Diamond based materials and nanostructures for advanced functional applications

This doctoral thesis is dedicated to the multidisciplinary exploration of the diverse applications of diamonds, harnessing their exceptional physical and chemical properties. Diamonds, characterized by their unique attributes, exhibit immense potential across various scientific domains and industrial sectors. The research in this thesis commenced with an extensive investigation into diamond growth technique s, with a primary focus on chemical vapor deposition (CVD). Through this method, we succeeded in expanding the spectrum of synthesized diamonds, both in terms of quality and size, thereby opening up new avenues for their utilization across a myriad of appl ications. The outcomes of this research have significantly broadened the applicability of diamonds in diverse fields such as electronics, optics, thermal management, life sciences, and materials science. Subsequently, our attention turned towards the devel opment of marine antibacterial properties. By scrutinizing the nanostructures present on diamond surfaces, we embarked on an exploration of their potential deployment in nanoelectronics devices, biomedicine, and material processing. This research is primar ily geared towards enhancing the antibacterial attributes of diamonds, thereby catering to the stringent demands of biomedical applications. Our efforts are directed at mitigating infection risks, preserving the sterility of medical equipment, averting cro ss contamination, and ushering in the era of highly sensitive biosensors and diagnostic tools.Furthermore, we have delved into the realm of diamond thermoelectric properties. Despite diamonds' inherent high thermal conductivity, which historically posed c hallenges for their use in thermoelectric applications, we have endeavored to enhance their thermoelectric performance through innovative physical modification methodologies. Leveraging the unique material characteristics of diamonds, we have unlocked thei r potential for extended longevity and stability in comparison to other thermoelectric materials. This achievement translates into reduced maintenance requirements, lower replacement frequencies, and ultimately, cost savings. Moreover, diamonds' steadfast stability equips them to maintain peak performance even in the harshest of environments, such as aerospace and energy conversion systems. In summation, this doctoral thesis undertakes a comprehensive exploration of diamonds' attributes, encompassing growth methodologies, marine antibacterial applications, and thermoelectric properties. Our research not only augments the scientific understanding of diamonds but also fosters innovation and paves the way for their diverse applications across several sectors.</p

Enhancement of the thermoelectric performance of (BiSb)2Te3 films by single target sputtering

In this study, (BiSb) 2Te3 films were deposited onto a glass substrate at 300 °C using radio frequency (RF) sputtering at various growth conditions. The effects of RF power, chamber gas pressure, and annealing temperature on the thermoelectric properties of the deposited films were investigated. An increase in the annealing temperature was found to enhance both the deposition rate and grain size. After optimizing the growth conditions and applying further annealing treatment, thin films grown at higher RF power exhibited higher electrical conductivity, attributable to an increase in carrier concentration. Additionally, films grown under 37.5 W RF power demonstrated an enhancement in the Seebeck coefficient, leading to a maximum power factor. The deposition chamber's base pressure was 10−6 mbar, and the optimal thermoelectric performance was achieved in the film grown under 0.04 mbar Ar+ partial pressure

Antibacterial properties of polycrystalline diamond films

Electronic and mechanical properties, and their biocompatibility, make diamond-based materials promising biomedical applications. The cost required to produce high quality single crystalline diamond films is still a hurdle to prevent them from commercial applications, but the emergence of polycrystalline diamond (PCD) films grown by chemical vapour deposition (CVD) method has provided an affordable strategy. PCD films grown on silicon wafer have been used throughout and were fully characterised by SEM, XPS, Raman spectroscopy and FTIR. The samples contain nearly pure carbon, with impurities originated from the CVD growth and the silicon etching process. Raman spectroscopy revealed it contained tetrahedral amorphous carbon with small tensile stress. The sp2 carbon content, comprised between 16.1 and 18.8%, is attributed to the diamond grain boundaries and iron-catalysed graphitisation. Antibacterial properties of PCD films were performed with two model bacteria, i.e. Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) using direct contact and shaking flask methods. The samples showed strong bacteriostatic properties against S. aureus and E. coli with the direct contact method and no influence on planktonic bacterial growth. These results suggest that the bacteriostatic mechanism of PCD films is linked to their surface functional groups (carbon radicals and –NH2 and –COOH groups) and that no diffusible molecules or components were involved

Morphology-dependent antibacterial properties of diamond coatings

Microorganisms promoted corrosion has caused significant loss to marine engineering and the antibacterial coatings have served as a solution that has gained attention. In this study, the chemical vapour deposition technique has been employed to grow three different types of diamond coatings, namely, ultrananocrystalline diamond (UNCD), nanocrystalline diamond (NCD), and microcrystalline diamond (MCD) coatings. The evolution of associated surface morphology and the surface functional groups of the grown coatings have demonstrated antibacterial activity in seawater environments. It is found that different ratio of sp3/sp2 carbon bonds on the diamond coatings influences their surface property (hydrophobic/hydrophilic), which changes the anti-adhesion behaviour of diamond coatings against bacteria. This plays a critical role in determining the antibacterial property of the developed coatings. The results show that the diamond coatings arising from the deposition process kill the bacteria via a combination of the mechanical effects and the functional groups on the surface of UNCD, NCD, and MCD coatings, respectively. These antibacterial coatings are effective to both Gram-negative bacteria (E. coli) and Gram-positive bacteria (B. subtilis) for 1–6 h of incubation time. When the contact duration is prolonged to 6 h or over, the MCD coatings begin to reduce the bacteria colonies drastically and enhance the bacteriostatic rate for both E. coli and B. subtilis.</p