Interfaces and surfaces are where the action happens. Catalysis, molecular recognition, charge transfer, polymerization and many other critical processes take place at the boundary between one medium and another. With the need to integrate new materials into devices, and applications ranging from catalysis to sensors, medicine to self-cleaning surfaces, and displays to lasers, fundamental and applied studies of surface and interface processes and optimization are of critical importance in developing new technology to meet today's challenges. The selection of recent research articles presented below illustrates the vast potential of this field.
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On the surface: The thermal decomposition of organometallic complexes with N-heterocyclic carbene ligands affords Pt nanoparticles that are soluble and stable in water for an indefinite period. The 13C–195Pt coupling observed by solid-state NMR spectroscopy confirms carbene coordination to the nanoparticle surface.
Explosive sensing: A structural mechanism that takes into account both the special conformation of oligophenyleneethynylene molecules at a thin-film surface and antenna effects enabled by exciton migration is presented (see figure). This mechanism explains why these crystallized fluorescent films exhibit excellent sensing properties toward nitroaromatic vapors despite the fact that they are nonporous.
Liquid, solid, or gel? High-performance electrolytes are important for the success of advanced energy-storage devices. From the view of battery structures and the electrolyte, this Review not only summarizes and discusses the up-to-date development of various electrolyte materials (liquids, solids, and gels), but also emphasizes a comprehensive understanding of electrolyte properties, which is critical for the design of high-performance electrolytes.
Si prefers alcohol: Low-temperature hydrosilylation led to a preferential surface grafting of the Si-O-C linkage instead of the classic Si-C linkage when reacted with an alcohol carrying a short bifunctional alkyne (see figure). Even in the presence of another alkyne competitor (trifluoroalkyne) at equimolar concentration, the Si-O-C bond remained the dominant linkage to the silicon surface through nucleophilic reaction.
Controllable Bioelectrocatalysis: The reversible activation of bioelectrocatalysis by external stimuli at stimuli-responsive supramolecular interfaces integrated with redox enzymes has been established, allowing potential applications in controllable biofuel cells, biosensors, bioelectronic devices, and for energy transduction and information storage. This Minireview outlines the current knowledge and important trends in this area.
Like oil and water: Superoleophobic surfaces with tunable adhesion were obtained by assembling mixed carboxylic acid on nanostructured aluminum substrates. The surface adhesion can be controlled by simply controlling the surface chemical composition (see figure).
Cu-trimer nodes: Using scanning tunneling microscopy and X-ray photoelectron spectroscopy, tetrahydroxybenzene (THB) is shown to dehydrogenate when adsorbed on a Cu(111) surface and form a highly reactive ligand. Density functional calculations confirm that the ligand stabilizes copper adatom trimers and creates a surface coordination network that is a two-dimensional analogue of metal–organic frameworks.
Sourcing luminescence: Imidazolium–silica-based nanoparticle networks (INNs) have been synthesized and characterized (see picture). A molecular model for the imidazolium–silica network is presented and described. The presence of water near the silica surface and its influence on the position of the counteranions in the INN has been shown.
The ferrocene-terminated Si (Si-Fc) as diodes: The diode nature of Si-Fc samples is attributed to the existence of a potential barrier between the Si substrate and the ferrocene layer. The diode nature of Si-Fc samples can be associated with some of its characteristics, such as the dependence of its cyclic voltammetry response on types of substrate and illumination.
Nanoparticle functionality: Iron oxide nanoparticles are functionalized by protected functional siloxanes. The functional group is deprotected on the nanoparticle itself, solving multiple issues related to the use of siloxanes. This procedure is highly reproducible and not limited to the discussed functionalities.
The long and short of it: A Au surface is modified by in situ reduction of aryldiazonium salts, and single-stranded DNA is covalently linked to the surface. A study of interactions of human Rad51 protein with DNA indicated that the presence of ADP promotes elongation of the Rad51 filament, whereas BRC4-28 peptide inhibits filament assembly.
Fluorescent nanomaterials: A one-step hydrothermal method to synthesize intercrossed carbon nanorings (see picture) with relatively pure hydroxy surface states is reported. The hydroxyl surface states make it possible to overcome aggregation-induced quenching effects and to emit scarce stable yellow-orange luminescence in both colloidal and solid states.
Staying on tip: RGD–Integrin binding in intact cell membranes is detected using controlled plasmonics between a cyclic-RGD peptide functionalized nanoparticle and a TERS tip. The observed TERS signal from the nanoparticles on cells matches the surface enhanced Raman signal for the purified αVβ3 Integrin receptor, demonstrating the selectivity. This enables the characterization of receptor binding in intact cell membranes.
