Free-standing, stable, single-sized, and highly pure ZnS nanosize particles or quantum dots are synthesized using a chemical route. The dimension of the quantum dots as estimated from x-ray diffraction was about 7 and 15 A. The optical band gap for these particles was 5.2 and 4.8 eV, respectively, as compared with the bulk energy gap of 3.8 eV. These results are compared wit.h the elfective mass approximation. The observations indicate that only particular-sized stable particles can be synthesized which should have minimum energy coniiguration. X-ray photoelectron spectroscopy was utilized for examining stoichiometry and purity of the sample.
ABSTRACT:The effect of rate of mass transfer on the surface morphology of electrochemically deposited polyaniline films was studied using scanning electron microscopy (SEM). The rate of mass transfer was controlled by varying the sheet resistance of electrode and the monomer concentration. Both these parameters are found to affect the deposition process and the surface morphology to a considerable extent. The polyaniline film deposited using 0.1 M monomer concentration on electrode with 50 0/0 sheet resistance shows a granular structure joined together with fine fibrils. Increase in the monomer concentration and decrease in the sheet resistance of the electrode lead to the enhancement in the growth of the polymer film as revealed from the current time transient measurements. The formation of fibres with different shapes such as rope-like, curved, cyclone-like, petal-like, wavy, wing-like, and criss-cross linking depends on the growth conditions of films. The sheet resistance of electrode mainly determines the number density of these fibres, whereas, the patterning is governed by the monomer concentration.KEY WORDS Polyaniline / Electrochemical Deposition / Morphology / Scanning Electron Microscopy (SEM) / Polyaniline has turned out to be a very promising electroconductive polymeric material because of its ease in preparation as well as good environmental stability. Attempts are being made to prepare thin films of this material having good thermal, mechanical and electrical properties so as to use these films for various applications as in electrochromic devices, batteries, smart windows etc. 1 • 2 For such kind of applications it is important that the surface of the film be quite smooth. Therefore, it becomes necessary to study the morphological properties of films deposited under various experimental conditions. This would help in establishing the optimum conditions for obtaining good quality films. Limited work in this regard have been published. 3 -5 deposition of poly(o-anisidine) films, while the monomer concentration determines the extent of formation of variable oxidation states of polymer. 6 The present study was undertaken to examine the effect of rate of mass transfer on the morphological properties by varying sheet resistance of electrode and monomer concentration on the electrochemically deposited polyaniline films using SEM technique.We have already reported that the sheet resistance of the electrode con trolls the rate of EXPERIMENT ALAll the chemicals used were of analytical reagent grade. The aqueous solutions were prepared using double distilled water. Transparent Sn0 2 : F thin films having coated on corning 7059 glass substrates were used as electrodes. Electrodes with three different sheet resistances* 1 as 50, 20 and 100/D (referred * 1 The sheet resistance, p,(0/0) is defined asp, =p/t where pis the reciprocal of conductivity (0cm) and tis the thickness of, film (cm) (cf,
Electrochemically deposited poly(o-anisidine) films exhibit a transition from insulating pernigraniline to conducting emeraldine salt phase by decreasing the pH of solution from 4.13 to -0.21 as observed from the optical spectra. A further decrease in pH does not affect the polymerization process. The sheet resistance of the substrate also has a remarkable influence in terms of rate and selectivity in the deposition of a particular phase. Morphological investigations indicate a change from a granular to a fibrillar type pattern with decrease in pH from 4.13 to -0.55. The substrate resistance and pH of solution are responsible for the voltammetric features. The polymerization mechanism mainly involves -NH,+ cationic coupling through preceeding chemical reactions. Thermograms exhibit a three-step decomposition pattern with large differences in the weight loss of individual steps. The final decomposition temperature of polymer varies with the pH of electrolyte solution, indicating the formation of different types of species during deposition.
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