Micro/Nano Manufacturing

Micro manufacturing involves dealing with the fabrication of structures in the size range of 0.1 to 1000 µm. The scope of nano manufacturing extends the size range of manufactured features to even smaller length scales—below 100 nm. A strict borderline between micro and nano manufacturing can hardly be drawn, such that both domains are treated as complementary and mutually beneficial within a closely interconnected scientific community. Both micro and nano manufacturing can be considered as important enablers for high-end products. This Special Issue of Applied Sciences is dedicated to recent advances in research and development within the field of micro and nano manufacturing. The included papers report recent findings and advances in manufacturing technologies for producing products with micro and nano scale features and structures as well as applications underpinned by the advances in these technologies

Polysaccharide and Silver Nanoparticles Based Hydrogels, Porous Materials, and Sensors

Cellulose based hydrogels and porous materials are gaining significant attention across a wide range of applications due to the natural abundance, biodegradability and physicochemical tunability of this polysaccharide. Cellulose nanofibrils (CNF) outperform cellulose fibers in terms of physicochemical tunability since CNF possess relatively high surface area. However, superior dispersibility of CNF in aqueous phase makes it challenging for traditional methods to dewater CNF suspensions to fabricate robust hydrogels and porous materials. In this dissertation, a novel scalable capillary based method to dewater CNF suspensions is invented as well as CNF hydrogels and porous materials with a broad range of porosity and mechanical properties were generated. CNF hydrogels and porous materials were further modified by creating a chemically crosslinked semi-interpenetrating (semi-IPN) network in the CNF matrices to enhance the mechanical robustness of these materials. Silver Nanoparticles have been incorporated xix into these semi-IPN networks to generate robust surface enhanced Raman scattering (SERS) substrates for trace level detection and quantification of organic molecules

Theoretical approach to atomic-scale nanoplasmonics as probed by light and swift electrons

223 P.This thesis tackles the theoretical description of atomic-scale features in plasmonic nanostructures asprobed by light and swift electrons. Plasmonic nanostuctures are known to localize and enhanceelectromagnetic fields in their proximity, and thus serve as building blocks to perform improved andenhanced molecular spectroscopy on them. We focus on the analysis of the effect of atomic-scale featuresin the overall response of plasmonic nanoparticles and nanocavities. We apply ab initio atomisticquantum time-dependent density functional theory (TDDFT) to unveil the near-field distribution aroundmetallic antennas, and describe "classically" various atomic-scale features such as continuous protrusionson the surfaces of the metal using a Boundary Element Method (BEM), providing an extra localization ofthe field. Moreover, we propose an analytical model to address the signal increase observed in surfaceenhancedRaman scattering (SERS) spectra related to local variations of the electron density associated toatomic-scale defects. Last, we identify the excitation of confined bulk plasmons (CBP) within theTDDFT calculations for the electron energy loss (EEL) probability of atomistic clusters, and provide asemi-analytical expression within a Hydrodynamic Model (HDM) to address such excitation

Recent Advances in Linear and Nonlinear Optics

Sight is the dominant sense of mankind to apprehend the world at the earth scale and beyond the frontiers of the infinite, from the nanometer to the incommensurable. Primarily based on sunlight and natural and artificial light sources, optics has been the major companion of spectroscopy since scientific observation began. The invention of the laser in the early sixties has boosted optical spectroscopy through the intrinsic or specific symmetry electronic properties of materials at the multiscale (birefringence, nonlinear and photonic crystals), revealed by the ability to monitor light polarization inside or on the surface of designed objects. This Special Issue of Symmetry features articles and reviews that are of tremendous interest to scientists who study linear and nonlinear optics, all oriented around the common axis of symmetry. Contributions transverse the entire breadth of this field, including those concerning polarization and anisotropy within colloids of chromophores and metal/semiconducting nanoparticles probed by UV-visible and fluorescence spectroscopies; microscopic structures of liquid–liquid, liquid–gas, and liquid–solid interfaces; surface- and symmetry-specific optical techniques and simulations, including second-harmonic and sum-frequency generations, and surface-enhanced and coherent anti-Stokes Raman spectroscopies; orientation and chirality of bio-molecular interfaces; symmetry breaking in photochemistry; symmetric multipolar molecules; reversible electronic energy transfer within supramolecular systems; plasmonics; and light polarization effects in materials

