Manisree Majumder

Synthesis of thiol capped CdS nanocrystallites using microwave irradiation and studies on their steady state and time resolved photoluminescence.

Synthesis of cadmium sulfide (CdS) nanocrystallites has been performed through the microwave (MW) assisted reaction of cadmium acetate with thiourea in N,N-dimethylformamide (DMF) in the presence of two capping agents, 1-butanethiol and 2-mercaptoethanol. Attempts were made to control the size and size distribution of the thiol capped CdS nanocrystallites by controlling the number of MW irradiations/exposures for a fixed time (duration). The prepared nanocrystallites have been characterized by UV-vis spectroscopy, FTIR, XRD, FESEM and TEM. The peak position of the absorption band of the 1-butanethiol caped CdS nanocrystals in DMF solution shifted towards longer wavelength with the increasing number of MW exposures indicating the growth of particle size. In contrast, the peak position of absorption band for the 2-mercaptoethanol capped CdS nanocrystals remained nearly at the same wavelength and only the intensity of the absorption band increased with the increasing number of MW exposures. The observed steady state photoluminescence (visible range) of the 1-butanethiol capped CdS nanocrystals in DMF solution shifted towards higher wavelength, showing a decrease in intensity, with the increase in the number of MW exposures. Whereas in the case of 2-mercaptoethanol capped CdS nanocrystals in DMF solution, the photoluminescence peak remained nearly at the same position showing a decrease in intensity with increase in the number of MW exposures. The interesting results on the size-dependent steady state and time resolved photoluminescence (PL) of the CdS nanocrystallites are discussed in the present article. Possible application of such studies in the area of biotechnology has been mentioned.

Electric field induced tunable bistable conductance switching and the memory effect of thiol capped CdS quantum dots embedded in poly(methyl methacrylate) thin films

Experimental results on conductivity switching and appearance of hysteresis in the current–voltage characteristics of thiol (benzyl mercaptan)-capped CdS quantum dots (QDs) embedded in a poly(methyl methacrylate) (PMMA) matrix are presented in this manuscript. The dependence of switching behavior has been studied under different conditions such as sample cell temperature, scan speed of voltage, illumination of light of various intensities, film thickness, size of thiol-capped CdS QDs etc. The voltage at which the conductivity switching occurs i.e. threshold voltage (Vth) appearing in the current–voltage characteristic curve, decreases with the increasing sample cell temperature and also with increasing intensity of photoexcitations but Vth increases with the increasing scan rate of voltage and size of thiol-capped CdS QDs. Between forward and reverse bias sweeps, the switching events exhibit hierarchy of hysteresis loops. The area within the hysteresis loops decreases with increasing sample cell temperature and ultimately disappear at higher temperatures. The switching events can be tuned by changing the external parameter (experimental conditions) such as sample cell temperature, scan speed of bias voltage, irradiation of light, size of thiol-capped CdS QDs etc. The switching mechanism and appearance of hysteresis have been attributed to an electric field-induced charge transfer from the polymer to the thiol-capped CdS QDs. The nanocomposites of PMMA and thiol-capped CdS nanocrystallites may be suitable for polymer based memory devices.

Silver Nanoparticles Dispersed in Poly(methyl methacrylate) Thin Films: Spectroscopic and Electrical Properties

Silver nanoparticles of different sizes were prepared following chemical route and using silver nitrate as starting material. The nanoparticles were dispersed in Poly(methyl methacrylate) (PMMA) matrix and thin films were prepared. The PMMA films with dispersed silver nanoparticles were characterized by UV‐Vis absorption spectroscopy and FESEM. The electrical measurements were carried out by using surface type cells. The absorption spectra of the films have shown plasmon peaks at different wavelengths with the variation in size of the silver nanoparticles. The film with dispersed silver nanoparticles showing plasmon peak at higher wavelength manifested increasing trend in dark current values with time at room temperature. On the contrary, the decreasing dark current values with time were observed in the case of the film showing plasmon peak at lower wavelength under similar measuring conditions. The photocurrent profile of the PMMA film with dispersed silver nanoparticles as a function of photoexcitation ...

Study of Quantum Yield and Photoluminescence of Thiol Capped CdS Nanocrystallites

For the preparation of thiol capped CdS nanocrystallites, the microwave (MW) assisted reaction of cadmium acetate with thiourea in N, N‐dimethylformamide (DMF) was controlled in the presence of two capping agents, 1‐butanethiol and 2‐mercaptoethanol. The peak position of the absorption band of the CdS nanocrystals in DMF solution shifted towards longer wavelength with increasing duration (by repeated exposure for a fixed time) of MW irradiation, for 1‐butanethiol caped CdS nanocrystals indicating growth of particle size. However, the peak position of absorption band remained nearly at the same wavelength and only the intensity of the absorption band increased with increasing duration of MW irradiation for the 2‐mercaptoethanol capped CdS nanocrystals. Photoluminescence (PL) of the CdS nanocrystals in solution with 1‐butanethiol as capping agent was observed to shift towards higher wavelength in the visible range of the spectrum showing a decrease in intensity with increase in the duration of exposure of M...