Studium možností funkcionalizace grafénu pomocí metod AFM a STM

Tato práce studuje metodou STM všechny fáze růstu, které se vyskytují v průběhu postupného žíhání substrátu SiC(0001), a které vedou ke vzniku hraniční vrstvy a jednovrstevného grafénu. Je zde prokázáno, že růst hraniční vrstvy je způsoben slučováním grafénových nanobublinek, které vznikaji v důsledku odpařování Si ze substrátu a že tento proces účinně soutěží s tvorbou málo probádané fáze 5√3x5√3 pro kterou jsme našli atomární model. Studovali jsme grafén zároveň nc-AFM a STM. Touto technikou se nám podařilo zvlášť určit topografické a elektronické vlastnosti povrchu grafénu na SiC(0001). Analýza odhalila, že drsnost grafénu získaná z map atomární síly je velmi nízká, v souladu s teoretickými předpověďmi. Dále jsme vyvinuli metodu přípravy vysoce kvalitního grafénu na SiC(0001) dopovaného příměsemi B a N. Kombinace experimentálních (STM, nc-AFM, XPS, NEXAFS) a teoretických (DFT a simulace STM) metod umožnila zjistit strukturální, chemické a elektronické vlastnosti jednotlivých substitučních příměsí v grafénu. Ukazujeme, že i pouhým STM lze dosáhnout chemického rozlišení příměsí B a N díky kvantově interferenčnímu jevu, který nastává v důsledku specifické elektronové struktury příměsi N. Chemická reaktivita příměsí B a N byla zkoumána spektroskopií sil pomocí nc-AFM.In this thesis, by means of STM we study all the stages that occur during stepwise annealing of the SiC(0001) substrate, and lead to the formation of buffer layer and to the single layer graphene. It is demonstrated that the buffer layer growth is initiated by merging of graphene nanobubbles arising due to Si depletion and that this process competes with formation of a largely neglected phase, the 5√3x5√3, for which we develop an atomistic model. We studied the single-layer graphene using a simultaneous nc-AFM/STM. By this technique we are able to separate the topographic and electronic contributions from the overall landscape. The analysis reveal that graphene roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. Furthermore, we report a method for preparation of high-quality B- and N-doped graphene on SiC(0001). We combine experimental (nc-AFM, STM, XPS, NEXAFS) and theoretical (total energy DFT simulated STM) studies to analyze the structural, chemical and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of B and N substitutional dopants can be achieved only with the STM due to the quantum interference effect, arising from the specific electronic structure of N dopant sites. Chemical reactivity...Katedra fyziky povrchů a plazmatuDepartment of Surface and Plasma ScienceMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Studying possibilities of graphene functionalization using AFM and STM techniques

In this thesis, by means of STM we study all the stages that occur during stepwise annealing of the SiC(0001) substrate, and lead to the formation of buffer layer and to the single layer graphene. It is demonstrated that the buffer layer growth is initiated by merging of graphene nanobubbles arising due to Si depletion and that this process competes with formation of a largely neglected phase, the 5√3x5√3, for which we develop an atomistic model. We studied the single-layer graphene using a simultaneous nc-AFM/STM. By this technique we are able to separate the topographic and electronic contributions from the overall landscape. The analysis reveal that graphene roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. Furthermore, we report a method for preparation of high-quality B- and N-doped graphene on SiC(0001). We combine experimental (nc-AFM, STM, XPS, NEXAFS) and theoretical (total energy DFT simulated STM) studies to analyze the structural, chemical and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of B and N substitutional dopants can be achieved only with the STM due to the quantum interference effect, arising from the specific electronic structure of N dopant sites. Chemical reactivity..

Substrate induced strain for on-surface transformation and synthesis

10.1039/d0nr01270jNanoscale12147500-750

On-surface Synthesis of [7]triangulene Quantum Ring via Antidot Engineering

The ability to engineer geometrically well-defined antidots in large triangulene homologues allows for creating an entire family of triangulene quantum ring (TQR) structures with tunable high-spin ground state and magnetic ordering, crucial for next-generation molecular spintronic devices. Herein, we report the synthesis of an open-shell [7]triangulene quantum ring ([7]TQR) molecule on Au(111) through the surface-assisted cyclodehydrogenation of a rationally-designed kekulene derivative. Bond-resolved scanning tunneling microscopy (BR-STM) unambiguously imaged the molecular backbone of a single [7]TQR with a triangular zigzag edge topology, which can be viewed as [7]triangulene decorated with a coronene-like antidot in the molecular centre. Additionally, dI/dV mapping reveals that both inner and outer zigzag edges contribute to the edge-localized and spin-polarized electronic states of [7]TQR. Both experimental results and spin-polarized density functional theory calculations indicate that [7]TQR retains its open-shell septuple ground-state (� = 3) on Au(111). This work demonstrates a new route for the design of high-spin graphene quantum rings as the key components for future quantum devices

