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14 Jul 2008

Volume 93, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 023303 (2008); http://dx.doi.org/10.1063/1.2953179 (3 pages)

Takafumi Kawanishi, Takaaki Fujiwara, Megumi Akai-Kasaya, Akira Saito, Masakazu Aono, Junichi Takeya, and Yuji Kuwahara
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Magnetostatic interactions between magnetic nanotubes

J. Escrig, S. Allende, D. Altbir, and M. Bahiana

Appl. Phys. Lett. 93, 023101 (2008); http://dx.doi.org/10.1063/1.2956681 (3 pages) | Cited 16 times

Online Publication Date: 14 July 2008

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The investigation of interactions between magnetic nanotubes is complex and often involves substantial simplifications. In this letter an analytical expression for the magnetostatic interaction, taking into account the geometry of the tubes, has been obtained. This expression allows for the definition of a critical vertical separation for relative magnetization between nanotubes and can be used for tailoring barcode-type nanostructures with prospective applications such as biological separation and transport.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials

High frequency columnar silicon microresonators for mass detection

J. Kehrbusch, E. A. Ilin, M. Hullin, and E. Oesterschulze

Appl. Phys. Lett. 93, 023102 (2008); http://dx.doi.org/10.1063/1.2957653 (3 pages) | Cited 9 times

Online Publication Date: 14 July 2008

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A simple but effective technological scheme for the fabrication of high frequency silicon columnar microresonators is presented. With the proposed technique the dimensions of the microresonators are controlled on a scale of at least 1 μm. Characterization of the mechanical properties of silicon columns gave resonant frequencies of the lowest flexural mode of 3–7 MHz with quality factors of up to 2500 in air and ∼ 8800 under vacuum condition. Columnar microresonators were operated as mass balance with a sensitivity of 1 Hz/fg. A mass detection limit of 25 fg was deduced from experiments.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Dr Mass and density

Synthesis and magnetic properties of Cu doped ZnO nanorods via radio frequency plasma deposition

Z. F. Wu, X. M. Wu, L. J. Zhuge, X. M. Chen, and X. F. Wang

Appl. Phys. Lett. 93, 023103 (2008); http://dx.doi.org/10.1063/1.2957037 (3 pages) | Cited 3 times

Online Publication Date: 14 July 2008

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Well-aligned Cu doped ZnO nanorods were synthesized by simple radio frequency plasma deposition in the absence of extra catalysts. The synthesized nanorods having a typical average diameter of about 60 nm, were about 700 nm in length and well aligned along the normal direction of the substrate. Magnetic measurements indicate that the nanorods are ferromagnetic at room temperature. The presence of considerable oxygen vacancies in the nanorods does allow possible defect mediated mechanisms (e.g., bound magnetic polarons) for mediating exchange coupling of the dopant Cu ions resulting in room temperature ferromagnetism.
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81.07.Bc Nanocrystalline materials
81.15.Jj Ion and electron beam-assisted deposition; ion plating
75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.jd Vacancies

Magnetic-field-modulated terahertz absorption spectra of a quantum ring

Yan Xie, Weidong Chu, and Suqing Duan

Appl. Phys. Lett. 93, 023104 (2008); http://dx.doi.org/10.1063/1.2957039 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2008

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The magnetic-field-modulated terahertz absorption spectra of a real GaAs quantum ring (QR) are studied by calculating the photon-participated tunneling current through the QR. We find that the absorption of photons can lead to a reduction in the tunneling current and this manifests as dips in the current versus magnetic field curves. There exists a saturation value for the depth of the current dip, which is described by a simple formula. A full width at half maximum less than 10 GHz can be reached for current dips induced by terahertz fields for Rabi frequencies smaller than 2.5 GHz. Our study provides a possible way to realize tunable detection of terahertz fields.
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73.63.Kv Quantum dots
73.40.Gk Tunneling
73.21.La Quantum dots
78.67.Hc Quantum dots
78.70.Gq Microwave and radio-frequency interactions

Improved and excellent humidity sensitivities based on KCl-doped TiO2 electrospun nanofibers

Qi Qi, Tong Zhang, and Lijie Wang

Appl. Phys. Lett. 93, 023105 (2008); http://dx.doi.org/10.1063/1.2957477 (3 pages) | Cited 14 times

