Interface Distances Research Articles

Theoretical design of rhombohedral-stacked MoS2-based ferroelectric tunneling junctions with ultra-high tunneling electroresistances.

The sliding ferroelectrics formed by rhombohedral-stacked transition metal dichalcogenides (R-TMDs) greatly broaden the ferroelectric candidate materials. However, the weak ferroelectricity and many failure behaviors (such as irreversible lattice strains or defects) regulated by applied stimuli hinder their application. Here we systematically explore the interface electronic and transport properties of R-MoS2-based van der Waals heterojunctions (vdWHJs) by first-principles calculations. We find that the polarization and the band non-degeneracy of 2R-MoS2 increase with decreasing interlayer distance (d1). Moreover, the polarization direction of graphene (Gra)/2R-MoS2 P↑ state can be switched with a small increase in d1 (about 0.124 Å) due to the weakening of the polarization field (Ep) by a built-in electric field (Ei). The equilibrium state of superposition (|Ep + Ei|) or weakening (|Ep - Ei|) can be modulated by interface distances, which prompts vertical strain-regulated polarization or Schottky barriers. Furthermore, Gra/2R-MoS2 and Gra/R-MoS2/WS2 vdW ferroelectric tunneling junctions (FTJs) demonstrate ultra-high tunneling electroresistance (TER) ratios of 1.55 × 105 and 2.61 × 106, respectively, as the polarization direction switches. Our results provide an avenue for the design of future R-TMD vdW FTJs.

Relationship between changes in interface characteristics and external voltage under compressing force in metal–graphene–metal stacks

Metal–graphene–metal (M–G–M) stacks have provided new specific methods for the integration of two-dimensional (2D) materials into three-dimensional (3D) electronic devices, such as transistors, supercapacitors, memristors and others. Intentional control of the local electronic properties in the stacks is the primary problem to be solved when developing hybrid structures with 2D and 3D elements. In order to do this, the physical mechanisms and processes that define the properties of the stacks must be thoroughly understood. This report introduces an approach based on the force curve analysis in terms of the interface characteristics in the M–G–M stack. In the study, the stack was produced by pressing the platinum probe of a scanning probe microscope into the surface of a gold-supported graphene monolayer, and the force curve was measured under applied direct current voltage. Based on the model of the van der Waals contact, the equilibrium interface distances and the built-in potential were obtained from the experimental results. The equilibrium state was proved to be weakly dependent on the applied voltage below a threshold level. Above this level, irreversible changes and the effect of the history of the tests were detected. The proposed method is acceptable to quantitatively describe the most essential characteristics in a local area of the M–G–M stack, essential for the construction of nano-scaled electronic devices.

Interface induced transition from Schottky-to-Ohmic contacts in single-walled carbon nanotube-based van der Waals Schottky heterostructures

The unique advantages of one-dimensional (1D) van der Waals (vdW) Schottky heterostructures in electronic devices have gradually been highlighted with the improvement of experimental technology in recent years. However, it is inevitable that metal and semiconductor contact will be in the 1D nanodevices, leading to many challenges in the formation of low-resistance Ohmic contacts due to the Fermi level pinning (FLP) effect. Herein, we employ density functional theory to explore a series of 1D armchair carbon nanotube (CNT)-based vdW Schottky heterostructures. By comparing three kinds of Schottky barrier heights (SBH) of S2-NT/CNT, S-NT/CNT, and Se-NT/CNT under different interface distances, we find that only S-NT/CNT can form an Ohmic contact when the interface distance is reduced to 3.01 Å. By analyzing the interface charge transfer, band alignment, and flexoelectric effect, we find that flexoelectric polarization can promote more charge transfer at the S-NT/CNT interface when interface distance becomes smaller, and energy band at the interface bends upwards and overlaps the Fermi level, resulting in the interface to change from a depletion region to an inversion layer and leading to the formation of p-type Ohmic contacts. The results achieved in this study provide a new avenue for the design of 1D vdW electronic devices.

