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15 May 2012

Volume 111, Issue 10 (partial)

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Preface to the International Symposium on Integrated Functionalities (ISIF 2010) Special Issue of Journal of Applied Physics Science and Technology of Integrated Functionalities

Ram Katiyar, Orlando Auciello, and Reji Thomas

J. Appl. Phys. 111, 102701 (2012); http://dx.doi.org/10.1063/1.4712272 (2 pages)

Online Publication Date: 16 May 2012

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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.-e Ferroelectricity and antiferroelectricity

Improved multiferroic properties in Sm-doped BiFeO3 thin films deposited using chemical solution deposition method

S. K. Singh, C. V. Tomy, T. Era, M. Itoh, and H. Ishiwara

J. Appl. Phys. 111, 102801 (2012); http://dx.doi.org/10.1063/1.4714650 (4 pages)

Online Publication Date: 16 May 2012

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Sm-substituted (0% to 10%) BiFeO3 thin films were fabricated by chemical solution deposition on Pt/Ti/SiO2/Si substrates. X-ray diffraction analysis revealed that no secondary phase appeared even if Bi atoms were substituted with Sm atoms up to 10 at. %. 7.5 at. % Sm-substituted films show improved electrical properties and substitution was effective in improving the coercive field in the films. Sm-substitution shows improved ferroelectric as well as magnetic properties of the films. There is a noticeable reduction in the leakage current density (10−4 A/cm2) and increase in the polarization (70 μC/cm2) when the Sm concentration is kept around 7.5%. The magnetic moment obtained from the saturated magnetization curves shows a value of 0.3 μB/Fe compared to 0.04 μB/Fe for the parent compound. The results are important since it increases the potential of the material as a multiferroic compound.
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75.70.Ak Magnetic properties of monolayers and thin films
77.22.Ej Polarization and depolarization
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.Nv Multiferroic/magnetoelectric films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Room temperature structural, morphological, and enhanced ferroelectromagnetic properties of xBa0.7Ca0.3TiO3−(1−x)BaFe0.2Ti0.8O3 multiferroic composites

V. S. Puli, I. Coondoo, N. Panwar, A. Srinivas, and R. S. Katiyar

J. Appl. Phys. 111, 102802 (2012); http://dx.doi.org/10.1063/1.4714657 (4 pages)

Online Publication Date: 16 May 2012

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Iron substituted barium titanate (BaTiO3, BT) has been found to exhibit both ferroelectric and ferromagnetic behavior at room temperature [Xu et al., Phys. Rev. B 79, 134109 (2009)]. However, ferroelectric properties of Fe-doped BT are not as pronounced as those of pure BT. It happens because iron doping causes hexagonal phase formation which inhibits ferroelectricity. We observed enhanced ferroelectric properties in x(Ba0.7Ca0.3)TiO3/(1−x)Ba(Fe0.2Ti0.8)O3 [(BCT-BFT) where x = 0.10, 0.15, 0.20] composites while maintaining the ferromagnetic characteristics. Structural and morphological studies reveal that composite with low content of BCT possesses dominating hexagonal phase, whereas tetragonal phase is more prominent in composite with higher BCT concentration. Such composite systems with enhanced ferroelectric and ferromagnetic behavior may be useful for room temperature multiferroic devices.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.bg Compositional effects
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Lf Composite materials
68.35.bt Other materials

Deposition of stress free c-axis oriented LiNbO3 thin film grown on (002) ZnO coated Si substrate

Swati Shandilya, Monika Tomar, and Vinay Gupta

J. Appl. Phys. 111, 102803 (2012); http://dx.doi.org/10.1063/1.4714664 (6 pages)

Online Publication Date: 16 May 2012

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C-axis oriented lithium niobate thin films have been deposited on Si substrate using RF sputtering technique. A thin buffer layer of c-axis (002) oriented ZnO on Si substrate has been used as a nucleating layer to promote the growth of (006) oriented LiNbO3 film. The processing gas composition and pressure are found to be very critical in obtaining stress free LiNbO3 film having desired (006) orientation. The LiNbO3 films deposited under unique combination of sputtering pressure (10 mTorr) and argon percentage (80%) in reactive gas (Ar + O2) composition become almost stress free having lattice parameter (1.3867 Å) close to the bulk value. The observed variation in the structural properties and optical phonon modes observed by Raman spectroscopic studies of the oriented LiNbO3 thin film with stress has been correlated with growth kinetics.
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68.55.aj Insulators
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators
81.15.Cd Deposition by sputtering
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Fe doped ZnO thin film for mediator-less biosensing application

