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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Multiwalled carbon nanotubes as ultrasensitive electrometers

L. Roschier, R. Tarkiainen, M. Ahlskog, M. Paalanen, and P. Hakonen

Appl. Phys. Lett. 78, 3295 (2001); http://dx.doi.org/10.1063/1.1362281 (3 pages) | Cited 15 times

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We show that it is possible to construct low-noise single-electron transistors (SETs) using free-standing multiwalled carbon nanotubes. The 1/fα-noise of our devices, 6×10−6e/math at 45 Hz, is close in the performance to the best metallic SETs of today. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
85.65.+h Molecular electronic devices
81.07.De Nanotubes
85.35.Gv Single electron devices
81.05.ub Fullerenes and related materials
07.68.+m Photography, photographic instruments; xerography
73.63.Fg Nanotubes

Wavelength dependence of laser-induced phase transformations in semiconductor quantum dots

M. Gajdardziska-Josifovska, V. Lazarov, J. Reynolds, and V. V. Yakovlev

Appl. Phys. Lett. 78, 3298 (2001); http://dx.doi.org/10.1063/1.1347226 (3 pages) | Cited 5 times

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We study the effect of wavelength on the laser-induced phase transformation in semiconductor quantum dots. In our earlier report [Yakovlev et al., Appl. Phys. Lett. 76, 2050 (2000)], we discovered that a nanosecond pulse of 532 nm radiation results in a phase transformation of CdS nanocrystals from an orthorhombic to cubic phase. In this study, we find that irradiation with the pulse of a different wavelength (355 nm) results in a completely different transformation to a hexagonal wurtzite phase and a significant broadening of nanocrystal size distribution. The nanocrystal stoichiometry remained unchanged by the laser irradiation, as verified by energy dispersive x-ray spectroscopy. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.82.Fk Semiconductors
64.70.K- Solid-solid transitions
61.66.Bi Elemental solids
61.66.Dk Alloys
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Displacement currents and the real part of high-frequency conductance of the resonant-tunneling diode

Michael N. Feiginov

Appl. Phys. Lett. 78, 3301 (2001); http://dx.doi.org/10.1063/1.1372357 (3 pages) | Cited 9 times

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I have shown that weak variation of the tunnel transparency of the collector barrier with bias has substantial (and frequently crucial) effect on the high-frequency properties of the resonant-tunneling diodes (RTDs). Also it has been shown that the real part of the RTD conductance can be negative and large at the frequencies much higher than the reciprocal quasibound-state lifetime in the quantum well between the barriers of RTD, if (as opposed to common practice) the RTD collector is heavily doped and does not have thick spacer layers. The displacement currents are responsible for the effects. A simple equivalent circuit of RTD is proposed, and it fairly well describes the published experimental data. © 2001 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
73.50.Mx High-frequency effects; plasma effects

Oxide-assisted growth and optical characterization of gallium-arsenide nanowires

W. S. Shi, Y. F. Zheng, N. Wang, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 78, 3304 (2001); http://dx.doi.org/10.1063/1.1371966 (3 pages) | Cited 29 times

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This letter reports the synthesis and optical characterization of GaAs nanowires obtained by oxide-assisted laser ablation of a mixture of GaAs and Ga2O3. The GaAs nanowires have lengths up to tens of micrometers and diameters in the range of 10–120 nm, with an average of 60 nm. The nanowires have a thin oxide layer covering a crystalline GaAs core with a [111] growth direction. Raman scattering and photoluminescence (PL) characterizations of GaAs nanowires reveal that the spectral peaks significantly shifted and broadened from those of bulk GaAs material. The changes in these spectra are mainly attributed to impurities, defects, and residual stress in the GaAs nanowires. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.67.Lt Quantum wires
81.07.Vb Quantum wires
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.65.La Quantum wires (patterned in quantum wells)
81.65.Mq Oxidation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Condensed phase growth of single-wall carbon nanotubes from laser annealed nanoparticulates

