Diamond is widely known for its extraordinary properties, such as high hardness, thermal conducti... more Diamond is widely known for its extraordinary properties, such as high hardness, thermal conductivity, electron mobility, energy bandgap and durability making it a very attractive material for many applications. Synthetic diamonds retain most of the attractive properties of natural diamond. Among the types of synthetic diamonds, nanocrystalline diamond (NCD) is being developed for electrical, tribological, optical, and biomedical applications. In this research work, NCD films were grown by the pulsed electron beam ablation (PEBA) method at different process conditions such as accelerating voltage, pulse repetition rate, substrate material and temperature. PEBA is a relatively novel deposition technique, which has been developed to provide researchers with a new means of producing films of equal or better quality than more conventional methods such as Pulsed Laser Deposition, Sputtering, and Cathodic Vacuum Arc. The deposition process parameters have been defined by estimating the temperature and pressure of the plasma particles upon impact with the substrates, and comparing the data with the carbon phase diagram. Film thickness was measured by visible reflectance spectroscopy technique and was in the range of 40-230 nm. The nature of chemical bonding, namely, the ratio (sp 3 /sp 3 +sp 2) and nanocrystallinity percentage were estimated using visible Raman spectroscopy technique. The films prepared from the ablation of a highly ordered pyrolytic graphite (HOPG) target on different substrates consisted mainly of nanocrystalline diamond material in association with a diamondlike carbon phase. The micro-structural properties and surface morphology of the films were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the NCD films were evaluated by nano-indentation.
Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single ... more Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single target and on different substrates at room temperature and under argon background gas at 0.5 Pa. The films have been deposited from a highly ordered pyrolytic graphite target on four different substrate materials, which include silicon, stainless steel, sapphire, and cubic boron nitride. Based on experimental measurement data, obtained from various analytical techniques, it has been observed that sp 3 bonded carbon content, grain size, film roughness, and nanocrystalline fraction of the films do not seem to be much affected by the type of substrate material used. The thickness of the films, in the range of ;70-90 nm, seems to be relatively the same irrespective of the substrate material. Hardness measurements have shown that film hardness, ranging between 18.5 and 19.5 GPa, is not remarkably influenced by the type of substrate material.
ABSTRACT Conditions for the formation of thin films of nanocrystalline diamond by electron-beam a... more ABSTRACT Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.
ECS Journal of Solid State Science and Technology, 2014
ABSTRACT We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed el... more ABSTRACT We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron beam ablation (channel-spark) from a single target on silicon and stainless steel substrates and under different process conditions. The films have been grown from highly ordered pyrolytic graphite at room temperature in an argon atmosphere under a pressure of 0.6 Pa. This study aims at elucidating the influence of the accelerating voltage (13, 14.5, and 16 kV) and electron beam pulse repetition rate (5 and 8 Hz) on film morphology, grain size, carbon-carbon sp3 content, and crystalline fraction. The films have been characterized using visible-reflectance spectroscopy, visible-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The correlations between measurement data and film properties are examined and discussed.
ABSTRACTPulsed electron beam ablation (15 keV, 1 kA, 100 ns) has been used to grow thin films of ... more ABSTRACTPulsed electron beam ablation (15 keV, 1 kA, 100 ns) has been used to grow thin films of nanocrystalline diamond on silicon substrates. The films have been grown at room temperature and 150°C, and under argon as the working background gas at a pressure of about 4 mTorr. Visible reflectance spectroscopic analysis has shown films thickness to range between about 55 nm and 115 nm. Visible-Raman spectroscopic measurements have confirmed the presence of sp3 carbon bonds with a substantial fraction in the deposited films, and surrounded by a graphitic phase. The morphological features of the films have been assessed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The films surface is relatively smooth at room temperature and for low thickness, and becomes rougher at high temperature and for thicker films.
Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single ... more Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single target and on different substrates at room temperature and under argon background gas at 0.5 Pa. The films have been deposited from a highly ordered pyrolytic graphite target on four different substrate materials, which include silicon, stainless steel, sapphire, and cubic boron nitride. Based on experimental measurement data, obtained from various analytical techniques, it has been observed that sp3 bonded carbon content, grain size, film roughness, and nanocrystalline fraction of the films do not seem to be much affected by the type of substrate material used. The thickness of the films, in the range of ∼70–90 nm, seems to be relatively the same irrespective of the substrate material. Hardness measurements have shown that film hardness, ranging between 18.5 and 19.5 GPa, is not remarkably influenced by the type of substrate material.
Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation o... more Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.
