The Synthesis and Characterization of LiFeAs and NaFeAs

The newest homologous series of superconducting As-pnictides, LiFeAs (Li111) and NaFeAs (Na111) have been synthesized and investigated. Both crystallize with the layered tetragonal anti-PbFCl-type structure in P4/nmm space group. Polycrystalline samples and single-crystals of Li111 and Na111 display superconducting transitions at ~ 18 K and 12-25 K, respectively. No magnetic order has been found in either compound, although a weak magnetic background is clearly in evidence. The origin of the carriers and the stoichiometric compositions of Li111 and Na111 were explored.Comment: submitted for publication in Physica C special issue on Fe-pnictide

CVD copper thin film deposition using (α-methylstyrene)Cu(I)(hfac)

A new volatile liquid copper precursor, (α-methylstyrene)Cu(I)(hfac), has been synthesized. A green liquid solution of (α-methylstyrene)Cu(I)(hfac), stabilized with Cu(hfac)2 and α-methylstyrene, can be used for CVD copper thin film deposition. In contrast, pure yellow (α-methylstyrene)Cu(I)(hfac) failed in CVD processing because of poor stability in the delivery system. The structure of solid crystalline [(α-methylstyrene)Cu(I)(hfac)]2[Cu(hfac)2], collected from the concentrated green liquid precursor solution, was obtained by x-ray crystallography. In copper thin film deposition using the green liquid precursor, a two-step water introduction process has been proposed for the purposes of obtaining good adhesion on metal nitride coated substrates and low bulk resistivity. The film purity was analyzed by SIMS. The effects of various process conditions have been studied, from which the film deposition activation energy was calculated as 12.82 Kcal/mol for deposition temperatures lower than 180°C. The resistivity of the copper thin films was measured as 1.92µΩ-cm when deposited at 190-200°C. Good film conformality and gap filling has also been demonstrated using this new copper precursor