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27 Feb 2012

Volume 100, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.
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Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast x-ray diffraction

M. Herzog, A. Bojahr, J. Goldshteyn, W. Leitenberger, I. Vrejoiu, D. Khakhulin, M. Wulff, R. Shayduk, P. Gaal, and M. Bargheer

Appl. Phys. Lett. 100, 094101 (2012); http://dx.doi.org/10.1063/1.3688492 (4 pages) | Cited 2 times

Online Publication Date: 27 February 2012

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We excite an epitaxial SrRuO3 thin film transducer by a pulse train of ultrashort laser pulses, launching coherent sound waves into the underlying SrTiO3 substrate. Synchrotron-based x-ray diffraction (XRD) data exhibiting separated sidebands to the substrate peak evidence the excitation of a quasi-monochromatic phonon wavepacket with sub-THz central frequency. The frequency and bandwidth of this sound pulse can be controlled by the optical pulse train. We compare the experimental data to combined lattice dynamics and dynamical XRD simulations to verify the coherent phonon dynamics. In addition, we observe a lifetime of 130 ps of such sub-THz phonons in accordance with the theory.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion

The band alignment of Cu2O/ZnO and Cu2O/GaN heterostructures

B. Kramm, A. Laufer, D. Reppin, A. Kronenberger, P. Hering, A. Polity, and B. K. Meyer

Appl. Phys. Lett. 100, 094102 (2012); http://dx.doi.org/10.1063/1.3685719 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2012

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Using photoelectron spectroscopy, we investigate the band alignments of the Cu2O/ZnO heterointerface and compare the findings with the corresponding values for Cu2O/GaN. While for Cu2O/ZnO, we find a valence band offset (VBO) of 2.17 eV and a conduction band offset (CBO) of 0.97 eV, both values are considerably reduced for Cu2O/GaN where the numbers are 1.47 eV (VBO) and 0.24 eV (CBO), respectively. The large CBO between ZnO and Cu2O will very likely result in low photovoltaic power conversion efficiencies as is the current status of Cu2O/ZnO solar cells.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures

Theoretical approach for plasma series resonance effect in geometrically symmetric dual radio frequency plasma

B. Bora, H. Bhuyan, M. Favre, E. Wyndham, and H. Chuaqui

Appl. Phys. Lett. 100, 094103 (2012); http://dx.doi.org/10.1063/1.3690870 (3 pages) | Cited 5 times

Online Publication Date: 29 February 2012

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Plasma series resonance (PSR) effect is well known in geometrically asymmetric capacitively couple radio frequency plasma. However, plasma series resonance effect in geometrically symmetric plasma has not been properly investigated. In this work, a theoretical approach is made to investigate the plasma series resonance effect and its influence on Ohmic and stochastic heating in geometrically symmetric discharge. Electrical asymmetry effect by means of dual frequency voltage waveform is applied to excite the plasma series resonance. The results show considerable variation in heating with phase difference between the voltage waveforms, which may be applicable in controlling the plasma parameters in such plasma.
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52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.80.Pi High-frequency and RF discharges
02.50.Ey Stochastic processes
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

Dependence of surface free energy on molecular orientation in polymer films

Urszula Stachewicz, Shuangwu Li, Emiliano Bilotti, and Asa H. Barber

Appl. Phys. Lett. 100, 094104 (2012); http://dx.doi.org/10.1063/1.3691186 (4 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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Surface free energy of mechanically drawn polycarbonate films was determined using contact angle measurements and shown to increase with orientation. The increase in polymer film surface free energy was attributed to increased polymer chain packing during orientation, supported by film density measurements, which provides enhanced intermolecular interactions. Surface free energy can therefore be increased by, or used to predict, polymer orientation.
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68.35.Md Surface thermodynamics, surface energies
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Acoustic omnidirectional superabsorber with arbitrary contour

Q. Wei, Y. Cheng, and X. J. Liu

Appl. Phys. Lett. 100, 094105 (2012); http://dx.doi.org/10.1063/1.3690899 (5 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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Using transformation acoustics we have constructed an arbitrarily contoured acoustic omnidirectional superabsorber (AOSA) which consists of a guiding shell of negative-index metamaterial and a sound absorptive cavity. A square AOSA with anisotropic parameters and a circular AOSA with isotropic parameters are demonstrated. The consistent results by numerical full-wave simulation, analytic scattering-theory derivation, and sound ray tracing show that the AOSA can completely absorb the incident acoustic waves with arbitrary incident angle. For theoretically unlimited bandwidth, the absorption across section of the AOSA in a fixed geometric size can be made arbitrarily larger than the size of itself. Interesting applications of the proposed superabsorber such as ventilated sound insulation window are further discussed.
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43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.25.Ed Effect of nonlinearity on velocity and attenuation

Schottky barrier formation at amorphous-crystalline interfaces of GeSb phase change materials

H. J. Kroezen, G. Eising, G. ten Brink, G. Palasantzas, B. J. Kooi, and A. Pauza

Appl. Phys. Lett. 100, 094106 (2012); http://dx.doi.org/10.1063/1.3691179 (4 pages)

Online Publication Date: 1 March 2012

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The electrical properties of amorphous-crystalline interfaces in phase change materials, which are important for rewritable optical data storage and for random access memory devices, have been investigated by surface scanning potential microscopy. Analysis of GeSb systems indicates that the surface potential of the crystalline phase is ∼30–60 mV higher than that of the amorphous phase. This potential asymmetry is explained qualitatively by the presence of a Schottky barrier at the amorphous-crystalline interface and supported also by quantitative Schottky model calculations.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Ps Atomic force microscopy (AFM)
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