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30 May 2011

Volume 98, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 223101 (2011); http://dx.doi.org/10.1063/1.3595266 (3 pages)

Takahiro Ohori, Yasuhide Ohno, Kenzo Maehashi, Koichi Inoue, Yutaka Hayashi, and Kazuhiko Matsumoto
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Bragg polariton luminescence from a GaN membrane embedded in all dielectric microcavity

E. Trichas, N. T. Pelekanos, E. Iliopoulos, E. Monroy, K. Tsagaraki, A. Kostopoulos, and P. G. Savvidis

Appl. Phys. Lett. 98, 221101 (2011); http://dx.doi.org/10.1063/1.3595481 (3 pages)

Online Publication Date: 31 May 2011

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We report on the development of a band gap-selective photochemical etching technique capable of producing 200 nm thick optical quality freestanding GaN membranes. The use of low electrolyte concentration combined with intense excitation by a laser source are shown to yield highly anisotropic etch profile with optical quality etched surfaces. Using this technique, high quality GaN microcavity is fabricated by embedding the GaN membrane inside an all-dielectric mirror cavity. In these structures, Bragg polariton photoluminescence is observed at room temperature.
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78.55.Cr III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
82.45.Mp Thin layers, films, monolayers, membranes
71.20.Nr Semiconductor compounds
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Highly catalytic counter electrodes for organic redox couple of thiolate/disulfide in dye-sensitized solar cells

Liang Wang, Mingxing Wu, Yurong Gao, and Tingli Ma

Appl. Phys. Lett. 98, 221102 (2011); http://dx.doi.org/10.1063/1.3595684 (3 pages) | Cited 4 times

Online Publication Date: 31 May 2011

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We synthesized a low-cost, highly catalytic tungsten carbide that was embedded in ordered mesoporous carbon (WC-OMC). This was used as a counter electrode (CE) in dye-sensitized solar cells (DSCs). For comparison, we also evaluated the catalytic activity of bare WC, and several normal carbon materials for the organic redox couple of thiolate/disulfide (T−/T2). The DSCs showed highly photovoltaic conversion efficiencies, ranging from 4.75% to 5.34%. The efficiency of the DSC composed of WC-OMC was 45% higher than that of Pt. Based on kinetic studies, the increased efficiency was caused by the increased exchange current density and decreased charge transfer resistance.
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81.05.U- Carbon/carbon-based materials
88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
81.05.Rm Porous materials; granular materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Optical dissolved oxygen sensor utilizing molybdenum chloride cluster phosphorescence

Ruby N. Ghosh, Per A. Askeland, Sage Kramer, and Reza Loloee

Appl. Phys. Lett. 98, 221103 (2011); http://dx.doi.org/10.1063/1.3595483 (3 pages)

Online Publication Date: 1 June 2011

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We report on an optical oxygen sensor for aqueous media. The phosphorescent signal from the indicator, K2Mo6Cl14, immobilized in a polymer matrix, is quenched by ground state 3O2. Continuous measurements (Δt = 10 s) over 36 h in oxygen atmospheres (0%–21%) were obtained with a signal to noise ratio better than 150. Photobleaching was not observed over ∼ 13 000 measurements. The senor response at 10, 22, and 37 °C water is governed by bimolecular collisional quenching, as evidenced by a linear fit to the Stern–Volmer equation for dissolved oxygen in the range 0<[O2]<3×10−4.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

A InGaN/GaN quantum dot green (λ = 524 nm) laser

Meng Zhang, Animesh Banerjee, Chi-Sen Lee, John M. Hinckley, and Pallab Bhattacharya

Appl. Phys. Lett. 98, 221104 (2011); http://dx.doi.org/10.1063/1.3596436 (3 pages) | Cited 4 times

Online Publication Date: 1 June 2011

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The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching with gallium. Emission above threshold is characterized by a peak at 524 nm (green) and linewidth of 0.7 nm. The lowest measured threshold current density is 1.2 kA/cm2 at 278 K. The slope and wall plug efficiencies are 0.74 W/A and ∼ 1.1%, respectively, at 1.3 kA/cm2. The value of T0 = 233 K in the temperature range of 260–300 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Generalized scattering control using cut-wire-based metamaterials