Achieving High-Quality Single-Atom Nitrogen Doping of Graphene/SiC(0001) by Ion Implantation and Subsequent Thermal Stabilization

We report a straightforward method to produce high-quality nitrogen-doped graphene on SiC(0001) using direct nitrogen ion implantation and subsequent stabilization at temperatures above 1300 K. We demonstrate that double defects, which comprise two nitrogen defects in a second-nearest-neighbor (meta) configuration, can be formed in a controlled way by adjusting the duration of bombardment. Two types of atomic contrast of single N defects are identified in scanning tunneling microscopy. We attribute the origin of these two contrasts to different tip structures by means of STM simulations. The characteristic dip observed over N defects is explained in terms of the destructive quantum interference

Electronic and Chemical Properties of Donor, Acceptor Centers in Graphene

Chemical doping is one of the most suitable ways of tuning the electronic properties of graphene and a promising candidate for a band gap opening. In this work we report a reliable and tunable method for preparation of high-quality boron and nitrogen co-doped graphene on silicon carbide substrate. We combine experimental (dAFM, STM, XPS, NEXAFS) and theoretical (total energy DFT and simulated STM) studies to analyze the structural, chemical, and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of boron and nitrogen substitutional defects can be achieved in the STM channel due to the quantum interference effect, arising due to the specific electronic structure of nitrogen dopant sites. Chemical reactivity of single boron and nitrogen dopants is analyzed using force–distance spectroscopy by means of dAFM

Tailoring Long-Range Superlattice Chirality in the Molecular Selfassemblies via Weak Fluorine-Mediated Interactions

Controllable fabrication of the enantiospecific molecular superlattices is a matter of imminent scientific and technological interest. Herein, we demonstrate that long-range superlattice chirality in molecular self-assemblies can be tailored by tuning the interplay of weak intermolecular non-covalent interactions. Different chiral recognition patterns are achieved in the two molecular self-assemblies comprised by two molecular enantiomers with identical steric conformations, derived from the hexaphenylbenzene – the smallest star-shaped polyphenylene. By means of high-resolution scanning tunneling microscopy measurements, we demonstrate that functionalization of star-shaped polyphenylene with fluorine (F) atoms leads to the formation of molecular self-assemblies with the distinct long-range chiral recognition patterns. We employed the density functional theory calculations to quantify F-mediated lone pair F ···π, C-H··· F, F···F interactions attributed to the tunable enantiospecific molecular self-organizations. Our findings underpin a viable route to tailor long-range chiral recognition patterns in supramolecular assemblies by engineering the weak non-covalent intermolecular interactions

Ultra-high Yield On-surface Synthesis and Assembly of Circumcoronene into Chiral Electronic Kagome-honeycomb Lattice

On-surface synthesis has revealed remarkable potential in the fabrication of a plethora of elusive nanographenes with tailored structural, electronic and magnetic properties unattainable by conventional wet-chemistry synthesis. Unfortunately, surface-assisted synthesis often involves multiple-step cascade reactions with competing pathways, leading to the formation of a diversity of products with limited yield, which reduces its feasibility towards the large-scale production for future technological applications. Here, we devise a new on-surface synthetic strategy for the ultra-high yield synthesis of a hexagonal nanographene with six zigzag edges, namely circumcoronene on Cu(111) via surfaceassisted intramolecular dehydrogenation of the rationally-designed precursor molecule, followed by methyl radical-radical coupling and aromatization. An elegant electrostatic interaction between circumcoronene and Cu(111) drives their self-organization into an extended superlattice, as revealed by bond-resolved low-temperature scanning probe microscopy and spectroscopy measurements. Density functional theory and tight-binding calculations reveal that unique hexagonal zigzag topology of circumcoronenes, along with their periodic electrostatic landscape confines two-dimensional (2D) electron gas in Cu(111) surface into chiral electronic Kagome-honeycomb lattice with two emergent electronic flat bands. Our findings open up a new route for the high-yield fabrication of elusive nanographenes with zigzag topologies and their novel 2D superlattices with possible nontrivial electronic properties towards their future technological applications