In this thesis, the effect of the sample properties on the characteristics of the hot carrier luminescence in graphene is investigated. The present work focuses on the two main issues described below. The first issue is the modification effects of near-infrared pulsed laser excitation on graphene. For excitation fluences several orders of magnitude lower than the optical damage threshold, the interaction with ultrafast laser pulses is found to cause a stable change in the properties of graphene. This photomodification also results in a decrease of the hot photoluminescence intensity. The detailed analysis shows that ultrafast photoexcitation leads to an increase in the local level of hole doping, as well as a change in the mechanical strain. The variation of doping and strain are linked with the enhanced adsorption of atmospheric oxygen caused by the distortion of the graphene surface. These findings demonstrate that ultrashort pulsed excitation can be invasive even if a relatively low laser power is used. Secondly, the variation of the hot photoluminescence intensity with the increasing charge carrier density in graphene is investigated. The electro-optical measurements performed using graphene field-effect transistors show a strong dependence of the photoluminescence intensity on the intrinsic carrier concentration. The emission intensity has a maximum value in undoped graphene and decreases with the increasing doping level. The theoretical calculations performed using a refined two-temperature model suggest that the reduction of the photoluminescence intensity is caused by an increase in the hot carrier relaxation rate. The modification of the carrier relaxation dynamics caused by photoinduced doping is probed directly using the two-pulse correlation measurements. The discovered sensitivity of the hot photoluminescence to the intrinsic carrier concentration can be utilised for spatially-resolved measurements of the Fermi level position in graphene samples, offering an advantage in resolution and speed.

Dynamic atomistic description of bio-inorganic interfaces represents a challenging problem for contemporary computational chemistry. A detailed analysis of processes occurring on the interface between biomolecule and inorganic material can help our understanding of various processes, ranging from chromatography and protein separation to protein immobilization techniques and their effect on enzyme activity or protein conformational stability. High complexity of bio- inorganic interfaces prevents detailed investigation using accurate, but computationally demanding ab initio methods. Since reliable empirical potentials are not available for these systems, the aim of this work is to develop force fields based on ab initio data as well as a general methodology for parameterization of such force fields. Our potential fitting procedure was carried out in an automated fashion based on molecular dynamics simulation. The resulting potentials were applied for investigation of inorganic material's influence on polypeptide conformations.

Les propriétés intrinsèques extraordinaires de ces matériaux de faible dimension dépendent fortement de l'environnement auquel ils sont soumis. Par conséquent, ils doivent être préparés, traités et caractérisés sans défauts. Dans cette thèse, je discute de la manière de contrôler l'environnement des nanomatériaux de faible dimension tels que le graphène, le MoS$_{2}$ et les nanotubes de carbone afin de préserver leurs propriétés physiques intrinsèques. De nouvelles solutions pour l'amélioration des propriétés sont discutées en profondeur. Dans la première partie, nous fabriquons des dispositifs d'hétérostructure à base de graphène de Van der Waals (VdW) de dernière génération, en contact avec les bords, encapsulés dans du nitrure de bore hexagonal (hBN), afin d'obtenir un transport balistique. Nous utilisons une technique basée sur des mesures de bruit 1 / f pour sonder le transport de masse et de bord lors de régimes Quantum Hall entiers et fractionnaires. Dans la deuxième partie, le même concept de fabrication des hétérostructures VdW a été étendu pour encapsuler la couche monocouche MoS $_{2}$ dans le hBN afin d'en modifier les propriétés optiques. À cet égard, nous présentons une étude approfondie sur l'origine et la caractérisation des défauts intrinsèques et extrinsèques et leur incidence sur les propriétés optiques. En outre, nous décrivons une technique pour sonder le couplage entre couches ainsi que la génération de lumière avec une résolution spatiale inférieure à la limite de diffraction de la lumière. Enfin, nous discutons d'un processus systémique naturel visant à améliorer les propriétés mécaniques de la soie polymérique naturelle à l'aide d'une nanotubes de carbone à paroi unique fabriqués par HipCO comme aliment pour le ver à soie. / The extraordinary intrinsic properties of low dimensional materials depend highly on the environment they are subjected to. Hence they need to be prepared, processed and characterized without defects. In this thesis, I discuss about how to control the environment of low dimensional nanomaterials such as graphene, MoS2 and carbon nanotubes to preserve their intrinsic physical properties. Novel solutions for property enhancements are discussed in depth. In the first part, we fabricate state-of-the-art, edge-contacted, graphene Van der Waals(VdW) heterostructuredevices encapsulated in hexagonal-boron nitride(hBN), to obtain ballistic transport. We use a technique based on 1/f-noise measurements to probe bulk and edge transport during integer and fractional Quantum Hall regimes. In the second part, the same fabrication concept of VdW heterostructures has been extended to encapsulate monolayer MoS2 in hBN to improve optical properties. In this regard we present an extensive study about the origin and characterization of intrinsic and extrinsic defects and their affect on optical properties. Further, we describe a technique to probe the interlayer coupling along with the generation of light with spatialresolution below the diffraction limit of light. Finally, we discuss a natural systemic process to enhance the mechanical properties of natural polymer silk using HipCO-made single walled carbon nanotubes as a food for silkworm.

