Yonghao Xiu | Georgia Institute of Technology (original) (raw)

Papers by Yonghao Xiu

Research paper thumbnail of Fabrication of surface micro-and nanostructures for superhydrophobic surfaces in electric and electronic applications

This chapter presents a mobile Web 2.0 framework for pedagogical change based upon the implementa... more This chapter presents a mobile Web 2.0 framework for pedagogical change based upon the implementation of over 30 mobile learning (m-learning) projects between 2006 and 2011. These projects explored the potential of m-learning as a catalyst for pedagogical change within architecture, product design, landscape architecture, contemporary music, computing, graphics design, performing and screen arts, accountancy law and finance, civil engineering, and journalism. The projects utilised mobile devices for student-generated content and for enabling student-generated learning contexts, bridging situated experiences with the formal classroom. Examples of the development and implementation of the framework are drawn from the context of the bachelor of product design programme at Unitec, New Zealand. The framework is founded upon contemporary social learning theory and illustrates the potential of mobile Web 2.0 tools to bridge pedagogically designed learning contexts between formal and informal learning and across international boundaries.

Research paper thumbnail of Methods of Promoting Adhesion Between Underfill and Conductive Bumps and Structures Formed Thereby

Research paper thumbnail of Methods to prevent filler entrapment in microelectronic device to microelectronic substrate interconnection structures

Research paper thumbnail of Metal-Assisted Chemical Etching of Substrates

Research paper thumbnail of Superhydrophobicity and UV stability of polydimethylsiloxane/polytetrafluoroethylene (PDMS/PTFE) coatings

International Symposium on Advanced Packaging Materials, 2006

The incorporation of polytetrafluoroethylene (PTFE) nanoparticles in curable polydimethylsiloxane... more The incorporation of polytetrafluoroethylene (PTFE) nanoparticles in curable polydimethylsiloxane (PDMS) matrix allows the formulation of superhydrophobic films with contact angles of ~155-160deg. Evaluation of the effect of PTFE particle size on the superhydrophobicity was conducted by using a larger particle size (2-5 mum); the resulting film yielded a contact angle of 140deg. However, after UV irradiation, the surface gradually lost superhydrophobicity. Changes in surface chemistry resulting from these processes were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Applications for this superhydrophobic film include the coating of microelectronic devices for self-cleaning and moisture protection

Research paper thumbnail of Controlled Growth of Well-Aligned Carbon Nanotubes and Their Assembly

International Symposium on Advanced Packaging Materials, 2006

Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, espe... more Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, especially for electrical interconnects and nanodevices, due to their excellent electrical, thermal and mechanical properties. In order to create interconnect structures comprised of CNT units, it is necessary to control the growth of CNTs in predefined orientations and configurations at a temperature compatible with current microelectronics fabrication process, and the interface with other materials such as metal electrodes. In this paper, we reported a very efficient method to grow well-aligned CNT films/arrays. For aligned CNT array growth, a lift-off process was used to pattern catalyst (Al2O3/Fe) islands to diameters of 13 or 20 mum After patterning, chemical vapor deposition (CVD) was invoked to deposit highly aligned CNT arrays using ethylene as the carbon source, and argon and hydrogen as carrier gases. The as-grown CNTs were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM). To circumvent the high carbon nanotube (CNT) growth temperature and poor adhesion with the substrates that currently plague CNT implementation, we proposed using novel CNT transfer technology, enabled by open-ended CNTs. The process is featured with separation of CNT growth and CNT device assembly. This novel technique shows promising applications for positioning of CNTs on temperature-sensitive substrates, and for the fabrication of field emitters, electrical interconnects, thermal management structures in microelectronics packaging

Research paper thumbnail of A combined etching process toward robust superhydrophobic SiC surfaces

Nanotechnology, 2012

Large-scale porous SiC was fabricated by a combination of Pt-assisted etching and reactive ion et... more Large-scale porous SiC was fabricated by a combination of Pt-assisted etching and reactive ion etching. It was found that the surface roughness of combined etchings increased dramatically in comparison with metal-assisted etching or reactive ion etching only. To reduce the surface energy, the porous SiC surface was functionalized with perfluorooctyl trichlorosilane, resulting in a superhydrophobic SiC surface with a contact angle of 169.2° and a hysteresis of 2.4°. The superhydrophobicity of the SiC surface showed a good long-term stability in an 85 °C/85% humidity chamber. Such superhydrophobicity was also stable in acidic or basic solutions, and the pH values showed little or no effect on the SiC surface status. In addition, enhancement of porosity-induced photoluminescence intensity was found in the superhydrophobic SiC samples. The robust superhydrophobic SiC surfaces may have a great potential for microfluid device, thermal ground plane, and biosensor applications.

