Le travail réalisé durant cette thèse s’est axé sur la compréhension des mécanismes de transport de charges impliqués dans l’électronique organique ainsi que sur l’ingénierie des propriétés semiconductrices d’interfaces supramoléculaires hybrides. Tout d’abord, l’origine intrinsèque des propriétés de transport de charges a été étudiée dans de petites molécules semiconductrices, similaires en structure chimiques, mais présentant des propriétés électriques nettement différentes. Puis, les propriétés électroniques de matériaux 2D ont été modulées à l’aide de monocouches auto-assemblées induisant des propriétés de dopage antagonistes. Enfin, des pérovskites hybrides ainsi que des petites molécules semiconductrices ont été utilisées comme matériaux actifs dans la détection d’oxygène et d’humidité, respectivement, formant alors des détecteurs à haute performance. L’ensemble de ces projets utilise les principes de la chimie supramoléculaire dans leur réalisation. / The work realized during this thesis was oriented toward the comprehension of the charge transport mechanism involved in organic electronics, and on the engineering of the semiconducting properties of hybrid supramolecular interfaces. Firstly, the intrinsic origin of the charge transport properties was studied for two semiconducting small molecules which are similar in terms of chemical structure but exhibit different electrical properties. Secondly, the electronic properties of 2D material were modulated with the help of self-assembled monolayers inducing antagonist doping properties. Finally, hybrid perovskites and semiconducting small molecules were used as active materials in oxygen and humidity sensing respectively, forming high-performance sensors. All the project employed the principles of the supramolecular chemistry in their realisation.

The 2-dimensional semiconductor family of materials called transition metal dichalcogenides (2d-TMDs) offers many technological advantages: low power consumption, atomically-precise interfaces, lack of nuclear spins and ease of functional integration with other 2d materials are just a few. In this work we harness the potential of these materials as a platform for quantum devices: develop a method by which we can deterministically create single-photon emitting sites in 2d-TMDs, in large-scale arrays. These we call quantum dots (QDs): quantum confinement potentials within semiconductor materials which can trap single-excitons. The single excitons recombine radiatively to emit single-photons. Single-photon sources are a crucial requirement for many quantum information technology (QIT) applications such as quantum cryptography and quantum communication. The QDs are formed by placing the flakes over substrates nano-patterned with protru- sions which induce local strain and provoke the quantum confinement of excitons at low temperatures. This method has been successfully tested in several TMD materials, hence achieving quantum light at different wavelengths. We present one of the very few systems where quantum confinement sites have been shown to be deterministically engineered in a scalable way. Moreover, we have demonstrated how the 2d-based QDs can be embedded within 2d- heterostructures to form functional quantum devices: we have used TMD monolayers along with other 2d-materials - graphene and hexagonal boron nitride - to create quan- tum light-emitting diodes that produce electrically-driven single-photons. Again, very few single-photon sources can be triggered electrically, and this provides a great ad- vantage when considering on-chip quantum technologies. Finally, we present experimental steps towards using our architecture as quantum bits: capturing single-spins inside the QDs, using field-effect type 2d-heterostructures. We are able to controllably charge the QDs with single-electrons and single-holes – a key breakthrough towards the use of spin and valley pseudospin of confined carriers in 2d-materials as a new kind of optically addressable matter qubit. This work presents the successful marriage of 2d-semiconductor technology with QIT, paving the way for 2-dimensional materials as platforms for scalable, on-chip quantum photonics.

The main goal of this thesis is to deposit metal particles on the surface of 2D nanoplatelets using a controlled cementation process. As a proof of concept, copper (Cu) and Graphene Nanoplatelets (GNP) were chosen as the representative metal and 2D nanoplatelets, respectively. Specific goals of this study include depositing nanometer scale Cu particles on the surface of GNP at a low concentration (approximately 5 vol.%) while maintaining clustering and impurities at a minimum. Parametric studies were done to attain these goals by investigating various metallic reducer types and morphologies, GNP surface activation process, acid volume % and copper (II) sulfate concentrations. Optimal conditions were obtained with Mg ribbon as a reducer, 3 minutes of activation, 1 vol.% of acetic acid and 0.01 M CuSO4. The GNP-Cu powder synthesized in this work is a precursor material to be consolidated via spark plasma sintering (SPS) to make a nacre-like, layered structure for future studies.

