Transmission electron microscopy (TEM) and scanning TEM (STEM) are indispensable tools for materials characterization. However, during a typical (S)TEM experiment, the sample is subject to a number of effects that can change its atomic structure. Of these, perhaps the least discussed are chemical modifications due to the non-ideal vacuum around the sample. With single-layer graphene, we show that even at relatively low pressures typical for many instruments, these processes can have a significant impact on the sample structure. For example, pore growth becomes up to two orders of magnitude faster at a pressure of ca. 10^{-6} mbar as compared to ultra-high vacuum (UHV; 10^{-10} mbar). Even more remarkably,the presence of oxygen at the sample also changes the observed atomic structure: When imaged in UHV, nearly 90% of the identifiable graphene edge configurations have the armchair structure, whereas armchair and zigzag structures are nearly equally likely to occur when the oxygen partial pressure in the column is higher. Our results both bring attention to the role of the often neglected vacuum composition of the microscope column, and show that control over it can allow atomic-scale tailoring of the specimen structure.
Using low-temperature high-magnetic-field scanning tunneling microscopy and spectroscopy (STM/STS), we systematically study a graphene quantum dot (GQD) defined by a circular graphene p-p junction. Inside the GQD, we observe a series of quasi-bound states arising from whispering-gallery-mode (WGM) confinement of the circular junction and directly visualize these quasi-bound states down to atomic dimensions. By applying a strong magnetic field, a large jump in energy of the quasi-bound states, which is about one-half the energy spacing between the quasi-bound states, is observed. Such a behavio…
Although the unconventional $π$-magnetism at the zigzag edges of graphene holds promise for a wide array of applications, whether and to what degree it plays a role in their chemistry remains poorly understood. Here, we investigate the addition of a hydrogen atom $-$ the simplest yet the most experimentally relevant adsorbate $-$ to zigzag graphene nanoribbons (ZGNRs). We show that the $π$-magnetism governs the chemistry of ZGNRs, giving rise to a site-dependent reactivity of the carbon atoms and driving the hydrogenation process to the nanoribbon edges. Conversely, the chemisorbed hydrogen at…
Transmission electron microscopy has been a promising candidate for mapping atomic orbitals for a long time. Here, we explore its capabilities by a first principles approach. For the example of defected graphene, exhibiting either an isolated vacancy or a substitutional nitrogen atom, we show that three different kinds of images are to be expected, depending on the orbital character. To judge the feasibility of visualizing orbitals in a real microscope, the effect of the optics aberrations is simulated. We demonstrate that, by making use of energy-filtering, it should indeed be possible to map…
The type and distribution of oxygen functional groups in graphene oxide (GO) and reduced graphene oxide (RGO) remain still a subject of great debate. Local analytic techniques are required to access the chemistry of these materials at a nanometric scale. Electron energy loss spectroscopy in a scanning transmission electron microscope can provide the suitable resolution, but GO and RGO are extremely sensitive to electron irradiation. In this work we employ a dedicated experimental setup to reduce electron illumination below damage limit. GO oxygen maps obtained at a few nanometers scale show se…
Drastic Minimization in the van der Waals Interaction with the Bottom Epitaxial Graphene Layer by the Diels-Alder Surface Chemistry of the Top Graphene Layer
We demonstrate that the sub-atomically focused beam of a scanning transmission electron microscope (STEM) can be used to controllably manipulate individual dopant atoms in a 2D graphene lattice. We demonstrate the manipulation of adsorbed source materials and the graphene lattice with the electron beam such that individual vacancy defects can be controllably passivated by Si substitutional atoms. We further demonstrate that these Si defects may be directed through the lattice via e-beam control or modified (as yet, uncontrollably) to form new defects which can incorporate new atoms into the gr…
The article discusses carbocatalysis provided with amorphous carbons. The discussion is conducted from the standpoint of the spin chemistry of graphene molecules, in the framework of which the amorphous carbocatalysts are a conglomerate of graphene-oxynitrothiohydride stable radicals presenting the basic structural units (BSUs) of the species. The chemical activity of the BSUs atoms is reliably determined computationally, which allows mapping the distribution of active sites in these molecular catalysts. The presented maps reliably evidence the BSUs radicalization provided with carbon atoms on…
Propagating atomic vibrational waves, phonons, rule important thermal, mechanical, optoelectronic and transport characteristics of materials. Thus the knowledge of phonon dispersion, namely the dependence of vibrational energy on momentum is a key ingredient to understand and optimize the material's behavior. However, despite its scientific importance in the last decade, the phonon dispersion of a freestanding monolayer of two dimensional (2D) materials such as graphene and its local variations has still remained elusive because of experimental limitations of vibrational spectroscopy. Even tho…
Whether or not specific ion effects determine the charge storage properties of aqueous graphene and graphite-based supercapacitors remains a highly debated topic. In this work we present a multiscale quantum mechanics classical molecular dynamics investigation of aqueous mono- and divalent salt electrolytes in contact with fully polarizable charged graphene sheets. By computing both the electrochemical double layer and quantum capacitance we observe a constant electrode specific capacitance with cationic radii and charge. Counterintuitively, we determine that a switch in the cation adsorption …
