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8 Dec 2008

Volume 93, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 93, 231101 (2008); http://dx.doi.org/10.1063/1.3040686 (3 pages)

Mads Brøkner Christiansen, Anders Kristensen, Sanshui Xiao, and Niels Asger Mortensen
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Energy gap modulation in V2O5 nanowires by gas adsorption

Byung Hoon Kim, Ansoon Kim, Soon-Young Oh, Sung-Soo Bae, Yong Ju Yun, and Han Young Yu

Appl. Phys. Lett. 93, 233101 (2008); http://dx.doi.org/10.1063/1.3044403 (3 pages) | Cited 5 times

Online Publication Date: 8 December 2008

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The current-voltage characteristics at various pressures (2–10 atm) and the scanning tunneling microscopy of vanadium pentoxide nanowires (VONs) with the inert gases (He, Ne, and Ar) and diatomic molecules (H2, N2, O2) have been investigated. The gas dependent conductance (G) is consistent with the inverse energy gap obtained from the scanning tunneling spectroscopy study for the gas-adsorbed single VON. The three possible interactions for gas adsorption of the VON have been discussed. Among them, we have found that the induced dipole-dipole interaction between adsorbed gases plays an important role in conductance variation in the gas adsorbed VON using the conductance per molecule (G/N).
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.47.-b Solid-gas/vacuum interfaces: types of surfaces
73.63.Nm Quantum wires
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
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Selective switch made from a graded nanosandwich chain

S. M. Wang, T. Li, H. Liu, F. M. Wang, S. N. Zhu, and X. Zhang

Appl. Phys. Lett. 93, 233102 (2008); http://dx.doi.org/10.1063/1.3023064 (3 pages) | Cited 7 times

Online Publication Date: 8 December 2008

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The magnetic plasmon (MP) modes in a metallic nanosandwich chain with a linearly increasing spacing along the chain has been investigated. Because of the graded coupling between nanosandwiches, the MP gradon with special field localization and large field amplitude can be found in the chain as well as the extended mode, which differs from the case of periodic chain. Using this property, we can precisely control the field in the chain and guide it to different ports at different frequencies, which works as a selective switch and may have potential application in integrated optics. Finally, we give out the underlying physical mechanism to help better understand and apply this graded chain.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
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Electrically driven single InGaN/GaN quantum dot emission

Anas F. Jarjour, Robert A. Taylor, Rachel A. Oliver, Menno J. Kappers, Colin J. Humphreys, and Abbes Tahraoui

Appl. Phys. Lett. 93, 233103 (2008); http://dx.doi.org/10.1063/1.3044395 (3 pages) | Cited 8 times

Online Publication Date: 9 December 2008

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Electroluminescence from single nitride-based quantum dots is reported. Clear single quantum dot emission is observed, which persists up to ∼ 85 K. This is achieved through the study of a quantum dot layer in the intrinsic region of a forward-biased vertical p-i-n diode. The current-voltage characteristic of the devices is examined at 4.3 K and observed to exhibit electrical bistability phenomena, which is explained in terms of charge accumulation in the InGaN layer. The dependence of the emission properties on current injection conditions are presented and related to the electrical properties of the device.
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73.63.Kv Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
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Electronic structure of single-walled carbon nanotubes on ultrathin insulating films

Hyung-Joon Shin, Sylvain Clair, Yousoo Kim, and Maki Kawai

Appl. Phys. Lett. 93, 233104 (2008); http://dx.doi.org/10.1063/1.3046114 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2008

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The electronic structures of single-walled carbon nanotubes on Ag(100) and on ultrathin insulating NaCl(100)/Ag(100) were studied using low-temperature scanning tunneling microscopy. The Fermi level of the nanotubes was shifted toward the conduction band on Ag(100), while it was shifted toward the valence band on NaCl films. We explain this opposite behavior by different basic mechanisms accounting for the Fermi level shifts. On the metal surface, the work function difference between the tube and the substrate determines the direction of the Fermi level shift. In the case of carbon nanotubes on insulating films, the electric field resulting from the dipole moment formed at the interface between the insulating film and the metal plays a decisive role in determining the Fermi level.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
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Scatterometry for in situ measurement of pattern reflow in nanoimprinted polymers

Heather J. Patrick, Thomas A. Germer, Yifu Ding, Hyun Wook Ro, Lee J. Richter, and Christopher L. Soles

Appl. Phys. Lett. 93, 233105 (2008); http://dx.doi.org/10.1063/1.3046117 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2008

