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26 Dec 2011

Volume 99, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 99, 261101 (2011); http://dx.doi.org/10.1063/1.3660243 (3 pages)

T. Schwarzbäck, H. Kahle, M. Eichfelder, R. Roßbach, M. Jetter, and P. Michler
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Trap-state whispering-gallery mode lasing from high-quality tin-doped CdS whiskers

R. B. Liu, X. J. Zhuang, J. Y. Xu, D. B. Li, Q. L. Zhang, K. Ding, P. B. He, C. Z. Ning, B. S. Zou, and A. L. Pan

Appl. Phys. Lett. 99, 263101 (2011); http://dx.doi.org/10.1063/1.3672032 (4 pages) | Cited 3 times

Online Publication Date: 27 December 2011

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High-quality surface tin-doped hexagonal CdS whiskers were synthesized by a well-controlled in situ source exchange chemical vapor deposition route. Under local light excitation, the detected microphotoluminescence from any positions along the length of these whiskers exhibits strong and multi-mode trap-state whispering-gallery (WG) mode emission. With elevating the pumping power, some of these WG modes start lasing at an ultra-low threshold, with lasing wavelength covering a broad range from ∼540 to ∼750 nm. Calculations using a plane-wave model of WG modes show that all these trap-state lasing modes are transverse magnetic polarized, which was well explained by a two-dimensional finite element simulation. The surface doped semiconductor structures have potential applications as low-threshold tunable micro/nanoscale lasers in optical storage, lighting, and optical communications.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Fundamental limits in the external quantum efficiency of single nanowire solar cells

Martin Heiss and Anna Fontcuberta i Morral

Appl. Phys. Lett. 99, 263102 (2011); http://dx.doi.org/10.1063/1.3672168 (3 pages) | Cited 7 times

Online Publication Date: 27 December 2011

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The fundamental limits for the measurement of the efficiency of single nanowire solar cell devices are presented. We evaluate the effect of the substrate, light polarization, and existence of Mie resonances in the absorption of the solar spectrum for nanowires with diameters from 10 to 300 nm. We find that the efficiency measured under such configuration can be underestimated between a factor 1.6 and 7.0 for GaAs nanowires and between 6.7 and 15.9 for silicon nanowires. These results constitute a reference for understanding the limits in the measurement of single nanowire devices.
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88.40.jj Silicon solar cells

Evolution of sheet resistance of thin Ni film deposited on porous anodic alumina substrate

Aree Song, Chul Sung Kim, and Taejoon Kouh

Appl. Phys. Lett. 99, 263103 (2011); http://dx.doi.org/10.1063/1.3672211 (4 pages) | Cited 1 time

Online Publication Date: 28 December 2011

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We have investigated the evolution of sheet resistance of thin nickel films, thermally evaporated on porous alumina substrates, based on in situ electron transport measurement. By comparing the porous films, having various surface area fractions, to the uniform film, following the scaling law in metal-insulator transition, we have been able to describe the growth and the resulting thickness-dependent sheet resistance of the porous film in light of the two-dimensional percolation model. The underlying pore array strongly affects the appearance of the film conductance, and the study suggests the possibility of modulating the electron transport characteristics with the constrained surface geometry.
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73.61.At Metal and metallic alloys
68.55.A- Nucleation and growth
81.15.Dj E-beam and hot filament evaporation deposition

Dependence of carbon nanotube field effect transistors performance on doping level of channel at different diameters: On/off current ratio

Shaahin G. Shirazi and Sattar Mirzakuchaki

Appl. Phys. Lett. 99, 263104 (2011); http://dx.doi.org/10.1063/1.3672220 (3 pages)

