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13 Aug 2012

Volume 101, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages)

Judson D. Ryckman and S. M. Weiss
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Strong current polarization and negative differential resistance in chiral graphene nanoribbons with reconstructed (2,1)-edges

Xiao-Fei Li, Ling-Ling Wang, Ke-Qiu Chen, and Yi Luo

Appl. Phys. Lett. 101, 073101 (2012); http://dx.doi.org/10.1063/1.4745506 (5 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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We investigate electronic structures and transport properties of chiral-graphene-nanoribbons (CGNRs) with reconstructed (2,1)-edges. First principles results reveal that the (2,1)-CGNRs can be either spin non-polarized or polarized, depending on whether the edges are H-saturated or unsaturated. H-saturated systems are semiconductors with width-dependent transmission gap, while unsaturated systems are metallic at non-polarized state or at antiferromagnetic state and they are semiconductors at ferromagnetic state. Moreover, unsaturated systems possess strong current polarizations (nearly 100%) and a striking negative differential resistance behavior (with a peak-to-valley ratio about 105). These remarkable properties suggest the potential application of (2,1)-CGNRs in molectronics and spintronics.
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73.22.Pr Electronic structure of graphene
71.15.-m Methods of electronic structure calculations
72.25.Dc Spin polarized transport in semiconductors
73.63.Bd Nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Field–effect transistors made of individual colloidal PbS nanosheets

Sedat Dogan, Thomas Bielewicz, Yuxue Cai, and Christian Klinke

Appl. Phys. Lett. 101, 073102 (2012); http://dx.doi.org/10.1063/1.4745786 (4 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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Two-dimensional materials are considered for future quantum devices and are usually produced by extensive methods like molecular beam epitaxy. We report on the fabrication of field–effect transistors using individual ultra-thin lead sulfide nanostructures with lateral dimensions in the micrometer range and a height of a few nanometers as conductive channel produced by a comparatively fast, inexpensive, and scalable colloidal chemistry approach. Contacted with gold electrodes, such devices exhibit p-type behavior and temperature-dependent photoconductivity. Trap states play a crucial role in the conduction mechanism. The performance of the transistors is among the ones of the best devices based on colloidal nanostructures.
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85.30.Tv Field effect devices

Polarization dependence of photocurrent in a metal-graphene-metal device

Minjung Kim, Ho Ang Yoon, Seungwoo Woo, Duhee Yoon, Sang Wook Lee, and Hyeonsik Cheong

Appl. Phys. Lett. 101, 073103 (2012); http://dx.doi.org/10.1063/1.4745787 (3 pages)

Online Publication Date: 13 August 2012

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The dependence of the photocurrent generated in a Pd/graphene/Ti junction device on the incident photon polarization is studied. Spatially resolved photocurrent images were obtained as the incident photon polarization is varied. The photocurrent is maximum when the polarization direction is perpendicular to the graphene channel direction and minimum when the two directions are parallel. This polarization dependence can be explained as being due to the anisotropic electron-photon interaction of Dirac electrons in graphene.
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85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.Tv Field effect devices

The site effects of B or N doping on I-V characteristics of a single pyrene molecular device

Zhi-Qiang Fan, Zhen-Hua Zhang, Ming Qiu, Xiao-Qing Deng, and Gui-Ping Tang

Appl. Phys. Lett. 101, 073104 (2012); http://dx.doi.org/10.1063/1.4745842 (5 pages)

Online Publication Date: 13 August 2012

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Using the non-equilibrium Green’s function method combined with the density functional theory, the electronic transport properties of boron (B) or nitrogen (N) doped pyrene molecular devices are investigated. The results show that effects of B or N doping on I-V characteristics of a single pyrene molecular device are not constant and can be changed by varying doped sites. More importantly, significant negative differential resistance (NDR) behaviors are found in B-doped pyrene molecular devices. The peak-to-valley ratio which is a typical character of NDR behavior is also sensitive to the B doped site.
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85.65.+h Molecular electronic devices
31.15.E- Density-functional theory
02.30.-f Function theory, analysis

ZnO/ZnSxSe1−x core/shell nanowire arrays as photoelectrodes with efficient visible light absorption

Zhenxing Wang, Xueying Zhan, Yajun Wang, Muhammad Safdar, Mutong Niu, Jinping Zhang, Ying Huang, and Jun He

Appl. Phys. Lett. 101, 073105 (2012); http://dx.doi.org/10.1063/1.4745918 (5 pages) | Cited 5 times

