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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Collecting photoelectrons with a scanning tunneling microscope nanotip

Ching-Yuan Chiu, Yuet-Loy Chan, Y. J. Hsu, and D. H. Wei

Appl. Phys. Lett. 92, 103101 (2008); http://dx.doi.org/10.1063/1.2894186 (3 pages) | Cited 10 times

Online Publication Date: 10 March 2008

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The collection of photoelectrons excited with a synchrotron via a nanotip placed near the surface of a sample is studied. Simulating the electron trajectory, we found that photoelectrons escaping from the surface are too weak to be the only source of electrons contributing to a photocurrent detected with a scanning tunneling microscope tip, as reported recently. The tunneling of low-energy electrons generated with synchrotron irradiation is suggested as an additional channel contributing to the photocurrent at a small separation between tip and sample. An image based on x-ray absorption is expected to attain a resolution comparable to a topographical image.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Ultrathin responsive polyelectrolyte brushes studied by infrared synchrotron mapping ellipsometry

Katy Roodenko, Yulia Mikhaylova, Leonid Ionov, Michael Gensch, Manfred Stamm, Sergiy Minko, Ulrich Schade, Klaus-Jochen Eichhorn, Norbert Esser, and Karsten Hinrichs

Appl. Phys. Lett. 92, 103102 (2008); http://dx.doi.org/10.1063/1.2892132 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2008

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An infrared microfocus spectroscopic mapping ellipsometer was set up at the Berlin electron synchrotron storage ring and used to study ultrathin polyacrylic acid brush films with 3 nm thickness. The pH-responsive properties of the brush on a gold-coated glass substrate were investigated. The chemical structure of the brush was resolved with a spatial resolution of 300 μm using the synchrotron mapping ellipsometer.
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61.66.Hq Organic compounds
61.41.+e Polymers, elastomers, and plastics
68.55.J- Morphology of films
78.30.Jw Organic compounds, polymers

Remarkable influence of the number of nanowires on plasmonic behaviors of the coupled metallic nanowire chain

H. S. Chu, W. B. Ewe, W. S. Koh, and E. P. Li

Appl. Phys. Lett. 92, 103103 (2008); http://dx.doi.org/10.1063/1.2892446 (3 pages) | Cited 8 times

Online Publication Date: 10 March 2008

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We investigate the plasmonic properties in terms of plasmonic resonances, near field intensity, and charge distribution of interacting nanowires chain which consists of small and large numbers of coupled silver nanowires. We show that the dominant resonance wavelength increases monotonically as the number of nanowires increases. On the other hand, the near field intensity is not only dependent on the chain length but also on the plasmonic resonances in the same chain length. The charge distribution is also demonstrated to fully understand the dependence of plasmonic properties on the chain length.
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73.22.Lp Collective excitations
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
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)

Degradation of carbon nanotube field emitters driven by anode adsorbed water

A. M. Fennimore, L. T. Cheng, D. H. Roach, G. A. M. Reynolds, R. R. Getty, and A. Krishnan

Appl. Phys. Lett. 92, 103104 (2008); http://dx.doi.org/10.1063/1.2892657 (3 pages) | Cited 5 times

Online Publication Date: 10 March 2008

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The field degradation of carbon nanotube field emitters in diode emission at constant current was demonstrated to be highly dependent upon the presence of water at partial pressures as low as 10−9 Torr. The anode surface was also seen to significantly impact the degradation rate, with metallic Al films yielding the worst degradation rates. Coating the anode surface with a carbon or polymer film lowered the degradation rate. It is suggested that a majority of the degradation seen in nanotube field emission devices is due to ionization of water adsorbed at the anode surface.
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85.35.Kt Nanotube devices
85.45.Db Field emitters and arrays, cold electron emitters
68.43.Mn Adsorption kinetics
82.45.Fk Electrodes

Synthesis of gold-silicon core-shell nanoparticles with tunable localized surface plasmon resonance

S. Mohapatra, Y. K. Mishra, D. K. Avasthi, D. Kabiraj, J. Ghatak, and S. Varma

Appl. Phys. Lett. 92, 103105 (2008); http://dx.doi.org/10.1063/1.2894187 (3 pages) | Cited 19 times