Desenvolvimento e caracterização de microagulhas apatíticas e bruhíticas para a libertação controlada de antibióticos

Mestrado em Materiais e Dispositivos BiomédicosAs microagulhas (MN) são microcomponentes inovadores na entrega de fármacos via transdérmica de forma quase impercetível para o paciente. De metais a polímeros, as MN têm sido fabricadas com uma grande variedade de materiais, embora com algumas restrições quanto à resistência mecânica (limitações relacionadas com a perfuração da pele), armazenamento e altos custos de fabrico. Na presente tese, foram utilizados cimentos à base de fosfato tricálcico (TCP) para o fabrico de MN brushíticas e apatíticas via micromoldagem. Foram sintetizados dois pós, -TCP e BTCP (bifásico, -TCP + -TCP). Partindo destes pós, foram preparadas pastas cimentícias na ausência e na presença de fármaco, variando a razão líquido/pó e caracterizadas em termos de tempos de presa inicial e final, parâmetros importantes para o enchimento e desmoldagem dos componentes. Os cimentos resultantes foram caracterizados em termos de porosidade, fases cristalinas, resistência mecânica, microestrutura da superfície e metodologia de secagem. As formulações de cimento que apresentaram os resultados mais promissores para o fabrico de MN foram utilizadas para estudar a taxa de libertação do fármaco. Uma solução aquosa de ácido cítrico com concentração adequada como líquido de presa revelou ser a mais adequada. O antibiótico levofloxacina (LEV) foi utilizado como fármaco modelo. Os resultados obtidos mostraram que a adição de LEV aumenta os tempos de presa iniciais e finais das pastas cimentícias e diminui as propriedades mecânicas dos cimentos. Uma libertação de fármaco de 100% foi alcançada para todas as formulações de cimento testadas após 48 horas de imersão. Do estudo cinético da libertação de fármaco verificou-se que o "Coupled Mechanism" foi o que melhor descreveu o mecanismo de libertação da LEV em todas as formulações de cimentos testadas. Com as pastas cimentícias foi possível obter microagulhas afiadas por enchimento de micromoldes e devidamente desmoldadas. Através da avaliação da sua resistência mecânica é possível prever que as MN obtidas apresentam estrutura e propriedades mecânicas adequadas para a perfuração da pele, uma vez que, é conhecido da literatura que a força necessária para que as agulhas perfurarem a pele humana é à volta de 1-5 N. Das várias agulhas testadas, os valores da força necessária para quebrar a ponta situam-se num intervalo de 57 a 110 N. As MN à base de cimentos de TCP apresentam características adequadas para serem utilizadas como meio de administração de fármacos via transdérmica com futuro em diversas aplicações médicas. O processo de produção utilizado traz imensas vantagens quando comparado com os métodos atuais para a produção de microcomponentes, sendo simples, económico e replicável.Microneedles (MN) are an up and coming technology offering almost inconspicuous transdermal drug delivery system. From metals to polymers, microneedles have been fabricated with a high variety of materials, although with some constraints regarding mechanical strength (limitations related to skin perforation), storage and high manufacturing costs. In the present thesis, self-setting bioceramics were used to fabricate brushitic and apatitic MN by micro-molding casting. Two precursor powders were synthesized to obtain -TCP and BTCP (biphasic,-TCP+-TCP) as main phases. Cement pastes were prepared in absence and in presence of drug, varying liquid to powder ratio and characterized in terms of initial and final setting times, important parameters for casting and de-molding procedures. The resulting cements were characterized for their porosity, crystalline phases, mechanical strength, surface morphology and drying methodology. The cement formulations that presented the most promising results for MN fabrication (flowability during casting and adequate mechanical properties for de-molding without damage) were used to study drug release rate. A citric acid solution with adequate concentration was the most suitable as setting liquid in both MN types. The antibiotic levofloxacin was used as a model drug. The results show that the addition of levofloxacin increases the setting times of the cement pastes and decreases the mechanical properties of the cements. A 100% drug release was achieved for all the tested cement formulations after 48 hours of immersion time. The drug release kinetics were evaluated being determined that the "coupled mechanism" is the one that best described the release mechanism of cements obtained from both powders. Sharp MN were successfully casted and de-molded. MN tip obtained in this work present adequate mechanical properties for skin perforation without breakage, since according to literature the insertion forces necessary for perforate human skin is around 1-5 N. Among all tested MN, the force necessary to break the tip is in the range 57 to 110 N. From the evaluated work, calcium phosphate cement based MN present adequate characteristics to be used as a promising drug delivery microcomponent for biomedical applications. The fabrication process used (micromolding) has several advantages when compared to the current production MN processes being simple, cost-effective and replicable

