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19 Mar 2012

Volume 100, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 121101 (2012); http://dx.doi.org/10.1063/1.3693413 (4 pages)

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta
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Reversible bistability of conductance on graphene/CuOx/Cu nanojunction

Sangku Kwon, Hyungtak Seo, Hyunsoo Lee, Ki-Joon Jeon, and Jeong Young Park

Appl. Phys. Lett. 100, 123101 (2012); http://dx.doi.org/10.1063/1.3694754 (4 pages) | Cited 3 times

Online Publication Date: 19 March 2012

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We report that a nanojunction composed of graphene, copper oxide, and Cu substrate exhibits resistive switching behavior, revealed with conductive probe atomic force microscopy at ultrahigh vacuum. The current-voltage curve measured between the titanium nitride-coated tip and the nanojunction exhibited reversible bistable resistance states. We propose that the switching behavior is controlled by the migration of oxygen ions in the copper oxide layer, leading to the reversible formation/disruption of a CuOx-associated charge tunneling barrier, which is consistent with glancing-angle x-ray photoelectron spectroscopy analysis.
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61.48.Gh Structure of graphene
73.40.Gk Tunneling
68.37.Ps Atomic force microscopy (AFM)

Construction of nanostructured electrodes on flexible substrates using pre-treated building blocks

Fuzhi Huang, Dehong Chen, Qi Li, Rachel A. Caruso, and Yi-Bing Cheng

Appl. Phys. Lett. 100, 123102 (2012); http://dx.doi.org/10.1063/1.3695080 (4 pages) | Cited 2 times

Online Publication Date: 19 March 2012

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A “building block” concept is introduced for the construction of electrodes for dye-sensitized solar cells (DSCs). The building blocks are prefabricated submicrometer- to micrometer-sized clusters, such as nanostructured mesoporous TiO2 spheres. This concept makes a number of approaches possible that are difficult to achieve through the conventional nanoparticle route for the preparation of flexible DSCs. Significantly, the building blocks can be physically and chemically pre-treated prior to electrode fabrication. Thus some of the intrinsic limitations of using plastic substrates can be overcome, such as applying heat treatment and TiCl4 treatment, affording a high power conversion efficiency of 7.5%.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.40.Gh Other heat and thermomechanical treatments
88.40.jr Organic photovoltaics
81.05.Rm Porous materials; granular materials
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials

Emission stability enhancement of a tip-type carbon-nanotube-based field emitter via hafnium interlayer deposition and thermal treatment

Jong-Pil Kim, Han-Beet Chang, Bu-Jong Kim, and Jin-Seok Park

Appl. Phys. Lett. 100, 123103 (2012); http://dx.doi.org/10.1063/1.3695173 (3 pages)

Online Publication Date: 20 March 2012

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Carbon nanotubes (CNTs) were deposited on a tip-type tungsten substrate via electrophoretic deposition, in which a hafnium thin film was used as an interlayer. The long-term (up to 24 h) emission stability of the CNT-based field emitter was remarkably enhanced when the hafnium interlayer was coated and thermally treated. This is attributed to the enhanced adhesion between the substrate and the CNTs. An x-ray photoelectron spectroscopy study and nano-scratch measurement provided a convincing evidence of the increase in the adhesive force.
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85.35.Kt Nanotube devices
81.15.Pq Electrodeposition, electroplating

Electrical characterization of back-gated bi-layer MoS2 field-effect transistors and the effect of ambient on their performances

Hao Qiu (邱浩), Lijia Pan (潘力佳), Zongni Yao (姚宗妮), Junjie Li (李俊杰), Yi Shi (施毅), and Xinran Wang (王欣然)

Appl. Phys. Lett. 100, 123104 (2012); http://dx.doi.org/10.1063/1.3696045 (3 pages) | Cited 16 times

Online Publication Date: 21 March 2012

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Two-dimensional transition-metal dichalcogenides such as MoS2 are promising channel materials for transistor scaling. Here, we report the performance and environmental effects on back-gated bi-layer MoS2 field-effect transistors. The devices exhibit Ohmic contacts with titanium at room temperature, on/off ratio higher than 107, and current saturation. Furthermore, we show that the devices are sensitive to oxygen and water in the ambient. Exposure to ambient dramatically reduces the on-state current by up to 2 orders of magnitude likely due to additional scattering centers from chemisorption on the defect sites of MoS2. We demonstrate that vacuum annealing can effectively remove the absorbates and reversibly recover the device performances. This method significantly reduces the large variations in MoS2 device caused by extrinsic factors.
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85.30.Tv Field effect devices
84.32.Dd Connectors, relays, and switches
61.72.Cc Kinetics of defect formation and annealing

