The continuous model of liquid crystals and the corresponding symmetry are discussed, from which the expression of the density of free energy is deducted. Based on the transformation of vector field, four typical important ways of distribution of the vector field are discussed and the stable conditions of the distribution are induced.
We have found that the silver colloids, which usually used as SERS active substrate, are inclined to aggregation on air water interface and forming a two dimension silver particle films. The formed silver particle films exhibit much higher surface Raman enhancement factor than silver colloids, and the power used on silver particle films is only about 1% of that on silver colloids. Combining with resonance Raman enhancement technique, we realize single molecular Raman detection under the common conditions by using this silver particle films as SERS active substrate.
