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15 Jun 2005

Volume 97, Issue 12, Articles (12xxxx)

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Absorption intensities and emission cross sections of principal intermanifold and inter-Stark transitions of Er3+(4f 11) in polycrystalline ceramic garnet Y3Al5O12

Dhiraj K. Sardar, Charles C. Russell, John B. Gruber, and Toomas H. Allik

J. Appl. Phys. 97, 123501 (2005); http://dx.doi.org/10.1063/1.1928327 (6 pages) | Cited 23 times

Online Publication Date: 16 June 2005

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A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds math of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+ math→math (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the math→math (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG samples were measured. From the radiative lifetimes determined from the JO model and the measured fluorescence lifetimes, the quantum efficiencies for both samples were determined. The comparative study of Er3+(4f11) ions performed suggests that polycrystalline ceramic YAG is an excellent alternative to single-crystal YAG rod for certain applications.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
75.50.Gg Ferrimagnetics
78.55.Hx Other solid inorganic materials
78.20.Jq Electro-optical effects

Ion irradiation of inhomogeneous Schottky barriers on silicon carbide

F. Roccaforte, S. Libertino, F. Giannazzo, C. Bongiorno, F. La Via, and V. Raineri

J. Appl. Phys. 97, 123502 (2005); http://dx.doi.org/10.1063/1.1928328 (9 pages) | Cited 9 times

Online Publication Date: 16 June 2005

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In this paper, the effects of ion irradiation on Schottky barriers formed on silicon carbide are discussed. After Si-ion irradiation at the near-interface region in Ti/4H-SiC contacts an increase of the Schottky barrier height from 1.05 to 1.21 eV was observed, accompanied by a lowering of the reverse leakage current. The combination of several methods allowed us to determine the physical properties of the Schottky barrier and to explain the mechanism responsible for the barrier height changes. In particular, the structural and electrical modifications of the interfacial region, both of Ti layer and SiC (i.e., different orientation of the Ti layer, irradiation-induced defects in the epilayer, dopant deactivation, and the consequent reduction of the surface electric field) are responsible for the increase of the Schottky barrier height and the reduction of the leakage current. The electrical characterization of the contacts at different temperatures also suggested that ion irradiation induced modifications in the inhomogeneous nature of the Ti Schottky barrier.
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73.30.+y Surface double layers, Schottky barriers, and work functions
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
73.40.Ns Metal-nonmetal contacts

Thermal-expansion behavior of a directionally solidified NiAl–Mo composite investigated by neutron diffraction and dilatometry

H. Bei, E. P. George, D. W. Brown, G. M. Pharr, H. Choo, W. D. Porter, and M. A. M. Bourke

J. Appl. Phys. 97, 123503 (2005); http://dx.doi.org/10.1063/1.1929853 (5 pages) | Cited 7 times

Online Publication Date: 16 June 2005

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The thermal expansion of directionally solidified NiAl–Mo eutectic alloys consisting of nanoscale Mo fibers embedded in a NiAl matrix was analyzed by neutron diffraction and dilatometry. From room temperature to 800 °C, perpendicular to the fiber direction, the NiAl and Mo phases expand independently with average coefficients of thermal expansion (CTEs) of 16.0×10−6 °C−1 and 5.8×10−6 °C−1, respectively. Parallel to the fiber direction, they coexpand up to 650 °C with an average CTE of 12.8×10−6 °C−1, but above this temperature the Mo fibers expand more than the NiAl matrix. This anomalous behavior is the result of the load transfer to the Mo fibers when the NiAl matrix softens. The average CTE of the composite parallel to the fiber direction was determined by dilatometry to be 13.0×10−6 °C−1, which is approximately 11% lower than the value predicted by a simple rule of mixtures using the CTEs of the constituent phases.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
65.40.De Thermal expansion; thermomechanical effects
81.30.Fb Solidification

Ductile relaxation in cracked metal-organic chemical-vapor-deposition-grown AlGaN films on GaN