<p>Controlling the surface chemistry of 2D materials is critical for the development of next generation applications including nanoelectronics and organic photovoltaics (OPVs). Further, next generation nanoelectronics devices require very specific 2D patterns of conductors and insulators with prescribed connectivity and repeating patterns less than 10 nm. However, both top-down and bottom-up approaches currently used lack the ability to pattern materials with sub 10-nm precision over large scales. Nevertheless, a class of monolayer chemistry offers a way to solve this problem through controlled long-range ordering with superior sub-10 nm patterning resolution. Graphene is most often functionalized noncovalently, which preserves most of its intrinsic properties (<i>i.e.,</i> electronic conductivity) and allows spatial modulation of the surface. Phospholipids such as 1,2-bis(10,12-tricsadiynoyl)-<i>sn­</i>-glycero-3-phosphoethanolamine (diyne PE) form lying down lamellar phases on graphene where both the hydrophilic head and hydrophobic tail are exposed to the interface and resemble a repeating cross section of the cell membrane. Phospholipid is made up of a complex headgroup structure and strong headgroup dipole which allows for a diverse range of chemistry and docking of objects to occur at the nonpolar membrane, these principals are equally as important at the nonpolar interface of 2D materials. A key component in the development of nanoelectronics is the integration of inorganic nanocrystals such as nanowires into materials at the wafer scale. Nanocrystals can be integrated into materials through templated growth on to surface of interest as well as through assembly processes (i.e. interfacial adsorption). </p> <p>In this work, I have demonstrated that gold nanowires (AuNWs) can be templated on striped phospholipid monolayers, which have an orientable headgroup dipoles that can order and straighten flexible 2-nm diameter AuNWs with wire lengths of ~1 µm. While AuNWs in solution experience bundling effects due to depletion attraction interactions, wires adsorb to the surface in a well separated fashion with wire-wire distances (e.g. 14 or 21 nm) matching multiples of the PE template pitch. This suggests repulsive interactions between wires upon interaction with dipole arrays on the surface. Although the reaction and templating of AuNWs is completed in a nonpolar environment (cyclohexane), the ordering of wires varies based on the hydration of the PE template in the presence of excess oleylamine, which forms hemicylindrical micelles around the hydrated headgroups protecting the polar environment. Results suggest that PE template experience membrane-mimetic dipole orientation behaviors, which in turn influences the orientation and ordering of objects in a nonpolar environment.</p> <p>Another promising material for bottom-up device applications is MoS₂substrates due to their useful electronic properties. However, being able to control the surface chemistry of different materials, like MoS₂, is relatively understudied, resulting in very limited examples of MoS₂substrates used in bottom-up approaches for nanoelectronics devices. Diyne PE templates adsorb on to MoS₂­in an edge-on conformation in which the alkyl tails stack on top of each other increasing the overall stability of the monolayer. A decrease in lateral spacing results in high local concentrations of orientable headgroups dipoles along with stacked tails which could affect the interactions and adsorption of inorganic materials (i.e. AuNW) at the interface. </p> <p>Here, I show that both diyne PE/HOPG and diyne PE/MoS₂ substrates can template AuNW of various lengths with long range ordering over areas up to 100 µm². Wires on both substrates experience repulsive interactions upon contact with the headgroup dipole arrays resulting in wire-wire distances greater than the template pitch (7 nm). As the wire length is shortened the measured distance between wires become smaller eventually resulting in tight packed ribbon phases. Wires within these ribbon phases have wire-wire distances equal to the template. Ribbon phases occur on diyne PE/HOPG substrates when the wire length is ~50 nm, whereas wire below ~600 nm produce ribbon phases on diyne PE/MoS_2­substrates. </p> <p>Another important aspect to future scientific development is the catalysis of organic reactions, specifically oxygenation of organic sulfides. Sulfide oxygenation is important for applications such as medicinal chemistry, petroleum desulfurization, and nerve agent detoxification. Both reaction rates and the use of inexpensive oxidants and catalysts are important for practical applications. Hydrogen peroxide and <i>tert</i>-butyl hydroperoxide are ideal oxidants due to being cost efficient and environmentally friendly. Hydrogen peroxide can be activated through transition metal base homogeneous catalysts. Some of the most common catalysts are homo- and hetero-polyoxometalates (POMs) due their chemical robustness. Heptamolybdate [Mo₇O₂₄]^6-is a member of the isopolymolybdate family and its ammonium salt is commercially available and low in cost.²² Heteropolyoxometalates have been widely studied as a catalyst for oxygenation reactions whereas heptamolybdate has been rarely studied in oxygenation reactions. </p> <p> Here I report sulfide oxygenation activity of both heptamolybdate and its peroxo derivate [Mo₇O₂₂(O₂)₂]^6-. Sulfide oxygenation of methyl phenyl sulfide (MPS) by H₂O₂to sulfoxide and sulfone occurs rapidly with 100 % utility of H₂O₂ in the presence of [Mo₇O₂₂(O₂)₂]^6-, suggesting the peroxo adduct is an efficient catalyst. However, heptamolybdate is a faster catalyst compared to [Mo₇O₂₂(O₂)₂]^6- for MPS oxygenation and all other sulfides tested under identical conditions. Pseudo-first order <i>k</i>_cat constants from initial rate kinetics show that [Mo₇O₂₄]^6-catalyzes sulfide oxygenation faster. The significant difference in the <i>k</i>_cat suggests differences in the active catalytic species, which was characterized by both UV-Vis and electrospray ionization mass spectrometry. ESI-MS suggest that the active intermediate of [Mo₇O₂₄]^6-under catalytic reaction conditions for sulfide oxygenation by H₂O₂ is [Mo₂O₁₁]^2-. These results show that heptamolybdate is a highly efficient catalyst for H₂O₂oxygenation of organic sulfides.</p>

