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17 May 2004

Volume 84, Issue 20, pp. 3957-4121

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4104 (2004); http://dx.doi.org/10.1063/1.1753068 (3 pages)

Tetsuya Akasaka, Toshio Nishida, Toshiki Makimoto, and Naoki Kobayashi
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Optical near-field mapping of excitons and biexcitons in naturally occurring semiconductor quantum dots

Ulrich Hohenester, Guido Goldoni, and Elisa Molinari

Appl. Phys. Lett. 84, 3963 (2004); http://dx.doi.org/10.1063/1.1741033 (3 pages) | Cited 17 times

Online Publication Date: 3 May 2004

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We calculate the near-field optical spectra of excitons and biexcitons in semiconductor quantum dots naturally occurring at interface fluctuations in GaAs-based quantum wells, using a nonlocal description of the response function to a spatially modulated electromagnetic field. The relative intensity of the lowest, far-field forbidden excitonic states is predicted; the spatial extension of the ground biexciton state is found, in agreement with recently published experiments. © 2004 American Institute of Physics.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors

Four-probe charge transport measurements on individual vertically aligned carbon nanofibers

Lan Zhang, Derek Austin, Vladimir I. Merkulov, Anatoli V. Meleshko, Kate L. Klein, Michael A. Guillorn, Douglas H. Lowndes, and Michael L. Simpson

Appl. Phys. Lett. 84, 3972 (2004); http://dx.doi.org/10.1063/1.1748849 (3 pages) | Cited 31 times

Online Publication Date: 3 May 2004

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We report four-probe I–V measurements on individual vertically aligned carbon nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I–V behavior at room temperature, with a resistivity of approximately 4.2×10−3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs. © 2004 American Institute of Physics.
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81.07.De Nanotubes
73.63.Fg Nanotubes
73.63.Rt Nanoscale contacts

In situ detection of faradaic current in probe oxidation using a dynamic force microscope

Hiromi Kuramochi, Kazunori Ando, Takashi Tokizaki, and Hiroshi Yokoyama

Appl. Phys. Lett. 84, 4005 (2004); http://dx.doi.org/10.1063/1.1748842 (3 pages) | Cited 17 times

Online Publication Date: 5 May 2004

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A faradaic current on the order of a sub-pico-ampere was detected while fabricating two-dimensional oxide nanostructures on H-passivated Si(001) surfaces. The detected faradaic current has been shown to faithfully reflect the degree of probe oxidation with a clear dependence on the variation of voltage and the tip speed. The faradaic current in dynamic mode can serve as a sensitive monitor of the nano-oxidation reaction for implementing precise closed-loop control of the oxide growth. © 2004 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Pr Micro- and nano-oxidation
68.37.Ps Atomic force microscopy (AFM)

Interaction of vapor-deposited Ti and Au with molecular wires

A. V. Walker, T. B. Tighe, J. Stapleton, B. C. Haynie, S. Upilli, D. L. Allara, and N. Winograd

Appl. Phys. Lett. 84, 4008 (2004); http://dx.doi.org/10.1063/1.1748844 (3 pages) | Cited 30 times

Online Publication Date: 5 May 2004

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We have investigated the interaction of vapor-deposited titanium and gold with a self-assembled monolayer (SAM) of 4-[4′-(phenylethynyl)-phenylethynyl]-benzenthiol, an unsubstituted oligo(phenylene-ethynylene), chemisorbed on a gold substrate, a typical SAM of interest for molecular electronics. Deposited titanium atoms are observed to react in a top-down fashion with the SAM molecules to form Ti–C bonds, destroying the monolayer structure. In contrast, deposited Au atoms undergo continuous penetration through the monolayer, even at high coverages, leaving the SAM “floating” on the Au substrate surface. © 2004 American Institute of Physics.
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68.43.Mn Adsorption kinetics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Multi-excitonic complexes in single InGaN quantum dots

R. Seguin, S. Rodt, A. Strittmatter, L. Reißmann, T. Bartel, A. Hoffmann, D. Bimberg, E. Hahn, and D. Gerthsen

Appl. Phys. Lett. 84, 4023 (2004); http://dx.doi.org/10.1063/1.1751214 (3 pages) | Cited 37 times

Online Publication Date: 5 May 2004

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Cathodoluminescence spectra employing a shadow mask technique of InGaN layers grown by metalorganic chemical vapor deposition on Si(111) substrates are reported. Sharp lines originating from InGaN quantum dots are observed. Temperature dependent measurements reveal thermally induced carrier redistribution between the quantum dots. Spectral diffusion is observed and was used as a tool to correlate up to three lines that originate from the same quantum dot. Variation of excitation density leads to identification of exciton and biexciton. Binding and anti-binding complexes are discovered. © 2004 American Institute of Physics.
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78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
71.35.-y Excitons and related phenomena

