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28 Oct 2002

Volume 81, Issue 18, pp. 3311-3500

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Control over exciton confinement versus separation in composite films of polyfluorene and CdSe nanocrystals

Y. C. Tseng, M. Tzolov, E. H. Sargent, P. W. Cyr, and M. A. Hines

Appl. Phys. Lett. 81, 3446 (2002); http://dx.doi.org/10.1063/1.1513214 (3 pages) | Cited 4 times

Online Publication Date: 22 October 2002

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Composite films of polyfluorene derivative poly(9,9-di-(2-ethylhexyl)-fluorenyl-2,7-diyl) and cadmium selenide nanocrystals were investigated using photomodulation spectroscopy exciting only the nanocrystal phase. Efficient charge separation resulting in hole injection into the polymer was observed in films in which the nanocrystals had been stripped of surface trioctylphosphine oxide passivating groups. The resulting induced absorption band centered at 1.2 eV was assigned to bipolarons or π-dimers formed on the polymer in the near vicinity of the polymer/nanocrystal interface. The intensity dependence of this band suggests bimolecular recombination, supporting the interpretation of the band as due to charge separation. The measured wide distribution of lifetimes for the photogenerated states confirms the glassy nature of the polymer. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
71.35.-y Excitons and related phenomena
71.38.Mx Bipolarons
78.66.Qn Polymers; organic compounds
61.41.+e Polymers, elastomers, and plastics
78.55.-m Photoluminescence, properties and materials
61.46.-w Structure of nanoscale materials
71.20.Rv Polymers and organic compounds

Distributions of noble metal Pd and Pt in mesoporous silica

J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, and Meilin Liu

Appl. Phys. Lett. 81, 3449 (2002); http://dx.doi.org/10.1063/1.1518158 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2002

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Mesoporous silica nanostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalytic properties for CO–CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
82.33.Ln Reactions in sol gels, aerogels, porous media
82.75.Fq Synthesis, structure determination, structure modeling
82.60.Qr Thermodynamics of nanoparticles
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis

Numerical simulation analysis of a near-field optical virtual probe

Tao Hong, Jia Wang, Liqun Sun, and Dacheng Li

Appl. Phys. Lett. 81, 3452 (2002); http://dx.doi.org/10.1063/1.1517401 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2002

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A near-field optical virtual probe based on the principle of near-field evanescent wave interference can be used in optical data storage, nanolithography, near-field optical imaging, and optical manipulation. This letter gives the numerical simulation results of the optical distribution of a near-field virtual probe and analyzes the dependence of the virtual probe’s on the aperture, the polarization, etc. The simulation results reveal that the transmission efficiency is higher than that of a nanoaperture metal-coated fiber probe. The size of the virtual probe is constant when the distance between the lens and recording media increases within a certain range so that the critical nanoseparation control in near-field system can be relaxed. © 2002 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.79.Bh Lenses, prisms and mirrors
02.70.Bf Finite-difference methods
07.79.Fc Near-field scanning optical microscopes

Oxidation and reduction behavior of Ge/Si islands

T. Sass, V. Zela, A. Gustafsson, I. Pietzonka, and W. Seifert

Appl. Phys. Lett. 81, 3455 (2002); http://dx.doi.org/10.1063/1.1517715 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2002

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We have investigated the oxidation/reduction behavior of dome-shaped three-dimensional islands of Ge on Si(001) grown by ultrahigh vacuum chemical vapor deposition. The oxidation was done by exposing the surfaces to H2O steam in N2. The reduction was done by H2, which selectively reduces only the GeO2. The results of the oxidation/reduction processes under varying conditions were analyzed by high-resolution transmission electron microscopy. We found that the selective reduction of such structures does not result in a perfect recovery of the former Ge dots, but results in phase-segregated Ge enrichments. In many cases these enrichments show epitaxial relationship with the underlying Si substrate. These structures are of potential interest for Ge dots embedded in an insulating material as well as for lateral epitaxial overgrowth of SiO2/Si(001) by Ge, using the reduced Ge dots as the seeds for epitaxy. © 2002 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.-b Specific chemical reactions; reaction mechanisms
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Growth of ordered, single-domain, alumina nanopore arrays with holographically patterned aluminum films