Surface plasmons are collective oscillations of free electrons excited at a metal-dielectric interface by incident light. They possess a broad set of interesting properties including a high degree of tunability, the generation of strong field enhancements close to the metal's surface and high sensitivity to their adjacent dielectric environment. It is possible to enhance the sensitivity of plasmonic systems by using narrow plasmon resonances. In this thesis two approaches to narrowing surface plasmon resonances have been studied: diffraction coupling of localised surface plasmon resonances in gold nanoarrays and the use of graphene-protected copper thin films. Applications of these approaches in hybrid systems have been considered for modulation, waveguiding, biosensing and field enhancements. Arrays of gold nanostripes fabricated on a gold sublayer have been used to create extremely narrow plasmon resonances using diffraction coupling of localised plasmon resonances with quality factors up to a value of $Q \sim 300$, among the highest reported in the literature. The nanostructures were designed to give the narrowest resonance at the telecommunication wavelength of 1.5 µm, allowing for this array geometry to be used in hybrid systems for proof-of-concept optoelectronic devices. The gold nanostripe array was used in a hybrid nanomechanical electro-optical modulator along with hexagonal boron nitride (hBN) and graphene. The modulator was fabricated with an air gap between the nanoarray and the hexagonal boron nitride/graphene. Applying a gate voltage across the device moves the hBN towards the nanoarray, resulting in broadband modulation effects from the ultraviolet through to the mid-infrared dependant on the motion of the hBN instead of graphene gating. The deposition of a 400 nm hafnium(IV) oxide film on top of the gold nanoarray created a structure capable of guiding modes at 1.5 µm. The hybrid air-dielectric-stripe waveguide is capable of guiding modes over a distance of 250 µm. Copper thin films have stronger plasmon resonances and higher phase sensitivity than gold thin films. Transferring a graphene sheet on the copper prevents oxidation of the copper. A feasibility study of this hybrid system has shown that phase-sensitive graphene-protected copper biosensing can detect HT-2 mycotoxin with over four orders of magnitude greater sensitivity than commercially-available gold-based surface plasmon resonance biosensing systems. In summary, two methods of attaining narrow plasmon resonances have been demonstrated and their promise in modulation, waveguiding and biosensing have been demonstrated.

The production of large area, high quality two-dimensional (2D) materials using chemical vapour deposition (CVD) has been an important and difficult topic in contemporary materials science research, after the discovery of the diverse and extraordinary properties exhibited by these materials. This thesis mainly focuses on the CVD synthesis of two 2D materials; bilayer graphene and monolayer tungsten disulphide (WS2). Various factors influencing the growth of each material were studied in order to understand how they affect the quality, uniformity, and size of the 2D films produced. Following this, these materials were combined to fabricate 2D vertical heterostructures, which were then spectroscopically examined and characterised. By conducting ambient pressure CVD growth with a flat support, it was found that high uniform bilayer graphene could be grown on the centimetre scale. The flat support provides for the consistent delivery of precursor to the copper catalyst for graphene growth. These results provide important insights not only into the upscaling of CVD methods for growing large area, high quality graphene and but also in how to transfer the product onto flexible substrates for potential applications as a transparent conducting electrode. Monolayer WS2 is of interest for use in optoelectronic devices due to its direct bandgap and high photoluminescence (PL) intensity. This thesis shows how the controlled addition of hydrogen into the CVD growth of WS2 can lead to separately distributed domains or centimetre scale continuous monolayer films at ambient pressure without the need for seed molecules, specially prepared substrates or low pressure vacuum systems. This CVD reaction is simple and efficient, ideal for mass-production of large area monolayer WS2. Subsequent studies showed that hexagonal domains of monolayer WS2 can have discrete segmentation in their PL emission intensity, forming symmetric patterns with alternating bright and dark regions. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. These results provide important insights into the spatially varying properties of these CVD-grown TMDs materials, which may be important for their effective implementation in fast photo sensors and optical switches. Finally, by introducing a novel non-aqueous transfer method, it was possible to create vertical stacks of mixed 2D layers containing a strained monolayer of WS2, boron nitride, and graphene. Stronger interactions between WS2 on graphene was found when swapping water for IPA, likely resulting from reduced contamination between the layers associated with aqueous impurities. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, a result which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with large area coverage and controllable thickness on the atomic level.

