Prior to inserting any substrates in the UHV-MBE chamber, the entire chamber and all its components are appropriately degassed to prevent any unwanted desorption of contaminants during deposition. Once the chamber and components are fully degassed, the final vacuum pressure is considered the base pressure of the system. Substrates are then inserted to the chamber, individually placed in the substrate heater/holder assembly, and final-cleaned by heating to $900^\circ \textrm{C}$. These necessary preparation steps are discussed in the following sections.