This thesis presents the design, manufacturing, and characterisation of a multimode metal oxide-based gas sensor. The aim of the multimode sensor is to enhance selectivity by integrating a chemiresistive sensor with a quartz crystal microbalance (QCM) into a single microscale device. The motivation for this work is the limited selectivity of low-cost gas sensors compared to laboratory systems, while the proposed design maintains the ambition of low-cost fabrication, small size, and industrial applicability. The proposed sensor combines interdigitated chemiresistive electrodes, a quartz resonator, platinum heaters, temperature-sensing functionality, and a metal-oxide-sensitive layer into a single device. The design is supported by analytical calculations and thermal simulations, after which the sensor is manufactured using standard MEMS-compatible processes, including lithography, lift-off metallisation, TEOS deposition, metal oxide printing, and packaging.

The fabricated sensor is characterised using a platinum-doped SnO2 sensing layer and a sequential electrical read-out of metal-oxide resistance and resonance frequency. The chemiresistive mode shows the strongest performance, including VOC-1 detection and an estimated limit of detection. The QCM sensor shows a resonance frequency of approximately 7.67 MHz at 50 °C and a Q-factor of about 550, but its performance is limited by low resonance quality and a relatively high detection limit. Nevertheless, combining both sensing principles yields gas-dependent relations between chemiresistive sensitivity and frequency response for VOC-1, VOC-2, and VOC-3. This demonstrates that the monolithic multimode concept provides additional discriminatory information compared with either sensing principle individually. It is concluded that monolithic integration of a chemiresistive and QCM sensor can enhance selectivity, but further optimisation of the resonator design, measurement electronics, and thermal control is required before the concept can be used as a robust, selective detector at low concentration levels. ... Read more

Boron-doped diamond (BDD) is widely regarded as a highly robust electrode material for electrochemical sensing due to its wide potential window, chemical stability, low background current, and resistance to fouling. However, despite its extensive application, the fundamental relationships between BDD material properties and electrochemical performance remain insufficiently understood. This dissertation systematically investigates boron-doped diamond from material fundamentals to scalable device implementation, with the aim of advancing its rational design for sensing applications.
Chapter 1 introduces electrochemical sensing principles and outlines the unique advantages of BDD electrodes. It discusses synthesis routes, key material characteristics, and how these properties influence electrochemical responses, forming the foundation of the research objectives.
Chapter 2 investigates microstructure–electroactivity relationships in free-standing polycrystalline BDD through spatially resolved electrochemical mapping. The study reveals how grain structure and local heterogeneity influence electrochemical activity, providing insights into structure–performance correlations.
Chapter 3 focuses on the role of sp² carbon in non-enzymatic glucose sensing using BDD electrodes. By systematically analyzing the contribution of non-diamond carbon phases, the work clarifies their impact on electrocatalytic activity and challenges common assumptions regarding the origin of electrochemical responses in BDD systems.
Chapter 4 explores heavily boron-doped diamond grown on scalable heteroepitaxial quasi-substrates. The results demonstrate pathways toward improved conductivity and scalability while maintaining desirable electrochemical properties, addressing material integration challenges.
Chapter 5 presents the fabrication of inkjet-printed BDD chip electrodes, highlighting a manufacturing-oriented approach toward miniaturized and application-ready sensing platforms. The electrochemical performance of the printed devices confirms their feasibility for practical implementation.
Finally, Chapter 6 summarizes the main findings and provides outlooks for future research directions, including further material optimization, scalable production strategies, and advanced sensing applications.
Overall, this dissertation bridges fundamental material understanding and practical device realization of boron-doped diamond electrodes. By systematically correlating microstructure, carbon phase composition, doping level, and fabrication strategy with electrochemical functionality, the work contributes to the rational development of high-performance BDD-based electrochemical sensors. ... Read more

Hot-filament chemical vapor deposition (HFCVD) has become the commercially most widely used technique for producing diamond thin-film coatings due to its scalability and relatively low cost. Maintaining the geometrical stability of the hot filament, however, is challenging since filament deformation varies the distance between the filament and the substrate. This study presents a dual optimization strategy for a newly developed HFCVD reactor, combining mechanical stabilization
with computational modeling.
Multiple novel hot filament clamp concepts were explored. From this, a novel hot filament clamp using tungsten support loops suspended from alumina (Al2O3) crossbeams was designed. Thermal simulations confirmed its feasibility, with alumina components reaching a maximum of 1250 °C, safely below the working temperature of this ceramic. 3D-printed prototypes allowed for the use of tab-and-slot connections with slight tolerances. The clamp was ultimately manufactured and assembled, although reactor maintenance prevented experimental evaluation of its influence on diamond deposition.
Hereafter, a COMSOL Multiphysics model of the reactor was developed. The substrate temperature distribution is modeled as a function of deposition parameters. Achieving more even substrate temperature distributions is beneficial for diamond quality. Parametric sweeps of key deposition parameters revealed that filament-filament spacing (D) had the strongest influence on substrate temperature uniformity. When D < 8.25 mm, the temperature range across the substrate increases.
In contrast, when D > 8.25 mm, the average substrate temperature decreases, and the amplitude of periodic temperature fluctuations grows. Additionally, simulations of sagged filaments showed a significant increase in standard deviation of substrate temperature, from μ = 3.67 °C to μ = 5.33 °C, highlighting the importance of maintaining filament geometry.
This work provides a mechanical solution to filament sagging and a framework for optimizing reactor parameters through simulation. The findings offer a pathway towards scalable, high-quality diamond film deposition in this setup. ... Read more

With the development of sensor miniaturization and intelligence, the application of flexible electrochemical sensors in health monitoring and drug testing is gradually emerging. The current research focuses on the electrode application of conductive nanomaterials, and carbon-based composites are increasingly widely used in the field of flexible sensors due to their excellent conductivity and flexibility. Among them, boron-doped diamond (BDD) has attracted much attention due to its excellent electrochemical properties and corrosion resistance, making it an ideal electrode material for integration in flexible sensors. The combination of 3D printing technology, especially fused deposition modeling (FDM), provides a new path for flexible electrode manufacturing with high efficiency and low cost.
In this study, we explored the FDM printing performance of TPU/CNT/BDD and TPU/CB composites and their potential as flexible electrodes. The results show that TPU/CNT/BDD printing is difficult and the resistance increases after printing. In contrast, the printing process of TPU/CB material is simple, repeatable, and maintains excellent structural stability and conductivity under mechanical stretching. In electrochemical tests, DMSO treatment can significantly improve the conductivity and redox activity of TPU/CB electrodes, indicating that this strategy has broad prospects for applications such as flexible electronic devices, wearable sensors and energy storage devices. ... Read more

Per- and polyfluoroalkyl substances (PFAS) are widely used in products such as non-stick coatings, waterproof fabrics, and firefighting foams due to their exceptional durability and chemical stability. However, their persistence in the environment and associated toxicity have raised increasing concerns about potential health risks, necessitating effective remediation strategies. Various physical, chemical, and biological PFAS remediation methods are available. However, many are limited to removal rather than complete degradation, and/or they are highly energy intensive. A promising method for degrading PFAS is electrochemical oxidation using boron-doped diamond electrodes. This process can be carried out in an electrochemical flow cell, where optimized flow dynamics can significantly enhance degradation efficiency.

This study focused on the rapid prototyping and optimization of a miniature electrochemical flow cell using 3D printing. By integrating computational fluid dynamics models, flow profiles were analyzed and refined to improve pollutant degradation performance. To evaluate the degradation efficiency of different cell configurations, rhodamine B (RhB) was employed as a model contaminant. The study compared two electrode geometries, E21 (21-hole disk) and E41 (41-hole disk), across volumetric flow rates of 25, 50, 75, 100, and 125 mL/min. Despite E41 having approximately 20% lower current densities, its decolorization rates were comparable to E21 across all tested flow rates, suggesting improved mass transfer due to favorable flow dynamics. CFD modeling showed at a volumetric flow rate of 125 mL/min, E41 exhibited 60% lower vorticity magnitude and 30% lower turbulent kinetic energy (TKE) compared to E21. It also demonstrated 18% more uniform vorticity magnitude and 28% more uniform TKE. The E21 configuration achieved a decolorization efficiency of 98.1%, while E41 slightly outperformed it with 98.4%. The corresponding energy consumption was calculated at 156.1 kWh/m³ for E21 and 166.6 kWh/m³ for E41.