Due to its truly two dimensional (2D) character and its particular lattice, single layer graphene (SLG) possesses exceptional properties: it is semimetallic, transparent, strong yet flexible ... Complementary features such as the insulating character of hexagonal boron nitride (h-BN) and semiconducting properties of transition metal dichalcogenides (TMDs) enable the whole spectrum of electronic devices to be built with combinations of these 2D materials. Due to this and the ease of exfoliation with a sticky tape, a vast amount of research was sparked. The mechanical exfoliation method, however, is only suitable for novel or proof-of-concept devices. The trend nowadays in electronics is towards transparent, lightweight, flexible, embedded smart devices and sensors in everyday objects such as windows and mirrors, garments, windshields, car seats, parachutes...These demands are already met inherently by these new materials, thus the challenges remaining are within their synthesis, deposition and processing, where more scalable ways of production and device fabrication need to be developed. This thesis explores innovative approaches using established techniques that aim to bridge the gap between proof-of-concept devices and real applications of 2D materials in future commercial level technologies. Methods to create graphene and engineer its properties are employed with a special focus on scalability and adaptability towards the industry. These graphene materials have been processed using pioneering schemes to create different optoelectronic devices and sensors. The techniques employed here for synthesis, transfer and deposition, device processing and characterization of graphene and derivatives, are suitable for their use in large manufacturing and mass-production. Depending on the application envisaged, different materials are used and optimize in order to balance good performance, cost-effectiveness and suitability/scalability of the process for the specific target the device was designed for.

abstract: Among the alternative processes for the traditional distillation, adsorption and membrane separations are the two most promising candidates and metal-organic frameworks (MOFs) are the new material candidate as adsorbent or membrane due to their high surface area, various pore sizes, and highly tunable framework functionality. This dissertation presents an investigation of the formation process of MOF membrane, framework defects, and two-dimensional (2D) MOFs, aiming to explore the answers for three critical questions: (1) how to obtain a continuous MOF membrane, (2) how defects form in MOF framework, and (3) how to obtain isolated 2D MOFs. To solve the first problem, the accumulated protons in the MOF synthesis solution is proposed to be the key factor preventing the continuous growth among Universitetet I Oslo-(UiO)-66 crystals. The hypothesis is verified by the growth reactivation under the addition of deprotonating agent. As long as the protons were sufficiently coordinated by the deprotonating agent, the continuous growth of UiO-66 is guaranteed. Moreover, the modulation effect can impact the coordination equilibrium so that an oriented growth of UiO-66 film was achieved in membrane structures. To find the answer for the second problem, the defect formation mechanism in UiO-66 was investigated and the formation of missing-cluster (MC) defects is attributed to the partially-deprotonated ligands. Experimental results show the number of MC defects is sensitive to the addition of deprotonating agent, synthesis temperature, and reactant concentration. Pore size distribution allows an accurate and convenient characterization of the defects. Results show that these defects can cause significant deviations of its pore size distribution from the perfect crystal. The study of the third questions is based on the established bi-phase synthesis method, a facile synthesis method is adopted for the production of high quality 2D MOFs in large scale. Here, pyridine is used as capping reagent to prevent the interplanar hydrogen bond formation. Meanwhile, formic acid and triethylamine as modulator and deprotonating agent to balance the anisotropic growth, crystallinity, and yield in the 2D MOF synthesis. As a result, high quality 2D zinc-terephthalic acid (ZnBDC) and copper-terephthalic acid (CuBDC) with extraordinary aspect ratio samples were successfully synthesized. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2019