J.-M. Bethoux and P. Vennéguès

J. Appl. Phys. 97, 123504 (2005); http://dx.doi.org/10.1063/1.1929856 (8 pages) | Cited 8 times

Online Publication Date: 16 June 2005

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A study of the strain relaxation of cracked (Al,Ga)N/GaN films grown by metal-organic chemical-vapor deposition on (0001) sapphire is presented. The strain measured by x-ray diffraction is shown to depend both on the film thickness and on the high-temperature exposure time (including both growth duration and annealing). These macroscopic observations are linked to the film microstructure by using transmission electron microscopy and cathodoluminescence observations. Relaxation may occur either by the introduction of long, straight, a+c misfit dislocations or by the introduction of additional cracks bordered by bowed a-type misfit dislocations. The nucleation mechanism and the efficiency in relaxing the misfit strain of these two features are discussed.
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81.05.Ea III-V semiconductors
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.M- Structural failure of materials
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.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Cc Kinetics of defect formation and annealing
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Temperature dependence of the absorption and refraction of Mg-doped congruent and stoichiometric LiNbO3 in the THz range

L. Pálfalvi, J. Hebling, J. Kuhl, Á. Péter, and K. Polgár

J. Appl. Phys. 97, 123505 (2005); http://dx.doi.org/10.1063/1.1929859 (6 pages) | Cited 48 times

Online Publication Date: 16 June 2005

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The absorption coefficient and the index of refraction of undoped and Mg-doped stoichiometric and congruent LiNbO3 crystals were determined for polarization parallel to the z axis in the far-infrared (FIR) 30−180-cm−1 frequency range for different Mg-doping levels and temperatures down to 10 K. For stoichiometric LiNbO3, smaller absorption and index of refraction were found, than for congruent samples. At a Mg content near the photorefractive threshold, the FIR absorption coefficient has the lowest value in the stoichiometric crystals, which are most suitable for efficient pulse generation in the terahertz range.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
61.72.S- Impurities in crystals
78.70.Gq Microwave and radio-frequency interactions

On conductivity changes in shocked potassium chloride

N. K. Bourne, D. Townsend, and M. Braithwaite

J. Appl. Phys. 97, 123506 (2005); http://dx.doi.org/10.1063/1.1929094 (6 pages) | Cited 1 time

Online Publication Date: 16 June 2005

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A previous work has reported that shock loading of ionic crystals produces an induced polarization and changes in electrical conductivity. However, previous measurements recorded an integrated electrical signal comprising the induced electrical field and that due to current flow. For this reason a differential system was designed to separate these effects that was adapted from that used in the investigation of the conductivity of hydrogen under shock. The measurement removes voltages produced in the shock-induced electrical field, allowing determination of those resulting from resistance changes. Although the mechanical response of potassium chloride to shock has been studied extensively, the electrical response is less studied. Here, experiments are reported in which it is shocked to various stresses in order to observe conductivity changes. The range of stresses induced includes several mechanical thresholds, including the elastic-plastic transition, the B1:B2 phase transformation, and the overdriving of the shock faster than the elastic wave. The behavior observed when single crystal and targets pressed from granular material (to close to full density) are shocked around each of these thresholds is presented. The effects of loading to a particular stress in a single step or in multiple steps are discussed.
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81.05.Rm Porous materials; granular materials
62.50.-p High-pressure effects in solids and liquids
72.80.Sk Insulators
62.30.+d Mechanical and elastic waves; vibrations
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Deep ultraviolet Raman scattering characterization of ion-implanted SiC crystals

S. Nakashima, T. Mitani, J. Senzaki, H. Okumura, and T. Yamamoto

J. Appl. Phys. 97, 123507 (2005); http://dx.doi.org/10.1063/1.1931039 (8 pages) | Cited 13 times

Online Publication Date: 16 June 2005

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Multiple energy phosphorous ions were implanted into 4H-SiC at room temperature and at an elevated temperature (500 °C) followed by annealing at various temperatures. Deep ultraviolet Raman microscopy was used to analyze the effect of the implantation dose and postannealing temperature on the recovery of surface layers damaged by the implantation. The Raman analysis showed that the recovery rate of the crystallinity increased with an increase in the annealing temperature. However, for highly dosed samples, recovery was not complete even with annealing temperatures up to 1700 °C. With room-temperature implantation, part of the implanted layer was converted into a 3C structure with heavy stacking faults. New Raman bands were observed at below 500 cm−1 in samples heavily dosed with 4.0×1016 cm−2 after annealing, which revealed that excess phosphorus precipitates. A downshift of the phonon Raman bands and a reduction in the LO–TO-phonon frequency splitting were observed in as-implanted samples and ones that are not completely recovered by annealing. This feature is discussed based on several mechanisms.
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78.30.Hv Other nonmetallic inorganics
81.05.Hd Other semiconductors
78.40.Fy Semiconductors
61.72.up Other materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.72.Cc Kinetics of defect formation and annealing
61.72.Nn Stacking faults and other planar or extended defects

