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15 Apr 2009

Volume 105, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 105, 081101 (2009); http://dx.doi.org/10.1063/1.3091395 (20 pages)

N. G. Rudawski, K. S. Jones, S. Morarka, M. E. Law, and R. G. Elliman
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Stressed multidirectional solid-phase epitaxial growth of Si

N. G. Rudawski, K. S. Jones, S. Morarka, M. E. Law, and R. G. Elliman

J. Appl. Phys. 105, 081101 (2009); http://dx.doi.org/10.1063/1.3091395 (20 pages) | Cited 10 times

Online Publication Date: 27 April 2009

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The study of the solid-phase epitaxial growth (SPEG) process of Si (variously referred to as solid-phase epitaxy, solid-phase epitaxial regrowth, solid-phase epitaxial crystallization, and solid-phase epitaxial recrystallization) amorphized via ion implantation has been a topic of fundamental and technological importance for several decades. Overwhelmingly, SPEG has been studied (and viewed) as a single-directional process where an advancing growth front between amorphous and crystalline Si phases only has one specific crystallographic orientation. However, as it pertains to device processing, SPEG must actually be considered as multidirectional (or patterned) rather than bulk in nature with the evolving growth interface having multiple crystallographic orientations. Moreover, due to the increasingly ubiquitous nature of stresses presented during typical Si-based device fabrication, there is great interest in specifically studying the stressed-SPEG process. This work reviews the progress made in understanding the multidirectional SPEG and, more importantly, stressed multidirectional SPEG process. For the work reviewed herein, (001) Si wafers with 〈110〉-aligned, intrinsically stressed Si3N4/SiO2 patterning consisting of square and line structures were used with unmasked regions of the Si substrate amorphized via ion implantation. It is revealed that the stresses generated in the Si substrate from the patterning, both in line and square structures, alter the kinetics and geometry of the multidirectional SPEG process and can influence the formation of mask-edge defects which form during growth to different degrees as per differences in the substrate stresses generated by each type of patterning. Likewise, it is shown that application of external stress from wafer bending during SPEG in specimens with and without patterning can also influence the geometry of the evolving growth interface. Finally, the effect of the addition of SPEG-enhancing impurities during multidirectional stressed growth is observed to alter the evolution of the growth interface, thus suggesting that stress influences on growth are much less than those from dopants. Within the context of prior work, attempts are made to correlate the prior observations in single-directional stressed SPEG with the observations from patterned stressed SPEG reviewed herein. However, as is argued in this review, it ultimately appears that much of the research performed on understanding the single-directional stressed-SPEG process cannot be reasonably extended to the multidirectional stressed-SPEG process.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.ag Semiconductors
64.70.kg Semiconductors
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Comparison of the x-ray spectroscopy response and charge transport properties of semi-insulating In/Al doped CdZnTe crystals

Y. Xu, P. J. Sellin, A. Lohstroh, W. Jie, T. Wang, C. Mills, P. Veeramani, and M. Veale

J. Appl. Phys. 105, 083101 (2009); http://dx.doi.org/10.1063/1.3097301 (6 pages)

Online Publication Date: 16 April 2009

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The x-ray spectroscopy performance of In/Al doped CdZnTe planar detectors based on as-grown crystals were investigated at room temperature, using a Tb x-ray source with a principle energy of 44.2 keV. The observed broadening in the photopeak resolution was attributed to incomplete charge carrier collection due to carrier trapping and scattering by the defects in the crystal. Alpha particle spectroscopy and pulse shape rise time analysis were used to measure the electron mobility lifetime product (μτ), as well as the mobility (μ) of the CdZnTe material grown with different dopant concentrations. To further clarify the role of the dopant and associated trapping states, temperature dependent alpha particle spectroscopy and pulse shapes were investigated at various applied bias fields over a temperature range from 200 to 300 K. CdZnTe doped with 1.5 ppm In exhibits excellent x-ray spectral resolution and charge transport properties, which implies a lower density of trapping centers in the crystal. The deep levels associated with Cdi2+ have been tentatively recognized as electron trapping centers and this is confirmed by the observed reduction in electron lifetime in CdZnTe crystal with 15 ppm In. Additionally, a shallower electron detrapping defect, with an activation energy of 0.14±0.02 eV, was also discovered to be simultaneously present in the crystal. In 30 ppm Al doped CdZnTe, however, the carrier mobility was significantly degraded due to scattering of the ionized centers attributed to the aluminum interstitial Ali.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.jj Interstitials
78.70.-g Interactions of particles and radiation with matter
61.72.uj III-V and II-VI semiconductors

