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22 Oct 2012

Volume 101, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 101, 171101 (2012); http://dx.doi.org/10.1063/1.4758996 (4 pages)

Wolfram H. P. Pernice and Harish Bhaskaran
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Temperature-dependent mechanical-resonance frequencies and damping in ensembles of gallium nitride nanowires

J. R. Montague, K. A. Bertness, N. A. Sanford, V. M. Bright, and C. T. Rogers

Appl. Phys. Lett. 101, 173101 (2012); http://dx.doi.org/10.1063/1.4761946 (5 pages)

Online Publication Date: 22 October 2012

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We have measured singly clamped cantilever mechanical-resonances in ensembles of as-grown gallium nitride nanowires (GaN NWs), from 12 K to 320 K. Resonance frequencies are approximately linearly dependent on temperature near 300 K with relative shifts of 40 ± 20 ppm/K, consistent with temperature-dependent elastic moduli. Below 100 K, we find that some GaN NWs have mechanical quality factors well above 400 000, at mechanical resonance frequencies near 1 MHz. We also observe a correlation between increased amplitude of dissipation and increased temperature dependence of resonance frequencies. The microwave homodyne detection technique we use is simple, allows for the investigation of as-grown or processed NWs, and is sensitive enough to observe the thermal motion of individual NWs while providing for the simultaneous measurement of large ensembles of NW mechanical resonances.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
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)
81.07.Gf Nanowires

Ordered graphene strips onto polymer backing prepared by laser scanning

O. Lyutakov, I. Huttel, J. Tuma, M. Kalbac, M. Janousek, P. Šimek, and V. Svorcik

Appl. Phys. Lett. 101, 173102 (2012); http://dx.doi.org/10.1063/1.4762817 (4 pages)

Online Publication Date: 22 October 2012

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The preparation of ordered array of graphene strips with arc lateral shape on graphene layer is described. In the next step, porphyrine doped polymer film was deposited onto graphene and the substrate was dissolved and the graphene film was revealed. Polymer film was modified by scanning laser beam and simultaneous mechanical movement of the sample. The creation of graphene ordered strips relies on graphene cutting due to polymer substrate distortion. Creation of ordered graphene strips was proved by scanning tunneling microscopy measurement. The method makes possible the creation of micro- and nano-ordered graphene strips.
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68.55.A- Nucleation and growth
42.62.-b Laser applications
68.65.Pq Graphene films
81.05.ue Graphene

Synthesis and local electrical characterization of ZnO microwalls grown on cracked GaN/Si(111) by aqueous method

Naisen Yu, Yunfeng Wu, Lifang Du, Haiying Du, Zhangwen Mao, Danyang Hu, Yong Wang, and Xueliang Zhu

Appl. Phys. Lett. 101, 173103 (2012); http://dx.doi.org/10.1063/1.4762824 (5 pages)

Online Publication Date: 22 October 2012

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ZnO microwalls have been grown on cracked GaN/Si(111) using aqueous method. The cracks of GaN direct ZnO grow and form two-dimensional microwall networks. Electrical characterization of individual upright standing ZnO microwall was performed by using conductive atomic force microscopy. Enhanced conductivity for the off-axis facet plane present on as-grown ZnO microwalls has been detected. Meanwhile, the local current-voltage characteristics shows that the sidewall has lower Schottky barrier height, it indicated that the off-axis sidewalls planes are more electrically active than c-plane ZnO. Furthermore, it will also provide a unique structure for surface-related applications, such as sensing, catalyzing, energy harvesting, etc.
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72.20.-i Conductivity phenomena in semiconductors and insulators
72.80.Ey III-V and II-VI semiconductors
81.10.Dn Growth from solutions
73.30.+y Surface double layers, Schottky barriers, and work functions

Oxygen plasma post process to obtain consistent conductance of carbon nanotubes in carbon nanotube field-effect transistors

Chi Woong Jang, Young Tae Byun, Deok Ha Woo, Seok Lee, and Young Min Jhon

Appl. Phys. Lett. 101, 173104 (2012); http://dx.doi.org/10.1063/1.4762829 (4 pages) | Cited 1 time

