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15 Apr 2006

Volume 99, Issue 8, Articles (08xxxx)

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Efficiency of silicon micromachining by femtosecond laser pulses in ambient air

David J. Hwang, Costas P. Grigoropoulos, and Tae Y. Choi

J. Appl. Phys. 99, 083101 (2006); http://dx.doi.org/10.1063/1.2187196 (6 pages) | Cited 11 times

Online Publication Date: 19 April 2006

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Femtosecond lasers have proven to be effective tools for precise micromachining. Taking advantage of the reduced heat diffusion and the sharp ablation threshold at comparatively low energy densities, subdiffraction limit sized craters have been machined on silicon wafers by single near infrared Ti:sapphire laser pulses using a high numerical aperture objective lens. Two different ablation regimes have been identified by varying the laser fluence. While two-photon absorption dominates in the low fluence regime, electronic diffusion is a major energy transport mechanism at higher laser fluences. Time-resolved pump-and-probe side-view imaging has been performed to investigate the energy coupling to the target specimen over a wide range of fluences (up to around 1000 J/cm2) at lateral beam dimensions of the order of micrometers. The decrease of the ablation efficiency in the high fluence regime (>10 J/cm2) is attributed to the strong interaction of the laser pulse with the laser-induced plasma.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.62.Cf Industrial applications
81.20.Wk Machining, milling
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Resonant modes in continuous metallic grids over ground and related spatial-filtering applications

Omar F. Siddiqui and George V. Eleftheriades

J. Appl. Phys. 99, 083102 (2006); http://dx.doi.org/10.1063/1.2189929 (8 pages) | Cited 4 times

Online Publication Date: 26 April 2006

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We use the theory of periodic structures, full-wave electromagnetic, and microwave circuit simulations to explain the resonant modes that propagate in metallic grids having rectangular unit cells constructed over a ground plane. We show that these metallic grids can support two types of resonant modes that have rectangular and hyperbolic isofrequency dispersion contours. By exploiting the spatial dispersion properties of these modes, a microwave 3 GHz/6 GHz harmonic splitter and a highly selective 5.8 GHz/6.2 GHz diplexer are designed and simulated. Furthermore, we provide experimental results for the diplexer and for the harmonic splitter, synthesized in microstrip technology. The proposed metallic grids utilize continuous unloaded transmission-line segments thus leading to spatial-filtering devices that are easy to fabricate and are scalable to terahertz frequencies and beyond.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Fm Reflectors, beam splitters, and deflectors
84.40.Dc Microwave circuits
84.40.Az Waveguides, transmission lines, striplines

Fabrication and characterization of erbium-doped toroidal microcavity lasers

J. Kalkman, A. Tchebotareva, A. Polman, T. J. Kippenberg, B. Min, and K. J. Vahala

J. Appl. Phys. 99, 083103 (2006); http://dx.doi.org/10.1063/1.2188050 (9 pages) | Cited 10 times

Online Publication Date: 27 April 2006

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Erbium-doped SiO2 toroidal microcavity lasers are fabricated on a Si substrate using a combination of optical lithography, etching, Er ion implantation, and CO2 laser reflow. Erbium is either preimplanted in the SiO2 base material or postimplanted into a fully fabricated microtoroid. Three-dimensional infrared confocal photoluminescence spectroscopy imaging is used to determine the spatial distribution of optically active Er ions in the two types of microtoroids, and distinct differences are found. Microprobe Rutherford backscattering spectrometry indicates that no macroscopic Er diffusion occurs during the laser reflow for preimplanted microtoroids. From the measured Er doping profiles and calculated optical mode distributions the overlap factor between the Er distribution and mode profile is calculated: Γ = 0.066 and Γ = 0.02 for postimplanted and preimplanted microtoroids, respectively. Single and multimode lasing around 1.5 μm is observed for both types of microtoroids, with the lowest lasing threshold (4.5 μW) observed for the preimplanted microtoroids, which possess the smallest mode volume. When excited in the proper geometry, a clear mode spectrum is observed superimposed on the Er spontaneous emission spectrum. This result indicates the coupling of Er ions to cavity modes.
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42.55.Sa Microcavity and microdisk lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
61.72.up Other materials
61.72.S- Impurities in crystals