Polaron dynamics in lithium niobate upon femtosecond pulse irradiation: Influence of magnesium doping and stoichiometry control

Satoru Sasamoto, Junji Hirohashi, and Satoshi Ashihara

J. Appl. Phys. 105, 083102 (2009); http://dx.doi.org/10.1063/1.3095763 (6 pages) | Cited 3 times

Online Publication Date: 16 April 2009

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The formation and relaxation dynamics of electron polarons in lithium niobate crystals were investigated by measuring transient absorption induced by blue femtosecond pulses. Anisotropy in the absorption change distinguished between small free polarons and small bound polarons, revealing that the dynamics were influenced by MgO doping and stoichiometry control. In crystals doped with MgO at concentrations above threshold, small free polarons were generated within 100 fs and decayed after tens of nanoseconds. In the presence of antisite defects, sequential formation of polaronic states occurred: electrons initially trapped as small free polarons became trapped as small bound polarons on picosecond time scale. The results are relevant for nonlinear optical applications of pulsed or high-power lasers.
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71.38.-k Polarons and electron-phonon interactions
61.72.up Other materials
61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys

Self-organized regular arrays of carbon nanocones induced by ultrashort laser pulses and their field emission properties

Q. Z. Zhao, F. Ciobanu, and L. J. Wang

J. Appl. Phys. 105, 083103 (2009); http://dx.doi.org/10.1063/1.3097391 (4 pages) | Cited 2 times

Online Publication Date: 17 April 2009

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Periodic, self-organized carbon nanocone structures with a spatial period of up to 170 nm (less than 1/5 laser wavelength) are induced by exposing a graphite surface to a single beam 800 nm ultrashort pulsed laser. When a linearly polarized laser beam is used, the nanocones are aligned perpendicularly to the direction of polarization. This paper also demonstrates the fabrication of large-area carbon nanocone structures. The resulting carbon nanocones show a field emission performance with a turn-on electric field of as low as 3.2 V/μm.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
79.70.+q Field emission, ionization, evaporation, and desorption
79.20.Ds Laser-beam impact phenomena
61.46.-w Structure of nanoscale materials

Optical absorption and emission of fully conjugated heterocyclic aromatic rigid-rod polyelectrolytes containing sulfonated pendants

Shih Jung Bai and Shen-Rong Han

J. Appl. Phys. 105, 083104 (2009); http://dx.doi.org/10.1063/1.3079516 (5 pages)

Online Publication Date: 20 April 2009

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Fully conjugated and rodlike poly[(1,7-dihydrobenzo[1,2-math:4,5-d′]diimidazole-2,6-diyl)-2-(2-sulfo)-p-phenylene] (sPBI) was synthesized and fabricated for monolayer light emitting diodes showing a threshold voltage of 4.5 V and an emission λmax of 530 nm. Intractable sPBI was derivatized for a fully conjugated water soluble rigid-rod polyelectrolyte sPBI-PS(Li+) which was doped with LiCF3SO3 or LiN(CF3SO2)2 for optical absorption, electrical conductivity, and luminescent emission. sPBI-PS(Li+) light emitting electrochemical cells doped with 0.41 and 1.01 wt % of LiN(CF3SO2)2 showed a threshold voltage of 2.8 V and a tenfold increase in electroluminescence intensity (at λmax = 514 nm) which did not increase with its conductivity.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
82.45.Wx Polymers and organic materials in electrochemistry
82.45.Gj Electrolytes
78.55.Kz Solid organic materials
66.30.hk Polymers

