To date, the scalable synthesis of elemental two-dimensional materials beyond graphene still remains elusive. Here, we introduce a versatile chemical vapor deposition (CVD) method to grow borophenes, as well as borophene heterostructures, by selectively using diborane originating from traceable byproducts of borazine. Specifically, metallic borophene polymorphs were successfully synthesized on Ir(111) and Cu(111) single-crystal substrates and conjointly with insulating hexagonal boron nitride (hBN) to form atomically precise lateral borophene-hBN interfaces or vertical van der Waals heterostructures. Thereby, borophene is protected from immediate oxidation by a single hBN overlayer. The ability to synthesize high-quality borophenes with large single-crystalline domains in the micrometer scale by a straight-forward CVD approach opens up opportunities for the study of their fundamental properties and for device incorporation.

Humidity sensing is fundamental in some applications, as humidity can be a strong interferent in the detection of analytes under environmental conditions. Ideally, materials sensitive or insensitive towards humidity are strongly needed for the sensors used in the first or second case, respectively. We present here the sensing properties of multi-layered graphene (MLG) upon exposure to different levels of relative humidity. We synthesize MLG by chemical vapor deposition, as shown by Raman spectroscopy, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Through an MLG-based resistor, we show that MLG is scarcely sensitive to humidity in the range 30%–70%, determining current variations in the range of 0.005%/%relative humidity (RH) well below the variation induced by other analytes. These findings, due to the morphological properties of MLG, suggest that defective MLG is the ideal sensing material to implement in gas sensors operating both at room temperature and humid conditions.

Catalytic activity is of pivotal relevance in enabling efficient and selective synthesis processes. Recently, covalent coupling reactions catalyzed by solid metal surfaces opened the rapidly evolving field of on-surface chemical synthesis. Tailored molecular precursors in conjunction with the catalytic activity of the metal substrate allow the synthesis of novel, technologically highly relevant materials such as atomically precise graphene nanoribbons. However, the reaction path on the metal substrate remains unclear in most cases, and the intriguing question is how a specific atomic configuration between reactant and catalyst controls the reaction processes. In this study, we cover the metal substrate with a monolayer of hexagonal boron nitride (h-BN), reducing the reactivity of the metal, and gain unique access to atomistic details during the activation of a polyphenylene precursor by sequential dehalogenation and the subsequent coupling to extended oligomers. We use scanning tunneling microscopy and density functional theory to reveal a reaction site anisotropy, induced by the registry mismatch between the precursor and the nanostructured h-BN monolayer. DOI: https://doi.org/10.1021/nn501906w Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-99013 Accepted Version Originally published at: Dienel, Thomas; Gomez-Diaz, Jaime; Seitsonen, Ari P; Widmer, Roland; Iannuzzi, Marcella; Radican, Kevin; Sachdev, Hermann; Muellen, Klaus; Hutter, Juerg; Groening, Oliver (2014). Dehalogenation and coupling of a polycyclic hydrocarbon on an atomically thin insulator. ACS Nano, 8(7):6571-6579. DOI: https://doi.org/10.1021/nn501906w Site-selective Dehalogenation and Ullmann-type Coupling of Polycyclic Hydrocarbons on a Metal-supported Atomically Thin Insulator Thomas Dienel *, Jaime Gómez-Díaz † , Ari P Seitsonen, Roland Widmer, Marcella Iannuzzi, Kevin Radican, Hermann Sachdev, Klaus Müllen, Jürg Hutter, and Oliver Gröning 1 Empa Swiss Federal Laboratories for Materials Science and Technology, nanotech@surfaces Laboratory, CH-8600 Dübendorf, Switzerland. 2 University of Zurich, Department of Chemistry, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland. 3 Max Planck Institute for Polymer Research, Department of Synthetic Chemistry, Ackermannweg 10, D-55128 Mainz, Germany. The persistent interest of chemists, physicists and material scientists in catalysis and catalytic reactions is fuelled by their pivotal relevance in enabling efficient synthesis processes. Recently, covalent coupling reactions catalysed by solid metal surfaces opened the rapidly evolving field of on-surface chemical synthesis. Using tailored molecular precursors in conjunction with the catalytic activity of the metal substrate allowed the synthesis of novel, technologically highly relevant materials like atomically precise graphene nanoribbons. However, the actual reaction site on the metal remains unclear in most cases and the intriguing question is how a specific atomic configuration between reactant and catalyst controls the reaction processes. With the reduced catalytic activity on hexagonal boron nitride (h-BN), the atomistic details of the sequential dehalogenation of a polyphenylene precursor, constituting the basic first step in many on-surface coupling reactions, prior to coupling to oligomers becomes accessible. Here, we use scanning tunneling microscopy (STM) and density functional theory (DFT) to study the reaction site anisotropy induced by the registry match between the precursor and the nano-patterned h-BN monolayer grown on Rh(111). The detailed understanding of the interaction between precursor molecules and substrates, as presented here, can pave the road to on-surface chemical synthesis of graphene derivatives on metal supported insulators. An atomically thin layer of the insulating h-BN is a natural counterpart for graphene; matching the graphene lattice – a single layer of sp-hybridised carbon atoms [1] – almost perfectly with a small mismatch of approx. 2%. Currently, fabrication of these two-dimensional materials follows two main approaches: i) the bottom-up synthesis by substrate supported chemical vapour deposition (CVD) with suitable precursors and ii) the topdown approach by exfoliation. The fabrication of graphene/h-BN heterostructures, leading to novel devices or devices with enhanced performance, usually relies on elaborate, sequential transfer processes of the produced layers [2]. The main obstacles in the transfer technique are possible misalignment, introduction of defects and contaminations, resulting from handling layers that are just one atom thick. Only recently, the direct CVD growth of graphene on h-BN was demonstrated offering superior properties [3, 4]. However, the growth conditions are harsh (long exposure time, high temperatures, several cycles, etc.) compared to the traditional CVD growth on metal substrates. Metals are favoured for their high catalytic activity, conversely bearing the disadvantage that the grown layers cannot be directly used for electronic device fabrication [5]. A common motif in catalytic reactions is the activation of a reactant, the intermittent complex formed between reactant and catalyst, and finally the coupling reaction [6]. A long-standing question in catalysis is the impact of the specific atomic configuration between catalyst and reactant on the catalytic efficiency. In other words, how does the specific atomic arrangement change the site activity and therefore influence the reaction pathways, energies and reaction yield? Thanks to the recent advances in surface science, we are witness of the tremendous progress in the understanding and development of on-surface chemical reactions and in the fabrication of nanostructured systems [6-8]. A widely used coupling reaction in this context is the Ullmann coupling [9, 10], where the reactive partners are created by dehalogenation of the precursors, which subsequently undergo the aryl-aryl coupling [11]. Recent examples are the formation of graphene nanoribbons and porous graphene on metal substrates [12-14]. The synthesis of porous graphene is based on the molecular precursor 5,5′,5′′,5′′′,5′′′′,5′′′′′-hexaiodo-cyclohexa-m-phenylene (I6-CHP), which dissociates all its iodine atoms on Cu(111), Ag(111) and even Au(111) already at room temperature. The catalytic activity on these metals is already so high that site specific effects are difficult to study and do not seem relevant for the synthesis process. This situation can be expected to be different for a surface supported, ultra-thin insulating spacer layer like monolayer h-BN. The lack of electronic states close to the Fermi level will reduce the catalytic activity, whereas the ultimate thinness still allows the dehalogenation process to be studied by STM. Furthermore, the interaction between the metal and h-BN layer generates distinct superstructures that can be adjusted by a variation of the underlying metal (Ni [15], Pt [16], Cu [17], Rh and Ru [16, 18-24], Fe and Cr [25, 26], etc). On Rh(111) the h-BN forms a highly corrugated “nanomesh” consisting of regions with strong bonding, so-called “pores”, separated by suspended “wire” regions, where the h-BN-Rh(111) interaction is weaker [16, 21, 24, 27-29]. Consequently, the structure of the nanomesh is a superposition of the 0.25 nm h-BN lattice and the network of pores with a lattice constant of 3.2 nm. As we show in the following, deposition of I6-CHP on the nanomesh leads to a distinct adsorption geometry imposing non-equivalency on the six iodine sites of the molecule, which is not intrinsic to the free I6-CHP. Adsorption geometry, sequential dehalogenation and the subsequent coupling of Ix-CHP species are analysed by low-temperature scanning tunneling microscopy (LT-STM at 5.5 K) and density functional theory (DFT). Our experimental and theoretical findings show that the dehalogenation process is surprisingly strongly influenced by the substrate and shed light on the challenges of growing nanostructures by CVD routes directly on an insulating substrate, the latter being of great advantage for future applications. Results and Discussion The molecular petri dish. Figure 1a displays an LT-STM image with low coverage (approx. 0.15 ML) of I6-CHP deposited onto the nanomesh (kept at RT during deposition). Empty pores are imaged as dark depressions [16, 21], while the adsorbed molecules have a flowerlike appearance originating from the apparent six-fold symmetric structure of a single I6-CHP. All molecules occupy single pores and are wellseparated from each other. Figure 1: Molecule I6-CHP and the nanomesh. a, STM image (-1.70 V, 40 pA) of I6-CHP molecules occupying some of the pores of the nanomesh (low coverage of 0.15 ML). b, High resolution STM image (-1.2 V, 32 pA) of a single molecule, revealing inner contrast of the h-BN layer and submolecular contrast of the molecule. c, Ball and stick model of the DFT derived position and orientation of the I6-CHP in the pore of the nanomesh (boron atoms of h-BN lattice enlarged; pore indicated by colour coding; black dots indicate top layer of rhodium atoms). The two insets show the different registries for the carbon-iodine bond: hollow position = A site; on top boron = B site (rhodium atoms are omitted for clarity reasons). This is a very different situation compared to molecules on other insulating thin films typically used in STM – like alkali metal salts (NaCl, KCl, etc.) on metals. The rather homogenous structure of these dielectric spacers is of manifold advantage to study individual molecules [30-32]. However, the adsorption energy landscape for molecular species usually shows only subtle corrugation and already at low coverage (well below a closed monolayer) immediate 2-dimensional domain formation is observed, with molecular close-packing or even aggregation into 3-dimensional structures similar to single crystal insulators [33

