Clare E. Troupe

The oxidation of (100) textured diamond

The thermal oxidation of highly textured (100) chemical vapour deposited (CVD) diamond has been investigated using a combination of high resolution X-ray photoelectron spectroscopy. The diamond samples were oxidised in dry O in a vacuum 2 furnace at temperatures up to 800 8C. The kinetics of oxidation of well-defined crystal facets of (100) diamond have been studied using in-situ laser interferometry and thermogravimetric analysis. Concomitant scanning probe microscopic examination of individual facets after oxidation revealed negligible changes to the surface roughness. Oxygen containing functional groups such as ether (COC) and carbonyl ()C_O) have been observed using X-ray photoelectron spectroscopy at all the surface coverages investigated. Even at higher coverages the formation of higher oxidation states such as carboxylic acid groupings was negligible (-2.5%). Angle resolved X-ray photoelectron spectroscopy measurements have been used to discriminate between surface and sub-surface oxygen. 2002 Elsevier Science B.V. All rights reserved.

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.

Scanning probe microscopy and spectroscopy of CVD diamond films

Abstract. The surface morphology and electronic properties of as-deposited CVD diamond films and the diamond films which have been subjected to boron ion implantation or hydrogen plasma etching have been systematically studied by high resolution scanning probe microscopy and spectroscopy techniques. AFM and STM image observations have shown that (a) both the as-deposited CVD diamond films and the boron ion implanted films exhibit similar hillock morphologies on (100) crystal faces and these surface features are formed during the deposition process; (b) boron ion implantation does not cause a discernible increase in surface roughness; (c) atomic flatness can be achieved on crystal faces by hydrogen plasma etching of the film surface. Scanning tunnelling spectroscopy analysis has indicated that (a) the as-deposited diamond films and the hydrogen plasma etched diamond films possess typical p-type semiconductor surface electronic properties; (b) the as-deposited diamond films subjected to boron implantation exhibit surface electronic properties which change from p-type semiconducting behaviour to metallic behaviour; (c) the damage in the boron implanted diamond films is restricted to the surface layers since the electronic properties revert to p-type on depth profiling.

Characterization of the surface morphology and electronic properties of microwave enhanced chemical vapor deposited diamond films

The surface morphology, electronic structure and atomic bonding configurations of chemical vapor deposition (CVD) diamond films prepared at different stages of the deposition process and subjected to different postdeposition surface treatments have been studied by scanning probe microscopy (SPM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS) surface analysis techniques. SPM image observations show that (a) in the biasing nucleation process, diamond crystallites grow in a three-dimensional manner and the nucleation density reaches 109–1010/cm2; (b) both as-deposited and boron ion implanted films exhibit a hillock morphology on (100) crystal faces; (c) atomic flatness can be achieved on crystal faces by hydrogen plasma etching. STS analysis indicates that (i) the films obtained after an initial biasing nucleation process show a metallic tunneling behavior; (ii) both as-deposited and hydrogen plasma etched CVD diamond films possess typical p-type semiconductor surface elec...

Study of the Interface Microstructures of CVD Diamond Films by TEM

Abstract. The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.

A novel STM-based depth profiling technique for the electronic characterisation of thin film materials

Abstract Material removal from a sample surface by operating a scanning tunneling microscope (STM) in the scanning tunneling spectroscopy (STS) mode can be controlled at the rate of a few angstroms per bias voltage ramping cycle. Monitoring the modified sample surface by tunneling spectroscopy allows determination of the electronic properties of the material. By combining these two capabilities, a novel type of depth profiling based on surface electronic properties has been proposed and studied. This depth profiling technique is based on the removal of small amounts of material obtained by operating the STM in the surface modification mode while simultaneously acquiring tunneling spectra from the material revealed by the tunneling electrons. The I – V curve profile is monitored on a pulse-by-pulse basis which allows the correlation of electronic properties with the etching depth. By this technique, the surface damage on the boron ion-implanted CVD diamond films and argon ion-etched CVD diamond films has been investigated. It has also been demonstrated that this technique can be used to measure thin film thickness. It is envisaged that this experimental technique could find applications in the characterisation of shallow-doped semiconductor devices.