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11 Aug 2003

Volume 83, Issue 6, pp. 1063-1275

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages)

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider
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Is there a thermodynamic size limit of nanowires grown by the vapor-liquid-solid process?

Teh Y. Tan, Na Li, and Ulrich Gösele

Appl. Phys. Lett. 83, 1199 (2003); http://dx.doi.org/10.1063/1.1599984 (3 pages) | Cited 28 times

Online Publication Date: 5 August 2003

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For nanowires grown by the vapor-liquid-solid (VLS) process, expressions of the thermodynamically allowed minimum sizes of the wire and the liquid droplet are derived using Si nanowires (SiNW) grown from metal–silicon (M–Si) liquid as the model case. The liquid droplet minimum size is determined by a unique set of external M and Si vapor phase pressure values. The SiNW minimum size expression contains two contributions, one depending on composition of the liquid and one depending on the droplet size. These expressions do not predict a limit on the attainable VLS SiNW minimum size, implying ever smaller SiNW can be grown until reaching some growth kinetic limit which is presently unknown. © 2003 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.-b Nanoscale materials and structures: fabrication and characterization

Infusing metal into self-organized semiconductor nanostructures

Hideo Kohno and Seiji Takeda

Appl. Phys. Lett. 83, 1202 (2003); http://dx.doi.org/10.1063/1.1599970 (2 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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We show that more complex nanoheterostructures can be formed readily by using templates through a self-organized process. We fabricated silicon/silicide/oxide-heterostructured nanowires by infusing metal into chains of crystalline-silicon nanospheres. The structure and composition were studied using transmission-electron-microscopy-based approaches. © 2003 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Lp Transmission electron microscopy (TEM)
61.46.-w Structure of nanoscale materials

Doping of the nanocrystalline semiconductor zinc oxide with the donor indium

Th. Agne, Z. Guan, X. M. Li, H. Wolf, Th. Wichert, H. Natter, and R. Hempelmann

Appl. Phys. Lett. 83, 1204 (2003); http://dx.doi.org/10.1063/1.1598289 (3 pages) | Cited 33 times

Online Publication Date: 5 August 2003

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Doping of the nanocrystalline semiconductor ZnO with the donor 111In was achieved by the incorporation of 111In atoms during the growth process followed by a hydrothermal treatment at 473 K. The incorporation of 111In on substitutional Zn sites was shown by the perturbed γγ angular correlation technique. The structural quality of nanocrystalline ZnO with a mean grain size of 11 nm is significantly improved by annealing at 473 K, as revealed by x-ray diffraction, transmission electron microscopy, optical absorption measurements, and photoluminescence spectroscopy. It is shown that the incorporation of 111In on undisturbed Zn sites in nanocrystalline ZnO seems to be supported by the onset of crystal growth and by the removal of intrinsic defects. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
78.55.Et II-VI semiconductors

Growth of vertically aligned carbon nanofibers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition

J. B. O. Caughman, L. R. Baylor, M. A. Guillorn, V. I. Merkulov, D. H. Lowndes, and L. F. Allard

Appl. Phys. Lett. 83, 1207 (2003); http://dx.doi.org/10.1063/1.1597981 (3 pages) | Cited 26 times

Online Publication Date: 5 August 2003

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Vertically aligned carbon nanofibers (VACNFs) have been grown using a low-pressure, plasma-enhanced, chemical vapor deposition process. The nanofibers are grown from a nickel catalyst that can be patterned to form arrays of individual, isolated VACNFs. The fibers are grown at pressures below 100 mTorr, using an inductively coupled plasma source with a radio-frequency bias on the sample substrate to allow for independent control of the ion energies. Plasma conditions are related to growth results by comparing optical emission from the plasma to the physical structure of the nanofibers. We find that the ratio of etching species in the plasma to depositing species is critical to the final shape of the carbon structures that are formed. © 2003 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Production, structure, and optical properties of ZnO nanocrystals embedded in CaF2 matrix

Y. C. Liu, H. Y. Xu, R. Mu, D. O. Henderson, Y. M. Lu, J. Y. Zhang, D. Z. Shen, X. W. Fan, and C. W. White

Appl. Phys. Lett. 83, 1210 (2003); http://dx.doi.org/10.1063/1.1591248 (3 pages) | Cited 25 times

Online Publication Date: 5 August 2003

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High-quality ZnO nanocrystals have been fabricated by zinc ion implantation (160 keV, 1×1017 ions/cm2) into a CaF2(111) single-crystal substrate followed by thermal annealing from 300 to 700 °C. X-ray diffraction results show that ZnO nanocrystals in CaF2(111) substrate have a (002) preferred orientation. The average grain size is ranging from 14 to 19 nm corresponding to the annealing temperatures from 500 to 700 °C. A very strong ultraviolet near-band edge emission is observed from 372 to 379 nm. The emission intensity is enhanced and linewidth is narrowed as the annealing temperature increases. The commonly observed visible green emission associated with deep-level defects in ZnO is suppressed. © 2003 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials

Chirality effect of single-wall carbon nanotubes on field emission

Shi-Dong Liang and N. S. Xu

Appl. Phys. Lett. 83, 1213 (2003); http://dx.doi.org/10.1063/1.1599983 (3 pages) | Cited 21 times

Online Publication Date: 5 August 2003

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The chirality effect of an opened-end single-wall carbon nanotube on field emission is studied by using the tunneling theory with the tight-binding approximation. The characteristic of the emission-current line density versus field is found to be dependence on the chirality of nanotubes. A metallic tube has a line density higher than that of a semiconducting one. Also, for semiconducting tubes, a tube of larger chiral angle has a line density higher than that of smaller chiral angle; a zigzag semiconducting tube has a smallest line density among the others. Further, the Fowler–Nordheim plots may have a nonlinear behavior in high current region. Finally, at temperature T<1000 K, the emission current is almost independent of temperature. Our results are explained by the energy band structure of nanotubes. © 2003 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.63.Fg Nanotubes
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Electrochemical properties of carbon nanofiber web as an electrode for supercapacitor prepared by electrospinning

C. Kim and K. S. Yang

Appl. Phys. Lett. 83, 1216 (2003); http://dx.doi.org/10.1063/1.1599963 (3 pages) | Cited 117 times

Online Publication Date: 5 August 2003

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Poly(acrylonitrile) solutions in dimethylformamide were electrospun to be webs consisting of 300 nm ultrafine fibers. The webs were oxidatively stabilized and activated by steam resulting in activated carbon nanofibers (ACNFs). The specific surface area of the ACNF activated at 700 °C was the highest but mesopore volume fraction of that was lowest. On the other hand, the ACNFs activated at 800 °C showed opposite trends to those activated at 700 °C. The high specific surface area, mainly due to the micropores, introduced maximum specific capacitance at low current density (173 F/g at 10 mA/g). The elevated volume fraction of mesopores gave maximum specific capacitance at high current density (120 F/g at 1000 mA/g). The behavior is explained on the basis of ion mobility in the pores. © 2003 American Institute of Physics.
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82.45.Fk Electrodes
82.47.Uv Electrochemical capacitors; supercapacitors
82.45.Yz Nanostructured materials in electrochemistry
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Visualization of individual carbon nanotubes with fluorescence microscopy using conventional fluorophores

Rohit Prakash, S. Washburn, Richard Superfine, Richard E. Cheney, and Michael R. Falvo

Appl. Phys. Lett. 83, 1219 (2003); http://dx.doi.org/10.1063/1.1599042 (3 pages) | Cited 19 times

Online Publication Date: 5 August 2003

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We demonstrate that individual carbon nanotubes (CNTs) can be visualized with fluorescence microscopy through noncovalent labeling with conventional fluorophores. Reversal of contrast in fluorescence imaging of the CNTs was observed when performing labeling procedure in a nonpolar solvent. Our results are consistent with a CNT-fluorophore affinity mediated by hydrophobic interaction. The reverse-contrast images also provide clear indication of nanotube location. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
87.64.M- Optical microscopy

Formation energy of Stone–Wales defects in carbon nanotubes

L. G. Zhou and San-Qiang Shi

Appl. Phys. Lett. 83, 1222 (2003); http://dx.doi.org/10.1063/1.1599961 (3 pages) | Cited 33 times

Online Publication Date: 5 August 2003

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A Stone–Wales (SW) defect is a dipole of 5–7 ring pair in a hexagonal network, which is one of the most important defective structures in carbon nanotubes (CNTs) that will affect mechanical, chemical, and electronic properties of CNTs. Using the extended Hückel method, we calculated the formation energy of SW defects in carbon nanotubes. The formation energy of SW defects was then fitted to a simple formula as a function of the tube radius and the orientation of a SW defect in the tube. This result provides a convenient tool for the study of thermodynamics and kinetics of SW defects, as well as the interaction of SW defects with other types of defects in CNTs. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials

Ion-induced chemical vapor deposition of copper films with nanocellular microstructures

F. Ross, C. V. Thompson, T. Chiang, and H. H. Sawin

Appl. Phys. Lett. 83, 1225 (2003); http://dx.doi.org/10.1063/1.1599964 (3 pages)

Online Publication Date: 5 August 2003

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Ion-induced chemical vapor deposition using a broad ion beam has been used to deposit nanocellular films. These films consist of closely packed 10–20 nm diameter copper rods separated by a carbonaceous residue, and growing in a direction normal to the substrate surface to lengths equal to the film thickness. The effects of ion flux, ion energy, and substrate temperature on rod spacing were investigated. A growth mechanism analogous to that leading to cellular structures during solidification from alloy melts is proposed and qualitatively described. Films with nanocellular structures are expected to have useful, highly anisotropic properties. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electrical properties of nanoceramics reinforced with ropes of single-walled carbon nanotubes

