Thin films

Physical deposition by ion bombardment – Sputtering

Sputter-type deposition is a moment transfer process in which atoms from a target are ejected or pulverized due to ion bombardment. The pulverized atoms travel until they reach a substrate, where they deposit to form the desired layer. As individual atoms, they are chemically active and quickly form compounds with the ions and atoms of the bombardment gas. For this reason, inert argon is used as a bombardment gas. For some applications, however, a reactive gas is purposely added to the argon so that the deposited film is a chemical compound rather than the elemental target materials. Spray deposition normally takes place at a pressure of 10-3 Torr. Therefore, the coating has a better conformation with the substrate geometry.

Physical deposition by electron beam – e-beam

Electron beam deposition takes place in a high vacuum (10-6 Torr). A focused beam of high-energy electrons is directed into a crucible containing the high-purity source material. The electrons that collide with the target heat the element until the phase change is solid-vapor, or solid-liquid-vapor. The steam flow is directed to the substrate, where it is condensed and deposited as a thin film. The high vacuum ensures highly directional deposit, which means that the film has more growth in the plane normal to the target.

MBE Technique

The MBE (molecular-beam epitaxy) technique refers to the process in which thin films or three-dimensional structures are formed on ordered and heated surfaces of monocrystalline substrates which, due to their characteristics as a network parameter and coefficient of thermal expansion, influence the formation of atomic arrangements. In this technique, the atoms or molecules come from solid sources with a high degree of purity, and can also be presented in a liquid state, as in the case of the chemical element gallium (Ga) used in the growth of compounds III-V. These charges are placed in effusion cells that are heated by power sources and monitored by PID controllers (proportional, integral and derivative) and, under ultra-high vacuum conditions (< 1.0 × 10−9 mbar), produce molecular beams with stable mass flow. Due to the rigor of the growing conditions, the MBE system makes it possible to produce films with high crystalline quality, in addition to accurately controlling the doping level (< 0.01 %), the film composition and the number of atomic monolayers. obtain multilayer heterostructures or two-dimensional films.