Progress in Surface Science最新文献

In this review we examine the influence of the line tension τ on droplets and particles at surfaces. The line tension influences the nucleation behavior and contact angle of liquid droplets at both liquid and solid surfaces and alters the attachment energetics of solid particles to liquid surfaces. Many factors, occurring over a wide range of length scales, contribute to the line tension. On atomic scales, atomic rearrangements and reorientations of submolecular components give rise to an atomic line tension contribution τ_atom (∼1 nN), which depends on the similarity/dissimilarity of the droplet/particle surface composition compared with the surface upon which it resides. At nanometer length scales, an integration over the van der Waals interfacial potential gives rise to a mesoscale contribution |τ_vdW| ∼ 1–100 pN while, at millimeter length scales, the gravitational potential provides a gravitational contribution τ_grav ∼ +1–10 μN. τ_grav is always positive, whereas, τ_vdW can have either sign. Near wetting, for very small contact angle droplets, a negative line tension may give rise to a contact line instability. We examine these and other issues in this review.

Sum-frequency generation vibrational spectroscopy (SFG-VS) was first developed in the 1980s and it has been proven a uniquely sensitive and surface/interface selective spectroscopic probe for characterization of the structure, conformation and dynamics of molecular surfaces and interfaces. In recent years, there have been many progresses in the development of methodology and instrumentation in the SFG-VS toolbox that have significantly broadened the application to complex molecular surfaces and interfaces. In this review, after presenting a unified view on the theory and methodology focusing on the SFG-VS spectral lineshape, as well as the new opportunities in SFG-VS applications with such developments, some of the controversial issues that have been puzzling the community are discussed. The aim of this review is to present to the researchers and students interested in molecular surfaces and interfacial sciences up-to-date perspectives complementary to the existing textbooks and reviews on SFG-VS.

Charge separation and transfer at the interface between two materials play a significant role in various atomic-scale processes and energy conversion systems. In this review, we present the mechanism and outcome of charge transfer in TiO₂, which is extensively explored for photocatalytic applications in the field of environmental science. We list several experimental and computational methods to estimate the amount of charge transfer. The effects of the work function, defects and doping, and employment of external electric field on modulating the charge transfer are presented. The interplay between the band bending and carrier transport across the surface and interface consisting of TiO₂ is discussed. We show that the charge transfer can also strongly affect the behavior of deposited nanoparticles on TiO₂ through built-in electric field that it creates. This review encompasses several advances of composite materials where TiO₂ is combined with two-dimensional materials like graphene, MoS₂, phosphorene, etc. The charge transport in the TiO₂-organohalide perovskite with respect to the electron-hole separation at the interface is also discussed.

Designing antibacterial surfaces has become extremely important to minimize Healthcare Associated Infections which are a major cause of mortality worldwide. A previous biocide-releasing approach is based on leaching of encapsulated biocides such as silver and triclosan which exerts negative impacts on the environment and potentially contributes to the development of bacterial resistance. This drawback of leachable compounds led to the shift of interest towards a more sustainable and environmentally friendly approach: contact-killing surfaces. Biocides that can be bound onto surfaces to give the substrates contact-active antibacterial activity include quaternary ammonium compounds (QACs), quaternary phosphoniums (QPs), carbon nanotubes, antibacterial peptides, and N-chloramines. Among the above, QACs and N-chloramines are the most researched contact-active biocides. We review the engineering of contact-active surfaces using QACs or N-chloramines, the modes of actions as well as the test methods. The charge-density threshold of cationic surfaces for desired antibacterial efficacy and attempts to combine various biocides for the generation of new contact-active surfaces are discussed in detail. Surface positive charge density is identified as a key parameter to define antibacterial efficacy. We expect that this research field will continue to attract more research interest in view of the potential impact of self-disinfective surfaces on healthcare-associated infections, food safety and corrosion/fouling resistance required on industrial surfaces such as oil pipes and ship hulls.

Metal–organic coordination structures are materials comprising reticular metal centers and organic linkers in which the two constituents bind with each other via metal–ligand coordination interaction. The underlying chemistry is more than a century old but has attracted tremendous attention in the last two decades owing to the rapidly development of metal–organic (or porous coordination) frameworks. These metal-coordination materials exhibit extraordinarily versatile topologies and many potential applications. Since 2002, this traditionally three-dimensional chemistry has been extended to two-dimensional space, that is, to synthesize metal–organic coordination structures directly on solid surfaces. This endeavor has made possible a wide range of so-called surface-confined metal–organic networks (SMONs) whose topology, composition, property and function can be tailored by applying the principle of rational design. The coordination chemistry manifests unique characteristics at the surfaces, and in turn the surfaces provide additional control for design structures and properties that are inaccessible in three-dimensional space.

In this review, our goal is to comprehensively cover the progress made in the last 15 years in this rapidly developing field. The review summarizes (1) the experimental and theoretical techniques used in this field including scanning tunneling microscopy and spectroscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, density functional theory, and Monte Carlo and kinetic Monte Carlo simulation; (2) molecular ligands, metal atoms, substrates, and coordination motifs utilized for synthesizing SMON; (3) representative SMON structures with different topologies ranging from finite-size discrete clusters to one-dimensional chains, two-dimensional periodical frameworks and random networks; and (4) the properties and potential applications of SMONs. We conclude the review with some perspectives.

