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6 Dec 2010

Volume 97, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages)

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie
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Imaging ellipsometry of graphene

Ulrich Wurstbauer, Christian Röling, Ursula Wurstbauer, Werner Wegscheider, Matthias Vaupel, Peter H. Thiesen, and Dieter Weiss

Appl. Phys. Lett. 97, 231901 (2010); http://dx.doi.org/10.1063/1.3524226 (3 pages) | Cited 7 times

Online Publication Date: 6 December 2010

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Imaging ellipsometry studies of graphene on SiO2/Si and crystalline GaAs are presented. We demonstrate that imaging ellipsometry is a powerful tool to detect and characterize graphene on any flat substrate. Variable angle spectroscopic ellipsometry is used to explore the dispersion of the optical constants of graphene in the visible range with high lateral resolution. In this way, the influence of the substrate on graphene’s optical properties can be investigated.
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78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Significant elastic anisotropy in Ti1−xAlxN alloys

Ferenc Tasnádi, Igor A. Abrikosov, Lina Rogström, Jonathan Almer, Mats P. Johansson, and Magnus Odén

Appl. Phys. Lett. 97, 231902 (2010); http://dx.doi.org/10.1063/1.3524502 (3 pages) | Cited 5 times

Online Publication Date: 6 December 2010

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Strong compositional-dependent elastic properties have been observed theoretically and experimentally in Ti1−xAlxN alloys. The elastic constant, C11, changes by more than 50% depending on the Al-content. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloys.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
62.65.+k Acoustical properties of solids
64.75.Op Phase separation and segregation in alloying
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Effect of substrate misorientation on the material properties of GaAs/Al0.3Ga0.7As tunnel diodes

H. W. Yu, E. Y. Chang, H. Q. Nguyen, J. T. Chang, C. C. Chung, C. I. Kuo, Y. Y. Wong, and W. C. Wang

Appl. Phys. Lett. 97, 231903 (2010); http://dx.doi.org/10.1063/1.3525158 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2010

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The effect of substrate misorientation on the material quality of the N++–GaAs/P++–AlGaAs tunnel diodes (TDs) grown on these substrates is investigated. It is found that the misorientation influences both surface roughness and interface properties of the N++–GaAs/P++–AlGaAs TDs. Smooth surface (rms roughness: 1.54 Å) and sharp interface for the GaAs/Al0.3Ga0.7As TDs were obtained when the (100) tilted 10° off toward [111] GaAs substrate was used. Besides, the oxygen content in N++–GaAs and P++–AlGaAs layers grown on the 10° off GaAs substrates was reduced due to the reduction of sticking coefficient and number of anisotropic sites.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Size-dependent strain in epitaxial (001) gadolinium-doped ceria nanoislands

Vyacheslav F. Solovyov, Marta Gibert, Teresa Puig, and Xavier Obradors

Appl. Phys. Lett. 97, 231904 (2010); http://dx.doi.org/10.1063/1.3527079 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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We report size-dependent strain in epitaxial gadolinium doped ceria nanoislands, which was determined by synchrotron x-ray diffraction. Reciprocal space sections of symmetric, (004) and asymmetric, (224) reflections are approximated by a model assuming size-dependent strain of the islands using real-space size distribution obtained by atomic force microscopy. We show that the islands smaller than 40 nm are subjected to a high level of lateral tensile strain and normal compression. The lateral to normal strain ratio determined from the reciprocal map analysis suggests that lateral tension is the primary stress generator, possibly due to oxygen vacancy ordering on the island-substrate interface.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology

Enhancing visibility of graphene on arbitrary substrates by microdroplet condensation

Hugo Gonçalves, Michael Belsley, Cacilda Moura, Tobias Stauber, and Peter Schellenberg

