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1 May 2010

Volume 107, Issue 9, Articles (09xxxx)

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back to top Lasers, Optics, and Optoelectronics

Enhancement of Faraday rotation effect in heterostructures with magneto-optical metals

Lijuan Dong, Haitao Jiang, Hong Chen, and Yunlong Shi

J. Appl. Phys. 107, 093101 (2010); doi:10.1063/1.3406152 (4 pages) | Cited 1 time

Online Publication Date: 3 May 2010

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We theoretically study the transmission and Faraday rotation effect in the heterostructure composed of an all-dielectric photonic crystal and a magnetic metal. Under the tunneling mechanism, the electromagnetic fields can totally enter the structure and localize at the interface between photonic crystal and magnetic metal. Because of the localized electromagnetic fields, the transmission and Faraday rotation in the heterostructure are simultaneously boosted.
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78.20.Ls Magneto-optical effects
42.70.Qs Photonic bandgap materials

Two-dimensional subwavelength-focused imaging using a near-field probe at a λ/4 working distance

Loïc Markley and George V. Eleftheriades

J. Appl. Phys. 107, 093102 (2010); doi:10.1063/1.3407518 (5 pages) | Cited 3 times

Online Publication Date: 4 May 2010

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Two-dimensional (2D) subwavelength imaging using a near-field antenna array probe is demonstrated experimentally at a probe-to-object separation distance of λ/4. Field perturbations caused by the presence of small objects are detected by monitoring the input reflection coefficient as the probe is scanned. The probe is designed to produce a subwavelength focal spot with a 0.217λ full-width half-maximum beam width. Propagating components are suppressed through destructive interference, enhancing the evanescent field enough to resolve objects spaced by 0.259λ. The poor resolving capability of a conventional single-element probe at this working distance is also addressed; it is shown that even objects spaced over a wavelength apart are inaccurately detected. A full 2D imaging experiment is carried out using eight scattered objects. The single element probe is unable to resolve any of the objects, while all but the two most closely spaced pairs are resolved by the array probe.
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84.40.Ba Antennas: theory, components and accessories

Effects of Li+ on structure and spectroscopic properties of Er3+/Li+ codoped Sb2O3–Na2O–SiO2 glasses

Lu Liu, Yuxiao Wang, Yunfeng Bai, Xueru Zhang, Kun Yang, Le Yang, and Yinglin Song

J. Appl. Phys. 107, 093103 (2010); doi:10.1063/1.3408315 (5 pages) | Cited 1 time

Online Publication Date: 4 May 2010

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Judd–Ofelt (JO) analysis of Er3+ ions spectral properties in Er3+ doped and Er3+/Li+ codoped Sb2O3–Na2O–SiO2 glasses are performed based on the optical absorption spectra at room temperature. Three phenomenological parameters Ω2, Ω4, and Ω6 are determined. The effects of Li+ on the JO parameters are discussed in terms of the variations in Er3+ bonding nature and ligand fields around Er3+ sites.
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61.43.Fs Glasses
78.55.-m Photoluminescence, properties and materials

Tunable slow light in semiconductor metamaterial in a broad terahertz regime

Qiang Bai (白强), Cong Liu (刘聪), Jing Chen, Chen Cheng (程晨), Ming Kang (康明), and Hui-Tian Wang (王慧田)

J. Appl. Phys. 107, 093104 (2010); doi:10.1063/1.3357291 (8 pages) | Cited 11 times

Online Publication Date: 4 May 2010

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We demonstrate theoretically and numerically that tunable slow light can be realized in planar semiconductor metamaterials with the unit cell composed of two different elements in a broad terahertz regime. In the unit cell, one element is a semiconductor split ring resonator and another one is a semiconductor cut wire. The interaction between the two elements of the unit cell, induced directly or indirectly by the incident electromagnetic wave, leads to a transparent window, resembling the classical analog of electromagnetically induced transparency. This transparent window, caused by the coupling of bright-bright modes or dark-bright modes, can be continuously tuned in a broad frequency regime. The strong normal phase dispersion in the vicinity of this transparent window results in the slow light effect. This scheme provides an alternative way to achieve tunable slow light in a broad frequency band and can find important applications in active and reversibly tunable slow light devices.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.40.-x Radiowave and microwave (including millimeter wave) technology