Upconversion properties of Tb3+–Yb3+ codoped fluorophosphate glasses

Yusuke Arai, Tatsuya Yamashidta, Takenobu Suzuki, and Yasutake Ohishi

J. Appl. Phys. 105, 083105 (2009); http://dx.doi.org/10.1063/1.3112010 (6 pages) | Cited 3 times

Online Publication Date: 22 April 2009

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Tb3+–Yb3+ codoped fluorophosphate glasses were synthesized and properties of the visible emission at 0.54 μm were investigated. The upconversion excitation efficiency from Yb3+ to Tb3+ was studied by evaluation of the cooperative energy transfer efficiency from Yb3+ to Tb3+ (ηCET) and the back-transfer efficiency from Tb3+ to Yb3+(ηBT), which gave a positive and negative contribution to upconversion excitation, respectively. The ηCET was as high as 30% and the ηBT was less than 1% in the fluorophosphate glass. This indicates that Tb3+–Yb3+ codoped fluorophosphate glass is promising as laser and gain medium in the 0.54 μm band.
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78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
42.70.Hj Laser materials

Feasibility study of high-resolution coherent diffraction microscopy using synchrotron x rays focused by Kirkpatrick–Baez mirrors

Yukio Takahashi, Yoshinori Nishino, Hidekazu Mimura, Ryosuke Tsutsumi, Hideto Kubo, Tetsuya Ishikawa, and Kazuto Yamauchi

J. Appl. Phys. 105, 083106 (2009); http://dx.doi.org/10.1063/1.3108997 (5 pages) | Cited 2 times

Online Publication Date: 23 April 2009

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High-flux coherent x rays are necessary for the improvement of the spatial resolution in coherent x-ray diffraction microscopy (CXDM). In this study, high-resolution CXDM using Kirkpatrick–Baez (KB) mirrors is proposed, and the mirrors are designed for experiments of the transmission scheme at SPring-8. Both the photon density and spatial coherence of synchrotron x rays focused by the KB mirrors are investigated by wave optical simulation. The KB mirrors can produce nearly diffraction-limited two-dimensional focusing x rays of ∼ 1 μm in size at 8 keV. When the sample size is less than ∼ 1 μm, the sample can be illuminated with full coherent x rays by adjusting the cross-slit size set between the source and the mirrors. From the estimated photon density at the sample position, the feasibility of CXDM with a sub-1‐nm spatial resolution is suggested. The present ultraprecise figuring process enables us to fabricate mirrors for carrying out high-resolution CXDM experiments.
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07.85.Tt X-ray microscopes

Analysis and optimisation of microcrystalline silicon solar cells with periodic sinusoidal textured interfaces by two-dimensional optical simulations

Andrej Čampa, Janez Krč, and Marko Topič

J. Appl. Phys. 105, 083107 (2009); http://dx.doi.org/10.1063/1.3115408 (5 pages) | Cited 10 times

Online Publication Date: 23 April 2009

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Two-dimensional optical model for simulation of thin-film solar cells with periodical textured interfaces is presented. The model is based on finite element method and uses triangular discrete elements for the structure description. The advantages of the model in comparison to other existing models are highlighted. After validation and verification of the developed simulator, simulations of a microcrystalline silicon solar cell with a sinusoidal grating texture applied to the interfaces are carried out. The analysis and optimization of the two grating parameters—period and height of the grooves—are performed with respect to the maximal short-circuit current density of the cell. Up to 45% increase in the current density is identified for the optimized structure, compared to that of the cell with flat interfaces. Optical losses in the periodically textured silver back reflector are determined.
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84.60.Jt Photoelectric conversion
02.60.Pn Numerical optimization
02.70.Dh Finite-element and Galerkin methods

