Metallic thin films composed of separated, three-dimensional nanostructures are promising candidates for numerous fields of applications such as electrodes in fuel cells and Li-ion batteries, nanostructured implant coatings and surface enhanced Raman sensors. The ability to tailor the shape of the nanostructures precisely represents a key issue for controlling the properties of such thin films. Oblique angle deposition in combination with electron beam evaporation represents a powerful method for sculpturing those thin films with nanometer scale precision. For this purpose, the substrate normal is tilted to an oblique angle θOAD with respect to the incoming particle flux. The particle trajectories can be considered as parallel. Caused by the oblique deposition geometry, shadowed regions are created between the developing nanostructures, where later arriving particles cannot condense. This favors the growth of tilted nano-sized columns that are inclined towards the incoming particle flux. Although substantial research has been performed in this field during the last decades, many questions concerning the growth processes of especially obliquely deposited metallic thin films remain unanswered.
This presentation focuses on highly porous Mo thin films that are grown by electron beam evaporation at an oblique angle θOAD = 84° and at room temperature. Natively and thermally oxidized Si(100) pieces have been used as substrates. In-plane pole figure measurements and reflection high-energy electron diffraction (RHEED) measurements are carried out to investigate the texture of the Mo thin films depending on the film thickness, which has been varied between 10 nm and 2.5 µm. Morphological features of the Mo thin films are studied by scanning electron microscopy. Moreover, a transmission electron microscope (TEM) lamella has been prepared, allowing the investigation of the texture formation depending on the film thickness via selective area electron diffraction (SAED) measurements. Further, a nano-sized electron beam has been applied to study the crystallinity of a single Mo column. High-resolution TEM images and SAED measurements indicate that tilted Mo columns deposited at room temperature tend to grow with a single crystalline microstructure.