Online Publication Date: 28 December 2011

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Choosing a suitable doping level of channel relevant to channel diameter is considered for determining the carbon nanotube field effect transistors’ performance which seem to be the best substitute of current transistor technology. For low diameter values of channel, the ratio of on/off current declines by increasing the doping level. But for higher diameter values, there is an optimum point of doping level in obtaining the highest on/off current ratio. For further verification, the variations of performance are justified by electron distribution function’s changes on energy band diagram of these devices. The results are compared at two different gate fields.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology

Room-temperature quantum-dot-like luminescence from site-controlled InGaN quantum disks

L. K. Lee, Lei Zhang, Hui Deng, and P.-C. Ku

Appl. Phys. Lett. 99, 263105 (2011); http://dx.doi.org/10.1063/1.3672441 (4 pages)

Online Publication Date: 28 December 2011

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We studied the optical properties of site-controlled InGaN quantum disks fabricated by the top-down approach. Room-temperature quantum-dot-like photoluminescence was observed from a single InGaN quantum disk. Size-dependent emission wavelength shift was measured and attributed to the quantum confinement in the disk plane. Theoretical modeling was carried out to explain the large blue shift due to size quantization. Temperature dependent luminescence was characterized and showed an abnormally large linewidth at low temperature and a linewidth saturation above 100 K. A sidewall charge center model was proposed to explain these phenomena.
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78.67.Hc Quantum dots
78.20.N- Thermo-optic effects
78.55.Cr III-V semiconductors

Simultaneous step meandering and bunching instabilities controlled by Ehrlich-Schwoebel barrier and elastic interaction

Yan-Mei Yu, Axel Voigt, Xiaoshu Guo, and Yong Liu

Appl. Phys. Lett. 99, 263106 (2011); http://dx.doi.org/10.1063/1.3666781 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2011

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Through phase-field simulations, we investigate simultaneous step meandering and bunching instabilities with the presence of Ehrlich-Schwoebel barrier and elastic interaction. The meandering instability induced by the Ehrlich-Schwoebel barrier is found to be dependent on the elastic interaction at low adatom deposition rate. The ordered step meandering-bunching structure is designed by using the predefined magnitude distribution of the force monopoles on vicinal surfaces based on interplay between the Ehrlich-Schwoebel barrier and the elastic interaction.
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68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
81.40.Jj Elasticity and anelasticity, stress-strain relations

Electrical noise characteristics of a doped silicon microcantilever heater-thermometer

Elise A. Corbin and William P. King

Appl. Phys. Lett. 99, 263107 (2011); http://dx.doi.org/10.1063/1.3673279 (3 pages)

Online Publication Date: 29 December 2011

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We measure the electrical noise characteristics of doped silicon microcantilevers during cantilever self-heating over the temperature range 296–781 K. The dominant noise source is 1/f below about 10 kHz, while at higher frequency, the dominant noise source is Johnson noise. The 1/f noise matches the Hooge model. The noise floor is about 10 nV/Hz1/2 and depends upon temperature, matching the theoretical Johnson noise. The Johnson noise-limited temperature resolution is about 1 μK/Hz1/2.
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07.10.Cm Micromechanical devices and systems
05.40.Ca Noise
07.20.Dt Thermometers

Size effect on magnetic coupling in all-ferromagnetic superlattices

P. Padhan and W. Prellier

Appl. Phys. Lett. 99, 263108 (2011); http://dx.doi.org/10.1063/1.3673295 (4 pages)

Online Publication Date: 29 December 2011

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The switching of ferromagnetic-to-antiferromagnetic coupling of magnetization in the superlattices consisting of two ferromagnetic metals La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) grown on (001) oriented SrTiO3 has been observed by changing the orientation of the field from out–of–plane to in–plane direction. Such switching of magnetic coupling strongly depends on the stacking order of La0.7Sr0.3MnO3 and SrRuO3 layers in the superlattice of 20 unit cell (u.c.)/n (= 3 or 5) u.c. thickness configuration. This is explained by the structural distortion in the MnO6 and RuO6 octahedra along the out-of-plane direction due to the observed stress.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
61.66.Fn Inorganic compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Balanced ternary addition using a gated silicon nanowire

