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1.
Nano Lett ; 21(20): 8770-8776, 2021 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-34653333

RESUMO

The spatial arrangement of adsorbates deposited onto a clean surface under vacuum typically cannot be reversibly tuned. Here we use scanning tunneling microscopy to demonstrate that molecules deposited onto graphene field-effect transistors (FETs) exhibit reversible, electrically tunable surface concentration. Continuous gate-tunable control over the surface concentration of charged F4TCNQ molecules was achieved on a graphene FET at T = 4.5K. This capability enables the precisely controlled impurity doping of graphene devices and also provides a new method for determining molecular energy level alignment based on the gate-dependence of molecular concentration. Gate-tunable molecular concentration is explained by a dynamical molecular rearrangement process that reduces total electronic energy by maintaining Fermi level pinning in the device substrate. The molecular surface concentration is fully determined by the device back-gate voltage, its geometric capacitance, and the energy difference between the graphene Dirac point and the molecular LUMO level.


Assuntos
Grafite , Capacitância Elétrica , Eletrônica , Microscopia de Tunelamento , Transistores Eletrônicos
2.
Nano Lett ; 21(17): 7100-7108, 2021 09 08.
Artigo em Inglês | MEDLINE | ID: mdl-34415771

RESUMO

Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be defect free. We report here scanning tunneling microscopy results that show graphite commonly used to prepare graphene devices can contain a significant amount of native defects. Extensive scanning of the surface allows us to determine the concentration of native defects to be 6.6 × 108 cm-2. We further study the effects of these native defects on the electronic properties of Bernal-stacked bilayer graphene. We observe gate-dependent intravalley scattering and successfully compare our experimental results to T-matrix-based calculations, revealing a clear carrier density dependence in the distribution of the scattering vectors. We also present a technique for evaluating the spatial distribution of short-scale scattering. Finally, we present a theoretical analysis based on the Boltzmann transport equation that predicts that the dilute native defects identified in our study are an important extrinsic source of scattering, ultimately setting the charge carrier mobility at low temperatures.


Assuntos
Grafite , Eletrônica , Microscopia de Tunelamento
4.
Chemistry ; 27(55): 13887-13893, 2021 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-34232531

RESUMO

Intermolecular interactions guide self-assembly on the surface. Precise control over these interactions by rational design of the molecule should allow fine control over the self-assembly patterns. Functional groups installed for electronic modulation often induce significant changes in the molecular dimensions, thereby disrupting the original assembly pattern. To overcome this challenge, we have employed a family of isosteric phenazine derivatives, DHP, DAP, and DBQD, to investigate the impacts of hydrogen bonding on two-dimensional molecular self-assembly. While these molecules are similar in size and chemical composition, the strength and directionality of hydrogen bonding differ significantly depending on the chemical structure of donor-acceptor pairs and prototropic tautomerization from positional isomerism. Scanning tunneling microscopy (STM) characterization of the assembled structures on Ag(111), Au(111), and Cu(100) surfaces revealed that minimal changes in molecular structure have a profound impact on the self-assembly patterns. While DHP exhibits highly ordered and robust assemblies, DAP and DBQD show either spatially confined or ill-defined assemblies. In conjunction with hydrogen bonding, prototropic tautomerism is a potent strategy to modulate molecular 2D lattices on surfaces.


Assuntos
Microscopia de Tunelamento , Ligação de Hidrogênio , Estrutura Molecular
5.
Int J Mol Sci ; 22(13)2021 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-34206862

RESUMO

We report an ultra-high vacuum low-temperature scanning tunneling microscopy (STM) study of the C60 monolayer grown on Cd(0001). Individual C60 molecules adsorbed on Cd(0001) may exhibit a bright or dim contrast in STM images. When deposited at low temperatures close to 100 K, C60 thin films present a curved structure to release strain due to dominant molecule-substrate interactions. Moreover, edge dislocation appears when two different wavy structures encounter each other, which has seldomly been observed in molecular self-assembly. When growth temperature rose, we found two forms of symmetric kagome lattice superstructures, 2 × 2 and 4 × 4, at room temperature (RT) and 310 K, respectively. The results provide new insight into the growth behavior of C60 films.


Assuntos
Microscopia de Tunelamento/métodos , Compostos Organometálicos/química , Cristalização , Polimerização , Estresse Mecânico , Temperatura , Vácuo
6.
Nano Lett ; 21(12): 5006-5012, 2021 06 23.
Artigo em Inglês | MEDLINE | ID: mdl-34061553

RESUMO

We demonstrate that nanocavity plasmons generated a few nanometers away from a molecule can induce molecular motion. For this, we study the well-known rapid shuttling motion of zinc phthalocyanine molecules adsorbed on ultrathin NaCl films by combining scanning tunneling microscopy (STM) and spectroscopy (STS) with STM-induced light emission. Comparing spatially resolved single-molecule luminescence spectra from molecules anchored to a step edge with isolated molecules adsorbed on the free surface, we found that the azimuthal modulation of the Lamb shift is diminished in case of the latter. This is evidence that the rapid shuttling motion is remotely induced by plasmon-molecule coupling. Plasmon-induced molecular motion may open an interesting playground to bridge the nanoscopic and mesoscopic worlds by combining molecular machines with nanoplasmonics to control directed motion of single molecules without the need for local probes.