Achieving a photonic band edge near visible wavelengths by metallic coatings

S. Y. Lin, D.-X. Ye, T.-M. Lu, J. Bur, Y. S. Kim, and K. M. Ho

J. Appl. Phys. 99, 083104 (2006); http://dx.doi.org/10.1063/1.2188049 (4 pages) | Cited 7 times

Online Publication Date: 1 May 2006

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A metallic coating method is used to modify the optical properties of a dielectric photonic lattice and to achieve a near visible photonic band edge. It is experimentally shown that the linear scaling rule of a metallic band edge versus lattice constant holds only for perfect conducting metals. When a metal deviates from a perfect conducting behavior near the plasma wavelength, the metallic photonic band edge is pinned and is nearly independent of lattice constant. For our tungsten photonic lattice, the pinning occurs at λ ≈ 1.5–2 μm. By using a thin copper coating ( ∼ 70 nm) to a dielectric photonic lattice, a photonic band edge at λ ∼ 750 nm is observed. This achievement is made possible by the fact that copper is a good conductor at visible wavelengths and the linear scaling rule holds. Finally, this coating method allows for tailoring photonic properties through material engineering at the nanometer scale.
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42.70.Qs Photonic bandgap materials
42.79.Wc Optical coatings

Effects of Si doping on normal incidence InAs/In0.15Ga0.85As dots-in-well quantum dot infrared photodetectors

R. S. Attaluri, S. Annamalai, K. T. Posani, A. Stintz, and S. Krishna

J. Appl. Phys. 99, 083105 (2006); http://dx.doi.org/10.1063/1.2189973 (3 pages) | Cited 6 times

Online Publication Date: 1 May 2006

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The effects of doping on InAs/In0.15Ga0.85As quantum dots-in-well infrared photodetectors have been studied by measuring the dark current, photocurrent, and spectral response. A significant reduction of dark current with decrease in doping concentration in the quantum dots has been observed. However, the photocurrent of the detectors increases with the doping. By measuring the background limited infrared photodetector temperature, we find that the optimum sheet doping concentration in these detectors is n = 3×1010 cm−2 (corresponding to about one electron per dot).
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals

High-efficiency generation of both forward and backward optical phase conjugations in one-dimensional nonlinear photonic crystals

Ping Xie and Zhao-Qing Zhang

J. Appl. Phys. 99, 083106 (2006); http://dx.doi.org/10.1063/1.2191575 (6 pages)

Online Publication Date: 3 May 2006

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By using only one pump beam, we show theoretically that both forward and backward phase conjugations can be generated simultaneously and efficiently in one-dimensional χ(3)-nonlinear photonic crystals of only a few micrometers in size. The photonic crystal considered here is a CdS/SiO2 superlattice. By using realistic optical parameters in our calculations, we find that the phase-conjugate generation efficiency can be enhanced by four to five orders of magnitude as compared with that in a homogeneous CdS medium of the same nonlinearity and length. The enhancement is caused by multiple reflections as well as strong field localization introduced by the shifted band-edge state, the gap localized state, or the shifted defect state.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Qs Photonic bandgap materials
78.66.Hf II-VI semiconductors

Laser damage threshold studies on urea L-malic acid: A nonlinear optical crystal

S. Vanishri, H. L. Bhat, A. Deepthy, V. P. N. Nampoori, E. de Matos Gomes, and M. Belsley

J. Appl. Phys. 99, 083107 (2006); http://dx.doi.org/10.1063/1.2193164 (5 pages) | Cited 2 times

Online Publication Date: 3 May 2006

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A detailed study of surface laser damage performed on a nonlinear optical crystal, urea L-malic acid, using 7 ns laser pulses at 10 Hz repetition rate from a Q-switched Nd:YAG laser at wavelengths of 532 and 1064 nm is reported. The single shot and multiple shot surface laser damage threshold values are determined to be 26.64±0.19 and 20.60±0.36 GW cm−2 at 1064 nm and 18.44±0.31 and 7.52±0.22 GW cm−2 at 532 nm laser radiation, respectively. The laser damage anisotropy is consistent with the Vickers mechanical hardness measurement performed along three crystallographic directions. The Knoop polar plot also reflects the damage morphology. Our investigation reveals a direct correlation between the laser damage profile and hardness anisotropy. Thermal breakdown of the crystal is identified as the possible mechanism of laser induced surface damage.
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42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.47.-p Spectroscopy of solid state dynamics
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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Equivalent ion temperature in Ta plasma produced by high energy laser ablation