The influences of atom relaxation on the DFT-calculated friction properties of the h-BN/h-BN and Gr/Gr interfaces

In this study, the h-BN/h-BN and Gr/Gr interface systems were employed to investigate the effects of the atomic relaxation on the DFT-calculated friction properties. The friction forces, the atom configurations and electron structures were simulated with and without the atomic relaxation during sliding. Besides, the different normal pressures corresponding to different interface distances were considered. It was found out that the effects of the atomic relaxation on the friction force could be ignored under lower pressures. However, it was prodigious under higher pressures, which can be attributed that the spontaneous motions of in-plane atoms were enhanced by the normal pressures. And the spontaneous atom motions decrease the system energy, which was also confirmed by the electronic structures.

A Theoretical Model to Predict Contact Electrification

Abstract Triboelectric nanogenerators (TENGs) are widely applied to latest nanogenerators which are based on contact electrification (CE). In order to predict the working process of TENGs effectively, this paper proposes a dynamics model to simulate the dynamic mechanism of CE. Taking Fe and polytetrafluoroethylene (PTFE) as contact materials, the field emission under a strong electric field could occur when the interface distance is small enough. The transferred charges in steady state and the differences of interface barrier are calculated by self-consistent field (SCF) method. The molecular dynamics (MD) simulation is carried out under the contact pressure and electric field. The structure results of MD simulation and the electric fields obtained by SCF calculation are the input parameters for each other which run alternately. According to dynamic interface distances and the differences of interface barrier, the dynamic transferred charges can be finally predicted by tunnel current density. The results reveal that the amounts of transferred electrons are positively corresponded to the external pressure and the energy conversion efficiency will reach the extreme value when the pressure is near 130 MPa.

Molecular Engineering of Hexaazatriphenylene Derivatives toward More Efficient Electron-Transporting Materials for Inverted Perovskite Solar Cells.

The electron-transporting material (ETM) in inverted perovskite solar cells (PSCs) plays important role in reducing hysteresis and realizing simple processing procedures, while the improvement of power conversion efficiency is limited by low electron mobility and weak perovskite/ETM interface interaction. In this work, three new ETMs (HAT-1, HAT-2, and HAT-3) were designed by introducing methoxyphenyl, imide, and naphthalene groups into the hexaazatriphenylene (HAT) skeleton, based on the ETM HATNASOC7 synthesized experimentally [Jen; Angew. Chem., Int. Ed. 2016, 55, 8999]. Theoretical calculations showed that the electron mobilities of HAT-1, HAT-2, and HAT-3 are 2.98, 3.79, and 13.21 times that of HATNASOC7, which is attributed to the increased C···C and O···H interactions in the newly designed ETMs. More importantly, the evidently decreased perovskite/ETM interface distances and the significantly increased adsorption energies revealed that the interface interactions were markedly enhanced with the newly designed ETMs by forming additional Pb···O interactions, which promote the electron injection. The deep understanding of perovskite/ETM interface properties sheds new light on the complex factors determining the PSC function and paves the way for the rational design of highly efficient and stable components for PSCs.

On distances between grain interfaces in macroscopic parameter space

There is a considerable activity in acquisition of large data sets of macroscopic grain boundary parameters. Analysis of these sets requires grouping boundaries with similar parameters, and thus one needs a measure of similarity or a distance between interfaces. A number of such functions have been previously defined. Interface distances are constructed in two steps: first, an underlying metric is devised, and then it is modified to account for equivalences between points in the space of macroscopic parameters. The paper characterizes and compares the known underlying distance functions. Features important for a function to be applicable as the interface distance are considered. The main aspects are the invariance with respect to symmetries in the parameter space and the property of metric intrinsicality which is essential for analysis of interface distributions. Also ways of devising alternative metrics are described, and suggestions for choosing a standard metric which may serve in conventional computations are given. Results of the metric characterization are of importance for laying out foundations of the statistical analysis of macroscopic grain boundary data.