Online Publication Date: 10 March 2008

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Gold-silicon core-shell nanoparticles embedded in silica matrix, evident by transmission electron microscopy and x-ray photoelectron spectroscopy were synthesized by atom beam cosputtering followed by thermal annealing. Optical absorption studies revealed localized surface plasmon resonance (LSPR), which showed regular redshift from 500 to 583 nm with increase in annealing temperature. The observed redshifts in the LSPR peaks are in close agreement with the theoretical calculations assuming Si nanoshells surrounding Au nanoparticles. The Au–Si core-shell formation is explained by Au–Si liquid nanodroplet formation at temperatures higher than the eutectic temperature, followed by phase separation during subsequent cooling.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations

Tuning coherent radiative thermal conductance in multilayer photonic crystals

Wah Tung Lau, Jung-Tsung Shen, Georgios Veronis, Shanhui Fan, and Paul V. Braun

Appl. Phys. Lett. 92, 103106 (2008); http://dx.doi.org/10.1063/1.2890433 (3 pages) | Cited 4 times

Online Publication Date: 10 March 2008

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We consider coherent radiative thermal conductance of a multilayer photonic crystal. The crystal consists of alternating layers of lossless dielectric slabs and vacuum, where heat is conducted only through photons. We show that such a structure can have thermal conductance below vacuum over the entire high temperature range due to the presence of partial band gap in most of the frequency range, as well as the suppression of evanescent tunneling between slabs at higher frequencies. The thermal conductance of this structure is highly tunable by varying the thickness of the vacuum layers.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.65.Ac Multilayers

A double substrate “sandwich” structure for fiber surface enhanced Raman scattering detection

Chao Shi, He Yan, Claire Gu, Debraj Ghosh, Leo Seballos, Shaowei Chen, Jin Z. Zhang, and Bin Chen

Appl. Phys. Lett. 92, 103107 (2008); http://dx.doi.org/10.1063/1.2883957 (3 pages) | Cited 18 times

Online Publication Date: 10 March 2008

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A double substrate “sandwiching” structure has been designed and tested for molecular detection using surface enhanced Raman scattering (SERS). With silver (Ag) nanoparticles as SERS substrates and rhodamine 6G (R6G) as a test molecule, the results show that the “sandwich” configuration exhibits significantly higher SERS enhancement compared to just one of the substrates or a simple sum of the signals from the two separate substrates. The improved SERS sensitivity is attributed to a stronger electromagnetic field enhancement by the double substrate sandwich structure.
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78.30.Jw Organic compounds, polymers
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.20.-n Methods of materials synthesis and materials processing
81.16.-c Methods of micro- and nanofabrication and processing

Directional growth of Ge on GaAs at 175 °C using plasma-generated nanocrystals

Erik V. Johnson, Gilles Patriarche, and Pere Roca i Cabarrocas

Appl. Phys. Lett. 92, 103108 (2008); http://dx.doi.org/10.1063/1.2895636 (3 pages) | Cited 6 times

Online Publication Date: 11 March 2008

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We demonstrate the directional growth of Ge on a GaAs {100} wafer at 175 °C using radio-frequency plasma-enhanced chemical vapor deposition at 13.56 MHz under conditions where nanocrystals are the primary contributors to film growth. High resolution transmission electron microscopy (HRTEM) verifies the transport of plasma-formed nanocrystals to the substrate surface where they are initially mobile. Furthermore, cross-sectional HRTEM images show directional growth on the GaAs wafer, wherein the incident Ge nanocrystals have adopted the orientation of the underlying lattice.
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68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Molecular understanding of the deposition of gold nanoclusters on TiO2(110)

Q. H. Zeng, K. Wong, X. C. Jiang, and A. B. Yu

Appl. Phys. Lett. 92, 103109 (2008); http://dx.doi.org/10.1063/1.2896610 (3 pages) | Cited 2 times

