Yonghao Xiu - Profile on Academia.edu (original) (raw)

Papers by Yonghao Xiu

Nanotechnology, Jul 18, 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.

Nano materials for microelectronic and photonic packaging

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.

IEEE Transactions on Components, Packaging and Manufacturing Technology, Jun 1, 2018

Flux materials are ubiquitously utilized in the microelectronics industry during back-end process... more Flux materials are ubiquitously utilized in the microelectronics industry during back-end processing. The Cu oxides or organic solderability preservatives present on Cu posts used in flip-chip packages must be removed by flux before solder reflow and die attachment to ensure a quality connection between the substrate and the die. However, flux residues can cause solder bridging, which renders the device useless. These residues must be studied in situ at the buried interface to determine fundamental interactions and how the residues can be eliminated. In this paper, model flux residues were investigated at the surface and the buried epoxy interface with sum frequency generation vibrational spectroscopy. Glutaric acid. served as the model flux, simulating fluxes that use dicarboxylic acids as one of the main components of the fluxing agent. It was found that the flux residues greatly change the buried interface on both Cu and silica surfaces, which affects properties such as adhesion. It was also observed that the fluxes require long washing times before they are completely removed. This paper is a step forward in flux residue analysis and will help the industry better understand molecular-level details of commonly used processes.

Journal of Applied Polymer Science, 2007

Polyhedral oligomeric silsesquioxanes (POSS) epoxy hybrid composites have attracted much research... more Polyhedral oligomeric silsesquioxanes (POSS) epoxy hybrid composites have attracted much research interest because of their unique structure, versatile synthetic approaches, and changeable properties through molecular tailoring. Octakis(dimethylsiloxypropylglycidyl ether)silsesquioxane and octakis(dimethylsiloxyethylcyclohexenyl epoxide)silsesquioxane were synthesized and cured with 4,4 0 -methylenebis(cyclohexylamine) and 4-methylhexahydrophthalic anhydride to prepare the highly crosslinked hybrid materials. The thermochemical data from DSC analysis and FTIR show that the curing reactions of POSS epoxy are more difficult than diglycidyl ether of bisphenol A (DGEBA) resin because of steric hindrance. The multifunctional structure of POSS can form highly crosslinked network throughout the composites, therefore the polymer main framework is frozen and cannot move freely. Some POSS composites do not show glass transitions and the observed relaxation for other POSS composites is likely due to the motion of tethers between POSS cores. The moduli of POSS composites, which decrease slowly with temperature increasing, are much higher than that of DGEBA resins at high temperatures. Although the coefficients of thermal expansion of POSS composites are larger than that of DGEBA resins at low temperatures, they are less dependent on temperature and relatively low at high temperatures. The unique thermal and mechanical properties of POSS composites make them potential candidates for applications in high temperature and temperature variable environments.

Langmuir, Oct 5, 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.

Journal of Colloid and Interface Science, Oct 1, 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 • .

IEEE Transactions on Components, Packaging and Manufacturing Technology, Oct 1, 2015

Delamination at heterogeneous metal/polymer interfaces during reliability testing of packaged dev... more Delamination at heterogeneous metal/polymer interfaces during reliability testing of packaged devices continues to be a reliability issue in microelectronic packaging. Although interfacial adhesion properties are largely determined by molecular structures at buried interfaces, structure-property relationships at buried metal/polymer interfaces are not well understood due to a lack of nondestructive interface sensitive analytical techniques. In this paper, methodology was developed to nondestructively characterize the molecular structure at buried copper/epoxy interfaces in situ using infrared-visible sum-frequency generation (SFG) vibrational spectroscopy. The methodology was applied to elucidate the relationship between molecular structure at the buried copper/epoxy interface and delamination behavior by correlating molecular structure with the locus of failure analysis. SFG and locus of failure analysis suggest that molecular ordering and silane behavior at the copper interface both contribute to a gradient in network structure and mechanical properties near the copper interface which was correlated with a locus of failure at an interfacial weak zone. The combined destructive and nondestructive characterization methodology developed here is general and can be directly applied to selectively characterize relationships between molecular structure at buried metal/polymer interfaces and interfacial properties such as adhesion, delamination, and interfacial moisture transport during Joint Electron Device Engineering Council qualification testing.

Biomimetic Lotus Effect Surfaces for Nanopackaging

Springer eBooks, 2021

Preparation of multi-functional silicon surface structures for solar cell applications

ABSTRACT Creation of superhydrophobic self-cleaning surfaces is an important objective for a vari... more ABSTRACT Creation of superhydrophobic self-cleaning surfaces is an important objective for a variety of applications. Indeed, numerous routes to generate superhydrophobic surfaces have been proposed. In this paper, a facile way of forming superhydrophobic surfaces is reported that uses Au assisted HF/H2O2 etching of silicon wafers. The Au layer was deposited onto a silicon wafer via e-Beam evaporation. By controlling the evaporation and etching times, the surface roughness can be manipulated and superhydrophobic surfaces with different optical properties can be generated. The effect of etchant concentration on superhydrophobicity was investigated by altering surface structures. Contact angles were measured with a CCD camera equipped goniometer; these values determined the water repellency. Light reflection on the as prepared black surfaces was measured to assess the efficiency for low cost solar cell applications. This approach offers a new way both to theoretically study the surface roughness effect and to investigate engineering applications of self-cleaning surfaces in solar cells, MEMS, anti-bacteria coating, and microfluidic devices.

