KRG RESEARCH PROJECTS
Biomimetic Hydrogels Nanocomposites for Responsive Wound Management Technology
Hydrogels have emerged in the biomedical field as alternatives to traditional wound dressings due to their well-defined structure and intrinsic properties such as swellability and biocompatibility. These supramolecular nanocomposites can be modified with various additives including metal ions, organic crosslinkers, antimicrobial agents, and conductive polymers to enhance these properties as well as promote responsive characteristics.
Design of a Multi-Layer Hydrogel Nanocomposite forReal-Time Monitoring
Development of a Biomimetic Supramolecular Hydrogel with Enhanced Antimicrobial Effectiveness
Our work investigates the incorporation of biomimetic additives such as amino acids into an alginate-based hydrogel to increase biomimicry of the supramolecular structure and aid in the proliferation of skin cells. Results have shown that the diversity in amino acid structure allows for a tunable material in which the pore structure can be tailored to obtain a material for specific wound types. Furthermore, metal nanoparticles have been incorporated to lyse bacterial cells that come in contact with the nanocomposite surface. These nanoparticles have also been further functionalized with antibiotics and capping agents to increase the rate of bacterial lysis.
This research focuses on the development of a conductive hydrogel nanocomposite to monitor the properties (oxygen diffusion and antimicrobial effectiveness) and lifetime (swellability) of a hydrogel. More specifically, this nanocomposite is a multi-layered system in which the first layer consists of a biomimetic, alginate hydrogel and the top scaffold is a bulk conductive polymer matrix that serves as the signal-response layer (i.e. receives charge from the biomimetic layer). Initial results show, as a simulated wound secretes, ions diffuse through the biomimetic hydrogel into the bulk conductive layer increasing the electron density to enhance the conductivity via p-doping. The changes in voltage and current are monitored and can be used to track the integrity of the matrix in real-time.
Design and Characterization of Supramolecular Nanocomposite Materials for Selective Water Remediation
Current water remediation technologies have focused on the selective removal of pollutants from complex wastewater systems. However, there is no singular existing treatment that can accommodate for all organic, inorganic, and biological pollutants in order to provide complete remediation. Our research explores the design and characterization of a supramolecular-based biomimetic adsorbent material using a β-Cyclodextrin incorporated into a cellulose-based network. The resultant nanocomposite exhibits effective textile dye adsorption and enhanced heavy metal ion sequestration from solution. With optimal synthetic design, the removal of 45% Cadmium (Cd2+) and 70% of Methylene Blue from solution has been shown. Additionally, optical microscopy and fluorescence spectroscopy are utilized to elucidate dye adsorption and heavy metal ion binding mechanisms.
Unraveling Mechanisms Relevant to Chemical Mechanical Planarization
Role of Molecular Structure on Controlling the Dynamic Equilibrium of the Electrochemical Ecosystem Present in Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP) Slurry Formulations
Chemical Mechanical Planarization (CMP) has emerged as a critical process step for achieving angstrom-level uniformity in advanced integrated circuit manufacturing and has ultimately led to the extension of Moore’s Law. CMP is used to effectively remove bulk material while limiting the number of defects during the polishing process; this can be achieved by finding the delicate balance between the chemical action of the nanoparticle/chemistry dispersion (slurry) and the mechanical force applied during the polishing process. Shallow Trench Isolation (STI) is used in the electrical isolation of the active components in an integrated circuit by actively removing oxide overburden and stopping on Si3N4 to achieve global planarity and limit defectivity. This planarity is achieved through the synergistic balance of an applied mechanical force and the incorporation of a colloidal dispersion containing ceria (CeO2) nanoparticles, rheology modifiers, and stability additives. In addition to the aforementioned additives, a main initiative of STI slurry formulation development has been centered around oxide rate control and selectivity enhancement. Current research has emphasized the addition of compounds that contain carboxylic acid, amine, and amino acid functionality. While the mechanism behind these additives is still of great debate, results have shown the importance of additive surface adsorption and nanoparticle surface redox properties. More specifically, in order to achieve optimal performance, the slurry additive must not impede the presence of surface oxygen vacancies on the nanoparticle, which are known to facilitate high oxide material removal rate (MRR). Slurry additives with redox activity as well as antioxidant properties show the highest MRR due to an increase in the surface oxygen vacancies and a decrease in the non-productive surface interactions. This research explores the structure activity relationship with known redox/antioxidant activity and their impact on the nucleophilic attack from the substrate to the nanoparticle surface oxygen vacancies. A suite of dynamic, analytical techniques such as dynamic atomic force microscopy (AFM), contact angle measurements, pre/post characterization of particle properties (size and zeta potential), coefficient of friction (COF), cyclic voltammetry, and UV-Vis spectroscopy, were employed. Results indicate a strong correlation between additive structure, slurry macro-environment, and overall CMP performance. The emphasis of this work is the application of electrochemistry in order to uncover relationships at the nanoparticle interface that directly impact the CMP performance. Understanding these molecular surface reactions can be directly correlated to device performance and can help further advance device manufacturing past the 7-nm technology node.
