Surface Science最新文献

In a recent publication [2D Materials, 8, 045033 (2021)], it was reported that the growth of a monolayer PdTe${}_2$ in ultra-high vacuum could be achieved by deposition of tellurium on a palladium (111) crystal surface and subsequent thermal annealing. By means of low-energy electron diffraction intensity (LEED-IV) structural analysis, we show that the obtained $\left(\sqrt{3}\times \sqrt{3}\right)\text{R30}°$ superstructure is in fact a TePd${}_2$ surface alloy. Attempts to produce a PdTe${}_2$ layer in ultra-high vacuum by increasing the Te content on the surface were not successful.

Although the structure of Cu(100)-($2\sqrt{2}\times \sqrt{2}$)R45°-O missing row reconstruction (MRR) has been well-established for decades, the detailed structure of its various boundaries remains an untilled area due to the difficulties in obtaining atomically resolved images. Herein, atomic arrangement of the phase boundaries existing in MRR structure was modeled on the basis of scanning tunneling microscopy (STM) investigations. By determining the periodicity and unit structure of MRR in STM images and extending them to boundary region, several types of phase boundaries were identified, resulted respectively from: (1) the mismatch between c(2 × 2)-O patches, (2) the regulation by step edges, and (3) the mismatch between Cu missing rows (MRs). With the modeled structure, it was revealed that the types of the c(2 × 2)-O mismatch induced phase boundaries (OMIPBs) are mainly dominated by the oxygen exposure and in-diffusion barrier. The step edge regulated phase boundaries (SERPBs) are always terminated with Cu-O chain and may represent an intermediate growth stage to larger MRR structure. Comparatively, Cu MRs mismatch is often reconciled by the differently oriented domains between them. As a result, the Cu MRs mismatch induced phase boundaries (CMRMIPBs) are only occasionally observed as Cu-O chains between mismatched Cu MRs that encounter shoulder-to-shoulder. For all studied boundaries, the surrounding MRR domains exhibit obvious orientation preference through inclined packing along the SP direction with the degree closely related with the width of the boundaries.

Based on theoretical calculation and experimental detection, SnO₂-modified graphene (SnO₂-graphene) was proposed as a gas-sensing material for the SF₆ characteristic decomposition products (SO₂, H₂S, SOF₂, SO₂F₂) in SF₆-insulated equipment. Based on density functional theory calculations, the most stable modifying structure of single and double SnO₂ on the surface of graphene is optimized. The adsorption structure, adsorption energy, and charge transfer of four gas molecules on the surface of SnO₂-graphene are calculated and analyzed. Then the total density of states (DOS) and partial density of states (PDOS) of the system before and after gas adsorption were compared and analyzed to explore the interaction mechanism between different gases and SnO₂-graphene. In experimental study, graphene was prepared by the modified Hummers oxidation–reduction method in the laboratory. four concentration gradients of SnO₂ modified on the surface of graphene, and then specific gas sensing experiments were carried out with 10, 25, 50, 100 ppm of the SF₆ characteristic decomposition products. The gap between simulation and experiment is compared and analyzed, which lays a theoretical and experimental foundation for the development of new specific sensors.

Lithium-sulfur (Li-S) batteries are especially competitive in the energy sector due to their excellent performances, like preferable energy density and economic benefits. Studying the adsorption of gas molecules on electrode materials has potential engineering significance for Li-S batteries since they have a highly osmotic potential, which causes unavoidable damage to batteries. In this work, the adsorption phenomenon of common gas molecules (H₂O, N₂, H₂, CO₂, and O₂) on the two-dimensional pyrite (2D-FeS₂) cathode material surface, as well as the effects on the electronic and electrochemical properties, were investigated by the first-principles calculations. The adsorption capabilities were estimated by adsorption energy and Mulliken population analysis. Simulation results demonstrated that whole adsorption energies were less than -1.0 eV and larger than -0.6 eV, which shows a physisorption nature. Among them, the O-S bond of O₂/2D-FeS₂ has the strongest strength. Electronic structure calculations suggested that 2D-FeS₂ maintained good conductivity after gas molecules were adsorbed, achieving efficient transfer between electron, lithium, and sulfur intermediates. Additionally, ab initio molecular dynamics (AIMD) simulations showed that Li⁺ exhibits excellent diffusion performance and low activation energy at different temperatures. 2D-FeS₂ still has a stable electrochemical working window (1.87 ∼ 2.47 V), while the theoretical open current voltage is damaged by gas molecule adsorption. Consequently, this work theoretically reveals the effect of gas molecules on the cathode materials for Li-S batteries, which has guide meaning for engineering.

