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15 Nov 2004

Volume 96, Issue 10, pp. 5393-5932

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Effects of polarizations of a laser on absorption in a paraboloid of revolution-shaped welding or drilling cavity

Ching-Yen Ho

J. Appl. Phys. 96, 5393 (2004); http://dx.doi.org/10.1063/1.1797543 (9 pages) | Cited 5 times

Online Publication Date: 5 November 2004

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The effects of polarizations on the apparent absorptivity or integrated energy absorbed by a paraboloid of revolution-shaped cavity subject to a laser beam are systematically and quantitatively investigated. The incident flux is considered to be a TEM00 mode of a Gaussian distribution specified by the wavelength, spot size, and focal location of the laser beam. Using a Monte Carlo method and neglecting the absorption within the plasma in the cavity, the results show that the predicted energy-transfer efficiency versus incident flux and cavity depth agrees well with the experimental data. The apparent absorption of p polarization is found to be always higher than that of s polarization, even though the latter causes higher energy fluxes absorbed than the former near the critical radius. The apparent absorptivity for s polarization as a function of cavity depth can be divided into three parts: an initial decrease, rapid increase, and gradual increase. Interestingly, the polarization of circularly polarized incoming rays is gradually transformed into s polarization in the course of multiple reflections. The apparent absorptivity as a function of polarizations, specular reflectivity, penetration depth, focal location, and absorptive and refractive indices is also presented.
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42.62.Cf Industrial applications

Electrically switchable spatial filter based on polymer-dispersed liquid crystal film

Andy Y.- G. Fuh and Tsung-Hsien Lin

J. Appl. Phys. 96, 5402 (2004); http://dx.doi.org/10.1063/1.1805185 (3 pages) | Cited 12 times

Online Publication Date: 5 November 2004

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This work demonstrates the feasibility of using polymer-dispersed liquid crystal (PDLC) films as electrically switchable spatial filters in the optical signal process. The fabrication relies on the fact that the size of the liquid crystal droplet formed in a PDLC film is inversely proportional to the intensity of curing. Controlling the driving voltage on the PDLC sample can filter particular spatial frequencies in the Fourier optical signal process. A simulation is also performed, and the results are highly consistent with those of experiments.
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61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
42.79.Ci Filters, zone plates, and polarizers
42.70.Df Liquid crystals
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.30.Kq Fourier optics

Nonvolatile two-step, two-color holography with continuous-wave lights for both congruent and near-stoichiometric LiNbO3:Fe

Yan Shen, Guoquan Zhang, Bo Fu, Qingjun Xu, and Jingjun Xu

J. Appl. Phys. 96, 5405 (2004); http://dx.doi.org/10.1063/1.1794361 (10 pages)

Online Publication Date: 5 November 2004

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We have studied theoretically the steady-state nonvolatile two-step, two-color holographic recording performance for both the congruent and the near-stoichiometric LiNbO3:Fe based on the two-center model (the deep-trap and the shallow-trap centers are Fe2+∕Fe3+ and NbLi4+∕NbLi5+, respectively). The results show that the direct electron exchange between the Fe2+∕Fe3+ centers and the NbLi4+∕NbLi5+ centers due to the tunneling effect dominates the charge-transfer process during the nonvolatile two-step, two-color holography and determines the two-step, two-color holography performance in LiNbO3:Fe. We have further studied the effects of the crystal stoichiometry on the performance of the two-step, two-color holography. It is shown that, as far as the total space-charge field is considered, the nonvolatile two-step, two-color holography performance in the near-stoichiometric LiNbO3:Fe is much better than that in the congruent LiNbO3:Fe within the intensity range reachable by the continuous-wave lights.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.J- Point defects and defect clusters
73.40.Gk Tunneling
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Periodic reverse-twist nematic domains obtained by microrubbing patterns