Controlling hydrocarbon transport and electron beam induced deposition on single layer graphene: toward atomic scale synthesis in the scanning transmission electron microscope
Graphene oxide is a rising star among 2D materials, yet its interaction with liquid water remains a fundamentally open question: experimental characterization at the atomic scale is difficult, and modelling by classical approaches cannot properly describe chemical reactivity. Here, we bridge the gap between simple computational models and complex experimental systems, by realistic first-principles molecular simulations of graphene oxide (GO) in liquid water. We construct chemically accurate GO models and study their behavior in water, showing that oxygen-bearing functional groups (hydroxyl and…
The fabrication of atomically precise structures with designer electronic properties is one of the emerging topics in condensed matter physics. The required level of structural control can either be reached through atomic manipulation using the tip of a scanning tunneling microscope (STM) or by bottom-up chemical synthesis. In this review, we focus on recent progress in constructing novel, atomically precise artificial materials: artificial lattices built through atom manipulation and graphene nanoribbons (GNRs) realized by on-surface synthesis. We summarize the required theoretical background…
Artificial diamond is created by exposing graphite to pressures on the order of 10\,GPa and temperatures of about 2000\,K. Here, we provide evidence that the pressure exerted by the tip of an atomic force microscope onto graphene over the carbon buffer layer of silicon carbide can lead to a temporary transition of graphite to diamond on the atomic scale. We perform atomic force microscopy with CO terminated tips and copper oxide (CuOx) tips to image graphene and to induce the structural transition. For a local transition, DFT predicts that a repulsive barrier of $\approx13$\,nN, followed by a …
Graphene is an attractive material for microelectronics applications, given such favourable electrical characteristics as high mobility, high operating frequency, and good stability. If graphene is to be implemented in electronic devices on a mass scale, then it must be compatible with existing semiconductor industry fabrication processes. Unfortunately, such processing introduces defects and impurities to the graphene, which cause scattering of the charge carriers and changes in doping level. Scattering results in degradation of electrical performance, including lower mobility and Dirac point…
The edge-functionalization of graphene nanoplatelets (GnP) was carried out exploiting diazonium chemistry, aiming at the synthesis of edge decorated nanoparticles to be used as building blocks in the preparation of engineered nanostructured materials for enhanced heat transfer. Indeed, both phenol functionalized and dianiline-bridged GnP (GnP-OH and E-GnP, respectively) were assembled in nanopapers exploiting the formation of non-covalent and covalent molecular junctions, respectively. Molecular dynamics allowed to estimate the thermal conductance for the two different types of molecular junct…
By bridging graphene and benzene through a well-defined sequence of polycyclic aromatic hydrocarbons and their inherent shell structure, J. Phys. Chem. C, 2018, 122, 17526, it is shown that graphene is actually a coherent arrangement of interwoven benzene molecules, which are coordinated by aromaticity, shell structure and topology, all interrelated. The exotic properties of graphene are in fact macroscopic manifestations of aromaticity. At the molecular level this is revealed as a dynamical flipping of the atomic pz-orbitals belonging to different sublattices, leading to a dynamical interchan…
Despite decades of research, the ultimate goal of nanotechnology--top-down manipulation of individual atoms--has been directly achieved with only one technique: scanning probe microscopy. In this Review, we demonstrate that scanning transmission electron microscopy (STEM) is emerging as an alternative method for the direct assembly of nanostructures, with possible applications in plasmonics, quantum technologies, and materials science. Atomically precise manipulation with STEM relies on recent advances in instrumentation that have enabled non-destructive atomic-resolution imaging at lower elec…
We report angle-resolved electron transmission measurements through freestanding graphene sheets in the energy range of 18 to 30 eV above the Fermi level. The measurements are carried out in a low-energy electron point source microscope, which allows simultaneously probing the transmission for a large angular range. The characteristics of low-energy electron transmission through graphene depend on its electronic structure above the vacuum level. The experimental technique described here allows mapping the unoccupied band structure of freestanding two-dimensional materials as a function of ener…
Graphene nano-flakes (GNFs) are predicted to host spin-polarized metallic edge states, which are envisioned for exploration of spintronics at the nanometer scale. To date, experimental realization of GNFs is only in its infancy because of the limitation of precise cutting or synthesizing methods at the nanometer scale. Here, we use low temperature scanning tunneling microscope (STM) to manipulate coronene molecules on a Cu(111) surface to build artificial triangular and hexagonal GNFs with either zigzag or armchair type of edges. We observe that the metallic edge states only exist in the GNFs …
