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Titanium and its alloys are protected by a compact and stable passive film, which confers resistance to corrosion by the primary halogen chloride (Cl - ) while being less effective against fluoride (F - ). Although researchers have recognized different macroscopic corrosion effects of these halide ions on titanium, the underlying mechanisms remain largely unexplored. In this work, the bonding of Cl - /F - with stable passive films was studied in neutral and acidic (pH = 2.3) conditions. The synergistic effect between the interfacial hydrogen bond (HB) structure and halogens on titanium corrosion was first revealed using first-principles calculation and Raman spectroscopy. F - forms more stable halogen-Ti bonds than Cl - , resulting in titanium degradation. The proton combined with F - exhibits a specific synergistic effect, causing corrosion of the passive film. The water hydrogen bond transformation index (HBTI) at the titanium/aqueous interface was 1.88 in an acidic solution containing F - , significantly higher than that in neutral/acid solutions containing Cl - (1.80/1.81) and a neutral solution containing F - (1.81). This work clarifies the structure-activity relationship between HBTI and the destruction of titanium passive films. We propose that the microstructure of the interfacial HB is an undeniable factor in the corrosion of titanium.

Ion adsorption and hydrogen bond (HB) network reconstruction in electric double layer (EDL) have a profound impact on the interface properties. The microstructure in the bulk phase of 1.00-21.30 wt.% Na 2 SO 3 aqueous solutions are investigated by X-ray scattering, confocal Raman spectroscopy, and classical molecular dynamics. The electronic properties of SO 3 2- adsorption and the geometric structure of the HB network in the EDL at the titanium TiO 2 (101) surface are studied by density functional theory (DFT) and classical molecular dynamics. The SO 3 2- strongly weakens the fully hydrogen-bonded water (FHW) and transforms it into partial hydrogen-bonded water (PHW). The HB transformation index (HBTI = PHW/FHW) shows a linear relationship with the mass fraction of Na 2 SO 3 . The TiO b -parallel adsorption configuration of SO 3 2- enhances the ionicity of the O b -Ti 6 bond, resulting in the formation of oxygen vacancies at the titanium passive film surface. Besides, SO 3 2- and Na + are enriched and thermodynamic supersaturated in the inner Helmholtz layer (IHL), and the ions are diluted in the outer Helmholtz layer (OHL). The diffusion coefficient of SO 3 2- and water molecules in EDL decreases seriously, which is easy to causes salt scaling on the surface of titanium passive film. This work provides evidence for the destruction of titanium passive film by SO 3 2- .

GeSe is an emerging promising light-harvesting material for photovoltaics due to its excellent optoelectronic properties, nontoxic and earth-abundant constituents, and high stability. In particular, perovskite-like antibonding states at the valence band maximum arising from Ge-4s and Se-4p coupling enable the bulk-defect-tolerant properties in GeSe. However, a fundamental understanding of surface-defect states in GeSe, another important factor for high-performance photovoltaics, is still lacking. Here, we investigate the surface-defect properties of GeSe through first-principle calculations. We find that different from common semiconductors possessing numerous surface dangling bonds, some GeSe surfaces are prone to reconstruction, thus eliminating the dangling bonds. The rearranged armchair edges exhibit unexpected benign defect properties, similar to those of bulk GeSe, arising from the formation of bulk-like [GeSe 3 ] tetrahedrons. We further show that the stable exposed (111) surfaces are hard to reconstruct due to the stiff structure but are effectively passivated by the addition of H.

Controlling droplet deposition with a minute amount of polymer additives is of profound practical importance in a wild range of applications. Previous work ascribed the relevant mechanisms to extensional viscosity, normal stress, wetting properties, etc., but the mechanism remains controversial. In this paper, we employ molecular dynamics simulations systematically for the first time to investigate the origin of rebound suppression for dilute polymer solution droplets on a flat superhydrophobic substrate. The results demonstrate that polymer-substrate interactions and impact velocities dominate the antirebound phenomenon. For low impact velocities, the dynamic characteristics of droplets are insensitive to polymer additives. However, large impact velocities will enhance the stretch behavior of polymer chains and make the chains closer to the substrate, increasing the probability of polymer molecules contacting the bottom substrate. With the cooperation of strong polymer-substrate interactions, polymer molecules can be absorbed easily by the bottom substrate, resisting the retraction process and leading to the onset of the antirebound behavior.

