Aerosol-Assisted Chemical Vapour Deposition (AACVD) of Silver Nanoparticle Decorated Tungsten Oxide Nanoneedle for Use in Oxygen Gas Sensing

Semiconducting metal oxides (SMOX) gas sensors, such as tungsten oxide (WO3), have been developed in depth for use in toxic gas detection, such as nitrogen oxides (NOx). With the addition of catalytic nanoparticles, like Ag, Pt, Pd and etc., the sensing properties, the three ‘S’ (sensitivity, selectivity and stability), can be significantly improved. This thesis details a two-step synthesis method for the fabrication of Ag nanoparticle decorated WO3 nanoneedle by using different silver metal precursors, including silver nitrate (AgNO3), silver 2-aminoethanol (Ag-EA), silver 1-aminopropan-2-ol (Ag-AP) and silver 2-methyl-2-aminopropan-1-ol (Ag-AMP), in a vapour deposition process. A series of experiments were conducted to investigate the parameters that affect the growth of the materials microstructure including deposition temperature, deposition time, flow rate of N2 carrier gas and concentration of precursor solution. Physical property characterization techniques including UV/Vis, XRD, XPS, SEM and TEM, have been systematically applied for all WO3 and Ag-decorated WO3 samples and sensor materials. Oxygen sensors’ have been considered as the critical component of Engine Management System for several decades. Gas sensing performance was carried out toward different O2 concentration between 1 and 20% at various operating temperatures. The sensing response revealed that the decoration of Ag nanoparticle on WO3 sensors significantly improved sensing properties as compared to undecorated WO3 sensors. An optimal gas response with silver-decorated WO3 is enhanced 400% compared to an undecorated WO3 sensor at an optimum operating temperature at 350 °C towards 20% oxygen at a relative humidity level ~ 85% by using AgNO3 as a precursor. An enhancement was also observed for the Ag decorated WO3 sensors fabricated using organometallic silver precursors, with a dramatically increasing in baseline resistance for these Ag@WO3 sensors. Sensing mechanisms, are proposed to explain the enhancement in sensing response

Functionalized epitaxial graphene as versatile platform for air quality sensors

The work presented in this thesis focuses on epitaxial graphene on SiC as a platform for air quality sensors. Several approaches have been tested and evaluated to increase the sensitivity, selectivity, speed of response and stability of the sensors. The graphene surfaces have been functionalized, for example, with different metal oxide nanoparticles and nanolayers using hollow-cathode sputtering and pulsed laser deposition. The modified surfaces were investigated to-wards topography, integrity and chemical composition with characterization methods such as atomic force microscopy and Raman spectroscopy. Interaction energies between several analytes and nanoparticle-graphene-combinations were calculated by density functional theory to find the optimal material for specific target gases, and to verify the usefulness of this approach. The impact of environmental influences such as operating temperature, relative humidity and UV irradiation on sensing properties was investigated as well. To further enhance sensor performances, the first-order time-derivative of the sensor’s resistance was introduced to speed up sensor response and a temperature cycled operation mode was investigated towards selectivity. Applying these methods in laboratory conditions, sensors with a quantitative readout of single ppb benzene and formaldehyde were developed. These results show promise to fill the existing gap of low-cost but highly sensitive and fast gas sensors for air quality monitoring.Financial support by the Swedish Foundation for Strategic Research (SSF) through the grants GMT14-0077 and RMA15-024

Nanoparticles in polyelectrolyte multilayer layer-by-layer (LbL) films and capsules : key enabling components of hybrid coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified

Plasmonics and its Applications

Plasmonics is a rapidly developing field that combines fundamental research and applications ranging from areas such as physics to engineering, chemistry, biology, medicine, food sciences, and the environmental sciences. Plasmonics appeared in the 1950s with the discovery of surface plasmon polaritons. Plasmonics then went through a novel propulsion in the mid-1970s, when surface-enhanced Raman scattering was discovered. Nevertheless, it is in this last decade that a very significant explosion of plasmonics and its applications has occurred. Thus, this book provides a snapshot of the current advances in these various areas of plasmonics and its applications, such as engineering, sensing, surface-enhanced fluorescence, catalysis, and photovoltaic devices