Guo-Dong Zhan, Joshua D. Kuntz, Javier E. Garay, and Amiya K. Mukherjee

Appl. Phys. Lett. 83, 1228 (2003); http://dx.doi.org/10.1063/1.1600511 (3 pages) | Cited 69 times

Online Publication Date: 5 August 2003

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Single-walled carbon nanotubes (SWCNTs) were used to convert insulating nanoceramics to metallically conductive composites. Dense SWCNT/Al2O3 nanocomposites with CNT contents ranging from 5.7 to 15 vol % and with nanocrystalline alumina matrices have been fabricated by spark-plasma-sintering that retains the integrity of SWCNT in the matrix. The conductivity of these composites increases with increasing content of CNTs. The conductivity has been increased to 3345 S/m in the 15 vol % SWCNT/Al2O3 nanocomposite at room temperature. This is an increase of 13 orders of magnitude over pure alumina and of more than 735% over previously reported results in CNT–ceramic composites. © 2003 American Institute of Physics.
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73.63.Fg Nanotubes
72.80.Tm Composite materials
81.07.De Nanotubes
81.05.Mh Cermets, ceramic and refractory composites
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
52.77.-j Plasma applications

III-nitride photonic crystals

T. N. Oder, J. Shakya, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 83, 1231 (2003); http://dx.doi.org/10.1063/1.1600839 (3 pages) | Cited 64 times

Online Publication Date: 5 August 2003

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We report the achievement of nanofabrication and characterization of a triangular lattice array of photonic crystals (PCs) with diameter/periodicity as small as 100/180 nm on an InGaN/GaN multiple quantum well using electron-beam lithography and inductively coupled plasma dry etching. Optical measurements of the PCs performed using near-field scanning optical microscopy showed a 60° periodic variation with the angle between the propagation direction of emission light and the PCs lattice. An unprecedented maximum enhancement factor of 20 was obtained for the emission light intensity at wavelengths as short as 475 nm at room temperature with emission light parallel to the Γ–K direction of the PCs lattice. The implications of these results to nitride-based optoelectronic devices, particularly in improving the light extraction efficiency in light-emitting diodes both for blue/green as well as UV emitters, are discussed. © 2003 American Institute of Physics.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
81.16.Nd Micro- and nanolithography
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.37.Uv Near-field scanning microscopy and spectroscopy

Noise and photoconductive gain in InAs quantum-dot infrared photodetectors

Zhengmao Ye, Joe C. Campbell, Zhonghui Chen, Eui-Tae Kim, and Anupam Madhukar

Appl. Phys. Lett. 83, 1234 (2003); http://dx.doi.org/10.1063/1.1597987 (3 pages) | Cited 28 times

Online Publication Date: 5 August 2003

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We report noise characteristics, carrier capture probability, and photoconductive gain of InAs quantum-dot infrared photodetectors with unintentionally doped active regions. At 77 K, a photoconductive gain of 750 was observed at a bias of 0.7 V. The high gain is a result of the low carrier capture probability: p = 0.0012. © 2003 American Institute of Physics.
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73.63.Kv Quantum dots
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Reflection of guided modes in a semiconductor nanowire laser

A. V. Maslov and C. Z. Ning

Appl. Phys. Lett. 83, 1237 (2003); http://dx.doi.org/10.1063/1.1599037 (3 pages) | Cited 78 times

Online Publication Date: 5 August 2003

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We analyze the waveguiding properties of semiconductor (GaN, ZnO, CdS) single nanowire lasers which were recently demonstrated experimentally. In particular, we compute the reflectivity for a few lowest-order guided modes (HE11, TE01, and TM01) from the nanowire facets. The reflectivity is shown to depend strongly on the mode type, lasing frequency and radius of the nanowire. By using the computed reflectivities, we make realisic estimates of the threshold gain and quality factor for the nanowire lasers. Our results shed light on the lasing mechanism of the nanowire lasers. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Nanowire-based very-high-frequency electromechanical resonator

A. Husain, J. Hone, Henk W. Ch. Postma, X. M. H. Huang, T. Drake, M. Barbic, A. Scherer, and M. L. Roukes

Appl. Phys. Lett. 83, 1240 (2003); http://dx.doi.org/10.1063/1.1601311 (3 pages) | Cited 141 times

Online Publication Date: 5 August 2003

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Fabrication and readout of devices with progressively smaller size, ultimately down to the molecular scale, is critical for the development of very-high-frequency nanoelectromechanical systems (NEMS). Nanomaterials, such as carbon nanotubes or nanowires, offer immense prospects as active elements for these applications. We report the fabrication and measurement of a platinum nanowire resonator, 43 nm in diameter and 1.3 μm in length. This device, among the smallest NEMS reported, has a fundamental vibration frequency of 105.3 MHz, with a quality factor of 8500 at 4 K. Its resonant motion is transduced by a technique that is well suited to ultrasmall mechanical structures. © 2003 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
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