Tunable middle infrared radiation generation in a GaSe crystal

Y. Z. Lu, X. B. Wang, X. W. Zhu, X. L. Zhang, D. L. Zuo, and Z. H. Cheng

J. Appl. Phys. 107, 093105 (2010); doi:10.1063/1.3415533 (4 pages) | Cited 1 time

Online Publication Date: 4 May 2010

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Tunable second harmonic generation of pulsed CO2 laser radiation in a GaSe crystal was demonstrated. The nonlinear optical properties of GaSe and phase-matching conditions were investigated, and the best fitted dispersion relationships for this crystal were also determined. External conversion efficiency of 0.1% with unfocused pumped radiation had been achieved and maximum single pulse energy of 0.19 mJ was generated at 5.3 μm.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Thermophotonic heat pump—a theoretical model and numerical simulations

Jani Oksanen and Jukka Tulkki

J. Appl. Phys. 107, 093106 (2010); doi:10.1063/1.3419716 (8 pages) | Cited 1 time

Online Publication Date: 4 May 2010

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We have recently proposed a solid state heat pump based on photon mediated heat transfer between two large-area light emitting diodes coupled by the electromagnetic field and enclosed in a semiconductor structure with a nearly homogeneous refractive index. Ideally the thermophotonic heat pump (THP) allows heat transfer at Carnot efficiency but in reality there are several factors that limit the efficiency. The efficient operation of the THP is based on the following construction factors and operational characteristics: (1) broad area semiconductor diodes to enable operation at optimal carrier density and high efficiency, (2) recycling of the energy of the emitted photons, (3) elimination of photon extraction losses by integrating the emitting and the absorbing diodes within a single semiconductor structure, and (4) eliminating the reverse thermal conduction by a nanometer scale vacuum layer between the diodes. In this paper we develop a theoretical model for the THP and study the fundamental physical limitations and potential of the concept. The results show that even when the most important losses of the THPs are accounted for, the THP has potential to outperform the thermoelectric coolers especially for heat transfer across large temperature differences and possibly even to compete with conventional small scale compressor based heat pumps.
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07.20.Pe Heat engines; heat pumps; heat pipes
85.60.Jb Light-emitting devices

Many-body design of highly strained GaInNAs electroabsorption modulators on GaInAs ternary substrates

Takeshi Fujisawa, Masakazu Arai, and Fumiyoshi Kano

J. Appl. Phys. 107, 093107 (2010); doi:10.1063/1.3360937 (7 pages) | Cited 1 time

Online Publication Date: 4 May 2010

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Electroabsorption in highly strained GaInAs and GaInNAs quantum wells (QWs) grown on GaInAs or quasi-GaInAs substrates is investigated by using microscopic many-body theory. The effects of various parameters, such as strain, barrier height, substrate composition, and temperature are thoroughly examined. It is shown that the value of the absorption coefficient strongly depends on the depth of the QWs under large bias electric field due to the small overlap integral of wave functions between the conduction and valence bands. The use of GaInNAs QWs makes the strain in the well layer very small. Further, the effective quantum-well depth is increased in GaInNAs QWs due to the anticrossing interaction between the conduction and N-resonant bands, making it possible to obtain larger absorption coefficient under large bias electric fields without using wide-band gap materials for barriers.
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42.79.Hp Optical processors, correlators, and modulators
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Phase properties of reflected light in photonic band gap