The research also explored the impact of gas bubble formation and initial RhB concentrations on system performance. Raman spectroscopy and scanning electron microscopy analyses were conducted to characterize electrode surfaces before and after use, providing insights into material durability and potential fouling behavior.

This research demonstrated that the flexibility of 3D printing enabled rapid prototyping and iterative testing, facilitating the exploration of various flow modifications. Future research will focus on evaluating the electrochemical flow cell’s effectiveness in degrading PFAS, with the expectation that optimized flow dynamics and electrode geometries will enhance the degradation rates of these persistent contaminants. Incorporating additional design modifications, such as flow-directing pillars, can be explored to promote more uniform flow profiles and potentially further enhance degradation efficiency. Such optimizations, developed on a miniature scale, lay the groundwork for future upscaling, with the potential to significantly impact real-world water treatment systems. ... Read more

This master thesis explores strain-induced quantum emitters in hexagonal boron nitride (hBN) as novel optical nanoprobes for Förster resonance energy transfer (FRET)-based biosensors. These types of emitters could outperform conventionally used fluorophores due to their high brightness, stability in harsh environments, biocompatibility and ease of integration with solid state devices. Ultimately, the aim is to combine optically-active hBN emitters with protein fingerprinting devices, which could impact the field of molecular diagnostics by detecting clinically relevant protein biomarkers.

To date, however, it is unclear which parameters are crucial for the generation of hBN quantum emitters with strain in both CVD grown and exfoliated hBN crystals. To address this gap in the field, this thesis systematically investigates the generation of strain by mechanically exfoliating pristine hBN crystals onto a variety of rigid micro/nanostructures with different aspect ratios, including 5 µm and 10 µm microbeads, femtosecond laser-ablated cavities, and CD/Blu-ray micro-nanostructures. We characterised the samples with fluorescence microscopy and atomic force microscopy in order to correlate the optical properties of the hBN with the topography of the substrate. Among the tested structures, samples displayed clear fluorescent emission at the location where the hBN was deposited on the femtosecond laser-ablated cavities with sharp edges. The presence of strain in these regions was verified with Raman spectroscopy, and the spectral properties of the fluorescent regions were determined with photoluminescence spectroscopy. We additionally studied the temporal behavior of the identified emitters and observed effects such as blinking with intensities reduced up to a 38 % and photobleaching with quantum emitters’ lifetimes between 6.57 s and 44.17 s.

While there were no clear threshold values of curvature, substrate structure height, and thickness of hBN that led to reproducible localized fluorescence, these findings open up further research opportunities for the use of strain engineering to generate quantum emitters in hBN.
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The hot-filament chemical vapor deposition (HF-CVD) method is widely used for the synthesis of thin films of polycrystalline diamond. These films are used in a broad range of applications, such as coating material on cutting tools, heat spreaders, and electrochemical sensors. HF-CVD offers some unique advantages in terms of simplicity, low equipment cost, and scalability.

Recently, a novel HF-CVD system has been designed and built at dept. PME (TU Delft), which should enable diamond deposition over relatively large substrate areas (i.e., two-inch wafers) by employing an array of multiple straight metallic filaments. However, the use of this setup so far has been primarily restricted due to the premature failure of the tungsten filaments. During the high-temperature chemical vapor deposition process, the filaments undergo large deformations due to carburization, leading to the formation of brittle metal carbides. In the initial configuration, the filaments were placed in a custom-made clamping device, obstructing their ability to expand and contract freely, resulting in residual mechanical stresses that caused premature failure of the filaments after cooling down. To enable diamond growth in this setup, a new approach is needed.

