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Unlock your guides8.1 Synthesis and characterization of quantum dots
3 min read•august 9, 2024
Quantum dots are tiny semiconductor crystals with unique optical and electronic properties. This section covers how to make them using and , as well as methods to control their size and modify their surfaces.
To fully understand quantum dots, we need to know how to analyze them. We'll look at techniques to study their structure, composition, and optical properties, including electron microscopy, X-ray methods, and various spectroscopy approaches.
Synthesis Methods
Colloidal Synthesis and Core-Shell Structures
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Top images from around the web for Colloidal Synthesis and Core-Shell Structures
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Heat-induced transformation of CdSe–CdS–ZnS core–multishell quantum dots by Zn diffusion into ... View original
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- Colloidal synthesis involves creating quantum dots in solution
- Precursor materials dissolved in solvents
- Heated to high temperatures (200-350°C) to initiate nucleation and growth
- Surfactants added to control growth and prevent agglomeration
- Core-shell structures enhance quantum dot properties
- Core made of one semiconductor material (CdSe)
- Shell of another material grown around core (ZnS)
- Improves and stability
- Reduces surface defects and non-radiative recombination
- Size control achieved through reaction conditions
- Temperature affects growth rate
- Reaction time determines final size
- Precursor concentration influences nucleation and growth
- modifies quantum dot properties
- Ligand exchange replaces original surfactants
- Adds desired functional groups (carboxyl, amine, thiol)
- Enables biocompatibility or specific binding
Size Control and Surface Modification Techniques
- process influences size distribution
- Smaller particles dissolve and redeposit on larger ones
- Leads to narrower size distribution over time
- for narrow size distribution
- Rapid injection of precursors into hot solvent
- Creates burst of nucleation followed by controlled growth
- approach for larger quantum dots
- Small quantum dots used as seeds
- Additional precursors added for continued growth
- Surface modification techniques
- improves stability and reduces toxicity
- enhances water solubility
- attaches biomolecules (antibodies, peptides)
Characterization Techniques
Structural and Compositional Analysis
- visualizes quantum dot structure
- High-resolution imaging of individual particles
- Measures size distribution and shape
- Lattice fringes reveal crystalline structure
- for elemental mapping
- Z-contrast imaging differentiates core and shell
- analyzes composition
- determines crystal structure
- Identifies crystalline phases present
- Estimates average crystallite size using Scherrer equation
- Reveals lattice parameters and strain
- for surface analysis
- Provides information on elemental composition
- Reveals chemical states of surface atoms
- Helps characterize surface
Optical and Electronic Property Measurements
- assesses optical properties
- Measures emission spectrum of quantum dots
- Reveals and size distribution
- determines absorption characteristics
- for carrier dynamics
- Measures fluorescence lifetime
- Provides information on radiative and non-radiative processes
- Quantum yield quantifies emission efficiency
- Ratio of emitted to absorbed photons
- using integrating sphere
- comparing to known standards
- for size and concentration
- Measures optical density across wavelengths
- First excitonic peak position correlates with size
- Beer-Lambert law used to determine concentration
- Electrochemistry for electronic structure
- Cyclic voltammetry reveals
- probes charge transfer processes
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