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25 Dec 2006

Volume 89, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 89, 263110 (2006); http://dx.doi.org/10.1063/1.2424541 (3 pages)

Ch. Deneke, U. Zschieschang, H. Klauk, and O. G. Schmidt
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Doping of germanium nanowires grown in presence of PH3

E. Tutuc, J. O. Chu, J. A. Ott, and S. Guha

Appl. Phys. Lett. 89, 263101 (2006); http://dx.doi.org/10.1063/1.2410238 (3 pages) | Cited 27 times

Online Publication Date: 26 December 2006

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The authors study the Au-catalyzed chemical vapor growth of germanium (Ge) nanowires in the presence of phosphine (PH3), used as a dopant precursor. The device characteristics of the ensuing nanowire field effect transistors (FETs) indicate n-type, highly doped nanowires. Using a combination of different nanowire growth sequences and their FET characteristics, the authors determine that phosphorus incorporates predominately via the conformal growth, which accompanies the acicular, nanowire growth. As such, the Ge nanowires grown in the presence of PH3 contain a phosphorus doped shell and an undoped core. The authors determine the doping level in the shell to be ≃ (1−4)×1019 cm−3.
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
68.65.La Quantum wires (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices

High performance ZnO nanowire field effect transistor using self-aligned nanogap gate electrodes

S. N. Cha, J. E. Jang, Y. Choi, G. A. J. Amaratunga, G. W. Ho, M. E. Welland, D. G. Hasko, D.-J. Kang, and J. M. Kim

Appl. Phys. Lett. 89, 263102 (2006); http://dx.doi.org/10.1063/1.2416249 (3 pages) | Cited 40 times

Online Publication Date: 26 December 2006

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A field effect transistor (FET) using a zinc oxide nanowire with significantly enhanced performance is demonstrated. The device consists of single nanowire and self-aligned gate electrodes with well defined nanosize gaps separating them from the suspended nanowire. The fabricated FET exhibits excellent performance with a transconductance of 3.06 μS, a field effect mobility of 928 cm2/V s, and an on/off current ratio of 106. The electrical characteristics are the best obtained to date for a ZnO transistor. The FET has a n-type channel and operates in enhancement mode. The results are close to those reported previously for p-type carbon nanotube (CNT) FETs. This raises the possibility of using ZnO as the n-type FET with a CNT as the p-type FET in nanoscale complementary logic circuits.
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85.30.Tv Field effect devices

Modulational transparency and femtosecond pulse train in Bragg reflectors with time-varying dielectric constant

Jiu Hui Wu, T. H. Cheng, A. Q. Liu, and Y. X. Wang

Appl. Phys. Lett. 89, 263103 (2006); http://dx.doi.org/10.1063/1.2410231 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2006

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A theoretical study is conducted to investigate the nonlinear properties of a one-dimensional (1D) periodic stratified structure with time-varying dielectric constants. When the dielectric constant is modulated temporally, the distributed Bragg reflector exhibits different throughputs depending on the modulation amplitude. Below or at the critical value, a periodic and stable femtosecond pulse train is generated; above this critical value, the modulational transparency is observed, as the reflectivity decreases rapidly, so that all incident radiation is completely transferred through the layered media. When the layer number is up to 15, the pulse train generated at the critical value is periodic with perfect reflectivity and zero rejection. These excellent optical properties may enhance the potential applications of the 1D periodic stratified structure in optical switches and laser optics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Bh Lenses, prisms and mirrors

Elastic deformation of nanometer-sized metal crystals in graphitic shells

L. Sun, J. A. Rodríguez-Manzo, and F. Banhart

Appl. Phys. Lett. 89, 263104 (2006); http://dx.doi.org/10.1063/1.2403898 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2006

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The elastic deformation of nanometer-sized metal crystals is achieved by encapsulating them in carbon nanotubes or carbon onions. Electron irradiation of these core-shell particles leads to high pressure in their center due to a shrinkage of the graphitic shells. Pressures in the range of 10–30 GPa are found by measuring the decrease in lattice spacings in the encapsulated metal crystals. Hence, it is quantitatively shown how closed graphitic shells can be applied as compression cells on the nanoscale.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.20.D- Elasticity
61.80.Fe Electron and positron radiation effects
61.82.Rx Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Physical manipulation of biological and chemical syntheses for nanoparticle shape and size control

S. B. Ogale, A. Ahmad, R. Pasricha, V. V. Dhas, and A. Syed

Appl. Phys. Lett. 89, 263105 (2006); http://dx.doi.org/10.1063/1.2424272 (3 pages) | Cited 3 times

