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28 Dec 1998

Volume 73, Issue 26, pp. 3803-3961

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Atomic structure and electronic properties of single-wall carbon nanotubes probed by scanning tunneling microscope at room temperature

A. Hassanien, M. Tokumoto, Y. Kumazawa, H. Kataura, Y. Maniwa, S. Suzuki, and Y. Achiba

Appl. Phys. Lett. 73, 3839 (1998); http://dx.doi.org/10.1063/1.122910 (3 pages) | Cited 44 times

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A detailed three-dimensional structural analysis of single-walled carbon nanotubes was carried out using a scanning tunneling microscope (STM) operated at room temperature in ambient conditions. On a microscopic scale, the images show tubes condensed in ropes as well as tubes which are separated from each other. For a single-wall nanotube rope, the outer portion is composed of highly oriented nanotubes with nearly uniform diameter and chirality. On separated nanotubes, atomically resolved images show variable chirality ranges between 0°–30°, and variable diameter (1–3 nm), with no one type dominant. From STM and scanning tunneling spectroscopy measurements we confirmed the correlation between chirality and the electronic properties, namely the tuning from metallic to semiconducting. We also observed a rectifying behavior correlated with the chiral angle of 25°, an important observation for nanodevices application. © 1998 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
72.80.Rj Fullerenes and related materials

Load transfer in carbon nanotube epoxy composites

L. S. Schadler, S. C. Giannaris, and P. M. Ajayan

Appl. Phys. Lett. 73, 3842 (1998); http://dx.doi.org/10.1063/1.122911 (3 pages) | Cited 531 times

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The mechanical behavior of multiwalled carbon nanotube/epoxy composites was studied in both tension and compression. It was found that the compression modulus is higher than the tensile modulus, indicating that load transfer to the nanotubes in the composite is much higher in compression. In addition, it was found that the Raman peak position, indicating the strain in the carbon bonds under loading, shifts significantly under compression but not in tension. It is proposed that during load transfer to multiwalled nanotubes, only the outer layers are stressed in tension whereas all the layers respond in compression. © 1998 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.30.Na Fullerenes and related materials
61.41.+e Polymers, elastomers, and plastics
62.20.D- Elasticity

Growth of highly oriented carbon nanotubes by plasma-enhanced hot filament chemical vapor deposition

Z. P. Huang, J. W. Xu, Z. F. Ren, J. H. Wang, M. P. Siegal, and P. N. Provencio

Appl. Phys. Lett. 73, 3845 (1998); http://dx.doi.org/10.1063/1.122912 (3 pages) | Cited 115 times

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Highly oriented, multiwalled carbon nanotubes were grown on polished polycrystalline and single crystal nickel substrates by plasma enhanced hot filament chemical vapor deposition at temperatures below 666 °C. The carbon nanotubes range from 10 to 500 nm in diameter and 0.1 to 50 μm in length depending on growth conditions. Acetylene is used as the carbon source for the growth of the carbon nanotubes and ammonia is used for dilution gas and catalysis. The plasma intensity, acetylene to ammonia gas ratio, and their flow rates, etc. affect the diameters and uniformity of the carbon nanotubes. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Effects of mechanical stress on electromigration-driven transgranular void dynamics in passivated metallic thin films

M. Rauf Gungor, Dimitrios Maroudas, and Leonard J. Gray

Appl. Phys. Lett. 73, 3848 (1998); http://dx.doi.org/10.1063/1.122913 (3 pages) | Cited 22 times

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The combined effects of mechanical stress and surface electromigration on the dynamics of transgranular voids in passivated metallic thin films are analyzed based on self-consistent dynamical simulations. Depending on the strength of the electric and stress fields, void morphological instabilities can lead to film failure by propagation from the void surface of either faceted slits or finer-scale crack-like features. Most importantly, there exists a narrow range of applied stress for given strength of electric field over which slit formation can be inhibited completely. © 1998 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.65.Rv Passivation
81.05.Bx Metals, semimetals, and alloys

Piezoelectric measurements with atomic force microscopy

J. A. Christman, R. R. Woolcott, A. I. Kingon, and R. J. Nemanich

Appl. Phys. Lett. 73, 3851 (1998); http://dx.doi.org/10.1063/1.122914 (3 pages) | Cited 102 times

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An atomic force microscope (AFM) is used to measure the magnitude of the effective longitudinal piezoelectric constant (d33) of thin films. Measurements are performed with a conducting diamond AFM tip in contact with a top electrode. The interaction between the tip and electric field present is a potentially large source of error that is eliminated through the use of this configuration and the conducting diamond tips. Measurements yielded reasonable piezoelectric constants of X-cut single-crystal quartz, thin film ZnO, and nonpiezoelectric SiO2 thin films. © 1998 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.79.Lh Atomic force microscopes
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films

Electric circuit model for MgO-doped ZrO2–TiO2 ceramic humidity sensor

M. K. Jain, M. C. Bhatnagar, and G. L. Sharma

Appl. Phys. Lett. 73, 3854 (1998); http://dx.doi.org/10.1063/1.122915 (3 pages) | Cited 12 times

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The MgO-doped ZrO2–TiO2 ceramic pellets were studied for its humidity-sensitive electrical conduction. An equivalent circuit model has been proposed to define the humidity-sensitive electrical properties. This model is in agreement with the experimental findings. The electrical conduction is largely controlled by the intergranular impedance except at very high humidities. The impedance of the pellets showed inductive behavior in high-humidity region. This behavior can be attributed to the spherical paths adopted by charge carrier because conduction is mainly through the spherical grain surface. © 1998 American Institute of Physics.
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07.07.Vx Hygrometers; hygrometry
72.80.Ga Transition-metal compounds
72.20.Fr Low-field transport and mobility; piezoresistance
85.30.De Semiconductor-device characterization, design, and modeling