Assuntos
Microscopia de Tunelamento , Nanotecnologia , Animais , Luminescência , Ovinos , Análise Espectral
7.
Nano Lett ; 21(13): 5493-5499, 2021 07 14.
Artigo em Inglês | MEDLINE | ID: mdl-34192467

RESUMO

A fundamental understanding and advancement of nanopatterning and nanometrology are essential in the future development of nanotechnology, atomic scale manipulation, and quantum technology industries. Scanning probe-based patterning/imaging techniques have been attractive for many research groups to conduct their research in nanoscale device fabrication and nanotechnology mainly due to its cost-effective process; however, the current tip materials in these techniques suffer from poor durability, limited resolution, and relatively high fabrication costs. Here, we report on employing GaN nanowires as a robust semiconductor material in scanning probe lithography (SPL) and microscopy (SPM) with a relatively low-cost fabrication process and the capability to provide sub-10 nm lithography and atomic scale (<1 nm) patterning resolution in field-emission scanning probe lithography (FE-SPL) and scanning tunneling microscopy (STM), respectively. We demonstrate that GaN NWs are great candidates for advanced SPL and imaging that can provide atomic resolution imaging and sub-10 nm nanopatterning on different materials in both vacuum and ambient operations.


Assuntos
Nanofios , Microscopia , Microscopia de Tunelamento , Nanotecnologia , Impressão
8.
Nat Chem ; 13(8): 766-770, 2021 08.
Artigo em Inglês | MEDLINE | ID: mdl-34031563

RESUMO

The funnelling of energy within multichromophoric assemblies is at the heart of the efficient conversion of solar energy by plants. The detailed mechanisms of this process are still actively debated as they rely on complex interactions between a large number of chromophores and their environment. Here we used luminescence induced by scanning tunnelling microscopy to probe model multichromophoric structures assembled on a surface. Mimicking strategies developed by photosynthetic systems, individual molecules were used as ancillary, passive or blocking elements to promote and direct resonant energy transfer between distant donor and acceptor units. As it relies on organic chromophores as the elementary components, this approach constitutes a powerful model to address fundamental physical processes at play in natural light-harvesting complexes.


Assuntos
Corantes Fluorescentes/química , Isoindóis/química , Compostos Organometálicos/química , Compostos de Zinco/química , Biomimética , Transferência de Energia , Fluorescência , Corantes Fluorescentes/efeitos da radiação , Isoindóis/efeitos da radiação , Luz , Microscopia de Tunelamento , Compostos Organometálicos/efeitos da radiação , Compostos de Zinco/efeitos da radiação
9.
Proc Natl Acad Sci U S A ; 118(11)2021 03 16.
Artigo em Inglês | MEDLINE | ID: mdl-33836601

RESUMO

Time- and space-resolved excited states at the individual nanoparticle level provide fundamental insights into heterogeneous energy, electron, and heat flow dynamics. Here, we optically excite carbon dots to image electron-phonon dynamics within single dots and nanoscale thermal transport between two dots. We use a scanning tunneling microscope tip as a detector of the optically excited state, via optical blocking of electron tunneling, to record movies of carrier dynamics in the 0.1-500-ps time range. The excited-state electron density migrates from the bulk to molecular-scale (∼1 nm2) surface defects, followed by heterogeneous relaxation of individual dots to either long-lived fluorescent states or back to the ground state. We also image the coupling of optical phonons in individual carbon dots with conduction electrons in gold as an ultrafast energy transfer mechanism between two nearby dots. Although individual dots are highly heterogeneous, their averaged dynamics is consistent with previous bulk optical spectroscopy and nanoscale heat transfer studies, revealing the different mechanisms that contribute to the bulk average.


Assuntos
Carbono/química , Nanopartículas/química , Imagem Individual de Molécula , Elétrons , Transferência de Energia , Fluorescência , Ouro/química , Microscopia de Tunelamento , Modelos Químicos , Fônons
10.
Chem Commun (Camb) ; 57(23): 2923-2926, 2021 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-33620361

RESUMO

The structure of a cyclic peptide with important biological functionalities, cyclosporin A (CsA), is investigated at the single molecule level. Its adsorption on Cu(111) under ultra-high vacuum is characterised with scanning tunnelling microscopy (STM) and density functional theory. With STM investigations, we demonstrate element specific on-surface coordination schemes of CsA with coadsorbed K, Co and Fe atoms. Thus, clear insights emerge in the behaviour of cyclic peptides at interfaces and their interactions with different metal atoms, providing control of the adsorption structure and assembly and paving the way for the integration of cyclic peptides in functional metal-organic nanostructures on surfaces.


