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7 Aug 2006

Volume 89, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 062501 (2006); http://dx.doi.org/10.1063/1.2259813 (3 pages)

Sangkook Choi, Ki-Suk Lee, and Sang-Koog Kim
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Efficient fabrication of field electron emitters from the multiwalled carbon nanotube yarns

Yang Wei, Ding Weng, Yuanchao Yang, Xiaobo Zhang, Kaili Jiang, Liang Liu, and Shoushan Fan

Appl. Phys. Lett. 89, 063101 (2006); http://dx.doi.org/10.1063/1.2236465 (3 pages) | Cited 26 times

Online Publication Date: 7 August 2006

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An efficient method has been developed to fabricate field electron emitters by cutting a continuous multiwalled carbon nanotube (MWNT) yarn into segments. The cross section of each segment was composed of open-ended MWNTs which serve as field emitters. The emission current can reach several milliamperes, and the emitters can work stably for a long time. The excellent field emission properties are attributed to the large enhancement factor over 100 000, dense emitting centers, and the robust structure. The emitters might be easily manipulated and assembled into devices, such as electron guns, x-ray tubes, pixel tubes, etc.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.35.Kt Nanotube devices

Sol-gel synthesis and nonlinear optical transmission in Zn(1−x)Mg(x)O (x ⩽ 0.2) thin films

C. S. Suchand Sandeep, Reji Philip, R. Satheeshkumar, and V. Kumar

Appl. Phys. Lett. 89, 063102 (2006); http://dx.doi.org/10.1063/1.2335375 (3 pages) | Cited 22 times

Online Publication Date: 7 August 2006

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Nanocrystalline Zn1−xMgxO thin films with an average particle diameter of 60 nm have been deposited on glass substrates using a sol-gel spin-coating technique. Within the range of compositions, 0 ⩽ x ⩽ 0.20, the optical band gap could be tuned between 3.40 and 3.83 eV. The nonlinear optical transmission in the visible spectral region is investigated using ultrafast (100 fs) and short (7 ns) laser pulses at off-resonant wavelengths. The observed nonlinearity is strong and is comparable to that recently obtained in ZnO nanocomposite layers ion-implanted with Cu+ ions.
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81.05.Dz II-VI semiconductors
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
78.66.Hf II-VI semiconductors
42.65.-k Nonlinear optics

Electrostatic charge distribution on single-walled carbon nanotubes

Chunyu Li and Tsu-Wei Chou

Appl. Phys. Lett. 89, 063103 (2006); http://dx.doi.org/10.1063/1.2335411 (3 pages) | Cited 9 times

Online Publication Date: 7 August 2006

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This letter reports a study of charge distribution on single-walled carbon nanotubes. An atomistic moment method is proposed based on classical electrostatics theory and the results of analysis are compared with those obtained from ab initio approach. It is shown that the classical electrostatics is applicable to solving electric problems of nanostructures and the present method is computationally efficient. The effect of tube length, tube diameter, and tube position on nanotube electrostatic charge distributions has also been examined.
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61.46.Fg Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems

Large area self-assembled masking for photonic applications

N. Nagy, A. E. Pap, E. Horváth, J. Volk, I. Bársony, A. Deák, and Z. Hórvölgyi

Appl. Phys. Lett. 89, 063104 (2006); http://dx.doi.org/10.1063/1.2335668 (3 pages) | Cited 13 times

Online Publication Date: 8 August 2006

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Ordered porous structures for photonic application were fabricated on p- and n-type silicon by means of masking against ion implantation with Langmuir-Blodgett (LB) films. LB films from Stöber silica spheres [ J. Colloid Interface Sci. 26, 62 (1968) ] of 350 nm diameter were applied in the boron and phosphorus ion-implantation step, thereby offering a laterally periodic doping pattern. Ordered porous silicon structures were obtained after performing an anodic etch and were then removed by alkaline etching resulting in the required two-dimensional photonic arrangement. The LB silica masks and the resulting silicon structures were studied by field emission scanning electron microscope analysis.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
61.72.uf Ge and Si
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
61.46.-w Structure of nanoscale materials
81.65.Cf Surface cleaning, etching, patterning