Michinori Honma, Keisuke Yamamoto, and Toshiaki Nose

J. Appl. Phys. 96, 5415 (2004); http://dx.doi.org/10.1063/1.1803946 (5 pages) | Cited 11 times

Online Publication Date: 5 November 2004

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A method for forming periodic 90° reverse-twist domains using a microscale rubbing pattern has been proposed; that is, an isolated 90° twist domain is surrounded by a 45° twist domain. Since liquid crystal (LC) materials exhibit elastic nature, the twist sense of the inner 90° twist domain prefers to be the same as that of the surrounding 45° twist domain. Two factors are investigated to obtain periodic 90° reverse-twist domains; (i) the injection process of LC material (isotropic or nematic phase) and (ii) the ratio of the area of the surrounding 45° twist domain and the whole area (the normalized area of the 45° twist domain). In the case of the injection in isotropic phase, it is revealed that periodic 90° reverse-twist domains can be obtained only when the area of the 45° twist domain is sufficiently large. On the other hand, in the case of injection in nematic phase, periodic 90° reverse-twist domains can successfully obtained regardless of the area of the 45° twist domain. Thus, the injection rocess is a very important factor to obtain periodic 90° reverse-twist domains. The fabricated LC cell with the periodic 90° reverse-twist domains is applied to LC grating. The almost linear relationship between the diffraction efficiency and the normalized area of the 45° twist domain is found and the high diffraction efficiency (0.39) near the theoretically maximum value (0.405) is obtained when the normalized area of the 45° twist domain is very small (0.1). The fabricated LC grating can function as a polarization-idependent and wavelength-independent LC grating.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
64.70.M- Transitions in liquid crystals
61.30.Jf Defects in liquid crystals
42.79.Dj Gratings
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Ionization and ablation phenomena in an ablative plasma accelerator

M. Keidar, I. D. Boyd, and I. I. Beilis

J. Appl. Phys. 96, 5420 (2004); http://dx.doi.org/10.1063/1.1805726 (9 pages) | Cited 9 times

Online Publication Date: 5 November 2004

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Several interrelated phenomena near the surface ablated into a discharge plasma, such as ablation and ionization in accelerated plasma are studied. Two characteristic ablation modes are identified, namely, ablation mode with a velocity at the Knudsen layer edge smaller than the local sound speed and a velocity at the Knudsen layer edge close to the sound speed. The existence of these two ablation modes is determined by the current density in the acceleration region. The nonequilibrium ionization region in the presence of strong electromagnetic plasma acceleration is studied. In the subsonic regime, the ionization region thickness is proportional to the ionization rate and inversely proportional to the magnetic field. Conditions for ionization equilibrium in the accelerating plasma are determined. The specific example of a micropulsed plasma thruster is considered. It is concluded that both the equilibrium and nonequilibrium ionization regimes occur in this device.
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52.75.Di Ion and plasma propulsion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Jm Ionization of plasmas
52.59.Dk Magneto-plasma accelerated plasmas
52.55.-s Magnetic confinement and equilibrium
52.25.Ya Neutrals in plasmas

Nonuniform radio-frequency plasma potential due to edge asymmetry in large-area radio-frequency reactors

A. A. Howling, L. Sansonnens, J. Ballutaud, Ch. Hollenstein, and J. P. M. Schmitt

J. Appl. Phys. 96, 5429 (2004); http://dx.doi.org/10.1063/1.1803608 (12 pages) | Cited 21 times

Online Publication Date: 5 November 2004

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In small area capacitive reactors, the rf and dc components of the plasma potential can be assumed to be uniform over all the plasma bulk because of the low plasma resistivity. In large area reactors, however, the rf plasma potential can vary over a long range across the reactor due to rf current flow and the nonzero plasma impedance. A perturbation in rf plasma potential, due to electrode edge asymmetry or the boundary of a dielectric substrate, propagates along the resistive plasma between capacitive sheaths. This is analogous to propagation along a lossy conductor in a transmission line and the damping length of the perturbation can be determined by the telegraph equation. Some consequences are the following: (i) The spatial variation in sheath rf amplitudes causes nonuniform rf power dissipation near to the reactor sidewalls. (ii) The surface charge and potential of a dielectric substrate can be negative and not only positive as for a uniform rf plasma potential. The variation of sheath dc potential across a dielectric substrate causes nonuniform ion energy bombardment. (iii) The self-bias voltage depends on the plasma parameters and on the reactor and substrate dimensions—not only on the ratio of electrode areas. (iv) The nonuniform rf plasma potential in presence of the uniform dc plasma potential leads to nonambipolar dc currents circulating along conducting surfaces and returning via the plasma. Electron current peaks can arise locally at the edge of electrodes and dielectric substrates. Perturbations to the plasma potential and currents due to the edge asymmetry of the electrodes are demonstrated by means of an analytical model and numerical simulations.
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52.58.Qv Electrostatic and high-frequency confinement
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.65.Vv Perturbative methods
52.25.Fi Transport properties
52.77.-j Plasma applications
52.40.Kh Plasma sheaths
52.30.-q Plasma dynamics and flow

