Hot Electron Engineering in Nano Structures
thesis
posted on 2017-01-04, 23:37 authored by Chathurangi KumarasingheWhen electromagnetic
radiation is applied to a nanoparticle, scattering, absorption, and transmission of this radiation can take
place. The absorbed radiation (photons) will increase the kinetic and potential
energy of electrons inside the particle, pushing them into excited states. These
excited electrons with high energy are not in thermal equilibrium with the
lattice of the nanoparticle
and hence are referred to as hot electrons.
Hot electrons are injected into the surrounding media if their energies are high enough to cross over the energy barrier at the interface between the nanoparticles and the surroundings. This results in generation of a photocurrent, which is found useful in many opto electronic applications. Therefore, hot electron generation and injection is a field of high scientific interest.
Localized surface plasmons (LSPs) generated in metallic nanoparticles via optical excitation create an enhanced electric field inside the nanoparticle, aiding the hot electron generation process. In smaller metallic nanoparticles, absorption is much more dominant than scattering and a larger proportion of excited electrons
end up in higher energy levels, making them ideal for hot electron injection related applications.
As the particle dimensions are reduced to nanoscale and become comparable to the wavelength of the electron wave function, the energy levels of electrons become highly discreet and geometrically dependent. The efficiency and magnitude of the hot electron injection process depends on the energy spectrum of the electrons, which is determined based on the shape and size of the nanoparticle. In this thesis, the shape and size dependent hot electron generation and injection behaviour of metallic nanoparticles, considering the quantized motion of the conduction electrons, are studied. The results of this study are used to design a hot electron based all-optical direction-switching device, which is extremely useful in nanoscale electronic circuitry.
The shape and size dependence of the electron energy levels cause the dielectric function of the nanoparticle to be geometry dependent as the dimensions of the particle are reduced. When analysing hot electron generation and other optical properties of nanoparticles, the dielectric function is a key input. Therefore, it is important to obtain a realistic dielectric function based on electron excitations
at different frequencies, considering the shape as well as the size of the particle by following a quantum-mechanical approach. Therefore, as a final part of this research, the quantum confinement effects on the frequency-dependent dielectric function of metallic nanoparticles and its influence on hot electron generation are studied.
This thesis is organized as follows. An introduction to hot electrons in nanoparticles and the objectives of this research are presented in Chapter 1, followed by a literature review of the mathematical techniques used to model hot electron generation and injection in Chapter 2. Chapters 3 and 4 present theoretical analyses of shape- and size-dependent hot electron behaviour and design guidelines for nanorods and nanotubes, respectively. A design of a novel all-optical hot electron based current-direction-switching device (CDSD) is presented in Chapter 5, while Chapter 6 discusses the effects of quantum confinement on the permittivity of a nanoparticle and how it effects hot electron generation. Chapter 7 presents a summary of contributions and suggestions for future research.
and hence are referred to as hot electrons.
Hot electrons are injected into the surrounding media if their energies are high enough to cross over the energy barrier at the interface between the nanoparticles and the surroundings. This results in generation of a photocurrent, which is found useful in many opto electronic applications. Therefore, hot electron generation and injection is a field of high scientific interest.
Localized surface plasmons (LSPs) generated in metallic nanoparticles via optical excitation create an enhanced electric field inside the nanoparticle, aiding the hot electron generation process. In smaller metallic nanoparticles, absorption is much more dominant than scattering and a larger proportion of excited electrons
end up in higher energy levels, making them ideal for hot electron injection related applications.
As the particle dimensions are reduced to nanoscale and become comparable to the wavelength of the electron wave function, the energy levels of electrons become highly discreet and geometrically dependent. The efficiency and magnitude of the hot electron injection process depends on the energy spectrum of the electrons, which is determined based on the shape and size of the nanoparticle. In this thesis, the shape and size dependent hot electron generation and injection behaviour of metallic nanoparticles, considering the quantized motion of the conduction electrons, are studied. The results of this study are used to design a hot electron based all-optical direction-switching device, which is extremely useful in nanoscale electronic circuitry.
The shape and size dependence of the electron energy levels cause the dielectric function of the nanoparticle to be geometry dependent as the dimensions of the particle are reduced. When analysing hot electron generation and other optical properties of nanoparticles, the dielectric function is a key input. Therefore, it is important to obtain a realistic dielectric function based on electron excitations
at different frequencies, considering the shape as well as the size of the particle by following a quantum-mechanical approach. Therefore, as a final part of this research, the quantum confinement effects on the frequency-dependent dielectric function of metallic nanoparticles and its influence on hot electron generation are studied.
This thesis is organized as follows. An introduction to hot electrons in nanoparticles and the objectives of this research are presented in Chapter 1, followed by a literature review of the mathematical techniques used to model hot electron generation and injection in Chapter 2. Chapters 3 and 4 present theoretical analyses of shape- and size-dependent hot electron behaviour and design guidelines for nanorods and nanotubes, respectively. A design of a novel all-optical hot electron based current-direction-switching device (CDSD) is presented in Chapter 5, while Chapter 6 discusses the effects of quantum confinement on the permittivity of a nanoparticle and how it effects hot electron generation. Chapter 7 presents a summary of contributions and suggestions for future research.