Qiao-Feng Dai, Sheng Lan, Li-Jun Wu, and He-Zhou Wang

J. Appl. Phys. 107, 093108 (2010); doi:10.1063/1.3383045 (6 pages)

Online Publication Date: 7 May 2010

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We find that the phase shifts of reflected light within band gap of two-dimensional photonic crystal (PC) are as follows: with frequency altering from the lower edge to the upper edge of first stop band, the reflection phase shift varies from −π to 0 for the PC’s unit cell with the high-index material near the center, while it varies from 0 to π for that with low-index material near the center. For the higher-order stop band, there exists a certain value of filling fraction, which makes the phase shifts in higher-order stop bands almost the same as that in the first stop band. When the filling fraction is far from that value, the phase shifts are significantly different. The further study on the Bloch modes demonstrates that their distribution of electric field and magnetic field determines the phase shifts. Moreover, we have found that, in the overlap area of transverse magnetic and transverse electric stop band, the phase difference between two polarizations of reflected light can remain invariant in a broad frequency region. Based on this property, the broadband and angle-insensitive phase retarders are designed. These interesting phase characteristics will bring about many potential applications.
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42.70.Qs Photonic bandgap materials
42.25.Gy Edge and boundary effects; reflection and refraction
42.79.Ci Filters, zone plates, and polarizers

Impurity-related photoluminescence line shape asymmetry in GaAs/AlAs multiple quantum wells: Fractional-dimensional space approach

Jurgis Kundrotas, Aurimas Čerškus, Gintaras Valušis, Agne Johannessen, Erik Johannessen, Paul Harrison, and Edmund H. Linfield

J. Appl. Phys. 107, 093109 (2010); doi:10.1063/1.3342673 (7 pages) | Cited 1 time

Online Publication Date: 10 May 2010

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The optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels were investigated at different excitation intensities. A fractional dimensionality model was used to describe the free hole-donor and free electron-acceptor transitions in the quantum wells. The measured photoluminescence spectra from samples of different doping level related to donor-impurity or acceptor-impurity induced effects in the photoluminescence lineshape, were compared within the framework of these model calculations. Both experimentally and theoretically it was shown that acceptor and donor related optical transitions and photoluminescence line shapes were related to the difference in the effective masses of holes and electrons. This effect also leads to a difference in the photoluminescence spectra in which the luminescence band for the donor related spectrum is narrower in comparison to the acceptor related spectrum.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.sd Impurity concentration
back to top Plasmas and Electrical Discharges

High power microwave generation from coaxial virtual cathode oscillator using graphite and velvet cathodes

Rakhee Menon, Amitava Roy, S. K. Singh, S. Mitra, Vishnu Sharma, Senthil Kumar, Archana Sharma, K. V. Nagesh, K. C. Mittal, and D. P. Chakravarthy

J. Appl. Phys. 107, 093301 (2010); doi:10.1063/1.3399650 (6 pages) | Cited 3 times

Online Publication Date: 3 May 2010

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High power microwave (HPM) generation studies were carried out in KALI-5000 pulse power system. The intense relativistic electron beam was utilized to generate HPMs using a coaxial virtual cathode oscillator. The typical electron beam parameters were 350 kV, 25 kA, and 100 ns, with a few hundreds of ampere per centimeter square current density. Microwaves were generated with graphite and polymer velvet cathode at various diode voltage, current, and accelerating gaps. A horn antenna setup with diode detector and attenuators was used to measure the microwave power. It was observed that the microwave power increases with the diode voltage and current and reduces with the accelerating gap. It was found that both the peak power and width of the microwave pulse is larger for the velvet cathode compared to the graphite cathode. In a coaxial vircator, velvet cathode is superior to the graphite cathode due to its shorter turn on time and better electron beam uniformity.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Effect of resonance in external radio-frequency circuit on very high frequency plasma discharge

Shahid Rauf, Zhigang Chen, and Ken Collins

J. Appl. Phys. 107, 093302 (2010); doi:10.1063/1.3406153 (6 pages) | Cited 2 times

Online Publication Date: 3 May 2010

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A fully electromagnetic plasma model for an asymmetric capacitively coupled plasma discharge is used to understand the interaction between the external radio-frequency (rf) distributed circuit and the plasma. The plasma is excited using a 150 MHz rf source connected to the top electrode, the bottom electrode is connected to a shorted transmission line, and the electrodes are separated from the chamber walls through dielectric rings. Under typical conditions, the electron density peaks in the center of the plasma chamber due to the standing electromagnetic wave and the rf current from the top electrode primarily returns through the bottom electrode. When the electrical length of the bottom transmission line is adjusted such that it presents a large (open-circuit) impedance at the plasma chamber interface, the rf return current shifts from the bottom electrode to the chamber wall. As a consequence, the peak in electron density also moves from the center of the chamber toward its outer periphery.
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52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources
84.30.-r Electronic circuits

