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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Parallel generation of nanochannels in fused silica with a single femtosecond laser pulse: Exploiting the optical near fields of triangular nanoparticles

F. Hubenthal, R. Morarescu, L. Englert, L. Haag, T. Baumert, and F. Träger

Appl. Phys. Lett. 95, 063101 (2009); http://dx.doi.org/10.1063/1.3186787 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2009

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We present experiments to prepare highly ordered nanochannels with subdiffraction dimensions on fused silica surfaces with femtosecond laser light. For this purpose, we exploit the strongly enhanced near field of highly ordered triangular gold nanoparticles. We demonstrate that after a single laser shot, 6 μm long nanochannels with a mean depth of 4 nm and an average width of 96 nm, i.e., well below the diffraction limit, are generated. These nanochannels are prepared by ablation, caused by the localization of the near field. The crucial parameters, besides the applied fluence, are the polarization direction of the incoming laser light with respect to the triangular nanoparticles and the size of the nanoparticles.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Size dependent thermoelectric properties of silicon nanowires

Lihong Shi, Donglai Yao, Gang Zhang, and Baowen Li

Appl. Phys. Lett. 95, 063102 (2009); http://dx.doi.org/10.1063/1.3204005 (3 pages) | Cited 26 times

Online Publication Date: 10 August 2009

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By using first-principles tight-binding electronic structure calculation and Boltzmann transport equation, we investigate the size dependence of thermoelectric properties of silicon nanowires (SiNWs). With cross section area increasing, the electrical conductivity increases slowly, while the Seebeck coefficient reduces remarkably. This leads to a quick reduction of cooling power factor with diameter. Moreover, the figure of merit also decreases with transverse size. Our results demonstrate that in thermoelectric application, NW with small diameter is preferred. We also predict that isotopic doping can increase the value of ZT significantly. With 50% 29Si doping (28Si0.5 29Si0.5 NW), the ZT can be increased by 31%.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.uf Ge and Si
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)
73.22.-f Electronic structure of nanoscale materials and related systems

Fluorescence enhancement and quenching of Eu3+ ions by Au–ZnO core-shell and Au nanoparticles

Krishna Kanta Haldar and Amitava Patra

Appl. Phys. Lett. 95, 063103 (2009); http://dx.doi.org/10.1063/1.3204012 (3 pages) | Cited 10 times

Online Publication Date: 10 August 2009

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We investigate the enhancement and quenching of Eu3+ emission in presence of Au–ZnO core-shell nanoparticles and Au nanoparticles. The quenching of Eu3+-emission in presence of Au nanoparticles is caused by change of nonradiative rate due to energy transfer. However, the enhancement of Eu3+-emission in presence of Au–ZnO core-shell nanoparticles is due to local field, which modifies the radiative and nonradiative rate. Enhancement and quenching of Eu3+ emission reflect the change in environment of Eu3+ from Au nanoparticles to Au–ZnO core-shell nanoparticles which is confirmed by the Judd–Ofelt parameter (Ω2) analysis.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
78.55.Et II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Formation of long-range ordered quantum dots arrays in amorphous matrix by ion beam irradiation

M. Buljan, I. Bogdanović-Radović, M. Karlušić, U. V. Desnica, G. Dražić, N. Radić, P. Dubček, K. Salamon, S. Bernstorff, and V. Holý

Appl. Phys. Lett. 95, 063104 (2009); http://dx.doi.org/10.1063/1.3204007 (3 pages) | Cited 8 times

Online Publication Date: 11 August 2009

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We demonstrate the production of a well ordered three-dimensional array of Ge quantum dots in amorphous silica matrix. The ordering is achieved by ion beam irradiation and annealing of a multilayer film. Structural analysis shows that quantum dots nucleate along the direction of the ion beam used for irradiation, while the mutual distance of the quantum dots is determined by the diffusion properties of the multilayer material rather than the distances between traces of ions that are used for irradiation.
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68.65.Hb Quantum dots (patterned in quantum wells)
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
68.65.Ac Multilayers
66.30.Ny Chemical interdiffusion; diffusion barriers

