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J. H. Chun - One of the best experts on this subject based on the ideXlab platform.

  • Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing
    Microsystem Technologies, 2014
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, Matthew Dirckx, J. H. Chun
    Abstract:

    Si Micromolds are common for fabrication of polymer-based microfluidic devices by hot-embossing because of the well established fabrication methods for Si, e.g., deep reactive ion etching, for favorable surface finish and accuracy. The problems with low yield, poor reproducibility, premature failure and limited lifetime of a Si Micromold are induced by high friction and surface adhesion generated during demolding. Therefore, Titanium (Ti) and molybdenum disulfide (MoS_2) coatings were deposited on Si Micromolds via magnetron co-sputtering at various combinations of target powers to improve its surface properties. Coating composition, crystallographic orientation, roughness, critical load, hardness, friction coefficient and surface energy were measured by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, scratch testing, nanoindentation, ball-on-disc tribometry and the contact angle method respectively. A statistical design of experiment matrix was used to investigate the effect of the Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings. From this designed experiment, it was observed that increasing MoS_2 target power was associated with increasing surface energy and decreasing friction coefficient and target powers had statistically significant effects on these parameters. Crystallinity, roughness and hardness of the coatings increased with increasing Ti concentration. A mathematical model of the effects of Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings has been fit to the experimental results using the response surface method. Uncoated and MoS_2–Ti coated Si Micromolds were used in hot-embossing for a comparative study on replication performance of uncoated and various coated Micromolds. Hotembossed PMMA microstructures showed that coating improve replication performance of Si Micromolds. Si Micromold coated with co-sputter of Ti and MoS_2 at power of 300 and 75 W respectively, showed better replication quality among the selected target powers.

  • Titanium–aluminum–polytetrafluoroethylene coated stainless steel Micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • titanium aluminum polytetrafluoroethylene coated stainless steel Micromold via co sputtering deposition replication performance and limitation in hot embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • Hot-embossing performance of silicon Micromold coated with self-assembled n-octadecyltrichlorosilane
    Sensors and Actuators B-chemical, 2011
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    Abstract Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si Micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si Micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the Micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si Micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the Micromolds and re-deposition of the OTS coatings on the coated Si Micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.

  • Improvement in lifetime and replication quality of Si Micromold using N:DLC:Ni coatings for microfluidic devices
    Sensors and Actuators B-chemical, 2010
    Co-Authors: B Saha, E. Liu, J. H. Chun, David E. Hardt, Shu Beng Tor, Nay Win Khun
    Abstract:

    Abstract In this paper the effect of surface properties of Micromolds on replication process was investigated by using nitrogen (N) and nickel (Ni) doped diamond-like carbon (N:DLC:Ni) coated and uncoated silicon (Si) Micromolds. Hot embossing is one of the most popular replication technologies for low cost and mass production. However higher friction and adhesion in hot-embossing process can shorten the lifetime of Micromolds. In the micro-hot-embossing process used for this study, the N:DLC:Ni coatings on the Si Micromolds successfully increased the lifetime of the Micromolds by 3–18 times. The N:DLC:Ni coatings were deposited on the Si Micromolds by magnetron co-sputtering at various Ni target powers. The surface and tribological properties of the molds such as bonding structure, surface roughness, surface energy, adhesive strength, friction coefficient and wear resistance were characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle measurement, micro-scratch test and ball-on-disk sliding test, respectively.

B Saha - One of the best experts on this subject based on the ideXlab platform.

  • Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing
    Microsystem Technologies, 2014
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, Matthew Dirckx, J. H. Chun
    Abstract:

    Si Micromolds are common for fabrication of polymer-based microfluidic devices by hot-embossing because of the well established fabrication methods for Si, e.g., deep reactive ion etching, for favorable surface finish and accuracy. The problems with low yield, poor reproducibility, premature failure and limited lifetime of a Si Micromold are induced by high friction and surface adhesion generated during demolding. Therefore, Titanium (Ti) and molybdenum disulfide (MoS_2) coatings were deposited on Si Micromolds via magnetron co-sputtering at various combinations of target powers to improve its surface properties. Coating composition, crystallographic orientation, roughness, critical load, hardness, friction coefficient and surface energy were measured by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, scratch testing, nanoindentation, ball-on-disc tribometry and the contact angle method respectively. A statistical design of experiment matrix was used to investigate the effect of the Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings. From this designed experiment, it was observed that increasing MoS_2 target power was associated with increasing surface energy and decreasing friction coefficient and target powers had statistically significant effects on these parameters. Crystallinity, roughness and hardness of the coatings increased with increasing Ti concentration. A mathematical model of the effects of Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings has been fit to the experimental results using the response surface method. Uncoated and MoS_2–Ti coated Si Micromolds were used in hot-embossing for a comparative study on replication performance of uncoated and various coated Micromolds. Hotembossed PMMA microstructures showed that coating improve replication performance of Si Micromolds. Si Micromold coated with co-sputter of Ti and MoS_2 at power of 300 and 75 W respectively, showed better replication quality among the selected target powers.

  • Titanium–aluminum–polytetrafluoroethylene coated stainless steel Micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • titanium aluminum polytetrafluoroethylene coated stainless steel Micromold via co sputtering deposition replication performance and limitation in hot embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • Hot-embossing performance of silicon Micromold coated with self-assembled n-octadecyltrichlorosilane
    Sensors and Actuators B-chemical, 2011
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    Abstract Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si Micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si Micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the Micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si Micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the Micromolds and re-deposition of the OTS coatings on the coated Si Micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.

  • Improvement in lifetime and replication quality of Si Micromold using N:DLC:Ni coatings for microfluidic devices
    Sensors and Actuators B-chemical, 2010
    Co-Authors: B Saha, E. Liu, J. H. Chun, David E. Hardt, Shu Beng Tor, Nay Win Khun
    Abstract:

    Abstract In this paper the effect of surface properties of Micromolds on replication process was investigated by using nitrogen (N) and nickel (Ni) doped diamond-like carbon (N:DLC:Ni) coated and uncoated silicon (Si) Micromolds. Hot embossing is one of the most popular replication technologies for low cost and mass production. However higher friction and adhesion in hot-embossing process can shorten the lifetime of Micromolds. In the micro-hot-embossing process used for this study, the N:DLC:Ni coatings on the Si Micromolds successfully increased the lifetime of the Micromolds by 3–18 times. The N:DLC:Ni coatings were deposited on the Si Micromolds by magnetron co-sputtering at various Ni target powers. The surface and tribological properties of the molds such as bonding structure, surface roughness, surface energy, adhesive strength, friction coefficient and wear resistance were characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle measurement, micro-scratch test and ball-on-disk sliding test, respectively.

E. Liu - One of the best experts on this subject based on the ideXlab platform.

  • Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing
    Microsystem Technologies, 2014
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, Matthew Dirckx, J. H. Chun
    Abstract:

    Si Micromolds are common for fabrication of polymer-based microfluidic devices by hot-embossing because of the well established fabrication methods for Si, e.g., deep reactive ion etching, for favorable surface finish and accuracy. The problems with low yield, poor reproducibility, premature failure and limited lifetime of a Si Micromold are induced by high friction and surface adhesion generated during demolding. Therefore, Titanium (Ti) and molybdenum disulfide (MoS_2) coatings were deposited on Si Micromolds via magnetron co-sputtering at various combinations of target powers to improve its surface properties. Coating composition, crystallographic orientation, roughness, critical load, hardness, friction coefficient and surface energy were measured by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, scratch testing, nanoindentation, ball-on-disc tribometry and the contact angle method respectively. A statistical design of experiment matrix was used to investigate the effect of the Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings. From this designed experiment, it was observed that increasing MoS_2 target power was associated with increasing surface energy and decreasing friction coefficient and target powers had statistically significant effects on these parameters. Crystallinity, roughness and hardness of the coatings increased with increasing Ti concentration. A mathematical model of the effects of Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings has been fit to the experimental results using the response surface method. Uncoated and MoS_2–Ti coated Si Micromolds were used in hot-embossing for a comparative study on replication performance of uncoated and various coated Micromolds. Hotembossed PMMA microstructures showed that coating improve replication performance of Si Micromolds. Si Micromold coated with co-sputter of Ti and MoS_2 at power of 300 and 75 W respectively, showed better replication quality among the selected target powers.