Organic-inorganic halide perovskite materials are emerging as a new class of photoelectric materials for its low cost, easy preparation, and, especially, outstanding optoelectronic properties. Although tremendous efforts have been made on the regulation and optimization of perovskite materials and their microscopic electrical properties for high-efficiency solar cells, few reports focus on the evolution of electrical properties with temperature changes, especially at the microscopic scale, which will directly affect the device performances at varying temperatures. Here, we map the contact potential difference and photocurrent distribution of MAPbI 3 at different temperatures in situ by Kelvin probe force microscopy and conductive atomic force microscopy, emphasizing the different influences of variable temperature and phase transition on the photoelectric properties of grains and grain boundaries (GBs). It is discovered that both the Fermi level and photocurrent decrease as the sample is heated from 30 to 80 °C gradually because of the variation of effective carrier concentration and the degradation of carrier mobility implicated by lattice vibration scattering. The difference between the Fermi level at GBs and that on the grains ascends first and then descends, peaking at 50 °C, near which MAPbI 3 transforms from a tetragonal phase to a cubic phase. This peak is speculated as a comprehensive consequence of the increasing difference of the Fermi level of semiconductors with different doping concentrations and the converging properties of grains and GBs with the temperature rising because the lower ion activation energy of the cubic phase at higher temperatures facilitates greatly the ions' movement between grains and GB. The variation trend of the difference of the photocurrent is the same. These findings advance the knowledge on the temperature-induced variations of microscopic photoelectrical properties of organic-inorganic hybrid perovskite materials, which may guide the development of strategies for improving their thermal stability.

Multifunctional supramolecular nanomaterials capable of targeted and multimodal therapy hold great potential to improve the efficiency of cancer therapeutics. Herein, we report a proof-of-concept nanoplatform for effective chemophotothermal therapy via the integration of folic acid-based active targeting and supramolecular nanovalves-based passive targeting. Inspired by facile surface engineering and designable layer-by-layer assembly concept, we design and synthesize PPy@UiO-66@WP6@PEI-Fa nanoparticles (PUWPFa NPs) to achieve efficient synergistic chemophotothermal therapy, taking advantage of the desirable photothermal conversion capability of polypyrrole nanoparticles (PPy NPs) and high drug-loading capacity of hybrid scaffolds. Significantly, pillararene-based pseudorotaxanes as pH/temperature dual-responsive nanovalves allow targeted drug delivery in pathological environment with sustained release over 4 days, which is complementary to photothermal therapy, and folic acid-conjugated polyethyleneimine (PEI-Fa) at the outmost layer through electrostatic interactions is able to enhance tumor-targeting and therapeutic efficiency. Such PUWPFa NPs showed efficient synergistic chemophotothermal therapy of cervical cancer both in vitro and in vivo. The present strategy offers not only the distinctly targeted drug delivery and release, but also excellent tumor inhibition efficacy of simultaneous chemophotothermal therapy, opening a new avenue for effective cancer treatment.

An understanding of the formation mechanism of solid electrolyte interphase (SEI) film at the nanoscale is paramount because it is one of the key issues at interfaces in lithium-ion batteries (LIBs). Herein, we explored the nucleation, growth, and formation of SEI film on highly oriented pyrolytic graphite (HOPG) substrate in ionic liquid-based electrolytes 1-butyl-1-methyl-pyrrolidinium bis(fluorosulfonyl)imide ([BMP] + [FSI] - ) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP] + [TFSI] - ) by in situ atomic force microscopy (AFM) and found that the types of anions have significant influence on the structure of the formed SEI. In [BMP] + [FSI] - containing LiFSI, a compact and thin SEI film prefers to grow in the plane of HOPG substrate, while a rough and loose film tends to form in [BMP] + [TFSI] - containing LiTFSI. On the basis of in situ AFM observations, the relationship between the SEI structure and the electrochemical performance was clarified.

Organic-inorganic hybrid perovskite single-crystalline thin films (SCTFs) are promising for enhancing photoelectric device performance due to high carrier mobility, long diffusion length, and carrier lifetime. However, bulk perovskite single crystals available today are not suitable for practical device application due to the unfavorable thickness. Herein, we report a facile space-confined solution-processed strategy to on-substrate grow various hybrid perovskite SCTFs in a size of submillimeter with adjustable thicknesses from nano- to micrometers. These SCTFs exhibit photoelectric properties comparable to bulk single crystals with low defect density and good air stability. The clear thickness-dependent colors allow fast visual selection of SCTFs with a suitable thickness for specific device application. The present substrate-independent growth of perovskite SCTFs opens up opportunities for on-chip fabrication of diverse high-performance devices.