Online Publication Date: 22 October 2012

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We modified the conductance of carbon nanotubes (CNTs) in carbon nanotube field-effect transistors by oxygen plasma post process (OPPP) to obtain consistent conductance after the CNTs were adsorbed by self-assembly monolayer method which is suitable for large scale mass production but hardly yields consistent conductance due to various complex factors involved. We have shown that the conductance of the CNTs can be tuned from 47 μS to zero by varying the OPPP time from 0 to 15 s. The reduction rate of the conductance was 9.8%/s implying that a tenth of the CNTs was removed every second.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices
73.63.Fg Nanotubes
68.43.Mn Adsorption kinetics

An “edge to edge” jigsaw-puzzle two-dimensional vapor-phase transport growth of high-quality large-area wurtzite-type ZnO (0001) nanohexagons

Jian-Min Li, Long-Gui Dai, Xiao-Ping Wan, and Xian-Lin Zeng

Appl. Phys. Lett. 101, 173105 (2012); http://dx.doi.org/10.1063/1.4761942 (5 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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The authors reported the synthesis of large but thin transparent regularly shaped single-crystalline zinc oxide (ZnO) (0001) hexagonal nanodisks (or nanohexagons) (the most probable area scale of 95 μm2 and 40–70 nm in thickness) by an indium assisted vapor-phase transport (VPT) growth route at ambient pressure. These large-area ZnO nanohexagons exhibit excellent luminescent properties with a strong ultraviolet emission band centered at about 384 nm and a very weak green band shoulder emission, leading to the further creation of a promising low-defect-concentration nanohexagons-based nanooptoelectronics. Finally, a two-dimensional VPT growth mechanism was proposed to understand the formation of high-quality wurtzite-type ZnO nanohexagons.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Why have not the hairs on the feet of gecko been smaller?

Yewang Su, Shijie He, Keh-Chih Hwang, and Baohua Ji

Appl. Phys. Lett. 101, 173106 (2012); http://dx.doi.org/10.1063/1.4762822 (4 pages)

Online Publication Date: 23 October 2012

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The nanometer size of the tiny hair is the key to the secret of strong stickiness of gecko's feet, by which the hair can achieve the maximum adhesion strength that is insensitive to the interfacial flaws with substrate surface. But the question why the hairs have not been smaller is not answered yet. In this study, we derived a geometric parameter of the surface structures considering lateral interaction among hairs, which gives a critical size below which these hairs will bunch together and cause failure of the adhesion, suggesting a lower limit of the dimension of hairs on gecko's feet.
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87.19.rm Structure

Enhanced field emission from large scale uniform monolayer graphene supported by well-aligned ZnO nanowire arrays

Zhicheng Yang, Qing Zhao, Yongxi Ou, Wei Wang, Heng Li, and Dapeng Yu

Appl. Phys. Lett. 101, 173107 (2012); http://dx.doi.org/10.1063/1.4763474 (5 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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Large scale, uniform single-layer graphene was transferred onto well-aligned ZnO nanowire arrays to produce high density nanoscale protrusions within graphene for efficient field emission. Polymethyl methacrylate (PMMA) was used as a supporting layer to provide a quasi-flat surface for graphene transfer. Highly efficient (maximum current density of ∼500 μA/cm2) and stable field emission with low turn-on fields (5.4 V/μm) was observed due to highly localized electric field, which is much better than those without using PMMA. F-N plot showed an unique up-bending feature of single-layer graphene. Our approach provides an efficient way to produce high quality single-layer graphene field emitters.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.21.Hb Quantum wires
73.61.Wp Fullerenes and related materials

CdSe quantum dots-poly(3-hexylthiophene) nanocomposite sensors for selective chloroform vapor detection at room temperature

S. P. Mondal, S. Bera, G. Narender, and S. K. Ray

Appl. Phys. Lett. 101, 173108 (2012); http://dx.doi.org/10.1063/1.4762861 (4 pages) | Cited 1 time

Online Publication Date: 24 October 2012

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Olive oil capped CdSe quantum dots (QDs) of average size ∼6 nm have been grown by a green chemical route synthesis for the fabrication of nanocomposite organic vapor sensing devices. A highly selective, room temperature chloroform vapor sensor has been fabricated using capped CdSe QDs and conducting polymer [poly(3-hexylthiophene)] nanocomposites. The nanocomposite sensor has been tested with the choloroform vapor of concentration varying from 100-1200 ppm at room temperature using different bias voltages. The recovery time of the sensor has been found to be improved on illumination with a monochromatic light of 600 nm, due to the photo-induced enhancement of charge transfer in nanocomposites.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.16.-c Methods of micro- and nanofabrication and processing