Online Publication Date: 11 March 2008

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The deposition of gold nanoclusters on rutile TiO2(110) surface is investigated by molecular dynamics simulation, with special reference to the effects of surface defect types (i.e., point, step, and groove) and deposition temperature. The results show that gold nanoclusters can be strongly attracted to the surface and a higher degree of defect results in a stronger attractive interaction. In addition, the aggregation behavior of gold nanoclusters is studied by simulation and experiment. The results indicate that the aggregation can be effectively controlled by introducing suitable surface defects or adding citrate ions into the solution. The findings are useful to the design and fabrication of supported Au–TiO2 catalysts with high catalytic activity.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.72.jd Vacancies
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Fabrication and characterization of a nanoelectromechanical switch with 15-nm-thick suspension air gap

Weon Wi Jang, Jeong Oen Lee, Jun-Bo Yoon, Min-Sang Kim, Ji-Myoung Lee, Sung-Min Kim, Keun-Hwi Cho, Dong-Won Kim, Donggun Park, and Won-Seong Lee

Appl. Phys. Lett. 92, 103110 (2008); http://dx.doi.org/10.1063/1.2892659 (3 pages) | Cited 30 times

Online Publication Date: 11 March 2008

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We developed titanium nitride (TiN) based nanoelectromechanical (NEM) switch with the smallest suspension air-gap thickness ever made to date by a “top-down” complementary metal-oxide semiconductor fabrication methods. Cantilever-type NEM switch with a 15-nm-thick suspension air gap and a 35-nm-thick TiN beam was successfully fabricated and characterized. The fabricated cantilever-type NEM switch showed an essentially zero off current, an abrupt switching with less than 3 mV/decade, and an on/off current ratio exceeding 105 in air ambient. Also achieved was an endurance of over several hundreds of switching cycles under dc and ac biases in air ambient.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Nanofluids with plasma treated diamond nanoparticles

Qingsong Yu, Young Jo Kim, and Hongbin Ma

Appl. Phys. Lett. 92, 103111 (2008); http://dx.doi.org/10.1063/1.2894520 (3 pages) | Cited 3 times

Online Publication Date: 11 March 2008

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In this study, diamond nanoparticles were plasma treated by glow discharges of methane and oxygen with an aim of improving their dispersion characteristics in a base fluid of water and enhancing the thermal conductivity of the resulting nanofluids. It was found that, after plasma treatment, stable nanofluids with improved thermal conductivity were obtained without using any stabilizing agents. With <0.15 vol % addition of plasma treated nanoparticles into water, a 20% increase in thermal conductivity was achieved and a 5%–10% increase in both fluid density and viscosity was observed.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
52.80.Hc Glow; corona
52.77.-j Plasma applications
66.20.-d Viscosity of liquids; diffusive momentum transport

Energy band and vacuum level alignment at a semiconductor-molecule-metal interface

Fabrizio Cleri

Appl. Phys. Lett. 92, 103112 (2008); http://dx.doi.org/10.1063/1.2896299 (3 pages) | Cited 2 times

Online Publication Date: 12 March 2008

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We calculated the atomic structure and energy-level alignment at a representative Si-molecule-metal interface. The covalently bonded Si-molecule interface largely determines the overall band offset and the highest occupied molecular orbital position, while charge transfer across the metal-molecule interface induces localized π levels, even in the absence of covalent bonding to the metal. We propose a scheme for the vacuum level adjustment, consistent with the formation of interfacial dipoles and charge transfer to the molecular layer. The highest occupied π level of the molecule should be the main electronic state involved in the transport properties, while interface dipoles appear to be related to the interface-induced states.
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73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization

Manganite thin film/ZnO nanowire (nanosheets) p-n junctions

Zhou Zhang, Yinghui Sun, Yonggang Zhao, Gongping Li, and Tom Wu

Appl. Phys. Lett. 92, 103113 (2008); http://dx.doi.org/10.1063/1.2896307 (3 pages) | Cited 19 times

Online Publication Date: 12 March 2008

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We have fabricated p-type La0.7Sr0.3MnO3 thin film/n-type ZnO nanowires (nanosheets) heterostructures. A lower-temperature growth with Zn source and a higher-temperature growth with ZnO/graphite source led to the formations of nanowires and nanosheets, respectively. While the nanosheets showed an epitaxial relationship with the manganite film, the high processing temperature resulted in interfacial diffusion and reaction, which were reflected in the x-ray diffraction, magnetic, and electrical transport measurements. The manganite thin film/ZnO nanowires (nanosheets) p-n junctions exhibited good rectification behaviors. Such heterostructures are promising to find potential applications in electronic and spintronic devices.
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66.30.Ny Chemical interdiffusion; diffusion barriers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.40.Ei Rectification
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)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.aj Insulators

