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1 Mar 2004

Volume 84, Issue 9, pp. 1435-1613

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Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages)

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber
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Field emission from gallium-doped zinc oxide nanofiber array

C. X. Xu, X. W. Sun, and B. J. Chen

Appl. Phys. Lett. 84, 1540 (2004); http://dx.doi.org/10.1063/1.1651328 (3 pages) | Cited 107 times

Online Publication Date: 25 February 2004

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Gallium-doped nanostructural zinc oxide fibers have been fabricated by vapor-phase transport method of heating the mixture of zinc oxide, gallium oxide, and graphite powders in air. The zinc oxide fibers grew along [002] direction, forming a vertically aligned array that is predominantly perpendicular to the substrate surface. With a gallium doping concentration of 0.73 at. %, the corresponding carrier concentration and resistivity were 3.77×1020 cm−3 and 8.9×10−4 Ω cm, respectively. The field emission of these vertically aligned ZnO fiber arrays showed a low field emission threshold (2.4 V/μm at a current density of 0.1 μA/cm2), high current density, and high field enhancement factor (2317). The dependence of emission current density on the electric field followed Fowler–Nordheim relationship. The enhanced field emission is attributed to the aligned structure, good crystal quality, and especially, the improved electrical properties (increased conductivity and reduced work function) of the nanofibers due to gallium doping. © 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
72.80.Ey III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Energy-level splitting of ligand-stabilized Au55 clusters observed by scanning tunneling spectroscopy

H. Zhang, U. Hartmann, and G. Schmid

Appl. Phys. Lett. 84, 1543 (2004); http://dx.doi.org/10.1063/1.1652227 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2004

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A monolayer of Au55 clusters stabilized by [P(C6H5)3]12Cl6 ligands was investigated at 7 K using a low-temperature ultrahigh vacuum scanning tunneling microscope. The topography of single clusters shows the actual arrangement of the C6H5 rings of ligand molecules. Characteristic charge-quantization phenomena usually obtained for metal particles were observed by current–voltage measurements. Spectroscopic data acquired at different locations within a cluster reveal energy levels with average spacing of 170 meV which can be attributed to the Au55 core. © 2004 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Synthesis of InN/InP core/sheath nanowires

Long-Wei Yin, Yoshio Bando, Ying-Chun Zhu, Dmitri Golberg, and Mu-Sen Li

Appl. Phys. Lett. 84, 1546 (2004); http://dx.doi.org/10.1063/1.1651331 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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Bulk quantities of InN/InP core/sheath nanowires with a diameter of 60–90 nm and a length of several micrometers were synthesized through a vapor reaction route. The nanowires consisted of single-crystalline InN core with 30–40 nm in diameter and amorphous InP sheath with a thickness of 20–25 nm. High-resolution transmission electron microscopy images indicated that most of the InN core is perfect crystalline; there also exists a high density of stacking faults and twins in the crystalline InN core in some of the synthesized nanowires. Indium nanoparticles found at the tip of the nanowires indicated a vapor-liquid-solid growth mechanism for formation of the InN/InP nanostructures. This type of InN/InP nanowire is important and may be further developed to be utilized as nanoscale field effect transistor and light-emitting diode. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.05.Gc Amorphous semiconductors
61.46.-w Structure of nanoscale materials
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries

Resonance Raman scattering of boron carbonitride nanotubes

C. Y. Zhi, X. D. Bai, and E. G. Wang

Appl. Phys. Lett. 84, 1549 (2004); http://dx.doi.org/10.1063/1.1652237 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2004

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Resonance Raman spectra of boron carbonitride (BCN) nanotubes synthesized by hot-filament chemical vapor deposition were investigated. The intensity of the D band is insensitive to laser excitation energy (Elaser), while the intensity of the G and G′ bands increases as Elaser increases, and saturates at Elaser = 2.67 eV. This particular resonance behavior is ascribed to an electronic transition process different from the π–π∗ transition that occurs in carbon materials. The dispersive behavior of the D-related bands also shows an inflection at Elaser = 2.67 eV and different ∂ω/∂Elaser compared to carbon materials. These results indicate there are special electronic and phonon structures in BCN nanotubes. © 2004 American Institute of Physics.
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78.67.Ch Nanotubes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Na Fullerenes and related materials

Field emission from vertically aligned conductive IrO2 nanorods

Reui-San Chen, Ying-Sheng Huang, Ya-Min Liang, Chim-Sung Hsieh, Dah-Shyang Tsai, and Kwong-Kau Tiong

Appl. Phys. Lett. 84, 1552 (2004); http://dx.doi.org/10.1063/1.1655703 (3 pages) | Cited 46 times

Online Publication Date: 25 February 2004

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We report on the preparation and field-emission properties of vertically aligned conductive IrO2 nanorods. The unique geometrical features of IrO2 nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (Eth ∼ 0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm2 is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO2 nanorods as an emitter material has been demonstrated. © 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A 7-nm nanocolumn structure fabricated by using a ferritin iron-core mask and low-energy Cl neutral beams

