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Inductively coupled plasmas for self-assembly of ordered carbon nanostructures
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Type
Thesis
Author
Tsakadze, Zviad
Supervisor
Xu, Shuyan
Abstract
There has been a great deal of interest in high-density, high uniform, low-temperature RF plasma sources for various areas of applications. Among the variety of the plasma sources, inductively coupled plasma (ICP) sources attracted a great interest because of their ability to generate high density (1010-1012 cm-3), large-area and large-volume plasma for fabrication and processing of unique materials.
In order to improve the uniformity of the electromagnetic fields and RF power density a new low-frequency ICP source with internal oscillating RF current (IOC) configuration has been developed and investigated. The obtained experimental results demonstrate the uniform power distribution into the presented device. The global plasma parameters, such as electron number density, effective electron temperature, plasma potential and electron energy distribution/probability functions obtained from a RF compensated Langmuir probe reveal that the internal RF currents significantly improve the radial and axial uniformity of the plasma density in the vacuum chamber. Optical emission spectroscopy (OES) measurements show that the intensities of different spectral lines in electrostatic (E) and electromagnetic (H) modes are higher than in conventional ICP source with external coil configuration.
ICP sources are very efficient for production of nano-films of diamond-like carbon (DLC) as well as many other new materials. This thesis is further extended to the investigation of the relationship between discharge parameters and composition of the deposited films. It has been found that plasma parameters strongly influence on the rates of molecular/radical gas-phase reactions, both are crucial for the composition of deposited films.
To demonstrate the usefulness of the low-frequency RF plasmas, different types of carbon nanostructures were produced and studied using conventional ICP source. Two different growth regimes were exploited : temperature controlled growth (TCG) regime with the preliminary heating of the substrate by the external source and floating temperature growth (FTG) regime when CNS have been produced by varying only DC substrate bias without any external substrate heating. Obtained results show that in TCG regime high density, large area, vertically aligned carbon nanotips can be grown at low substrate temperatures (t=300oC-350oC). X-ray Diffraction (XRD) spectra exhibit high degree of crystallization. Raman spectra demonstrate two peaks, G (~ 1580 cm-1) peak attributed to the crystalline graphite and D peak (~ 1350 cm-1) resulting from disordered-inducing Raman scattering from sp2 carbons. With a decrease of the substrate temperature, the ratio ID / IG grows indicating the number of nano-sized sp2 clusters increases which play an important role in the field emission from nanostructured carbons. At the same time amorphous carbon content decreases at lower temperatures.
In the FTG regime the different types of CNS such as nanoparticles, nanotips and pyramid-like structures were grown at various applied biases. XRD spectra show high degree of crystallization whereas Raman spectra exhibit excellent carbon graphitization. The ratio ID / IG grows indicating gradual sp2 clustering. It has been also found that G peak shifts from high frequency at V s = 100V to low frequency at V s = 300V indicating the increased contents of sp2 carbon bonds. OES measurements reveal that atomic hydrogen plays important role in the growth of carbon nanostructures.
The growth and characterization of carbon nanostructures using ICP source show that high density, large area vertically aligned carbon nanostructures can be produced at low substrate temperatures and using a suitable applied substrate bias without any external substrate heating.
In order to improve the uniformity of the electromagnetic fields and RF power density a new low-frequency ICP source with internal oscillating RF current (IOC) configuration has been developed and investigated. The obtained experimental results demonstrate the uniform power distribution into the presented device. The global plasma parameters, such as electron number density, effective electron temperature, plasma potential and electron energy distribution/probability functions obtained from a RF compensated Langmuir probe reveal that the internal RF currents significantly improve the radial and axial uniformity of the plasma density in the vacuum chamber. Optical emission spectroscopy (OES) measurements show that the intensities of different spectral lines in electrostatic (E) and electromagnetic (H) modes are higher than in conventional ICP source with external coil configuration.
ICP sources are very efficient for production of nano-films of diamond-like carbon (DLC) as well as many other new materials. This thesis is further extended to the investigation of the relationship between discharge parameters and composition of the deposited films. It has been found that plasma parameters strongly influence on the rates of molecular/radical gas-phase reactions, both are crucial for the composition of deposited films.
To demonstrate the usefulness of the low-frequency RF plasmas, different types of carbon nanostructures were produced and studied using conventional ICP source. Two different growth regimes were exploited : temperature controlled growth (TCG) regime with the preliminary heating of the substrate by the external source and floating temperature growth (FTG) regime when CNS have been produced by varying only DC substrate bias without any external substrate heating. Obtained results show that in TCG regime high density, large area, vertically aligned carbon nanotips can be grown at low substrate temperatures (t=300oC-350oC). X-ray Diffraction (XRD) spectra exhibit high degree of crystallization. Raman spectra demonstrate two peaks, G (~ 1580 cm-1) peak attributed to the crystalline graphite and D peak (~ 1350 cm-1) resulting from disordered-inducing Raman scattering from sp2 carbons. With a decrease of the substrate temperature, the ratio ID / IG grows indicating the number of nano-sized sp2 clusters increases which play an important role in the field emission from nanostructured carbons. At the same time amorphous carbon content decreases at lower temperatures.
In the FTG regime the different types of CNS such as nanoparticles, nanotips and pyramid-like structures were grown at various applied biases. XRD spectra show high degree of crystallization whereas Raman spectra exhibit excellent carbon graphitization. The ratio ID / IG grows indicating gradual sp2 clustering. It has been also found that G peak shifts from high frequency at V s = 100V to low frequency at V s = 300V indicating the increased contents of sp2 carbon bonds. OES measurements reveal that atomic hydrogen plays important role in the growth of carbon nanostructures.
The growth and characterization of carbon nanostructures using ICP source show that high density, large area vertically aligned carbon nanostructures can be produced at low substrate temperatures and using a suitable applied substrate bias without any external substrate heating.
Date Issued
2004
Call Number
QD96.I47 Tsa
Date Submitted
2004