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15 Aug 2004

Volume 96, Issue 4, pp. 1775-2410

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Intermode conversion in a near-field optical fiber probe

M. I. Bakunov, S. B. Bodrov, and M. Hangyo

J. Appl. Phys. 96, 1775 (2004); http://dx.doi.org/10.1063/1.1769091 (6 pages) | Cited 1 time

Online Publication Date: 2 August 2004

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The propagation of light in metal-coated fiber probes used in scanning near-field optical microscopy is studied computationally by means of the cross-section method. In contrast to previous work focusing on the behavior of the HE11 mode in the vicinity of the end aperture of the probe, we trace the propagation of the incident fundamental mode of the optical fiber through the tapered probe. The transformation of the fiber mode into the probe modes, intermode conversion, and modes cutoff are consistently calculated. In particular, it is shown that in the conventional gradual tapered probe only a few percent of the input power are transformed into the HE11 mode which has the smallest cutoff radius. In addition, an easily manufacturable modification of the shape of the probe’s tip that can provide a tenfold enhancement in optical near-field intensity has been proposed.
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42.81.Bm Fabrication, cladding, and splicing
42.81.Dp Propagation, scattering, and losses; solitons

Phase retrieval with two-beam off-axis x-ray holography

Yoshiki Kohmura, Tatsuyuki Sakurai, Tetsuya Ishikawa, and Yoshio Suzuki

J. Appl. Phys. 96, 1781 (2004); http://dx.doi.org/10.1063/1.1769098 (4 pages) | Cited 3 times

Online Publication Date: 2 August 2004

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A wave front dividing x-ray interferometer with a prism was applied to two-beam off-axis holography. Complex amplitudes at the detector plane, which were derived from the hologram using the fringe scanning method, were inversely transformed to those at the exit surface of the specimen. The x-ray phase shift due to the amorphous carbon particles was quantitatively determined with the background of the phase image being as small as approximately λ∕100 at 12.4 keV.
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42.40.Kw Holographic interferometry; other holographic techniques
42.40.Eq Holographic optical elements; holographic gratings

Optimizing the nematic liquid crystal relaxation speed by magnetic field

Bin Wang, Xinghua Wang, and Philip J. Bos

J. Appl. Phys. 96, 1785 (2004); http://dx.doi.org/10.1063/1.1767289 (5 pages)

Online Publication Date: 2 August 2004

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Nematic liquid crystalline materials have been widely used in electro-optical control of visible light. However, when IR light is considered, the thickness of the liquid crystal layer must be increased which causes the relaxation time of the material to be slower than required for many applications. In this paper we use a magnetic field to increase the speed of thick nematic devices. We show that above a particular magnetic field strength, thicker cells relax more quickly than thinner ones. Also, we find that there exists an optimal voltage range for devices of a particular thickness and with a particular applied magnetic field. Devices that allow a half-wave modulation of 1.55 μm light in less than 5 ms are shown to be possible with the use of a 2 T magnetic field.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Fiber laser relaxation oscillation noise suppression through the use of self-biased intracavity loss modulator

G. Zhu, Q. Wang, H. Dong, and N. K. Dutta

J. Appl. Phys. 96, 1790 (2004); http://dx.doi.org/10.1063/1.1773919 (4 pages) | Cited 1 time

Online Publication Date: 2 August 2004

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We demonstrate a technique for suppressing the intensity noise of erbium doped fiber lasers. We show that by introducing negative feedback into the system through the use of a self-biased intracavity loss modulator, the relaxation oscillation noise of the fiber laser could be suppressed by as much as 20 dB. To explain the observed noise reduction phenomenon, a simple theory based on the linearized rate equation has been developed and is supported by experimental measurements. We also derive a formula for estimating the maximum achievable intensity noise suppression ratio.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.79.Hp Optical processors, correlators, and modulators

Modal foundations of close-packed optical arrays with particular application to infrared and millimeter-wave astronomical interferometry