Silver-based nanocomposite materials for marine antifouling applications

Biofouling of marine surfaces is an age-old problem that affects natural and man-made surfaces exposed to the aquatic environment. The tenacious attachment of seaweed and invertebrates to man-made surfaces, notably on ship hulls, has incurred undesirable economic losses. The initial stage of the biofouling process has been attributed to the attachment of marine bacteria and their subsequent formation of biofilm which attract the settlement of larger sessile organisms including barnacles and seaweed. Silver nanostructured materials have a well-documented history as antimicrobial agents against pathogenic bacteria due to their ability to penetrate cell walls and interfere with crucial cellular processes. However, there is a surprising lack of information on their activity against marine biofilm bacteria that have critical roles in the initiation of marine fouling processes. This PhD project explores the antifouling properties of novel silver nanocomposite materials as potent antifouling agents against targeted organisms present in marine environments. The study consists of the syntheses of novel silver nanocomposite materials using various templates/matrices such as ion-exchange polymeric microspheres, zeolites, TiO2 nanotubes and graphene nanosheets. These materials were characterized through various instrumentation techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray powder diffraction (XRD), UV-visible (UV-vis) spectrophotometry, transmission electron microscopy (TEM), accelerated surface area porosimetry (ASAP), thermal gravimetric analysis (TGA), and Raman spectroscopy to elucidate their physical properties. Their antifouling effects were evaluated on Halomonas pacifica, a model marine microfouling bacterium, through an established static biofilm assay. In addition, the biological effects of these silver nanocomposites were also studied on marine microalgae Dunaliella tertiolecta and Isochrysis sp. Silver-polymer nanocomposite (Ag-PNC) microspheres were formed through a rapid chemical synthesis procedure at room temperature via the reduction of silver nitrate by sodium borohydride. The introduction of Ag nanoparticles (AgNPs) enhanced the thermal stability of the Dowex microspheres by shifting the glass transition temperature to above 300°C and the material decomposition occurred above 460°C. XRD analysis confirmed the presence of metallic Ag, while UV-vis absorption studies showed the characteristic surface plasmon resonance (SPR) for AgNPs ranging from 406 – 422 nm maximum absorption wavelengths. SEM imaging revealed the uniform distribution of AgNPs with diameters between 20 – 60 nm on the surface of the microbeads. The Ag-PNC materials, diluted to a concentration of 1 mg/mL in marine broth, showed a potent inhibitory effect on H. pacifica biofilm formation, with up to 76% decrease of biofilm when contrasted with the polymeric microspheres without Ag. Ag-PNCs also caused significant growth inhibition of D. tertiolecta and Isochrysis sp. Silver-zeolite nanocomposite clusters (AgZ) were formed through a low temperature chemical reduction method using the environmentally friendly trisodium citrate. The stable and porous inner structure of ZSM-5 zeolites performed a dual role as a stable size-control template and a reservoir of antimicrobial nanosilver. SEM revealed the globular and cluster-like morphology of the AgZ composites, with a homogenous distribution of silver particles on the surface of the clusters. EDX results displayed an increasing Ag loading with higher concentrations of Ag precursor, up to 10 wt% Ag. The UV-visible absorption displayed the characteristic SPR absorption maximum ranging from 408 – 500 nm. The AgZ clusters