Hydrothermal Synthesis and Characterization of Cadmium Selenide Nanocrystals.

Cadmium Selenide;Quantum Dot;Hydrothermal Synthesis;High-temperature Water;Nanocrystal;Chemical Engineering;Engineering;Chemical Engineering

Williams, Juandria V.Thompson, Jr., Levi T. ;

University of Michigan

关键词: Cadmium Selenide;    Quantum Dot;    Hydrothermal Synthesis;    High-temperature Water;    Nanocrystal;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/58451/jvw_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Cadmium Selenide (CdSe), a type of semiconductor nanocrystal, is of interest because its optical properties can be tuned by varying its size, thus yielding a material that has potential application in electronics and biology.Conventional preparations of CdSe primarily use organic solvents.We explored the use of high-temperature liquid water (HTW) as an alternative reaction medium because of its environmental benignity and solvent properties which could potentially mimic the function of the conventional organic-based mediums.The base case experimental conditions for the feasibility study (non-isothermal conditions) produced nanocrystals that exhibited quantum confinement behavior. The quantum yield (QY) for the base case nanocrystals was 1.5%, but was easily increased to ~7% by adding a cadmium sulfide (CdS) shell.The nanocrystal mean size increased with increasing reaction time, temperature, stabilizer concentration and Cd:Se molar ratio.The mean size decreased with increasing pH. Under isothermal synthesis conditions, nanocrystals smaller than those produced in the feasibility study were obtained when using the same process parameters..The mean nanocrystal size did not increase with reaction temperature, but did increase with time and stabilizer concentration.The mean size also decreased with increasing pH and Cd:Se molar ratio.An increase in the Cd:Se molar ratio, pH and Cd:stabilizer molar ratio increased the QY.The reaction temperature and time had no affect on QY.We used red-shift rates and reaction completion times to determine an activation energy Q for the CdSe growth in HTW. We calculated Q = 0.48 ± 0.06 eV/molecule from the red-shift rate method and Q = 0.42 ± 0.08 eV/molecule using reaction completion times.Compared with organic-based systems, these values are lower, possibly due to the less bulky cadmium complex used.The kinetics analysis shows that the synthesis in HTW could be both reaction- and diffusion-controlled.This work indicates that HTW is a viable alternative reaction medium.Nanocrystals can be grown that exhibit quantum confinement, and certain process parameters have a profound effect on the nanocrystal’s quality.Further studies can identify the optimum process conditions to produce the nanocrystal with the highest quality.