THE PROBLEM OF HOT-SPOTS IN MICROWAVE EQUIPMENT USED FOR PREPARATORY TECHNIQUES - THEORY AND PRACTICE

Electron microscopists who wants to use a microwave (MW) oven to stimulate preparatory processes are sooner or later confronted with the problem of hot spots. It soon becomes clear to the user of any MW oven that the energy distribution-thus the speed of absorbing energy, and hence warming up-varies topographically. The unaware can observe variations in results when the principles of topographic order are not followed meticulously. To understand the hot-spot phenomenon a certain theoretical knowledge is needed, as presented in this paper. In the 10 years that we have used MW ovens for our preparatory techniques we have learned how to solve the problem of hot spots. Thermographic paint can be applied to record energy distribution. In our studies, we have used a fiberoptic thermometer to follow precisely in time the temperature in the MW-exposed media, and these observations have provided us with the needed insight to obtain reproducible results. We argue that only when temperature curves are given by the authors can their recipes be used successfully in other laboratories.