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6 Jul 2009

Volume 95, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 95, 013107 (2009); http://dx.doi.org/10.1063/1.3167775 (3 pages)

T. Y. Tsai, C. Y. Lee, N. H. Tai, and W. H. Tuan
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Size-dependent thermopower in nanocrystalline nickel

Ajay Soni and Gunadhor S. Okram

Appl. Phys. Lett. 95, 013101 (2009); http://dx.doi.org/10.1063/1.3167302 (3 pages) | Cited 6 times

Online Publication Date: 6 July 2009

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Thermopower (Sn) of compacted nanocrystalline Ni of average particle size D = 38, 32, and 25 nm at low temperatures (5–300 K) is reported here. Sn exhibits striking deviations from bulk thermopower Sbulk behavior revealing evolution of Sn with change in D. As D decreases, there is significant decrease in Sn, gradual disappearance of phonon drag minimum and sign change to positive below 38 K compared to usual negative Sbulk. They have been attributed to electron and phonon scattering at grain boundaries and phonon confinement. Small minima observed near 25 K in thermopower difference ΔS are correlated with superparamagnetic transitions.
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72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.38.-k Polarons and electron-phonon interactions
63.20.kd Phonon-electron interactions
63.22.Kn Clusters and nanocrystals
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
75.50.Tt Fine-particle systems; nanocrystalline materials

Investigating the role of hydrogen in indium oxide tubular nanostructures as a donor or oxygen vacancy passivation center

Mukesh Kumar, R. Chatterjee, S. Milikisiyants, A. Kanjilal, M. Voelskow, D. Grambole, K. V. Lakshmi, and J. P. Singh

Appl. Phys. Lett. 95, 013102 (2009); http://dx.doi.org/10.1063/1.3159786 (3 pages) | Cited 3 times

Online Publication Date: 6 July 2009

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Electron paramagnetic resonance (EPR) spectroscopy of hydrogen-doped indium oxide (IO) tubular nanostructures shows presence of paramagnetic oxygen vacancies (VO) at room temperature. For temperatures below 80 K, the EPR spectra exhibit two distinct split resonances correspond to S = ½ hydrogen electron spin. Interestingly, presence of hydrogen EPR resonances is accompanied by absence of EPR signal of VO, which is restored above 80 K with the concomitant disappearance of signature resonances from hydrogen. The temperature dependent donor and passivation behavior of hydrogen has been directly observed in metal oxide. This could provide valuable explanations of various VO induced controversial properties of IO nanostructures.
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76.30.Mi Color centers and other defects
61.72.jd Vacancies
81.65.Rv Passivation

Spin relaxation in silicon coupled quantum dots

Wei Pan, Xiao Zhu Yu, and Wen Zhong Shen

Appl. Phys. Lett. 95, 013103 (2009); http://dx.doi.org/10.1063/1.3167817 (3 pages) | Cited 3 times

Online Publication Date: 6 July 2009

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We present a detailed investigation for spin relaxation processes in silicon coupled quantum dots. Low-field magnetoconductance measurements have been employed to deduce phase dephasing and spin relaxation rates. On the basis of the dephasing theory containing triplet channel interaction, we have demonstrated that small energy transfer scattering process is the dominant dephasing mechanism, and strong electron-electron interaction results in an interdot spin-exchange relaxation process. Triplet-singlet relaxation is found to be another important spin relaxation process in the inner quantum dots, taking into account the triplet-singlet splitting induced by spin-orbit coupling.
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72.20.My Galvanomagnetic and other magnetotransport effects
68.65.Hb Quantum dots (patterned in quantum wells)
73.63.Kv Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Confined energy states in quantum dots detected by a resonant differential capacitance method

O. Engström, M. Kaniewska, and M. Kaczmarczyk

Appl. Phys. Lett. 95, 013104 (2009); http://dx.doi.org/10.1063/1.3168408 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2009

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A novel method is demonstrated for revealing the presence of confined energy states in quantum dots. The samples used are Schottky diodes with quantum dots inserted in a plane inside its depletion region. By measuring the voltage derivative of the differential diode capacitance and plotting the data as contour diagrams on a voltage versus temperature plane, the confined charge carrier states are visualized as peaks. To confirm this interpretation, experimental data are compared with theory based on statistics earlier used for understanding data from deep level transient spectroscopy on the same type of samples.
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73.63.Kv Quantum dots
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes

Giant birefringence induced by plasmonic nanoslit arrays

Shen-Yu Hsu, Kuang-Li Lee, En-Hong Lin, Ming-Chang Lee, and Pei-Kuen Wei

Appl. Phys. Lett. 95, 013105 (2009); http://dx.doi.org/10.1063/1.3167772 (3 pages) | Cited 10 times

Online Publication Date: 7 July 2009

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Large phase differences between transverse electric (TE) and transverse magnetic (TM) waves were investigated in plasmonic nanoslit arrays. The phase of the TE wave shifts ahead because of its low propagation constant. On the other hand, the phase of the TM wave is retarded due to the propagation of surface plasmons. The opposite phase shift forms a giant birefringence. Its magnitude was dependent on the width of nanoslits. The birefringence magnitude was ∼ 1 for 300-nm-wide nanoslits and up to ∼ 2.7 for 100 nm ones. The spectroscopic measurements indicate that waveplates made of gold nanoslits have large bandwidths.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
78.20.Fm Birefringence

Thermoelectric properties of nanoporous Ge

Joo-Hyoung Lee and Jeffrey C. Grossman

Appl. Phys. Lett. 95, 013106 (2009); http://dx.doi.org/10.1063/1.3159813 (3 pages) | Cited 7 times

Online Publication Date: 7 July 2009

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We computed thermoelectric properties of nanoporous Ge (np-Ge) with aligned pores along the [001] direction through a combined classical molecular dynamics and first-principles electronic structure approach. A significant reduction in the lattice thermal conductivity of np-Ge leads to a 30-fold increase in the thermoelectric figure-of-merit (ZT) compared to that of bulk. Detailed comparisons with the recently proposed np-Si show that although the maximum ZT (ZTmax) of Ge is nine times larger than that of Si in the bulk phase, ZTmax of np-Ge is twice as large as that of np-Si due to the similarity in lattice thermal conductivity of the two np systems. Moreover, ZTmax is found to occur at a carrier concentration two orders of magnitude lower than that for with np-Si due to the dissimilarities in their electronic structure.
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72.20.Pa Thermoelectric and thermomagnetic effects
61.43.Gt Powders, porous materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
72.80.Cw Elemental semiconductors
71.20.Mq Elemental semiconductors
81.05.Cy Elemental semiconductors
66.70.Df Metals, alloys, and semiconductors
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Transfer of patterned vertically aligned carbon nanotubes onto plastic substrates for flexible electronics and field emission devices

T. Y. Tsai, C. Y. Lee, N. H. Tai, and W. H. Tuan

Appl. Phys. Lett. 95, 013107 (2009); http://dx.doi.org/10.1063/1.3167775 (3 pages) | Cited 27 times

Online Publication Date: 7 July 2009

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A direct transfer method for fabricating flexible electronics without the assistance of an adhesive layer and stamp is reported in this paper. This rapid and simple method provides an approach for the application of vertically aligned carbon nanotubes (VA-CNTs) on plastic substrates. After transfer, the VA-CNTs maintained their initial orientation in the designed pattern and showed sufficient adhesion to the substrate under extreme bending conditions. The flexible device performed an emission on the transparent substrate and showed a low turn-on of 1.13 V/μm. This VA-CNT-based flexible device, which exhibits electrical resistance sensitive to bending, is also described herein.
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85.35.Kt Nanotube devices
85.65.+h Molecular electronic devices

Formation and shape control of InAsSb/InP (001) nanostructures

W. Lei, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 95, 013108 (2009); http://dx.doi.org/10.1063/1.3160738 (3 pages) | Cited 8 times

Online Publication Date: 7 July 2009

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This paper presents a study on the formation and shape control of InAsSb/InP nanostructures on InP (001) substrates. For the formation of InAsSb nanostructures, incorporation of Sb atoms into InAs islands results in significant morphology change in the islands due to the surfactant effect of Sb atoms and the large strain in the system. And, shape control of InAsSb/InP nanostructures is achieved by optimizing their growth parameters. Low growth temperature and high growth rate will induce the formation of InAsSb elongated quantum dots, while high growth temperature and low growth rate will promote the formation of InAsSb quantum wires or dashes.
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81.16.-c Methods of micro- and nanofabrication and processing
68.65.Hb Quantum dots (patterned in quantum wells)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
81.07.Bc Nanocrystalline materials

