Preparation and structure of quantum-sized cadmium sulﬁde grown in amphiphilic oligomer Langmuir–Blodgett ﬁlms Lin Song Li, Lianhua Qu, Ran Lu, Xiaogang Peng 1 , Yingying Zhao, Tie Jin Li* Department of Chemistry, Jilin University, Changchun 130023, People’s Republic of China Abstract An amphiphilic oligomer, polymaleic acid with octadecanol ester (PMAO), with ratios of 2:1, 3.7:1 and 6:1 between the carboxylic groups and the hydrocarbon chains, was synthesized and has been used as a matrix to form and grow quantum dot-sized CdS particles. The formation of quantum-sized CdS particles during exposure of Langmuir–Blodgett (LB) ﬁlms of CdPMAO to hydrogen sulﬁde has been studied using Fourier transform infrared spectroscopy and UV-vis absorption spectra. This showed that hydrogen bonding of the PMAO molecules were replaced by the metal ion (Cd 2 + ) bridges to form the bridging complex structures before the reaction with H 2 S. The intensities of the asymmetric n a (COO - ) and symmetric n s (COO - ) stretching modes were reduced after the reaction. But the presence of the asymmetric n a (COO - ) and symmetric n s (COO - ) stretching mode in spectra implied that not all the CdPMAO oligomers in the ﬁlm were converted to PMAO after exposure to H 2 S gas. The result from the UV-vis absorption spectra indicated that the CdS within PMAO LB ﬁlms showed a larger blue shift of the optical absorption edge with the decrease of the ratio between the carboxylic groups and the hydrocarbon chains. Moreover, it could be deduced that the size of the aggregate of the sulﬁdes within PMAO LB ﬁlms was smaller than that formed in stearic acid LB ﬁlms.  1998 Elsevier Science S.A. All rights reserved Keywords: Langmuir–Blodgett technique; CdS nanoparticle; Oligomer; Inorganic–organic alternating ﬁlm 1. Introduction Progress in the preparation, characterization, and utiliza- tion of nanostructured materials has been spectacular [1–3]. For conﬁnement within a low dimension, the Langmuir– Blodgett (LB) technique allows one to sequentially deposit a single layer of semiconductor nanoparticles within an insulating lattice. Indeed, size-quantized CdS, PbS, CdSe and Cdl 2 particles have been generated in situ by the expo- sure of the appropriate metal carboxylate Y-type LB ﬁlms to H 2 S (or H 2 Se and HI, respectively) [4–8]. Polymers as ver- satile materials have also been introduced in the research on LB ﬁlms. The most common method of producing quantum- state (Q-state) particles in LB ﬁlms involves the use of long- chain carboxylic acids. By using polymers instead of simple acids, improvements in the thermal and mechanical stability of the matrix can be achieved. A kind of LB matrix (polymaleic acid with octadecanol ester, i.e. PMAO) which can be used for the ordered synth- esis and ordered assembly of the inorganic nanoparticles and the results on PMAO with X:Y = 2:1, where X is the number of carboxyl groups and Y is the number of hydro- carbon chains, was reported previously [9]. From the mole- cular formula, it can be seen that the ratio of carboxylic groups to hydrocarbon chains is always larger than 1. We have obtained several kinds of PMAO with different X:Y ratios (2:1, 3.7:1 and 6:1). In this paper, we investigate the CdS within PMAO LB ﬁlms with different X:Y ratios in detail. The LB ﬁlms of PMAO salts with different ratios between carboxylic groups and hydrocarbon chains were deposited onto the substrates. The LB ﬁlms of the CdPMAO were reacted with H 2 S at reduced pressure, quantum-sized cadmium sulﬁde particles were grown in the hydrophilic interface of LB ﬁlms and Thin Solid Films 327–329 (1998) 408–411 0040-6090/98/$ - see front matter  1998 Elsevier Science S.A. All rights reserved PII S0040-6090(98)00673-7 * Corresponding author. Tel.: +86 431 8922331; ext., 243; fax: +86 431 8923907; e-mail: tjli@mail.edu.cn 1 Present address: Department of Chemistry, University of California, Berkeley, CA 94720, USA.