A microfluidic device was fabricated to separate different conducting parts of multi-walled carbo... more A microfluidic device was fabricated to separate different conducting parts of multi-walled carbon nanotubes (MWCNTs). The device consists of a curing PDMS fluidic-flow chamber covered on electrode coated glass. The electrode was designed to generate non-uniform electric field by patterning via lithography. A range of frequencies with low applied voltage was utilized to induce different sign of dielectrophoresis force. Two different separation schemes based on positive and negative dielectrophoresis were employed to separate different conducting parts in unsorted MWCNTs. From Raman spectroscopy, conducting MWCNTs collected by positive dielectrophoresis showed little variation in the intensities of D-band and G-band ratio while the less conducting MWCNTs collected by negative dielectrophoresis showed decreasing intensities in these positions. The ID/IG ratio in the samples collected by both separation schemes is decreasing compared to the unsorted samples. The electric properties of the samples were characterized by a dielectrophoresis frequency spectra method. The conductance in positive dielectrophoresis collected sample is the greatest while the conductance in negative dielectrophoresis collected sample is the smallest. The trend in the conductance in unsorted and sorted samples is confirmed by current-voltage measurements.
Abstract In this study, diamond-like carbon (DLC) films were deposited on silicon substrates usin... more Abstract In this study, diamond-like carbon (DLC) films were deposited on silicon substrates using different hydrogen and acetylene mixing ratios with the same total flow rate by RF plasma-enhanced chemical vapor deposition. By altering the ratios of ion and neutral radicals, different precursor combinations resulted in different film properties. To obtain the optimal precursor combinations, the morphological, structural, hydrophilic, mechanical, and biocompatibility properties were probed by AFM, Raman spectra, contact angle measurements, nanoindentation, and ECV-304 cell cultures, respectively. The results showed that, for DLC films with high hydrogen contents, the depleted carbon gas and high hydrogen etching resulted in a lower film thickness and smoother surface morphology. In terms of the film structure, the hydrogen-rich DLC films possessed a higher I D /I G ratio and an upward G-peak position shift due to an increase in the sp 2 grain size and bond-angle order. The high hydrogen content also led to increase in the residual stress, hardness, and the Young's modulus. The primary mechanisms for this increase were determined to be due to extensive hydrogen bombardment and the presence of covalent bonds. In biocompatibility, the cell number for ECV-304 ascended if the hydrogen precursor ratio was increased. The mechanism for this increase was characterized by protein absorption associated with hydrophilicity. The results of this research demonstrated that the DLC deposited at moderate hydrogen levels might possess the best overall film properties.
The etching in SiO2 is a crucial step in fabricating thin film transistor. For large area etching... more The etching in SiO2 is a crucial step in fabricating thin film transistor. For large area etching, high density plasma which independently controls ion energy and ion flux is preferable than conventional RIE etcher for its high etching capability. In an attempt to understand how the bias power of N-slot ICP affects the etching rate and uniformity, we study the correlation among bias power, inductive power, etching rate and uniformity. The results show that the etching rate is proportional to the bias power up to 800 W which has the best uniformity. Beyond that power, the etching rate enters the different slope and the uniformity become worse. This phenomenon might be attributed to the combined effects of resist etching and polymer film growth. For N-slot ICP system, high etching rate and good uniformity can be obtained only when the bias power is in the moderate range.
The collection and manipulation of small objects is important in bioassays. One commonly used for... more The collection and manipulation of small objects is important in bioassays. One commonly used force to manipulate small objects is electroosmosis which has the advantages of easy fabrication and small power consumption. Many factors affect the electroosmosis like surface charge density, applied voltage and frequency. For ac electroosmosis, frequency affects flow pattern and particle collection. In this study, the role of frequency is investigated by experiments and verified by numerical simulation. The electroosmosis collecting chip is made of two parallel electrodes separated by a spacer. The chip consists of a top ITO electrode and a bottom electrode made by Corning 1737 glass with different patterned sputtered Cr electrode. The spinning photoresist on the bottom electrode is used as dielectric layer and the electrodes are separated by a curing PDMS spacer. The amine-modified polystyrene particles were collected by varying frequency. To further investigate the mechanism, numerical...
