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11 Feb 2013

Volume 102, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 063701 (2013); http://dx.doi.org/10.1063/1.4790115 (5 pages)

In-Tsang Lin, Hong-Chang Yang, and Jyh-Horng Chen
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Sub-volt broadband hybrid plasmonic-vanadium dioxide switches

Arash Joushaghani, Brett A. Kruger, Suzanne Paradis, David Alain, J. Stewart Aitchison, and Joyce K. S. Poon

Appl. Phys. Lett. 102, 061101 (2013); http://dx.doi.org/10.1063/1.4790834 (4 pages) | Cited 2 times

Online Publication Date: 11 February 2013

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The insulator-metal phase transition of a correlated-electron material, vanadium dioxide, is used to demonstrate electrically controlled, compact, broadband, and low voltage plasmonic switches. The devices are micron-scale in length and operate near a wavelength of 1550 nm. The switching bandwidths exceed 100 nm and 400 mV is sufficient to attain extinction ratios in excess of 20 dB. The results illustrate the promise of using phase transition materials for efficient and ultra-compact plasmonic switches and modulators.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Electro-refractive effect in Ge/SiGe multiple quantum wells

J. Frigerio, P. Chaisakul, D. Marris-Morini, S. Cecchi, M. S. Roufied, G. Isella, and L. Vivien

Appl. Phys. Lett. 102, 061102 (2013); http://dx.doi.org/10.1063/1.4792271 (4 pages)

Online Publication Date: 11 February 2013

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We report on the electro-refractive effect in Ge/SiGe multiple quantum wells grown by low energy plasma enhanced chemical vapor deposition. The electro-refractive effect was experimentally characterized by the shift of Fabry-Perot fringes in the transmission spectra of a 64 μm long slab waveguide. A refractive index variation up to 1.3 × 10−3 was measured with an applied electric field of 88 kV/cm at 1475 nm, 50 meV below the excitonic resonance, with a VπLπ figure of merit of 0.46 V cm. The device performances are promising for the realization of Mach Zehnder modulators in the Ge-Si material platform.
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78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Subwavelength superfocusing with a dipole-wave-reciprocal binary zone plate

Jun Wang, Fei Qin, Dao Hua Zhang, Dongdong Li, Yueke Wang, Xiaonan Shen, Ting Yu, and Jinghua Teng

Appl. Phys. Lett. 102, 061103 (2013); http://dx.doi.org/10.1063/1.4791581 (4 pages)

Online Publication Date: 12 February 2013

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We propose an idea of using a convergent dipole wave at the aperture, radiated from a dipole at distance of z0, to produce a perfect focusing at z0. We verified this idea through simulation and experimental observation. It is demonstrated that the zone plate designed based on the idea can provide a subwavelength superfocusing by effectively bending the surface waves in a Fresnel region of 100 nm to a couple of wavelengths and is suitable for a situation where a superresolution at a micro working distance is essential.
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42.79.Ci Filters, zone plates, and polarizers
42.25.Fx Diffraction and scattering

Frequency-modulated light scattering in colloidal suspensions

Liang Mei, Sune Svanberg, and Gabriel Somesfalean

Appl. Phys. Lett. 102, 061104 (2013); http://dx.doi.org/10.1063/1.4792220 (4 pages)

Online Publication Date: 12 February 2013

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Frequency-modulated light field fluctuations due to moving particles in colloidal suspensions are examined using heterodyne interferometry. The power spectrum is the combined result of a time-of-flight-related frequency distribution due to light scattering and frequency shifts due to the Doppler effect. An approximation model is developed based on diffusion theory and verified experimentally. The potential for application towards comprehensive diagnosis of both particle dynamics and optical properties of the examined media is discussed.
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82.70.Dd Colloids
82.70.Kj Emulsions and suspensions
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Mobility enhancement of top contact pentacene based organic thin film transistor with bi-layer GeO/Au electrodes

Mir Waqas Alam, Zhaokui Wang, Shigeki Naka, and Hiroyuki Okada

Appl. Phys. Lett. 102, 061105 (2013); http://dx.doi.org/10.1063/1.4792235 (3 pages)