Aligning microcavity resonances in silicon photonic-crystal slabs using laser-pumped thermal tuning

Jun Pan, Yijie Huo, Kazuhiko Yamanaka, Sunil Sandhu, Luigi Scaccabarozzi, Rolf Timp, Michelle L. Povinelli, Shanhui Fan, M. M. Fejer, and James S. Harris

Appl. Phys. Lett. 92, 103114 (2008); http://dx.doi.org/10.1063/1.2896615 (3 pages) | Cited 14 times

Online Publication Date: 12 March 2008

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We report the postfabrication alignment of multiple microcavity resonances in silicon photonic-crystal (PhC) slabs using laser-pumped thermal tuning. The thermal gradient resulting from a focused laser spot was used to differentially tune the resonant wavelengths of two microcavities spaced about 50 μm apart. The resonant wavelengths could be brought closer together, over a tunable range of more than 5 nm. A cross over in the resonant wavelengths was demonstrated, showing that two microcavities can be tuned to the identical wavelength. The results show that differential thermal tuning can be used to remove slight fabrication differences in nominally identical microcavities, relaxing the fabrication tolerances that will be required to realize coupled-resonator structures in PhCs.
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84.40.Az Waveguides, transmission lines, striplines
42.55.Tv Photonic crystal lasers and coherent effects
42.70.Qs Photonic bandgap materials
42.60.Fc Modulation, tuning, and mode locking
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Self-assembling conditions of 1O4Sr clusters in ZnTe:(Sr, O)

V. A. Elyukhin

Appl. Phys. Lett. 92, 103115 (2008); http://dx.doi.org/10.1063/1.2896617 (3 pages) | Cited 3 times

Online Publication Date: 12 March 2008

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Self-assembling (SA) conditions of 1O4Sr tetrahedral clusters in ZnTe:(Sr, O) with the Sr concentration of up to 0.02 and in the ultradilute oxygen limit are represented. The cause of SA is a decrease of the strain energy after the formation of the clusters. SA occurs at temperatures of 573, 773, and 973 K if the Sr contents reach 1.23×10−4, 1.26×10−3, and 4.97×10−3, respectively. At the melting temperature of ZnTe, SA is absent at the considered Sr and oxygen concentrations. A temperature when all oxygen atoms are in clusters depends on the Sr and oxygen contents.
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61.72.uj III-V and II-VI semiconductors

Fabrication of electromechanical switch using interconnected single-walled carbon nanotubes

Zhuo Chen, Lianming Tong, Zhongyun Wu, and Zhongfan Liu

Appl. Phys. Lett. 92, 103116 (2008); http://dx.doi.org/10.1063/1.2884311 (3 pages) | Cited 7 times

Online Publication Date: 12 March 2008

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We demonstrated a prototype of nanoelectromechanical switch which was fabricated with single-walled carbon nanotubes (SWCNTs). An alternating current electric field was utilized to assemble interconnected SWCNTs suspended over the focused ion beam lithography fabricated trenches on the electrode surface. By controlling the electromechanical coupling between the electrostatic and elastostatic forces acting on the SWCNTs, we realized the on and off states of the SWCNT switches. Both two-terminal and three-terminal measurements have been conducted and indicated repeatable switch effects.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.Kt Nanotube devices
85.40.Hp Lithography, masks and pattern transfer

Subwavelength modulation of surface relief and refractive index in preirradiated liquid-crystalline polymer films

Haifeng Yu, Atsushi Shishido, and Tomiki Ikeda

Appl. Phys. Lett. 92, 103117 (2008); http://dx.doi.org/10.1063/1.2894073 (3 pages) | Cited 2 times

