L-α-dipalitoylphosphatidylcholine(DPPC) is a phospholipid, and a lung surfactant is used for dielectric surface patterning. In this technique, the self-assembling property of DPPC along with meniscus oscillation, which occurs in LangmuirBlodgett transfer, results in a spatially inhomogeneous distribution of two different phases of DPPC. This way, nanometre height rigid, tightly packed, and durable lateral structures separated by micron size channels are grown on the dielectric surface using the Langmuir-Blodgett deposition technique. The effect of surface modification and deposition parameters on the growth of the patterned surface is studied in detail. A simplified relationship between the surface energy of substrate and deposition parameters is explained in this work. Thus, deposition parameters can be tuned based on the modification of the surface gives more control over the growth of these structures. Lastly, the effect of post-annealing temperatures on the patterned surface is investigated. In conclusion, an easy, affordable, and less timeconsuming method of dielectric surface patterning using phospholipid is investigated, which has potential applications in improving the properties (such as charge mobility and contact resistance) of OFET, TFT and in bioelectronics.
At a glance
- Experimental DPPC films on mica and barium titanate substrates
- Post-annealing experiment at 60°C, 70°C, 80°C and 90°C
- X-ray reflectivity measurements at the Indian Beamline, Photon Factory
- 61 sources in the bibliography
Table of Contents
1. Introduction
1.1. Self-assembly
1.2. DPPC
2. Literature survey
2.1. Stripe pattern formation using Langmuir-Blodgett deposition technique
2.2. Effect of surface treatment on self-organized DPPC monolayer
2.3. Selective deposition of organic molecules onto DPPC templates
2.4. Effect of temperature on self-assembly of amphiphilic molecules
3. Experimental techniques
3.1. Langmuir-Blodgett deposition technique
3.2. Sol-gel technique
3.3. Spin-coating technique
3.4. Atomic force microscopy(AFM)
3.5. Optical Microscopy
3.6. X-ray photoelectron spectroscope(XPS)
3.7. X-ray reflectivity(XRR)
4. Problem Statement
5. Growth of Self-assembled monolayer (SAM) on Mica substrate
5.1. Chemicals and equipment:
5.2. Langmuir monolayer preparation:
5.3. Monolayer transfer on substrate:
5.1. Experimental Results
5.4.1. Pressure - Area Isotherm:
5.4.2. AFM measurement:
5.5. Discussion:
6. Growth of Patterned SAM of DPPC on BTO surface
6.1. Experimental section:
6.1. Results:
6.2.1. XPS measurements:
6.2.2. XRR measurements:
6.2.3. AFM and optical microscopy measurements:
6.3. Discussion:
7. Effect of post-annealing temperature on pattern SAM of DPPC on dielectric surface
7.1. Experimental section:
7.2. Results:
7.3. Discussion:
8. Conclusion
Objectives and Themes
This thesis investigates the growth of self-assembled DPPC films by Langmuir-Blodgett deposition, asking how substrate properties, deposition conditions and post-annealing temperature influence film morphology and pattern formation.