Effects of doping on the kinetics of laser-induced low-temperature crystallization of amorphous silicon

Yu. L. Khait, R. Beserman, A. Chack, and W. Beyer

J. Appl. Phys. 97, 123508 (2005); http://dx.doi.org/10.1063/1.1921337 (4 pages) | Cited 1 time

Online Publication Date: 20 June 2005

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Substantial effects of boron and phosphorus doping on the kinetics of laser-induced crystallization (LIC) in hydrogenated amorphous silicon (a-Si:H) are reported. A kinetic nanoscopic electron-related LIC model that suggests predictions and explanations of observed effects of B and P doping on the LIC temperatures and crystallite size in a-Si:H is presented. The LIC is considered to be the integral effect of a huge number of nanoscale picosecond material reconstructions, each of which is generated by a nanoscopic short-lived (picosecond) large-energy fluctuation. The LIC in doped a-Si:H occurs at temperatures substantially lower than those found in the crystallization in a furnace. Crystallite size in B-doped a-Si:H is half of that in P-doped and undoped material.
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81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.uf Ge and Si

Observation of a spin one native defect in as-grown high-purity semi-insulating 4H SiC

M. E. Zvanut, Haiyan Wang, Mpumelelo Richards, and V. V. Konovalov

J. Appl. Phys. 97, 123509 (2005); http://dx.doi.org/10.1063/1.1928329 (4 pages)

Online Publication Date: 20 June 2005

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Electron paramagnetic resonance measurements of high-purity semi-insulating 4H SiC reveals a spectrum characteristic of an S = 1 defect, which appears only after exposure to light with a wavelength less than 690 nm. Analysis of the hyperfine structure of the spectrum suggests that the defect is an intrinsic pair or defect∕impurity complex. The center is stable in an inert ambient up to temperatures of 1200 °C, but a 1-h, 1600 °C anneal reduces the concentration by at least an order of magnitude. Because the spectrum is not affected by removal of the excitation light, it is concluded that the center is the ground state of an S = 1 defect. A study of the angular dependence of the spectrum shows that g = 2.0052, ∣D∣ = (329±14)×10−4 cm−1, and ∣E∣<19×10−4 cm−1.
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76.30.Mi Color centers and other defects
71.55.Ht Other nonmetals
61.72.Cc Kinetics of defect formation and annealing

Adhesion of polymer coatings studied by laser-induced delamination

A. Fedorov and J. Th. M. De Hosson

J. Appl. Phys. 97, 123510 (2005); http://dx.doi.org/10.1063/1.1929858 (7 pages) | Cited 3 times

Online Publication Date: 20 June 2005

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This paper concentrates on the laser-induced delamination technique, aimed at measuring the practical work of adhesion of thin polymer coatings on metal substrates. In this technique an infrared laser-pulsed beam is used to create an initial blister. Upon increasing the pulse intensity, the size of the blister grows, resulting in partial delamination of the film. In this work the blister profiles and the blister pressure were obtained from independent measurements. Alongside experiments, a simple model is developed to provide the equations necessary for calculating the blister strain energy, height, and the gas pressure inside the blister. The model is essentially based on an elastic behavior of the polymer film. The blister height and the blister pressure predicted by the model were confronted with the experimental observations and a fair agreement was found. The adhesion properties of the polyethylene terephthalate films on a steel substrate were characterized in terms of the maximum stress required for delamination and the practical work of adhesion. The relation between the two are discussed. Because the blister formation and subsequent delamination take place on a time scale of microseconds, it is argued that the viscous properties of the film do not manifest on this time scale and the contribution of plastic deformation of the film is rather small.
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68.35.Np Adhesion
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
68.60.Bs Mechanical and acoustical properties
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds

Epitaxial growth and characteristics of N-doped anatase TiO2 films grown using a free-radical nitrogen oxide source

