Atom Probe Field Ion Microscopy of Surface Zones, Coatings and Interfaces

Doctoral thesis, 1995

This thesis is focused on developingmethods for high resolution microanalysis of coatings on a substrate, andsurface zones of a bulk sample using atom probe field ion microscopy,APFIM. The APFIM technique is described and some examples of its applications to semiconductors,cemented carbides and intermetallic compounds are given. The main part of the thesis is concerned with the formation of Schottky andohmic contacts on highly-doped GaAs. Three different metal coatings wereanalysed, gold, silver and gold-germanium, all of them formed on an APFIMspecimen of the semiconductor. The gold and silver coatings were studied on atomically clean as well asair exposed GaAs surfaces. Intermixing occurred for Au on a clean surfacewhereas Ag showed an atomically abrupt interface. Oxygen seemed to stopintermixing between Au and GaAs, but promoted diffusion of Ag into the semiconductor. Deposition of thegold-germanium alloy was only made on oxidised GaAs surfaces and the effectof heat treatment on this contact was studied. After heat treatment a thinlayer containing a few at.% of Ge in the GaAs was observed beneath an almost pure layer of Au. A technique for preparing APFIM specimens of the near surface zone of acemented carbide sample was developed, using a combination of dimplegrinding, electropolishing and ion milling. The first results obtained froma specimen prepared with this methodare presented. The possible applicability of this technique to metal/GaAsinterfaces and CVD-coated cemented carbides is discussed. APFIM analysis for the determination of the platinum distribution in anordered Cu3Au(4 at.% Pt) alloy is presented with a particularinterest in problems related to quantitative analysis near and at grainboundaries.