The interlayer gallery between two adjacent sheets of van der Waals materials is expected to modify properties of atoms and molecules confined at the atomic interfaces. Here, we directly image individual hydrogen atom intercalated between two graphene sheets and investigate its dynamics by scanning tunnelling microscope (STM). The intercalated hydrogen atom is found to be remarkably different from atomic hydrogen chemisorbed on external surface of graphene. Our STM measurements, complemented by first-principles calculations, show that the hydrogen atom intercalated between two graphene sheets …
The light-like dispersion of graphene monolayer results in many novel electronic properties in it1, however, this gapless feature also limits the applications of graphene monolayer in digital electronics2. A rare working solution to generate a moderate bandgap in graphene monolayer is to cut it into one-dimensional (1D) nanometre-wide ribbons3-13. Here we show that a wide bandgap can be created in a unique 1D strained structure, i.e., graphene-nanoribbon-like (GNR-like) structure, of a continuous graphene sheet via strong interaction between graphene and the metal substrate, instead of cutting…
Ordered atomic-scale superlattices on surface hold great interest both for basic science and for potential applications in advanced technology. However, controlled fabrication of superlattices down to atomic scale has proven exceptionally challenging. Here we demonstrate the segregation-growth and self-organization of ordered S atomic superlattices confined at the interface between graphene and S-rich Cu substrates. Scanning tunneling microscope (STM) studies show that, by finely controlling the growth temperature, we obtain well-ordered S (sub)nanometer-cluster superlattice and monoatomic sup…
Understanding Graphene-Perovskite Interactions: From Flake Chemistry to Crystallisation and Solar Cell Performance
CIC nanoGUNE（纳米材料中心）；Fisika Saila, Centro Fı́sica Materiales CSIC-UPV/EHU（巴斯克国家研究委员会-巴斯克国立大学物质物理中心物理系）；Centre for Advanced Materials and Technologies (CEZAMAT), Warsaw University of Technology（华沙理工大学先进材料与技术中心）；Key Laboratory for Special Functional Materials of Ministry of Education, School of Nanoscience and Materials Engineering, Henan University（河南大学纳米科学与工程学部委部省共建特殊功能材料重点实验室）；Instituto de Ciencia de los Materiales (ICMUV), Universitat de Valencia（瓦伦西亚大学材料科学研究所）；Donostia International Physics Center（圣塞巴斯蒂安国际物理中心）；Ikerbasque, Basque Foundation for Science（伊克尔巴斯科，巴斯克科学基金会）；Polymat, University of the Basque Country UPV/EHU（巴斯克国立大学聚合物材料研究中心）；BCMaterials, Basque Center for Materials, Applications and Nanostructures, UPV/EHU Science Park（巴斯克材料、应用与纳米结构中心）
Surface impurities and contamination often seriously degrade the properties of two-dimensional materials such as graphene. To remove contamination, thermal annealing is commonly used. We present a comparative analysis of annealing treatments in air and in vacuum, both ex situ and "pre-situ", where an ultra-high vacuum treatment chamber is directly connected to an aberration-corrected scanning transmission electron microscope. While ex situ treatments do remove contamination, it is challenging to obtain atomically clean surfaces after ambient transfer. However, pre-situ cleaning with radiative …
By using the state-of-the-art microscopy and spectroscopy in aberration-corrected scanning transmission electron microscopes, we determine the atomic arrangements, occupancy, elemental distribution, and the electronic structures of dislocation cores in the 10°tilted SrTiO3 bicrystal. We identify that there are two different types of oxygen deficient dislocation cores, i.e., the SrO plane terminated Sr0.82Ti0.85O3-x (Ti3.67+, 0.48<x<0.91) and TiO2 plane terminated Sr0.63Ti0.90O3-y (Ti3.60+, 0.57<y<1). They have the same Burgers vector of a[100] but different atomic arrangements and chemical pro…
The Ångström-sized probe of the scanning transmission electron microscope can visualize and collect spectra from single atoms. This can unambiguously resolve the chemical structure of materials, but not their isotopic composition. Here we differentiate between two isotopes of the same element by quantifying how likely the energetic imaging electrons are to eject atoms. First, we measure the displacement probability in graphene grown from either $^{12}$C or $^{13}$C and describe the process using a quantum mechanical model of lattice vibrations coupled with density functional theory simulations…
The present theoretical study proposes the enhanced interaction of nanostructures with monosaccharides. It has been demonstrated that the interactions with and without metal adsorption do in fact show that the adsorption energies change accordingly. It is important to note that the chemistry of reactions can also be influenced as a result of this change in dynamics.
Electron-beam (e-beam) manipulation of single dopant atoms in an aberration-corrected scanning transmission electron microscope is emerging as a method for directed atomic motion and atom-by-atom assembly. Until now, the dopant species have been limited to atoms closely matched to carbon in terms of ionic radius and capable of strong covalent bonding with carbon atoms in the graphene lattice. In situ dopant insertion into a graphene lattice has thus far been demonstrated only for Si, which is ubiquitously present as a contaminant in this material. Here, we achieve in situ manipulation of Pt at…
The burgeoning field of atomic level material control holds great promise for future breakthroughs in quantum and memristive device manufacture and fundamental studies of atomic-scale chemistry. Realization of atom-by atom control of matter represents a complex and ongoing challenge. Here, we explore the feasibility of controllable motion of dopant Si atoms at the edges of graphene via the sub-atomically focused electron beam in a scanning transmission electron microscope (STEM). We demonstrate that the graphene edges can be cleaned of Si atoms and then subsequently replenished from nearby sou…