We investigate the structural, surface and electronic properties of small silicon clusters Si${}_n$ (for $n=2$ to 15) using HF, DFT and FN-DMC calculations. We analyze the atomic configurations, surface properties and electronic structures and show that the radius and average surface area of the clusters can be modeled by a Jellium-type model. We found that the surface tension $\sigma$ of the clusters decreases with increasing cluster size in the range of the clusters under investigation. An estimate of the surface tension for bulk silicon yields ${\sigma }_{bulk}=0.88\left(3\right)$ J/m² in agreement with recent experiments. The average bond length of the clusters shows a non-monotonic behavior. Smaller clusters exhibit a high spin state influenced by electron correlation, especially during the 2D to 3D structural transition, which occurs at $n=4$ to $n=5$. We also find that the Si₄, Si₁₀ and Si₁₂ clusters exhibit enhanced stability due to electron correlation. Our results are consistent with the experiments on bond length, binding energy and dissociation energy.

With increasing importance of germanium (Ge) for semiconductor quantum technologies, the necessity of growing defect-free Ge films has become crucial. Here, Ge homoepitaxial growth experiments were conducted using molecular beam epitaxy (MBE). This requires a smooth (${\sigma }_{rms}\le 10$ Å) and contamination-free substrate surface. We have shown that common ex-situ wet chemical cleaning methods are not sufficient. Foreign atoms like carbon stick to the substrate surface and tend to form clusters which results in macroscopic growth defects which are referred here as pits. The density of such pits is in the range of $10^6$ to $10^9$ cm⁻². The formation and characteristics of the pits have been investigated. Pits emerge after a growth at 370 °C with a thickness of above 5 nm . At growth temperatures lower than 300 °C, the density of pits increases, while it decreases at temperatures higher than 400 °C. Pits can be faceted with the main facets being {1 1 3} and {3 15 23}.

Furthermore, a procedure is presented involving a Ge buffer growth at room temperature with a high growth rate (0.02 nm/s). This leads to a coverage of present contamination and the formation of a new substrate surface which prevent pit formation.

The geometrical confinement directly affects many crucial properties of polymer thin films by interfacial interactions. A key to understanding the role of these interfacial interactions is to specifically probe the confined interface at the molecular level and in situ. However, the direct and nondestructive detection of interfacial polymer structures under confinement is very difficult. In this study, specific interface-sensitive sum frequency generation (SFG) spectroscopy was applied to study the deuterated PS (d₈-PS) film confined between hydrogenated poly (methyl methacrylate) (PMMA) films at the molecular level and in situ. The results showed that the ordering/orientation of the PS chain (backbone and phenyl group) evolved at the buried d₈-PS/PMMA interface during annealing. The tilt angle of the PS phenyl group increased while the twist angle decreased with elevated annealing temperature. Both overall SFG ssp and ppp intensities decreased after annealing at 433 K for 24 h, indicating that PS chains entangled with or penetrated the PMMA chains at the confined interface. This study qualitatively and quantitatively revealed the interfacial structure and structural evolution of the PS chain confined between PMMA films in situ during annealing, which is beneficial to the molecular-level understanding of the interfacial chain conformational relaxation of polymers under confinement.

Reconstructed surfaces of the A15-compound superconductor V${}_3$Si(100) that are possibly induced by the segregation of bulk impurities serve as platforms to study the dependence of Yu–Shiba–Rusinov states induced by a single Fe atom on the adsorption site. Their number, energy and electron–hole asymmetry vary strongly with the atomic environment of the Fe atom. These variations are indicative of different Fe $d$-orbitals being active in the site-dependent exchange coupling with the substrate Cooper pairs. Spatially resolved spectroscopy gives rise to a short decay length of the Yu–Shiba–Rusinov states and thereby suggests the three-dimensional character of the scattering process underlying the bound states.

The effect of O-atom doping on the electronic and optical properties of monolayer MoS₂ under shear deformation has been systematically investigated using first principles. The results show that shear deformation reduces the structural stability of the doped system. The forbidden band width of the doped system decreases sequentially with increasing shear deformation, while conductivity increases. The density of states of both intrinsic and doped systems is primarily contributed by the 4d and 3p orbitals of the Mo and S atoms, respectively. Analysis of the optical properties reveals that shear deformation enhances the static permittivity of the doped systems, leading to an increased ability to bind charges. Additionally, absorption and reflection peaks of all doped systems occur in the ultraviolet region. Compared to the doped system without shear deformation, absorption peaks of the remaining doped systems shift towards the high energy region, resulting in enhanced utilization of ultraviolet light. In the energy range of 16.7–17.3 eV, peak energy loss of all doped systems decreases sequentially, suggesting that shear deformation can reduce energy loss. These results demonstrate that shear deformation can modulate the optoelectronic properties of O-doped monolayer MoS₂ and provide a theoretical foundation for practical applications in semiconductor devices.