Nanomaterials have been studied extensively in the last decade in the context of many applications such as polymer composites, energy harvesting systems, sensors, ‘transparent’-like materials, field-effect transistors (FETs), spintronic devices, gas sensors and biomedical applications. Graphene, a recently discovered two-dimensional form of carbon has captured the interest of material scientists, and physicists alike due to its excellent electrical, mechanical and thermal properties. Graphene has also kindled a tremendous interest among chemists and cell biologists to create cellular-electronic interface in the context of bio-electronic devices as it can enable fabricating devices with enhanced potential as compared to conventional bio-electronics. Graphene’s unique electronic properties and sizes comparable with biological structures involved in cellular communication makes it a promising nanostructure for establishing active interfaces with biological systems. In the recent past Field effect transistors (FETs) have been successfully fabricated using carbon nanotubes (CNTs) and nanowires (NWs) and electrical characterization of these FETs were done by interfacing them with various cell cultures, tissues and muscle cells. In these cases, exceptionally high surface area to thickness ratio of FETs provides high percentage of collectible signals and the cells that are used for the study are typically placed on the FET. In this thesis, we examine a different approach towards forming bio-electronic interfaces by covering the graphene oxide (reduced) sheets on the yeast cells. Graphene oxide and reduced graphene oxide sheets as two-dimensional electronic materials have very high charge carrier mobility, extremely high surface area to thickness ratio, mechanical modulus and elasticity. We report the synthesis of graphene oxide using wet chemistry method, reduction of graphene oxide using different reducing agents and electrical characterization of graphene oxide’s conductivity. Micro-meter sized graphene sheets are used to encapsulate the yeast cells with the aid of calcium and gold nanoparticle chains. We also demonstrate that graphene sheets form electrically conductive layers on the yeast cells and developing an electromechanical coupling with the cell. The mechanical and electrical characteristics of graphene sheets are highly dependent on the cell volume and structure which are in turn related to the environment around the cell. Furthermore, using the same principle of electromechanical coupling we study the dynamics of cell surface stresses and cell volume modification, which are of importance in processes such as cell growth, division, and response to physiological factors such as osmotic stresses.

In the recent past, graphene has been discovered and studied as one of the most promising materials after silicon and carbon nanotube. Its atomically thin structure, pristine dangling bonds free surface and interface, ultra-fast charge transport capability, semi-metallic behavior, ultra-strong mechanical ruggedness, promising photonic properties and bio-compatibility makes it a material to explore from all different perspectives to identify potential application areas which can augment the quality of our life. Therefore, in this doctoral work the following critical studies have been carried out meticulously with key findings are listed below: (1) A simplistic and sustainable growth process of double or multi-layer graphene (up to 4” substrate coverage with uniformity) using low-cost atmospheric chemical vapor deposition (APCVD) technique. [presented in MRS Fall Meeting 2012 and in IEEE SIECPC 2012) (2) A buried metallic layer based contact engineering process to overcome the sustained challenge of contact engineering associated with low-dimensional atomically thin material. (presented in IEEE Nano 2013 and archieved in conference proceedings) (3) Demonstration of a fin type graphene transistor (inspired by multi-gate architecture) with a mobility of 11,000 cm2/V.s at room temperature with an applied drive-in voltage of ±1 volt to demonstrate for the first time a pragmatic approach for graphene transistor for mobile applications which can maintain its ultra-fast charge transport behavior with ultra-low power consumption. [Published in ACS Nano 2013] (4) Further a meticulous study has been done to understand the harsh environment compatibility of graphene for its potential use in underwater and space applications. [Published as Cover Article in physica solidi status – Rapid Research Letters, 2014] (5) Due to its highly conductive nature and low surface-to-volume ratio it has been used to replace conventional gold based anodic material in microbial fuel cells (used for water purification in self-sustained mode) to demonstrate its effectiveness as a sustainable low-cost mechanically robust transparent material. [Published in ACS Nano 2013, in Energy Technology 2014 as a Cover Article and in Nature Publishing Group Asia Materials 2014] (6) Extensive study to stabilize graphene surface and to use the phenomena for development of a sensor which can monitor the quality of water. [presented in MRS Fall Meeting 2013 and in MRS Fall Meeting 2014] (7) By using graphene as an expose transistor architecture with ultra-scale high-k dielectric, to develop a series of sensor for glucose monitoring. Sensitivity, selectivity, response rate and refresh time has been studied and optimized. [pending review in Nature Scientific Reports 2015] (8) From the lessons learnt during the development of glucose monitoring sensor cell, a sophisticated low-cost ultra-low power mobile graphene based non-invasive sensor has been assembled and clinically trialed in collaboration with King Faisal Hospitals in Jeddah and in Makkah. [pending review in Science 2015] As a future direction, this thesis also discusses potential of graphene growth on electrochemically deposited metallic seed layers and consequential usage in stretchable and transparent graphene antenna development for fully flexible only graphene based integrated electronic system integration.