Adsorption geometry and stability of organic molecules on surfaces are key parameters that determine the observable properties and functions of hybrid inorganic/organic systems (HIOSs). Despite many recent advances in precise experimental characterization and improvements in first-principles electronic structure methods, reliable databases of structures and energetics for large adsorbed molecules are largely amiss. In this review, we present such a database for a range of molecules adsorbed on metal single-crystal surfaces. The systems we analyze include noble-gas atoms, conjugated aromatic molecules, carbon nanostructures, and heteroaromatic compounds adsorbed on five different metal surfaces. The overall objective is to establish a diverse benchmark dataset that enables an assessment of current and future electronic structure methods, and motivates further experimental studies that provide ever more reliable data. Specifically, the benchmark structures and energetics from experiment are here compared with the recently developed van der Waals (vdW) inclusive density-functional theory (DFT) method, DFT + vdW^surf. In comparison to 23 adsorption heights and 17 adsorption energies from experiment we find a mean average deviation of 0.06 Å and 0.16 eV, respectively. This confirms the DFT + vdW^surf method as an accurate and efficient approach to treat HIOSs. A detailed discussion identifies remaining challenges to be addressed in future development of electronic structure methods, for which the here presented benchmark database may serve as an important reference.

Superhydrophobic films were prepared using dispersions of fluorinated multi-walled carbon nanotubes (MWCNTs) or nanofibers (CNFs) in toluene. The grafting of polystyrene allowed stable dispersions to be obtained. The grafting of polystyrene (PS), polyacrylic acid (PAA) and polyaniline (PANI) onto nanofibers and MWCNTs was first evidenced by solid state NMR and Infrared Spectroscopy. The graft polymerization of styrene, acrylic acid and aniline monomers was initiated by radicals (dangling bonds) formed due to the initial fluorination. The process appeared as highly versatile and efficient for different polymers. The consumption of those radicals in the course of grafting was evidenced by EPR, through decrease of the spin density. The hydrophobic/hydrophilic character was tuned according to the grafted polymer nature, i.e. hydrophobic with PS or hydrophilic with PAA. Finally, in order to reach superhydrophobicity, films were prepared from CNFs or MWCNTs, irrespective of their average diameter, that allowed adequate structuring of the surface. The presence of fluorine atoms on their surface also favors superhydrophobicity. Water contact angles of 155 ± 2° and 159 ± 2° were measured for the films casted from fluorinated CNFs or MWCNTs with grafted polystyrene, respectively.

Semiconducting nanowires (NWs) are firm candidates for novel nanoelectronic devices and a fruitful playground for fundamental physics.

Ultra-thin nanowires, with diameters below 10 nm, present exotic quantum effects due to the confinement of the wave functions, e.g. widening of the electronic band-gap, deepening of the dopant states. However, although several reports of sub-10 nm wires exist to date, the most common NWs have diameters that range from 20 to 200 nm, where these quantum effects are absent or play a very minor role. Yet, the research activity on this field is very intense and these materials still promise to provide an important paradigm shift for the design of emerging electronic devices and different kinds of applications. A legitimate question is then: what makes a nanowire different from bulk systems? The answer is certainly the large surface-to-volume ratio.

In this article we discuss the most salient features of surface physics and chemistry in group-IV semiconducting nanowires, focusing mostly on Si NWs. First we review the state-of-the-art of NW growth to achieve a smooth and controlled surface morphology. Next we discuss the importance of a proper surface passivation and its role on the NW electronic properties. Finally, stressing the importance of a large surface-to-volume ratio and emphasizing the fact that in a NW the surface is where most of the action takes place, we discuss molecular sensing and molecular doping.

Molecular oxygen (O₂) is a paramagnetic linear molecule, yet the effect of its molecular alignment and electron spin on the dynamics of O₂ adsorption has remained unclear. Recently, it has been however shown that the use of magnetic hexapolar field allows us to prepare a single spin-rotational state [($J\text{,}M$) = (2, 2)] selected O₂ beam for which both the molecular alignment and the spin state of O₂ are well defined. State-resolved studies of O₂ sticking on Si(1 0 0), Al(1 1 1), Ni(1 1 1) surfaces conducted with this beam have clarified that the O₂ sticking probability depends strongly on the molecular alignment and the spin orientation of O₂ relative to the surface. The mechanism of O₂ adsorption on Al(1 1 1) has been disputed in the past few decades, but the observed steric effect has provided a reasonable picture for it. The preparation method of the state-selected O₂ beam and its application to the alignment- and spin-resolved O₂ sticking studies are reviewed.

Graphene, a single atomic layer of graphite, has been the focus of recent intensive studies due to its novel electronic and structural properties. Metals grown on graphene also have been of interest because of their potential use as metal contacts in graphene devices, for spintronics applications, and for catalysis. All of these applications require good understanding and control of the metal growth morphology, which in part reflects the strength of the metal–graphene bond. Also of importance is whether the interaction between graphene and metal is sufficiently strong to modify the electronic structure of graphene. In this review, we will discuss recent experimental and computational studies related to deposition of metals on graphene supported on various substrates (SiC, SiO₂, and hexagonal close-packed metal surfaces). Of specific interest are the metal–graphene interactions (adsorption energies and diffusion barriers of metal adatoms), and the crystal structures and thermal stability of the metal nanoclusters.