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11 Jun 2012

Volume 100, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages)

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci
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High-performance photodetectors for visible and near-infrared lights based on individual WS2 nanotubes

Chaoying Zhang, Sheng Wang, Leijing Yang, Yang Liu, Tingting Xu, Zhiyuan Ning, Alla Zak, Zhiyong Zhang, Reshef Tenne, and Qing Chen

Appl. Phys. Lett. 100, 243101 (2012); http://dx.doi.org/10.1063/1.4729144 (5 pages) | Cited 3 times

Online Publication Date: 11 June 2012

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We propose that a photodetector based on nanotubes formed from layered structure may have a faster response than nanowires or nanobelts. The layered compound tungsten disulfide (WS2) can absorb visible and near-infrared lights. We fabricated photodetectors based on individual WS2 nanotubes. The photodetectors exhibited a remarkable response to excitation with 633 and 785 nm light. The nanotube-based photodetectors exhibited short rise and decay times of a few hundred μs, high on/off ratio, and high spectral responsivity and external quantum efficiency. Our results imply that WS2 nanotubes are prospective candidates for high-performance nanoscale optoelectronic devices.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Enhanced performance by incorporation of zinc oxide nanowire array for organic-inorganic hybrid solar cells

C. P. Liu, Z. H. Chen, H. E. Wang, S. K. Jha, W. J. Zhang, I. Bello, and J. A. Zapien

Appl. Phys. Lett. 100, 243102 (2012); http://dx.doi.org/10.1063/1.4728985 (3 pages) | Cited 1 time

Online Publication Date: 12 June 2012

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We study the solar power conversion efficiency in hybrid solar cells based on zinc oxide (ZnO)/antimony trisulfide (Sb2S3)/poly-3(hexylthiophene) heterojunctions. The incorporation of ZnO nanowire arrays (NAs) structure results in power conversion efficiency of 2.9%, or 20% higher than the control device. Absorption spectra and numerical simulation analysis provide strong evidence revealing that the enhanced performance is mainly induced by (1) enhanced optical absorption from light-trapping effect of NAs and (2) reduced bulk recombination rate in Sb2S3 from shortened electron injection pathway into ZnO. Significantly, numerical simulations show that the expected interface recombination increase from larger interfacial area effects is negligible.
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88.40.jp Multijunction solar cells
88.40.hj Efficiency and performance of solar cells

Plasma control of morpho-dimensional selectivity of hematite nanostructures

U. Cvelbar, I. Levchenko, G. Filipič, M. Mozetič, and K. Ostrikov

Appl. Phys. Lett. 100, 243103 (2012); http://dx.doi.org/10.1063/1.4729053 (5 pages)

Online Publication Date: 12 June 2012

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Highly controllable fabrication of the nanowire, nanocone, and mixed nanowire/nanowall arrays of iron oxide (hematite, α-Fe2O3) nanostructures in a simple, environment-friendly process is achieved by exposing the metal foils to low-temperature oxygen plasmas. Very dense forests of thin (≈50 nm) and long (up to several μm) nanowires are grown on the electrically biased substrates, whereas the use of the electrically insulated substrate resulted in the formation of a mixed array of nanowires and nanowalls. The proposed mechanism of the nanostructure growth is supported by the numerical simulations demonstrating the key role of the plasma environment in the growth morphology selection.
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81.16.-c Methods of micro- and nanofabrication and processing
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)
02.60.-x Numerical approximation and analysis
52.77.-j Plasma applications

Light contact and surfing state dynamics of air bearing sliders in hard disk drives

Yung-Kan Chen, Jinglin Zheng, and David B. Bogy

Appl. Phys. Lett. 100, 243104 (2012); http://dx.doi.org/10.1063/1.4729055 (4 pages)

Online Publication Date: 12 June 2012

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We report experimental findings and simulation results that identify distinct dynamical phases during the light touchdown between the flying head and ultra-thin perfluoropolyether lubricant layer in resolution of Angstroms. Using an accurately controlled power supply with thermal fly-height control sliders, we observe that during light touchdown, the slider could reach the surfing phase, which is characterized by relatively low amplitude contact signals. The surfing state also contains a distinct frequency content and exhibits Angstrom-level modulations in the mobile part of the lubricant layers.
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89.20.Kk Engineering
46.55.+d Tribology and mechanical contacts
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Cabrera-Mott kinetics of oxidation of metal nanowires

Vladimir P. Zhdanov and Bengt Kasemo

Appl. Phys. Lett. 100, 243105 (2012); http://dx.doi.org/10.1063/1.4729059 (2 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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The Cabrera-Mott model, implying that oxidation of a metal is limited by the field-facilitated activated jumps of metal ions at the metal-oxide interface, was originally proposed to interpret growth of thin oxide films on planar metal surfaces. Recently, the model was used to describe oxidation of spherical nanoparticles with small radius of curvature. Here, we analyze oxidation of nanowires. The increase of the oxide thickness with increasing time for a nanowire is shown to be slower than that for a nanoparticle with the same radius, but faster than in the case of a planar surface.
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81.65.Mq Oxidation
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)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Pr Micro- and nano-oxidation

Metal cluster’s effect on the optical properties of cesium bromide thin films

Kuldeep Kumar, P. Arun, Chhaya Ravi Kant, and Bala Krishna Juluri

Appl. Phys. Lett. 100, 243106 (2012); http://dx.doi.org/10.1063/1.4729061 (4 pages)

