. Polarization holographic gratings have been registered using two orthogonally circularly polarized light beams. The results are qualitatively similar to those of photoinduced anisotropy, that is, stability of the registered grating and larger values of diffraction efficiency for the block copolymer as compared with the random copolymers. The recording of holographic gratings with submicron period in films several microns thick, showing both polarization and angular selectivity, has also been demonstrated. Block copolymers showed a lamellar block nanosegregated morphology. The interaction among azo chromophores within the nanosegregated azo blocks seems to be the reason for the stability and the photoresponse enhancement in the block copolymer as compared with the statistical ones.
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42.40.Ht Hologram recording and readout methods
42.70.Ln Holographic recording materials; optical storage media
42.70.Jk Polymers and organics
42.79.Wc Optical coatings
42.40.Eq Holographic optical elements; holographic gratings
42.79.Ci Filters, zone plates, and polarizers

Refractive indices and elasto-optic coefficients of GaN studied by optical waveguiding

S. Pezzagna, J. Brault, M. Leroux, J. Massies, and M. de Micheli

J. Appl. Phys. 103, 123112 (2008); http://dx.doi.org/10.1063/1.2947598 (7 pages) | Cited 5 times

Online Publication Date: 25 June 2008

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Asymmetric GaN planar waveguides were grown on (0001) sapphire by molecular beam epitaxy or by metal-organic chemical vapor deposition. The GaN chromatic dispersion is measured in these samples by the prism coupling method at several discrete wavelengths over a large spectral domain (458–1550 nm). Two-term Sellmeier equations are adequate to fit the ordinary no and extraordinary ne refractive index curves as a function of wavelength. GaN waveguides were also grown on AlxGa1−xN and AlN cladding layers, and the GaN refractive indices are further measured from these samples. On the other hand, the biaxial stress state of each sample is determined by measuring the A, B, and C free exciton transition energies by low temperature (10 K) reflectivity measurements. The refractive indices versus in-plane stress σ1 reveal linear variations in the studied range and the slopes ∂n/∂σ1 are determined. It is found that these variations are more than seven times larger for the ordinary index than for the extraordinary index depending on the optical wavelength. We report here for the first time the measurement of the elasto-optic coefficients (p11+p12) and p13 of GaN in the visible wavelength range.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Gn Optical waveguides and couplers
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
71.35.-y Excitons and related phenomena

Lasing from photonic structure: Cholesteric-voltage controlled nematic-cholesteric liquid crystal

Mikhail I. Barnik, Lev M. Blinov, Vladimir V. Lazarev, Serguei P. Palto, Boris A. Umanskii, and Nikolay M. Shtykov

J. Appl. Phys. 103, 123113 (2008); http://dx.doi.org/10.1063/1.2948937 (7 pages) | Cited 5 times

Online Publication Date: 27 June 2008

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Experimental investigation and numerical simulation have been made of spectral and lasing properties of thin planar hybrid structures consisting of two layers of a cholesteric liquid crystal (ChLC) and a homogeneously aligned layer of a nematic liquid crystal between them. The light optical path in the nematic layer was controlled by an electric field. In the reference structure the ChLC layers were not doped, and the field controlled transmission spectra have been studied in detail. In the other two structures, both the ChLC layers were doped by the same laser dye (but different in the two structures) and the feedback necessary for lasing was controlled by the field induced phase retardation of the nematic layer. Therefore, the field control of the lasing spectra has been demonstrated. Numerical simulations of the transmission and lasing spectra are in good agreement with experimental data. The multilayer device described can be used as a field controllable planar microlaser.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.70.Df Liquid crystals
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Analysis and improvement of an X-band magnetically insulated transmission line oscillator

Yu-wei Fan, Hui-huang Zhong, Han-wu Yang, Zhi-qiang Li, Ting Shu, Jun Zhang, Yong Wang, and Ling Luo

J. Appl. Phys. 103, 123301 (2008); http://dx.doi.org/10.1063/1.2940129 (4 pages) | Cited 13 times

Online Publication Date: 17 June 2008

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An X-band magnetically insulated transmission line oscillator has been investigated theoretically and experimentally in our laboratory. However, severe pulse shortening and electrode erosion are observed in the experiments. The theoretical analyses show that anode plasma formation in the load region is the essential reason for the pulse shortening and electrode erosion. In order to eliminate or at least minimize anode plasma formation in the load region, an improved beam dump is presented. The theoretical analyses show that anode plasma formation can be eliminated or at least minimized in the improved beam dump.
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84.30.Ng Oscillators, pulse generators, and function generators
84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources

Effects of collisions and finite ion temperature on the sheath structure of cylindrical probes in low-pressure electronegative discharges

