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5 Nov 2007

Volume 91, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 91, 191106 (2007); http://dx.doi.org/10.1063/1.2804016 (3 pages)

A. Pikulin, N. Bityurin, G. Langer, D. Brodoceanu, and D. Bäuerle
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Decoherence of nuclear spins due to dipole-dipole interactions probed by resistively detected nuclear magnetic resonance

T. Ota, G. Yusa, N. Kumada, S. Miyashita, T. Fujisawa, and Y. Hirayama

Appl. Phys. Lett. 91, 193101 (2007); http://dx.doi.org/10.1063/1.2804011 (3 pages) | Cited 6 times

Online Publication Date: 5 November 2007

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We study decoherence of nuclear spins in a GaAs quantum well structure using resistively detected nuclear magnetic resonance. The transverse decoherence time T2 of 75As nuclei is estimated from Rabi-type coherent oscillations as well as by using spin-echo techniques. By analyzing T2 obtained by decoupling techniques, we extract the role of dipole-dipole interactions as sources of decoherence in GaAs. Under the condition that the device is tilted in an external magnetic field, we exhibit enhanced decoherence induced by the change in strength of the direct dipole-dipole interactions between first nearest-neighbor nuclei. The results agree well with simple numerical calculations.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
76.60.Lz Spin echoes
81.07.St Quantum wells

In situ growth rate control of carbon nanotubes by optical imaging method

Itaru Gunjishima, Takashi Inoue, and Atsuto Okamoto

Appl. Phys. Lett. 91, 193102 (2007); http://dx.doi.org/10.1063/1.2809369 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2007

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Feedback control of the growth rate of carbon nanotubes (CNTs) was performed. By measuring the CNTs thickness using an optical microscope and an image processor, and instantaneous calculation of growth rate, continuous data of CNT thickness/growth rate versus growth time curves were obtained. The growth rate for the constant growth condition degraded as time progressed. In contrast, growth rate degradation was suppressed by optimizing the growth conditions by changing the growth parameters such as growth temperature, pressure, and gas flow rate. As a result, a larger thickness was obtained under the varied growth condition in the measurement time range.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.Fg Nanotubes
81.07.De Nanotubes

Nonvolatile Si/SiO2/SiN/SiO2/Si type polycrystalline silicon thin-film-transistor memory with nanowire channels for improvement of erasing characteristics

Shih-Ching Chen, Ting-Chang Chang, Po-Tsun Liu, Yung-Chun Wu, Jing-Yi Chin, Ping-Hung Yeh, Li-Wei Feng, S. M. Sze, Chun-Yen Chang, and Chen-Hsin Lien

Appl. Phys. Lett. 91, 193103 (2007); http://dx.doi.org/10.1063/1.2798600 (3 pages) | Cited 2 times

Online Publication Date: 5 November 2007

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A silicon-oxide-nitride-oxide-silicon type polycrystalline silicon thin-film transistor (poly-Si TFT) with nanowire channels was investigated for both transistor and memory applications. The poly-Si TFT memory device has superior electrical characteristics, such as higher drain current, smaller threshold voltage, and steeper subthreshold slope. Also, the simulation result on electrical field reveals that the electrical field across the tunnel oxide is enhanced and that across the blocking oxide is reduced at the corner regions. This will lead to the parasitic gate injection activity and the erasing speed can be apparently improved in the memory device due to the pronounced corner effect and narrow channel width.
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85.30.Tv Field effect devices
84.30.Sk Pulse and digital circuits

Patterning of an amine-terminated nanolayer by extreme ultraviolet

Sangwoon Moon, Sukmin Chung, Cheolho Jeon, Chong-Yun Park, Han-Na Hwang, Chan-Cuk Hwang, Hajin Song, and Hyun-Joon Shin

Appl. Phys. Lett. 91, 193104 (2007); http://dx.doi.org/10.1063/1.2803216 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2007