Excimer laser nanostructuring of nickel thin films for the catalytic growth of carbon nanotubes

S. J. Henley, C. H. P. Poa, A. A. D. T. Adikaari, C. E. Giusca, J. D. Carey, and S. R. P. Silva

Appl. Phys. Lett. 84, 4035 (2004); http://dx.doi.org/10.1063/1.1751226 (3 pages) | Cited 15 times

Online Publication Date: 5 May 2004

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Pulse laser ablation and subsequent laser nanostructuring at room temperature has been employed to produce nanostructured Ni on SiO2/Si substrates for catalytic growth of carbon nanotubes. The resultant nanostructured surface is seen to consist of nanometer sized hemispherical droplets whose mean diameter is controlled by the initial metal thickness, which in turn is readily controlled by the number of laser pulses. Vertically aligned multiwall carbon nanotube mats were then grown using conventional plasma enhanced chemical vapor deposition. We show that within a single processing technique it is possible to produce the initial metal-on-oxide thin film to a chosen thickness but also to be able to alter the morphology of the film to desired specifications at low macroscopic temperatures using the laser parameters. The influence of the underlying oxide is also explored to explain the mechanism of nanostructuring of the Ni catalyst. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.16.Mk Laser-assisted deposition

Self-assembled magnetic nanostripes by organic patterning

X. Ma, H. L. Meyerheim, J. Barthel, J. Kirschner, S. Schmitt, and E. Umbach

Appl. Phys. Lett. 84, 4038 (2004); http://dx.doi.org/10.1063/1.1751228 (3 pages) | Cited 7 times

Online Publication Date: 5 May 2004

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Selective adsorption of Fe deposited on the organic molecule 3,4,9,10-perylene-tetracarboxylic-3, 4,9,10-dianhydride (PTCDA) is used to prepare a self assembled magnetic nanostripe structure on a vicinal Ag surface. Scanning tunneling microscopy reveals that after PTCDA deposition on the Ag(10 8 7) surface a grating-like domain pattern is formed. It consists of alternating stripes of molecule-covered facets and uncovered (111) terraces. Fe adsorption takes place selectively on the molecule-covered stripes forming disk-shaped super-paramagnetic islands with a polar easy magnetization axis. © 2004 American Institute of Physics.
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81.16.Dn Self-assembly
75.75.-c Magnetic properties of nanostructures
81.16.Rf Micro- and nanoscale pattern formation

Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

L. J. Klein, K. A. Slinker, J. L. Truitt, S. Goswami, K. L. M. Lewis, S. N. Coppersmith, D. W. van der Weide, Mark Friesen, R. H. Blick, D. E. Savage, M. G. Lagally, Charlie Tahan, Robert Joynt, M. A. Eriksson, J. O. Chu, et al.

Appl. Phys. Lett. 84, 4047 (2004); http://dx.doi.org/10.1063/1.1751612 (3 pages) | Cited 34 times

Online Publication Date: 5 May 2004

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We report the fabrication and electrical characterization of a single electron transistor in a modulation doped silicon/silicon–germanium heterostructure. The quantum dot is fabricated by electron beam lithography and subsequent reactive ion etching. The dot potential and electron density are modified by laterally defined side gates in the plane of the dot. Low temperature measurements show Coulomb blockade with a single electron charging energy of 3.2 meV. © 2004 American Institute of Physics.
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85.35.Gv Single electron devices
81.07.Ta Quantum dots
81.16.Nd Micro- and nanolithography
73.23.Hk Coulomb blockade; single-electron tunneling
73.61.Le Other inorganic semiconductors
73.61.Cw Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning

Strong quantum-confinement effects in the conduction band of germanium nanocrystals

C. Bostedt, T. van Buuren, T. M. Willey, N. Franco, L. J. Terminello, C. Heske, and T. Möller

Appl. Phys. Lett. 84, 4056 (2004); http://dx.doi.org/10.1063/1.1751616 (3 pages) | Cited 53 times

Online Publication Date: 5 May 2004

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Quantum-confinement effects in the conduction band of deposited germanium nanocrystals are measured to be greater than in similar-sized silicon nanocrystals. The germanium particles are condensed out of the gas phase and their electronic properties are determined with x-ray absorption spectroscopy. The conduction band edge shifts range from 0.2 eV for 2.7 nm particles up to 1.1 eV for 1.2 nm particles. © 2004 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Bistable nanoelectromechanical devices

Kirk J. Ziegler, Daniel M. Lyons, Justin D. Holmes, Donats Erts, Boris Polyakov, Håkan Olin, Krister Svensson, and Eva Olsson

Appl. Phys. Lett. 84, 4074 (2004); http://dx.doi.org/10.1063/1.1751622 (3 pages) | Cited 25 times

