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23 Aug 2010

Volume 97, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 97, 081901 (2010); http://dx.doi.org/10.1063/1.3457448 (3 pages)

Zhaofeng Li, Rongkuo Zhao, Thomas Koschny, Maria Kafesaki, Kamil Boratay Alici, Evrim Colak, Humeyra Caglayan, Ekmel Ozbay, and C. M. Soukoulis
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Selective electroless coating of palladium nanoparticles on metallic single-walled carbon nanotube

Yiyu Feng, Peng Lv, Xuequan Zhang, Yu Li, and Wei Feng

Appl. Phys. Lett. 97, 083101 (2010); http://dx.doi.org/10.1063/1.3483615 (3 pages) | Cited 2 times

Online Publication Date: 23 August 2010

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The selective electroless coating of palladium (Pd) nanoparticles on metallic single-walled carbon nanotube (SWNT) was studied. The remarkable increase in conductivity of SWNT/Pd films up to fourfold higher than pure SWNT was due to p-type doping and Ohmic contact. Metallic behavior of SWNT/Pd-Field effect transistor (on/off ratio = 1.2) was attributed to more hole carriers and no electrostatic barrier between nanotube and Pd. G-band and radial breathing mode in Raman indicates a definitive increase in the proportion of metallic SWNT. Results indicate Pd are selectively coated on metallic SWNT with more negative potential allowing for the electroless Pd2+ reduction.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.65.-b Surface treatments
68.55.A- Nucleation and growth
73.40.Ns Metal-nonmetal contacts
73.61.-r Electrical properties of specific thin films
85.30.Tv Field effect devices

Effects of surface chemistry on thermal conductance at aluminum–diamond interfaces

Kimberlee C. Collins, Shuo Chen, and Gang Chen

Appl. Phys. Lett. 97, 083102 (2010); http://dx.doi.org/10.1063/1.3480413 (3 pages) | Cited 12 times

Online Publication Date: 23 August 2010

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Synthetic diamond has potential as a heat spreading material in small-scale devices. Here, we report thermal conductance values at interfaces between aluminum and diamond with various surface terminations over a range of temperatures from 88 to 300 K. We find that conductance at oxygenated diamond interfaces is roughly four times higher than at hydrogen-treated diamond interfaces. Furthermore, we find that Al grain structure formation is not strongly dependent on diamond surface chemistry, which suggests that interfacial bonding influences thermal conductance. The results reported here will be useful for device design and for advancing models of interfacial heat flow.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.-y Defects and impurities in crystals; microstructure

Acoustic phonon scattering in Bi2Te3/Sb2Te3 superlattices

Yaguo Wang, Carl Liebig, Xianfan Xu, and Rama Venkatasubramanian

Appl. Phys. Lett. 97, 083103 (2010); http://dx.doi.org/10.1063/1.3483767 (3 pages) | Cited 7 times

Online Publication Date: 24 August 2010

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Ultrafast time-resolved measurements were conducted to investigate long-wavelength acoustic phonon scattering and velocity reduction in Bi2Te3/Sb2Te3 superlattices. We show that both these phenomena suppress heat transfer process, with the phonon scattering contributing more in differentiating the lattice thermal conductivities among films with different periods. Measurements of reduction in the acoustic phonon amplitudes support the decrease in the thermal conductivity for certain superlattice periods, which is not predicted by acoustic mismatch theory. This study is a direct measurement of coherent acoustic phonons in superlattices which is of significant interest to thermoelectrics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.65.Cd Superlattices

Bulk Cr tips with full spatial magnetic sensitivity for spin-polarized scanning tunneling microscopy

A. Schlenhoff, S. Krause, G. Herzog, and R. Wiesendanger

Appl. Phys. Lett. 97, 083104 (2010); http://dx.doi.org/10.1063/1.3474659 (3 pages) | Cited 2 times

Online Publication Date: 24 August 2010

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A full magnetic characterization of bulk Cr tips has been achieved using spin-polarized scanning tunneling microscopy at low temperature. A detailed bias-dependent study of the spatial magnetic sensitivity on the system of 1.5 monolayers of Fe/W(110) reveals that all magnetic directions in space are sensed over a wide bias range, thereby indicating a canted magnetization direction being a typical feature of bulk Cr tips. Consequently, using Cr as tip material allows any standard scanning tunneling microscope setup to be extended by the spin-polarized mode.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
72.25.Ba Spin polarized transport in metals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Magnetically tunable self-assembly of colloidal rings

Kwan H. Li and Benjamin B. Yellen

Appl. Phys. Lett. 97, 083105 (2010); http://dx.doi.org/10.1063/1.3483137 (3 pages) | Cited 9 times

