Alec Deslandes

Characterization of PVD Lumogen films for wavelength conversion applications

Lumogen Yellow S0790 is a commercial azomethine based pigment and is used for enhancing CCD devices for detecting ultraviolet radiation. In this work we report on the crystal structure and morphology of the raw material, as-deposited and post-annealed films, as well as the influence these have on the subsequent optical properties. Our measurements of physical vapour deposited (PVD) Lumogen films indicate that commercial Lumogen powder is crystalline in its as-received state, with a melting point of 273.3°C and boiling point of 328.6°C. Furthermore, we have found that as-deposited films on room temperature substrates possess an inherent crystalline structure, which has not been reported previously, but also that the material’s structure changes into a completely different crystalline form upon annealing for 90 hours at 80°C.

Plasma Fluorination of Highly Ordered Pyrolytic Graphite and Single Walled Carbon Nanotube Surfaces

A simple room temperature fluorination process for highly ordered pyrolytic graphite (HOPG) and single walled carbon nanotube (SWCNT) surfaces is presented and discussed. Graphite and SWCNT surfaces are functionalised using radio frequency SF6 plasma. Samples were characterised before and after treatment using XPS, EDX, SEM, and STM techniques. It is found that functionalisation of SWCNT surfaces occurs rapidly indicating an efficient fluorination process with minimal damage to the carbon surfaces, and furthermore, without presence of sulphur-containing functional groups

Observation of a helium ion energy threshold for retention in tungsten exposed to hydrogen/helium mixture plasma

Helium retention is measured in tungsten samples exposed to mixed H/He plasma in the Magnum-PSI linear plasma device. It is observed that there is very little He retention below helium ion impact energies of 9.0 +- 1.4 eV, indicating the existence of a potential barrier which must be overcome for implantation to occur. The helium retention in samples exposed to plasma at temperaturesu2009u2009>1000u2009K is strongly correlated with nano-bubble formation measured using grazing incidence small-angle x-ray scattering. The diameters of nano-bubbles were not found to increase with increasing helium concentration, indicating that additional helium must be accommodated by increasing the bubble concentration or an increase in bubble pressure. For some samples pre-irradiation with heavy ions of 2.0 MeV energy is investigated to simulate the effects of neutron damage. It is observed that nano-bubble sizes are comparable between samples pre-irradiated with heavy-ions, and those without heavy-ion pre-irradiation.

Deuterium retention and near-surface modification of ion-irradiated diamond exposed to fusion-relevant plasma

Chemical vapour deposited diamond was irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. Ion-irradiated samples were then exposed to a deuterium plasma in MAGPIE with ion flux of ~1.3 × 1021 ions m−2 s−1. Raman and near edge x-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the degree of disorder and sp2-bonding induced by the ion irradiation. The signals of sp2-bonded and disordered carbon were observed to decrease after exposure to the deuterium plasma, although sharp Raman peaks indicative of vacancy and interstitial defects induced by the MeV ions were less affected. Recovery of a diamond-like surface after plasma exposure was evident in the NEXAFS spectra. Elastic recoil detection analysis showed that the ion-damaged diamond retained more deuterium than diamond exposed only to deuterium plasma. For the case of unirradiated samples, diamond retained more deuterium than graphite. However, for the case of the ion-irradiated samples, diamond exhibited less deuterium retention than graphite.

Plasma modified carbon surfaces for supporting sensor architectures

Carbon possesses a number of properties that make it ideal for use in sensor and electrical applications. Using radio frequency plasma with various precursor gases it is possible to prepare carbon surfaces for further molecular attachment or functionalisation. Research in our laboratory has involved studies of plasma fluorination, hydrogenation and methanation of highly ordered pyrolytic graphite (HOPG) (as it serves as a highly ordered, single crystal, model substrate for other more complex forms of carbon), glassy carbon in the form of pyrolysed photoresist films (PPF) and single-walled carbon nanotubes (SWCNTs). Treated surfaces have been characterised using a variety of investigatory surface techniques. In this article we report on results obtained using X-ray Photoelectron Spectroscopy (XPS) for probing the chemical nature of the surface and hence the extent of treatment; Time of Flight Secondary-Ion Mass Spectrometry (ToFSIMS) has been utilised to examine the molecular surface structure and in particular, determine the extent of surface hydrogenation; Scanning Tunnelling Microscopy (STM) measurements provide information on the morphology of treated surfaces, in particular the damage and change in surface structures caused by various plasma treatments. We show in this work that the morphology, mechanisms and extent of modification of the plasma-modified surface obtained is strongly influenced by various experimental conditions. For instance, etching and/or nucleation and growth features are observed, with the type of features and their distribution strongly dependent on the precursor gas that is used to support the plasma. Other important parameters are operating pressure, RF power and exposure time.

Effect of Annealing upon Retention of He and H in Irradiated SiC

Silicon carbide (3C-β SiC) samples were irradiated with He ions of energy up to 30 keV and a fluence up to 1016/cm2, to produce damage in the near-surface region. A duplicate set of He ion irradiated SiC samples, as well as undamaged SiC, were also irradiated with H2+ ions of energy up to 20 keV and a similar fluence, to study the interaction of H species with pristine SiC and with He radiation-damaged SiC. Samples were annealed in steps of 200 K, from 473 K to 1273 K, and the retention of H and He were measured using elastic recoil detection analysis with 7.8 MeV C3+ ions, after each anneal step. Modification to the surface following irradiation is observed via Raman spectroscopy, which exhibits development of damage states such as disordered carbon and Si-Si peaks. Only minor changes in the H and He profiles were observed up to 1073 K, however after the 1273 K anneal the H and He profiles changed considerably, with a marked difference between samples irradiated only with He and those irradiated with He and H.

Langmuir probe characterization of low-frequency oscillations in a radio-frequency SF6 plasma

A low-frequency oscillation (<100u2009Hz) has been observed in a low-pressure (1–50u2009mTorr) radio-frequency (RF) inductively coupled plasma, produced in sulfur hexafluoride. Langmuir probe studies have characterized this oscillation with respect to RF power, gas pressure and probe proximity to the antenna. The experimental parameter space within which this oscillation is observed is mapped with respect to power and pressure for the reaction chamber in use. The oscillation is observed in Langmuir probe currents for positive probe bias, and has a strong dependence on experimental conditions, as well as probe position within the chamber. The propagation speed of the instability away from the source is found to be 16u2009mu2009s−1.

Characterisation of methane plasma treated carbon surfaces

Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was used to investigate the chemical nature of methane plasma treated graphite surfaces. Principle Component Analysis (PCA) was applied to the SIMS data, revealing chemical changes to the surfaces, in particular the extent of hydrogenation. The hydrogen content of the HOPG surface is observed to increase with systematic increases in power of the plasma treatment. These results are supported by Elastic Recoil Detection Analysis (ERDA) measurements that show a similar increase in hydrogen content. Scanning Tunneling Microscopy (STM) measurements provide insight into the morphological changes to the surface caused by the treatment, via investigating plasma-created features that are observed to increase in coverage with the increases in plasma power.

Preparation of Carbon Surfaces for Sensing Applications via Plasma Hydrogenation

Graphite (HOPG) has been exposed to radio frequency (RF) plasmas of hydrogen and methane to produce hydrogen-terminated carbon surfaces, and hence model the use of plasma hydrogenated carbon as a substrate in sensing applications. Etching and/or growth and nucleation features are observed in scanning tunneling microscopy images. Surface coverage and size of features are found to depend upon the choice of source gas. Preliminary time of flight secondary ion mass spectrometry measurements suggest these features and the hydrogen content of the surfaces are related