Shibu Saha, Monika Tomar, and Vinay Gupta

J. Appl. Phys. 111, 102804 (2012); http://dx.doi.org/10.1063/1.4714670 (5 pages)

Online Publication Date: 16 May 2012

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Fe doped ZnO (FZO) thin film is prepared by pulsed laser deposition for its application as mediator-less biosensing matrix. Fe doping introduces redox centre in ZnO along with shallow donor level and promotes the electron transfer capability due to substitution of Fe at Zn sites. Glucose oxidase (GOx), chosen as model enzyme, was immobilized on surface of the prepared matrix. Cyclic voltammetry and photometric assay show that the developed bio-electrode, GOx/FZO/indium tin oxide/Glass is sensitive to glucose concentration with enhanced response (0.2 µA mM−1 cm−2) and low Km (3.01 mM). The results show promising application of Fe doped ZnO thin film as an attractive matrix for mediator-less biosensing.
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87.80.Kc Electrochemical techniques
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.45.Fk Electrodes
82.47.Rs Electrochemical sensors
82.80.Fk Electrochemical methods
87.14.ej Enzymes

Structural and magnetic properties of N doped ZnO thin films

Kajal Jindal, Monika Tomar, R. S. Katiyar, and Vinay Gupta

J. Appl. Phys. 111, 102805 (2012); http://dx.doi.org/10.1063/1.4714686 (5 pages)

Online Publication Date: 16 May 2012

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Experimental investigations and first-principle calculations based on density functional theory are effectively combined to shed light on origin of room temperature ferromagnetism in nitrogen doped ZnO (ZnO:N) based intrinsic dilute magnetic semiconductors. ZnO:N thin films grown by pulsed laser deposition show a well defined M-H hysteresis loop at room temperature, reflecting ferromagnetic behavior in contrast to undoped ZnO thin films grown under the same processing condition. Isotropic behavior of magnetism in ZnO:N reveals the dominant contribution of N incorporation on the magnetism and is attributed to p-p interaction between nitrogen and neighboring oxygen atoms having potential for room temperature spintronic applications.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Fg Pulsed laser ablation deposition
68.55.ag Semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Nr Semiconductor compounds
75.50.Dd Nonmetallic ferromagnetic materials

ZnO nanowire based visible-transparent ultraviolet detectors on polymer substrates

Hongbin Yu, Ebraheem Ali Azhar, Tej Belagodu, Swee Lim, and Sandwip Dey

J. Appl. Phys. 111, 102806 (2012); http://dx.doi.org/10.1063/1.4714698 (5 pages)

Online Publication Date: 16 May 2012

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The fabrication and characterization of fully visible-transparent and flexible ultraviolet (UV) detectors, on polyethylene 2,6-naphthalate (PEN) with active channels of zinc oxide nanowires and ohmic indium tin oxide contacts, are reported and discussed. The fabricated detector has an average transmittance of 80% in the visible spectral range and is most responsive at or below 370 nm, the onset of UV light, with a UV/vis rejection ratio of 1.42 × 103. A five orders of magnitude difference in the photocurrent, between UV illumination and dark conditions, are also observed. The single-sided UV response further shows that the PEN substrate performs well as a UV reflector. The noise analysis on the nanowire UV detector indicates a noise equivalent power and detectivity (D*) of 5.88 × 10−13 WHz−0.5 and 2.13 × 109 cm Hz0.5 W−1, respectively.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Threshold resistive and capacitive switching behavior in binary amorphous GeSe

Doo Seok Jeong, Hyungkwang Lim, Goon-Ho Park, Cheol Seong Hwang, Suyoun Lee, and Byung-ki Cheong

J. Appl. Phys. 111, 102807 (2012); http://dx.doi.org/10.1063/1.4714705 (8 pages)

Online Publication Date: 16 May 2012

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A threshold switching (TS) event in a binary amorphous GeSe film placed between Pt top and bottom electrodes was examined. This GeSe film exhibits fast (<40 ns) TS behavior. The observed TS of the resistance was found to be accompanied with the TS of the capacitance. A mechanism for the TS of the GeSe film was suggested by revisiting the previous controversy about the thermal versus non-thermal electronic mechanism. The non-thermal electronic mechanism envisaging the double-injection of electronic carriers can qualitatively account for the measured threshold resistive and capacitive switching, whereas the TS behavior simulated using the thermal mechanism is inconsistent with the experimental observation.
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72.60.+g Mixed conductivity and conductivity transitions
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors

Materials for phase-change memory with elevated temperature stability

Kin-Fu Kao, Yung-Ching Chu, Ming-Jinn Tsai, and Tsung-Shune Chin

J. Appl. Phys. 111, 102808 (2012); http://dx.doi.org/10.1063/1.4714711 (6 pages)

Online Publication Date: 16 May 2012

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Thermal stability is one of the key issues in phase-change memory. We try to tackle it by developing new compositions based on Ga-Te-Sb system. Thermal stability is exemplified using Ga18Te12Sb70 which shows crystallization-temperature (Tx) 248 °C and activation energy of non-isothermal crystallization 5.9 eV. Films were isothermally soaked at 5 ∼ 30 °C below Tx to estimate the failure-time when electrical resistance dropped to a half of the original. Arrhenius plot attained using logarithm failure-time versus reciprocal temperature were extrapolated to the temperature corresponding to 10-year failure (T10y) as 183 °C. Pre-crystallization structure upon heating to 2 ∼ 5 °C below Tx reflects stable amorphous phase of the alloy up to at least 240 °C. Memory-cells made of Ga18Te12Sb70 can be set-reset at 20 ∼ 500 ns with electrical currents around 66% those of our Ge2Sb2Te5 cells. We suggest that compositions Ga18–25Te8–12Sb67–70 are optimal to ensure Tx > 240 °C, T10y > 180 °C and with low operation-currents.
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84.30.Sk Pulse and digital circuits

A comparative study of ultraviolet photoconductivity relaxation in zinc oxide (ZnO) thin films deposited by different techniques

Harish Kumar Yadav and Vinay Gupta

J. Appl. Phys. 111, 102809 (2012); http://dx.doi.org/10.1063/1.4714715 (5 pages)

Online Publication Date: 16 May 2012

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Photoresponse characteristics of ZnO thin films deposited by three different techniques namely rf diode sputtering, rf magnetron sputtering, and electrophoretic deposition has been investigated in the metal-semiconductor-metal (MSM) configuration. A significant variation in the crystallinity, surface morphology, and photoresponse characteristics of ZnO thin film with change in growth kinetics suggest that the presence of defect centers and their density govern the photodetector relaxation properties. A relatively low density of traps compared to the true quantum yield is found very crucial for the realization of practical ZnO thin film based ultraviolet (UV) photodetector.
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72.40.+w Photoconduction and photovoltaic effects
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.bg Semiconductors

Combinatorial growth of oxide nanoscaffolds and its influence in osteoblast cell adhesion

Claudia Y. Acevedo-Morantes, Roberto A. Irizarry-Ortiz, Pablo G. Caceres-Valencia, Surinder P. Singh, and Jaime E. Ramirez-Vick

J. Appl. Phys. 111, 102810 (2012); http://dx.doi.org/10.1063/1.4714727 (7 pages)

Online Publication Date: 17 May 2012

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We report a novel method for high-throughput investigations on cell-material interactions based on metal oxide nanoscaffolds. These scaffolds possess a continuous gradient of various titanium alloys allowing the compositional and morphological variation that could substantially improve the formation of an osseointegrative interface with bone. The model nanoscaffold has been fabricated on commercially pure titanium (cp-Ti) substrate with a compositional gradients of tin (Sn), chromium (Cr), and niobium (Nb) deposited using a combinatorial approach followed by annealing to create native oxide surface. As an invitro test system, the human fetal osteoblastic cell line (hFOB 1.19) has been used. Cell-adhesion of hFOB 1.19 cells and the suitability of these alloys have been evaluated for cell-morphology, cell-number, and protein adsorption. Although, cell-morphology was not affected by surface composition, cell-proliferation rates varied significantly with surface metal oxide composition; with the Sn- and Nb-rich regions showing the highest proliferation rate and the Cr-rich regions presenting the lowest. The results suggest that Sn and Nb rich regions on surface seems to promote hFOB 1.19 cell proliferation and may therefore be considered as implant material candidates that deserve further analysis.
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87.17.Rt Cell adhesion and cell mechanics
87.15.km Protein-protein interactions
87.15.R- Reactions and kinetics
87.17.Pq Morphogenesis