Surface layer magneto-optical effect on one-dimensional magneto-photonic crystal

Reina Nishino and Shigeki Yamada

J. Appl. Phys. 105, 083108 (2009); http://dx.doi.org/10.1063/1.3115462 (5 pages) | Cited 1 time

Online Publication Date: 23 April 2009

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Surface-layer magneto-optical effects of propagating and reflected light were calculated for photonic crystals of magnetic materials using a finite-difference time-domain algorithm. The magneto-optical effect of the reflected light on the photonic band-gap range strongly depended on the dielectric constant of the surface layer, although no such surface effect was observed near the first photonic band edge. When the dielectric constant of the surface layer was low, the polarization rotation angle of the reflected light increased with the frequency of the light, and reached a maximum value just below the second photonic band. This frequency dependence should be associated with the group delay time of the reflected light, and thus the large delay time just below the second photonic band should be caused by the localization mode in the surface layer. Due to the localized surface mode, the influence of the absorption of the medium on the polarization rotation angle strongly depends on the dielectric constant of the surface layer.
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42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects
77.22.Ch Permittivity (dielectric function)

Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms

H. Hagman, P. Sjölund, S. J. H. Petra, M. Nylén, A. Kastberg, H. Ellmann, and J. Jersblad

J. Appl. Phys. 105, 083109 (2009); http://dx.doi.org/10.1063/1.3097466 (9 pages) | Cited 1 time

Online Publication Date: 24 April 2009

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A low noise time-of-flight detection system for laser cooled atoms has been constructed and incrementally optimized. Here, a thorough description of the construction is presented along with an analysis of the capabilities of the system. The quality of the detection (the resolution, the reproducibility, the sensitivity, etc.) is crucial for, e.g., the ability to see details in the velocity distribution profile, which is of interest for fundamental studies of statistical physics and of the laser cooling processes, and for detection of small initial velocities of an atomic cloud, important, e.g., when studying small drifts induced by Brownian motors and ratchets. We estimate the signal-to-noise ratio of our signal to be better than 1000:1 for a typical single shot, and we discuss the effect of the initial atomic cloud size, the probe size, and the effects of the wave packet spread during the fall time on the measured quantities. We show that the shape of the velocity distribution is well conserved during the mapping done in the detection, i.e., in the convolution with the probe beam, and that velocities as small as a few percent of the single photon recoil velocity can be resolved.
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37.10.De Atom cooling methods
32.80.-t Photoionization and excitation

Ultrafast photovoltaic effects in miscut Nb-doped SrTiO3 single crystals

Na Zhou, Kun Zhao, Hao Liu, Zhiqing Lu, Hui Zhao, Lu Tian, Wenwei Liu, and Songqing Zhao

J. Appl. Phys. 105, 083110 (2009); http://dx.doi.org/10.1063/1.3116555 (3 pages) | Cited 4 times

Online Publication Date: 27 April 2009

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Picosecond photovoltaic effect in miscut Nb-doped SrTiO3 single crystal has been observed under ultraviolet pulsed laser irradiation at ambient temperature without an applied bias. The 10%–90% rise time and the full width at half maximum are 828 and 670 ps, respectively, which is faster than that of exact cut Nb-doped SrTiO3 single crystal. A model based on terrace structure is put forward to explain the observation.
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72.40.+w Photoconduction and photovoltaic effects
78.47.J- Ultrafast spectroscopy (<1 psec)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Strongly subluminal regime of optical-to-terahertz conversion in GaP

M. I. Bakunov, M. V. Tsarev, S. B. Bodrov, and M. Tani

J. Appl. Phys. 105, 083111 (2009); http://dx.doi.org/10.1063/1.3110064 (9 pages) | Cited 1 time

Online Publication Date: 27 April 2009

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We introduce and investigate a special regime of terahertz generation in electro-optic crystals with ultrashort laser pulses, in which neither phase-matching nor Cherenkov radiation mechanism are efficient. This regime occurs under the conditions that the optical group refractive index is larger than the low-frequency phase refractive index of the crystal, and the spectral bandwidth of the laser pulse is smaller than the frequency of the phase-matched terahertz wave. In this regime, that can be realized for a Ti:sapphire laser in GaP, terahertz generation is provided by transient processes at the crystal boundaries. We study the peculiarities of the terahertz emission from a slab of GaP excited with a Ti:sapphire laser. In particular, we demonstrate a possibility to implement a pointlike source of terahertz radiation that can increase the resolution of terahertz apertureless near-field microscopy.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Excitation resolved color conversion of CdSe/ZnS core/shell quantum dot solids for hybrid white light emitting diodes