Research paper thumbnail of Epoxy/h-BN composites for thermally conductive underfill material

Electronic Components and Technology Conference, 2009

In order to enhance thermal conductivity of underfill materials, hexagonal boron nitride (h-BN) w... more In order to enhance thermal conductivity of underfill materials, hexagonal boron nitride (h-BN) was employed as a thermally conductive filler. The relationship between the filler morphology and its effects on the thermal conductivity is focused in this study. Two different h-BN fillers with different morphologies were applied to generate an efficient thermal transport path through the filler and epoxy resin

Research paper thumbnail of Controlling the morphology and uniformity of a catalyst-infiltrated cathode for solid oxide fuel cells by tuning wetting property

Journal of Power Sources, 2010

Infiltration has been widely used in surface modification of porous electrodes in solid oxide fue... more Infiltration has been widely used in surface modification of porous electrodes in solid oxide fuel cells (SOFCs). The stability and performance of a porous electrode infiltrated with a catalyst depend sensitively on the composition, morphology, and nanostructure of the catalyst. In this contribution, we report our findings on investigation into the effect of wetting property on the formation of catalyst coatings through an infiltration process. It is observed that aqueous solutions containing catalyst precursors wet SOFC electrolyte materials (e.g., yttria-stabilized zirconia or YSZ) better than cathode materials (e.g., La0.6Sr0.4Co0.2Fe0.8O3−δ or LSCF). Controlling the wetting of catalyst precursor solutions on porous electrode backbones can dramatically improve the uniformity of the infiltrated catalyst layer on porous cathode backbone, thus enhancing the electrochemical performance of infiltrated cathodes, especially at low operating temperatures.

Research paper thumbnail of Nano materials for microelectronic and photonic packaging

IEEE International Conference on Portable Information Devices, 2008

This paper addresses the state of art nano science and technology regarding next generation high ... more This paper addresses the state of art nano science and technology regarding next generation high density microelectronics and photonics packaging applications, including carbon nanotubes (CNTs) for electrical/thermal devices, nano lead-free alloy, molecular wires for electrical interconnects, etc.

Research paper thumbnail of Modifying the anti-wetting property of butterfly wings and water strider legs by atomic layer deposition coating: surface materials versus geometry

Nanotechnology, 2008

Although butterfly wings and water strider legs have an anti-wetting property, their working cond... more Although butterfly wings and water strider legs have an anti-wetting property, their working conditions are quite different. Water striders, for example, live in a wet environment and their legs need to support their weight and bear the high pressure during motion. In this work, we have focused on the importance of the surface geometrical structures in determining their performance. We have applied an atomic layer deposition technique to coat the surfaces of both butterfly wings and water strider legs with a uniform 30 nm thick hydrophilic Al 2 O 3 film. By keeping the surface material the same, we have studied the effect of different surface roughness/structure on their hydrophobic property. After the surface coating, the butterfly wings changed to become hydrophilic, while the water strider legs still remained super-hydrophobic. We suggest that the super-hydrophobic property of the water strider is due to the special shape of the long inclining spindly cone-shaped setae at the surface. The roughness in the surface can enhance the natural tendency to be hydrophobic or hydrophilic, while the roughness in the normal direction of the surface is favorable for forming a composite interface.

