A novel approach of multilayered thin film based on layer-by-layer deposition using colloidal nanoparticles was carried out in this work. The films were made by the self-assembly of oppositely charged metal and dielectric nanoparticles, alternately capped with polymers. Synthesized colloidal suspensions of gold nanoparticles (~20nm) and silica nanoparticles (~30nm) were used as the building blocks for the self-organisation of the films. Capping with PDDA and chitosan was used effectively to control the optical absorption of the surface plasmon resonance peaks of the gold nanoparticles. Using different combinations of layer formation, absorption characteristics in the near-ultraviolet (NUV), green and blue region were controlled through capping and varying the thickness of the film. Capping with chitosan or PDDA reduced the absorption peak of the coated silica nanoparticles in a similar fashion. Peak absorption in the UV range was achieved by assembling bare silica nanoparticles layers onto layers of gold nanoparticles. Transmission color was controlled (less than 1% color distance per added bi-layer) by changing the film thickness.
Optical modeling of multilayer thin films constructed with oppositely charged nanoparticles helped us to understand phenomenon such as surface plasmon resonance, absorbance, transmittance and reflectance. Maxwell-Garnett effective medium theory in this case is applied in quasi-static limit to multilayer composite consisting of host material silica and inclusion material gold nanoparticles. Maxwell Garnett optical simulations is correlated with experimental spectra obtained for the thin film composites. The thickness of layers, size and spacing of metal inclusion is varied to alter the optical properties for the required device applications.
The multilayered thin film of gold and silica resembles a structure consisting of large charge sheets of metal separated by a dielectric layer. When the applied electric potential reaches a threshold value, it drives the electrons to tunnel through the charge sheets producing a rectification effect. Therefore current-voltage measurements of the multilayer thin films were performed to calculate the threshold voltages. The electrical capacitance in these multilayer devices was modified with the change in thickness of the dielectric layers between two conducting layers and calculated by capacitance-voltage measurements of multilayer stack. [...]
Table of Contents
1 Introduction
1.1 Background
1.2 Statement of the problem
1.3 Objective of research work
1.4 Hypothesis
1.5 Scope and limitations of research work
1.6 Organization of the research thesis
2 Literature Review
2.1 'Top-down' versus 'bottom-up' assembly
2.2 Colloidal nanoparticles
2.2.1 Colloidal gold nanoparticle
2.2.2 Colloidal silica nanoparticles
2.3 Polyelectrolytes
2.3.1 Chitosan
2.3.2 PDDA poly(diallyldimethylammonium chloride)
2.4 Surface passivation of colloidal nanoparticles
2.5 Stabilisation of nanoparticles
2.5.1 Electrostatic stabilization
2.5.2 Steric stabilisation
2.6 Surface plasmon resonance
2.7 Layer-by-layer self assembly
2.8 The forces guiding colloidal assembly
2.9 The role of pH buffers
2.10 The formation and structure of thin films
2.11 Wettability of thin films
2.12 Electrical properties of metal-insulator films
2.13 Quantum tunneling
2.14 Fowler-Nordheim (F-N) tunneling
2.15 Thermal properties of thin films
2.16 Optical properties of thin multilayered structures
2.17 Effective medium theory
2.18 Maxwell-Garnett model
2.19 Thin film optical filter
3 Methodology
3.1 Synthesis of colloidal nanoparticles
3.2 Surface passivation of colloidal nanoparticles using different polymers
3.3 Synthesis and surface modification of gold nanoparticles
3.4 Synthesis and surface modification of silica nanoparticles
3.5 Thin film architectures
3.6 Layer-by-layer self assembly using dip coating system
3.7 Thin film fabrication using layer-by-layer self assembly
3.8 Types of substrates
3.9 Synthesis of pH buffers for colloidal solutions of gold & silica nanoparticles
3.10 Fabrication of gold-silica thin films arrays
3.11 Measurement of WCA (Water Contact Angle) over glass substrates
3.12 Optical characterisation of thin multilayer films
3.13 Optical absorbance of gold silica thin film through air and water medium
3.14 Study of the light interference through gold-silica thin film
3.15 Electrical characterisation of gold-silica multilayer thin films
3.16 Measurement of electrical rectification for gold-silica thin film
3.17 DC-capacitance measurements for gold-silica thin films
3.18 Current-Voltage measurements with change in temperature
3.19 Current measurement with variable temperature and fixed voltage
3.20 Application of Maxwell-Garnett theory to metal-dielectric multilayer films
3.21 Transmission Electron Microscopy
3.22 Scanning Electron Microscopy
3.23 Simulation of optical spectra gold-silica thin films
4 Results and discussions
4.1 Synthesis of colloidal nanoparticles
4.2 Particle Size Distribution of gold and silica nanoparticles
4.3 Glass substrate functionalisation
4.4 Measurement of WCA (Water Contact Angle)
4.5 Growth of gold-silica multilayers
4.6 Effect of pH of buffers for fabrication of multilayers
4.7 Fabrication of gold-silica multilayer thin films
4.8 Optical absorbance of chitosan capped gold-silica thin films
4.9 Optical absorbance of PDDA capped gold-silica thin films
4.10 Thin film fabrication using different volume ratio of gold nanoparticles
4.11 Optical filter application
4.12 Deconvolution of optical absorbance graphs for gold-silica multilayers
4.13 Effect of the film thickness on filter transmittance
4.14 Application of Maxwell-Garnett theory to gold-silica multilayer films
4.15 Optical absorbance of gold silica thin film through air and water medium
4.16 Study of the light interference through gold-silica thin film
4.17 Optical transmission through gold-silica thin film
4.18 Electrical characterisation of gold-silica multilayer thin films
4.19 DC-capacitance measurements for gold-silica thin films
4.20 Measurement of Rectification for gold-silica thin
4.21 Current-voltage measurements with change in temperature
4.22 Current measurement with variable temperature and fixed voltage
4.23 Fowler-Nordheim (F-N) plot for gold-silica multilayer films
4.24 Multilayer thickness measurements
5 Conclusions and future recommendations
Research Objectives and Core Themes
This research explores the development of multilayered thin films constructed from colloidal gold and silica nanoparticles. The primary objective is to investigate the optical and electrical properties of these nanocomposites, which are fabricated using a layer-by-layer (LbL) deposition technique. A central research question is how nanoparticle size, layer architecture, and deposition parameters—specifically the role of polyelectrolyte capping and pH buffers—influence the resulting structural and functional characteristics of the thin film.