In this paper, the pinning and depinning mechanism of the contact line during droplet evaporation on chemically stripe-patterned surfaces is numerically investigated using a thermal multiphase lattice Boltzmann (LB) model with liquid-vapor phase change. A local force balance in the context of diffuse interfaces is introduced to explain the equilibrium states of droplets on chemically patterned surfaces. It is shown that when the contact line is pinned on a hydrophobic-hydrophilic boundary, different contact angles can be interpreted as the variation of the length of the contact line occupied by each component. The stick-slip-jump behavior of evaporating droplets on chemically patterned surfaces is well captured by the LB simulations. Particularly, a slow movement of the contact line is clearly observed during the stick (pinning) mode, which shows that the pinning of the contact line during droplet evaporation on chemically stripe-patterned surfaces is actually a dynamic pinning process and the dynamic equilibrium is achieved by the self-adjustment of the contact lines occupied by each component. Moreover, it is shown that when the surface tension varies with the temperature, the Marangoni effect has an important influence on the depinning of the contact line, which occurs when the horizontal component (toward the center of the droplet) of the force caused by the Marangoni stress overcomes the unbalanced Young's force toward the outside.

Halogen bonding has attracted much attention recently as an important driving force for supramolecular assembly and crystal engineering. Herein, we demonstrate for the first time the formation of a halogen bond-based open porous network on a graphite surface using ethynylpyridine and aryl-halide based building blocks. We found that the electrical stimuli of a scanning tunneling microscopy (STM) tip can induce the formation of a binary supramolecular structure on the basis of halogen bond formation between terminal pyridyl groups and perfluoro-iodobenzene. This electrical manipulation method can be applied to engineer a series of linear or porous structures by selecting halogen bond donor and acceptor fragments with different symmetries, as the directional interactions ultimately determine the structural outcome.

Silicon nanowires (SiNWs) have attracted great attention as promising anode materials for lithium ion batteries (LIBs) on account of their high capacity and improved cyclability compared with bulk silicon. The interface behavior, especially the solid electrolyte interphase (SEI), plays a significant role in the performance and stability of the electrodes. We report herein an in situ single nanowire atomic force microscopy (AFM) method to investigate the interface electrochemistry of silicon nanowire (SiNW) electrode. The morphology and Young's modulus of the individual SiNW anode surface during the SEI growth were quantitatively tracked. Three distinct stages of the SEI formation on the SiNW anode were observed. On the basis of the potential-dependent morphology and Young's modulus evolution of SEI, a mixture-packing structural model was proposed for the SEI film on SiNW anode.

Hybrid bilayers consisting of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and meso-tetra(4-pyridyl)porphine (TPyP) have been successfully constructed on Au(111) and investigated by electrochemical scanning tunneling microscopy (ECSTM). Under the guidance of the electrostatic interaction between negatively charged sulfonate groups and positively charged pyridyl groups, the underlying HPTS arrays act as templates for the deposition of cationic TPyPs, forming two types of TPyP/HPTS complex bilayers. The present work provides a feasible way to fabricate hybrid multilayers on the electrode surface via electrostatic interaction, which has great significance for the design of molecular nanodevices.

The ordered array of nanovoids in nanoporous networks, such as honeycomb, Kagome, and square, provides a molecular template for the accommodation of "guest molecules". Compared with the commonly studied guest molecules featuring high symmetry evenly incorporated into the template, guest molecules featuring lower symmetry are rare to report. Herein, we report the formation of a distinct patterned superlattice of guest molecules by selective trapping of guest molecules into the honeycomb network of trimesic acid (TMA). Two distinct surface patterns have been achieved by the guest inclusion induced adaptive reconstruction of a 2D molecular nanoporous network. The honeycomb networks can synergetically tune the arrangement upon inclusion of the guest molecules with different core size but similar peripherals groups, resulting in a trihexagonal Kagome or triangular patterns.