Online Publication Date: 12 February 2013

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The enhancement of the charge injection and field effect mobility by inserting a thin (5 nm) germanium oxide (GeO) interlayer between the Au electrode and pentacene layer in a top contact pentacene based organic thin-film transistor (OTFTs) was reported. In comparison with the pentacene-based OTFT with only-Au electrode, the device performance has been considerably improved, which exhibits the highest field effect mobility of 0.96 cm2/Vs. The improvement was attributed to significant reduction of barrier height at Au/pentacene interfaces and smoothed surface of pentacene layer after inserting a thin GeO layer.
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85.30.Tv Field effect devices

Harnessing second-order optical nonlinearities at interfaces in multilayer silicon-oxy-nitride waveguides

Dylan F. Logan, Ali B. Alamin Dow, Dmitri Stepanov, Payam Abolghasem, Nazir P. Kherani, and Amr S. Helmy

Appl. Phys. Lett. 102, 061106 (2013); http://dx.doi.org/10.1063/1.4792272 (4 pages)

Online Publication Date: 12 February 2013

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We demonstrate multi-layer silicon-oxy-nitride (SiON) waveguides as a platform for broadband tunable phase-matching of second-order nonlinear interactions arising at material interfaces. Second-harmonic generation (SHG) is measured with a 2 ps pulsed pump of 1515–1535 nm wavelength, where 6 nW power is generated by an average pump power of 30 mW in a 0.92 mm long device. The wavelength acceptance bandwidth of the SHG is as broad as 20 nm due to the low material dispersion of SiON waveguides. The waveguide structure provides a viable method for utilizing second order nonlinearity for light generation and manipulation in silicon photonic circuits.
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42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.-a Optical materials

Highly tunable-emittance radiator based on semiconductor-metal transition of VO2 thin films

Ali Hendaoui, Nicolas Émond, Mohamed Chaker, and Émile Haddad

Appl. Phys. Lett. 102, 061107 (2013); http://dx.doi.org/10.1063/1.4792277 (4 pages)

Online Publication Date: 12 February 2013

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This paper describes a VO2-based smart structure with an emittance that increases with the temperature. A large tunability of the spectral emittance, which can be as high as 0.90, was achieved. The transition of the total emittance with the temperature was fully reversible according to a hysteresis cycle, with a transition temperature of 66.5 °C. The total emittance of the device was found to be 0.22 and 0.71 at 25 °C and 100 °C, respectively. This emittance performance and the structure simplicity are promising for the next generation of energy-efficient cost-effective passive thermal control systems of spacecrafts.
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72.60.+g Mixed conductivity and conductivity transitions

Improvement of volume holographic performance by plasmon-induced holographic absorption grating

Chengmingyue Li, Liangcai Cao, Jingming Li, Qingsheng He, Guofan Jin, Shiman Zhang, and Fushi Zhang

Appl. Phys. Lett. 102, 061108 (2013); http://dx.doi.org/10.1063/1.4792312 (3 pages)

Online Publication Date: 13 February 2013

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We report on the enhanced holographic performance by employing a strong volume holographic absorption grating induced by localized surface plasmon resonance effect in a bulk gold nanoparticles doped photopolymer. The contributions of plasmon-induced volume holographic absorption grating is characterized through the Kogelnik's coupled wave model and demonstrated experimentally by using two-beam interference technology. At the 0.05 vol. % concentration of the gold nanoparticles in the bulk photopolymer, 101.8% increase in the diffraction efficiency and more than four times suppression of the first side lobe in angular selectivity have been achieved.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Integrated sensor for ultra-thin layer sensing based on hybrid coupler with short-range surface plasmon polariton and dielectric waveguide

Boyu Fan, Fang Liu, Xiaoyan Wang, Yunxiang Li, Kaiyu Cui, Xue Feng, and Yidong Huang

Appl. Phys. Lett. 102, 061109 (2013); http://dx.doi.org/10.1063/1.4792319 (4 pages)

Online Publication Date: 13 February 2013

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Based on a hybrid coupler composed of short-range surface plasmon polariton (SRSPP) and dielectric waveguides, an integrated sensor for ultra-thin layer sensing has been realized. The simulation and experiment results demonstrate that the thickness variation of detection layer (polymer layer) about several nanometers could be detected. The measured thickness-detection sensitivity is as high as 0.67 dB/nm. And the sensitive region for thickness variation of polymer layer can be adjusted widely by varying the thickness of the SRSPP waveguide.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Low-threshold and quasi-single-mode random laser within a submicrometer-sized ZnO spherical particle film