Online Publication Date: 5 May 2004

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A combined transmission electron microscopy-scanning tunneling microscopy (TEM-STM) technique has been used to investigate the force interactions of silicon and germanium nanowires with gold electrodes. The I(V) data obtained typically show linear behavior between the gold electrode and silicon nanowires at all contact points, whereas the linearity of I(V) curves obtained for germanium nanowires were dependent on the point of contact. Bistable silicon and germanium nanowire-based nanoelectromechanical programmable read-only memory (NEMPROM) devices were demonstrated by TEM-STM. These nonvolatile NEMPROM devices have switching potentials as low as 1 V and are highly stable making them ideal candidates for low-leakage electronic devices. © 2004 American Institute of Physics.
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84.30.Sk Pulse and digital circuits
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Hi Surface barrier, boundary, and point contact devices
82.37.Gk STM and AFM manipulations of a single molecule
68.37.Lp Transmission electron microscopy (TEM)
73.40.Mr Semiconductor-electrolyte contacts

Initial growth of vertically aligned carbon nanofibers

Hongtao Cui, Xiaojing Yang, Michael L. Simpson, Douglas H. Lowndes, and Maria Varela

Appl. Phys. Lett. 84, 4077 (2004); http://dx.doi.org/10.1063/1.1751624 (3 pages) | Cited 37 times

Online Publication Date: 5 May 2004

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Samples of vertically aligned carbon nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite “cups” in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.16.Hc Catalytic methods
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Effects of the one-dimensional quantum barriers in pyramidal quantum dots

F. Michelini, M.-A. Dupertuis, and E. Kapon

Appl. Phys. Lett. 84, 4086 (2004); http://dx.doi.org/10.1063/1.1753054 (3 pages) | Cited 9 times

Online Publication Date: 5 May 2004

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We investigated theoretically the effects of the one-dimensional barriers on the electronic states in a quantum dot grown on a nonplanar substrate. These peculiar barriers drastically modify the confined carrier wave functions and their energies. Connecting the quantum wire to the pyramidal quantum dot leads to an enhancement in the ground to first excited state separation energy and a simultaneous large reduction of the energy size sensitivity. © 2004 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots

SU-8 for real three-dimensional subdiffraction-limit two-photon microfabrication

W. H. Teh, U. Dürig, G. Salis, R. Harbers, U. Drechsler, R. F. Mahrt, C. G. Smith, and H.-J. Güntherodt

Appl. Phys. Lett. 84, 4095 (2004); http://dx.doi.org/10.1063/1.1753059 (3 pages) | Cited 38 times

Online Publication Date: 5 May 2004

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We report the inherent utility of two-photon-absorption (TPA) in the fabrication of real three-dimensional (3D) structures with subdiffraction-limit resolution, based on SU-8 as the threshold polymer media. We exploit the nonlinear velocity dependence of TPA photopolymerization as the shutter mechanism for disruptive 3D lithography. We show that low numerical aperture optics can be used for the rapid microfabrication of ultrahigh-aspect ratio photoplastic pillars, planes, and cage structures. © 2004 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Formation of highly aligned ZnO tubes on sapphire (0001) substrates

B. P. Zhang, N. T. Binh, K. Wakatsuki, Y. Segawa, Y. Yamada, N. Usami, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 84, 4098 (2004); http://dx.doi.org/10.1063/1.1753061 (3 pages) | Cited 84 times

Online Publication Date: 5 May 2004

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ZnO tubes were epitaxially grown on sapphire (0001) substrates by metalorganic chemical vapor deposition. The tubes grew along the substrate normal and were characterized by hexagon-shaped cross sections. All of the tubes possessed the same epitaxial relationships with respect to the substrate. Both reactor pressure and growth temperature were found to play an important role in the formation of ZnO tubes. Spiral column growth mode was found to be responsible for the formation of ZnO tubes. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.05.Dz II-VI semiconductors

Hydrogen adsorption and desorption by potassium-doped superactivated carbon

Yoshitsugu Kojima and Nobuaki Suzuki

Appl. Phys. Lett. 84, 4113 (2004); http://dx.doi.org/10.1063/1.1753654 (3 pages) | Cited 10 times

Online Publication Date: 5 May 2004

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Potassium-doped superactivated carbon can adsorb 1.6 wt % of hydrogen at room temperature under 5 MPa. This value was greater than that of potassium-doped graphite (hydrogen adsorption capacity: 1.0 wt %). Kinetics of the hydrogen adsorption of the potassium-doped superactivated carbon was remarkably improved. The hydrogen stored in the potassium-doped superactivated carbon was mainly released at high temperatures (440–1370 K). The high hydrogen adsorption capacity and the improved kinetics of this system may be derived from the small-sized graphen and the high surface area. © 2004 American Institute of Physics.
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68.43.Mn Adsorption kinetics
81.07.-b Nanoscale materials and structures: fabrication and characterization
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