Nanowire Zinc Oxide MOSFET Pressure Sensor

Fabrication and characterization of a new kind of pressure sensor using self-assembly Zinc Oxide (ZnO) nanowires on top of the gate of a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is presented. Self-assembly ZnO nanowires were fabricated with a diameter of 80 nm and 800 nm height (80:8 aspect ratio) on top of the gate of the MOSFET. The sensor showed a 110% response in the drain current due to pressure, even with the expected piezoresistive response of the silicon device removed from the measurement. The pressure sensor was fabricated through low temperature bottom up ultrahigh aspect ratio ZnO nanowire growth using anodic alumina oxide (AAO) templates. The pressure sensor has two main components: MOSFET and ZnO nanowires. Silicon Dioxide growth, photolithography, dopant diffusion, and aluminum metallization were used to fabricate a basic MOSFET. In the other hand, a combination of aluminum anodization, alumina barrier layer removal, ZnO atomic layer deposition (ALD), and wet etching for nanowire release were optimized to fabricate the sensor on a silicon wafer. The ZnO nanowire fabrication sequence presented is at low temperature making it compatible with CMOS technology

Nanostructures Defined by The Local Oxidation of Ferromagnetic GaMnAs Layer

The results of Local Anodic Oxidation (LAO) on the thin GaMnAs layers are reported. The ferromagnetic GaMnAs layers were prepared by low temperature MBE growth in a Veeco Mod Gen II machine. The LAO process was performed with the AFM microscope Smena NT-MDT placed in the sealed box with the controlled humidity in the range 45-80%. The oxide was grown in the semi-contact mode of the AFM. Sample was positively biased with respect to the AFM tip with the bias from 6 to 24 V. The conductive diamond coated AFM tips with the radius 30 nm were utilized for the oxidation. The tip speed during the oxidation was changed from 400 nm/s to 1.5 μm/s. The tip force was also changed during the oxidation. The height of oxide nanolines increases with applied voltage from 3 to 18 nm. The width of these lines was approximately 100 nm at half of the maximum

Biotribocorrosion of Hard-on-Hard Bearing Surfaces in Orthopaedic Hip Replacements

Following higher than acceptable failure rates, the most recent generation of Metal-on-Metal THRs have all but been removed from the market. Many recent studies in the literature attribute their failure to higher wear rates as a result of so-called ‘adverse loading’ scenarios. In order to investigate the in situ corrosive degradation of 28 mm Metal-on-Metal and Metal-on-Ceramic Total Hip Replacement components under these ‘adverse loading’ scenarios, two hip simulators were instrumented with three-electrode electrochemical cells. Various DC electrochemical analysis techniques, including Linear Polarisation Resistance and Potentiostatic Polarisation, were used to quantify the corrosion currents released from the bearings during sliding. Under 0.8 mm of Microseparation the corrosion currents were found to increase by a near order of magnitude compared to Standard Gait; which resulted in an increase of estimated corrosive volume loss from approximately 0.03 - 0.05 mm3 to as much as 0.24 mm3. A similar increase was observed for Metal-on-Ceramic bearings whereby the contribution of corrosion to total material loss from the bearing shifted from approximately 4 - 8 % to as much as 17 %. Under potentiostatic polarisation the resultant anodic current transient was found to increase with increased angle of acetabular inclination. The magnitude of peak current increased from approximately 5 - 10 µA at 30° inclination to 80 - 120 µA at 50°. Corrosion at the bearing surface of 28 mm Total Hip Components was found to be a significant source of corrosive material loss and ion release. This was also sensititve to the articulations conditions and did not necessarily scale linearly with total mass loss. Consideration of the mechanisms of degradation is therefore critical to pre-clinical assessment of devices in order to better predict in vivo performance

Boosting solar energy harvesting with ordered nanostructures fabricated by anodic aluminum oxide templates

