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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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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) | Cited 1 time

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

Improvement of heat transfer efficiency at solid-gas interfaces by self-assembled monolayers

Zhi Liang, William Evans, Tapan Desai, and Pawel Keblinski

Appl. Phys. Lett. 102, 061907 (2013); http://dx.doi.org/10.1063/1.4792530 (5 pages) | Cited 1 time

Online Publication Date: 13 February 2013

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Using molecular dynamics simulations, we demonstrate that the efficiency of heat exchange between a solid and a gas can be maximized by functionalizing solid surface with organic self-assembled monolayers (SAMs). We observe that for bare metal surfaces, the thermal accommodation coefficient (TAC) strongly depends on the solid-gas interaction strength. For metal surfaces modified with organic SAMs, the TAC is close to its theoretical maximum and is essentially independent from the SAM-gas interaction strength. The analysis of the simulation results indicates that softer and lighter SAMs, compared to the bare metal surfaces, are responsible for the greatly enhanced TAC.
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44.35.+c Heat flow in multiphase systems
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Sn and Nb modified ultrafine Ti-based bulk alloys with high-strength and enhanced ductility

G. H. Cao, R. Schneider, D. Gerthsen, R. Chulist, R. Schaarschuch, C.-G. Oertel, and W. Skrotzki

Appl. Phys. Lett. 102, 061908 (2013); http://dx.doi.org/10.1063/1.4792592 (4 pages)

Online Publication Date: 13 February 2013

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Sn and Nb modified ultrafine eutectic Ti−Fe alloys with high strength and plasticity prepared by cold crucible levitation melting were tested in compression at room temperature. (Ti70.5Fe29.5)93.15Sn3.85Nb3 alloy exhibited an ultimate compressive strength of 2.36 GPa at 15% plastic strain. Electron microscopy revealed that lamellar structures in Ti70.5Fe29.5 alloy could be tailored by the addition of Sn and Nb to obtain a globular structure. The microstructural refinement, morphology of phase constituents, and their relationships to the mechanical properties are discussed.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
64.70.dj Melting of specific substances

Iso-structural phase transition in YMnO3 nanosized particles

Saurabh Tripathi and Valeri Petkov

Appl. Phys. Lett. 102, 061909 (2013); http://dx.doi.org/10.1063/1.4791596 (4 pages)

Online Publication Date: 13 February 2013

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Structure studies on multiferroic YMnO3 particles with size varying between 467 ± 42 nm (bulk) and 28 ± 3 nm was carried out using high-energy synchrotron x-ray diffraction. Analysis of the diffraction data reveals that when the particles size decreases to about 121 nm an iso-structural phase transition takes place. The transition is accompanied by a substantial change in the unit cell volume and the ratio (c/a) of the parameters of the hexagonal lattice of YMnO3. The phase transition is similar to the one reported in bulk YMnO3 heated to temperatures of about 920 K. In this letter, we argue that the phase transition in nanosized YMnO3 is of an order-disorder type.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
75.85.+t Magnetoelectric effects, multiferroics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.60.Cn Order-disorder transformations
64.70.Nd Structural transitions in nanoscale materials

Resonant Raman scattering from CdS nanocrystals enhanced by interstitial Mn

P. Q. Zhao, L. Z. Liu, H. T. Xue, X. L. Wu, J. C. Shen, and Paul K. Chu

Appl. Phys. Lett. 102, 061910 (2013); http://dx.doi.org/10.1063/1.4792512 (4 pages)

Online Publication Date: 14 February 2013

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Different Raman scattering effects are observed from CdS and Mn-doped CdS nanocrystals (NCs) with an average size of 5.1 nm synthesized by the reverse-micelle method. The intensity of the longitudinal optical (LO) phonon spectrum acquired from the Mn-doped CdS NCs is more than 20 times larger than that from the undoped CdS NCs. Spectroscopic and theoretical analyses reveal that the enhancement is caused by the interstitial Mn dopants, which decrease the NC surface deformation potential due to the small dielectric constant of the metal resulting in enhanced coupling between the LO phonon and surface plasmon.
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78.30.Fs III-V and II-VI semiconductors
63.20.kk Phonon interactions with other quasiparticles
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
77.22.Ch Permittivity (dielectric function)

Vortical structures of supersonic flow over a delta-wing on a flat plate

D. P. Wang, Z. X. Xia, Y. X. Zhao, Q. H. Wang, and B. Liu

Appl. Phys. Lett. 102, 061911 (2013); http://dx.doi.org/10.1063/1.4790286 (4 pages)

Online Publication Date: 14 February 2013

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Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flow over a delta-winged vortex generator on a flat plate was experimentally investigated in a supersonic quiet wind tunnel at Ma = 2.68. The fine structures of the flow field, shock waves, separation vortices, wake, and boundary layer transition were observed in the NPLS images. According to the time-correlation of the NPLS images and the measurement results of particle image velocimetry, the structural model of the flow field was improved further, and coherent wake structures were observed, which is of significance theoretically and in engineering application.
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47.32.Ff Separated flows
47.40.Ki Supersonic and hypersonic flows
47.40.Nm Shock wave interactions and shock effects
47.80.Jk Flow visualization and imaging
47.85.Np Fluidics

Quantitative scanning thermal microscopy of ErAs/GaAs superlattice structures grown by molecular beam epitaxy

K. W. Park, H. P. Nair, A. M. Crook, S. R. Bank, and E. T. Yu

Appl. Phys. Lett. 102, 061912 (2013); http://dx.doi.org/10.1063/1.4792757 (5 pages)

Online Publication Date: 15 February 2013

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A proximal probe-based quantitative measurement of thermal conductivity with ∼100–150 nm lateral and vertical spatial resolution has been implemented. Measurements on an ErAs/GaAs superlattice structure grown by molecular beam epitaxy with 3% volumetric ErAs content yielded thermal conductivity at room temperature of 9 ± 2 W/m K, approximately five times lower than that for GaAs. Numerical modeling of phonon scattering by ErAs nanoparticles yielded thermal conductivities in reasonable agreement with those measured experimentally and provides insight into the potential influence of nanoparticle shape on phonon scattering. Measurements of wedge-shaped samples created by focused ion beam milling provide direct confirmation of depth resolution achieved.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
66.70.Df Metals, alloys, and semiconductors
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