Assuntos
Ciclosporina/química , Metais/química , Adsorção , Teoria da Densidade Funcional , Dimerização , Microscopia de Tunelamento , Modelos Moleculares , Conformação Molecular , Nanoestruturas/química , Propriedades de Superfície
11.
J Am Chem Soc ; 142(47): 19814-19818, 2020 11 25.
Artigo em Inglês | MEDLINE | ID: mdl-33179492

RESUMO

Peptide-based biomimetic nanostructures and metal-organic coordination networks on surfaces are two promising classes of hybrid materials which have been explored recently. However, despite the great versatility and structural variability of natural and synthetic peptides, the two directions have so far not been merged in fabrication of metal-organic coordination networks using peptides as building blocks. Here we demonstrate that cyclic peptides can be used as ligands to form highly ordered, two-dimensional, peptide-based metal-organic coordination networks. The networks are formed on a Au(111) surface through coadsorption of cyclic dialanine with Cu-adatoms under Ultra-High Vacuum (UHV) conditions. Scanning Tunneling Microscopy (STM) in combination with X-ray Photoelectron spectroscopy (XPS) has been utilized to characterize the network structures at submolecular resolution and expound the chemical changes involved in network coordination. The networks involve a motif of three cyclic dialanine molecules coordinating to a central Cu-adatom. Interestingly the networks expose pores functionalized by the side chain of the cyclic peptide, suggesting a general method to form functionalized porous metal-organic networks on surfaces.


Assuntos
Estruturas Metalorgânicas/química , Peptídeos Cíclicos/química , Cobre/química , Dipeptídeos/química , Ouro/química , Microscopia de Tunelamento , Espectroscopia Fotoeletrônica , Porosidade , Propriedades de Superfície
12.
Molecules ; 25(17)2020 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-32824933

RESUMO

The on-surface C-H bond activation and coupling reaction is a powerful approach to constructing fine-tuned surface nanostructures. It is quite challenging to control its regioselectivity due to the inertness of the C-H bond involved. With scanning tunneling microscopy/spectroscopy and theoretical calculations, the C-H activation and sequential intramolecular dehydrocyclization of meso-tetra(p-methoxyphenyl)porphyrinatocobalt(II) was explored on Au(111), showing that the methoxy groups in the molecule could kinetically mediate the selectivity of the intramolecular reaction over its intermolecular coupling counterpart. The experimental results demonstrate that the introduced protecting group could help augment the selectivity of such on-surface reaction, which can be applied to the precise fabrication of functional surface nanostructures.


Assuntos
Complexos de Coordenação/química , Ouro/química , Modelos Teóricos , Nanoestruturas/química , Porfirinas/química , Microscopia de Tunelamento , Propriedades de Superfície
13.
Molecules ; 25(13)2020 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-32605152

RESUMO

The effect of deposition time on the surface coverage of sublimation deposited solid-phase glycine and proline molecules onto a Ge(100) surface was studied at room temperature using scanning tunneling microscopy (STM). The STM images obtained at various coverages of glycine and proline adsorbed on the Ge(100) surface showed that (i) the adsorption rate for both molecules gradually decreased with increasing deposition time, obeying the Langmuir adsorption model, and (ii) the coverage of glycine on the Ge(100) surface is higher than that of proline under the same deposition conditions, which may be due to the differences in their molecular weight or molecular sticking probability.


Assuntos
Glicina/química , Prolina/química , Adsorção , Microscopia de Tunelamento , Conformação Molecular , Peso Molecular , Propriedades de Superfície , Temperatura
14.
Nature ; 582(7812): 375-378, 2020 06.
Artigo em Inglês | MEDLINE | ID: mdl-32555487

RESUMO

Imaging of biomolecules guides our understanding of their diverse structures and functions1,2. Real-space imaging at sub-nanometre resolution using cryo-electron microscopy has provided key insights into proteins and their assemblies3,4. Direct molecular imaging of glycans-the predominant biopolymers on Earth, with a plethora of structural and biological functions5-has not been possible so far6. The inherent glycan complexity and backbone flexibility require single-molecule approaches for real-space imaging. At present, glycan characterization often relies on a combination of mass spectrometry and nuclear magnetic resonance imaging to provide insights into size, sequence, branching and connectivity, and therefore requires structure reconstruction from indirect information7-9. Here we show direct imaging of single glycan molecules that are isolated by mass-selective, soft-landing electrospray ion beam deposition and imaged by low-temperature scanning tunnelling microscopy10. The sub-nanometre resolution of the technique enables the visualization of glycan connectivity and discrimination between regioisomers. Direct glycan imaging is an important step towards a better understanding of the structure of carbohydrates.


