Structure Of Solid Surfaces Research Articles

Surface structure-based model to calculate thermal and optical properties in nanoscale and quantum dot semiconductors

Surface combination structure was used to design the construction of nano and quantum films, particles, and dots. The created model was applied to tetrahedral semiconductor nanoparticles and quantum dots with a successful performance. It works better than reported experimental data across the whole size range, from the bulk state to the critical size of quantum dots. The model helps to figure out the melting point that changes with the nanosize scale as applied on Si and Sn, which are simple tetrahedral semiconductors, and for CdS and CdSe, which are among II-VI group compounds. It was also used to calculate melting-related parameters such as cohesive energy, Debye temperature, vibrational entropy, and melting enthalpy. The nanosize dependence of the lattice volume and the atom's ionization energy describes the solid surface structure. From the model, an equation was obtained to calculate the energy gaps in Si, CdS, and CdSe particles that are nano- and quantum-dot-sized, and the results are compared to the experimental data that goes with these particles.

Formation of emission in diode lasers with evaporation of various impurities on the main semiconductor crystal having affinity to electron

The introduction contains a summary of modern provisions that make it impossible to interpret many phenomena occurring in diode laser systems on the basis of commonly accepted physical conceptions. The work demonstrates their inadequacy. The goal and tasks of studies have been formulated. Analysis of a solid and its internal structure (crystal) is provided. It is demonstrated that interaction of plane surface clusters determines the surface structure of solids, while the interaction between three-dimensional clusters determines the internal structure of solids (crystals). Each atom inside the crystal interacts with the first, second and third coordination layer. The value of conduction band energy is determined by displacement of the ionization boundary. For implementation of diode lasers, the distribution of electrons by Fermi-Dirac energies must have a sufficiently diffused maximum. N-conductivity emerges when ionization of negative ions occurs, the energy of affinity of which is located near the conduction band. Р-conductivity is determined by ionization of negative ions, the energy of affinity of which is located near the valence band. Р-n junction is mostly formed when two-atom molecules enter the band gap. In this case, some of the atoms have an affinity for an electron with the value of such affinity located is near the conduction band, while other atoms have an affinity for an electron near the valence band. Interband transition energy contains three components: 1 – Fermi level position energy; 2 – energy of external applied electrical field, and 3 – induced energy formed by positive charge in the valence band. Generation of laser emission takes place when two-atom molecules are adsorbed on the surface of the semiconductor crystal, in which atoms have an affinity to the electron for some of the atoms near the conduction band and for other atoms near the valence band. Maximum emission intensity occurs when external applied electrical voltage fully compensates the energy of affinity to the electron located near the conduction band.

Thermal transport across flat and curved gold-water interfaces: Assessing the effects of the interfacial modeling parameters.

The present investigation assesses a variety of parameters available in the literature to model gold-water interfaces using molecular dynamics simulations. The study elucidates the challenges of characterizing the solid-liquid affinity of highly hydrophilic gold-water interfaces via wettability. As an alternative, the local pairwise interaction energy was used to describe the solid-liquid affinity of flat and curved surfaces, where for the latter, the calculation of a contact angle becomes virtually impossible. Regarding the heat transfer properties of different interface models (flat and curved), partly conclusive trends were observed between the total pairwise interaction energy and the thermal boundary conductance. It was observed that the solid surface structure, interfacial force field type, and force field parameters created a characteristic bias in the interfacial water molecules (liquid structuring). Consequently, a study of the liquid depletion layer provided better insight into the interfacial heat transfer among different interfaces. By computing the density depletion length, which describes the deficit or surplus of energy carries (water molecules) near the interface, a proper characterization of the thermal boundary conductance was obtained for the different gold-water interfaces. It was observed that the interfacial heat transfer is favored when the water molecules organize in cluster-like structures near the interface, by a surplus of water molecules at the interface, i.e., lower density depletion length, and by the closeness of water to the solid atoms.

Multifunctional Edible Oil-Impregnated Nanoporous Oxide Layer on AISI 304 Stainless Steel.

