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28 Feb 2011

Volume 98, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 093502 (2011); http://dx.doi.org/10.1063/1.3531756 (3 pages)

Marina S. Leite, Robyn L. Woo, William D. Hong, Daniel C. Law, and Harry A. Atwater
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Luminescence decay dynamics of self-assembled germanium islands in silicon

B. Julsgaard, P. Balling, J. Lundsgaard Hansen, A. Svane, and A. Nylandsted Larsen

Appl. Phys. Lett. 98, 093101 (2011); http://dx.doi.org/10.1063/1.3559230 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2011

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The dynamics of the luminescence decay from self-assembled germanium islands embedded in crystalline silicon has been studied for temperatures varied between 16 K and room temperature. We separate the time scale for various dynamical processes by time-resolved emission spectroscopy and identify a characteristic time scale of Auger recombination processes around 10 ns largely independent on temperature, while two slower decay components appear on time scales around 1 μs and 10 μs, respectively, at low temperatures.
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81.16.Dn Self-assembly
78.47.jd Time resolved luminescence
79.60.-i Photoemission and photoelectron spectra
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Synthesis and waveguiding of single-crystalline LiNbO3 nanorods

Jingyun Huang, Zhong Chen, Zesong Zhang, Chongyu Zhu, Haiping He, Zhizhen Ye, Guangyuan Qu, and Limin Tong

Appl. Phys. Lett. 98, 093102 (2011); http://dx.doi.org/10.1063/1.3557524 (3 pages) | Cited 5 times

Online Publication Date: 28 February 2011

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Single-crystalline LiNbO3 nanorods with a trigonal rhombic crystal structure are synthesized through hydrothermal reaction with KOH, LiOH⋅H2O, and Nb2O5 as source materials. LiNbO3 nanorods were along the [110] crystallographic direction. KOH was found to be essential for the formation of one dimensional nanostructures. Meanwhile, waveguiding performance of the LiNbO3 nanorods was investigated. The as-synthesized nanorods exhibit broadband waveguiding capability in the experiments. High temperature annealing was also proved to be effective in enhancing the transmission of the nanowire waveguides by reducing the defects in the nanorods.
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42.82.Et Waveguides, couplers, and arrays
81.10.Dn Growth from solutions
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
42.70.-a Optical materials

Metal-dispersed porous graphene for hydrogen storage

Pakpoom Reunchan and Seung-Hoon Jhi

Appl. Phys. Lett. 98, 093103 (2011); http://dx.doi.org/10.1063/1.3560468 (3 pages) | Cited 15 times

Online Publication Date: 28 February 2011

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First-principles calculations are carried out to study the role of various metal atoms on porous graphene for molecular hydrogen (H2) adsorption. The binding sites of each metal atom on porous graphene are investigated and the binding energies are determined. It is shown that H2 exhibits different adsorption characteristics onto alkaline, alkaline-earth, or transition metals in porous graphene. In particular, Ca-decorated porous graphene is investigated and found to be feasible for high-capacity hydrogen storage. Our results provide a general picture on the interactions of H2 with porous graphene decorated with various metals.
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88.30.R- Hydrogen storage
61.43.Gt Powders, porous materials
68.43.Mn Adsorption kinetics

Direct evidence of dopant segregation in Gd-doped ceria

Zhi-Peng Li, Toshiyuki Mori, Graeme John Auchterlonie, Jin Zou, and John Drennan

Appl. Phys. Lett. 98, 093104 (2011); http://dx.doi.org/10.1063/1.3556650 (3 pages) | Cited 14 times

Online Publication Date: 1 March 2011

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Microstructures and segregations of dopants and associated oxygen vacancies in gadolinium-doped ceria (GDC) have been characterized by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM). Diffuse scattering was detected in 25 at. % GDC (25GDC) in comparison to 10GDC, which is ascribed to nanodomain formation in 25GDC. HRTEM, dark-field, and STEM Z-contrast imaging investigations all provide direct evidence for dopant segregation in doped ceria. It is illustrated that dopant cations cannot only segregate in grain interior forming larger nanodomains but also at grain boundary forming smaller ones. Detailed analyses about nanodomain formation and related dopant segregation behaviors are then elucidated.
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64.75.-g Phase equilibria
61.72.-y Defects and impurities in crystals; microstructure
61.72.jd Vacancies

Nanometer-scale molecular deposition using the surface Plasmon polariton interference field on a metal film

Yaling Yin, Tao Li, Ping Xu, Hua Jin, and Shining Zhu

Appl. Phys. Lett. 98, 093105 (2011); http://dx.doi.org/10.1063/1.3560306 (3 pages)