The small volume of sample and fast response time are the primary features of micro fluidic syste... more The small volume of sample and fast response time are the primary features of micro fluidic system. It is essential for expensive samples. Microvalve is a key to regulate the flow movement component in an integrated microfluidic system. The working principle of conventional microvalves relies on its mechanical or electromagnetic properties. These valves are neither biocompatible nor are suitable for bioassays. Stimuli-response hydrogels whose properties of efficient mode of energy conversion (chemical to mechanical), excellent biocompatibility and the combination of multiple function (sensing and actuation) have become the leading candidate as engineered microscale components. In this paper, we study the feasibility of thermo-sensitive hydrogel as a valve on the microchip. A metal resistor was used as the temperature regulator. The results show that the miniaturization fabrication of the hydrogel depends on many factors like the volume of the hydrogel (the size of the valve), the vacuum condition (the evaporation rate) and the deposition substrate. The degree of swelling and deswelling of the hydrogel valve depends on the size of the hydrogel. This micro fluidic system is regulated by temperature change of the aqueous solution. The integration with other fluidic component is crucial for practical application.
Carbon nanotubes have been extensively studied due to their unique property and potential applica... more Carbon nanotubes have been extensively studied due to their unique property and potential application like field emission. For successful implementation, it is essential to know the properties of carbon nanotubes. In this work, we propose a simple method to estimate the electric property of multi walled carbon nanotubes (MWCNTs) by ac dielectrophoresis. Dielectrophoresis is a phenomenon resulted from the inhomogeneous electric field and has been used to sort out colloids with different dielectric properties. When applied ac dielectrophoresis, the movement of the colloids depends on the polarizability of the colloids relative to the medium as well as the applied frequency. In certain frequency, the direction of dielectrophoresis force will change and this crossover frequency is related to the electric property of colloids. Since the crossover frequency is a function of the particle's dielectric property, as a result, if the crossover frequency can be obtained, then the electric property of MWCNTs can be estimated. In a preliminary experiment, NanoAmor MWCNTs (95+%, core diameter: 5-10 nm, outside diameter 20-40 nm, length 5-15 mum) mixed with alcohol, DI water and the surfactant was injected onto a dielectrophoresis microfluidic chip to measure the crossover frequency. These MWCNTs were under negative dielectrophoresis (repelled from high electric field) for frequencies over 12 KHz, and were under positive dielectrophoresis (attracted to the high electric field) for frequencies under 1 KHz. These results were compared with the CM factor frequency spectrum with known electric properties. The results show that for positive dielectrophoresis in low frequency and negative dielectrophoresis in high frequency is a characteristic of conducting materials which indicates that these MWCNTs are conducting in nature. One application of this technique is the characterization of electric property of SWCNT which is currently under investigation.
In this study, the specimens in disc style were prepared by changing the coating sequence and coa... more In this study, the specimens in disc style were prepared by changing the coating sequence and coating thickness of titanium nitride and titanium carbonitride films on S45C steel substrate as the top and the second layers of a multilayer system. These arrangements were made in order to investigate the mechanical properties of the composite films like the adhesion strength, load carrying capacity, hardness, surface topography and surface microstructure. The experimental results show that the specimens Ž. Ž. with the TirTi C,N rTiN film have a relatively higher composite hardness than the TirTiNrTi C,N film. The trend exhibited in Ž. the coating film hardness of ceramic coating film is similar to the composite hardness. The specimens with the TirTi C,N rTiN Ž. film have a lower critical friction force and critical track distance compared with the TirTiNrTi C,N film. For the specimen with Ž. the TirTi C,N rTiN film, peaks protruding over the flat surface are quantitatively increased by the increase in the coating film thickness. Nevertheless, either the peak parameter Rz or the amplitude parameter Ry after coating thick films is strongly affected by the Ra value of steel substrate before coating and the uniformity of the surface morphology can thus be improved. However, Ž. for the specimens with the TirTiNrTi C,N film, increasing the total film thickness decreased the asperity, but also eliminated the morphological uniformity.