The electron donor-acceptor dyads are an emerging class of materials showing important applications in nonlinear optics, dye-sensitized solar cells, and molecular electronics. Investigation of their structure and electron transfer at the molecular level provides insights into the structure-property relationship and can benefit the design and preparation of electron donor-acceptor dyad materials. Herein, the interface adstructure and electron transfer of buckyferrocene Fe(C60Me5)Cp, a typical electron donor-acceptor dyad, is directly probed using in situ electrochemical scanning tunneling microscopy (STM) combined with theoretical simulations. It is found that the adsorption geometry and assembled structure of Fe(C60Me5)Cp is significantly affected by the electrochemical environments. In 0.1 M HClO4 solution, Fe(C60Me5)Cp forms well-ordered monolayers and multilayers on Au(111) surfaces with molecular dimer as the building block. In 0.1 M NaClO4 solution, typical six-fold symmetric close-packed monolayer with vertically adsorbed Fe(C60Me5)Cp is formed. Upon electrochemical oxidation, the oxidized Fe(C60Me5)Cp shows higher brightness in an STM image, which facilitates the direct visualization of the interfacial electrochemical electron transfer process. Theoretical simulation indicates that the electrode potential-activated, one-electron transfer from Fe(C60Me5)Cp to the electrode leads to the change of the delocalization character of the frontier orbital in the molecule, which is responsible for the STM image contrast change. This result is beneficial for understanding the structure and property of single electron donor-acceptor dyads. It also provides a direct approach to study the electron transfer of electron donor-acceptor compounds at the molecular level.

Surface covalent organic frameworks (SCOFs), featured by atomic thick sheet with covalently bonded organic building units, are promised to possess unique properties associated with reduced dimensionality, well-defined in-plane structure, and tunable functionality. Although a great deal of effort has been made to obtain SCOFs with different linkages and building blocks via both "top-down" exfoliation and "bottom-up" surface synthesis approaches, the obtained SCOFs generally suffer a low crystallinity, which impedes the understanding of intrinsic properties of the materials. Herein, we demonstrate a self-limiting solid-vapor interface reaction strategy to fabricate highly ordered SCOFs. The coupling reaction is tailored to take place at the solid-vapor interface by introducing one precursor via vaporization to the surface preloaded with the other precursor. Following this strategy, highly ordered honeycomb SCOFs with imine linkage are obtained. The controlled formation of SCOFs in our study shows the possibility of a rational design and synthesis of SCOFs with desired functionality.

Surface modifications of a Au(111) electrode with 4-bromobenzenediazonium tetrafluoroborate (BBD) in acetonitrile (ACN) and 0.1 M HClO4 have been characterized by scanning tunneling microscopy (STM). In ACN, STM results reveal the formation of disordered thin organic films. The involvement of the radical as an intermediate is evidenced by the negative effect of radical scavengers on organic thin film formation. In contrast, the 4,4'-dibromobiphenyl monolayer is observed when the aqueous solution is used as a medium to carry out the grafting experiment. The biphenyl compound is considered to be generated by a radical-radical coupling reaction.

The adsorption behaviors of subphthalocyanine (SubPc) and subnaphthalocyanine (SubNc) on the Au(111) surface were investigated by electrochemical scanning tunneling microscopy (ECSTM). Two types of ordered adlayer structures of SubPc were observed at 550 mV versus the reversible hydrogen electrode (RHE). All of the SubPc molecules take the Cl-down adsorption configuration on Au(111) in both structures. The ordered adlayers exist in the potential range between 350 and 650 mV. The SubNc molecules adsorb on Au(111) in a less-ordered pattern than the SubPc molecules. The present work provides direct evidence for understanding the potential-controlled adsorption behaviors of SubPc and SubNc on the Au(111) surface.

Hydrogen bonds with high selectivity and directionality are significant in harnessing molecules to form 2D supramolecular nanostructures. The competition and reorganization of hydrogen bond partners determine the ultimate molecular assembly and pattern in a 2D supramolecular system. In this study, multicomponent assemblies of a monodendron (5-benzyloxy-isophthalic acid derivative, BIC) and pyridylethynyl derivatives [1,4-bis(4-pyridylethynyl)-2,3-bis-dodecyloxy-benzene (PBPC12) and 1,4-bis(4-pyridylethynyl)-2,3-bis-octadecyloxy-benzene (PBPC18)] have been studied by scanning tunneling microscopy (STM) on a graphite surface. BIC molecules are able to associate with PBPC12 and PBPC18 molecules to induce the rearrangement of hydrogen bond partners and form coassembly structures. Interestingly, BIC acts as a template molecule in the coassembly process, and these multicomponent structures exhibit similar structural features to the assembly structures of BIC itself. The structural details of the coassembled structures are revealed by high-resolution STM images, and their relationship with the original BIC assemblies is discussed. These results provide important insights into the design and fabrication of hydrogen-bond-directed multicomponent molecular nanostructures on solid surfaces.