with metallic silver loading of up to 10 wt% Ag, diluted to a concentration of 1 mg/mL, reduced H. pacifica biofilm attachment of up to 81% compared to pure zeolite alone. XRD analysis clearly indicated the presence of metallic Ag while the ZSM-5 zeolite crystalline framework remained largely intact after the Ag crystal growth process. Brunauer-Emmett-Teller (BET) analysis showed a reduction in surface area of up to 44% with the incorporation of AgNPs into the zeolite, indicating the formation and growth of Ag within the internal pores and channels of the zeolite. Although the introduction and crystal growth of silver nanoparticles within the porous structure of the zeolite caused a change from a mesoporous to a largely macroporous structure, the integrity of the zeolite template was preserved. Silver-titania nanotube (Ag/TNT) composite material was prepared through a novel 2-step hydrothermal synthesis method. Titania nanotubes were chosen as a support material for the AgNPs as its greater specific surface area on the inner and outer surfaces of its tubular structure lead to enhanced properties. The morphology, particle size, chemical content, crystal structure, optical properties and surface area were systematically characterized. Determination of biofilm inhibitory properties revealed that Ag/TNT (concentration of 0.1 mg/mL) with the lowest silver content (0.95 wt% Ag) decorated with AgNPs of approximately 3 nm reduced biofilm formation of H. pacifica by 98% compared to pure titania nanotubes and bulk silver alone. Growth inhibition of D. tertiolecta and Isochrysis sp. were also observed. Interestingly, the antifouling properties were improved with a size decrease of AgNPs. The work shows that titania nanotubes are a stable and effective support for the anchoring and growth of AgNPs. The addition of very low amounts of Ag enhanced the antifouling property of pure TiO2 to produce an extremely potent antifouling effect on the targeted organisms. Graphene-Ag (GAg) nanocomposites were prepared from a novel and mild hydrothermal synthesis method which bypasses the formation of graphene oxide. The GAg nanocomposite combines the antimicrobial property of silver nanoparticles and the unique structure of graphene as a support material, with potent marine antifouling properties. The results show that GAg nanocomposites displayed significant biofilm inhibition property on H. pacifica and antiproliferative effects on D. tertiolecta and Isochrysis sp. As low as 1.3 wt% of Ag loading on a GAg sample, diluted to a concentration of 0.1 mg/mL, inhibited biofilm formation from H. pacifica. The GAg sample with 4.9 wt% Ag loading was associated with a biofilm inhibition of 99.6%. The marine antifouling properties of GAg nanocomposites were a synergy of the biocidal AgNPs anchored on the flexible graphene sheets, thereby providing maximum active contact surface areas to the target organisms. The GAg material was characterized with SEM, EDX, TEM, XRD and Raman spectroscopy. In addition, the GAg material exhibited the surface-enhanced Raman scattering (SERS) effect. The AgNPs were estimated to be between 72-86 nm, observed supported on micron-scaled graphene flakes. These results strongly suggest that the 4 types of silver-based nanocomposite materials are promising marine antifouling agents. The addition of very low amounts of Ag enhanced the antifouling property of the support structure, and the nanocomposites were shown to be more effective on the targeted organisms compared to the matrix material or bulk silver alone. In addition, the precursor materials used in the syntheses are affordable and easily available, whilst the synthetic methods and conditions are facile, environmentally friendly, and capable of producing high yields