Hideki Fujiwara, Ryo Niyuki, Yoshie Ishikawa, Naoto Koshizaki, Takeshi Tsuji, and Keiji Sasaki

Appl. Phys. Lett. 102, 061110 (2013); http://dx.doi.org/10.1063/1.4792349 (4 pages)

Online Publication Date: 13 February 2013

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An unique random laser exhibiting quasi-single-mode and low lasing threshold is developed by a homogenized submicrometer-sized zinc oxide particle film dispersed with intentionally introduced polymer particles as point defects. Such unique random lasing is dominantly initiated at the defect sites, although multi-mode peaks with a collapsed broad emission spectrum are observed at the defect-free sites as in the conventional random lasers. Thus our proposed simple structure can possibly provide the controllability of lasing properties even in random structures.
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42.55.-f Lasers
42.70.Jk Polymers and organics

Large photoresponse of Cu:7,7,8,8-tetracyanoquinodimethane nanowire arrays formed as aligned nanobridges

Rabaya Basori, K. Das, Prashant Kumar, K. S. Narayan, and A. K. Raychaudhuri

Appl. Phys. Lett. 102, 061111 (2013); http://dx.doi.org/10.1063/1.4792470 (4 pages)

Online Publication Date: 13 February 2013

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We report large photoresponse in an array of Cu:TCNQ (TCNQ-7,7,8,8-tetracyanoquinodimethane) nanowires fabricated as nanobridge device. The device shows highest photoresponse for excitation wavelength = 405 nm. The current gain at zero bias can reach ∼104 with an illumination power density of 2 × 106 W/m2. The zero bias responsivity is ∼0.3 mA/W, which increases upto 1 A/W for an applied bias of 2.0 V. Dark and illuminated I-V data are analyzed by a model of two Schottky diodes connected back-to-back, which shows that the predominant photocurrent in the device arises from the photoconductive response of the nanowires.
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85.30.Kk Junction diodes
85.60.-q Optoelectronic devices

Polarization of the edge emission from Ag/InGaAsP Schottky plasmonic diode

C. Wang, H. J. Qu, W. X. Chen, G. Z. Ran, H. Y. Yu, B. Niu, J. Q. Pan, and W. Wang

Appl. Phys. Lett. 102, 061112 (2013); http://dx.doi.org/10.1063/1.4792508 (4 pages)

Online Publication Date: 13 February 2013

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Electrical plasmonic sources with compact sizes are a fundamental component in plasmonics. Here, we report a simple plasmonic diode having an Ag/InGaAsP quantum well Schottky structure. The polarization ratio (TM:TE) of the edge-emission photoluminescence for the quantum wells is about 2:1 and increases to about 3:1 after covered by Ag. As contrast, the electroluminescence polarization ratio exceeds 10:1 at a low current, indicating a high plasmon generation efficiency but drops gradually as current increasing; simultaneously, the peak wavelength red shifts evidently, which are attributed to the recombination zone shift and quantum confinement Stark effect.
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85.30.Kk Junction diodes

Enhanced depth of field laser processing using an ultra-high-speed axial scanner

M. Duocastella and C. B. Arnold

Appl. Phys. Lett. 102, 061113 (2013); http://dx.doi.org/10.1063/1.4791593 (4 pages)

Online Publication Date: 13 February 2013

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Lasers are ubiquitous in materials processing, but the requirement of precise control of the focal plane in order to ensure optimal performance constitutes a time limiting step for high-throughput laser manufacturing. Here, we overcome this limitation by axially scanning the focus at high speeds using an acoustically driven liquid lens. We demonstrate this approach by processing silicon surfaces, and we find it is possible to enhance the depth-of-field by an order of magnitude without loss in lateral resolution. These results open the door to a fundamental change in the paradigm for laser processing by eliminating the need in z-focus control.
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42.62.-b Laser applications
42.79.Ls Scanners, image intensifiers, and image converters