One dimensional carbon nanotubes (CNTs) and two-dimensional layered materials like graphene, MoS2, hexagonal boron nitride (hBN), etc. with different electrical and mechanical properties are great candidates for many applications in the future. In this study the synthesis and growth of carbon nanotubes on both conducting graphene and graphite substrates as well as insulating hBN substrate with precise crystallographic orientation is achieved. We show that the nanotubes have a clear preference to align to specific crystal directions of the underlying graphene or hBN substrate. On thicker flakes of graphite, the edges of these 2D materials can control the orientation of these carbon nanotubes. This integrated aligned growth of materials with similar lattices provides a promising route to achieving intricate nanoscale electrical circuits. Furthermore, short channel nanoscale devices consisting of the heterostructure of 1D and 2D materials are fabricated. In these nanoscale devices the nanogap is created due to etching of few layer graphene flake through hydrogenation and the channel is either carbon nanotubes or 2D materials like graphene and MoS2. Finally the transport properties of these nanoscale devices is studied.

Dans le domaine des nanosciences, la recherche sur les matériaux possédant des dimensions réduites a connu des progrès spectaculaires. Tandis que de nombreux travaux ont été fait initialement sur le graphène, l'attention s'est ensuite portée vers d'autres matériaux bidimensionnels, tels que le nitrure de bore hexagonal ou encore les dichalcogénures de métaux de transition. Néanmoins, il est toujours nécessaire de trouver des matériaux possédant des caractéristiques équivalentes ou supérieures à celles des composés déjà connus. Dans le cadre de cette thèse, nous avons utilisé le calcul ab initio et plus particulièrement la théorie de la fonctionnelle de la densité pour prédire et comprendre les propriétés de trois familles de matériaux bidimensionnels. Premièrement, en prenant la structure du phosphorène comme structure de référence et en remplaçant le phosphore par des atomes voisins dans le tableau périodique, nous avons pu obtenir des matériaux inconnus jusqu'ici. Ensuite, nous nous sommes intéressés à des matériaux à base d'halogénures tels que AcOBr ou BaFCl, parmi d'autres. Enfin, nous avons mis l'accent sur des composés bidimensionnels quaternaires, tels que ScP2AgSe6, P2AgSe6Bi, P2CuBiSe6 et CuInP2 S6. Pour chaque matériau, nous avons démontré qu'il était dynamiquement stable et étudié sa structure électronique, et pour certains l'effet d'un champ électrique sur le matériau, ce qui ouvre la porte à de futures études expérimentales dans le domaine / In the field of nanosciences, research on materials with reduced dimensions has seen spectacular progress. While many works were initially done on graphene, the attention then came to other two-dimensional materials, such as hexagonal boron nitride or transition metal dichalcogenides. Nevertheless, it is still necessary to find materials with characteristics equivalent to or superior to those of the already known compounds. In this thesis, we used ab initio calculations and more particularly density functional theory to predict and understand the properties of three families of two-dimensional materials. First, taking the phosphorene structure as the reference and replacing phosphorus with neighboring atoms in the periodic table, we have been able to obtain unknown materials so far. Then we looked at halide materials such as AcOBr or BaFCl, among others. Finally, we have focused on two-dimensional quaternary compounds, such as ScP2AgSe6, P2AgSe6Bi, P2CuBiSe6 and CuInP2S6. For each compound, we demonstrated that it was dynamically stable and studied its electronic structure, and for some the effect of an electric field on the material, which opens the door for future experimental studies in the field

This thesis explores structural and electronic properties of layered materials at the nanometre scale. Room temperature and low temperature ultrahigh vacuum scanning probe microscopy (scanning tunneling microscopy, scanning tunneling spectroscopy, atomic force microscopy) is used as the primary characterization method. The main findings in this thesis are: (a) observations of the atomic lattice and imaging local lattice defects of semiconducting ReS2 by scanning tunneling microscopy, (b) measurement of the electronic band gap of ReS2 by scanning tunneling spectroscopy, and (c) scanning tunneling microscopy study of 1T-TaS2 lattice and chemically functionalizing its defects with magnetic molecules.