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27 Oct 2008

Volume 93, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 93, 172501 (2008); http://dx.doi.org/10.1063/1.3005561 (3 pages)

Yan Wang, X. F. Han, and X.-G. Zhang
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Rapid degradation of CdSe/ZnS colloidal quantum dots exposed to gamma irradiation

Nathan J. Withers, Krishnaprasad Sankar, Brian A. Akins, Tosifa A. Memon, Tingyi Gu, Jiangjiang Gu, Gennady A. Smolyakov, Melisa R. Greenberg, Timothy J. Boyle, and Marek Osiński

Appl. Phys. Lett. 93, 173101 (2008); http://dx.doi.org/10.1063/1.2978073 (3 pages) | Cited 4 times

Online Publication Date: 28 October 2008

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Effects of 137Cs gamma irradiation on photoluminescent properties of CdSe/ZnS colloidal quantum dots are reported. Optical degradation is evaluated by tracking the dependence of photoluminescence intensity on irradiation dose. CdSe/ZnS quantum dots show poor radiation hardness, and severely degrade after less than 20 kR exposure to 662 keV gamma photons.
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61.80.Ed γ-ray effects
82.70.Dd Colloids
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots

Electrical resistivity of individual molecular-assembly nanowires of amphiphilic bis-tetrathiafulvalene macrocycle/2,3,5,6-tetrafluoro- 7,7,8,8-tetracyano-p-quinodimethane charge transfer complex characterized by point-contact current-imaging atomic force microscopy

Ryo Tsunashima, Yuki Noda, Yoko Tatewaki, Shin-ichiro Noro, Tomoyuki Akutagawa, Takayoshi Nakamura, Takuya Matsumoto, and Tomoji Kawai

Appl. Phys. Lett. 93, 173102 (2008); http://dx.doi.org/10.1063/1.3009556 (3 pages) | Cited 2 times

Online Publication Date: 29 October 2008

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Resistivity of individual molecular-assembly nanowires was characterized using the point-contact current-imaging atomic force microscope (PCI-AFM). Current images were simultaneously obtained along with topographic images, from which the mean electrical resistivity of each nanowire was deduced to be approximately 180 Ω cm, which was about two orders of magnitude lower than that measured on bulk Langmuir–Blodgett films (103–105 Ω cm).
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73.63.Nm Quantum wires
81.16.Dn Self-assembly

Phase and photoelectrochemical behavior of solution-processed Fe2O3 nanocrystals for oxidation of water under solar light

Pramod H. Borse, Hwichan Jun, Sun Hee Choi, Suk Joon Hong, and Jae Sung Lee

Appl. Phys. Lett. 93, 173103 (2008); http://dx.doi.org/10.1063/1.3005557 (3 pages) | Cited 15 times

Online Publication Date: 29 October 2008

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Monodispersed iron-oxide nanocrystals of controlled sizes (5–16 nm) were prepared by the thermal decomposition of iron-oleate complex to fabricate photoanode films for photoelectrochemical oxidation of water under simulated solar light. The smallest 5 nm particles were made mostly of γ-Fe2O3, but other sizes showed mixed phases with Fe3O4, whose fraction increased with size. Size-dependent photoanodic currents were also observed, showing maximum photocurrent density for 12 nm particles. The high photocurrents were attributed to the lowered electron-hole recombination rates for the nanocrystals with the sizes comparable to the hole diffusion length.
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82.50.Hp Processes caused by visible and UV light
73.63.Bd Nanocrystalline materials
72.40.+w Photoconduction and photovoltaic effects
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Quantum confinement effect in ZnO thin films grown by pulsed laser deposition

J. C. Nie, J. Y. Yang, Y. Piao, H. Li, Y. Sun, Q. M. Xue, C. M. Xiong, R. F. Dou, and Q. Y. Tu

Appl. Phys. Lett. 93, 173104 (2008); http://dx.doi.org/10.1063/1.3010376 (3 pages) | Cited 18 times

Online Publication Date: 29 October 2008

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High quality crystalline nanostructured ZnO thin films were fabricated by pulsed laser deposition on (0001) sapphire substrates. The films were investigated by x-ray diffraction, scanning electron microscopy, and optical absorption spectroscopy. The exciton peak energy from absorption spectra was used to determine the band gap energy Eg, which was found to increase systematically with the decrease in the mean grain size and ranged from 3.388 to 3.647 eV. This is consistent with the quantum confinement model and, up until now, not observed in a convincing manner in the ZnO thin films.
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81.15.Fg Pulsed laser ablation deposition
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds
68.55.ag Semiconductors

Writing nanotriboelectric charge bits on insulator surface

J. Y. Son and Geunhee Lee

Appl. Phys. Lett. 93, 173105 (2008); http://dx.doi.org/10.1063/1.3010739 (2 pages) | Cited 2 times

Online Publication Date: 29 October 2008

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We demonstrated nanotriboelectric charge bits on the surface of insulating SiO2 thin film, prepared by thermo-oxidation of Si substrate with about 100 nm in thickness, by Kelvin probe force microscope. We wrote and read nanotriboelectric charge bits with the various experimental parameters such as contact force, rubbing speed, and repeat number. We could write the nanotriboelectric charge bits with the minimum line width of about 17 nm.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.25.+i Surface conductivity and carrier phenomena
68.55.aj Insulators
81.65.Mq Oxidation

Revisiting the separation dependent surface enhanced Raman scattering

Y.-J. Liu, Z.-Y. Zhang, Q. Zhao, and Y.-P. Zhao

Appl. Phys. Lett. 93, 173106 (2008); http://dx.doi.org/10.1063/1.3009301 (3 pages) | Cited 13 times