Conical air prism arrays as an embedded reflector for high efficient InGaN/GaN light emitting diodes

Volodymyr V. Lysak, Ji Hye Kang, and Chang-Hee Hong

Appl. Phys. Lett. 102, 061114 (2013); http://dx.doi.org/10.1063/1.4773559 (3 pages)

Online Publication Date: 14 February 2013

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The effect of the combination of triangular prisms and cones as air-void structures arrays on the enhancement of light extraction efficiency of InGaN light-emitting diodes (LEDs) is investigated. The arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 74% and far-field angle as low as 125° is realized with a compact arrangement of arrays compared with that of a conventional LED.
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85.60.Jb Light-emitting devices

Strong enhancement of Eu+3 luminescence in europium-implanted GaN by Si and Mg codoping

J. K. Mishra, T. Langer, U. Rossow, S. Shvarkov, A. Wieck, and A. Hangleiter

Appl. Phys. Lett. 102, 061115 (2013); http://dx.doi.org/10.1063/1.4793207 (3 pages) | Cited 1 time

Online Publication Date: 14 February 2013

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A strong enhancement of Eu3+ luminescence in europium-implanted GaN samples is obtained by codoping with silicon (Si) and magnesium (Mg), simultaneously. The Eu3+ intensity in the 5D0 to 7F2 transition region is found to be 30 times higher compared to europium-implanted undoped GaN. The major contribution to this overall enhancement is due a weak peak present only in europium-implanted Mg-doped GaN at 2.0031 eV (618.9 nm) which is strongly enhanced by codoping both Mg and Si. The excitation process of europium ions is proposed to take place through a donor-acceptor pair related energy transfer mechanism.
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78.55.Cr III-V semiconductors
61.72.U- Doping and impurity implantation
71.55.Eq III-V semiconductors
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Hole doping of graphene supported on Ir(111) by AlBr3

N. A. Vinogradov, K. A. Simonov, A. A. Zakharov, J. W. Wells, A. V. Generalov, A. S. Vinogradov, N. Mårtensson, and A. B. Preobrajenski

Appl. Phys. Lett. 102, 061601 (2013); http://dx.doi.org/10.1063/1.4790579 (5 pages)

Online Publication Date: 11 February 2013

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In this letter, we report an easy and tenable way to tune the type of charge carriers in graphene, using a buried layer of AlBr3 and its derivatives on the graphene/Ir(111) interface. Upon the deposition of AlBr3 on graphene/Ir(111) and subsequent temperature-assisted intercalation of graphene/Ir(111) with atomic Br and AlBr3, pronounced hole doping of graphene is observed. The evolution of the graphene/Br-AlBr3/Ir(111) system at different stages of intercalation has been investigated by means of microbeam low-energy electron microscopy/electron diffraction, core-level photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy.
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61.72.up Other materials
81.05.ue Graphene
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
79.60.-i Photoemission and photoelectron spectra
79.60.Jv Interfaces; heterostructures; nanostructures

Strain relaxation by pitting in AlN thin films deposited by metalorganic chemical vapor deposition

I. Bryan, A. Rice, L. Hussey, Z. Bryan, M. Bobea, S. Mita, J. Xie, R. Kirste, R. Collazo, and Z. Sitar

Appl. Phys. Lett. 102, 061602 (2013); http://dx.doi.org/10.1063/1.4792694 (4 pages)

Online Publication Date: 14 February 2013

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Strain relaxation mechanisms were investigated in epitaxial AlN layers deposited on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition. It was revealed that epitaxial AlN layers under tensile strain can exhibit micro-cracks and nano-pits. A correlation existed between the amount of strain and number of pits in localized areas. Pit densities as high as 1010 cm−2 were observed in areas where the tensile strain reached ∼0.4%, while unstrained areas of the film showed step flow growth. These nano-pits occurred as a strain relaxation mechanism and were not related to intrinsic defects, such as threading dislocations or inversion domains.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
81.05.Ea III-V semiconductors

Experimental evidence of the atmospheric convective transport contribution to sessile droplet evaporation

F. Carle, B. Sobac, and D. Brutin

Appl. Phys. Lett. 102, 061603 (2013); http://dx.doi.org/10.1063/1.4792058 (4 pages)

