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13 Sep 2010

Volume 97, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages)

Sarah E. Baker, Michael D. Pocha, Allan S. P. Chang, Donald J. Sirbuly, Stefano Cabrini, Scott D. Dhuey, Tiziana C. Bond, and Sonia E. Létant
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Inhibited single-electron transfer by electronic band gap of two-dimensional Au quantum dot superlattice

Rui Xu, Yi Sun, Ji-Yong Yang, Lin He, Jia-Cai Nie, Lingling Li, and Yadong Li

Appl. Phys. Lett. 97, 113101 (2010); http://dx.doi.org/10.1063/1.3489436 (3 pages) | Cited 2 times

Online Publication Date: 13 September 2010

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The electronic density of states of two-dimensional (2D) Au quantum dot superlattice are explored by using cryogenic scanning tunneling microscopy and scanning tunneling spectroscopy. The 2D Au superlattice opens up a gap in its electronic density of states. The single-electron transfer of a single Au quantum dot can be effectively inhibited by this “artificial” forbidden gap. This finding opens a route toward modulating electronic energy band of solid on the basis of 2D metal quantum dot superlattice, which may generate materials with electronic properties for possible future electronic devices.
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73.21.La Quantum dots
73.21.Cd Superlattices
71.20.-b Electron density of states and band structure of crystalline solids

Edge dopant energy levels of graphene nanoribbons

Yang Lu and Jing Guo

Appl. Phys. Lett. 97, 113102 (2010); http://dx.doi.org/10.1063/1.3489690 (3 pages)

Online Publication Date: 14 September 2010

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Edge doping of graphene flakes and graphene nanoribbons (GNRs) was achieved in recent experiments. Atomistic self-consistent simulations are performed in this study to compute the edge dopant energy levels of GNRs. The results indicate that the energy required to ionize the edge dopant in a sub-10 nm wide GNR increases considerably as the GNR width decreases and it is sensitive to electrostatic environment such as the substrate and gate insulator materials. These unusual behaviors of dopants in a GNR are due to its quasi-one-dimensional structure and monolayer-thin body.
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81.05.ue Graphene
85.30.Tv Field effect devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.22.Pr Electronic structure of graphene

Properties of hybrid organic-inorganic systems: Au nanoparticles embedded into an organic CuPc matrix

V. Yu. Aristov, O. V. Molodtsova, C. Laubschat, V. M. Zhilin, I. M. Aristova, V. V. Kveder, and M. Knupfer

Appl. Phys. Lett. 97, 113103 (2010); http://dx.doi.org/10.1063/1.3488809 (3 pages) | Cited 2 times

Online Publication Date: 15 September 2010

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The evolution of the morphology and the electronic structure of the hybrid organic-inorganic system composed of gold nanoparticles (NPs) distributed in an organic matrix—copper phthalocyanine (CuPc)—as a function of nominal gold content was studied by transmission electron microscopy and by surface and bulk sensitive spectroscopic methods. The gold atoms deposited onto the CuPc surface diffuse into the organic matrix and self-assemble to NPs. There is no formation of a continuous metallic Au film on top of the CuPc film up to large nominal coverage of about 130 Å considered in the present study. The gold is assembled in well defined NPs with metallic properties.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Lp Transmission electron microscopy (TEM)
71.20.Rv Polymers and organic compounds

Incomplete screening by epitaxial graphene on the Si face of 6H–SiC(0001)

Andreas Sandin, Alex Pronschinske, J. E. (Jack) Rowe, and Daniel B. Dougherty

Appl. Phys. Lett. 97, 113104 (2010); http://dx.doi.org/10.1063/1.3484966 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2010

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A biased scanning tunneling microscope (STM) tip is used to study the ability of carriers in graphene to screen external electrostatic fields by monitoring the effect of tunneling-junction width on the position of image potential-derived surface states. These states are unusually sensitive to local electric fields due to the STM tip in both single layer and bilayer epitaxial graphene. This is attributed to the incomplete screening of applied fields in epitaxial graphene on SiC(0001). Our observations imply that charged impurity scattering is likely to be a dominant factor in the transport properties of epitaxial graphene on SiC.
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81.05.ue Graphene
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
73.61.Wp Fullerenes and related materials
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
73.20.At Surface states, band structure, electron density of states

Nanopore-array-dispersed semiconductor quantum dots as nanosensors for gas detection

Zhouying Zhao, Teresa M. Dansereau, Marina A. Petrukhina, and Michael A. Carpenter

Appl. Phys. Lett. 97, 113105 (2010); http://dx.doi.org/10.1063/1.3489366 (3 pages) | Cited 5 times

Online Publication Date: 15 September 2010

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CdSe quantum dots (QDs) and anodic aluminum oxide (AAO) nanopore arrays were integrated to form an optically active element for chemical vapor detection. The introduction of porous AAO as a platform for QD dispersion is found to have twofolds of merit for QD based chemical sensing. First, AAO intensifies QD photoluminescence (PL), thus increasing the measurable responses, due both to redistributing high intensity near-fields for efficient excitation of QDs and introducing strong scattering effects for enhanced extraction of the resulting QD emission. Second, the nanopores of AAO retard film-wetting effects which occur at higher target chemical exposures and result in an inverted PL response as seen from QDs or QD-polymer films cast on nonporous substrates. The PL and response sensitivity of QDs on AAO is further increased through the use of an Au coated silicon support which increases the overall reflectivity of the composite material stack. These strategies enable QD-based materials to be used for sensitive detection of chemical vapors with monotonic trends across large concentration ranges, for example, 10–9400 ppm xylenes. This method is readily extendable to other systems and opens the door to the development of QD-based optical or optoelectronic devices.
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82.53.Mj Femtosecond probing of semiconductor nanostructures
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.60.-q Optoelectronic devices