Online Publication Date: 27 December 2006

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A nanosynthesis scheme is demonstrated which renders excellent control of nanoparticle shape, size, and dispersity in a solution based synthesis process. The scheme, termed as percolative microcavity synthesis, involves the use of a granular medium with percolative microcavities which facilitate nearly similar grain size/shape dependent reaction zones limiting intrinsic growth inhomogeneities, enabling particle size/shape control. The viability of the process is demonstrated for the synthesis of gold nanoparticles by a plant extract based biological method as well as a chemical method.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Retarded oxidation of Si nanowires

C. C. Büttner and M. Zacharias

Appl. Phys. Lett. 89, 263106 (2006); http://dx.doi.org/10.1063/1.2424297 (3 pages) | Cited 24 times

Online Publication Date: 27 December 2006

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Retarded thermal oxidation of Si nanowires is investigated. The oxidation behavior strongly depends on the wire curvature. The effect starts to evolve for a curvature larger than 0.05 nm, i.e., an original nanowire radius of 35 nm. For longer oxidation time and lower oxidation temperature, the effect of retarded oxidation gets stronger. The average values of the oxidation rate for small wires are reduced nearly by a factor of 2 compared to bulk ⟨100⟩ silicon. The authors suggest that the increased stress is responsible for the mechanism of retarded oxidation which cannot be decreased by the viscous flow of the oxide.
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81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
68.65.La Quantum wires (patterned in quantum wells)
68.35.Gy Mechanical properties; surface strains

Probing adsorption sites on thin oxide films by dynamic force microscopy

M. Heyde, G. H. Simon, H.-P. Rust, and H.-J. Freund

Appl. Phys. Lett. 89, 263107 (2006); http://dx.doi.org/10.1063/1.2424432 (3 pages) | Cited 22 times

Online Publication Date: 27 December 2006

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Site specific atomically resolved dynamic force spectroscopy measurements were performed on a thin MgO film grown on Ag(001). The microscope is operated in ultrahigh vacuum at low temperature to ensure defined imaging condition, high stability, and drift reduction. Atomically resolved dynamic force microscopy images have been combined with site specific frequency shift versus distance measurements. The frequency shift is measured as a function of z and the lateral displacement. With these measurement characteristics the authors are currently probing inequivalent surface sites on thin MgO films to extract atomic-scale information on surface chemical reactivity and possible adsorption sites for metal atoms and small clusters.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Nanoscale voltage tunable tunnel rectifier by gold nanostructures embedded in SiO2

F. Ruffino, M. G. Grimaldi, F. Giannazzo, F. Roccaforte, and V. Raineri

Appl. Phys. Lett. 89, 263108 (2006); http://dx.doi.org/10.1063/1.2424433 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2006

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Conductive-atomic force microscopy is used to electrically characterize a nanometric metal-SiO2–Si (n+) system with Au nanocluster inclusions in SiO2. The system shows a marked rectifying behavior at room temperature with a threshold voltage function of the cluster size. This behavior is interpreted crossing physical considerations on metal-oxide-semiconductor structure and on double barrier tunnel junction device. The system fabricated and analyzed is proposed as a possible basic component for nanoelectronic circuits working at room temperature.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Gv Single electron devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Ei Rectification
73.23.Hk Coulomb blockade; single-electron tunneling

Control of fine-structure splitting and excitonic binding energies in selected individual InAs/GaAs quantum dots

R. Seguin, A. Schliwa, T. D. Germann, S. Rodt, K. Pötschke, A. Strittmatter, U. W. Pohl, D. Bimberg, M. Winkelnkemper, T. Hammerschmidt, and P. Kratzer

Appl. Phys. Lett. 89, 263109 (2006); http://dx.doi.org/10.1063/1.2424446 (3 pages) | Cited 28 times

Online Publication Date: 27 December 2006

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A systematic study of the impact of annealing on the electronic properties of single InAs/GaAs quantum dots (QDs) is presented. Single QD cathodoluminescence spectra are recorded to trace the evolution of one and the same QD over several steps of annealing. A substantial reduction of the excitonic fine-structure splitting upon annealing is observed. In addition, the binding energies of different excitonic complexes change dramatically. The results are compared to model calculations within 8-band k∙p theory and the configuration interaction method, suggesting a change of electron and hole wave function shape and relative position.
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71.35.-y Excitons and related phenomena
71.15.Nc Total energy and cohesive energy calculations
73.21.La Quantum dots
78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Cc Kinetics of defect formation and annealing

InGaAs/GaAs/alkanethiolate radial superlattices

Ch. Deneke, U. Zschieschang, H. Klauk, and O. G. Schmidt

Appl. Phys. Lett. 89, 263110 (2006); http://dx.doi.org/10.1063/1.2424541 (3 pages) | Cited 14 times