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We use optical scatterometry to extract the time evolution of the profile of nanoimprinted lines in low and high molecular mass polymer gratings during reflow at the glass transition temperature. The data are obtained continuously during the anneal using a spectroscopic ellipsometer and analyzed using a rigorous-coupled-wave model. We show excellent agreement of scatterometry results with ex situ measurements of line height by atomic force microscopy and specular x-ray reflectivity. The in situ scatterometry results reveal differences in the shape evolution of the grating lines indiscernible by other methods.
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81.70.Fy Nondestructive testing: optical methods
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
61.41.+e Polymers, elastomers, and plastics
42.79.Dj Gratings
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Retrieving effective parameters for quasiplanar chiral metamaterials

Christoph Menzel, Carsten Rockstuhl, Thomas Paul, and Falk Lederer

Appl. Phys. Lett. 93, 233106 (2008); http://dx.doi.org/10.1063/1.3046127 (3 pages) | Cited 15 times

Online Publication Date: 9 December 2008

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We introduce and compare two approaches for retrieving quantitatively the effective chirality of metamaterials at normal incidence. The retrieval employs either the reflected and transmitted amplitude of a plane wave illuminating a finite three-dimensional (3D) metamaterial or the dispersion relation of the pertinent Bloch modes in an infinite metamaterial. Both approaches are applied to characterize a 3D metamaterial consisting of a stack of metallic gammadions separated by dielectric films. It will be shown that the results coincide if transitional effects between the metamaterial and the environment can be neglected.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Wc Optical coatings
78.20.Ek Optical activity
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Growth behaviors of ultrathin ZnSe nanowires by Au-catalyzed molecular-beam epitaxy

Y. Cai, T. L. Wong, S. K. Chan, I. K. Sou, D. S. Su, and N. Wang

Appl. Phys. Lett. 93, 233107 (2008); http://dx.doi.org/10.1063/1.3037024 (3 pages) | Cited 4 times

Online Publication Date: 9 December 2008

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Ultrathin ZnSe nanowires grown by Au-catalyzed molecular-beam epitaxy show an interesting growth behavior of diameter dependence of growth rates. The smaller the nanowire diameter, the faster is its growth rate. This growth behavior is totally different from that of the nanowires with diameters greater than 60 nm and cannot be interpreted by the classical theories of the vapor-liquid-solid mechanism. For the Au-catalyzed nanowire growth at low temperatures, we found that the surface and interface incorporation and diffusion of the source atoms at the nanowire tips controlled the growth of ultrathin ZnSe nanowires.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.Pa Diffusion in nanoscale solids
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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Spin precession induced by an effective magnetic field in a two-dimensional electron gas

Genhua Liu, Yonghai Chen, Caihong Jia, and Zhanguo Wang

Appl. Phys. Lett. 93, 233108 (2008); http://dx.doi.org/10.1063/1.3042095 (3 pages)

Online Publication Date: 9 December 2008

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We theoretically study the spatial behaviors of the spin precession in a two-dimensional electron system with spin-orbit interaction. Through analysis of interaction between the spin and the effective magnetic field in the system, we obtain the general conditions to generate a persistent spin helix and predict a persistent spin helix pattern in [001]-grown quantum wells. Particularly, we demonstrate that the phase of spin can be locked to propagate in a quantum well with SU(2) symmetry.
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72.25.-b Spin polarized transport
73.63.Hs Quantum wells
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
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Ferroelectric devices created by pressure modulated stencil deposition

Paul M. te Riele, Guus Rijnders, and Dave H. A. Blank

Appl. Phys. Lett. 93, 233109 (2008); http://dx.doi.org/10.1063/1.3030991 (3 pages) | Cited 4 times

Online Publication Date: 10 December 2008

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Ferroelectric Pb(ZrxTi1−x)O3 sandwiched between SrRuO3 electrodes devices were fabricated by a single stencil deposition method. By varying the pressure, the dimension of the deposited pattern could be controlled. The dimension becomes larger in the high pressure shockwave regime, which is typical for pulsed laser deposition. The particle interactions result in an increased amount of broadening. At lower pressures, the deposited material is still in the correct crystalline phase and broadening is minimized. Top electrodes are isolated from the bottom electrode by controlling the broadening of the ferroelectric medium. With this method, multilayered oxide devices can be created in situ.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.15.Fg Pulsed laser ablation deposition
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An in situ electrical study on primary hydrogen spillover from nanocatalysts to amorphous carbon support