Stafford Withington, Michael P. Hobson, and Edward S. Campbell

J. Appl. Phys. 96, 1794 (2004); http://dx.doi.org/10.1063/1.1767621 (9 pages) | Cited 13 times

Online Publication Date: 2 August 2004

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A scheme is presented for modeling the behavior of multimode, multielement, close-packed optical systems. The scheme is of particular importance when describing the operation of astronomical interferometers. The basic idea is to find, through singular value decomposition, the fields on the sky and at the detectors, to which the individual telescopes of an array can couple. In the paper, we call these fields eigenfields. Eigenfields are more fundamental than eigenmodes, which are the field distributions that can pass through an optical system unchanged in form, and provide mutually orthogonal basis sets for propagating the second-order statistical properties of a source through the individual telescopes, through the beam combiners, and onto the detectors. Using our scheme it is possible to model many different kinds of interferometer, to include the noise generated by the optical components themselves and to calculate the power coupled into coherent, partially coherent, and incoherent detectors.
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95.55.Br Astrometric and interferometric instruments
42.79.-e Optical elements, devices, and systems
02.60.Dc Numerical linear algebra
02.10.Ud Linear algebra
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Ly Interferometers

Optical modulation in photonic band gap structures by surface acoustic waves

Srinivasan Krishnamurthy and Paulo V. Santos

J. Appl. Phys. 96, 1803 (2004); http://dx.doi.org/10.1063/1.1767974 (8 pages) | Cited 8 times

Online Publication Date: 2 August 2004

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We investigate theoretically the modulation of light beams in photonic band gap (PBG) structures by surface acoustic waves (SAWs). In these structures, the propagation of light beams can be actively controlled through an external acoustic stimulus. We have extended the mathematically rigorous transfer matrix method to calculate the light flow in PBG structures subjected to the spatial- and time-dependent dielectric function modulation induced by the SAW. The calculational procedure, which applies for SAWs with a frequency much smaller than that of the light, is employed to determine the transmission spectra of a one-dimensional Bragg stack with a cavity and that of a two-dimensional GaAs PBG structure with periodic air holes. We demonstrate that these two structures can be configured as an on∕off optical switch with very high contrast ratios and, in the two-dimensional case as an efficient wavelength-tunable optical filter.
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42.70.Qs Photonic bandgap materials
42.79.Hp Optical processors, correlators, and modulators
42.65.Pc Optical bistability, multistability, and switching, including local field effects
68.35.Iv Acoustical properties
77.22.Ch Permittivity (dielectric function)
42.79.Ci Filters, zone plates, and polarizers
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Spectrometry of 0.46 and 13.56 MHz Ar∕SF6 inductive plasma discharges

M. Tuszewski, W. K. Scarborough, and R. R. White

J. Appl. Phys. 96, 1811 (2004); http://dx.doi.org/10.1063/1.1769599 (8 pages) | Cited 3 times

Online Publication Date: 2 August 2004

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The neutral and positive ion species of two inductively coupled plasma (ICP) discharges, operated with low-pressure argon and sulfur hexafluoride (Ar∕SF6) gas mixtures, are studied with optical emission and mass spectrometry. Similar discharges sustained in the two ICPs show significantly different species. The spectra of the 0.46 MHz hemispherical ICP suggest nearly pure Ar∕SF6 discharges. The spectra of the 13.56 MHz planar ICP reveal many species containing silicon and oxygen, from etching of the quartz dielectric. Etch rate measurements support these observations.
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52.80.-s Electric discharges
52.50.Dg Plasma sources
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.Bn Etching and cleaning

Interaction between the electromagnetic fields and the plasma in a microwave plasma reactor

G. J. M. Hagelaar, K. Hassouni, and A. Gicquel

J. Appl. Phys. 96, 1819 (2004); http://dx.doi.org/10.1063/1.1769607 (10 pages) | Cited 14 times

Online Publication Date: 2 August 2004

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We investigate the interaction between electromagnetic (EM) fields and a hydrogen plasma in a resonance-type microwave plasma reactor, by combining an elementary theoretical analysis and a self-consistent two-dimensional numerical model. We show that the EM fields in the reactor are strongly modified by the presence of plasma; due to absorption the standing wave patterns of the field intensity are less pronounced. In turn, the electric field controls the electron temperature and the plasma formation. For typical conditions (field frequency 2.45 GHz, gas pressure 10–200 mbar, gas temperature 2000–3000 K) it is not just the electric field that controls the plasma, but rather the reduced electric field, i.e., the ratio of electric field strength to gas particle density. We show that the dependence of the reduced field on the gas temperature has a reinforcing effect on plasma formation and may cause jumps in the spatial plasma configuration as a function of power or pressure. We also show that the plasma size is limited by the skin effect.
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52.75.-d Plasma devices
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.-b Plasma production and heating
52.65.-y Plasma simulation
52.25.Fi Transport properties

Simulations studies on influence of He concentration on discharge of alternating current plasma display panels in He-Ne-Xe mixture

Insook Lee and K. Y. Choi

J. Appl. Phys. 96, 1829 (2004); http://dx.doi.org/10.1063/1.1773920 (6 pages) | Cited 5 times

Online Publication Date: 2 August 2004

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With recent experiments to add He gas to the conventional Ne-Xe discharge gas mixture for high luminous efficiency plasma display panels, we have performed simulations on a coplanar structured alternating current plasma display panel sustained in the He-Ne-Xe gas mixture, by using the two-dimensional fluid model simulator. As the He concentration increases, luminance and luminous efficiencies increase but power consumption decreases, which agrees well with the recent experimental findings. He atoms increase the number of Xe*(3P2) in the excited state and thus, the dimer emission is increased while the resonant line is reduced with the He content. As a result, the total vacuum ultraviolet emission is increased and higher luminance and higher luminous efficiency can be obtained. The enhanced mobilities of the ions in the gas mixture by adding He gas to the mixture also play an important role in increasing luminous efficiency.
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52.75.-d Plasma devices
52.65.-y Plasma simulation
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.80.Vp Discharge in vacuum
78.40.Ha Other nonmetallic inorganics
52.30.-q Plasma dynamics and flow

Two-dimensional space-time-resolved emission spectroscopy on atmospheric pressure glows in helium with impurities

C. Anderson, M. Hur, P. Zhang, L. Mangolini, and U. Kortshagen

J. Appl. Phys. 96, 1835 (2004); http://dx.doi.org/10.1063/1.1773923 (5 pages) | Cited 14 times

Online Publication Date: 2 August 2004

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The time dependence of the spectral emission of an atmospheric pressure glow discharge in helium with impurities has been studied with a two-dimensional spatial resolution. Emissions from He I (3s3S→2p3P:λ=706.5 nm) and N2(C3Πu→B3Πg:λ=337.1 nm) are used to qualitatively map the distributions of high- and low-energy electrons, respectively. The emission from N2+(B2∑u+→X2∑g+:λ=391.4 nm) provides qualitative information about the relative spatial distribution of He* metastable atoms within the discharge gap. The results demonstrate a radial spreading of the discharge during the current pulse as well as the formation of a ringlike, radially propagating cathode layer late in the current pulse.
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52.80.Hc Glow; corona
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Mechanisms of vapor permeation through multilayer barrier films: Lag time versus equilibrium permeation

G. L. Graff, R. E. Williford, and P. E. Burrows

J. Appl. Phys. 96, 1840 (2004); http://dx.doi.org/10.1063/1.1768610 (10 pages) | Cited 81 times

Online Publication Date: 2 August 2004

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Multilayer, thin-film organic/inorganic composite barrier layers have recently been reported to achieve water vapor permeation rates of <10−5 g∕m2∕day at 25 °C∕40%RH on polyethylene terephthalate substrates. Using both transient and steady-state vapor permeation measurements combined with classical Fickian diffusion models, we determine the mechanism of vapor permeation through such barrier structures and show that results obtained to date are limited not by equilibrium diffusion but by lag-time effects caused by the extremely long effective path length for the diffusing gas. The implications for further improvement of flexible thin-film vapor barriers are discussed.
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66.30.Dn Theory of diffusion and ionic conduction in solids
68.35.Fx Diffusion; interface formation