Transitions between corona, glow, and spark regimes of nanosecond repetitively pulsed discharges in air at atmospheric pressure

David Z. Pai, Deanna A. Lacoste, and Christophe O. Laux

J. Appl. Phys. 107, 093303 (2010); doi:10.1063/1.3309758 (15 pages) | Cited 12 times

Online Publication Date: 6 May 2010

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In atmospheric pressure air preheated from 300 to 1000 K, the nanosecond repetitively pulsed (NRP) method has been used to generate corona, glow, and spark discharges. Experiments have been performed to determine the parameter space (applied voltage, pulse repetition frequency, ambient gas temperature, and interelectrode gap distance) of each discharge regime. In particular, the experimental conditions necessary for the glow regime of NRP discharges have been determined, with the notable result that there exists a minimum and maximum gap distance for its existence at a given ambient gas temperature. The minimum gap distance increases with decreasing gas temperature, whereas the maximum does not vary appreciably. To explain the experimental results, an analytical model is developed to explain the corona-to-glow (C-G) and glow-to-spark (G-S) transitions. The C-G transition is analyzed in terms of the avalanche-to-streamer transition and the breakdown field during the conduction phase following the establishment of a conducting channel across the discharge gap. The G-S transition is determined by the thermal ionization instability, and we show analytically that this transition occurs at a certain reduced electric field for the NRP discharges studied here. This model shows that the electrode geometry plays an important role in the existence of the NRP glow regime at a given gas temperature. We derive a criterion for the existence of the NRP glow regime as a function of the ambient gas temperature, pulse repetition frequency, electrode radius of curvature, and interelectrode gap distance.
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52.80.Hc Glow; corona
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

Simulations of direct-current air glow discharge at pressures ∼ 1 Torr: Discharge model validation

Shankar Mahadevan and Laxminarayan L. Raja

J. Appl. Phys. 107, 093304 (2010); doi:10.1063/1.3374711 (11 pages)

Online Publication Date: 6 May 2010

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Computational simulations of air glow discharge phenomena in the pressure range typical of plasma actuator applications for high speed flow control are presented. The model is based on a self-consistent, multispecies, and multitemperature continuum description of the plasma. A reduced air plasma model suitable for multidimensional simulations with 11 species and 21 gas phase chemical reactions is validated against experimental results in the literature. The discharge model predicts experimentally observed glow mode discharge operation, the current-voltage characteristics of the discharge, and spatial profiles of the electron temperature and positive ion number densities. For pressures of order 1 Torr, O2+ and N2+ are the dominant positive ion species in the discharge, and the concentration of O− negative ion is comparable to electron concentration. The two-dimensional structure of the discharge is predicted by the model is found to be in agreement with qualitative observations from the experiments.
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52.80.Hc Glow; corona
52.65.-y Plasma simulation
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.-b Plasma properties
52.20.Fs Electron collisions

H-atom interaction with amorphous hydrocarbon films: Effect of surface temperature, H flux and exposure time

A. Erradi, R. Clergereaux, and F. Gaboriau

J. Appl. Phys. 107, 093305 (2010); doi:10.1063/1.3369286 (6 pages) | Cited 2 times

Online Publication Date: 7 May 2010

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In the present paper, we study the interaction between atomic hydrogen generated in a microwave afterglow with amorphous hydrogenated carbon films. A simple surface model is described and compared with the experimental results. Erosion rate is time dependent and exhibits a transient regime before reaching a constant value. Estimate of the modified film thickness by ellipsometry shows that thickness increases with time and becomes constant and equal to 1.4 nm when reaching the permanent regime. In addition, this limit is independent on the conditions, e.g., on hydrogen flux and temperature. Erosion rate depends linearly on hydrogen flux arriving at the surface and shows an exponential increase with surface temperature. A simple model proposed in the paper is in good agreement with the experimental data and allows giving an estimate of the erosion activation energy Ea = 0.2 eV. This value is in agreement with the energy involved in the reaction between hydrogen atom and carbon atom in sp3 hybridization.
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81.05.U- Carbon/carbon-based materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
68.55.jd Thickness
52.80.Hc Glow; corona