Field electron emission from individual diamond cone formed by plasma etching

Q. Wang, Z. L. Wang, J. J. Li, Y. Huang, Y. L. Li, C. Z. Gu, and Z. Cui

Appl. Phys. Lett. 89, 063105 (2006); http://dx.doi.org/10.1063/1.2266991 (3 pages) | Cited 11 times

Online Publication Date: 8 August 2006

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Field electron emission properties of individual diamond cone were investigated using a customized double-probe scanning electron microscope system. The diamond cone was formed by maskless ion sputtering process in bias-assisted hot filament chemical vapor deposition system. The as-formed sharp diamond cone coated with high-sp2-content amorphous carbon exhibited high emission current of about 80 μA at an applied voltage of 100 V. The field emission was stable and well in consistent with the conventional Fowler-Nordheim emission mechanism, due to a stabilization process in surface work function. It has demonstrated the possibility of using individual diamond cone as a point electron emission source, because of its high field electron emission ability and stable surface state after the process of work function stabilization.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.65.Cf Surface cleaning, etching, patterning
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
52.77.Bn Etching and cleaning

Acoustic directional radiation and enhancement caused by band-edge states of two-dimensional phononic crystals

Chunyin Qiu and Zhengyou Liu

Appl. Phys. Lett. 89, 063106 (2006); http://dx.doi.org/10.1063/1.2335975 (3 pages) | Cited 13 times

Online Publication Date: 8 August 2006

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The authors numerically investigate the radiation of a line acoustic source placed inside a phononic crystal of square lattice. Their results show that it is possible to obtain a highly directional acoustic source with a large radiation enhancement, operating at the band-edge frequency of the phononic crystal. The angular distributions of the radiation power and the radiation enhancement factor are strongly dependent on the position of the acoustic source relative to the unit cell in which it is placed. A simple realization of a highly directional acoustic source with a half-power angular width of about 5.2° is presented.
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63.20.-e Phonons in crystal lattices
62.65.+k Acoustical properties of solids
71.20.-b Electron density of states and band structure of crystalline solids

Selective growth of Ge islands on nanometer-scale patterned SiO2/Si substrate by molecular beam epitaxy

Tae-Sik Yoon, Zuoming Zhao, Jian Liu, Ya-Hong Xie, Du yeol Ryu, Thomas P. Russell, Hyun-Mi Kim, and Ki-Bum Kim

Appl. Phys. Lett. 89, 063107 (2006); http://dx.doi.org/10.1063/1.2335976 (3 pages) | Cited 10 times

Online Publication Date: 8 August 2006

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The authors studied the selective growth of Ge islands by molecular beam epitaxy on Si(001) covered with nanometer-scale patterned SiO2 mask generated using self-assembled diblock copolymer. Selective growth is made possible by Ge adatoms desorbing from the SiO2 surface as well as diffusing into the exposed Si area. For the Ge coverage of 2 nm, multiple islands are observed along the periphery of individual exposed Si areas. At 3.5 nm coverage, the coalescence of small islands with significant strain relaxation becomes evident. The ramifications of the multiple islands morphology and their coalescence on potential device applications are discussed.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.43.Mn Adsorption kinetics
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.65.Hb Quantum dots (patterned in quantum wells)

In situ scanning tunneling microscopy during metal-organic vapor phase epitaxy

Bert Rähmer, Markus Pristovsek, Markus Breusing, Raimund Kremzow, and Wolfgang Richter

Appl. Phys. Lett. 89, 063108 (2006); http://dx.doi.org/10.1063/1.2335580 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2006

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The authors report the first ever in situ scanning tunnelling microscopy measurements in metal-organic vapor phase epitaxy (MOVPE) using an active cooling shield for operation up to 650 °C. Apart from fundamental considerations and constraints, some MOVPE specific problems are discussed. The authors present images representing the current status and discuss the effect of tip interaction with the MOVPE process.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.79.Cz Scanning tunneling microscopes

Magnetic properties of FePt nanodots formed by a self-assembled nanodot deposition method

C. K. Yin, T. Fukushima, T. Tanaka, M. Koyanagi, J. C. Bea, H. Choi, M. Nishijima, and M. Miyao

Appl. Phys. Lett. 89, 063109 (2006); http://dx.doi.org/10.1063/1.2335588 (3 pages) | Cited 10 times