Online Publication Date: 1 March 2011

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We explore the possibility of using the surface plasmon polariton interference field to deposit neutral molecules onto a silver film perforated with two double-slits. The Monte Carlo simulated results show that the deposited molecular pattern is the periodic line array with a width resolution of ∼ 10 nm and a period of 530 nm when the molecular beam is well-collimated. Dependences of the deposition resolution on the system parameters, the potential applications and improvements are also discussed in some detail.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Nb Molecular nanostructures
61.46.-w Structure of nanoscale materials
73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electron beam heating effects during environmental scanning electron microscopy imaging of water condensation on superhydrophobic surfaces

K. Rykaczewski, J. H. J. Scott, and A. G. Fedorov

Appl. Phys. Lett. 98, 093106 (2011); http://dx.doi.org/10.1063/1.3560443 (3 pages) | Cited 12 times

Online Publication Date: 1 March 2011

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Superhydrophobic surfaces (SHSs) show promise as promoters of dropwise condensation. Droplets with diameters below ∼ 10 μm account for the majority of the heat transferred during dropwise condensation but their growth dynamics on SHS have not been systematically studied. Due to the complex topography of the surface environmental scanning electron microscopy is the preferred method for observing the growth dynamics of droplets in this size regime. By studying electron beam heating effects on condensed water droplets we establish a magnification limit below which the heating effects are negligible and use this insight to study the mechanism of individual drop growth.
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68.03.Fg Evaporation and condensation of liquids
61.80.Fe Electron and positron radiation effects
68.08.Bc Wetting

High frequency resistance of single-walled and multiwalled carbon nanotubes

Y. Yang, C. Y. Tan, W. Q. Sun, W. Li, C. K. Ong, Y. Liu, Y. Li, and S. Y. Xu

Appl. Phys. Lett. 98, 093107 (2011); http://dx.doi.org/10.1063/1.3558909 (3 pages) | Cited 3 times

Online Publication Date: 1 March 2011

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The electrical resistances of individual single-walled carbon nanotubes (SWCNTs), SWCNT arrays, and multiwalled carbon nanotube (MWCNT) bundles have been measured from frequency of 10 MHz to 16 GHz, using vector network analyzer and ground-source-ground probe on coplanar waveguide (CPW) structured sample stages. Full-wave electromagnetic simulation of the structure has also been performed. Analysis of the experimental and stimulated data indicates that the resistances of individual SWCNTs, SWCNT arrays, and MWCNT bundles are nearly independent of frequency within the frequency range under study. We have also calculated the parasitic capacitance of the CPW open structure, and the results indicate that the parasitic capacitance can greatly influence the high frequency measurement because of high impedance of SWCNT samples.
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73.63.Fg Nanotubes
84.40.Az Waveguides, transmission lines, striplines

Functionalized graphene nanoroads for quantum well device

Y. G. Zhou, P. Yang, Z. G. Wang, H. Y. Xiao, X. T. Zu, X. Sun, M. A. Khaleel, and F. Gao

Appl. Phys. Lett. 98, 093108 (2011); http://dx.doi.org/10.1063/1.3560981 (3 pages) | Cited 1 time

Online Publication Date: 2 March 2011

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Using density functional theory, a series of calculations of structural and electronic properties of Si-substituted graphene were conducted. Through substituting C atoms by Si atoms on graphene in the present study, we found that the band gap of graphene can be continuously tuned with differently substitutional concentration. To utilize such substitution-induced band gap changes, we proposed a special design to fabricate graphene-based quantum well device.
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81.05.ue Graphene
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Atomic-resolution scanning transmission electron microscopy through 50-nm-thick silicon nitride membranes

Ranjan Ramachandra, Hendrix Demers, and Niels de Jonge

Appl. Phys. Lett. 98, 093109 (2011); http://dx.doi.org/10.1063/1.3561758 (3 pages) | Cited 5 times

Online Publication Date: 2 March 2011

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Silicon nitride membranes can be used for windows of environmental chambers for in situ electron microscopy. We report that aberration corrected scanning transmission electron microscopy (STEM) achieved atomic resolution on gold nanoparticles placed on both sides of a 50-nm-thick silicon nitride membrane at 200 keV electron beam energy. Spatial frequencies of 1/1.2 Å were visible for a beam semi-angle of 26.5 mrad. Imaging though a 100-nm-thick membrane was also tested. The achieved imaging contrast was evaluated using Monte Carlo simulations of the STEM imaging of a sample of with a representative geometry and composition.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Vertical ZnO nanorod/Si contact light-emitting diode

Sang Wuk Lee, Hak Dong Cho, Gennady Panin, and Tae Won Kang

Appl. Phys. Lett. 98, 093110 (2011); http://dx.doi.org/10.1063/1.3562608 (3 pages) | Cited 9 times

