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6 Aug 2012

Volume 101, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang
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Scanning gate microscopy on a graphene nanoribbon

Nikola Pascher, Dominik Bischoff, Thomas Ihn, and Klaus Ensslin

Appl. Phys. Lett. 101, 063101 (2012); http://dx.doi.org/10.1063/1.4742862 (4 pages)

Online Publication Date: 6 August 2012

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The metallic tip of a scanning probe microscope operated at a temperature of 1.7 K is used to locally induce a potential in a graphene nanoribbon. Images of the conductance through the device as a function of tip-position show that two centers of enhanced conductance are formed inside the structure. By applying a linescan-technique, it can be demonstrated that these two features correspond to two charge localizations, exhibiting the characteristics of quantum dots. Scanning gate microscopy allows us to characterize them with high resolution both in real space and as a function of energy.
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73.21.La Quantum dots
07.79.-v Scanning probe microscopes and components
61.46.-w Structure of nanoscale materials
68.37.-d Microscopy of surfaces, interfaces, and thin films

An electromechanical membrane resonator

D. Hatanaka, I. Mahboob, H. Okamoto, K. Onomitsu, and H. Yamaguchi

Appl. Phys. Lett. 101, 063102 (2012); http://dx.doi.org/10.1063/1.4742868 (5 pages)

Online Publication Date: 6 August 2012

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An electrically active membrane-based mechanical resonator was fabricated from a GaAs/AlGaAs heterostructure. The mechanical motion of the membrane was piezoelectrically excited and detected. The piezoelectric transducer could also excite a range of resonance modes in the membrane that were identified and mapped via optical interferometry. Furthermore, the various mode shapes combined with the piezoelectric transduction could be used to execute mechanical-logic-gates. The development of an electrically active membrane-based mechanical resonator paves the way towards responsive electromechanical detectors and highly functional opto-electro-mechanical systems.
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84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Largely enhanced photocurrent via gap-mode plasmon resonance by a nanocomposite layer of silver nanoparticles and porphyrin derivatives fabricated on an electrode

Katsuhiko Kanaizuka, Shigeta Yagyu, Manabu Ishizaki, Hiroki Kon, Takanari Togashi, Masatomi Sakamoto, and Masato Kurihara

Appl. Phys. Lett. 101, 063103 (2012); http://dx.doi.org/10.1063/1.4742870 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Photocurrent generation efficiency via the photoactive dyes, porphyrins, was strongly enhanced by construction of a nanocomposite structure, which consists of an undercoat layer of (3-mercaptopropyl)trimethoxysilane and densely and homogeneously attached silver nanoparticles on an electrode. The employed 5 -(4-carboxyphenyl)-10,15,20-triphenylporphyrins, 1, were embedded on the silver nanoparticle surface through their carboxylate moiety. The photo-absorption of 1 was significantly influenced by normal and gap-mode plasmon bands. The photocurrent of the nanocomposite structure was more strongly enhanced via the Q band excitation of 1, overlapped with the gap-mode plasmon band in the absorption wavelength range, and also showed stable photocurrent.
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72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
81.16.-c Methods of micro- and nanofabrication and processing
82.45.-h Electrochemistry and electrophoresis
61.46.-w Structure of nanoscale materials
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Resistive switching and activity-dependent modifications in Ni-doped graphene oxide thin films

S. Pinto, R. Krishna, C. Dias, G. Pimentel, G. N. P. Oliveira, J. M. Teixeira, P. Aguiar, E. Titus, J. Gracio, J. Ventura, and J. P. Araujo

Appl. Phys. Lett. 101, 063104 (2012); http://dx.doi.org/10.1063/1.4742912 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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The resistive switching (RS) mechanism in Ni-doped graphene oxide (GO) devices is studied. We found that RS depends strongly on the fabrication method of the GO sheet and on the electrode material. Resistive switching in GO-devices can be caused by the diffusion of ions from metallic electrode or by the migration of oxygen groups, depending on the fabrication process. We also show that GO-based structures possess activity-dependent modification capabilities, emphasized by the increase/decrease of device conductance after consecutive voltage sweeps of opposite polarity. Our results allow a better understanding of bipolar RS, towards future non-volatile memories and neuromorphic systems.
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85.65.+h Molecular electronic devices
73.61.Wp Fullerenes and related materials