Online Publication Date: 8 August 2006

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Fe50Pt50 nanodots dispersed in a SiO2 film (Fe50Pt50 nanodot film) were formed by a self-assembled nanodot deposition (SAND) method in which Fe50Pt50 and SiO2 are cosputtered in a high vacuum rf magnetron sputtering equipment. Fe50Pt50 pellets are laid on a SiO2 target in a sputtering chamber to form the Fe50Pt50 nanodot film in the SAND method. The size and density of Fe50Pt50 nanodot were controlled by changing the ratio of the total area of Fe50Pt50 pellets to that of SiO2 target. The Fe50Pt50 nanodot size decreases and its density increases when the ratio decreases. As-deposited Fe50Pt50 nanodots self-assembled to a face-centered-cubic phase of single-crystal structure. The Fe50Pt50 nanodot films were annealed to evaluate the nanodot size controllability, the magnetic anisotropy, and the thermal stability. Fully ordered L10 face-centered-tetragonal Fe50Pt50 nanodots with high magnetocrystalline anisotropy (Ku ≅ 8.7×107 ergs/cm3) were obtained by in situ annealing at 600 °C for 1 h in a high vacuum ambience. Furthermore, the Fe50Pt50 nanodot film with a monolayer of Fe50Pt50 nanodots was formed by annealing at 800 °C due to the agglomeration of Fe50Pt50 nanodots in the SiO2 film.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.Dn Self-assembly
81.15.Cd Deposition by sputtering
61.46.-w Structure of nanoscale materials

Structure and conductivity of self-assembled films of gold nanoparticles

J. B. Pełka, M. Brust, P. Gierłowski, W. Paszkowicz, and N. Schell

Appl. Phys. Lett. 89, 063110 (2006); http://dx.doi.org/10.1063/1.2245376 (3 pages) | Cited 18 times

Online Publication Date: 8 August 2006

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Self-assembled thin films of gold nanoparticles of 4–5 nm, prepared on glass using aliphatic dithiols of different hydrocarbon chain lengths as interparticle linker molecules, have been studied by x-ray methods and dc conductivity. X-ray data revealed small spacer-dependent cluster size variations in the films. Conductivity, in the temperature range of 4.2–300 K, showed a strong relation with spacer length, indicating that different mechanisms of conduction from metal-like through hopping to tunneling dominate, depending on temperature range and particle spacing. The results demonstrate that the electronic and optical properties of such films can be precisely controlled by interparticle distance.
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73.63.Bd Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology
72.20.Ee Mobility edges; hopping transport
73.40.Gk Tunneling

In situ electrode manipulation for three terminal field emission characterization of individual carbon nanotubes

R. C. Smith, J. D. Carey, D. C. Cox, and S. R. P. Silva

Appl. Phys. Lett. 89, 063111 (2006); http://dx.doi.org/10.1063/1.2335604 (3 pages) | Cited 2 times

Online Publication Date: 8 August 2006

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In situ three terminal electron field emission characterization of an isolated multiwalled carbon nanotube has been performed, where both anode and gate electrodes are attached to high precision piezodrivers. All measurements are performed in a scanning electron microscope allowing accurate knowledge of the local environment of the nanotube to be obtained. It is shown that the presence of the grounded gate electrode screens the applied field by approximately 32%. This technique in positioning the gate and anode electrodes allows for an estimate of the gate transparency factor and demonstrates characterization of individual carbon nanotubes without the need for fabrication of arrays of emitters.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes

Lack of dependence of the Raman frequency of optical vibrational modes on excitation wavelength in polar nanosemiconductors

Shu-Lin Zhang, Yanbin Zhang, Wei Liu, Zhengdong Fu, Yan Yan, Jing Chen, Rui Ma, Yang Song, Jun Zhao, Lv-Shun Xu, Songnan Wu, Min Gao, Hongdong Li, Yadong Li, and Fangli Yuan

Appl. Phys. Lett. 89, 063112 (2006); http://dx.doi.org/10.1063/1.2335622 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2006