We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron be... more We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron beam ablation (channel-spark) from a single target on silicon and stainless steel substrates and under different process conditions. The films have been grown from highly ordered pyrolytic graphite at room temperature in an argon atmosphere under a pressure of 0.6 Pa. This study aims at elucidating the influence of the accelerating voltage (13, 14.5, and 16 kV) and electron beam pulse repetition rate (5 and 8 Hz) on film morphology, grain size, carbon-carbon sp3 content, and crystalline fraction. The films have been characterized using visible-reflectance spectroscopy, visible-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The correlations between measurement data and film properties are examined and discussed.
al. Structural and optical properties of diamond and nano-diamond films grown by microwave plasma... more al. Structural and optical properties of diamond and nano-diamond films grown by microwave plasma CVD, J. Diamond Relat.
Polytetrafluoroethylene (PTFE) has been prepared by pulsed electron deposition technique on glass... more Polytetrafluoroethylene (PTFE) has been prepared by pulsed electron deposition technique on glass and silicon substrates. Deposition of the thin films has been carried out in the temperature range from room temperature to 300 °C, pressure range from 133.32 × 10−3 Pa to 799.93 × 10−3 Pa, and discharge voltages between 10 kV and 16 kV. Argon or nitrogen has been used as a background gas during the deposition of the films. Attenuated Total Reflection Fourier Transform Infrared spectroscopy shows absorption peaks in the films at 644 cm−1, 1154 cm−1 and 1210 cm−1 consistent with those of PTFE target material. Atomic force microscopy and spectroscopic reflectometry reveal the clustered nature of the films and other morphological characteristics. Surface wettability of the films, expressed via the contact angle, has been measured via static angle goniometry. PTFE films increase the contact angle from about 32° (bare glass) and 43° (bare silicon) to up to 90° and 110° for PTFE-coated glass and silicon substrates, respectively. The contact angle decreases with an increase in both pressure and temperature, while it increases then decreases as the discharge voltage increases.
Cocoa is a common ingredient for various food and confectionery products. Industrial production o... more Cocoa is a common ingredient for various food and confectionery products. Industrial production of this ingredient however is normally not optimised, due to the lack of appropriate analytical tools. Furthermore, cocoa processing is normally operated in semi-continuous mode, and this adds to the difficulty in optimising the various unit operations involved. In this work, a computer-aided process simulation tool was used to model and debottleckneck an industrial cocoa manufacturing process, with the aim to identify an economically viable production scheme that would double the current production rate.
Diamond is widely known for its extraordinary properties, such as high hardness, thermal conducti... more Diamond is widely known for its extraordinary properties, such as high hardness, thermal conductivity, electron mobility, energy bandgap and durability making it a very attractive material for many applications. Synthetic diamonds retain most of the attractive properties of natural diamond. Among the types of synthetic diamonds, nanocrystalline diamond (NCD) is being developed for electrical, tribological, optical, and biomedical applications. In this research work, NCD films were grown by the pulsed electron beam ablation (PEBA) method at different process conditions such as accelerating voltage, pulse repetition rate, substrate material and temperature. PEBA is a relatively novel deposition technique, which has been developed to provide researchers with a new means of producing films of equal or better quality than more conventional methods such as Pulsed Laser Deposition, Sputtering, and Cathodic Vacuum Arc. The deposition process parameters have been defined by estimating the temperature and pressure of the plasma particles upon impact with the substrates, and comparing the data with the carbon phase diagram. Film thickness was measured by visible reflectance spectroscopy technique and was in the range of 40-230 nm. The nature of chemical bonding, namely, the ratio (sp 3 /sp 3 +sp 2) and nanocrystallinity percentage were estimated using visible Raman spectroscopy technique. The films prepared from the ablation of a highly ordered pyrolytic graphite (HOPG) target on different substrates consisted mainly of nanocrystalline diamond material in association with a diamondlike carbon phase. The micro-structural properties and surface morphology of the films were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the NCD films were evaluated by nano-indentation.
Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single ... more Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single target and on different substrates at room temperature and under argon background gas at 0.5 Pa. The films have been deposited from a highly ordered pyrolytic graphite target on four different substrate materials, which include silicon, stainless steel, sapphire, and cubic boron nitride. Based on experimental measurement data, obtained from various analytical techniques, it has been observed that sp 3 bonded carbon content, grain size, film roughness, and nanocrystalline fraction of the films do not seem to be much affected by the type of substrate material used. The thickness of the films, in the range of ;70-90 nm, seems to be relatively the same irrespective of the substrate material. Hardness measurements have shown that film hardness, ranging between 18.5 and 19.5 GPa, is not remarkably influenced by the type of substrate material.
ABSTRACT Conditions for the formation of thin films of nanocrystalline diamond by electron-beam a... more ABSTRACT Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.
ECS Journal of Solid State Science and Technology, 2014
ABSTRACT We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed el... more ABSTRACT We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron beam ablation (channel-spark) from a single target on silicon and stainless steel substrates and under different process conditions. The films have been grown from highly ordered pyrolytic graphite at room temperature in an argon atmosphere under a pressure of 0.6 Pa. This study aims at elucidating the influence of the accelerating voltage (13, 14.5, and 16 kV) and electron beam pulse repetition rate (5 and 8 Hz) on film morphology, grain size, carbon-carbon sp3 content, and crystalline fraction. The films have been characterized using visible-reflectance spectroscopy, visible-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The correlations between measurement data and film properties are examined and discussed.