Research paper thumbnail of Superhydrophobic optically transparent silica films formed with a eutectic liquid

Thin Solid Films, 2009

A eutectic liquid (choline chloride and urea) that served as a templating agent in sol–gel proces... more A eutectic liquid (choline chloride and urea) that served as a templating agent in sol–gel processing was used to prepare thin silica films on glass microscope slides. Subsequent extraction of the eutectic liquid yielded a film with a rough surface. After treating the film surface with a fluoroalkyl silane, the surface became superhydrophobic with a contact angle ∼ 170° and a contact angle hysteresis < 10°. The optical transmittance of the film coated on the glass slide was comparable to that of the microscope glass slide. Atomic Force Microscopy (AFM) was used to characterize the surface structures; a tipless probe allowed measurement of the force of interaction with superhydrophobic surfaces. The interaction force between the AFM probe and the superhydrophobic surface was reduced greatly compared to that between the probe and the flat surface treated with fluoroalkyl silane.

Research paper thumbnail of UV and thermally stable superhydrophobic coatings from sol–gel processing

Journal of Colloid and Interface Science, 2008

A method for the preparation of inorganic superhydrophobic silica coatings using sol–gel processi... more A method for the preparation of inorganic superhydrophobic silica coatings using sol–gel processing with tetramethoxysilane and isobutyltrimethoxysilane as precursors is described. Incorporation of isobutyltrimethoxysilane into silica layers resulted in the existence of hydrophobic isobutyl surface groups, thereby generating surface hydrophobicity. When combined with the surface roughness that resulted from sol–gel processing, a superhydrophobic surface was achieved. This surface showed improved UV and thermal stability compared to superhydrophobic surfaces generated from polybutadiene by plasma etching. Under prolonged UV tests (ASTM D 4329), these surfaces gradually lost superhydrophobic character. However, when the as-prepared superhydrophobic surface was treated at 500 °C to remove the organic moieties and covered with a fluoroalkyl layer by a perfluorooctylsilane treatment, the surface regained superhydrophobicity. The UV and thermal stability of these surfaces was maintained upon exposure to temperatures up to 400 °C and UV testing times of 5500 h. Contact angles remained >160° with contact angle hysteresis ∼2°.The UV stability was significantly improved after the hydrophobic surface groups (isobutyl) were replaced by fluoroalkyl groups.

Research paper thumbnail of Silicon Surface Structure-Controlled Oleophobicity

Langmuir, 2010

Superoleophobic surfaces display contact angles &amp;amp;amp;amp;gt;150 degrees with liquids ... more Superoleophobic surfaces display contact angles &amp;amp;amp;amp;gt;150 degrees with liquids that have lower surface energies than does water. The design of superoleophobic surfaces requires an understanding of the effect of the geometrical shape of etched silicon surfaces on the contact angle and hysteresis observed when different liquids are brought into contact with these surfaces. This study used liquid-based metal-assisted etching and various silane treatments to create superoleophobic surfaces on a Si(111) surface. Etch conditions such as the etch time and etch solution concentration played critical roles in establishing the oleophobicity of Si(111). When compared to Young&amp;amp;amp;amp;#39;s contact angle, the apparent contact angle showed a transition from a Cassie to a Wenzel state for low-surface-energy liquids as different silane treatments were applied to the silicon surface. These results demonstrated the relationship between the re-entrant angle of etched surface structures and the contact angle transition between Cassie and Wenzel behavior on etched Si(111) surfaces.

Research paper thumbnail of Electrowetting of Aligned Carbon Nanotube Films

Journal of Physical Chemistry B, 2006

Electrowetting is one approach to reducing the interfacial tension between a solid and a liquid. ... more Electrowetting is one approach to reducing the interfacial tension between a solid and a liquid. In this method, an electrical potential is applied across the solid/liquid interface which modifies the wetting properties of the liquid on the solid without changing the composition of the solid and liquid phases. Electrowetting of aligned carbon nanotube (CNT) films is investigated by the sessile drop method by dispensing deionized (DI) water or 0.03 M NaCl droplets (contacted by Au wire) onto aligned CNT films assembled on a copper substrate. The results demonstrate that electrowetting can greatly reduce the hydrophobicity of the aligned CNTs; the contact angle saturation for DI water and 0.03 M NaCl droplets occurs at 98 and 50 degrees , respectively. The combined effects of the geometrical roughness and the electrical potential on the contact angle are briefly discussed and modeled. Such a strategy may be invoked to controllably reduce the interfacial tension between carbon nanotubes (CNTs) and polymer precursors when infiltrating the monomers into the prealigned nanotube films.