Chikai Lin, Zhenzhen Yang, Tao Xu, and Yufeng Zhao

Appl. Phys. Lett. 93, 233110 (2008); http://dx.doi.org/10.1063/1.3046120 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2008

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Primary hydrogen spillover has been studied using a unique electrical method. We observed that at ambient temperature, when a discontinuous nanogranular Pd film is on the top of an amorphous carbon film, the electrical conductance of the carbon film decreases in pressurized hydrogen. In comparison, in the absence of this Pd layer, the conductance of the carbon film remains unchanged in pressurized hydrogen. The observed decrease in the current in the Pd/carbon structure is ascribed to the hydrogenation of the dangling carbon bonds and sp2-sp3 transition in the amorphous carbon by the primary spillover hydrogen atoms from Pd nanoclusters.
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73.61.-r Electrical properties of specific thin films
72.20.Fr Low-field transport and mobility; piezoresistance
61.43.Er Other amorphous solids
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.55.-a Thin film structure and morphology
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
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Conformable coating of SiO2 on hydrothermally grown ZnO nanorods

B. H. Chu, L. C. Leu, C. Y. Chang, F. Lugo, D. Norton, T. Lele, B. Keselowsky, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 93, 233111 (2008); http://dx.doi.org/10.1063/1.3033407 (3 pages) | Cited 3 times

Online Publication Date: 10 December 2008

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Coating silicon dioxide on hydrothermally grown ZnO nanorods is demonstrated using a low temperature plasma enhanced chemical vapor deposition (PECVD) system. Wurtzite structured ZnO nanorods were prepared by spin coating ZnO nanocrystals onto plastics or glass substrates. Then, the nanorods were subsequently grown in a zinc nitrate solution. SiO2 was deposited by PECVD at 50 °C. No current could be measured through the patterned metal dots on the SiO2 coated sample, which indicates that SiO2 was covered seamlessly across the entire substrate. Photoluminescence measurements indicated that the SiO2 layer covering the nanorods did not alter the optical properties of the ZnO.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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Directing the transportation of a water droplet on a patterned superhydrophobic surface

Qian Feng Xu, Jian Nong Wang, Ian H. Smith, and Kevin D. Sanderson

Appl. Phys. Lett. 93, 233112 (2008); http://dx.doi.org/10.1063/1.3039874 (3 pages) | Cited 12 times

Online Publication Date: 10 December 2008

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Directional transportation of a ball-like water droplet on a superhydrophobic (SH) surface has been experimentally demonstrated. A SH surface with a water contact angle of as high as 160° and a sliding angle close to 0° is prepared by a sol-gel method based on removable polymeric nanospheres. A designed path line is then created on the prepared SH surface. The contact angle possesses anisotropy on the patterned SH surface. When the tilted angle of the patterned SH surface and the volume of the water droplet are proper, the sliding of a ball-like water droplet follows the designed line precisely.
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68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
68.47.Mn Polymer surfaces
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Crystalline silicon carbide nanocones and heterostructures induced by released iron nanoparticles

Zhenyu Liu, Lijie Ci, V. Srot, N. Y. Jin-Phillipp, Peter A. van Aken, M. Rühle, and Judith C. Yang

Appl. Phys. Lett. 93, 233113 (2008); http://dx.doi.org/10.1063/1.3043580 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2008

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We present the formations of crystalline silicon carbide (SiC) nanocones and heterostructures catalyzed by iron nanoparticles, originally encapsulated in graphite-like carbon shells, via the vapor-liquid-solid process. We propose that the nanocone shape is due to the release of iron nanoparticles from their carbon shells followed by agglomeration, where the increasing size of the iron nanoparticle during SiC growth creates the nanocone shape. The release and agglomeration model may explain the formation of multisegmented SiC nanostructures. The encapsulation and controlled release of the metal catalyst is a promising method for the synthesis of unusual one-dimensional nanostructures and complex heterostructures.
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81.16.-c Methods of micro- and nanofabrication and processing
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Absence of elastic clamping in quantitative piezoelectric force microscopy measurements of nanostructures

David A. Scrymgeour and Julia W. P. Hsu

Appl. Phys. Lett. 93, 233114 (2008); http://dx.doi.org/10.1063/1.3040055 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2008