  • Titanium–aluminum–polytetrafluoroethylene coated stainless steel Micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • titanium aluminum polytetrafluoroethylene coated stainless steel Micromold via co sputtering deposition replication performance and limitation in hot embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • Hot-embossing performance of silicon Micromold coated with self-assembled n-octadecyltrichlorosilane
    Sensors and Actuators B-chemical, 2011
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    Abstract Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si Micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si Micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the Micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si Micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the Micromolds and re-deposition of the OTS coatings on the coated Si Micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.

  • Improvement in lifetime and replication quality of Si Micromold using N:DLC:Ni coatings for microfluidic devices
    Sensors and Actuators B-chemical, 2010
    Co-Authors: B Saha, E. Liu, J. H. Chun, David E. Hardt, Shu Beng Tor, Nay Win Khun
    Abstract:

    Abstract In this paper the effect of surface properties of Micromolds on replication process was investigated by using nitrogen (N) and nickel (Ni) doped diamond-like carbon (N:DLC:Ni) coated and uncoated silicon (Si) Micromolds. Hot embossing is one of the most popular replication technologies for low cost and mass production. However higher friction and adhesion in hot-embossing process can shorten the lifetime of Micromolds. In the micro-hot-embossing process used for this study, the N:DLC:Ni coatings on the Si Micromolds successfully increased the lifetime of the Micromolds by 3–18 times. The N:DLC:Ni coatings were deposited on the Si Micromolds by magnetron co-sputtering at various Ni target powers. The surface and tribological properties of the molds such as bonding structure, surface roughness, surface energy, adhesive strength, friction coefficient and wear resistance were characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle measurement, micro-scratch test and ball-on-disk sliding test, respectively.

David E. Hardt - One of the best experts on this subject based on the ideXlab platform.

  • Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing
    Microsystem Technologies, 2014
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, Matthew Dirckx, J. H. Chun
    Abstract:

    Si Micromolds are common for fabrication of polymer-based microfluidic devices by hot-embossing because of the well established fabrication methods for Si, e.g., deep reactive ion etching, for favorable surface finish and accuracy. The problems with low yield, poor reproducibility, premature failure and limited lifetime of a Si Micromold are induced by high friction and surface adhesion generated during demolding. Therefore, Titanium (Ti) and molybdenum disulfide (MoS_2) coatings were deposited on Si Micromolds via magnetron co-sputtering at various combinations of target powers to improve its surface properties. Coating composition, crystallographic orientation, roughness, critical load, hardness, friction coefficient and surface energy were measured by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, scratch testing, nanoindentation, ball-on-disc tribometry and the contact angle method respectively. A statistical design of experiment matrix was used to investigate the effect of the Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings. From this designed experiment, it was observed that increasing MoS_2 target power was associated with increasing surface energy and decreasing friction coefficient and target powers had statistically significant effects on these parameters. Crystallinity, roughness and hardness of the coatings increased with increasing Ti concentration. A mathematical model of the effects of Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings has been fit to the experimental results using the response surface method. Uncoated and MoS_2–Ti coated Si Micromolds were used in hot-embossing for a comparative study on replication performance of uncoated and various coated Micromolds. Hotembossed PMMA microstructures showed that coating improve replication performance of Si Micromolds. Si Micromold coated with co-sputter of Ti and MoS_2 at power of 300 and 75 W respectively, showed better replication quality among the selected target powers.

  • Titanium–aluminum–polytetrafluoroethylene coated stainless steel Micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • titanium aluminum polytetrafluoroethylene coated stainless steel Micromold via co sputtering deposition replication performance and limitation in hot embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • Hot-embossing performance of silicon Micromold coated with self-assembled n-octadecyltrichlorosilane
    Sensors and Actuators B-chemical, 2011
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    Abstract Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si Micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si Micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the Micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si Micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the Micromolds and re-deposition of the OTS coatings on the coated Si Micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.

