In this work is presented the investigation on the morphology cadmium selenide quantum dots (CdSe QD) crystals, growth on glass substrates by dip coating. Two different samples have used for the film formation: one with CdSe QD and the second one with CdSe QD covered with the tripeptide L-glutathione. Both samples were synthesized using the technique of water-in-oil microemulsion, and the Dioctyl sulfosuccinate sodium salt (AOT) was used as the surfactant. The film obtained by the first sample (CdSe QD without stabilizing agent) shows the better properties: the pattern of the film is more regular and the striations are well defined with a square shape; moreover it exhibits a powerful fluorescence emission.
Furthermore, the dip-coating was carried out at different speed to verify if the film formation follows the theoretical prediction. The height of each film obtained at a different rate (using the first sample) was measured, and the results were compared with the theory using the Landau-Levich equation. It was verified a full correspondence between the experimental data and theoretical model.
Table of Contents
AIM OF THE WORK
CHAPTER 1
INTRODUCTION
1.1 Quantum Dot
1.2 Quantum Dots Synthesis
1.3 Dip Coating
1.4 Application
1.4.1 Tissue Regeneration
1.4.2 QD Solar Cells
CHAPTER 2
EXPERIMENTAL PART
2.1 Materials
2.2 Preparation Methods
2.2.1 Synthesis Methods for CdSe qd
2.3 Coating Procedure
2.4 Characterization Techniques
2.4.1 Fluorescence Microscopy
2.4.2 Atomic Force Microscopy (AFM)
CHAPTER 3
RESULTS AND DISCUSSION
CHAPTER 4
SUMMARY AND CONCLUSIONS
Research Objectives and Core Topics
This thesis investigates the morphological characteristics and film formation processes of cadmium selenide (CdSe) quantum dot crystals on glass substrates using the dip-coating technique. The primary research goal is to compare the film properties of pure CdSe quantum dots with those stabilized by L-glutathione, while also evaluating whether the deposition process aligns with theoretical predictions derived from the Landau-Levich equation.
- Synthesis of colloidal CdSe quantum dots via water-in-oil microemulsion.
- Evaluation of the impact of the L-glutathione stabilizer on film morphology and fluorescence.
- Analysis of dip-coating parameters and their influence on film thickness and uniformity.
- Correlation of experimental findings with the Landau-Levich theoretical model.
- Characterization of crystal surface morphology using Fluorescence Microscopy and Atomic Force Microscopy (AFM).
Excerpt from the Thesis
1.1 Quantum Dot
When one of the dimensions of the semiconductor crystalline material becomes comparable with the size of the so-called exciton Bohr radius, there are the phenomena of quantum confinement, leading to the formation of discrete energy levels. The Bohr radius refers to the Bohr model that permits to calculate the radius of the electron orbit around the nucleus by the equation: r = 4πε0 n^2ħ^2/mZe^2.
The Coulomb force acting on the electron and the orbital angular momentum of the electron (to which have been applied the quantization condition) is considered in such model. The exciton is referred to the electrons and hole existing in a material which are subject to Coulomb interaction, and the optical nature of semiconductors can be understood by investigating the properties of the excitons. The distance between the electron and the hole within an exciton is called Bohr radius of the exciton, which typically in semiconductors is of few nanometers.
The electron motion (charge carrier) confined within the nanostructure can be described, in the first approximation, similar to the movement of a particle in the box through the resolution of the Schroedinger equation to it associated: -ħ^2/2m(∂^2ψ/∂x^2 + ∂^2ψ/∂y^2) = Eψ.
This equation is a time-independent bidimensional equation where ħ is the Planck´s constant ħ = h/2π, m is the mass of the particle, ψ is the wave function, x and y the dimension of “box” and E the total energy of the particle.
Chapter Summaries
AIM OF THE WORK: Defines the investigation of CdSe quantum dot morphology on glass substrates and the assessment of dip-coating as a method for controlled film formation.
CHAPTER 1: Provides a theoretical introduction to quantum dots, their synthesis via microemulsion, the physics of dip-coating, and their potential applications in fields like tissue engineering and solar cells.
CHAPTER 2: Details the materials used for the synthesis, the experimental setup for the double microemulsion process, and the technical specifications of the dip-coating and characterization equipment.
CHAPTER 3: Presents the results of the dip-coating experiments, comparing the morphology and fluorescence of different samples and validating these findings against the Landau-Levich theoretical predictions.
CHAPTER 4: Concludes the thesis by summarizing how deposition parameters and stabilizing agents influence film characteristics, confirming the viability of using the Landau-Levich equation for predictive film deposition.
Keywords
CdSe Quantum Dots, Dip Coating, Microemulsion, Landau-Levich Equation, Nanocrystals, Fluorescence Microscopy, Atomic Force Microscopy, Surface Morphology, Thin Films, L-glutathione, Quantum Confinement, Semiconductor, Photoluminescence, Crystal Growth, Sol-gel.
Frequently Asked Questions
What is the primary objective of this research?
The research aims to investigate how crystal growth and morphology of CdSe quantum dots are influenced by dip-coating parameters and the presence of the stabilizing agent L-glutathione.
What technique is used to synthesize the quantum dots?
The quantum dots are synthesized using the water-in-oil microemulsion technique, which allows for the creation of stable, monodisperse nanocrystals.
How is the dip-coating process evaluated in this study?
The dip-coating process is evaluated by measuring the resulting film thickness and morphology at various withdrawal speeds, comparing the results against the theoretical predictions of the Landau-Levich equation.
What is the role of L-glutathione in this experiment?
L-glutathione acts as a stabilizer to control the growth of the quantum dots; however, the study finds that its presence significantly alters the film's structure and fluorescence properties compared to unstabilized samples.
Which characterization tools were essential for this study?
Fluorescence Microscopy and Atomic Force Microscopy (AFM) were the primary tools used to examine the emission spectra and surface morphology of the deposited films.
How does withdrawal speed affect the film structure?
The research observes that withdrawal speed impacts the spacing between striations and the overall deposit thickness, with a specific threshold speed identified where the deposition behavior shifts.
What were the unexpected findings regarding L-glutathione?
It was observed that films containing L-glutathione showed irregular wave-like striations and an absence of fluorescence, which contrasted with the regular square-shaped striations and strong fluorescence seen in unstabilized samples.
How does the thickness of the film behave in relation to the speed?
At lower speeds, the film height is heavily influenced by evaporation; as speed increases, the liquid entrainment effect begins to dominate, leading to different growth regimes as described by the Landau-Levich model.
- Arbeit zitieren
- Christian Bellacanzone (Autor:in), 2013, Film Formation of Cadmium Selenide Quantum Dots (CdSe QD) by Dip-Coating, München, GRIN Verlag, https://www.grin.com/document/950425
