Microplasma chemical reaction enhancement by laser modification of dielectric surface topography

A newly developed etching technique, infrared laser ablation, for microplasma device fabrication is introduced. The ablated surface provides a topography that is distinct from the surface created by conventional techniques. Chemical, optical, and electrical experiments have been conducted to observe the difference in performance between devices fabricated with the conventional and with the new technique. Carbon dioxide (CO2) dissociation and ozone (O3) generation have been observed to verify the difference. Using the new laser ablation technique, CO2 dissociation energy efficiency has been increased from 13.5 ± 3.1% to 17.4 ± 5.7%. Furthermore, introducing 10% H2 (by vol.) into CO2 with the laser-ablated device has increased the energy efficiency to 23.5 ± 4.6%. In short, total energy efficiency increase of ~75% has been achieved by combining microplasmas with the new ablation technique and the H2 mixing. Optical emission spectroscopy observation shows that the CO2+ Fox-Duffendack-Barker system is dominant at low H2 flow rates, but the CO Angstrom bands start to dominate as H2 in the reactant mixture composition is increased. Using the residual gas analyzer (RGA), mass 30 (ethane or formaldehyde) and mass 46 (ethanol or formic acid) have been observed when H2 is mixed into the CO2 microplasmas. Calculated from the RGA signal, the maximum amount of ethanol generated is ~0.4 sccm when 100 sccm (80% CO2 and 20% H2 by vol.) is flowed into a single microplasma device (“chip”). Using the laser-ablated device, the efficiency of generating O3 has been increased by 7-11% depending on the flow rate. Microcavities within the microchannel generated by laser ablation have been observed, and the average cavity diameter has been calculated to be ~33 μm, with cavity density of ~300 mm-2. Intensified charge coupled device (ICCD) images of these cavities indicate that they discharge at lower applied voltage, while the observed optical emission intensity has been measured at ~2 times higher than typical microplasma regions at any given voltage. Furthermore, the laser-ablated device that contains cavities has higher electrical conductivities. Stark broadening has been measured, and the electron density has been calculated to be 1.2×10^16 ± 0.8×10^15 cm-3 and 1.1×10^16 ± 0.8×10^15 cm-3 for the laser-ablated and powder-ablated chips, respectively. Current-voltage (i.e. I-V) characteristics of laser-ablated chips show ~6% lower breakdown voltage. Also, higher current, compared to that of powder-ablated chips, at any given voltage has been observed for the laser-ablated chips. Owing to the higher surface area of laser-ablated chips, these electrical observations agree with increased field emission effect. As the dimensions of individual cavities will play an important role in further optimizing the plasma-surface interaction, production of uniform cavities has been attempted. Uniform truncated upside-down conical shapes with bottom and top diameters of ~150 μm and ~300 μm, respectively, have been fabricated. The laser ablation technique also has shown procedural advantages over the conventional technique. From a new microchannel design to a complete microplasma chip, micropowder ablation takes ~150 hours, whereas laser ablation technique requires only ~27 hours. Furthermore, no need for consumable chemicals, such as photoresist or silicone molds, makes the laser ablation technique a safer and more economical option as a surface ablation tool for microplasma production

Microplasmas for Advanced Materials and Devices

Microplasmas are low-temperature plasmas that feature microscale dimensions and a unique high-energy-density and a nonequilibrium reactive environment, which makes them promising for the fabrication of advanced nanomaterials and devices for diverse applications. Here, recent microplasma applications are examined, spanning from high-throughput, printing-technology-compatible synthesis of nanocrystalline particles of common materials types, to water purification and optoelectronic devices. Microplasmas combined with gaseous and/or liquid media at low temperatures and atmospheric pressure open new ways to form advanced functional materials and devices. Specific examples include gas-phase, substrate-free, plasma-liquid, and surface-supported synthesis of metallic, semiconducting, metal oxide, and carbon-based nanomaterials. Representative applications of microplasmas of particular importance to materials science and technology include light sources for multipurpose, efficient VUV/UV light sources for photochemical materials processing and spectroscopic materials analysis, surface disinfection, water purification, active electromagnetic devices based on artificial microplasma optical materials, and other devices and systems including the plasma transistor. The current limitations and future opportunities for microplasma applications in materials related fields are highlighted.</p