Preparation of Superhydrophobic Silica Thin Films for Antistiction of MEMS Devices Using a Novel Sol-Gel Process

Based on the theory of superhydrophobicity for low surface energy coatings, we describe a superhy... more Based on the theory of superhydrophobicity for low surface energy coatings, we describe a superhydrophobic antistiction silica coating for MEMS devices. The process uses a novel sol-gel process sequence with a eutectic liquid as a templating agent. The eutectic liquid displays negligible vapor pressure and very low melting point (12degC at ambient conditions) to reduce solvent loss during the high

A Novel Method to Prepare Superhydrophobic, Self-Cleaning and Transparent Coatings for Biomedical Applications

ABSTRACT In this paper, a novel method of preparing nanostructured ultra-thin films for transpare... more ABSTRACT In this paper, a novel method of preparing nanostructured ultra-thin films for transparent superhydrophobic coatings is reported for the first time by Y. Xiu et al. A solgel process that uses a eutectic liquid solvent was employed. This solvent serves as both a low vapor pressure, low melting point liquid and a templating agent in the solgel process. UV-visible spectra indicate that after coating a glass microscope slide, with the transparent superhydrophobic coating, the light transmittance improved relative to that of a bare glass slide. The superhydrophobic surface is biocompatible because of the extremely low surface energy that results from the combination of a fluoroalkyl chain attached to the surface and the surface nanostructure. Preliminary studies suggest that the superhydrophobic coating may effectively prevent surface contamination by bacteria.

Journal of Electronic Materials, Feb 1, 2006

The remarkable properties of carbon nanotubes (CNTs) make them attractive for microelectronic app... more The remarkable properties of carbon nanotubes (CNTs) make them attractive for microelectronic applications, especially for interconnects and nanoscale devices. In this paper, we report an efficient process to grow well-aligned CNT films and high-aspect-ratio CNT arrays with very high area distribution density (>1600 m -2 ). Chemical vapor deposition (CVD) was invoked to deposit highly aligned CNTs on Al 2 O 3 /Fe coated silicon substrates of several square centimeter area using ethylene as the carbon source, and argon and hydrogen as carrier gases. The nanotubes grew at a high rate of ∼100 m/min. for nanotube films at 800°C, while the nanotube arrays grew at ∼140 m/min. even at 750°C, due to the base growth mode. The CNTs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS). The results demonstrated that the CNTs are of high purity and form densely aligned arrays with controllable size and height. The as-grown CNT structures have considerable potential for thermal management and electrical interconnects for microelectronic devices.

Langmuir, Aug 19, 2008

Silicon is employed in a variety of electronic and optical devices such as integrated circuits, p... more Silicon is employed in a variety of electronic and optical devices such as integrated circuits, photovoltaics, sensors, and detectors. In this paper, Au-assisted etching of silicon has been used to prepare superhydrophobic surfaces that may add unique properties to such devices. Surfaces were characterized by contact angle and contact angle hysteresis. Superhydrophobic surfaces with reduced hysteresis were prepared by Au-assisted etching of pyramid-structured silicon surfaces to generate hierarchical surfaces. Consideration of the Laplace pressure on hydrophobized hierarchical surfaces gives insight into the manner by which contact is established at the liquid/composite surface interface. Light reflectivity from the etched surfaces was also investigated to assess application of these structures to photovoltaic devices.

Two Scale Roughness, Self-Cleaning, and Low Reflectivity Silicon Surface for Solar Cell Applications

Acs Symposium Series, 2010

Si surface modification is of great significance for a variety of applications, such as hydrophob... more Si surface modification is of great significance for a variety of applications, such as hydrophobic treatment, surface passivation of photovoltaic devices, and microelectronic devices. In this study, a facile way of forming superhydrophobic surfaces is reported that uses Au assisted HF/H 2 O 2 etching of silicon wafers. The Au layer was deposited onto a silicon wafer via e-beam evaporation. By controlling the evaporation and etching times, the micro/nano scale roughness can be manipulated and superhydrophobic surfaces with reduced hysteresis can be generated. Light reflection on the as prepared black surfaces was measured to assess the efficiency for low cost solar cell applications. The two scale roughnes surface showed a much reduced reflectance compared to that of pyramid textured silicon surfaces which are commonly employed in high efficiency solar cells. This approach offers a new way both to theoretically study the surface roughness effect and to investigate engineering applications of self-cleaning surfaces in solar cells.

Reduction of Underfill Filler Settling in Integrated Circuit Packages

Epoxy-Amine Underfill Materials for Semiconductor Packages

IEEE Transactions on Components, Packaging and Manufacturing Technology, 2015

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 b 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.

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.

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