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25 Apr 2011

Volume 98, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 98, 171102 (2011); http://dx.doi.org/10.1063/1.3582035 (3 pages)

Shigeru Nakayama, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa
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Li-doped B2C graphene as potential hydrogen storage medium

Hui An, Chun-sheng Liu, Zhi Zeng, Chao Fan, and Xin Ju

Appl. Phys. Lett. 98, 173101 (2011); http://dx.doi.org/10.1063/1.3583465 (3 pages) | Cited 5 times

Online Publication Date: 25 April 2011

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Based on first-principles density functional theory, we show that Li-doped B2C graphene can serve as a high-capacity hydrogen storage medium with the gravimetric density of 7.54 wt %. The present results indicate that the strong binding of Li onto the substrate comes from the hybridizations of B 2p and C 2p orbitals with the partial occupancy of Li 2p orbitals. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of H2 molecules and the resulting adsorption energy is in the range of 0.12–0.22 eV/H2. The system reported here is favorable for the reversible hydrogen adsorption/desorption at the room temperature.
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88.30.rd Inorganic metal hydrides
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.43.Mn Adsorption kinetics
84.60.Ve Energy storage systems, including capacitor banks
68.43.Nr Desorption kinetics
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Graphyne- and graphdiyne-based nanoribbons: Density functional theory calculations of electronic structures

L. D. Pan, L. Z. Zhang, B. Q. Song, S. X. Du, and H.-J. Gao

Appl. Phys. Lett. 98, 173102 (2011); http://dx.doi.org/10.1063/1.3583507 (3 pages) | Cited 20 times

Online Publication Date: 25 April 2011

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We report on the configurations and electronic properties of graphyne and graphdiyne nanoribbons with armchair and zigzag edges investigated with first principles calculations. Our results show that all the nanoribbons are semiconductors with suitable band gaps similar to silicon. And their band gaps decrease as widths of nanoribbons increase. We also find that the band gap is at the Γ point for all graphdiyne ribbons and it is at the X point for all graphyne ribbons. Of particular interest, the band gap of zigzag graphyne nanoribbons show a unique “step effect” as the width increases. This property is good for tuning of the energy band gap, as in a certain range of the ribbon width, the energy gap remains constant and in reality the edge cannot be as neat as that in a theoretic model.
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81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Effect of surface passivation on dopant distribution in Si quantum dots: The case of B and P doping

Jie Ma, Su-Huai Wei, Nathan R. Neale, and Arthur J. Nozik

Appl. Phys. Lett. 98, 173103 (2011); http://dx.doi.org/10.1063/1.3583663 (3 pages) | Cited 4 times

Online Publication Date: 25 April 2011

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Despite many efforts, the doping behavior in Si quantum dots (QDs) is still not well understood. Theoretical work shows that boron as an acceptor prefers to stay near the surface and phosphorous as a donor may stay close to the center in a perfectly hydrogen passivated QD. However, experiment studies seem suggesting an opposite trend. Using first-principle methods, we show that the discrepancy could be explained by the imperfectness of surface passivation of the QD. We find that, in QDs with hydrogen deficient or oxygen rich surfaces, phosphorous prefers the surface sites and boron may stay inside, consistent with experiment observations.
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61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
81.65.Rv Passivation
71.15.-m Methods of electronic structure calculations

Strong coupling between a photonic crystal nanobeam cavity and a single quantum dot

Ryuichi Ohta, Yasutomo Ota, Masahiro Nomura, Naoto Kumagai, Satomi Ishida, Satoshi Iwamoto, and Yasuhiko Arakawa

Appl. Phys. Lett. 98, 173104 (2011); http://dx.doi.org/10.1063/1.3579535 (3 pages) | Cited 8 times

Online Publication Date: 26 April 2011

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We demonstrated the strong coupling between a one-dimensional photonic crystal nanobeam cavity and a single quantum dot (QD). Thanks to a high quality factor ( ∼ 25 000) with small mode volume [0.38×(n/λ)3] of the nanobeam cavity, an anticrossing behavior with a vacuum Rabi splitting of 226 μeV was observed. The ratio of the QD-cavity coupling strength to the cavity decay rate, which is a figure of merit of quantum optical applications, is estimated to 2.1. This is the highest value among any QD-based cavity quantum electrodynamics systems reported so far.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.70.Qs Photonic bandgap materials
42.79.-e Optical elements, devices, and systems

Electrical current mediated interconversion between graphene oxide to reduced grapene oxide

H. F. Teoh, Y. Tao, E. S. Tok, G. W. Ho, and C. H. Sow

Appl. Phys. Lett. 98, 173105 (2011); http://dx.doi.org/10.1063/1.3580762 (3 pages) | Cited 3 times

Online Publication Date: 26 April 2011

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In this work, we demonstrate that graphene oxide (GO) can be reversibly converted to reduced-graphene-oxide (rGO) through the use of electric current. Strong electric field could cause ionization of water molecules in air to generate H+ ions at cathode, causing GO to be reduced. When the bias is reversed, the same electrode becomes positive and OH− ions are produced. According to Le Chatelier Principle, it then favors the reverse reaction, converting rGO back to GO, GO+2H++2e− = >rGO+H2O. X-ray spectroscopy and Raman spectroscopy were carried to verify the conversion reversibility in the reversed process.
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81.05.ue Graphene
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.48.Gh Structure of graphene
78.30.Na Fullerenes and related materials