Rapid and universal coatings were developed by mussel-inspired dendritic polyglycerol that mimics mussel foot proteins with regard to functional groups, molecular weight, and molecular structure. Multiple further modifications can be achieved by either pre- or post-functionalization and control of surface roughness.
Sub-monolayer photochemistry: A Tetraphenylporphyrin derivative carrying para-amino-phenyl functional groups is used to obtain extended and highly ordered molecular wires on Ag(110) through a photochemical approach. A low-to-high density approach is used in order to not sterically prevent the conformational adaptation of the molecules during the reaction (see figure).
Nanotube-based organic photovoltaics: An easily dispersible multiwalled carbon nanotube (MWCNT) derivative is prepared, and provides a platform for the synthesis of the phenyl butyric acid methyl ester derivative. Subsequently, pristine MWCNTs and the amide and ester derivatives are studied to provide an insight into influence of nanotube morphology on photovoltaic characteristics.
The subunit stoichiometry of archaeal RNase P, a multi-subunit ribonucleoprotein complex, was determined by surface-induced dissociation coupled with ion mobility mass spectrometry. Native MS studies with the proteins showed RPP21·RPP29 and (POP5·RPP30)2 complexes, but indicated a 1:1 composition for all subunits when either one or both protein complexes bind the cognate RNA.
Electrolytic spray deposition was employed for the formation of nanoparticle spots on various substrates in air. These materials are rugged, versatile substrates for surface-enhanced Raman spectroscopy, in which they lead to good enhancements. Lithographic applications of this method of ion deposition were also investigated.
Interfacing: Stabilizing the surface of lithium metal is an important challenge that must be overcome to enable lithium–air or lithium–sulfur batteries to succeed. Controlling the interface between the electrolyte and lithium is thus critical. By attaching vinyl-containing silanes to the hydroxy-terminated surface of lithium metal, a critical functional group is introduced at this interface that can be used to tailor this critical interaction (see figure; scale bars: 500 μm).
It makes sense: Anion transfer for highly hydrophilic phosphate and hydroxide anions into a water-immiscible organic phase is driven with a manganese(II/III) redox system and facilitated with a hydrophobic oil-based boronic acid. It is shown that phosphate transfer is facilitated by boronic acid. Improved boronic acid facilitators and nanotrench electrodes are discussed in terms of future feasibility for phosphate sensing applications.
Choosing a position: The controlled formation of hydrophobic fibers by careful choice of the position of the hydrophobic substituent has been achieved. The 3-position of 3,4-propylenedioxythiophene is the best to preserve the presence of nanofibers when a voluminous substituent is introduced, owing to longer polymer chains and higher hydrophobicity (see figure).
To nano or not to nano? Assessment of the mixing thermodynamics and the effect of the particle size on Fe-Ti spinel oxides leads to an intriguing conclusion about the heats of mixing on both macro and nanoscale. The energetics of the nanosized spinel oxides turn out to be predictable based only on knowledge of their macroscale energetics and surface energies, which are consistent regardless of composition. The findings have important implications for designing nanoscale spinel oxides with desirable properties.
Self-reduction: A general route for the direct growth of metal particles on TiO2 nanosheets with (001) exposed facets by an oxygen-vacancy-driven self-redox reaction is reported. Because there is no need for thermal treatment to remove stabilizing agents, the structure of the nanoparticles can also be retained, preserving the active sites associated with the high activity (see scheme).
Friction force fluctuation and tribocurrent generation at metal–insulator interfaces show a strong correlation during sliding contacts. The reported results suggest that these two phenomena have a common origin that must be associated with the occurrence of strong electrostatic interactions at the interface.
Pick and choose: A three-step strategy for synthesizing Ag-MS (M=Zn, Cd) nanoheterostructures by following a solution–liquid–solid (SLS; see figure) mechanism with Ag2S nanoparticles as catalysts, followed by conversion of Ag2S sections of the heterostructures into silver nanoparticles by selective extraction of sulfur, is reported.
Enzymes and electrodes in sync: Modification of carbonaceous electrodes with mediators with the appropriate redox potential, and a fast electron-transfer rate, creates an “electron sink” on the electrode surface. This effect pulls electrons from the cofactor, increasing the electron-transfer rate and generating higher current densities.
A core–shell nanostructure with three distinct components enables the efficient production of H2 from water and significant electron harvesting under visible-light irradiation because of enhanced hot-electron injection, the formation of a Schottky junction, and high-performance electron filtering. The electron transfer pathway is elucidated through steady-state and time-resolved photoluminescence spectroscopy.
