Two of the tungsten boats listed on this page are a combination of the refractory metal tungsten and an alumina barrier (Al2O3) coating over the tab area. The exposed metal area comprising the bottom of the boat allows the sample to be in good thermal contact with the source.

The barrier will tend to help concentrate the heat towards the center. The alumina barrier will inhibit an evaporant (if used as a sample instead of an aperture) from creeping toward the heat sink or from wetting the entire boat.

The tungsten boats, baskets and filaments are manufactured from high grade tungsten. Of all metals in pure form, tungsten has the highest melting point (3422°C / 6192°F), the lowest vapor pressure at temperatures above 1650°C (3000°F) and has the highest tensile strength. Tungsten also has the lowest coefficient of thermal expansion of any pure metal.

This combination of properties makes tungsten the ideal material for evaporation sources. During evaporation, it can alloy with some materials such as Al or Au. In this case, another evaporation source material should be used such as alumina coated boats or baskets. Other materials useful for evaporation sources are molybdenum and tantalum.