Online Publication Date: 13 June 2012

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Cesium bromide (CsBr) films grown on glass substrates by thermal evaporation showed prominent absorption peaks in the UV-visible region. Interestingly, these absorption spectra showed peaks which red shifted over time in ambient exposure. Structural and morphological studies suggested decrease in particle size overtime which was unusual. Electron micrographs show the formation of “daughter” cesium nanorods from parent CsBr particles. Theoretical calculations show the optical behavior observed to be due to localized surface plasmon resonance resulting from cesium nanorods.
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78.66.Nk Insulators
78.68.+m Optical properties of surfaces
68.55.aj Insulators
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Ha Other nonmetallic inorganics

Direct observation of inner and outer G′ band double-resonance Raman scattering in free standing graphene

Zhiqiang Luo, Chunxiao Cong, Jun Zhang, Qihua Xiong, and Ting Yu

Appl. Phys. Lett. 100, 243107 (2012); http://dx.doi.org/10.1063/1.4729407 (4 pages)

Online Publication Date: 14 June 2012

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In contrary to the widely reported single and symmetric peak feature of G′ band in Raman spectrum of graphene, we herein report the observation of splitting in G′ band in free standing graphene. Our experimental findings provide a direct and strong support for the previous theoretical prediction that the coexistence of the outer and inner processes in the double-resonance Raman scattering would cause the splitting of G′ mode. The investigation of the influence of trigonal warping effect on the spectral features of G′ subbands further verified the theoretical interpretation established on the anisotropic electronic structure of graphene.
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78.30.Na Fullerenes and related materials
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
78.67.Wj Optical properties of graphene

Structural and optical properties of InAs/AlAsSb quantum dots with GaAs(Sb) cladding layers

Paul J. Simmonds, Ramesh Babu Laghumavarapu, Meng Sun, Andrew Lin, Charles J. Reyner, Baolai Liang, and Diana L. Huffaker

Appl. Phys. Lett. 100, 243108 (2012); http://dx.doi.org/10.1063/1.4729419 (5 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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We investigate the effect of GaAs1−xSbx cladding layer composition on the growth and properties of InAs self-assembled quantum dots surrounded by AlAs0.56Sb0.44 barriers. Lowering Sb-content in the GaAs1−xSbx improves the morphology of the InAs quantum dots and reduces cladding layer alloy fluctuations. The result is a dramatic increase in photoluminescence intensity from the InAs quantum dots, with a peak at 0.87 eV. The emission energy exhibits a cube root dependence on excitation power, consistent with the type-II band alignment of the quantum dots. The characteristics of this quantum dot system show promise for applications such as intermediate band solar cells.
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78.66.Fd III-V semiconductors
68.35.bg Semiconductors
68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
73.21.La Quantum dots
78.55.Cr III-V semiconductors

A compact lab-on-a-chip nanosensor for glycerol detection

Jiheng Zhao, Ali Hashmi, Jie Xu, and Wei Xue

Appl. Phys. Lett. 100, 243109 (2012); http://dx.doi.org/10.1063/1.4729424 (4 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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Real-time monitoring of glycerol concentration has significant meaning in many lab-on-a-chip applications. The existing sensors for glycerol detection have complicated fabrication and testing procedures and are not truly compatible with microfluidic systems for on-site detection. In this study, we explore the possibility of using an integrated single-walled carbon nanotubes nanosensor for glycerol detection. Our device enables real-time, in-channel detection of the concentration of static or flowing aqueous glycerol solutions. Sensor resistance is found to increase with an increasing glycerol-to-water weight ratio and is sensitive to flow velocity. We also highlight the sensing mechanisms for both conditions.
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87.80.Ek Mechanical and micromechanical techniques
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
47.85.Np Fluidics
82.80.-d Chemical analysis and related physical methods of analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Efficient manipulation of surface plasmon polariton waves in graphene

Hong Ju Xu, Wei Bing Lu, Wei Zhu, Zheng Gao Dong, and Tie Jun Cui

Appl. Phys. Lett. 100, 243110 (2012); http://dx.doi.org/10.1063/1.4729557 (4 pages) | Cited 1 time

Online Publication Date: 14 June 2012

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The propagation of surface plasmon polariton (SPP) wave can be controlled by tunable graphene conductivity via electrostatic gating and/or chemical doping. Here, we propose an alternative way to manipulate the SPP waves efficiently by designing the thickness of dielectric cladding on the graphene. Meanwhile, the SPP wave properties can be changed gradually rather than abruptly through designing the topology of cladding. Compared to the traditional method, the proposed approach is more convenient for machining with lower scattering loss. A plasmonic Luneburg lens has been realized using this method, which opens a useful way to achieve the planar plasmonic devices.
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81.05.ue Graphene
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.79.Bh Lenses, prisms and mirrors

Quantum dot photodegradation due to CdSe-ZnO charge transfer: Transient absorption study

K. Žídek, K. Zheng, P. Chábera, M. Abdellah, and T. Pullerits

Appl. Phys. Lett. 100, 243111 (2012); http://dx.doi.org/10.1063/1.4729382 (4 pages) | Cited 4 times

Online Publication Date: 15 June 2012

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We study changes in ultrafast transient absorption due to photodegradation of quantum dots attached to ZnO nanowire. The time-resolved measurements reveal impact of photodegradation on three distinct kinetic components present in transient absorption τ ∼ 7 ps, 80 ps, and 7.5 ns). In addition, we observe superlinear dependence of photodegradation rate on concentration of excited electrons. The data are used to evaluate the mean electron back-recombination time of ∼1 μs.
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78.67.Hc Quantum dots
78.47.jb Transient absorption
88.40.jm Thin film III-V and II-VI based solar cells
73.61.Ga II-VI semiconductors
73.63.Kv Quantum dots
78.66.Hf II-VI semiconductors
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