eTraining Introduction

Specimen Preparation

Leica Ultracut UCT

Histology

JEOL JSM-6400 SEM

Hitachi S-4700 FE-SEM

Hitachi FB-2000A FIB

Microanalysis

Veeco Dim 3000 AFM

Fluorescence Microscopes

Support

Coating

Specimen Coating

The topic Reasons for Coating under Specimen Preparation addresses the rationale for coating and which coating to use for a particular problem. In this topic are the basic principles behind the coating machines available in the ACMAL facility, namely high vacuum evaporation and sputter coating systems.

In both of the two systems the specimen is sealed in a vacuum environment. There are three reasons why a vacuum environment is important. First, a vacuum minimizes collisions between evaporated/sputtered materials and other atoms or molecules encountered before reaching the specimen. Second, the degree of volatile contamination on the specimen and in the chamber itself affects the coating quality. The chamber vacuum removes these contaminants. Last, high voltage is used in the evaporation/sputtering process, and in air the voltage would jump or arc to ground. This is dangerous to an operator.

SputteringSputtering

Sputtering refers to the way in which the conductive metal in a target is liberated when the target is hit with fast-moving, heavy particles. The freed metal atoms are deposited onto the specimen surface.

This event is accomplished in a vacuumed chamber filled with an inert gas, such as argon, and under the influence of a charge produced by an anode at the top and a cathode at the bottom.


EvaporatorHigh Vacuum Evaporation

Carbon or noble metals and their alloys are used in high vacuum evaporation. In either case, the material to be evaporated is heated until it evaporates or explodes. The freed material then deposits onto the specimen.

For metal coating, metal wire is placed in a tungsten wire "boat" and heated until evaporation. For carbon coating, sharpened carbon rods are placed in contact with each other.

As evaporation takes place, a spring drives the exploding rod against the other fixed rod, resulting in a greater amount of evaporated material. Heat is produced in both cases, so the operator should use care in order to avoid burns when handling the materials post-coating.

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