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A lack of dependence of the Raman frequency of optical vibrational modes on excitation wavelength in polar nanosemiconductors was observed. This is in contrast to the earlier observed dependence in nonpolar nanomaterials: carbon nanotubes and Si nanowires. This difference has been ascribed to the different crystallographic natures of their Raman spectra: crystalline for nonpolar and amorphous for polar nanosemiconductors. The result has been explored theoretically to the Raman spectra being insensitive to sample sizes and thus indicates that the size confinement effect, a basic effect in nanomaterials, does not exhibit in the optical vibrational modes of polar nanosemiconductors.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Ch Nanotubes
78.67.Lt Quantum wires

Indium oxide “rods in dots” nanostructures

G. Q. Ding, W. Z. Shen, M. J. Zheng, and Z. B. Zhou

Appl. Phys. Lett. 89, 063113 (2006); http://dx.doi.org/10.1063/1.2335665 (3 pages) | Cited 6 times

Online Publication Date: 9 August 2006

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The authors have demonstrated a special indium oxide (In2O3) “rods in dots” nanostructure with high nanorod sheet density of over 1012 cm−2. The approach has been realized through depositing controllable individual In2O3 nanorods in both number and shape within a single porous alumina membrane (PAM) nanochannel under radio frequency magnetron sputtering. The authors further discussed in detail effects of the PAM configurations (pore diameter and thickness) and sputtering conditions (substrate temperature and argon pressure) on the formation of the In2O3 nanostructure.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
61.46.-w Structure of nanoscale materials

Probing nanoscale local lattice strains in advanced Si complementary metal-oxide-semiconductor devices

J. Huang, M. J. Kim, P. R. Chidambaram, R. B. Irwin, P. J. Jones, J. W. Weijtmans, E. M. Koontz, Y. G. Wang, S. Tang, and R. Wise

Appl. Phys. Lett. 89, 063114 (2006); http://dx.doi.org/10.1063/1.2336085 (3 pages) | Cited 16 times

Online Publication Date: 9 August 2006

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Local lattice strains in nanoscale Si complementary metal-oxide-semiconductor (MOS) transistors are directly measured by convergent beam electron diffraction (CBED). Through both high spatial resolution and high strain sensitivity of the CBED technique, compressive strains on the order of 10−3 from a p-type MOS transistor with a sub-100 nm gate length are detected. One-dimensional quantitative strain mapping is demonstrated. The tensile strains from a ⟨100⟩ channel n-type MOS transistor are observed at the ⟨910⟩ zone axis. It is found that the strain increases with the thickness of the silicon nitride-capping layer, which is consistent with the device’s electrical behavior.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Defect-free 100-layer strain-balanced InAs quantum dot structure grown on InP substrate

Z. H. Zhang, K. Y. Cheng, C. F. Xu, and K. C. Hsieh

Appl. Phys. Lett. 89, 063115 (2006); http://dx.doi.org/10.1063/1.2335605 (3 pages)

Online Publication Date: 9 August 2006

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A high quality 100-layer InAs quantum dot (QD) structure was successfully grown on InP substrate. The overall compressive strain caused by InAs QDs on InAlGaAs/InP is effectively balanced by inserting tensile-strained InGaAs strain-balance layers immediately above QD layers. The cross-sectional transmission electron microscopy images show a low defect density of less than 106 cm−2 and a smooth interface between QD layers throughout the whole structure. In addition, the intense room temperature photoluminescence indicates a good optical quality of the multilayer QD structure.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Cr III-V semiconductors

Noise in carbon nanotube field effect transistor

Fei Liu, Kang L. Wang, Daihua Zhang, and Chongwu Zhou

Appl. Phys. Lett. 89, 063116 (2006); http://dx.doi.org/10.1063/1.2335777 (3 pages) | Cited 12 times

Online Publication Date: 10 August 2006

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Low frequency noise power spectrum density of carbon nanotubes is presented. It is shown that the input-referred noise of carbon nanotubes increases quadratically as gate voltage is overdriven, suggesting that mobility fluctuation is the dominant mechanism contributing to the noise in carbon nanotube field effect transistors. The comparison of source-drain current noise power spectrum densities of carbon nanotubes in air and in vacuum indicates that a part of device noise is due to charge fluctuations from attached air molecules.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Charge-dipole model to compute the polarization of fullerenes

A. Mayer, Ph. Lambin, and R. Langlet

Appl. Phys. Lett. 89, 063117 (2006); http://dx.doi.org/10.1063/1.2337524 (3 pages) | Cited 15 times