Localized surface functionalization with atmospheric-pressure microplasma jet for cell-on-a-chip applications

Surface properties of biopolymers are crucial for providing topographical and chemical cues to affect cellular behaviors, such as attachment, spreading, viability, proliferation, and differentiation. As an effective surface modification technique, plasma treatment is often applied to enhance surface wettability, adhesion, and biocompatibility of polymers. This study concentrates on developing technical platforms, experimental procedures, and computational-statistical models to manipulate and control the cellular functions on specifically modified polymer surfaces. A novel freeform microplasma-generated maskless surface patterning process was developed to create spatially defined topological and chemical features on biopolymer surface. Global and localized plasma functionalization was performed on polycaprolactone (PCL) samples to introduce biophysical, biochemical, biological and structural cues to enhance cellular response including attachment, proliferation and differentiation. A plasma computational-statistical model was developed to predict the changes in biopolymer surface physicochemical properties following the oxygen based plasma surface functionalization. Furthermore, an integrated system including localized plasma functionalization was specifically designed for the development of biologically inspired devices. The capabilities, benefits, and challenges of the integrated multifunctional biofabrication system to develop cell-on-a-chip device were also illustrated. The objective of this thesis is to contribute scientific and engineering knowledge to the utilization of plasma chemistry to enhance surface functionalization, development of an engineering model for local plasma treatment, and integration of biofabrication processes to assemble cell-on-a-chip devices.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 201

Characterization and stabilization of atmospheric pressure DC microplasmas and their application to thin film deposition

Ph.D., Mechanical Engineering -- Drexel University, 200

The fabrication and application of carbon nanotube-based hybrid nanomaterials

The evolution of technology has reached a stage where the performances and dimension needed are outpacing what conventional materials can deliver. This has been made more acute with the further necessity of miniaturisation. Therefore, new materials which can overcome this bottleneck are required. Over the past few decades, it was found that when a material is reduced to the nanoscale, they can exhibit properties unparallel by their bulk counterparts. Therefore these nanomaterials poise as a promising candidate for future applications. Of the many nanomaterials, carbon nanotube (CNT) is among the most emblematic. CNT is a hollow one-dimensional structure comprising solely of carbon atoms. They are fascinating as they exhibit physical attributes which surpass many conventional materials and their nanoscale dimension allows greater flexibility in their deployments. However, the utilisation of CNTs is currently frustrated by a host of intrinsic and extrinsic factors. As a result, there are usually significant disparity between their predicted capability and real-world performance. Therefore, the practical application of CNTs remains unfeasible. The premise of this thesis is that by employing CNTs in conjunction with other materials, the hurdles which plague their utilisation may be overcome. Here, the concept of CNT-based hybrid nanomaterials is presented. This thesis demonstrates that by engineering complementary interaction between two materials, many challenges which hamper the utilisations of CNTs and other nanomaterials can indeed be negated. Furthermore, their synergistic interaction allows the performance of the CNT-based hybrid nanomaterials to be superior to their uncoupled precursors. Therefore, this could be a viable strategy to incorporating nanomaterials in a range of applications