Insulating hexagonal boron nitride monolayers (hBN) are best known for being resistant to chemical functionalization. This property makes hBN an excellent substrate for graphene heterostructures, but limits its application as an active element in nanoelectronics where tunable electronic properties are needed. Moreover, the two-dimensional-materials' community wishes to learn more about the adsorption and intercalation characteristics of alkali metals on hBN, which have direct relevance to several electrochemistry experiments that are envisioned with layered materials. Here we provide results on ionic functionalization of hBN/metal interfaces with K and Li dopants. By combining angle-resolved photoemission spectroscopy (ARPES), x-ray photoelectron spectroscopy, and density functional theory calculations, we show that the metallic substrate readily ionizes the alkali dopants and exposes hBN to large electric fields and band-energy shifts. In particular, if hBN is in between the negatively charged substrate and the positive alkali ion, this allows us to directly study, using ARPES, the effects of large electric fields on the electron energy bands of hBN.

We report on the bottom-up fabrication of BN-substituted heteroaromatic networks achieved by surface-assisted polymerization and subsequent cyclodehydrogenation of specifically designed BN-substituted precursor monomers based on a borazine core structural element. To get insight into the cyclodehydrogenation pathway and the influence of molecular flexibility on network quality, two closely related precursor monomers with different degrees of internal cyclodehydrogenation have been employed. Scanning tunneling microscopy shows that, for both monomers, surface-assisted cyclodehydrogenation allows for complete monomer cyclization and the formation of covalently interlinked BN-substituted polyaromatic hydrocarbon networks on the Ag(111) surface. In agreement with experimental observations, density functional theory calculations reveal a significantly lower energy barrier for the cyclodehydrogenation of the conformationally more rigid precursor monomer, which is also reflected in a higher degree of long-range order of the obtained heteroaromatic network. Our proof-of-concept study will allow for the fabrication of atomically precise substitution patterns within BNC heterostructures.

Buckling nanopatterns of monoatomic layer 2D materials on metal substrates attract significant attention due to their rich interface morphology affecting electronic applications. An experimental–theoretical study of a 2D boron–nitrogen–carbon (B x /2 N x /2 C 1− x ) alloy on a Ru(0001) surface is conducted and a profound relation between the composition x and the degree of buckling is discovered. Experimentally, real carbon–boron–nitrogen alloys on the Ru(0001) surface are demonstrated and various morphologies of pure and mixed compounds are shown. Density functional theory calculations are further carried out using the supercells of graphene, hexagonal boron nitride (h‐BN), and random BNC on Ru(0001), as well as Monte Carlo simulations for elucidating the kinetics of their growth. The results show that unlike pure compounds (h‐BN or C), the carbon–boron–nitrogen mix on Ru(0001) mostly exists in an uncorrugated form, thus greatly improving the interface contact. The likely cause of the diminished corrugation is a softening of bond angular interactions in the alloy relative to the pure phases.