In this research, different placements of the filaments within the existing clamping device were tested to determine the optimized placement that ensures a longer filament lifespan. Additionally, a preliminary experimental parameter study was performed to investigate the effects of different deposition parameters (i.e., filament-substrate distance, stage temperature, and methane concentration) on the diamond growth on Si (100) substrates.
The optimized filament placement was achieved by simply resting the tungsten filament on both electrodes without additional fixations. In this configuration, the filaments could be used for multiple interrupted deposition runs, and even after 162 hours of usage, the filaments remained intact. The average carburization time required to reach a constant filament power consumption and to initiate the thin-film growth of diamond was found to be 8 hours when using 0.5 vol.% methane and 5 hours when using 1.0 vol.%. As the carburization proceeded, the filaments elongated and exhibited a sagging effect. The growth experiments showed that dense polycrystalline diamond films can be synthesized in this setup with growth rates ranging from ~50 nm/h to 300 nm/h depending on the deposition parameters. As diamond growth is a temperature-driven process, the substrate temperature was found to have a particularly strong effect on the film growth rate in the investigated range of 360 to 780 °C. Finally, based on the experimental results, new designs for the clamping device are proposed to maintain straight filaments during the deposition process in future experiments.

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Additive manufacturing technologies are widely gaining more attention, resulting in the development or modification of 3D-printing techniques and materials. At the same time, economical and ecological aspects force the industry to develop materials that are easier and quicker to manufacture, while attaining their desired properties. The electrochemistry field can certainly take advantage of this fabrication tool for sensing and energy-related processes. In particular, the fabrication of flexible sensing devices could extensively benefit from the currently developed 3D-printing techniques, such as fused-deposition modelling (FDM) and stereolithography (SLA), as they provide a good platform for the integration of flexible materials (polymers). Mechanical flexibility of the electrodes is desirable for biomedical sensing applications, as it improves contact between sensor and skin or neural tissue by adopting the shape and decreases mechanical stress.

Boron-doped diamond (BDD) is a popular material for electrodes because it exhibits metal-like conductivity when sufficiently doped with boron atoms. BDD possesses highly desired electrochemical characteristics such as wide potential window and low background current, while attaining diamond’s chemical stability and biocompatibility. The hardness of diamond, however, has hindered its applications in flexible electrodes due to the mechanical property mismatch between diamond and flexible substrates. Moreover, common manufacturing techniques that focus on flexible BDD electrodes are time-consuming and require complex material transferring steps.

In this work, two 3-D printing techniques, FDM and SLA, have been employed to explore the possibility to prepare 3D-printed flexible BDD-based electrodes. The effect of selected 3D printing technique, particle concentration, treatment process on the mechanical, morphological, electrical and electrochemical properties of the developed composites was thoroughly investigated. A common feature for both SLA and FDM fabrication processes, the presence of BDD particles in the polymer composites resulted in enhanced mechanical properties such as Young’s modulus (increased by 230% and 75%, for FDM and SLA, respectively), but caused a reduction in tensile strength and elongation at break. The FDM-based composites additionally allowed higher weight percent of BDD fillers to be introduced, 40 wt.% in contrast to only 12.5 wt.% achieved by SLA. For this reason, further development of composite electrodes was devoted to FDM, which allowed higher weight percentage of fillers to be introduced in the polymer.

Herein, we report, an innovative, flexible, 3D-printed conductive composite was developed through FDM that displayed promising mechanical and electrochemical characteristics. By using a unique combination of a flexible polymer, thermoplastic polyurethane (TPU), and fillers, BDD particles and carbon nanotubes (CNTs), a conductive composite material was fabricated which enabled its use as a flexible electrode. Three different compositions were fabricated that each consisted of TPU, CNTs and BDD, with CNT-to-BDD ratios of 1:0, 1:1, and 1:2. For the TPU/CNT/BDD electrodes, the electrical conductivity was significantly improved with the addition of BDD particles and displayed an increase of over 7 times (up to 1.2 S/m) compared to without BDD. This effect was similarly visible in the electrochemical characterization, and well-developed peaks were observed in the presence of two commonly used redox markers [Fe(CN)6]3−/4− and [Ru(NH3)6]3+/2+ with increasing BDD concentration. Surface treatment of the TPU/CNT/BDD electrodes drastically enhanced electrochemical properties such as double-layer capacitance (Cdl) by 250 times, but also reported significant increase in peak current intensities for both redox markers. A prominent drop in peak-to-peak separation (∆EP) for [Ru(NH3)6]3+/2+] redox marker was noticed when the electrodes were incorporated with BDD particles. From 178 mV for TPU/CNT, it decreased to 110 mV for the highest BDD-loaded electrode (TPU/CNT/BDD(1:2)). The detection of dopamine was successfully achieved through the fabricated BDD-based composite electrodes. This study provides a state-of-the art, novel composite material that is characterized by excellent flexibility, attractive electrical conductivity and promising electrochemical characteristics. It provides insights into the interactions between composite components and their impact on the electrical and electrochemical properties of the 3D-printed surfaces.
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Boron-doped diamond (BDD) is a popular material for electrodes and it exhibits metal-like conductivity when a sufficient quantity of boron atoms is incorporated in the diamond lattice. BDD has distinct advantages over alternative electrode materials. It has diamond’s chemical stability and biocompatibility in conjunction with excellent electrochemical characteristics including large potential window and low background current. Thus, BDD has great potential as an electrode material in electrochemical sensors for the detection of pharmaceutical compounds.

