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12 Dec 2005

Volume 87, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 87, 243101 (2005); http://dx.doi.org/10.1063/1.2147713 (3 pages)

Y.-S. Choi, K. Hennessy, R. Sharma, E. Haberer, Y. Gao, S. P. DenBaars, S. Nakamura, E. L. Hu, and C. Meier
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GaN blue photonic crystal membrane nanocavities

Y.-S. Choi, K. Hennessy, R. Sharma, E. Haberer, Y. Gao, S. P. DenBaars, S. Nakamura, E. L. Hu, and C. Meier

Appl. Phys. Lett. 87, 243101 (2005); http://dx.doi.org/10.1063/1.2147713 (3 pages) | Cited 39 times

Online Publication Date: 5 December 2005

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GaN-based photonic-crystal membrane nanocavities with Q factors up to 800 have been realized at the wavelength of ∼ 480 nm. The tuning behavior agrees well with numerical calculations using the finite-difference time-domain method. Theoretically, the lowest energy mode of a cavity that consists of seven missing holes in the Γ-K direction promises a Q factor as high as 4×104 with a mode volume of about 1.3×(λ/n)3.
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42.70.Qs Photonic bandgap materials
81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization

Orientational self-assembled field-effect transistors based on a single-walled carbon nanotube

Xianglong Li, Yunqi Liu, Dachuan Shi, Yanming Sun, Gui Yu, Daoben Zhu, Hongmin Liu, Xinyu Liu, and Dexin Wu

Appl. Phys. Lett. 87, 243102 (2005); http://dx.doi.org/10.1063/1.2137464 (3 pages) | Cited 4 times

Online Publication Date: 5 December 2005

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We fabricate single-walled carbon nanotube field-effect transistors (SWNT FETs) with a simple, low-cost, high-efficiency, and solution-based orientational self-assembly method. The SWNT was first functionalized with thiol groups, then suspended in an N,N-dimethylformamide solution, and finally self-assembled on predefined gold contact pads by an orientational N2 blow. A relatively high mobility of 9.2×102 cm2/V s and an on∕off ratio greater than 105 at a bias voltage of −1 V have been achieved as a result of directly covalent interaction between end-thiolated SWNT and gold contacts, which favors the fabrication of SWNT FETs as compared to the SWNT FETs bearing the similar geometry but relies on random deposition. Therefore, this orientational self-assembly approach should be a valuable tool in the mass fabrication of high-performance SWNT FETs and SWNT-based molecular-scale electronic devices.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
81.16.Dn Self-assembly

Direct imaging of core-shell structure in silver-gold bimetallic nanoparticles

Z. Y. Li, J. Yuan, Y. Chen, R. E. Palmer, and J. P. Wilcoxon

Appl. Phys. Lett. 87, 243103 (2005); http://dx.doi.org/10.1063/1.2139851 (3 pages) | Cited 23 times

Online Publication Date: 5 December 2005

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High-angle annular dark field imaging in the electron microscope has been exploited to reveal the internal structure of monodispersed, bimetallic gold (Au) - silver (Ag) nanoparticles of ∼ 4 nm diameter, prepared using a seed-growth wet chemical method and passivated with an organic layer. Starting with a 3 nm Ag seed particle, deposition of Au atoms to a final overall atomic ratio of Ag:Au = 1:2 leads to nanoparticles with an Ag-rich core and an Au-rich shell, as expected. If the overall atomic ratio is 2:1, the core∕shell structure is not observed. The physical significance of these observations is discussed in terms of the stability of particles of nanoscale dimensions.
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61.46.-w Structure of nanoscale materials

High emission current density microwave-plasma-grown carbon nanotube arrays by postdepositional radio-frequency oxygen plasma treatment

Z. Chen, D. den Engelsen, P. K. Bachmann, V. van Elsbergen, I. Koehler, J. Merikhi, and D. U. Wiechert

Appl. Phys. Lett. 87, 243104 (2005); http://dx.doi.org/10.1063/1.2140893 (3 pages) | Cited 20 times

Online Publication Date: 5 December 2005

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Highly stable field emission current densities of more than 6 A/ cm2 along with scalable total field emission currents of ∼ 300 μA per 70 μm diameter carbon nanotube (CNT)-covered electron emitter dot are reported. Microwave-plasma chemical vapor deposition, along with a novel catalyst sandwich structure and postdepositional radio-frequency (rf) oxygen plasma treatment lead to well-structured vertically aligned CNTs with excellent and scalable emission properties. Scanning electron and transmission electron microscope investigations reveal that postdepositional treatment reduces not only the number but modifies the structure of the CNTs. Well-structured microwave-plasma-grown nanotubes become amorphous during rf oxygen plasma treatment and the measured work functions of CNTs change from 4.6 eV to 4.0 eV before and after treatment, respectively. Our experiments outline a novel fabrication route for structured CNT arrays with improved and scalable field emission characteristics.
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81.07.De Nanotubes
81.05.U- Carbon/carbon-based materials
81.16.-c Methods of micro- and nanofabrication and processing
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.45.Db Field emitters and arrays, cold electron emitters
73.30.+y Surface double layers, Schottky barriers, and work functions