Slippery liquid-infused porous surface (SLIPS) realized on commercial materials provides various functionalities, such as corrosion resistance, condensation heat transfer, anti-fouling, de/anti-icing, and self-cleaning. In particular, perfluorinated lubricants infused in fluorocarbon-coated porous structures have showed exceptional performances with durability; however, they caused several issues in safety, due to their difficulty in degradation and bio-accumulation. Here, we introduce a new approach to create the multifunctional lubricant-impregnated surface with edible oils and fatty acid, which are also safe to human body and degradable in nature. The edible oil-impregnated anodized nanoporous stainless steel surface shows a significantly low contact angle hysteresis and sliding angle, which is similar with general surface of fluorocarbon lubricant-infused systems. The edible oil impregnated in the hydrophobic nanoporous oxide surface also inhibits the direct contact of external aqueous solution to a solid surface structure. Due to such de-wetting property caused by a lubricating effect of edible oils, the edible oil-impregnated stainless steel surface shows enhanced corrosion resistance, anti-biofouling and condensation heat transfer with reduced ice adhesion.

Structure of an Ultrathin Oxide on Pt3 Sn(111) Solved by Machine Learning Enhanced Global Optimization.

Determination of the atomic structure of solid surfaces typically depends on comparison of measured properties with simulations based on hypothesized structural models. For simple structures, the models may be guessed, but for more complex structures there is a need for reliable theory‐based search algorithms. So far, such methods have been limited by the combinatorial complexity and computational expense of sufficiently accurate energy estimation for surfaces. However, the introduction of machine learning methods has the potential to change this radically. Here, we demonstrate how an evolutionary algorithm, utilizing machine learning for accelerated energy estimation and diverse population generation, can be used to solve an unknown surface structure—the (4×4) surface oxide on Pt3Sn(111)—based on limited experimental input. The algorithm is efficient and robust, and should be broadly applicable in surface studies, where it can replace manual, intuition based model generation.

Structure of an Ultrathin Oxide on Pt3Sn(111) Solved by Machine Learning Enhanced Global Optimization.

Determination of the atomic structure of solid surfaces typically depends on comparison of measured properties with simulations based on hypothesized structural models. For simple structures, the models may be guessed, but for more complex structures there is a need for reliable theory-based search algorithms. So far, such methods have been limited by the combinatorial complexity and computational expense of sufficiently accurate energy estimation for surfaces. However, the introduction of machine learning methods has the potential to change this radically. Here, we demonstrate how an evolutionary algorithm, utilizing machine learning for accelerated energy estimation and diverse population generation, can be used to solve an unknown surface structure-the (4×4) surface oxide on Pt3Sn(111)-based on limited experimental input. The algorithm is efficient and robust, and should be broadly applicable in surface studies, where it can replace manual, intuition based model generation.

In situ lattice tuning of quasi-single-crystal surfaces for continuous electrochemical modulation.

The ability to control the atomic-level structure of a solid represents a straightforward strategy for fabricating high-performance catalysts and semiconductor materials. Herein we explore the capability of the mechanically controllable surface strain method in adjusting the surface structure of a gold film. Underpotential deposition measurements provide a quantitative and ultrasensitive approach for monitoring the evolution of surface structures. The electrochemical activities of the quasi-single-crystalline gold films are enhanced productively by controlling the surface tension, resulting in a more positive potential for copper deposition. Our method provides an effective way to tune the atom arrangement of solid surfaces with sub-angstrom precision and to achieve a reduction in power consumption, which has vast applications in electrocatalysis, molecular electronics, and materials science.

Spectral analysis on effects of solid surface structures on mechanism of local heat transport across solid-liquid interface

Spectral analysis on effects of solid surface structures on mechanism of local heat transport across solid-liquid interface

Effect of solid surface structure on the condensation flow of Argon in rough nanochannels with different roughness geometries using molecular dynamics simulation

In this study, the molecular dynamics method is applied for condensation flow inside rough and smooth nanochannels by attaching the roughness on the lower walls. The influence of roughness geometry and height on the condensation characteristics is studied, and the corresponding distribution of density, velocity, and temperature are obtained. Also, the influence of rough surfaces on the condensation rate and the number of atoms that shift the liquid phase is investigated. Results indicate that the rough surface decreases the density fluctuations in its neighboring as well as the velocity level and temperature near the lower wall. Moreover, rough surfaces trap more atoms in the liquid film, which empower the condensation process of flow. It is concluded that the behavior of condensation flow in rough nanochannels is dependent on the roughness geometry and height so that by enhancement of the roughness height, the flow is more affected.