Online Publication Date: 27 December 2006

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A radial InGaAs/GaAs/1-hexadecanethiol superlattice is fabricated by the roll-up of a strained InGaAs/GaAs bilayer passivated with a molecular self-assembled monolayer. The technique allows the formation of multiperiod inorganic/organic hybrid heterostructures. The authors investigate the radial superlattices in a detailed transmission electron microscopy study. The structure consists of 11 tightly bonded semiconductor/organic layers with thicknesses and chemical compositions accurately controlled by epitaxial growth and self-assembly. Their chemical analysis reveals that neither any detectable oxygen contamination nor amorphization is present at the superlattice interfaces.
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81.07.Pr Organic-inorganic hybrid nanostructures
68.65.Cd Superlattices
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
81.65.Rv Passivation
82.80.-d Chemical analysis and related physical methods of analysis

Photoluminescence studies of type-II diluted magnetic semiconductor ZnMnTe/ZnSe quantum dots

M. C. Kuo, J. S. Hsu, J. L. Shen, K. C. Chiu, W. C. Fan, Y. C. Lin, C. H. Chia, W. C. Chou, M. Yasar, R. Mallory, A. Petrou, and H. Luo

Appl. Phys. Lett. 89, 263111 (2006); http://dx.doi.org/10.1063/1.2424654 (3 pages) | Cited 8 times

Online Publication Date: 28 December 2006

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Type-II diluted magnetic semiconductor ZnMnTe quantum dots (QDs) in ZnSe matrix grown by molecular beam epitaxy were investigated by conventional and magnetophotoluminescence (PL) spectroscopy. The QD emission exhibits a type-II characteristic in excitation power dependence of PL peak energy. A nonzero circular polarization of PL at the absence of magnetic field was observed. This phenomenon is attributed to the accumulation of interface charges confined in adjacent layers. The magneto-optical measurement demonstrates a magnetic-induced degree of circular polarization in the PL spectra, indicating the Mn incorporation into the QD system.
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75.50.Pp Magnetic semiconductors
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.20.Ls Magneto-optical effects

Nonresonant carrier tunneling in arrays of silicon nanocrystals

R. Lockwood, A. Hryciw, and A. Meldrum

Appl. Phys. Lett. 89, 263112 (2006); http://dx.doi.org/10.1063/1.2424656 (3 pages) | Cited 16 times

Online Publication Date: 28 December 2006

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Silicon nanocrystals are of interest in the nascent field of silicon microphotonics, with potential applications as waveguide amplifiers, light-emitting diodes, and silicon-based lasers. Comparing computational simulations and experiment, it is shown that nonresonant carrier tunneling in ensembles of silicon nanocrystals is a controlling factor in the luminescence. In thin film silicon nanocrystal composites, only the larger particles can be luminescent as a result of rapid carrier tunneling, suggesting that these applications may only be achieved for well-isolated nanocrystals or for arrays with a narrow distribution of sizes.
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73.61.Cw Elemental semiconductors
73.40.Gk Tunneling
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors

Field emission of electrons from a Cs-doped single carbon nanotube of known chiral indices

Gongpu Zhao, Qi Zhang, Han Zhang, Guang Yang, Otto Zhou, Lu-Chang Qin, and Jie Tang

Appl. Phys. Lett. 89, 263113 (2006); http://dx.doi.org/10.1063/1.2420796 (3 pages) | Cited 7 times

Online Publication Date: 29 December 2006

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The authors report the effects of Cs doping on the field emission properties of a five-shell single carbon nanotube. The chiral indices of each shell of this carbon nanotube have been determined using nanobeam electron diffraction, which has four semiconducting shells and one metallic shell in the middle. From the Fowler-Nordheim plots, a reduction from 4.8 to 3.8 eV has been observed in the work function of the single carbon nanotube before and after Cs doping.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes
73.63.Fg Nanotubes
61.72.up Other materials
73.30.+y Surface double layers, Schottky barriers, and work functions

Interface characteristics of vertically aligned carbon nanofibers for interconnect applications

Yusuke Ominami, Quoc Ngo, Makoto Suzuki, Alexander J. Austin, Cary Y. Yang, Alan M. Cassell, and Jun Li

Appl. Phys. Lett. 89, 263114 (2006); http://dx.doi.org/10.1063/1.2423241 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2006

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The authors characterize the detailed interface structure of Ni-catalyzed vertically aligned carbon nanofibers (CNFs) prepared by plasma-enhanced chemical vapor deposition for interconnect applications. Stacked graphitic layers and cup-shape structures of CNFs around the interface region have been observed using high-resolution scanning transmission electron microscopy. The interaction between the Ni catalyst and Ti layer dramatically affects the CNF structure during initial growth. The effect of interface nanostructures on contact resistance is also discussed.
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61.46.-w Structure of nanoscale materials
73.40.Cg Contact resistance, contact potential
81.05.U- Carbon/carbon-based materials
81.16.Hc Catalytic methods
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Multiline spectra of single CdSe/ZnS core-shell nanorods

