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7 Feb 2005

Volume 86, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 063101 (2005); http://dx.doi.org/10.1063/1.1861133 (3 pages)

Choongho Yu, Qing Hao, Sanjoy Saha, Li Shi, Xiangyang Kong, and Z. L. Wang
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Integration of metal oxide nanobelts with microsystems for nerve agent detection

Choongho Yu, Qing Hao, Sanjoy Saha, Li Shi, Xiangyang Kong, and Z. L. Wang

Appl. Phys. Lett. 86, 063101 (2005); http://dx.doi.org/10.1063/1.1861133 (3 pages) | Cited 55 times

Online Publication Date: 31 January 2005

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We have assembled tin dioxide nanobelts with low-power microheaters for detecting dimethyl methylphosphonate (DMMP), a nerve agent simulant. The electrical conductance of a heated nanobelt increased for 5% upon exposure to 78 parts per billion DMMP in air. The nanobelt conductance recovered fully quickly after the DMMP was shut off, suggesting that the single-crystal nanobelt was not subject to poisoning often observed in polycrystalline metal oxide sensors. While the sensitivity can be improved via doping nanobelts with catalytic additives, directed assembly or growth of nanobelts on microsystems will potentially allow for the large-scale fabrication of nanosensor arrays.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.-c Methods of micro- and nanofabrication and processing

Interdot carrier transfer in asymmetric bilayer InAs/GaAs quantum dot structures

Yu. I. Mazur, Zh. M. Wang, G. G. Tarasov, Min Xiao, G. J. Salamo, J. W. Tomm, V. Talalaev, and H. Kissel

Appl. Phys. Lett. 86, 063102 (2005); http://dx.doi.org/10.1063/1.1861980 (3 pages) | Cited 37 times

Online Publication Date: 1 February 2005

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Transient photoluminescence from a series of asymmetric InAs quantum-dot bilayers with a GaAs barrier layer thickness varying from 30 to 60 monolayers between the quantum-dot planes is investigated. The interdot carrier transfer process is analyzed. In the framework of a three-level system, interdot carrier transfer times between 200 and 2500 ps are derived and compared with similar data from the literature. Within the semiclassical Wentzel–Kramers–Brillouin approximation, the observed “transfer time-barrier thickness-relation” supports nonresonant tunneling as the microscopic carrier transfer mechanism.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.40.Gk Tunneling

Quantum size effects in n-PbTe/p-SnTe/n-PbTe heterostructures

E. I. Rogacheva, O. N. Nashchekina, A. V. Meriuts, S. G. Lyubchenko, M. S. Dresselhaus, and G. Dresselhaus

Appl. Phys. Lett. 86, 063103 (2005); http://dx.doi.org/10.1063/1.1862338 (3 pages) | Cited 12 times

Online Publication Date: 1 February 2005

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The dependencies of the thermoelectric properties of n-PbTe/p-SnTe/n-PbTe heterostructures on the SnTe quantum well width (dSnTe = 0.5–6.0 nm) at fixed PbTe barrier layers thicknesses were studied. It was established that the thickness dependencies of the Seebeck coefficient, electrical conductivity, the Hall coefficient, charge carrier mobility, and the thermoelectric power factor are distinctly nonmonotonic. The observed effect is attributed to the size quantization of the energy spectrum of the hole gas in a SnTe quantum well.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Lw Thermoelectric effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Mx High-frequency effects; plasma effects

Nanometer-scale gaps between metallic electrodes fabricated using a statistical alignment technique

P. Steinmann and J. M. R. Weaver

Appl. Phys. Lett. 86, 063104 (2005); http://dx.doi.org/10.1063/1.1862342 (3 pages) | Cited 7 times