3D thermodynamic analysis of superhydrophobicity of cylinder microtextured surfaces

Superhydrophobic surfaces have attracted great interest due to their self-cleaning, dust-proofing and friction-reducing properties. Related papers have proposed methods and theoretical bases for preparing these surfaces in order to achieve excellent superhydrophobicity. However, the influence of the roughness of the solid surface structure on its superhydrophobicity requires further in-depth thermodynamic analysis. In this paper, three-dimensional (3D) cylinder microtextured surface models are selected based on thermodynamic analysis. On this basis, a simulation diagram of the three-phase contact line of a circular cylinder section in a 3D model is presented. The effects of the intrinsic contact angle and geometrical parameters of the cylinder microtexture on free energy and the free energy barrier, as well as contact angle hysteresis, are theoretically investigated. The obtained results reveal the necessity of the transition between the non-composite state and composite state. The transition criteria between the non-composite and composite wetting states are obtained from the perspective of thermodynamic analysis and theoretical equations. The calculated results are basically consistent with the theoretical calculations and experimental results. This method provides theoretical guidance for the design of superhydrophobic surfaces.

Construction and manipulation of self-assemble structures on solid surfaces

Construction of two-dimensional (2D) molecular crystals on solid surfaces is an important way to synthesize supermolecular materials and functionalize solid surfaces. In this review, we provide an overview of the formation mechanism of the 2D self-assembled molecular crystals, and the control of the structures and electronic structures by combining theoretical calculations with scanning tunneling microscopy (STM). Here we focus on the molecular self-assembled structures dominated by weak interactions. Several key factors are listed, for example, the electronic structures of solid surfaces, the configuration of molecules, the interaction of molecules, the interaction between molecules and substrates, and the bromine adatom assisted self-assembly. Finally, we assess future directions of research in this field, where the overall consideration of all the aspects we discussed is important.

Surface chemistry of solid catalysts

<p indent=0mm>Surface chemistry of solid catalysts is an interdiscipline research area of surface science and catalysis science. It aims at fundamental understandings of heterogeneous catalysis of solid surfaces and establishments of structure-activity relation of solid catalysts at the atomic and molecular levels via surface chemistry studies of solid catalysts. Surface chemistry studies of solid catalysts are challenging due to complex and poorly-uniform structure of solid surfaces. This review introduces a novel approach based on model catalysts ranging from single crystals to nanocrystals and summaries the research progress employing such an approach, including the establishment of “oxygen vacancy-controlled reactivity of hydroxyl groups on oxide surfaces” concept, the reveal of facet effect in oxide catalysis, and the demonstration of structural sensitivity of gold catalysis. Surface chemistry studies of model catalysts ranging from single crystals to nanocrystals are hopeful to realize the ultimate research goal of fundamental catalysis studies- from the fundamental understandings at the atomic and molecular levels to the structural design and controlled synthesis of efficient catalysts.

What is the Smallest Atom as a Probe for Characterizing Nanostructures?

In gas adsorption techniques for characterizing the surface structure of solids and the porosity of porous materials, a smaller adsorptive is expected to be useful as a probe to detect finer structures. According to the periodic table, the smallest noble gas atom is helium. However, in cryogenic systems, light atoms such as helium behave as atoms larger than the size estimated from their electron shell structures because of the uncertainty in the position of the atom arising from quantum effects. Here, to unveil the smallest atom as a probe, we perform path integral grand canonical Monte Carlo simulations for the adsorption of noble gases on pore and solid surface models at the respective boiling temperature of each noble gas. First, we show that helium gas behaves exactly as an atom larger than its classically estimated size at low temperatures; in pores, however, it is smaller than in the bulk phase because quantum delocalization is suppressed by the pore walls and helium anomalously acts as a spheroidal atom in confined space. Second, a systematic comparison of the simulation results reveals that neon can enter an extremely small space helium is unable to enter, suggesting that the effective size of the atom at cryogenic temperatures is determined by the size of the electron cloud and wave nature of an atomic nucleus; consequently, neon is the smallest and most suitable noble gas as a probe to access more in-depth information on atomistic scale nanostructures.