Graphene membrane-based NEMS for study of interface interaction

Abstract The scheme and operational principles of graphene-based nanoelectromechanical system (NEMS) for study of interaction between graphene and surface of a sample is proposed. In such a NEMS multilayer graphene membrane bends due to van der Waals attraction between surface of graphene membrane and surface of a sample attached to a manipulator. An analysis of the NEMS total energy balance shows that the NEMS is bistable and abrupt transition between the stable states occurs if the sample is moved toward and backward the membrane. The detection of the interface distances corresponding to these transitions can be used to fit parameters of interatomic potentials for interaction between atoms of the surfaces of the graphene membrane and the sample. The analytical expression for dependences of this transition distances on NEMS sizes and parameters of the potential are derived on example of Lennard-Jones potential. For graphene-graphene interaction the transition distance is estimated to be from several nanometers to several tens nanometers for possible sizes of the proposed NEMS and thus can be measurable for example by transmission electron microscopy . Possibility of this NEMS implementation and application to study graphene-metal interaction are discussed.

First-principles investigations on the contact electrification mechanism between metal and amorphous polymers for triboelectric nanogenerators

Chemical modification on contact pair materials is an important means to enhance the output of triboelectric nanogenerators (TENGs) as the electrification performance of contact materials depends critically on their molecular structures. However, limited understanding on the contact electrification mechanism between metal and amorphous polymer leads to the lack of theoretical basis on chemical modification ideas. On the basis of the typical amorphous polymers used in TENGs, polyethylene terephthalate (PET) and polyimide (Kapton), the method of first-principles research on amorphous polymers contact electrification is explored and the charge transfer mechanism between metal and amorphous polymer is studied. It is found that the electron acceptor in PET and Kapton is always the lowest unoccupied molecular orbital (LUMO) under different contact configurations and interface distances, which provides a clear direction for chemical modification on triboelectric materials. On the other hand, the major functional groups gaining electrons in PET and Kapton are found to be the carboxyl (-COOH) and the imide (-C(=O)NC(=O)-), respectively. Moreover, the contributions of double-bonded oxygen atoms in the carboxyl of PET and the imide of Kapton to contact electrification are significantly greater than that of single-bonded oxygen atoms in the carboxyl of PET and the ether of Kapton, respectively. This indicates that the contributions made by the same atomic species in different molecular groups to contact electrification are significantly different, which provides novel ideas for the chemical modification on triboelectric materials.

One‐Step Solid‐Phase Synthesis of 2D Ultrathin CdS Nanosheets for Enhanced Visible‐Light Photocatalytic Hydrogen Evolution

Photocatalysts with 2D ultrathin nanosheet structures are gradually attracting significant interest from researchers because of their excellent photoelectric and physicochemical properties. However, the efficient fabrication of 2D CdS nanosheets with high crystallinity and ultrathin thickness still faces huge challenges. In this work, 2D ultrathin CdS nanosheets are synthesized through a simple one‐step solid‐phase strategy using CdSO4 · 8/3H2O as precursors in the CH4N2S atmosphere. The 2D ultrathin CdS nanosheet obtained by calcining at 300 °C for 4 h shows superior photocatalytic activity: the photocatalytic rate of hydrogen generation reaches 149.67 μmol h−1, and the corresponding apparent quantum efficiency is 36.7% at 450 nm. The enhanced photocatalytic activity and excellent photocatalytic stability are realized through the high crystallinity and ultrathin 2D nanosheet structure of CdS, which provide a high surface‐to‐volume ratio and enriched active adsorption sites. The 2D ultrathin nanosheet structure prevents the surface sulfide ions from being oxidized because of the extremely short interface distances and photocatalytic carrier transport, resulting in effective photocorrosion inhibition. Controlled experiments also show that the precursors ZnSO4 · 7H2O and Cd(Ac)2 · 2H2O are converted to 2D ZnS and CdS nanosheets through the one‐step solid‐phase method, illustrating that this simple one‐step solid‐phase strategy can be extended to the fabrication of other metal sulfide photocatalysts with 2D nanostructures.

