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6 Aug 2001

Volume 79, Issue 6, pp. 705-888

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Fabrication of epitaxial CoSi2 nanowires

P. Kluth, Q. T. Zhao, S. Winnerl, S. Lenk, and S. Mantl

Appl. Phys. Lett. 79, 824 (2001); http://dx.doi.org/10.1063/1.1390318 (3 pages) | Cited 8 times

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We have developed a method for fabricating epitaxial CoSi2 nanowires using only conventional optical lithography and standard silicon processing steps. This method was successfully applied to ultrathin epitaxial CoSi2 layers grown on Si(100) and silicon-on-insulator substrates. A nitride mask induces a stress field near its edges into the CoSi2/Si heterostructure and leads to the separation of the CoSi2 layer in this region during a rapid thermal oxidation step. A subsequent etching step and a second oxidation generate highly homogenous silicide wires with dimensions down to 50 nm. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.16.Nd Micro- and nanolithography
81.07.Lk Nanocontacts
85.40.Sz Deposition technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Hp Lithography, masks and pattern transfer
81.16.Pr Micro- and nano-oxidation
81.65.Cf Surface cleaning, etching, patterning

Coherent nanoscale islands on La0.5Ca0.5MnO3 thin films and the enhancement of magnetoresistance

W. Z. Gong, B. R. Zhao, C. Cai, and Y. Lin

Appl. Phys. Lett. 79, 827 (2001); http://dx.doi.org/10.1063/1.1384003 (3 pages) | Cited 6 times

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A low cost reproducible fabrication process has been developed to prepare La0.5Ca0.5MnO3 (LCMO) films with well distributed uniform nanoscale dots using pulsed-laser deposition. It was found that the growth of the dots was closely related to the strain in the film during the growth process. The diameter and density of dots could be controlled within the range of 30–120 nm and 2×108–2×109/cm2, respectively. The magnetoresistance effect of such LCMO films is also enhanced, which may be caused by the spin-dependent scattering of carriers due to the existence of the dots. © 2001 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology
75.75.-c Magnetic properties of nanostructures
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
72.25.Rb Spin relaxation and scattering

Continuous-wave two-photon excitation of individual CdS nanocrystallites

A. M. van Oijen, R. Verberk, Y. Durand, J. Schmidt, J. N. J. van Lingen, A. A. Bol, and A. Meijerink

Appl. Phys. Lett. 79, 830 (2001); http://dx.doi.org/10.1063/1.1391231 (3 pages) | Cited 6 times

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By use of low-temperature confocal microscopy, continuous-wave two-photon fluorescence images are obtained of individual CdS nanocrystallites embedded in a polymer matrix. The quadratic dependence of the emission rate on the applied laser power proves that the observed fluorescence originates from the simultaneous absorption of two photons. From the experimental data the two-photon absorption cross-section σ(2) could be determined, resulting in a value smaller than that known from literature. The work presented is a first step towards high-resolution fluorescence-excitation spectroscopy on the electronic states in the band edge, inaccessible by conventional one-photon spectroscopy. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
73.22.Dj Single particle states

Ultraviolet–visible near-field microscopy of phase-separated blends of polyfluorene-based conjugated semiconductors

R. Stevenson, R. Riehn, R. G. Milner, D. Richards, E. Moons, D.-J. Kang, M. Blamire, J. Morgado, and F. Cacialli

Appl. Phys. Lett. 79, 833 (2001); http://dx.doi.org/10.1063/1.1389822 (3 pages) | Cited 27 times

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We have used fluorescence scanning near-field microscopy to characterize polymer blends for electroluminescent applications, and thereby identify compositional nonhomogeneities. In particular, we have focused on the binary system constituted by poly(9,9′-dioctylfluorenealt-benzothiadiazole) and poly(9,9′-dioctylfluorene) (PFO), known to give efficiencies of up to 22 cd/A in light-emitting devices with suitable electrodes. Our primary aim was the assignment of the morphological features revealed in shear-force and atomic-force images of spin-coated films, and suggestive of phase separation on a 300-nm-length scale. From analysis of the fluorescence images (325 and 488 nm excitation), and quantitative correlation of optical and topographic data, we identify the raised features with PFO-rich regions. However, the limited variation in fluorescence intensity reveals a high extent of mixing within each phase on the length scale accessible in our experiment, approximately 100 nm for our focused-ion-beam-processed probe apertures. © 2001 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.Kz Solid organic materials
64.75.-g Phase equilibria
78.66.Qn Polymers; organic compounds

Dimensional effects on field emission properties of the body for single-walled carbon nanotube

Gang Zhou, Wenhui Duan, and Binglin Gu

Appl. Phys. Lett. 79, 836 (2001); http://dx.doi.org/10.1063/1.1388871 (3 pages) | Cited 29 times

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In this letter, by use of the first-principles calculations, field emission properties of the body are investigated for a series of dimension-variational single-walled carbon nanotubes (SWNTs). We find that in the course of increasing tube diameter, at low emission currents, field emission properties worsen, chemical stability enhances and binding energy increases, which indicates that optimized field emitter could be achieved; while at high applied voltages, the highest emission current density may appear for the SWNT with some peculiar dimension. We predict that the body of the SWNT could behave as a peculiar field emitter with high threshold voltage and high current density. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.22.-f Electronic structure of nanoscale materials and related systems
71.15.-m Methods of electronic structure calculations