ABSTRACTPulsed electron beam ablation (15 keV, 1 kA, 100 ns) has been used to grow thin films of ... more ABSTRACTPulsed electron beam ablation (15 keV, 1 kA, 100 ns) has been used to grow thin films of nanocrystalline diamond on silicon substrates. The films have been grown at room temperature and 150°C, and under argon as the working background gas at a pressure of about 4 mTorr. Visible reflectance spectroscopic analysis has shown films thickness to range between about 55 nm and 115 nm. Visible-Raman spectroscopic measurements have confirmed the presence of sp3 carbon bonds with a substantial fraction in the deposited films, and surrounded by a graphitic phase. The morphological features of the films have been assessed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The films surface is relatively smooth at room temperature and for low thickness, and becomes rougher at high temperature and for thicker films.
Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single ... more Nanocrystalline diamond films have been deposited by pulsed electron beam ablation from a single target and on different substrates at room temperature and under argon background gas at 0.5 Pa. The films have been deposited from a highly ordered pyrolytic graphite target on four different substrate materials, which include silicon, stainless steel, sapphire, and cubic boron nitride. Based on experimental measurement data, obtained from various analytical techniques, it has been observed that sp3 bonded carbon content, grain size, film roughness, and nanocrystalline fraction of the films do not seem to be much affected by the type of substrate material used. The thickness of the films, in the range of ∼70–90 nm, seems to be relatively the same irrespective of the substrate material. Hardness measurements have shown that film hardness, ranging between 18.5 and 19.5 GPa, is not remarkably influenced by the type of substrate material.
Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation o... more Conditions for the formation of thin films of nanocrystalline diamond by electron-beam ablation of a graphite target are studied. The analysis is based on the predictions of the analytical solutions of two models describing the expansion of the plasma plume into a background gas and toward a substrate. The models allow the calculation of the pressure and temperature of ablated nanoparticles upon impact with the substrate where the film is deposited. The calculation data are reported on the phase diagram of carbon and are used to assess conditions under which the diamond phase is likely to form on the substrate. The results show that decreasing gas pressure and target to substrate distance, over the practical range of accelerating voltage, is conducive to diamond formation.
We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron be... more We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron beam ablation (channel-spark) from a single target on silicon and stainless steel substrates and under different process conditions. The films have been grown from highly ordered pyrolytic graphite at room temperature in an argon atmosphere under a pressure of 0.6 Pa. This study aims at elucidating the influence of the accelerating voltage (13, 14.5, and 16 kV) and electron beam pulse repetition rate (5 and 8 Hz) on film morphology, grain size, carbon-carbon sp3 content, and crystalline fraction. The films have been characterized using visible-reflectance spectroscopy, visible-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The correlations between measurement data and film properties are examined and discussed.
al. Structural and optical properties of diamond and nano-diamond films grown by microwave plasma... more al. Structural and optical properties of diamond and nano-diamond films grown by microwave plasma CVD, J. Diamond Relat.
Polytetrafluoroethylene (PTFE) has been prepared by pulsed electron deposition technique on glass... more Polytetrafluoroethylene (PTFE) has been prepared by pulsed electron deposition technique on glass and silicon substrates. Deposition of the thin films has been carried out in the temperature range from room temperature to 300 °C, pressure range from 133.32 × 10−3 Pa to 799.93 × 10−3 Pa, and discharge voltages between 10 kV and 16 kV. Argon or nitrogen has been used as a background gas during the deposition of the films. Attenuated Total Reflection Fourier Transform Infrared spectroscopy shows absorption peaks in the films at 644 cm−1, 1154 cm−1 and 1210 cm−1 consistent with those of PTFE target material. Atomic force microscopy and spectroscopic reflectometry reveal the clustered nature of the films and other morphological characteristics. Surface wettability of the films, expressed via the contact angle, has been measured via static angle goniometry. PTFE films increase the contact angle from about 32° (bare glass) and 43° (bare silicon) to up to 90° and 110° for PTFE-coated glass and silicon substrates, respectively. The contact angle decreases with an increase in both pressure and temperature, while it increases then decreases as the discharge voltage increases.
Cocoa is a common ingredient for various food and confectionery products. Industrial production o... more Cocoa is a common ingredient for various food and confectionery products. Industrial production of this ingredient however is normally not optimised, due to the lack of appropriate analytical tools. Furthermore, cocoa processing is normally operated in semi-continuous mode, and this adds to the difficulty in optimising the various unit operations involved. In this work, a computer-aided process simulation tool was used to model and debottleckneck an industrial cocoa manufacturing process, with the aim to identify an economically viable production scheme that would double the current production rate.
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Papers by Omar Alshekhli