Since its isolation in 2004, the research landscape around graphene and other 2D materials has expanded rapidly and now encompasses fields as diverse as electronic engineering and drug delivery. For biomedical applications, one of the most desirable properties of the graphene family of nanomaterials (GFNs) is their 2D geometry; the high surface area to volume ratio that is characteristic of nanomaterials is taken to its extreme in a material that can be viewed as being entirely surface. This particular property alongside the versatility with which they may be functionalised both makes GFNs well positioned to function as the foundation of highly tailored and multifunctional therapeutics platforms. In this project, two GFN types, namely pristine graphene and graphene oxide, were prepared to form suspensions suitable for application to therapeutics delivery. Firstly, experiments using four essential amino acids with pristine graphitic material were undertaken to assess whether graphene flakes could be suitably exfoliated and suspended using sonication in the presence of aqueous solutions of these biocompatible molecules. A positive correlation was found between the hydrophobicity of the amino acid and the presence of one or more aromatic rings in the amino acid, and the efficacy of exfoliation both in terms of concentration achieved in suspension and flake thinness. However, the system itself was found to be highly complex, both with regards to the sonication used to exfoliate the graphitic flakes, and the interactions between the amino acids and the flakes. These considerations limited the wider applicability of this form of graphene preparation for therapeutics delivery applications. Secondly, work was performed on graphene oxide (GO), a GFN far more studied in the literature, but notoriously heterogeneous. Therefore much of the work completed focused on its characterisation. A combination of established and novel fluorescence-based characterisation methods were used to fully characterise three preparations of GO, before preliminary experiments were undertaken to test their interactions with cell components. The work showed that the inherent fluorescence of GO can be exploited to improve suspension characterisation; raster image correlation spectroscopy (RICS) was used to measure the apparent hydrodynamic radii of the flakes and flow cytometry was used to provide insight into the interactions between GO flakes and serum components. Preliminary cellular experiments confirmed that flow cytometry could be also employed to assess particular graphene characteristics in the context of cell culture, demonstrating the relatively low toxicity of PEGylated GO compared to unfunctionalised GO. Finally, as the therapeutics target for this project was leukaemia, a targeting ligand was designed and synthesised that could bind to CXCR4 - a receptor that is overexpressed on CLL B-cells, as well as many other cancer types. The ligand was synthesised such that it could easily be attached to GO, however its molecular structure is flexible enough that it can be attached to a number of different therapeutics materials. It was confirmed using both competition and functional assays that the molecule was antagonistic, and was able to deliver a conjugated fluorescent molecule specifically to the CXCR4 receptors on primary CLL B-cells. The work presented in this thesis illustrates the complexity that affects the use of GFNs in biomedicine, but also confirms the potential for their future development. The field is still young, and therapeutics delivery is likely to benefit from advances in the preparation of pristine graphene, and from methods to minimise the heterogeneity of GO. These steps will support a route towards clinical application. In addition, as the field of 2D materials expands, other materials with enviable surface area to volume ratios may come to the fore. Furthermore, this thesis has shown the value of exploring novel approaches to the characterisation of GFNs, and has identified approaches that may be exploited to improve applications of GFNs in biomedicine. Additionally, the aim of using GFNs as a platform for a multifunctional therapeutics delivery vehicle was developed with regards to the attractive CXCL12/CXCR4 axis, which is relevant in a large number of disease states including over 20 cancers, by demonstrating a flexible targeting ligand that could be used to exploit the CXCR4 receptor as a drug delivery target.

