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27 Sep 2010

Volume 97, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 133303 (2010); http://dx.doi.org/10.1063/1.3491815 (3 pages)

Yoshihide Fujisaki, Yoshiki Nakajima, Daisuke Kumaki, Toshihiro Yamamoto, Shizuo Tokito, Takahiro Kono, Jun-ichi Nishida, and Yoshiro Yamashita
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Fast imaging with alternative signal for dynamic atomic force microscopy

Chibum Lee and Srinivasa M. Salapaka

Appl. Phys. Lett. 97, 133101 (2010); http://dx.doi.org/10.1063/1.3495987 (3 pages) | Cited 1 time

Online Publication Date: 27 September 2010

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In this paper, a method for imaging in amplitude-modulation atomic force microscopy is developed which enables accurate sample-profile imaging even at high scanning speeds where existing methods that use the actuator input signal fail. The central concept is to use a model of the vertical positioning actuator to compensate for the artifacts introduced due to its compliance in high scanning frequencies. We provide experiments that compare sample-profile estimates from our method with the existing methods and demonstrate significant improvement (by 70%) in the estimation bandwidth. The proposed design allows for specifying a trade-off between the sample-profile estimation error and estimation bandwidth.
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07.79.Lh Atomic force microscopes
42.30.Lr Modulation and optical transfer functions
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Magnetic properties in graphene-graphane superlattices

Joo-Hyoung Lee and Jeffrey C. Grossman

Appl. Phys. Lett. 97, 133102 (2010); http://dx.doi.org/10.1063/1.3495771 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2010

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The magnetic properties of graphene-graphane superlattices with zigzag interfaces and separately varying widths are investigated by first-principles density functional calculations. It is demonstrated that magnetic states are energetically more stable than nonmagnetic ones due to the Stoner-type instability, and that antiferromagnetic spin configuration across the graphene strip is found to be the ground state, whereas the ferromagnetic ordering becomes metastable. The magnetic moments in the ferromagnetic states show a monotonic increase and saturation with the width of the graphene strip, independent of the graphane width due to the π-character of the spin densities. These findings point toward an alternative route for graphene-based applications without requiring physical cutting as in graphene nanoribbons.
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75.75.-c Magnetic properties of nanostructures
68.35.Ct Interface structure and roughness
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.40.Mg Numerical simulation studies

Metal-enhanced chemiluminescence from chromium, copper, nickel, and zinc nanodeposits: Evidence for a second enhancement mechanism in metal-enhanced fluorescence

Micah Weisenberg, Yongxia Zhang, and Chris D. Geddes

Appl. Phys. Lett. 97, 133103 (2010); http://dx.doi.org/10.1063/1.3492849 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2010

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Over the past decade metal-fluorophore interactions, metal-enhanced fluorescence, have attracted significant research attention, with the technology now becoming common place in life science applications. In this paper, we address the underlying mechanisms of metal-enhanced fluorescence (MEF) and experimentally show using chemiluminescence solutions that MEF is indeed underpinned by two complimentary mechanisms, consistent with the recent reports by Geddes and co-workers [ Zhang et al., J. Phys. Chem. C 113, 12095 (2009)] and their enhanced fluorescence hypothesis.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
78.66.Bz Metals and metallic alloys
78.60.Ps Chemiluminescence
78.55.Hx Other solid inorganic materials
81.16.-c Methods of micro- and nanofabrication and processing

In situ microscopy of rapidly heated nano-Al and nano-Al/WO3 thermites

Kyle T. Sullivan, Wen-An Chiou, Richard Fiore, and Michael R. Zachariah

Appl. Phys. Lett. 97, 133104 (2010); http://dx.doi.org/10.1063/1.3490752 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2010

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The initiation and reaction mechanism of nano-Al and nano-Al thermites in rapid heating environments is investigated in this work. A semiconductor-based grid/stage was used, capable of in situ heating of a sample from room temperature to 1473 K, and at a rate of 106 K/s, inside an electron microscope. Nano-Al was rapidly heated in a transmission electron microscope, and before and after images indicate that the aluminum migrates through the shell, consistent with a diffusion-based mechanism. A nano-Al/WO3 composite was then heated in a scanning electron microscope. The results indicate that a reactive sintering mechanism is occurring for the nano-Al/WO3 thermite, as the products are found to be in surface contact and significantly deformed after the heating pulse.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
66.30.Pa Diffusion in nanoscale solids
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Resonance frequency shift of a carbon nanotube with a silver nanoparticle adsorbed at various positions