The influence of copper top electrodes on the resistive switching effect in TiO2 thin films studied by conductive atomic force microscopy

Lin Yang, Carsten Kuegeler, Krzysztof Szot, Andreas Ruediger, and Rainer Waser

Appl. Phys. Lett. 95, 013109 (2009); http://dx.doi.org/10.1063/1.3167810 (3 pages) | Cited 16 times

Online Publication Date: 9 July 2009

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Titanium dioxide thin films (30 nm) are deposited on platinized substrates by atomic layer deposition and locally studied by conductive atomic force microscopy showing repetitive bipolar resistive switching. Experiments using macroscopic copper top electrodes, which are electroformed, bipolar switched, and removed again from the TiO2–Pt stack, prove the formation of local conductive filaments with bipolar switching properties. The localized filaments can be switched repetitively with a resistance ratio of 30. Our findings underline that Cu diffusion and the formation of filaments are the major mechanism for the resistive switching in Cu/TiO2/Pt cells.
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72.60.+g Mixed conductivity and conductivity transitions
68.55.at Other materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.37.Ps Atomic force microscopy (AFM)

Experimental determination of the spring constant of an individual multiwalled carbon nanotube cantilever using fluorescence measurement

Soongeun Kwon, Hyojun Park, Hyung Cheoul Shim, Hyung Woo Lee, Yoon Keun Kwak, and Soohyun Kim

Appl. Phys. Lett. 95, 013110 (2009); http://dx.doi.org/10.1063/1.3176403 (3 pages) | Cited 4 times

Online Publication Date: 9 July 2009

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We report an experimental method to determine the spring constant of a multiwalled carbon nanotube (MWNT) cantilever as a mechanical piconewton force transducer. Electrostatic actuation was employed to investigate the mechanical properties of a MWNT cantilever. In order to measure nanotube’s deflection during actuation, fluorescent dyes were noncovalently attached to the end of the nanotubes. Also, the length dependence of the spring constant is studied by adjusting the length of MWNT via electrochemical etching. The results show that the spring constant of a MWNT cantilever is as small as 0.001 N/m and tunable in the range of 0.001–0.05 N/m.
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07.07.Mp Transducers
85.35.Kt Nanotube devices
81.65.Cf Surface cleaning, etching, patterning

Indium-zinc-oxide nanobelts with superlattice structure

B. Alemán, P. Fernández, and J Piqueras

Appl. Phys. Lett. 95, 013111 (2009); http://dx.doi.org/10.1063/1.3176974 (3 pages) | Cited 13 times

Online Publication Date: 9 July 2009

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Indium-zinc-oxide (IZO) nanobelts have been grown by a thermal evaporation-deposition method with ZnO and In2O3 powders as precursors. The nanobelts have a superlattice structure that is explained by the formation of In–O and In/Zn–O layers, which appears to favor the formation of nanorings. X-ray analytical methods indicate that the approximate composition of the compound is Zn4In2O7. Cathodoluminescence of the nanobelts in scanning electron microscope shows a dominant emission at 2.37 eV, which is suggested to be a characteristic band of the IZO structure.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.65.Cd Superlattices
78.60.Hk Cathodoluminescence, ionoluminescence

Temperature dependent electrical resistivity of a single strand of ferromagnetic single crystalline nanowire

M. Venkata Kamalakar, A. K. Raychaudhuri, Xueyong Wei, Jason Teng, and Philip D. Prewett

Appl. Phys. Lett. 95, 013112 (2009); http://dx.doi.org/10.1063/1.3174918 (3 pages) | Cited 2 times

Online Publication Date: 10 July 2009

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We have measured the electrical resistivity of a single strand of a ferromagnetic Ni nanowire of diameter 55 nm using a four-probe method in the temperature range 3–300 K. The wire used is chemically pure and is a high quality oriented single crystalline sample in which the temperature independent residual resistivity is determined predominantly by surface scattering. Precise evaluation of the temperature dependent resistivity (ρ) allowed us to identify quantitatively the electron-phonon contribution (characterized by a Debye temperature θR) as well as the spin-wave contribution, which is significantly suppressed upon size reduction.
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73.63.-b Electronic transport in nanoscale materials and structures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Ds Spin waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.38.-k Polarons and electron-phonon interactions
75.50.Cc Other ferromagnetic metals and alloys