Here we present the formation of predominantly sp(2)-coordinate carbon with magnetic- and heteroatom-induced structural defects in a graphene lattice by a stoichiometric dehalogenation of perchlorinated (hetero)aromatic precursors [hexachlorobenzene, C6Cl6 (HCB), and pentachloropyridine, NC5Cl5 (PCP)] with transition metals such as copper in a combustion synthesis. This route allows the build-up of a carbon lattice by a chemistry free of hydrogen and oxygen compared to other pyrolytic approaches and yields either nitrogen-doped or -undoped graphene domains depending on the precursor. The resulting carbon was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoelectron spectroscopy (XPS), and SQUID magnetometry to gain information on its morphological, chemical, and electronic structure and on the location of the nitrogen atoms within the carbon lattice. A significant lowering of the magnetization was observed for the nitrogen-doped carbon obtained by this method, which exhibits less ordered graphene domains in the range of approximately 10-30 nm as per TEM analysis compared to the nondoped carbon resulting from the reaction of HCB with larger graphene domains as per TEM and the presence of a 2D mode in the Raman spectra. The decrease of the magnetization by nitrogen doping within the sp(2)-coordinate carbon lattice can be attributed to an increase in pyrrole-type defects along with a reduction in radical defects originating from five-membered carbon ring structures as well as changes in the π-electron density of edge states.

The characterization of graphene by electron and optical spectroscopy is well established and has led to numerous breakthroughs in material science. Yet, it is interesting to note that these characterization methods are almost never carried out on the same sample, i.e., electron spectroscopy uses epitaxial graphene while optical spectroscopy relies on cleaved graphene flakes. In order to bring coherence and convergence to this branch, a universal and easy-to-prepare substrate is needed. Here we suggest that chemical vapour deposition (CVD) grown graphene on thin monocrystalline Ir(1 1 1) films, which are grown heteroepitaxially on Si(1 1 1) wafers with an yttria stabilized zirconia (YSZ) buffer layer, perfectly meets these needs. We investigate graphene prepared in this way by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, angle-resolved photoemission spectroscopy (ARPES), resonance Raman spectroscopy, and scanning tunnelling microscopy (STM). Our results highlight the excellent crystalline quality of graphene, comparable to graphene prepared on Ir(1 1 1) bulk single crystals. This synthesis route allows for large-area, inexpensive growth on standardized disposable substrates, suitable for both optical and electron spectroscopic characterization, which meets the needs of many researchers in the field.

Borophene—stable, single-atom-thick layers of boron—displays remarkable properties [Also see Report by Mannix et al. ]

We identify the influence of nitrogen-doping on charge- and magnetotransport of single layer graphene by comparing doped and undoped samples. Both sample types are grown by chemical vapor deposition (CVD) and transferred in an identical process onto Si/SiO2 wafers. We characterize the samples by Raman spectroscopy as well as by variable temperature magnetotransport measurements. Over the entire temperature range, the charge transport properties of all undoped samples are in line with literature values. The nitrogen doping instead leads to a 6-fold increase in the charge carrier concentration up to 4 × 10(13) cm(-2) at room temperature, indicating highly effective doping. Additionally it results in the opening of a charge transport gap as revealed by the temperature dependence of the resistance. The magnetotransport exhibits a conspicuous sign change from positive Lorentz magnetoresistance (MR) in undoped to large negative MR that we can attribute to the doping induced disorder. At low magnetic fields, we use quantum transport signals to quantify the transport properties. Analyses based on weak localization models allow us to determine an orders of magnitude decrease in the phase coherence and scattering times for doped samples, since the dopants act as effective scattering centers.

Graphite particles were treated in a nitrogen radio frequency-plasma (RF-plasma) at different excitation power. The morphological as well as chemical surface modifications were investigated by Raman spectroscopy, SEM, and XPS. Changes of the sp2/sp3 bonding ratio and selective surface terminations by functional groups were achieved. Especially, a direct functionalization of the graphites with nitrile groups was evidenced by a characteristic signal at 2240cm−1 in the Raman spectra after a high energy RF-nitrogen plasma treatment. A total nitrogen content of up to 11at.% was reached by the applied conditions. The increased polarity of the surfaces was confirmed by contact angle measurements. The nitrile functionalization may serve as synthetic scaffold for the development of new routes towards the chemical surface modification of carbon substrates. Furthermore, the modified graphites can be processed by common exfoliation techniques yielding nitrogen modified graphene nanoplatelets directly in polar and non-polar solvents.