Online Publication Date: 13 August 2012

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ZnO/ZnSxSe1−x core/shell nanowires have been synthesized on n+-type silicon substrate via a two-step chemical vapor deposition method. Transmission electron microscopy reveals that ZnSxSe1−x can be deposited on the entire surface of ZnO nanowire, forming coaxial heterojunction along ZnO nanowire with very smooth shell surface and high shell thickness uniformity. The photoelectrode after deposition of the ternary alloy shell significantly improves visible light absorption efficiency. Electrochemical impedance spectroscopy results explicitly indicate that the introduction of ZnSxSe1−x shell to ZnO nanowires effectively improves the photogenerated charge separation process. Our finding opens up an efficient means for achieving high efficient energy conversion devices.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
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Repeatable unipolar/bipolar resistive memory characteristics and switching mechanism using a Cu nanofilament in a GeOx film

S. Z. Rahaman, S. Maikap, W. S. Chen, H. Y. Lee, F. T. Chen, M. J. Kao, and M. J. Tsai

Appl. Phys. Lett. 101, 073106 (2012); http://dx.doi.org/10.1063/1.4745783 (5 pages) | Cited 3 times

Online Publication Date: 14 August 2012

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This paper investigates the repeatable unipolar/bipolar resistive switching memory characteristics in a copper/germanium-oxide/tungsten (Cu/GeOx/W) structure. The switching mechanism occurs because of the lower barrier height for hole injection rather than electron injection. Therefore, Cu ions, as a positive charge, migrate before initiating growth at the GeOx/W interface and dissolving at the GeOx/Cu interface. The diameter of the Cu nanofilament increases linearly from 0.13 Å to 25 nm as current compliances increase from 1 nA to 10 mA, as calculated using the other approach. The crystalline Cu nanofilament was also confirmed by high-resolution transmission electron microscopy analysis under SET. Good data retention with high resistance ratios of 102–105 (and >104 at 85 °C) and ∼109 was obtained under the bipolar and unipolar modes, respectively. Therefore, a maximum memory size of 5000 Pbit/in2 can be designed in the future.
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84.30.Sk Pulse and digital circuits

Highly luminescing multi-shell semiconductor nanocrystals InP/ZnSe/ZnS

Kyungnam Kim, Hangyeoul Lee, Jaewook Ahn, and Sohee Jeong

Appl. Phys. Lett. 101, 073107 (2012); http://dx.doi.org/10.1063/1.4745844 (4 pages) | Cited 2 times

Online Publication Date: 14 August 2012

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We design, synthesize, and characterize multi-shell quantum dot structure of an indium phosphide core surrounded by zinc chalcogenide shells. A simple mathematical model describing the wave function of electronhole pairs enabled us to design ZnSe and ZnS shells to confine the carriers inside the core region effectively. The result indicates that the designed multi-shell quantum dots show improved optical properties that are more robust against chemical and photo-environmental changes.
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81.07.Ta Quantum dots
78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
81.05.Gc Amorphous semiconductors

Mechanochemistry of shock-induced nanobubble collapse near silica in water

K. Nomura, R. K. Kalia, A. Nakano, P. Vashishta, and A. C. T. van Duin

Appl. Phys. Lett. 101, 073108 (2012); http://dx.doi.org/10.1063/1.4746270 (4 pages)

Online Publication Date: 14 August 2012

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We have performed million-atom reactive molecular dynamics simulations to study shock-induced bubble collapse near an amorphous silica surface. We observe the formation of water jet during the bubble collapse, which collides on to the silica surface causing a hemispherical pit. Fragment analysis reveals substantial ionization activities in water followed by rapid increase in H3O+ population during the pit formation. We have identified a shock-induced H3O+ ion formation mechanism, in which transient five-coordinated silicon atoms play a pivotal role.
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47.55.dr Interactions with surfaces
02.70.Ns Molecular dynamics and particle methods
47.11.Mn Molecular dynamics methods
47.40.Nm Shock wave interactions and shock effects

Synthesis and morphological transition of Ni2+ doped Rh-In2O3 nanocrystals under LiNO3 molten salts

Qingbo Sun, Yuping Zeng, and Dongliang Jiang

Appl. Phys. Lett. 101, 073109 (2012); http://dx.doi.org/10.1063/1.4746388 (4 pages)

Online Publication Date: 14 August 2012

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Rhombohedral corundum-type metastable phase of Ni2+ doped indium oxide nanocrystals is directly synthesized via an easy LiNO3 molten salt route by dehydrated reactions of Ni2+ doped indium oxohydroxide precursors. Due to higher viscosity of molten salt solvents, their morphological transition from one-dimensional nanorods to zero-dimensional nanoparticles is realized under continuous corrosion of interfaces. Meanwhile, diluted ferromagnetism of indium oxide is also accomplished by incorporating Ni2+ ions. The mechanisms about structural evolutions and magnetic changes for Ni2+ doped indium oxide nanocrystals are discussed, too.
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81.16.Be Chemical synthesis methods
61.72.up Other materials
75.75.Cd Fabrication of magnetic nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials

Oxidation of graphene in ozone under ultraviolet light

Y. C. Cheng, T. P. Kaloni, Z. Y. Zhu, and U. Schwingenschlögl

Appl. Phys. Lett. 101, 073110 (2012); http://dx.doi.org/10.1063/1.4746261 (4 pages) | Cited 1 time

