Near-field thermal radiation occurs when the distance between two surfaces at different temperatures is less than the characteristic wavelength of thermal radiation. While theoretical studies predict that the near-field radiative heat transfer could exceed Planck’s blackbody limit in the far-field by orders of magnitudes depending on the materials and gap distance, experimental measurement of super-Planckian near-field radiative heat flux is extremely challenging in particular at sub-100-nm vacuum gaps and few has been demonstrated. The objective of this thesis is to develop a novel thermal metrology based on AFM bi-material cantilever and experimentally measure near-field thermal radiation.

The experiment setup is completed and validated by measuring the near-field radiative heat transfer between a silica microsphere and a silica substrate and comparing with theoretical calculations. The bi-material AFM cantilever made of SiNi and Au bends with temperature changes, whose deflection is monitored by the position-sensitive diode. After careful calibration, the bi-material cantilever works as a thermal sensor, from which the near-field radiative conductance and tip temperature can be deduced when the silica substrate approaches the silica sphere attached to the cantilever by a piezo stage with a resolution of 1 nm from a few micrometers away till physical contact. The developed novel near-field thermal metrology will be used to measure the near-field radiative heat transfer between the silica microsphere and planar SiC surface as well as nanostructured SiC metasurface. This research aims to enhance the fundamental understandings of radiative heat transfer in the near-field which could lead to advances in microelectronics, optical data storage and thermal systems for energy conversion and thermal management.

Photovoltaics (PV) is one of the promising options for maintaining sustainable energy supply because it is environmentally friendly, a non-polluting and low-maintenance energy source. Despite the many advantages of PV, solar energy currently accounts for only 1% of the global energy portfolio for electricity generation. This is because the cost of electricity from PV remains about a factor of two higher than the fossil fuel (10¢/kWh). Widely-used commercial methods employed to generate PV energy, such as silicon or thin film-based technologies, are still expensive as they are processed through vacuum-based techniques. Therefore, it is desirable to find an alternative method that is open-air and continuous process for the mass production of solar cells.

The objective of the research in this thesis is to develop low-cost spray pyrolysis technique to synthesize oxides thin films for applications in solar cells. Chapter 4 and 5 discuss spray-deposited dielectric oxides for their applications in Si solar cells. In Chapter 4, a successful deposition of Al2O3 is demonstrated using water as the solvent which ensures a lower cost and safer process environment. Optical, electrical, and structural properties of spray-deposited Al2O3 are investigated and compared to the industrial standard Atomic Layer Deposition (ALD) Al2O3/Plasma Enhanced Chemical Vapor Deposition (PECVD) SiNx stack, to reveal the suitability of spray-deposited Al2O3 for rear passivation and optical trapping in p-type Si Passivated Emitter and Rear Cell (PERC) solar cells. In Chapter 5, The possibility of using low-cost spray-deposited ZrO2 as the antireflection coating for Si solar cells is investigated. Optical, electrical and structural properties of spray-deposited ZrO2 films are studied and compared to the industrial standard antireflection coating PECVD SiNx. In Chapter 6, spray-deposited hematite Fe2O3 and sol-gel prepared anatase TiO2 thin films are sulfurized by annealing in H2S to investigate the band gap narrowing by sulfur doping and explore the possibility of using ternary semiconductors for their application as solar absorbers.

In this research, the effect of the crystal structure of the parent phase on the morphology of nanoporous gold is explored. Specifically, Cu-Au alloys are studied. For this experiment, Cu0.75Au0.25 is heat treated to achieve an ordered phase Cu3Au and a disordered random solid solution, face centered cubic, Cu0.75Au0.25 phase, which are then dealloyed to form nanoporous gold (NPG). Using a morphology digital image analysis software called AQUAMI, SEM images of the NPG morphology were characterized to collect data on the ligament length, ligament diameter, porosity size, etc. of the samples. It was determined that the NPG formed from the ordered parent phase had an average ligament diameter that was 10 nm larger than the NPG formed from the disordered parent phase. This may be due to the ordered crystal structure allowing for faster gold diffusion and coarsening resulting in an increased average ligament size. Further future work is needed in order to obtain further evidence to support this hypothesis.

This paper discusses the possibility of utilizing 2D molybdenum disulfide (MoS2) as a nanozyme to detect dopamine colorimetric assays, first by detecting color change in liquid solutions due to oxidation and then second on paper-based assays. MoS2 samples dispersed in methylcellulose (MC) solution were prepared using liquid-phase exfoliation through sonication. The dopamine (DOPA) and hydrogen peroxide (H¬¬2O2) solutions were prepared separately in specific concentrations. The solutions were mixed in a well plate and colorimetric results were analyzed by a plate reader, revealing a quantitative relationship between dopamine concentration and absorbance. Subsequent testing was conducted using paper assays, where combined solutions of DOPA and H2O2 were dropped onto paper with printed wax wells that contained dried MoS2. An analysis of the color change was conducted using a smartphone application called Color Grab to detect the red, green, and blue (RGB) values. Plotting the RGB results across the dopamine concentrations revealed a positively correlated relationship between the two factors, suggesting that a predictive model could be developed to predict dopamine concentrations based on measured colorimetric values.