Controllable aggregates of silver nanoparticle induced by methanol for surface-enhanced Raman scattering

Zhiliang Zhang and Yongqiang Wen

Appl. Phys. Lett. 101, 173109 (2012); http://dx.doi.org/10.1063/1.4764024 (4 pages)

Online Publication Date: 24 October 2012

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In this work, a series of highly sensitive surface-enhanced Raman scattering substrates have been achieved based on the controllable aggregation of silver nanoparticles. In such system, hexadecylamine-capped silver nanoparticles were ink-jet printed on glass substrates and subsequently dipped into methanol solution. An aggregation was induced due to preferential dissolution of hexadecylamine into methanol and partial removal of the protective layers on silver nanoparticle surfaces, which exhibited stable and controllable Raman enhancement effect. This strategy could be further extended to construct various chemical and biological functional sensors.
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81.16.-c Methods of micro- and nanofabrication and processing
78.40.Kc Metals, semimetals, and alloys
78.30.Er Solid metals and alloys
78.68.+m Optical properties of surfaces
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Microcantilever Q control via capacitive coupling

Magdalena Huefner, Adam Pivonka, Jeehoon Kim, Cun Ye, Martin A. Blood-Forsythe, Martin Zech, and Jennifer E. Hoffman

Appl. Phys. Lett. 101, 173110 (2012); http://dx.doi.org/10.1063/1.4764025 (4 pages)

Online Publication Date: 24 October 2012

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We introduce a versatile method to control the quality factor Q of a conducting cantilever in an atomic force microscope (AFM) via capacitive coupling to the local environment. Using this method, Q may be reversibly tuned to within ∼ 10% of any desired value over several orders of magnitude. A point-mass oscillator model describes the measured effect. Our simple Q control module increases the AFM functionality by allowing greater control of parameters such as scan speed and force gradient sensitivity, which we demonstrate by topographic imaging of a VO2 thin film in high vacuum.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
07.10.Cm Micromechanical devices and systems
84.30.Ng Oscillators, pulse generators, and function generators

The compressibility of nanocrystalline Pt

A. S. Mikheykin, V. P. Dmitriev, S. V. Chagovets, A. B. Kuriganova, N. V. Smirnova, and I. N. Leontyev

Appl. Phys. Lett. 101, 173111 (2012); http://dx.doi.org/10.1063/1.4758000 (4 pages)

Online Publication Date: 25 October 2012

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High-pressure behavior of carbon supported Pt nanoparticles (Pt/C) with an average particle size of 10.6 nm was investigated by in situ high-pressure synchrotron radiation x-ray diffraction up to 14 GPa at ambient temperature. Our results show that the compressibility of Pt/C nanoparticles decreases substantially as the particle size decreases. An interpretation based upon the available mechanisms of structural compliance in nanoscale vs bulk materials was proposed.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

An optical leveling technique for parallel near-field photolithography system

Zhuming Liu, Xinyong Chen, Yuan Zhang, John Weaver, and Clive J. Roberts

Appl. Phys. Lett. 101, 173112 (2012); http://dx.doi.org/10.1063/1.4764912 (4 pages)

Online Publication Date: 25 October 2012

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An optical leveling technique is reported for a compact parallel (multi-cantilever) scanning near-field photolithography (SNP) prototype. This instrument operates in liquid and was designed to overcome the challenge of low sample throughput of previous serial scanning SNPs. A combination of zone plate lens array, probe array, and standard atomic force microscope feedback technique are employed to deliver parallel probe operation in the current SNP. Compared to the commonly used two-end or multi-end “force feedback” alignment techniques, the optical levelling technique applied provides a simple solution to maintaining all levers in an array within the near-field region. As a proof-of-principle experiment, the operation of the prototype was demonstrated by producing nano-scale patterns in parallel using scanning near-field photolithography.
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85.40.Hp Lithography, masks and pattern transfer

Role of surface charge, morphology, and adsorbed moieties on thermal conductivity enhancement of nanofluids

S. Anbumozhi Angayarkanni and John Philip

Appl. Phys. Lett. 101, 173113 (2012); http://dx.doi.org/10.1063/1.4764050 (4 pages)