Online Publication Date: 1 February 2005

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We describe a fabrication process for the creation of nanoscale gaps between metallic electrodes based on a statistical alignment method. This technique is appropriate for applications in which a sparse array of gaps, connected to macroscopic electrodes and pads, is required, for example the study of single molecule electrical conduction. This process relies on aligning two separate levels of electron beam lithography defining opposing arrays of metallic wires, so that the gap may be defined between wires of two dissimilar materials, such as nickel and gold. Lithographic definition of gaps small enough to permit tunneling was reliable and had high yield. Fitting an analytical model of tunnel conductance to measured electrical characteristics of a typical gap demonstrates a gap spacing of 1.3±0.7 nm. The process is compatible with most conventional electron-beam lithography systems and does not require the use of unusually high resolution or accurate pattern placement.
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81.16.Nd Micro- and nanolithography
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Gk Tunneling

Fabrication of self-organized conical microstructures by excimer laser irradiation of cyanoacrylate-carbon nanotube composites

Yuming Liu, Liang Liu, and Shoushan Fan

Appl. Phys. Lett. 86, 063105 (2005); http://dx.doi.org/10.1063/1.1862775 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2005

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Self-organized conical microstructures are fabricated by 308 nm XeCl excimer laser irradiation of cyanoacrylate-carbon nanotube composites in air. The morphology of the surface on the composite films is studied, varying the total number and fluence of the applied laser pulses. A simple mechanism of the fabrication based on the evaporation of cyanoacrylate and the burning of carbon nanotubes is proposed. The conical peak structures of cyanoacrylate-carbon nanotube composite films show good field-emission properties. Similar structures are also observed on carbon nanotube arrays.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials
61.82.Ms Insulators
61.82.Pv Polymers, organic compounds

Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles

D. M. Schaadt, B. Feng, and E. T. Yu

Appl. Phys. Lett. 86, 063106 (2005); http://dx.doi.org/10.1063/1.1855423 (3 pages) | Cited 257 times

Online Publication Date: 2 February 2005

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Surface plasmon resonances in metallic nanoparticles are of interest for a variety of applications due to the large electromagnetic field enhancement that occurs in the vicinity of the metal surface, and the dependence of the resonance wavelength on the nanoparticle’s size, shape, and local dielectric environment. Here we report an engineered enhancement of optical absorption and photocurrent in a semiconductor via the excitation of surface plasmon resonances in spherical Au nanoparticles deposited on the semiconductor surface. The enhancement in absorption within the semiconductor results in increased photocurrent response in Si pn junction diodes over wavelength ranges that correspond closely to the nanoparticle plasmon resonance wavelengths as determined by measurements of extinction spectra. These observations suggest a variety of approaches for improving the performance of devices such as photodetectors, imaging arrays, and photovoltaics.
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78.68.+m Optical properties of surfaces
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
85.30.Kk Junction diodes
72.40.+w Photoconduction and photovoltaic effects
73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Kc Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials

Mechanism of stress relaxation in Ge nanocrystals embedded in SiO2

I. D. Sharp, D. O. Yi, Q. Xu, C. Y. Liao, J. W. Beeman, Z. Liliental-Weber, K. M. Yu, D. N. Zakharov, J. W. Ager, D. C. Chrzan, and E. E. Haller

Appl. Phys. Lett. 86, 063107 (2005); http://dx.doi.org/10.1063/1.1856132 (3 pages) | Cited 27 times

Online Publication Date: 2 February 2005

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Ion-beam-synthesized math nanocrystals embedded in an amorphous silica matrix exhibit large compressive stresses in the as-grown state. The compressive stress is determined quantitatively by evaluating the Raman line shift referenced to the line position of free-standing nanocrystals. Postgrowth thermal treatments lead to stress reduction. The stress relief process is shown to be governed by the diffusive flux of matrix atoms away from the local nanocrystal growth region. A theoretical model that quantitatively describes this process is presented.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
61.72.Cc Kinetics of defect formation and annealing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Am Elemental semiconductors and insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering
66.30.J- Diffusion of impurities
61.46.-w Structure of nanoscale materials
61.43.Er Other amorphous solids
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Ion-beam-induced nanosmoothening and conductivity enhancement in ultrathin metal films

