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2 Aug 2010

Volume 97, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 97, 051101 (2010); http://dx.doi.org/10.1063/1.3470591 (3 pages)

Pascal Böhi, Max F. Riedel, Theodor W. Hänsch, and Philipp Treutlein
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Self-assembled GaAs islands on Si by droplet epitaxy

C. Somaschini, S. Bietti, N. Koguchi, F. Montalenti, C. Frigeri, and S. Sanguinetti

Appl. Phys. Lett. 97, 053101 (2010); http://dx.doi.org/10.1063/1.3475923 (3 pages) | Cited 5 times

Online Publication Date: 2 August 2010

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We presented an innovative fabrication technique for the self-assembly of GaAs islands on Si substrates by droplet epitaxy. The islands show highly tunable density (from 107 to some 109 islands/cm2) and size (from 75 to 250 nm), and small size dispersion (below 10%). The islands, made by single relaxed crystals with lattice parameters close to the GaAs bulk, show well defined shapes, with a high aspect ratio. The low thermal budget required for the island self-assembly, together with the high scalability of the process, make these islands good candidates for local artificial substrates or local strain sources with the required lattice parameters, band alignment, and crystalline quality as now required for the implementation of high quality devices on Si.
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68.55.A- Nucleation and growth
68.55.ag Semiconductors
61.50.-f Structure of bulk crystals

Amplified nanopatterning by self-organized shadow mask ion lithography

D. Chiappe, A. Toma, Z. Zhang, C. Boragno, and F. Buatier de Mongeot

Appl. Phys. Lett. 97, 053102 (2010); http://dx.doi.org/10.1063/1.3473770 (3 pages) | Cited 4 times

Online Publication Date: 2 August 2010

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The self-organized formation of high aspect ratio dielectric nanostructures can be guided and sped-up recurring to a sacrificial metal film during ion beam sputtering. Following ion irradiation, the metal film evolves into a disconnected array of laterally ordered nanowires, which guide etching of the dielectric substrate. While the amplification rate of large scale features can be described simply in terms of the ratio of the sputtering yields of substrate and film, for small scale features the amplification rate depends on the interplay and lateral range of the smoothing and erosive mechanisms of the two materials.
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85.40.Hp Lithography, masks and pattern transfer

Aqueous-based synthesis of atomic gold clusters: Geometry and optical properties

S. Rath, S. Nozaki, D. Palagin, V. Matulis, O. Ivashkevich, and S. Maki

Appl. Phys. Lett. 97, 053103 (2010); http://dx.doi.org/10.1063/1.3467261 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2010

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Gold clusters synthesized by the solution-based growth technique have exhibited ultraviolet (UV) light emission with nearly zero Stokes shift. Atomic arrangement decided optical properties of the Au microclusters have been studied extensively. In addition to the time-of-flight mass spectra, the comparison of experimental and theoretical emission and absorption spectra confirms the presence of Au8 clusters with the planar hexagon+1-shaped geometry. The observed UV emission is attributed to the transition from the highest occupied to the lowest unoccupied molecular orbitals of the hexagon+1 structured Au8 clusters.
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36.40.Vz Optical properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
32.30.Jc Visible and ultraviolet spectra
32.10.Bi Atomic masses, mass spectra, abundances, and isotopes

Charge carrier separation induced by intrinsic surface strain in pristine ZnO nanowires

Liangzhi Kou, Chun Li, Zi-Yue Zhang, Changfeng Chen, and Wanlin Guo

Appl. Phys. Lett. 97, 053104 (2010); http://dx.doi.org/10.1063/1.3467262 (3 pages) | Cited 2 times

Online Publication Date: 2 August 2010

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We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs.
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73.21.Hb Quantum wires
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio

Multiwavelength micro-Raman analysis of strain in nanopatterned ultrathin strained silicon-on-insulator

O. Moutanabbir, M. Reiche, A. Hähnel, M. Oehme, and E. Kasper

Appl. Phys. Lett. 97, 053105 (2010); http://dx.doi.org/10.1063/1.3475399 (3 pages) | Cited 6 times

Online Publication Date: 2 August 2010

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We developed a heterostructure to assess accurately the strain evolution upon nanopatterning of 15 nm thick tensile strained silicon-on-insulator (SSOI). Here the long-standing concern of substrate background in micro-Raman analysis was circumvented by the introduction of a Ge layer underneath the buried oxide. Unprecedented insights into the strain behavior in SSOI nanostructures were obtained by combining deep UV and visible micro-Raman probes. We found that the formation of edges results in a strong relaxation near the surface parallel to an increase in the strain at the Si/oxide interface. This disparity in the strain evolution between surface and interface leads to the coexistence of compressive and tensile strained regions within the same structure at a lateral dimension of 50 nm. This heterogeneous distribution of strain should be taken into account in the design and fabrication of SSOI-based nanodevices.
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81.16.Rf Micro- and nanoscale pattern formation
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Selective growth and piezoelectric properties of highly ordered arrays of vertical ZnO nanowires on ultrathin alumina membranes

Liaoyong Wen, Zhengzheng Shao, Yaoguo Fang, Kin Mun Wong, Yong Lei, Lifeng Bian, and Gerhard Wilde

Appl. Phys. Lett. 97, 053106 (2010); http://dx.doi.org/10.1063/1.3474615 (3 pages) | Cited 4 times