N. Le Thomas, M. Allione, Y. Fedutik, U. Woggon, M. V. Artemyev, and E. A. Ustinovich

Appl. Phys. Lett. 89, 263115 (2006); http://dx.doi.org/10.1063/1.2425019 (3 pages) | Cited 6 times

Online Publication Date: 29 December 2006

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Single-nanorod spectroscopy at low temperature is used to study the exciton states of individual CdSe/ZnS core-shell nanorods. By analyzing the LO-phonon assisted recombination the authors may distinguish between charged and exchange-splitted excitons. Four different types of single-nanorod emission spectra are found and assigned to neutral, positively, and negatively charged excitons and multiexciton states. The spatially separate confinement of two localized excitons in one, individual nanorod is discussed.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.35.Pq Charged excitons (trions)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Bd Nanocrystalline materials
78.55.Et II-VI semiconductors

Catalyst-free growth of uniform ZnO nanowire arrays on prepatterned substrate

Y. D. Wang, K. Y. Zang, S. J. Chua, and C. G. Fonstad

Appl. Phys. Lett. 89, 263116 (2006); http://dx.doi.org/10.1063/1.2425036 (3 pages) | Cited 4 times

Online Publication Date: 29 December 2006

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Uniform and ordered ZnO nanowire arrays have been fabricated on the nanopatterned SiO2/GaN substrate without metal catalysts using hydrothermal synthesis. The nanopatterns on SiO2/GaN substrate with an average diameter of 65 nm are produced by inductively coupled plasma etching using anodic alumina template as a mask, which provides nucleation sites for the vertical ZnO nanowires growth. High quality of the aligned uniform ZnO nanowire arrays grown on GaN substrate was confirmed by x-ray diffraction, transmission electron microscopy, and photoluminescence. This growth technique provides a cost-effective approach to fabricate ordered nanowire arrays with controlled size, which may benefit the nanowire device applications.
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81.05.Dz II-VI semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Be Chemical synthesis methods
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors

Impacts of ammonia background flows on structural and photoluminescence properties of InN dots grown on GaN by flow-rate modulation epitaxy

W. C. Ke, L. Lee, C. Y. Chen, W. C. Tsai, W.-H. Chang, W. C. Chou, M. C. Lee, W. K. Chen, W. J. Lin, and Y. C. Cheng

Appl. Phys. Lett. 89, 263117 (2006); http://dx.doi.org/10.1063/1.2425038 (3 pages) | Cited 8 times

Online Publication Date: 29 December 2006

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Structural and photoluminescence (PL) properties of InN dots grown on GaN by metal organic vapor phase epitaxy using the flow-rate modulation technique, and their dependence on growth conditions, were investigated. An ammonia (NH3) background flow was intentionally supplied during indium deposition periods to control the kinetics of adatoms and hence the morphology of InN dots. Samples prepared under lower NH3 background flows generally exhibit narrower and more intense PL signals peaked at lower emission energies. The authors point out that the NH3 background flow is an important parameter that controls not only the nucleation process but also the emission property of InN dots.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase

High-density, uniform InSb/GaSb quantum dots emitting in the midinfrared region

V. Tasco, N. Deguffroy, A. N. Baranov, E. Tournié, B. Satpati, A. Trampert, M. S. Dunaevskii, and A. Titkov

Appl. Phys. Lett. 89, 263118 (2006); http://dx.doi.org/10.1063/1.2425041 (3 pages) | Cited 9 times

Online Publication Date: 29 December 2006

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The authors have developed a multistep molecular-beam epitaxy growth technique which allows them to grow InSb quantum dots with high structural perfection and high density. This technique consists in the deposition at a very low temperature followed by a properly designed annealing step. Fully strained InSb/GaSb quantum dots with a density exceeding 7×1010 cm−2 and lateral sizes in the 20–30 nm range have been obtained. Narrow photoluminescence emission is obtained around 3.5 μm up to room temperature.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

One-dimensional ferroelectric monodomain formation in single crystalline BaTiO3 nanowire

Zhaoyu Wang, Jie Hu, and Min-Feng Yu

Appl. Phys. Lett. 89, 263119 (2006); http://dx.doi.org/10.1063/1.2425047 (3 pages) | Cited 25 times

Online Publication Date: 29 December 2006

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The authors report the existence of one-dimensional and stable formation of ferroelectric monodomain in single crystalline BaTiO3 nanowire. Piezoresponse force microscopy operated in both vertical and lateral modes showed ferroelectric polarization switching along the axial (lateral) direction of nanowire, while the polarization along the transversal (vertical) direction was strongly suppressed. Such a one-dimensional polarization formation was also found to be highly stable and nonretentive in that switched polarization spontaneously returned to its original orientation at the instant of removing the applied poling voltage.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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