Hiroaki Matsui, Hitoshi Tabata, Noriyuki Hasuike, Hiroshi Harima, and Bunsho Mizobuchi

J. Appl. Phys. 97, 123511 (2005); http://dx.doi.org/10.1063/1.1929889 (8 pages) | Cited 22 times

Online Publication Date: 20 June 2005

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This paper reports on a systematic investigation of nitrogen (N) doping in single-crystalline TiO2 films possessing an anatase phase. TiO2 films heavily doped with N were grown with high crystallinity by employing a pulsed laser ablation technique using a close lattice-matched LaAlO3 (100) substrate and NO as the source gases for N doping. math and math isotope tracing by secondary-ion-mass spectroscopy confirmed that N and O atoms were simultaneously incorporated into the films as a consequence of the gas phase reactions between Ti-related chemical species ablated by the laser and NO free radicals. The films yielded an absorption band at around 3.0 eV, as expected from the yellowish color, with band tailing becoming stronger with increasing N concentration. It is suggested that N-related complex defects in TiO2 acted as carrier compensation centers. Micro-Raman spectroscopy with a spatial resolution of 1 μm2 revealed host-lattice defects and generation of secondary phases at the microscopic scale by N doping. This work showed that the visible absorption band in N-doped TiO2 films can be attributed to small structural modifications consisting of N-related complex defects and secondary phases formed at the microscopic scale. These structural modifications were associated with a concomitant enhancement in photocatalytic activity.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Fg Pulsed laser ablation deposition
61.72.up Other materials
78.66.Nk Insulators
78.30.Am Elemental semiconductors and insulators
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.66.Li Other semiconductors
78.40.Ha Other nonmetallic inorganics

Charge-carrier transport and triplet exciton diffusion in a blue electrophosphorescent emitting layer

Noriyuki Matsusue, Satoshi Ikame, Yuichiro Suzuki, and Hiroyoshi Naito

J. Appl. Phys. 97, 123512 (2005); http://dx.doi.org/10.1063/1.1929886 (5 pages) | Cited 17 times

Online Publication Date: 20 June 2005

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Charge-carrier transport and triplet exciton diffusion in iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2′]picolinate (FIrpic) doped in 4,4′-N, N′-dicarbazole-biphenyl (CBP) thin films have been studied by time-of-flight (TOF) transient photocurrent and steady-state photocurrent measurements. With increasing FIrpic concentration, hole TOF transients become highly dispersive and the hole drift mobility is decreased. In contrast, the electron transit signals become unobservable. The TOF results are found to be consistent with those of steady-state photocurrent measurements of FIrpic-doped CBP thin films; the photocurrent spectra are symbatic and antibatic when the illuminated electrode is positively and negatively biased, respectively. The diffusion lengths of triplet excitons in FIrpic-doped CBP thin films are determined from the symbatic photocurrent spectra.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
66.30.-h Diffusion in solids
71.35.-y Excitons and related phenomena
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence

Bright green electroluminescence from Tb3+ in silicon metal-oxide-semiconductor devices

J. M. Sun, W. Skorupa, T. Dekorsy, M. Helm, L. Rebohle, and T. Gebel

J. Appl. Phys. 97, 123513 (2005); http://dx.doi.org/10.1063/1.1935766 (7 pages) | Cited 31 times

Online Publication Date: 20 June 2005

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Bright green electroluminescence with luminance up to 2800 cd/m2 is reported from indium-tin-oxide∕SiO2:Tb/Si metal-oxide-semiconductor devices. The SiO2:Tb3+ gate oxide was prepared by thermal oxidation followed by Tb+ implantation. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and the annealing temperature. The optimized device shows a high external quantum efficiency of 16% and a luminous efficiency of 2.1 lm/W. The excitation processes of the strong green electroluminescence are attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent crossrelaxation from math to math energy levels. Light-emitting devices with micrometer size fabricated by the standard metal-oxide-semiconductor technology are demonstrated.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing
61.72.up Other materials

Optical models for cavity profiles in high-dose helium-implanted and annealed silicon measured by ellipsometry