ABSTRACT Diamond-like carbon (DLC) films have many excellent properties such as high hardness, lo... more ABSTRACT Diamond-like carbon (DLC) films have many excellent properties such as high hardness, low friction coefficient, chemical inertness, and biocompatibility. Their good biocompatibility is a result of their chemical composition containing only carbon and hydrogen which are biologically compatible. Previous studies on biocompatibility of DLC films focus primarily on morphological issues like roughness and wettability. However, we believe that the stress and the associated surface properties in the films are equally important. In exploring these effects, the silicon substrates were roughened with 30 wt.% KOH in different etching time. The substrate roughness was increased by longer etching time. Three different types of samples – silicon without DLC film, smooth silicon with DLC thin film and rough silicon with DLC – were prepared by culturing the human endothelial cell ECV304 for 72 h. The DLC films were examined by AFM, Raman spectroscopy, XPS, sessile drop and surfcorder to study the morphology, chemical bonding, wettability and residual stress. For DLC surface properties, as the substrate roughness increases, the residual stress increases and the sp3/sp2 ratio decreases. Meanwhile, the surface became more hydrophobic. The stress caused by the substrate roughness seems to be correlated with the surface properties of DLC. As for the ECV304 cell culture, the viability for bare silicon without DLC is almost zero. This indicates that silicon is not biocompatible for ECV 304. The cell number of ECV in DLC/rough substrate is less than that in DLC/smooth substrate in a 72-hour cell culture. This implies that a DLC/Si whose surface properties are associated with higher stress is adverse to ECV cell culture.
ATR-FTIR apparatus is used to measure the curing rate of PMDA-ODA polyimide film in order to avoi... more ATR-FTIR apparatus is used to measure the curing rate of PMDA-ODA polyimide film in order to avoid sinusoidal interference fringe. From the corrected height method, the curing rate is found to have positive correlative trend with the curing temperature. It was shown that the curing rate under 300 C is 92.1% than that under 400 C for one hour. The curing degree related to the mechanical properties was further demonstrated by nanoindentation. The results show that the higher the curing rate the higher the nano-hardness and nano-modulus due to the thermal imidization of polyimide characteristic. The nano-hardness ratio of curing degree at 300 C over curing degree at 400 C is 0.89, while the nano-modulus of which is 0.95.
Water contact angle has been measured to indirectly assess the sp 2 /sp 3 ratio and hydrogen cont... more Water contact angle has been measured to indirectly assess the sp 2 /sp 3 ratio and hydrogen content of DLCH film under post N 2 annealed treatment with O 2 content under 100 ppm. XPS spectrum is used to measure the C1s bonding type and calculate the sp 2 /sp 3 ratio. The surface morphology of DLCH film was examined by SEM and AFM. From experimental results, it seems the surface morphology was not a critical factor on water contact angle value, at least for DLCH film. A quantitative correlation between water contact angle and sp 2 /sp 3 ratio of DLCH film is established from which the hydrogen content can be estimated by the sp 2 /sp 3 ratio as well as Angus equation.
The present work describes the hybrid layers consisting of 1-mm-thick hydrogenated diamond-like c... more The present work describes the hybrid layers consisting of 1-mm-thick hydrogenated diamond-like carbon (DLCH) film deposited by ion beam deposition (IBD) method as the bottom layer and spin coating polyimide (PI) film at a thickness of 6 mm as the top layer. Optical microscopy shows that all DLCH film, PI film and PI/DLCH film have smooth surface and are free from cracks or wrinkles. Water contact angle measurement shows that the annealed DLCH film has the higher relative adhesive tension and adhesive work than that of PI film. Raman spectra show that the DLCH film can avoid severe graphitization & degradation at 300 C during annealing treatment, and FTIR spectra also exhibit that the PI film will reach 95% imidization during the curing step at 300 C. PI film can act on DLCH film as the stress buffer. This is demonstrate from warpage measurement showing that top PI film with tensile stress can partially reduce the compressive stress over bottom DLCH film with 6.7% warpage reduction. The electrical resistivity of PI/DLCH/Si is similar to that of PI/Si is resulted from the PI passivation effect.