D. B. Geohegan, H. Schittenhelm, X. Fan, S. J. Pennycook, A. A. Puretzky, M. A. Guillorn, D. A. Blom, and D. C. Joy

Appl. Phys. Lett. 78, 3307 (2001); http://dx.doi.org/10.1063/1.1371796 (3 pages) | Cited 17 times

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Single-wall carbon nanotubes (SWNT) were grown to micron lengths by laser-annealing nanoparticulate soot containing short (∼50 nm long) nanotube “seeds.” The “seeded” nanoparticulate soot was produced by restricting the time spent by an ablation plume inside an 800 °C oven following laser vaporization of a C–Ni–Co target. The soot collected from the laser vaporization apparatus was placed inside graphite crucibles under argon, and heated by a CO2 laser. In situ pyrometry was used to estimate the sample temperature. Length distributions of SWNT bundles in the unannealed and annealed samples were measured by transmission electron microscopy and field emission scanning electron microscopy. Annealing treatments exceeding 1600 °C produced no increase in nanotube length, while lower temperatures in the 1000–1300 °C range were optimal for growth. These experiments indicate that SWNT grow by the conversion of condensed phase nanomaterial during annealing, a similar mechanism to that proposed for growth during normal laser–vaporization production. © 2001 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Mk Laser-assisted deposition

Free-standing SiGe-based nanopipelines on Si (001) substrates

O. G. Schmidt and N. Y. Jin-Phillipp

Appl. Phys. Lett. 78, 3310 (2001); http://dx.doi.org/10.1063/1.1373408 (3 pages) | Cited 35 times

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Thin solid films form nanopipelines if the films are released from a substrate and put back onto their own surface. We give a detailed description of free-standing SiGe-based nanopipelines created on Si (001) substrates. The initial layer sequence is grown by molecular beam epitaxy and comprises SiGe-based epitaxial layers grown on a Ge sacrificial layer. After selectively etching away the Ge sacrificial layer, SiGe nanopipelines have formed on the surface. Nanopipelines as long as 20 μm with diameters ranging from 50 to 530 nm are fabricated. We show that SiGe nanopipelines perform multiple revolutions if selective etching is carried out long enough. Adding carbon to Si epitaxial layers is proposed to extend the design freedom of Si-based nanopipelines and nanotubes. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials
81.65.Cf Surface cleaning, etching, patterning
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors

Optimized contact configuration for the study of transport phenomena in ropes of single-wall carbon nanotubes

J. Appenzeller, R. Martel, P. Avouris, H. Stahl, and B. Lengeler

Appl. Phys. Lett. 78, 3313 (2001); http://dx.doi.org/10.1063/1.1373413 (3 pages) | Cited 26 times

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The study of the intrinsic transport properties of carbon nanotubes suffers from the difficulties in fabricating noninvasive contacts. Here, we present a scheme for the investigation of transport phenomena in metallic single-wall carbon nanotubes by means of a special four-terminal measurement configuration. To suppress the impact of the contacts on the measured conductance in a tube, we found a combination of top and bottom contacts to the rope of single-wall nanotubes to be most appropriate. Our experimental findings demonstrate that a linear decrease of the sample resistance can be observed under these circumstances without the common increase of resistance for decreasing temperatures. © 2001 American Institute of Physics.
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73.63.Fg Nanotubes
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.40.Cg Contact resistance, contact potential

Production of ordered silicon nanocrystals by low-energy ion sputtering

Raúl Gago, Luis Vázquez, Rodolfo Cuerno, María Varela, Carmen Ballesteros, and José María Albella

Appl. Phys. Lett. 78, 3316 (2001); http://dx.doi.org/10.1063/1.1372358 (3 pages) | Cited 115 times

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We report on the production of ordered assemblies of silicon nanostructures by means of irradiation of a Si (100) substrate with 1.2 keV Ar+ ions at normal incidence. Atomic force and high-resolution transmission electron microscopies show that the silicon structures are crystalline, display homogeneous height, and spontaneously arrange into short-range hexagonal ordering. Under prolonged irradiation (up to 16 h) all dot characteristics remain largely unchanged and a small corrugation develops at long wavelengths. We interpret the formation of the dots as a result of an instability due to the sputtering yield dependence on the local surface curvature. © 2001 American Institute of Physics.
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81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Bc Nanocrystalline materials
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.46.-w Structure of nanoscale materials
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Gallium arsenide crystalline nanorods grown by molecular-beam epitaxy