To date, technical development has boosted the efficiencies of solar energy conversion devices with conventional planar architectures to be close to the respective theoretical values, which are hard to be further improved without reforming the device structures. Alternatively, ordered nanostructure arrays have recently emerged as efficacious scaffolds to construct devices for converting energy more efficiently due to their advantageous optical effects. To meet the global energy requirements for producing renewable energy efficiently, a general approach is needed to fabricate diverse ordered nanostructure arrays. In the meantime, the approach should allow for fine tuning in every set of nanounits towards obtaining desired properties. Herein, we utilized anodic aluminum oxide (AAO) templates to provide a versatile method for constructing ordered nanostructure arrays from one to two dimensions. Firstly, arrays of one-dimensional Au nanowires comprising two components of pillar and truncated pyramid were fabricated. Then, periodic one-dimensional Janus hetero-nanostructures with programmable morphologies, compositions, dimensions, and interfacial junctions were realized. Finally, two-dimensional superlattice photonic crystals with two sets of nanopores were constructed via a combination of the AAO template and the structural replication technique. Subsequently, these as-obtained nanostructures were integrated into photoelectrochemical water-splitting cells and solar-to-thermal conversion systems, which significantly boosted solar energy harvesting performance. In conjunction with theoretical simulations, we further elucidated that the enhanced light harvesting ability can be ascribed to twofold facts: photonic effects and surface plasmon resonance which thus provide a route to manipulate light at the nanoscale.In dieser Dissertation habe ich drei Arten von hochgeordneten Nanostrukturen realisiert, einschließlich 1D-PTP-Au-Core / CdS-Shell-Array, Au-NW / TiO2-NT-Janus-Hetero-Nanostruktur-Array und 2D-Metall-SPhCs. Diese fortschrittlichen Architekturen könnten als vielseitige Gerüste zum Aufbau energiebezogener Geräte eingesetzt werden und haben ein großes Potenzial, die Gesamtleistung drastisch zu verbessern und die durch die planare Konfiguration auferlegten Grenzen zu durchbrechen. Insbesondere die geordneten Nanostruktur-Arrays mit mehreren Komponenten sind von großer Bedeutung, und die entsprechenden Geräte können die Vorteile dieser nanostrukturierten Komponenten kombinieren, wodurch die relevante Leistung systematisch verbessert wird. Darüber hinaus ermöglichen die hohe Regelmäßigkeit der Nanostrukturverteilung, die Gleichmäßigkeit der Nanounits sowie die steuerbaren Größen und Profile der Nanostruktur die resultierenden Architekturen als leistungsfähige Plattform, um die spezifischen Energieumwandlungsreaktionen mikroskopisch zu untersuchen. Diese Ergebnisse könnten wiederum die weitere Entwicklung der relevanten Geräte leiten

The Fundamentals of Fretting Crevice Corrosion of Metallic Biomaterials for Orthopedic Implants