The bonding and crystalline structures of oil-fried fly ash collected from a power plant were ana... more The bonding and crystalline structures of oil-fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X-ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D peaks under 2000 or 2700 • C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 • C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 • C. The XRD spectral line shape of refined, unburned carbon heated at 2700 • C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders.
Nanoindentation measurements using the Berkovich diamond tip with a load up to 700 and 210 mN wer... more Nanoindentation measurements using the Berkovich diamond tip with a load up to 700 and 210 mN were performed on 1-μm hydrogenated diamond-like carbon (DLCH) films and 6-μm polyimide (PI) films under different thermal treatment. The average nanohardness and elastic modulus from nanoindentation measurements are 25.13 and 192.18 GPa for as-deposited DLCH film and 22.93 and 174.22 GPa for as-annealed DLCH film, respectively. The ID/IG ratio of Raman spectra is 1.72 for as-deposited DLCH film and 2.04 for as-annealed DLCH film. The average nanohardness and elastic modulus from nanoindentation measurements are 0.37 and 5.58 GPa for 300 as-cured PI film and 0.42 and 5.19 GPa for 400 as-cured PI film, respectively. The relative cured rate is 92.1% for 300 as-cured PI film and 100% for 400 as-cured PI film. Both the nanohardness and elastic modulus derived from nanoindentation test results can correlate well with the trend of Raman spectra and FTIR spectra for hard DLCH film and soft PI film...
A microfluidic device was fabricated to separate different conducting parts of multi-walled carbo... more A microfluidic device was fabricated to separate different conducting parts of multi-walled carbon nanotubes (MWCNTs). The device consists of a curing PDMS fluidic-flow chamber covered on electrode coated glass. The electrode was designed to generate non-uniform electric field by patterning via lithography. A range of frequencies with low applied voltage was utilized to induce different sign of dielectrophoresis force. Two different separation schemes based on positive and negative dielectrophoresis were employed to separate different conducting parts in unsorted MWCNTs. From Raman spectroscopy, conducting MWCNTs collected by positive dielectrophoresis showed little variation in the intensities of D-band and G-band ratio while the less conducting MWCNTs collected by negative dielectrophoresis showed decreasing intensities in these positions. The ID/IG ratio in the samples collected by both separation schemes is decreasing compared to the unsorted samples. The electric properties of the samples were characterized by a dielectrophoresis frequency spectra method. The conductance in positive dielectrophoresis collected sample is the greatest while the conductance in negative dielectrophoresis collected sample is the smallest. The trend in the conductance in unsorted and sorted samples is confirmed by current-voltage measurements.
Abstract In this study, diamond-like carbon (DLC) films were deposited on silicon substrates usin... more Abstract In this study, diamond-like carbon (DLC) films were deposited on silicon substrates using different hydrogen and acetylene mixing ratios with the same total flow rate by RF plasma-enhanced chemical vapor deposition. By altering the ratios of ion and neutral radicals, different precursor combinations resulted in different film properties. To obtain the optimal precursor combinations, the morphological, structural, hydrophilic, mechanical, and biocompatibility properties were probed by AFM, Raman spectra, contact angle measurements, nanoindentation, and ECV-304 cell cultures, respectively. The results showed that, for DLC films with high hydrogen contents, the depleted carbon gas and high hydrogen etching resulted in a lower film thickness and smoother surface morphology. In terms of the film structure, the hydrogen-rich DLC films possessed a higher I D /I G ratio and an upward G-peak position shift due to an increase in the sp 2 grain size and bond-angle order. The high hydrogen content also led to increase in the residual stress, hardness, and the Young's modulus. The primary mechanisms for this increase were determined to be due to extensive hydrogen bombardment and the presence of covalent bonds. In biocompatibility, the cell number for ECV-304 ascended if the hydrogen precursor ratio was increased. The mechanism for this increase was characterized by protein absorption associated with hydrophilicity. The results of this research demonstrated that the DLC deposited at moderate hydrogen levels might possess the best overall film properties.