Self-assembly of single dielectric nanoparticle layers and integration in polymer-based solar cells

Jonathan E. Allen, Biswajit Ray, M. Ryyan Khan, Kevin G. Yager, Muhammad A. Alam, and Charles T. Black

Appl. Phys. Lett. 101, 063105 (2012); http://dx.doi.org/10.1063/1.4744928 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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A single, self-assembled layer of highly uniform dielectric alumina nanoparticles improves the photovoltaic performance of organic semiconductor bulk heterojunction solar cells. The block copolymer based self-assembly approach is readily amenable to the large areas required for solar cell fabrication. A fraction of the performance gain results from incident light scattering which increases active layer absorption and photocurrent output, consistent with device simulations. The nanoparticle layer also roughens the device electrode surface, increasing contact area and improving device fill factor through more efficient charge collection.
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81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
85.30.De Semiconductor-device characterization, design, and modeling
88.40.hj Efficiency and performance of solar cells
88.40.jr Organic photovoltaics
72.40.+w Photoconduction and photovoltaic effects

Ion dynamics at porous alumina surfaces

Shinnosuke Hattori, Rajiv K. Kalia, Aiichiro Nakano, Ken-ichi Nomura, and Priya Vashishta

Appl. Phys. Lett. 101, 063106 (2012); http://dx.doi.org/10.1063/1.4742869 (4 pages)

Online Publication Date: 7 August 2012

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Anodic porous alumina has broad applications for fabricating self-assembled nanostructures, for which atomistic understanding of ionic transport at pore surfaces is indispensable. Here, molecular-dynamics simulation of amorphous alumina with a cylindrical pore under electric field shows correlated anion (oxygen)-cation (aluminum) transport at the pore surface, as opposed to ordinary drift motion in the bulk. In particular, this phenomenon leads to “inverted” cation transport at the surface. Detailed analyses of simulation data reveal atomistic mechanisms of the correlated transport based on surface-structural relaxation and covalent oxygen-aluminum bond networks. These transport mechanisms have significant implications for alumina anodization processes.
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66.30.Dn Theory of diffusion and ionic conduction in solids
61.43.Bn Structural modeling: serial-addition models, computer simulation
61.43.Gt Powders, porous materials

Influence of the magnetic field on the plasmonic properties of transparent Ni anti-dot arrays

Emil Melander, Erik Östman, Janine Keller, Jan Schmidt, Evangelos Th. Papaioannou, Vassilios Kapaklis, Unnar B. Arnalds, B. Caballero, A. García-Martín, J. C. Cuevas, and Björgvin Hjörvarsson

Appl. Phys. Lett. 101, 063107 (2012); http://dx.doi.org/10.1063/1.4742931 (4 pages) | Cited 1 time

Online Publication Date: 7 August 2012

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Extraordinary optical transmission is observed due to the excitation of surface plasmon polaritons in 2-dimensional hexagonal anti-dot patterns of pure Ni thin films, grown on sapphire substrates. A strong enhancement of the polar Kerr rotation is recorded at the surface plasmon related transmission maximum. Angular resolved reflectivity measurements under an applied field reveal an enhancement and a shift of the normalized reflectivity difference upon reversal of the magnetic saturation (transverse magneto-optical Kerr effect-TMOKE). The change of the TMOKE signal clearly shows the magnetic field modulation of the dispersion relation of SPPs launched in a 2D patterned ferromagnetic Ni film.
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81.05.Bx Metals, semimetals, and alloys
81.07.Ta Quantum dots
73.21.La Quantum dots
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
78.67.Hc Quantum dots