Advanced Thermoelectric Materials for Energy Harvesting Applications

Electrical energy consumption is negatively affecting our environment and contributing to climate change. Therefore the research and industrial communities are working hard to minimize energy consumption using promising energy-efficient and renewable energy technologies. We know that it is possible to convert heat energy into electrical energy using thermoelectric devices; this heat energy can be from the sun or from an electro-mechanical device. However, thermoelectric devices traditionally suffer from lower efficiencies of energy conversion. This book, Advanced Thermoelectric Materials for Energy Harvesting Applications, is a researchintensive textbook consisting of eight chapters organized into three sections. Section 1 consists of Chapters 2, 3, and 4, which cover advanced thermoelectric materials and the topics of organic/inorganic thermoelectric materials, quantum theory of the Seebeck coefficient for the advancement of thermoelectric superconducting material, and the limits of Bismuth Telluride-based thermoelectric materials. Section 2, containing Chapters 5 and 6, evaluates behaviors and performance of thermoelectric devices. Section 3, containing Chapters 7 and 8, focuses on energy harvesting applications of thermoelectric devices. This book will be of interest to a wide range of individuals, such as scientists, engineers, researchers, and undergraduate and postgraduate students in the field of advanced thermoelectric materials

Surface plasmons for enhanced mid-infrared graphene photodetection

Information photonics, which deals with the manipulation, detection, generation and transmission of light across a broad wavelength range has undoubtedly shaped and transformed our daily life, from mobile and communication devices to computing and the internet. Although the research and application of photonic devices based on silicon and other semiconductor materials have shown potentials towards the next information revolution, several intrinsic limitations have shown up, resulting from the common drawbacks of semiconductors, such as large footprint, limited absorption bandwidth and complex and expensive manufacturing process. Therefore, the exploration of new material is highly demanded and the integration with other research fields, such as electronics, is crucial. Integrated optoelectronics, which bridges optics and electronics through manipulating, detecting and generating optical signals with electronic signals, provides the ability to tackle some of the existing challenges, because it not only inherits the mature processing protocols and theories from well-developed integrated electronics but also assimilates advantages from optics. Among integrated optoelectronics devices, photodetectors, devices that transduce absorbed photons into measurable electrical signals, are ubiquitous. They are the key components for optical communications, imaging, security, night-vision, spectroscopy and motion detection. Current commercial photodetectors have thrived on the development of band theory and the maturity of semiconductor growth and manufacturing; however, current mid-infrared photodetectors are intrinsically limited by high dark current, low working temperature and responsivity and expensive cost resulting from the narrow band gap of semiconductor alloys and restrictive materials growth process. Nevertheless, the mid-infrared wavelength plays a crucial role in the applications of spectroscopy, security and industry, chemical and biological sensing. Therefore, exploration and investigation of novel materials for mid-infrared photodetection is critical. Graphene, a one-atom-thick layer of sp2-bonded carbon atoms tightly packed in a hexagonal lattice, has shown potential as a substitute material for silicon for the next information revolution because of its extraordinary optical, electronic, mechanical and thermal properties. These exceptional properties make it a promising candidate for a comprehensive range of applications, such as energy and storage, electronics, biomedical, flexible and wearables, photonics and optoelectronics. For example, the intrinsic surface plasmons based on a graphene platform surpass conventional plasmons because of its exceptional characteristics including tuneability, adjustability and relatively low dissipation, which implies that novel manufactured devices based on graphene surface plasmons can operate with low power consumption and driving voltage, small footprint and unrivalled speed. Moreover, the broadband absorption from UV to THz, ultrafast carrier mobility and tuneable Fermi level are prominent for mid-infrared photodetection. Common mid-infrared photodetection focuses on wavelength; if other states of light, such as polarisation and phase could be detected at same time, detection bandwidth could be broadened, and detection functionality increased. Compared with wavelength detection, the detection of circular polarisation states is much less explored, especially at the mid-infrared wavelength range. Chirality, a geometric property of a structure, can be utilised to detect polarisation states of light due to the reason that chiral structures behave differently for incident light with different circular polarisation states. The main objective of this thesis is to explore both theoretically and experimentally new types of mid-infrared graphene photodetectors enhanced by surface plasmons to address the main drawbacks of mid-infrared photodetection, such as low working temperature, low responsivity, high costs and lacking detection of polarisation states. The primary achievements are summarised as follows: To simultaneously detect the spin angular momentum states of mid-infrared region from 3 to 5 µm, we employ a photodetection structure that contains a zigzag chiral metal structure and a