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We establish that clamping effects, which limit accurate determination of piezoelectric responses in bulk materials and films using piezoelectric force microscopy (PFM), are not present when measuring discrete nanostructures with radii less than five times the tip radius. This conclusion is established by comparing the piezoelectric response in ZnO rods using two electrode configurations: one with the conducting atomic force microscopy tip acting as the top electrode and the other using a uniform metal top electrode. The distributions of piezoelectric coefficients measured with these two types of electrode configurations are the same. Hence, clamping issues do not play a role in the piezoelectric property measurement of nanomaterials using PFM. The role of conduction electrons on the piezoelectric measurement in both cases is also discussed.
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77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
82.45.Fk Electrodes
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The enhancement of ZnO nanowalls photoconductivity induced by CdS nanoparticle modification

F. Fang, D. X. Zhao, B. H. Li, Z. Z. Zhang, J. Y. Zhang, and D. Z. Shen

Appl. Phys. Lett. 93, 233115 (2008); http://dx.doi.org/10.1063/1.3045952 (3 pages) | Cited 17 times

Online Publication Date: 11 December 2008

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10 nm sized hexagonal CdS nanoparticles were decorated on the surface of well-aligned ZnO nanowall through a facile hydrothermal approach. The effects of CdS-cap layer on the optical and photoelectrical properties of ZnO nanowalls have been studied. It was found the CdS acted not only as a passivation layer to suppress the detrimental surface states of ZnO nanowalls, which reduced the deep-level emissions, but also as an interfacial carrier transport layer to reduce the probability of carrier recombination. Due to this effect a significant enhancement in ultraviolet photoconductivity of ZnO nanowalls was observed by the surface modification with CdS nanoparticles.
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72.40.+w Photoconduction and photovoltaic effects
81.65.Rv Passivation
73.20.-r Electron states at surfaces and interfaces
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Surface optical Raman modes in InN nanostructures

Satyaprakash Sahoo, M. S. Hu, C. W. Hsu, C. T. Wu, K. H. Chen, L. C. Chen, A. K. Arora, and S. Dhara

Appl. Phys. Lett. 93, 233116 (2008); http://dx.doi.org/10.1063/1.3040681 (3 pages) | Cited 12 times

Online Publication Date: 11 December 2008

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Raman spectroscopic investigations are carried out on one-dimensional nanostructures of InN, such as nanowires and nanobelts synthesized by chemical vapor deposition. In addition to the optical phonons allowed by symmetry A1, E1, and E2 (high) modes, two additional Raman peaks are observed around 528 and 560 cm−1 for these nanostructures. Calculations for the frequencies of surface optical (SO) phonon modes in InN nanostructures yield values close to those of the new Raman modes. A possible reason for large intensities for SO modes in these nanostructures is also discussed.
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78.30.-j Infrared and Raman spectra
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
63.22.Gh Nanotubes and nanowires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Chemical patterning of Ag(111): Spatially confined oxide formation induced by electron beam irradiation

S. Günther, R. Reichelt, J. Wintterlin, A. Barinov, T. O. Menteş, M. Á. Niño, and A. Locatelli

Appl. Phys. Lett. 93, 233117 (2008); http://dx.doi.org/10.1063/1.3040685 (3 pages) | Cited 3 times

Online Publication Date: 11 December 2008

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Low energy electron irradiation of a Ag(111) surface during NO2 adsorption at 300 K induces formation of Ag oxide. Using a spatially confined electron beam, small Ag2O spots could be grown with a sharp, ∼ 100 nm wide, boundary to the nonirradiated metallic surface. Since the structure size will mainly depend on the sharpness of the irradiating electron beam, this process has the potential of a single step nanostructuring process. Temperature treatment offers an easy way to manipulate the boundary between oxide and metallic silver by steering a chemical front.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.Mn Adsorption kinetics
81.65.Mq Oxidation
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys
81.16.Rf Micro- and nanoscale pattern formation
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Ag-modified silicon nanowires substrate for ultrasensitive surface-enhanced raman spectroscopy

Ming-Wang Shao, Ming-Liang Zhang, Ning-Bew Wong, Dorothy Duo-duo Ma, Hui Wang, Weiwei Chen, and Shuit-Tong Lee

Appl. Phys. Lett. 93, 233118 (2008); http://dx.doi.org/10.1063/1.2969292 (3 pages) | Cited 23 times