Four-dimensional spectral low-loss energy-filtered transmission electron tomography of silicon nanowire-based capacitors

G. Haberfehlner, P. Bayle-Guillemaud, G. Audoit, D. Lafond, P. H. Morel, V. Jousseaume, T. Ernst, and P. Bleuet

Appl. Phys. Lett. 101, 063108 (2012); http://dx.doi.org/10.1063/1.4742932 (4 pages)

Online Publication Date: 7 August 2012

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We show the potential of low-loss energy filtered transmission electron microscopy combined with tomography for four-dimensional structural characterization of nanowire-based capacitors. This method allows reconstructing local low-loss spectra within the whole device giving access to the chemical distribution. We used this capability to extract information about plasmon peaks from the different materials within the nanowire leading to the reconstruction of a three-dimensional model of the device. Additionally, the reconstructed low-loss spectra are compared to spectra acquired in classical two-dimensional scanning geometries across the whole nanowire and across a thin focused ion beam-prepared lamella of the nanowire.
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84.32.Tt Capacitors

Orientation-dependent friction between a carbon nanotube and graphite

W.-C. Chang, W.-C. Lai, H.-S. Liao, S. C. Wang, M. S. Ho, K.-Y. Huang, L. J. Chen, and C. S. Chang

Appl. Phys. Lett. 101, 063109 (2012); http://dx.doi.org/10.1063/1.4744576 (3 pages)

Online Publication Date: 7 August 2012

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We performed experiments to measure the friction force against the relative orientation between the carbon nanotube probe and graphite substrate. As the sample stage revolved one full circle, six sharp peaks were registered and each separated by 60°. Furthermore, these six peaks formed into three pairs, exhibiting the threefold symmetry, which can be explained with contribution beyond the top layer of the graphite. Yet, due to the prominent layer structure of the graphite, the energy loss caused by friction was dissipated mostly through its top layer.
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81.05.uf Graphite
62.20.Qp Friction, tribology, and hardness
81.07.De Nanotubes
81.40.Pq Friction, lubrication, and wear

Ultra-high current density carbon nanotube field emitter structure on three-dimensional micro-channeled copper

Indranil Lahiri, Joyce Wong, Zilu Zhou, and Wonbong Choi

Appl. Phys. Lett. 101, 063110 (2012); http://dx.doi.org/10.1063/1.4745010 (5 pages)

Online Publication Date: 7 August 2012

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High-current field emitter with extended stability has been focus of many researchers, which can be fulfilled by application of engineered nanomaterials and beneficial design. In the present research, such a field emitter is designed and fabricated, involving growth of interface controlled carbon nanotubes along micro-channels of 3-dimensional copper template. The emitter offers very high emission current density (270 mA/cm2, peak), low turn-on field (1.1 V/μm), moderate threshold field (1.69 V/μm), emission stability for extended operation, and excellent resistance to structural damage. Higher conductivity of Cu, lower interfacial resistance, strong interfacial bonding, and unique 3-dimensional design leads to such 23-27 times higher current density, providing a potential approach to field emission devices.
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85.35.Kt Nanotube devices
79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes

Local-strain mapping on Ag(111) islands on Nb(110)

T. Tomanic, C. Sürgers, R. Heid, M. Alcántara Ortigoza, K.-P. Bohnen, D. Stöffler, and H. v. Löhneysen

Appl. Phys. Lett. 101, 063111 (2012); http://dx.doi.org/10.1063/1.4745011 (4 pages)

Online Publication Date: 7 August 2012

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The local in-plane strain of Ag(111) islands on the Nb(110) surface has been derived from the lateral variation of the electronic density of states measured by scanning tunneling spectroscopy. The onset energy Ess of the Shockley-type surface-state band is shifted to higher energies compared to the bulk due to thermal strain arising from the difference in thermal expansion between Nb and Ag and cooling by 565 K. A quantitative dependence of Ess from the strain is obtained by density-functional theory calculations. This allows a mapping of the local strain of individual Ag islands on the nanometer scale.
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73.20.-r Electron states at surfaces and interfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Ultra-sensitive strain sensors based on piezoresistive nanographene films