  • Improvement in lifetime and replication quality of Si Micromold using N:DLC:Ni coatings for microfluidic devices
    Sensors and Actuators B-chemical, 2010
    Co-Authors: B Saha, E. Liu, J. H. Chun, David E. Hardt, Shu Beng Tor, Nay Win Khun
    Abstract:

    Abstract In this paper the effect of surface properties of Micromolds on replication process was investigated by using nitrogen (N) and nickel (Ni) doped diamond-like carbon (N:DLC:Ni) coated and uncoated silicon (Si) Micromolds. Hot embossing is one of the most popular replication technologies for low cost and mass production. However higher friction and adhesion in hot-embossing process can shorten the lifetime of Micromolds. In the micro-hot-embossing process used for this study, the N:DLC:Ni coatings on the Si Micromolds successfully increased the lifetime of the Micromolds by 3–18 times. The N:DLC:Ni coatings were deposited on the Si Micromolds by magnetron co-sputtering at various Ni target powers. The surface and tribological properties of the molds such as bonding structure, surface roughness, surface energy, adhesive strength, friction coefficient and wear resistance were characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle measurement, micro-scratch test and ball-on-disk sliding test, respectively.

Shu Beng Tor - One of the best experts on this subject based on the ideXlab platform.

  • Effect of sputtering power on friction coefficient and surface energy of co-sputtered titanium and molybdenum disulfide coatings and its performance in micro hot-embossing
    Microsystem Technologies, 2014
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, Matthew Dirckx, J. H. Chun
    Abstract:

    Si Micromolds are common for fabrication of polymer-based microfluidic devices by hot-embossing because of the well established fabrication methods for Si, e.g., deep reactive ion etching, for favorable surface finish and accuracy. The problems with low yield, poor reproducibility, premature failure and limited lifetime of a Si Micromold are induced by high friction and surface adhesion generated during demolding. Therefore, Titanium (Ti) and molybdenum disulfide (MoS_2) coatings were deposited on Si Micromolds via magnetron co-sputtering at various combinations of target powers to improve its surface properties. Coating composition, crystallographic orientation, roughness, critical load, hardness, friction coefficient and surface energy were measured by X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, scratch testing, nanoindentation, ball-on-disc tribometry and the contact angle method respectively. A statistical design of experiment matrix was used to investigate the effect of the Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings. From this designed experiment, it was observed that increasing MoS_2 target power was associated with increasing surface energy and decreasing friction coefficient and target powers had statistically significant effects on these parameters. Crystallinity, roughness and hardness of the coatings increased with increasing Ti concentration. A mathematical model of the effects of Ti and MoS_2 target powers on the friction coefficient and surface energy of the coatings has been fit to the experimental results using the response surface method. Uncoated and MoS_2–Ti coated Si Micromolds were used in hot-embossing for a comparative study on replication performance of uncoated and various coated Micromolds. Hotembossed PMMA microstructures showed that coating improve replication performance of Si Micromolds. Si Micromold coated with co-sputter of Ti and MoS_2 at power of 300 and 75 W respectively, showed better replication quality among the selected target powers.