Online Publication Date: 10 August 2006

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The authors present a charge-dipole model for the calculation of the polarization of fullerenes and carbon nanotubes. By expressing the electrostatic interactions in terms of normalized propagators, the technique achieves a better consistency and an improved stability. In its most elementary form, the model depends on a single parameter and provides an excellent agreement with reference data. The technique is illustrated with a C720 fullerene and enables one to quantify the role of free charges in the polarization of these structures. The positioning of these charges suggests that field-induced adsorption of small molecules should be enhanced at pentagonal rings and defects.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.46.Fg Nanotubes
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
68.43.Mn Adsorption kinetics

Engineering patterns of Co nanoclusters on thin film Al2O3/NiAl(100) using scanning tunneling microscopy manipulation techniques

Shrikrishina D. Sartale, Ku-Liang Lin, Chou-I Chiang, Meng-Fan Luo, and Chien-Cheng Kuo

Appl. Phys. Lett. 89, 063118 (2006); http://dx.doi.org/10.1063/1.2221394 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2006

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We present precise engineering of patterns of Co nanoclusters grown on ordered Al2O3/NiAl(100) surface using the scanning tunneling microscopy (STM) manipulation technique. The clusters are attracted to the STM tip by lowering the bias below a threshold value and translated and relocated to another position by reversing the polarity. This facile manipulation technique in combination with the self-organized patterning on this system reported earlier might play a decisive role in nanotechnology for various applications where patterned nanoclusters are desired.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Ta Atom manipulation
81.16.Dn Self-assembly
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Catalyst-free growth of In(As)P nanowires on silicon

M. Mattila, T. Hakkarainen, H. Lipsanen, H. Jiang, and E. I. Kauppinen

Appl. Phys. Lett. 89, 063119 (2006); http://dx.doi.org/10.1063/1.2336599 (3 pages) | Cited 34 times

Online Publication Date: 10 August 2006

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The catalyst-free metal organic vapor phase epitaxial growth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowire growth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InP nanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.
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81.07.Vb Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.La Quantum wires (patterned in quantum wells)
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Switchable nanometer contacts: Ultrathin Ag nanostructures on Si(100)

G. Gardinowski, J. Schmeidel, H. Pfnür, T. Block, and C. Tegenkamp

Appl. Phys. Lett. 89, 063120 (2006); http://dx.doi.org/10.1063/1.2336650 (3 pages) | Cited 8 times

Online Publication Date: 10 August 2006

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The fabrication and characterization of metallic nanometer-sized gaps suitable for conductivity measurements of single molecules were studied. Controlled gap formation by electromigration (EM) is demonstrated in contiguous and ultrathin Ag structures wetting the Si(100) substrate. The gaps obtained are in the range of nanometers or even subnanometers, as revealed by lateral conductivity measurements and scanning tunneling microscopy carried out under ultrahigh vacuum conditions. Annealing to 300 K closes the gap by enabling surface diffusion of Ag, and another cycle of opening by EM at 80 K can be performed. The functionality of the contacts is demonstrated by insertion of ferrocenedithiol molecules into the gap.
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73.63.Rt Nanoscale contacts
81.16.-c Methods of micro- and nanofabrication and processing
68.35.Fx Diffusion; interface formation
66.30.Qa Electromigration
81.40.Gh Other heat and thermomechanical treatments

Thermal conductivity of tubular and core/shell nanowires

Ravi Prasher

Appl. Phys. Lett. 89, 063121 (2006); http://dx.doi.org/10.1063/1.2336720 (3 pages) | Cited 16 times

Online Publication Date: 10 August 2006

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Analytical solution of the Boltzmann transport equation (BTE) for phonon transport in tubular and core-shell nanowire is obtained. Thermal conductivity calculated from the analytical solution of BTE is in excellent agreement with a recently reported numerical model [ R. Yang et al., Nano Lett. 5, 1111 (2005) ]. Results show that thermal conductivity of tubular and core-shell nanowire can be significantly smaller than the bulk thermal conductivity.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials

Growth of ultrahigh-density quantum-confined germanium dots on SiO2 thin films

I. Berbezier, A. Karmous, A. Ronda, A. Sgarlata, A. Balzarotti, P. Castrucci, M. Scarselli, and M. De Crescenzi

Appl. Phys. Lett. 89, 063122 (2006); http://dx.doi.org/10.1063/1.2221875 (3 pages) | Cited 10 times

