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19 Sep 2011

Volume 99, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 121101 (2011); http://dx.doi.org/10.1063/1.3617472 (3 pages)

M. Davanço, M. T. Rakher, W. Wegscheider, D. Schuh, A. Badolato, and K. Srinivasan
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High efficiency switching using graphene based electron “optics”

Redwan N. Sajjad and Avik W. Ghosh

Appl. Phys. Lett. 99, 123101 (2011); http://dx.doi.org/10.1063/1.3640224 (3 pages) | Cited 6 times

Online Publication Date: 19 September 2011

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We demonstrate a way to open a gate-tunable transmission gap across graphene p-n junction by introducing an additional barrier in the middle that replaces Klein tunneling with regular tunneling, allowing us to modulate current by several orders of magnitude. The gap arises by angularly sorting electrons by their longitudinal energy and filtering out the hottest, normally incident electrons with the tunnel barrier, and the rest through total internal reflection. Using analytical and atomistic numerical studies, we show that the barrier causes graphene p-n junction act as a metamaterial with metal-insulator transition and overcome the KTln10/decade limit for subthreshold conduction.
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81.05.ue Graphene
85.65.+h Molecular electronic devices
73.40.Gk Tunneling
72.60.+g Mixed conductivity and conductivity transitions

Kelvin probe force microscopy characterization of TiO2 (110)-supported Au clusters

Hong Jing Chung, Ayhan Yurtsever, Yoshiaki Sugimoto, Masayuki Abe, and Seizo Morita

Appl. Phys. Lett. 99, 123102 (2011); http://dx.doi.org/10.1063/1.3641418 (3 pages) | Cited 7 times

Online Publication Date: 19 September 2011

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We present a combined non-contact atomic force microscopy and Kelvin probe force microscopy (KPFM) investigation of the structural and electrical properties of Au nanoclusters on a TiO2 model-oxide surface at room temperature. The KPFM images reveal an increase in the local contact potential difference (LCPD) of Au clusters with respect to the supporting TiO2 surface. Variation of the LCPD shift with a broad range of tip-cluster distances verifies that the obtained KPFM images are not a cause of the topographic artifacts. Based on the LCPD shift, both in the distance-dependent bias spectroscopy and KPFM images, we provide new evidence supporting the charge transfer formation from the surface to the Au cluster. We attribute the increment of the LCPD over an Au cluster site to the presence of surface dipoles, created by the charge transfer, pointing towards the substrate.
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61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials

Chemical states and photoluminescence of Si0.3Ge0.7-nitride film formed by N2+ gas

Y. M. Lee, S. H. Jang, M. Han, and M.-C. Jung

Appl. Phys. Lett. 99, 123103 (2011); http://dx.doi.org/10.1063/1.3641475 (3 pages)

Online Publication Date: 19 September 2011

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We investigated chemical states and photoluminescence of Si0.3Ge0.7-nitride film with a surface that was modified by N2+ ion implantation and rapid thermal annealing (RTA). By increasing the implantation time, the chemical bonding between Si and Ge was directly broken, and subnitrides were formed. We also observed the N2 vibration mode peak in the x-ray absorption spectra, but after RTA, this peak disappeared completely. SiNx was transformed to the stable Si3N4. However, GeNx with various chemical states, including Ge3N4 and nanocrystalline Ge, were formed. Photoluminescence observations at room temperature showed strong visible luminescence at wavelengths of 460 and 515 nm.
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78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
61.72.up Other materials
68.35.bt Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Fabrication of nanometer scale gaps for thermo-tunneling devices

M. H. Tanielian, R. B. Greegor, J. A. Nielsen, and C. G. Parazzoli

Appl. Phys. Lett. 99, 123104 (2011); http://dx.doi.org/10.1063/1.3641897 (3 pages)

Online Publication Date: 19 September 2011

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We report a fabrication approach for making nanometer wide gaps between two planar metallic electrodes, which can be utilized for the formation of thermo-tunneling devices. The technique is a three dimensional variant of the electromigration techniques used for creating nanometer sized gaps on planar surfaces. The gap is formed by applying a low level voltage between two parallel electrodes, each deposited on separate wafers that have been bonded together. I-V and thermal characterization of the gap show very good agreement with modeling results, indicating a tunneling gap on the order of 0.5-1 nm.
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81.16.-c Methods of micro- and nanofabrication and processing
85.80.Fi Thermoelectric devices
82.45.Fk Electrodes
66.30.Qa Electromigration

