Schottky barrier heights of tantalum oxide, barium strontium titanate, lead zirconate titanate and strontium bismuth tantalate

Schottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 - 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.

Local hydrogen reactions of H*2 in a-Si:H

Hydrogen rearrangements at the H*2 complex are used as a model of low energy, local transitions in the two-hydrogen density of states of hydrogenated amorphous silicon (a-Si:H). These are used to account for the low activation energy motion of H observed by nuclear magnetic resonance, the low energy defect annealing of defects formed by bias stress in thin film transistors, and the elimination of hydrogen from the growth zone during the low temperature plasma deposition of a-Si:H. © 1998 Elsevier Science B.V. All rights reserved.

Surface atomic properties of tetrahedral amorphous carbon

The surface energy and surface atomic structure of tetrahedral amorphous carbon has been calculated by an ab-initio method. The surface atoms are found to reconstruct into sp2 sites often bonded in graphitic rings. Placing the dangling bonds on adjacent surface atoms lower their energy by π-bonding and this is the source of the low surface energy. The even lower surface energy of hydrogenated amorphous carbon (a-C:H) is due to the hydrogenation of all broken surface bonds. © 2005 Elsevier B.V. All rights reserved.

Growth of ultrahigh density vertically aligned carbon nanotube forests for interconnects.

We present a general catalyst design to synthesize ultrahigh density, aligned forests of carbon nanotubes by cyclic deposition and annealing of catalyst thin films. This leads to nanotube forests with an area density of at least 10(13) cm(-2), over 1 order of magnitude higher than existing values, and close to the limit of a fully dense forest. The technique consists of cycles of ultrathin metal film deposition, annealing, and immobilization. These ultradense forests are needed to use carbon nanotubes as vias and interconnects in integrated circuits and thermal interface materials. Further density increase to 10(14) cm(-2) by reducing nanotube diameter is possible, and it is also applicable to nanowires.

An electrokinetic sensor for studying immersed surfaces, using focused ultrasound

A novel method for obtaining information on the charge density of an immersed surface is presented. The technique uses focused ultrasound to excite oscillatory fluid motion in the plane of the solid-liquid interface, over a localised area. The displacement current (resulting from the motion of fluid-borne ions in the outer double-layer) is detected by electrodes in the liquid. The method is demonstrated as a means for monitoring protein adsorption, and for monitoring interactions between two different proteins. A second electrokinetic effect at the interface is identified, isolated from the first, and shown to provide additional information on the compressibility and charge density of the double-layer. © 2001 Elsevier Science B.V. All rights reserved.

Low temperature growth of carbon nanotubes and nanofibres

This paper reviews work on low temperature growth of carbon nanotubes, on Si, on plastic, on carbon cloth, using sputtered and colloidal catalysts, and with nano-imprinted patterning. © 2005 Materials Research Society.

Capacitive nanoelectromechanical switch based on suspended carbon nanotube array

We present the fabrication and high frequency characterization of a capacitive nanoelectromechanical system (NEMS) switch using a dense array of horizontally aligned single-wall carbon nanotubes (CNTs). The nanotubes are directly grown onto metal layers with prepatterned catalysts with horizontal alignment in the gas flow direction. Subsequent wetting-induced compaction by isopropanol increases the nanotube density by one order of magnitude. The actuation voltage of 6 V is low for a NEMS device, and corresponds to CNT arrays with an equivalent Young's modulus of 4.5-8.5 GPa, and resistivity of under 0.0077 Ω·cm. The high frequency characterization shows an isolation of -10 dB at 5 GHz. © 2010 American Institute of Physics.

Growth rate of YBCO single grains containing Y-2411(M)

Y-Ba-Cu-O (YBCO) single grains have the potential to generate large trapped magnetic fields for a variety of engineering applications, and research on the processing and properties of this material has attracted world-wide interest. In particular, the introduction of flux pinning centres to the large grain microstructure to improve its current density, Jc, and hence trapped field, has been investigated extensively over the past decade. Y 2Ba4CuMOx [Y-2411(M)], where M = Nb, Ta, Mo, W, Ru, Zr, Bi and Ag, has been reported to form particularly effective flux pinning centres in YBCO due primarily to its ability to exist as nano-size inclusions in the superconducting phase matrix. However, the addition of the Y-2411(M) phase to the precursor composition complicates the melt-processing of single grains. We report an investigation of the growth rate of single YBCO grains containing Y-2411(Bi) phase inclusions and Y2O3. The superconducting properties of these large single grains have been measured specifically to investigate the effect of Y2O3 on broadening the growth window of these materials. © 2010 IOP Publishing Ltd.

Three-dimensional carbon nanowall structures

The authors report the growth of carbon nanowalls in freestanding, three-dimensional aggregates by microwave plasma-enhanced chemical vapor deposition. Carbon nanowalls extrude from plasma sites into three-dimensional space. The growth is catalyst-free and not limited by nucleating surfaces. The growth mechanism is discussed and compared with similar carbon nanomaterials. High surface area of as-grown carbon nanowalls indicates a potential for electrochemical applications. Field emission measurements show a low field turn-on and long-term stability. The results establish a scalable production method and possible applications using field emission or high surface area. © 2007 American Institute of Physics.

Stress reduction and bond stability during thermal annealing of tetrahedral amorphous carbon

A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600-700°C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100°C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material. © 1999 American Institute of Physics.

High rate deposition of ta-C:H using an electron cyclotron wave resonance plasma source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 1.5 nm/s over a 4-inch diameter and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized as having an sp3 content of up to 77%, plasmon energy of 27 eV, refractive index of 2.45, hydrogen content of about 30%, optical gap of up to 2.1 eV and RMS surface roughness of 0.04 nm. © 1999 Elsevier Science S.A. All rights reserved.

High rate deposition of Ta-C:H using an electron cyclotron wave resonance plasma source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 900 angstrom/min and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized in terms of its bonding, stress and friction coefficient. The results indicated that the ta-C:H produced using this source fulfills the necessary requirements for applications requiring enhanced tribological performance.

The preparation, characterization and tribological properties of TA-C : H deposited using an electron cyclotron wave resonance plasma beam source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 900 Å/min over a 4″ diameter and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized in terms of its sp3 content, mass density, intrinsic stress, hydrogen content, C-H bonding, Raman spectra, optical gap, surface roughness and friction coefficient. The results obtained indicated that the film properties were maximized at an ion energy of approximately 167 eV, corresponding to an energy per daughter carbon ion of 76 eV. The relationship between the incident ion energy and film densification was also explained in terms of the subsurface implantation of carbon ions into the growing film.