Doping nanowires grown by the vapor-liquid-solid mechanism

E. J. Schwalbach and P. W. Voorhees

Appl. Phys. Lett. 95, 063105 (2009); http://dx.doi.org/10.1063/1.3204543 (3 pages) | Cited 5 times

Online Publication Date: 11 August 2009

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The ability to dope semiconductor nanowires during growth is an important step toward making functional devices. We develop a model for steady state vapor-liquid-solid growth of a ternary semiconductor-catalyst-dopant nanowire. Our analysis shows that the relative flux of dopant atoms through the liquid controls the mole fraction of dopant in the solid wire, and that local equilibrium constrains the catalyst composition in the solid and the compositions of the dopant and catalyst in the liquid. We find that the phase diagram can be used to determine an upper limit on the dopant composition in the solid.
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81.16.Hc Catalytic methods
61.72.U- Doping and impurity implantation
81.07.Vb Quantum wires
81.07.-b Nanoscale materials and structures: fabrication and characterization

Theoretical study of hierarchical structures and heredity effect of silicon solidifying on carbon nanotube

H. Li, Y. F. Li, K. M. Liew, J. X. Zhang, X. F. Liu, and R. H. Fan

Appl. Phys. Lett. 95, 063106 (2009); http://dx.doi.org/10.1063/1.3200227 (3 pages) | Cited 1 time

Online Publication Date: 12 August 2009

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The growth of silicon atoms at the heterogeneous surface of carbon nanotubes (CNTs) is studied by means of molecular dynamics simulations. The results indicate that silicon atoms are concentrated to form an “annual ring” structure around CNTs. The structures of CNTs have strong correlation with the stacking sequence of silicon atoms. Heredity effect can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around CNTs results in the formation of annual ring structures.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.72.Nn Stacking faults and other planar or extended defects
64.60.Q- Nucleation
64.70.dg Crystallization of specific substances

Ultrathin lead oxide film on Pb(111) and its application in single spin detection

Ying-Shuang Fu, Shuai-Hua Ji, Tong Zhang, Xi Chen, Xu-Cun Ma, Jin-Feng Jia, and Qi-Kun Xue

Appl. Phys. Lett. 95, 063107 (2009); http://dx.doi.org/10.1063/1.3205118 (3 pages)

Online Publication Date: 12 August 2009

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The morphology and electronic structure of ultrathin PbO films on silicon-supported Pb islands have been investigated with a low temperature scanning tunneling microscope. It is found that the PbO film acts as an insulating layer to electronically decouple the adsorbates from the metallic substrate. Due to the increased lifetime of spin excitation, the Zeeman splitting of individual manganese phthalocyanine molecules adsorbed on PbO could be detected with spin-flip inelastic tunneling spectroscopy. The ultrathin insulating films like PbO provide an effective way to control the electronic coupling in the nanometer scale.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
71.20.Ps Other inorganic compounds
68.43.Mn Adsorption kinetics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Spontaneous high-speed transport of subnanoliter water droplet on gradient nanotextured surfaces

Hwa Seng Khoo and Fan-Gang Tseng

Appl. Phys. Lett. 95, 063108 (2009); http://dx.doi.org/10.1063/1.3197574 (3 pages) | Cited 7 times

Online Publication Date: 13 August 2009

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We present water droplets that undergo spontaneous self-directed motion upon contact with a chemically patterned nanotextured surface with wedge-shaped gradient. The surface exhibits two distinct wetting properties and low hysteresis. The droplet velocity depends on the droplet position and gradient angle. A wide range of droplet volume can be transported and a droplet velocity as high as 0.5 m/s has been achieved herein. Ascension of water droplets with all-round acclivity and a subnanoliter droplet movement were also demonstrated. We conclude that it is the combination of surface tension gradient and nanowetting actuation that governs the droplet motion.
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47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.85.Np Fluidics
47.55.D- Drops and bubbles
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena

Avalanche multiplication of photocarriers in nanometer-sized silicon dot layers

Yoshiyuki Hirano, Kenta Okamoto, Susumu Yamazaki, and Nobuyoshi Koshida

Appl. Phys. Lett. 95, 063109 (2009); http://dx.doi.org/10.1063/1.3205119 (3 pages) | Cited 2 times

Online Publication Date: 13 August 2009

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Photocurrent under reverse bias has been studied for metal-semiconductor diodes consisting of nanocrystalline Si dot (3.1 nm in mean diameter) embedded in SiO2. The samples were prepared on n+-type Si wafers by sequential dry processing based on low-pressure chemical vapor deposition and subsequent thermal oxidation. The temperature dependence measurements show that the quantum efficiency under an electric field of 9×105 V/cm reaches 2400% at 77 K. This high quantum efficiency is presumably caused by the avalanche multiplication of photoexcited carriers in the Si-nanodot layers. The Si-nanodot layer is potentially useful as a highly sensitive image-sensor target compatible with low-voltage operation.
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73.63.Kv Quantum dots
72.20.Ht High-field and nonlinear effects
72.40.+w Photoconduction and photovoltaic effects

Dependence of anisotropic surface plasmon lifetimes of two-dimensional hole arrays on hole geometry

K. C. Hui, J. T. K. Wan, J. B. Xu, and H. C. Ong

Appl. Phys. Lett. 95, 063110 (2009); http://dx.doi.org/10.1063/1.3205121 (3 pages) | Cited 1 time

Online Publication Date: 13 August 2009

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The dependences of surface plasmon lifetimes of two-dimensional Au hole arrays on aspect ratio, hole length, and depth have been studied by angle-dependent reflectivity. Long lifetimes can be obtained from the arrays by reducing the hole length and depth and increasing the aspect ratio. In addition, our results can be qualitatively discussed under the framework of coupled-charge model, indicating the interaction between holes can lead to an increase of surface plasmon lifetime. We believe such interaction can find applications in biosensing such as surface plasmon resonance spectroscopy.
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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
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.22.Lp Collective excitations
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Electronic structure of epitaxial graphene nanoribbons on SiC(0001)

I. Deretzis and A. La Magna

Appl. Phys. Lett. 95, 063111 (2009); http://dx.doi.org/10.1063/1.3202397 (3 pages) | Cited 10 times

Online Publication Date: 14 August 2009

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We present electronic structure calculations of few-layer epitaxial graphene nanoribbons on SiC(0001). Trough an atomistic description of the graphene layers and the substrate within the extended Hückel theory and real/momentum space projections we argue that the role of the heterostructure’s interface becomes crucial for the conducting capacity of the studied systems. The key issue arising from this interaction is a Fermi level pinning effect introduced by dangling interface bonds. Such phenomenon is independent from the width of the considered nanostructures, compromising the importance of confinement in these systems.
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73.22.-f Electronic structure of nanoscale materials and related systems
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Tx Fullerenes and related materials; intercalation compounds
81.05.ub Fullerenes and related materials

qPlus atomic force microscopy of the Si(100) surface: Buckled, split-off, and added dimers

A. Sweetman, S. Gangopadhyay, R. Danza, N. Berdunov, and P. Moriarty

Appl. Phys. Lett. 95, 063112 (2009); http://dx.doi.org/10.1063/1.3197595 (3 pages) | Cited 2 times

Online Publication Date: 14 August 2009

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Dimer configurations at the Si(100) surface have been studied with noncontact atomic force microscopy in the qPlus mode at 77 K, using both large (10 nm peak to peak) and small (0.5 nm peak to peak) oscillation amplitudes. In addition to the p(2×1), p(2×2), and c(4×2) reconstructions of the pristine surface, a variety of defect types including ad-dimers, vacancies, and split-off dimers have been imaged. Our data appear at odds with the currently accepted structural model for split-off dimers. At low oscillation amplitudes the degree of apparent dimer buckling can be “tuned” by varying the frequency shift set point.
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68.35.bg Semiconductors
61.72.jd Vacancies
68.35.Dv Composition, segregation; defects and impurities
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