Dielectric properties and electrical conduction of high-k LaGdO3 ceramics

S. P. Pavunny, R. Thomas, A. Kumar, N. M. Murari, and R. S. Katiyar

J. Appl. Phys. 111, 102811 (2012); http://dx.doi.org/10.1063/1.4714721 (5 pages)

Online Publication Date: 18 May 2012

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The temperature and frequency dependent dielectric properties and leakage conduction mechanism in LaGdO3 (LGO) ceramics have been studied, and this material has been identified as a potential high-k candidate for the future complementary metal-oxide-semiconductor (CMOS) and dynamic random access memory (DRAM) technology nodes. The dielectric constant and the loss tangent at 100 kHz were ∼21.5 and ∼0.003, respectively, at ambient conditions without any significant temperature and voltage dependence. The ac conductivity shows the typical features of universal dynamic response (UDR) and obey the double power law σac = σdc+Aωn1+Bωn2 with three types of temperature dependent conduction processes involved; (i) a dc plateau (< 3 kHz) due to long range translational hopping, (ii) a mid frequency region due to the short range hopping (3–100 kHz), and (iii) a high frequency region due to localized or reorientational hopping (100–1000 kHz). The temperature dependent dc conductivity follows the Arrhenius relation with activation energies of 0.05 eV in the 200–400 K range and 0.92 eV in the 400–600 K range. The leakage current behavior reveals bulk limited Poole-Frenkel (PF) conduction mechanism and the estimated optical dielectric constant (ɛ∞) is 3.6.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
72.20.Ee Mobility edges; hopping transport
72.20.Ht High-field and nonlinear effects
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Inhomogeneous nanostructured honeycomb optical media for enhanced cathodo- and under-x-ray luminescence

N. V. Gaponenko, V. S. Kortov, M. V. Rudenko, V. A. Pustovarov, S. V. Zvonarev, A. I. Slesarev, I. S. Molchan, G. E. Thompson, L. S. Khoroshko, and S. Ya. Prislopskii

J. Appl. Phys. 111, 103101 (2012); http://dx.doi.org/10.1063/1.4717740 (6 pages)

Online Publication Date: 17 May 2012

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Photo-, radio-, and pulse cathodoluminescence spectra from sol-gel derived titania, doped with strontium and terbium, deposited on porous anodic alumina (PAA) films are reported. The morphology and qualitative elemental depth distributions have been examined by transmission electron microscopy, scanning electron microscopy, and radio-frequency glow discharge optical emission spectroscopy. PAA films with pore and cell sizes ranging from 170 to 190 and 240 to 270 nm, respectively, have been generated on aluminum and monocrystalline silicon substrates followed by spin-on sol-gel derived coating with the subsequent thermal treatment. The resultant PAA surface is not coated with a continuous xerogel film; the xerogel is mainly distributed near the pore bases, leaving much of the pore volume unfilled. The xerogel/PAA structures reveal terbium-related luminescence under x-ray excitation and cathodoluminescence. The same xerogels generated on monocrystalline silicon revealed no cathode- or under-x-ray luminescence. Thus, PAA enhances strongly the cathode- and under x-ray luminescence from terbium and strontium-doped titania xerogels confined in the porous matrix. The fabricated structures are considered as a type of low-cost, thin-film convertor of x-rays, and cathode ray irradiation into visible light, with an average cell size of the convertor of about 250 nm.
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81.07.Bc Nanocrystalline materials
42.70.-a Optical materials
78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence

Plasmonic dispersion engineering of coupled metal nanoparticle-film systems

Jeff DiMaria and Roberto Paiella

J. Appl. Phys. 111, 103102 (2012); http://dx.doi.org/10.1063/1.4717763 (5 pages)

Online Publication Date: 17 May 2012

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The plasmonic dispersion properties of thin silver films in close proximity of square-periodic arrays of silver nanocylinders are investigated via transmission measurements and numerical simulations. Due to their nanoscale thicknesses, these films support hybrid surface plasmon modes extended across both interfaces, whose dispersion curves exhibit a large geometrically tunable energy splitting. Furthermore, the spatial and spectral overlap between these modes and the nanoparticles’ localized plasmonic resonances produces an additional anticrossing in the dispersion spectrum. The resulting plasmonic excitations are attractive for applications given their wide tunability, coupling to free-space radiation, and ability to extend into an optically active substrate.
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73.22.Lp Collective excitations
78.66.Bz Metals and metallic alloys
78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Optical switch based on electrowetting liquid lens