P. Petrik, M. Fried, T. Lohner, O. Polgár, J. Gyulai, F. Cayrel, and D. Alquier

J. Appl. Phys. 97, 123514 (2005); http://dx.doi.org/10.1063/1.1937469 (6 pages) | Cited 1 time

Online Publication Date: 20 June 2005

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Cavities created by He implantation with a dose of 5×1016 cm−2 and energy of 40 keV into single-crystalline silicon and annealing at 650–1000 °C for 15–60 min were characterized by multiple angles of incidence spectroscopic ellipsometry. Optical models of increasing complexity were developed assuming the cavity layer either to be homogeneous, or to have a Gaussian profile, or sublayers with independently fitted cavity ratios. Cavity profiles of different annealing conditions were compared and cross-checked by transmission electron microscopy. A strategy for the ellipsometric evaluation was proposed to reduce the computation time and the probability of getting in local minima using complex models with numerous parameters. High sensitivity on the angle of incidence was found, and the choice and the determination of the angle of incidence were discussed.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.Cc Kinetics of defect formation and annealing

Ultraviolet electroabsorption modulator based on AlGaN/GaN multiple quantum wells

I. Friel, C. Thomidis, and T. D. Moustakas

J. Appl. Phys. 97, 123515 (2005); http://dx.doi.org/10.1063/1.1937471 (4 pages) | Cited 12 times

Online Publication Date: 20 June 2005

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An ultraviolet electroabsorption modulator based on AlGaN/GaN quantum wells is demonstrated. Enhanced excitonic absorption in the quantum wells at around 3.48 eV was achieved using a Schottky contact to partially cancel the polarization-induced electric fields in the quantum well layers. A change in the absorption coefficient greater than 4×104 cm−1 was obtained for a modest reverse bias of 10 V. The observed blueshift in the exciton energy was smaller than that predicted by theoretical calculations. This is accounted for by variations in the background carrier concentration in the wells with reverse bias.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects

Writing of nonlinear optical Sm2(MoO4)3 crystal lines at the surface of glass by samarium atom heat processing

M. Abe, Y. Benino, T. Fujiwara, T. Komatsu, and R. Sato

J. Appl. Phys. 97, 123516 (2005); http://dx.doi.org/10.1063/1.1938269 (7 pages) | Cited 22 times

Online Publication Date: 20 June 2005

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Some glasses such as 21.25Sm2O3.63.75MoO3.15B2O3 (mol %) giving the formation of nonlinear optical Sm2(MoO4)3 crystals through conventional crystallization in an electric furnace and through continuous-wave Nd: yttrium aluminum garnet (YAG) laser (wavelength: 1064 nm) irradiation (samarium atom heat processing) have been developed. It is proposed from x-ray diffraction analyses, micro-Raman-scattering spectra, and second-harmonic generation measurements that the crystal structure of Sm2(MoO4)3 formed by the crystallization is the β′-phase structure with an orthorhombic (noncentrosymmetric) symmetry. The lines consisting of nonlinear optical β′-Sm2(MoO4)3 crystals are written at the surface of glasses by YAG laser irradiation (laser power: P = 0.4 W, laser scanning speed: S = 1–10 μm/s), and, in particular, homogeneous crystal lines are formed at the laser scanning speed of 1 μm/s. Refractive index changes (not crystallization) are also induced by YAG laser irradiation of P = 0.4 W and a high laser scanning speed of S = 25 μm/s. The crystallization mechanism in the laser-irradiated region has been proposed. The present study demonstrates that the samarium atom heat processing is a technique for the writing of rare earth containing optical nonlinear/ferroelectric crystal lines in glass.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.62.-b Laser applications
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.66.Fn Inorganic compounds
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.K- Solid-solid transitions
77.80.-e Ferroelectricity and antiferroelectricity
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

The initial rate of vapor-solid interaction and its application in the detection of vapor at ultra low concentrations