Carbon tips as electrodes for single-molecule junctions

Andres Castellanos-Gomez, Stefan Bilan, Linda A. Zotti, Carlos R. Arroyo, Nicolás Agraït, Juan Carlos Cuevas, and Gabino Rubio-Bollinger

Appl. Phys. Lett. 99, 123105 (2011); http://dx.doi.org/10.1063/1.3643031 (3 pages) | Cited 1 time

Online Publication Date: 20 September 2011

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We study electron transport through single-molecule junctions formed by an octanethiol molecule bonded with the thiol anchoring group to a gold electrode and the opposing methyl endgroup to a carbon tip. Using the scanning tunneling microscope based break junction technique, we measure the electrical conductance of such molecular junctions. We observe the presence of well-defined conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.
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73.63.-b Electronic transport in nanoscale materials and structures
85.65.+h Molecular electronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.40.-c Electronic transport in interface structures

Temperature-dependent photoluminescence properties of porous silicon nanowire arrays

Haiping He (何海平), Chao Liu (刘超), Luwei Sun (孙陆威), and Zhizhen Ye (叶志镇)

Appl. Phys. Lett. 99, 123106 (2011); http://dx.doi.org/10.1063/1.3643047 (3 pages) | Cited 4 times

Online Publication Date: 20 September 2011

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Luminescent porous silicon nanowire arrays are prepared through metal-assisted chemical etching. Photoluminescence (PL) and cathodoluminescence (CL) reveal that both the nanowire arrays and individual nanowire exhibit intense orange emission around 1.9 eV at room temperature. The emission linewidth increases monotonously and significantly with decreasing temperature. Combined with PL decay measurements, the results indicate that there are two transitions contributing to the broad emission at low temperatures. In addition, negative thermal quenching of the PL intensity due to surface states is observed. A multi-level transition model is proposed to interpret the experimental results.
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78.55.Ap Elemental semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Gh Other heat and thermomechanical treatments
78.67.Uh Nanowires

High-purity hydrogen generation by ultraviolet illumination with the membrane composed of titanium dioxide nanotube array and Pd layer

Masashi Hattori, Kei Noda, and Kazumi Matsushige

Appl. Phys. Lett. 99, 123107 (2011); http://dx.doi.org/10.1063/1.3643052 (3 pages) | Cited 2 times

Online Publication Date: 20 September 2011

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High-purity hydrogen generation was observed by using a membrane composed of a bilayer of an anodized titanium dioxide nanotube array (TNA) and a hydrogen permeable metal. This membrane was fabricated by transferring a TNA embedded in a titanium foil onto a sputtered 10-μm-thick palladium film. Alcohols are reformed photocatalytically and concurrently generated hydrogen is purified through the Pd layer. H2 with a purity of more than 99% was obtained from liquid alcohols under ultraviolet illumination onto the membrane. Thus, we demonstrated the integration of photocatalytic hydrogen production and purification within a single membrane.
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88.30.E- Hydrogen production with renewable energy
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
82.45.Mp Thin layers, films, monolayers, membranes
82.50.Hp Processes caused by visible and UV light
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Rectifying and negative differential resistance behaviors of a functionalized Tour wire: The position effects of functional groups

Gordon Kwong, Zhenhua Zhang, and Jinbo Pan

Appl. Phys. Lett. 99, 123108 (2011); http://dx.doi.org/10.1063/1.3641421 (3 pages) | Cited 5 times

Online Publication Date: 20 September 2011

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Based on Tour wire, we construct four D-π-A molecular devices with different positional functional groups, in an attempt to explore the position effects of functional groups on their electronic transport properties and to show that some interesting physical phenomena can emerge by only varying the position of functional groups. The first-principles calculations demonstrate that the position of functional groups can affect the rectifying behaviors (rectification direction and ratio) significantly and determines whether or not the negative differential resistance (NDR) can be observed as well as the physical origin of the NDR phenomenon.
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85.65.+h Molecular electronic devices