Sedat Nizamoglu and Hilmi Volkan Demir

J. Appl. Phys. 105, 083112 (2009); http://dx.doi.org/10.1063/1.3109151 (5 pages) | Cited 5 times

Online Publication Date: 28 April 2009

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In this paper, for their use as nanoluminophors on color-conversion white light emitting diodes (LEDs), we present spectrally resolved relative quantum efficiency and relative color (photon) conversion efficiency of CdSe/ZnS core/shell nanocrystal (NC) emitters in the solid-state film. We observe that both the averaged relative quantum efficiency and the averaged relative photon conversion efficiency of these NC solids increase with the increasing photon pump energy. Therefore, the excitation LED platform emitting at shorter wavelengths facilitates such NC luminophor solids to be more efficiently pumped optically. Furthermore, we investigate the spectral time-resolved spectroscopy of NCs in solution and in film with 0.4–2.4 nmol integrated number of NCs in the spectral range of 610–660 nm. We observe that the average lifetime of NCs increases toward longer wavelengths as the number of in-film NCs increases. With the increased amount of NCs, the average lifetime increases even further and the emission of NCs is shifted further toward red. This is attributed to the enhanced nonradiative energy transfer between these NCs due to the inhomogeneous size distribution. Thus, in principle, for fine tuning of the collective color of NCs for color-conversion LEDs, it is important to control the energy transfer by changing the integrated number of NCs.
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78.67.Hc Quantum dots
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.65.Hb Quantum dots (patterned in quantum wells)
85.60.Jb Light-emitting devices
78.55.Et II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Efficient Nd3+→Yb3+ energy transfer in Nd3+,Yb3+:Gd3Ga5O12 multicenter garnet crystal

Zhitai Jia, Andrea Arcangeli, Xutang Tao, Jian Zhang, Chunming Dong, Minhua Jiang, Lucia Bonelli, and Mauro Tonelli

J. Appl. Phys. 105, 083113 (2009); http://dx.doi.org/10.1063/1.3115442 (6 pages) | Cited 8 times

Online Publication Date: 28 April 2009

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For seeking better laser crystals with good optical properties and high efficiency, especially for application in a high power solid-state laser, Yb3+,Nd3+:Gd3Ga5O12 crystal (abbreviated as Yb,Nd:GGG below) was grown by Czochralski method. A complete optical characterization was reported including absorption and emission spectra at different temperatures and fluorescence lifetimes. Very efficient Nd3+ 4F3/2→Yb3+ 2F5/2 energy transfer was found whereas the back transfer was completely quenched at low temperature (T<200 K). From the data of Nd3+ fluorescence lifetime and emission spectrum we achieved the energy-transfer efficiency as large as 94% at 77 K and 84% at 300 K, respectively. After fitting the decay curve we got the energy-transfer microparameter with a value of 2.1×10−39 cm6 s−1 at 300 K.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
78.55.Hx Other solid inorganic materials
81.10.Fq Growth from melts; zone melting and refining
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
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Terrestrial gamma-ray flashes caused by neutron bursts above thunderclouds