The etching in SiO2 is a crucial step in fabricating thin film transistor. For large area etching... more The etching in SiO2 is a crucial step in fabricating thin film transistor. For large area etching, high density plasma which independently controls ion energy and ion flux is preferable than conventional RIE etcher for its high etching capability. In an attempt to understand how the bias power of N-slot ICP affects the etching rate and uniformity, we study the correlation among bias power, inductive power, etching rate and uniformity. The results show that the etching rate is proportional to the bias power up to 800 W which has the best uniformity. Beyond that power, the etching rate enters the different slope and the uniformity become worse. This phenomenon might be attributed to the combined effects of resist etching and polymer film growth. For N-slot ICP system, high etching rate and good uniformity can be obtained only when the bias power is in the moderate range.
The collection and manipulation of small objects is important in bioassays. One commonly used for... more The collection and manipulation of small objects is important in bioassays. One commonly used force to manipulate small objects is electroosmosis which has the advantages of easy fabrication and small power consumption. Many factors affect the electroosmosis like surface charge density, applied voltage and frequency. For ac electroosmosis, frequency affects flow pattern and particle collection. In this study, the role of frequency is investigated by experiments and verified by numerical simulation. The electroosmosis collecting chip is made of two parallel electrodes separated by a spacer. The chip consists of a top ITO electrode and a bottom electrode made by Corning 1737 glass with different patterned sputtered Cr electrode. The spinning photoresist on the bottom electrode is used as dielectric layer and the electrodes are separated by a curing PDMS spacer. The amine-modified polystyrene particles were collected by varying frequency. To further investigate the mechanism, numerical...
The small volume of sample and fast response time are the primary features of micro fluidic syste... more The small volume of sample and fast response time are the primary features of micro fluidic system. It is essential for expensive samples. Microvalve is a key to regulate the flow movement component in an integrated microfluidic system. The working principle of conventional microvalves relies on its mechanical or electromagnetic properties. These valves are neither biocompatible nor are suitable for bioassays. Stimuli-response hydrogels whose properties of efficient mode of energy conversion (chemical to mechanical), excellent biocompatibility and the combination of multiple function (sensing and actuation) have become the leading candidate as engineered microscale components. In this paper, we study the feasibility of thermo-sensitive hydrogel as a valve on the microchip. A metal resistor was used as the temperature regulator. The results show that the miniaturization fabrication of the hydrogel depends on many factors like the volume of the hydrogel (the size of the valve), the vacuum condition (the evaporation rate) and the deposition substrate. The degree of swelling and deswelling of the hydrogel valve depends on the size of the hydrogel. This micro fluidic system is regulated by temperature change of the aqueous solution. The integration with other fluidic component is crucial for practical application.