Tato práce se zabývá oblastí dvourozměrných materiálů, jejich přípravou a analýzou. Pravděpodobně nejznámějším zástupcem dvourozměrných materiálů je grafen. Tento 2D allotrop uhlíku, někdy nazývaný „otec 2D materiálů“, v sobě spojuje neobyčejnou kombinaci elektrických, tepelných a mechanických vlastností. Grafen získal mnoho pozornosti a byl také připraven mnoha metodami. Jedna z těchto metod však stále vyniká nad ostatními kvalitou produkovaného grafenu. Mechanická exfoliace je ve srovnání s jinými technikami velmi jednoduchá, takto připravený grafen je však nejkvalitnější. Práce je také zaměřena na optimalizaci procesu tvorby heterostruktur složených z vrstev grafenu a hBN. Dle prezentovaného postupu bylo připraveno několik van der Waalsových heterostruktur, které byly analyzovány Ramanovskou spektroskopií, mikroskopií atomových sil a nízkoenergiovou elektronovou mikroskopií. Měření pohyblivosti nosičů náboje bylo provedeno v GFET uspořádání. Získané hodnoty pohyblivosti prokázaly vynikající transportní vlastnosti exfoliovaného grafenu v porovnání s grafenem připraveným jinými metodami. V práci popsaný proces přípravy je tedy vhodný pro výrobu kvalitních heterostruktur.