Online Publication Date: 11 December 2008

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We report a unique substrate for surface-enhanced raman spectroscopy (SERS) based on silver nanoparticles-embedded silicon nanowires (SiNWs). The SiNWs were prepared by thermal evaporation of SiO powder via oxide-assisted growth, oxide removed with HF, and then used to reduce silver ions to form a highly decorated Ag-embedded surface. Such modified SiNWs substrates yielded ultrahigh SERS sensitivity, which could detect 25 μl of 1×10−16M Rhodamine 6G, 1×10−16M crystal violet, and 1×10−14M nicotine in methanol solutions. An Ag-modified SiNW strand could also enable SERS detection of 25 μl of 1×10−8 mg/ml calf thymus DNA. The possible mechanisms for the ultrahigh SERS sensitivity were discussed.
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78.30.Am Elemental semiconductors and insulators
87.80.-y Biophysical techniques (research methods)
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ZnO nanowire arrays: Optical scattering and sensitization to solar light

Ramón Tena-Zaera, Jamil Elias, and Claude Lévy-Clément

Appl. Phys. Lett. 93, 233119 (2008); http://dx.doi.org/10.1063/1.3040054 (3 pages) | Cited 35 times

Online Publication Date: 11 December 2008

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Arrays of ZnO nanowires with different lengths (0.5–2 μm) and diameters (100–330 nm) were electrodeposited to study the influence of the nanowire dimensions on light scattering. The nanowire length and diameter were found to be major parameters in modifying the intensity and the wavelength of the scattered radiation, respectively. A significant scattering for the whole visible wavelength range was attained in arrays of ZnO nanowires of ∼ 1.5 μm in length and ∼ 330 nm in diameter. ZnO nanowire arrays were sensitized to solar light with a conformally deposited thin CdSe layer. A clear correlation between light scattering before coating and absorption in the resulting ZnO/CdSe core-shell nanostructures was found. The enhancement in the scattering for wavelengths where CdSe exhibits a relatively low absorption coefficient resulted in an effective absorption, in the 400–725 nm range of the AM1.5 solar spectrum, as high as 88% with a CdSe shell thickness of ∼ 20 nm only.
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78.67.Lt Quantum wires
78.40.Fy Semiconductors
84.60.Jt Photoelectric conversion
68.65.La Quantum wires (patterned in quantum wells)
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Multilevel sensitization of Er3+ in low-temperature-annealed silicon-rich SiO2

Oleksandr Savchyn, Ravi M. Todi, Kevin R. Coffey, and Pieter G. Kik

Appl. Phys. Lett. 93, 233120 (2008); http://dx.doi.org/10.1063/1.3044480 (3 pages) | Cited 11 times

Online Publication Date: 12 December 2008

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The dynamics of Er3+ excitation in low-temperature-annealed Si-rich SiO2 are studied. It is demonstrated that Si-excess-related indirect excitation is fast (transfer time τtr<27 ns) and occurs into higher lying Er3+ levels as well as directly into the first excited state (4I13/2). By monitoring the time-dependent Er3+ emission at 1535 nm, the multilevel nature of the Er3+ sensitization is shown to result in two types of excitation of the 4I13/2 state: a fast excitation process (τtr<27 ns) directly into the 4I13/2 level and a slow excitation process due to fast excitation into Er3+ levels above the 4I13/2 level, followed by internal Er3+ relaxation with a time constant τ32>2.3 μs. The fast and slow excitations of the 4I13/2 level account for an approximately equal fraction of the excitation events: 45%–50% and 50%–55%, respectively.
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71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials
61.72.Cc Kinetics of defect formation and annealing
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Effect of viscosity of base fluid on thermal conductivity of nanofluids

Tsung-Han Tsai, Long-Sheng Kuo, Ping-Hei Chen, and Chin-Ting Yang

Appl. Phys. Lett. 93, 233121 (2008); http://dx.doi.org/10.1063/1.3046732 (3 pages) | Cited 18 times

Online Publication Date: 12 December 2008

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This study aims to investigate the effect of viscosity of the base fluid on the thermal conductivity of nanofluids in which Fe3O4 nanoparticles are suspended in the base fluid composed of diesel oil and polydimethylsiloxane. Viscosity of the base fluid is varied by changing the volumetric fractions between both fluids. The measured thermal conductivity of nanofluids gradually approaches the value predicted by the Maxwell equation by increasing the viscosity. It demonstrates that the viscosity of nanofluids does affect the thermal conductivity of nanofluids, and the Brownian motion of suspended particles could be an important factor that enhances the thermal conductivity of nanofluids.
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66.20.-d Viscosity of liquids; diffusive momentum transport
66.25.+g Thermal conduction in nonmetallic liquids
82.70.Kj Emulsions and suspensions
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