T. H. Chung

J. Appl. Phys. 103, 123302 (2008); http://dx.doi.org/10.1063/1.2939578 (7 pages) | Cited 3 times

Online Publication Date: 17 June 2008

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The spatial distributions of electric potential and velocity and density of positive ions are calculated in the surroundings of a negatively biased cylindrical probe immersed in electronegative plasmas. The model equations are solved on the scale of the electron Debye length. The solutions provide the variation of plasma variables along the distance from the plasma bulk region to the probe surface. The control parameters are the ratio of the negative ion density to the electron density, the ratios of the electron temperature to the positive and negative ion temperatures, and the ratio of the rate coefficient for the momentum transfer collision to that for the ionization. Especially, the effects of collision and finite temperature of positive ions are investigated. As the positive ion temperature increases, the sheath width decreases and the positive ion current collected by the probe increases. As the ratio of the rate coefficient for the momentum transfer collision to that for the ionization increases, the sheath edge approaches the plasma region, and the positive ion current to the probe decreases.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas
52.80.-s Electric discharges
52.70.Ds Electric and magnetic measurements

Elimination of dimethyl methylphosphonate by plasma flame made of microwave plasma and burning hydrocarbon fuel

S. C. Cho, H. S. Uhm, Y. C. Hong, Y. G. Park, and J. S. Park

J. Appl. Phys. 103, 123303 (2008); http://dx.doi.org/10.1063/1.2939799 (4 pages) | Cited 1 time

Online Publication Date: 18 June 2008

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Elimination of dimethyl methylphosphonate (DMMP) in liquid phase was studied by making use of a microwave plasma burner, exhibiting a safe removal capability of stockpiled chemical weapons. The microwave plasma burner consisted of a fuel injector and a plasma flame exit connected in series to a microwave plasma torch. The burner flames were sustained by injecting hydrocarbon fuels into the microwave plasma torch in air discharge. The Fourier transform infrared spectra indicated near perfect elimination of DMMP in the microwave plasma burner. This was confirmed by gas chromatography spectra as supporting data, revealing the disappearance of even intermediary compounds in the process of DMMP destruction. The experimental results and the physical configuration of the microwave plasma burner may provide an effective means of on-site removal of chemical warfare agents found on a battlefield.
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82.33.Vx Reactions in flames, combustion, and explosions
52.77.-j Plasma applications
82.80.Bg Chromatography

Soft x-ray emission from a pulsed gas discharge in a pseudosparklike electrode geometry

Klaus Bergmann, Felix Küpper, and Markus Benk

J. Appl. Phys. 103, 123304 (2008); http://dx.doi.org/10.1063/1.2940786 (8 pages) | Cited 7 times

Online Publication Date: 23 June 2008

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The mechanism of the soft x-ray generation in a pulsed high current discharge is investigated by means of time and space resolved characterization of the extreme ultraviolet emitting regions and discussion of the related electrical circuit parameters. The plasma is ignited in a pseudosparklike electrode geometry. In a discharge of 15 J, stored electrical energy characteristic emission of different gases (oxygen, argon, and nitrogen) is excited in the spectral range from 2 to 5 nm. Special interest is devoted to the 2.88 nm line emission of heliumlike nitrogen ions within the spectral range of the water window to be used for x-ray microscopy. For the nitrogen discharge, an admixture of xenon leads to axial shorter plasma emission as well as to a smaller diameter below 300 μm of the short wavelength emission. Investigation of the xenon related emission in the range of 10–16 nm indicates that radiative cooling is a possible reason for the observed decrease in the radius. Time and spatial resolved images show that the x-ray emission exhibits an axial dynamic in addition to the usual compression occurring in pinch plasmas.
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52.80.-s Electric discharges
52.55.Ez Theta pinch

Characterization of ZnO plasma in a radio frequency sputtering system

N. V. Joshy, Johney Isaac, and M. K. Jayaraj

J. Appl. Phys. 103, 123305 (2008); http://dx.doi.org/10.1063/1.2948940 (7 pages) | Cited 3 times

Online Publication Date: 25 June 2008

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Plasma generated by the radio frequency (rf) magnetron sputtering of gallium doped zinc oxide (ZnO) has been studied using cylindrical Langmuir probe and optical emission spectroscopy. The electron density and electron temperature were calculated for various rf powers at different spatial positions along the propagation direction of the plume. The electron density was found to increase with argon gas pressure whereas electron temperature decreased. The focusing of the plasma due to the magnetic field of the magnetron was observed at 3 cm distance from the target at low rf powers, while shift in the focusing of the plume was observed for high sputtering powers. Plasma potential of the plume was also evaluated at all sputtering conditions and its spatial variations were studied. Optical emission spectra of the plume were recorded at various spatial positions of the plume to get qualitative estimate of species in the plasma at various sputtering conditions. ZnO thin films were deposited on glass substrates placed at 3 and 6 cm distances from the target at different sputtering conditions. X-ray diffraction and scanning electron microscopy studies were carried out to investigate the crystallographic properties and the surface morphology of films deposited at these distances in relation to the plasma parameters.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Investigation of strain relaxation mechanisms and transport properties in epitaxial SmNiO3 films