Of particular interest is the monitoring of the antidepressants venlafaxine (VF) and desvenlafaxine (DVF). These pharmaceuticals are prescribed to those suffering from major depressive disorder, generalized anxiety disorder, panic disorder and/or social anxiety disorder. However, they can have adverse effects on the health and behaviour of aquatic life, and harmful quantities have already been detected in nature. Monitoring of DVF and VF in a patient’s blood and urine is required to ensure correct dosage levels, which in turn could mitigate environmental pollution. An electrochemical sensor with BDD electrodes would be well-suited for this application.

In this research, two distinct BDD electrode materials were used for the electrochemical detection of VF and DVF. For initial experimentation, a robust and well-established free-standing BDD electrode type was utilized in a voltammetric study. Optimized detection conditions were achieved on hydrogen-terminated BDD for DVF and oxygen-terminated BDD for VF in a 0.1 M H2SO4 solution (pH 0.6), yielding limits of detection (LOD) of 0.31 µM and 0.17 µM and limits of quantification (LOQ) of 0.94 µM and 0.57 µM for VF and DVF, respectively. The scan rate study demonstrated that the oxidation reactions for both compounds are diffusion controlled. VF and DVF have excellent repeatability in the presence of several interfering compounds, such as inorganic ions, sucrose, glucose, and dopamine. To assess the suitability of the detection method, electroanalysis of VF and DVF in synthetic human serum, synthetic urine, and river water was conducted. Besides, a commercially available BDD electrode chip was employed for VF and DVF detection under optimized conditions. The measurement results of the different BDD electrodes were compared; in particular, when the less robust commercial electrode chip was used, larger values of LOD (1.9 µM and 8.0 µM) and LOQ (5.8 µM and 24.1 µM) were reached for VF and DVF, respectively. The fabrication of analogue BDD-based electrochemical sensors by utilizing direct inkjet printing of diamond nanoparticles on silicon substrates was evaluated in parallel. Various electrode designs were successfully printed, however subsequent chemical vapor deposition of thin-film BDD did not satisfy the required electrode quality. Notwithstanding, the use of a BDD electrode allows for the creation of a modification-free and promising practical method for VF and DVF detection.
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Diamond is known for its outstanding material properties, including highest hardness, excellent chem­ ical resistance and high thermal conductivity. Diamond, which is normally formed in high pressure and temperature environments, can also be produced as polycrystalline thin films in reduced pressure environments through chemical vapor deposition (CVD). Microfabricated diamond microstructures find their applications in a variety of micro­devices and sensors exploiting diamond’s physical and chemical properties. Current diamond microfabrication methods are limited to simple 2D and 2.5D structures, and rely on costly processes to pattern the diamond films after their growth. At present, a method to produce ar­ bitrary 3D diamond microstructures is not available, thereby limiting the exploitation of microstructured diamond . Therefore, a novel bottom­up approach to produce diamond loaded microstructures using the principle of two­photon polymerization (2PP) was explored in this MSc thesis project. The diamond loaded microstructures were developed through a monodispersed nanodiamond loaded photoresist (1 weight percentage), produced by mixing photoresist SU­8 2075 with an acetone based nanofluid containing diamond nanoparticles ranging from 3.5 to 6.0 nm in size. Using the loaded resin, the 2PP process was optimized for micropillar arrays of 20 microns in diameter and height. As a result, by utilizing the optimized parameters, microstructures with features of 2 microns and aspect ratios of 1:5 were obtained. Furthermore, the loaded microstructures showed to have a Young’s modulus of 3.2 ± 0.22 GPa compared to 2.4 ± 0.10 GPa for the base resin, thus exhibiting an increase of 33%. The obtained diamond loaded microstructures are expected to form a base for future pyrolysis and CVD processes, thereby enabling the fabrication of complex 3D diamond coated glassy carbon core­ shell microstructures. These microstructures with high surface­to­volume ratios might solve the largest bottleneck in the advance of hierarchical boron­doped diamond microelectrodes for various electro­ chemical applications. ... Read more

