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The advances in electronics have been achieved by downscaling the physical size of devices’ components to the nanometer range. However, already in the late 1990s, it was clear that the dimensional scaling of silicon-based technologies had reached its limits. Therefore, to meet the requirements and expectations of future applications, novel materials need to be employed and integrated within the current infrastructure, which is mainly based on silicon. In this scenario, two-dimensional (2D) materials might offer many advantages. Indeed, the integration of graphene, the first among 2D materials, with complementary metal-oxide semiconductor (CMOS) compatible platforms is expected to be the breakthrough point in the research field. In order to control the integration process, the properties of the interface between graphene and substrate need to be thoroughly investigated. However, graphene presents some fundamental weaknesses. Thus, in parallel to graphene’s investigation, research on novel 2D materials beyond graphene has boosted over recent years. Therefore, this Ph.D. thesis focus on the case of graphene deposited on Ge(110) via chemical vapor deposition and potential alternatives to graphene, focusing specifically on silicene. The thesis begins with a brief motivation for novel electronics, a background on graphene’s electronic properties, and state-of-the-art graphene/Ge interface studies. The following chapter gives an overview of the main experimental techniques used in this work. The graphene/Ge(110) interface investigation describes the system’s structural, electronic, and chemical properties. The study is structured to induce modification in the interface by different thermal annealings in vacuum. Upon each annealing, the interface is systematically characterized with different techniques to correlate the various properties and offer the full picture of the system. The last part of the thesis focuses on potential 2D materials that could overco

Combining scanning tunneling microscopy and angle-resolved photoemission spectroscopy, we demonstrate how to tune the doping of epitaxial graphene from p to n by exploiting the structural changes that occur spontaneously on the Ge surface upon thermal annealing. Furthermore, using first-principle calculations, we build a model that successfully reproduces the experimental observations. Since the ability to modify graphene electronic properties is of fundamental importance when it comes to applications, our results provide an important contribution toward the integration of graphene with conventional semiconductors.

We show abrupt changes in the electronic properties of graphene with different types of binding to oxygen. Whereas oxygen bonded to the basal plane in the form of functional groups p-type dopes graphene, we prove that substitutional (i.e. in-plane) oxygen n-type dopes it. Moreover, we determine that impurity scattering potentials introduced by these substitutional atoms are notably larger than those of conventional donors, e.g. nitrogen. Both facts ultimately result in a conduction asymmetry in the system with holes being scattered more strongly than electrons. These findings provide essential insights into the impact of oxygen in carbon nanomaterials such as graphene oxide, oxidized carbon nanotubes or novel two-dimensional pi-conjugated organic frameworks, promising compounds for a wide range of applications including flexible electronics, catalysis, energy storage or biomedicine., Funding Agencies|Danish National Research FoundationDanmarks Grundforskningsfond [DNRF103]; EU Graphene Flagship Core 2 [785219]; EU Graphene Flagship Core 3 [785219]; Villum Young Investigator Program [19130]; Programma per Giovani Ricercatori-Rita Levi Montalcini 2017; NAS of Ukraine [0120U102265]; Provincial Council of Gipuzkoa [2021-CIEN-000070-01]; Basque Department of Education [PIBA-2020-1-0014]; VinnovaVinnova [201902878]; Spanish Ministry of Science and InnovationSpanish Government [PID2019-107338RB-C66]; European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant) [863098]; MICINN Ramon y Cajal program [RYC2019-028443-I]

The family of two-dimensional materials has been expanding rapidly over the last few years. Within it, a special place is occupied by silicene, germanene, and stanene due to their inherent compatibility with the existing semiconductor technology (notably for the case of silicene and germanene). Although obtaining them is not trivial due to the lack of layered bulk counterparts from which they could be mechanically exfoliated, they have been recently synthesized on a number of metallic substrates. The remarkable interaction between metals and these puckered materials, however, strongly modifies their intrinsic electronic properties, and also jeopardizes their integration into functional devices. In this context, first experimental efforts are now being devoted to the synthesis of silicene, germanene, and stanene on nonmetal substrates. Here, we review these pioneering works, present the ongoing debate, analyze, and discuss the major technical challenges and finally suggest possible novel solutions worth exploring.

The availability of an accurate, nondestructive method for measuring thickness and continuity of two-dimensional (2D) materials with monolayer sensitivity over large areas is of pivotal importance for the development of new applications based on these materials. While simple optical contrast methods and electrical measurements are sufficient for the case of metallic and semiconducting 2D materials, the low optical contrast and high electrical resistivity of wide band gap dielectric 2D materials such as hexagonal boron nitride (hBN) hamper their characterization. In this work, we demonstrate a nondestructive method to quantitatively map the thickness and continuity of hBN monolayers and bilayers overlarge areas. The proposed method is based on acquisition and subsequent fitting of ellipsometry spectra of hBN on Si/SiO2 substrates. Once a proper optical model is developed, it becomes possible to identify and map the commonly observed polymer residuals from the transfer process and obtain submonolayer thickness sensitivity for the hBNfilm. With some assumptions on the optical functions of hBN, the thickness of an as-transferred hBN monolayer on SiO2 is measured as 4.1 Å ± 0.1 Å, whereas the thickness of an air-annealedhBN monolayer on SiO2 is measured as 2.5 Å ±0.1 Å. We argue that the difference in the two measured values is due to the presence of a water layer trapped between the SiO2 surface and the hBN layer in the latter case. The procedure can be fully automated to wafer scale and extended to other 2D materials transferred onto any polished substrate, as long as their optical functions are approximately known.

Systems comprising single and multilayer graphene deposited on metals and immersed in acid environments have been investigated, with the aim of elucidating the mechanisms involved, for instance, in hydrogen production or metal protection from corrosion. In this work, a relevant system, namely chemical vapor deposited (CVD) multilayer graphene/Ni (MLGr/Ni), is studied when immersed in a diluted sulfuric electrolyte. The MLGr/Ni electrochemical and morphological properties are studied in situ and interpreted in light of the highly oriented pyrolytic graphite (HOPG) electrode behavior, when immersed in the same electrolyte. Following this interpretative framework, the dominant role of the Ni substrate in hydrogen production is clarified.

Applying protective or barrier layers to isolate a target item from the environment is a common approach to prevent or delay its degradation. The impermeability of two-dimensional materials such as graphene and hexagonal boron nitride (hBN) has generated a great deal of interest in corrosion and material science. Owing to their different electronic properties (graphene is a semimetal, whereas hBN is a wide-bandgap insulator), their protection behaviour is distinctly different. Here we investigate the performance of graphene and hBN as barrier coatings applied on copper substrates through a real-time study in two different oxidative conditions. Our findings show that the evolution of the copper oxidation is remarkably different for the two coating materials.