Strain balanced quantum posts

D. Alonso-Álvarez, B. Alén, J. M. Ripalda, J. M. Llorens, A. G. Taboada, F. Briones, M. A. Roldán, J. Hernández-Saz, D. Hernández-Maldonado, M. Herrera, and S. I. Molina

Appl. Phys. Lett. 98, 173106 (2011); http://dx.doi.org/10.1063/1.3583455 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2011

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Quantum posts are assembled by epitaxial growth of closely spaced quantum dot layers, modulating the composition of a semiconductor alloy, typically InGaAs. In contrast with most self-assembled nanostructures, the height of quantum posts can be controlled with nanometer precision, up to a maximum value limited by the accumulated stress due to the lattice mismatch. Here, we present a strain compensation technique based on the controlled incorporation of phosphorous, which substantially increases the maximum attainable quantum post height. The luminescence from the resulting nanostructures presents giant linear polarization anisotropy.
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81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots

Ballistic thermoelectricity in double-bend nanowires

Jun Zhou and Ronggui Yang

Appl. Phys. Lett. 98, 173107 (2011); http://dx.doi.org/10.1063/1.3583670 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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We investigate ballistic thermoelectric transport in double-bend nanowires. The geometric confinement induces quantum interference effect, which results in large Seebeck coefficient. The Seebeck coefficient (both the sign and the amplitude) is tunable by changing the structural parameters of the double-bend nanowires. Geometry-controlled ballistic thermoelectric effect could potentially be explored to design thermoelectric devices such as thermocouples at nanoscale.
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73.23.Ad Ballistic transport
73.63.Nm Quantum wires

Formation of graphene sheets through laser exfoliation of highly ordered pyrolytic graphite

Min Qian, Yun Shen Zhou, Yang Gao, Jong Bok Park, Tao Feng, Su Mei Huang, Zhuo Sun, Lan Jiang, and Yong Feng Lu

Appl. Phys. Lett. 98, 173108 (2011); http://dx.doi.org/10.1063/1.3584021 (3 pages) | Cited 5 times

Online Publication Date: 28 April 2011

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Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation.
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81.05.ue Graphene
42.62.-b Laser applications

Three-dimensional mapping of nickel oxidation states using full field x-ray absorption near edge structure nanotomography

George J. Nelson, William M. Harris, John R. Izzo, Jr., Kyle N. Grew, Wilson K. S. Chiu, Yong S. Chu, Jaemock Yi, Joy C. Andrews, Yijin Liu, and Piero Pianetta

Appl. Phys. Lett. 98, 173109 (2011); http://dx.doi.org/10.1063/1.3574774 (3 pages) | Cited 11 times

Online Publication Date: 28 April 2011

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The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.
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82.47.Ed Solid-oxide fuel cells (SOFC)
82.45.Fk Electrodes
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
78.70.Dm X-ray absorption spectra
68.37.Yz X-ray microscopy

Self-assembled ordered arrays of nanoscale germanium Esaki tunnel diodes

Kaigui Zhu, Wu Wang, Qingyi Shao, Dongning Zhao, Yongfeng Lu, and Natale Ianno

Appl. Phys. Lett. 98, 173110 (2011); http://dx.doi.org/10.1063/1.3583673 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2011

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We have self-assembled regimented arrays of vertical ∼ 100 nm diameter Ge Esaki tunnel diodes using nanosphere lithography. Measurements of the current-voltage characteristics of individual nanodiodes using conductive atomic force microscopy at room temperature reveal pronounced negative differential resistance under forward bias, with a peak to valley ratio of 2–4. These diode arrays could constitute a neuromorphic circuit architecture exhibiting collective computational activity.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.-p Nanoelectronic devices

Plasmonic interferences in two-dimensional stacked double-disk array

Zong-Suo Zhang, Zhong-Jian Yang, Jian-Bo Li, Zhong-Hua Hao, and Qu-Quan Wang

Appl. Phys. Lett. 98, 173111 (2011); http://dx.doi.org/10.1063/1.3583999 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2011

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We numerically investigate the resonant spectral features of the two-dimensional stacked double-disk array. Narrow plasmon line shapes are observed on resonance spectra which are similar to the case of single-disk array. The electric field shows that the narrow plasmon modes are produced by the dark plasmon mode coupling to the diffraction which may be due to the retardation effect. The narrow mode and the dark mode overlap on resonance spectra, resulting in a Fano-like spectrum. The intensities of the electric fields for these narrow modes arising from the dark mode coupling are much stronger than that of the bright modes.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

L. Seravalli, G. Trevisi, P. Frigeri, D. Rivas, G. Muñoz-Matutano, I. Suárez, B. Alén, J. Canet-Ferrer, and J. P. Martínez-Pastor

Appl. Phys. Lett. 98, 173112 (2011); http://dx.doi.org/10.1063/1.3584132 (3 pages) | Cited 4 times

Online Publication Date: 29 April 2011

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See Also: Publisher's Note

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We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 108 cm−2 dot density and metamorphic InxGa1−xAs (x = 0.15,0.30) confining layers result in emission wavelengths at 1.3 μm. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows.
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81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
73.21.La Quantum dots
78.67.Hc Quantum dots
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