Plasma structure and behavior in a disk magnetohydrodynamic generator

Tomoyuki Murakami, Yoshihiro Okuno, and Hiroyuki Yamasaki

J. Appl. Phys. 96, 5441 (2004); http://dx.doi.org/10.1063/1.1803929 (9 pages) | Cited 15 times

Online Publication Date: 5 November 2004

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We describe the structure and behavior of a nonequilibrium cesium-seeded helium plasma in a disk-shaped magnetohydrodynamic generator. Excellent time-resolved optical measurements clarify the spatial distribution of the electron temperature. A correlation analysis and the visualization of the plasma structure reveal its propagation phenomena from upstream to downstream and the transformation from a homogeneous quasisteady state to a self-consistent periodical state. A linear perturbation analysis suggests that the inhomogeneous plasma structure associated with the unique electron temperature behavior is closely related to ionization instability due to weak seed ionization.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.25.Fi Transport properties
84.60.Lw Magnetohydrodynamic conversion
52.65.Vv Perturbative methods
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Jm Ionization of plasmas

Time evolution of plasma afterglow produced by femtosecond laser pulses

A. E. Martirosyan, C. Altucci, A. Bruno, C. de Lisio, A. Porzio, and S. Solimeno

J. Appl. Phys. 96, 5450 (2004); http://dx.doi.org/10.1063/1.1803920 (6 pages) | Cited 12 times

Online Publication Date: 5 November 2004

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In this paper we investigate the time evolution of laser plasmas generated in atmospheric air by ultrashort (100 fs) laser pulses. The detected quantity is the time integrated photon yield emitted by the plasma, which monotonically depends on the amount of energy transferred by the laser pulses to the plasma. We study the effect of a preionizing pulse on the efficiency of plasma generation by a second “probe” pulse and demonstrate that preionization results into a considerable increase of the overall photon yield emitted by the plasma. An explanation of this phenomenon relies on the fact that the larger the electron density experienced by the probe pulse, the more effective the energy transfer from the probe pulse to the residual plasma, the more intense is the light from the plasma. With this concept in mind and by relying on a pump-probe technique, we also measure the total photon yield emitted by the plasma produced by the combination of the two pulses, as a function of their relative delay time. We observe a considerable increase in the plasma brightness for delay times much longer than the laser pulse duration. This phenomenon is associated with an increase of the electron density even after the end of the pump pulse, due to secondary electron-impact ionization originating from highly-energetic primary photoelectrons, and to superelastic electron-molecule collisions. We also develop a simplified model describing the time evolution of the electron and ion densities and the electron temperature. From the calculated time evolution of these quantities produced by a single laser pulse, we can predict with a good approximation the main features of the plasma generated by an ultrashort laser pulse.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Jm Ionization of plasmas
52.20.Fs Electron collisions
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Electron cyclotron resonance deposition, structure, and properties of oxygen incorporated hydrogenated diamondlike amorphous carbon films

G. Adamopoulos, C. Godet, T. Zorba, K. M. Paraskevopoulos, and D. Ballutaud

J. Appl. Phys. 96, 5456 (2004); http://dx.doi.org/10.1063/1.1804624 (6 pages) | Cited 2 times

Online Publication Date: 5 November 2004

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Oxygen-incorporated hydrogenated amorphous carbon films were grown by the integrated distributed electron cyclotron resonance plasma technique from a mixture of acetylene and oxygen. It has been found that the increase of the oxygen to acetylene gas ratio results in more oxygen incorporation up to O∕(O+C)=0.2 with a decrease in the hydrogen concentration within the film as measured by the nuclear reaction analysis (NRA) and a combination of the elastic recoil detection analysis and Rutherford backscattering techniques. The spectroscopic ellipsometry in the range of 1.5–5 eV showed a negligible decrease of the E04 optical band gap for increasing the oxygen content. At the same time, the decrease of the refractive index from 2.2 to 2.0 denotes the decrease of the films density, which was independently estimated by NRA. The visible (488 nm) Raman spectroscopy showed that the increase of the oxygen content favors the clustering of the six-fold sp2C rings. The Fourier transform infrared spectroscopy gives evidence of both C–O and C�O bonding configurations. No evidence of O–H bonds formation is found. Simultaneously, the chemisorption of CO2 seems to increased with increasing the oxygen to acetylene gas ratio, which is consistent with the lower film density. The previously trends denote the “softening” of the films, which is consistent with the significant decrease (of about 35%) of the compressive stress allowing the growth of thicker but still transparent films.
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68.55.A- Nucleation and growth
81.05.U- Carbon/carbon-based materials
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
52.77.Dq Plasma-based ion implantation and deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Pg Disordered solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
82.80.Nj Fourier transform mass spectrometry
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Interfacial roughening during solid phase epitaxy: Interaction of dopant, stress, and anisotropy effects