Zhijun Sun and Hong Koo Kim

Appl. Phys. Lett. 81, 3458 (2002); http://dx.doi.org/10.1063/1.1517719 (3 pages) | Cited 44 times

Online Publication Date: 22 October 2002

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Highly-ordered, single-domain ( ∼ cm2), alumina nanopore arrays with controlled symmetry were obtained by anodizing prepatterned aluminum films that were deposited on silica substrates. Holographic lithography, in conjunction with a conformal deposition process, was utilized to form nanoscale corrugations on aluminum film surface prior to anodization. Both the order and symmetry of pore arrays were found to be well controlled and guided by the periodic surface corrugations from the initial stage of pore growth. Ordered nanopore arrays grown on foreign substrates are promising as a host or template for forming various nanodevices and their on-chip integration. © 2002 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Rm Porous materials; granular materials
81.16.Pr Micro- and nano-oxidation
81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
42.40.My Applications

Controlled fabrication of silver or gold nanoparticle near-field optical atomic force probes: Enhancement of second-harmonic generation

Inna Barsegova, Aaron Lewis, Artium Khatchatouriants, Alexandra Manevitch, Andrei Ignatov, Noel Axelrod, and Chaim Sukenik

Appl. Phys. Lett. 81, 3461 (2002); http://dx.doi.org/10.1063/1.1507618 (3 pages) | Cited 10 times

Online Publication Date: 22 October 2002

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A simple method is described for producing silver and gold nanoparticles at the tip of an atomic force microscope sensor. It is shown that these nanoparticles can enhance the nonlinear optical phenomenon of second-harmonic generation of a molecular system such as a styryl dye. © 2002 American Institute of Physics.
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81.07.Wx Nanopowders
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)

Electric-field-aligned growth of single-walled carbon nanotubes on surfaces

Ant Ural, Yiming Li, and Hongjie Dai

Appl. Phys. Lett. 81, 3464 (2002); http://dx.doi.org/10.1063/1.1518773 (3 pages) | Cited 32 times

Online Publication Date: 22 October 2002

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Aligned single-walled carbon nanotubes are grown onto the surfaces of SiO2/Si substrates in electric fields established across patterned metal electrodes. Calculations of the electric field distribution under the designed electrode structures, the directing ability of electric fields, and the prevention of surface van der Waals interactions are used to rationalize the aligned growth. The capability of synthesizing oriented single-walled nanotubes on surfaces shall open up many opportunities in organized architectures of nanotubes for molecular electronics. © 2002 American Institute of Physics.
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81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.65.+h Molecular electronic devices

Nanowires of metal borates

Renzhi Ma, Yoshio Bando, and Tadao Sato

Appl. Phys. Lett. 81, 3467 (2002); http://dx.doi.org/10.1063/1.1517178 (3 pages) | Cited 37 times

Online Publication Date: 22 October 2002

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Nanowires of metal borates Al18B9O33 and MgB4O7 were synthesized by thermal evaporation of mixed powders containing metal oxide (Al2O3 or MgO) and boron oxide. Typical widths of these nanowires are in the range of 10 to ∼ 100 nm and lengths are in the range of several to several tens of micrometers. The nanowires were studied using a high-resolution transmission electron microscope equipped with electron energy loss spectrometer and energy dispersive x-ray spectrometer. The metal borate nanowires fabricated in this way are single crystals. It is proposed that these metal borate nanowires are grown in a vapor–solid process, in which both the metal oxide and boron oxide vapors were simultaneously involved. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
79.20.Uv Electron energy loss spectroscopy
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Field emission properties of porous diamond-like films produced by chemical vapor deposition

