The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy

Groß, Leo; Mohn, Fabian; Moll, Nikolaj; Liljeroth, Peter; Meyer, Gerhard

doi:10.1126/science.1176210

Cited by 1,601 publications

(2,004 citation statements)

References 31 publications

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“…Herein we report the on‐surface synthesis of the complete series from heptacene ( 2 ) up to previously unknown undecacene ( 6 ) through the dehydrogenation of the corresponding tetrahydroacene precursors 1 (Scheme 1). In order to confirm the generation of intrinsically unstable higher acenes, high resolution nc‐AFM imaging with a CO functionalized tip was applied,18a which provided doubtless structural and chemical identification of the synthesized compounds. The generation of the acene series was complemented by scanning tunneling spectroscopy (STS) measurements, which revealed the resonances associated with HOMO and LUMO orbitals and therefore allowed us to quantify the transport electronic gap evolution upon extension of the molecule board for acenes physisorbed on Au(111).…”

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Higher Acenes by On‐Surface Dehydrogenation: From Heptacene to Undecacene

et al. 2018

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A unified approach to the synthesis of the series of higher acenes up to previously unreported undecacene has been developed through the on‐surface dehydrogenation of partially saturated precursors. These molecules could be converted into the parent acenes by both atomic manipulation with the tip of a scanning tunneling and atomic force microscope (STM/AFM) as well as by on‐surface annealing. The structure of the generated acenes has been visualized by high‐resolution non‐contact AFM imaging and the evolution of the transport gap with the increase of the number of fused benzene rings has been determined on the basis of scanning tunneling spectroscopy (STS) measurements.

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confidence: 99%

Higher Acenes by On‐Surface Dehydrogenation: From Heptacene to Undecacene

et al. 2018

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“…21,22 Picking up atoms and small molecules with the tip, in particular CO, has proven to be particularly useful in achieving high resolution. 5 Although CO is important in catalysis, the C bonds to the tip, thus presenting the wrong end of the molecule to the surface to learn about how CO interacts with surfaces. Rather the CO termination yields NC-AFM images that closely resemble textbook molecular structures; 5 Figure 3C showing pentacene, for example, received great attention in the popular press.…”

Section: Tip Terminationmentioning

confidence: 99%

Noncontact Atomic Force Microscopy: An Emerging Tool for Fundamental Catalysis Research

Altman¹,

Baykara

Schwarz³

2015

Acc. Chem. Res.

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CONSPECTUS:Although atomic force microscopy (AFM) was rapidly adopted as a routine surface imaging apparatus after its introduction in 1986, it has not been widely used in catalysis research. The reason is that common AFM operating modes do not provide the atomic resolution required to follow catalytic processes; rather the more complex noncontact (NC) mode is needed. Thus, scanning tunneling microscopy has been the principal tool for atomic scale catalysis research. In this Account, recent developments in NC-AFM will be presented that offer significant advantages for gaining a complete atomic level view of catalysis. The main advantage of NC-AFM is that the image contrast is due to the very short-range chemical forces that are of interest in catalysis. This motivated our development of 3D-AFM, a method that yields quantitative atomic resolution images of the potential energy surfaces that govern how molecules approach, stick, diffuse, and rebound from surfaces. A variation of 3D-AFM allows the determination of forces required to push atoms and molecules on surfaces, from which diffusion barriers and variations in adsorption strength may be obtained. Pushing molecules towards each other provides access to intermolecular interaction between reaction partners. Following reaction, NC-AFM with CO-terminated tips yields textbook images of intramolecular structure that can be used to identify reaction intermediates and products. Because NC-AFM and STM contrast mechanisms are distinct, combining the two methods can produce unique insight. It is demonstrated for surface-oxidized Cu(100) that simultaneous 3D-AFM/STM yields resolution of both the Cu and O atoms. Moreover, atomic defects in the Cu sublattice lead to variations in the reactivity of the neighboring O atoms. It is shown that NC-AFM also allows a straightforward imaging of work function variations which has been used to identify defect charge states on catalytic surfaces and to map charge transfer within an individual molecule. These advances highlight the potential for NC-AFM-based methods to become the cornerstone upon which a quantitative atomic scale view of each step of a catalytic process may be gained. Realizing this potential will rely on two breakthroughs: (1) development of robust methods for tip functionalization and (2) simplification of NC-AFM instrumentation and control schemes. Quartz force sensors may offer paths forward in both cases. They allow any material with an atomic asperity to be used as a tip, opening the door to a wide range of surface functionalization chemistry. In addition, they do not suffer from the instabilities that motivated the initial adoption of complex control strategies that are still used today.