Online Publication Date: 2 March 2011

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Blue-white light emission was obtained from glass/indium tin oxide (ITO)/n-ZnO nanorod array (NRA)/p+-Si vertical contact light emitting diodes (VCLEDs). The nanoscale p-n heterojunction VCLEDs were formed by direct engagement n−-tips of n-ZnO NRA grown vertically on an ITO/glass substrate with p+-Si wafer. Proposed configuration of the VCLED allows creating a high density ( ∼ 109 cm−2) of self-assembled ZnO/Si nanodiodes with point junctions of high quality due to structural perfection of the Si wafer and the tips of ZnO nanorods as well as providing a high injection current and light emission from the NRA VCLED required for solid state lighting.
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85.60.Jb Light-emitting devices
42.86.+b Optical workshop techniques

Dependence of transport on adatom location for armchair-edge graphene nanoribbons

Xiongwen Chen, Kehui Song, Benhu Zhou, Haiyan Wang, and Guanghui Zhou

Appl. Phys. Lett. 98, 093111 (2011); http://dx.doi.org/10.1063/1.3555445 (3 pages) | Cited 3 times

Online Publication Date: 2 March 2011

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We study the transport property for armchair-edge graphene nanoribbons (AGNRs) with an adatom coupling to a semi-infinite quantum wire. Using the nonequilibrium Green’s function (NEGF) approach with tight-binding approximation, we demonstrate that the tunneling current through the system is sensitively dependent on both the AGNR width and adatom location. Interestingly, when the adatom locates onto a carbon atom in the 3jth chain from the edge of a metallic AGNR, the system shows a transmission gap accompanied by a threshold voltage like a semiconducting AGNR. This effect may be useful in scanning tunneling microscopy experimental characterization on graphene samples.
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72.80.Vp Electronic transport in graphene
61.48.Gh Structure of graphene
73.40.Gk Tunneling
73.63.Nm Quantum wires
61.46.-w Structure of nanoscale materials

Assembly of CdSe nanoparticles on graphene for low-temperature fabrication of quantum dot sensitized solar cell

Shengrui Sun, Lian Gao, Yangqiao Liu, and Jing Sun

Appl. Phys. Lett. 98, 093112 (2011); http://dx.doi.org/10.1063/1.3558732 (3 pages) | Cited 7 times

Online Publication Date: 2 March 2011

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Quantum dot sensitized solar cell (QDSSC) was fabricated in a low-temperature process based on graphene-CdSe composite, which was prepared by the procedures of immobilizing CdSe on graphene oxide (GO) and reduction in GO. It was found that the charge separation between excited CdSe and graphene could be tapped to generate photocurrent from photocurrent measurements, which established the ability of graphene to collect and transport electrons. By optimizing the CdSe-to-GO ratio at 4.5:1, the obtained graphene-CdSe-based cells exhibited significantly higher short-circuit photocurrent and energy conversion efficiency (5.8 mA/cm2 and 0.72%, respectively) than the reported values of the C60 or carbon nanotube related QDSSC, demonstrating that the graphene-CdSe composite is an attractive candidate in energy conversion devices.
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88.40.H- Solar cells (photovoltaics)
81.07.Ta Quantum dots
72.40.+w Photoconduction and photovoltaic effects

Polarization independent visible color filter comprising an aluminum film with surface-plasmon enhanced transmission through a subwavelength array of holes

Daisuke Inoue, Atsushi Miura, Tsuyoshi Nomura, Hisayoshi Fujikawa, Kazuo Sato, Naoki Ikeda, Daiju Tsuya, Yoshimasa Sugimoto, and Yasuo Koide

Appl. Phys. Lett. 98, 093113 (2011); http://dx.doi.org/10.1063/1.3560467 (3 pages) | Cited 7 times

Online Publication Date: 2 March 2011

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The enhanced transmission through periodic arrays of sub-wavelength holes in optically-thick metallic films has many potential applications, such as in wavelength filters, light extraction from light emission diodes, and subwavelength photolithography. A color filter comprising arrays of subwavelength holes in an aluminum film has been fabricated. In addition to the simplicity of the process, the aluminum film enables the excitation of visible-range surface plasmons due to its high plasma frequency. Periodic nanostructures in the aluminum film open the way for new visible color filters.
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42.79.Ci Filters, zone plates, and polarizers
42.86.+b Optical workshop techniques

Strain engineering of band offsets in Si/Ge core-shell nanowires

Shouting Huang and Li Yang

Appl. Phys. Lett. 98, 093114 (2011); http://dx.doi.org/10.1063/1.3561773 (3 pages) | Cited 6 times