Local regularization methods for inverse Volterra equations applicable to the structure of solid surfaces

Deconvolution of appearance potential spectra is an old strategy commonly used to investigate electronic properties of solids in the surface region. Recently, this strategy was found to be effective in the study of nanostructures. In this context, the density of unoccupied states in the surface region of a solid is recovered from the measured AP-spectrum data from the governing equation $k*x*x=g$, where $k$ is a Lorentzian type function, $g$ is a measured APS-signal and $x$ is the density function to be recovered. As an important step in solving for $x$, we need to solve the autoconvolution problem $x*x=f$, which is a nonlinear ill-posed Volterra problem. In this paper, we first improve upon the existing local regularization theory developed in [{\bf9}] for solving the autoconvolution problem, allowing for $L_p$ data, where $1 \le p \le \infty$. We prove the solutions of the regularized equation $x_\alpha^\delta \in L_\infty(0,1)$ (smoother than $x_\alpha^\delta \in L_2(0,1)$ as in [{\bf9}]) converge to the true solution $\overline{x}$ of the autoconvolution equation in $L_\infty$ norm (stronger than $L_2$ norm as in [{\bf9}]) when the noise level in the data shrinks to 0. It is worth noting that we obtain the improved convergence theory while imposing less restrictions on the true solution $\overline{x}$; namely $\overline{x} \in C^1(0,1)$ in contrast to $\overline{x}\in W^{2,\infty}(0,1)$. Further, for the stable deconvolution of appearance potential spectra, we apply the local regularization methods to solve a combination of two ill-posed Volterra problems: the linear problem of determining $f$ from $f*k=g$ and then the nonlinear autoconvolution problem of determining $x$ from $x*x=f$. The results include a convergence theory and a fast sequential numerical method which essentially preserves the causal nature of the combined deconvolution problem. Numerical examples are included to show the effectiveness and efficiency of the methods.

Design and Performance Aspects of a Custom-Built Ambient Pressure Photoelectron Spectrometer toward Bridging the Pressure Gap: Oxidation of Cu, Ag, and Au Surfaces at 1 mbar O2 Pressure

The critical features of a custom-built laboratory version ambient pressure photoelectron spectrometer (Lab-APPES) are presented. A double front cone differential pumping arrangement and an aperture free design employed in the electrostatic lens regime improve the data collection and data quality. In contrast to the conventional X-ray photoelectron spectrometers (XPS) operating at ultrahigh vacuum (UHV), it is possible to explore the electronic structure of solid surfaces under working conditions or closer to working conditions with Lab-APPES. Especially surface-dependent phenomena can be explored up to 1 mbar pressure and up to 873 K by conventional heating methods and at least up to 1273 K by a laser heating method. Simultaneous XPS and reaction kinetic measurements on solid surfaces make the Lab-APPES an important tool to measure the dynamic electronic structure changes on material surfaces under reaction conditions. The interaction of O2 with polycrystalline foils of Cu, Ag, and Au from UHV to 1 mbar ...

Solid surface structure affects liquid order at the polystyrene–self-assembled-monolayer interface

We present a combined x-ray and neutron reflectivity study characterizing the interface between polystyrene (PS) and silanized surfaces. Motivated by the large difference in slip velocity of PS on top of dodecyl-trichlorosilane (DTS) and octadecyl-trichlorosilane (OTS) found in previous studies, these two systems were chosen for the present investigation. The results reveal the molecular conformation of PS on silanized silicon. Differences in the molecular tilt of OTS and DTS are replicated by the adjacent phenyl rings of the PS. We discuss our findings in terms of a potential link between the microscopic interfacial structure and dynamic properties of polymeric liquids at interfaces.

Reactive Solid Surface Morphology Variation via Ionic Diffusion

In gas-solid reactions, one of the most important factors that determine the overall reaction rate is the solid morphology, which can be characterized by a combination of smooth, convex and concave structures. Generally, the solid surface structure varies in the course of reactions, which is classically noted as being attributed to one or more of the following three mechanisms: mechanical interaction, molar volume change, and sintering. Here we show that if a gas-solid reaction involves the outward ionic diffusion of a solid-phase reactant then this outward ionic diffusion could eventually smooth the surface with an initial concave and/or convex structure. Specifically, the concave surface is filled via a larger outward diffusing surface pointing to the concave valley, whereas the height of the convex surface decreases via a lower outward diffusion flux in the vertical direction. A quantitative 2-D continuum diffusion model is established to analyze these two morphological variation processes, which shows consistent results with the experiments. This surface morphology variation by solid-phase ionic diffusion serves to provide a fourth mechanism that supplements the traditionally acknowledged solid morphology variation or, in general, porosity variation mechanisms in gas-solid reactions.

