Positively charged silver colloid and negatively gold colloid were prepared in aqueous solution for surface-enhanced Raman scattering (SERS) by the chemical reduction of metallic ions in aqueous solution with sodium borohydride solution in ice-cooled condition, respectively. SERS from glycine molecules in above mentioned colloidal systems were recorded respectively and compared with each other. The results show that the mixture of silver and gold colloids could form aggregation different from that of single silver colloid and gold colloid and bring about the favorable effect on SERS behavior for adsorbed glycine.
In this paper, we propose a new scheme to generate a dark hollow-beam, which includes dark hollow-beam optical pipe and hollow-beam optical dipole trap, through using a system composed of a four steps phase plate and a spherical lens. This kind of light beam can be used to focus, guide and trap the cold atom. We also calculate the intensity distributing and characteristic parameters of a dark hollow-beam and the optical dipole potential which manipulate the cold atoms of 85Rb. At last, we analyze and demonstrate the experimental feasibility of the scheme.