Determination of the thickness of pulsed laser deposited cylindrical Co films by their magnetoelastic effects

C. Favieres and V. Madurga

J. Appl. Phys. 96, 1850 (2004); http://dx.doi.org/10.1063/1.1768611 (7 pages) | Cited 2 times

Online Publication Date: 2 August 2004

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Soft magnetic Co films, with a grain size of 1–2 nm and thickness between ≈1.3 and tens of nanometers were pulsed laser deposited on rotating metallic wire substrates, conferring them cylindrical geometry. These films showed a magnetostrictive property, making it possible to measure and study the magnetoelastic inverse Wiedemann effect, (IWE) of the longitudinal magnetic flux in the film as a function of the circular applied magnetic field, Φz−Hϕ. The IWE of these films was explained by the assumption of magnetic wall nucleation and magnetization rotation processes. This explanation allowed us to establish the relation of Φz with the spontaneous magnetization Ms and with the film's thickness. Then using the measured Φz and the known value of Ms: (1) we determine the thickness of the film by means of an inductive method; (2) we analyze the inaccuracy of the determined film thickness; (3) we achieve the limit of tfilm,min=1.3±0.3 nm in thickness for measuring the films’ magnetic properties.
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75.50.Cc Other ferromagnetic metals and alloys
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
81.15.Fg Pulsed laser ablation deposition
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.A- Nucleation and growth
75.30.Gw Magnetic anisotropy

A two-dimensional model of the deformation of photoresist structures using elastoplastic polymer properties

K. Yoshimoto, M. P. Stoykovich, H. B. Cao, J. J. de Pablo, P. F. Nealey, and W. J. Drugan

J. Appl. Phys. 96, 1857 (2004); http://dx.doi.org/10.1063/1.1768614 (9 pages) | Cited 23 times

Online Publication Date: 2 August 2004

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A model was developed for predicting the collapse behavior of photoresist structures due to the drying of rinse liquids during wet chemical processing. The magnitude of the capillary forces was estimated using the classical thermodynamics of surface tension, and the deformation of the structure was modeled using beam bending mechanics that accounts for both elastic and plastic modes of deformation. The two-dimensional model can predict the critical beam height of collapse as a function of the wetting behavior of the rinse liquid on the beam, the elastic and plastic mechanical properties of the polymeric photoresist, and the beam dimensions. Collapse behavior was predicted for polymer nanostructures with elastoplastic mechanical properties similar to those of bulk poly(methyl methacrylate). We have compared the collapse predictions from our model with the results of models that account only for elastic or plastic deformation behavior. Regimes in the elastic-plastic mechanical property space for which it is necessary to use the developed beam bending model have been highlighted. It is shown that in some cases the inclusion of both elastic and plastic mechanical properties is necessary for modeling the collapse behavior of polymer beams fabricated using the lithographic process.
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81.40.Lm Deformation, plasticity, and creep
61.41.+e Polymers, elastomers, and plastics
85.40.Hp Lithography, masks and pattern transfer
62.20.F- Deformation and plasticity
68.03.Cd Surface tension and related phenomena
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Effects of anisotropic k⋅p interactions on energy bands and optical properties of type-II interband cascade lasers

Yao-Ming Mu and S. S. Pei

J. Appl. Phys. 96, 1866 (2004); http://dx.doi.org/10.1063/1.1763243 (14 pages) | Cited 1 time

Online Publication Date: 2 August 2004

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The validity of an eight-band k⋅p method with the axial approximation for modeling the band structures and optical properties of type-II interband cascade lasers is assessed by comparing its results with those from the standard eight-band k⋅p method. Explicit expressions for anisotropic k⋅p interaction terms, which are neglected by the axial approximation, are obtained. Then the band structures and optical properties of practical type-II interband cascade lasers are calculated using both eight-band k⋅p methods and the numerical results are discussed in detail. It is found that the axial approximation may be problematical for the simulation of type-II interband cascade lasers.
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42.55.Px Semiconductor lasers; laser diodes
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations

Time-dependent inelastic deformation of shocked soda-lime glass

C. Hari Manoj Simha and Y. M. Gupta

J. Appl. Phys. 96, 1880 (2004); http://dx.doi.org/10.1063/1.1763992 (11 pages) | Cited 14 times

Online Publication Date: 2 August 2004

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Plate impact experiments were carried out to understand inelastic deformation in soda-lime glass shocked between 3 and 10.8 GPa. In-material, wave profile measurements were obtained using longitudinal and lateral stress gauges (4.6–10.8 GPa), and electromagnetic particle velocity gauges (2.9–6 GPa) at comparable sample thicknesses. The 4.6 and 6 GPa experiments revealed time-dependent material inelastic response along with time-dependent loss of material strength. Because of the unsteady, two wave structure observed in the longitudinal wave profiles in conjunction with the time-dependent changes in the lateral stress data, previous interpretations of the shocked soda-lime glass response in terms of a propagating failure wave are not valid. At higher peak stresses (∼10 GPa), the experimental results do not display time-dependent strength loss. The shock wave response of soda-lime glass over the 4–10 GPa range is complex, and material strength and inelastic deformation features depend significantly on the peak stress. Using the experimental results, a phenomenological continuum model incorporating the various material phenomena was developed. Wave profile simulations using the continuum model show reasonable overall agreement with the experimental profiles at different stress levels. Because of the approximate nature of the continuum model, all of the experimental details were not reproduced in the wave propagation simulations. It is likely that around and above 10 GPa, other material phenomena not included in our model may need to be considered.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids

Electrical activation in silicon-on-insulator after low energy boron implantation

Antonio F. Saavedra, Kevin S. Jones, Mark E. Law, Kevin K. Chan, and Erin C. Jones

J. Appl. Phys. 96, 1891 (2004); http://dx.doi.org/10.1063/1.1769095 (8 pages) | Cited 7 times

Online Publication Date: 2 August 2004

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We have investigated the electrical activation of implanted boron in silicon-on-insulator (SOI) material using Hall effect, four-point probe, and secondary ion mass spectrometry. Boron was implanted at energies ranging from 1 keV to 6.5 keV with a dose of 3×1014 cm−2 into bonded SOI wafers with surface silicon thickness ranging from 300 math to 1600 math. In one sample set, furnace anneals at 750 °C were performed in a nitrogen ambient for times ranging from 5 min to 48 h. A second sample consisted of isochronal furnace anneals performed from 450 °C to 1050 °C for 30 min. Significantly less activation of boron is observed in SOI at temperatures below 750 °C, regardless of the implant energy and surface silicon thickness. Between 750 °C and 900 °C, the active dose of boron in SOI is similar to that of bulk Si. As the implant energy increases, the fractional activation in thin SOI increases, due to a reduction in boron interstitial clusters (BIC) in the surface Si layer. It is concluded that an increase in the BIC population is the likely source of the low activation observed in SOI. This may be due to an increase in the interstitial supersaturation within the surface Si layer, due to the interface acting as a reflective boundary for interstitials.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.up Other materials
61.72.J- Point defects and defect clusters
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
72.20.My Galvanomagnetic and other magnetotransport effects
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Influence of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells

X. H. Zheng, H. Chen, Z. B. Yan, D. S. Li, H. B. Yu, Q. Huang, and J. M. Zhou

J. Appl. Phys. 96, 1899 (2004); http://dx.doi.org/10.1063/1.1769099 (5 pages) | Cited 6 times

Online Publication Date: 2 August 2004

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We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14 min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300 K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50 K for the sample with the shorter deposition time, and above 100 K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination centers based on a fit to Arrhenius plot of the normalized integrated PL intensity over the entire temperature range. The first centers at higher temperatures show less difference for the two samples. The second centers at lower temperatures can be attributed to the trapping of carriers at the rough interface for the sample with the shorter deposition time and to the thermal quenching of bound excitons for the sample with the longer deposition time, respectively.
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68.65.Fg Quantum wells
73.21.Fg Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
81.40.Gh Other heat and thermomechanical treatments
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Photoluminescence characteristics of Pb-doped, molecular-beam-epitaxy grown ZnSe crystal layers