Appl. Phys. Lett. 97, 231905 (2010); http://dx.doi.org/10.1063/1.3527081 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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In order to take advantage of the enormous potential of graphene for future electronic microcircuits and other applications it is necessary to develop reliable, rapid, and widely applicable methods to visualize graphene-based structures. We report here on a microdroplet condensation technique, which allows for quick visual identification of graphene on a variety of substrates, including some which were previously considered unsuitable for the visualization of carbon layers. The technique should also be applicable to visualize artificially patterned graphene structures which are expected to be key technologically enabling components in electronic microcircuits and other applications.
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78.67.Wj Optical properties of graphene
61.48.Gh Structure of graphene
78.30.Na Fullerenes and related materials

Photoluminescence and extinction enhancement from ZnO films embedded with Ag nanoparticles

M. Liu, S. W. Qu, W. W. Yu, S. Y. Bao, C. Y. Ma, Q. Y. Zhang, J. He, J. C. Jiang, E. I. Meletis, and C. L. Chen

Appl. Phys. Lett. 97, 231906 (2010); http://dx.doi.org/10.1063/1.3525171 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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ZnO films embedded with Ag nanoparticles are deposited at 750 °C with a reactive radio-frequency magnetron sputtering. The films are found to have a large enhancement in the intensity of photoluminescence emission and in the extinction of incident light. The enhancement is assigned to be from the interaction between the localized surface plasmons in the Ag nanoparticels and the light. The surface plasmons in the films can be excited in a wide range, from ultraviolet to near infrared wavelength of light.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors

Identification of zinc and oxygen vacancy states in nonpolar ZnO single crystal using polarized photoluminescence

J. Liu, Y. Zhao, Y. J. Jiang, C. M. Lee, Y. L. Liu, and G. G. Siu

Appl. Phys. Lett. 97, 231907 (2010); http://dx.doi.org/10.1063/1.3525714 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2010

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Polarized photoluminescence spectra of the nonpolar ZnO single crystals annealed at different temperatures in air were investigated, for which the whole emission spectra from visible up to ultraviolet range for zinc and oxygen defects states are taken separately via the parallel and the crossed polarization geometries, respectively. It is also deduced from the spectra that the density of oxygen vacancy defects attains minimum for the sample annealed at 400 °C, and above which both anharmonic effects of ultraviolet emission and enhancement of defect-related deep band emission band due to the increase of oxygen and zinc vacancy defects are observed.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies

Promotion of hydrogen production using spectrally controlled thermal radiation

Yuriko Maegami, Fumitada Iguchi, and Hiroo Yugami

Appl. Phys. Lett. 97, 231908 (2010); http://dx.doi.org/10.1063/1.3525164 (3 pages)

Online Publication Date: 10 December 2010

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By controlling the thermal radiation spectrum using surface grating technologies, we promote the methane steam reforming to produce hydrogen. We fabricated a two-dimensional surface grating to tune its thermal emittance peak to the vibrational absorption bands of methane and water. We demonstrated that hydrogen production strongly depends on the spectral intensity within the resonant wavelength range, and that the hydrogen production rate is four times greater than that obtained when the spectrally controlled thermal radiation is not tuned to vibrational resonances. The optical excitation of the vibrational energy levels of gas molecules is found to effectively promote hydrogen production.
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88.30.E- Hydrogen production with renewable energy

Effect of relative humidity on contact angle and particle deposition morphology of an evaporating colloidal drop

Viral H. Chhasatia, Abhijit S. Joshi, and Ying Sun

Appl. Phys. Lett. 97, 231909 (2010); http://dx.doi.org/10.1063/1.3525167 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2010

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The deposition behavior of inkjet-printed aqueous colloidal drops on a glass substrate has been investigated by using fluorescence microscopy and a high resolution goniometer. Real-time side-view images of a pinned colloidal drop show that the contact angle during evaporation is a function of the relative humidity (RH). The RH also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively driven flow inside the drop that drives the suspended particles toward the contact line. Results show that the particle deposition area and pattern change significantly with the RH.
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68.03.Fg Evaporation and condensation of liquids
47.57.J- Colloidal systems
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
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