## I. INTRODUCTION 

Since their discovery in 1994 [1–4], superconducting rare earth nickel borocarbides R Ni$_{2}$B$_{2}$C [ R ϵ { Y, Dy . . . Tm, Lu } ] have been extensively investigated for their structural, magnetic and superconductive properties. In particular, the interaction between rare earth magnetism and superconductivity has been studied in detail. The results have been pub- lished in several extensive review articles [5–8]. During the years, all those compounds have then been synthesized as single crystals using different methods. Traditionally, small plate-shaped crystals of the highest quality were grown from a Ni$_{2}$B flux [9, 10]. Recently, the increasing experience on the growth of these materials using a travelling floating zone technique (TFZ) and a subsequent thermal treatment resulted in much larger crystals of also very high quality [11, 12]. Therefore, the precise investigation of properties of this class of materials such as thermodynamical, superconductive or magnetic properties, which are highly dependant on the sample purity, became again an interesting field of research (see for examples: [13–16]. Since that time, there was much interest to grow textured thin films of these materials using epitaxial growth. Different groups successfully prepared borocarbide thin films and studied their structural, intrinsic and extrinsic properties [17–25]. All those films were fabricated using physical vapor deposition techniques (PVD) on unbuffered or metal buffered oxidic single crystal substrates. Basically, several specific challenges have to be met for the preparation of intermetallic Borocarbide thin films: 1.) High crystallization temperature: The crystalline bulk phase formation temperature is about 1550 ℃ . While the first films were produced by room temperature sputtering and annealed afterwords[26], a successful in situ preparation of epitaxial c–axis–oriented borocarbide thin films was not re- ported for growth temperatures below 700 ℃ . 2.) High sensitivity of the rare earth material against oxidation: Oxygen incorporation into the borocarbide phase has to be prevented during thin film growth. As a first consequence, ultra high vacuum (UHV) conditions are necessary for physical vapor deposition. Secondly, oxygen interdiffusion into the film must be either hindered choosing suitable buffer materials or has to be at least controlled in a way that enables clean borocarbide phase growth on top. 3.) High diffusion of metallic buffer materials: The use of refractory metal buffers such as tungsten can suppress the oxidation of the rare earth but at the same time, interface reactions resulting in compounds as for example tungsten carbide may lead to changes of the composition of the borocarbide phase 