J. A. Mol, J. van der Heijden, J. Verduijn, M. Klein, F. Remacle, and S. Rogge

Appl. Phys. Lett. 99, 263109 (2011); http://dx.doi.org/10.1063/1.3669536 (3 pages)

Online Publication Date: 29 December 2011

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Ternary logic has the lowest cost of complexity, here, we demonstrate a CMOS hardware implementation of a ternary adder using a silicon metal-on-insulator single electron transistor. Gate dependent rectifying behavior of a single electron transistor (SET) results in a robust three-valued output as a function of the potential of the single electron transistor island. Mapping logical, ternary inputs to the three gates controlling the potential of the single electron transistor island allows us to perform complex, inherently ternary operations, on a single transistor.
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84.30.Sk Pulse and digital circuits
85.35.Gv Single electron devices

Direct imaging of the spatial diffusion of excitons in single semiconductor nanowires

M. A. Fickenscher, H. E. Jackson, L. M. Smith, J. M. Yarrison-Rice, J. H. Kang, S. Paiman, Q. Gao, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 99, 263110 (2011); http://dx.doi.org/10.1063/1.3671367 (4 pages) | Cited 5 times

Online Publication Date: 29 December 2011

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We use spatially and temporally resolved photoluminescence to measure exciton diffusion in single zinc blende GaAs/AlGaAs core/shell and mixed phase InP nanowires. Excitons in the single phase GaAs/AlGaAs nanowires are seen to diffuse rapidly throughout the nanowire with a measured diffusion constant ranging from 45 to 100 cm2/s, while in the mixed phase, InP nanowire electrons and holes are seen to rapidly localize to the quantum confined states in the zinc blende and wurtzite segments, respectively. The diffusion constant in the GaAs/AlGaAs nanowire is similar to the best hole mobilities observed in modulation doped heterostructures.
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73.21.Hb Quantum wires
73.63.Nm Quantum wires
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
71.35.-y Excitons and related phenomena
72.20.Fr Low-field transport and mobility; piezoresistance

Suppressed blinking behavior of thioglycolic acid capped CdTe quantum dot by amine functionalization

Abhijit Mandal and Naoto Tamai

Appl. Phys. Lett. 99, 263111 (2011); http://dx.doi.org/10.1063/1.3671075 (4 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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Prepared water soluble thioglycolic acid capped CdTe quantum dots (QDs) were further surface functionalized by ethylene diamine (EDA). Amine functionalized CdTe QDs demonstrate enhanced luminescence intensity at ensemble measurements and suppressed luminescence intermittency behavior at the single molecule level. A clear decrease in the power law exponent for “on” time behavior is observed in amine modified CdTe QDs. Our results show that surface of CdTe QDs modified by EDA can lead to an important physical mechanism to enhance fluorescence intensity, reduce blinking, and increase photostability.
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78.67.Hc Quantum dots
73.63.Kv Quantum dots
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors

Controlling the conformations and transport of DNA by free energy landscaping

Elijah Shelton, Zhijun Jiang, Shutong Wang, and Derek Stein

Appl. Phys. Lett. 99, 263112 (2011); http://dx.doi.org/10.1063/1.3673277 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2011

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We demonstrate free energy landscaping, a method for controlling the transport and conformations of DNA in nanofluidic devices with a nanotopography. A device that funnels molecules into traps where they adopt the shapes of letters illustrates the principle. We analyze how the nanotopography establishes regions of lower free energy and how entropic forces compete with advection, Brownian motion, and, importantly, excluded volume interactions; a rise in the density of DNA can be induced to facilitate its escape from a trap at a controlled location. An ability to guide DNA into solvent-permeable traps makes free energy landscaping applicable to genetic analyses.
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87.14.gk DNA
87.80.St Genomic techniques
05.40.Jc Brownian motion
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