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18 May 2009

Volume 94, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 203301 (2009); http://dx.doi.org/10.1063/1.3133902 (3 pages)

Zihong Liu, Joon Hak Oh, Mark E. Roberts, Peng Wei, Bipul C. Paul, Masaki Okajima, Yoshio Nishi, and Zhenan Bao
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Electrochemical fabrication and magnetization properties of CoCrPt nanowires and nanotubes

S. Shamaila, D. P. Liu, R. Sharif, J. Y. Chen, H. R. Liu, and X. F. Han

Appl. Phys. Lett. 94, 203101 (2009); http://dx.doi.org/10.1063/1.3139059 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2009

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Magnetization properties of CoCrPt alloy nanocylinders (nanowires and nanotubes) fabricated by low cost electrodeposition method have been investigated. Angular dependence of coercivity depicts curling mode of magnetization reversal process for CoCrPt nanowires (NWs) while for nanotubes (NTs) there is a transition from curling to coherent mode as a function of field angle. The effective anisotropy during reversal process is determined from a competition between the magnetostatic interactions, surface effects, and shape anisotropy in NTs while in NWs shape anisotropy is the dominant anisotropy. Furthermore, magnetization and remanence curves describe that the surface effects and dipolar coupling are increased in NTs as compared to the NWs due to their geometry. These results depict that the magnetization properties are influenced by the geometry of nanocylinders, which can become good candidate for ultrahigh density magnetic recording media.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Pq Electrodeposition, electroplating
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Influence of surface-related states on the carrier dynamics in (Ga,In)N/GaN single quantum wells

Andreas Othonos, G. Itskos, D. D. C. Bradley, M. D. Dawson, and I. M. Watson

Appl. Phys. Lett. 94, 203102 (2009); http://dx.doi.org/10.1063/1.3139079 (3 pages) | Cited 2 times

Online Publication Date: 18 May 2009

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We report on the influence of surface-related states on the relaxation of carriers within single (Ga,In)N/GaN quantum wells. Two identical samples that differ only in the thickness of the top GaN cap layer were studied. Photoluminescence and pump-probe measurements reveal significant variations in the quantum well integrated emission and the carrier relaxation decay times in the two samples, when probing both the ground and excited states of the wells. The variations are attributed to the presence of an efficient nonradiative relaxation channel associated with the proximity of the quantum well excitations to the surface-related states in the thin-cap sample.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.67.De Quantum wells
73.20.At Surface states, band structure, electron density of states

Lattice thermal conductivity of graphene flakes: Comparison with bulk graphite

D. L. Nika, S. Ghosh, E. P. Pokatilov, and A. A. Balandin

Appl. Phys. Lett. 94, 203103 (2009); http://dx.doi.org/10.1063/1.3136860 (3 pages) | Cited 83 times

Online Publication Date: 19 May 2009

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The authors proposed a simple model for the lattice thermal conductivity of graphene in the framework of Klemens approximation. The Gruneisen parameters were introduced separately for the longitudinal and transverse phonon branches through averaging over phonon modes obtained from the first principles. The calculations show that Umklapp-limited thermal conductivity of graphene grows with the increasing linear dimensions of graphene flakes and can exceed that of the basal planes of bulk graphite when the flake size is on the order of a few micrometers. The obtained results are in agreement with experimental data and reflect the two-dimensional nature of phonon transport in graphene.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Radio frequency nanowire resonators and in situ frequency tuning

Wayne Y. Fung, Eric N. Dattoli, and Wei Lu

Appl. Phys. Lett. 94, 203104 (2009); http://dx.doi.org/10.1063/1.3139750 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2009

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We report the fabrication and characterization of radio frequency nanoelectromechanical resonators based on semiconductor nanowires with a dual-gate configuration. Suspended nanowire resonators were fabricated with little residual tension using a dry transfer method and lithographically defined metal electrodes. Fundamental flexural modes of the nanowire resonators were actuated and detected electrically at room temperature using the on-chip gates and a mixing circuit. The dual-gate setup in turn enabled us to tune the nanowire resonant frequency up or down in situ through elastic hardening and capacitive softening effects, respectively. Selective actuation of the out-of-plane or the in-plane vibrational mode was also reported.
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68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Peculiar three-dimensional ordering in (In,Ga)As/GaAs(311)B quantum dot superlattices

M. Hanke, M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, Sh. Seydmohamadi, G. J. Salamo, T. D. Mishima, and M. B. Johnson

Appl. Phys. Lett. 94, 203105 (2009); http://dx.doi.org/10.1063/1.3141404 (3 pages) | Cited 2 times

Online Publication Date: 20 May 2009

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The impact of the GaAs spacer layer thickness on the three-dimensional ordering in (In,Ga)As/GaAs(311)B quantum dot superlattices was investigated by high-resolution x-ray diffraction, cross-sectional transmission electron microscopy, and atomic force microscopy. Dramatic changes in both planar and vertical ordering could be observed. A distinct correlation was found in that the azimuthal angle of inclined vertical inheritance of the dot positions is perpendicular to the planar direction between the dot chains within individual quantum dot layers. These directions are close to [130] or [math03].
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68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Cd Superlattices
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.37.Ps Atomic force microscopy (AFM)