The presence of harmful pollutants and toxic pathogens in water is a risk to both living beings and the environment. Water treatment plays a crucial role in the removal of these contaminants through different stages of filtration. Among the existing pollutants, a family of per-and polyfluoroalkyl substances (PFAS) escapes from all treatment methods and ends up in our food, water and, finally, in our blood. Current treatment methods are not effective due to their inability to break the strong C-F bonds in PFAS. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are the most widely studied PFAS due to their widespread contamination of various environmental and biological matrices. Due to the global ban of PFOA, a short-chain fluorinated compound named GenX (the ammonium salt of hexafluoropropylene oxide dimer acid) is currently used as an alternative. However, recent studies have shown that GenX has higher toxicity compared to PFOA and is more easily soluble in water, thus making it more difficult for removal. Hence, this research surveys the potential of using boron-doped diamond (BDD) anodes, which are known to have the largest potential window and high stability over time, for GenX degradation. During the electrochemical advanced oxidation process (EAOP), the highly reactive hydroxyl radicals (OH•) produced at the BDD surface break the C-F bonds to form fluoride (Fˉ) and CO2 products. Till date, very limited research is reported on the GenX degradation and they present a contradiction on the effect of sulfate radicals (SO4•ˉ), considered for their high redox potential, in the GenX degradation. In the present study, we investigate the degradation and defluorination efficiency of GenX using boron-doped diamond anodes in EAOP. This study aims to elucidate the first step in the degradation mechanism of GenX and to clarify the contradictions previously reported on the role of sulfate radicals. Experiments are performed separately with sodium sulfate and sodium perchlorate to assess the effect of SO4•ˉ. The results demonstrate that sulfate radicals are ineffective in GenX degradation due to the steric hindrance by the -CF3 branch which blocks the trajectory of SO4•ˉ for electron transfer reaction. The effects of electrolyte concentration, current density, and chloride radicals on the degradation and defluorination are investigated for the first time to provide in-depth understanding of the degradation mechanism. A possible degradation pathway is proposed by determination of the intermediate products using mass spectrometry. From the proposed pathway, it is inferred that GenX completely mineralizes to CO2 and Fˉ via formation of three intermediates. By comparing the electrochemical degradation of GenX with that of PFOA, it is observed that the presence of the -CF3 branch increases the complexity of electron transfer in the GenX degradation even though the mineralization rate is faster for GenX than for PFOA due to lesser number of intermediates. Hence, the direct electron transfer from GenX to the BDD anode is observed to be the rate-determining step in the GenX degradation. Additionally, by comparing different BDD anodes based on their material properties and surface morphology, it is observed that the presence of sp2 regions which act as active sites for effective electron transfer is necessary to initiate the GenX degradation mechanism. Electrochemical degradation of GenX using the BDD anodes has resulted in the complete mineralization to CO2 and Fˉ which supports EAOP using BDD anodes as a promising approach towards effective PFAS degradation.
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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. ... Read more

