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27 Jun 2005

Volume 86, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 86, 263107 (2005); http://dx.doi.org/10.1063/1.1952585 (3 pages)

B. Yang, M. S. Marcus, D. G. Keppel, P. P. Zhang, Z. W. Li, B. J. Larson, D. E. Savage, J. M. Simmons, O. M. Castellini, M. A. Eriksson, and M. G. Lagally
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Abnormal temperature dependence of conductance of single Cd-doped ZnO nanowires

Q. H. Li, Q. Wan, Y. G. Wang, and T. H. Wang

Appl. Phys. Lett. 86, 263101 (2005); http://dx.doi.org/10.1063/1.1954878 (3 pages) | Cited 12 times

Online Publication Date: 20 June 2005

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Positive temperature coefficient of resistance is observed on single Cd-doped ZnO nanowires. The current along the nanowire increases linearly with the bias and saturates at large biases. The conductance is greatly enhanced either by ultraviolet illumination or infrared illumination. However, the conductance decreases with increasing temperature, in contrast to the reported temperature behavior either for ZnO nanostructures or for CdO nanoneedles. The increase of the conductance under illumination is related to surface effect and the decrease with increasing temperature to bulk effect. These results show that Cd doping does not change surface effect but affects bulk effect. Such a bulk effect could be used to realize on-chip temperature-independent varistors.
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73.63.Nm Quantum wires
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Plasmon effects on infrared spectra of GaN nanocolumns

Takeshi Iwanaga, Toshihiko Suzuki, Shigeru Yagi, and Teruaki Motooka

Appl. Phys. Lett. 86, 263102 (2005); http://dx.doi.org/10.1063/1.1957113 (3 pages) | Cited 1 time

Online Publication Date: 20 June 2005

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Infrared (IR) transmission spectra of GaN nanocolumns were analyzed. In addition to the bulk GaN optical phonon signal, a broad absorption peak was observed from undoped and Mg-doped nanocolumns. The central position and width of the broad peak changed with the growth condition and Mg concentration. Based on the Lorentz–Drude model composed of phonon and plasmon modes associated with depolarization fields in GaN nanocolumns, IR transmission spectra were fitted by adjusting the free-electron concentration and scattering rate. Dependence of these values on the column size and impurity concentration is discussed.
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78.30.Fs III-V and II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
61.72.S- Impurities in crystals
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Preparation of tungsten oxide nanowires from sputter-deposited WCx films using an annealing/oxidation process

Shui-Jinn Wang, Chao-Hsuing Chen, Rong-Ming Ko, Yi-Cheng Kuo, Chin-Hong Wong, Chien-Hung Wu, Kai-Ming Uang, Tron-Min Chen, and Bor-Wen Liou

Appl. Phys. Lett. 86, 263103 (2005); http://dx.doi.org/10.1063/1.1957115 (3 pages) | Cited 19 times

Online Publication Date: 20 June 2005

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The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited WCx films using a simple annealing/oxidization process was reported. It was found that thermal annealing of WCx films at 680 °C for 30 min in nitrogen followed by oxidation at 450 °C for 30 min in pure oxygen would yield dense and well-crystallized monoclinic W18O49 (010) nanowires with a typical length/diameter of about 0.15–0.2 μm/10–20 nm. The formation of W18O49 nanowires is attributed to the nuclei of immature W2C nanowires experiencing a regrowth process, accompanied by carbon depletion and the oxidization of tungsten during the subsequent oxidization process.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Dn Self-assembly
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials

Temperature dependence of the field emission of multiwalled carbon nanotubes

Cher Ming Tan, Junji Jia, and Weibo Yu

Appl. Phys. Lett. 86, 263104 (2005); http://dx.doi.org/10.1063/1.1957117 (3 pages) | Cited 18 times

Online Publication Date: 20 June 2005

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The field emission characteristics of multiwalled carbon nanotubes at various temperatures are studied. It is found that the turn-on field and emission current at a given applied electric field are dependent on the ambient temperature of the nanotube. This dependence is believed to be due to the change in the work function of the nanotube on temperature, and the dependence of the work function with temperature is calculated. The direct application of such temperature dependence is a simple and low-cost nanothermometer.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions
73.63.Fg Nanotubes