Development and Diagnostics of Novel Non-Thermal PlasmaTreatment Systems

Non-thermal plasma (NTP) has been a point of interest in many areas over the last few decades. Much research has been,and continues to beundertaken,to understand the fundamentals of plasma discharges. This is such a broad topic due to the very nature and variable dependencies that set the conditions for plasma discharge to occur. This can come in the form of electrode geometry and spacing, dielectric barrier thickness, humidity of environment, material selection for electrodes and dielectric barriers, the power supply used, and the operating gas(es) used. A lot of these influencing factors can be set and kept constant, but still result invariation from system to system. However, the most important aspect comes from the power supply used and the gas(es) employedas the operating environmentfor plasma discharge. The power supply is important as there can be multiple variables applied to generate plasma andvarying each one can havea significant impact on how it behaves. Examples of such parameters include the frequency, duty cycle, voltage, current, and the number of pulses per unit time for the associate power. Gas supplies create the potential for certain chemistries to arise that allow for the processing of many types of samples. For these reasons, it is crucial that diagnostics and monitoring continue to be carried out on the many plasma systems available and currently under development so that the understanding of the multitude of possibilities that arise when using NTP for application purposes can be furthered and set with more confidence. By doing this, not only are the processes and physical properties of plasma better understood, but the mechanisms and reasons for the changes in surface properties, food modification, or biological responses are better elucidated,enablingmore efficient application methods to be developed

Microplasma Discharges in High Pressure Gases Scaling Towards the Sub-micron Regime

Atmospheric pressure microplasmas are uniquely characterized by their very high energy densities and also by their small discharge sizes. These properties allow for unique applications in plasma processing technologies. We have investigated the operational characteristics of microplasmas at higher energy densities and smaller sizes by operating microplasma configurations at high pressure conditions. We studied the discharge and analyzed its variation with changes in current and pressure. The discharge was analyzed by microscopic visualization and data from the images and was processed to measure the current density and estimate charged particle density. By increasing the pressure beyond 200 psi and by minimizing the discharge current required for sustaining the plasma, we have been able to achieve discharge sizes of 7 mu m in nitrogen and as small as 20 μm in helium. Optical emission spectroscopic studies were carried out to measure gas temperature and vibrational temperature using the nitrogen 2nd positive system. With increase in pressure, the transition from non-equilibrium plasma to equilibrium plasma was also studied using the OES temperature measurements. iv Temperature measurements are also used to estimate normalized current densities. Normalized current density results obtained after introducing the corrected effective pressure based on the increased gas temperature are close to the value of 400 mu A /cm^2*Torr^2 obtained for low pressure normal glow discharges in nitrogen. This research presents further validation of the general operational characteristics of microplasmas being pressure scaled versions of normal glow discharges. Attained energy densities are ten to twenty times higher than in atmospheric pressure microplasmas. Discharge sizes are also significantly smaller, decreasing with increasing pressure, but the scaling is with density ‘nd’ rather than pressure ‘Pd’ due to the increase in gas temperature with pressure, indicating a dependence on collisional processes. We can infer that at higher pressures, the operational characteristics of more complex plasma discharges like dielectric barrier discharges, RF plasmas, etc. follow scaling patterns, transitions and limits similar to the microplasma discharge studied in this thesis

BioMEMS

As technological advancements widen the scope of applications for biomicroelectromechanical systems (BioMEMS or biomicrosystems), the field continues to have an impact on many aspects of life science operations and functionalities. Because BioMEMS research and development require the input of experts who use different technical languages and come from varying disciplines and backgrounds, scientists and students can avoid potential difficulties in communication and understanding only if they possess a skill set and understanding that enables them to work at the interface of engineering and biosciences. Keeping this duality in mind throughout, BioMEMS: Science and Engineering Perspectives supports and expedites the multidisciplinary learning involved in the development of biomicrosystems. Divided into nine chapters, it starts with a balanced introduction of biological, engineering, application, and commercialization aspects of the field. With a focus on molecules of biological interest, the book explores the building blocks of cells and viruses, as well as molecules that form the self-assembled monolayers (SAMs), linkers, and hydrogels used for making different surfaces biocompatible through functionalization. The book also discusses: Different materials and platforms used to develop biomicrosystems Various biological entities and pathogens (in ascending order of complexity) The multidisciplinary aspects of engineering bioactive surfaces Engineering perspectives, including methods of manufacturing bioactive surfaces and devices Microfluidics modeling and experimentation Device level implementation of BioMEMS concepts for different applications. Because BioMEMS is an application-driven field, the book also highlights the concepts of lab-on-a-chip (LOC) and micro total analysis system (μTAS), along with their pertinence to the emerging point-of-care (POC) and point-of-need (PON) applications