Langmuir and langmuir blodgett studies of cadmium selenide (CdSe) quantum dots

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Chemistry, Turkey

Approval Date: 2017




Various methods can be used to prepare layered thin films with the sensitivity of molecular level. Langmuir Blodgett method, draws attraction since its discovery both in thin film production and in transferring the films produced onto a solid surface. Langmuir films have the application areas of biosensors, coating studies, electronic molecular and optoelectronic devices and semi-permeable barriers. In this work, firstly the alignment of silver nanoparticles on air water interphase was planned. Therefore, to provide optimum conditions for LB film of silver nanoparticles we tried to obtain stable cetyltrimethylammonium bromide (CTAB) films on deionized water subphase. However, at low concentration of CTAB (0.07 mg/mL) we could not get stable monolayers. To increase the stability of monolayer of CTAB, a new technique namely "gluing technique" was used and its effect on the stability of CTAB monolayers were investigated by using Poly(4-styrenesulfonate) (PSS) as gluing reagent. As a result of both surface pressure versus mean molecular area (π – MMA) isotherms and hysteresis experiments it was concluded that more stable monolayers of CTAB were obtained at low concentration with gluing technique. However, in the continuation part of the study; hoping that the fluorescence emission of the nanoparticles that were arranged on the surface can be seen by using hand-hold UV light, we decided to prepare LB thin films of Cadmium Selenide (CdSe) quantum dots instead of silver nanoparticles. Their synthesis and characterization were done by thermal decomposition method and fluorescence spectrometry respectively. The emission intensity of the QDs, at the excitation wavelength of 400 nm, was observed at 558 nm. The morphological characterization of quantum dots was done with Transmission Electron Microscopy (TEM). The monolayer formation of CdSe quantum dots and their mixture with stearic acid (SA) were achieved on water air sub-phase. During these studies, parameters corresponding compression rate and volume of CdSe quantum dots that spread onto sub-phase were optimized. Addition of SA as a spacer was improved spreading property of QDs and consequently facilitated the stable monolayer formation. Langmuir monolayer of CdSe quantum dots deposited on to the glass substrates and first characterization of these layers were done with Confocal Microscopy. In accordance of the information acquired with confocal microscopy, the selection of thin films of quantum dots that would be characterized by TEM was selected. TEM patterns have clearly shown that the homogeneous and closely arranged CdSe quantum dots films were obtained on the entire surface of the substrate.