Online Publication Date: 14 July 2008

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Pure and KCl-doped TiO2 nanofibers have been synthesized by electrospinning and calcination technique. The measurement results by the sensors fabricated from these fibers at the working electrodes show that KCl-doped TiO2 nanofibers hold the improved humidity sensing properties with the resistance varying more than four orders of magnitude in the range of 11%–95% relative humidity, while the resistance of pure TiO2 nanofibers changes only about two orders of magnitude. An ion-controlled model has been established to explain the results further. Additionally, excellent sensing characteristics (rapid response and recovery behavior and good stability) have been also found based on KCl-doped TiO2 nanofibers, which endows our product with the potentials for humidity sensors.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments

Pattern level assembly of Ge quantum dots on Si with focused ion beam templating

M. Gherasimova, R. Hull, M. C. Reuter, and F. M. Ross

Appl. Phys. Lett. 93, 023106 (2008); http://dx.doi.org/10.1063/1.2957676 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2008

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Array level assembly mechanisms are described for controlled nucleation of Ge quantum dots (QDs) on Si(100) surfaces templated by low dose focused ion beam pulses. The registration rates of QD positions with the target sites approach 100% for site separations of 100 nm and above, but incomplete occupancy is observed at closer distances. We investigate the dependence of the QD array perfection on the site separation, and identify the competition between the intended nucleation sites for the supply of Ge adatoms as a key factor limiting the large area registration fidelity.
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81.07.Ta Quantum dots
81.05.Cy Elemental semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.65.Hb Quantum dots (patterned in quantum wells)

Probing quantum confinement of single-walled carbon nanotubes by resonant soft-x-ray emission spectroscopy

Jun Zhong, Jauwern Chiou, Chungli Dong, Li Song, Chang Liu, Sishen Xie, Huiming Cheng, Way-Faung Pong, Chinglin Chang, Yangyuan Chen, Ziyu Wu, and Jinghua Guo

Appl. Phys. Lett. 93, 023107 (2008); http://dx.doi.org/10.1063/1.2959058 (3 pages) | Cited 2 times

Online Publication Date: 15 July 2008

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We report the band-structure changes near Fermi level for single-walled carbon nanotubes (SWNTs) with diameters down to 1 nm from the study of soft-x-ray absorption and resonant emission spectroscopy. The observed quantum confinement of SWNTs affects both π and σ bands and bandgap through the rehybridization of π and σ orbitals. The significant changes of electronic structure are proved to be a measure for the mean diameter of the macroscopic amounts of SWNTs.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.70.En X-ray emission spectra and fluorescence

Carbon nanotube formation by laser direct writing

Yu-Tsung Wu, Huan-Chieh Su, Chung-Min Tsai, Kuo-Liang Liu, Guo-Dung Chen, Ren-Hong Huang, and Tri-Rung Yew

Appl. Phys. Lett. 93, 023108 (2008); http://dx.doi.org/10.1063/1.2959061 (3 pages)

Online Publication Date: 15 July 2008

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This letter presents carbon nanotube (CNT) formation by laser direct writing using 248 nm KrF excimer pulsed laser in air at room temperature, which was applied to irradiate amorphous carbon (a-C) assisted by Ni catalysts underneath for the transformation of carbon species into CNTs. The CNTs were synthesized under appropriate combination of laser energy density and a-C thickness. The growth mechanism and key parameters to determine the success of CNT formation were also discussed. The demonstration of the CNT growth by laser direct writing in air at room temperature opens an opportunity of in-position CNT formation at low temperatures.
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81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.16.Hc Catalytic methods
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Organometallic vapor phase epitaxial growth of GaN on ZrN/AlN/Si substrates

Mark H. Oliver, Jeremy L. Schroeder, David A. Ewoldt, Isaac H. Wildeson, Vijay Rawat, Robert Colby, Patrick R. Cantwell, Eric A. Stach, and Timothy D. Sands

Appl. Phys. Lett. 93, 023109 (2008); http://dx.doi.org/10.1063/1.2953541 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2008