Hiroki Wakatsuchi and Christos Christopoulos

Appl. Phys. Lett. 98, 221105 (2011); http://dx.doi.org/10.1063/1.3597628 (3 pages)

Online Publication Date: 2 June 2011

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We numerically show how multiple band scattering parameters for arbitrary polarization can be easily designed by using cut-wire-based (CW-based) metamaterials, which enable us to control six fundamental scattering properties, i.e., reflection, transmission, absorption, and polarization independence, dependence and change. The structure shown here is composed of three-independent metamaterial designs, each of which has a different scattering profile. The use of the simple CW-based metamaterials is expected to facilitate complex scattering parameter design, which potentially contributes to the development of more complex and multiple band metamaterial applications.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Experimental investigation on line width compression of stimulated Brillouin scattering in water

Lei Zhang, Dong Zhang, Zhuo Yang, Jinwei Shi, Dahe Liu, Wenping Gong, and Edward S. Fry

Appl. Phys. Lett. 98, 221106 (2011); http://dx.doi.org/10.1063/1.3595338 (3 pages)

Online Publication Date: 3 June 2011

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Line width compression of stimulated Brillouin scattering (SBS) in water was investigated experimentally. The results show that, when the water temperature is low, the compressing effect is obvious. However, when the temperature is higher than 25 °C, the line width is almost not compressed in water. Also, the pulse duration compression of SBS was measured simultaneously, and appeared an inherent relation to line width compression. It reveals that the line width can be simply measured by measuring the compressed pulse duration of SBS.
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42.65.Es Stimulated Brillouin and Rayleigh scattering
78.35.+c Brillouin and Rayleigh scattering; other light scattering

High-efficiency silicon-compatible photodetectors based on Ge quantum dots

S. Cosentino, Pei Liu, Son T. Le, S. Lee, D. Paine, A. Zaslavsky, D. Pacifici, S. Mirabella, M. Miritello, I. Crupi, and A. Terrasi

Appl. Phys. Lett. 98, 221107 (2011); http://dx.doi.org/10.1063/1.3597360 (3 pages) | Cited 2 times

Online Publication Date: 3 June 2011

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We report on high responsivity, broadband metal/insulator/semiconductor photodetectors with amorphous Ge quantum dots (a-Ge QDs) as the active absorbers embedded in a silicon dioxide matrix. Spectral responsivities between 1–4 A/W are achieved in the 500–900 nm wavelength range with internal quantum efficiencies (IQEs) as high as ∼ 700%. We investigate the role of a-Ge QDs in the photocurrent generation and explain the high IQE as a result of transport mechanisms via photoexcited QDs. These results suggest that a-Ge QDs are promising for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Scattering suppression in plasmonic optics using a simple two-layer dielectric structure

E. A. Bezus, L. L. Doskolovich, and N. L. Kazanskiy

Appl. Phys. Lett. 98, 221108 (2011); http://dx.doi.org/10.1063/1.3597620 (3 pages)

Online Publication Date: 3 June 2011

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We demonstrate that a planar structure consisting of two isotropic dielectric layers can be used to minimize parasitic scattering in plasmonic elements. It is shown using rigorous electromagnetic simulations that the utilization of the proposed structure allows reducing the scattering losses by an order-of-magnitude (1%–2%). The proposed approach can be used for the design of various plasmonic elements such as lenses, reflectors, and plasmonic crystals.
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42.25.Fx Diffraction and scattering

Microfluidic refractive-index sensors based on small-hole microstructured optical fiber Bragg gratings

A. Ping Zhang, Guofeng Yan, Shaorui Gao, Sailing He, Bongkyun Kim, Jooeun Im, and Youngjoo Chung

Appl. Phys. Lett. 98, 221109 (2011); http://dx.doi.org/10.1063/1.3597623 (3 pages) | Cited 3 times