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The adsorption of NH3 molecules on the Si(100)2×1 surface constructs a cleaner and more well-defined amine layer than self-assembled monolayer such as aminosilylated layer, which make it possible to study photoinduced reactions between amines and monochromatic light with shorter wavelength than ultraviolet, i.e., extreme ultraviolet and soft x ray. We report that the molecular layer of amine groups reacts with extreme ultraviolet and soft x ray, which can be used to make fine patterns on the amine-terminated layer. The amine patterning with the leading postoptical lithography using extreme ultraviolet could be applied to fabricating future molecular nanodevices.
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81.16.Rf Micro- and nanoscale pattern formation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Mn Adsorption kinetics
81.16.Nd Micro- and nanolithography
82.50.Kx Processes caused by X-rays or γ-rays

Stimulated emission of CdS nanowires grown by thermal evaporation

Hui Pan, Guichuan Xing, Zhenhua Ni, Wei Ji, Yuan Ping Feng, Zhe Tang, Daniel H. C. Chua, Jianyi Lin, and Zexiang Shen

Appl. Phys. Lett. 91, 193105 (2007); http://dx.doi.org/10.1063/1.2807840 (3 pages) | Cited 12 times

Online Publication Date: 7 November 2007

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High-quality CdS nanowires with wurtzite structure were produced by thermal evaporation of CdS powder. The nanowires were core-shell structures, consisting of crystalline core and amorphous/polycrystal shell. The intensity of the second-order longitudinal phonon mode in the Raman spectrum of the CdS nanowires is higher than that of the first-order mode due to exciton-phonon coupling. The photoluminescence of the CdS nanowires is power dependent, and the photoluminescence peak at 516.5 nm becomes narrower with increase in excitation power, indicating the stimulated emission characteristics of CdS nanowires. The population inversion generated by two-photon absorption is mainly attributed to the occurrence of stimulated emission.
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81.16.-c Methods of micro- and nanofabrication and processing
68.65.La Quantum wires (patterned in quantum wells)
78.67.Lt Quantum wires
78.45.+h Stimulated emission
78.30.Fs III-V and II-VI semiconductors

Fabrication of L10-PdCoFe nanocrystalline particles with tilted magnetic easy axis

András Kovács and Yoshihiko Hirotsu

Appl. Phys. Lett. 91, 193106 (2007); http://dx.doi.org/10.1063/1.2806225 (3 pages) | Cited 2 times

Online Publication Date: 7 November 2007

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Tilted magnetic easy axis L10-PdCoFe nanoparticles were fabricated by sequential evaporation and postdeposition annealing. The MgO(110) substrate was used to prepare the faceted Pd seed crystals with {100} surfaces tilted by 45° from the surface normal. A bcc–Co–Fe layer formed on the seed Pd crystals. The L10-FeCoPd nanoparticles were formed immediately after the start of interdiffusion of Pd and Co, Fe atoms. Their tetragonal c axes were mutually tilted by 45°. The shape of the Pd seed nanocrystals and the top-down interdiffusion are the main factors influencing tilted easy axis L10 particle formation. Magnetic properties of L10-FeCoPd nanoparticles are also discussed.
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81.07.Bc Nanocrystalline materials
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
66.30.Ny Chemical interdiffusion; diffusion barriers

Power dependence of the photocurrent lineshape in a semiconductor quantum dot

A. Russell and Vladimir I. Fal’ko

Appl. Phys. Lett. 91, 193107 (2007); http://dx.doi.org/10.1063/1.2803850 (3 pages)

Online Publication Date: 7 November 2007

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We propose a kinetic theory to describe the power dependence of the photocurrent lineshape in optically pumped quantum dots at low temperatures in both zero and finite magnetic fields. We show that there is a crossover power Pc, determined by the electron and hole tunneling rates, where the photocurrent no longer reflects the exciton lifetime. For P>Pc, we show that the photocurrent saturates due to the slow hole escape rate, whereas the linewidth increases with power. We analyze the spin-doublet lineshape in high magnetic fields and determine to what measure it reflects the degree of circular polarization of incident light.
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72.40.+w Photoconduction and photovoltaic effects
79.60.-i Photoemission and photoelectron spectra
73.21.La Quantum dots
73.63.Kv Quantum dots
73.40.Gk Tunneling