Research paper thumbnail of Self-Assembled Monolayer-Assisted Chemical Transfer of In Situ Functionalized Carbon Nanotubes

Journal of The American Chemical Society, 2008

A low-temperature flexible process, named &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more A low-temperature flexible process, named &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;chemical transfer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;, was developed to assemble well-aligned carbon nanotube (ACNT) structures onto various substrates. The technology was featured by (1) in situ functionalization of ACNTs with reactive functional groups during the CVD process and (2) covalently bonded interface with a self-assembled monolayer (SAM) of conjugated thiol molecules as the bridging ligand and conduction path at the ACNT/gold interface. The effectiveness of the in situ functionalization was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). I-V response and the interfacial strength of the chemically transferred structure were studied. Results showed an Ohmic contact, low electrical resistivity, and improved CNT-substrate adhesion. This novel technique shows promising applications for positioning ACNTs as electrical interconnects or thermal interface materials on temperature-sensitive substrates.

Research paper thumbnail of Biomimetic Creation of Hierarchical Surface Structures by Combining Colloidal Self-Assembly and Au Sputter Deposition

Langmuir, 2006

Surfaces of hexagonally packed silica spheres have been functionalized with silanes containing di... more Surfaces of hexagonally packed silica spheres have been functionalized with silanes containing different hydrocarbon or fluorocarbon chains. The resulting chemical and physical structures were studied to establish the effect of surface hydrophobicity on the measured contact angles on the rough surfaces. The results were used to assess the effects of surface modifications on the parameters in the Cassie equation. To achieve superhydrophobicity via a biomimetic approach, we created two-scale structures by first forming hexagonally packed SiO 2 spheres, followed by Au deposition on the spheres and heat treatment to form Au nanoparticles on sphere surfaces. Contact angles over 160°were achieved. This work provides improved understanding of the effect of the surface roughness and solid surface fraction on superhydrophobicity.

Research paper thumbnail of Superhydrophobicity on Two-Tier Rough Surfaces Fabricated by Controlled Growth of Aligned Carbon Nanotube Arrays Coated with Fluorocarbon

Langmuir, 2005

Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with tw... more Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with two-tier (micro and nano) roughness, but experimental studies are few due to the difficulties in fabricating such surfaces in a controllable way. The objective of this work is to experimentally study the wetting and hydrophobicity of water droplets on two-tier rough surfaces for comparison with theoretical analyses. To compare wetting on micropatterned silicon surfaces with wetting on nanoscale roughness surfaces, two model systems are fabricated: carbon nanotube arrays on silicon wafers and carbon nanotube arrays on carbon nanotube films. All surfaces are coated with 20 nm thick fluorocarbon films to obtain low surface energies. The results show that the microstructural characteristics must be optimized to achieve stable superhydrophobicity on microscale rough surfaces. However, the presence of nanoscale roughness allows a much broader range of surface design criteria, decreases the contact angle hysteresis to less than 1 degrees , and establishes stable and robust superhydrophobicity, although nanoscale roughness could not increase the apparent contact angle significantly if the microscale roughness dominates.

Research paper thumbnail of Hierarchical Silicon Etched Structures for Controlled Hydrophobicity/Superhydrophobicity

Nano Letters, 2007

Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surf... more Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.

Research paper thumbnail of Eutectic liquid in Sol-Gel process for superhydrophobic silica thin films — antistiction of MEMS devices

2007 12th International Symposium on Advanced Packaging Materials: Processes, Properties, and Interfaces, 2007

The creation of superhydrophobic surfaces that mimick lotus leaves is a relatively new research f... more The creation of superhydrophobic surfaces that mimick lotus leaves is a relatively new research field that has attracted considerable attention. It shows promising applications in self-cleaning, microfluidics, bio-antifouling, and anticorrosion etc. Generally two requirements must be satisfied in order to achieve superhydrophobicity. First, the surface must be hydrophobic with a contact angle greater than 90°. Second, the surface needs to