F. Conchon, A. Boulle, R. Guinebretière, E. Dooryhée, J.-L. Hodeau, C. Girardot, S. Pignard, J. Kreisel, F. Weiss, L. Libralesso, and T. L. Lee

J. Appl. Phys. 103, 123501 (2008); http://dx.doi.org/10.1063/1.2938845 (8 pages) | Cited 4 times

Online Publication Date: 16 June 2008

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This article deals with strain relaxation in SmNiO3 epitaxial films deposited by chemical vapor deposition on SrTiO3 substrates. Thanks to x-ray reciprocal space mapping, we demonstrate that the strain relaxation is driven both “chemically” and “mechanically” by the formation of oxygen vacancies and misfit dislocations, respectively. Besides, a careful interpretation of the resistivity measurements allows us to highlight a correlation between the formation of oxygen vacancies, the stabilization of Ni3+, and the metal-insulator transition in the SmNiO3 films. Furthermore, using coplanar and grazing incidence diffraction, the shape of the strain gradient within the films is retrieved. This latter is calculated using a versatile scattering model involving B-spline functions. Finally, particular planar faults (Ruddlesden–Popper faults) that give rise to extended diffuse scattering on transverse scans are analyzed using a recent phenomenological model.
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68.60.Bs Mechanical and acoustical properties
73.61.-r Electrical properties of specific thin films
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions

Probing the underlying physics of ejecta production from shocked Sn samples

M. B. Zellner, W. Vogan McNeil, J. E. Hammerberg, R. S. Hixson, A. W. Obst, R. T. Olson, J. R. Payton, P. A. Rigg, N. Routley, G. D. Stevens, W. D. Turley, L. Veeser, and W. T. Buttler

J. Appl. Phys. 103, 123502 (2008); http://dx.doi.org/10.1063/1.2939253 (7 pages) | Cited 9 times

Online Publication Date: 16 June 2008

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This effort investigates the underlying physics of ejecta production for high explosive (HE) shocked Sn surfaces prepared with finishes typical to those roughened by tool marks left from machining processes. To investigate the physical mechanisms of ejecta production, we compiled and re-examined ejecta data from two experimental campaigns [ W. S. Vogan et al., J. Appl. Phys. 98, 113508 (1998); M. B. Zellner et al., ibid. 102, 013522 (2007) ] to form a self-consistent data set spanning a large parameter space. In the first campaign, ejecta created upon shock release at the back side of HE shocked Sn samples were characterized for samples with varying surface finishes but at similar shock-breakout pressures PSB. In the second campaign, ejecta were characterized for HE shocked Sn samples with a constant surface finish but at varying PSB.
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62.50.Ef Shock wave effects in solids and liquids
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
68.35.Gy Mechanical properties; surface strains
64.60.Ht Dynamic critical phenomena

Terahertz spectroscopy of carbon nanotubes embedded in a deformable rubber

R. Rungsawang, V. G. Geethamma, E. P. J. Parrott, D. A. Ritchie, and E. M. Terentjev

J. Appl. Phys. 103, 123503 (2008); http://dx.doi.org/10.1063/1.2939268 (4 pages) | Cited 7 times

Online Publication Date: 16 June 2008

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The dielectric response and anisotropic properties of natural rubber with embedded multiwall carbon nanotubes (CNTs) are studied in the 0.2–3 THz frequency range using terahertz transmission spectroscopy. Natural rubber acts as an invisible and insulating medium in this frequency range, allowing examination of isolated CNTs. The complex dielectric function is obtained with different CNT loadings by using a superposition formula. In highly loaded composites, we find a significant increase in the imaginary part of the dielectric function, related to a change in conductivity due to percolation. The deformable rubber matrix allows the alignment of CNTs by stretching. We investigated the response of aligned nanotubes to polarized terahertz radiation and it shows the evidence of primary electron transport along the tube axis.
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78.70.Gq Microwave and radio-frequency interactions
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.63.Fg Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
64.60.ah Percolation
78.67.Ch Nanotubes