Jing Zhao, Congli He, Rong Yang, Zhiwen Shi, Meng Cheng, Wei Yang, Guibai Xie, Duoming Wang, Dongxia Shi, and Guangyu Zhang

Appl. Phys. Lett. 101, 063112 (2012); http://dx.doi.org/10.1063/1.4742331 (5 pages) | Cited 3 times

Online Publication Date: 7 August 2012

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Graphene shows promise on strain sensor applications, but the piezoresistive sensitivity of perfect graphene is low due to its weak electrical conductivity response upon structural deformation. In this paper, we used nanographene films for ultra-sensitive strain sensors. The piezoresistive sensitivity of nanographene films with different thicknesses and conductivities was systematically investigated and a nearly inverse proportional correlation was found. A gauge factor over 300, the highest so far for graphene-based strain sensors, was achieved. A charge tunneling model was used to explain the piezoresistive characteristics of nanographene films, which indicates our results provide a different rout toward ultra-sensitive strain sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Pz Instruments for strain, force, and torque
46.80.+j Measurement methods and techniques in continuum mechanics of solids
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Transfer printing of flexible hybrid inductor-capacitor filters via pre-etched silicon-on-insulator mother wafer

Liang Pang, Hui-Chan Seo, and Kyekyoon (Kevin) Kim

Appl. Phys. Lett. 101, 063113 (2012); http://dx.doi.org/10.1063/1.4742341 (4 pages) | Cited 1 time

Online Publication Date: 7 August 2012

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An approach for the processing of flexible electronics is presented. To protect the functional insulator in the structure, hybrid inductor-capacitor (LC) filters were fabricated on the pre-etched silicon-on-insulator wafer, where the selectively patterned semi-stable Si-supporting membranes were sufficiently robust to support the entire device fabrication process, yet flexible enough to facilitate the subsequent transfer printing via adhesive stamp. When the LC filters were transferred to an elastomeric substrate, 20% compressibility was achieved, giving rise to “wavy” deformation of the devices and up to 9% variation in the electronic properties. Beyond the 20% strain, local delamination of the films resulted in mechanical instability.
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84.30.Vn Filters
84.32.Hh Inductors and coils; wiring
84.32.Tt Capacitors

Eliminating the fine structure splitting of excitons in self-assembled InAs/GaAs quantum dots via combined stresses

Jianping Wang, Ming Gong, Guang-Can Guo, and Lixin He

Appl. Phys. Lett. 101, 063114 (2012); http://dx.doi.org/10.1063/1.4745188 (4 pages) | Cited 1 time

Online Publication Date: 8 August 2012

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Eliminating the fine structure splitting (FSS) of excitons in self-assembled quantum dots (QDs) is essential to the generation of high quality entangled photon pairs. It has been shown that the FSS has a lower bound under uniaxial stress. In this letter, we show by a extended two-level model that the FSS of excitons in a general self-assembled InGaAs/GaAs QD can be fully suppressed via combined stresses along the [110] and [010] directions. The results of the model Hamiltonian are confirmed by atomic empirical pseudopotential calculations. For all the QDs we calculated, the FSS can be tuned to be vanishingly small (<0.1 μeV), which is sufficient small for high quality entangled photon emission.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
03.67.Bg Entanglement production and manipulation
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.35.-y Excitons and related phenomena
73.21.La Quantum dots

Optimization of nanotube thermal interconnects for near-field radiative heat transport

Andrei Nemilentsau and Slava V. Rotkin

Appl. Phys. Lett. 101, 063115 (2012); http://dx.doi.org/10.1063/1.4745202 (4 pages)