Atmospheric-pressure plasma treatment to modify hydrogen storage properties of multiwalled carbon nanotubes

Kyu Sung Han, Hyun Seok Kim, Min Sang Song, Min Sik Park, Sang Soo Han, Jai Young Lee, Jeung Ku Kang, and Yoon Kee Kim

Appl. Phys. Lett. 86, 263105 (2005); http://dx.doi.org/10.1063/1.1957119 (3 pages) | Cited 6 times

Online Publication Date: 21 June 2005

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We prepared multiwalled carbon nanotubes by a floating catalyst method using thermal chemical vapor deposition, but then the structures of the nanotubes were modified by the atmospheric-pressure plasma treatment to enable practical applications to hydrogen storage media. As is usually observed in multiwalled carbon nanotubes grown by thermal chemical vapor deposition, the as-grown multiwalled carbon nanotubes showed closed-cap structures and continuous walls that could not provide enough sites for hydrogen storage at ambient conditions. A thermal desorption spectra analysis showed that hydrogen was released at a temperature range of 100–150 K, where the total amount of evolved hydrogen was 4.9 wt %. However, after the atmospheric-pressure plasma treatment performed to open closed caps and create nanopores in multiwalled carbon nanotubes, it was found that the modified structures of the nanotubes released hydrogen not only at a subambient temperature range of 100–150 K, but also at an ambient temperature range of 300–330 K. The amount of released hydrogen was 5.1 wt % and 0.6 wt %, respectively.
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81.07.De Nanotubes
81.05.Rm Porous materials; granular materials
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
52.77.-j Plasma applications
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Vx Thermal desorption
84.60.-h Direct energy conversion and storage

Studies of the self-ordering process in FePt self-ordered magnetic array media

C. Verdes, J. Ahner, P. M. Jones, N. Shukla, R. W. Chantrell, and D. Weller

Appl. Phys. Lett. 86, 263106 (2005); http://dx.doi.org/10.1063/1.1953879 (3 pages) | Cited 6 times

Online Publication Date: 21 June 2005

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A model of self-organization in FePt particulate thin films is described. The model is based on Monte Carlo methods and describes the self-organization process from the colloidal state as a result of the evaporation of the solvent and the consequent compression of the film due to surface tension forces. The model predicts the self-ordered state for systems with very narrow particle size distributions (standard deviation of the lognormal distribution σ<0.05). Various forms of interparticle potentials were considered. A comparison of the model with experimental data shows that the interparticle potential must contain an attractive term, in addition to the repulsive term normally expected to arise from the surfactant. Quantum chemistry calculations show that an attractive potential does indeed exist between overlapping oleic acid molecules. Although the ordering predicted by the model is predominantly hexagonal, the conditions for the formation of a square lattice are investigated, and an explanation for the observation of square lattices in some systems is proposed.
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81.16.Dn Self-assembly
68.03.Cd Surface tension and related phenomena
75.50.Bb Fe and its alloys
82.70.Dd Colloids

Template-directed carbon nanotube network using self-organized Si nanocrystals

B. Yang, M. S. Marcus, D. G. Keppel, P. P. Zhang, Z. W. Li, B. J. Larson, D. E. Savage, J. M. Simmons, O. M. Castellini, M. A. Eriksson, and M. G. Lagally

Appl. Phys. Lett. 86, 263107 (2005); http://dx.doi.org/10.1063/1.1952585 (3 pages) | Cited 12 times

Online Publication Date: 22 June 2005

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We demonstrate a way to direct carbon nanotube growth using Si nanocrystals that are self-ordered via the thermal decomposition of thin silicon-on-insulator substrates. The Si nanocrystals are about 90 nm wide and 100–150 nm tall, with 200 nm spacing. Nanotubes connect the silicon nanocrystals to form a network. Nanotubes selectively appear between tops of the Si nanocrystals. We show that the flow pattern of the carbon feedstock in the chemical vapor deposition growth process is disturbed by the geometric effect of the Si nanocrystals, providing a mechanism for growth between the tops of the Si nanocrystals.
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81.07.De Nanotubes
81.16.Dn Self-assembly
81.16.Be Chemical synthesis methods
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Device modeling of long-channel nanotube electro-optical emitter