Online Publication Date: 3 June 2011

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A microstructured optical fiber (MOF) Bragg grating is presented for microfluidic sensing applications. The MOF is specially designed to be with a large amount of microholes for developing ultrasensitive sensors based on inner coating and surface effects. With the fabrication of fiber Bragg grating (FBG), such an MOF sensor has been demonstrated for monitoring the fluid flowing through microholes. Experimental results reveal that the sensitivity of the sensor depends on both the refractive-index range of measurement and the order of fiber modes. The temperature dependency of the sensor has also been measured and compared with that of conventional FBGs.
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42.81.Pa Sensors, gyros
42.81.Wg Other fiber-optical devices
42.82.Cr Fabrication techniques; lithography, pattern transfer
07.10.Cm Micromechanical devices and systems
42.15.Eq Optical system design
42.79.Dj Gratings

Two-dimensional carrier density distribution inside a high power tapered laser diode

R. Pagano, M. Ziegler, J. W. Tomm, I. Esquivias, J. M. G. Tijero, J. R. O’Callaghan, N. Michel, M. Krakowski, and B. Corbett

Appl. Phys. Lett. 98, 221110 (2011); http://dx.doi.org/10.1063/1.3596445 (3 pages)

Online Publication Date: 3 June 2011

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The spontaneous emission of a GaAs-based tapered laser diode emitting at λ = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems

Terahertz spectroscopy of Ni–Ti alloy thin films

A. D. Jameson, J. W. Kevek, J. L. Tomaino, M. Hemphill-Johnston, M. J. Paul, M. Koretsky, E. D. Minot, and Yun-Shik Lee

Appl. Phys. Lett. 98, 221111 (2011); http://dx.doi.org/10.1063/1.3596456 (3 pages)

Online Publication Date: 3 June 2011

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We investigate the carrier dynamics in nickel–titanium (Ni–Ti) alloy thin films using terahertz transmission spectroscopy. Analyzing the power transmission data and the transmitted waveforms, we obtained the alloy resistivity as a function of Ti concentration. Sharp changes in the resistivity were observed at the Ti fractions of 22%, 44%, and 62%, indicating that structural disorder is greatly enhanced when the alloy undergoes a phase transition.
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78.70.Gq Microwave and radio-frequency interactions
64.70.K- Solid-solid transitions
73.61.At Metal and metallic alloys

MgZnO-based metal-semiconductor-metal solar-blind photodetectors on ZnO substrates

Qinghong Zheng, Feng Huang, Kai Ding, Jin Huang, Dagui Chen, Zhibing Zhan, and Zhang Lin

Appl. Phys. Lett. 98, 221112 (2011); http://dx.doi.org/10.1063/1.3596479 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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Using lattice matched ZnO substrates, wurtzite single crystalline Mg0.49Zn0.51O films were obtained by reactive magnetron cosputtering method, and the heterostructures of MgZnO/ZnO were fabricated into metal-semiconductor-metal solar-blind photodetectors (SBPDs). Calculated and experimental results demonstrate that the response of the ZnO substrate can be suppressed by adopting a thick MgZnO epilayer. The SBPD with a 2 μm thick MgZnO epilayer shows a peak responsivity of 304 mA/W at 260 nm under 10 V bias, which is comparable to the highest value ever reported in MgZnO-based SBPDs. A rejection ratio (R260 nm/R365 nm) over 5×102 is also observed, indicating fully suppression of the signal from ZnO substrate.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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He+O2+H2O plasmas as a source of reactive oxygen species

D. X. Liu, F. Iza, X. H. Wang, M. G. Kong, and M. Z. Rong

Appl. Phys. Lett. 98, 221501 (2011); http://dx.doi.org/10.1063/1.3592775 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2011

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The effect of water in the chemistry of atmospheric-pressure He+O2 plasmas is studied by means of a comprehensive global model. Water enables the generation of reactive oxygen species (ROS) cocktails that are rich not only in O, O2∗, and O3 but also in OH and H2O2. Due to its polar nature, water also leads to cluster formation, possibly affecting the plasma dynamics. Since the lifetime of many of the ROS is short, the plasma chemistry plays two roles: (i) direct interaction with superficial cells and (ii) triggering of a secondary chemistry that propagates the plasma treatment to regions away from the plasma-surface interface.
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52.77.-j Plasma applications
52.50.Dg Plasma sources
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.40.Hf Plasma-material interactions; boundary layer effects

Transition from dielectric barrier discharge to microhollow discharge in parallel-plate electrodes with intercavity microholes