graphene layer. The localised surface plasmons can be excited within this designed photodetection structure to enhance the light absorption of graphene layer and distinct the spin angular momentum states by producing photocurrent with different direction. First, to understand how the nano-engineered chiral structure affects spin angular momentum and the potential size of the circular dichroism, we performed a detailed theoretical simulation of the hybrid structure and optimised all geometric parameters. To unveil the physical mechanisms behind the high graphene absorption and circular dichroism, we performed an electric field analysis of the left-handed and right-handed structure with left circularly polarised (LCP) and right circularly polarised (RCP) light at resonant wavelength. It is shown that the hybrid structures with different chirality resonant differently for the incident light with left-circular polarised state and right-circular polarised state respectively. In addition, the circular dichroism originates from the different absorption for LCP and RCP because the zigzag chiral structures resonant differently. Instructed by these theoretical investigations, we fabricated mid-infrared graphene photodetectors that contain a zigzag gold structure, graphene layer and SiO2/Si substrate, via steps including graphene transfer, photolithography, electron beam lithography and electron beam deposition. To qualitatively and quantitatively characterise our fabricated devices, we performed characterisations with SEM; the error of all measured structure sizes was less than 3.1% compared with designed values, which proves the high precision and uniformity of the fabricated devices. Moreover, to characterise the optical properties of our fabricated devices, FTIR measurements were taken. Considering that incident light is not pure plane wave and not all the light is vertically illuminated on the devices, the simulated and measured extinction spectra and circular dichroism spectra were highly consistent. To electrically characterise these photodetectors, we conducted photocurrent measurements with our home-made photocurrent characterisation system. Results show that responsivity of 0.36 µA/Wwas achieved for left-handed (LHD) structure with LCP light illumination (0.33 µA/Wfor right-handed (RHD) structure with RCP light illumination) and the circular dichroism was approximately 75% both LHD and RHD structures. Most importantly, photocurrent with different circulation direction was produced when the incident light possessed different circular polarisation states, which is the novel contribution of our proposed simultaneous mid-infrared spin angular momentum photodetector. Surface plasmons supported by a gold chiral structure possesses a parasitic absorption problem. Moreover, chirality originates from the chiral structure and the monolayer graphene only acts as a transport layer for the photodetector. Hence, to fully implement the potential of graphene and take advantage of its exceptional optical and electrical properties, we investigated a mid-infrared photodetector based on a grapheme nanomesh (GNM) structure. Tuneable intrinsic graphene plasmons is introduced to enhance light absorption (i.e., to enhance the responsivity of device). Further, band gap engineering was utilised to improve the electron-hole separation efficiency and restrict dark current. To fully understand the impacts of geometric size and graphene properties on band gap engineering and intrinsic graphene plasmons and investigate whether they can work side by side, we performed a thorough theoretical analysis of this proposed GNMstructure. First, we calculated the band gap of four representative types of GNM structures and their dependence on the period length of the unit cell and diameter of the hole. Then we investigated the impact of these two parameters on absorption magnitude of the GNMlayer and resonant wavelength of photodetectors. The band gap energy of the GNM is larger than the energy of thermal fluctuation at room temperature implying the opened band gap can effectively restrict dark current. As it was smaller than graphene plasmons energy, this proves that incident mid-infrared light at resonant wavelength can be absorbed and excited electrons can jump from valence band to conduction band. Thus, this proves that band gap engineering and graphene plasmons can work side by side to improve performance. Experimentally, GNM structures with period length of 100 nm and hole diameters from 40 nm to 80 nm were achieved. The geometric characterisation results show that the experimental size was within ± 5% of the design size. The resistance change under different back-gate voltages proved the tuneability of fabricated devices. Most importantly, the shifted resonant peaks shown on extinction spectra manifested the resonant graphene local surface plasmon supported by the GNM platform and the tunability of the Fermi level of the GNM layer. In summary, this thesis demonstrates novel research on mid-infrared photodetection and offers two significant contributions. The first is the increase in detector functionality by simultaneously detecting the LCP and RCP light. The second is the improvement in performance of mid-infrared photodetectors by boosting responsivity and restricting dark current. A simultaneous mid-infrared spin angular momentum photodetector was proposed, theoretically investigated and experimentally achieved. Furthermore, a mid-infrared photodetector based on GNM was thoroughly explored. Band gap engineering and graphene plasmons were introduced and investigated and it was proved they can work side by side to improve responsivity and restrict dark current. Moreover, the device was fabricated and characterised according to geometric, electrical and optical aspects. All these contributions form the basis for future advances