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“…Most of these observables, however, are accessible only under limited circumstances. For instance, electronic properties are measurable only on conducting samples while atomic-resolution force microscopy requires careful preparation of samples in ultrahigh vacuum 5,6 or liquid environments 7 .Here we demonstrate a scanning probe imaging method that extends the range of accessible quantities to label-free imaging of chemical species operating on arbitrary samples -including insulating materials -under ambient conditions. Moreover, it provides three-dimensional depth information, thus revealing subsurface features.…”

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confidence: 97%

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Nanoscale nuclear magnetic imaging with chemical contrast

et al. 2015

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Scanning probe microscopy is one of the most versatile windows into the nanoworld, providing imaging access to a variety of sample properties, depending on the probe employed.Tunneling probes map electronic properties of samples 1 , magnetic and photonic probes image their magnetic and dielectric structure 2,3 while sharp tips probe mechanical properties like surface topography, friction or stiffness 4 . Most of these observables, however, are accessible only under limited circumstances. For instance, electronic properties are measurable only on conducting samples while atomic-resolution force microscopy requires careful preparation of samples in ultrahigh vacuum 5,6 or liquid environments 7 .Here we demonstrate a scanning probe imaging method that extends the range of accessible quantities to label-free imaging of chemical species operating on arbitrary samples -including insulating materials -under ambient conditions. Moreover, it provides three-dimensional depth information, thus revealing subsurface features. We achieve these results by recording nuclear magnetic resonance signals from a sample surface with a recently introduced scanning probe, a single nitrogen-vacancy center in diamond. We demonstrate NMR imaging with 10 nm resolution and achieve chemically specific contrast by separating fluorine from hydrogen rich regions.Our result opens the door to scanning probe imaging of the chemical composition and atomic structure of arbitrary samples. A method with these abilities will find widespread application in material science even on biological specimens down to the level of single macromolecules.The development of a scanning probe sensor able to image nuclear spins has been a long and outstanding goal of nanoscience, proposed shortly after the invention of scanning probe microscopy itself 8 . To date, this goal is most closely met by magnetic resonance force microscopy (MRFM), an extension of atomic-force-microscopy with sensitivity to spins, which has successfully imaged nanoscale distributions of nuclear spins in three dimensions 9 .However, its operation is experimentally challenging, requiring low (sub-Kelvin) temperature and long (weeks/image) acquisition times, which has so far precluded its adoption as a routine technique. To surmount these problems, single electron spins with optical readout capability have been proposed as an alternative local probe for spin distributions 10 . This complementary approach has become a realistic prospect since recent research has established the nitrogenvacancy center, a color defect in diamond 11 , as a candidate system for this scheme 12,13 . This center serves as an atomic-sized magnetic field sensor, which has proven sufficiently sensitive to detect the field of single nuclear spins in its diamond lattice environment [14][15][16] as well as ensembles of 10-10 4 spins in a nanometer-sized sample volume on the diamond surface [17][18][19] .Here we employ a single NV center as a scanning probe to image distributions of nuclear spins in an external sample. All our ...

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The Chemical Structure of a Molecule Resolved by Atomic Force Microscopy

Cited by 1,601 publications

References 31 publications

Higher Acenes by On‐Surface Dehydrogenation: From Heptacene to Undecacene

Higher Acenes by On‐Surface Dehydrogenation: From Heptacene to Undecacene

Noncontact Atomic Force Microscopy: An Emerging Tool for Fundamental Catalysis Research

Nanoscale nuclear magnetic imaging with chemical contrast

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