Radiation-induced defects in calcium fluoride and their influence on material properties under 193 nm laser irradiation

Calcium fluoride (CaF2) is one of the key lens materials in deep-ultraviolet microlithography because of its transparency at 193 nm and its nearly perfect optical isotropy. Its physical and chemical properties make it applicable for lens fabrication. The key feature of CaF2 is its extreme laser stability. rnAfter exposing CaF2 to 193 nm laser irradiation at high fluences, a loss in optical performance is observed, which is related to radiation-induced defect structures in the material. The initial rapid damage process is well understood as the formation of radiation-induced point defects, however, after a long irradiation time of up to 2 months, permanent damage of the crystals is observed. Based on experimental results, these permanent radiation-induced defect structures are identified as metallic Ca colloids.rnThe properties of point defects in CaF2 and their stabilization in the crystal bulk are calculated with density functional theory (DFT). Because the stabilization of the point defects and the formation of metallic Ca colloids are diffusion-driven processes, the diffusion coefficients for the vacancy (F center) and the interstitial (H center) in CaF2 are determined with the nudged elastic band method. The optical properties of Ca colloids in CaF2 are obtained from Mie-theory, and their formation energy is determined.rnBased on experimental observations and the theoretical description of radiation-induced point defects and defect structures, a diffusion-based model for laser-induced material damage in CaF2 is proposed, which also includes a mechanism for annealing of laser damage. rn

Describing and explaining the foreign expansion of network managing electronic business companies (NM-EBCs)

This study deals with the internationalization behavior of a new and specific type of e-business company, namely the network managing e-business company (NM-EBC). The business model of such e-business companies is based on providing a platform and applications for users to connect and interact, on gathering and channeling the inputs provided by the users, and on organizing and managing the cross-relationships of the various participants. Examples are online communities, matching platforms, and portals. Since NM-EBCs internationalize by replicating their business model in a foreign market and by building up and managing a network of users, who provide input themselves and interact with each other, they have to convince users in foreign markets to join the network and hence to adopt their platform. We draw upon Rogers’ Diffusion of Innovations Theory and Network Theory to explain the internationalization behavior of NM-EBCs. These two theories originate from neighboring disciplines and have not yet been used to explain the internationalization of firms. We combine both theories and formulate hypotheses about which strategies NM-EBCs may choose to expand abroad. To test the applicability of our theory and to gain rich data about the internationalization behavior of these firms, we carried out multiple case studies with internationally active Germany-based NM-EBCs.