Surface Science最新文献

In this report we describe new findings on the structure, composition and thermal stability of Fe${}_x$Ni${}_{1-x}$ nanoparticles, synthesized via a magnetron sputtering source and deposited on a clean W(110) surface. The elemental distribution of the nanoparticles was determined by energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS). The melting behavior of the nanoparticles was studied under UHV by scanning tunneling microscopy (STM) upon heating. Notably, it has been observed that the nanoparticle’s core is characterized by an enrichment of Ni atoms, while the shell shows a higher amount of Fe atoms. Specifically, in the case of Fe_0.75Ni_0.25 and Fe_0.25Ni_0.75, where a Ni core is surrounded by a Fe shell, all nanoparticles completely liquefy after heating at 540 K. In contrast, the Fe_0.50Ni_0.50 nanoparticles, which exhibit a homogeneous distribution of both elements, only begin to melt around 540 K.

The growth of Pt islands at submonolayer coverages on Ag(111) at room temperature were investigated with scanning tunneling microscopy. A two-step mechanism for growth of the islands is proposed. First, Pt replaces Ag substrate atoms through a place-exchange process. Next, Pt adatoms nucleate at substitutional Pt sites and Pt islands subsequently grow from these sites. At room temperature, Ag atoms migrate to cover Pt islands, creating vacancy pits on the terraces and bays on the step edges. Ag atoms nucleate at corner sites of the Pt islands, and the layer of Ag atoms on the Pt islands grow from these sites.

Calcite (calcium carbonate) is the most abundant carbonate in the Earth's crust. Due to its omnipresence it plays a prominent role in fields such as geochemistry, biomineralization and industrial processes. Moreover, the interaction of water with the most stable cleavage plane, calcite (10.4), has been studied intensively, elucidating atomic-scale details of water binding and structure formation on this surface. Interestingly, calcite (10.4) reconstructs under ultrahigh vacuum conditions, exhibiting a (2 × 1) surface unit cell. Although first indications of this reconstruction have been presented more than 20 years ago, a clear confirmation of the existence has been provided only very recently. Here, we study the tip-assisted diffusion of water molecules on calcite (10.4) under ultrahigh vacuum conditions. By recording images series using dynamic atomic force microscopy we follow the movement of water molecules on the surface kept at 140 K. Analyzing the change in consecutive images allows for elucidating details of the molecular movement on the surface. Most notably, the analysis reveals that water molecules occupy one type of adsorption position exclusively, while the other type is not adopted. Our analysis thus demonstrates that the (2 × 1) reconstruction manifests itself in the movement of single water molecules on this surface.

We investigate tracer diffusion at the domain boundaries in an adsorption layer, an effect that corresponds to grain boundary diffusion in 3D polycrystalline solids. Experiments were performed on adsorbed O atoms on a Ru(0001) surface in a layer of CO molecules. The CO molecules form a $\left(\sqrt{3}x\sqrt{3}\right)R{30}^{\circ }$ structure which displays translational domains. High-speed scanning tunneling microscopy (STM) was used to image the motion of the O atoms. The data show that single O atoms preferentially move along the domain walls which in the STM movies appear as disordered, fluctuating stripes between the ordered domains. The diffusion coefficient of the O atoms is one order of magnitude higher than the diffusion coefficient in the ordered domains. By comparison with previous experiments on completely disordered CO layers, it is concluded that the diffusion is similarly promoted by the enhanced fluctuations in the disordered domain walls.

Surface site activation enhances the sensing properties of the CeO₂ (110) surface. Herein, the adsorption of nitrogen dioxide (NO₂) on pristine and modified CeO₂ (110) surfaces has been studied in detail using quantum chemical calculation. The introduction of the single praseodymium atom on the CeO₂ surface reduces its band gap from 1.93 to 0.53 eV, which in turn enhances the adsorption energy from -0.58 (pristine) to -1.34 eV (doped) and also prolongs the desorption time, indicating stronger adsorption ability. The density of states (DOS) and projected density of states (PDOS) analyses reveal that Pr doping modifies the electronic properties of the CeO₂ (110) surface which improves NO₂ sensitivity. Further, it is also observed that 0.57 eV increase in the work function for NO₂ adsorption on Pr doped CeO₂ surface, indicating stronger interaction compared to the pristine CeO₂. In contrast, reduced CeO₂ surfaces do not exhibit any significant change in sensing properties. Thus, it is understood that Pr-doped CeO₂ (Pr/CeO₂) surfaces exhibit better stability and sensitivity towards NO₂ adsorption compared to pristine and reduced surfaces. Therefore, this study provides insight into the rational design of advanced gas sensing materials based on modified CeO₂ (110) surfaces, contributing to the development of an efficient air quality monitoring system.

Carboxylic acid-modified anatase TiO${}_2$-water interfaces are widely relevant, yet understanding of their molecular scale structure is limited. To help improve this understanding, we here construct a deep neural network potential (DP) that accurately represents the potential energy surface of the formic (FA) and acetic acid (AA)-covered anatase TiO${}_2$(101) (A101) interfaces with water predicted by Density Functional Theory (DFT) with the SCAN exchange–correlation functional. Long time-scale (ns) Molecular Dynamics simulations employing such DP provide insight into the hydration structure at the interface, showing how the water density profile and radial distribution functions depend on the coverage and adsorption configurations of the acids. The developed model sets the stage for estimating the adsorption energetics of these small carboxylic acids on the A101 surface in an aqueous environment.

Molybdenum disulfide (MoS₂) features an atomically flat surface without dangling bonds. Molecular self-assembly on this surface provides an effective route to constructing heterostructure devices. In this work, we show the successful synthesis of M₃(1,4,5,8,9,12-hexaazatriphenylene, HAT)₂ (M = Ni, Co) conjugated metal–organic frameworks (c-MOFs) on a MoS₂ surface. In the frameworks, HAT molecules constitute a honeycomb lattice while the metal atoms constitute a Kagome lattice. The random orientations of the frameworks with respect to the substrate and irregular domain shapes indicate that the frameworks interact weakly with the MoS₂. The successful synthesis of 2D c-MOFs on inert substrates opens a door for the construction of advanced 2D van der Waals heterojunctions.

Based on the first principles, we have calculated the influence of the applied electric field and doped X (X = N, P, As, Sb) atoms on the optoelectronic properties and phonon dispersion of the monolayer 2D material SnSe₂. The calculation results show that intrinsic SnSe₂ is a semiconductor with a band gap value of 0.884 eV. The doping of X atoms improves the energy band tunability of the monolayer SnSe₂ system and becomes more stable. The N-doped SnSe₂ system has the most stable structure and the best doping performance. When the electric field strength of 0.3 V/Å is applied on the surface of the N-doped system, the band gap of the system increases. The energy gap gradually decreases when the electric field strength continues to increase from 0.3 V/Å to 0.9 V/Å. At an applied electric field strength of 0.9 V/Å, the system changes from semiconductor to metallic properties. As far as the optical properties are concerned, the applied electric field increases the static refractive index of the system, the imaginary part of the photoconductivity increases, the energy loss function decreases, and the light absorption performance improves. The applied electric field successfully enhanced the optical properties of the SnSe₂ system. The applied electric field strength of 0.9 V/Å doped N system has the best optical properties. This provides a new way to explore the optoelectronic devices based on the SnSe₂ doped system.