William Barvosa-Carter, Michael J. Aziz, A.-V. Phan, T. Kaplan, and L. J. Gray

J. Appl. Phys. 96, 5462 (2004); http://dx.doi.org/10.1063/1.1790580 (7 pages) | Cited 16 times

Online Publication Date: 5 November 2004

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The effects of externally applied stress and rate-enhancing dopants on interfacial roughness during the solid phase epitaxial growth of ion-implantation-doped Si are investigated using cross-sectional transmission electron microscopy and time-resolved reflectivity. We find long-wavelength roughness in the absence of an applied stress that arises solely from the dopant-gradient. With the addition of a compressive stress, the interface roughens further with an enhanced magnitude and a dramatically reduced wavelength. We discuss the experimental results in the context of a simulation that includes our current understanding of stress, dopant-gradient, and interface anisotropy effects. We find a rich interplay between these effects in determining growth morphology evolution, and demonstrate the successes and current limitations of the model.
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68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases
61.72.S- Impurities in crystals
61.72.uf Ge and Si
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Accurate determination of optical constants of textured SnO2 using low incidence angle spectroscopic ellipsometry

P. D. Paulson and Steven S. Hegedus

J. Appl. Phys. 96, 5469 (2004); http://dx.doi.org/10.1063/1.1797544 (9 pages) | Cited 5 times

Online Publication Date: 5 November 2004

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Accurate optical constants (n and k) of textured SnO2 films were obtained in the range of 0.85–4.6 eV using spectroscopic ellipsometry. The angular dependence of the spectroscopic ellipsometer measurement was determined at incident angles 30°, 50°, and 70° from normal to the sample surface. Depolarization components due to texturing and substrate backside reflection were separately analyzed using the measurement on polished and unpolished samples. Depolarization due to substrate backside reflection was modeled accurately. By performing the measurements at a low angle of incidence (30°), where the depolarization due to texturing is at a minimum and therefore can be neglected in the optical model, one can obtain the accurate values of n and k.
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78.66.Nk Insulators
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Study of HfO2 films deposited on strained Si1−xGex layers by atomic layer deposition

J.-F. Damlencourt, O. Weber, O. Renault, J.-M. Hartmann, C. Poggi, F. Ducroquet, and T. Billon

J. Appl. Phys. 96, 5478 (2004); http://dx.doi.org/10.1063/1.1805184 (6 pages) | Cited 11 times

Online Publication Date: 5 November 2004

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This paper focuses on the growth of HfO2 by atomic layer deposition (ALD) at 350°C on pseudomorphic Si1−xGex thin films (x=15% and 25%). Two different Si1−xGex surface preparations (chemical oxidation and HF “last” treatment) have been investigated to obtain the highest HfO2 film quality with the thinnest interfacial layer possible. The initial stages of the ALD growth on these different surfaces (i.e., hafnium adsorption and chlorine contamination) analyzed by total x-ray fluorescence show that HF last treated Si1−xGex surfaces are more convenient than chemically oxidized ones to grow high quality HfO2 layers. This result is confirmed by x-ray photoelectron spectroscopy investigations of the interfacial layer structure as a function of the surface treatment. As-deposited and annealed thin HfO2 layers (2.5, 3.5, 5, and 8 nm) grown on HF last treated Si0.75Ge0.25 strained layers were analyzed by mercury probe. An equivalent oxide thickness as low as 0.7 nm was obtained for a 2.5 nm as-deposited HfO2 film. Mobility results show that a 22% mobility enhancement is obtained in the entire effective field range with HfO2∕SiGe compared to the HfO2∕Si reference.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments
68.43.Mn Adsorption kinetics
81.65.Mq Oxidation
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures

Defect levels and types of point defects in high-purity and vanadium-doped semi-insulating 4H–SiC