Metallic medical devices have been widely used in clinical applications, especially for joint arthroplasty or joint replacement surgery. Fretting corrosion, one of the most common forms of mechanically-assisted corrosion (MAC), has become a major concern associated with orthopedic medical devices. Crevice corrosion, a second mechanism of corrosion related to metallic medical devices, is a second factor of corrosion for many circumstances in medical devices that is an additional factor in the overall corrosion performance of these implants. It is a form of localized corrosion of metal surfaces present within the gap or crevice between two adjoining interfaces. The relationship and interplay between fretting and crevice corrosion is poorly understood and the observed damage seen in retrievals, which includes pitting, selective dissolution, intergranular and interphase corrosion has not been adequately duplicated in in vitro tests of mechanically assisted crevice corrosion.CoCrMo alloy, T-i6Al-4V alloy and stainless steel are the principal alloys in use today in orthopedics and are the focus of corrosion related studies. In addition, alternative materials, including ceramic materials with trusted biocompatibility, are also playing an increasingly-important role in medical device implantation. Here, we performed a series of studies intended to explore the fundamentals of fretting crevice corrosion of metallic biomaterials for orthopedic implants. We first studied CoCrMo alloy fretting corrosion debris generation and distribution using a range of characterization techniques and a custom-made fretting corrosion testing system. These several analytical surface techniques include SEM/EDS, AFM, and XPS. They were used to determine what debris was generated and to where it was distributed. Also, solution chemistry measurement (using ICP-MS) after testing was included to determine which ions and in what proportion remained in the solution. Next, a tribocorrosion model, which linked fretting mechanics, current and potential, was developed to predict currents and potential shifts resulting from fretting corrosion based on tribocorrosion theory. The model was tested against controlled fretting corrosion test conditions for its ability to predict the current-time and potential-time response. This model established a strong connection between mechanical and electrochemical aspects to demonstrate that potential and current affect each other during tribocorrosion and both are affected by other electrochemical factors (electrode area, impedance, contact mechanics, etc.) In the next step, fretting-initiated crevice corrosion in stainless steel alloys was observed and described, where fretting disruption of the surface initiated a self-sustained crevice corrosion reaction that continued even in the absence of additional fretting. The result was to comprehensively investigate fretting initiated-crevice corrosion (FICC) mechanism of stainless steel and to explore the factors, including potential and fretting duration that leads to this process. Lastly, device testing using the MTS servo-hydraulic test frame was performed to measure fretting corrosion performance of Si3N4 heads/Ti-6Al-4V modular tapers for total hip replacements in vitro and compared their behavior to standard CoCrMo heads/Ti-6Al-4V modular tapers tested under identical conditions. It was shown that using a Si3N4 ceramic head on metal trunnion significantly reduced the fretting corrosion reactions present

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

A flexible single-step 3D nanolithography approach via local anodic oxidation : theoretical and experimental studies