V. P. Mammana, T. E. A. Santos, A. P. Mammana, V. Baranauskas, Helder J. Ceragioli, and A. C. Peterlevitz

Appl. Phys. Lett. 81, 3470 (2002); http://dx.doi.org/10.1063/1.1517724 (3 pages) | Cited 11 times

Online Publication Date: 22 October 2002

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The field emission properties of “porous diamond-like” carbon structures have been characterized. A hot filament chemical vapor deposition system fed with ethyl alcohol vapor diluted in helium was used to deposit the samples. Morphological analysis by field emission scanning electron microscopy revealed that they had a highly porous structure, which was attributed to the modification of the kinetics of the carbon deposition process due to the presence of helium as a buffer gas. Micro-Raman spectroscopy showed two peaks in the graphene and microcrystalline graphite frequencies and a new peak at 1620 cm−1. Low threshold fields (Et) and hysteresis in the current versus voltage characteristic have been observed, and a model to explain the hysteresis is proposed. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials
81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Vj Field emission and field-ion microscopy
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses
85.45.Db Field emitters and arrays, cold electron emitters

Selective manipulation of InAs quantum dot electronic states using a lateral potential confinement layer

Eui-Tae Kim, Zhonghui Chen, and Anupam Madhukar

Appl. Phys. Lett. 81, 3473 (2002); http://dx.doi.org/10.1063/1.1517710 (3 pages) | Cited 14 times

Online Publication Date: 22 October 2002

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To further the objective of controlled manipulation of the electronic states in epitaxial island quantum dots (QDs), we introduce the notion of a lateral potential confinement layer (LPCL) whose judicious placement during island capping allows selective impact on ground and excited electron and hole states. The energy states of InAs/In0.15Ga0.85As QDs are manipulated using 10-monolayer-thick In0.15Al0.25Ga0.60As LPCLs positioned at the bottom, upper, and top region of the QDs. The changes in the photoluminescence (PL) and PL excitation spectra reveal the nature of the electronic transitions impacted selectively through the spatial charge distributions of the states involved. © 2002 American Institute of Physics.
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73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena

Self-similarity in abrasion of metals by nanosharp asperities of hard carbon containing films

Feodor M. Borodich, Stephen J. Harris, and Leon M. Keer

Appl. Phys. Lett. 81, 3476 (2002); http://dx.doi.org/10.1063/1.1519099 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2002

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We discuss a remarkably simple power-law relationship observed between the abrasion rate of an initially spherical slider by hard carbon-containing films and the number of sliding cycles n to which the film has been subjected. The power-law relationship is valid up to 4 orders of magnitude in n. We model this phenomenon by connecting it with nanocharacteristics of the coatings. It is proposed to explain the phenomenon by a statistically self-similar variation of the pattern of relatively sharp nanometer-scale asperities of the films. © 2002 American Institute of Physics.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.05.U- Carbon/carbon-based materials
81.65.-b Surface treatments

Nanofabrication of integrated magnetoelectronic devices using patterned self-assembled copolymer templates

M. Bal, A. Ursache, M. T. Tuominen, J. T. Goldbach, and T. P. Russell

Appl. Phys. Lett. 81, 3479 (2002); http://dx.doi.org/10.1063/1.1517400 (3 pages) | Cited 29 times

Online Publication Date: 22 October 2002

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Conventional lithographic exposure is used to selectively degrade regions of a self-assembled diblock copolymer film to obtain a honeycomblike nanoporous array template with arbitrary lateral design. Combined with other lithographic process steps, this enables the fabrication of arrays of nanostructures interfaced to electrical probes for device applications. To demonstrate, a unique magnetotransport device is fabricated, consisting of an array of electrodeposited Co nanowires standing atop a thin gold film patterned into a four-probe resistor configuration. Magnetoresistance measurements, performed at various temperatures and magnetic field orientations, reveal the coexistence of anisotropic magnetoresistance and giant magnetoresistance. © 2002 American Institute of Physics.
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81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
75.75.-c Magnetic properties of nanostructures
75.47.De Giant magnetoresistance
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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