I. Introduction

The evaporator for making the films consists of a large brass baseplate connected by a 2" line to a vacuum system. There are two electrodes connecting through the baseplate to provide mechanical support for, and electric power to, a filament "boat" or heater. The boat is a dimpled strip of molybdenum and is heated by high-current, low-voltage electric power controlled by a variable autotransformer. There is also a movable shutter between the filament and substrate holder.

The substrate holder is a removable brass cylinder surrounding the electrodes and shutter. The end of the cylinder places the substrates the correct distance from the filament for good film thickness and also acts as a mask to shape the film to the correct pattern. There is a hole in the cylinder to observe the evaporation.

The baseplate and cylinder are enclosed in a removable glass bell jar, which has a rubber gasket for vacuum sealing and a metal screen safety guard. The metal screen safety guard should be in place at all times when the bell jar is under vacuum.

II. Preparing the Sample
 

1. Start the vacuum system in accordance with its instructions so it will be operating when needed. The instructions are given in Appendix A. (This takes approximately 45 minutes time.)

2. Bring the bell jar up to atmospheric pressure by opening the air inlet valve. Remove the screen guard and then the bell jar, placing the bell jar in the wooden cradle to prevent it rolling off the table and to keep dirt from the gasket. If the bell jar adheres to the baseplate after being brought up to atmospheric pressure, twist or rotate it to help loosen the bond of the seal. Remove the substrate holder cylinder.

3. Clean all the parts of the evaporator with Kimwipes and Methanol, including the bell jar and cylinder. DO NOT USE METHANOL ON RUBBER GASKET AT BASE OF BELL JAR! Cleaning the seal is unnecessary.

4. Get 2 or 3 small coils of silver wire from the white envelope and place them in the dimple of the filament boat. Center the shutter over the boat and set the cylinder and mask in place, checking to see that the hole in the side of the cylinder is positioned so that the evaporation can be observed.

5. Clean two microscope slides. Films will be evaporated on both simultaneously; one will be used in the actual Hall measurement, the other to measure the film thickness. Since the two films were evaporated side by side, the film thicknesses will be the same. Cleanliness is essential for the production of pure thin films. To clean the slide, wipe with a clean Kimwipe which has been dampened with alcohol.

6. Place the slides in the substrate holder Then carefully set the bell jar in place by lowering it over the cylinder so that the entire bottom edge makes contact at the same moment with the base plate. Seat the bell jar on the base plate by giving it a slight twist. Place the metal guard over the bell jar.

7. Be sure the air inlet valve is closed. Evacuate the bell jar following the vacuum system instructions.

8. Turn on the filament power switch. Slowly rotate the control knob in a clockwise direction while observing the filament boat. It may be difficult to see at first, but as it begins to glow red you will be able to observe the silver metal. Slowly increase the current until the silver just melts, then reduce it to allow the silver to resolidiñ’. (You can tell when this happens by observing the convection currents on the surface of the molten silver bead.) Hold the temperature at this point. The pressure should rise as the heat outgases the silver and the metal components of the evaporator The shutter protects the substrate from the contaminants and from the radiant heat. When the pressure returns to normal, move the shutter to one side and raise the temperature until the silver boils away or evaporates. Do not raise the temperature once the evaporation starts, as too much current will burn out the filament. The silver vapor condenses as a mirror-finish thin film on all cool surfaces, i.e. the substrates, cylinder, bell jar, etc.

After the slides have been taken out, remove the excess film that has been evaporated on the base plate, cylinder, bell jar and other parts of the evaporator using Kimwipes, methanol and "elbow grease." Replace the cylinder, bell jar and guard and evacuate the bell jar so it will be clean for the next evaporation. Turn off the vacuum system as it will no longer be needed, following instructions in Appendix A.