Rational synthesis and tunable optical properties of quasialigned Zn1−xMgxO nanorods

J. G. Lu, Y. Z. Zhang, Z. Z. Ye, Y. J. Zeng, J. Y. Huang, and L. Wang

Appl. Phys. Lett. 91, 193108 (2007); http://dx.doi.org/10.1063/1.2806939 (3 pages) | Cited 8 times

Online Publication Date: 8 November 2007

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Quasialigned, single-crystal Zn1−xMgxO (x = 0–0.32) nanorods were synthesized on Si substrates by thermal evaporation. Zn1−xMgxO nanorods grew along the [0001] crystal direction and had uniform hexagonal planes with diameters of 420–120 nm. The predominant ultraviolet luminescence could be tuned from 379 (x = 0) to 305 nm (x = 0.32) at room temperature. This blueshift indicated the band gap engineering in Zn1−xMgxO nanorods. Temperature-dependent photoluminescence was used to illustrate the free-exciton emission from Zn1−xMgxO nanorods. The exciton binding energy decreased from 59 (x = 0) to 49 meV (x = 0.18) and then increased to 54 meV (x = 0.32).
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73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Nr Semiconductor compounds
71.23.Ft Quasicrystals
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
71.15.Nc Total energy and cohesive energy calculations

Suppression of fatigue crack growth in carbon nanotube composites

W. Zhang, R. C. Picu, and N. Koratkar

Appl. Phys. Lett. 91, 193109 (2007); http://dx.doi.org/10.1063/1.2809457 (3 pages) | Cited 21 times

Online Publication Date: 9 November 2007

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Fatigue is one of the primary causes for catastrophic failure in structural materials. Here, we report an order-of-magnitude reduction in the fatigue crack propagation rate for an epoxy system with the addition of ∼ 0.5 wt. % of carbon nanotube additives. Using fractography analysis and fracture mechanics modeling, we show that the crack suppression is caused by crack bridging, which results in an effective crack-closing stress due to the pull out of nanotube fibers in the wake of the crack tip. Carbon nanotubes therefore show potential to significantly enhance the reliability and operating life of structural polymers that are susceptible to fatigue failure.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Three-dimensional kinetic Monte Carlo simulation of prepatterned quantum-dot island growth

E. Pan, M. Sun, P. W. Chung, and R. Zhu

Appl. Phys. Lett. 91, 193110 (2007); http://dx.doi.org/10.1063/1.2812572 (3 pages) | Cited 7 times

Online Publication Date: 9 November 2007

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A special prepatterning method is proposed for spatially ordered self-organizing quantum dots on anisotropic semiconductor substrates. Using three-dimensional kinetic Monte Carlo simulations, atoms are deposited with varying intermediate interruption times. We demonstrate the effect of interruption time and long-range anisotropic strain energy on island size uniformity and lateral alignment.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Quantum-confined and tunable optical emission from sub-10-nm silicon oxide nanowires in aqueous suspension

Z. Y. Zhang, X. L. Wu, J. C. Shen, L. L. Xu, and Paul K. Chu

Appl. Phys. Lett. 91, 193111 (2007); http://dx.doi.org/10.1063/1.2806228 (3 pages) | Cited 3 times

Online Publication Date: 9 November 2007

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Silicon oxide nanowires (SiONWs) smaller than 10 nm were synthesized by vaporization of SiO2 powders without catalytic assistance. The SiONWs resemble bamboos and the knots comprise Si nanocrystals of different orientations. A SiONW water suspension prepared ultrasonically was subjected to photoluminescence and photoluminescence excitation spectral examinations. Strong blue emission which arises from band-to-band recombination in the quantum confined Si nanocrystals in the knots is observed. Our results show that the emission characteristics can be tuned by adjusting the size of the knots.
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82.70.Kj Emulsions and suspensions
78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
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