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Triadic bioactive CaPTi thin films synthesized by concurrent sputtering deposition
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Type
Thesis
Author
Long, Jidong
Supervisor
Xu, Shuyan
Abstract
This thesis addresses the problem concerned with the development and experimental investigation of novel bioactive triadic CaPTi thin films synthesized by means of a reactive concurrent sputtering deposition method.
Two types of plasma sources, namely, an internal current driven inductively coupled plasma source and a capacitively coupled RF magnetron plasma sputtering deposition system, are studied comparatively for synthesis of CaPTi thin films. The results demonstrated that RF magnetron sputtering deposition technique is a powerful method for synthesis of CaPTi thin films on Ti6A14V alloy. The experiments indicate that various parameters of plasma discharge can strongly affect the film formation and properties, including elemental composition, bonding state, crystal structure, interface bonding strength, and biocompatibility.
Experiments show that a threshold power is required for the formation of crystalline CaPTi thin films. At a low power, a sufficient sputtering yield for the thin film growth cannot be produced. The externally applied bias voltage strongly affects the composition, phase content and crystal structure of the thin films. With an increase of the bias voltage, the percentage of calcium rises while the percentage of phosphorus decreases. As a result, the CaJP ratio sharply increases. The experiments show that thin films synthesized at a low bias voltage (0 - 75 V) have a composition close to the stoichiometric value of hydroxyapatite (HA). At a lower bias, HA is the dominant content in the films. When bias is increased to a level of 200 V, the percentage of HA phase largely decreases and the dominant phase changes into calcium oxide. XRD experiments show that the thin films have a better crystallinity at low bias voltages. The interface bonding strength assessment experiments show that the thin films synthesized at a low bias voltage have high adhesion. With rising of bias, the adhesion sharply decreases.
The working gas pressure has a profound effect on the chemical composition of the films. In a low-pressure range of 12 - 18 mTorr, the composition of the film is close to that of hydroxyaptite. As the working gas pressure increases, the CdP ratio is observed to decrease. Low pressure (12 - 18 mTorr) is also favorable for better crystallization of the film. The adhesive strength the thm films synthesized at a low pressure is also higher than that at a high pressure.
The formation and properties of the films are closely connected to the substrate temperature. The CdP ratio slightly increases with the increase of the temperature. For compound phase in the film the meta-stable phosphate phase transforms into the stable phosphate as the temperature rises to above 5 50°C. Crystallization o f thin films h as a clear improvement at a high temperature. The adhesive strength is found higher for the thin films obtained at a high temperature than those obtained at a low temperature.
Introduction of water vapor has no clear influence on the composition of the CaPTi films. However, water vapor can affect the crystallization. When the percentage of water in the working gas reaches around 14%, the crystallization is the best. In addition, introduction of water vapor makes it possible to achieve good crystallization at a relative low temperature. On the other hand, the results of scratch test show that water vapor decreases the adhesion of the films.
Gaseous species studies reveal that in the HA+Ti sputtering plasma, CaO is the dominant species in the gas phase. Other calcium phosphate-related species, such as PO, PHO, and CaOH etc., are also found. Calcium phosphate compounds are formed by the recombination of these species on the surface of the substrates. The results of the OES measurements show that the concentration of the calcium phosphate- related species in the gas phase has a rising tendency with an increase of RF power, working gas pressure and bias voltage. Water-related gaseous species (H2, H, OH-, 0, and 02) have been investigated using the optical emission spectroscopy The results show that water vapor has a strong quenching effect on the plasma and results in a big decrease in sputtering yield and deposition rate.
In vitro cell culture experiments show that the CaPTi thin films with good crystallinity have good compatibility. On the other hand, the thin films with poor crystallization do not support the adhesion of the cells.
Two types of plasma sources, namely, an internal current driven inductively coupled plasma source and a capacitively coupled RF magnetron plasma sputtering deposition system, are studied comparatively for synthesis of CaPTi thin films. The results demonstrated that RF magnetron sputtering deposition technique is a powerful method for synthesis of CaPTi thin films on Ti6A14V alloy. The experiments indicate that various parameters of plasma discharge can strongly affect the film formation and properties, including elemental composition, bonding state, crystal structure, interface bonding strength, and biocompatibility.
Experiments show that a threshold power is required for the formation of crystalline CaPTi thin films. At a low power, a sufficient sputtering yield for the thin film growth cannot be produced. The externally applied bias voltage strongly affects the composition, phase content and crystal structure of the thin films. With an increase of the bias voltage, the percentage of calcium rises while the percentage of phosphorus decreases. As a result, the CaJP ratio sharply increases. The experiments show that thin films synthesized at a low bias voltage (0 - 75 V) have a composition close to the stoichiometric value of hydroxyapatite (HA). At a lower bias, HA is the dominant content in the films. When bias is increased to a level of 200 V, the percentage of HA phase largely decreases and the dominant phase changes into calcium oxide. XRD experiments show that the thin films have a better crystallinity at low bias voltages. The interface bonding strength assessment experiments show that the thin films synthesized at a low bias voltage have high adhesion. With rising of bias, the adhesion sharply decreases.
The working gas pressure has a profound effect on the chemical composition of the films. In a low-pressure range of 12 - 18 mTorr, the composition of the film is close to that of hydroxyaptite. As the working gas pressure increases, the CdP ratio is observed to decrease. Low pressure (12 - 18 mTorr) is also favorable for better crystallization of the film. The adhesive strength the thm films synthesized at a low pressure is also higher than that at a high pressure.
The formation and properties of the films are closely connected to the substrate temperature. The CdP ratio slightly increases with the increase of the temperature. For compound phase in the film the meta-stable phosphate phase transforms into the stable phosphate as the temperature rises to above 5 50°C. Crystallization o f thin films h as a clear improvement at a high temperature. The adhesive strength is found higher for the thin films obtained at a high temperature than those obtained at a low temperature.
Introduction of water vapor has no clear influence on the composition of the CaPTi films. However, water vapor can affect the crystallization. When the percentage of water in the working gas reaches around 14%, the crystallization is the best. In addition, introduction of water vapor makes it possible to achieve good crystallization at a relative low temperature. On the other hand, the results of scratch test show that water vapor decreases the adhesion of the films.
Gaseous species studies reveal that in the HA+Ti sputtering plasma, CaO is the dominant species in the gas phase. Other calcium phosphate-related species, such as PO, PHO, and CaOH etc., are also found. Calcium phosphate compounds are formed by the recombination of these species on the surface of the substrates. The results of the OES measurements show that the concentration of the calcium phosphate- related species in the gas phase has a rising tendency with an increase of RF power, working gas pressure and bias voltage. Water-related gaseous species (H2, H, OH-, 0, and 02) have been investigated using the optical emission spectroscopy The results show that water vapor has a strong quenching effect on the plasma and results in a big decrease in sputtering yield and deposition rate.
In vitro cell culture experiments show that the CaPTi thin films with good crystallinity have good compatibility. On the other hand, the thin films with poor crystallization do not support the adhesion of the cells.
Date Issued
2002
Call Number
TK7871.15.F5 Lon
Date Submitted
2002