Jun Watanabe and Masaaki Nagatsu

Appl. Phys. Lett. 98, 221502 (2011); http://dx.doi.org/10.1063/1.3595320 (3 pages)

Online Publication Date: 31 May 2011

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Parallel-plate electrodes with microholes were used to study microhollow discharges (MHDs) triggered by dielectric barrier discharge (DBD) generated by applying a low-frequency high ac voltage under atmospheric conditions. The results obtained reveal that MHD is ignited simultaneously with spiky DBD signals generated by applying two cycles of time-truncated sinusoidal waves. The discharge ignition voltage of MHD was about 1 kV lower for electrodes with intercavity holes than for electrodes with conventional straight holes. This reduction is due to the triggering effect of self-generated DBD.
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52.80.Hc Glow; corona

How deep can plasma penetrate into a biofilm?

Z. Xiong, T. Du, X. Lu, Y. Cao, and Y. Pan

Appl. Phys. Lett. 98, 221503 (2011); http://dx.doi.org/10.1063/1.3597622 (3 pages) | Cited 3 times

Online Publication Date: 2 June 2011

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It is well known that plasma can deactivate various types of microorganisms. However, one fundamental key question has never been addressed, namely, how deep can plasma penetrate into multilayer biofilms. In this letter, Porphyromonas gingivalis (PG) biofilms (10 days growth, which has about 30 layers of PG cells with a thickness of about 15 μm) are treated with a cold plasma plume. It is found that the plasma can penetrate the biofilms and effectively deactivate all the bacteria in the 15 μm thick biofilms. Moreover, it was found that most of the dead cells’ structures in the biofilms are not damaged. From the optical emission spectra of the plasma, it can be concluded that it is O and OH, rather than O2−, N2+, or UV emission that play the major role in the deactivation processes.
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87.50.wf Biophysical mechanisms of interaction
87.17.-d Cell processes
87.80.-y Biophysical techniques (research methods)

On the mechanical efficiency of dielectric barrier discharge plasma actuators

R. H. M. Giepman and M. Kotsonis

Appl. Phys. Lett. 98, 221504 (2011); http://dx.doi.org/10.1063/1.3597652 (3 pages)

Online Publication Date: 3 June 2011

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The mechanical power production and electrical power consumption of the dielectric barrier discharge plasma actuator is investigated for different operating conditions. The ratio of these two values delivers the mechanical efficiency of the actuator as a flow acceleration device. The general trend is that higher carrier frequencies and voltages lead to higher values of the efficiency. The values that were found for the mechanical efficiency are very small, the highest recorded value is only 0.18%.
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52.80.-s Electric discharges
52.25.Fi Transport properties
52.77.-j Plasma applications
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Multidirectional surface-wave splitters

Yong Jin Zhou and Tie Jun Cui

Appl. Phys. Lett. 98, 221901 (2011); http://dx.doi.org/10.1063/1.3595281 (3 pages) | Cited 5 times

Online Publication Date: 31 May 2011

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We propose a multidirectional surface-wave splitter excited by a cylindrical wire. Such a splitter could function as a plasmonic wavelength-division multiplexer, since electromagnetic waves at the designed frequencies will be confined and guided along different multiple grating structures that are placed around the cylindrical wire. The experimental verification of the proposed splitter has been implemented in the microwave frequencies. The measurement results have excellent agreements to the full-wave simulations to show the good performance of the splitter. We also propose and simulate a multidirectional surface-wave splitter in the terahertz frequency to validate the concept.
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42.79.Fm Reflectors, beam splitters, and deflectors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
42.79.Dj Gratings

Interface engineering of high-Mg-content MgZnO/BeO/Si for p-n heterojunction solar-blind ultraviolet photodetectors

H. L. Liang, Z. X. Mei, Q. H. Zhang, L. Gu, S. Liang, Y. N. Hou, D. Q. Ye, C. Z. Gu, R. C. Yu, and X. L. Du

Appl. Phys. Lett. 98, 221902 (2011); http://dx.doi.org/10.1063/1.3595342 (3 pages) | Cited 1 time