M. E. Zvanut, V. V. Konovalov, Haiyan Wang, W. C. Mitchel, W. D. Mitchell, and G. Landis

J. Appl. Phys. 96, 5484 (2004); http://dx.doi.org/10.1063/1.1797547 (6 pages) | Cited 12 times

Online Publication Date: 5 November 2004

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Electron paramagnetic resonance (EPR) spectroscopy and photo-induced EPR are used to examine the point defects in vanadium-doped 4H–SiC and high-purity semi-insulating (HPSI) 4H–SiC grown by physical vapor transport. Both types of samples often exhibit a 1.1-eV activation energy, Ea, as extracted from the temperature-dependent Hall/resistivity measurements; however, different defects are related to the same Ea in each case. In the vanadium-doped wafers, the EPR data reveal both V4+ and V3+ in the same sample; thus, the 1.1-eV Hall activation energy is tentatively interpreted as the V3+∕4+ acceptor level. However, this conclusion cannot be confirmed because additional defects complicate the photoresponse of vanadium. The carbon vacancy, which is detected in all the HPSI wafers, exhibits a range of photothresholds similar to the various values measured for Ea. The photo-EPR and temperature-dependent Hall/resistivity measurements made before and after a 1600 °C anneal suggest that several different types of nonuniformly distributed defects participate in compensation of the HPSI material and that annealing selectively removes those with different defect levels.
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81.05.Hd Other semiconductors
76.30.Mi Color centers and other defects
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.up Other materials
61.72.S- Impurities in crystals
61.72.J- Point defects and defect clusters

Electron-beam-induced current study of grain boundaries in multicrystalline silicon

J. Chen, T. Sekiguchi, D. Yang, F. Yin, K. Kido, and S. Tsurekawa

J. Appl. Phys. 96, 5490 (2004); http://dx.doi.org/10.1063/1.1797548 (6 pages) | Cited 53 times

Online Publication Date: 5 November 2004

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The effects of grain boundary (GB) character and impurity contamination on the recombination activity of grain boundaries (GBs) in multicrystalline silicon (mc-Si) were systematically studied through an electron-beam-induced current (EBIC) technique. First, clean GBs of various characters were checked at 300 and 100 K. The EBIC contrasts of these GBs were in the same range of 0%–2% at 300 K and 2%–4% at 100 K, suggesting that the recombination activity of clean GBs is weak and the GB character has no significant effect on it. Second, the effect of impurities was studied by comparing the EBIC contrasts of the same type of the GBs in mc-Si with different Fe contamination levels. The recombination activity of GBs became stronger as the contamination level rose. The variation in the recombination activity related to the GB character was also observed in these specimens. The random or high-Σ GBs showed a stronger EBIC contrast than the low-Σ GBs. Moreover, we found that the EBIC contrast was not uniform along one Σ3 GB. In a clean mc-Si, the variation in the EBIC contrast of different parts of the Σ3 GB was 1% at 300 K, whereas it was more than 10% in the contaminated mc-Si. This indicates that not only the GB character but also the GB plane would affect the recombination activity of GBs. These results suggest that the recombination activity of GBs is principally determined by the gettering ability of GBs. Specifically, that random GBs may have the strongest gettering ability, whereas Σ3 {111} has the weakest.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Mm Grain and twin boundaries
61.72.S- Impurities in crystals
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Interdiffusion and structural change in an InGaAs dots-in-a-well structure by rapid thermal annealing

Young Min Park, Young Ju Park, Kwang Moo Kim, Jin Dong Song, Jung II Lee, Keon-Ho Yoo, Hyung Seok Kim, and Chan Gyung Park

J. Appl. Phys. 96, 5496 (2004); http://dx.doi.org/10.1063/1.1805191 (4 pages) | Cited 8 times

Online Publication Date: 5 November 2004

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Post-growth rapid thermal annealing (RTA) has been used to investigate an interdiffusion and the structural change in an InGaAs dots-in-a-well (DWELL) structure grown by molecular beam epitaxy using an alternately supplying InAs and GaAs sources. In the case of the as-grown sample, which has a metastable quantum structure due to an intentional deficit of source materials, it is found that an InGaAs quantum well (QW) coexists with the premature quantum dots (QDs), and an intermediate layer exists between the QW and the QDs. Through the RTA process at 600 and 800 °C for 30 s, metastable structure changes into a normal DWELL structure composed of QDs and QW as a result of the intermixing of premature QDs and the intermediate layer.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Fg Quantum wells
68.35.Fx Diffusion; interface formation
78.67.Hc Quantum dots
81.07.St Quantum wells
81.07.Ta Quantum dots
78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