On demand-direct synthesis of Si and Ge nanowires on a single platform by focused laser illumination

David J. Hwang, Sang-gil Ryu, Eunpa Kim, Costas P. Grigoropoulos, and Carlo Carraro

Appl. Phys. Lett. 99, 123109 (2011); http://dx.doi.org/10.1063/1.3643042 (3 pages) | Cited 1 time

Online Publication Date: 21 September 2011

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Laser irradiation can incur spatially confined and rapid heating that enables precisely controlled nucleation and subsequent growth of nanomaterials. This localization of the laser-driven growth can realize on-demand, direct synthesis of nanowires composed of multiple elements on a single platform. In this study, silicon and germanium nanowires are grown by laser-induced vapor-liquid-solid mechanism in a hetero-array configuration by simply switching the reactant gas precursors as the growth of nanowires is limited within the heat-affected zone induced by the laser. Energy dispersive x-ray and Raman spectroscopies were performed to observe the elemental composition and crystallinity of as-grown nanowires, respectively.
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81.16.Mk Laser-assisted deposition
68.55.ag Semiconductors
78.67.Uh Nanowires
81.07.Gf Nanowires
78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors

Self-assembly of metallic nanoparticles into plasmonic rings

Thomas Lerond, Julien Proust, Hélène Yockell-Lelièvre, Davy Gérard, and Jérôme Plain

Appl. Phys. Lett. 99, 123110 (2011); http://dx.doi.org/10.1063/1.3643057 (3 pages) | Cited 1 time

Online Publication Date: 21 September 2011

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Metallic nanoparticles are self-assembled into plasmonic nanorings. The self-assembly is evaporation-induced and is driven using a template of dielectric microspheres. We obtain well-ordered arrays of metallic nanorings over large areas. The inner and outer diameters of the rings, as well as the pitch of the array, are fully controllable. The optical resonances supported by the plasmonic rings are then characterized using extinction spectroscopy. Our approach opens a simple and inexpensive road to create plasmonic structures that can find applications as metamaterials or substrates for enhanced spectroscopies.
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81.16.Dn Self-assembly
78.66.Bz Metals and metallic alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Self-assembly on (111)-oriented III-V surfaces

Paul J. Simmonds and Minjoo Larry Lee

Appl. Phys. Lett. 99, 123111 (2011); http://dx.doi.org/10.1063/1.3640501 (3 pages) | Cited 2 times

Online Publication Date: 21 September 2011

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We demonstrate the self-assembly of tensile strained GaP into three-dimensional dots on GaAs(111)A. Size and areal density of the dislocation-free GaP dots are readily tunable with both substrate temperature and deposition thickness. GaP dot growth obeys island scaling theory, allowing us to predict dot size distributions a priori.
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81.16.Dn Self-assembly
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Morphology and structure of mono- and few-layer graphene produced by jet cavitation

Min Yi, Jinzhi Li, Zhigang Shen, Xiaojing Zhang, and Shulin Ma

Appl. Phys. Lett. 99, 123112 (2011); http://dx.doi.org/10.1063/1.3641863 (3 pages) | Cited 3 times

Online Publication Date: 21 September 2011

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We prepared mono- and few-layer graphene with micrometer-sized dimensions in aqueous solution by a jet cavitation method starting from common crystal graphite, which is totally green, facile, low-cost, and laborsaving. The graphene yield by our method is estimated as ∼4 wt. % by statistical analysis. Diverse microscopy is used to characterize the morphology, microstructure, and near-edge fine structure of the prepared nanosheets. It is found that partial folding allows realization of rotational stacking fault in otherwise perfect samples. The folded graphene with Morié patterns could be ideal specimens for experimentally probing band structure and electronic properties of graphene with different stacking styles.
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61.48.Gh Structure of graphene
47.55.dp Cavitation and boiling
47.60.Kz Flows and jets through nozzles
82.45.Mp Thin layers, films, monolayers, membranes
73.20.At Surface states, band structure, electron density of states
02.50.-r Probability theory, stochastic processes, and statistics