Electronic transport characteristics of electrolyte-gated conducting polyaniline nanowire field-effect transistors

Seung-Yong Lee, Gyoung-Rin Choi, Hyuneui Lim, Kyung-Mi Lee, and Sang-Kwon Lee

Appl. Phys. Lett. 95, 013113 (2009); http://dx.doi.org/10.1063/1.3176444 (3 pages) | Cited 2 times

Online Publication Date: 10 July 2009

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We investigate the electronic transport characteristics of an electrolyte-gated conducting polyaniline (PANI) nanowire field-effect transistor (FET) assembled between two Au electrodes on SiO2/Si substrate using nanochannel-assisted chemical oxidative polymerization. This is the first demonstration that the current-voltage characteristics for a PANI nanowire FET exhibit significant hysteresis, which is typically greater on the positive sweep of the potential than on the negative sweep. We suggest that this hysteresis is due to changes in the PANI structure and the effects of Coulombic repulsion in PANI nanowires on oxidation process. We also present degradation properties of PANI nanowire FETs with electrochemical gate potential.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
81.65.Mq Oxidation

Surface reactions during atomic layer deposition of Pt derived from gas phase infrared spectroscopy

W. M. M. Kessels, H. C. M. Knoops, S. A. F. Dielissen, A. J. M. Mackus, and M. C. M. van de Sanden

Appl. Phys. Lett. 95, 013114 (2009); http://dx.doi.org/10.1063/1.3176946 (3 pages) | Cited 22 times

Online Publication Date: 10 July 2009

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Infrared spectroscopy was used to obtain absolute number information on the reaction products during atomic layer deposition of Pt from (methylcyclopentadienyl)trimethylplatinum [(MeCp)PtMe3] and O2. From the detection of CO2 and H2O it was established that the precursor ligands are oxidatively decomposed during the O2 pulse mainly. Oxygen atoms chemisorbed at the Pt lead to likewise ligand oxidation during the (MeCp)PtMe3 pulse however the detection of a virtually equivalent density of CO2 and CH4 also reveals a concurrent ligand liberation reaction. The surface coverage of chemisorbed oxygen atoms found is consistent with the saturation coverage reported in surface science studies.
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81.65.Mq Oxidation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
78.30.Er Solid metals and alloys

Evolution of photoluminescence properties of Si1−xGex nanocrystals synthesized by laser-induced pyrolysis

L. B. Ma, T. Schmidt, O. Guillois, and F. Huisken

Appl. Phys. Lett. 95, 013115 (2009); http://dx.doi.org/10.1063/1.3176948 (3 pages) | Cited 3 times

Online Publication Date: 10 July 2009

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Silicon nanocrystals (NCs) doped with germanium were synthesized by CO2 laser-induced pyrolysis. Photoluminescence (PL) spectra were measured for a Si0.92Ge0.08 NC sample as a function of time, starting one day after synthesis. The position of the PL peak and the following blueshift during aging are consistent with radiative recombination of quantum-confined excitons. At the same time, the evolution of the excited state lifetime was found to saturate after approximately 10 days. In accordance with theoretical calculations, the terminal radiative decay rate was found to be two times faster than for pure Si NCs at the same emission energy.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.Be Chemical synthesis methods
71.35.-y Excitons and related phenomena
81.07.Bc Nanocrystalline materials
78.55.Ap Elemental semiconductors

Prediction of energetically optimal single-walled carbon nanotubes for hydrogen physisorption

W. J. Fan, R. Q. Zhang, Boon K. Teo, B. Aradi, and Th. Frauenheim

Appl. Phys. Lett. 95, 013116 (2009); http://dx.doi.org/10.1063/1.3158597 (3 pages) | Cited 3 times

Online Publication Date: 10 July 2009

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Hydrogen storage by carbon nanotubes (CNTs) is a challenging issue still in debate. Using an approximate density functional method augmented with a van der Waals dispersion term, we have shown that there are binding maxima for H2/single-walled carbon nanotube (SWCNT) complexes at (5, 5) and (8, 0) tubes for armchair and zigzag CNTs, respectively, with binding energies around three times as large as that of H2 on graphene surface. We predict that SWCNTs with diameters of 6–7 Å are energetically optimal candidates for physisorption of molecular hydrogen.
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84.60.-h Direct energy conversion and storage
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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