A Standardized Method to Quantify ER-Mitochondrial Interfaces in Electron Mircographs

The interaction sites between endoplasmic reticulum (ER) and mitochondria are signaling hubs in the cell implicated in calcium transfer, lipid metabolism, autophagy, and cell death among other functions. Transmission electron microscopy (TEM) is commonly used to visualize the geometry of these interfaces, but metrics used to describe and compare between conditions, as well as the techniques of measurement are not standardized. Here we describe a pair of scripts for ImageJ that allow for rapid, reproducible and flexible quantification of interface geometries. One script is focused on measuring the physical apposition of the membranes while the other considers the potential exposure of the outer mitochondrial membrane (OMM) to calcium released from the ER. In both cases, the user simply traces the OMM and nearby ER membranes; the script bins the interface distances and returns the length of the OMM that participates in an interface of a given gap width, as well as the total OMM and ER lengths. A ‘score’ based on the inverse-square of the distance is also generated as an attempt to make a single value representing ‘interface-ness’. The additive nature of these measures allows cell-wise totals to be calculated for a given TEM section. While this approach standardizes the measurement technique for a number of parameters of ER-mitochondrial interfaces, it remains to be seen which parameters best correspond with physiological changes in different models.

The thyrohyoid membrane as a target for ultrasonography-guided block of the internal branch of the superior laryngeal nerve

Study objectiveThe objective was to present a proof of concept for a simple and consistently successful ultrasonograpy (US)-guided technique to block the internal branch of the superior laryngeal nerve (iSLN). DesignThis was a volunteer and cadaver anatomy study. SettingThe setting was an anesthesiology department and an anatomy laboratory at a medical school MeasurementsH13-6 MHz US scans were performed in 40 healthy volunteers positioned supine and with extended necks. The goals were to identify the thyrohyoid membrane, measure its depth (in centimeters) using the shortest vertical distance from the skin, and record the scanning time (in seconds) needed to obtain the optimal image.Anatomical dissection was performed with an operating microscope bilaterally on 5 adult cadaver heads, fixed in formalin, to expose the point of iSLN penetration through the thyrohyoid membrane. The distance between the greater horn of the hyoid bone and the nerve entry point into the thyrohyoid membrane was measured. Ultrasonography-guided in-plane injections were performed unilaterally with 22-gauge 50-mm nerve block needles in 3 fresh cadavers with 2-mL lidocaine/methylene blue mixture deposited under direct vision just superficial to the thyrohyoid membrane to evaluate technical feasibility and injectate spread. Main resultsAnatomically, the iSLN was identified in all formalin-preserved cadavers, with hyoid bone greater horn to nerve-membrane interface distances measuring 1.0-2.4 cm (mean, 2.0 cm; SD, 0.5).Sonographically, the iSLN was not visualized, whereas the hyoid bone and the thyrohyoid membrane were visualized in all volunteers. The mean distance from skin to thyrohyoid membrane was 1.69 cm (SD, 0.38). The mean time needed to scan was 15 seconds (SD, 2.3). After US-guided injection, the dye deposition was observed around the iSLN in all cadaver specimens. ConclusionsA simpler and consistently reproducible US-guided iSLN block is feasible using the thyrohyoid membrane as target plane for local anesthetic injection. Clinical trials are needed to determine its effectiveness and safety, needle entry point, trajectory, and local anesthetic volume.

A method for improved accuracy in three dimensions for determining wheel/rail contact points

Searching for the contact points between wheels and rails is important because these points represent the points of exerted contact forces. In order to obtain an accurate contact point and an in-depth description of the wheel/rail contact behaviours on a curved track or in a turnout, a method with improved accuracy in three dimensions is proposed to determine the contact points and the contact patches between the wheel and the rail when considering the effect of the yaw angle and the roll angle on the motion of the wheel set. The proposed method, with no need of the curve fitting of the wheel and rail profiles, can accurately, directly, and comprehensively determine the contact interface distances between the wheel and the rail. The range iteration algorithm is used to improve the computation efficiency and reduce the calculation required. The present computation method is applied for the analysis of the contact of rails of CHINA (CHN) 75 kg/m and wheel sets of wearing type tread of China's freight cars. In addition, it can be proved that the results of the proposed method are consistent with that of Kalker's program CONTACT, and the maximum deviation from the wheel/rail contact patch area of this two methods is approximately 5%. The proposed method, can also be used to investigate static wheel/rail contact. Some wheel/rail contact points and contact patch distributions are discussed and assessed, wheel and rail non-worn and worn profiles included.