Assuntos
Polissacarídeos/análise , Polissacarídeos/química , Imagem Individual de Molécula , Manosídeos/análise , Manosídeos/química , Microscopia de Tunelamento
15.
J Am Chem Soc ; 142(21): 9809-9817, 2020 05 27.
Artigo em Inglês | MEDLINE | ID: mdl-32311259

RESUMO

Coordination-driven self-assembly has been extensively employed to construct a variety of discrete structures as a bottom-up strategy. However, mechanistic understanding regarding whether self-assembly is under kinetic or thermodynamic control is less explored. To date, such mechanistic investigation has been limited to distinct, assembled structures. It still remains a formidable challenge to study the kinetic and thermodynamic behavior of self-assembly systems with multiple assembled isomers due to the lack of characterization methods. Herein, we use a stepwise strategy which combined self-recognition and self-assembly processes to construct giant metallo-supramolecules with 8 positional isomers in solution. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, we were able to unambiguously differentiate 14 isomers on the substrate which correspond to 8 isomers in solution. Through measurement of 162 structures, the experimental probability of each isomer was obtained and compared with the theoretical probability. Such a comparison along with density functional theory (DFT) calculation suggested that although both kinetic and thermodynamic control existed in this self-assembly, the increased experimental probabilities of isomers compared to theoretical probabilities should be attributed to thermodynamic control.


Assuntos
Complexos de Coordenação/química , Termodinâmica , Complexos de Coordenação/síntese química , Teoria da Densidade Funcional , Cinética , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Microscopia de Tunelamento , Estrutura Molecular
16.
Nat Chem ; 12(5): 468-474, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32284575

RESUMO

For the past three decades, the coordination-driven self-assembly of three-dimensional structures has undergone rapid progress; however, parallel efforts to create large discrete two-dimensional architectures-as opposed to polymers-have met with limited success. The synthesis of metallo-supramolecular systems with well-defined shapes and sizes in the range of 10-100 nm remains challenging. Here we report the construction of a series of giant supramolecular hexagonal grids, with diameters on the order of 20 nm and molecular weights greater than 65 kDa, through a combination of intra- and intermolecular metal-mediated self-assembly steps. The hexagonal intermediates and the resulting self-assembled grid architectures were imaged at submolecular resolution by scanning tunnelling microscopy. Characterization (including by scanning tunnelling spectroscopy) enabled the unambiguous atomic-scale determination of fourteen hexagonal grid isomers.


Assuntos
Complexos de Coordenação/química , Estruturas Metalorgânicas/química , Metais/química , Nanoestruturas/química , Isomerismo , Ligantes , Microscopia de Tunelamento , Modelos Moleculares , Estrutura Molecular , Peso Molecular
17.
Nucleosides Nucleotides Nucleic Acids ; 39(8): 1083-1087, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32345125

RESUMO

Electrical properties of metal-mediated DNA duplexes (metallo-DNA) have been of particular interest because of their potential applications in DNA-based nanoelectronics. We prepared HgII-mediated DNA duplex with NH2 anchors and measured the electrical conductance of single-molecule metallo-DNA via scanning tunneling microscopy-based break junction method in the buffered solution. Three conductance values were observed that may correspond to different conformations of the metallo-DNA molecule bridged over metallic electrodes.


Assuntos
DNA/química , Mercúrio/química , Condutividade Elétrica , Eletrodos , Microscopia de Tunelamento , Soluções , Água/química
18.
J Am Chem Soc ; 142(13): 6196-6205, 2020 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-32150680

RESUMO

During the past few decades, the study of the single polymer chain has attracted considerable attention with the goal of exploring the structure-property relationship of polymers. It still, however, remains challenging due to the variability and low atomic resolution of the amorphous single polymer chain. Here, we demonstrated a new strategy to visualize the single metallopolymer chain with a hexameric or trimeric supramolecule as a repeat unit, in which Ru(II) with strong coordination and Fe(II) with weak coordination were combined together in a stepwise manner. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM) and scanning tunneling spectroscopy (STS), we were able to directly visualize both Ru(II) and Fe(II), which act as staining reagents on the repeat units, thus providing detailed structural information for the single polymer chain. As such, the direct visualization of the single random polymer chain is realized to enhance the characterization of polymers at the single-molecule level.


Assuntos
Complexos de Coordenação/química , Ferro/química , Polímeros/química , Rutênio/química , Técnicas de Química Sintética , Complexos de Coordenação/síntese química , Microscopia de Tunelamento , Polímeros/síntese química
19.
Science ; 367(6476): 368, 2020 01 24.
Artigo em Inglês | MEDLINE | ID: mdl-31974236
20.
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
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