N. A. Morrison

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.

Properties of amorphous carbon-silicon alloys deposited by a high plasma density source

The addition of silicon to hydrogenated amorphous carbon can have the advantageous effect of lowering the compressive stress, improving the thermal stability of its hydrogen, and maintaining a low friction coefficient up to high humidity. Most experiments to date have been on hydrogenated amorphous carbon–silicon alloys (a-C1−xSix:H) deposited by rf plasma enhanced chemical vapor deposition. This method gives alloys with sizeable hydrogen content and only moderate hardness. Here we use a high plasma density source known as the electron cyclotron wave resonance source to prepare films with higher sp3 content and lower hydrogen content. The composition and bonding in the alloys is determined by x-ray photoelectron spectroscopy, Rutherford backscattering, elastic recoil detection analysis, visible and ultraviolet (UV) Raman spectroscopy, infrared spectroscopy, and x-ray reflectivity. We find that it is possible to produce relatively hard, low stress, low friction, almost humidity insensitive a-C1−xSix:H allo...

Nitrogen Incorporation into Tetrahedral Hydrogenated Amorphous Carbon

Structural changes induced by the incorporation of nitrogen into ta-C : H films have been studied by Electron Energy Loss Spectroscopy, X-Ray Photoelectron Spectroscopy, Fourier Transformed Infrared Spectroscopy and Ultraviolet-Visible Spectroscopy. ta-C:H films have been synthesised using a low pressure Electron Cyclotron Wave Resonance (ECWR) source which provides a plasma beam with a high degree of ionisation and dissociation. Nitrogen was incorporated by adding N 2 to the C 2 H 2 plasma used for the deposition of ta-C : H films. The N/C atomic ratio in the films rises rapidly until the N 2 /C 2 H 2 gas ratio reaches three, and then increases more gradually, while the deposition rate decreases steeply. Chemical sputtering of the forming films and the formation of molecular nitrogen within the films limit the maximum nitrogen content to about N/C = 0.6. For low nitrogen content the films retain their diamond-like properties, however as N/C atomic ratio increases, a polymeric-like material is formed, with > C=N- structures and terminating C=N and NH groups that decrease the connectivity of the network.

Hydrogen content estimation of hydrogenated amorphous carbon by visible Raman spectroscopy

In the present study, we report the hydrogen content estimation of the hydrogenated amorphous carbon (a‐C:H) films using visible Raman spectroscopy in a fast and nondestructive way. Hydrogenated diamondlike carbon films were deposited by the plasma enhanced chemical vapor deposition, plasma beam source, and integrated distributed electron cyclotron resonance techniques. Methane and acetylene were used as source gases resulting in different hydrogen content and sp2∕sp3 fraction. Ultraviolet-visible (UV-Vis) spectroscopic ellipsometry (1.5–5eV) as well as UV-Vis spectroscopy were provided with the optical band gap (Tauc gap). The sp2∕sp3 fraction and the hydrogen content were independently estimated by electron energy loss spectroscopy and elastic recoil detection analysis-Rutherford back scattering, respectively. The Raman spectra that were acquired in the visible region using the 488nm line shows the superposition of Raman features on a photoluminescence (PL) background. The direct relationship of the sp2...

Diamond-based glucose sensors

Abstract A series of diamond-based glucose sensors, based on the interaction of glucose with the enzyme glucose oxidase (GOD), has been produced. For each sensor, the sensitivity to glucose was assessed and, with some devices, the range of glucose concentrations over which the sensor showed a linear response was determined. The sensing electrode formed one electrode of an electrochemical cell, and a tungsten counter electrode formed the other. All the sensors were diamond-based, with the nature of the working electrode being the distinguishing feature. The first device was a diamond platinum-GOD sensor. However, this device was prone to interference from other electroactive chemicals in the blood such as vitamin C and acetaminophen. To minimise the metal content of the sensors, two further sensors were produced using heavily boron doped diamond as the conducting electrode in place of the platinum. In the first case, the GOD was immobilised on to the surface of the diamond by electrochemical deposition, and in the second, the GOD was “wired” directly to the electrode by covalent bonding to the electrode surface.

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 A/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 sp 3 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.