Ion energy distribution near a plasma meniscus with beam extraction for multi element focused ion beams

Jose V. Mathew, Samit Paul, and Sudeep Bhattacharjee

J. Appl. Phys. 107, 093306 (2010); doi:10.1063/1.3369287 (5 pages) | Cited 2 times

Online Publication Date: 7 May 2010

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An earlier study of the axial ion energy distribution in the extraction region (plasma meniscus) of a compact microwave plasma ion source showed that the axial ion energy spread near the meniscus is small ( ∼ 5 eV) and comparable to that of a liquid metal ion source, making it a promising candidate for focused ion beam (FIB) applications [ J. V. Mathew and S. Bhattacharjee, J. Appl. Phys. 105, 96101 (2009) ]. In the present work we have investigated the radial ion energy distribution (IED) under the influence of beam extraction. Initially a single Einzel lens system has been used for beam extraction with potentials up to −6 kV for obtaining parallel beams. In situ measurements of IED with extraction voltages upto −5 kV indicates that beam extraction has a weak influence on the energy spread (±0.5 eV) which is of significance from the point of view of FIB applications. It is found that by reducing the geometrical acceptance angle at the ion energy analyzer probe, close to unidirectional distribution can be obtained with a spread that is smaller by at least 1 eV.
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52.50.Dg Plasma sources
41.75.Cn Negative-ion beams
52.59.-f Intense particle beams and radiation sources

Micron-focused ion beamlets

Abhishek Chowdhury and Sudeep Bhattacharjee

J. Appl. Phys. 107, 093307 (2010); doi:10.1063/1.3371688 (5 pages) | Cited 2 times

Online Publication Date: 10 May 2010

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A multiple beam electrode system (MBES) is used to provide focused ion beamlets of elements from a compact microwave plasma. In this study, a honeycomb patterned plasma electrode with micron size apertures for extracting ion beamlets is investigated. The performance of the MBES is evaluated with the help of two widely adopted and commercially available beam simulation tools, AXCEL-INP and SIMION, where the input parameters are obtained from our experiments. A simple theoretical model based upon electrostatic ray optics is employed to compare the results of the simulations. It is found that the results for the beam focal length agree reasonably well. Different geometries are used to optimize the beam spot size and a beam spot ∼ 5–10 μm is obtained. The multiple ion beamlets will be used to produce microfunctional surfaces on soft matter like polymers. Additionally, the experimental set-up and plans are presented in the light of above applications.
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29.25.Ni Ion sources: positive and negative
41.85.Ar Particle beam extraction, beam injection
52.40.Mj Particle beam interactions in plasmas
52.65.-y Plasma simulation
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Growth of Bi doped cadmium zinc telluride single crystals by Bridgman oscillation method and its structural, optical, and electrical analyses