L. Torrisi, S. Gammino, L. Andó, L. Laska, J. Krasa, K. Rohlena, J. Ullschmied, J. Wolowski, J. Badziak, and P. Parys

J. Appl. Phys. 99, 083301 (2006); http://dx.doi.org/10.1063/1.2189932 (5 pages) | Cited 8 times

Online Publication Date: 17 April 2006

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High energy laser, 400 ps pulse duration, irradiating heavy targets in vacuum produce intense plasma and generate emission of various energetic ion groups. The ion intensity is high along the normal to the irradiated target surface and high charge state and high velocity ions are produced. The characteristics of the ion streams were investigated by using an electrostatic ion energy analyzer and different ion collectors were placed at various angles with respect to the target normal. The ion energy distribution as a function of the ion charge state was measured and the comparison of the properties of different ion groups generated by laser beams at two different energies was carried out. Measurements point out that five ion groups or more can be generated by the laser interaction with the preformed plasma, with different “equivalent ion temperatures.” Slow, thermal, fast, and very fast ions follow a Boltzmann-like distribution; the equivalent temperatures of different ion groups were estimated to reach values up to about 80 keV.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Tx Emission, absorption, and scattering of particles
52.38.Mf Laser ablation
52.70.Nc Particle measurements
52.25.Fi Transport properties

In situ simple method for measuring size and density of nanoparticles in reactive plasmas

Shota Nunomura, Makoto Kita, Kazunori Koga, Masaharu Shiratani, and Yukio Watanabe

J. Appl. Phys. 99, 083302 (2006); http://dx.doi.org/10.1063/1.2189951 (7 pages) | Cited 13 times

Online Publication Date: 25 April 2006

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A laser-light-scattering (LLS) method for measuring the size and density of nanoparticles generated in reactive plasmas has been developed. The size and density of the nanoparticles are determined from their thermal coagulation that takes place after turning off the discharge. The measurable size and density range of the LLS method is np⪆1013 (m−3/2)×dp−5/2L−2ng−1, where np, dp, L, and ng are the density, size, and diffusion length of the nanoparticles, and the density of a background gas, respectively. The method has been demonstrated by measurement of the size and density of nanoparticles formed by the radio-frequency discharge of dimethyldimethoxysilane Si(CH3)2(OCH3)2 diluted with Ar. Using a simple optical setup for the LLS measurement, nanoparticles are detected down to ≈ 1 nm in size when they are generated at a density of ≈ 1012 cm−3. The developed method is widely applicable to other systems in which thermal coagulation takes place.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges
52.77.-j Plasma applications
52.25.Tx Emission, absorption, and scattering of particles
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Ambient gas effects on the dynamics of laser-produced tin plume expansion

S. S. Harilal, Beau O’Shay, Yezheng Tao, and Mark S. Tillack

J. Appl. Phys. 99, 083303 (2006); http://dx.doi.org/10.1063/1.2188084 (10 pages) | Cited 25 times

Online Publication Date: 28 April 2006

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Controlling the debris from a laser-generated tin plume is one of the prime issues in the development of an extreme ultraviolet lithographic light source. An ambient gas that is transparent to 13.5 nm radiation can be used for controlling highly energetic particles from the tin plume. We employed a partial ambient argon pressure for decelerating various species in the tin plume. The kinetic energy distributions of tin species were analyzed at short and large distances using time and space resolved optical emission spectroscopy and a Faraday cup, respectively. A fast-gated intensified charged coupled device was used for understanding the hydrodynamics of the plume’s expansion into argon ambient. Our results indicate that the tin ions can be effectively mitigated with a partial argon pressure ∼ 65 mTorr. Apart from thermalization and deceleration of plume species, the addition of ambient gas leads to other events such as double peak formation in the temporal distributions and ambient plasma formation.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.30.-q Plasma dynamics and flow
42.72.Bj Visible and ultraviolet sources