Research paper thumbnail of Fabrication of surface micro-and nanostructures for superhydrophobic surfaces in electric and electronic applications

This chapter presents a mobile Web 2.0 framework for pedagogical change based upon the implementa... more This chapter presents a mobile Web 2.0 framework for pedagogical change based upon the implementation of over 30 mobile learning (m-learning) projects between 2006 and 2011. These projects explored the potential of m-learning as a catalyst for pedagogical change within architecture, product design, landscape architecture, contemporary music, computing, graphics design, performing and screen arts, accountancy law and finance, civil engineering, and journalism. The projects utilised mobile devices for student-generated content and for enabling student-generated learning contexts, bridging situated experiences with the formal classroom. Examples of the development and implementation of the framework are drawn from the context of the bachelor of product design programme at Unitec, New Zealand. The framework is founded upon contemporary social learning theory and illustrates the potential of mobile Web 2.0 tools to bridge pedagogically designed learning contexts between formal and informal learning and across international boundaries.

Research paper thumbnail of Methods of Promoting Adhesion Between Underfill and Conductive Bumps and Structures Formed Thereby

Research paper thumbnail of Methods to prevent filler entrapment in microelectronic device to microelectronic substrate interconnection structures

Research paper thumbnail of Metal-Assisted Chemical Etching of Substrates

Research paper thumbnail of Superhydrophobicity and UV stability of polydimethylsiloxane/polytetrafluoroethylene (PDMS/PTFE) coatings

International Symposium on Advanced Packaging Materials, 2006

The incorporation of polytetrafluoroethylene (PTFE) nanoparticles in curable polydimethylsiloxane... more The incorporation of polytetrafluoroethylene (PTFE) nanoparticles in curable polydimethylsiloxane (PDMS) matrix allows the formulation of superhydrophobic films with contact angles of ~155-160deg. Evaluation of the effect of PTFE particle size on the superhydrophobicity was conducted by using a larger particle size (2-5 mum); the resulting film yielded a contact angle of 140deg. However, after UV irradiation, the surface gradually lost superhydrophobicity. Changes in surface chemistry resulting from these processes were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Applications for this superhydrophobic film include the coating of microelectronic devices for self-cleaning and moisture protection

Research paper thumbnail of Controlled Growth of Well-Aligned Carbon Nanotubes and Their Assembly

International Symposium on Advanced Packaging Materials, 2006

Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, espe... more Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, especially for electrical interconnects and nanodevices, due to their excellent electrical, thermal and mechanical properties. In order to create interconnect structures comprised of CNT units, it is necessary to control the growth of CNTs in predefined orientations and configurations at a temperature compatible with current microelectronics fabrication process, and the interface with other materials such as metal electrodes. In this paper, we reported a very efficient method to grow well-aligned CNT films/arrays. For aligned CNT array growth, a lift-off process was used to pattern catalyst (Al2O3/Fe) islands to diameters of 13 or 20 mum After patterning, chemical vapor deposition (CVD) was invoked to deposit highly aligned CNT arrays using ethylene as the carbon source, and argon and hydrogen as carrier gases. The as-grown CNTs were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM). To circumvent the high carbon nanotube (CNT) growth temperature and poor adhesion with the substrates that currently plague CNT implementation, we proposed using novel CNT transfer technology, enabled by open-ended CNTs. The process is featured with separation of CNT growth and CNT device assembly. This novel technique shows promising applications for positioning of CNTs on temperature-sensitive substrates, and for the fabrication of field emitters, electrical interconnects, thermal management structures in microelectronics packaging

Research paper thumbnail of A combined etching process toward robust superhydrophobic SiC surfaces

Nanotechnology, 2012

Large-scale porous SiC was fabricated by a combination of Pt-assisted etching and reactive ion et... more Large-scale porous SiC was fabricated by a combination of Pt-assisted etching and reactive ion etching. It was found that the surface roughness of combined etchings increased dramatically in comparison with metal-assisted etching or reactive ion etching only. To reduce the surface energy, the porous SiC surface was functionalized with perfluorooctyl trichlorosilane, resulting in a superhydrophobic SiC surface with a contact angle of 169.2° and a hysteresis of 2.4°. The superhydrophobicity of the SiC surface showed a good long-term stability in an 85 °C/85% humidity chamber. Such superhydrophobicity was also stable in acidic or basic solutions, and the pH values showed little or no effect on the SiC surface status. In addition, enhancement of porosity-induced photoluminescence intensity was found in the superhydrophobic SiC samples. The robust superhydrophobic SiC surfaces may have a great potential for microfluid device, thermal ground plane, and biosensor applications.