Online Publication Date: 17 August 2012

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Based on first-principles calculations, the process of graphene oxidation in ozone under ultraviolet light is explored by studying the effects of O(3P) on the structural and electronic properties of a graphene sheet. On initial absorption of O(3P), an epoxy group is formed on the graphene sheet and the Dirac cone is shifted away from the Brillouin zone corners without carrier doping. When the oxidation progresses, an adjacent C-C bond is broken, a vacancy is formed, and CO and/or CO2 molecules are released.
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73.22.Pr Electronic structure of graphene
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states
61.48.Gh Structure of graphene

Enhanced vibration damping of carbon fibers-ZnO nanorods hybrid composites

A. Alipour Skandani, N. Masghouni, S. W. Case, D. J. Leo, and M. Al-Haik

Appl. Phys. Lett. 101, 073111 (2012); http://dx.doi.org/10.1063/1.4746398 (4 pages)

Online Publication Date: 17 August 2012

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In this study, ZnO nanorods are grown on the surface of polyacrylonitrile based carbon fibers using a low temperature hydrothermal synthesis technique. Bi-layered carbon fiber-ZnO nanorod hybrid composite with epoxy matrix is prepared and tested for vibrational attenuations using dynamic mechanical analysis. Results revealed that the growth of ZnO nanorods on top of carbon fiber increases the damping performance by 50% while causing a slight decrease (∼7%) on the storage modulus. The enhanced damping of the hybrid composites can be related to the frictional mechanisms between the ZnO nanorod/epoxy and nanorod/nanorod interfaces combined with piezoelectric effect of ZnO.
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63.22.Np Layered systems
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
63.50.-x Vibrational states in disordered systems
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)

Highly ordered self-assembled nanoscale periodic faceting in GaAs(631) homoepitaxial growth

E. Cruz-Hernández, S. Shimomura, and V. H. Méndez-García

Appl. Phys. Lett. 101, 073112 (2012); http://dx.doi.org/10.1063/1.4746423 (4 pages) | Cited 2 times

Online Publication Date: 17 August 2012

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We report on the self-assembly of large-order-correlated nanoscale faceting on GaAs(631)A substrates grown by molecular beam epitaxy. The surface morphology of the grown samples as a function of the growth temperature and the As-beam equivalent pressure was studied using atomic force microscopy. A two-dimensional autocorrelation function analysis was performed in order to quantitatively determine the uniformity of the surface corrugation. By optimizing the growth conditions, correlated faceted areas as large as 1.7 × 1.7 μm2 are obtained. The highly ordered surface corrugation discussed here provides useful insights to prepare highly ordered facet planes for the self organized growth of quantum wires.
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81.07.Vb Quantum wires
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Dn Self-assembly
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)
68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces

Universal ultrafast sandpaper assisting rubbing method for room temperature fabrication of two-dimensional nanosheets directly on flexible polymer substrate

Yan Yu, Shenglin Jiang, Guangzu Zhang, Wenli Zhou, Xiangshui Miao, Yike Zeng, Jing Wang, Jungang He, and Ling Zhang

Appl. Phys. Lett. 101, 073113 (2012); http://dx.doi.org/10.1063/1.4746755 (4 pages)

Online Publication Date: 17 August 2012

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In this letter, a universal ultrafast sandpaper assisting rubbing method was proposed to fabricate two-dimensional nanosheets (graphene, hexagonal boron nitride, tungsten disulfide, molybdenum disulfide) directly on flexible polymer substrate under room temperature. By two steps of rubbing progresses totally within 2 min, raw materials could be evolved to be thinner and to be attached onto polymer substrate. The final products showed high surface stability, which would be very useful during applications, and the physical mechanisms of surface stability were discussed. The micro-morphology evolutions of two-dimensional powders and sandpapers were tested to study the physical mechanisms of the method.
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81.07.Wx Nanopowders
61.43.Gt Powders, porous materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

How to fabricate a semihydrogenated graphene sheet? A promising strategy explored

Jian Zhou and Qiang Sun

Appl. Phys. Lett. 101, 073114 (2012); http://dx.doi.org/10.1063/1.4746756 (4 pages) | Cited 1 time

Online Publication Date: 17 August 2012

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There has been a long-standing dream to synthesize a semihydrogenated graphene sheet. Here, we propose a promising strategy based on physical method instead of chemical method to avoid the current problems in synthesizing. By applying pressure on a fluorinated BN sheet supported on a graphene sheet, we can induce a structural transition for H atoms jumping from the graphane sheet to fluorinated BN sheet, thus transforming the graphane sheet to a graphone sheet. Moreover, hole doping can reduce the pressure required for such structural transition. This strategy is more feasible and controllable as compared to the existing experimental techniques.
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81.05.ue Graphene
81.65.-b Surface treatments
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