Less is more: Pt–Pd–graphene stack structures (see picture) are prepared by a new method that allows control of the thickness of the Pt shell. This thickness correlates with performance in the hydrogen-evolution reaction (HER). As a result of surface polarization, the HER activity actually increases with decreasing Pt thickness, opening possibilities of using less Pt.
A strong effect: The controversy over vibrational properties of sulfate adsorption on Pt(111) surface originates from the different adsorption models in use. Ab initio molecular dynamics simulations employing different models yield a unified interpretation for various experimental and simulation results. The model (right side) that best approximates the experimental environments reproduces the experimentally observed Stark effect.
Atomic cartography: Atom-probe tomography reveals the atomic structure of Au@Ag nanoparticles. The atomic arrangement of the particle is reconstructed with a resolution of ±0.5 nm and shows that the surface coverage of Ag is influenced by the presence of residues from the synthesis. There is also a relationship between the particle’s surface curvature and the Ag surface coverage (surface excess, ΓAg).
Chain effects: A perfluoroalkyl (Rf) group with (CF2)9 or longer spontaneously aggregates in a hexagonal manner through the stratified dipole-arrays aggregation mechanism, which explains Rf-specific bulk properties (see picture).
Surface travel in less time: Simulating multiple excited-state trajectories of complex systems is challenging due to the computational costs. Interpolation, in combination with a conventional molecular mechanics approach, is presented as a method for overcoming this issue.
Making changes with visible light: Recent developments in the direct photocatalysis of plasmonic-metal nanoparticles are described, with a focus on the role of the localized surface plasmon resonance (LSPR) effect in plasmonic metals and their applications in organic transformations (see figure). The role of light irradiation in the catalyzed reactions and the light-excited energetic electron reaction mechanisms will be highlighted.
The deposition of functional polymers from the vapor phase enables new frontiers for device fabrication and technological development. Chemical vapor deposition (CVD) methods have a marked footprint in a wide range of applications from biotechnology to conducting polymers for solar cells. Finally, CVD process implementation to an industrial scale and commercialization are also discussed.
Power of the light: Plasmon-mediated synthetic methods are excellent techniques for controlling the growth and final shape of metal nanostructures. These reactions use visible light irradiation and excitation of plasmonic seeds to drive the chemical reduction of metal ions, usually Ag+, by citrate. The underlying physical and chemical factors that influence structural selection are outlined along with some important design considerations for controlling particle shape.
On the right track: Recent advances in noncontact atomic force microscopy (nc-AFM) have enabled the bond-resolved imaging of reaction pathways. In particular, unprecedented insights into complex enediyne cyclization cascades on silver surfaces were gained by single-molecule imaging.
Tip-enhanced Raman spectroscopy combines scanning probe techniques with Raman spectroscopy. Latest developments permit the chemical mapping of individual adsorbed molecules by monitoring molecular vibrations with sub-nanometer resolution. Increased efficiency and reduced photodegradation make this method suitable for studies of adsorbed organic and biomolecules in surface science, catalysis, biochemistry, and related fields.
Developments in instrumentation for “high-speed AFM” (HSAFM) have been ongoing since the 1990s, and now nanometer resolution imaging and lithography at video rate is readily achievable. This review provides a summary of different approaches to and advances in the development of high-speed AFMs, highlights important discoveries made with new instruments, and discusses new possibilities for HSAFM in materials science.
Various cellular and extracellular matrix's cues are decoupled via surface patterning to elucidate the role of each factor, such as the effect of cell shape on differentiation of stem cells. The pertinent patterning techniques are introduced. Chemical contrast, surface topography, matrix stiffness, and nanoscaled features of substrate surfaces to regulate cell fate are summarized. The cell geometry cues on cell adhesion and differentiation are highlighted.
The interfaces derived from two phases, including liquid-solid, gas-liquid, liquid-liquid, gas-solid and solid-solid interface, provides a plentiful and crucial space for adsorption, assembly, synthesis and catalysis. In this review, we summarize recent developments in preparing mesoporous materials based on the interfacial assembly and engineering.
Flick of the nanoswitch: STM studies on reversible supramolecular self-assemblies based on H-bonded supramolecular networks, azobenzenes, a triple-decker complex, and guanine and catechol motifs are discussed in this Focus Review. These functional structures can undergo reversible phase transformation when triggered by a suitable external stimulus at the solid–liquid interface, and thus they may be used for fabricating molecular switches and other nanomachines.
Simply sliding: The study of nanoscale tribology offers great potential in the fields of friction, wear, and lubrication. By considering a variety of hexagonal layered materials, including graphene, hexagonal boron nitride, and molybdenum disulfide, it is shown how a simple geometrical parameter, named the “registry index”, can capture the interlayer sliding energy landscape (see picture) as calculated by using advanced electronic structure methods as well as experimentally measured frictional behavior.