Dipankar Chandra, Jack R. Frazier, Jill Ringo, and Carlos E. Aramayo

J. Appl. Phys. 97, 123517 (2005); http://dx.doi.org/10.1063/1.1944203 (11 pages)

Online Publication Date: 20 June 2005

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The initial interaction between mercury vapor and gold film surfaces was determined from the response of gold-coated piezoresistive silicon cantilevers maintained at a constant temperature. It was found that for low mercury vapor concentration the cantilever response, indicative of interaction strength, exhibits weak dependence on mercury concentration and that the interaction remains confined to the gold film surface, with no detectable alteration of either its solid surface or bulk properties. A Freundlich isotherm [ H. Freundlich, Colloid and Capillary Chemistry (E.P. Dutton, New York, 1922) ] can approximate several characteristics of this interaction. For high mercury vapor concentration, the interaction extends to the entire volume of the gold film and deviates strongly from a Freundlich isotherm dependence. The initial interaction rate decreases slowly with decreasing mercury vapor concentration as determined from the response rate of change of a piezoresistive cantilever at equilibrium with condensed mercury. The mercury concentration could be confirmed independently of this process down to 0.09 part per billion. With continued cooling of the condensed mercury source, the initial interaction rate continues to decrease slowly, indicating probable detection at concentrations ranging to less than 1 part per quadrillion, though no independent confirmation of the mercury partial pressure is possible in this range. The cantilever response also increases strongly with decreasing platform surface temperature. Similar results were obtained for the interaction of ethanol vapor and the surface of a positive photoresist layer coating on piezoresistive silicon cantilevers. These characteristics will permit the development of new sensors in detecting vapors at ultra low concentrations.
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68.43.Mn Adsorption kinetics
68.47.De Metallic surfaces
82.80.-d Chemical analysis and related physical methods of analysis

Annealing behavior of low-energy ion-implanted phosphorus in silicon

S. Ruffell, I. V. Mitchell, and P. J. Simpson

J. Appl. Phys. 97, 123518 (2005); http://dx.doi.org/10.1063/1.1929861 (6 pages) | Cited 13 times

Online Publication Date: 20 June 2005

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Phosphorous diffusion in silicon has been investigated for room-temperature implants of low energy (5, 10, and 30 keV) and fluence between 1×1014 and 5×1015 cm−2, followed by rapid thermal annealing in the temperature range of 600–1000 °C. Depth profiles were extracted by time-of-flight secondary-ion-mass spectroscopy. For 5-keV energy implants below 1×1015 cm−2 fluence, phosphorus preferentially diffused outwards, i.e., toward the sample surface. Nuclear reaction analysis in combination with chemical stripping of the oxide shows that as much as 50% of the P in annealed samples can accumulate at the surface oxide during a 30-s anneal. At all implant energies, indiffusion of P dominates in the regimes of higher fluence, higher anneal temperature, and longer anneal times.
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81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
66.30.J- Diffusion of impurities
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Mass transport phenomena during lithographic polymerization of nematic monomers monitored with interferometry

Bianca M. I. van der Zande, Jan Steenbakkers, Johan Lub, Christian M. Leewis, and Dirk J. Broer

J. Appl. Phys. 97, 123519 (2005); http://dx.doi.org/10.1063/1.1935129 (8 pages) | Cited 10 times

Online Publication Date: 20 June 2005

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Photopolymerization of liquid-crystalline diacrylates is a versatile tool to make optical films for liquid-crystal display (LCD) enhancement. The constant drive towards LCD’s having an improved front-of-screen performance demands optical films with properties that can be adjusted on (sub) pixel level. Birefringent films made from liquid-crystalline diacrylates allow for the required adjustment of the optical property on (sub) pixel level. In this paper we report on the composition of the acrylate mixture that results in planarly aligned nematic films usable as optical retarder in transflective LCD’s as well as the mass transport phenomena that take place during heating of a mask-exposed birefringent film of liquid-crystalline diacrylates. The mass transport phenomena are studied by interferometry as a function of temperature and time. Upon heating a pronounced surface corrugation arises from the latent image formed during the mask exposure. The surface profile largely depends on lateral feature sizes. For 1×1-mm2 areas the exposed areas rise compared to the nonexposed areas, whereas the opposite is observed for 100×100-μm2 areas. Finally, the direction of the mass transport depends on the molecular orientation of the liquid-crystalline diacrylate. The protrusion formed by lengthwise diffusion is 1.7 times higher than that formed by sidewise diffusion.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
82.35.-x Polymers: properties; reactions; polymerization
78.20.Fm Birefringence

Cathodoluminescence imaging and spectroscopy of excited states in InAs self-assembled quantum dots