Yoh Mita, Ryoichi Kuronuma, Masanori Inoue, Shoichiro Sasaki, and Yoshinobu Miyamoto

J. Appl. Phys. 96, 1904 (2004); http://dx.doi.org/10.1063/1.1769101 (5 pages)

Online Publication Date: 2 August 2004

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The characteristic green photoluminescence emission and related phenomena in Pb-doped, molecular-beam-epitaxy (MBE)-grown ZnSe crystal layers were investigated to explore the nature of the center responsible for the green emission. The intensity of the green emission showed a distinct nonlinear dependence on excitation intensity. Pb-diffused polycrystalline ZnSe was similarly examined for comparison. The characteristic green emission has been observed only in MBE-grown ZnSe crystal layers with moderate Pb doping. The results of the investigations on the growth conditions, luminescence, and related properties of the ZnSe crystal layers suggest that the green emission is due to isolated Pb replacing Zn and surrounded with regular ZnSe lattice with a high perfection.
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81.05.Dz II-VI semiconductors
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Hf II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Interfacial properties of strained piezoelectric InGaAs∕GaAs quantum wells grown by metalorganic vapor phase epitaxy on (111)A GaAs

Soohaeng Cho, A. Sanz-Hervás, Jongseok Kim, A. Majerfeld, and B. W. Kim

J. Appl. Phys. 96, 1909 (2004); http://dx.doi.org/10.1063/1.1765862 (5 pages) | Cited 3 times

Online Publication Date: 2 August 2004

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In this work we employed photoreflectance spectroscopy over the temperature range 11-300 K to investigate the heterointerfaces of a strained piezoelectric InGaAs∕GaAs single quantum well structure grown on a (111)A GaAs substrate by metalorganic vapor phase epitaxy. Photoreflectance spectroscopy measurements in combination with a theoretical analysis using the quantum well structural parameters obtained by high-resolution x-ray diffractometry enabled us to evaluate separately the abruptness and roughness of the quantum well interfaces. The excellent agreement between the experimental and calculated transition energies for a quantum well structure with a well width of 41 math and 13% In demonstrates that the heterointerfaces are abrupt. From a theoretical analysis of the temperature dependence of the photoreflectance broadening parameters, based on the Bose-Einstein phonon-coupling model, we determined the longitudinal optical phonon energy and the electron-phonon coupling strength. This analysis shows an interface roughness of less than ±1 monolayer. These results in conjunction with the observation of a narrow photoluminescence linewidth of 9.1 meV indicate the achievement of essentially atomically smooth interfaces in a highly strained (∼1%) piezoelectric InGaAs∕GaAs quantum well structure.
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81.07.St Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
68.65.Fg Quantum wells
68.35.Ct Interface structure and roughness
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

High energy (MeV) ion-irradiated π-conjugated polyaniline: Transition from insulating state to carbonized conducting state

S. K. Park, S. Y. Lee, C. S. Lee, H. M. Kim, J. Joo, Y. W. Beag, and S. K. Koh

J. Appl. Phys. 96, 1914 (2004); http://dx.doi.org/10.1063/1.1769603 (5 pages) | Cited 5 times

Online Publication Date: 2 August 2004

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High energy (MeV) C2+, F2+, and Cl2+ ions were irradiated onto π-conjugated polyaniline emeraldine base (PAN-EB) samples. The energy of an ion beam was controlled to a range of 3–4.5 MeV, with the ion dosage varying from 1×1012 to 1×1016 ions∕cm2. The highest dc conductivity (σdc) at room temperature was measured to be ∼60 S∕cm for 4.5 MeV Cl2+ ion-irradiated PAN-EB samples with a dose of 1×1016 ions∕cm2. We observed the transition of high energy ion-irradiated PAN-EB samples from insulating state to conducting state as a function of ion dosage based on σdc and its temperature dependence. The characteristic peaks of the Raman spectrum of the PAN-EB samples were reduced, while the D-peak (disordered peak) and the G peak (graphitic peak) appeared as the ion dose increased. From the analysis of the D and G peaks of the Raman spectra of the systems compared to multiwalled carbon nanotubes, ion-irradiated graphites, and annealed carbon films, the number of the clusters of hexagon rings with conducting sp2-bonded carbons increased with ion dosage. We also observed the increase in the size of the nanocrystalline graphitic domain of the systems with increasing ion dosage. The intensity of normalized electron paramagnelic resonance signal also increased in correlation with ion dose. The results of this study demonstrate that π-conjugated pristine PAN-EB systems changed from insulating state to carbonized conducting state through high energy ion irradiation with high ion dosage.
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61.80.Jh Ion radiation effects
72.80.Le Polymers; organic compounds (including organic semiconductors)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
76.30.Lh Other ions and impurities
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions

Morphological instability of NiSi1−uGeu on single-crystal and polycrystalline Si1−xGex

J. Seger, T. Jarmar, Z.-B. Zhang, H. H. Radamson, F. Ericson, U. Smith, and S.-L. Zhang

J. Appl. Phys. 96, 1919 (2004); http://dx.doi.org/10.1063/1.1766088 (10 pages) | Cited 13 times

Online Publication Date: 2 August 2004

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The morphological stability of NiSi1−uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1−xGeu is studied (u can be different from x). The agglomeration of NiSi1−uGeu films on Si0.7Ge0.3 occurs at 550°C after rapid thermal processing for 30 s, independently of the crystallinity of the Si1−xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1−xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1−uGeu on sc-Si1−xGex are found to be the stored strain energy in the Si1−xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1−uGeu on poly-Si1−xGex and is not affected by the degree of crystallinity of Si1−xGex. The total free-energy change also includes terms corresponding to the entropy of mixing of Si and Ge in both Si1−xGex and NiSi1−uGeu. Calculations show that the strain energy and the total free-energy change can be 5–7 times (with 30 at.% Ge) the surface/interface and grain-boundary energies in a NiSi film or the grain-boundary energy in an underlying poly-Si. These latter energies are responsible for the agglomeration of NiSi on sc- and poly-Si. The agglomeration takes place primarily via the interdiffusion of Si and Ge between Si1−xGex and NiSi1−uGeu. A structure likely to improve the stability of NiSi1−uGeu∕Si1−xGex is discussed.
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68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
65.40.G- Other thermodynamical quantities

Inspection of an end quenched 0.15%–0.2% C, 0.6%–0.9% Mn steel jominy bar with photothermal radiometric techniques

Yue Liu, Natalie Baddour, Andreas Mandelis, and Chinhua Wang

J. Appl. Phys. 96, 1929 (2004); http://dx.doi.org/10.1063/1.1771478 (5 pages) | Cited 1 time

Online Publication Date: 2 August 2004

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The effect of the cooling rate on hardness and thermal conductivity in a metallurgical Jominy bar made of 0.15%–0.2% C, 0.6%–0.9% Mn (AISI 1018) steel, by means of a water end-quenched heat treatment process without diffusion-controlled case depth, is studied with photothermal radiometry (PTR). It is concluded that our two PTR techniques, common-mode rejection demodulation and conventional 50% duty-cycle square-wave frequency scan, are sensitive to low hardness values and gradients, unlike the high values all previous photothermal studies have dealt with to-date. Both PTR methods have yielded an anticorrelation between thermal conductivity and microhardness in this case as in previous cases with heat-treated and diffusion-controlled case depth profiles. It is shown that the cooling rate strongly affects both hardness and thermal conductivity in the Jominy-bar heat-treating process.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.Bx Metals, semimetals, and alloys
66.30.Xj Thermal diffusivity
81.40.Gh Other heat and thermomechanical treatments