Exohedral doping of single-walled boron nitride nanotube by atomic chemisorption

Jia Zhang, Kian Ping Loh, Shuo Wang Yang, and Ping Wu

Appl. Phys. Lett. 87, 243105 (2005); http://dx.doi.org/10.1063/1.2140876 (3 pages) | Cited 13 times

Online Publication Date: 5 December 2005

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The adsorption of atoms on the tube walls of (8,0) boron nitride nanotubes (BNNTs) has been studied using the density functional theory. Adsorption of either H or F (exohedral doping) on the B site imparts hole carrier conduction characteristics on the BNNT; however, co-adsorption on both of the B and N dimer pairs results in compensation.
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61.72.up Other materials
68.43.Mn Adsorption kinetics
73.63.Fg Nanotubes

Single standing carbon nanotube array in gate holes using a silicon nitride cap layer

Sung Hoon Lim, Hyun Sik Yoon, Jong Hyun Moon, Kyu Chang Park, and Jin Jang

Appl. Phys. Lett. 87, 243106 (2005); http://dx.doi.org/10.1063/1.2142079 (3 pages) | Cited 9 times

Online Publication Date: 6 December 2005

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We studied the growth of a single standing carbon nanotube (CNT) which was grown by plasma-enhanced chemical vapor deposition in the gate hole formed by conventional photolithography in the silicon nitride. The number of CNT per hole increases with increasing the gate hole diameter and a single CNT could be grown in a 3 μm hole. A single standing CNT in a gate hole exhibited the turn-on field of 1.6 V/μm and the current density of 16 μA at 3.3 V/μm. The emission currents follow the Fowler–Nordheim equation with a field enhancement factor of 1.14×107.
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85.35.Kt Nanotube devices
52.77.Dq Plasma-based ion implantation and deposition

High-gain and low-threshold InAs quantum-dot lasers on InP

P. Caroff, C. Paranthoen, C. Platz, O. Dehaese, H. Folliot, N. Bertru, C. Labbé, R. Piron, E. Homeyer, A. Le Corre, and S. Loualiche

Appl. Phys. Lett. 87, 243107 (2005); http://dx.doi.org/10.1063/1.2146063 (3 pages) | Cited 55 times

Online Publication Date: 6 December 2005

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InAs quantum-dot (QD) laser structures are grown on (113)B-oriented InP substrate by gas-source molecular-beam epitaxy. Following an optimized growth procedure, a high density of 1.1×1011 cm−2 of uniformly sized QDs is achieved. Broad-area lasers containing three stacked QD layers have been realized and tested. Laser emission on the ground-state transition (λ = 1.59 μm) is obtained at room temperature (RT), at a threshold current density as low as 190 A/cm2. Ground-state modal gain and transparency current density is measured to be 7 cm−1 and 23 A/cm2 per dot layer. Ground-state laser emission is also demonstrated from low temperature (100 K, Jth = 33 A/cm2) to high temperature (350 K), exhibiting an insensitive threshold in the [100, 170] K range, and a 55 K characteristic temperature at RT.
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42.55.Px Semiconductor lasers; laser diodes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots

Current-driven domain-wall motion in magnetic wires with asymmetric notches

A. Himeno, S. Kasai, and T. Ono

Appl. Phys. Lett. 87, 243108 (2005); http://dx.doi.org/10.1063/1.2140884 (2 pages) | Cited 21 times

Online Publication Date: 6 December 2005

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Current-driven domain-wall (DW) motion in magnetic wires with asymmetric notches was investigated by means of magnetic force microscopy. It was found that the critical current density necessary for the current-driven DW motion depended on the propagation direction of the DW. The DW moved more easily in the direction along which the slope of the asymmetric notch was less inclined.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys

Packing-dependent pore structures in single-walled carbon nanotube arrays

C. H. Sun, F. Li, H. M. Cheng, and G. Q. Lu

Appl. Phys. Lett. 87, 243109 (2005); http://dx.doi.org/10.1063/1.2139993 (3 pages)

Online Publication Date: 6 December 2005

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Based on a self-similar array model of single-walled carbon nanotubes (SWNTs), the pore structure of SWNT bundles is analyzed and compared with that obtained from the conventional triangular model and adsorption experimental results. In addition to the well known cylindrical endo-cavities and interstitial pores, two types of newly defined pores with diameters of 2–10 and 8–100 nm are proposed, inter-bundle pores and inter-array pores. In particular, the relationship between the packing configuration of SWNTs and their pore structures is systematically investigated.
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61.43.Gt Powders, porous materials

Optically transparent bionanofiber composites with low sensitivity to refractive index of the polymer matrix