The equation of state of a fluorinated tripolymer

J. C. F. Millett, N. K. Bourne, and G. T. Gray

J. Appl. Phys. 96, 5500 (2004); http://dx.doi.org/10.1063/1.1805193 (5 pages) | Cited 4 times

Online Publication Date: 5 November 2004

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The Hugoniot of the fluorinated tripolymer Viton B has been quantified in terms of shock stress, shock velocity, and particle velocity. The shock velocity—particle velocity curve was found to be linear, thus suggesting no changes in phase occurred in the experimental stress range investigated. Comparisons of the calculated hydrodynamic pressures and measured stresses also showed close agreement, with only small differences apparent at the highest stresses. It is believed that this shows Viton B has a low shock-induced shear strength that only becomes significant at high impact stresses. Comparison of the Hugoniots of Viton B, polytetrafluroethylene, and polyvinylidene difluoride shows that the former is slightly steeper. The authors suggest that this is due to the −CF3 side group having a strengthening effect.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids

Evolution equation for a thin epitaxial film on a deformable substrate

W. T. Tekalign and B. J. Spencer

J. Appl. Phys. 96, 5505 (2004); http://dx.doi.org/10.1063/1.1766084 (8 pages) | Cited 23 times

Online Publication Date: 5 November 2004

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We consider a continuum model for the evolution of an epitaxially strained dislocation-free thin solid film on a deformable substrate in the absence of vapor deposition. By using a thin-film approximation we derived a nonlinear evolution equation. We examined the nonlinear evolution equation and found that there is a critical film thickness below which every film thickness is stable and a critical wave number above which every film thickness is stable. Preliminary numerical results indicate that the equation possesses island-like steady state solutions.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Md Surface thermodynamics, surface energies
68.60.-p Physical properties of thin films, nonelectronic

Simulation of correlated diffusion of Si and B in thermally grown SiO2

Masashi Uematsu, Hiroyuki Kageshima, Yasuo Takahashi, Shigeto Fukatsu, Kohei M. Itoh, and Kenji Shiraishi

J. Appl. Phys. 96, 5513 (2004); http://dx.doi.org/10.1063/1.1806253 (7 pages) | Cited 2 times

Online Publication Date: 5 November 2004

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Simultaneous diffusion of Si and B in thermally grown SiO2 is modeled taking into account the effect of SiO molecules generated at the Si∕SiO2 interface and diffusing into SiO2 to enhance both Si and B diffusion. Based on the model, we simulated experimental profiles of coimplanted 30Si and B in 28SiO2, which showed increasing diffusivities with decreasing distance from the interface. The simulation results show that the SiO diffusion is so slow that the SiO concentration at the near-surface region critically depends on the distance from the interface. In addition, the simulation explains that the diffusivities of both Si and B increase with longer annealing times because more SiO molecules arrive from the interface. Furthermore, we examined the effect of high-concentration B on the diffusivities of Si and B in SiO2, both of which increase with higher B concentration. The experimental results were simulated assuming that the diffusivity of SiO, which enhances the diffusivities of Si and B, increases with higher B concentration. The present results indicate that Si and B diffusion in SiO2 are correlated via SiO molecules; namely, the enhancement of SiO diffusion at high B concentrations also causes enhanced diffusion of both Si and B.
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66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Wm Other nonelectronic physical properties
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.72.S- Impurities in crystals
81.40.Gh Other heat and thermomechanical treatments

Measurement of the compression isentrope for 6061-T6 aluminum to 185 GPa and 46% volumetric strain using pulsed magnetic loading

D. B. Hayes, C. A. Hall, J. R. Asay, and M. D. Knudson

J. Appl. Phys. 96, 5520 (2004); http://dx.doi.org/10.1063/1.1803108 (8 pages) | Cited 8 times

Online Publication Date: 5 November 2004

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The Z accelerator at Sandia National Laboratories was used to measure the compression isentrope of 6061-T6 aluminum to 185 GPa. The isentropic compression experimental technique uses a rapidly increasing, planar magnetic field to simultaneously subject multiple planar aluminum samples of different thicknesses to a ramped magnetic stress load. This magnetic stress load causes a ramped compression wave to propagate in the aluminum. Motion histories at the rear surface of each aluminum sample are measured through a LiF window using laser velocity interferometry. Backward and forward integration of the one-dimensional equations of motion are used to analyze the data. Imposing the requirement that each motion history comes from the same magnetic stress load is sufficient to determine both the stress load and the stress-strain behavior of the aluminum. Because of shocks that grow in the LiF, the usual VISAR interferometer analysis was modified. The measured compression curve obtained on different aluminum samples for volumetric strains to 46% agrees to within about 2% of peak stress with an isentrope obtained from the often-used Mie-Grüneisen equation of state that was derived from previous Hugoniot data.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids

Rapid dissociation of merocyanine dye aggregates by reduced pressure in mixed Langmuir-Blodgett films