Enhanced CO2 Solubility in Hybrid MCM-41: Molecular Simulations and Experiments

Grand canonical Monte Carlo simulations are performed in a hybrid adsorbent model in order to interpret the CO(2) solubility behavior. The hybrid adsorbent is prepared by confining a physical solvent (OMCTS) into the pores of a mimetic MCM-41 solid support. As a result, simulated adsorption isotherms of CO(2) nicely match the experimental data for three distinctive systems: bulk solvent, raw MCM-41, and hybrid MCM-41. The microscopic mechanisms underlying the apparition of enhanced solubility are then clearly identified. In fact, the presence of solvent molecules favors the layering of CO(2) molecules within the pores; therefore, the CO(2) solubility in the hybrid adsorbent markedly increases in comparison to that found in the raw adsorbent as well as in the bulk solvent. In addition, a good understanding of confined solvents' properties and solid surface structures is essential to fully evaluate the efficiency of hybrid adsorbents in capturing CO(2). The sorbent-solid interactions along with the solvent molecular size's impact on CO(2) solubility are therefore investigated in this study. We found that an ideal hybrid system should possess a weak solvent-solid interaction but a strong solvent-CO(2) interaction. Besides, an optimal solvent size is obtained for the enhanced CO(2) solubility in the hybrid system. According to the simulation results, the solvent layer builds pseudomicropores inside the mesoporous MCM-41, enabling more CO(2) molecules to be absorbed under the greater influence of spatial confinement and surface interaction. In addition, the molecular sieving effect is clearly observed in the case of larger solvent molecular sizes.

ChemInform Abstract: Magnetoadsorption and Magnetodesorption of NO on Iron Oxides: Role of Magnetism and Surface Structures of Solids.

The magnetic field effects on NO adsorption on iron oxides were observed at 303 K. Ferrimagnetic magnetite and maghemite showed magnetic field induced adsorption (magnetoadsorption); i.e., NO adsorption was promoted with an increase in external magnetic field (1-7.6 kG). Hematite (parasitic ferromagnetism) also showed magnetoadsorptivity. Antiferromagnetic iron oxyhydroxides ({alpha}-, {beta}-, and {gamma}-FeOOH) showed magnetic field induced desorption (magnetodesorption). On the other hand, an antiferromagnetic NiO and a ferrimagnetic {delta}-FeOOH exhibited magnetoadsorptivity and magnetodesorptivity, respectively. The magnetoadsorptivity of magnetites depended on the preheating conditions and that of {delta}-FeOOH was independent of its magnetism susceptibility. The results suggest that surface sites and porosity, i.e., adsorption state of NO, rather than solid magnetism would play an important role in the magnetic interactions between solid surfaces and NO molecules under a magnetic field.

Role of solid surface structure on evaporative phase change from a completely wetting corner meniscus

The transport processes that occur at small length scales are greatly influenced by interfacial and intermolecular forces. Surface roughness at the nanoscale generates additional intermolecular interactions that arise due to the increased surface area. In this work, we have experimentally studied how the magnitude as well as the shape of surface roughness influences the microscale transport processes that occur in the contact line region of a liquid corner meniscus. The surface roughness contribution to the interaction potential was calculated and a direct relationship between the wetting properties of the liquid and the underlying surface properties was obtained. Since the underlying roughness alters the surface potential, the shape of the meniscus and in turn, the resulting capillary and disjoining pressure forces also changed. Atomic force microscopy was utilized to obtain a detailed characterization of the shape of the prepared surfaces. Surface morphology features were obtained from a height-height correlation function. These features were related to the wetting and transport properties of the meniscus at the contact line. Finally, the modified capillary and disjoining pressure forces on the structured surfaces were observed to influence the evaporative heat transfer from the corner meniscus.