This study explored the interactions between alkaline hydrothermal pretreatment (AHPT) operational conditions temperature (°C), NaOH concentration (M) and residence time (min) on the compositional characteristics of the solid (SH) and liquid hydrolysate (LH) obtained from AHPT of sugarcane bagasse (SCB), empty fruit bunch (EFB) and agave bagasse (AB). The experimental design was carried out with a three factors five levels (−훼, −1, 0, 1, and +훼) central composite rotatable design. Response variables for the liquid hydrolysate included glucose, xylose and arabinose content. Whereas the effects on the solid hydrolysate were evaluated with delignification and solids recovery (%). Biogas production and in situ biogas upgrading by co digestion of SH and NaOH rich LH was evaluated against mono digestion of raw and treated fibers. Therefore, methane production and methane content in the biogas were also considered response variables. Compositional characteristics were fiber dependent. Glucose, xylose and arabinose were found in SCB and AB LHs whereas for EFB LH cellobiose was also detected. A significant (p-value <0.05) linear interaction between treatment temperature and glucose release was found for SCB and AB. EFB showed significant (p-value <0.05) a quadratic interaction between temperature and retention time with glucose release. Arabinose presented a significant (p-value <0.05) linear positive interaction with temperature and NaOH concentration in all fibers. Delignification of SCB had a significant (p-value <0.05) negative correlation with the coupled effect of temperature and NaOH concentration. Solids recovery showed a significant (p-value <0.05) negative interaction with temperature and NaOH concentration for all fibers. Methane production from SCB hydrolysates co digestion presented significant (p-value <0.05) interaction with NaOH concentration and retention time. EFB hydrolysates co digestion presented a significant (p-value <0.05) interaction with temperature and NaOH concentration. Methane content in biogas presented a significant (p-value <0.05) linear interaction with temperature and NaOH concentration. No energy gain from pretreated SCB was observed. A maximum energy gain of 3.5MJ Kg-1 for pretreated empty fruit bunch. Agave bagasse presented a maximum net energy gain of 4.8 MJ Kg-1.Keywords: Empty fruit bunch; sugarcane bagasse; agave bagasse; hexoses; pentoses; lignin degradation. ... Read more

Rapid industrialization and use of carbon based fuels has caused a drastic increase in the atmospheric CO₂ levels in the last few decades. The rising anthropogenic CO₂ levels pose a significant threat to the environment as evidenced by the increase in the mean global temperature levels, and the rising ocean levels. To mitigate the challenges associated with rising CO₂ levels, there is an urgent need to move towards carbon neutral sources of energy and to curb carbon emission from large scale point emitters such as industries. Additionally, emitted CO₂ could be converted into energy dense organic fuels using carbon-neutral forms of energy. This not only helps in reducing the carbon emissions but also balances the intermittent nature of renewable energy supply. CO₂ could also be converted into platform chemicals such as ethylene/CO, which can be further up-converted or directly used in industry. Ethylene is particularly interesting due to its high
energy density and wide industrial usage as a precursor in the polymer industry. Electroreduction of CO₂ provides one such approach to electrochemically convert CO₂ produced at large scale emitters to useful organic compounds. Different metallic catalysts are known to catalyse the electrochemical reduction towards different products, which follows from Sabatier’s principle. In this study copper is used as the model catalyst due to its unique ability to electrochemically convert CO₂ to multi-carbon products, such as ethylene. From a cell design perspective conventional electrochemical reduction of CO₂ in aq. media suffers from low production rates due to the low solubility of CO₂ in aq. electrolytes which makes it not feasible from an industrial standpoint. To overcome the low production rates, this study was carried out on novel gas diffusion electrodes. Another factor limiting the implementation of CO₂ electrolysers on an industrial scale, is the scalability of the catalyst synthesis. To improve this, electrodeposition of copper catalysts was employed. Electrodeposition is a well-established industrial technique and integrable within the existing infrastructure. Electrodeposition facilitates in-situ growth of the catalyst on gas diffusion layers, thereby providing a facile alternative to the conventional multi-step process for catalyst synthesis. Different morphologies of copper were synthesized by varying the electrodeposition process parameters. Copper nanowires were also synthesized by using templated electro-deposition techniques. The catalysts were characterised before and after the CO₂ reduction experiments by Scanning ElectronMicroscopy, and X- Ray Diffraction. CO₂ reduction experiments using the synthesised copper catalysts were carried out over a range of potentials. A peak Faradaic Efficiency (FE%) of 15% was measured at -1.5 V vs RHE (uncompensated) for ethylene, 19% FE at -1.1 V vs RHE for formic acid, and 13% FE at -1.5 V vs RHE for methane. It was also seen that the catalyst suffered from stability issues which were overcome by using pulsed electrolysis. Using pulsed electrolysis the lifetime of the catalyst was increased from 30 minutes to 15 hours. ... Read more