L'isolement du graphène, une monocouche de graphite composée d'un plan d’atomes de carbone, a démontré qu'il est possible de séparer un seul plan d'épaisseur atomique, que l'on appelle matériau bidimensionnel (2D), à partir des solides de Van de Waals (vdW). Grâce à leur stabilité, différents matériaux 2D peuvent être empilés pour former les hétérostructures de vdW. L'interaction vdW à l'interface étant suffisamment faible, les propriétés spécifiques de chaque matériau demeurent globalement inchangées dans l’empilement. En utilisant une démarche théorique et computationnelle basée sur la théorie de la fonctionnelle de la densité (DFT) et le formalisme de Keldysh-Green, nous avons étudié l'hétérostructure graphène/MoS₂ . Le principal intérêt des propriétés spécifiques du graphène et du MoS₂ pour la conception d'un transistor à effet de champ réside dans la mobilité du graphène, à la base d'un transistor haute performance et dans le gap électronique du MoS₂, à la base de la commutation du dispositif. Tout d'abord, nous avons étudié les effets de la rotation entre les deux couches sur les propriétés électroniques à l'interface, en démontrant que les propriétés électroniques globales ne sont pas affectées par l'orientation. En revanche, les images STM (microscope à effet tunnel) sont différentes pour chaque orientation, en raison d'un changement de densité de charge locale. Dans un deuxième temps, nous avons utilisé l’interface graphène/MoS₂ en tant que modèle très simple de Transistor à Effet de Champ. Nous avons analysé le rôle des hétérostructures de vdW sur la performance du transistor, en ajoutant des couches alternées de graphène et MoS₂ sur l'interface graphène/MoS₂. Il a ainsi été démontré que la forme de la DOS au bord du gap est le paramètre le plus important pour la vitesse de commutation du transistor, alors que si l’on ajoute des couches, il n’y aura pas d’amélioration du comportement du transistor, en raison de l'indépendance des interfaces dans les hétérostructures de vdW. Cependant, cela démontre que, dans le cadre de la DFT, on peut étudier les propriétés de transport des hétérostructures de vdW plus complexes en séparant chaque interface et en réduisant le temps de calcul. Les matériaux 2D sont également étudiés ici en tant que pointe pour STM et AFM (microscope à force atomique) : une pointe de graphène testée sur MoS₂ avec défauts a été comparée aux résultats correspondants pour une pointe en cuivre. La résolution atomique a été obtenue et grâce à l'interaction de vdW entre la pointe et l’échantillon, il est possible d’éviter les effets de contact responsables du transfert d'atomes entre la pointe et l'échantillon. En outre, l'analyse des défauts est très utile du fait de la présence de nouveaux pics dans le gap du MoS₂ : ils peuvent ainsi être utilisés pour récupérer un pic de courant et donner des perspectives pour améliorer la performance des transistors. / The isolation of graphene, a single stable layer of graphite, composed by a plane of carbon atoms, demonstrated the possibility to separate a single layer of atomic thickness, called bidimensional (2D) material, from the van der Waals (vdW) solids. Thanks to their stability, 2D materials can be used to form vdW heterostructures, a vertical stack of different 2D crystals maintained together by the vdW forces. In principle, due to the weakness of the vdW interaction, each layer keeps its own global electronic properties. Using a theoretical and computational approach based on the Density Functional Theory (DFT) and Keldish-Green formalism, we have studied graphene/MoS₂ heterostructure. In this work, we are interested in the specific electronic properties of graphene and MoS₂ for the conception of field effect transistor: the high mobility of graphene as a basis for high performance transistor and the gap of MoS₂ able to switch the device. First, the graphene/MoS₂ interface is electronically characterized by analyzing the effects of different orientations between the layers on the electronic properties. We demonstrated that the global electronic properties as bandstructure and Density of State (DOS) are not affected by the orientation, whereas, by mean of Scanning Tunneling Microscope (STM) images, we found that different orientations leads to different local DOS. In the second part, graphene/MoS₂ is used as a very simple and efficient model for Field Effect Transistor. The role of the vdW heterostructure in the transistor operation is analyzed by stacking additional and alternate graphene and MoS₂ layers on the simple graphene/MoS₂ interface. We demonstrated that the shape of the DOS at the gap band edge is the fundamental parameter in the switch velocity of the transistor, whereas the additional layers do not improve the transistor behavior, because of the independence of the interfaces in the vdW heterostructures. However, this demonstrates the possibility to study, in the framework of DFT, the transport properties of more complex vdW heterostructures, separating the single interfaces and reducing drastically the calculation time. The 2D materials are also studied in the role of a tip for STM and Atomic Force Microscopy (AFM). A graphene-like tip, tested on defected MoS₂, is compared with a standard copper tip, and it is found to provide atomic resolution in STM images. In addition, due to vdW interaction with the sample, this tip avoids the contact effect responsible for the transfer of atoms between the tip and the sample. Furthermore, the analysis of defects can be very useful since they induce new peaks in the gap of MoS₂: hence, they can be used to get a peak of current representing an interesting perspective to improve the transistor operation.

<div> Challenges in the semiconductor industry have resulted in the discovery of a plethora of promising materials and devices such as the III-Vs (InGaAs, GaSb, GaN/InGaN) and 2D materials (Transition-metal dichalcogenides [TMDs]) with wide-ranging applications from logic devices, optoelectronics to biomedical devices. Performance of these devices suffer significantly from scattering processes such as polar-optical phonons (POP), charged impurities and remote phonon scattering. These scattering mechanisms are long-ranged, and a quantitative description of such devices require non-local scattering calculations that are computationally expensive. Though there have been extensive studies on coherent transport in these materials, simulations are scarce with scattering and virtually non-existent with non-local scattering. </div><div> </div><div>In this work, these scattering mechanisms with full non-locality are treated rigorously within the Non-Equilibrium Green's function (NEGF) formalism. Impact of non-locality on charge transport is assessed for GaSb/InAs nanowire TFETs highlighting the underestimation of scattering with local approximations. Phonon, impurity scattering, and structural disorders lead to exponentially decaying density of states known as Urbach tails/band tails. Impact of such scattering mechanisms on the band tail is studied in detail for several bulk and confined III-V devices (GaAs, InAs, GaSb and GaN) showing good agreement with existing experimental data. A systematic study of the dependence of Urbach tails with dielectric environment (oxides, charged impurities) is performed for single and multilayered 2D TMDs (MoS2, WS2 and WSe2) providing guideline values for researchers. </div><div><br></div><div>Often, empirical local approximations (ELA) are used in the literature to capture these non-local scattering processes. A comparison against ELA highlight the need for non-local scattering. A physics-based local approximation model is developed that captures the essential physics and is computationally feasible.</div>

