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Near-field optical elements for free space focussing of terahertz (THz) radiation were studied using analytical and numerical approaches for conical waveguides. One of the most promising candidates, a self-similar logarithmic periodical coupling structure (LPCS) embedded into a conical parabolic waveguide, was further experimentally studied with respect to spectral transmission losses using a scaled model at GHz frequencies. Since both studies confirmed the expected broadband high transmission properties of LPCS structures compared to conventional conical waveguides, a prototype structure for THz frequencies as realized by a X-ray lithography technique is presented. Published by Elsevier B.V.

The LIGA process combines X-ray lithography with electroplating and molding. It is a technique used worldwide for the fabrication of high aspect ratio microstructures. In Germany, this technique will be established as a production line to manufacture micro system devices. A project named (modular production method using the LIGA process) MODULIGA has the goal to link together the activities of the German LIGA centers Forschungszentrum Karlsruhe / Institut fur Mikrostrukturtechnik, Karlsruhe (FZK/IMT), Institut fur Mikrotechnik, Mainz (IMM) and Berliner Elektronenspeicherring-Gesellschaft fur Synchrotronstrahlung, Berlin (BESSY). LIGA process steps will be standardized and interface specifications will be defined to establish a modular production method. Interface specifications are defined for masks, substrate and resist, exposure technology, development and finally electroplating. The standards are defined by testing criteria. The challenges and the current status of standardization will be described.

Both X-ray lithography beamlines at BESSY can be operated in three different modes: one coming from a dipole (1.3 T) is used for standard exposures for patterning PMMA and SU-8, while the other beamline, coming from a straight section of the storage ring, can be operated in soft wavelength mode (0.4 T) or alternatively in wave length shifter mode (4T). Using the soft wave length mode, copying processes for X-ray mask can be carried, while the very hard radiation generated in the wave length shifter (WLS) modes best for patterning ultra thick PMMA layers up to several mm in thickness. In WLS mode the higher magnetic field of 4T is shifting the critical photon energy to 7.7 keV compared to a standard dipole magnet with 2.5 keV. The lateral intensity homogeneity of this beamline is very high. Tests for using the WLS mode for ultra deep X-ray lithography (UDXRL) were performed and delivered very good results. PMMA layers of up to 4 mm in thickness were patterned successfully. Similar patterning methods to fabricate high aspect ratio micro parts were reported in literature.

Fluoroalkylsilanes (FAS) prove to be an interesting water-repellent coating for the recently discussed “superhydrophobic surfaces”. The FAS investigated here form a self-assembled monolayer when brought into contact with a surface. They arrange at a high degree of orientation with their molecular axis perpendicular to the substrate surface. The film stability and the film thickness were observed using X-ray photoelectron spectroscopy. The orientation of the FAS molecules was investigated with polarization-dependent X-ray absorption near edge spectroscopy (XANES). Furthermore using density functional theory the molecular structure was calculated in order to aid in the interpretation of the polarization dependence of the XANES spectrum at F K-edge.