Ž . Materials Science and Engineering C 8–9 1999 171–177 www.elsevier.comrlocatermsec Formation of CdS nanoclusters within LB films of calixarene derivatives and study of their size-quantization A.V. Nabok a, ) , A.K. Ray a , A.K. Hassan a , J.M. Titchmarsh b , F. Davis c , T. Richardson d , A. Starovoitov e , S. Bayliss e a Sheffield Hallam UniÕersity, Physical Electronics and Fibre Optics Research Laboratories, School of Engineering, Pond Street, Sheffield, S1 1WB, UK b Sheffield Hallam UniÕersity, Material Research Institute, Sheffield, UK c Gillette UKRDL, Reading, UK d The UniÕersity of Sheffield, Department of Physics, Sheffield, UK e De Montfort UniÕersity, Solid State Research Centre, Leicester, UK Abstract Cadmium sulphide nanoclusters formed in Langmuir–Blodgett films of various calixarene derivatives were studied by means of UV–visible spectroscopy, AFM, TEM and electron diffraction. It has been shown that calixarene cavitands of different size yield a similar kind of CdS nanoclusters as characterised by the first exciton transition near 3.2 eV. In contrast to that, CdS clusters formed within LB films of stearic acid or formaldehyder2,6-dihydroxybenzoic acid copolymer have much lower exciton energy of 2.7 eV, corresponding to greater CdS clusters. The value of 2 nm and 4 nm in diameter were obtained, respectively, for CdS clusters in calixarene and stearic acid LB films by using Ramakhrishna’s results of direct calculations of the band structure. AFM and TEM results confirm the difference in size of those CdS clusters. Electron diffraction data show that CdS nanoclusters have zinc blende structure rather than wurtzite, and the lattice parameters of 0.583 "0.009 nm and 0.567 "0.012 nm were obtained for the clusters formed within stearic acid and calixarene matrices, respectively. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Semiconductor nanoclusters; CdS; Size-quantization; AFM; TEM; Electron diffraction 1. Introduction Recent achievements of colloid chemistry in producing nanostructured II–VI and III–V semiconductor materials wx 1 provide a real alternative for the costly MBE technol- ogy. Moreover, quantum phenomena, such as single-elec- w x tron tunnelling 2,3 , can be observed at room temperature in semiconductor nanoclusters produced by ‘‘wet technol- ogy’’. Production of metal sulphide nanoclusters within LB films of fatty acid salts by their reduction with H S 2 wx gas 4 has recently been extended by using calixarene LB wx film as a matrix material 5 . It has been suggested that the presence of calixarenes restricts segregation of CdS by capturing some of CdS molecules within molecular cavi- ties. As a result, CdS nanoparticles with the size of 1.5 " 0.3 nm, which is the smallest that has ever been reported, were formed, and well-resolved electron transi- tions between levels of size-quantization were observed ) Corresponding author. Tel.: q44-114-225-3512; fax: q44-114-225- 3433 w x 5,6 . However, the mechanism of the formation of CdS clusters within calixarene matrix is still unknown. For instance, the formation of CdS clusters does not affect the layer-by-layer structure of calixarene LB films, as has been shown by both the low angle X-ray diffraction and ellip- wx sometry 6 . This fact can be explained either by the formation of very small 3D CdS clusters comparable in size with the calixarene cavity, or by the formation of 2D crystals within each calixarene bilayer. From this point of view, the study of LB films of different calixarene derivatives, possessing inner cavities of various sizes, can aid our understanding of the process of formation of CdS nanoclusters. Also, direct observation of CdS clusters using techniques such as STM and AFM, Ž . or transmission electron microscopy TEM is necessary. Since both the size and crystallography of the semiconduc- tor nanoclusters have a dramatic effect on their exciton w x spectra 7,8 , the results of TEM and electron diffraction are particularly interesting. Thus, the main objectives of the present work are to study in more detail the formation of CdS nanoclusters in LB films of various calixarene 0928-4931r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0928-4931 99 00012-0