G. S. Paiva

J. Appl. Phys. 105, 083301 (2009); http://dx.doi.org/10.1063/1.3089230 (4 pages) | Cited 1 time

Online Publication Date: 17 April 2009

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In this work, it is suggested that upward pulses of fast neutrons, which are produced by energetic intracloud lightning, will form terrestrial gamma-ray flashes (TGFs) through neutron inelastic scattering by atoms in the atmosphere. About 1015 fast neutrons produce gamma-ray photons that compose the TGF pulse in altitude of about 20 km, in good agreement with the altitude of TGF source estimated by Dwyer and Smith [Geophys. Res. Lett. 32, L22804 (2005) ].
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92.60.Qx Storms
92.60.Pw Atmospheric electricity, lightning
92.60.H- Atmospheric composition, structure, and properties
92.60.Nv Cloud physics and chemistry
92.60.Vb Radiative processes, solar radiation

Laser ablation of metallic targets with high fluences: Self-consistent approach

Madhusudhan Kundrapu and Michael Keidar

J. Appl. Phys. 105, 083302 (2009); http://dx.doi.org/10.1063/1.3098198 (9 pages)

Online Publication Date: 17 April 2009

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Ablation of metallic target using Gaussian profile laser pulse with duration of 30 ns and fluence extending up to 100 J/cm2 is studied. A self-consistent model that involves numerical simulation to obtain the thickness of a hydrodynamic layer is proposed. The influence of the hydrodynamic layer thickness on Knudsen layer properties, and hence the rate of evaporation, is demonstrated. Self-consistent model is compared with model based on assumption about sonic speed at the Knudsen layer outer edge and validated with experimental results for Al alloy and Cu. Finally, sample calculations are performed using the proposed model to obtain depth of evaporation of Al alloy for single pulse duration.
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79.20.Ds Laser-beam impact phenomena
64.70.fm Thermodynamics studies of evaporation and condensation
42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Tailoring carbon nanotips in the plasma-assisted chemical vapor deposition: Effect of the process parameters

B. B. Wang and K. Ostrikov

J. Appl. Phys. 105, 083303 (2009); http://dx.doi.org/10.1063/1.3112025 (9 pages) | Cited 4 times

Online Publication Date: 20 April 2009

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Carbon nanotips have been synthesized from a thin carbon film deposited on silicon by bias-enhanced hot filament chemical vapor deposition under different process parameters. The results of scanning electron microscopy indicate that high-quality carbon nanotips can only be obtained under conditions when the ion flux is effectively drawn from the plasma sustained in a CH4+NH3+H2 gas mixture. It is shown that the morphology of the carbon nanotips can be controlled by varying the process parameters such as the applied bias, gas pressure, and the NH3/H2 mass flow ratios. The nanotip formation process is examined through a model that accounts for surface diffusion, in addition to sputtering and deposition processes included in the existing models. This model makes it possible to explain the major difference in the morphologies of the carbon nanotips formed without and with the aid of the plasma as well as to interpret the changes of their aspect ratio caused by the variation in the ion/gas fluxes. Viable ways to optimize the plasma-based process parameters to synthesize high-quality carbon nanotips are suggested. The results are relevant to the development of advanced plasma-/ion-assisted methods of nanoscale synthesis and processing.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Cd Deposition by sputtering
68.35.Fx Diffusion; interface formation
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Deposition of silicon dioxide films using an atmospheric pressure microplasma jet