Online Publication Date: 31 May 2011

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High-quality wurtzite MgZnO film was deposited on Si(111) substrate via a delicate interface engineering using BeO, by which solar-blind ultraviolet photodetectors were fabricated on the n-MgZnO(0001)/p-Si(111) heterojunction. A thin Be layer was deposited on clean Si surface with subsequent in situ oxidation processes, which provides an excellent template for high-Mg-content MgZnO growth. The interface controlling significantly improves the device performance, as the photodetector demonstrates a sharp cutoff wavelength at 280 nm, consistent with the optical band gap of the epilayer. Our experimental results promise potential applications of this technique in integration of solar-blind ultraviolet optoelectronic device with Si microelectronic technologies.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Gz Photodetectors (including infrared and CCD detectors)
68.55.ag Semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Hf II-VI semiconductors

Another kinetic mechanism of stabilizing multiple-layer surface steps

Ruoxin Zhang and Hanchen Huang

Appl. Phys. Lett. 98, 221903 (2011); http://dx.doi.org/10.1063/1.3595938 (3 pages) | Cited 3 times

Online Publication Date: 31 May 2011

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This letter reports that a large three-dimensional Ehrlich–Schwoebel (3D ES) barrier kinetically stabilizes multiple-layer surface steps. The report is based on (1+1)D lattice kinetic Monte Carlo simulations of Cu{111} surfaces. The larger 3D ES barrier leads to slower diffusion over multiple-layer steps, thereby slower dissociation and higher stability. The higher stability of multiple-layer surface steps, in turn, facilitates the operation of the 3D ES barrier; a positive feedback relationship. The mechanism of kinetically stabilizing multiple-layer surface steps allows another way of controlling surface morphology to promote the growth of either nanorods or smooth thin films.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.35.bd Metals and alloys
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Thermal conductivity as a metric for the crystalline quality of SrTiO3 epitaxial layers

Dong-Wook Oh, Jayakanth Ravichandran, Chen-Wei Liang, Wolter Siemons, Bharat Jalan, Charles M. Brooks, Mark Huijben, Darrell G. Schlom, Susanne Stemmer, Lane W. Martin, Arun Majumdar, Ramamoorthy Ramesh, and David G. Cahill

Appl. Phys. Lett. 98, 221904 (2011); http://dx.doi.org/10.1063/1.3579993 (3 pages) | Cited 3 times

Online Publication Date: 31 May 2011

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Measurements of thermal conductivity Λ by time-domain thermoreflectance in the temperature range 100<T<300 K are used to characterize the crystalline quality of epitaxial layers of a prototypical oxide, SrTiO3. Twenty samples from five institutions using two growth techniques, molecular beam epitaxy and pulsed laser deposition (PLD), were analyzed. Optimized growth conditions produce layers with Λ comparable to bulk single crystals. Many PLD layers, particularly those that use ceramics as the target material, show surprisingly low Λ. For homoepitaxial layers, the decrease in Λ created by point defects correlates well with the expansion of the lattice parameter in the direction normal to the surface.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
61.72.J- Point defects and defect clusters
61.66.Fn Inorganic compounds

Size-dependent photochromism-based holographic storage of Ag/TiO2 nanocomposite film

Runyuan Han, Xintong Zhang, Lingling Wang, Rui Dai, and Yichun Liu

Appl. Phys. Lett. 98, 221905 (2011); http://dx.doi.org/10.1063/1.3595399 (3 pages)

Online Publication Date: 2 June 2011

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The influence of size distribution of Ag nanoparticles (NPs) on photochromic behavior and holographic storage dynamics of Ag/TiO2 films was investigated using a 532 nm laser as excitation source and recording beams, respectively. Experimental results suggest that small Ag NPs are subject to easier photoinduced oxidative dissolution than large Ag NPs under the 532 nm excitation, and contribute to the rapid growth of holographic grating in the initial stage. These observations were discussed in terms of size-dependent silver redox potential influencing both interfacial electron transfer among Ag NPs and TiO2 matrix and subsequent dissolution of Ag NPs, as well as surface plasmon resonance absorption property of Ag NPs also related to their size distribution.
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42.70.Ln Holographic recording materials; optical storage media
42.79.Vb Optical storage systems, optical disks
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.68.+m Optical properties of surfaces
42.40.Eq Holographic optical elements; holographic gratings
42.40.My Applications

