研究目的
Investigating the buildup of strain in InP quantum dots with the addition of shells of ZnSe and ZnS, and understanding the influence of material stiffness on the strain.
研究成果
The study shows that the lattice mismatch between InP and ZnSe or ZnS leads to compressive strain in the InP core and tensile strain in the shell material. The material stiffness, represented by the Young’s modulus, is an additional parameter to consider when optimizing core/shell QDs for strain. ZnS, with a higher Young’s modulus, requires less material to develop stress on the InP lattice at the interface compared to ZnSe.
研究不足
The limited element contrast in TEM does not permit to differentiate between core and shell. The assignment of the ZnS-related strain values is less accurate than for the ZnSe shells due to the less robust fit of the fundamental Raman band with three Lorentzian functions.
1：Experimental Design and Method Selection:
Raman spectroscopy was used to investigate the strain in InP quantum dots with ZnSe and ZnS shells. The method selection was based on its nondestructive nature and sensitivity to strain.
2：Sample Selection and Data Sources:
InP QDs with 3.2 nm diameter were used as cores. ZnSe shells with 2, 5, 9, and 13 monolayers and ZnS shells with 1, 2, and 3 monolayers were synthesized.
3：2 nm diameter were used as cores. ZnSe shells with 2, 5, 9, and 13 monolayers and ZnS shells with 1, 2, and 3 monolayers were synthesized.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: JEOL 2200 FS microscope for TEM images, Perkin Elmer Lambda 950 spectrometer for absorption spectra, 514 nm ArKr ion laser for excitation, HORIBA LabRAM HR Raman microscope equipped with a 1800 grooves/mm grating and a Peltier-cooled CCD for acquiring Raman spectra.
4：Experimental Procedures and Operational Workflow:
QD solutions were drop-casted on silicon wafers. Raman spectra were recorded in a confocal backscattering geometry. The laser power was kept at a few hundred microwatts to avoid sample heating or destruction.
5：Data Analysis Methods:
The widths and center frequencies of the LO bands were determined by fitting Lorentzian functions to the spectra. The strain was evaluated using the frequency shifts obtained from the fits.
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