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An intermediate ZrN/AlN layer stack that enables the epitaxial growth of GaN on (111) silicon substrates using conventional organometallic vapor phase epitaxy at substrate temperatures of ∼ 1000 °C is reported. The epitaxial (111) ZrN layer provides an integral back reflector and Ohmic contact to n-type GaN, whereas the (0001) AlN layer serves as a reaction barrier, as a thermally conductive interface layer, and as an electrical isolation layer. Smooth (0001) GaN films less than 1 μm thick grown on ZrN/AlN/Si yield 0002 x-ray rocking curve full width at half maximum values as low as 1230 arc sec.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors

Realization of regular arrays of nanoscale resistive switching blocks in thin films of Nb-doped SrTiO3

Ruth Muenstermann, Regina Dittmann, Krzysztof Szot, Shaobo Mi, Chun-Lin Jia, Paul Meuffels, and Rainer Waser

Appl. Phys. Lett. 93, 023110 (2008); http://dx.doi.org/10.1063/1.2959074 (3 pages) | Cited 22 times

Online Publication Date: 16 July 2008

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We report on the realization of short-range-ordered arrays of nanoscale resistive switching blocks in epitaxial Nb-doped SrTiO3 thin films. These blocks can be individually addressed by the tip of a conductive tip atomic force microscope and reversibly switched between a high and a low resistance state reaching an Roff to Ron ratio of up to 50. Scanning micrometer-scale areas with an appropriately biased tip, all blocks within the scanned area can be switched between the two resistive states. We suggest a connection between these nanoscale switching blocks and defect-rich nanoclusters which were detected with high resolution transmission electron microscopy.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ng Insulators
68.55.aj Insulators

Photovoltaic effect and charge storage in single ZnO nanowires

Zhi-Min Liao, Jun Xu, Jing-Min Zhang, and Da-Peng Yu

Appl. Phys. Lett. 93, 023111 (2008); http://dx.doi.org/10.1063/1.2957470 (3 pages) | Cited 19 times

Online Publication Date: 16 July 2008

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Asymmetric Schottky barriers between ZnO nanowire and metal electrode have been fabricated at the two ends of the nanowire. An obvious photocurrent generated from the device at zero voltage bias can be switched on/off with quick response by controlling the light irradiation. Moreover, the device can still afford a current at zero bias after switching off light illumination, which is ascribed to the charge storage effect in single ZnO nanowires. The underlying mechanisms related to the photovoltaic effect and charge storage were discussed.
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72.40.+w Photoconduction and photovoltaic effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.30.+y Surface double layers, Schottky barriers, and work functions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Ion exchange in glass using femtosecond laser irradiation

Shingo Kanehira, Kiyotaka Miura, and Kazuyuki Hirao

Appl. Phys. Lett. 93, 023112 (2008); http://dx.doi.org/10.1063/1.2959820 (3 pages) | Cited 23 times

Online Publication Date: 16 July 2008

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We explain the occurrence of ion exchange and an index profile around the focal point inside a commercial crown glass formed by femtosecond laser irradiation. The index profile in the photoinduced area has a ring-shaped pattern, which indicates that local densification occurred in the glass. An irregular surface reflecting the density distribution is formed around the focal point by dry etching process using a focused ion beam. By the irradiation of femtosecond laser pulses, the effect of ion exchange between the focal point and the surrounding area is also observed in the area in which local densification occurred.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Cf Surface cleaning, etching, patterning
78.47.-p Spectroscopy of solid state dynamics
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
64.70.P- Glass transitions of specific systems
61.43.Fs Glasses

High-sensitivity pesticide detection via silicon nanowires-supported acetylcholinesterase-based electrochemical sensors

Shao Su, Yao He, Mingliang Zhang, Kun Yang, Shiping Song, Xiaohong Zhang, Chunhai Fan, and Shuit-Tong Lee

Appl. Phys. Lett. 93, 023113 (2008); http://dx.doi.org/10.1063/1.2959827 (3 pages) | Cited 13 times