Online Publication Date: 8 August 2012

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Near-field radiative heat transfer between vertical single-wall nanotube (SWNT) forest and different substrates was computed using experimental parametrization for dielectric response of α-quartz, α-sapphire, GaAs, 6H-BN, h-SiC, Au, Ag, Al, Ni, Ti, Cu materials. Rational choice of material and optical matching at the interface allow one to achieve maximum near-field Kapitza conductance of the SWNT forest exceeding 60  MW/(K m2) on polar dielectrics at 300 K. Such an efficient thermal coupling is due to the near-field overlap of surface polaritons of the substrate and SWNT plasmons, further enhanced by tweaking the forest thickness.
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85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation

Electron beam induced current in InSb-InAs nanowire type-III heterostructures

C. Y. Chen, A. Shik, A. Pitanti, A. Tredicucci, D. Ercolani, L. Sorba, F. Beltram, and H. E. Ruda

Appl. Phys. Lett. 101, 063116 (2012); http://dx.doi.org/10.1063/1.4745603 (3 pages) | Cited 2 times

Online Publication Date: 9 August 2012

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InSb-InAs nanowire heterostructure diodes investigated by electron beam induced current (EBIC) demonstrate an unusual spatial profile where the sign of the EBIC signal changes in the vicinity of the heterointerface. A qualitative explanation confirmed by theoretical calculations is based on the specific band diagram of the structure representing a type-III heterojunction with an accumulation layer in InAs. The sign of the EBIC signal depends on the specific parameters of this layer. In the course of measurements, the diffusion length of holes in InAs and its temperature dependence are also determined.
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85.30.Kk Junction diodes

Molecular resolution of a dioleoyl-Sn-glycero-phosphocholine lipid bilayer in liquid by phase modulation atomic force microscopy

Antonin Hoel, Toshihisa Osaki, Shoji Takeuchi, Sebastian Volz, and Hideki Kawakatsu

Appl. Phys. Lett. 101, 063117 (2012); http://dx.doi.org/10.1063/1.4745184 (3 pages)

Online Publication Date: 9 August 2012

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We present a molecular resolved image of a supported lipid bilayer using atomic force microscopy in liquid conditions. Due to the well-known molecular diffusion processes with velocities of a few nm/s occurring in free-standing membranes, this type of mapping is difficult to achieve. We have obtained a sub-nanometer scale resolution of a dioleoyl-sn-glycero-phosphocholine membrane because of the high sensitivity of our phase modulated microscope and the slowed down diffusion due to the interaction with the substrate. A pair function analysis has revealed local disordered and gel phases with an order range limited to the first neighbour.
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87.16.D- Membranes, bilayers, and vesicles
82.70.Gg Gels and sols
87.14.Cc Lipids
87.15.Vv Diffusion

Stabilization of gold doped single-walled carbon nanotube film by electropolymerization

Hyungduk Yun and Sanghyo Kim

Appl. Phys. Lett. 101, 063118 (2012); http://dx.doi.org/10.1063/1.4745198 (4 pages)

Online Publication Date: 9 August 2012

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We report poly(3,4-ethylenedioxythiophene) (PEDOT) as a conducting polymer useful for stabilizing gold chloride (HAuCl4)-doped single-walled carbon nanotube (SWCNT) film. A specific area was sprayed with SWCNT on a polyethylene terephthalate substrate supported by a slide glass, followed by HAuCl4 doping. The SWCNT film was electropolymerized with 3,4-ethylenedioxythiophene (EDOT). Transparency of 91% at 550 nm wavelength with 150 Ω/sq of sheet resistance was achieved with this method. Unlike general AuCl3 doped SWCNT film, the sheet resistance remained stable for up to 4 months. The electropolymerization of PEDOT on the doped film could eliminate the hygroscopic effects through the redox reaction between EDOT and gold chloride salts.
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78.67.Ch Nanotubes
82.30.-b Specific chemical reactions; reaction mechanisms
82.35.Cd Conducting polymers
78.30.Na Fullerenes and related materials