Partha Mitra and Arthur F. Hebard

Appl. Phys. Lett. 86, 063108 (2005); http://dx.doi.org/10.1063/1.1861953 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2005

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We present a systematic in situ study of the effect of postdeposition low-energy (200 eV) ion bombardment on resistance and surface topography of ultrathin iron (<50 Å) and copper (<130 Å) films. The ion-beam-induced nanosmoothening occurs while material is being removed and gives rise to an initial decrease in resistance followed by a steady increase as the film is subsequently uniformly eroded. The shunt resistance associated with the resistance decrease is found to be independent of the thickness of the underlying film, thus indicating that the conductivity enhancement is due primarily to surface modification.
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81.05.Bx Metals, semimetals, and alloys
61.80.Jh Ion radiation effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Rs Electrical and magnetic properties related to treatment conditions
73.61.At Metal and metallic alloys
81.40.Wx Radiation treatment (particle and electromagnetic)
81.16.-c Methods of micro- and nanofabrication and processing
61.82.Bg Metals and alloys
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.35.B- Structure of clean surfaces (and surface reconstruction)

Imaging temperature-dependent field emission from carbon nanotube films: Single versus multiwalled

S. Gupta, Y. Y. Wang, J. M. Garguilo, and R. J. Nemanich

Appl. Phys. Lett. 86, 063109 (2005); http://dx.doi.org/10.1063/1.1850616 (3 pages) | Cited 9 times

Online Publication Date: 2 February 2005

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Field emission properties of vertically aligned single- and multiwalled carbon nanotube films at temperatures up to 1000 °C are investigated by electron emission microscopy, enabling real-time imaging of electron emission to provide information on emission site density, the temporal variation of the emission intensity, and insight into the role of adsorbates. The nanotube films showed an emission site density of 104 ∼ 105/cm2, which is compared to the areal density (from 1012–1013/cm2 to 108–109/cm2). At ambient temperature, the emission indicated temporal fluctuation ( ∼ 6%–8%) in emission current with minimal changes in the emission pattern. At elevated temperatures, the emission site exhibited an increase in emission site intensity. From the experimental observations, it is proposed that the chemisorbed molecules tend to desorb presumably at high applied electric fields (field-induced) in combination with thermal effects (thermal-induced) and provide a contrasting comparison between semiconducting (single-walled) and metallic (multiwalled) nanotubes.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
68.55.-a Thin film structure and morphology
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Vertically integrated optics for ballistic electron emission luminescence microscopy

Ian Appelbaum, Wei Yi, K. J. Russell, V. Narayanamurti, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 86, 063110 (2005); http://dx.doi.org/10.1063/1.1861961 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2005

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We have integrated a photon detector directly into a ballistic electron emission luminescence (BEEL) heterostructure, just below a luminescent quantum well. Results from solid-state metal-base hot-electron transistors fabricated with this collector design indicate that more than 10% of the photons emitted by the quantum well excite photoelectrons in the detector region. The improved photonic coupling and effective collection angle in this scheme improves the BEEL signal by many orders of magnitude as compared to far-field detection with the most sensitive single-photon counters, enabling BEEL microscopy in systems with no optical components.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
42.82.Gw Other integrated-optical elements and systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Tracing deeply buried InAs/GaAs quantum dots using atomic force microscopy and wet chemical etching

G. Fasching, K. Unterrainer, W. Brezna, J. Smoliner, and G. Strasser

Appl. Phys. Lett. 86, 063111 (2005); http://dx.doi.org/10.1063/1.1862332 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2005

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We present cross-sectional atomic-force-microscope measurements of buried self-assembled quantum dots. The used method needs a minimum of time and sample preparation (cleaving and etching) to obtain the dot density, dot distribution, and give an estimate of the dot dimensions. Etching only the cleaved surface of the sample opens up the opportunity to determine the properties of a buried dot layer before or even after device fabrication.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Dielectric properties of WS2-coated multiwalled carbon nanotubes studied by energy-loss spectroscopic profiling