Shau-Chieh Wang, Yuan-Chih Chang, Der-Hsien Lien, Tung Hsu, and Chia-Seng Chang

Appl. Phys. Lett. 97, 133105 (2010); http://dx.doi.org/10.1063/1.3493176 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2010

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We positioned a single silver nanoparticle along the length of a carbon nanotube based resonator, and investigated the resonance frequency shift subject to the particle’s position. We found that a curve derived from the classical continuum model can fit well to our experimental data, implying the applicability of the analytical formula even in the nanometer range. We also used the finite element simulation to elicit the subtle frequency difference caused by the radial angle of nanoparticle’s position in reference to the vibrating plane of the resonator. This effect was found to have an insignificant correction to our measurement.
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68.43.Mn Adsorption kinetics

Frequency shift and attenuation of hypersonic surface acoustic phonons under metallic gratings

Jyothi Sadhu, J. H. Lee, and Sanjiv Sinha

Appl. Phys. Lett. 97, 133106 (2010); http://dx.doi.org/10.1063/1.3493183 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2010

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Using aluminum gratings of varying duty cycles, we report picoseconds acoustics measurements of frequency shift and attenuation in surface acoustic phonons in silicon at ∼ 15 GHz. We observe that the frequency shifts nonlinearly with the duty cycle, particularly in the range of 0.3 to 0.5. The data deviate from the perturbation model as a sinusoidal function of the duty cycle. The attenuation peaks at 0.5 duty cycle which is in good agreement with an eigenmode analysis of the composite structure. This work elucidates the mechanism of surface acoustic phonon scattering at periodic interfaces.
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68.35.Iv Acoustical properties
63.20.-e Phonons in crystal lattices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Tuning the thermal conductivity of graphene nanoribbons by edge passivation and isotope engineering: A molecular dynamics study

Jiuning Hu, Stephen Schiffli, Ajit Vallabhaneni, Xiulin Ruan, and Yong P. Chen

Appl. Phys. Lett. 97, 133107 (2010); http://dx.doi.org/10.1063/1.3491267 (3 pages) | Cited 16 times

Online Publication Date: 28 September 2010

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Using classical molecular dynamics simulation, we have studied the effect of edge-passivation by hydrogen (H-passivation) and isotope mixture (with random or superlattice distributions) on the thermal conductivity of rectangular graphene nanoribbons (GNRs) (of several nanometers in size). We find that the thermal conductivity is considerably reduced by the edge H-passivation. We also find that the isotope mixing can reduce the thermal conductivities, with the superlattice distribution giving rise to more reduction than the random distribution. These results can be useful in nanoscale engineering of thermal transport and heat management using GNRs.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
73.61.Wp Fullerenes and related materials
61.46.-w Structure of nanoscale materials
61.48.Gh Structure of graphene
81.05.ue Graphene
81.65.Rv Passivation

Au nanoparticles on graphitic petal arrays for surface-enhanced Raman spectroscopy

Chandra Sekhar Rout, Anurag Kumar, Guoping Xiong, Joseph Irudayaraj, and Timothy S. Fisher

Appl. Phys. Lett. 97, 133108 (2010); http://dx.doi.org/10.1063/1.3493656 (3 pages) | Cited 9 times

Online Publication Date: 28 September 2010

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We report a unique substrate for surface-enhanced Raman scattering (SERS) based on Au nanoparticle-decorated, thin graphitic petals. The petals were grown on Si substrates by microwave plasma chemical vapor deposition without catalyst, followed by Au nanoparticle decoration on the oxygen plasma-treated petals by electrodeposition. The substrates possess high surface area and sharp nanoscale features that enable high SERS sensitivity to detect 1×10−7 M rhodamine 6G in methanol solution. The obtained SERS enhancement is comparable to the best values reported in the literature and is determined to result from high surface area and increased density of Au nanoparticles on the petal surfaces.
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78.30.Jw Organic compounds, polymers
81.07.Wx Nanopowders
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Pq Electrodeposition, electroplating
81.16.-c Methods of micro- and nanofabrication and processing
52.77.Dq Plasma-based ion implantation and deposition