Research paper thumbnail of Epoxy/h-BN composites for thermally conductive underfill material

Electronic Components and Technology Conference, 2009

In order to enhance thermal conductivity of underfill materials, hexagonal boron nitride (h-BN) w... more In order to enhance thermal conductivity of underfill materials, hexagonal boron nitride (h-BN) was employed as a thermally conductive filler. The relationship between the filler morphology and its effects on the thermal conductivity is focused in this study. Two different h-BN fillers with different morphologies were applied to generate an efficient thermal transport path through the filler and epoxy resin

Research paper thumbnail of Controlling the morphology and uniformity of a catalyst-infiltrated cathode for solid oxide fuel cells by tuning wetting property

Journal of Power Sources, 2010

Infiltration has been widely used in surface modification of porous electrodes in solid oxide fue... more Infiltration has been widely used in surface modification of porous electrodes in solid oxide fuel cells (SOFCs). The stability and performance of a porous electrode infiltrated with a catalyst depend sensitively on the composition, morphology, and nanostructure of the catalyst. In this contribution, we report our findings on investigation into the effect of wetting property on the formation of catalyst coatings through an infiltration process. It is observed that aqueous solutions containing catalyst precursors wet SOFC electrolyte materials (e.g., yttria-stabilized zirconia or YSZ) better than cathode materials (e.g., La0.6Sr0.4Co0.2Fe0.8O3−δ or LSCF). Controlling the wetting of catalyst precursor solutions on porous electrode backbones can dramatically improve the uniformity of the infiltrated catalyst layer on porous cathode backbone, thus enhancing the electrochemical performance of infiltrated cathodes, especially at low operating temperatures.

Research paper thumbnail of Nano materials for microelectronic and photonic packaging

IEEE International Conference on Portable Information Devices, 2008

This paper addresses the state of art nano science and technology regarding next generation high ... more This paper addresses the state of art nano science and technology regarding next generation high density microelectronics and photonics packaging applications, including carbon nanotubes (CNTs) for electrical/thermal devices, nano lead-free alloy, molecular wires for electrical interconnects, etc.

Research paper thumbnail of Modifying the anti-wetting property of butterfly wings and water strider legs by atomic layer deposition coating: surface materials versus geometry

Nanotechnology, 2008

Although butterfly wings and water strider legs have an anti-wetting property, their working cond... more Although butterfly wings and water strider legs have an anti-wetting property, their working conditions are quite different. Water striders, for example, live in a wet environment and their legs need to support their weight and bear the high pressure during motion. In this work, we have focused on the importance of the surface geometrical structures in determining their performance. We have applied an atomic layer deposition technique to coat the surfaces of both butterfly wings and water strider legs with a uniform 30 nm thick hydrophilic Al 2 O 3 film. By keeping the surface material the same, we have studied the effect of different surface roughness/structure on their hydrophobic property. After the surface coating, the butterfly wings changed to become hydrophilic, while the water strider legs still remained super-hydrophobic. We suggest that the super-hydrophobic property of the water strider is due to the special shape of the long inclining spindly cone-shaped setae at the surface. The roughness in the surface can enhance the natural tendency to be hydrophobic or hydrophilic, while the roughness in the normal direction of the surface is favorable for forming a composite interface.