Carbon nanotubes have been extensively studied due to their unique property and potential applica... more Carbon nanotubes have been extensively studied due to their unique property and potential application like field emission. For successful implementation, it is essential to know the properties of carbon nanotubes. In this work, we propose a simple method to estimate the electric property of multi walled carbon nanotubes (MWCNTs) by ac dielectrophoresis. Dielectrophoresis is a phenomenon resulted from the inhomogeneous electric field and has been used to sort out colloids with different dielectric properties. When applied ac dielectrophoresis, the movement of the colloids depends on the polarizability of the colloids relative to the medium as well as the applied frequency. In certain frequency, the direction of dielectrophoresis force will change and this crossover frequency is related to the electric property of colloids. Since the crossover frequency is a function of the particle's dielectric property, as a result, if the crossover frequency can be obtained, then the electric property of MWCNTs can be estimated. In a preliminary experiment, NanoAmor MWCNTs (95+%, core diameter: 5-10 nm, outside diameter 20-40 nm, length 5-15 mum) mixed with alcohol, DI water and the surfactant was injected onto a dielectrophoresis microfluidic chip to measure the crossover frequency. These MWCNTs were under negative dielectrophoresis (repelled from high electric field) for frequencies over 12 KHz, and were under positive dielectrophoresis (attracted to the high electric field) for frequencies under 1 KHz. These results were compared with the CM factor frequency spectrum with known electric properties. The results show that for positive dielectrophoresis in low frequency and negative dielectrophoresis in high frequency is a characteristic of conducting materials which indicates that these MWCNTs are conducting in nature. One application of this technique is the characterization of electric property of SWCNT which is currently under investigation.
In this study, the specimens in disc style were prepared by changing the coating sequence and coa... more In this study, the specimens in disc style were prepared by changing the coating sequence and coating thickness of titanium nitride and titanium carbonitride films on S45C steel substrate as the top and the second layers of a multilayer system. These arrangements were made in order to investigate the mechanical properties of the composite films like the adhesion strength, load carrying capacity, hardness, surface topography and surface microstructure. The experimental results show that the specimens Ž. Ž. with the TirTi C,N rTiN film have a relatively higher composite hardness than the TirTiNrTi C,N film. The trend exhibited in Ž. the coating film hardness of ceramic coating film is similar to the composite hardness. The specimens with the TirTi C,N rTiN Ž. film have a lower critical friction force and critical track distance compared with the TirTiNrTi C,N film. For the specimen with Ž. the TirTi C,N rTiN film, peaks protruding over the flat surface are quantitatively increased by the increase in the coating film thickness. Nevertheless, either the peak parameter Rz or the amplitude parameter Ry after coating thick films is strongly affected by the Ra value of steel substrate before coating and the uniformity of the surface morphology can thus be improved. However, Ž. for the specimens with the TirTiNrTi C,N film, increasing the total film thickness decreased the asperity, but also eliminated the morphological uniformity.
ABSTRACT Diamond-like carbon (DLC) films have many excellent properties such as high hardness, lo... more ABSTRACT Diamond-like carbon (DLC) films have many excellent properties such as high hardness, low friction coefficient, chemical inertness, and biocompatibility. Their good biocompatibility is a result of their chemical composition containing only carbon and hydrogen which are biologically compatible. Previous studies on biocompatibility of DLC films focus primarily on morphological issues like roughness and wettability. However, we believe that the stress and the associated surface properties in the films are equally important. In exploring these effects, the silicon substrates were roughened with 30 wt.% KOH in different etching time. The substrate roughness was increased by longer etching time. Three different types of samples – silicon without DLC film, smooth silicon with DLC thin film and rough silicon with DLC – were prepared by culturing the human endothelial cell ECV304 for 72 h. The DLC films were examined by AFM, Raman spectroscopy, XPS, sessile drop and surfcorder to study the morphology, chemical bonding, wettability and residual stress. For DLC surface properties, as the substrate roughness increases, the residual stress increases and the sp3/sp2 ratio decreases. Meanwhile, the surface became more hydrophobic. The stress caused by the substrate roughness seems to be correlated with the surface properties of DLC. As for the ECV304 cell culture, the viability for bare silicon without DLC is almost zero. This indicates that silicon is not biocompatible for ECV 304. The cell number of ECV in DLC/rough substrate is less than that in DLC/smooth substrate in a 72-hour cell culture. This implies that a DLC/Si whose surface properties are associated with higher stress is adverse to ECV cell culture.