Lei Li, Chao Liu, Hua-Rong Peng, and Qiong-Hua Wang

J. Appl. Phys. 111, 103103 (2012); http://dx.doi.org/10.1063/1.4717715 (4 pages)

Online Publication Date: 18 May 2012

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multimedia

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In this paper, we propose an optical switch based on an electrowetting liquid lens. The device consists of an electrowetting liquid lens and a non-transparent cap with a pin hole. When the lens is actuated to be positive, the incident light can be converged on the pin hole and pass through the hole with less attenuation. When the lens is deformed to be negative, the incident light is diverged and most of light is blocked by the cap. Our results show that the system can provide high contrast ratio (∼800:1) and reasonable response time (∼88 ms). The proposed optical switch has potential application in light shutters, variable optical attenuators, and adaptive irises.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Bh Lenses, prisms and mirrors

A simple analysis of interband absorption in quantum well structure of III-V ternary and quaternary semiconductors

Anup Dey, Biswajit Maiti, and Debasree Chanda (Sarkar)

J. Appl. Phys. 111, 103104 (2012); http://dx.doi.org/10.1063/1.4718414 (9 pages)

Online Publication Date: 18 May 2012

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A simple generalized theory is presented for the determination of interband optical absorption coefficient (IOAC) around band edges, in quantum well (QW) structure of non-parabolic semiconducting materials whose band structures obey the three band model of Kane. The dependence of absorption coefficient on wave-vector (math) has also been investigated. IOAC has been calculated for a wide range of III–V compound semiconductors, such as InAs, InSb, Hg1−xCdxTe, and In1−xGaxAsyP1−y lattice matched to InP. It has been found that IOAC for QWs increases in steps with increasing photon energy and the positions of jumps of the coefficient are more closely spaced in the three band model of Kane than those with parabolic energy band approximations in all the cases. IOAC for QWs is largely dependent on the polarization direction of the incident light and on the well dimension as well. The expressions of IOAC presented in this article can easily be extended to incorporate the effects of different external conditions like strain, electric, and magnetic fields on IOAC. It has also been shown that under certain limiting conditions the expressions for IOAC reduces to the previously known results for wide band gap materials and this is the indication for it to be a generalized theory for IOAC.
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78.67.De Quantum wells
73.21.Fg Quantum wells
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

The use of optical microscopy to examine crystallite nucleation and growth in thermally annealed plasma enhanced chemical vapor deposition and hot wire chemical vapor deposition a-Si:H films

A. H. Mahan, M. S. Dabney, R. C. Reedy, Jr., D. Molina, and D. S. Ginley

J. Appl. Phys. 111, 103501 (2012); http://dx.doi.org/10.1063/1.4712045 (5 pages)

Online Publication Date: 16 May 2012

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We report a simple method to investigate crystallite nucleation and growth in stepwise, thermally annealed plasma enhanced chemical vapor deposition and hot wire chemical vapor deposition a-Si:H films. By confining film thicknesses to the range 500–4000 Å, optical microscopy in the reflection mode can be used to readily detect crystallites in the thermally annealed a-Si:H lattice. Measurements of the crystallite density versus annealing time for identically prepared films of different thickness show that the crystallite nucleation rate is smaller for thinner films, suggesting that crystallite nucleation is homogeneous, in agreement with previous results. A comparison of film nucleation rates with those obtained by other methods on identically prepared films shows excellent agreement, thus establishing the validity of the current technique. The potential effect of impurity (oxygen) incorporation during the stepwise annealing in air is shown not to affect crystallite nucleation and growth, in that SIMS oxygen profiles for stepwise versus continuous annealing show not only similar impurity profiles but also similar bulk impurity densities.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
71.55.Cn Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.05.Cy Elemental semiconductors