- Fabrication of multilayered thin films using colloidal self-assembly.
- Characterization of optical phenomena such as surface plasmon resonance and light interference.
- Evaluation of electrical properties including quantum tunneling, rectification, and capacitance.
- Optimization of the LbL dip-coating process for uniform and reproducible film growth.
Excerpt from the Book
2.7 Layer-by-layer self assembly
In most of the applications of layers using deposition by adsorption from solution, the application by spraying was initiated by Schlenoff [121] and the use of spin-coaters was introduced by Wang and Hong [122-123] . The advantage of these deposition techniques is that that only small quantity of solutions are required to coat relatively larger surfaces. The concept of electrostatic interactions of charged colloids and multilayer films composed began with Iler's, who exploited the sequential deposition of positive alumina fibrils and negative silica colloids in the year 1966 [124]. However this novel process was not widely used until the early 1990s, until Decher and coworkers, at Gutenberg University in Germany, succeeded in development of multilayer films that were optically transparent through the use of different polyelectrolytes [125]. This concept of self assembly demonstrated the use of size-independent substrates to build periodic nanostructures.
The basic idea behind the electrostatic self assembly is simple as shown in figure 2.10. A single layer of film is assembled through the use of ionic bond formation on the oppositely charged substrate. After that the loosely adsorbed molecules are removed by rinsing in ultrapure water three or four times and the substrate is then immersed in the relative colloidal solution to form a single anionic/cationic monolayer. The process of rinsing is repeated in ultrapure water. In this way, a single bilayer of anionic/cationic material is fabricated. Repeating this self assembly process produces a multilayered thin film structure.
Summary of Chapters
1 Introduction: Provides background on colloidal nanoparticles and defines the core problem of fabricating multilayered thin films with controlled electrical and optical characteristics.
2 Literature Review: Discusses the theoretical framework including colloidal synthesis, polyelectrolyte roles, surface plasmon resonance, and established models like Maxwell-Garnett for effective medium theory.
3 Methodology: Details the experimental procedures, including the LbL dip-coating setup, chemical synthesis of gold/silica particles, and the various analytical techniques used for characterization.
4 Results and discussions: Analyzes experimental data regarding film growth, optical absorbance, thickness measurements, and electrical performance of the fabricated multilayer devices.
5 Conclusions and future recommendations: Summarizes key research findings and suggests potential future applications in fields such as photonics, electronics, and desalination.
Keywords
Colloidal Nanoparticles, Layer-by-Layer Assembly, Multilayer Thin Films, Gold Nanoparticles, Silica Nanoparticles, Surface Plasmon Resonance, Maxwell-Garnett Theory, Polyelectrolytes, Quantum Tunneling, Electrical Rectification, Nanocomposites, Thin Film Fabrication, Optical Absorbance, Dip-Coating, Surface Passivation.
Frequently Asked Questions
What is the core focus of this research?
The research focuses on the fabrication and characterization of multilayered thin films composed of gold and silica nanoparticles using a layer-by-layer self-assembly approach.
What are the primary research themes?
Key themes include the synthesis of stable colloidal suspensions, the role of polyelectrolyte capping agents, optical spectroscopy of nanocomposites, and the investigation of electronic properties like tunneling and capacitance.
What is the main objective of the thesis?
The objective is to successfully create and optimize multilayered thin films and to thoroughly understand their unique optical and electrical properties through experimental analysis and theoretical modeling.
Which scientific methods are employed?
The research uses wet chemical synthesis, layer-by-layer dip-coating deposition, transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-Vis spectroscopy, and electrical measurements like current-voltage (I-V) and capacitance characterization.
What is covered in the main body of the work?
The main body covers the detailed literature review of self-assembly, the step-by-step methodologies for thin film fabrication, and a comprehensive analysis of the results related to structural, optical, and electrical properties.
Which keywords characterize this work?
Key terms include Colloidal Nanoparticles, Layer-by-Layer Assembly, Surface Plasmon Resonance, Maxwell-Garnett Theory, and Quantum Tunneling.
How does the author handle nanoparticle aggregation during film growth?
The author uses polyelectrolytes such as chitosan and PDDA to passivate the nanoparticle surface, providing both electrostatic and steric stabilization to prevent uncontrolled aggregation.
What specific role do pH buffers play in this process?
pH buffers are crucial for controlling the ionization of polyelectrolytes and maintaining the colloidal stability of the nanoparticle solutions during the long-term sequential dipping process.
How does the thickness of the thin film influence its properties?
The study shows that increasing the number of bilayers affects the optical absorption and the electrical sheet resistance, allowing for the tuning of film properties for specific device applications.
- Arbeit zitieren
- Dr Zaheer Abbas Khan (Autor:in), 2011, Fabrication and characterisation of multilayer thin film using self assembly of colloidal gold and silica nanoparticles, München, GRIN Verlag, https://www.grin.com/document/334799