Planar polar liquid crystalline alignment in nanostructured porous silicon one-dimensional photonic crystals

Shahar Mor, Vicente Torres-Costa, Raúl J. Martín-Palma, and I. Abdulhalim

Appl. Phys. Lett. 97, 113106 (2010); http://dx.doi.org/10.1063/1.3489428 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2010

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The ability of liquid crystals (LCs) to flow and fill nanopores assists in using them for infiltration into porous nanophotonic structures such as nanostructured porous silicon (nanoPS). The reflectivity spectra at normal incidence from periodic nanostructured nanoPS filters infiltrated with nematic LC is found to exhibit polarization dependence. This is experimental evidence that the LC molecules in the nanoPS matrix are aligned such that an effective anisotropy exists parallel to the substrate plane. From the theoretical fit the preferred configuration was found to be the planar-polar geometry which is shown to be biaxial.
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61.30.-v Liquid crystals
81.07.Bc Nanocrystalline materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
81.05.Cy Elemental semiconductors

High emission current density, vertically aligned carbon nanotube mesh, field emitter array

Chi Li, Yan Zhang, Mark Mann, David Hasko, Wei Lei, Baoping Wang, Daping Chu, Didier. Pribat, Gehan A. J. Amaratunga, and William I. Milne

Appl. Phys. Lett. 97, 113107 (2010); http://dx.doi.org/10.1063/1.3490651 (3 pages) | Cited 5 times

Online Publication Date: 16 September 2010

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A vertically aligned carbon nanotube mesh emitter array has been fabricated and tested, giving a current density of up to 1.5 A/cm2, and a threshold field of 1.5 V/μm for a current density 1 mA/cm2. Low temperature carbon nanotube growth is used to fabricate the carbon nanotube mesh emitter arrays significantly reducing the cost of the fabrication of large area electron emitters. This system exhibits ultralong lifetime.
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81.07.De Nanotubes
61.46.Fg Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.45.Db Field emitters and arrays, cold electron emitters
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Single quantum dot nanowire photodetectors

M. P. van Kouwen, M. H. M. van Weert, M. E. Reimer, N. Akopian, U. Perinetti, R. E. Algra, E. P. A. M. Bakkers, L. P. Kouwenhoven, and V. Zwiller

Appl. Phys. Lett. 97, 113108 (2010); http://dx.doi.org/10.1063/1.3484962 (3 pages) | Cited 11 times

Online Publication Date: 16 September 2010

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We report InP nanowire photodetectors with a single InAsP quantum dot as light absorbing element. With excitation above the InP band gap, the nanowire photodetectors are efficient (quantum efficiency of 4%). Under resonant excitation of the quantum dot, the photocurrent amplitude depends on the linear polarization direction of the incident light. The photocurrent is enhanced (suppressed) for a polarization parallel (perpendicular) to the axis of the nanowire (contrast 0.83). The active detection volume under resonant excitation is 7×103 nm3. These results show the promising features of quantum dots embedded in nanowire devices for electrical light detection at high spatial resolution.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Gv Single electron devices
85.35.Ds Quantum interference devices

Production of hollow hemisphere shells by pure Kirkendall porosity formation in Au/Ag system

Györgyi Glodán, Csaba Cserháti, Imre Beszeda, and Dezső L. Beke

Appl. Phys. Lett. 97, 113109 (2010); http://dx.doi.org/10.1063/1.3490675 (3 pages) | Cited 8 times

Online Publication Date: 17 September 2010

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Interdiffusion has been studied in Ag/Au hemispherical core-shell structures on sapphire substrate. In isothermal heat treatments first a relatively fast growth of nanovoids was observed, which was followed by a slower shrinkage process. The void formation is interpreted by pure Kirkendall-porosity formation since Ag-50%Au solid solution has been formed in the shell. In contrary, in all previous publications on hollow nanoshell formation a chemical reaction took place and the shell consisted of the reaction product (i.e., of sulphide or oxide). Furthermore, in these cases the shrinkage was observed at temperatures higher than the formation temperature.
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66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
61.72.Qq Microscopic defects (voids, inclusions, etc.)
82.30.-b Specific chemical reactions; reaction mechanisms

Picosecond optical spectroscopy of a single negatively charged self-assembled InAs quantum dot

Erik D. Kim, Katherine Truex, Yanwen Wu, A. Amo, Xiaodong Xu, D. G. Steel, A. S. Bracker, D. Gammon, and L. J. Sham

Appl. Phys. Lett. 97, 113110 (2010); http://dx.doi.org/10.1063/1.3487783 (3 pages) | Cited 1 time

Online Publication Date: 17 September 2010

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We demonstrate an experimental technique for the transient read-out of the optical transitions in a single negatively charged self-assembled InAs quantum dot (QD) using resonant picosecond optical pulses and control of the QD charge state. Observable phenomena include trion (negatively charged exciton) decay, Rabi oscillations between the electron and trion states and the precession of electron and heavy-hole spins about an externally applied dc magnetic field.
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73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Pq Charged excitons (trions)
78.67.Hc Quantum dots
78.47.J- Ultrafast spectroscopy (<1 psec)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
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