Reducing the dimensionality of a material can effectively influence its properties. Compared to the knowledge on actinide bulk materials concerning their structure, behavior, and reactivity, much less is known regarding the materials with reduced dimensions (thin films, colloids, nanoparticles, clusters, isolated atoms in a matrix). The surface science laboratory installations at the Institute for Transuranium Elements (ITU) provide a combination of a reactive sputter deposition set-up for thin film production with photoemission spectroscopy instrumentation. This allows for characterization of the surface elemental composition of thin film materials, to draw conclusions regarding the chemical environment of the constitutive elements and to gather information on the electronic structure of the materials. X-ray photoelectron spectroscopy (XPS), probing the sample up to tens of monolayers (ML) deep, and UV photoelectron spectroscopy (UPS), with a probing depth of one to four MLs, are used. In this chapter, we focus on the investigation of surface reactions, and some examples are given to show how the electronic structure of 5f materials is influenced by reducing the materials’ dimensions. Additional characterization methods are applied to show that the films can also serve as structural models: characterization of the film surfaces by SEM–EDX (scanning electron microscopy combined with energy dispersive X-ray spectroscopy) and AFM (atomic force microscopy) are carried out. In the case of bulk characterization, X-ray diffraction (XRD) is used to give insight in crystallinity. The designed thin film models are used in gas adsorption (O2, Oatom, H2, Hatom) and electrochemical experiments probing their redox behavior. Specific examples are presented to illustrate this approach to mechanistic understanding.