Silver-based nanocomposite materials for marine antifouling applications

Biofouling of marine surfaces is an age-old problem that affects natural and man-made surfaces exposed to the aquatic environment. The tenacious attachment of seaweed and invertebrates to man-made surfaces, notably on ship hulls, has incurred undesirable economic losses. The initial stage of the biofouling process has been attributed to the attachment of marine bacteria and their subsequent formation of biofilm which attract the settlement of larger sessile organisms including barnacles and seaweed. Silver nanostructured materials have a well-documented history as antimicrobial agents against pathogenic bacteria due to their ability to penetrate cell walls and interfere with crucial cellular processes. However, there is a surprising lack of information on their activity against marine biofilm bacteria that have critical roles in the initiation of marine fouling processes. This PhD project explores the antifouling properties of novel silver nanocomposite materials as potent antifouling agents against targeted organisms present in marine environments. The study consists of the syntheses of novel silver nanocomposite materials using various templates/matrices such as ion-exchange polymeric microspheres, zeolites, TiO2 nanotubes and graphene nanosheets. These materials were characterized through various instrumentation techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray powder diffraction (XRD), UV-visible (UV-vis) spectrophotometry, transmission electron microscopy (TEM), accelerated surface area porosimetry (ASAP), thermal gravimetric analysis (TGA), and Raman spectroscopy to elucidate their physical properties. Their antifouling effects were evaluated on Halomonas pacifica, a model marine microfouling bacterium, through an established static biofilm assay. In addition, the biological effects of these silver nanocomposites were also studied on marine microalgae Dunaliella tertiolecta and Isochrysis sp. Silver-polymer nanocomposite (Ag-PNC) microspheres were formed through a rapid chemical synthesis procedure at room temperature via the reduction of silver nitrate by sodium borohydride. The introduction of Ag nanoparticles (AgNPs) enhanced the thermal stability of the Dowex microspheres by shifting the glass transition temperature to above 300°C and the material decomposition occurred above 460°C. XRD analysis confirmed the presence of metallic Ag, while UV-vis absorption studies showed the characteristic surface plasmon resonance (SPR) for AgNPs ranging from 406 – 422 nm maximum absorption wavelengths. SEM imaging revealed the uniform distribution of AgNPs with diameters between 20 – 60 nm on the surface of the microbeads. The Ag-PNC materials, diluted to a concentration of 1 mg/mL in marine broth, showed a potent inhibitory effect on H. pacifica biofilm formation, with up to 76% decrease of biofilm when contrasted with the polymeric microspheres without Ag. Ag-PNCs also caused significant growth inhibition of D. tertiolecta and Isochrysis sp. Silver-zeolite nanocomposite clusters (AgZ) were formed through a low temperature chemical reduction method using the environmentally friendly trisodium citrate. The stable and porous inner structure of ZSM-5 zeolites performed a dual role as a stable size-control template and a reservoir of antimicrobial nanosilver. SEM revealed the globular and cluster-like morphology of the AgZ composites, with a homogenous distribution of silver particles on the surface of the clusters. EDX results displayed an increasing Ag loading with higher concentrations of Ag precursor, up to 10 wt% Ag. The UV-visible absorption displayed the characteristic SPR absorption maximum ranging from 408 – 500 nm. The AgZ clusters