AFM and X-ray studies of films formed by thermal evaporation and by the LB technique

Abstract

The object of this research was to compare multilayers formed by thermal evaporation and the LB technique and to investigate their structure by atomic force microscopy (AFM) and X-ray diffraction. Films of a wide range of amphiphilic materials were formed by thermal evaporation in vacuo onto substrates maintained at temperatures chosen to maximise order as evidenced by low angle X-ray diffraction. Where it was possible multilayers of these material were also formed by the Langmuir-Blodgett (LB) technique. The X-ray diffraction patterns obtained from films formed in the two different ways are very similar. Studies of these films made by AFM show that, in most cases, there is substantial surface structure and terracing in the case of films formed by both techniques. We have made particular studies of films of cadmium stearate. Multilayers of this material made by thermal evaporation appear to consist of platelets having a Y-structure whose planes are parallel to the substrate. LB films of this material show terracing but also flat areas. Even these areas contain circular defects less than a micron in diameter which tend to multiply and grow with time. The best thermally evaporated films we obtained were formed from N-methylstearamide. These films had relatively smooth surfaces showing only small steps and had a good Y-layer structure as evidenced by X-ray diffraction.