Research paper thumbnail of Superhydrophobic optically transparent silica films formed with a eutectic liquid

Thin Solid Films, 2009

A eutectic liquid (choline chloride and urea) that served as a templating agent in sol–gel proces... more A eutectic liquid (choline chloride and urea) that served as a templating agent in sol–gel processing was used to prepare thin silica films on glass microscope slides. Subsequent extraction of the eutectic liquid yielded a film with a rough surface. After treating the film surface with a fluoroalkyl silane, the surface became superhydrophobic with a contact angle ∼ 170° and a contact angle hysteresis < 10°. The optical transmittance of the film coated on the glass slide was comparable to that of the microscope glass slide. Atomic Force Microscopy (AFM) was used to characterize the surface structures; a tipless probe allowed measurement of the force of interaction with superhydrophobic surfaces. The interaction force between the AFM probe and the superhydrophobic surface was reduced greatly compared to that between the probe and the flat surface treated with fluoroalkyl silane.

Research paper thumbnail of UV and thermally stable superhydrophobic coatings from sol–gel processing

Journal of Colloid and Interface Science, 2008

A method for the preparation of inorganic superhydrophobic silica coatings using sol–gel processi... more A method for the preparation of inorganic superhydrophobic silica coatings using sol–gel processing with tetramethoxysilane and isobutyltrimethoxysilane as precursors is described. Incorporation of isobutyltrimethoxysilane into silica layers resulted in the existence of hydrophobic isobutyl surface groups, thereby generating surface hydrophobicity. When combined with the surface roughness that resulted from sol–gel processing, a superhydrophobic surface was achieved. This surface showed improved UV and thermal stability compared to superhydrophobic surfaces generated from polybutadiene by plasma etching. Under prolonged UV tests (ASTM D 4329), these surfaces gradually lost superhydrophobic character. However, when the as-prepared superhydrophobic surface was treated at 500 °C to remove the organic moieties and covered with a fluoroalkyl layer by a perfluorooctylsilane treatment, the surface regained superhydrophobicity. The UV and thermal stability of these surfaces was maintained upon exposure to temperatures up to 400 °C and UV testing times of 5500 h. Contact angles remained >160° with contact angle hysteresis ∼2°.The UV stability was significantly improved after the hydrophobic surface groups (isobutyl) were replaced by fluoroalkyl groups.

Research paper thumbnail of Silicon Surface Structure-Controlled Oleophobicity

Langmuir, 2010

Superoleophobic surfaces display contact angles &amp;amp;amp;amp;gt;150 degrees with liquids ... more Superoleophobic surfaces display contact angles &amp;amp;amp;amp;gt;150 degrees with liquids that have lower surface energies than does water. The design of superoleophobic surfaces requires an understanding of the effect of the geometrical shape of etched silicon surfaces on the contact angle and hysteresis observed when different liquids are brought into contact with these surfaces. This study used liquid-based metal-assisted etching and various silane treatments to create superoleophobic surfaces on a Si(111) surface. Etch conditions such as the etch time and etch solution concentration played critical roles in establishing the oleophobicity of Si(111). When compared to Young&amp;amp;amp;amp;#39;s contact angle, the apparent contact angle showed a transition from a Cassie to a Wenzel state for low-surface-energy liquids as different silane treatments were applied to the silicon surface. These results demonstrated the relationship between the re-entrant angle of etched surface structures and the contact angle transition between Cassie and Wenzel behavior on etched Si(111) surfaces.

Research paper thumbnail of Electrowetting of Aligned Carbon Nanotube Films

Journal of Physical Chemistry B, 2006

Electrowetting is one approach to reducing the interfacial tension between a solid and a liquid. ... more Electrowetting is one approach to reducing the interfacial tension between a solid and a liquid. In this method, an electrical potential is applied across the solid/liquid interface which modifies the wetting properties of the liquid on the solid without changing the composition of the solid and liquid phases. Electrowetting of aligned carbon nanotube (CNT) films is investigated by the sessile drop method by dispensing deionized (DI) water or 0.03 M NaCl droplets (contacted by Au wire) onto aligned CNT films assembled on a copper substrate. The results demonstrate that electrowetting can greatly reduce the hydrophobicity of the aligned CNTs; the contact angle saturation for DI water and 0.03 M NaCl droplets occurs at 98 and 50 degrees , respectively. The combined effects of the geometrical roughness and the electrical potential on the contact angle are briefly discussed and modeled. Such a strategy may be invoked to controllably reduce the interfacial tension between carbon nanotubes (CNTs) and polymer precursors when infiltrating the monomers into the prealigned nanotube films.