Observation of electric field enhancement in a water streamer using Kerr effect

G. S. Sarkisov, N. D. Zameroski, and J. R. Woodworth

J. Appl. Phys. 99, 083304 (2006); http://dx.doi.org/10.1063/1.2189215 (6 pages)

Online Publication Date: 28 April 2006

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We report the observation of the Kerr effect in a streamer head in experiments with electrical breakdown of water. The propagation of the streamer in water is associated with localized enhancement of the electric field surrounding the streamer head. Polarizational measurements show that the electric field around the streamer head is estimated to be 1.7–2.2 MV/cm, which is approximately six times higher than the maximum interelectrode electric field of 0.37 MV/cm. Electrostatic simulations support the experimental data.
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52.80.Wq Discharge in liquids and solids
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements

Surface reactions during etching of organic low-k films by plasmas of N2 and H2

Kenji Ishikawa, Yoshikazu Yamaoka, Moritaka Nakamura, Yuichi Yamazaki, Satoshi Yamasaki, Yasushi Ishikawa, and Seiji Samukawa

J. Appl. Phys. 99, 083305 (2006); http://dx.doi.org/10.1063/1.2191567 (6 pages) | Cited 11 times

Online Publication Date: 3 May 2006

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Surface reactions during etching of organic low-k film by N2 and H2 plasmas were studied through observations of the surface resident species using in situ infrared spectroscopy and in vacuo electron-spin-resonance techniques. We observed surface modifications by the formation of CN and NH bonds after exposure to plasmas generated from N2 and H2. The number of carbon dangling bonds were greater in processes where H2 was present. The passivation of carbon dangling bonds leads to CH3, NH3, and CN functionalities, which are the precursors for etching products that are desorbed, which includes volatile forms such as HCN and C2N2.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
77.55.-g Dielectric thin films
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Generation of ion-acoustic waves in an inductively coupled, low-pressure discharge lamp

J. C. Camparo and C. M. Klimcak

J. Appl. Phys. 99, 083306 (2006); http://dx.doi.org/10.1063/1.2191568 (7 pages) | Cited 4 times

Online Publication Date: 3 May 2006

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For a number of years it has been known that the alkali rf-discharge lamps used in atomic clocks can exhibit large amplitude intensity oscillations. These oscillations arise from ion-acoustic plasma waves and have typically been associated with erratic clock behavior. Though large amplitude ion-acoustic plasma waves are clearly deleterious for atomic clock operation, it does not follow that small amplitude oscillations have no utility. Here, we demonstrate two easily implemented methods for generating small amplitude ion-acoustic plasma waves in alkali rf-discharge lamps. Furthermore, we demonstrate that the frequency of these waves is proportional to the square root of the rf power driving the lamp and therefore that their examination can provide an easily accessible parameter for monitoring and controlling the lamp’s plasma conditions. This has important consequences for precise timekeeping, since the atomic ground-state hyperfine transition, which is the heart of the atomic clock signal, can be significantly perturbed by changes in the lamp’s output via the ac-Stark shift.
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52.35.Dm Sound waves
52.80.Pi High-frequency and RF discharges
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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Extended Mie-Grüneisen molecular model for time dependent dielectric breakdown in silica detailing the critical roles of O–SiO3 tetragonal bonding, stretched bonds, hole capture, and hydrogen release

J. W. McPherson

J. Appl. Phys. 99, 083501 (2006); http://dx.doi.org/10.1063/1.2189930 (13 pages) | Cited 9 times

Online Publication Date: 17 April 2006

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An extended Mie-Grüneisen molecular model is presented, which describes a bond-breakage process for O–SiO3 tetragonal molecules in silica and the trap-generation process that occurs during time dependent dielectric breakdown (TDDB) testing. This quantitative molecular model correctly describes important physics routinely reported for silica TDDB testing: the generation of E′ centers, a breakdown strength of Ebd ∼ 15 MV/cm, an effective dipole-moment range of peff = 7–13e Å, and a zero-field activation energy range for bond breakage of ΔHo* = 1−2 eV. The bond-breakage/trap-generation mechanism is shown to occur when the Si ion transitions from its primary energy minimum (with fourfold coordination) to a secondary saddle point (with threefold coordination). The molecular model also shows clearly that current induced hole capture and hydrogen release can play critically important roles in the TDDB process.
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77.22.Jp Dielectric breakdown and space-charge effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Spectroscopic assessment of Tm3+:GdAl3(BO3)4 crystal as a potential diode pumped laser near 1.9 μm

