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Two-dimensional (2D) van der Waals heterostructures combine the distinct properties of individual 2D materials, resulting in metamaterials, ideal for emergent electronic, optoelectronic, and spintronic phenomena. A significant challenge in harnessing these properties for future hybrid circuits is their large-scale realization and integration into graphene interconnects. In this work, we demonstrate the direct growth of molybdenum disulfide (MoS2) crystals on patterned graphene channels. By enhancing control over vapor transport through a confined space chemical vapor deposition growth technique, we achieve the preferential deposition of monolayer MoS2 crystals on monolayer graphene. Atomic resolution scanning transmission electron microscopy reveals the high structural integrity of the heterostructures. Through in-depth spectroscopic characterization, we unveil charge transfer in Graphene/MoS2, with MoS2 introducing p-type doping to graphene, as confirmed by our electrical measurements. Photoconductivity characterization shows that photoactive regions can be locally created in graphene channels covered by MoS2 layers. Time-resolved ultrafast transient absorption (TA) spectroscopy reveals accelerated charge decay kinetics in Graphene/MoS2 heterostructures compared to standalone MoS2 and upconversion for below band gap excitation conditions. Our proof-of-concept results pave the way for the direct growth of van der Waals heterostructure circuits with significant implications for ultrafast photoactive nanoelectronics and optospintronic applications.

Graphene, the atomically thin material of carbon atoms, first isolated experimentally in 2004, exhibits remarkable properties and holds potential for applications in quantum, electrical, and spin-based devices. The chemical vapor deposition (CVD) method enables graphene production on a large scale, merging its exceptional characteristics with scalability and high-quality implementation. Despite the extraordinary promise of CVD graphene with structural imperfections, the main challenge for graphene electronics and spintronics lies in achieving reliability at the device and circuit levels with scalable materials and interfaces. To address these, it is essential to understand the intricacies, endurance, and performance issues in graphene devices. In this thesis, to understand graphene interfaces in devices, we first explored a critical aspect of graphene's interaction with metal oxides, particularly titanium oxide (TiOx) and aluminum oxide (AlOx), and their implications for graphene-based nanoelectronic and spintronic devices. Investigating the electrical characteristics of graphene, both with and without oxides, uncovers the distinct behaviors of TiOx and AlOx when interfaced with graphene, highlighting the charge transfer-induced p-type doping and the formation of sp3 defects, traps, and impurities, especially at the AlOx/graphene interface. These findings bring new insights for graphene spintronic devices while opening possibilities for novel functionalities such as hybrid resistive switching devices. Advancing further towards van der Waals heterostructures in these studies, we could also observe the impact of monolayer MoS2 on graphene’s properties. Next, we explored how CVD graphene devices withstand high current stress to elucidate device durability and resilience. We examine the impact of extreme electric currents on channel structures and resistive tunnel barrier interfaces, focusing on their feasibility for high-capacity electronic and spintronic applications.

Neuromorphic computing mimics the brain's architecture to create energy-efficient devices. Reconfigurable synapses are crucial for neuromorphic computing, which can be achieved through memory-resistive (memristive) switching. Graphene-based memristors have shown nonvolatile multibit resistive switching with desirable endurance. Through first-principles calculations, we study the structural and electronic properties of graphene in contact with an ultra-thin alumina overlayer and demonstrate how one can use charge doping to exert direct control over its interfacial covalency, reversibly switching between states of conductivity and resistivity in the graphene layer. We further show that this proposed mechanism can be stabilized through the p-type doping of graphene, e.g., by naturally occurring defects, the passivation of dangling bonds or defect engineering.

Emergent technologies are required in the field of nanoelectronics for improved contacts and interconnects at nano and micro-scale. In this work, we report a highly-efficient nanolithography process for the growth of cobalt nanostructures requiring an ultra-low charge dose (15 mu C cm(-2), unprecedented in single-step charge-based nanopatterning). This resist-free process consists in the condensation of a similar to 28 nm-thick Co-2(CO)(8) layer on a substrate held at -100 degrees C, its irradiation with a Ga+ focused ion beam, and substrate heating up to room temperature. The resulting cobalt-based deposits exhibit sub-100 nm lateral resolution, display metallic behaviour (room-temperature resistivity of 200 mu omega cm), present ferromagnetic properties (magnetization at room temperature of 400 emu cm(-3)) and can be grown in large areas. To put these results in perspective, similar properties can be achieved by room-temperature focused ion beam induced deposition and the same precursor only if a 2 x 10(3) times higher charge dose is used. We demonstrate the application of such an ultra-fast growth process to directly create electrical contacts onto graphene ribbons, opening the route for a broad application of this technology to any 2D material. In addition, the application of these cryo-deposits for hard masking is demonstrated, confirming its structural functionality.

Despite structural and processing-induced imperfections, wafer-scale chemical vapor deposited (CVD) graphene today is commercially available and has emerged as a versatile form that can be readily transferred to desired substrates for various nanoelectronic and spintronic applications. In particular, over the past decade, significant advancements in CVD graphene synthesis methods and experiments realizing high-quality charge and spin transport have been achieved. These include growth of large-grain graphene, new processing methods, high-quality electrical transport with high-carrier mobility, micron-scale ballistic transport, observations of quantum and fractional quantum Hall effect, as well as the spintronic performance of extremely long spin communication over tens of micrometers at room temperature with robust spin diffusion lengths and spin lifetimes. In this short review, we discuss the progress in recent years in the synthesis of high-quality, large-scale CVD graphene and improvement of the electrical and spin transport performance, particularly towards achieving ballistic and long-distance spin transport that show exceptional promise for next-generation graphene electronic and spintronic applications.