Online Publication Date: 11 August 2006

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The spontaneous formation of nanometric and highly dense ( ∼ 3×1012 cm−2) Ge droplets on thin SiO2 film on Si(001) is investigated by scanning tunneling microscopy and spectroscopy. Ge dots have been grown by depositing Ge on the clean SiO2 surface at room temperature and then annealing the sample at 500 °C. Ge dots appear to be free of germanium oxides and characterized by a flat surface with the onset of {113} faceting. I-V curves show that they have an energy gap of approximately 1.8 eV, well above that of bulk Ge. Fabrication of nanometer-sized, highly dense pure Ge droplets is very promising for nanoelectronics applications.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
61.72.Cc Kinetics of defect formation and annealing
71.20.Mq Elemental semiconductors

Growth of RuO2 nanorods in reactive sputtering

Yu-Tsun Lin, Chun-Yu Chen, Chang-Po Hsiung, Kai-Wen Cheng, and Jon-Yiew Gan

Appl. Phys. Lett. 89, 063123 (2006); http://dx.doi.org/10.1063/1.2269180 (3 pages) | Cited 8 times

Online Publication Date: 11 August 2006

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The synthesis of RuO2 nanorods with reactive sputtering was demonstrated in this work. The synthesis process is very much like the metal organic chemical vapor deposition, except that RuO3 generated with reactive sputtering under high oxygen-to-argon flow ratio (>5 SCCM/15 SCCM) (SCCM denotes cubic centimeter per minute at STP) and high substrate temperature (>300 °C) is used in place of the metal organic precursor. RuO2 nanorods tend to grow steadily with constant aspect ratio ( ∼ 27) and the field-emission characteristics appear very sensitive to their spatial distribution.
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81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Cd Deposition by sputtering
79.70.+q Field emission, ionization, evaporation, and desorption

Electric-field-induced microstructural transformation of carbon nanotubes

Qiaoliang Bao, Han Zhang, and Chunxu Pan

Appl. Phys. Lett. 89, 063124 (2006); http://dx.doi.org/10.1063/1.2227620 (3 pages) | Cited 8 times

Online Publication Date: 11 August 2006

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In the present work, microstructural transformation of carbon nanotubes (CNTs) from the “herringbone” into highly crystalline structure in an electric field was experimentally observed by using a high-resolution transmission electron microscope and the growth mechanism was modeled and discussed by using a finite element method. It is found that the CNT microstructures can be changed by an electric field through the influence of the electrostatic force on the carbon surface and bulk diffusion on/in a deformed catalyst particle. Preliminary experiment revealed that an isomeric “graphite-nongraphite-graphite-nongraphite⋯” CNTs could be synthesized when a pulsed electric field is applied, which are expected to exhibit special properties and promising applications.
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81.07.De Nanotubes
64.70.K- Solid-solid transitions
61.46.Fg Nanotubes
66.30.-h Diffusion in solids
61.72.-y Defects and impurities in crystals; microstructure
68.37.Lp Transmission electron microscopy (TEM)

Quantifying oxygen diffusion in ZnO nanobelt

Jin Liu, Puxian Gao, Wenjie Mai, Changshi Lao, Zhong L. Wang, and Rao Tummala

Appl. Phys. Lett. 89, 063125 (2006); http://dx.doi.org/10.1063/1.2236214 (3 pages) | Cited 13 times

Online Publication Date: 11 August 2006

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A method is presented for quantifying oxygen diffusion behavior in a nanodevice fabricated using individual ZnO nanowire/nanobelt. A nanodevice was built using a single nanobelt. Defects are introduced into nanobelt during specific nanofabrication procedure. Then, after the device being exposed to atmosphere for several days, oxygen in air diffused into the nanobelt and significantly changed the conductivity of the device. By comprising the experimentally measured conductivity and that of simulated result, the diffusion coefficient of oxygen in ZnO nanowires/nanobelts has been derived.
Show PACS
85.35.-p Nanoelectronic devices
66.30.-h Diffusion in solids
73.63.-b Electronic transport in nanoscale materials and structures
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