V. Carcelén, P. Hidalgo, J. Rodríguez-Fernández, and E. Dieguez

J. Appl. Phys. 107, 093501 (2010); doi:10.1063/1.3275054 (4 pages)

Online Publication Date: 3 May 2010

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The II-VI compound semiconductor cadmium zinc telluride (CZT) is very useful for room temperature radiation detection applications. In the present research, we have successfully grown Bi doped CZT single crystals with two different zinc concentrations (8 and 14 at. %) by the Bridgman oscillation method, in which one experiment has been carried out with a platinum (Pt) tube as the ampoule support. Pt also acts as a cold finger and reduces the growth velocity and enhances crystalline perfection. The grown single crystals have been studied with different analysis methods. The stoichiometry was confirmed by energy dispersive by x-ray and inductively coupled plasma mass spectroscopy analyses and it was found there is no incorporation of impurities in the grown crystal. The presence of Cd and Te vacancies was determined by cathodoluminescence studies. Electrical properties were assessed by I-V analysis and indicated higher resistive value (8.53×108 Ω cm) for the crystal grown with higher zinc concentration (with Cd excess) compare to the other (3.71×105 Ω cm).
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81.10.Fq Growth from melts; zone melting and refining
61.72.U- Doping and impurity implantation
72.80.Ey III-V and II-VI semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.jd Vacancies
78.60.Hk Cathodoluminescence, ionoluminescence
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

An analysis of temperature-dependent photocurrent-spectra in photoconductive CuGaSe2 layers

S. Y. Yun, K. J. Hong, T. S. Jeong, and C. J. Youn

J. Appl. Phys. 107, 093502 (2010); doi:10.1063/1.3399770 (5 pages)

Online Publication Date: 3 May 2010

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The photocurrent (PC) variation in photoconductive CuGaSe2 (CGS) layers had been investigated as a function of temperature. Three peaks A, B, and C of the PC spectra were associated with the band-to-band transitions. Thus, the parameters of the crystal-field splitting (Δcr) and spin-orbit splitting (Δso) were directly acquired through the PC measurement. The Δcr and Δso were 0.0903 eV and 0.2130 eV at 10 K, respectively. From the relations of peak position and temperature, the temperature dependence of the band-gap energy is well described by Eg(T) = Eg(0)−(8.63×10−4)T2/(336+T). Also, the Eg(0) is estimated to be 1.7952, 1.8855, and 2.0985 eV at the valence-band states of Γ7(A), Γ6(B), and Γ7(C), respectively. However, the behavior of the PC was different from that generally observed in other semiconductors, the PC intensities decreased with decreasing temperature. From the relation of log Jph versus 1/T, where Jph is the PC density, two dominant levels were observed, one at high temperature and the other at low temperature. By comparing the results of the PC and photoluminescence, we confirmed that the activation energy of 82.7 meV at high temperatures is related to the dissociation energy of donor level due to Se vacancies. Consequently, we suggest that in photoconductive CGS layers, the trapping center due to native defects and impurities limits the PC signal with decreasing temperature.
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81.05.Hd Other semiconductors
71.20.Nr Semiconductor compounds
72.40.+w Photoconduction and photovoltaic effects
78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors
73.61.Le Other inorganic semiconductors

Size dependent strengthening mechanisms in sputtered Fe/W multilayers

Nan Li, K. Y. Yu, J. Lee, H. Wang, and X. Zhang

J. Appl. Phys. 107, 093503 (2010); doi:10.1063/1.3400130 (7 pages) | Cited 4 times

Online Publication Date: 3 May 2010

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We investigate size dependent strengthening mechanisms in sputtered Fe/W multilayers with individual layer thickness, h, varying from 1 to 200 nm. Microstructure analyses reveal that Fe/W has incoherent bcc/bcc interface when h is greater than 5 nm. When h decreases to 1–2.5 nm, the interface becomes semicoherent, and Fe and W show significant lattice distortions comparing to their bulk counterpart due to interface constraint. The layer thickness dependent drastic variations in x-ray diffraction profiles are simulated well by using an analytical model. Film hardness increases with decreasing h, and approaches a maximum value of 12.5 GPa when h is 1 nm. The layer thickness dependent film hardnesses are compared with analytical models. Koehler’s image force plays a major role in determining the maximum strength of composites at smaller h.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.05.Bx Metals, semimetals, and alloys

Optical spectroscopy investigation on distribution of Eu3+ in nanostructured glass ceramics