Ultraviolet photodetectors based on selectively grown ZnO nanorod arrays

L. W. Ji, S. M. Peng, Y. K. Su, S. J. Young, C. Z. Wu, and W. B. Cheng

Appl. Phys. Lett. 94, 203106 (2009); http://dx.doi.org/10.1063/1.3141447 (3 pages) | Cited 16 times

Online Publication Date: 20 May 2009

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Metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with ZnO nanorods (NRs) have been fabricated and characterized in this investigation. The NR arrays were selectively grown on the gap of interdigitated electrodes by chemical solution method through a photolithography process. Compared to a traditional ZnO MSM photodetector with no NRs, the fabricated NR UV photodetector showed much higher photoresponsity. As a result, it can be attributed to high surface-to-volume ratio of ZnO NRs and such a high photoresponse could strongly depend on oxygen adsorption/desorption process in the presence of trap states at the NR surface.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.16.Nd Micro- and nanolithography

A highly efficient two level diamond based single photon source

D. A. Simpson, E. Ampem-Lassen, B. C. Gibson, S. Trpkovski, F. M. Hossain, S. T. Huntington, A. D. Greentree, L. C. L. Hollenberg, and S. Prawer

Appl. Phys. Lett. 94, 203107 (2009); http://dx.doi.org/10.1063/1.3141450 (3 pages) | Cited 22 times

Online Publication Date: 20 May 2009

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An unexplored diamond defect center that is found to emit stable single photons at a measured rate of 1.6 MHz at room temperature is reported. The center, identified in chemical vapor deposition grown diamond crystals, exhibits a sharp zero phonon line at 734 nm with a full width at half maximum of ∼ 4 nm. The photon statistics confirm that the center is a single emitter and provides direct evidence of a true two level single quantum system in diamond.
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78.55.Hx Other solid inorganic materials
81.10.Bk Growth from vapor

A simple design of flat hyperlens for lithography and imaging with half-pitch resolution down to 20 nm

Yi Xiong, Zhaowei Liu, and Xiang Zhang

Appl. Phys. Lett. 94, 203108 (2009); http://dx.doi.org/10.1063/1.3141457 (3 pages) | Cited 19 times

Online Publication Date: 20 May 2009

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We propose that a hyperlens can be used for photolithography to generate deep subwavelength arbitrary patterns from diffraction-limited masks. Numerical simulation shows that half-pitch resolution down to 20 nm is possible from a mask with 280 nm period at working wavelength 375 nm. We also extend the hyperlens projection concept from cylindrical interfaces to arbitrary interfaces. An example of a flat interface hyperlens is numerically demonstrated for lithography purposes.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Bh Lenses, prisms and mirrors

Improved thermoelectric properties of Mg2SixGeySn1−x−y nanoparticle-in-alloy materials

S. Wang and N. Mingo

Appl. Phys. Lett. 94, 203109 (2009); http://dx.doi.org/10.1063/1.3139785 (3 pages) | Cited 8 times

Online Publication Date: 21 May 2009

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We theoretically find that introducing nanoparticles into Mg2SixGeySn1−x−y alloys considerably improves their thermoelectric figure of merit (ZT). We have computed the thermal conductivity versus nanoparticle size of this class of nanocomposites for nine different material types at various temperatures. We provide validity ranges of nanoparticle concentration that will not reduce the thermoelectric power factor, but will considerably decrease the thermal conductivity. ZT enhancements of two times the alloy values are within reach. In particular, n-type Mg2Si0.4Sn0.6 with Mg2Si or Mg2Ge nanoparticles stand out as one of the best materials for intermediate temperature (800 K) applications, providing a good nontoxic alternative to PbTe.
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72.15.Jf Thermoelectric and thermomagnetic effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

GeTe/Sb7Te3 superlatticelike structure for lateral phase change memory

Hongxin Yang, Chong Tow Chong, Rong Zhao, Hock Koon Lee, Jianming Li, Kian Guan Lim, and Luping Shi

Appl. Phys. Lett. 94, 203110 (2009); http://dx.doi.org/10.1063/1.3139776 (3 pages) | Cited 15 times

Online Publication Date: 22 May 2009

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A series of superlatticelike (SLL) structure incorporated with two phase-change materials GeTe and Sb7Te3 was applied in lateral phase change memory. Power consumption and lifetime were used as two criteria to optimize the SLL structure. It was found that with the thickness ratio of GeTe to Sb7Te3 at 1.6, the RESET current could be as low as 1.5 mA and the endurance could reach as high as 5.3×106 cycles. By varying the thickness ratio of GeTe to Sb7Te3, the crystallization temperature of SLL structures and the performance of lateral phase change memory with these SLL structures can be controlled.
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68.65.Cd Superlattices
84.30.Sk Pulse and digital circuits
64.70.kg Semiconductors
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