Online Publication Date: 16 July 2008

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We report the use of a silicon-based nanocomplex, i.e., gold nanoparticles-coated silicon nanowires, for the improvement of acetylcholinesterase (AChE)-based electrochemical sensors for pesticide detection. Owing to the high electrical conductivity of the nanocomplex and its compatibility with the enzyme, the sensor exhibited significantly enhanced performance. The AChE enzyme bound to the surface possessed Michaelis–Menton constant of 81 μM, resembling that in its free form. The sensor showed rapid response toward substrate acetylcholine in the concentration range of 1.0 μM–1.0 mM. This AChE nanosensor could detect as low as 8 ng/L dichlorvos, an organophosphate pesticide.
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82.47.Rs Electrochemical sensors
82.80.Fk Electrochemical methods
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Cantilevers with integrated sensor for time-resolved force measurement in tapping-mode atomic force microscopy

A. F. Sarioglu and O. Solgaard

Appl. Phys. Lett. 93, 023114 (2008); http://dx.doi.org/10.1063/1.2959828 (3 pages) | Cited 9 times

Online Publication Date: 16 July 2008

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We present a micromachined cantilever with an integrated high-bandwidth resonator for direct measurement of tip-sample interaction forces in tapping-mode atomic force microscopy. Force measurements are achieved by a diffraction grating that serves as a differential displacement sensor for the tip motion relative to the cantilever body. Time-resolved tip-sample interaction force measurement is demonstrated on a silicon sample following calibration of the probe structure. By using lock-in detection, the harmonics of periodic tip-sample interaction have been utilized to obtain high-contrast, material specific images. The harmonic images of patterned silicon/silicon nitride control samples and triblock copolymers are presented.
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07.10.Pz Instruments for strain, force, and torque
07.79.Lh Atomic force microscopes
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.79.Dj Gratings
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Highly ordered arrays of macroscopically long Pb nanobelts with atomic-level controlled thickness and width on Si

Z. L. Guan, R. Wu, Y. X. Ning, C. L. Song, L. Tang, D. Hao, Xu-Cun Ma, J. F. Jia, X. Chen, Q. K. Xue, Z. M. Liao, and D. P. Yu

Appl. Phys. Lett. 93, 023115 (2008); http://dx.doi.org/10.1063/1.2955823 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2008

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We report growth of ordered arrays of superlong Pb nanobelts using Al decorated Si(111) substrates as a template. By depositing Al at substrate temperature of 650–700 °C, each original Si(111) terrace is divided into two distinct strips, a γ-phase strip and a mixed √7×√7 and √3×√3 structure strip. In situ scanning tunneling microscopy observation reveals that Pb atoms preferentially nucleate on the γ-phase strips and form uniform array of nanobelts with a width from 10 to 100 nm and a thickness from 2.3 to 20 nm, which can delicately be controlled by Al coverage and Pb coverage.
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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

Atomically sharp catalyst-free wurtzite GaAs/AlGaAs nanoneedles grown on silicon

Michael Moewe, Linus C. Chuang, Shanna Crankshaw, Chris Chase, and Connie Chang-Hasnain

Appl. Phys. Lett. 93, 023116 (2008); http://dx.doi.org/10.1063/1.2949315 (3 pages) | Cited 30 times

Online Publication Date: 16 July 2008

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We report a catalyst-free, self-assembled growth mode generating single-crystal wurtzite phase ultrasharp GaAs/AlGaAs nanoneedles on both GaAs and Si substrates via low-temperature metal-organic chemical vapor deposition. The needles exhibit record-narrow tip diameters of 2–4 nm wide and sharp 6°–9° taper angles. The length is dependent on growth time and up to 3–4 μm nanoneedles are attained. The structures do not exhibit twinning defects, contrary to typical GaAs nanowires grown by vapor-liquid-solid catalyzed growth. AlGaAs layered nanoneedle structures are also demonstrated.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.-w Structure of nanoscale materials

Angular dependent luminescence of individual suspended ZnO nanorods

Wenliang Li, Min Gao, Rui Cheng, Xiaoxian Zhang, Sishen Xie, and Lian-Mao Peng

Appl. Phys. Lett. 93, 023117 (2008); http://dx.doi.org/10.1063/1.2957982 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2008

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We report angular dependent microphotoluminescence measurements on individual suspended ZnO nanorods attached to sharp metal tips. The luminescence measured along and perpendicular to the axis of the same single nanorod indicates quantitatively that >99% of the near band edge emission can be confined effectively in the nanorods and emitted from the end facets. The radially confined luminescence is dominated by P bands and LO phonon replicas of the free exciton emission and P bands. The measurements along the length of the nanorods show that the confinement is evidently influenced by the surface structure.
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78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Breaking single-walled carbon nanotube bundles by Joule heating