Yoshiaki Hirano, Takurou N. Murakami, Yuhki K. Nakamura, Yoshinori Fukushima, Yoshikazu Tokuoka, and Norimichi Kawashima

J. Appl. Phys. 96, 5528 (2004); http://dx.doi.org/10.1063/1.1803109 (6 pages) | Cited 2 times

Online Publication Date: 5 November 2004

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We have examined the influence of reduced pressure on the redshifted and the blueshifted aggregates formed in the mixed Langmuir-Blodgett (LB) films of the merocyanine dye–arachidic acid (MS–C20) binary and the MS–C20–n-octadecane (MS-C20-AL18) ternary systems with the molar mixing ratios of [MS]:[C20]:[AL18]=1:2:x in the range of 0≦x≦5.0. The peak of the redshifted band at 590 nm in the binary system remains constant before and after the reduced pressure treatments. On the other hand, not only the peaks of the blueshifted bands at 505 nm and 520 nm but also the redshifted shoulder at around 580 nm in the ternary systems drastically diminishes after the treatments, indicating the dissociation of the MS aggregates. The long axis of AL18 molecules with the all-trans conformation, which tends to fill the MS empty spaces, is aligned along the stacking direction of the mixed LB films before the treatments, whereas almost all the AL18 molecules are absent after the treatments. Therefore, the dissociation is considered to be ascribed to the removal of the AL18 molecules with the uniaxial orientation in the mixed LB films by reduced pressure, leading to a change in the MS aggregation state.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.18.Fg Liquid thin film structure: measurements and simulations
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.40.Me Organic compounds and polymers
78.30.C- Liquids
78.66.Qn Polymers; organic compounds

Study of the interaction of tris-(8-hydroxyquinoline) aluminum (Alq3) with potassium using vibrational spectroscopy: Examination of possible isomerization upon K doping

Y. Sakurai, Y. Hosoi, H. Ishii, Y. Ouchi, G. Salvan, A. Kobitski, T. U. Kampen, D. R. T. Zahn, and K. Seki

J. Appl. Phys. 96, 5534 (2004); http://dx.doi.org/10.1063/1.1776626 (9 pages) | Cited 15 times

Online Publication Date: 5 November 2004

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The geometrical structure of potassium-doped Alq3 [tris-(8-hydroxyquinoline) aluminum] and the interaction between the Alq3 molecule and potassium were studied using infrared reflection absorption spectroscopy (IRRAS), surface-enhanced Raman scattering (SERS), and density functional theory calculations. A major aim of this study was to examine the theoretically predicted isomerization of Alq3 molecules from the meridional form to the facial form upon alkali-metal doping. The observed spectra show significant changes with the deposition of potassium on a thin Alq3 film. The calculated IR spectra of the K-Alq3 complex differ significantly between the meridional and facial forms, and the calculation for the meridional form agrees fairly well with the observed spectrum. This demonstrates that (1) the Alq3 molecule does not change to a facial isomer with the deposition of potassium, but retains the meridional form, in contrast to the reported theoretical prediction, and (2) the structure of the complex as evaluated from geometry optimization is reliable. We also found that the calculated IR spectrum of the K-Alq3 complex with Alq3 in its meridional form is significantly different from that of the isolated anion in the same isomeric form, which probably reflects nonuniform interaction between K and the three ligands of Alq3. On the other hand, the calculated spectra of Alq3 and the K-Alq3 complex in the facial form are similar, possibly because the K atom in the suggested structure lies on the axis of threefold symmetry, leading to an equivalent effect on the three ligands. Even though vibrational spectra of alkali-metal-doped organic materials are usually interpreted on the basis of an isolated anion, the results presented here show that care should be taken in interpreting the spectra of doped organic materials without considering the presence of the counter ion. The observed SERS spectra and theoretical calculations of the Raman spectra show similar trends when compared to the IRRAS results. The present results show that vibrational spectroscopy can be used as a sensitive tool for discerning subtle differences between isomers as well as between complexes and isolated anions.
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82.30.Qt Isomerization and rearrangement
78.30.Jw Organic compounds, polymers
78.66.Qn Polymers; organic compounds

