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1.
J Chem Phys ; 152(23): 234301, 2020 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-32571057

RESUMO

The hydrogen-bonding networks of water have strong intra- and intermolecular vibrational coupling which influences the energy dissipation and proton transfer in water. Disentangling and quantitative characterization of different coupling effects in water at a single-molecular level still remains a great challenge. Using tip-enhanced inelastic electron tunneling spectroscopy (IETS) based on low-temperature scanning tunneling microscopy, we report the direct quantitative assessment of the intermolecular coupling constants of the OH-stretch vibrational bands of an isolated water tetramer adsorbed on a Au(111)-supported NaCl(001) bilayer film. This is achieved by distinguishing various coupled modes of the H-bonded O-H stretching vibrations through tip-height dependent IET spectra. In contrast, such vibrational coupling is negligible in the half-deuterated water tetramer owing to the large energy mismatch between the OH and OD stretching modes. Not only do these findings advance our understanding on the effects of local environment on the intermolecular vibrational coupling in water, but also open up a new route for vibrational spectroscopic studies of extended H-bonded network at the single-molecular level.

2.
Nature ; 577(7788): 60-63, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31894149

RESUMO

The formation and growth of water-ice layers on surfaces and of low-dimensional ice under confinement are frequent occurrences1-4. This is exemplified by the extensive reporting of two-dimensional (2D) ice on metals5-11, insulating surfaces12-16, graphite and graphene17,18 and under strong confinement14,19-22. Although structured water adlayers and 2D ice have been imaged, capturing the metastable or intermediate edge structures involved in the 2D ice growth, which could reveal the underlying growth mechanisms, is extremely challenging, owing to the fragility and short lifetime of those edge structures. Here we show that noncontact atomic-force microscopy with a CO-terminated tip (used previously to image interfacial water with minimal perturbation)12, enables real-space imaging of the edge structures of 2D bilayer hexagonal ice grown on a Au(111) surface. We find that armchair-type edges coexist with the zigzag edges usually observed in 2D hexagonal crystals, and freeze these samples during growth to identify the intermediate edge structures. Combined with simulations, these experiments enable us to reconstruct the growth processes that, in the case of the zigzag edge, involve the addition of water molecules to the existing edge and a collective bridging mechanism. Armchair edge growth, by contrast, involves local seeding and edge reconstruction and thus contrasts with conventional views regarding the growth of bilayer hexagonal ices and 2D hexagonal matter in general.


Assuntos
Gelo , Microscopia de Tunelamento , Cristalização
3.
Front Chem ; 7: 626, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31572715

RESUMO

The structure and dynamics of interfacial water, determined by the water-interface interactions, are important for a wide range of applied fields and natural processes, such as water diffusion (Kim et al., 2013), electrochemistry (Markovic, 2013), heterogeneous catalysis (Over et al., 2000), and lubrication (Zilibotti et al., 2013). The precise understanding of water-interface interactions largely relies on the development of atomic-scale experimental techniques (Guo et al., 2014) and computational methods (Hapala et al., 2014b). Scanning probe microscopy has been extensively applied to probe interfacial water in many interdisciplinary fields (Ichii et al., 2012; Shiotari and Sugimoto, 2017; Peng et al., 2018a). In this perspective, we review the recent progress in the noncontact atomic force microscopy (nc-AFM) imaging and AFM simulation techniques and discuss how the newly developed techniques are applied to study the properties of interfacial water. The nc-AFM with the quadrupole-like CO-terminated tip can achieve ultrahigh-resolution imaging of the interfacial water on different surfaces, trace the reconstruction of H-bonding network and determine the intrinsic structures of the weakly bonded water clusters and even their metastable states. In the end, we present an outlook on the directions of future AFM studies of interfacial water as well as the challenges faced by this field.

4.
Nature ; 563(7729): E18, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30135587

RESUMO

In this Letter, the links to Supplementary Videos 5, 7, 9 and 10 were incorrect, and there were some formatting errors in the Supplementary Video legends. These errors have been corrected online.

5.
Nature ; 557(7707): 701-705, 2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29760468

RESUMO

Ion hydration and transport at interfaces are relevant to a wide range of applied fields and natural processes1-5. Interfacial effects are particularly profound in confined geometries such as nanometre-sized channels6-8, where the mechanisms of ion transport in bulk solutions may not apply9,10. To correlate atomic structure with the transport properties of hydrated ions, both the interfacial inhomogeneity and the complex competing interactions among ions, water and surfaces require detailed molecular-level characterization. Here we constructed individual sodium ion (Na+) hydrates on a NaCl(001) surface by progressively attaching single water molecules (one to five) to the Na+ ion using a combined scanning tunnelling microscopy and noncontact atomic force microscopy system. We found that the Na+ ion hydrated with three water molecules diffuses orders of magnitude more quickly than other ion hydrates. Ab initio calculations revealed that such high ion mobility arises from the existence of a metastable state, in which the three water molecules around the Na+ ion can rotate collectively with a rather small energy barrier. This scenario would apply even at room temperature according to our classical molecular dynamics simulations. Our work suggests that anomalously high diffusion rates for specific hydration numbers of ions are generally determined by the degree of symmetry match between the hydrates and the surface lattice.

6.
Nano Lett ; 18(5): 2937-2942, 2018 05 09.
Artigo em Inglês | MEDLINE | ID: mdl-29601201

RESUMO

The atomic structures of self-assembled silicon nanoribbons and magic clusters on Ag(110) substrate have been studied by high-resolution noncontact atomic force microscopy (nc-AFM) and tip-enhanced Raman spectroscopy (TERS). Pentagon-ring structures in Si nanoribbons and clusters have been directly visualized. Moreover, the vibrational fingerprints of individual Si nanoribbon and cluster retrieved by subnanometer resolution TERS confirm the pentagonal nature of both Si nanoribbons and clusters. This work demonstrates that Si pentagon can be an important element in building silicon nanostructures, which may find important applications for future nanoelectronic devices based on silicon.

7.
Nat Commun ; 9(1): 122, 2018 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-29317638

RESUMO

Scanning probe microscopy has been extensively applied to probe interfacial water in many interdisciplinary fields but the disturbance of the probes on the hydrogen-bonding structure of water has remained an intractable problem. Here, we report submolecular-resolution imaging of the water clusters on a NaCl(001) surface within the nearly noninvasive region by a qPlus-based noncontact atomic force microscopy. Comparison with theoretical simulations reveals that the key lies in probing the weak high-order electrostatic force between the quadrupole-like CO-terminated tip and the polar water molecules at large tip-water distances. This interaction allows the imaging and structural determination of the weakly bonded water clusters and even of their metastable states with negligible disturbance. This work may open an avenue for studying the intrinsic structure and dynamics of ice or water on surfaces, ion hydration, and biological water with atomic precision.

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