We investigate the electronic properties of graphene upon water adsorption and study the influence of the SiO2 substrate in this context using density functional calculations. Perfect suspended graphene is rather insensitive to H2O adsorbates, as doping requires highly oriented H2O clusters. For graphene on a defective SiO2 substrate, we find a strongly different behavior: H2O adsorbates can shift the substrate's impurity bands and change their hybridization with the graphene bands. In this way, H2O can lead to doping of graphene for much lower adsorbate concentrations than for free hanged graphene. The effect depends strongly on the microscopic substrate properties.
The contact of water with graphene is of fundamental importance and of great interest for numerous promising applications, but how graphene interacts with water remains unclear. Here we used atomic force microscopy to investigate hydrophilic mica substrates with some regions covered by mechanically exfoliated graphene layers in water. In water containing air gas close to the saturation concentration (within ~40%), cap-shaped nanostructures and ordered stripe domains were observed on graphene-covered regions, but not on pure mica regions. These structures did not appear on graphene when samples…
We demonstrate the temperature-mediated and completely reversible process of desorption-readsorption of water on a few layers of epitaxial graphene on a 4H-SiC(0001) substrate. We show that under ambient conditions water forms solid structures on top of the second and third layers of graphene. In the case of strained or highly defective graphene domains, these features produce strongly correlated and reproducible patterns, implying importance of the underlying defects for the initial stages of water adsorption. Hydrophobicity increases with number of graphene layers. Evolution of the water lay…
Surface adsorption is one of the fundamental processes in numerous fields, including catalysis, environment, energy and medicine. The development of an adsorption model which provides an effective prediction of binding energy in minutes has been a long term goal in surface and interface science. The solution has been elusive as identifying the intrinsic determinants of the adsorption energy for various compositions, structures and environments is non-trivial. We introduce a new and flexible model for predicting adsorption energies to metal substrates. The model is based on easily computed, int…
Although very similar in many technological applications, graphene and MoS2 bear significant differences if exposed to humid environments. As an example, lubrication properties of graphene are reported to improve while those of MoS2 to deteriorate: it is unclear whether this is due to oxidation from disulfide to oxide or to water adsorption on the sliding surface. By means of ab initio calculations we show here that these two layered materials have similar adsorption energies for water on the basal planes. They both tend to avoid water intercalation between their layers and to display only mil…
Thermal batteries based on a reversible adsorption-desorption of a working fluid rather than the conventional vapor compression is a promising alternative to exploit waste thermal energy for heat reallocation. In this context, there is an increasing interest to find novel porous solids able to adsorb a high energy density of working fluid under low relative vapor pressure condition combined with an easy ability of regeneration (desorption) at low temperature, which are the major requirements for adsorption driven heat pumps and chillers. The porous crystalline hybrid materials named Metal-Orga…
The atomic scale insights into the interaction of water with oxide surface are essential for elucidating the mechanism of physiochemical processes in various scientific and practical fields, since the water is ubiquitous and coats multifarious material surface under ambient conditions. By utilizing periodic density functional theory calculations with van der Waals corrections, herein we report for the first time the energetically and thermodynamically favorable homolytic dissociative adsorption behavior of water over magnesia (001) films deposited on metal substrate. The water adsorption on pr…
The discovery of fullerenes has stimulated extensive exploration of the resulting behavior of adsorbed films. Our study addresses the planar substrates graphene-fluoride (GF) and graphane (GH) in comparison to graphene. We present initial results concerning the potential energy, energy bands and low density behavior of 4He and 3He films on such different surfaces. For example, while graphene presents an adsorption potential that is qualitatively similar to that on graphite, GF and GH yield potentials with different symmetry, a number of adsorption sites double that on graphene/graphite and a l…