To expand the utilization of cellulose beyond its traditional uses, it is necessary to modify the surface of the fibers. This paper summarizes the modification of cellulose by controlled polymerization methods such as ATRP, RAFT, ROP, and ROMP. The combination of the excellent properties of cellulose with functional polymers creates new materials of great potential in advanced material applications.
See beneath the surface! Surface analysis of biologically relevant composites leads to an improved understanding of the chemistry of nanocomposite constituents and the interactions between them (see picture).
Real-time surface microscopy and in situ spectroscopy can provide unique insight into graphene and other 2D materials on metal substrates. The power of in situ microscopy in realizing and probing important functionalities in 2D materials is illustrated by reviewing recent progress in understanding scalable graphene growth on metals, processing by selective chemistry at the graphene/metal interface, and important properties such as band structure, work function, etc.
Due to the recent development of bottom-up and top-down approaches for material design and fabrication at the nanoscale, giant chiroptical effects have been reported from plasmonic nanostructures. These effects are exhibited both in the linear and in the nonlinear optical regimes and are sensitive to the chirality of nanostructures, the chirality of the experiments and the chirality of light itself.
Graphene is a unique platform for surface-enhanced Raman spectroscopy (SERS). The multi-role of graphene played in SERS is overviewed, including as a Raman probe, as a substrate, as an additive, and as a building block of a flat surface for SERS. Apart from versatile improvements on SERS performance towards applications, graphene-involved SERS studies are also expected to shed light on the fundamental mechanism of the SERS effect.
The sweet spot of nanomedicine: Carbohydrates are key to cellular signalling pathways and major contributors to molecular recognition events at the cell surface. Novel nanomaterials that probe multivalent binding events between carbohydrates and their biological binding partners are driving discovery at this interface (see figure).
Creating patterns of extreme wettability on surfaces leads to new functionalities and possibilities in a wide variety of applications. We highlight novel applications of superhydrophilic-superhydrophobic patterned surfaces that are currently being explored, from miniaturized cell and chemical screening platforms to surface tension confined microchannels for separation and diagnostic devices, and give an outlook on the progress in this field.
New insights in capillary interactions between nanofilaments have led to versatile and scalable methods to build complex structures that cannot be achieved by any other processing technique. Understanding the control of this process is conducive to the development of high-performance battery and capacitor electrodes as well as photovoltaics, electrical interconnects, and other smart materials.
Catechols participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of certain metals ions. Accordingly, many scientists worldwide have been studying and mimicking these natural systems to develop new active materials and coatings. A detailed revision of a wide variety of relevant studies in this field is discussed in this Review.
In this review, a brief introduction to surface modification using poly(N-vinylpyrrolidone) and its copolymers and their potential biomedical applications is presented. Some perspectives on future research in the areas are also discussed.
In a molecularly decorated surface, the molecular tiles are “glued” to the surface by binding constants and possibly further “glued” to each other by cooperativity factors. At odds with mosaics, these “glues” come with the tiles and cannot be removed or supplemented. Binding polynomials quantify glue amounts from experimental data and may predict molecular self-organization on surfaces that can be exploited in organic (opto-)electronics.
Dynamic surfaces: Construction and applications of dynamic surfaces on which surface properties can be modulated by an external stimulus on user demand are reviewed, with focus on self-assembled monolayers with dynamicity that stems from (bio)chemical conversions on the surface in response to stimuli such as electrical potential, light, enzymes, and pH (see picture).
Monolayer zeolite? The application of a variety of “surface-science” techniques to elucidate the surface structures and mechanisms of chemical reactions at zeolite surfaces has long been considered as almost impossible. The growth of a thin aluminosilicate film on a metal single crystal under controlled conditions results in adequate and well-defined model systems for zeolite surfaces.
In a different light: In a provocative look at nanoscience, Nobel Laureate Roald Hoffmann considers the structural and electronic perplexities of dimensionality, the consequences of bond severance in nano-object formation, the implications of simple acid-base chemistry for stabilization of nanostructures, and what lessons might be learned from surface science on structural relaxation and reconstruction.
Bubble, bubble: Why does champagne bubble? Why does it stop bubbling? Does the vintage affect its fizz? Chemistry can answer these and other questions about the wine that is so often associated with celebrations and anniversaries.
Scratching the surface: For over 100 years the interactions of molecules at surfaces have been studied at the Fritz Haber Institute of the Max Planck Society, Berlin. Nobel Laureate Gerhard Ertl looks back at some of the key developments in this time, and the people who made them.