- Molecular self-assembly and DPPC phase behaviour
- Langmuir-Blodgett deposition on mica and barium titanate
- Surface pressure, dipping speed and substrate surface energy
- Characterization by AFM, optical microscopy, XPS and XRR
- Post-annealing and changes in patterned films
Excerpt from the Book
1.2. DPPC
L-α-Dipalmitoylphosphatidylcholine(DPPC) is a phospholipid consisting of two palmitic acids attached to a phosphatidylcholine head-group. It has a melting point of 41˚C and is found in a solid/gel phase at 37˚C. It is amphiphilic in nature, which is due to its hydrophilic head composed by the phosphatidylcholine group and its hydrophilic tail, formed by two palmitic acids. This allows DPPC molecules to self-assemble easily and form micelles, monolayers, bilayers, and liposomes spontaneously whenever it comes in contact with an aqueous medium [23]. DPPC structure undergoes reorientation on the water surface with time. When studied on the surface of the water, DPPC film roughness increases up to several nanometres at longer time scales, which proves its self-assembly nature[24]. This is because phospholipid attract towards each other due to the electrostatic interaction between phosphate and choline groups[25]. At the air-water interface, DPPC molecules self-assemble to forms a monolayer. By increasing the surface pressure DPPC undergoes phase transition in the following order: gaseous phase(G), the coexistence of liquid-expanded and gaseous phases(LE-G), liquid-expanded phase(LE), the coexistence of liquid-expanded and liquid-condensed phases(LE-LC), liquid-condensed phase(LC) and solid phase(S). All these phases can be observed in a pressure-area (PA) isotherm curve obtained using an LB deposition system. When DPPC molecules are in the LC phase, it becomes incompressible. Further compression causes the collapse of the monolayer to form an irreversible 3D structure, which is the solid phase[26]. DPPC has a high collapse surface pressure because of a bigger head group with two hydrophobic chains[27]. The shape of the PA isotherm curve depends on the impurities, monolayer leakage during compression, and compression rate, as investigated by Susan et al.[25]. An increase in temperature causes an upward shift in surface pressure, shortens the coexistence of LE and LC region, and makes it less horizontal. The temperature does not affect the limiting high surface pressure area[25]. However, a recent study by Bykov et al.[26] states that an increase in temperature from 25 ˚C to 35 ˚C causes a decrease in surface elasticity in the region of high surface pressure of DPPC monolayer and reduction in limiting high surface pressure. Another literature by Carmel et al.[23] states that the reorganization of molecules occurs in DPPC bilayer with an increase in temperature when deposited on a hydrophobic substrate. Thus, the temperature has a strong influence on the self-assembling property of DPPC.
Chapter Summaries
1. Introduction: Introduces surface patterning, molecular self-assembly and the properties and phase behaviour of DPPC.
2. Literature survey: Reviews research on stripe formation, substrate treatment, selective deposition and temperature-dependent self-assembly.
3. Experimental techniques: Explains the deposition, substrate preparation and microscopy and X-ray characterization methods used in the project.
4. Problem Statement: Sets out the experiments on mica and barium titanate and the investigation of deposition and annealing parameters.
5. Growth of Self-assembled monolayer (SAM) on Mica substrate: Describes monolayer preparation and transfer at different dipping speeds, followed by pressure-area and AFM measurements.
6. Growth of Patterned SAM of DPPC on BTO surface: Presents preparation and characterization of DPPC films on barium titanate and discusses the proposed mechanism of pattern formation.
7. Effect of post-annealing temperature on pattern SAM of DPPC on dielectric surface: Examines patterned films after annealing at different temperatures and discusses changes in their morphology.
8. Conclusion: Brings together the observations on substrate effects, deposition conditions and post-annealing.
Keywords
DPPC, self-assembly, Langmuir-Blodgett deposition, patterned films, phospholipid monolayers, barium titanate, mica, surface pressure, surface energy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray reflectivity, post-annealing
Frequently Asked Questions
What is the thesis about?
It investigates the deposition and morphology of self-assembled DPPC films on mica and dielectric surfaces.
What are its central themes?
The central themes are molecular self-assembly, surface patterning, deposition parameters, substrate properties and thermal treatment.
What is the primary research objective?
The objective is to study the growth of patterned DPPC films and the influence of deposition conditions and post-annealing on their morphology.
What scientific methods are used?
The author prepares films by Langmuir-Blodgett deposition and uses atomic force microscopy, optical microscopy, X-ray photoelectron spectroscopy and X-ray reflectivity for characterization.
What does the main body cover?
It covers the preparation and characterization of DPPC monolayers on mica, patterned films on barium titanate and the effects of post-annealing.
Which keywords characterize the work?
Key terms include DPPC, self-assembly, Langmuir-Blodgett deposition, barium titanate, surface morphology and post-annealing.
How are the barium titanate substrates prepared?
Barium titanate is synthesized by a sol-gel technique, spin-coated onto glass and annealed before DPPC deposition.
Which annealing temperatures are examined?
The reported temperatures are 60°C, 70°C, 80°C and 90°C; an unannealed sample is also described.
- Quote paper
- Satyabrat Behera (Author), 2020, Growth of Self-Assembled Patterned Films on Dielectric Surfaces Using Langmuir-Blodgett Deposition Technique, Munich, GRIN Verlag, https://www.grin.com/document/1445647