Online Publication Date: 3 August 2010

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A well controlled and cost effective method of fabricating highly ordered arrays of vertical zinc oxide (ZnO) nanowires or nanopores is demonstrated where an ultrathin alumina membrane (UTAM) itself is utilized as a substrate for the selective growth of the ordered arrays. A thin film of gold was thermally evaporated on the UTAM followed by the growth of highly regular ZnO nanowires using chemical vapor deposition (CVD). Alternatively, highly ordered ZnO nanopores arrays were also grown by CVD on the bare UTAM. Additionally, piezoelectric currents were generated from the ZnO nanowires during the conductive atomic force microscopy probe tip scan across the array.
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81.07.Gf Nanowires
73.30.+y Surface double layers, Schottky barriers, and work functions
77.65.-j Piezoelectricity and electromechanical effects
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Controlling the electrical transport properties of graphene by in situ metal deposition

Yujie Ren, Shanshan Chen, Weiwei Cai, Yanwu Zhu, Chaofu Zhu, and Rodney S. Ruoff

Appl. Phys. Lett. 97, 053107 (2010); http://dx.doi.org/10.1063/1.3471396 (3 pages) | Cited 16 times

Online Publication Date: 3 August 2010

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The deposition effect of metals on graphene was studied by in situ field effect transistor (FET) measurements in high vacuum. Metals such as gold (Au), silver (Ag), and copper (Cu) were deposited onto clean graphene surfaces, followed by FET measurements. The results show that Ag and Cu cause a shift in the Fermi level in the graphene from the Dirac point into the conduction band while Au causes a shift into the valence band. The induced carrier concentration was estimated at 2–6×1012/cm2. The shifts in the Fermi level of the graphene are explained by the different work functions of these metals.
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73.63.-b Electronic transport in nanoscale materials and structures
73.22.Pr Electronic structure of graphene
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Dj E-beam and hot filament evaporation deposition
68.55.A- Nucleation and growth

Switching capability of double-sided grating with horizontal shift

Hideo Iizuka, Nader Engheta, Hisayoshi Fujikawa, Kazuo Sato, and Yasuhiko Takeda

Appl. Phys. Lett. 97, 053108 (2010); http://dx.doi.org/10.1063/1.3476349 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2010

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A TiO2 grating beam splitter on the SiO2 layer is designed using the modal analysis. Normal incident light couples to the −1st/+1st-order transmission diffraction with a 49.6% efficiency for each and with a 50° refraction angle that is larger than the critical angle for the SiO2-air interface. The SiO2 interlayer is sandwiched between the two gratings. The finite-integration-technique investigation shows its switching capability due to the quarter-period shift between the gratings, with the zeroth-order transmission smaller than 5% for the “off” state and larger than 95% for the “on” state from 553 to 654 nm wavelength regime.
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42.79.Fm Reflectors, beam splitters, and deflectors

Plasmon assisted single photon emission of CdSe/CdS nanocrystals deposited on random gold film

I. Mallek-Zouari, S. Buil, X. Quélin, B. Mahler, B. Dubertret, and J.-P. Hermier

Appl. Phys. Lett. 97, 053109 (2010); http://dx.doi.org/10.1063/1.3467264 (3 pages) | Cited 4 times

Online Publication Date: 4 August 2010

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We have investigated the modifications of the fluorescence properties of single CdSe/CdS nanocrystals deposited close to a semicontinuous gold film. We report a reduction by a factor of ten of the monoexcitonic state decay rate. Due to the structure of the plasmon resonances, the decay depends on the nanocrystal position. Through the detailed study of the collection efficiency, we show that a large fraction of the plasmons are converted in far field single photons. These results demonstrate the great interest of plasmonic devices to control the single photon emission of colloidal nanocrystals.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
79.60.-i Photoemission and photoelectron spectra

Direct determination of the crystallographic orientation of graphene edges by atomic resolution imaging

S. Neubeck, Y. M. You, Z. H. Ni, P. Blake, Z. X. Shen, A. K. Geim, and K. S. Novoselov

Appl. Phys. Lett. 97, 053110 (2010); http://dx.doi.org/10.1063/1.3467468 (3 pages) | Cited 14 times

Online Publication Date: 4 August 2010

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In this letter, we show how high-resolution scanning tunneling microscopy (STM) imaging can be used to reveal that certain edges of micromechanically exfoliated single layer graphene crystals on silicon oxide follow either zigzag or armchair orientation. Using the cleavage technique, graphene flakes are obtained that very often show terminating edges seemingly following the crystallographic directions of the underlying honeycomb lattice. Performing atomic resolution STM-imaging on such flakes, we were able to directly prove this assumption. Raman imaging carried out on the same flakes further validated our findings.
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61.48.Gh Structure of graphene
81.05.ue Graphene
78.30.Na Fullerenes and related materials

Differential reflection spectroscopy of a single quantum dot strongly coupled to a photonic crystal cavity

Erik D. Kim, Arka Majumdar, Hyochul Kim, Pierre Petroff, and Jelena Vučković

Appl. Phys. Lett. 97, 053111 (2010); http://dx.doi.org/10.1063/1.3469922 (3 pages) | Cited 1 time

Online Publication Date: 4 August 2010

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We demonstrate the use of periodically modulated Coulomb shifts in quantum dot (QD) transition energies to obtain differential reflection spectra of a photonic crystal nanocavity containing strongly coupled dots. Measured spectra isolate the change in the empty cavity optical reflectivity spectrum due to the presence of each dot. This technique permits the probing of coupled QD-cavity systems possessing cavity modes of arbitrary polarization, making it attractive for use in both cavity quantum electrodynamics studies and quantum information applications.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
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