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Chapter 1 describes work towards the synthesis of graphene nanoribbons with varying widths and edge structures. Interest in graphene comes from the high electron mobility at room temperature, exceptional thermal conductivity, and superior mechanical properties.¹ These properties enable graphene’s use in numerous applications such as transparent conducting electrodes, gas detection, transistors, energy storage devices, and polymer composites.¹ Density functional theory has predicted that the electronic properties of GNRs differ with changes in length, width, and differences in edge structure.⁵ First polyacetylene ladder polymers were developed as intermediates for nanoribbons with zig-zag edge structures. Experiments have shown evidence for polyacetylene structures within the material although conversion is too low to be used as a precursor for graphene nanoribbons. Next tetraethynylethene monomers were synthesized to study their use as monomers for Bergman polymerization in hopes of producing armchair edged nanoribbons. Polymers were made with both alkyl and carboxylic acid functionality. ortho-Acylphenols are useful reagents in the synthesis of many natural products, pharmaceuticals, agrichemicals, flavors, and fragrances²⁷,²⁸. For this reason, ketone directed hydroxylation of arenes catalyzed by Pd was developed by Dong and coworkers. During this work it was discovered that 1-acetylnaphthalene would polymerize under the reaction conditions. Chapter 2 describes the author’s efforts to understand the polymerization mechanism through the synthesis of a variety of substituted acetylnaphthalene derivatives and their polymerization. / text

Graphene has displayed much promise as an electrical conductor and as a optical material. To date there is a large body of literature dedicated to the equilibrium properties of graphene. In this thesis the properties of graphene out of equilibrium are probed. Through combined optical and transport measurements the behaviour of hot electrons are probed at temperatures over five orders of magnitude from 50mK to 2000K. This wide range of temperatures allows access to the behaviour of quantum corrections at the lowest temperatures to the highest energy phonon modes. From ultrafast femtosecond laser pulses to steady state heating from an electric field the cooling of hot electron populations through coupling to various phonon modes in the graphene and the substrate are explored. Additionally the effect of an electric field on the weak localisation correction to the conductivity was separated from heating effects using applied magnetic fields combined with careful modelling of the heat transport properties of the graphene. Finally the desorption dynamics of oxygen bound to the surface are shown using a combination of transport and two pulse correlation technique using an ultrafast laser. Surprisingly the cooling of hot carriers in graphene at low energies shows substrate surface phonons as an important cooling mechanism, highlighting the importance of substrate choice in future graphene devices. In contrast at the very highest energy scales accessed only by photoexcitation the cooling is shown not to be influenced by the presence of a substrate, but out-of-plane phonon modes increase cooling of the hot optical phonons.

Epitaxial multilayer h-BN(0001) heterostructures and graphene/h-BN heterostructures have many potential applications in spintronics. The use of h-BN and graphene require atomically precise control and azimuthal alignment of the individual layers in the structure. These in turn require fabrication of devices by direct scalable methods rather than physical transfer of BN and graphene flakes, and such scalable methods are also critical for industrially compatible development of 2D devices. The growth of h-BN(0001) multilayers on Co and Ni, and graphene/h-BN(0001) heterostructures on Co have been studied which meet these criteria. Atomic Layer Epitaxy (ALE) of BN was carried out resulting in the formation of macroscopically continuous h-BN(0001) multilayers using BCl3 and NH3 as precursors. X-ray photoemission spectra (XPS) show that the films are stoichiometric with an average film thickness linearly proportional to the number of BCl3/NH3 cycles. Molecular beam epitaxy (MBE) of C yielded few layer graphene in azimuthal registry with BN/Co(0001) substrate. Low energy electron diffraction (LEED) measurements indicate azimuthally oriented growth of both BN and graphene layers in registry with the substrate lattice. Photoemission data indicate B:N atomic ratios of 1:1. Direct growth temperatures of 600 K for BN and 800 to 900 K for graphene MBE indicate multiple integration schemes for applications in spintronics.

