Lithium Li Evaporation Process Notes
Lithium is classified as an alkali metal on the Periodic Table. It is the least dense of all metals and one of only three other metals that can float on water. It is silvery-white in appearance and very soft with a density of 0.53 g/cc, a melting point of 181°C, and a vapor pressure of 10-4 Torr at 407°C. Lithium is also highly flammable and easily oxidizes when exposed to air. While lithium and its compounds serve a variety of industries, it is mainly used to make rechargeable batteries which are found in smartphones, tablets, cars, and in many other products. Lithium, along with its alloys and compounds, is evaporated under vacuum to make batteries, fuel cells, and to form optical coatings.
Lithium Li Specifications
|Color/Appearance||Silvery White/Gray, Metallic|
|Thermal Conductivity||85 W/m.K|
|Melting Point (°C)||181|
|Coefficient of Thermal Expansion||46 x 10-6/K|
|Theoretical Density (g/cc)||0.53|
|Thermal Evaporation Techniques||
|E-Beam Crucible Liner Material||Tantalum|
|Temp. (°C) for Given Vap. Press. (Torr)||
|Comments||Metal reacts quickly in air.|
Empirical Determination of Z-Factor
Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:
- Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
- Place a new substrate adjacent to the used quartz sensor.
- Set QCM Density to the calibrated value; Tooling to 100%
- Zero thickness
- Deposit approximately 1000 to 5000 A of material on the substrate.
- Use a profilometer or interferometer to measure the actual substrate film thickness.
- Adjust the Z Factor of the instrument until the correct thickness reading is shown.
Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.