Yang Wei, Peng Liu, Kaili Jiang, Liang Liu, and Shoushan Fan

Appl. Phys. Lett. 93, 023118 (2008); http://dx.doi.org/10.1063/1.2957986 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2008

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Electrical breakdown induced by Joule heating was employed to make a well-aligned surface structure from single-walled carbon nanotube (SWCNT) bundles. The surfaces at the breaking ends are tip abundant and composed of SWCNTs of high quality. In addition, the radial breathing mode frequencies of the CNT tips have a downshift than the as-grown SWCNTs, due to the higher thermal stability of wider SWCNTs and the strong intertube interactions. The ends can provide emission currents of about 100 μA, and a pixel based on these potential electron emitters was developed for lateral field emission displays.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Fd Field emission displays (FEDs)

Large-scale silica nanowire array grown on liquid tin and its applications as Hg (II) scavenger

Hui Wang, Xiao-Hong Zhang, Dorothy Duo Duo Ma, and Shuit-Tong Lee

Appl. Phys. Lett. 93, 023119 (2008); http://dx.doi.org/10.1063/1.2955836 (3 pages) | Cited 3 times

Online Publication Date: 16 July 2008

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Silica (SiO2) nanowire array has been prepared in large scale through thermal evaporation of SiO via oxide-assisted growth on Sn substrate. During growth the Sn substrate became a liquid, whose fluid surface induced the growth of SiO2 (from SiO disproportionation) into an aligned nanowire array on Sn surface. The liquid Sn itself further served as the solvent to dissolve elemental Si produced from SiO disproportionation. The high-density nanowire array is a type of microporous silica with a large surface area, which can serve as an efficient absorbent for scavenging heavy metal ions such as Hg (II) from water after surface modification with mercapto groups (–SH).
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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.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.75.Bc Solubility

Evaporation-induced assembly of biomimetic polypeptides

Joseph Keyes, Michael Junkin, Joseph Cappello, Xiaoyi Wu, and Pak Kin Wong

Appl. Phys. Lett. 93, 023120 (2008); http://dx.doi.org/10.1063/1.2957992 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2008

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We report an evaporation assisted plasma lithography (EAPL) process for guided self-assembly of a biomimetic silk-elastinlike protein (SELP). We demonstrate the formation of SELP structures from millimeter to submicrometer range on plasma-treatment surface templates during an evaporation-induced self-assembly process. The self-assembly processes at different humidities and droplet volumes were investigated. The process occurs efficiently in a window of optimized operating conditions found to be at 70% relative humidity and 8 μl volume of SELP solution. The EAPL approach provides a useful technique for the realization of functional devices and systems using these biomimetic materials.
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87.14.E- Proteins
36.20.-r Macromolecules and polymer molecules
52.77.-j Plasma applications
81.16.Dn Self-assembly

Nanophotonic split-ring resonators as dichroics for molecular spectroscopy

A. W. Clark, A. Glidle, D. R. S. Cumming, and J. M. Cooper

Appl. Phys. Lett. 93, 023121 (2008); http://dx.doi.org/10.1063/1.2956389 (3 pages) | Cited 11 times

Online Publication Date: 16 July 2008

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We describe the design and fabrication of nanostructured silver split-ring resonators and demonstrate their application as dichroic sensors for multipurpose visible wavelength molecular spectroscopy. By producing arrays of these identical nanostructures, with critical dimensions of 30–150 nm, we demonstrate the controllable generation of plasmonic resonances at two common visible laser wavelengths, produced as a consequence of the polarization of the light with respect to structural geometry. We show the application of these devices in surface enhanced Raman spectroscopy, using their dichroic properties to perform molecular sensing of a self-assembled monolayer of 2-mercaptopyridine at both 532 and 633 nm.
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07.60.Rd Visible and ultraviolet spectrometers
33.55.+b Optical activity and dichroism

Annealing effect on the optical properties of implanted silicon in a silicon nitride matrix