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

AbstractA compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedralamorphous 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 thedeposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized as having an sp 3 content ofup 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 surfaceroughness of 0.04 nm. q1999 Elsevier Science S.A. All rights reserved.Keywords: Electron cyclotron wave resonance; Tetrahedral amorphous carbon; High rate deposition 1. IntroductionThe magnetic storage disk consists of an AlMg substrate,a NiP base layer, a Cr texturing layer, and a layer of ferro-magnetic polycrystalline Co alloy which acts as the storagemedium. The disk rotates rapidly and a read-write head‘flies’ just above the disk on a hydrodynamic air bearing.It is found necessary to coat the disk and the head surfacewith a protective layer, to prevent wear and mechanicaldamage during head crashes. Diamond-like carbon (DLC)is nowadays the only material for this application, as it isable to make a smooth, very continuous film of low thick-ness.The storage density of these disks is increasing rapidly,presently by about 50% per year [1], a similar rate to thespeed increase of microprocessors. The density increase ispossible by using ever smaller areas to hold each bit of data,and this requires lower head flying heights, and so thinnerDLC layers. The next generation of disks requires DLClayers of order 10 nm thickness with a roughness of under1 nm [2].Presently, the DLC overcoats are hydrogenated amor-phous carbon (a-C:H) deposited by reactive sputtering ofgraphite in an Ar, hydrogen atmosphere. Sputtering isused because it is used for the metal layers. However,there is doubt whether the quality of a-C:H formed by sput-tering is suitable for future generations of magnetic disk.Other technologies are being considered.Suitable technologies for carbon coating must be able tomake continuous films of 5 nm thickness, under 1 nm rough-ness, at deposition rates of 10–20 nm in 8 s (that is, over 1.2nm/s), with good uniformity over a certain area.One such technology is the filtered cathodic vacuum arc(FCVA)[3,4]. This method creates an intense plasma beam ofcarbon ions which is then passed through an axial magneticfilter to remove particulates. This method is capable of form-ing highly smooth films of 0.05 nm RMS roughness and ofvery high hardness, 80 GPa at a high deposition rate of up to3 nm/s [4]. The extreme properties of the tetrahedral amor-phous carbon (ta-C) produced arise from the deposition froman almost fully ionised plasma beam.Plasma enhanced chemical vapour deposition (PECVD)is another method frequently used to make a-C:H. However,PECVD must be carried out at a lower than usual pressure inorder to give highly ionised plasma beams suitable for thebest a-C:H. The plasma beam source (PBS) is one suchsource [5,6]. This is a RF excited, capacitively coupledsource in which magnetic confinement is used to allow theplasma to operate at a low pressure of 10

Chemical sputtering of ta-C: Implications for the deposition of carbon nitride

The majority of attempts to synthesize the theoretically predicted superhard phase β−C3N4 have been driven towards the use of techniques which maximize both the carbon sp3 levels and the amount of nitrogen incorporated within the film. However, as yet no attempt has been made to understand the mechanism behind the resultant chemical sputter process and its obvious effect upon film growth. In this work, however, the chemical sputtering process has been investigated through the use of an as-deposited tetrahedrally bonded amorphous carbon film with a high density nitrogen plasma produced using an rf-based electron cyclotron wave resonance source. The results obtained suggested the presence of two distinct ion energy dependent regimes. The first, below 100 eV, involves the chemical sputtering of carbon from the surface, whereas the second at ion energies in excess of 100 eV exhibits a drop in sputter rate associated with the subplantation of nitrogen within the carbon matrix. Furthermore, as the sample temper...

Directional nickel-induced fielded aided lateral crystallization of amorphous silicon

For application to active matrix liquid crystal displays (AMLCDs), a low temperature (<900 K) process for the production of polycrystalline silicon is required to permit the use of inexpensive glass substrates. This would allow the integration of drive electronics onto the display panel. Current low temperature processes include excimer laser annealing and solid phase crystallization, both of which are currently unsuitable for the fabrication of low cost, large area devices. The addition of small amounts of metal (e.g., Ni) to the amorphous silicon has been shown to significantly reduce the solid phase crystallization temperature. The rate of this solid phase metal induced crystallization can also be increased as a result of the presence of an electric field. The work presented here reports directional crystallization of amorphous silicon thin films during heat treatment in the presence of an electric field. Models are proposed for metal induced crystallization with and without an applied electric field i...

Methane chemistry involved in a low-pressure electron cyclotron wave resonant plasma discharge

Radio frequency (rf) generated methane plasmas are commonly employed in the deposition of hydrogenated amorphous carbon (a-C:H) thin films. However, very little is known about the rf discharge chemistry and how it relates to the deposition process. Consequently, we have characterized a low-pressure methane plasma and compared the results with those obtained theoretically by considering the steady-state kinetics of the chemical processes present in a low-pressure plasma reactor, in order to elucidate the dominant reaction channels responsible for the generation of the active precursors required for film growth. Mass spectrometry measurements of the gas phase indicated little variation in the plasma chemistry with increasing electron temperature. This was later attributed to the partial saturation of the electron-impact dissociation and ionization rate constants at electron temperatures in excess of ∼4 eV. The ion densities in the plasma were also found to be strongly dependent upon the parent neutral conce...