Online Publication Date: 14 February 2013

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We investigate the contribution of the natural convective transport in the vapor phase on the evaporation rate of an evaporating sessile droplet. When comparing the experimental data with the quasi-steady diffusion-controlled evaporation model, an increasing deviation with substrate temperature that was attributed to the effect of the natural convection on the vapor field has been recently highlighted. To validate this analysis, we present experimental results obtained with two gravity levels: 1 g and μg. The contribution of the natural convection is analyzed with the Grashof number, and an empirical model is developed combining diffusive and convective transport.
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47.55.D- Drops and bubbles
68.03.Fg Evaporation and condensation of liquids
66.10.C- Diffusion and thermal diffusion

Gold ion implantation induced high conductivity and enhanced electron field emission properties in ultrananocrystalline diamond films

K. J. Sankaran, H. C. Chen, B. Sundaravel, C. Y. Lee, N. H. Tai, and I. N. Lin

Appl. Phys. Lett. 102, 061604 (2013); http://dx.doi.org/10.1063/1.4792744 (4 pages)

Online Publication Date: 15 February 2013

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We report high conductivity of 185 (Ω cm)−1 and superior electron field emission (EFE) properties, viz. low turn-on field of 4.88 V/μm with high EFE current density of 6.52 mA/cm2 at an applied field of 8.0 V/μm in ultrananocrystalline diamond (UNCD) films due to gold ion implantation. Transmission electron microscopy examinations reveal the presence of Au nanoparticles in films, which result in the induction of nanographitic phases in grain boundaries, forming conduction channels for electron transport. Highly conducting Au ion implanted UNCD films overwhelms that of nitrogen doped ones and will create a remarkable impact to diamond-based electronics.
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73.61.Wp Fullerenes and related materials
79.70.+q Field emission, ionization, evaporation, and desorption
61.72.up Other materials
81.05.ug Diamond
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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Noncontact and simultaneous measurement of the d33 and d31 piezoelectric strain coefficients

Mohammad H. Malakooti and Henry A. Sodano

Appl. Phys. Lett. 102, 061901 (2013); http://dx.doi.org/10.1063/1.4791573 (5 pages)

Online Publication Date: 11 February 2013

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Here, digital image correlation is demonstrated to be an accurate tool for the noncontact, non-destructive, and rapid characterization of the converse effect of piezoelectric materials. The longitudinal (d33) and transverse (d31) piezoelectric strain coefficients of lead zirconate titanate-5H wafers are measured simultaneously by imaging the wafer's cross section. The results are validated through laser interferometry and the large piezoresponse at switching domains is observed in strain-electric field butterfly loops. The proposed technique is simple and low cost requiring only an optical microscope and unlike indirect measurement methods requires little sample preparation and no information regarding the mechanical properties of the specimen.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Cg PZT ceramics and other titanates

Influence of surface oxidation on the valence electron energy-loss spectrum of wurtzite aluminum nitride

Michael R. S. Huang, Rolf Erni, and Chuan-Pu Liu

Appl. Phys. Lett. 102, 061902 (2013); http://dx.doi.org/10.1063/1.4790395 (4 pages)

Online Publication Date: 11 February 2013

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The influence of surface oxidation on the low-loss spectrum of aluminum nitride (AlN) is investigated in electron energy-loss spectroscopy with scanning transmission electron microscopy. Contrary to intrinsic bulk AlN, oxidized AlN exhibits considerable spectral broadening both in the full width at half maximum of bulk plasmon and the subsidiary features. The modification in the low-loss lineshapes due to oxidation significantly complicates the determination of the dielectric function intrinsic to AlN. Simulations based on dielectric theory qualitatively consist with the experimental results while incorporating thick overlayers, further suggesting that the surface oxide of AlN can be rough and porous in nature.
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81.65.Mq Oxidation
77.22.Ch Permittivity (dielectric function)
79.20.Uv Electron energy loss spectroscopy

Thermal properties of carbon nanowall layers measured by a pulsed photothermal technique

A. Achour, B. E. Belkerk, K. Ait Aissa, S. Vizireanu, E. Gautron, M. Carette, P.-Y. Jouan, G. Dinescu, L. Le Brizoual, Y. Scudeller, and M.-A. Djouadi