In situ reflectance difference spectroscopy of N-plasma doped ZnTe grown by molecular beam epitaxy

D. Stifter, M. Schmid, K. Hingerl, A. Bonanni, M. Garcia-Rocha, and H. Sitter

Appl. Phys. Lett. 73, 3857 (1998); http://dx.doi.org/10.1063/1.122916 (3 pages) | Cited 11 times

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In situ reflectance difference spectroscopy (RDS) has been performed during growth and nitrogen-doping of ZnTe thin films fabricated by molecular beam epitaxy. The doping level of the ZnTe samples can be determined by evaluating the RD spectra in the vicinity of the E1 and E1+Δ1 transitions. RDS features in this spectral range were used to optimize online the doping performance of the N-plasma cell. Furthermore, doping-induced surface processes have been investigated, like surface saturation with activated N species and surface Fermi level pinning occurring at ambient pressure. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
61.72.uj III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.At Surface states, band structure, electron density of states

Molecular dynamics-based ion-surface interaction models for ionized physical vapor deposition feature scale simulations

Daniel G. Coronell, David E. Hansen, Arthur F. Voter, Chun-Li Liu, Xiang-Yang Liu, and Joel D. Kress

Appl. Phys. Lett. 73, 3860 (1998); http://dx.doi.org/10.1063/1.122917 (3 pages) | Cited 22 times

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A procedure is presented for incorporating the results of atomistic simulations of ion–surface interactions into integrated circuit topographic simulations of ionized physical vapor deposition (PVD). Energy and angular dependent sticking probabilities for energetic Cu atoms impacting a {111} Cu surface, obtained from molecular dynamics simulations, were implemented in a simple Monte Carlo flux model. The resulting flux-averaged Cu sticking probability was found to vary significantly with position within submicron features and with the feature geometry. This illustrates the shortcomings of a constant (energy and angle independent) sticking probability model for ionized PVD. © 1998 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Effect of the linewidth reduction on the characteristic time spread in C49–C54 phase transition

S. Privitera, F. La Via, M. G. Grimaldi, and E. Rimini

Appl. Phys. Lett. 73, 3863 (1998); http://dx.doi.org/10.1063/1.122918 (3 pages) | Cited 11 times

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The kinetics of the C49–C54 phase transformation in TiSi2 narrow strips for width in the 0.5–1.3 μm range was investigated by sheet resistance measurements. The experimental data follow the Johnson–Mehl–Avrami equation for the fraction of the transformed material, with an exponent equal to 1 for all of the analyzed linewidths. Nucleation sites saturation occurs and the growth is one-dimensional along the length of the strip. The characteristic time, as obtained by the fit, increases as 1/W, W being the width of the strip, and a nucleation density of about 0.05 sites/μm2 has been obtained. The distribution of the characteristic times around the average value increases with decreasing the linewidth. The amplitude of the dispersion is in quantitative agreement with the statistical fluctuation of the number of nucleation sites. © 1998 American Institute of Physics.
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64.70.K- Solid-solid transitions
73.61.At Metal and metallic alloys
61.72.Cc Kinetics of defect formation and annealing
64.60.Q- Nucleation

Observation of incident angle dependent phonon absorption in hydrogenated amorphous silicon nitride thin films

Tong Li and Jerzy Kanicki

Appl. Phys. Lett. 73, 3866 (1998); http://dx.doi.org/10.1063/1.122919 (3 pages) | Cited 4 times

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We have demonstrated the existence of longitudinal- and transverse-like optical modes of Si–N bond in vibrational absorption spectrum of hydrogenated amorphous silicon nitride thin films. One of the longitudinal-like optical resonances coincides with the transverse-like mode of Si–O bond, and the other closely neighbors the bending mode of N–H bond. We have also shown that the conventionally assigned asymmetric stretching mode of Si–N bond is merely a transverse-like mode of the bond. The microstructures of both longitudinal- and transverse-like modes can well be apprehended by a p-polarized beam at an oblique incidence light, especially at Brewster angle incidence. The spectrum distortion induced by interference fringes can be eliminated at this condition. © 1998 American Institute of Physics.
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78.66.Nk Insulators
78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Structural characterization of thin GaN epilayers directly grown on on-axis 6H–SiC(0001) by plasma-assisted molecular beam epitaxy

B. Yang, A. Trampert, B. Jenichen, O. Brandt, and K. H. Ploog

Appl. Phys. Lett. 73, 3869 (1998); http://dx.doi.org/10.1063/1.122920 (3 pages) | Cited 11 times

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The structural properties of a series of thin (0.2–0.6 μm) GaN epilayers directly grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy are studied. X-ray reciprocal space maps of the GaN(0002) reflection reveal negligible inhomogeneous strain within the layer but a comparatively large orientational spread of the GaN c axis. X-ray rocking curve measurements show, however, that this mosaicity steadily decreases with film thickness. In fact, the density of threading defects detected by transmission electron microscopy is found to decrease drastically with the distance away from the GaN/SiC interface, finally reaching a value of less than 5×109 cm−2 at a layer thickness of 0.5 μm. The formation mechanisms of the threading dislocations in the GaN films are discussed in consideration of the specific GaN/SiC interface structure. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
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