V. Raballand, J. Benedikt, S. Hoffmann, M. Zimmermann, and A. von Keudell

J. Appl. Phys. 105, 083304 (2009); http://dx.doi.org/10.1063/1.3108541 (6 pages) | Cited 16 times

Online Publication Date: 21 April 2009

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Organic and inorganic silicon dioxide films have been deposited by means of an atmospheric pressure microplasma jet. Tetramethylsilane (TMS), oxygen, and hexamethyldisiloxane (HMDSO) are injected into argon as plasma forming gases. In the case of TMS injection, inorganic films are deposited if an admixture of oxygen is used. In the case of HMDSO injection, inorganic films can be deposited at room temperature even without any oxygen admixture: at low HMDSO flow rates [<0.1 SCCM (SCCM denotes cubic centimeters per minute at STP),<32 ppm], the SiOxHz films contain no carbon and exhibit oxygen-to-silicon ratio close to 2 according to x-ray photoelectron spectroscopy. At high HMDSO flow rates (>0.1 SCCM,>32 ppm), SiOxCyHz with up to 21% of carbon are obtained. The transition from organic to inorganic film is confirmed by Fourier transform infrared spectroscopy. The deposition of inorganic SiO2 films from HMDSO without any oxygen admixture is explained by an ion-induced polymerization scheme of HMDSO.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.at Other materials
79.60.Dp Adsorbed layers and thin films
52.77.Dq Plasma-based ion implantation and deposition
82.35.-x Polymers: properties; reactions; polymerization
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Synthesis of ultrathin carbon films by direct current filtered cathodic vacuum arc

H.-S. Zhang and K. Komvopoulos

J. Appl. Phys. 105, 083305 (2009); http://dx.doi.org/10.1063/1.3098254 (7 pages) | Cited 24 times

Online Publication Date: 21 April 2009

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Filtered cathodic vacuum arc was used to synthesize ultrathin carbon films on silicon substrates. The depth profiles, near-surface chemical composition, fractions of tetrahedral (sp3) and trigonal (sp2) carbon atom hybridizations, roughness, and hardness of the carbon films were determined from Monte Carlo (T-DYN) simulations and x-ray reflectivity (XRR), x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surface force microscopy (SFM) measurements, respectively. Films of thickness of only a few nanometers possessed smaller sp3 fractions than much thicker films. The effective hardness was found to depend on the sp3 fraction and silicon-carbon composition profile. The formation of different carbon atom bonds, film growth mechanisms, and optimum process conditions for synthesizing ultrathin carbon films are interpreted in the context of T-DYN, XRR, XPS, AFM, and SFM results and surface bombardment, adsorption, and diffusion mechanisms.
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81.05.U- Carbon/carbon-based materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.at Other materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
68.60.Bs Mechanical and acoustical properties

Fluid simulation of the E-H mode transition in inductively coupled plasma

Shu-Xia Zhao, Xiang Xu, Xue-Chun Li, and You-Nian Wang

J. Appl. Phys. 105, 083306 (2009); http://dx.doi.org/10.1063/1.3112009 (10 pages) | Cited 4 times

Online Publication Date: 21 April 2009

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One self-consistent method combined with the electromagnetic theory and fluid model is developed to investigate the E-H mode transition of argon inductively coupled plasma (ICP) by adjusting the external electric parameters of the reactor. ICP dynamic characteristics of radial and axial space are also studied when E and H modes coexist. By regulating the radio-frequency current in the coil and voltage across the powered end of the coil and the ground, the E-H mode transition is observed, accompanied by the substantial variations in the electromagnetic field and plasma parameters (density, temperature, and deposited power). Besides, the evolution characteristics of ICP are examined when the discharge mechanism transforms from an E-mode dominated to an H-mode dominated.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.-y Plasma simulation
52.25.-b Plasma properties
52.80.-s Electric discharges

S-band relativistic magnetron operation with an active plasma cathode

Y. Hadas, A. Sayapin, T. Kweller, and Ya. E. Krasik

J. Appl. Phys. 105, 083307 (2009); http://dx.doi.org/10.1063/1.3108590 (7 pages) | Cited 3 times

Online Publication Date: 22 April 2009

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Results of experimental research on a relativistic S-band magnetron with a ferroelectric plasma source as a cathode are presented. The cathode plasma was generated using a driving pulse ( ∼ 3 kV, 200 ns) applied to the ferroelectric cathode electrodes via inductive decoupling prior to the beginning of an accelerating pulse (200 kV, 150 ns) delivered by a linear induction accelerator. The magnetron and generated microwave radiation parameters obtained for the ferroelectric plasma cathode and the explosive emission plasma were compared. It was shown that the application of the ferroelectric plasma cathode allows one to avoid a time delay in the appearance of the electron emission to achieve a better matching between the magnetron and linear induction accelerator impedances and to increase significantly ( ∼ 30%) the duration of the microwave pulse with an ∼ 10% increase in the microwave power. The latter results in the microwave radiation generation being 30% more efficient than when the explosive emission cathode is used, where efficiency does not exceed 20%.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
52.50.Dg Plasma sources