Yunlong Yu, Fangyi Weng, Daqin Chen, Ping Huang, and Yuansheng Wang

J. Appl. Phys. 107, 093504 (2010); doi:10.1063/1.3402458 (5 pages) | Cited 1 time

Online Publication Date: 3 May 2010

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The time-resolved luminescence spectra of the Eu3+ doped SiO2–Al2O3–NaF–YF3–EuF3 precursor glass reveal that Eu3+ ions locate in both the oxygen-coordination environment and the fluorine-coordination one. After crystallization induced by heat treatment, the orthorhombic YF3 nanocrystals with mean size of 22 nm embedded homogeneously in the glassy matrix. The Stark splitting emission, the low electric dipole 5D0→7F2 transition, the disappearance of the O2−–Eu3+ charge transfer band and the reduction in Ω2 value indicate the partition of Eu3+ into the YF3 lattice. Moreover, the nearly single-exponential luminescence decay curves of the Eu3+:5D0 and 5D1 levels for the 0.1% Eu3+ doped glass ceramic evidence that Eu3+ ions mainly occupy the Y3+ sites.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
81.05.Pj Glass-based composites, vitroceramics
78.55.Hx Other solid inorganic materials
78.47.jd Time resolved luminescence
61.72.up Other materials

Phase transformation of Mg–Fe alloys

Yasuhiro Yoneda, Hiroshi Abe, Takeshi Ohshima, and Hirohisa Uchida

J. Appl. Phys. 107, 093505 (2010); doi:10.1063/1.3402498 (6 pages)

Online Publication Date: 3 May 2010

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An Mg–Fe alloy system prepared through mechanical alloying (MA) was structurally analyzed. MA can produce single-phase bcc alloys using Mg concentrations up to about 15 mol %. Use of conventional average structure analysis and x-ray pair-distribution function method enabled the long-range and short-range order structures of the Mg–Fe alloys to be bridged. The substituted Mg atoms were randomly arranged in the low-Mg composition but started to have an order structure. The partially ordered Mg–Fe alloy undergoes an austenitic (cubic) to martensitic (orthorhombic) phase change, as increasing Mg composition.
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81.05.Bx Metals, semimetals, and alloys
81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.66.Dk Alloys
64.70.kd Metals and alloys

Structural, electronic, and optical properties of α, β, and γ-TeO2

Yanlu Li, Weiliu Fan, Honggang Sun, Xiufeng Cheng, Pan Li, and Xian Zhao

J. Appl. Phys. 107, 093506 (2010); doi:10.1063/1.3406135 (7 pages) | Cited 2 times

Online Publication Date: 3 May 2010

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First-principles calculations of the structural, electronic, and optical properties of TeO2 polymorphs were performed with the density functional theory plane-wave pseudopotential method. The results reveal that all the three crystalline TeO2 phases are wide-gap semiconductors and the lone electron pairs have contributions near the Fermi energy level. The layer structure of β-TeO2 leads to the obvious anisotropy of the complex dielectric function. Considering the lattice contribution of dielectric constants, we predict the static dielectric constants of TeO2 polymorphs. For α-TeO2, the calculated values of 19.0 for ε1⊥ and 25.3 for ε1∥ agree well with the experimental value, and the β- and γ-phases also belong to the high dielectric constant materials. Besides, a special collective plasma resonance for γ-TeO2 has been found in lower energy. It corresponds to the small peak in the imaginary part of dielectric function, and reflects the abrupt reduction in the reflectivity spectrum.
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71.20.Nr Semiconductor compounds
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)
78.68.+m Optical properties of surfaces
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Giant electrorheological fluid comprising nanoparticles: Carbon nanotube composite