This thesis deals with the analytical study of vibration of carbon nanotubes and graphene plates. First, a brief overview of the traditional Bresse-Timoshenko models for thick beams and Uflyand-Mindlin models for thick plates will be conducted. It has been shown in the literature that the conventionally utilized mechanical models overcorrect the shear effect and that of rotary inertia. To improve the situation, two alternative versions of theories of beams and plates are proposed. The first one is derived through the use of equilibrium equations and leads to a truncated governing differential equation in displacement. It is shown, by considering a power series expansion of the displacement, that this is asymptotically consistent at the second order. The second theory is based on slope inertia and results in the truncated equation with an additional sixth order derivative term. Then, these theories will be extended in order to take into account some scale effects such as interatomic interactions that cannot be neglected for nanomaterials. Thus, different approaches will be considered: phenomenological, asymptotic and continualized. The basic principle of continualized models is to build continuous equations starting from discrete equations and by using Taylor series expansions or Padé approximants. For each of the different models derived in this study, the natural frequencies will be determined, analytically when the closed-form solution is available, numerically when the solution is given through a characteristic equation. The objective of this work is to compare the models and to establish the eventual superiority of a model on others. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

Graphene is the first 2D material consisting of carbon atoms densely packed into planar structures. Graphene oxide (GO) is the intermediate derivative of chemically-produced graphene, which retains 2D basal plane structures but is also decorated with functional groups along the basal plane and edges. This functionality allows self-assembly of planar sheets into a paper-like material. However, formations of both intrinsic defects within the sheet structures as well as larger scale extrinsic defects in the paper are expected to significantly degrade mechanical performance. Strength provides the most direct evidence of defect related mechanical behaviour and is therefore targeted for understanding defect effects in GO paper. Such evaluations are crucial both from a technological perspective of realizing designed functions and from a fundamental interest in understanding structure-mechanics in 2D nanomaterials. A complete strategy of performing mechanical testing at different length scales is thus reported to provide a comprehensive description of GO strength. Both conventional larger scale mechanical testing as well as novel smaller length scale evaluations, using in situ atomic force microscopy (AFM) combined with scanning electron microscopy (SEM) and optical microscopy as well as structural probing using synchrotron FT-IR microspectroscopy, were applied to GO materials. Results showed that large structural defects determined mechanical properties of GO papers due to stress concentration effects whereas smaller scale intrinsic effects were defined by interfacial defects and stress concentrations within sheets. Synchrotron FT-IR microspectroscopy provided molecular deformation mechanisms in GO paper, which highlighted the interaction between in-plane C=C and cross-linking C=O bonds. A comprehensive description of macroscopic GO paper using evaluations of strength at the range of length scales studied was attempted, with a good correlation between predictions and experimental observations. This thesis therefore provides a hierarchical understanding of the defects impact on the strength of graphene-based materials from the macroscale to the nanoscale.

Graphene is a novel material that has exceptional electrical properties. In this work the graphene-based devices were developed towards three applications. Graphene-glass electrodes were fabricated and characterised towards understanding the electrochemical nature of graphene. It was shown that graphene could serve as an electrochemical electrode towards use as a sensing platform due to its fast electron transfer characteristics and thus exhibited potential as a platform for electrochemical sensing of electroactive species. Further, the Graphene-on-Glass electrodes were shown to be used as a working electrode to create a reversible electrochromic device where the optical transparency of the Graphene was modulated, and the electrochemical characteristics of the Graphene device were examined. A proof-of-concept detection for the presence of a biomarker for Sepsis was developed. Large-area, functionalised graphene was shown to able to electronically sense the presence of the binding events of the Anti-PCT antibody, PCT molecule and differentiate from their bulk solution. The device was able to detect the presence of PCT over the medically relevant range. This sensor combines the exceptional electrical properties of graphene leading to high sensitivity, which when functionalized also yields high specificity as a sensor platform and offers a new route for diagnosis of Sepsis electronically in real time measurements. Lastly, a hybrid graphene FET array that is embedded under microfluidic channels was developed. The effect of water on the device was measured and the utility of such devices towards sensing in aqueous media is discussed. Further, it is shown that the microfluidic channels of varying widths are able to transport water along the graphene FET array, such that individual graphene strips can sense them. This measurement scheme is extremely useful and can be adapted to a host of other sensing applications which would benefit from dynamic and precise control on the detection of the analyte.