Preparation of size-controlled hexagonal CdS nanocrystallites and the characteristics of their surface structures

Hexagonal CdS nanocrystallites have been easily prepared by reacting Cd2+ and S2- (H2S or Na2S) in N,N-dimethylformamide (DMF) without adding any surface stabilizers. The mean diameter of the nanocrystallites can be rigorously controlled over the range 1.8-4.2 nm with keeping the hexagonal crystalline structure by varying the sulfur source (H2S and Na2S) and by regulating the preparation temperature. Use of Na2S as a sulfur source produces smaller CdS nanocrystallites than use of H2S. The size control and stability of CdS nanocrystallites are discussed in terms of the characteristics of the surface structures based on in situ Cd K-edge EXAFS analysis.