Ordered indium-oxide nanowire arrays and their photoluminescence properties

M. J. Zheng, L. D. Zhang, G. H. Li, X. Y. Zhang, and X. F. Wang

Appl. Phys. Lett. 79, 839 (2001); http://dx.doi.org/10.1063/1.1389071 (3 pages) | Cited 110 times

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Ordered semiconductor In2O3 nanowire arrays are uniformly assembled into hexagonally ordered nanochannels of anodic alumina membranes (AAMs) by electrodeposition and oxidizing methods. Their microstructures were characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A blue-green photoluminescence (PL) band in the wavelength range of 300–650 nm was observed in the In2O3/AAM assembly system. The PL intensity and peak position depend on the annealing temperature, which is mainly attributed to the singly ionized oxygen vacancy in the In2O3 nanowire array system. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.-f Electronic structure of nanoscale materials and related systems
81.15.Pq Electrodeposition, electroplating
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals
61.72.Cc Kinetics of defect formation and annealing

Selective thermal desorption of ultrathin aluminum oxide layers induced by electron beams

Manisha Kundu, Noriyuki Miyata, and Masakazu Ichikawa

Appl. Phys. Lett. 79, 842 (2001); http://dx.doi.org/10.1063/1.1391236 (3 pages) | Cited 1 time

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The mechanism of electron-beam-induced selective thermal desorption of ultrathin aluminum-oxide layer (∼0.4 nm) on Si(001) surface was investigated by using scanning reflection electron microscopy, reflection high-energy electron diffraction, and Auger electron spectroscopy. We found that the change in the aluminum-oxide layer composition induced by electron-stimulated oxygen desorption accounted for the selective thermal desorption of the oxide layer. A systematic increase in the vacuum-annealing temperature to 500 °C, 600 °C and 720 °C resulted in the formation of three-dimensional metal aluminum clusters, desorption of these clusters, and creation of a nanometer-scale clean Si(001)-2×1 open window in the selected electron-beam-irradiated area. © 2001 American Institute of Physics.
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68.43.Rs Electron stimulated desorption
79.20.La Photon- and electron-stimulated desorption
79.20.Fv Electron impact: Auger emission
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)

Multilevel nanoimprint lithography with submicron alignment over 4 in. Si wafers

Wei Zhang and Stephen Y. Chou

Appl. Phys. Lett. 79, 845 (2001); http://dx.doi.org/10.1063/1.1391400 (3 pages) | Cited 25 times

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We demonstrate that multilevel nanoimprint lithography (NIL) with submicron alignment over an entire 4 in. Si wafer can be achieved. Average alignment accuracy of 1 μm with a standard deviation 0.4 μm in both X and Y directions was obtained in ten consecutive tests of multilevel NIL. The multilevel alignment was achieved by aligning the wafer and the mask with an aligner, fixing them with a holder, and imprinting in an imprint machine. The issues that are critical to the alignment accuracy, such as relative movement during the press, relative thermal expansion, wafer bending, and resist, are discussed. The alignment accuracy currently achieved on the system is limited by the aligning accuracy of the aligner, instead of the process of multilevel NIL. © 2001 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
06.60.Sx Positioning and alignment; manipulating, remote handling

Double textured cylindrical block copolymer domains via directional solidification on a topographically patterned substrate

Cheolmin Park, Joy Y. Cheng, Michael J. Fasolka, Anne M. Mayes, C. A. Ross, Edwin L. Thomas, and Claudio De Rosa

Appl. Phys. Lett. 79, 848 (2001); http://dx.doi.org/10.1063/1.1389766 (3 pages) | Cited 29 times

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Directional solidification of cylinder forming block copolymer films confined between a directionally crystallizing solvent (benzoic acid) and a topographically patterned silicon substrate imparts a particular orientation to the block copolymer microdomains that is dependent of the solidification direction and the local film thickness. The substrate features (30 nm high, 2μm wide square mesas on a 4μm sq lattice) shape the film morphology by periodically modulating the local film thickness. Thicker regions between substrate features (plateaus) exhibit in-plane cylinders aligned in the crystallization direction and thinner regions over the substrate features (mesas) display vertically aligned cylindrical domains. This approach is a simple and general technique for engineering an intended domain orientation in specific areas of a block copolymer film. Development of this method for nanolithographic applications is demonstrated through oxygen plasma reactive ion etching of the patterned cylindrical domains. © 2001 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.30.Fb Solidification
81.65.Cf Surface cleaning, etching, patterning
81.16.Nd Micro- and nanolithography
61.41.+e Polymers, elastomers, and plastics

Modification of the three-phonon Umklapp process in a quantum wire

A. Khitun and K. L. Wang

Appl. Phys. Lett. 79, 851 (2001); http://dx.doi.org/10.1063/1.1391230 (3 pages) | Cited 12 times

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We have investigated the modification of the three-phonon Umklapp process in a quantum wire caused by the effect of phonon confinement. Our formalism rigorously takes into account variations in phonon group velocity as well as the presence of an energy gap between the phonon modes due to the quantization of the radial phonon wave vector. Numerical calculations of the Umklapp relaxation rate were carried out for Si wires. Based on the obtained results we predict the suppression of the acoustic phonon modes decay at low temperatures that can lead to the unusual thermal conductivity increase. We also present a simplified empiric formula for the Umklapp relaxation rate calculation in a quantum wire. © 2001 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.K- Phonon interactions
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.65.La Quantum wires (patterned in quantum wells)
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