Research paper thumbnail of Self-Assembled Monolayer-Assisted Chemical Transfer of In Situ Functionalized Carbon Nanotubes

Journal of The American Chemical Society, 2008

A low-temperature flexible process, named &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;am... more A low-temperature flexible process, named &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;chemical transfer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;, was developed to assemble well-aligned carbon nanotube (ACNT) structures onto various substrates. The technology was featured by (1) in situ functionalization of ACNTs with reactive functional groups during the CVD process and (2) covalently bonded interface with a self-assembled monolayer (SAM) of conjugated thiol molecules as the bridging ligand and conduction path at the ACNT/gold interface. The effectiveness of the in situ functionalization was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). I-V response and the interfacial strength of the chemically transferred structure were studied. Results showed an Ohmic contact, low electrical resistivity, and improved CNT-substrate adhesion. This novel technique shows promising applications for positioning ACNTs as electrical interconnects or thermal interface materials on temperature-sensitive substrates.

Research paper thumbnail of Biomimetic Creation of Hierarchical Surface Structures by Combining Colloidal Self-Assembly and Au Sputter Deposition

Langmuir, 2006

Surfaces of hexagonally packed silica spheres have been functionalized with silanes containing di... more Surfaces of hexagonally packed silica spheres have been functionalized with silanes containing different hydrocarbon or fluorocarbon chains. The resulting chemical and physical structures were studied to establish the effect of surface hydrophobicity on the measured contact angles on the rough surfaces. The results were used to assess the effects of surface modifications on the parameters in the Cassie equation. To achieve superhydrophobicity via a biomimetic approach, we created two-scale structures by first forming hexagonally packed SiO 2 spheres, followed by Au deposition on the spheres and heat treatment to form Au nanoparticles on sphere surfaces. Contact angles over 160°were achieved. This work provides improved understanding of the effect of the surface roughness and solid surface fraction on superhydrophobicity.

Research paper thumbnail of Superhydrophobicity on Two-Tier Rough Surfaces Fabricated by Controlled Growth of Aligned Carbon Nanotube Arrays Coated with Fluorocarbon

Langmuir, 2005

Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with tw... more Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with two-tier (micro and nano) roughness, but experimental studies are few due to the difficulties in fabricating such surfaces in a controllable way. The objective of this work is to experimentally study the wetting and hydrophobicity of water droplets on two-tier rough surfaces for comparison with theoretical analyses. To compare wetting on micropatterned silicon surfaces with wetting on nanoscale roughness surfaces, two model systems are fabricated: carbon nanotube arrays on silicon wafers and carbon nanotube arrays on carbon nanotube films. All surfaces are coated with 20 nm thick fluorocarbon films to obtain low surface energies. The results show that the microstructural characteristics must be optimized to achieve stable superhydrophobicity on microscale rough surfaces. However, the presence of nanoscale roughness allows a much broader range of surface design criteria, decreases the contact angle hysteresis to less than 1 degrees , and establishes stable and robust superhydrophobicity, although nanoscale roughness could not increase the apparent contact angle significantly if the microscale roughness dominates.

Research paper thumbnail of Hierarchical Silicon Etched Structures for Controlled Hydrophobicity/Superhydrophobicity

Nano Letters, 2007

Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surf... more Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.

Research paper thumbnail of Eutectic liquid in Sol-Gel process for superhydrophobic silica thin films — antistiction of MEMS devices

2007 12th International Symposium on Advanced Packaging Materials: Processes, Properties, and Interfaces, 2007

The creation of superhydrophobic surfaces that mimick lotus leaves is a relatively new research f... more The creation of superhydrophobic surfaces that mimick lotus leaves is a relatively new research field that has attracted considerable attention. It shows promising applications in self-cleaning, microfluidics, bio-antifouling, and anticorrosion etc. Generally two requirements must be satisfied in order to achieve superhydrophobicity. First, the surface must be hydrophobic with a contact angle greater than 90°. Second, the surface needs to