S. Khatsevich, D. H. Rich, Eui-Tae Kim, and A. Madhukar

J. Appl. Phys. 97, 123520 (2005); http://dx.doi.org/10.1063/1.1935743 (8 pages) | Cited 7 times

Online Publication Date: 20 June 2005

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We have examined state filling and thermal activation of carriers in buried InAs self-assembled quantum dots (SAQDs) with excitation-dependent cathodoluminescence (CL) imaging and spectroscopy. The InAs SAQDs were formed during molecular-beam epitaxial growth of InAs on undoped planar GaAs (001). The intensities of the ground- and excited-state transitions were analyzed as a function of temperature and excitation density to study the thermal activation and reemission of carriers. The thermal activation energies associated with the thermal quenching of the luminescence were measured for ground- and excited-state transitions of the SAQDs, as a function of excitation density. By comparing these activation energies with the ground- and excited-state transition energies, we have considered various processes that describe the reemission of carriers. Thermal quenching of the intensity of the QD ground- and first excited-state transitions at low excitations in the ∼ 230–300-K temperature range is attributed to dissociation of excitons from the QD states into the InAs wetting layer. At high excitations, much lower activation energies of the ground and excited states are obtained, suggesting that thermal reemission of single holes from QD states into the GaAs matrix is responsible for the observed temperature dependence of the QD luminescence in the ∼ 230–300-K temperature range. The dependence of the CL intensity of the ground-and first excited-state transition on excitation density was shown to be linear at all temperatures at low-excitation density. This result can be understood by considering that carriers escape and are recaptured as excitons or correlated electron–hole pairs. At sufficiently high excitations, state-filling and spatial smearing effects are observed together with a sublinear dependence of the CL intensity on excitation. Successive filling of the ground and excited states in adjacent groups of QDs that possess different size distributions is assumed to be the cause of the spatial smearing.
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73.21.La Quantum dots
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Gh Other heat and thermomechanical treatments

Electron transport of a quantum wire containing a finite-size impurity under terahertz electromagnetic-field illumination

Guanghui Zhou, Yuan Li, Fang Cheng, and Wenfu Liao

J. Appl. Phys. 97, 123521 (2005); http://dx.doi.org/10.1063/1.1939085 (6 pages) | Cited 1 time

Online Publication Date: 20 June 2005

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We investigate theoretically the electron-transport properties for a semiconductor quantum wire containing a single finite-size attractive impurity under an external terahertz electromagnetic-field illumination in the ballistic limit. Within the effective-mass free-electron approximation, the scattering matrix for the system has been formulated by means of a time-dependent mode matching method. Some interesting properties of the electron transmission for the system have been shown through numerical examples. It is found that in the case of a relatively large field amplitude and a frequency resonant with that corresponding to the difference between the two lowest lateral energy levels in the impurity region, the field-induced intersubband transition dominates the process as it does in the absence of the impurity. Furthermore, there is a steplike structure on the transmission as a function of the incident electron energy. However, in the case of a small field amplitude and nonresonant frequencies, both multiple symmetry Breit-type resonance peaks and asymmetry Fano-type dip lines appear in the electron transmission dependence on the incident energy due to the presence of the impurity and the external field. Therefore, within a certain energy range the transmission as a function of the field frequency and∕or field amplitude shows a rich structure. Moreover, the transmission dependence on the strength and size of the impurity is also discussed. Our results suggest that the electron-transport properties of a quantum wire are affected by the interplay effects between the impurity and the applied field.
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73.63.Nm Quantum wires
73.50.Mx High-frequency effects; plasma effects
73.23.Ad Ballistic transport
73.50.Fq High-field and nonlinear effects

Physical structures of SiO2 ultrathin films probed by grazing incidence x-ray reflectivity