The formation of a desired nanostructure with concomitant patterns and functions is of utmost importance in the field of surface molecular engineering and nanotechnology. We here present a flexible host-guest assembly, which steers the formation of linear molecular nanostructures on surfaces by a hydrogen-bond-mediated assembly process. A linear monodendron molecular template with periodic hydrogen-bond binding sites is shown to accommodate a variety of molecules with pyridylethynyl terminals. The unit cell parameters in the transverse direction of the linear pattern can be tuned from 3.4 to 7.3 nm in response to the packing of the guest molecules with different sizes, shapes, and aggregation number. The introduction of hydrogen-bonding partners into the host template and into guest molecules is responsible for the steering of the linear pattern of guest molecules. The modular approach could greatly facilitate the ordering of guest molecules with desired functional moieties.

The two-dimensional (2D) self-assembled networks of 2,7,12-trihexyloxytruxene (Tr) are shown to accommodate coronene guest molecules on highly oriented pyrolytic graphite (HOPG) surfaces. The host-guest structures are revealed by scanning tunneling microscopy (STM) at liquid/solid interfaces. The effect of solvents on the host-guest structures is intensively investigated in different solvents such as 1,2,4-trichlorobenzene (TCB), 1-phenyloctane, 1-octanol, and tetradecane. In contrast to the similar 2D hexagonal self-assembly of Tr host template on HOPG in different solvents, the formation of host-guest nanostructures of coronene in Tr 2D network strongly depend on the polarity of the solvents. The thermodynamic equilibrium during the host-guest assembly process is discussed, and the solvent-guest interaction is proposed as a main contributor for the observed solvent effect in the 2D host-guest self-assembly process. The results are significant to surface host-guest chemistry and nanopatterning.

Spontaneous symmetry-breaking of a racemic mixture of supramolecular triginal prisms into chiral domains on a Au(111) surface is observed by scanning tunneling microscopy (STM). High-resolution STM analysis enables the structural aspects of each enantiomeric domain to be elucidated. The ability to resolve chirality on achiral surfaces has potential applications in heterogeneous stereoselective synthesis and catalysis.

NMR and STM studies revealed that the hydrazide-quinolinone-based building block 5 exhibited a monomer-dimer-polymer equilibrium, while its acyclic analogue 6, due to conformational flexibility, exhibited a more complicated mode of aggregation and formed a gel in dichloromethane/hexane.

The adlayers formed by a series of aza- and/or oxo-bridged calix[2]arene[2]triazines on Au(111) surfaces were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. 1,3-Alternate configurations of these molecules are preserved on gold surfaces as in their three-dimensional crystals. STM images show that the cavity sizes of these molecules are finely tuned by substituting the bridging nitrogen atom with oxygen atoms, which change the strengths and densities of the intermolecular hydrogen bonds. Hydrogen bond interaction influences the molecular orientation and conformation in the adlayers, and it plays a key role in the formation of these two-dimensional supramolecular architectures. Coadsorption of calix[2]arene[2]triazine with 1,3,5-tris(5-carboxyamyloxy)benzene (TCAB) intervenes with the intermolecular hydrogen bond formations among the calix[2]arene[2]triazine molecules and consequently causes a conformational transition of the calixarene molecules from rhombic to square. These results demonstrate the role of hydrogen bonds in molecular assembly formations.

This communication provides a facile method for distributing and dispersing molecules within a molecular template. Using the self-assembled template of oligo(phenylene-ethynylene) (OPE), organic molecules such as coronene (COR) and biomolecules such as tripeptide are controllably distributed and dispersed within this molecular template on highly oriented pyrolytic graphite (HOPG) surfaces. COR molecules were controllably distributed into various regular arrays by simply adjusting the molecular molar ratio, while tripeptide molecules were uniformly positioned at the vacancies of the OPE template.