a
Department of Solar Energy and Environmental Physics, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel
E-mail: jeff@bgu.ac.il
;
Fax: +972-8-659-6921
b
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel