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Introduction to Carbon Coating & Vacuum Evaporation Incorporating Carbon & Metal Carbon and Metal Evaporators K250X, K450X, K950X & K975X

Table of Contents:

1. Introduction
2. Physical Considerations
3. Physical Considerations (Part 2)
4. Turbo Pumped, High Vacuum Systems
5. Surface Treatment

INTRODUCTION

Carbon Films, because of their mechanical stability, good electrical conductivity, and low background signal are commonly used in sample preparation techniques for Electron Microscopy (EM).

Thin films of the order of up to 5 nm (50A) are used in Transmission Electron Microscopy (TEM) as particle support and as isolating layers in autoradiography. Thick films somewhat more than 5 nm (50A) are used in Scanning Electron Microscopy (SEM) also for support, in addition to coating for X-Ray Microanalysis. It may also be a requirement to subsequently treat support films by means of Glow Discharge.

In general there is a need for all these films to be fine grain, even coating, with uniform and reproducible film thickness.

The advent of Carbon fibre has resulted in a new principle for Evaporation of Carbon in EM applications. The basis is a carbon filament, which at high temperature burns very quickly somewhat in the order of 1 second, or less, from which has evolved the terminology Carbon 'Flash' Evaporation. The resulting short coating times and reduced total power input distinguishes it from the somewhat longer process of carbon rod evaporation.

It is further distinguished in total cycle time, which is approx. 4 minutes including pumping and outgassing, by the fact that it can be carried out at Rotary Vacuum Pump pressures. These pressures (relative Vacuum) of the range 0.05 to 0.01 Torr giving mean free paths of the order of 1 to 5mm respectively.

Evaporation under these conditions is not unidirectional as the particles engage in a number of collisions before they arrive at the surface, enhancing the possibility of a uniform coating, even on sculptured surfaces.

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