Diffusion of O2 in C60 crystal by measuring the decay of electrical conductivity

Chih-Ming Yang, Jian-Liang Liao, and Kuan-Cheng Chiu

J. Appl. Phys. 96, 1934 (2004); http://dx.doi.org/10.1063/1.1771819 (5 pages) | Cited 11 times

Online Publication Date: 2 August 2004

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The time dependence of the decay of dark electrical conductivity σ(t) from C60 crystals under air exposure was investigated at different temperatures. The decay of σ(t) can be fitted via a stretched exponential function, indicating that the diffusion of O2 in C60 crystal follows a hierarchically constrained dynamic. The diffusivity of molecular oxygen in C60 crystal is estimated using the least-square fitted time constant, and an activation energy EA=1.5 eV corresponding to the diffusion process is deduced from the Arrhenius plot. The mechanism of the diffusion process is then discussed.
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66.30.J- Diffusion of impurities
72.40.+w Photoconduction and photovoltaic effects
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
73.50.Pz Photoconduction and photovoltaic effects
61.72.J- Point defects and defect clusters
73.61.Wp Fullerenes and related materials

Molecular dynamics simulations of boron diffusion in SiGe

Liguo Wang and Paulette Clancy

J. Appl. Phys. 96, 1939 (2004); http://dx.doi.org/10.1063/1.1766410 (8 pages) | Cited 2 times

Online Publication Date: 2 August 2004

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Transient enhanced diffusion (TED) of boron poses a limit to the formation of ultrashallow junctions. To suppress TED of boron, other species (e.g., Ge) can be introduced into the Si substrate. Experiments have shown that boron diffusivity decreased rapidly as Ge concentration increased to 40% Ge. There is no consensus on the cause for this decrease in diffusivity. Here, an ab initio derived energy database was used to fit classical potential models in order to simulate boron diffusion in SiGe on larger length and time-frames than are possible using ab initio models. In this paper, a set of Stillinger-Weber potential parameters for Ge-B and Si-Ge-B has been constructed, allowing a molecular dynamics study of boron diffusion in SiGe alloys to be carried out. Molecular dynamics simulations of boron B diffusion in Si compared to that in SiGe alloys suggest that different trapping mechanisms dominate: B in Si is trapped in substitutional positions, whereas B in SiGe alloys is trapped in interstitial positions. The number of boron interstitials increases as Ge concentration increases, reaches a maximum at 50% Ge, and then decreases as the amount of Ge increases to 100%. Concordantly, the number of Si∕Ge interstitials followed the opposite trend: Their numbers decreased, reached a minimum at 50% Ge and then increased again as the Ge concentration increased. This confirmed ab initio predictions and provided an exploration to the origin of retarded boron diffusion in SiGe alloys.
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61.72.J- Point defects and defect clusters
66.30.J- Diffusion of impurities

Effects of degree of three-dimensional order and Fe impurities on photoluminescence of boron nitride

B. Yao, Li Liu, W. H. Su, Z. X. Shen, L. Liu, W. X. Sun, and J. Ding

J. Appl. Phys. 96, 1947 (2004); http://dx.doi.org/10.1063/1.1772880 (6 pages) | Cited 6 times

Online Publication Date: 2 August 2004

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Amorphous boron nitride (a-BN) was produced by ball milling of hexagonal BN (h-BN). Turbostratic BN (t-BN) and mesographite BN (m-BN) with different degrees of three-dimensional order (DTDO) were subsequently prepared by annealing the a-BN at different temperatures. The photoluminescence (PL) of the BN samples with different structures and DTDOs was investigated in the visible region from 460 to 800 nm. The h-, a-, and t-BN samples, which have completely ordered, disordered and two-dimensionally ordered structures, respectively, emitted weak continuums. The m-BN samples with three-dimensionally ordered structures gave discrete PL bands, which we attributed to the presence of NB antisites or a complex formed by an Fe atom and a B vacancy in the BN layer. The intensity and energy of the PL bands changed greatly with DTDO and could be tuned by varying the annealing temperature. The strongest PL bands at 593 and 612 nm were observed in one of the m-BN samples produced at an annealing temperature of 1100 °C, and their intensity was about 1000 times the intensity of h-BN. Unintentional Fe contamination did not affect the PL nature of the m-BN samples but increased the PL intensities of some bands greatly.
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81.05.Ea III-V semiconductors
81.05.Gc Amorphous semiconductors
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
61.72.Yx Interaction between different crystal defects; gettering effect
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