Online Publication Date: 29 October 2008

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Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Er Solid metals and alloys

Enhanced luminescence efficiency due to carrier localization in InGaN/GaN heterostructures grown on nanoporous GaN templates

C. B. Soh, S. Y. Chow, L. Y. Tan, H. Hartono, W. Liu, and S. J. Chua

Appl. Phys. Lett. 93, 173107 (2008); http://dx.doi.org/10.1063/1.3005409 (3 pages) | Cited 6 times

Online Publication Date: 30 October 2008

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Low defect density GaN was achieved through dislocation annihilation by regrowing GaN on strain relaxed nanoporous GaN template formed by UV-enhanced electrochemical etching. The InGaN/GaN single and multiple quantum wells grown on this nanoporous GaN template show enhanced indium incorporation due to strain relaxation. The step edges of regrown GaN on these nanoporous GaN act as effective nucleation sites for impinging indium atoms during growth. Evidence shows fluctuation in the quantum well width caused by indium segregation leading to carrier localization. A higher luminescence efficiency of InGaN/GaN quantum wells is achieved through a combination of excitons localization, higher energy barrier for nonradiative recombination of carriers with dislocations and the reduction in defect density of the materials grown on the nanoporous GaN template.
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78.55.Cr III-V semiconductors
78.55.Mb Porous materials
78.67.De Quantum wells
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
61.72.Lk Linear defects: dislocations, disclinations

Indirect-to-direct band gap transitions in phosphorus adsorbed 〈112〉 silicon nanowires

X. B. Yang and R. Q. Zhang

Appl. Phys. Lett. 93, 173108 (2008); http://dx.doi.org/10.1063/1.3012372 (3 pages) | Cited 12 times

Online Publication Date: 30 October 2008

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Using first-principles calculations, we investigated the modification of the band structures of 〈112〉 silicon nanowires (SiNWs) that were adsorbed with phosphorus atoms. We found that the phosphorus atom adsorption on the (110) and (111) facets causes considerable modifications in the conduction bands. Interestingly, the modifications result in the indirect band gap characteristic enhancement for the adsorption on the (110) facet and induce an indirect-to-direct band gap transition for the adsorption on the (111) facet due to the distribution of the local density of states that are parallel to the (110) facet. The finding has significant implications for SiNWs in optoelectronic applications.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.21.Hb Quantum wires
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Mq Elemental semiconductors
73.20.At Surface states, band structure, electron density of states

Quantum-dot crystal defects

S. Kiravittaya and O. G. Schmidt

Appl. Phys. Lett. 93, 173109 (2008); http://dx.doi.org/10.1063/1.3013461 (3 pages) | Cited 1 time

Online Publication Date: 30 October 2008

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The authors investigate the formation of quantum-dot crystal (QDC) defects during the growth of two-dimensional QDCs on flat surfaces. The flat surface is modulated by the periodic strain fields of a buried quantum-dot (QD) seed layer, which in turn is grown onto a patterned substrate surface. Two types of QDC defects, QD vacancies, and QD interstitials are observed whenever the QD density controlled by the growth conditions does not match the areal density of the patterned sites. Our kinetic Monte Carlo growth simulations take into account the realistic strain profile of buried QDs and are able to describe the occurrence of both types of QDC defects during the growth of seeded QDCs.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.jj Interstitials
61.72.jd Vacancies
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Single live cell refractometer using nanoparticle coated fiber tip

Jung-Yan Lee, Chia-Wei Lee, En-Hong Lin, and Pei-Kuen Wei

Appl. Phys. Lett. 93, 173110 (2008); http://dx.doi.org/10.1063/1.3009205 (3 pages) | Cited 6 times

Online Publication Date: 30 October 2008

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We present a nano-optical probe for real-time refractive index measurement of single live cell. The probe was made of a tapered fiber tip coated with 13 nm diameter gold nanoparticles. The evanescent wave near the tip excited localized surface plasmon resonance of gold nanoparticles. By measuring the optical intensity scattered from the nanoparticles, the probe showed an intensity sensitivity up to ∼ 5400% per refractive index unit. The 3T3 fibroblast cell was tested by inserting the probe into the cytoplasm. Refractive index as measured by the localized plasmonic effect was 1.3506, consistent with the results measured by holographic methods.
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87.85.Rs Nanotechnologies-applications
07.60.Hv Refractometers and reflectometers
42.81.Pa Sensors, gyros
87.16.-b Subcellular structure and processes

Phonon-engineered mobility enhancement in the acoustically mismatched silicon/diamond transistor channels

Denis L. Nika, Evghenii P. Pokatilov, and Alexander A. Balandin

Appl. Phys. Lett. 93, 173111 (2008); http://dx.doi.org/10.1063/1.3007986 (3 pages) | Cited 10 times

Online Publication Date: 31 October 2008

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The authors have shown that the low-field electron drift mobility in the ultrathin silicon films can be enhanced if they are embedded within acoustically hard materials such as diamond. The increase results from phonon spectrum modification in the acoustically mismatched silicon/diamond heterostructure and suppression of the deformation-potential electron-phonon scattering. The room temperature mobility in silicon films with 2 nm thickness can be increased by a factor of 2–3 depending on the hardness and thickness of the barrier layers. The obtained results suggest a new phonon-engineering approach for increasing the speed and drive current of downscaled electronic devices.
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85.30.Tv Field effect devices
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