  • Titanium–aluminum–polytetrafluoroethylene coated stainless steel Micromold via co-sputtering deposition: Replication performance and limitation in hot-embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • titanium aluminum polytetrafluoroethylene coated stainless steel Micromold via co sputtering deposition replication performance and limitation in hot embossing
    Sensors and Actuators B-chemical, 2012
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    a b s t r a c t Stainless steel Micromold is an alternative of silicon (Si) Micromold in the fabrication of polymeric microfluidic devices because of the brittleness and short lifetime of Si mold. High adhesion and friction of stainless steel Micromold can cause the distortion of the microstructures of polymeric products. In this work, titanium (Ti), aluminum (Al) and polytetrafluoroethylene (PTFE) were co-sputter deposited on stainless steel Micromolds to improve their surface properties. The sputtering power applied to the PTFE target was varied to control the PTFE concentration in the Ti-Al-PTFE coatings, which affected the bond- ing structure, surface roughness, friction and contact angle of coatings characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), confocal microscopy, ball-on-disc tribometer and goniometer, respectively. It was observed that the Ti-Al-PTFE coatings were a mixture of carbide, PTFE- like material and amorphous carbon. The surface roughness of coated Micromolds decreased with the increase in the PTFE concentration. The Ti-Al-PTFE coating deposited with 50 W sputtering power on the PTFE target showed the lowest friction coefficient and surface energy of about 0.17 and 13.1 × 10−3 N/m, respectively. The coated stainless steel Micromolds showed a better replication performance compared to the bare stainless steel Micromolds in terms of the quality of polymeric microfluidic devices fabricated using hot embossing process. This work also investigated the coating properties at the sidewalls of the Micromold channels and the limitations of the Ti-Al-PTFE coatings for application in hot-embossing. © 2012 Elsevier B.V. All rights reserved.

  • Hot-embossing performance of silicon Micromold coated with self-assembled n-octadecyltrichlorosilane
    Sensors and Actuators B-chemical, 2011
    Co-Authors: B Saha, E. Liu, David E. Hardt, Shu Beng Tor, J. H. Chun
    Abstract:

    Abstract Self-assembled monolayer (SAM) coatings of n-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] were deposited on Si Micromolds for micro hot-embossing by dipping the Si molds into an anhydrous toluene solvent containing OTS. The coated samples were designated as OTS20, OTS40, OTS60 and OTS80 with respect to deposition time of 20, 40, 60 and 80 min to study the effect of deposition time on the coating quality. The composition, surface roughness, friction coefficient, thermal stability and surface energy were measured using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), nanotribological test and contact angle test, respectively. The thermal stability of the OTS coatings was determined by measuring water contact angle after heating at various temperatures. The XPS and AFM results showed that a prolonged deposition induced a denser and thicker coating structure and more aggregation of OTS, which also increased the surface roughness. A comparative study of the uncoated and OTS60 coated Si Micromolds depicted that the OTS coatings had a good potential to improve the surface quality and efficiency of the molds. The OTS60 coating was evaluated after heat treatment at embossing temperature of 130 °C for a better understanding of the failure mechanism of the Micromolds, which showed that the surface properties of the molds remained unchanged at the embossing temperature. Further characterization of the damaged Si Micromolds showed that the peel-off of the coatings after a number of replications was the main reason for the failure of the molds. It was found that periodic re-cleaning of the Micromolds and re-deposition of the OTS coatings on the coated Si Micromolds could extend the lifetime of the molds up to about 112 embossing operations per mold.

  • Improvement in lifetime and replication quality of Si Micromold using N:DLC:Ni coatings for microfluidic devices
    Sensors and Actuators B-chemical, 2010
    Co-Authors: B Saha, E. Liu, J. H. Chun, David E. Hardt, Shu Beng Tor, Nay Win Khun
    Abstract:

    Abstract In this paper the effect of surface properties of Micromolds on replication process was investigated by using nitrogen (N) and nickel (Ni) doped diamond-like carbon (N:DLC:Ni) coated and uncoated silicon (Si) Micromolds. Hot embossing is one of the most popular replication technologies for low cost and mass production. However higher friction and adhesion in hot-embossing process can shorten the lifetime of Micromolds. In the micro-hot-embossing process used for this study, the N:DLC:Ni coatings on the Si Micromolds successfully increased the lifetime of the Micromolds by 3–18 times. The N:DLC:Ni coatings were deposited on the Si Micromolds by magnetron co-sputtering at various Ni target powers. The surface and tribological properties of the molds such as bonding structure, surface roughness, surface energy, adhesive strength, friction coefficient and wear resistance were characterized by micro-Raman spectroscopy, atomic force microscopy (AFM), contact angle measurement, micro-scratch test and ball-on-disk sliding test, respectively.