Real-time observation of lithium fibers growth inside a nanoscale lithium-ion battery

Hessam Ghassemi, Ming Au, Ning Chen, Patricia A. Heiden, and Reza S. Yassar

Appl. Phys. Lett. 99, 123113 (2011); http://dx.doi.org/10.1063/1.3643035 (3 pages) | Cited 3 times

Online Publication Date: 22 September 2011

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Formation of lithium dendrite/fibers during charging-discharging cycles not only causes short circuit but is also known as a major safety issue. In this work, an electrochemical cell was constructed inside a transmission electron microscope to observe the real-time nucleation and growth of the lithium fibers inside a nanoscale Li-ion battery. Our results show that during the lithiation process, the lithium ions nucleate at the interface of anode and electrolyte and then grow into fibers. These fibers grew parallel to the direction of the applied electric field. Such observations can assist the nanoscale design of better electrodes and electrolyte materials needed for safe and high power Li-ion batteries.
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82.47.Aa Lithium-ion batteries
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Lp Transmission electron microscopy (TEM)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Thermally induced currents in graphene-based heterostructure

Minggang Zeng, Yuanping Feng, and Gengchiau Liang

Appl. Phys. Lett. 99, 123114 (2011); http://dx.doi.org/10.1063/1.3641478 (3 pages) | Cited 2 times

Online Publication Date: 22 September 2011

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We investigate thermally induced currents in a zigzag graphene nanoribbon (ZGNR) heterostructure, consisting of hydrogen-terminated ZGNR (ZGNR-H) and oxygen-terminated ZGNR (ZGNR-O), under different electronic and magnetic states. Compared to a pure ZGNR-H system, the heterostructure displays a considerably larger thermally induced current due to its asymmetric transmission spectrum. Moreover, the magnetized ZGNR-H/ZGNR-O shows spin filter and magnetoresistance effects, suggesting potential applications of the ZGNR-H/ZGNR-O heterostructures in thermoelectric and spintronics devices.
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72.80.Vp Electronic transport in graphene
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Dc Spin polarized transport in semiconductors

Shift of isoelectric point in extended nanospace investigated by streaming current measurement

Kyojiro Morikawa, Kazuma Mawatari, Yutaka Kazoe, Takehiko Tsukahara, and Takehiko Kitamori

Appl. Phys. Lett. 99, 123115 (2011); http://dx.doi.org/10.1063/1.3644481 (3 pages) | Cited 4 times

Online Publication Date: 23 September 2011

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Isoelectric points in extended nanochannels (580-2720 nm) fabricated on fused-silica substrates were measured using the streaming current method. The isoelectric point obtained in a 2720 nm channel was almost the same as the isoelectric point reported for the bulk (2.6-3.2). However, the isoelectric point in the extended nanochannel (580 nm) was decreased to less than 2.0. This result provides important information for the modeling of ion transport in extended nanospace.
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47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics

The theoretical search for half-metallic material: The non-stoichiometric peroskite oxide Sr2FeCoO6−δ

Haiping Wu, Yan Qian, Weishi Tan, Chuanyun Xiao, Kaiming Deng, and Ruifeng Lu

Appl. Phys. Lett. 99, 123116 (2011); http://dx.doi.org/10.1063/1.3644493 (3 pages) | Cited 4 times

Online Publication Date: 23 September 2011

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The non-stoichiometric peroskite oxide Sr2FeCoO6−δ is investigated and predicted to be half-metallic material using density-functional calculations. The results reveal that Sr2FeCoO5 shows antiferromagnetic half-metallic behavior and exhibits magnetic moment ordering with the magnetic moments of 2.97 and 3.72 μB on Fe(1) and Fe(2) sites, 2.96 and 3.20 μB on Co(1) and Co(2) sites antiparallel to those of Fe, and about 0.05 μB on O sites parallel to those of Co, respectively. Moreover, Sr2FeCoO4 and Sr2FeCoO6 both have half-metallic character. This hints that Sr2FeCoO6−δ possesses half-metallic nature in a large range of δ.
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71.20.Ps Other inorganic compounds
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
61.66.Bi Elemental solids
61.66.Dk Alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
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