Plastics make up a large proportion of solid waste that ends up in landfills and pollute ecosystems, and do not readily decompose. Composites from fungus mycelium are a recent and promising alternative to replace plastics. Mycelium is the root-like fibers from fungi that grow underground. When fed with woody biomass, the mycelium becomes a dense mass. From there, the mycelium is placed in mold to take its shape and grow. Once the growth process is done, the mycelium is baked to end the growth, thus making a mycelium brick. The woody biomass fed into the mycelium can include materials such as sawdust and pistachio shells, which are all cheap feedstock. In comparison to plastics, mycelium bricks are mostly biodegradable and eco-friendly. Mycelium bricks are resistant to water, fire, and mold and are also lightweight, sustainable, and affordable. Mycelium based materials are a viable option to replace less eco-friendly materials. This project aims to explore growth factors of mycelium and incorporate nanomaterials into mycelium bricks to achieve strong and sustainable materials, specifically for packaging materials. The purpose of integrating nanomaterials into mycelium bricks is to add further functionality such as conductivity, and to enhance properties such as mechanical strength.

Flame retardants (FRs) are applied to variety of consumer products such as textiles and polymers for fire prevention and fire safety. Substantial research is ongoing to replace traditional FRs with alternative materials that are less toxic, present higher flame retardancy and result in lower overall exposure as there are potential health concerns in case of exposure to popular FRs. Carbonaceous nanomaterials (CNMs) such as carbon nanotubes (CNTs) and graphene oxide (GO) have been studied and applied to polymer composites and electronics extensively due to their remarkable properties. Hence CNMs are considered as potential alternative materials that present high flame retardancy. In this research, different kinds of CNMs coatings on polyester fabric are produced and evaluated for their use as flame retardants. To monitor the mass loading of CNMs coated on the fabric, a two-step analytical method for quantifying CNMs embedded in polymer composites was developed. This method consisted of polymer dissolution process using organic solvents followed by subsequent programmed thermal analysis (PTA). This quantification technique was applicable to CNTs with and without high metal impurities in a broad range of polymers. Various types of CNMs were coated on polyester fabric and the efficacy of coatings as flame retardant was evaluated. The oxygen content of CNMs emerged as a critical parameter impacting flame retardancy with higher oxygen content resulting in less FR efficacy. The most performant nanomaterials, multi-walled carbon nanotubes (MWCNTs) and amine functionalized multi-walled carbon nantoubes (NH2-MWCNT) showed similar FR properties to current flame retardants with low mass loading (0.18 g/m2) and hence are promising alternatives that warrant further investigation. Chemical/physical modification of MWCNTs was conducted to produce well-dispersed MWCNT solutions without involving oxygen for uniform FR coating. The MWCNTs coating was studied to evaluate the durability of the coating and the impact on the efficacy during use phase by conducting mechanical abrasion and washing test. Approximately 50% and 40% of MWCNTs were released from 1 set of mechanical abrasion and washing test respectively. The losses during simulated usage impacted the flame retardancy negatively.

Ultrasonication-mediated liquid-phase exfoliation has emerged as an efficient method for producing large quantities of two-dimensional materials such as graphene, boron nitride, and transition metal dichalcogenides. This thesis explores the use of this process to produce a new class of boron-rich, two-dimensional materials, namely metal diborides, and investigate their properties using bulk and nanoscale characterization methods. Metal diborides are a class of structurally related materials that contain hexagonal sheets of boron separated by metal atoms with applications in superconductivity, composites, ultra-high temperature ceramics and catalysis. To demonstrate the utility of these materials, chromium diboride was incorporated in polyvinyl alcohol as a structural reinforcing agent. These composites not only showed mechanical strength greater than the polymer itself, but also demonstrated superior reinforcing capability to previously well-known two-dimensional materials. Understanding their dispersion behavior and identifying a range of efficient dispersing solvents is an important step in identifying the most effective processing methods for the metal diborides. This was accomplished by subjecting metal diborides to ultrasonication in more than thirty different organic solvents and calculating their surface energy and Hansen solubility parameters. This thesis also explores the production and covalent modification of pristine, unlithiated molybdenum disulfide using ultrasonication-mediated exfoliation and subsequent diazonium functionalization. This approach allows a variety of functional groups to be tethered on the surface of molybdenum disulfide while preserving its semiconducting properties. The diazonium chemistry is further exploited to attach fluorescent proteins on its surface making it amenable to future biological applications. Furthermore, a general approach for delivery of anticancer drugs using pristine two-dimensional materials is also detailed here. This can be achieved by using two-dimensional materials dispersed in a non-ionic and biocompatible polymer, as nanocarriers for delivering the anticancer drug doxorubicin. The potency of this supramolecular assembly for certain types of cancer cell lines can be improved by using folic-acid-conjugated polymer as a dispersing agent due to strong binding between folic acid present on the nanocarriers and folate receptors expressed on the cells. These results show that ultrasonication-mediated liquid-phase exfoliation is an effective method for facilitating the production and diverse application of pristine two-dimensional metal diborides and transition metal dichalcogenides.