Microscaled and nanoscaled platinum sensors

Aditya Rajagopal, Sameer Walavalkar, Samson Chen, Luke Guo, Tom Gwinn, and Axel Scherer

Appl. Phys. Lett. 97, 133109 (2010); http://dx.doi.org/10.1063/1.3494088 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2010

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We show small and robust platinum resistive heaters and thermometers that are defined by microlithography on silicon substrates. These devices can be used for a wide range of applications, including thermal sensor arrays, programmable thermal sources, and even incandescent light emitters. To explore the miniaturization of such devices, we have developed microscaled and nanoscaled platinum resistor arrays with wire widths as small as 75 nm, fabricated lithographically to provide highly localized heating and accurate resistance (and hence temperature) measurements. We present some of these potential applications of microfabricated platinum resistors in sensing and spectroscopy.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Preparation of superhydrophobic nanodiamond and cubic boron nitride films

Y. B. Zhou, Y. Yang, W. M. Liu, Q. Ye, B. He, Y. S. Zou, P. F. Wang, X. J. Pan, W. J. Zhang, I. Bello, and S. T. Lee

Appl. Phys. Lett. 97, 133110 (2010); http://dx.doi.org/10.1063/1.3494269 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2010

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Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150° and a sliding angle smaller than 10° were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
68.08.Bc Wetting
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.03.Cd Surface tension and related phenomena

Acoustic microstreaming for droplet breakup in a microflow-focusing device

Yin Nee Cheung and Huihe Qiu

Appl. Phys. Lett. 97, 133111 (2010); http://dx.doi.org/10.1063/1.3495986 (3 pages)

Online Publication Date: 29 September 2010

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This study reports on the breaking up of droplets which can be manipulated with acoustic fields. The oscillation of vortex in a breaking droplet is observed. The droplet size is dependent on the flow-rate combination of the two fluids as well as the frequency and power of the acoustic actuation. Acoustic microstreaming flow is observed in the dispersed phase at the cross-junction of the device. The microstreaming flow causes a stratified vortex flow structure within the dispersed phase. Two stratified vortex centers at the side poles of the droplet are found.
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47.55.df Breakup and coalescence
47.55.Hd Stratified flows
47.32.C- Vortex dynamics
82.70.Kj Emulsions and suspensions
47.55.db Drop and bubble formation

Localized ultraviolet photoresponse in single bent ZnO micro/nanowires

Wen Guo, Ya Yang, Junjie Qi, Jing Zhao, and Yue Zhang

Appl. Phys. Lett. 97, 133112 (2010); http://dx.doi.org/10.1063/1.3495939 (3 pages) | Cited 3 times

Online Publication Date: 30 September 2010

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The localized ultraviolet photoresponse in single bent ZnO micro/nanowires bridging two Ohmic contacts has been investigated. The ZnO micro/nanowire has a higher photoresponse sensitivity of about 190% at the bent region (bending strain: about 4%) than that at the straight region (about 50%). The rise and decay time constants are almost the same in the straight and bent regions of the ZnO micro/nanowire. A possible mechanism has been proposed and discussed. The bent ZnO micro/nanowires could be potentially useful for fabricating the coupled piezoelectric and optoelectronic nanodevices.
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81.07.Gf Nanowires
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors

Surface plasmon beam splitting by the photon tunneling through the plasmonic nanogap

Seung-Yeol Lee, Junghyun Park, Inchul Woo, Namkyoo Park, and Byoungho Lee

Appl. Phys. Lett. 97, 133113 (2010); http://dx.doi.org/10.1063/1.3496012 (3 pages) | Cited 5 times

Online Publication Date: 30 September 2010

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A compact device that splits a surface plasmon beam by using double triangular prisms coated on a metal surface is proposed. Due to the photon tunneling effect of the evanescent plasmon mode between the two plasmonic prisms, the incident plasmon beam from one plasmonic prism can be partially transmitted to the other, resulting in the splitting of the plasmon beam. Theoretical study and simulation results for the power dividing ratio of the device are in good agreement with the experimental demonstration. It is believed that the results show their great potential for the realization of the plasmonic interferometer system.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Bh Lenses, prisms and mirrors
42.70.Jk Polymers and organics
42.79.Wc Optical coatings