Online Publication Date: 12 March 2008

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We present a simple method to record subwavelength gratings (SWGs) in an azobenzene (AZ)-containing liquid-crystalline polymer by preirradiation. Since the cooperative motions of mesogens are eliminated in a cis-AZ-rich isotropic phase by the pretreatment, the subwavelength modulation of surface relief and refractive index (RI) was obtained. The surface relief of less than 10 nm and the RI modulation were detected by atomic force microscopy. A large phase retardation and formed birefringence were obtained in the recorded SWGs in which a possible schematic illustration of AZ was proposed.
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78.66.Qn Polymers; organic compounds
78.20.Fm Birefringence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.15.+e Liquid thin films
61.80.-x Physical radiation effects, radiation damage
61.82.Pv Polymers, organic compounds

Buckling of ZnO nanowires under uniaxial compression

M. Riaz, O. Nur, M. Willander, and P. Klason

Appl. Phys. Lett. 92, 103118 (2008); http://dx.doi.org/10.1063/1.2894184 (3 pages) | Cited 20 times

Online Publication Date: 12 March 2008

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Instability and buckling characterization of vertical well aligned single crystal of ZnO nanowires grown on SiC substrate was done quantitatively by nanoindentation technique. The critical load was found to be 477 μN and the corresponding buckling energy was 3.46×10−11 J. Based on the Euler model for long nanowire and Johnson model which is an extension of the Euler model for intermediate nanowire, the modulus of elasticity of single wire was calculated. Also, the critical buckling stress and strain were determined for the as grown single wire of ZnO. We found how the modulus of elasticity is dependent on the slenderness ratio.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.mq Buckling
81.40.Lm Deformation, plasticity, and creep
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)

Hard-x-ray microscopy with Fresnel zone plates reaches 40 nm Rayleigh resolution

Y. S. Chu, J. M. Yi, F. De Carlo, Q. Shen, Wah-Keat Lee, H. J. Wu, C. L. Wang, J. Y. Wang, C. J. Liu, C. H. Wang, S. R. Wu, C. C. Chien, Y. Hwu, A. Tkachuk, W. Yun, et al.

Appl. Phys. Lett. 92, 103119 (2008); http://dx.doi.org/10.1063/1.2857476 (3 pages) | Cited 61 times

Online Publication Date: 12 March 2008

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Substantial improvements in the nanofabrication and characteristics of gold Fresnel zone plates yielded unprecedented resolution levels in hard-x-ray microscopy. Tests performed on a variety of specimens with 8–10 keV photons demonstrated a first-order lateral resolution below 40 nm based on the Rayleigh criterion. Combined with the use of a phase contrast technique, this makes it possible to view features in the 30 nm range; good-quality images can be obtained at video rate, down to 50 ms/frame. The important repercussions on materials science, nanotechnology, and the life sciences are discussed.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.85.Tt X-ray microscopes
42.79.Ci Filters, zone plates, and polarizers
42.25.Fx Diffraction and scattering
42.65.Es Stimulated Brillouin and Rayleigh scattering

Two-dimensional signatures for molecular identification

Muhammad Qazi, Thomas Vogt, and Goutam Koley

Appl. Phys. Lett. 92, 103120 (2008); http://dx.doi.org/10.1063/1.2897295 (3 pages) | Cited 3 times

Online Publication Date: 13 March 2008

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Simultaneous measurements of the conductance and surface work function (SWF) changes on nanostructured graphite layers have been performed to detect several gaseous analyte molecules. It has been observed that the gradient of the SWF versus conductance response plotted for specific analyte molecules is constant irrespective of their concentration or fractional occupancy of surface adsorption sites. The SWF and conductance changes have been found to be uncorrelated for different analyte molecules, resulting in unique gradients that can be used as two-dimensional signatures for molecular identification.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ng Insulators
68.43.Mn Adsorption kinetics
73.25.+i Surface conductivity and carrier phenomena
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.63.Bd Nanocrystalline materials

Theoretical investigation of size and shape effects on the melting temperature and energy bandgap of TiO2 nanostructures

G. Guisbiers, O. Van Overschelde, and M. Wautelet

Appl. Phys. Lett. 92, 103121 (2008); http://dx.doi.org/10.1063/1.2897297 (3 pages) | Cited 17 times