Surface stress effects on the resonant properties of silicon nanowires

Harold S. Park

J. Appl. Phys. 103, 123504 (2008); http://dx.doi.org/10.1063/1.2939576 (10 pages) | Cited 24 times

Online Publication Date: 16 June 2008

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The purpose of the present work is to quantify the coupled effects of surface stresses and boundary conditions on the resonant properties of silicon nanowires. We accomplish this by using the surface Cauchy–Born model, which is a nonlinear, finite deformation continuum mechanics model that enables the determination of the nanowire resonant frequencies including surface stress effects through solution of a standard finite element eigenvalue problem. By calculating the resonant frequencies of both fixed/fixed and fixed/free 〈100〉 silicon nanowires with unreconstructed {100} surfaces using two formulations, one that accounts for surface stresses and one that does not, it is quantified how surface stresses cause variations in nanowire resonant frequencies from those expected from continuum beam theory. We find that surface stresses significantly reduce the resonant frequencies of fixed/fixed nanowires as compared to continuum beam theory predictions, while small increases in resonant frequency with respect to continuum beam theory are found for fixed/free nanowires. It is also found that the nanowire aspect ratio, and not the surface area to volume ratio, is the key parameter that correlates deviations in nanowire resonant frequencies due to surface stresses from continuum beam theory.
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61.46.-w Structure of nanoscale materials
68.35.Gy Mechanical properties; surface strains
68.65.La Quantum wires (patterned in quantum wells)

Coherent A1g and Eg phonons of antimony

Kunie Ishioka, Masahiro Kitajima, and Oleg V. Misochko

J. Appl. Phys. 103, 123505 (2008); http://dx.doi.org/10.1063/1.2940130 (5 pages) | Cited 3 times

Online Publication Date: 16 June 2008

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We report the ultrafast dynamics of the coherent A1g and Eg phonons of antimony as a function of temperature and optical polarization. Like in bismuth, the two phonon modes exhibit nearly π/2 difference in their initial phase, suggesting their different coupling strengths with photoexcited electrons. The dependence of the phonon amplitude on the optical polarization and temperature indicates the generation of the coherent A1g phonons through both displacive and Raman processes, rather than a purely displacive one. In contrast, the generation of the coherent Eg phonons can be understood within Raman framework alone.
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78.47.J- Ultrafast spectroscopy (<1 psec)
81.05.Bx Metals, semimetals, and alloys

Electromigration behavior of lead-free solder flip chip bumps on NiP/Cu metallization

J. W. Jang, L. N. Ramanathan, and D. R. Frear

J. Appl. Phys. 103, 123506 (2008); http://dx.doi.org/10.1063/1.2940133 (5 pages) | Cited 2 times

Online Publication Date: 16 June 2008

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The electromigration behavior of Sn–2.5Ag and Sn–0.7Cu (in wt %) flip chip solder joints on electroless NiP/Cu metallization at a current density of 1.3×104 A/cm2 was studied. For Sn-2.5 Ag solder, electromigration at 115 °C for 250 h showed a selective dissolution of Ni from the electroless NiP layer forming crystallized Ni3P. At 140 °C, the damage to the NiP layer was accelerated and instability of the NiP/Cu interface was observed. For eutectic Sn–0.7Cu solder, the electromigration behavior at a higher temperature was evaluated. At 180 °C, the NiP/Cu under bump metallurgy (UBM) started to show damage after 50 h. At 200 °C, the entire NiP/Cu layer was damaged, and P in the NiP layer moved to the edge of the anode much faster than the other species forming CuP2 intermetallics. NiP/Cu UBM experiences selective dissolution of Ni at lower temperatures, and the damage of the entire UBM occurred abruptly at the higher temperature.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
64.75.Bc Solubility

On the formation of complexes between Mn acceptors and hydrogen in GaP and GaMnP alloys

B. Clerjaud, D. Wasik, R. Bouanani-Rahbi, G. Strzelecka, A. Hruban, and M. Kamińska

J. Appl. Phys. 103, 123507 (2008); http://dx.doi.org/10.1063/1.2939089 (5 pages) | Cited 2 times

Online Publication Date: 17 June 2008

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The observation of the local vibrational stretching mode of the manganese-hydrogen complex in GaP by infrared spectroscopy is reported. It is shown that when manganese is in the impurity regime, the complex only forms in very small concentrations in samples in which the Fermi level is about 0.3 eV above the valence band maximum. The reasons for this behavior are analyzed. It is argued that in GaMnP alloys, the formation of manganese-hydrogen complexes is more likely than in the impurity regime, but a full passivation of the manganese by hydrogen is not possible. However, the fraction of passivated manganese can impede ferromagnetism.
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71.55.-i Impurity and defect levels
71.20.-b Electron density of states and band structure of crystalline solids
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