Guohua Jia, Chaoyang Tu, Jianfu Li, Xiuai Lu, Zhaojie Zhu, Zhenyu You, Yan Wang, and Baichang Wu

J. Appl. Phys. 99, 083502 (2006); http://dx.doi.org/10.1063/1.2188079 (3 pages) | Cited 1 time

Online Publication Date: 17 April 2006

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The spectroscopic properties of GdAl3(BO3)4:Tm3+ single crystal for the Tm3+ transition near 1.9 μm are presented. The absorption cross section, the emission cross section, and the potential laser gain near 1.9 μm are investigated for both σ and π polarizations. The broad absorption band at about 797 nm and high value of the above cross section are promising features for obtaining a laser diode pumped Tm3+ laser. The maximum emission cross sections are 1.29×10−20 and 6.60×10−20 cm2 at 1.85 μm for the σ and π polarizations, respectively. The potential laser gain curves indicate that more than 200 nm tunability range is expected for this material.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.60.Fc Modulation, tuning, and mode locking
78.30.Hv Other nonmetallic inorganics

Characterization of porous low-k films using variable angle spectroscopic ellipsometry

M. T. Othman, J. A. Lubguban, A. A. Lubguban, S. Gangopadhyay, R. D. Miller, W. Volksen, and H.-C. Kim

J. Appl. Phys. 99, 083503 (2006); http://dx.doi.org/10.1063/1.2189018 (7 pages) | Cited 11 times

Online Publication Date: 19 April 2006

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Variable angle spectroscopic ellipsometry (VASE™) is used as a tool to characterize properties such as optical constant, thickness, refractive index depth profile, and pore volume fraction of single and bilayer porous low-k films. The porous films were prepared using sacrificial pore generator (porogen) approach. Two sets of porous films with open- and closed-pore geometries were measured. Three models were used for data analysis: Cauchy, Bruggeman effective medium approximation (BEMA), and graded layer. Cauchy, a well-known model for transparent films, was used to obtain thickness and optical constant, whereas BEMA was utilized to calculate the pore volume fraction from the ellipsometric data. The Cauchy or BEMA models were then modified as graded layers, resulting in a better fit and a better understanding of the porous film. The depth profile of the porous film implied a more porous layer at the substrate-film interface. We found 3%–4% more porosity at the interface compared with the bulk for both films. This work shows that VASE™, a nondestructive measurement tool, can be used to characterize single- and multigraded layer porous films quickly and effectively.
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77.55.-g Dielectric thin films
61.43.Gt Powders, porous materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Grain-boundary relaxation and its effect on plasticity in nanocrystalline Fe

D. Jang and M. Atzmon

J. Appl. Phys. 99, 083504 (2006); http://dx.doi.org/10.1063/1.2187417 (7 pages) | Cited 6 times

Online Publication Date: 20 April 2006

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Grain-boundary relaxation in nanocrystalline Fe was studied by high-resolution transmission electron microscopy (HREM), and its effect on plasticity was characterized by nanoindentation. Samples with grain size of 9.8 nm were synthesized by mechanical attrition and subsequently annealed at low temperatures (80 and 100 °C) without affecting the grain size. While the hardness is not significantly affected by annealing, the strain-rate sensitivity peaks as a function of annealing time, suggesting two competing processes. HREM images show grain-boundary relaxation during annealing. Initially disconnected lattice planes were observed to evolve into a more continuous and ordered structure with regularly spaced grain-boundary dislocations.
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61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Energy transfer and frequency upconversion involving triads of Pr3+ ions in (Pr3+, Gd3+) doped fluoroindate glass

Diego J. Rátiva, Cid B. de Araújo, and Younes Messaddeq

J. Appl. Phys. 99, 083505 (2006); http://dx.doi.org/10.1063/1.2189207 (5 pages)

Online Publication Date: 20 April 2006

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Blue and ultraviolet luminescence in (Pr3+, Gd3+) doped fluoroindate glass is studied for excitation in the red region ( ≈ 590 nm). Frequency upconversion (UC) is observed due to energy transfer (ET) among three Pr3+ ions initially excited to the math state corresponding to the ET process math+math+math→math+math+math. Additionally, UC luminescence from states math and math of Gd3+ is observed for an excitation wavelength resonant with transitions of the Pr3+ ions. The characterization of the luminescence signals allowed to determine ET rate among the Pr3+ ions and provides evidence of interconfigurational ET between Gd3+ and Pr3+ ions.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz

High quality YBa2Cu3O7−δ films with controllable in-plane orientations grown on yttria-stabilized zirconia substrates

P. A. Lin, R. L. Lo, and C. C. Chi

J. Appl. Phys. 99, 083506 (2006); http://dx.doi.org/10.1063/1.2194228 (6 pages) | Cited 1 time

Online Publication Date: 21 April 2006

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The pulsed-laser deposition (PLD) technique was used to grow high TC superconducting YBa2Cu3O7−δ (YBCO) films on both virgin and ion-bombarded yttria-stabilized zirconia (YSZ) substrates. To pattern high TC films for device applications, the ion milling technique is often used to turn virgin YSZ substrates into ion-bombarded substrates. Multilayered processes require the growth of high TC films on these ion-bombarded substrates. The purpose of this work was to investigate the growing conditions for these two kinds of substrate surfaces. We found that high quality 0° in-plane orientation films can be grown on either substrate when the growth temperature is about 810 °C. The thin film grown at this temperature has TC of about 90.3 K and JC of about 4×106 A cm−2 at 77 K. On virgin substrates, the in-plane orientations of YBCO films grown within the temperature range of 790–730 °C exhibit a mixture of 0° and 45° domains. As the growth temperature decreases, the dominant orientation shifts gradually from 0° to 45°. On the other hand, on ion-bombarded YSZ substrates, the in-plane orientation of YBCO films grown within the same temperature range shows that the 45° domain is more prominent. Furthermore, 9° subpeaks appear around the 0° peak on ion-bombarded YSZ substrates. At a lower growth temperature of around 690 °C, only the 45° domain exists on the virgin substrate, while a small amount of 0° domain is present with the majority of 45° domain on the ion-bombarded substrate. The TC and JC of the films grown at around 690 °C on virgin substrates are as good as films grown at high temperatures, despite the difference in the in-plane orientations.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology

Influence of postdeposition annealing on the structural and optical properties of cosputtered Mn doped ZnO thin films

Harish Kumar Yadav, K. Sreenivas, and Vinay Gupta

J. Appl. Phys. 99, 083507 (2006); http://dx.doi.org/10.1063/1.2188083 (8 pages) | Cited 22 times

Online Publication Date: 27 April 2006

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The influence of postgrowth annealing on the structural and optical properties of rf cosputtered Mn doped ZnO thin films deposited on glass substrate at room temperature has been investigated. All as deposited Zn1−xMnxO films are highly textured, with the c axis of the wurtzite structure along the growth direction. The as grown films are in a state of compressive stress and a reduction in stress with postgrowth annealing treatment are observed. The band gap of Mn doped ZnO films (3.34 eV) is slightly larger than the pure ZnO film (3.30 eV) and is found to decrease with an increase in annealing temperature for all the samples. The optical dispersion of refractive index with photon energy in Zn1−xMnxO films with varying x and different annealing temperature is studied in the light of single oscillator and Pikhtin-Yas’kov [Sov. Phys. Semicond. 15, 81 (1981)] model, respectively.
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68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Direct imaging of electron-beam interaction region

D. R. Luber and N. M. Haegel

J. Appl. Phys. 99, 083508 (2006); http://dx.doi.org/10.1063/1.2189934 (5 pages) | Cited 1 time

Online Publication Date: 1 May 2006

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We demonstrate a method for charge recombination imaging in the scanning electron microscope and employ this technique to directly image the two-dimensional projection of the generation volume as a function of electron energy and probe current. Using GaAs and SiC bulk samples, we observe the lateral extent of the generation volume increasing as a function of increasing e-beam accelerating voltage, in excellent agreement with previous work. This work also reveals significant variations in minority carrier distribution within the volume for low-Z compared to the high-Z material. The roles of sample geometry and carrier diffusion are discussed. The direct imaging technique used in this work is well suited for further studies of the nature of the effective interaction region for cathodoluminescence or electron-beam induced current studies in any luminescent material.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.60.Hk Cathodoluminescence, ionoluminescence

Stranski-Krastanov GaN/AlN quantum dots grown by metal organic vapor phase epitaxy