Vlad Stolojan, S. R. P. Silva, Michael J. Goringe, R. L. D. Whitby, Wang K. Hsu, D. R. M. Walton, and Harold W. Kroto

Appl. Phys. Lett. 86, 063112 (2005); http://dx.doi.org/10.1063/1.1861985 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2005

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We investigate experimentally the electronic properties of the coating for multiwalled carbon nanotubes covered in tungsten disulfide (WS2) of various thicknesses. Coatings of thicknesses between 2 and 8 monolayers (ML) are analyzed using energy-loss spectroscopic profiling (ELSP), by studying the variations in the plasmon excitations across the coated nanotube, as a function of the coating thickness. We find a change in the ELSP for coatings above 5 ML thickness, which we interpret in terms of a change in its dielectric properties.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
61.46.-w Structure of nanoscale materials

Transmission electron microscopy and electron energy-loss spectroscopy analysis of manganese oxide nanowires

G. H. Du, Z. Y. Yuan, and G. Van Tendeloo

Appl. Phys. Lett. 86, 063113 (2005); http://dx.doi.org/10.1063/1.1861963 (3 pages) | Cited 23 times

Online Publication Date: 3 February 2005

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Single-crystalline MnOOH and Mn3O4 nanowires have been prepared by hydrothermal treatment of commercial bulky manganese oxide particles. β-MnO2 and α-Mn2O3 nanowires were prepared by calcination of MnOOH nanowires. Transmission electron microscopy analysis demonstrates that MnOOH nanowires grow directly from MnO2 raw particles. The diameter of the nanowires is 20–70 nm, while the length can reach several micrometers. MnOOH nanowires grow preferentially along the [010] direction and Mn3O4 nanowires prefer to grow along the [001] direction; the long dimension of both β-MnO2 and α-Mn2O3 nanowires is along [001]. Electron energy-loss spectroscopy analysis shows that the position of the prepeak of the oxygen K edge shifts to higher energy and the energy separation between the two main peaks of the oxygen K edge decreases with decreasing manganese oxidation state. The manganese-white-line ratios (L3/L2) were calculated.
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81.07.Bc Nanocrystalline materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.46.-w Structure of nanoscale materials
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
79.20.Uv Electron energy loss spectroscopy

Long spin relaxation in self-assembled InAlAs quantum dots observed by heterodyne four-wave mixing

T. Watanuki, S. Adachi, H. Sasakura, and S. Muto

Appl. Phys. Lett. 86, 063114 (2005); http://dx.doi.org/10.1063/1.1861978 (3 pages) | Cited 11 times

Online Publication Date: 4 February 2005

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Exciton spin relaxation in self-assembled InAlAs quantum dots was investigated by three-pulse four-wave mixing under resonant conditions. The concept of the spin grating holds well for quantum dots and the measurements combined with optical heterodyne detection at 10 K demonstrates that the exciton spin relaxation lasts up to a few nanoseconds and the time constant is ∼ 5 times larger than the exciton recombination time on average.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.55.Cr III-V semiconductors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Fabrication and photoluminescence properties of porous CdSe

I. M. Tiginyanu, E. Monaico, V. V. Ursaki, V. E. Tezlevan, and Robert W. Boyd

Appl. Phys. Lett. 86, 063115 (2005); http://dx.doi.org/10.1063/1.1864240 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2005

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We report the results of a study of the growth of pores in n-CdSe single crystals using anodic etching techniques. Upon anodization in dark, a nonuniform distribution of pores was produced. However, anodic dissolution of the material under in situ UV illumination proves to result in uniform distribution of pores stretching perpendicularly to the initial surface of the specimen. The porous structures exhibit less luminescence than the bulk samples. These results pave the way for cost-effective manufacturing of CdSe-based semiconductor nanotemplates for nanofabrication.
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81.05.Dz II-VI semiconductors
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.55.Mb Porous materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Gt Powders, porous materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.82.Fk Semiconductors
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