ATR-FTIR apparatus is used to measure the curing rate of PMDA-ODA polyimide film in order to avoi... more ATR-FTIR apparatus is used to measure the curing rate of PMDA-ODA polyimide film in order to avoid sinusoidal interference fringe. From the corrected height method, the curing rate is found to have positive correlative trend with the curing temperature. It was shown that the curing rate under 300 C is 92.1% than that under 400 C for one hour. The curing degree related to the mechanical properties was further demonstrated by nanoindentation. The results show that the higher the curing rate the higher the nano-hardness and nano-modulus due to the thermal imidization of polyimide characteristic. The nano-hardness ratio of curing degree at 300 C over curing degree at 400 C is 0.89, while the nano-modulus of which is 0.95.
Water contact angle has been measured to indirectly assess the sp 2 /sp 3 ratio and hydrogen cont... more Water contact angle has been measured to indirectly assess the sp 2 /sp 3 ratio and hydrogen content of DLCH film under post N 2 annealed treatment with O 2 content under 100 ppm. XPS spectrum is used to measure the C1s bonding type and calculate the sp 2 /sp 3 ratio. The surface morphology of DLCH film was examined by SEM and AFM. From experimental results, it seems the surface morphology was not a critical factor on water contact angle value, at least for DLCH film. A quantitative correlation between water contact angle and sp 2 /sp 3 ratio of DLCH film is established from which the hydrogen content can be estimated by the sp 2 /sp 3 ratio as well as Angus equation.
The present work describes the hybrid layers consisting of 1-mm-thick hydrogenated diamond-like c... more The present work describes the hybrid layers consisting of 1-mm-thick hydrogenated diamond-like carbon (DLCH) film deposited by ion beam deposition (IBD) method as the bottom layer and spin coating polyimide (PI) film at a thickness of 6 mm as the top layer. Optical microscopy shows that all DLCH film, PI film and PI/DLCH film have smooth surface and are free from cracks or wrinkles. Water contact angle measurement shows that the annealed DLCH film has the higher relative adhesive tension and adhesive work than that of PI film. Raman spectra show that the DLCH film can avoid severe graphitization & degradation at 300 C during annealing treatment, and FTIR spectra also exhibit that the PI film will reach 95% imidization during the curing step at 300 C. PI film can act on DLCH film as the stress buffer. This is demonstrate from warpage measurement showing that top PI film with tensile stress can partially reduce the compressive stress over bottom DLCH film with 6.7% warpage reduction. The electrical resistivity of PI/DLCH/Si is similar to that of PI/Si is resulted from the PI passivation effect.
The bonding and crystalline structures of oil-fried fly ash collected from a power plant were ana... more The bonding and crystalline structures of oil-fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X-ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D peaks under 2000 or 2700 • C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 • C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 • C. The XRD spectral line shape of refined, unburned carbon heated at 2700 • C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders.
Nanoindentation measurements using the Berkovich diamond tip with a load up to 700 and 210 mN wer... more Nanoindentation measurements using the Berkovich diamond tip with a load up to 700 and 210 mN were performed on 1-μm hydrogenated diamond-like carbon (DLCH) films and 6-μm polyimide (PI) films under different thermal treatment. The average nanohardness and elastic modulus from nanoindentation measurements are 25.13 and 192.18 GPa for as-deposited DLCH film and 22.93 and 174.22 GPa for as-annealed DLCH film, respectively. The ID/IG ratio of Raman spectra is 1.72 for as-deposited DLCH film and 2.04 for as-annealed DLCH film. The average nanohardness and elastic modulus from nanoindentation measurements are 0.37 and 5.58 GPa for 300 as-cured PI film and 0.42 and 5.19 GPa for 400 as-cured PI film, respectively. The relative cured rate is 92.1% for 300 as-cured PI film and 100% for 400 as-cured PI film. Both the nanohardness and elastic modulus derived from nanoindentation test results can correlate well with the trend of Raman spectra and FTIR spectra for hard DLCH film and soft PI film...
Uploads
Papers by Chehung Wei