Characterization of coupled micro/nanoresonators using inverse eigenvalue analysis

Bhaskar Choubey, Carl Anthony, Nor Hayati Saad, Mike Ward, Ross Turnbull, and Steve Collins

Appl. Phys. Lett. 97, 133114 (2010); http://dx.doi.org/10.1063/1.3491802 (3 pages) | Cited 1 time

Online Publication Date: 1 October 2010

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This paper reports a method of determining the system matrix of a nearest neighbor coupled array of micro/nanomechanical resonators. The simple method requires contacts to only one element of the array to determine two sets of eigenvalues related to the system matrix. The elements of the system matrix are then determined from these eigenvalues. This system matrix can then be used to determine the characteristics of the individual resonators or as the starting point for a perturbation analysis to determine the changes observed when a functionalized array of resonators is used as a sensor.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.Oj Nanoelectromechanical systems (NEMS)
07.10.Cm Micromechanical devices and systems

Effect of metal grain size on multiple microwave resonances of Fe/TiO2 metal-semiconductor composite

Qiang Zhang, Caifu Li, Yanna Chen, Zheng Han, Han Wang, Zhanjie Wang, Dianyu Geng, Wei Liu, and Zhidong Zhang

Appl. Phys. Lett. 97, 133115 (2010); http://dx.doi.org/10.1063/1.3496393 (3 pages) | Cited 6 times

Online Publication Date: 1 October 2010

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The dielectric resonance and multiple magnetic resonances which correspond to multiple microwave absorptions in the 2–18 GHz range have been studied in the composite Fe/TiO2. The Fe grain size is found to have great impact on the dielectric resonance in this metal-semiconductor composite. The polarization mechanism is attributed to interfacial polarization. The multiple magnetic resonances can be ascribed to the natural resonance and exchange resonances, which can be explained by Aharoni’s exchange resonance theory.
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73.40.Ns Metal-nonmetal contacts
78.70.Gq Microwave and radio-frequency interactions
77.22.Ej Polarization and depolarization

Recombination dynamics in ZnO nanowires: Surfaces states versus mode quality factor

J. S. Reparaz, F. Güell, M. R. Wagner, G. Callsen, R. Kirste, S. Claramunt, J. R. Morante, and A. Hoffmann

Appl. Phys. Lett. 97, 133116 (2010); http://dx.doi.org/10.1063/1.3496444 (3 pages) | Cited 2 times

Online Publication Date: 1 October 2010

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In this work, we investigate the influence of finite size on the recombinations dynamics of ZnO nanowires. We demonstrate that diameter as well as length of nanowires determine the lifetime of the neutral donor bound excitons. Our findings suggest that while the length is mainly responsible for different mode quality factors of the cavity-like nanowires, the diameter determines the influence of surface states as alternative recombinations channels for the optical modes trapped in the nanocavity. In addition, comparing nanowires grown using different catalyst we show that the surfaces states strongly depend on each precursor characteristics.
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81.07.Gf Nanowires
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.67.Uh Nanowires
73.20.At Surface states, band structure, electron density of states
78.68.+m Optical properties of surfaces

Mechanically-exfoliated stacks of thin films of Bi2Te3 topological insulators with enhanced thermoelectric performance

V. Goyal, D. Teweldebrhan, and A. A. Balandin

Appl. Phys. Lett. 97, 133117 (2010); http://dx.doi.org/10.1063/1.3494529 (3 pages) | Cited 32 times

Online Publication Date: 1 October 2010

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The authors report on “graphene-like” mechanical exfoliation of single-crystal Bi2Te3 films and thermoelectric characterization of the stacks of such films. Thermal conductivity of the resulting “pseudosuperlattices” was measured by the “hot disk” and “laser flash” techniques. The room temperature in-plane (cross-plane) thermal conductivity of the stacks decreases by a factor of ∼ 2.4 (3.5) as compared to bulk. The thermal conductivity reduction with preserved electrical properties leads to strong increase in the thermoelectric figure of merit. It is suggested that the film thinning to few-quintuples and tuning of the Fermi level can help in achieving the topological-insulator surface transport regime with an extraordinary thermoelectric efficiency.
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73.50.Lw Thermoelectric effects
72.20.Pa Thermoelectric and thermomagnetic effects
68.65.Cd Superlattices
73.61.Le Other inorganic semiconductors
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