The exceptional material properties of bulk diamond like high stiffness, high thermal conductivity, wide optical transparency, chemical inertness and bio-compatibility make it the material of choice in many high-end applications. Most present-day diamond micro-devices are fabricated by costly and time-consuming top-down methods, such as focussed ion beam milling or reactive ion etching. Hence, bottom-up methods that incorporate selective seeding and chemical vapour deposition (CVD) to produce micro-patterned poly-crystalline diamond are of interest. The present work introduces two novel methods for the bottom-up synthesis of nanocrystalline diamond micro-structures. The first method is based on the precise dispensing of nanodiamond dispersions from a hollow AFM cantilever and is used to manufacture freestanding diamond micro-resonators which are analysed on their frequency response. The second method incorporates maskless lithography to create stencils for selective seeding and enables patterned diamond growth on the single digit micrometer scale. A future step of growing such micro-structures in electrically conductive diamond could open up a vast new range up applications. ... Read more

Boron-doped diamond (BDD) is an attractive electrode material. When sufficiently boron-doped, diamond has metal-like conductivity and in comparison with other electrode materials has several advantages, such as lowand stable background current, reduced biofouling, broad potentialwindow, corrosion resistance and chemical stability. However, current fabrication processes rely on top-down techniques, that often require cleanrooms and expensive micro fabrication techniques. This research focuses on a low-cost bottom-up fabrication technique by using an inkjet printing process to locally increase the substrate seeding density. Thin-film BDD can then be selectively grown into electrode geometries. The BDD electrodes can be used as more robust and better performing electrodes for detectingmicropollutants in environmental monitoring or for detecting biomarkers in saliva, sweat or blood, in health monitoring. Inkjet manufacturing is an emerging production process in micro fabrication. Due to its accuracy, material efficiency, and given that it is a digital process, inkjet printing is a strong candidate for bottom-up fabrication of low-cost and customizable BDD (micro)-electronics. Two inkjet printers were used to investigate themicro fabrication technique for a BDD chip electrode. A hacked desktop Epson printer was used to demonstrate the capabilities of selective seeding using ’diamond’ ink on silicon substrates and to grow patterned thin-film intrinsic diamond. However, the printer lacks the required control to produce continuous structures with high accuracy. A second method for selective seeding was employed by using a PIXDRO LP-50 commercial research printer, which has a high resolution, motion controlled print bed. With the application of surface treatments, such as oxygen plasma, on the silicon substrate and the development of different inks, continuous films of nanocrystaline diamond with line resolution of approximately 60 μm are produced in a final chemical vapor deposition (CVD) growth step. In addition, by loading the printer with a silver ink part of the diamond film has been coated with silver, which demonstrates that a reference electrodes or electrode leads can be manufactured with the same production technique. This research demonstrates the potential for the bottom-up fabrication of chip electrodes using the inkjet printing process. Furthermore, as this process is not limited to the production of BDD electrodes, it opens the path towards bottom-up fabrication of other (boron-doped) diamond sensor devices, such as gas sensors or 2D heaters. ... Read more

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.
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In this MSc thesis report, the process of developing a laser aiming solution for the purpose of bird repelling will be described. This process consists roughly of five phases: Setting up requirements, generating concepts, picking and developing a single concept, building and finally testing this concept.

The current laser aiming solution is not satisfactory for many applications where safety is critical. The laser technology used by Bird Control Group to repel the birds can be dangerous to the human eye under certain circumstances. Therefore, a more accurate aiming solution is required.

A concept where the source is stationary and the laser beam is reflected with a mirror is chosen over a moving source configuration, as the moving mass in that configuration is much lower (around 4% of the moving source configuration). This means the system can reach much higher speeds and react to higher frequency input signals due to the higher eigenfrequencies of the system.

The completed prototype proved to be two orders of magnitude more accurate than the current solution, while also being much faster when required. Both of these factors and other factors contributed to the success of this project. ... Read more