Self-sustained waves of exothermic dissolution in reactive multilayer nano-foils

A. S. Rogachev, S. G. Vadchenko, and A. S. Mukasyan

Appl. Phys. Lett. 101, 063119 (2012); http://dx.doi.org/10.1063/1.4745201 (4 pages)

Online Publication Date: 9 August 2012

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The phenomenon of exothermic waves in reactive multilayer nano-foils demonstrates unusually high propagating rates (up to 100 m/s), which generate numerous applications and continuously motivate attempts for understanding its mechanism. In this work, based on the studies of the “quenched” exothermic waves, we have found that the driving mechanism of this phenomenon is a direct exothermic dissolution of one solid reactant in the molten layer of the other. The suggested mechanism of the exothermic wave in the Ni/Al multilayer nano-foil allows non-contradictory explanation of its main features.
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64.75.Bc Solubility

Modelling of piezoresistive response of carbon nanotube network based films under in-plane straining by percolation theory

Y. Miao, Q. Yang, L. Chen, R. Sammynaiken, and W. J. Zhang

Appl. Phys. Lett. 101, 063120 (2012); http://dx.doi.org/10.1063/1.4742893 (4 pages)

Online Publication Date: 10 August 2012

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Carbon nanotube (CNT) networks used for strain detection are one of the encouraging findings in the application of sensors. Recently, our group has discovered that in-plane strain sensors built from CNT films without surfactants exhibit a high piezoresistive response in CNT networks. In this paper, a study on modeling of piezoresistive response of CNT network based films without surfactants by percolation theory for in-plane strain detection is presented. In particular, within a conductive region, a model was built to predict piezoresistive response of CNT networks and the model predicted result shows an agreement with the experimental result.
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73.50.Dn Low-field transport and mobility; piezoresistance
72.10.Bg General formulation of transport theory
72.20.Fr Low-field transport and mobility; piezoresistance

Quantum dot solar cells using 2-dimensional array of 6.4-nm-diameter silicon nanodisks fabricated using bio-templates and neutral beam etching

Makoto Igarashi, Mohd Fairuz Budiman, Wugen Pan, Weiguo Hu, Noritaka Usami, and Seiji Samukawa

Appl. Phys. Lett. 101, 063121 (2012); http://dx.doi.org/10.1063/1.4745195 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2012

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Quantum dot solar cells consisting of a sub-10-nm highly ordered and dense 2-dimensional (2D) array of Si nanodisks (Si-NDs) as a quantum dot superlattice with a SiC interlayer are achieved. The Si-NDs are fabricated with an original top-down process involving a 2D array of bio-templates with a 4.5-nm-diameter iron core and damage-free neutral beam etching (Si-ND diameter: 6.4 nm). The Si-ND array has a high optical absorption coefficient due to miniband formation. As a result, the cells achieve open-circuit voltage of 0.556 V, short-circuit current density of 31.3 mA/cm2, a 72% fill factor, and 12.6% conversion efficiency.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Nanoscale contacts between semiconducting nanowires and metallic graphenes

Seongmin Kim, David B. Janes, Sung-Yool Choi, and Sanghyun Ju

Appl. Phys. Lett. 101, 063122 (2012); http://dx.doi.org/10.1063/1.4745210 (5 pages)

Online Publication Date: 10 August 2012

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Here we report on the metal–semiconductor junction characteristics of a semiconducting ZnO nanowire grown directly on a metallic graphene film. The extracted specific contact resistivity of the graphene–ZnO nanowire contact (1.5 × 10−5 Ω·cm2) is comparable to that reported for Al–ZnO contacts. Based on the assumption that thermionic-field emission is the dominant mechanism, we obtained a zero-bias effective barrier height of 0.413 eV for the graphene–ZnO nanowire Schottky contact. We thus demonstrate that as a result of the enhanced tunneling at the contact, the graphene–nanowire contact exhibits near-ohmic current–voltage characteristics with a low contact resistance.
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73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
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