Surface Plasmon Resonance for Biosensing

The rise of photonics technologies has driven an extremely fast evolution in biosensing applications. Such rapid progress has created a gap of understanding and insight capability in the general public about advanced sensing systems that have been made progressively available by these new technologies. Thus, there is currently a clear need for moving the meaning of some keywords, such as plasmonic, into the daily vocabulary of a general audience with a reasonable degree of education. The selection of the scientific works reported in this book is carefully balanced between reviews and research papers and has the purpose of presenting a set of applications and case studies sufficiently broad enough to enlighten the reader attention toward the great potential of plasmonic biosensing and the great impact that can be expected in the near future for supporting disease screening and stratification

Coupling colloidal chemistry with coordination chemistry: Design of hybrid nanomaterials by the assembly of plasmonic nanoparticles and functional coordination complexes

Nanotechnology involves the design, characterization, production and application of structures, devices and systems by the control of the shape and size at the nanometer scale involving different fields. In the last decade, nanotechnology development has boosted the interest in hybrid nanomaterials. These materials are a complimenting combination of two (or more) nanoparticles (NPs) with enhanced performance characteristics that offer exciting opportunities. It allows the possibility of integrating materials with different physical and chemical properties to widen the range of practical applications. In this context, Au NPs have recently attracted a lot of attention due to the great opportunities that Au offers at the nanoscale. In fact, their facile synthesis and functionalization can be exploited for constructing hybrid nanoparticles showing multi-functionality. In this manner, different Au hybrid nanostructures have been developed exhibiting diverse sizes, shapes and compositions displaying novel physicochemical properties, opening the door to potential new applications. On the other hand, Coordination Polymers (CPs) possess besides interesting electronic properties, potential advantages over conventional inorganic nanomaterials such as structural and chemical versatility, high specific area and biodegradability, among others. Therefore, the integration of both Au and CPs in a single heterostructure has emerged as an appealing topic. However, suitable chemical design appears as one of the key factors to improve their applicability. The work described in this thesis is motivated by the purpose of designing and studying novel hybrid nanostructures formed by combining Au NPs with different CPs: i) Prussian Blue and its Analogues (PB and PBA), ii) Spin-Crossover compounds (SCO) and iii) Metal-Organic Frameworks (MOF). Taking into account the numerous possible heterostructures, it will be discussed why these tailored hybrid NPs are the most appropriate for magneto-optical, electrochemical and electrical applications. In chapter 1, it is described the optical properties and the synthesis of Au NPs as well as the main research efforts that have been made to combine CPs incorporating Au functionalities within the overall hybrid nanomaterials. The main results of this thesis are divided into three parts depending on the potential applications: magneto-optics, electrochemistry and electrical conductivity. Chapter 2 deals with the preparation of hybrid systems formed by metallic NPs decorated by electrostatic attraction onto PBA NPs of different sizes and nature. In this approach, the capping agent of the plasmonic NP is modified, thus, allowing to select the plasmonic NP (isotropic or anisotropic) and, therefore, to tune the plasmon band position in a broad range of the visible spectrum. The heterostructure keeps its plasmonic and magnetic properties becoming a suitable hybrid material for magneto-optical applications. In chapter 3, different heterostructures composed of Au and PBA (of NiFe and CoFe) are synthesized and evaluated as electrocatalysts for the oxygen evolution reaction. The core@shell heterostructures are found to be the most appropriate to exploit the Au properties (conductivity and electronegativity). In this way, through a suitable chemical design it can be greatly enhanced the electrochemical activity and stability of the electroactive PBA. In chapter 4, a straightforward protocol is carried out to overgrow a thin SCO over different plasmonic NPs. Moreover, this synthetic route was extended to MOF. It is observed that thanks to the metallic core and the naked surface of the ultrathin SCO/MOF shell, these core@shell NPs are more conductive than the pristine SCO NPs when contacted to electrodes. In future work, further development will be done by taking advantage of the plasmon properties of the plasmonic core to get a light-induced spin transition (SCO) and to promote the adsorption/desorption of guest molecules (MOF) to obtain advanced sensing devices. This Ph.D. thesis is expected to represent a significant advancement in the development of novel heterostructures as a result of the incorporation of Au NPs to CPs