Plasmons in graphene nanostructures

Haifeng Yin and Hong Zhang

J. Appl. Phys. 111, 103502 (2012); http://dx.doi.org/10.1063/1.4706566 (6 pages)

Online Publication Date: 16 May 2012

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The collectivity of the electronic motion in graphene nanostructures is studied by time-dependent density functional theory (TDDFT). Compared with the plasmon in the homogeneous graphene, the plasmon in the graphene nanostructure has some different properties due to the effect of the size and the all dimensional confinement. In lower-energy resonance zone, spectral band is greatly broadening, even extending to the near-infrared spectral area, and the photoabsorption strength line splits. The absorption spectrum also depends on the edge configuration of the graphene nanostructure. The armchair-edge and the zigzag-edge play different roles in the absorption spectrum. Moreover, our results also demonstrate that most low-energy resonances are localized in the boundary region.
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73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.30.Na Fullerenes and related materials
61.48.Gh Structure of graphene

A monoclinic-tetragonal ferroelectric phase transition in lead-free (K0.5Na0.5)NbO3-x%LiNbO3 solid solution

Wenwei Ge, Yang Ren, Jialiang Zhang, Christopher P. Devreugd, Jiefang Li, and D. Viehland

J. Appl. Phys. 111, 103503 (2012); http://dx.doi.org/10.1063/1.4716027 (6 pages)

Online Publication Date: 16 May 2012

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A monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na0.5)NbO3-5%LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements. At ambient temperature, the lattice parameters of this monoclinic structure were (am, bm, cm; β) = (4.015 Å, 3.944 Å, 3.987 Å; 90.34°). This monoclinic phase transformed to a tetragonal (P4mm) one on heating between 340 K and 360 K. The results demonstrate the presence of structurally bridging low symmetry monoclinic phase in (K0.5Na0.5)NbO3-x%LiNbO3 solid solution system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.
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77.80.bg Compositional effects
61.66.Fn Inorganic compounds
77.65.-j Piezoelectricity and electromechanical effects
77.80.Dj Domain structure; hysteresis
64.70.K- Solid-solid transitions
77.84.Ek Niobates and tantalates

Z-scan study of nonlinear absorption in reduced LiNbO3 crystals

S. M. Kostritskii and M. Aillerie

J. Appl. Phys. 111, 103504 (2012); http://dx.doi.org/10.1063/1.4716470 (6 pages)

Online Publication Date: 17 May 2012

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The nonlinear absorption (NLA) was studied by open-aperture Z-scan experiments in the chemically reduced nominally pure LiNbO3 crystals at cw-illumination with the red (644 nm) and green (514.5 nm) laser beams. The magnitude of the measured NLA is considerably different from the reported Z-scan results obtained in as-grown LiNbO3. The positive sign of NLA obtained with the red light has been related to the generation of the small bound polarons absorbing in red and near-IR ranges. Application of green light results in the light-induced transparency, i.e., the Z-scan traces show negative sign of NLA. Intensity dependence of Z-scan traces allows for conclusion that the photo-induced dissociation of small NbLi4+:NbNb4+ bipolarons and sequent generation of small polarons gives the dominating contribution to the nonlinear optical absorption in reduced crystals with a large bipolarons concentration.
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71.38.Mx Bipolarons
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.37.Np Single molecule reaction kinetics, dissociation, etc.
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators

Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

Zilong Hua, Heng Ban, Marat Khafizov, Robert Schley, Rory Kennedy, and David H. Hurley

J. Appl. Phys. 111, 103505 (2012); http://dx.doi.org/10.1063/1.4716474 (7 pages)

Online Publication Date: 17 May 2012

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A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k = (e2/D)1/2. To generalize this approach, sensitivity analysis is conducted for materials having a range of thermal conductivities. Application to nuclear fuel is consider by performing experimental validation using two materials (CaF2 and SiO2) having thermal properties representative of fresh and high burnup nuclear fuel. The measured conductivities compare favorably with literature values.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
42.62.-b Laser applications