Z. H. Cen, T. P. Chen, L. Ding, Y. Liu, M. Yang, J. I. Wong, Z. Liu, Y. C. Liu, and S. Fung

Appl. Phys. Lett. 93, 023122 (2008); http://dx.doi.org/10.1063/1.2962989 (3 pages) | Cited 9 times

Online Publication Date: 17 July 2008

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Optical properties of implanted Si in a silicon nitride (Si3N4) thin film have been determined with spectroscopic ellipsometry based on the Tauc–Lorentz (TL) model and the Bruggeman effective medium approximation. It is shown that the suppressed dielectric functions of the implanted Si are dominated by the energy transitions related to the critical point E2. The effect of thermal annealing on the dielectric functions of the implanted Si has been investigated. The analysis of the dielectric functions based on the evolution of the TL parameters can provide an insight into the structural changes in the implanted Si embedded in the Si3N4 matrix caused by the annealing.
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81.40.Gh Other heat and thermomechanical treatments
78.66.-w Optical properties of specific thin films
77.55.-g Dielectric thin films

Paramagnetic point defects at SiO2/nanocrystalline Si interfaces

A. Stesmans, M. Jivanescu, S. Godefroo, and M. Zacharias

Appl. Phys. Lett. 93, 023123 (2008); http://dx.doi.org/10.1063/1.2952276 (3 pages) | Cited 8 times

Online Publication Date: 17 July 2008

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A K- and Q-band electron spin resonance study, combining two detection modes, on structures composed of Si nanoparticles ( ∼ 2 nm across) embedded in a SiO2 matrix obtained by annealing of SiO/SiO2 superstructures unveils the observed principal Si dangling bond signal as solely comprised of the intrinsic Pb(0) and Pb1 Si/SiO2 interface defect spectra, of comparable densities. Based on independent particle density counting, about one Pb-type defect is found at every 1.4 Si nanoparticles. Relying on the known properties of Pb-type defects in standard microscopic Si/SiO2, the data would comply with Si nanocrystallites with morphology, schematically, of [100] truncated (111) octahedrons. Both types and densities of observed point defects indicate a structure of quality much alike that of standard thermal Si/SiO2.
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61.72.J- Point defects and defect clusters
76.30.-v Electron paramagnetic resonance and relaxation
71.55.-i Impurity and defect levels

Nonlinear optical tuning of photonic crystal microcavities by near-field probe

Silvia Vignolini, Francesca Intonti, Laurent Balet, Margherita Zani, Francesco Riboli, Anna Vinattieri, Diederik S. Wiersma, Marcello Colocci, Lianhe Li, Marco Francardi, Annamaria Gerardino, Andrea Fiore, and Massimo Gurioli

Appl. Phys. Lett. 93, 023124 (2008); http://dx.doi.org/10.1063/1.2960259 (3 pages) | Cited 11 times

Online Publication Date: 17 July 2008

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We report on a nonlinear way to control and tune the dielectric environment of photonic crystal microcavities exploiting the local heating induced by near-field laser excitation at different excitation powers. The temperature gradient due to the optical absorption results in an index of refraction gradient which modifies the dielectric surroundings of the cavity and shifts the optical modes. Reversible tuning can be obtained either by changing the excitation power density or by exciting in different points of the photonic crystal microcavity.
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42.65.-k Nonlinear optics
42.70.Mp Nonlinear optical crystals
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Relationship between the molecular orbital structure of the dyes and photocurrent density in the dye-sensitized solar cells

R. Jose, A. Kumar, V. Thavasi, K. Fujihara, S. Uchida, and S. Ramakrishna

Appl. Phys. Lett. 93, 023125 (2008); http://dx.doi.org/10.1063/1.2957988 (3 pages) | Cited 22 times

Online Publication Date: 17 July 2008

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Through a combined experimental and theoretical investigation we have shown that the efficiency of charge injection in dye-sensitized solar cells constituted from dyes having a single carboxylic group is determined by the extent to which the lowest unoccupied molecular orbital (LUMO) of the dye falls on its anchoring group. This conclusion was brought by calculating the LUMO surface of three indoline dyes and comparing the conversion efficiency of dye-sensitized solar cells fabricated using those dyes. The Ruthenium based N3 dye was used as standard both in the calculation and experiment.
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84.60.Jt Photoelectric conversion
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