Boron diffusion in strained Si: A first-principles study

Li Lin, Taras Kirichenko, Sanjay K. Banerjee, and Gyeong S. Hwang

J. Appl. Phys. 96, 5543 (2004); http://dx.doi.org/10.1063/1.1803630 (5 pages) | Cited 3 times

Online Publication Date: 5 November 2004

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We investigate B diffusion in strained Si by using first-principles density functional theory calculations. An enhancement and an anisotropy of B diffusion in biaxial tensile strained Si are found. The diffusion barrier along the strain plane (channel) is decreased while the barrier in the vertical direction (depth) remains unchanged. This anisotropy comes from the orientation dependence of the saddle point in the diffusion pathway. The formation enthalpy of B-I pair also decreases in strained Si. According to our calculations, for strained Si on a Si0.8Ge0.2 buffer layer, which is widely used in strained metal oxide semiconductor field-effect-transistor, an enhancement of B diffusivity along the channel by a factor ∼4 and a factor ∼2 in the vertical direction are expected for typical rapid thermal anneals.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Investigation of incubation in ArF excimer laser irradiated poly(methyl-methacrylate) using pulsed force mode atomic force microscopy

B. Hopp, T. Smausz, J. Kokavecz, N. Kresz, Z. Bor, S. Hild, and O. Marti

J. Appl. Phys. 96, 5548 (2004); http://dx.doi.org/10.1063/1.1803632 (4 pages) | Cited 3 times

Online Publication Date: 5 November 2004

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An atomic force microscopic method to study the incubation states of UV laser irradiated polymer samples is presented. Targets were illuminated by different number of pulses at 5.8 and 8.9 mJ∕cm2 fluences. The induced adhesive and morphological changes were investigated simultaneously by an atomic force microscope equipped with a pulsed force mode extension. Importantly, below 100 pulses morphological changes were not observable while significant changes in the adhesion were found as a result of the incubation at 8.9 mJ∕cm2 fluence. This method allows the imaging and detection of the whole laser modified area with nanometer resolution.
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82.35.Gh Polymers on surfaces; adhesion
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments

Biexcitonic effect on optical nutation in semiconductor quantum wires

Pranay K. Sen, Manish K. Bafna, and Saral K. Gupta

J. Appl. Phys. 96, 5552 (2004); http://dx.doi.org/10.1063/1.1794895 (5 pages) | Cited 3 times

Online Publication Date: 5 November 2004

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We have proposed a simplified theoretical model to examine the optical nutation in one-dimensional semiconductor quantum wires. We explored the role of excitons, biexcitons, and the effect of confinement in enhancing transient optical processes in such semiconductor nanostructures. We apply the time dependent perturbation technique to the coherent radiation-semiconductor interaction for a three-level system in the near band gap resonant excitation regime. We have incorporated the relaxation and dephasing mechanisms phenomenologically. The induced polarization is calculated theoretically and the role of biexciton density on the polarization is analyzed. Numerical estimations of refractive and absorptive optical nutation have been made for a GaAs∕AlxGa1−xAs quantum wire duly shined by femtosecond pulse Ti: sapphire laser. Our results agree qualitatively with available experimental observations.
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81.05.Ea III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Influence of Bi doping upon the phase change characteristics of Ge2Sb2Te5

K. Wang, D. Wamwangi, S. Ziegler, C. Steimer, and M. Wuttig

J. Appl. Phys. 96, 5557 (2004); http://dx.doi.org/10.1063/1.1803612 (6 pages) | Cited 32 times

Online Publication Date: 5 November 2004

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The influence of Bi doping upon the phase change characteristics of Ge2Sb2Te5 alloys has been investigated using four-point-probe electrical resistance measurements, grazing incidence x-ray diffraction (XRD), x-ray reflectometry (XRR) and variable incident angle spectroscopic ellipsometry, a static tester and atomic force microscopy. For a Ge2Sb2Te5 alloy doped with 3% Bi, two transition temperatures are observed in the temperature dependent sheet resistance measurements at 136 °C and 236 °C, respectively. The evolution of structures upon annealing, investigated by XRD, reveals that the first transition is caused by the crystallization of the amorphous film to a NaCl-type structure, while the second transition is related to the transition to a hexagonal structure. The density values of 5.87±0.05 g cm−3, 6.33±0.05 g cm−3, and 6.41±0.05 g cm−3 are measured by XRR for the film in the amorphous, NaCl-type, and hexagonal structure, respectively. Ultrafast crystallization, which is correlated with a single NaCl-structure phase and the reduced activation barrier, is demonstrated. Sufficient optical contrast is exhibited and can be correlated with the density change upon crystallization.
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81.05.Gc Amorphous semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
64.70.D- Solid-liquid transitions
61.72.S- Impurities in crystals
73.61.Jc Amorphous semiconductors; glasses
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
78.66.Jg Amorphous semiconductors; glasses
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics
68.37.Ps Atomic force microscopy (AFM)
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