Online Publication Date: 25 October 2012

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The role of surface charge, morphology, and adsorbed moieties on thermal conductivity is studied using soft micellar systems and alumina nanofluids of size varying from 2.5 to 30 nm. The thermal conductivity of soft systems of different sizes, surface charges, and morphologies is found to follow effective medium theory of poor thermal conductors. It is observed that the adsorption of surface active moieties on alumina nanoparticles does not lower the enhanced thermal conductivity of nanofluids but significantly enhances the stability and dispersibility of nanomaterials. Further, the cationic and non-ionic surfactants provide optimal thermal to rheological property enhancements.
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68.43.Mn Adsorption kinetics
68.03.Fg Evaporation and condensation of liquids
66.25.+g Thermal conduction in nonmetallic liquids

Highly enhanced Raman scattering from coupled vertical silicon nanowire arrays

M. Khorasaninejad, N. Dhindsa, J. Walia, S. Patchett, and S. S. Saini

Appl. Phys. Lett. 101, 173114 (2012); http://dx.doi.org/10.1063/1.4764057 (5 pages) | Cited 1 time

Online Publication Date: 25 October 2012

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Vertical silicon nanowire (SiNW) arrays were fabricated in square lattices with varying diameters, pitches, and lengths, in order to investigate the effects on Raman scattering enhancement. An increase in absolute intensity of the 520 cm−1 vibrational mode by a factor of 15 was achieved for 1.1 μm long SiNWs with diameter of 115 nm arranged 400 nm apart. An oscillatory behaviour in the Raman intensity was also observed with increasing diameter, which is a result of constructive and destructive interferences within the array. A maximum Raman enhancement per unit volume (REV) of 838 was achieved for 115 nm diameter SiNWs with a length of 1.1 μm. The experimental REV results were supported and modelled quantitatively using finite difference time domain simulations.
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81.05.Cy Elemental semiconductors
78.67.Uh Nanowires
78.30.Am Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.-c Methods of micro- and nanofabrication and processing

Superelastic memory effect in in-situ NbTi-nanowire-NiTi nanocomposite

Shijie Hao, Lishan Cui, Daqiang Jiang, Yandong Wang, Xiaobing Shi, Jiang Jiang, Dennis E. Brown, and Yang Ren

Appl. Phys. Lett. 101, 173115 (2012); http://dx.doi.org/10.1063/1.4764538 (3 pages)

Online Publication Date: 26 October 2012

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An in-situ NbTi-nanowire-NiTi composite wire fabricated by conventional metallurgical processing has the remarkable ability of remembering its previous stress/strain states where it was unloaded during multiple-step cyclic loading. In situ synchrotron x-ray diffraction studies revealed that an interactive stress between NbTi nanowires and NiTi matrix was introduced and retained after a load/unload cycle due to their strain mismatch. The different levels of interactive stress in different regions of the specimen resulted in a superelastic memory effect. Furthermore, the final loading curve could remember all previous loading histories, which may be of use in practical applications.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
62.23.Pq Composites (nanosystems embedded in a larger structure)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.Rf Micro- and nanoscale pattern formation
81.40.Jj Elasticity and anelasticity, stress-strain relations

Temperature dependence of reversible switch-memory in electron field emission from ultrananocrystalline diamond

M. Tordjman, A. Bolker, C. Saguy, and R. Kalish

Appl. Phys. Lett. 101, 173116 (2012); http://dx.doi.org/10.1063/1.4764907 (4 pages)

Online Publication Date: 26 October 2012

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Temperature dependence of reversible hysteretic switching in electron field emission from surface transfer doped ultrananocrystalline diamond (UNCD) thin films is reported. Sharp jumps (up to 3 orders of magnitude) of the current, at specific ramp up and down extracting electric field values, are found. The memory-window, i.e., hysteresis widths, of the emitted current is controllable by heating (50 °C to 250 °C). The temperature dependence of the hysteresis is explained as being due to conductivity properties of the transfer doped UNCD film namely, by the electrons supply to emission sites. These results may find application in memory-switch devices with tunable properties.
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73.25.+i Surface conductivity and carrier phenomena
73.61.Wp Fullerenes and related materials
79.70.+q Field emission, ionization, evaporation, and desorption
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth
81.05.ug Diamond
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