Jiaxing Li, Xiuqing Gong, Shuyu Chen, Weijia Wen, and Ping Sheng

J. Appl. Phys. 107, 093507 (2010); doi:10.1063/1.3407503 (5 pages) | Cited 4 times

Online Publication Date: 3 May 2010

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We have fabricated suspensions exhibiting the giant electrorheological (GER) effect comprising nanoparticles—multiwall carbon nanotubes (MCNTs) composite particles dispersed in silicone oil. This type of GER fluids display dramatically enhanced antisedimentation characteristic without sacrificing the yield stress. The nanoparticles-nanotubes composites were fabricated by modifying the coprecipitation method with MCNTs and urea-coated barium titanyl-oxylate (BTRU) nanoparticles as the components. The composite solid particles are denoted MCNT-BTRU. In the best cases, stabilized suspensions with MCNT-BTRU particles dispersed in silicone oil have been maintained for several months without any appreciable sedimentation being observed. Both the sedimentary and rheological properties of the MCNT-BTRU suspension were systematically studied and compared with their BTRU counterparts. Yield stress as high as 194 kPa was obtained in the MCNT-BTRU suspensions. The MCNT-BTRU based GER fluids, with their antisedimentation characteristic, may have broad engineering applications.
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47.65.Gx Electrorheological fluids
83.60.La Viscoplasticity; yield stress
81.16.-c Methods of micro- and nanofabrication and processing
82.70.Kj Emulsions and suspensions
81.30.Mh Solid-phase precipitation

87Rb and 133Cs nuclear magnetic resonance study of the structural properties of mixed RbxCs2−xZnCl4 (x = 0, 1, and 2) crystals

Ae Ran Lim

J. Appl. Phys. 107, 093508 (2010); doi:10.1063/1.3406146 (6 pages) | Cited 2 times

Online Publication Date: 4 May 2010

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The structures of mixed RbxCs2−xZnCl4 (x = 0, 1, and 2) single crystals grown by using the slow evaporation method were determined with x-ray diffraction. In addition, the NMR spectra and the spin-lattice relaxation times, T1, of the 87Rb and 133Cs nuclei of the three crystals were determined by using nuclear magnetic resonance (NMR) spectroscopy. The spin-lattice relaxation times, T1, of the Cs-based compounds are very much longer than those of the Rb-based compounds. The differences between the T1 values of the Rb and Cs nuclei are due to the difference between their electric quadrupole moments. Further, we analyzed the crystallographic structures of these crystals by considering the occupation probabilities (Rb or Cs) of the two cationic sites. Our NMR experimental results confirm that there are two crystallographically inequivalent Rb sites, Rb(1) and Rb(2), in Rb2ZnCl4 and two crystallographically inequivalent Cs sites, Cs(1) and Cs(2), in Cs2ZnCl4. And, only one Rb site and only one Cs site in RbCsZnCl4 was obtained. The Cs and Rb occupation rates of each of the two available sites, A1 and A2, were determined from the NMR signals.
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61.66.-f Structure of specific crystalline solids
76.60.Es Relaxation effects
68.03.Fg Evaporation and condensation of liquids
81.10.Dn Growth from solutions

Theoretical investigation of the high pressure structure, lattice dynamics, phase transition, and thermal equation of state of titanium metal

Cui-E Hu, Zhao-Yi Zeng, Lin Zhang, Xiang-Rong Chen, Ling-Cang Cai, and Dario Alfè

J. Appl. Phys. 107, 093509 (2010); doi:10.1063/1.3407560 (10 pages) | Cited 4 times

Online Publication Date: 4 May 2010

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We report a detailed first-principles calculation to investigate the structures, elastic constants, and phase transition of Ti. The axial ratios of both α-Ti and ω-Ti are nearly constant under hydrostatic compression, which confirms the latest experimental results. From the high pressure elastic constants, we find that the α-Ti is unstable when the applied pressures are larger than 24.2 GPa, but the ω-Ti is mechanically stable at all range of calculated pressure. The calculated phonon dispersion curves agree well with experiments. Under compression, we captured a large softening around Γ point of α-Ti. When the pressure is raised to 35.9 GPa, the frequencies around the Γ point along Γ-M-K and Γ-A in transverse acoustical branches become imaginary, indicating a structural instability. Within quasiharmonic approximation, we obtained the full phase diagram and accurate thermal equations of state of Ti. The phase transition ω-Ti→α-Ti→β-Ti at zero pressure occurs at 146 K and 1143 K, respectively. The predicted triple point is at 9.78 GPa, 931 K, which is close to the experimental data. Our thermal equations of state confirm the available experimental results and are extended to a wider pressure and temperature range.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
81.30.Bx Phase diagrams of metals, alloys, and oxides
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
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