Geospatial approach for defining the Wildland-Urban Interface in the Alpine environment

Problems related to fire hazard and fire management have become in recent decades one of the most relevant issues in the Wildland-Urban Interface (WUI), that is the area where human infrastructures meet or intermingle with natural vegetation. In this paper we develop a robust geospatial method for defining and mapping the WUI in the Alpine environment, where most interactions between infrastructures and wildland vegetation concern the fire ignition through human activities, whereas no significant threats exist for infrastructures due to contact with burning vegetation. We used the three Alpine Swiss cantons of Ticino, Valais and Grisons as the study area. The features representing anthropogenic infrastructures (urban or infrastructural components of the WUI) as well as forest cover related features (wildland component of the WUI) were selected from the Swiss Topographic Landscape Model (TLM3D). Georeferenced forest fire occurrences derived from the WSL Swissfire database were used to define suitable WUI interface distances. The Random Forest algorithm was applied to estimate the importance of predictor variables to fire ignition occurrence. This revealed that buildings and drivable roads are the most relevant anthropogenic components with respect to fire ignition. We consequently defined the combination of drivable roads and easily accessible (i.e. 100m from the next drivable road) buildings as the WUI-relevant infrastructural component. For the definition of the interface (buffer) distance between WUI infrastructural and wildland components, we computed the empirical cumulative distribution functions (ECDF) of the percentage of ignition points (observed and simulated) arising at increasing distances from the selected infrastructures. The ECDF facilitates the calculation of both the distance at which a given percentage of ignition points occurred and, in turn, the amount of forest area covered at a given distance. Finally, we developed a GIS ModelBuilder routine to map the WUI for the selected buffer distance. The approach was found to be reproducible, robust (based on statistical analyses for evaluating parameters) and flexible (buffer distances depending on the targeted final area covered) so that fire managers may use it to detect WUI according to their specific priorities.

Schlieren visualization of fluid dynamics effects in direct analysis in real time mass spectrometry.

The success of ambient analysis using plasma-based ion sources depends heavily on fluid dynamics and mass transport efficiency in the sample region. To help characterize the influence of these determining factors, visualization of the gas flow profile for a Direct Analysis in Real Time (DART) ion source at the mass spectrometer atmospheric pressure (AP) interface was performed using the Schlieren technique. The DART helium flow pattern was imaged in model systems incorporating different interface designs, i.e. skimmer or capillary inlet, and for sampling strategies using several types of traditional DART sample probes including a glass capillary, swab, and drug tablet. Notably, Schlieren experiments were conducted on instruments equipped with the gas-ion separator tube (GIST) adapter and Vapur® pump, and on setups featuring the transmission mode (TM) DART module used in standard practice. DART sources were seen to expel a collimated, highly laminar helium stream across interface distances up to ~8 cm. The helium stream was robust to the influence of gas temperature (50-500 °C) and flow rate (≤3.5 L min(-1) ), but considerable DART gas deflection or full disruption was observed in each sampling scenario. The severity of the flow disturbance depended on probe size and placement, the GIST/Vapur® settings, or counter-current gas movements present at the interface. The real-time Schlieren visualizations introduced in this work provide new insight on the fluid dynamics within the DART-MS sample gap while also helping to identify those experimental parameters requiring optimization for improved transmission.

Large scale characterization of the LC13 TCR and HLA-B8 structural landscape in reaction to 172 altered peptide ligands: a molecular dynamics simulation study.