Masaya Nogi, Keishin Handa, Antonio Norio Nakagaito, and Hiroyuki Yano

Appl. Phys. Lett. 87, 243110 (2005); http://dx.doi.org/10.1063/1.2146056 (3 pages) | Cited 37 times

Online Publication Date: 7 December 2005

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Transparent polymers were reinforced by bacterial cellulose (BC) nanofibers, which are 10×50 nm ribbon-shaped fibers. They exhibited high luminous transmittance at a fiber content as high as 60 wt %, and low sensitivity to a variety of refractive indices of matrix resins. Due to the nanofiber size effect, high transparency was obtained against a wider distribution of refractive index of resins from 1.492 to 1.636 at 20 °C. The optical transparency was also surprisingly insensitive to temperature increases up to 80 °C. As such, BC nanofibers appear to be viable candidates for optically transparent reinforcement.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.07.Bc Nanocrystalline materials
87.16.Gj Cell walls
42.70.Jk Polymers and organics

Direct enumeration of alloy configurations for electronic structural properties

Peter A. Graf, Kwiseon Kim, Wesley B. Jones, and Gus L. W. Hart

Appl. Phys. Lett. 87, 243111 (2005); http://dx.doi.org/10.1063/1.2142091 (3 pages) | Cited 6 times

Online Publication Date: 8 December 2005

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We present and apply an approach to directly enumerate the band gaps and effective masses of all possible zinc blende-based alloy configurations whose unit cell contains up to a specified number of atoms. This method allows us to map the space of band gaps and effective masses versus alloy composition and atomic configuration. We demonstrate that a large number of band gaps and effective masses are available. We also discuss convergence of the method with respect to unit cell size and the combined optimization of band gap and effective mass for AlGaAs and GaInP semiconductor alloys.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Self-assembled InAs quantum dots on patterned GaAs(001) substrates: Formation and shape evolution

S. Kiravittaya, A. Rastelli, and O. G. Schmidt

Appl. Phys. Lett. 87, 243112 (2005); http://dx.doi.org/10.1063/1.2143125 (3 pages) | Cited 35 times

Online Publication Date: 8 December 2005

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We report on the formation of ordered and size homogeneous InAs quantum dot (QD) arrays on patterned GaAs(001) substrates. A material depletion region is observed around the patterned area while a long-range homogeneous distribution of QDs is found inside the patterned area. A sample with less InAs deposition shows a gradient in the material distribution over the patterned area. Based on these observations we propose a simple model to describe the QD formation in the patterned area. The QD shape evolution is also investigated and discussed.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly

Are fluorinated boron nitride nanotubes n-type semiconductors?

H. J. Xiang, Jinlong Yang, J. G. Hou, and Qingshi Zhu

Appl. Phys. Lett. 87, 243113 (2005); http://dx.doi.org/10.1063/1.2142290 (3 pages) | Cited 33 times

Online Publication Date: 8 December 2005

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The structural and electronic properties of fluorine (F)-doped boron nitride nanotubes (BNNTs) are studied using density functional methods. Our results indicate that F atoms prefer to substitute N atoms, resulting in substantial changes of BN layers. However, F substitutional doping results in no shallow impurity states. The adsorption of F atoms on B sites is more stable than that on N sites. BNNTs with adsorbed F atoms are p-type semiconductors, suggesting the electronic conduction in F-doped multiwalled BNNTs with large conductivity observed experimentally might be of p-type due to the adsorbed F atoms, but not n-type as supposed before.
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73.63.Fg Nanotubes
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.uj III-V and II-VI semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
68.43.Mn Adsorption kinetics

Enhancement and limits of the photoelectrochemical response from anodic TiO2 nanotubes

R. Beranek, H. Tsuchiya, T. Sugishima, J. M. Macak, L. Taveira, S. Fujimoto, H. Kisch, and P. Schmuki

Appl. Phys. Lett. 87, 243114 (2005); http://dx.doi.org/10.1063/1.2140085 (3 pages) | Cited 109 times

Online Publication Date: 9 December 2005

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TiO2 nanotube layers were grown on titanium by a self-organized anodic oxidation. The layers consist of arrays of individual tubes with a length of ∼ 2 μm, a diameter of ∼ 100 nm, and a wall thickness of ∼ 10 nm. These layers can be annealed to an anatase structure which strongly increases the photocurrent efficiency. Moreover, the nanotube layers can—under certain conditions—exhibit a drastically enhanced photocurrent compared to compact anatase layers. These strong changes in the photoresponse are attributed to the characteristics of the space charge layer within the tube wall.
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81.07.De Nanotubes
82.45.Yz Nanostructured materials in electrochemistry
82.50.-m Photochemistry
81.16.Dn Self-assembly
81.65.Mq Oxidation
82.45.Cc Anodic films
81.40.Gh Other heat and thermomechanical treatments
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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