Efficient high-harmonic radiations by chirped laser-pulse interactions with electrons in the presence of a magnetic field

Devki Nandan Gupta and Hyyong Suk

J. Appl. Phys. 105, 083308 (2009); http://dx.doi.org/10.1063/1.3106143 (4 pages) | Cited 1 time

Online Publication Date: 24 April 2009

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We present numerical investigations for high-order harmonic generations by a high-intensity chirped-laser interaction with vacuum electrons in the presence of an axial static magnetic field. Combined role of frequency chirp of the laser and a magnetic field enhances the electron acceleration and leads electron energy gain after passing of the laser pulse that generates high-harmonic radiations until the magnetic field diminishes. The result shows that high-harmonic radiations in the range of soft x-rays up to about 10 nm can be generated with common experimental parameters by the proposed scheme of this paper.
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34.80.Qb Laser-modified scattering
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Spectroscopic analysis of the excitation transfer from background air to diffusing aluminum laser produced plasma

M. Ribière, D. Karabourniotis, and B. G. Chéron

J. Appl. Phys. 105, 083309 (2009); http://dx.doi.org/10.1063/1.3116186 (7 pages) | Cited 2 times

Online Publication Date: 24 April 2009

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During the relaxation of the plasma plume generated by laser ablation of an aluminum target, a pronounced intensity enhancement is observed at the central wavelength of the 396.15 nm self-reversed resonant line. This spectral special feature is analyzed and related to the interaction of the plasma edge with the background air excited by the shockwave, prompt electrons, and extreme ultraviolet radiation produced at the earliest times of the ablation. In this article, the electron density, the aluminum ground state, and resonant level populations are determined from the fitting of the 396.15 nm calculated line profile to the experimental one at two background pressures (100 and 1000 Pa). The evolution of these densities is derived from experiments performed at delays, after the laser pulse arrival, ranging from 120 to 180 ns.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Tc Shock waves and discontinuities
52.40.Hf Plasma-material interactions; boundary layer effects

Theoretical investigation of the fundamental mode frequency of A6 magnetron

Yu-Wei Fan, Jing Liu, Hui-Huang Zhong, Ting Shu, and Zhi-Qiang Li

J. Appl. Phys. 105, 083310 (2009); http://dx.doi.org/10.1063/1.3116202 (5 pages) | Cited 2 times

Online Publication Date: 24 April 2009

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The fundamental mode frequency of A6 magnetron is investigated theoretically by the equivalent circuit method, and an exact theoretical formula as a function of structure dimensions is derived. The theoretical results are compared with the simulation and experimental results, and the relative errors, which are calculated according to the theoretical and simulation or experimental frequencies, are less than 3%. So the validity of the theoretical formula is verified. In addition, this approach can also be used in other configurations but some changes need to be made in the formula according to the specific structures.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Reducing current loss of laser-driven fast electron beams propagating in solid-density plasmas

C. T. Zhou, X. T. He, J. M. Cao, X. G. Wang, and S. Z. Wu

J. Appl. Phys. 105, 083311 (2009); http://dx.doi.org/10.1063/1.3116728 (7 pages) | Cited 1 time

Online Publication Date: 27 April 2009

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A scheme to reduce the current loss of laser-driven energetic electron beams propagating in solid-density targets is proposed. In the scheme, two intense laser pulses irradiate the solid target consisting of two materials, one enveloping the other. Because of the resistivity and density gradients at the material interface, the first pulse generates tens of megagauss robust interface magnetic fields that can considerably reduce the divergence of the electron beam generated by the second pulse. It is shown that by using a coaxial gold-aluminum target instead of a simple gold target, beam current loss can be lowered by about 30%.
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52.40.Mj Particle beam interactions in plasmas
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