The interplay between T cell receptors (TCRs) and peptides bound by major histocompatibility complexes (MHCs) is one of the most important interactions in the adaptive immune system. Several previous studies have computationally investigated their structural dynamics. On the basis of these simulations several structural and dynamical properties have been proposed as effectors of the immunogenicity. Here we present the results of a large scale Molecular Dynamics simulation study consisting of 100 ns simulations of 172 different complexes. These complexes consisted of all possible point mutations of the Epstein Barr Virus peptide FLRGRAYGL bound by HLA-B*08:01 and presented to the LC13 TCR. We compare the results of these 172 structural simulations with experimental immunogenicity data. We found that simulations with more immunogenic peptides and those with less immunogenic peptides are in fact highly similar and on average only minor differences in the hydrogen binding footprints, interface distances, and the relative orientation between the TCR chains are present. Thus our large scale data analysis shows that many previously suggested dynamical and structural properties of the TCR/peptide/MHC interface are unlikely to be conserved causal factors for peptide immunogenicity.

Generation of CO2-rich melts during basalt magma ascent and degassing

To test mechanisms of basaltic magma degassing, continuous decompressions of volatile-bearing (2.7–3.8 wt% H2O, 600–1,300 ppm CO2) Stromboli melts were performed from 250–200 to 50–25 MPa at 1,180–1,140 °C. Ascent rates were varied from 0.25 to ~1.5 m/s. Glasses after decompression show a wide range of textures, from totally bubble-free to bubble-rich, the latter with bubble number densities from 104 to 106 cm−3, similar to Stromboli pumices. Vesicularities range from 0 to ~20 vol%. Final melt H2O concentrations are homogeneous and always close to solubilities. In contrast, the rate of vesiculation controls the final melt CO2 concentration. High vesicularity charges have glass CO2 concentrations that follow theoretical equilibrium degassing paths, whereas glasses from low vesicularity charges show marked deviations from equilibrium, with CO2 concentrations up to one order of magnitude higher than solubilities. FTIR profiles and maps reveal glass CO2 concentration gradients near the gas–melt interface. Our results stress the importance of bubble nucleation and growth, and of volatile diffusivities, for basaltic melt degassing. Two characteristic distances, the gas interface distance (distance either between bubbles or to gas–melt interfaces) and the volatile diffusion distance, control the degassing process. Melts containing numerous and large bubbles have gas interface distances shorter than volatile diffusion distances, and degassing proceeds by equilibrium partitioning of CO2 and H2O between melt and gas bubbles. For melts where either bubble nucleation is inhibited or bubble growth is limited, gas interface distances are longer than volatile diffusion distances. Degassing proceeds by diffusive volatile transfer at the gas–melt interface and is kinetically limited by the diffusivities of volatiles in the melt. Our experiments show that CO2-oversaturated melts can be generated as a result of magma decompression. They provide a new explanation for the occurrence of CO2-rich natural basaltic glasses and open new perspectives for understanding explosive basaltic volcanism.

Foot Pain and Cycling: a survey of frequency, type, location, associations and amelioration of foot pain