Dislocation cross-slip in GaN single crystals under nanoindentation

J. Huang, K. Xu, X. J. Gong, J. F. Wang, Y. M. Fan, J. Q. Liu, X. H. Zeng, G. Q. Ren, T. F. Zhou, and H. Yang

Appl. Phys. Lett. 98, 221906 (2011); http://dx.doi.org/10.1063/1.3593381 (3 pages)

Online Publication Date: 2 June 2011

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The dislocation multiplication and movement mechanism in GaN single crystals has been studied using nanoindentation and cathodoluminescence. Dislocation loops can multiply and move from plane to plane by cross-slip, thus producing a wide plastic deformation in GaN during indentation. This mechanism is further supported by the remarkable movement of indentation induced dislocations during annealing. Furthermore, the so-called pop-in events, in which the indenter suddenly enters deeper into the material without the application of any additional force, can be better understood by considering the cross-slip mechanism.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.me Fatigue
78.60.Hk Cathodoluminescence, ionoluminescence

Formation of Zn defects in willemite-type Zn2GeO4 during supercooled liquid-crystal phase transition

Yoshihiro Takahashi, Masataka Ando, Rie Ihara, and Takumi Fujiwara

Appl. Phys. Lett. 98, 221907 (2011); http://dx.doi.org/10.1063/1.3597300 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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This letter elucidates the formation mechanism of interstitial Zn defects in wide band-gap semiconductive willemite-type Zn2GeO4 via nanocrystallization in a zincogermanate glass. The results of time-development structural observations suggest that Zn2GeO4 nanocrystals precipitate in the nanometric Zn-condensed region, which occurs prior to nanocrystallization. The Zn-condensed environment probably promotes the capture of Zn ions in the interstitial sites of the Zn2GeO4 structure during the structural ordering of the supercooled liquid phase. The Zn-condensation mechanism is also discussed.
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61.72.jj Interstitials
64.70.dg Crystallization of specific substances
64.70.mj Experimental studies of liquid crystal transitions
64.70.pp Liquid crystals
64.70.Nd Structural transitions in nanoscale materials
81.16.Pr Micro- and nano-oxidation

First-principles studies of complex hydride YMn2H6 and its synthesis from metal hydride YMn2H4.5

Motoaki Matsuo, Kazutoshi Miwa, Satoshi Semboshi, Hai-Wen Li, Mika Kano, and Shin-ichi Orimo

Appl. Phys. Lett. 98, 221908 (2011); http://dx.doi.org/10.1063/1.3597363 (3 pages) | Cited 2 times

Online Publication Date: 3 June 2011

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First-principles calculations were performed for a complex hydride YMn2H6 to investigate its electronic structure and thermodynamic stability. The results indicated that an Y atom and one of two Mn atoms were ionized as Y3+ and Mn2+, respectively, and another Mn atom bound covalently to H atoms to form a [MnH6]5− complex anion. Based on the enthalpy change of −65 kJ/mol estimated from the calculation, we experimentally verified a possible low-pressure synthesis of YMn2H6 from a metal hydride YMn2H4.5. X-ray diffractometry confirmed the formation of YMn2H6 after hydrogenation below 5 MPa, much lower than the previously reported value of 170 MPa.
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71.20.Ps Other inorganic compounds
65.40.-b Thermal properties of crystalline solids
71.15.-m Methods of electronic structure calculations

An electroactuation system based on nanofluids

Baoxing Xu, Yu Qiao, Yibing Li, Qulan Zhou, and Xi Chen

Appl. Phys. Lett. 98, 221909 (2011); http://dx.doi.org/10.1063/1.3597367 (3 pages) | Cited 1 time

Online Publication Date: 3 June 2011

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We propose the conceptual design of an electrically controlled actuation system by adjusting the relative hydrophobicity of a nanoporous material/liquid mixture. When the variation in wettability is amplified by the large surface area, a considerable mechanical work is output. The energy density, power density, and efficiency are explored and their variations with pore size, solid phase, and liquid phase are explored. An infiltration experiment on a nanoporous silica system is performed to qualitatively validate these findings.
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07.10.Cm Micromechanical devices and systems
47.85.Np Fluidics
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