Online Publication Date: 24 August 2010

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We present a technique using ferrofluid to induce bidisperse suspensions of superparamagnetic and diamagnetic beads to assemble into colloidal ring configurations. The separation distance between particles within the ring can be tuned by adjusting the ferrofluid concentration, which has the effect of enhancing the effective dipole moment of one of the components while screening the dipole moment of the other, leading to a wealth of different ring configurations.
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81.16.Dn Self-assembly
75.50.Mm Magnetic liquids
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Cd Fabrication of magnetic nanostructures
75.30.Cr Saturation moments and magnetic susceptibilities

Hydrogen storage cycling of MgH2 thin film nanocomposites catalyzed by bimetallic Cr Ti

Beniamin Zahiri, Babak Shalchi Amirkhiz, and David Mitlin

Appl. Phys. Lett. 97, 083106 (2010); http://dx.doi.org/10.1063/1.3479914 (3 pages) | Cited 11 times

Online Publication Date: 26 August 2010

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We examine hydrogen sorption cycling of 1.5 μm thick magnesium thin films containing a bimetallic chromium titanium catalyst. At 200 °C these nanocomposites absorb 5 wt % hydrogen in several seconds, and desorb in 10–20 minutes. In several compositions, there is negligible hydrogenation kinetics or capacity degradation even at over 100 cycles. Equally importantly, the ternary films require minimal activation, achieving rapid magnesium hydride formation and decomposition from cycle one. Pressure-composition isotherms display well-known enthalpies of MgH2. Transmission electron microscopy analysis supports a hypothesis that such extreme kinetics is due to the presence of a nanodispersed Cr Ti phase in Mg matrix.
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88.30.rd Inorganic metal hydrides
65.40.G- Other thermodynamical quantities

DNA-decorated graphene chemical sensors

Ye Lu, B. R. Goldsmith, N. J. Kybert, and A. T. C. Johnson

Appl. Phys. Lett. 97, 083107 (2010); http://dx.doi.org/10.1063/1.3483128 (3 pages) | Cited 34 times

Online Publication Date: 26 August 2010

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Graphene is a two-dimensional material with exceptional electronic properties and enormous potential for applications. Graphene’s promise as a chemical sensor material has been noted but there has been little work on practical chemical sensing using graphene, and in particular, how chemical functionalization may be used to sensitize graphene to chemical vapors. Here we show one route towards improving the ability of graphene to work as a chemical sensor by using single stranded DNA as a sensitizing agent. The resulting devices show fast response times, complete and rapid recovery to baseline at room temperature, and discrimination between several similar vapor analytes.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.ue Graphene

Growth and electronic properties of GaN/ZnO solid solution nanowires

Wei-Qiang Han, Yan Zhang, Chang-Yong Nam, C. T. Black, and E. E. Mendez

Appl. Phys. Lett. 97, 083108 (2010); http://dx.doi.org/10.1063/1.3483132 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2010

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We have grown single-crystal (Ga1−xZnx)(N1−xOx) solid-solution nanowires using nanostructured ZnGa2O4 precursor prepared by a sol-gel method. From electrical transport measurements in individual nanowire field-effect transistors, we have identified the conduction as n-type and obtained a background carrier density ( ∼ 1019 cm−3) and an electron mobility ( ∼ 1 cm2/V s) that are consistent with chemical disorder and a large number of charge traps, as confirmed by the devices’ photocurrent response. From the dependence of the device photoresponse on incident light wavelength, we have determined the energy band gap of (Ga0.88Zn0.12)(N0.88O0.12) to be as much as ∼ 0.6 eV lower than that of GaN or ZnO.
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81.16.-c Methods of micro- and nanofabrication and processing
72.40.+w Photoconduction and photovoltaic effects
85.30.Tv Field effect devices
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.21.Hb Quantum wires
73.63.Nm Quantum wires

Bolometric terahertz detection in pinched-off quantum point contacts

J. W. Song, G. R. Aizin, J. Mikalopas, Y. Kawano (河野行雄), K. Ishibashi (石橋幸治), N. Aoki (青木伸之), J. L. Reno, Y. Ochiai (落合勇一), and J. P. Bird

Appl. Phys. Lett. 97, 083109 (2010); http://dx.doi.org/10.1063/1.3475488 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2010

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Terahertz (>1 THz) irradiation of pinched-off quantum point contacts (QPCs) generates a pronounced photo-current due to radiation-induced heating. This response is reproduced by a model of temperature-dependent transmission through a saddle potential, confirming its bolometric nature.
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73.23.-b Electronic transport in mesoscopic systems
72.40.+w Photoconduction and photovoltaic effects
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