Density Functional Theory calculations are used to investigate the role of substrate-induced cooperative effects on the adsorption of water on a partially oxidized transition metal surface, O(2x2)/Ru(0001). Focussing particularly on the dimer configuration, we analyze the different contributions to its binding energy. A significant reinforcement of the intermolecular hydrogen-bond (H-bond), also supported by the observed frequency shifts of the vibration modes, is attributed to the polarization of the donor molecule when bonded to the Ru atoms in the substrate. This result is further confirmed…
We study adsorption at periodically corrugated substrates formed by scoring rectangular grooves into a planar solid wall which interacts with the fluid via long-range (dispersion) forces. The grooves are assumed to be macroscopically long but their depth, width and separations can all be molecularly small. We show that the entire adsorption process can be divided into three parts consisting of (i) \emph{filling} the grooves by a capillary liquid; (ii) \emph{depinning} of the liquid-gas interface from the wall edges; and (iii) \emph{unbinding} of the interface from the top of the wall, which is…
At present, Pt nanoparticle catalysts in fuel cells suffer from aggregation and loss of chemical activity. In this work, graphdiyne, which has natural porous structure, was proposed as substrate with high adsorption ability to stabilize Pt nanoparticles. Using multiscale calculations by ab initio method and the ReaxFF potential, geometry optimizations, molecular dynamics simulations, Metropolis Monte Carlo simulations and minimum energy paths calculations were performed to investigate the adsorption energy and the rates of desorption and migration of Pt nanoparticles on graphdiyne and graphene…
Near-surface Defects Break Symmetry in Water Adsorption on CeO$_{2-x}$(111)
National Institute for Materials Science (NIMS)（物质材料研究机构）；Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid（马德里自治大学凝聚态理论物理系）；Instituto de Catálisis y Petroleoquímica (CSIC)（催化与石油化工研究所（西班牙国家研究委员会））；Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid（马德里自治大学凝聚态物理中心）；Graduate School of Engineering Science, Osaka University（大阪大学工学研究科）
An efficient technique for the evaluation of the Gibbs adsorption of a liquid on a solid substrate is presented. The behavior of a water nanodroplet on a silicon surface is simulated with molecular dynamics. An external field with varying strength is applied on the system to tune the solid-liquid interfacial contact area. A linear dependence of droplet's volume on the contact area is observed. Our modified Young--Laplace equation is used to explain the influence of the Gibbs adsorption on the nanodroplet volume contraction. Fitting of the molecular dynamics results with these of an analytical …
Silicene and germanene derivatives constructed from periodic dumbbell units play a crucial role in multilayers of these honeycomb structures. Using first-principles calculations based on density functional theory, here we investigate the dumbbell formation mechanisms and energetics of Group IV atoms adsorbed on graphene, silicene, germanene and stanene monolayer honeycomb structures. The stabilities of the binding structures are further confirmed by performing ab-initio molecular dynamics calculations at elevated temperatures, except for stanene which is subject to structural instability upon …
Epitaxial silicene, which is one single layer of silicon atoms packed in a honeycomb structure, demonstrates a strong interaction with the substrate that dramatically affects its electronic structure. The role of electronic coupling in the chemical reactivity between the silicene and the substrate is still unclear so far, which is of great importance for functionalization of silicene layers. Here, we report the reconstructions and hybridized electronic structures of epitaxial 4x4 silicene on Ag(111), which are revealed by scanning tunneling microscopy and angle-resolved photoemission spectrosc…
Using surface-tension measurements, we study the brush-limited adsorption dynamics of a range of amphiphilic polymers, PAAH-$α$-$\textrm{C}_n$ composed of a poly(acrylic acid) backbone, PAAH, grafted with a fraction $α$ of alkyl moieties, containing either $n=8$ or $n=12$ carbon atoms, at pH conditions where the PAAH backbone is not charged. At short times, the surface tension decreases more sharply as the degree of grafting increases while at long times, the adsorption dynamics becomes logarithmic in time and is slower as the degree of grafting increases. This logarithmic behavior at long tim…
We have investigated how the recently-developed water-leaching method for atomically-flat SrTiO3 (STO) substrates affects the transport properties of LaAlO3 (LAO) and STO heterointerfaces. Using pulsed laser deposition at identical growth conditions, we have synthesized epitaxial LAO thin-films on two different STO substrates, which are prepared by water-leaching and buffered hydrofluoric acid (BHF) etching methods. The structural, transport, and optical properties of LAO/STO heterostructures grown on water-leached substrates show the same high-quality as the samples grown on BHF-etched substr…