Tomohiro Kubota, Tomohiro Baba, Seiji Samukawa, Hiroyuki Kawashima, Yukiharu Uraoka, Takashi Fuyuki, and Ichiro Yamashita

Appl. Phys. Lett. 84, 1555 (2004); http://dx.doi.org/10.1063/1.1655701 (3 pages) | Cited 25 times

Online Publication Date: 25 February 2004

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A 7-nm silicon column structure was fabricated by using a Cl neutral beam we developed. The neutral beam achieved a high etching selectivity to a ferritin iron-core mask by using charge-free and damage-free etching processes. The silicon etching selectivity ratio to the iron core was measured to be about 59. The iron core in the ferritin was 7 nm in diameter, which was identical to that of the etched nanocolumn. This indicates that neutral-beam etching transferred the structure and size of the iron core to the silicon substrate. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Switchable cantilever for a time-of-flight scanning force microscope

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber

Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2004

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We have developed a cantilever device for applying a time-of-flight scanning force microscope (TOF–SFM) system. The cantilever device consists of a switchable cantilever with an integrated bimorph actuator, an integrated extraction electrode to minimize the ion extraction voltage, and an interlocking structure for precise tip–EE alignment. The TOF–SFM with the cantilever device allows quasisimultaneous topographical and chemical analyses of solid surfaces to be performed in the same way as with the conventional scanning probe technique. The switching properties of the bimorph actuator are demonstrated for use in two operating systems. Field emission measurements and a TOF analysis of a Pt-coated tip are conducted with the TOF–SFM. © 2004 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.-d Chemical analysis and related physical methods of analysis
79.70.+q Field emission, ionization, evaporation, and desorption

Investigation of azobenzene side group orientation in polymer surface relief gratings by means of photoelectron spectroscopy

O. Henneberg, Th. Geue, U. Pietsch, M. Saphiannikova, and B. Winter

Appl. Phys. Lett. 84, 1561 (2004); http://dx.doi.org/10.1063/1.1651654 (3 pages) | Cited 4 times

Online Publication Date: 25 February 2004

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The molecular orientation of azobenzene side groups in polymer films before (nonpatterned) and after (patterned) development of a surface relief grating has been investigated by photoelectron spectroscopy using synchrotron radiation. The photoemission spectra obtained for 60–100 eV photons of a patterned and a nonpatterned surface are similar when the polarization vector of the synchrotron light is parallel to the grating vector. However, for perpendicular excitation, considerable spectral intensity differences can be observed for 9–14 eV electron binding energy. The observed changes are attributed to the formation of well-oriented azobenzenes at the surface. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
79.60.Ht Disordered structures
78.66.Qn Polymers; organic compounds

Phonon confinement in oxide-coated silicon nanowires

Somnath Bhattacharyya and Saumyadip Samui

Appl. Phys. Lett. 84, 1564 (2004); http://dx.doi.org/10.1063/1.1651648 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2004

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Raman spectroscopy of micron-long crystalline Si nanowires covered with a thick SiO2 layer showed a downshift and asymmetric broadening of the Raman first order TO phonon peak when compared with the bulk (q = 0) mode. The Raman shift and broadening were attributed to phonon confinement in the nanowires. A phenomenological phonon confinement model, incorporating the effects of nanowire diameter distribution, is presented. This model is shown to accurately describe the broadening of the Raman peak and is consistent with the microstructure of Si nanowires. In addition to the work a distribution of the phonon wave vector was directly taken into consideration replacing the diameter distribution to fit the Raman TO peak. The effects of the nano-Si:SiO2 boundary on the Raman spectra are discussed in terms of softening of the phonon confinement. © 2004 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Am Elemental semiconductors and insulators
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

2H nuclear magnetic resonance spectroscopy of deuterium adsorption on single-walled carbon nanotubes

Kai Shen and Tanja Pietraß

Appl. Phys. Lett. 84, 1567 (2004); http://dx.doi.org/10.1063/1.1652231 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2004

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2H nuclear magnetic resonance (NMR) spectroscopy was employed to study the interaction between deuterated hydrogen gas and single walled carbon nanotubes before and after purification. Transmission electron micrographs revealed strong bundling of the tubes. After purification, very little amorphous carbon and no graphitic particles were present, implying that the interactions observed are truly due to the nanotubes. In the parent material, the NMR signal is dominated by interaction of hydrogen with residual metal catalyst particles. For purified material, hydrogen in the gas phase is discernible from adsorbed hydrogen. The two phases do not exchange with each other on a ms time scale. The hydrogen molecules move among different adsorption sites, presumably outer tube surfaces and interstitial channels. This process is diffusion limited in the pressure range investigated. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics
76.60.Es Relaxation effects
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
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