A DIGITAL DATA ACQUISITION SYSTEM FOR INELASTIC ELECTRON TUNNELLING SPECTROSCOPY

A digital inelastic electron tunnelling spectrometer has been designed, constructed and implemented. Full details of hardware software and calibration are presented. The spectrometer has been used in a detailed inelastic electron tunnelling spectroscopy (IETS) study of benzoate anion (C6H5C00) absorbed at monolayer coverage on aluminium oxide. Mode energy and intensity measurements of high accuracy are reported. Small (<0.4 meV) non-systematic increases in absorbed mode energies occur when the oxidised electrode is positively biased. Possible causes of this phenomenon are discussed. Natural linewidths, as small as 0.45 meV, and variations in observed mode energy and lineshape with modulation voltage for selected modes have been studied at low temperatures (0.2 K), with a normal, and a superconducting, lead, (Pb) counter-electrode. The intensity of inelastic interactions involving aluminium oxide/ hydroxyl excitations have been measured, In contrast to molecular modes, they occur more strongly when the oxidised electrode is positively biased, suggesting that the zone of interaction may lie closer to this electrode. The digital system has been used to study elastic tunnelling in junctions comprising aluminium Oxide and aluminium oxide/organic Insulators. Several barrier modelling techniques have been employed. Barrier parameters obtained are intercompared and contrasted with those deduced by others. The nature of the organic adlayer and counter-electrode material are both found to exert a strong influence on the barrier potential distribution. lETS has been used to study liquid and vapour phase adsorption of (i) Oi-cyanoacrylate adhesives (CH2C(CN)COOR) (ii) alkoxysilane coupling agents (RSi(OR’)3) on aluminium oxide. High-quality tunnel spectra are presented and assigned. Evidence suggests that a-cyanoacrylates adsorb through formation of carbonyl - surface hydroxyl hydrogen bonds, conventional polymerisation inhibition by SO2 during adsorption results in a more physically uniform adlayer, but does not prevent polymerisation at the monomolecular level. No dominant absorption mechaism or adlayer structure is indicated in the case of alkoxysilanes, but several possibilities are discussed.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1983

Author dc:creator

• Reynolds, Stephen

Licence

• https://dora.dmu.ac.uk/bitstreams/a1accba8-6614-4035-92af-295810671244/download