A new method for synthesizing broadband antireflective (AR) surfaces at microwave and millimeter wave frequencies is demonstrated. The AR surface, we call an inverse motheye, was formed by machining a multi-layer grating of subwavelength circular holes into a non-absorptive dielectric. This created low reflected energies ( 30 dB) over reasonably large bandwidths and incidence angles. An optimization algorithm, based on a direct pattern search, integrated with a rigorous electromagnetic model was used to design the grating geometries. Experimental results are provided at Ka-band demonstrating the validity of the method.

The chemistry of a series of ansa-bridged ethylene-bis(hexamethylindenyl)zirconium and hafnium complexes has been explored. Treatment of EBI*Li 2 3 THF 0.38 with MCl 4 3 THF 2 (M = Zr, Hf) gives rac-EBI*MCl 2 (rac-2, rac-3) and meso-EBI*MCl 2 (meso-2, meso-3) (M=Zr and Hf), respectively. The rac-and meso-isomers can be separated by fractional crystallization. meso-EBI*ZrMe 2 (meso-4) can be prepared by alkylation of meso-2 with MeLi 3 LiBr. The molecular structures of racand meso-2 and racand meso-3 have been determined by single-crystal X-ray crystallography. A comprehensive structural comparison between these compounds and related ansa metallocenes has been carried out. racand meso-2 and racand meso-3 in the presence of modified methylaluminoxane (MMAO) are very active catalyst precursors for the polymerization of ethene to give high-density polyethene (HDPE) with molecular weights (M w ) in the range 100 000-220 000 and polydispersities (M w /M n ) of ca. 2.6. The activities of both catalyst precursors racand meso-2 are some of the highest reported in the literature, at 61 800 and 38 200 kg PE /mol met/h/bar, respectively.

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