Online Publication Date: 13 March 2008

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In this letter, we report a theoretical investigation concerning the size effect on the melting temperature and energy bandgap of TiO2 nanostructures. Within the thermodynamical approach, we predict a structural phase transition from rutile to anatase for the sizes around 40, 29, and 48 nm, respectively, in the cases of spherical nanoparticles, cylindrical nanowires, and nanotubes. For spherical nanoparticles, this means that the more stable phase is anatase for sizes smaller than ∼ 40 nm and rutile for sizes larger than ∼ 40 nm. The energy bandgap of these structures is also estimated.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
71.20.Nr Semiconductor compounds
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
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)

Photosensitization of nonlinear scattering and photoacoustic emission from single-walled carbon nanotubes

I.-Yin Sandy Lee, Tomomi Matsuo, and Honoh Suzuki

Appl. Phys. Lett. 92, 103122 (2008); http://dx.doi.org/10.1063/1.2897302 (3 pages)

Online Publication Date: 13 March 2008

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Enhancement of laser-induced nonlinear scattering has been observed from an aqueous suspension of single-walled carbon nanotubes (SWCNTs) doped with near-infrared dye chromophores. The underlying mechanism involves cavitation triggered by optical heating and bubble pulsation, which are further enhanced by the dye adsorbed on SWCNT surfaces, resulting in the scattering enhancement and a modification of the accompanying photoacoustic waveform. These photosensitizing effects suggest potential feasibility of dye-doped nanotubes as optically switchable nanoemitters of ultrasound for biomedical applications such as ultrasonic therapy and imaging.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
78.67.Ch Nanotubes
87.85.Rs Nanotechnologies-applications
87.63.D- Ultrasonography
43.80.Qf Medical diagnosis with acoustics
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction

Near-field optical characterization of surface-plasmon-mediated light emission from electrically biased metal-insulator-semiconductor tunnel junctions

J. Seidel, T. Göhler, S. Grafström, and L. M. Eng

Appl. Phys. Lett. 92, 103123 (2008); http://dx.doi.org/10.1063/1.2898201 (3 pages) | Cited 1 time

Online Publication Date: 13 March 2008

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We report on near-field optical observations of surface-plasmon-mediated light emission in electrically biased metal-insulator-semiconductor (MIS) tunnel junctions fabricated from Au and p-type Si with a native oxide layer as the tunneling barrier. Our junctions exhibit stable broadband macroscopic light emission in the visible spectrum. Inspection of the optical near-field reveals highly localized hot spots due to local plasmon excitation and scattering, which are investigated with spectral distinction. Such MIS tunneling junctions are compatible with common complementary metal-oxide semiconductor technology and thus open up an interesting route toward the development of novel integrated optoelectronic and plasmonic devices.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

Cantilever based optical interfacial force microscope

Jeremy R. Bonander and Byung I. Kim

Appl. Phys. Lett. 92, 103124 (2008); http://dx.doi.org/10.1063/1.2898524 (3 pages) | Cited 7 times

Online Publication Date: 14 March 2008

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We developed a cantilever based optical interfacial force microscopy (COIFM) that employs a microactuated silicon cantilever and optical detection method to establish the measurement of the single molecular interactions using the force feedback technique. Through the direct measurement of the COIFM force-distance curves, we have demonstrated that the COIFM is capable of unveiling structural and mechanical information on interfacial water at the single molecular level over all distances between two hydrophilic surfaces.
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07.79.Lh Atomic force microscopes

High quality mechanical and optical properties of commercial silicon nitride membranes

B. M. Zwickl, W. E. Shanks, A. M. Jayich, C. Yang, A. C. Bleszynski Jayich, J. D. Thompson, and J. G. E. Harris

Appl. Phys. Lett. 92, 103125 (2008); http://dx.doi.org/10.1063/1.2884191 (3 pages) | Cited 33 times

Online Publication Date: 14 March 2008

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We have measured the optical and mechanical loss of commercial silicon nitride membranes. We find that 50 nm thick, 1 mm2 membranes have mechanical Q>106 at 293 K, and Q>107 at 300 mK, well above what has been observed in devices with comparable dimensions. The near-IR optical loss at 293 K is less than 2×10−4. This combination of properties make these membranes attractive candidates for studying quantum effects in optomechanical systems.
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42.79.-e Optical elements, devices, and systems
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