Yasushi Azuma, Jiangwei Fan, Isao Kojima, and Shiqiang Wei

J. Appl. Phys. 97, 123522 (2005); http://dx.doi.org/10.1063/1.1941469 (5 pages) | Cited 4 times

Online Publication Date: 21 June 2005

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The effects of contamination overlayer and density as well as surface and interface roughnesses on the x-ray reflectivity of a SiO2 ultrathin film are discussed from viewpoints of experiment and theory. Grazing incidence x-ray reflectivity (GIXRR) is used to accurately measure physical structures of SiO2 ultrathin films grown on Si substrate by effectively resolving deviations caused by a contamination overlayer (i.e., H2O and carbonaceous compounds). GIXRR results indicate that only the thickness accuracy of a SiO2 film is largely affected by the overlayer. The thickness of a SiO2 film obtained from GIXRR peak extrema and theoretical fitting reveals that if a SiO2 film with the thickness of 2.64 nm is considered as a single layer, the H2O overlayer with a thickness of 0.55 nm makes the thickness of the SiO2 film increase to 3.09 nm, and the deviation is about 17% from its corrected thickness. By evaluating the GIXRR results of three repeating measurements of a nominal 4‐nm SiO2 film, its density, thickness, and surface and interface roughnesses are 2.43±0.01 g/cm3, 3.99±0.03 nm, and 0.40±0.02 nm and 0.25±0.02 nm, respectively.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.60.Wm Other nonelectronic physical properties
68.47.Gh Oxide surfaces
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films

The thermoluminescence activation energy and frequency factor of the main glow of CaSO4:Tm phosphor determined by heating rate method including very slow rates of heating

K. Shinsho, Y. Suzuki, Y. Yamamoto, and A. Urushiyama

J. Appl. Phys. 97, 123523 (2005); http://dx.doi.org/10.1063/1.1947898 (4 pages) | Cited 4 times

Online Publication Date: 21 June 2005

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The typical thermoluminescent phosphor of CaSO4:Tm was investigated using a heating rate method including very slow rates of heating, down to 0.0008 °C s−1. The sufficiently slow rates of heating clearly resolved at least eight narrow components in the main glow. The analysis of the peak temperature values and the half-widths of the resolved components in the glow curves by using various heating rates resulted in the distinctly higher activation energy (E) of 1.67–2.01 eV and a higher frequency factor (s) of 1019 s−1 for the resolved components, compared to earlier reported values of E in the range of 0.94–1.42 eV and values of s in the range of 109–1013 s−1, respectively.
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78.60.Kn Thermoluminescence
81.40.Gh Other heat and thermomechanical treatments

A theoretical analysis of quantum dash structures

J. H. Wei and K. S. Chan

J. Appl. Phys. 97, 123524 (2005); http://dx.doi.org/10.1063/1.1938272 (12 pages) | Cited 12 times

Online Publication Date: 21 June 2005

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The gain and related characteristics of quantum dash structures are modeled and analyzed using a parabolic effective-mass theory and the density-matrix theory. Size fluctuation is included in the model and its effects are analyzed. Comparison of performance in terms of these characteristics has been made with quantum well (QW) and quantum wire structures. Owing to size fluctuation, quantum dashes have broad gain spectra, which allow wavelength tuning without significant increase in the injected carrier density. Quantum dashes have smaller differential gain than quantum wells, while the linewidth enhancement factors are similar for these two structures. Due to their broad gain profiles, quantum dashes have much smaller large-signal chirp (change of refractive index). These characteristics can be further improved by blueshifting the emission energy without significant change in the injected carrier density. After detuning, the differential gain can be improved only to half of quantum well’s values and the large-signal chirp can be reduced to one-tenth of the QW’s value.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ion dynamics and mixed mobile ion effect in fluoride glasses

S. Ghosh and A. Ghosh

J. Appl. Phys. 97, 123525 (2005); http://dx.doi.org/10.1063/1.1939084 (5 pages)

Online Publication Date: 21 June 2005

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We report the ionic relaxation and mixed mobile ion effect in 50ZrF4−10BaF2−10YF3−(30−x)LiF−xNaF fluoride glass series, where fluorine anions participate in the diffusion process in addition to alkali cations, unlike mixed alkali oxide glasses and crystals. By analyzing the ion dynamics in the framework of a power-law model as well as modulus formalism we have observed mixed mobile ion effect in the dc conductivity and its activation energy, the crossover frequency and its activation energy, the conductivity relaxation frequency and its activation energy, and also in the decoupling index. We have correlated these phenomena with the fractal dimension of the conduction pathways in the mixed alkali fluoride glasses compared to the single alkali glasses. We have shown that the relaxation dynamics in mixed alkali fluoride glasses is independent of temperature but dependent on glass composition.
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81.05.Kf Glasses (including metallic glasses)
66.30.H- Self-diffusion and ionic conduction in nonmetals
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