Abstract Liquid repellent layers can be fabricated by coating a fractal-like layer of candle soot particles with a silicon oxide layer, combusting the soot at 600 °C and subsequently silanizing with perfluoroalkylsilanes. Drops of different liquids deposited on these so called “superamphiphobic” layers easily roll off thanks to the low liquid-solid adhesion. The lower value of the surface tension of liquids that can be repelled depends on details of the processing. Here, we analyze the influence of the soot deposition duration and height with respect to the flame on the structure and wetting properties of the superamphiphobic layer. The mean diameter of the soot particles depends on the distance from the wick. Close to the wick, the average diameter of the particles varies between 30 and 50 nm as demonstrated by scanning electron microscopy (SEM). Close to the top of the flame, the particles size decreases to 10–20 nm. By measuring the mass of superamphiphobic layers and their thickness by laser scanning confocal microscopy (LSCM) in reflection mode, we could determine that the average porosity is 0.91. The height-dependent structural differences affect the apparent contact and roll-off angles. Lowest contact angles are measured when soot is deposited close to the wick due to wax that is not completely burnt, smearing out the required overhanging structures. The small particle size close to the top of the flame also reduces contact angles, again due to decreasing size of overhangs. Sooting in the middle of the flame led to optimal liquid repellency. Furthermore, for sooting times longer than 45 s the properties of the layer did not change with sooting time, verifying the self-similarity of the layer.

Thermally induced chemical vapor deposition (CVD) was used to study the formation of nitrogen-doped graphene and carbon films on copper from aliphatic nitrogen-containing precursors consisting of C1- and C2-units and (hetero)aromatic nitrogen-containing ring systems. The structure and quality of the resulting films were correlated to the influence of the functional groups of the precursor molecules and gas phase composition. They were analyzed with SEM, TEM, EDX, XPS, and Raman spectroscopy. The presence of (N-doped) graphene was confirmed by the 2D mode of the Raman spectra. The isolated graphene films obtained from nitrogen-containing precursors reveal a high conductivity and transparency compared to standard graphene CVD samples. Precursors with amine functional groups (e.g., methylamine) can lead to a direct formation of graphene even without additional hydrogen present in the gas phase. This is not observed for, e.g., methane under comparable CVD conditions. Therefore, the intermediate gas phase species (e.g., amine radicals) can significantly enhance the graphene film growth kinetics. Kinetic and thermodynamic effects can be invoked to discuss the decay of the precursors.

Catalytic activity is of pivotal relevance in enabling efficient and selective synthesis processes. Recently, covalent coupling reactions catalyzed by solid metal surfaces opened the rapidly evolving field of on-surface chemical synthesis. Tailored molecular precursors in conjunction with the catalytic activity of the metal substrate allow the synthesis of novel, technologically highly relevant materials such as atomically precise graphene nanoribbons. However, the reaction path on the metal substrate remains unclear in most cases, and the intriguing question is how a specific atomic configuration between reactant and catalyst controls the reaction processes. In this study, we cover the metal substrate with a monolayer of hexagonal boron nitride (h-BN), reducing the reactivity of the metal, and gain unique access to atomistic details during the activation of a polyphenylene precursor by sequential dehalogenation and the subsequent coupling to extended oligomers. We use scanning tunneling microscopy and density functional theory to reveal a reaction site anisotropy, induced by the registry mismatch between the precursor and the nanostructured h-BN monolayer.

The realization of graphene-based, next-generation electronic applications essentially depends on a reproducible, large-scale production of graphene films via chemical vapor deposition (CVD). We demonstrate how key challenges such as uniformity and homogeneity of the copper metal substrate as well as the growth chemistry can be improved by the use of carbon dioxide and carbon dioxide enriched gas atmospheres. Our approach enables graphene film production protocols free of elemental hydrogen and provides graphene layers of superior quality compared to samples produced by conventional hydrogen/methane based CVD processes. The substrates and resulting graphene films were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Raman microscopy, sheet resistance and transport measurements. The superior quality of the as-grown graphene films on copper is indicated by Raman maps revealing average G band widths as low as 18 ± 8 cm(-1) at 514.5 nm excitation. In addition, high charge carrier mobilities of up to 1975 cm(2)/(V s) were observed for electrons in transferred films obtained from a carbon dioxide based growth protocol. The enhanced graphene film quality can be explained by the mild oxidation properties of carbon dioxide, which at high temperatures enables an uniform conditioning of the substrates by an efficient removal of pre-existing and emerging carbon impurities and a continuous suppression and in situ etching of carbon of lesser quality being co-deposited during the CVD growth.