Probing Surface Oxidation State Influence Relevant to STI CMP
Shallow trench isolation (STI) allows for the continued miniaturization of devices by separating active circuits with a dielectric material, tetraethyl orthosilicate (TEOS). However, device functionality requires the chemical mechanical planarization (CMP) process to remove excess material using a CeO2-based colloidal dispersion. While this process is effective in achieving planarity, it is known to introduce contaminants such as: abrasive nanoparticles, polyurethane pad debris, and organic residues on the dielectric substrate. Therefore, a post-CMP cleaning step is incorporated to limit these defects. While the current industrial methods focus on using redox chemistry to facilitate CeO2 state change, our research focuses on particle encapsulation mechanisms with polyelectrolyte and surfactant-based systems. We investigate the non-covalent interactions at the chemistry/particle/wafer interface through techniques such as dynamic light scattering, adsorption studies, and coefficient of friction measurements. This has allowed our group to determine that incorporating soft, supramolecular structures in cleaning increases cleaning efficiency and limits defectivity.
Effect of Molecular Structure on Modulation of Passivation Films on Copper CMP
Copper (Cu) chemical mechanical planarization (CMP) is a critical step in the manufacturing of ultra-large-scale integrated (ULSI) semiconductor devices. Utilizing abrasive silica (SiO2) nanoparticles, among other additives, Cu CMP slurries are formulated to enhance removal rate through both increased chemical and mechanical interactions. However there exists an intrinsic balance in achieving high mechanical removal and minimizing the chemical etching of the surface to achieve global planarity. In order to control the rate of chemical corrosion, film formers are used to passivate the surface of Cu. Therefore, it is crucial to understand how changes in the passivation agent molecular structure will impact the Cu CMP process. More specifically, our work aims to mechanistically investigate the film formation mechanism using a suite of novel techniques such as open circuit potential/corrosion current, dynamic contact angle, and coefficient of friction, amongst standard polishing methods. Results have shown that aromatic film formers, such as benzotriazole (BTA) and 1,4 triazole (TAZ), demonstrate the ability to effectively passivate the Cu surface through the formation of supramolecular complexes. Thus, the strategic implementation of film formers gives tunability to Cu CMP, especially in terms of MRR control over chemical etching/dishing.
Novel Oxidizers and Pressure Responsive Composite Nanoparticles for through Silicon Via (TSV) Chemical Mechanical Planarization (CMP) Applications
Through silicon vias (TSV) has emerged as a critical process due to the vertical alignment necessary to produce 3D integrated circuit devices. As a result of the large overburden, a slurry that achieves a high Cu removal rate with minimal dishing is essential for producing highly planar and defect free substrates. Standard Cu slurries utilize a mixture of hydrogen peroxide and glycine to facilitate the formation of hydroxyl radicals as the primary mechanism of removing Cu. While hydrogen peroxide-based slurries are effective in removing Cu in traditional Cu CMP process, they are ineffective in removing typical TSV overburdens, requiring long polish times and large quantities of slurry. Therefore, we focus on investigating novel oxidizing agents and complexing agents that have shown to increase the MRR to rates greater than 1.5 microns/min. Furthermore, we are working on developing a pressure responsive, multi-layer composite nanoparticle. Layers are held together either covalently or non-covalently to the nanoparticle core using additives with amine, amino acid, and surfactant functionalities. The additives can respond to an applied force and shear at the slurry-pad interface, resulting in the controlled release of the slurry chemistry. Results show that at higher downforces removal rates are at an excess of 1 micron/min, while at low downforces the removal rates are below 0.2 micron/min, while obtaining a uniform surface with low surface roughness.
Probing Absorption Mechanisms Related to Nanoparticle/Filter
Media Interactions for CMP Applications
Next generation technology has led to the need and the development of responsive polymeric filtration media to reduce surface defectivity. Therefore, it has become essential to probe the molecular level interactions at the slurry chemistry/polymer filtration media interface, in order to correlate this to key performance metrics. Our work revealed that altering the structure of the media and complexing agent can affect the non-covalent interaction between the media, slurry additives, and the nanoparticle. Further characterization of the interactions at the media interface iss implemented by measuring the change in rate of plugging (ROP), rate of diffusion (ROD), and activation energy.
Want to know more?
Read our publication on Unraveling Slurry Chemistry/Nanoparticle/Polymeric Membrane Adsorption Relevant to Cu CMP Filtration Applications!
Synthesis and Characterization of Nanocomposite Materials for Tunable Antimicrobial Efficiency
Our research focuses on designing and incorporating nanoparticles into composite materials for various applications. The antimicrobial activity of these systems is evaluated using a custom design optical tweezer. The optical manipulation technique of this instrument, coupled with fluorescent indicators is used to probe bacterium-substrate interactions while observing real-time cell viability. These materials can be tuned to provide targeted levels of antimicrobial efficiency within various polymeric matrices.
Design and Characterization of a Conductive Cellulose Nanocomposite Anode for Enhancement of Microbial Fuel Cell Efficiency
Microbial fuel cells (MFCs) have gained attention as a source of renewable energy because of their ability to directly convert natural substrates into electric potential; however, this technology is limited due to minimal power production and high operational cost.
Our work focuses on developing nanocomposite anodes to optimize bacteria-surface interactions to enhance fuel cell performance. The cellulose-based conductive polymers increase the binding efficiency and the electrical output of the MFC using a biomimetic, cost effective material. Functionalization of the electrode matrix as well as surface modifications allow for tunability of dye adsorption, photochemical properties, and bacteria absorption.