The field of nanotechnology has experienced rapid growth in recent years, fuelled by the increasing need for high-performance next-generation nano/quantum devices/products possessing 3D nanostructures with sub-10 nm feature sizes. As a result, there is a high demand for a new flexible nanofabrication technique capable of generating various 3D nanostructures with high precision and efficiency. Local anodic oxidation (LAO) nanolithography is a promising nanofabrication technique for the in-lab prototyping of nanoproducts due to its high precision, low environmental requirement, and ease of use. However, challenges remain with current LAO nanofabrication techniques to meet the processing demands of next-generation nanoproducts. These challenges include limited throughput, high defect rates, and inflexibility in generating various nanostructures. Consequently, the existing 3D LAO nanofabrication methods suffer from high costs and inefficiencies. Addressing these challenges is crucial for advancing the capabilities of LAO nanolithography and unlocking its full potential in nanofabrication. In this thesis, a novel flexible single-step nanofabrication approach was developed to generate diverse 3D nanostructures with sub-10 nm feature sizes through pulse-modulated LAO nanolithography. Compared with other tool and condition control methods, pulse modulation is easier to achieve with precise tunability, enabling flexible, high-precision, and cost-effective 3D nanofabrication. A clear and in-depth understanding of the manufacturing mechanisms at the atomic and molecular scales is crucial in determining the influencing factors during the manufacturing process. This thesis thus first used the reactive force field (ReaxFF) molecular dynamics simulation method to investigate the reaction mechanisms of the LAO process. A comprehensive analysis of bonding, molecular, and charge indicates that the bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film and the consumption of H2O. In contrast, the oxidised surface’s chemical composition remained unchanged during the bias-induced oxidation process. In addition, parametric studies further revealed the dependence of electric field strength and humidity on the bias-induced oxidation process and their respective influencing mechanisms. A good agreement was achieved through qualitative comparison between simulation and experimental results. Secondly, this thesis proposed a new pulse-modulated LAO nanolithography approach to realise flexible and efficient fabrication of various 3D nanostructures. The process was designed on the principle that the amplitude or width of the pulse can control the lateral and vertical growth of each nanodot while the tuning of pulse periods can determine the position of each nanodot based on certain tip scan speeds and trajectories. Feasibility tests were conducted on an atomic force microscope (AFM) to demonstrate the capability of this approach in fabricating various nanostructures with the minimum linewidth at sub-10 nm and height variations at sub-nm. Finally, nanofabrication experiments were conducted to investigate the capabilities of pulse-modulated LAO nanolithography in achieving flexible, accurate, and efficient fabrication of 3D nanostructures. Based on the systematic parametric study on the effects of pulse period, amplitude, and width through the LAO experiment, a process model was developed to provide a clear and detailed interpretation of the nanofabrication process. This model links the geometry of 3D nanostructures with arrays of pulse periods, amplitudes, and widths, allowing for active control of the LAO process. The fabrication of several 3D nanostructures was experimentally validated by comparing the fabricated and predicted results, demonstrating good agreement. The fabricated three-dimensional curved surface could achieve the average form accuracy and precision at sub-nm levels. Higher efficiency was achieved by using a high scan rate, enabling the creation of a nanoscale lens structure consisting of four thousand nanodots within 50 seconds. The efficiency and accuracy of the proposed flexible single-step nanofabrication approach were, therefore, fully demonstrated.The field of nanotechnology has experienced rapid growth in recent years, fuelled by the increasing need for high-performance next-generation nano/quantum devices/products possessing 3D nanostructures with sub-10 nm feature sizes. As a result, there is a high demand for a new flexible nanofabrication technique capable of generating various 3D nanostructures with high precision and efficiency. Local anodic oxidation (LAO) nanolithography is a promising nanofabrication technique for the in-lab prototyping of nanoproducts due to its high precision, low environmental requirement, and ease of use. However, challenges remain with current LAO nanofabrication techniques to meet the processing demands of next-generation nanoproducts. These challenges include limited throughput, high defect rates, and inflexibility in generating various nanostructures. Consequently, the existing 3D LAO nanofabrication methods suffer from high costs and inefficiencies. Addressing these challenges is crucial for advancing the capabilities of LAO nanolithography and unlocking its full potential in nanofabrication. In this thesis, a novel flexible single-step nanofabrication approach was developed to generate diverse 3D nanostructures with sub-10 nm feature sizes through pulse-modulated LAO nanolithography. Compared with other tool and condition control methods, pulse modulation is easier to achieve with precise tunability, enabling flexible, high-precision, and cost-effective 3D nanofabrication. A clear and in-depth understanding of the manufacturing mechanisms at the atomic and molecular scales is crucial in determining the influencing factors during the manufacturing process. This thesis thus first used the reactive force field (ReaxFF) molecular dynamics simulation method to investigate the reaction mechanisms of the LAO process. A comprehensive analysis of bonding, molecular, and charge indicates that the bias-induced oxidation led mainly to the creation of Si–O–Si bonds in the oxide film and the consumption of H2O. In contrast, the oxidised surface’s chemical composition remained unchanged during the bias-induced oxidation process. In addition, parametric studies further revealed the dependence of electric field strength and humidity on the bias-induced oxidation process and their respective influencing mechanisms. A good agreement was achieved through qualitative comparison between simulation and experimental results. Secondly, this thesis proposed a new pulse-modulated LAO nanolithography approach to realise flexible and efficient fabrication of various 3D nanostructures. The process was designed on the principle that the amplitude or width of the pulse can control the lateral and vertical growth of each nanodot while the tuning of pulse periods can determine the position of each nanodot based on certain tip scan speeds and trajectories. Feasibility tests were conducted on an atomic force microscope (AFM) to demonstrate the capability of this approach in fabricating various nanostructures with the minimum linewidth at sub-10 nm and height variations at sub-nm. Finally, nanofabrication experiments were conducted to investigate the capabilities of pulse-modulated LAO nanolithography in achieving flexible, accurate, and efficient fabrication of 3D nanostructures. Based on the systematic parametric study on the effects of pulse period, amplitude, and width through the LAO experiment, a process model was developed to provide a clear and detailed interpretation of the nanofabrication process. This model links the geometry of 3D nanostructures with arrays of pulse periods, amplitudes, and widths, allowing for active control of the LAO process. The fabrication of several 3D nanostructures was experimentally validated by comparing the fabricated and predicted results, demonstrating good agreement. The fabricated three-dimensional curved surface could achieve the average form accuracy and precision at sub-nm levels. Higher efficiency was achieved by using a high scan rate, enabling the creation of a nanoscale lens structure consisting of four thousand nanodots within 50 seconds. The efficiency and accuracy of the proposed flexible single-step nanofabrication approach were, therefore, fully demonstrated