<div>With the transistor dimensions scaling down to a few atoms, quantum phenomena - like quantum tunneling and entanglement - will dictate the operation and performance of the next generation of electronic devices, post-CMOS era. While quantum tunneling limits the scaling of the conventional transistor, Tunneling Field Effect Transistor (TFET) employs band-to-band tunneling for the device operation. This mechanism can reduce the sub-threshold swing (S.S.) beyond the Boltzmann's limit, which is fundamentally limited to 60 mV/dec in a conventional Si-based metal-oxide-semiconductor field-effect transistor (MOSFET). A smaller S.S. ensures TFET operation at a lower supply voltage and, therefore, at lesser power compared to the conventional Si-based MOSFET.</div><div><br></div><div>However, the low transmission probability of the band-to-band tunneling mechanism limits the ON-current of a TFET. This can be improved by reducing the body thickness of the devices i.e., using 2-Dimensional (2D) materials or by utilizing heterojunction designs. In this thesis, two promising methods are proposed to increase the ON-current; one for the 2D material TFETs, and another for the III-V heterojunction TFETs.</div><div><br></div><div>Maximizing the ON-current in a 2D material TFET by determining an optimum channel thickness, using compact models, is presented. A compact model is derived from rigorous atomistic quantum transport simulations. A new doping profile is proposed for the III-V triple heterojunction TFET to achieve a high ON-current. The optimized ON-current is 325 uA/um at a supply voltage of 0.3 V. The device design is optimized by atomistic quantum transport simulations for a body thickness of 12 nm, which is experimentally feasible.</div><div> </div><div>However, increasing the device's body thickness increases the atomistic quantum transport simulation time. The simulation of a device with a body thickness of over 12 nm is computationally intensive. Therefore, approximate methods like the mode-space approach are employed to reduce the simulation time. In this thesis, the development of the mode-space approximation in modeling the triple heterojunction TFET is also documented.</div><div><br></div><div>In addition to the TFETs, quantum computing is an emerging field that utilizes quantum phenomena to facilitate information processing. An extra chapter is devoted to the electronic structure calculations of the Si:P delta-doped layer, using the empirical tight-binding method. The calculations agree with angle-resolved photoemission spectroscopy (ARPES) measurements. The Si:P delta-doped layer is extensively used as contacts in the Phosphorus donor-based quantum computing systems. Understanding its electronic structure paves the way towards the scaling of Phosphorus donor-based quantum computing devices in the future.</div>

As part of the EU SmartVista project to develop a multi-modal wearable sensor for health diagnostics, field-effect transistor (FET) based biosensors were explored, with glucose as the analyte, and carbon nanotubes (CNTs) or monolayer MoS2 as the semiconducting sensing layer.  Numerous arrays of CNT-FETs and MoS2-FETs were fabricated by photolithographic methods and packaged as integrated circuits.  Functionalization of the sensing layer using linkers and enzymes was performed, and the samples were characterized by atomic force microscopy, scanning electron microscopy, optical microscopy, and electrical measurements. ON/OFF ratios of 102 p-type and &lt; 102 n-type were acheived, respectively, and the work helped survey the viability of realizing such sensors in a wearable device. / EU Horizon 2020 - SmartVista (825114)

Two dimensional (2D) materials, such as graphene, phosphorene and transition metal chalcogenides, have received a great attention in recent years due to their unique physical and chemical properties. A majority of 2D materials is intrinsically non-magnetic, therefore, their applications in spintronics are limited. The design and synthesis of new 2D materials with intrinsic magnetism and high spin-polarization remains a challenge. Computational discovery of new 2D materials with desired magnetic and electronic properties is the subject of this thesis. Using density functional theory with PBE, PBE+U and HSE06 functionals, we have systematically investigated the structure, electronic, magnetic and topological properties of novel 2D materials. Investigated materials include MXenes and layered transition-metal trihalides, both with great potential applications in spintronic devices. Four different classes of materials showing unique magnetic properties were investigated and reported in this thesis. (1) Asymmetrically functionalized MXenes were studied. The coexistence of the fully compensated antiferromagnetic order (zero magnetization) and completely spin-polarized semiconductivity was found for the first time. Moreover, the spin carrier orientation and induced transition from bipolar antiferromagnetic...