Suitable templates to steer the formation of nanostructure arrays on surfaces are indispensable in nanoscience. Recently, atomically thin sp(2)-bonded layers such as graphene or boron nitride (BN) grown on metal supports have attracted considerable interest due to their potential geometric corrugation guiding the positioning of atoms, metallic clusters or molecules. Here, we demonstrate three specific functions of a geometrically smooth, but electronically corrugated, sp(2)/metal interface, namely, BN/Cu(111), qualifying it as a unique nanoscale template. As functional adsorbates we employed free-base porphine (2H-P), a prototype tetrapyrrole compound, and tetracyanoquinodimethane (TCNQ), a well-known electron acceptor. (i) The electronic moirons of the BN/Cu(111) interface trap both 2H-P and TCNQ, steering self-organized growth of arrays with extended molecular assemblies. (ii) We report an effective decoupling of the trapped molecules from the underlying metal support by the BN, which allows for a direct visualization of frontier orbitals by scanning tunneling microscopy (STM). (iii) The lateral molecular positioning in the superstructured surface determines the energetic level alignment; i.e., the energy of the frontier orbitals, and the electronic gap are tunable.

A cobalt-nitrogen-doped porous carbon that exhibits a ribbon-shape morphology, high surface area, mesoporous structure, and high nitrogen and cobalt content is fabricated for high-performance self-supported oxygen reduction electrocatalytsts through template-free pyrolysis of cobalt porphyrin-based conjugated mesoporous polymer frameworks.

Graphene is seen as potential successor to silicon [1,2] due to its high charge carrier mobility, which could facilitate ultra high speed electronic devices. Chemical vapour deposition (CVD) synthesis of graphene on single crystal metal surfaces [3] represents a widely used approach, which offers scalable methods for the large-scale production of high-quality graphene layer but it is severely limited by the high cost. The scalable approach of graphene formation reported here provides an important route to the low cost mass production of epitaxial graphene on silicon-based multilayer substrates, which are already available in 4-inch wafers [4]. We have investigated the selective formation of graphene on single crystal Ir(111) films, grown heteroepitaxially on Si(111) wafers with yttria stabilized zirconia (YSZ) buffer layers, using several hydrocarbons and substrate temperatures during CVD synthesis. This surface-induced chemical growth mechanism has been investigated using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), near edge X-ray absorpion fine structure (NEXAFS), and angle-resolved photoemission spectroscopy (ARPES), showing that monolayer graphene grown on Ir(111) films on YSZ/Si(111) is comparable in surface quality to graphene/Ir(111) bulk single crystals and it represents a good way for an up-scalable and low cost synthesis of graphene. Using higher CVD temperatures, ARPES clearly shows double bands characteristic of bilayer graphene formation.

Time-dependent photoemission spectroscopy is employed to study the kinetics of the hydro-genation/deuteration reaction of graphene. Resulting in an unusual kinetic isotope effect, the graphene deuteration reaction proceeds faster than hydrogenation and leads to substantially higher maximum coverages of deuterium (D/C approximate to 35% vs H/C approximate to 25%). These results can be explained by the fact that in the atomic state H and D have a lower energy barrier to overcome in order to react with graphene, while in the molecular form the bond between two atoms must be broken before the capture on the graphene layer. More importantly, D has a higher desorption barrier than H due to quantum mechanical zero-point energy effects related to the CD or CH stretch vibration. Molecular dynamics simulations based on a quantum mechanical electronic potential can reproduce the experimental trends and reveal the contribution of the constituent chemisorption, reflection, and associative desorption processes of H or D atoms onto graphene. Regarding the electronic structure changes, a tunable electron energy gap can be induced by both deuteration and hydrogenation.

Ultrathin films of boron nitride (BN) have recently attracted considerable interest given their successful incorporation in graphene nanodevices and their use as spacer layers to electronically decouple and order functional adsorbates. Here, we introduce a BN monolayer grown by chemical vapor deposition of borazine on a single crystal Cu support, representing a model system for an electronically patterned but topographically smooth substrate. Scanning tunneling microscopy and spectroscopy experiments evidence a weak bonding of the single BN sheet to Cu, preserving the insulating character of bulk hexagonal boron nitride, combined with a periodic lateral variation of the local work function and the surface potential. Complementary density functional theory calculations reveal a varying registry of the BN relative to the Cu lattice as origin of this electronic Moiré-like superstructure.