Appl. Phys. Lett. 102, 061903 (2013); http://dx.doi.org/10.1063/1.4791686 (4 pages) | Cited 1 time

Online Publication Date: 12 February 2013

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We report the thermal properties of carbon nanowall layers produced by expanding beam radio-frequency plasma. The thermal properties of carbon nanowalls, grown at 600 °C on aluminium nitride thin-film sputtered on fused silica, were measured with a pulsed photo-thermal technique. The apparent thermal conductivity of the carbon at room temperature was found to increase from 20 to 80 Wm−1 K−1 while the thickness varied from 700 to 4300 nm, respectively. The intrinsic thermal conductivity of the carbon nanowalls attained 300 Wm−1 K−1 while the boundary thermal resistance with the aluminium nitride was 3.6 × 10−8 Km2 W−1. These results identify carbon nanowalls as promising material for thermal management applications.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
52.77.Dq Plasma-based ion implantation and deposition
61.46.-w Structure of nanoscale materials
65.40.Ba Heat capacity
81.16.-c Methods of micro- and nanofabrication and processing
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.

Influence of structural anisotropy to anisotropic electron mobility in a-plane InN

H. Ahn, J.-W. Chia, H.-M. Lee, and S. Gwo

Appl. Phys. Lett. 102, 061904 (2013); http://dx.doi.org/10.1063/1.4792209 (4 pages)

Online Publication Date: 12 February 2013

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This study reports on the anisotropic electron transport properties and a correlation between the electron mobility (μ) and the stacking faults (SFs) in the a-plane InN film. Electron mobilities measured by terahertz time-domain spectroscopy and Hall effect measurement along the in-plane [math100] (c⊥) orientation were much higher than those of the in-plane [0001] (c∥) orientation. This result shows a sharp contrast to higher defect density for the c⊥ orientation as measured by x-ray diffraction. The electrons transporting through the planar SFs aligned along the c⊥ direction are expected to experience more scattering by defects, resulting in lower μ for the c∥ orientation.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
61.72.Nn Stacking faults and other planar or extended defects
78.70.Gq Microwave and radio-frequency interactions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Resonance ultrasonic thermography: Highly efficient contact and air-coupled remote modes

Igor Solodov and Gerd Busse

Appl. Phys. Lett. 102, 061905 (2013); http://dx.doi.org/10.1063/1.4792236 (3 pages)

Online Publication Date: 12 February 2013

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A frequency match between the driving ultrasonic wave and characteristic frequency of a defect provides an efficient energy pumping from the wave directly into the defect. The application of the concept of local defect resonance is shown to enhance substantially the efficiency of vibro-thermal conversion in ultrasonic thermography (ULT). Therefore, the resonance modes of ultrasonic thermography require much lower acoustic power to activate defects that makes it possible to avoid high-power ultrasonic instrumentation and proceed to a remote ultrasonic thermography version by using air-coupled ultrasonic excitation.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Stability of MnB2 with AlB2-type structure revealed by first-principles calculations and experiments

Huiyang Gou, Gerd Steinle-Neumann, Elena Bykova, Yoichi Nakajima, Nobuyoshi Miyajima, Yuan Li, Sergey V. Ovsyannikov, Leonid S. Dubrovinsky, and Natalia Dubrovinskaia

Appl. Phys. Lett. 102, 061906 (2013); http://dx.doi.org/10.1063/1.4792273 (5 pages)

Online Publication Date: 12 February 2013

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MnB2 with the ReB2-type structure has been theoretically predicted to be a superhard material which could be synthesized at ambient pressure. However, this phase has not been observed experimentally to date. In the present work, we show that even applying moderate pressure does not facilitate the formation of ReB2-structured MnB2. Our high-pressure high-temperature experiments resulted in the synthesis of single crystals of MnB2 with the previously known AlB2-type structure. This is at odds with results from density functional theory-based calculations using the generalized gradient approximation (GGA). The discrepancy with the computational prediction was reconciled by including on-site repulsion (GGA + U), which found the anti-ferromagnetically ordered AlB2-type structure energetically favored over the ReB2-structure for MnB2.
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61.66.Fn Inorganic compounds
62.20.Qp Friction, tribology, and hardness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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