Hae Gwon Lee, Hee Chang Jeon, Tae Won Kang, and Tae Whan Kim

Appl. Phys. Lett. 78, 3319 (2001); http://dx.doi.org/10.1063/1.1359783 (3 pages) | Cited 12 times

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Gallium arsenide (GaAs) crystalline nanorods were grown by molecular-beam epitaxy (MBE). Scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray fluorescence measurements showed that the grown GaAs nanorods were straight single crystals with diameters between 70 and 80 nm, lengths of up to 5 μm, and were doped with Si impurity. The formation mechanism of the Si-doped GaAs crystalline nanorods is described. These results indicate that Si-doped GaAs crystalline nanorods can be grown by using the MBE technique and that the nanorods hold promise for potential applications in next-generation electronic and optoelectronic devices. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
61.46.-w Structure of nanoscale materials
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Direct three-dimensional patterning using nanoimprint lithography

Mingtao Li, Lei Chen, and Stephen Y. Chou

Appl. Phys. Lett. 78, 3322 (2001); http://dx.doi.org/10.1063/1.1375006 (3 pages) | Cited 43 times

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We demonstrated that nanoimprint lithography (NIL) can create three-dimensional patterns, sub-40 nm T-gates, and air-bridge structures, in a single step imprint in polymer and metal by lift-off. A method based on electron beam lithography and reactive ion etching was developed to fabricate NIL molds with three-dimensional protrusions. The low-cost and high-throughput nanoimprint lithography for three-dimensional nanostructures has many significant applications such as monolithic microwave integrated circuits and nanoelectromechanical system. © 2001 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.40.Lj Microwave integrated electronics

Investigation of switching effects between the drains of an electron Y-branch switch

L. Worschech, B. Weidner, S. Reitzenstein, and A. Forchel

Appl. Phys. Lett. 78, 3325 (2001); http://dx.doi.org/10.1063/1.1372341 (3 pages) | Cited 25 times

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By using high-resolution electron beam lithography and wet etching, Y-branched electron waveguides with lengths down to 70 nm have been fabricated on modulation-doped GaAs/AlGaAs heterostructures. Small positive bias applied between the source and the two drain electron reservoirs leads to enhanced switching of electrons into either of the two branches when a lateral external electric field is applied. The switching manifests itself by pronounced sawtooth oscillations in the conductance between source and one branch of an electron Y-branch switch as the gate voltage at the other branch is changed when the corresponding gate voltage is fixed. © 2001 American Institute of Physics.
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85.35.Ds Quantum interference devices
81.16.Nd Micro- and nanolithography
81.07.Lk Nanocontacts
73.23.Ad Ballistic transport
81.65.Cf Surface cleaning, etching, patterning

Structural transformation, amorphization, and fracture in nanowires: A multimillion-atom molecular dynamics study

Phillip Walsh, Wei Li, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta, and Subhash Saini

Appl. Phys. Lett. 78, 3328 (2001); http://dx.doi.org/10.1063/1.1374237 (3 pages) | Cited 14 times

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Multimillion-atom molecular dynamics simulations of silicon diselenide nanowires are used to study mechanical properties and changes in nanowire structure under strain. The nanowires transform from a body-centered orthorhombic structure to a body-centered tetragonal structure under uniaxial strain, which causes an unexpected elongation in one of the transverse directions. For larger strains, the nanowires undergo a process of local amorphization, followed by fracture at one of the resulting crystalline–amorphous interfaces. The critical strain for fracture is 15%. Local temperature and stress distributions after failure are interpreted in terms of the local amorphization. © 2001 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
61.46.-w Structure of nanoscale materials
64.70.Nd Structural transitions in nanoscale materials
62.20.M- Structural failure of materials
61.43.Bn Structural modeling: serial-addition models, computer simulation
62.20.D- Elasticity
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