Enhanced atomic corrugation in dynamic force microscopy—The role of repulsive forces

L. Lichtenstein, C. Büchner, S. Stuckenholz, M. Heyde, and H.-J. Freund

Appl. Phys. Lett. 100, 123105 (2012); http://dx.doi.org/10.1063/1.3696039 (3 pages) | Cited 2 times

Online Publication Date: 22 March 2012

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Full range two dimensional (2D) force mapping was performed by means of low temperature dynamic force microscopy (DFM) on a highly complex surface structure. For this purpose, we used a thin film of vitreous silica on a Ru(0001)-support, which is a 2D structural equivalent to silica glass. The 2D spectroscopy shows that the contrast generating shift in vertical distance between two sites on the surface is twice as large on the repulsive branch of the frequency shift-distance curve as compared to the attractive branch. The results give insight into the origin of the formation of atomic resolution in DFM.
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68.35.bj Amorphous semiconductors, glasses
61.43.Fs Glasses
68.55.aj Insulators
68.37.Ps Atomic force microscopy (AFM)

Fabrication of submicron devices on the (011) cleave surface of a cleaved-edge-overgrowth GaAs/AlGaAs crystal

A. M. Chang, Hao Zhang, L. N. Pfeiffer, and K. W. West

Appl. Phys. Lett. 100, 123106 (2012); http://dx.doi.org/10.1063/1.3694052 (4 pages)

Online Publication Date: 22 March 2012

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We describe the fabrication of submicron devices on the (011) cleave surface of a GaAs heterostructure crystal, in which this surface is extremely narrow. Special purpose devices are produced, which take advantage of the unique characteristics of cleaved-edge-overgrowth. The successful fabrication relies on understanding the surface tension of the electron beam polymethyl methacrylate resist, the workable degree of variation in resist thickness, and on gluing the crystal onto a backing substrate to increase structural strength. We demonstrate functional gate-controlled quantum point contact constrictions placed 9 μm from one edge of the cleave surface.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Effect of bending stress on structures and quantum conduction of Cu nanowires

C. He, W. X. Zhang, Z. Q. Shi, J. P. Wang, and H. Pan

Appl. Phys. Lett. 100, 123107 (2012); http://dx.doi.org/10.1063/1.3696052 (3 pages)

Online Publication Date: 23 March 2012

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The ballistic transport properties of Cu nanowires under different bending stresses are investigated for future application in flexible displays and flexible solar cell using first-principles density-function theory. The stability and quantum conduction of both nonhelical and helical atomic strands are reduced by applying a bending stress f. With increasing of f, the helical wire becomes disorder, suffering a phase transition to similar nonhelical one and collapsing eventually. Our calculations show that the maximum bearable bending stress is fmax = 3 nN for the helical atomic strands while is more stable than fmax = 2.5 nN for the nonhelical atomic strands.
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73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects
73.63.Nm Quantum wires
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Ultrahigh efficient single-crystalline TiO2 nanorod photoconductors

R. S. Chen, C. A. Chen, H. Y. Tsai, W. C. Wang, and Y. S. Huang

Appl. Phys. Lett. 100, 123108 (2012); http://dx.doi.org/10.1063/1.3694926 (4 pages) | Cited 6 times

Online Publication Date: 23 March 2012

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Photoconductive gain and normalized gain, which determine the device and material properties on photoconduction, respectively, have been defined for single-crystalline titanium dioxide (TiO2) nanorods (NRs) with various diameter sizes. The gain values of the NR photodetectors can reach 105 easily at a low bias of 0.1 V. By excluding the contributions of experimental parameters, the optimal normalized gain of the indirect-bandgap TiO2 NRs at 5.4 × 10−5 m2V−1 is comparable with that estimated from the direct-bandgap ZnO nanowires. The average normalized gain value at 3.3 ± 2.2 × 10−5 m2V−1 obtained from eight individual TiO2 NRs with diameters ranging from 120 to 1250 nm is also over three orders of magnitude higher than the polycrystalline nanotube counterpart. The results demonstrate the superior photoconductivity efficiency in boundary-free titania one-dimensional nanostructure, which is crucial for ultraviolet photodetector, dye-sensitized solar cell, and photochemical device applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
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