J. Tersoff, Marcus Freitag, James C. Tsang, and Phaedon Avouris

Appl. Phys. Lett. 86, 263108 (2005); http://dx.doi.org/10.1063/1.1957116 (3 pages) | Cited 21 times

Online Publication Date: 22 June 2005

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We present a simple analytic model of long single-wall nanotube electro-optical emitters, along with experimental measurements using improved devices with reduced hysteresis. The model describes well the voltage-controlled motion of the emission spot, and provides a clear picture of the physical mechanism of device operation. It also indicates that the electric field is strongly enhanced at the emission spot, and that device performance can be greatly improved by the use of thinner gate oxides.
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85.35.Kt Nanotube devices
42.79.-e Optical elements, devices, and systems

Synthesis of blue-light-emitting Si1−xGex oxide nanowires

J. H. He, W. W. Wu, S. W. Lee, L. J. Chen, Y. L. Chueh, and L. J. Chou

Appl. Phys. Lett. 86, 263109 (2005); http://dx.doi.org/10.1063/1.1949283 (3 pages) | Cited 14 times

Online Publication Date: 22 June 2005

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Blue-light-emitting Si1−xGex oxide nanowires have been grown on epitaxial Si0.8Ge0.2 alloys on silicon by thermal annealing in a quartz tube furnace in N2 ambient. The photoluminescence spectrum of Si1−xGex oxide nanostructures exhibits the blue-light emission with a peak at 415 nm, compared with the Si oxide nanowires with a peak at 470 nm. Nanowires with uncommon shapes, such as sunflowerlike and radiolarialike shape, have been observed. A field emission scanning electron microscope was used to monitor the growth of nanowires on the same patterned catalytic Au region. The growth can be understood in term of vapor-liquid-solid mechanism.
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81.07.Vb Quantum wires
81.05.Hd Other semiconductors
78.67.Lt Quantum wires
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
61.72.Cc Kinetics of defect formation and annealing
68.37.Vj Field emission and field-ion microscopy

Potassium chloride nanowire formation inside a microchannel glass array

Daqing Zhang, Sam Moore, Jiang Wei, Abdullah Alkhateeb, Dev Gangadean, Hasan Mahmood, Justin Lantrips, David N. Mcllroy, Aaron D. LaLonde, M. Grant Norton, James S. Young, and Chongmin Wang

Appl. Phys. Lett. 86, 263110 (2005); http://dx.doi.org/10.1063/1.1977202 (3 pages) | Cited 2 times

Online Publication Date: 23 June 2005

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The synthesis of KCl nanowires has been achieved by atomic layer deposition inside high aspect ratio channels of microchannel glass. The average diameter of the KCl nanowires is 250 nm, with a minimum observed diameter of 50 nm, and lengths up to 5 μm. The Cl precursor was TaCl5, while the source of K was determined to be impurities in the microchannel glass substrate. The process for KC1 nanowire formation is a three-step chemical process that simultaneously etches K from the substrate concomitant with the formation of chlorine gas. It is postulated that the curvature of the channels may influence the diameters of the KCl nanowires.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
61.46.-w Structure of nanoscale materials
81.65.Cf Surface cleaning, etching, patterning

Controllable method for the preparation of metalized probes for efficient scanning near-field optical Raman microscopy

J. J. Wang, Y. Saito, D. N. Batchelder, J. Kirkham, C. Robinson, and D. A. Smith

Appl. Phys. Lett. 86, 263111 (2005); http://dx.doi.org/10.1063/1.1978983 (3 pages) | Cited 16 times

Online Publication Date: 23 June 2005

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A modification of the mirror reaction method has been used to metalize atomic force microscope (AFM) probes for apertureless near-field optical microscopy. The method produces a single silver particle of controllable size at the apex of the AFM tip with no detrimental effects on the AFM probe. A particle of the order 80 nm in diameter appears to provide the best tip-enhanced Raman signal using 488 nm excitation. The near-field Raman spatial resolution of one such probe was shown to be as high as 24 nm using single-walled carbon nanotubes as a test sample.
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07.79.Lh Atomic force microscopes
07.79.Fc Near-field scanning optical microscopes
81.16.-c Methods of micro- and nanofabrication and processing

In-plane strain distribution in the surface region of thin silicon overlayers on insulator

Hiroo Omi, Tomoaki Kawamura, Seiji Fujikawa, Yoshiyuki Tsusaka, Yasushi Kagoshima, and Junji Matsui

Appl. Phys. Lett. 86, 263112 (2005); http://dx.doi.org/10.1063/1.1977208 (3 pages) | Cited 6 times

Online Publication Date: 24 June 2005

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A thin silicon nano-overlayer (SNOL) fabricated by oxidation and etchback in a separation by implantation of oxygen wafer was investigated by grazing incident x-ray diffraction at incident angles between 0.01° and 0.1° below the critical angle of total reflection (0.18° ). We measured {220} reflections by probing the sample in depth and found that the SNOL has finite domains under strain close to the surface. We also found that annealing the sample up to 1000 °C significantly reduced inhomogeneous in depth strain and increased the size of the domains in the surface region of the SNOL.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si

Lateral quantum-dot replication in three-dimensional quantum-dot crystals

S. Kiravittaya, H. Heidemeyer, and O. G. Schmidt

Appl. Phys. Lett. 86, 263113 (2005); http://dx.doi.org/10.1063/1.1954874 (3 pages) | Cited 17 times

Online Publication Date: 24 June 2005

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Single quantum dots (QDs) reproduce into pairs of QDs with increasing separation distance during the growth of a three-dimensional QD crystal. Kinetic Monte Carlo simulations—that rely on strain profiles deduced from experiment—can describe this lateral replication process, which is triggered by a distinct ridge structure that evolves during the overgrowth of two-dimensional periodic QD arrays.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Highly sensitive strain detection in strained silicon by surface-enhanced Raman spectroscopy

Norihiko Hayazawa, Masashi Motohashi, Yuika Saito, and Satoshi Kawata

Appl. Phys. Lett. 86, 263114 (2005); http://dx.doi.org/10.1063/1.1984105 (3 pages) | Cited 18 times

Online Publication Date: 24 June 2005

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We used surface-enhanced Raman spectroscopy to observe selective amplification of the vibration mode of Si–Si in strained silicon. By covering the silver island film on a strained silicon layer, the Raman signal from the strained silicon can be detected with a high sensitivity compared with the overwhelming background signal from the underlying silicon layer. This technique allowed us to carry out micro-Raman spectroscopy on strained silicon. This technique can be a precursor for nano-Raman spectroscopy using a tip-enhanced Raman microscope with a sharpened metallic probe tip.
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68.60.Bs Mechanical and acoustical properties
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
63.20.-e Phonons in crystal lattices

Effects of in situ vacuum annealing on the surface and luminescent properties of ZnS nanowires

R. A. Rosenberg, G. K. Shenoy, F. Heigl, S.-T. Lee, P.-S. G. Kim, X.-T. Zhou, and T. K. Sham

Appl. Phys. Lett. 86, 263115 (2005); http://dx.doi.org/10.1063/1.1984096 (3 pages) | Cited 26 times

Online Publication Date: 24 June 2005

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We have monitored the changes that occur in the x-ray-excited optical luminescence, absorption, and photoemission spectra as a function of vacuum annealing time and temperature for ZnS nanowires. All measurements were done in situ. Initial heating causes desorption of surface oxides and a concurrent reduction in the intensity of all the luminescence peaks, which we attribute to the creation of surface states that quench the luminescence. Extended annealing causes diffusion of Au from the particle used to nucleate the wire growth, which results in an increase in intensity of its associated luminescent band at 520 nm. Changes were also observed in the Zn L- and S K-edge x-ray absorption spectra, which are consistent with this interpretation.
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81.05.Dz II-VI semiconductors
81.07.Vb Quantum wires
78.67.Lt Quantum wires
61.72.Cc Kinetics of defect formation and annealing
78.55.Et II-VI semiconductors
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.43.Mn Adsorption kinetics
66.30.J- Diffusion of impurities
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