D. S. Martin

Reflection anisotropy spectroscopy

Reflection anisotropy spectroscopy (RAS) is a non-destructive optical probe of surfaces that is capable of operation within a wide range of environments. In this review we trace the development of RAS from its origins in the 1980s as a probe of semiconductor surfaces and semiconductor growth through to the present where it is emerging as a powerful addition to the wide range of existing ultra-high vacuum (UHV) surface science techniques. The principles, instrumentation and theoretical considerations of RAS are discussed. The recent progress in the application of RAS to investigate phenomena at metal surfaces is reviewed, and applications in fields including electrochemistry, molecular assembly, liquid crystal device fabrication and remote stress sensing are discussed. We show that the experimental study of relatively simple surfaces combined with continuing progress in the theoretical description of surface optics promises to unlock the full potential of RAS. This provides a firm foundation for the application of the technique to the challenging fields of ambient, high pressure and liquid environments. It is in these environments that RAS has a clear advantage over UHV-based probes for investigating surface phenomena, and its surface sensitivity, ability to monitor macroscopic areas and rapidity of response make it an ideal complement to scanning probe techniques which can also operate in such environments.

EFFECTS OF A NANOPARTICULATE SILICA SUBSTRATE ON CELL ATTACHMENT OF CANDIDA ALBICANS

Aims:  To investigate the influence of silica nanoparticles on the attachment and growth of Candida albicans cells.

Ecdysone promotes growth of imaginal discs through the regulation of Thor in D. melanogaster

Animals have a determined species-specific body size that results from the combined action of hormones and signaling pathways regulating growth rate and duration. In Drosophila, the steroid hormone ecdysone controls developmental transitions, thereby regulating the duration of the growth period. Here we show that ecdysone promotes the growth of imaginal discs in mid-third instar larvae, since imaginal discs from larvae with reduced or no ecdysone synthesis are smaller than wild type due to smaller and fewer cells. We show that insulin-like peptides are produced and secreted normally in larvae with reduced ecdysone synthesis, and upstream components of insulin/insulin-like signaling are activated in their discs. Instead, ecdysone appears to regulate the growth of imaginal discs via Thor/4E-BP, a negative growth regulator downstream of the insulin/insulin-like growth factor/Tor pathways. Discs from larvae with reduced ecdysone synthesis have elevated levels of Thor, while mutations in Thor partially rescue their growth. The regulation of organ growth by ecdysone is evolutionarily conserved in hemimetabolous insects, as shown by our results obtained using Blattella germanica. In summary, our data provide new insights into the relationship between components of the insulin/insulin-like/Tor and ecdysone pathways in the control of organ growth.

The adsorption of aromatic acids onto the graphite basal surface

Abstract The adsorption of benzoic acid, toluic acid, and salicylic acid from solution onto the graphite basal surface has been studied using atomic force microscopy (AFM). A systematic study of these three related planar aromatic acids is conducted in order to observe the influence of the functional side-group upon adsorption. It is found that upon adsorption all three acids orient with the benzene ring parallel to the graphite surface. On the graphite terraces, the benzoic acid decoration follows a Stranski–Krastanov growth mode whereas toluic acid follows Volmer–Weber growth. Salicylic acid forms a fibrous aggregate network. In addition to the terraces, graphite steps and near-surface bulk defects are found to be important sites for adsorption. The AFM tip is used to create irreversible nanoscale modifications of adsorbate structures.

VARIATIONS IN THE LIFETIME OF 3d HOLE STATES IN ULTRATHIN Fe FILMS GROWN ON Cu(100) DEDUCED FROM THE LMM AUGER SPECTRA OF Fe

The Fe LMM Auger and Auger vacancy satellite spectra of ultrathin Fe films grown on Cu(100) have been measured using photon excitation energies above and below the L2 ionisation edge, and in coincidence with the Fe 2p3/2 and Fe 2p1/2 photoelectrons. A comparison of the relative intensities of the satellites and main Auger transitions indicates that the M4,5 holes of L3M4,5 double hole states are localised for longer than the L3 lifetime for the 0.3 and 10 ML coverages but have a lifetime comparable to that of L3 holes for the 1 ML coverage. The results for the 1 ML coverage are supported by the results of the coincidence experiments. The reasons for the variation in the lifetime of M4,5 holes are discussed in terms of changes in the number of Fe–Fe neighbours and the density of states at the Fermi energy in these systems.

Influence of the heterojunction on the field emission from tetrahedral amorphous carbon on Si

In order to study the influence of the back barrier on the electron emission properties of tetrahedral amorphous carbon (ta-C), we have deposited identical films on p and n+ Si. The valence and conduction band offsets were measured for ta-C on p and n+ Si using in situ x-ray photoelectron spectroscopy and optical spectroscopy. From the band measurements it is shown that there is a substantial back barrier to emission. We show that for films having very similar properties, the electron emission can be influenced by the ta-C/Si heterojunction.

The adsorption of n-dodecane and n-pentane onto highly oriented pyrolytic graphite studied by atomic force microscopy

Abstract Atomic force microscopy has been used to study structures formed on the surface of highly oriented pyrolytic graphite following the evaporation of n-dodecane (C 12 H 26 ) and n-pentane (C 5 H 12 ). Previous work on the evaporation of n-hexadecane (C 16 H 34 ) revealed the graphite surface to be decorated with two species of isolated features on the terraces and continuous features at the steps. Models were proposed describing the orientations of the molecules within the features which were dependent on the length of the n-alkane molecule. Experiments have now been performed with shorter-chain alkanes, which show that the structural models derived from the hexadecane system also apply to the observed structures composed of dodecane and pentane.

The evaporation of n-hexadecane from highly oriented pyrolytic graphite studied by atomic force microscopy

The evaporation of n-hexadecane from highly oriented pyrolytic graphite (HOPG) has been investigated using tapping mode atomic force microscopy. Four evaporation times of 5, 10, 15, and 25 min have been studied. The same gross features are observed for all evaporation times, namely two types of isolated features located on the terraces and continuous features associated with steps on the graphite surface. Extensive measurements have been performed on the observed features allowing a detailed comparison between evaporation times. Models describing the molecular orientations within the features are proposed.

'Near-field optical microscopy with an infra-red free electron laser applied to cancer diagnosis'

We show that the combination of a scanning near field optical microscope and an infra-red free electron laser yields chemical images with sub-cellular spatial resolution that have the potential to provide a diagnostic for oesophageal adenocarcinoma.

Detection of DNA hybridisation on a functionalised diamond surface using reflection anisotropy spectroscopy

The analysis of single-stranded DNA attached to a polycrystalline diamond surface by reflection anisotropy spectroscopy (RAS) demonstrates that the DNA is oriented essentially vertically to the surface. RAS is able to detect the hybridisation between the attached strand and the homologous sequence.