The foot – pedal interface is the primary site for energy transfer from the cyclist to the bicycle, with anecdotal evidence that foot injuries from cycling are common. However, there is little research regarding the prevalence, aetiology and/or management of such injuries. 1) What is the distribution of age, gender, foot/pedal interface use and distances cycled amongst cyclists who experience foot pain? 2) What type of pain and what region of the foot do cyclists experience pain? 3) What amelioration techniques are used for this cycling foot pain? 4) Are there key groups of cyclists at greater risk of foot pain than others?. Cyclists over 18 years of age riding a non-stationary, upright bicycle at least once a week (minimum of one hour) were invited to participate in an electronic questionnaire. The electronic link to the survey was distributed through three large databases Bike SA, (the peak representative body for South Australian cyclists), Mega Bike (a large bicycle shop in Adelaide) and staff and students of the School of Health Sciences at the University of South Australia. The survey asked about cycling participation, pedal interface and foot pain. The survey was returned by 397 participants (93.9% responses eligible for analysis). Foot pain was reported by 53.9% respondents. The forefoot, inclusive of the toenails, toes and ball of the foot, was the highest reported region of foot pain (61%). The pain was described as ‘burning’ and ‘numbness’. ‘Stopping’ for a period of time during the cycle and ‘removing their shoes’, ‘walking around’, ‘massaging’ and ‘stretching’ the foot was the most commonly reported amelioration technique. The group of cyclists at greatest risk of experiencing foot pain are those who ride with an attached (cleated-in, strap, cage) foot-pedal interface. This paper found a high frequency of foot pain in cyclists (53.9% of cohort). The pain was overwhelmingly described as ‘burning’ and ‘numbness’ with the forefoot region most implicated. ‘Stopping’ for a period of time during the cycle and ‘removing their shoes’, ‘walking around’, ‘massaging’ and ‘stretching’ the foot was the most commonly reported amelioration technique. The group of cyclists who are at the greatest risk of experiencing foot pain are those who ride with an attached foot-pedal interface (2.6 odds ratio); followed by the combination of those who use an attached foot-pedal interface and who are 26 years of age or older (2.2 odds ratio). Our study highlights the importance of addressing the current knowledge gap regarding foot pain and cycling and the need to investigate effective interventions for this problem.

Atomic and electronic structure of simple metal/graphene and complex metal/graphene/metal interfaces

Structural, electronic, and magnetic properties of simple interfaces (graphene on top of a metallic substrate) and complex interfaces (a single metallic adlayer on a simple graphene/metal system, either on top or between the graphene and metallic substrate) have been studied using density functional theory. Two types of simple interface with strong (Ni/graphene) and weak (Cu/graphene) bonding were considered. In addition to binding energies and interface distances, which are used to quantify the strength of graphene-substrate interactions, the bonding in simple and complex interfaces was analyzed using charge density distributions and bond orders. Substantial enhancement of the metallic substrate/graphene binding was observed in complex interfaces, consisting of a Ni monolayer on top of a simple {Ni or Cu}/graphene interface. The increase of substrate-graphene bonding in such complex interfaces is accompanied by weakening of in-plane C-C bonds in graphene, as quantified by the bond orders. A weak ferrimagnetism in graphene, i.e., unequal magnetic moments $\ensuremath{-}0.04{\ensuremath{\mu}}_{B}$ and $+0.06{\ensuremath{\mu}}_{B}$ on the C atoms, is induced by a ferromagnetic Ni substrate. The strength of graphene-substrate interactions is also reflected in simulated scanning tunneling microscopy images.

Interfacial interactions between local defects in amorphous SiO2and supported graphene

We present a density functional study of graphene adhesion on a realistic SiO$_2$ surface taking into account van der Waals (vdW) interactions. The SiO$_2$ substrate is modeled at the local scale by using two main types of surface defects, typical for amorphous silica: the oxygen dangling bond and three-coordinated silicon. The results show that the nature of adhesion between graphene and its substrate is qualitatively dependent on the surface defect type. In particular, the interaction between graphene and silicon-terminated SiO$_2$ originates exclusively from the vdW interaction, whereas the oxygen-terminated surface provides additional ionic contribution to the binding arising from interfacial charge transfer ($p$-type doping of graphene). Strong doping contrast for the different surface terminations provides a mechanism for the charge inhomogeneity of graphene on amorphous SiO$_2$ observed in experiments. We found that independent of the considered surface morphologies, the typical electronic structure of graphene in the vicinity of the Dirac point remains unaltered in contact with the SiO$_2$ substrate, which points to the absence of the covalent interactions between graphene and amorphous silica. The case of hydrogen-passivated SiO$_2$ surfaces is also examined. In this situation, the binding with graphene is practically independent of the type of surface defects and arises, as expected, from the vdW interactions. Finally, the interface distances obtained are shown to be in good agreement with recent experimental studies.