Thickness-Controlled Synthesis of Colloidal PbS Nanosheets and Their Thickness-Dependent Energy Gaps (original) (raw)
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Correlation between structural and optical properties of PbS nanocrystals
Journal of Crystal Growth, 1996
PbS semiconductor nanocrystals have been synthesized in order to study the modifications of their optical properties in relation to their size. The synthesis has been carried out by using the techniques of colloid chemistry. A fast evolution of the optical absorption spectrum has been noticed following synthesis. Immediately after the synthesis reaction, the samples exhibit a structured absorption spectrum with three well-defined excitonic peaks. Within a few minutes, the peaks progressively disappear and a structureless spectrum occurs. A procedore of stabilization of the colloids has been set up in order to allow the study of the structural and optical properties at different stages of their evolution. Fiber-like nanocrystals (2.5 x 25 nm) and platelets have been found in the early stages of the synthesis and nearly cubic nanocrystals (13 nm) are found in later stages of evolution.
Preparation and optical studies of PbS nanoparticles
In the present report formation of nano-sized PbS in MA/octene-1 copolymer matrix at 80 C temperature is being reported. A size and distribution of particles were observed in AFM results and the images are correlated with the results on X-ray diffraction measurements. The structure and phase of the PbS nanoparticles were characterized by X-ray diffraction (XRD). XRD studies reveal that as-synthesized PbS nanoparticles are in single phase cubic structure and the grain size have been calculated 10–15 nmfrom XRD results. The size distribution was further supported by UV/Vis absorption and photoluminescence (PL) spectroscopy of the colloid nanoparticles. The obtained nanocomposites show an emission peak at 418 nm.
Journal of Physical Chemistry B, 2006
The internal structure of PbSe nanocrystals was deduced using synchrotron X-ray photoemission spectroscopy for three different sizes of nanocrystals. The photoemission data revealed the layered structure of PbSe nanocrystals with the crystalline PbSe core surrounded by a nonstoichiometric Pb 1-x Se shell, finally passivated by a capping agent in the outermost layer. A detailed analysis of the experimental data yielded quantitative information on the thickness of three different layers, which is unavailable through any other technique; moreover, the overall sizes of the nanocrystals probed by transmission electron microscopy were in agreement with the corresponding quantity obtained in the present experiment. The present results provide a plausible explanation for the strong variation in the photoluminescence intensity with size observed for these nanocrystals.
Colloidal PbS Nanosheets with Tunable Energy Gaps
MRS Proceedings, 2015
ABSTRACTUltrathin colloidal PbS nanosheets are synthesized using organometallic precursors with chloroalkane cosolvents, resulting in tunable thicknesses ranging from 1.2 nm to 4.6 nm. We report the first thickness-dependent photoluminescence spectra from lead-salt nanosheets. The one-dimensional confinement energy of these quasi-two-dimensional nanosheets is found to be proportional to1/Linstead of1/L2(Lis the thickness of the nanosheet), which is consistent with results calculated using density functional theory as well as tight-binding theory.
Synthesis and Characterization of Nanostructured PbS Thin film
In the present work, PbS Nanocrystals with rod shaped structure have been successfully prepared by chemical bath deposition method. The structure was determined by X-ray diffraction studies. The XRD data revealed the formation of cubic phase of PbS with the preferential orientation (2 0 0). The average crystallite size was found to be 7.82 nm. SEM images confirm the formation of nanorods of PbS. The optical properties were studied by recording absorption spectra in the wavelength range of 200-900 nm. The optical bandgap and refractive index was found to be 1.47eV and 2.97, respectively. The electrical resistance was measured using four probe method and it was found to be 0.67MΩ.
Synthesis and characterization of PbSe and PbSe/PbS core–shell colloidal nanocrystals
Journal of Crystal Growth, 2002
A new colloidal procedure, for the synthesis of PbSe and PbSe/PbS core-shell semiconductor nanocrystals (NCs), is reported. The synthesis includes the reaction between tributyl-phosphine selenium and lead 2-ethyl-hexanoate, under inert gas at room temperature. High-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectroscopy (EDS), absorption and photoluminescence (PL) spectroscopy were used to characterize the samples. The EDS and HRTEM confirmed the existence of rock-salt cubic structures of the PbSe. Furthermore, the HRTEM showed the formation of PbSe/PbS core-shell structures, with epitaxial shell layer with thickness varying between 1 and 4 ML. The absorption spectra of these materials exhibited distinct transitions, related to the e1-h1, e2-h2 and e2-h3 and e2-h1 transitions. These bands are blue shifted with decrease in the NCs diameter. However, the e1-h1 is slightly red shifted with increase in the PbS shell thickness. The last effect can be due to an electronic mixing of the PbSe and PbS conduction states. The PL measurements showed a substantial increase of the exciton emission in the core-shell structures, arising by an efficient chemical passivation of the PbSe core. r