D. Simeonov, E. Feltin, J.-F. Carlin, R. Butté, M. Ilegems, and N. Grandjean

J. Appl. Phys. 99, 083509 (2006); http://dx.doi.org/10.1063/1.2189975 (6 pages) | Cited 11 times

Online Publication Date: 1 May 2006

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We report a thorough study of the growth of self-assembled GaN/AlN quantum dots (QDs). These QDs were grown on sapphire substrates using the Stranski-Krastanov (SK) growth mode by means of low-pressure metal organic vapor phase epitaxy. The influence of the V∕III ratio on the QD height, shape, and density is studied. Emissions above (3.8 eV) and below (2.8 eV) the band gap of GaN are observed for small dots (1.3 nm) and large ones (4.4 nm), respectively. Special emphasis was given to the SK growth mode transition and the parameters influencing the QD formation. The two-dimensional–three-dimensional transition is studied continuously by photoluminescence mapping showing its high sensitivity to the V∕III ratio.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.67.Hc Quantum dots

Capture barrier for DX centers in gallium doped Cd1−xMnxTe

Ewa Placzek-Popko, Anna Nowak, Jan Szatkowski, and Kazimierz Sieranski

J. Appl. Phys. 99, 083510 (2006); http://dx.doi.org/10.1063/1.2191573 (5 pages) | Cited 1 time

Online Publication Date: 3 May 2006

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We report on the capture barrier for the gallium related DX center in Cd0.99Mn0.01Te. In order to determine the barrier height, two methods were applied: an analysis of the persistent photoconductivity decay and the optical deep level transient spectroscopy technique. Over a range of temperatures varying from 77 to 105 K, the capture barrier height, deduced from the decay time constants of photoconductivity, has been found to be equal to 0.22 eV. An apparent hole trap, observed with the optical deep level transient spectroscopy, was attributed to the thermally activated capture cross section of a DX center with a 0.23 eV capture barrier. The obtained data are close to 0.21 eV, the value of the capture barrier which we determined earlier with the help of the deep level transient spectroscopy method.
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71.55.Gs II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Ey III-V and II-VI semiconductors

Residual internal stress in partially crystallized photothermorefractive glass: Evaluation by nuclear magnetic resonance spectroscopy and first principles calculations

J. W. Zwanziger, U. Werner-Zwanziger, E. D. Zanotto, E. Rotari, L. N. Glebova, L. B. Glebov, and J. F. Schneider

J. Appl. Phys. 99, 083511 (2006); http://dx.doi.org/10.1063/1.2191731 (6 pages) | Cited 7 times

Online Publication Date: 4 May 2006

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In some circumstances, the mechanical and optical properties of multiphase brittle materials strongly depend on the level of residual micromechanical stresses that arise upon cooling due to thermal and elastic mismatch between the constituent phases. Here we study the residual internal stress in a partially crystallized oxyfluoride glass, best known as photothermorefractive (PTR) glass. This material is composed of a glass matrix with embedded nanosize sodium fluoride (NaF) crystals. Using both the Selsing model and solid-state nuclear magnetic resonance in combination with first principles calculations we found that the crystals are under a tensile stress field of approximately 610–800 MPa. For this stress level the estimated critical crystal diameter for spontaneous cracking is about 2300–1900 nm, which greatly exceeds the observed diameters of 7–35 nm. Hence no spontaneous cracking is expected for the PTR glasses. First principles calculations indicate that the stress induced change of the refractive index of the NaF crystals is about −0.08%, which agrees with the observed refractive index changes.
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76.60.-k Nuclear magnetic resonance and relaxation
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Influence of bias stressing and irradiation on poly-three-hexylthiophene based field effect transistors

R. A. B. Devine

J. Appl. Phys. 99, 083701 (2006); http://dx.doi.org/10.1063/1.2189936 (5 pages) | Cited 2 times

Online Publication Date: 19 April 2006

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Preliminary measurements of positive and negative bias stress and radiation effects in poly-three-hexylthiophene based field effect transistors are reported. Radiation up to 0.5 Mrad (SiO2) is found to have little effect on channel carrier mobility though bias stressing does. A strong positive bias stress induced positive threshold voltage shift is suppressed when devices are simultaneously irradiated. There is no evidence for significant radiation effects in the organic semiconductor. Recovery effects are observed following removal of bias stress and radiation.
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85.30.Tv Field effect devices
61.82.Fk Semiconductors
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