In the past decade

preparation of nanoparticles whose sizes and size distribution can be well controlled has become an important subject in materials science fields. Many methods have been developed in preparation of semiconductor nanoparticles

such as Langmuir-Blodgett (LB) films

colloid-chemical

electrochemical

electrophoresis

thermolysis of organometallic compounds in solution

template and self-assembled monolayers etc. The self-assembled monolayer was reported by Sagtiv in 1983. Hereafter the method has attracted wide interesting due to its simple operation

easy preparation

and no need of complex instruments

but it meets great difficulties to obtain a desirable size distribution.A new method for preparation of nearly monodisperse CdS nanoparticles by self-assembled monolayers of mercaptoacetic acid and oxalic acid is reported. The mercaptoacetic acid plays an important role in the formation of the CdS nanoparticles. The preparation procedures were shown in Fig. 1. There include three major steps:First

preparing of self-assembled monolayers of mercaptoacetic acid and oxalic acid on aluminum substrate; Second

immersing the substrate into solution containing Cd

2+

to exchange ions; Third

Cd

2+

reaction with H

2

S gas to form CdS nanoparticles. In the formation process of the nanoparticles

CdS molecular formed at mercaptoacetic acid will play a role of nuclear center. The CdS nanoparticles were characterized by SEM

XRD

XPS and PL

respectively. SEM image indicates that the average size is about 45nm

which is well agreement with XRD result. Room temperature PL spectrum shows that CdS has a wide emission band in the range from 500 to 800nm about and the emission peak is at 675nm

which is attributed to surface defects.