Phononic and structural response to strain in wurtzite-gallium nitride nanowires

G. C. Loh, E. H. T. Teo, and B. K. Tay

J. Appl. Phys. 111, 103506 (2012); http://dx.doi.org/10.1063/1.4716476 (7 pages)

Online Publication Date: 17 May 2012

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Gallium nitride (GaN) nanowires exist in a myriad of cross-sectional shapes. In this study, a series of classical molecular dynamics simulations is performed to investigate the strain-phononics-structure relationship in rectangular and triangular wurtzite-GaN nanowires. The thermal conductivity of the nanowires is linearly dependent on the uniaxial strain in both compressive and tensile regimes, and shows no significant dissimilitude for the same amount of strain exerted on the two types of nanowire. This is coherent with an analytical approach using the Boltzmann transport theory. However, the thermomechanical behaviour at the vertex regions shows palpable differences between the two subfamilies, relative to the non-vertex faceted regions, as the structural morphology is most disparate at the vertices. Furthermore, the degree of strain asymmetry is a strong determinant of the vibrational response and consequently thermal conductance.
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63.22.Gh Nanotubes and nanowires
66.70.Df Metals, alloys, and semiconductors
81.40.Lm Deformation, plasticity, and creep
61.46.Np Structure of nanotubes (hollow nanowires)
62.20.F- Deformation and plasticity
62.23.Hj Nanowires

Azimuthal dependence of switching field strength for nematic liquid crystal bistability on patterned alignment layers

Jun-ichi Niitsuma, Makoto Yoneya, and Hiroshi Yokoyama

J. Appl. Phys. 111, 103507 (2012); http://dx.doi.org/10.1063/1.4716681 (6 pages)

Online Publication Date: 17 May 2012

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We investigate the azimuthal dependence of the switching field strength for nematic liquid crystal bistability on patterned alignment layers to determine the validity of a switching theory proposed by Kim et al. [Appl. Phys. Lett. 78, 3055 (2001)] and to evaluate higher-order azimuthal anchoring coefficients. Director behavior during switching is described in detail for general azimuthal directions of an applied electric field and the experimental results are explained on the basis of the theory. We obtain azimuthal anchoring coefficients up to the second higher-order term in an expansion of the anchoring energy function. Detailed analysis of the director behavior reveals a close analogy between the proposed model of nematic liquid crystal bistability and a coherent rotation (Stoner-Wohlfarth) model of ferromagnetism. This suggests a reversal-asymmetric property of the substrate-nematic interface director, differing from the reversal symmetry of the bulk nematic director, as far as the nematic bistability switching is concerned.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Prediction of glass forming ability and glass forming range for electrodeposited binary Co-W alloys

Ashish Singh, Nikhilesh Iyer, and Sandip P. Harimkar

J. Appl. Phys. 111, 103508 (2012); http://dx.doi.org/10.1063/1.4717723 (5 pages)

Online Publication Date: 17 May 2012

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This paper reports on the transition of crystalline to amorphous structure with increasing W content in electrodeposited binary Co-W alloys. The glass forming ability of the electrodeposited Co-based alloys, including Co-W alloy, is analyzed using deep eutectic criteria based on reduced liquidus temperature and relative composition ratio. MD simulations based on solid solution models indicated glass forming ability above 20 at. % W for Co-rich Co-W alloys, which is in good agreement with the experimental observations.
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64.70.P- Glass transitions of specific systems
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution

Energetic instability of polygonal micro- and nanowires

Harris Wong

J. Appl. Phys. 111, 103509 (2012); http://dx.doi.org/10.1063/1.4717709 (8 pages)

Online Publication Date: 18 May 2012

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Micro- and nanowires are commonly used in biological sciences, micro- and nanoelectronics, and optoelectronics, and their morphological stability needs to be understood and controlled. Previous linear-stability analyses of infinitely-long circular wires have shown that the critical wavelength for instability approaches infinity if the wire surface is facetted. Thus, Rayleigh’s instability is suppressed in finite facetted circular wires and possibly in finite facetted polygonal wires. This work studies the energetic stability of long facetted regular-polygonal and rectangular wires that are not in thermodynamic equilibrium. The long wire is assumed to break up into N identical equilibrium crystals with the same cross-sectional shape as the wire. The length of the wire is Nλ and that of the crystal is L. The surface energy of the system is found to decrease after breakup if λ/L>9/4-2/3N+… for N ≫ 1. This instability criterion holds for regular-polygonal wires of arbitrary sides and for rectangular wires of arbitrary aspect ratios. The criterion also applies to infinitely long equilibrium wires if N is set to infinity. Previous experimental studies of pore channels in sapphire have revealed that the facetted channels break up not by Rayleigh’s instability, but by tip shedding. The observed “crystal” separation to length ratio agrees with the above instability criterion.
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61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
68.35.Md Surface thermodynamics, surface energies
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