with metallic silver loading of up to 10 wt% Ag, diluted to a concentration of 1 mg/mL, reduced H. pacifica biofilm attachment of up to 81% compared to pure zeolite alone. XRD analysis clearly indicated the presence of metallic Ag while the ZSM-5 zeolite crystalline framework remained largely intact after the Ag crystal growth process. Brunauer-Emmett-Teller (BET) analysis showed a reduction in surface area of up to 44% with the incorporation of AgNPs into the zeolite, indicating the formation and growth of Ag within the internal pores and channels of the zeolite. Although the introduction and crystal growth of silver nanoparticles within the porous structure of the zeolite caused a change from a mesoporous to a largely macroporous structure, the integrity of the zeolite template was preserved. Silver-titania nanotube (Ag/TNT) composite material was prepared through a novel 2-step hydrothermal synthesis method. Titania nanotubes were chosen as a support material for the AgNPs as its greater specific surface area on the inner and outer surfaces of its tubular structure lead to enhanced properties. The morphology, particle size, chemical content, crystal structure, optical properties and surface area were systematically characterized. Determination of biofilm inhibitory properties revealed that Ag/TNT (concentration of 0.1 mg/mL) with the lowest silver content (0.95 wt% Ag) decorated with AgNPs of approximately 3 nm reduced biofilm formation of H. pacifica by 98% compared to pure titania nanotubes and bulk silver alone. Growth inhibition of D. tertiolecta and Isochrysis sp. were also observed. Interestingly, the antifouling properties were improved with a size decrease of AgNPs. The work shows that titania nanotubes are a stable and effective support for the anchoring and growth of AgNPs. The addition of very low amounts of Ag enhanced the antifouling property of pure TiO2 to produce an extremely potent antifouling effect on the targeted organisms. Graphene-Ag (GAg) nanocomposites were prepared from a novel and mild hydrothermal synthesis method which bypasses the formation of graphene oxide. The GAg nanocomposite combines the antimicrobial property of silver nanoparticles and the unique structure of graphene as a support material, with potent marine antifouling properties. The results show that GAg nanocomposites displayed significant biofilm inhibition property on H. pacifica and antiproliferative effects on D. tertiolecta and Isochrysis sp. As low as 1.3 wt% of Ag loading on a GAg sample, diluted to a concentration of 0.1 mg/mL, inhibited biofilm formation from H. pacifica. The GAg sample with 4.9 wt% Ag loading was associated with a biofilm inhibition of 99.6%. The marine antifouling properties of GAg nanocomposites were a synergy of the biocidal AgNPs anchored on the flexible graphene sheets, thereby providing maximum active contact surface areas to the target organisms. The GAg material was characterized with SEM, EDX, TEM, XRD and Raman spectroscopy. In addition, the GAg material exhibited the surface-enhanced Raman scattering (SERS) effect. The AgNPs were estimated to be between 72-86 nm, observed supported on micron-scaled graphene flakes. These results strongly suggest that the 4 types of silver-based nanocomposite materials are promising marine antifouling agents. The addition of very low amounts of Ag enhanced the antifouling property of the support structure, and the nanocomposites were shown to be more effective on the targeted organisms compared to the matrix material or bulk silver alone. In addition, the precursor materials used in the syntheses are affordable and easily available, whilst the synthetic methods and conditions are facile, environmentally friendly, and capable of producing high yields