In this dissertation, three complex material systems including a novel class of hyperuniform composite materials, cellularized collagen gel and low melting point alloy (LMPA) composite are investigated, using statistical pattern characterization, stochastic microstructure reconstruction and micromechanical analysis. In Chapter 1, an introduction of this report is provided, in which a brief review is made about these three material systems. In Chapter 2, detailed discussion of the statistical morphological descriptors and a stochastic optimization approach for microstructure reconstruction is presented. In Chapter 3, the lattice particle method for micromechanical analysis of complex heterogeneous materials is introduced. In Chapter 4, a new class of hyperuniform heterogeneous material with superior mechanical properties is investigated. In Chapter 5, a bio-material system, i.e., cellularized collagen gel is modeled using correlation functions and stochastic reconstruction to study the collective dynamic behavior of the embed tumor cells. In chapter 6, LMPA soft robotic system is generated by generalizing the correlation functions and the rigidity tunability of this smart composite is discussed. In Chapter 7, a future work plan is presented.

Two-dimensional transition metal dichalcogenides (TMDCs) such as

molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2) are attractive for use in biotechnology, optical and electronics devices due to their promising and tunable electrical, optical and chemical properties. To fulfill the variety of requirements for different applications, chemical treatment methods are developed to tune their properties. In this dissertation, plasma treatment, chemical doping and functionalization methods have been applied to tune the properties of TMDCs. First, plasma treatment of TMDCs results in doping and generation of defects, as well as the synthesis of transition metal oxides (TMOs) with rolled layers that have increased surface-to-volume ratio and are promising for electrochemical applications. Second, chemical functionalization is another powerful approach for tuning the properties of TMDCs for use in many applications. To covalently functionalize the basal planes of TMDCs, previous reports begin with harsh treatments like lithium intercalation that disrupt the structure and lead to a phase transformation from semiconducting to metallic. Instead, this work demonstrates the direct covalent functionalization of semiconducting MoS2 using aryl diazonium salts without lithium treatments. It preserves the structure and semiconducting nature of MoS2, results in covalent C-S bonds on basal planes and enables different functional groups to be tethered to the MoS2 surface via the diazonium salts. The attachment of fluorescent proteins has been used as a demonstration and it suggests future applications in biology and biosensing. The effects of the covalent functionalization on the electronic transport properties of MoS2 were then studied using field effect transistor (FET) devices.

Carbon nanomaterials have caught tremendous attention in the last few decades due to their unique physical and chemical properties. Tremendous effort has been made to develop new synthesis techniques for carbon nanomaterials and investigate their properties for different applications. In this work, carbon nanospheres (CNSs), carbon foams (CF), and single-walled carbon nanotubes (SWNTs) were studied for various applications, including water treatment, energy storage, actuators, and sensors.

A facile spray pyrolysis synthesis technique was developed to synthesize individual CNSs with specific surface area (SSA) up to 1106 m2/g. The hollow CNSs showed adsorption of up to 300 mg rhodamine B dye per gram carbon, which is more than 15 times higher than that observed for conventional carbon black. They were also evaluated as adsorbents for removal of arsenate and selenate from water and displayed good binding to both species, outperforming commercial activated carbons for arsenate removal in pH > 8. When evaluated as supercapacitor electrode materials, specific capacitances of up to 112 F/g at a current density of 0.1 A/g were observed. When used as Li-ion battery anode materials, the CNSs achieved a discharge capacity of 270 mAh/g at a current density of 372 mA/g (1C), which is 4-fold higher than that of commercial graphite anode.

Carbon foams were synthesized using direct pyrolysis and had SSA up to 2340 m2/g. When used as supercapacitor electrode materials, a specific capacitance up to 280 F/g was achieved at current density of 0.1 A/g and remained as high as 207 F/g, even at a high current density of 10 A/g.

A printed walking robot was made from common plastic films and coatings of SWNTs. The solid-state thermal bimorph actuators were multifunctional energy transducers powered by heat, light, or electricity. The actuators were also investigated for photo/thermal detection. Electrochemical actuators based on MnO2 were also studied for potential underwater applications.

SWNTs were also used to fabricate printable electrodes for trace Cr(VI) detection, which displayed sensitivity up to 500 nA/ppb for Cr(VI). The limit of detection was shown to be as low as 5 ppb. A flow detection system based on CNT/printed electrodes was also demonstrated.