Online Publication Date: 3 March 2011

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We present first-principles studies on how to engineer band lineups of nanosized radial heterojunctions, Si/Ge core-shell nanowires. Our calculation reveals that band offsets of these one-dimensional nanostructures can be tailored by applying the axial strain. In particular, the valence band offset can be efficiently tuned in a wide range and even be diminished with applied strain. Two mechanisms contributing to this strain engineering of band offsets are discussed. Our proposed approach to control band offsets in nanosized heterojunctions may be of practical interest for nanoelectronics and photovoltaic applications.
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73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.65.La Quantum wires (patterned in quantum wells)

Enhanced photosensitivity of electro-oxidized epitaxial graphene

Mikhail E. Itkis, Feihu Wang, Palanisamy Ramesh, Elena Bekyarova, Sandip Niyogi, Xiaoliu Chi, Claire Berger, Walt A. de Heer, and Robert C. Haddon

Appl. Phys. Lett. 98, 093115 (2011); http://dx.doi.org/10.1063/1.3562316 (3 pages) | Cited 1 time

Online Publication Date: 3 March 2011

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We report the enhanced photosensitivity of epitaxial graphene (EG) after electrochemical oxidation in nitric acid. The onset of photoconductivity appears at a photon energy of ∼ 1.7 eV while the responsivity reaches 2.5 A/W at a wavelength of 470 nm (blue light, energy 2.64 eV) and further increases to 200 A/W in the UV spectral range (3.5 eV, 350 nm). The observed photoresponse is attributed to the formation of deep traps at the electro-oxidized EG interface, which release charge carriers under illumination and prolong the life time of the photocarriers. Potential applications of electro-oxidized EG in ultraviolet photodetection are discussed.
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73.61.Wp Fullerenes and related materials
73.50.Pz Photoconduction and photovoltaic effects
81.65.Mq Oxidation
82.45.Aa Electrochemical synthesis
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.65.+h Molecular electronic devices

Binding mechanisms of molecular oxygen and moisture to graphene

Yinxiao Yang and Raghu Murali

Appl. Phys. Lett. 98, 093116 (2011); http://dx.doi.org/10.1063/1.3562317 (3 pages) | Cited 12 times

Online Publication Date: 4 March 2011

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We report on the binding mechanisms of oxygen and water to graphene by comparing the doping of graphene in a dry O2 environment versus in ambient. It is seen that dry oxygen dopes graphene from the basal plane while the ambient dopes graphene from the edges or from the substrate in the vicinity of the edge. Upon vacuum annealing, doping is fully reversible in the former case and only partially reversible in the latter case. We observe a thickness-dependent doping as a result of the difference in host sites for doping (basal plane versus edge). Finally, hysteresis is shown to be triggered even in dry oxygen.
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73.61.Wp Fullerenes and related materials
61.72.U- Doping and impurity implantation
61.72.Cc Kinetics of defect formation and annealing
81.05.ue Graphene

Volumetric plasmonic resonator architecture for thin-film solar cells

Mustafa Akin Sefunc, Ali Kemal Okyay, and Hilmi Volkan Demir

Appl. Phys. Lett. 98, 093117 (2011); http://dx.doi.org/10.1063/1.3560446 (3 pages) | Cited 11 times

Online Publication Date: 4 March 2011

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We propose and demonstrate a design concept of volumetric plasmonic resonators that relies on the idea of incorporating coupled layers of plasmonic structures embedded into a solar cell in enhanced optical absorption for surface-normal and off-axis angle configurations, beyond the enhancement limit of individual plasmonic layers. For a proof-of-concept demonstration in a thin-film organic solar cell that uses absorbing materials of copper phthalocyanine/perylene tetracarboxylic bisbenzimidazole, we couple two silver grating layers such that the field localization is further extended within the volume of active layers. Our computational results show a maximum optical absorption enhancement level of ∼ 67% under air mass 1.5 global illumination considering both polarizations.
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88.40.H- Solar cells (photovoltaics)
88.40.jr Organic photovoltaics
42.79.Wc Optical coatings

Superhydrophobic surface at low surface temperature

Min He, Huiling Li, Jianjun Wang, and Yanlin Song

Appl. Phys. Lett. 98, 093118 (2011); http://dx.doi.org/10.1063/1.3558911 (3 pages) | Cited 9 times

Online Publication Date: 4 March 2011

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Superhydrophobic surfaces have aroused great attention for promising applications, e.g., anti-ice/frost. However, most surfaces which are superhydrophobic at room temperature lose their superhydrophobicity at low surface temperatures. Here, surfaces with different area fractions of the solid surface in contact with the liquid (f1) were designed. It is found that surfaces with f1 equal to or smaller than 0.068 maintain the superhydrophobicity when the surface temperature approaches the dew-point. These results are crucial to understand the correlation between the surface morphology and the superhydrophobicity around the dew-point, and design effective surfaces with desired wettability.
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68.08.Bc Wetting
68.35.B- Structure of clean surfaces (and surface reconstruction)
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