Electrochemical sensing is a powerful tool for the rapid detection of (bio)molecules in fluids, and is frequently used in clinical analysis and diagnostics. Diamond is arguably the best electrode material for its robustness, wide potential window, very low background current, biocompatibility and self-cleaning features. Nowadays, there is a new trend leading to electrodes getting smaller. One of the current challenges in the development of diamond micro-electrodes is to increase the sensitivity of the diamond electrode, while the electrode’s dimensions decrease. An interesting biomolecule to detect is glucose. 2.8% of the world population suffers from diabetes, these people need to measure their blood sugar level and manage this level by dispensing insulin in their body when needed. A glucose sensor is used to determine the amount of glucose in the blood. Boron-doped diamond (BDD) is an interesting material for the non-enzymatic detection of glucose. In this thesis project, study has been done to the nanostructuring and functionalisation effects on the performance of sensing glucose by using diamond electrodes. Measurements have been done with different types of electrodes: bare BDD, acid cleaned BDD, BDD functionalised with gold nanoparticles, BDD with a nanowire surface structure, and BDD with a nanowire surface structure and gold nanoparticles on top. It was found possible to detect glucose with three of these samples: bare BDD, BDD with gold nanoparticles, and the nanostructured BDD functionalised with the gold nanoparticles. The other two electrode types did not give any reduction/oxidation peaks, which is attributed to the oxygenated surface resulting from their fabrication processes. The three glucose-detecting electrodes showed linear behaviour in a range of 1-10 $mM$, which is in line with the detection range of glucose in human blood. The sensitivities achieved with bare BDD, BDD with gold nanoparticles, and the nanostructured BDD functionalised with the gold nanoparticles are 0.022, 0.429, and 0.136 mA/mMcm^{2}, respectively. The addition of gold particles improves the sensitivity for glucose substantially and works like an electrocatalyst. Making use of electrocatalysts is an interesting and useful functionalisation for direct non-enzymatic glucose sensing, because sensing glucose with bare BDD is a kinetically very slow process. Results of such high sensitivities for BDD with gold nanoparticles were not published in literature yet, so this is a promising achievement that asks for continuation of research in this field.

Boron-doped diamond (BDD) is an electrode material applied in high end advanced oxidation processes and electrochemical sensing. BDD has a low background current, is robust and has a high affinity for the production of oxidizing radicals. BDD shows better degradation rates compared to competing electrode materials, and can also be used to detect trace amounts of compounds. The surface properties of BDD electrodes, such as the crystal sizes present on the electrode surface and the presence of non diamond content, influence their degradation and sensing performance. Electrochemical advanced oxidation processes using BDD electrodes are one of the methods investigated in literature to remove recalcitrant micro-pollutants from wastewater. Wastewater treatment at present faces a challenge to eliminate micro-pollutants of increasing complexity and toxicity. One of the compounds that could potentially benefit from the application of BDD electrodes in its removal from wastewater and detection in human blood and analogues is nevirapine. Nevirapine (NVP) is an antiretroviral on the World Health Organization’s list of essential medicines, used extensively in HIV treatment. NVP has been detected in wastewater in the continents where it is deployed as treatment, and has shown resistance to ordinary wastewater treatment. The removal of NVP from wastewater and the detection of NVP in human blood are current challenges considered in academic research. NVP has not been used in detection or degradation studies using BDD electrodes before. In this study, two types of electrodes were used to attempt to electrochemically degrade and detect NVP. The application of electrochemical activation in combination with micro-crystalline BDD electrodes for NVP sensing is a promising lead into new research to detect low concentrations of NVP using in-situ electrode cleaning. The results obtained indicate further research into the interaction between NVP and the surface of BDD electrodes as well as electrochemical activation could provide a stable detection method to asses NVP at levels competitive to those reported in literature. The research into degradation of NVP using BDD electrodes indicates the practical challenges the interaction between NVP and BDD surfaces poses, for the removal of NVP from wastewater using electrochemical advanced oxidation processes.

Micro-/nanoimprint lithography is a high-throughput, high-resolution, and low-cost mass production fabrication process often used for creating microfluidic devices and optical components. In the imprint lithography process, a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacements. These stamps are exposed to high pressures and temperatures and need to be able to withstand these circumstances in order to be durable. Diamond is potentially the ideal surface material for an imprint lithography stamp, since it has a high hardness, a high thermal conductivity coefficient, a low thermal expansion coefficient, it is chemically inert and highly wear resistant. Up until now, only molds made completely out of diamond have been used for imprint lithography. These molds were fabricated using single crystal or polished Chemical Vapor Deposited (CVD) diamond, which were then micro-structured by focused ion beam, reactive ion etching or e-beam lithography. Unfortunately, the availability of large area, single crystal diamond is very limited, and therefore extremely costly. On the other hand, diamond synthesis by chemical vapor deposition provides the possibility to deposit polycrystalline diamond films on areas up to tens of cm2. However, it is a rather slow process where typical growth rates are about 1 μm/hour, and thus production of full diamond stamps is time consuming and expensive. In this thesis, two new methods for the fabrication of CVD diamond imprint lithography molds have been developed. In the first method, a layer of 0.5 μm CVD diamond is deposited on micro-structured silicon. The second method makes use of porous silicon templates through which diamond can be grown, resulting in micro-structured diamond molds. Since polishing micro-structured diamond layers is not possible, the molds were coated with an anti-adhesion layer in order to facilitate release of the mold after imprinting. Both methods proved to be suited for imprinting into a cyclic olefin copolymer developed by TOPAS (grade 6013). With the first method, imprint dimensions of 1 μm with a depth of 350 nm were realized, and imprint dimensions of 2.5 μm with a depth of 2 μm were realized with the second fabrication method. These new approaches greatly reduce complexity of the fabrication process for durable stamps, and thereby the costs involved in creating imprint lithography stamps.

A better understanding of the wear mechanism of materials is essential to selecting suitable materials to prolong service time and reduce costs. Wear resistance is not an intrinsic material property but a response to a system including multiples parameters determined by the material, the counter body, the load condition, and the environment. Wear is a common cause of materials degradation, as well as Corrosion. When mechanical wear and corrosion co-exist, they interact with each other and, often, enhance each other, resulting in faster material failure than the situation where only a single factor exists. This thesis presents the study of the interaction between corrosion and wear with the goal of obtaining a better understanding of the wear mechanism to guide the material selection. To study the wear mechanism, a pin on disc tribometer was employed to precisely control the load, rotational speed, and corrosion environment. A potentiostat was also used to provide well-defined corrosion environment (corrosion is quantified by the current and potential). By connecting the pin on disc with a potentiostat, a well-controlled mechanical and chemical (electrochemical) system was employed to perform wear experiments. Results show that the influence of corrosion on wear is found to be much more complex than simply enhancing, as proposed at the onset of my PhD research. The new findings in this thesis show that the influence of corrosion is highly dependent on the specific situation and the corresponding wear mechanism. Corrosion may increase wear rate when the process is governed by cyclic formation and removal of surface corrosion products. Corrosion may decrease wear rate when the process is governed by the galvanic micro coupling effect. Corrosion may not influence wear rate when the process is dominated by impacting.@en