ZnO and Zn 1-x Cd x O nanocrystallites obtained by oxidation of precursor Langmuir–Blodgett multilayers Sukhvinder Singh a , R.S. Srinivasa b , S.S. Talwar a , S.S. Major a, ⁎ a Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076, India b Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai-400076, India Abstract ZnO and Zn 1-x Cd x O nanocrystallites were prepared by oxidation of zinc arachidate–arachidic acid and zinc arachidate–cadmium arachidate– arachidic acid LB multilayers, respectively. The metal content of the multilayers was controlled by manipulation of subphase composition and pH. Precursor multilayers were oxidized in the temperature range of 400 °C–700 °C. The formation of ZnO and Zn 1-x Cd x O was confirmed by UV– Visible spectroscopy. Uniformly distributed, isolated and nearly mono-dispersed nanocrystallites of ZnO (11±3 nm) and Zn 1-x Cd x O (18 ± 6 nm) were obtained. Keywords: ZnO; Zn 1-x Cd x O; Nanocrystallites; Langmuir–Blodgett 1. Introduction Zinc oxide, a wide band gap semiconductor is an attractive material for a variety of applications [1]. There is a growing interest in ZnO nanostructures owing to expected improvements in room temperature lasing due to quantum size effects [2]. Formation of ZnO has been reported in low dimensional forms, showing interesting size dependent effects [3]. Alloying ZnO with CdO allows the engineering of its band gap towards the design of novel optoelectronic devices [4]. Langmuir–Blodgett (LB) multilayers of zinc arachidate (ZnA) and cadmium arachidate (CdA) have been used to form zinc oxide and cadmium oxide films by oxidation of the corresponding precursor multilayers [5–7]. In the present work, the oxidation of ZnA and mixed ZnA–CdA LB multilayers has been carried out to form nanocrystallites of ZnO and Zn 1-x Cd x O on quartz and freshly cleaved mica substrates. 2. Experimental details ZnA and ZnA–CdA mixed multilayers were prepared using a KSV 3000 LB instrument. A solution of arachidic acid (AA) in chloroform (1 mg/ml) was spread on subphase containing ZnCl 2 and CdCl 2 in varying proportions and a total concentra- tion of 5×10 - 4 M in de-ionized and ultra filtered water. The subphase temperature was maintained at 10 ± 1 °C and subphase pH was varied in the range 5.0–6.2. Quartz, CaF 2 and freshly cleaved mica substrates were used. The as-deposited multilayers were heat treated for 30 minutes in a stream of oxygen at atmospheric pressure in the temperature range of 400–700 °C. FTIR spectra were obtained with a Perkin Elmer Spectrum1 instrument and UV–Visible spectra with a Perkin Elmer Lambda 950 spectrophotometer. Atomic force microscopy (AFM) studies were carried out using a Nanoscope IV Multimode SPM. 3. Results and discussion The zinc content of ZnA multilayers was varied by changing the subphase pH at which the multilayers were transferred and was monitored by studying their FTIR spectra. Typical results are shown in Fig. 1(a). The spectrum of the multilayer transferred at a subphase pH of 6.2 shows a strong absorption at ∼ 1540 cm - 1 , assigned to the asymmetric stretching of COO - [8]. The presence of this band and the absence of C_O stretching band of unionized carboxylic acid which is expected at ∼ 1700 cm - 1 , confirm that this multilayer consists of pure