ReaxFF molecular dynamics simulation study of nanoelectrode lithography oxidation process on silicon (100) surface

The nanoelectrode lithography has been strengthened in recent years as one of the most promising methods due to its high reproducibility, low cost and ability to manufacture nano-sized structures. In this work, the mechanism and the parametric influence in nanoelectrode lithography have been studied qualitatively in atomic scale using ReaxFF MD simulation. This approach was originally developed by van Duin and co-workers to investigate hydrocarbon chemistry. We have investigated the water adsorption and dissociation processes on Si (100) surface as well as the characteristics (structure, chemical composition, morphology, charge distribution, etc.) of the oxide growth. The simulation results show two forms of adsorption of water molecules: molecular adsorption and dissociative adsorption. After breaking the adsorbed hydroxyls, the oxygen atoms insert into the substrate to form the Si−O−Si bonds so as to make the surface oxidized. The influence of the electric field intensity (1.5 – 7 V/nm) and the relative humidity (20 – 90%) on the oxidation process have also been discussed. Nevertheless, the results obtained from the simulations have been compared qualitatively with the experimental results and they show in good agreements. Variable charge molecular dynamics allowed us to characterize the nanoelectrode lithography process from an atomistic point of view

Novel Nanostructured Titania and Titania Nanocomposites for Photovoltaics and Photocatalysis

With the consumption of energy continually increasing around the world and the main source of this energy, fossil fuels, slowly being depleted, the need for alternate sources of energy is becoming more and more pertinent. Demand for solar energy has experienced exponential increase over the last decade. Nanostructured TiO2 has attracted significant attention due to its nontoxicity, low cost and wide applications in photovoltaics and photocatalysis. This research is focused on novel synthesis and surface modification of TiO2 nanotube arrays for applications in advanced dye-sensitized solar cells (DSSCs) and efficient photocatalysis. The first part of this work entails fast synthesis of bamboo-type TiO2 nanotube arrays with large surface area via anodization of Ti substrates for applications as photo-anodes in high-efficiency DSSCs. In addition, titania nanotubes are modified with other nanomaterials for further increased efficiency of DSSCs. For example, uniformly-sized Ag nanoparticles are deposited onto TiO2 nanotube array via pulse electrodeposition for plasmon effect, leading to enhanced light absorption in DSSCs. Also, reduced graphene oxide nanosheets are deposited onto a TiO2 nanotube array using electrophoretic deposition, for increased electronic conductivity and improved electron transport in DSSCs. Additionally, ultra-thin two dimensional TiO2 nanosheets are synthesized via exfoliation of layered protonated titanate into separate layers using bulky organic ions, for application as photo-anodes with enhanced light scattering and dye loading in high-efficiency DSSCs. The second part of the work concentrates on synthesis of Ag-modified bamboo-type TiO2 nanotube arrays for efficient photocatalysis. Such novel titania-based nanocomposite structure provides large surface area for organic pollutant absorption and subsequent degradation; the ordered structure of nanotube array also offers direct pathway for fast electron transport. Moreover, Ag nanoparticles deposited onto TiO2 nanotubes function as reservoirs for photogenerated electrons to improve charge separation and facilitate catalytic reactions