Coverage and nearest-neighbor dependence of adsorbate diffusion

Wong, Kin; Rao, Bommisetty V.; Pawin, Greg; Ulin-Avila, Erick; Bartels, Ludwig

doi:10.1063/1.2124687

Cited by 27 publications

(40 citation statements)

References 29 publications

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“…Importantly, it appears always in a confined area of the surface (see Mielke_movie2_diff in Supplemental Material [26]). We suggest that the presence of other adsorbates triggers the adatom diffusion, as observed for enhanced atomic or molecular diffusion [44][45][46][47], and more specifically for FeO where the presence of water molecules stimulates the cascadelike motion of hydrogen atoms [48]. We have tested whether water molecules from the rest gas in the vacuum chamber play such a role here [26], but could not find any evidence.…”

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confidence: 98%

Observing single-atom diffusion at a molecule-metal interface

et al. 2016

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The dynamics at the interface between a close-packed porphyrin monolayer and Au(111) is investigated by time-dependent scanning tunneling microscopy, detecting the motion of single-interface adatoms in real space. Imaging sequences reveal predominant switching of the molecular appearance in adjacent molecules, pointing to a spatial correlation that is consistent with adatom diffusion from one molecule to the next. In some cases, the number of switching molecules is drastically increased, indicating collective switching events. In addition to the thermally induced motion of adatoms at the interface, also voltage pulses from the microscope tip can induce the process-revealing different yields in agreement with the model of adatom hopping. DOI: 10.1103/PhysRevB.94.035416 The interface between organic molecules and metal substrates plays a key role for many properties that are important, for instance, in catalytically driven reactions [1,2] and for charge transport [3]. The study of such systems gives detailed insight into fundamental processes that take place at an organic-inorganic interface. For an in-depth understanding, it is advantageous to use a scanning tunneling microscope (STM) for imaging because it provides information about the local environment of each individual molecule, which is important since the molecular properties might differ locallydue to defects, step edges, or different areas of a surface reconstruction [4,5]. For instance, individual C 60 molecules were found to change between dark and bright appearances in STM images, caused by the diffusion of surface [6] or bulk [7] vacancies, charge transfer between molecule and surface [8], or adsorption on small metal islands [9].Adatoms are known to diffuse on close-packed metal surfaces if the thermal energy is sufficient for their detachment from step edges [10]. When molecules are adsorbed on such a surface, the adatoms can interact with and even be trapped by molecules [11][12][13][14][15], leading to characteristic metallic nanostructures that reflect the molecular shape [16][17][18]. In addition to these self-organized structures, manipulation of single adatoms has been used to bring them in contact with molecules [19,20]. So far, real space studies of the molecule-surface interaction have been done mainly under static conditions [21,22] or focus on the lateral diffusion of molecules on surfaces [23][24][25]. Here, we report the dynamic behavior at the molecule-metal interface by observing the motion of individual gold adatoms underneath a molecular monolayer on Au(111) in time.As a molecular system we have chosen tetrabromophenylporphyrin [Br 4 TPP; Fig. 1(a) The appearance of our molecules strongly depends on the applied bias voltage: At −0.5 V all molecules appear at a similar height, while at around −1 V two dark and one bright molecular appearances can be found [ Fig. 1(b)]. The two dark molecules could be identified as two tautomers without a gold adatom, while bright molecules have a single gold adatom underneath, causing the shift i...

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confidence: 98%

Observing single-atom diffusion at a molecule-metal interface

et al. 2016

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“…8,17 The method offers advantages over following diffusion trajectories: it does not require varying the temperature to obtain an Arrhenius plot; and it allows paths that include rare sites that nonetheless may have a large impact on catalysis. For different initial and final sites, repeating the measurement in the reverse direction would provide the energy difference between the sites.…”

Section: Measuring the Forces Required To Translate Atoms And Moleculesmentioning

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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“…7) are in constant motion below 30 K, a remarkable result since CO on Cu(111) does not begin to diffuse till ∼33 K [57]. Since CO adatoms are confined in pores, one can monitor the diffusion rate as a function of a fixed number density.…”

Section: Applications Of the Array Of Poresmentioning

confidence: 99%

Patterns of Organics on Substrates with Metallic Surface States: Why?, So??

Einstein

Bartels

Morales-Cifuentes

2018

e-J. Surf. Sci. Nanotech.

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This paper modestly expands an invited talk at ISSS-8 with the same title. After reviewing the relevant interactions between adsorbates on substrates with metallic surface states [especially Cu(111)], it focuses on organic adsorbates. Of particular interest are those which form honeycomb lattices with pores of various sizes. The nature of the confined states derived from the surface-state electrons is discussed as their effect on admolecules inside the pores.

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Coverage and nearest-neighbor dependence of adsorbate diffusion

Cited by 27 publications

References 29 publications

Observing single-atom diffusion at a molecule-metal interface

Observing single-atom diffusion at a molecule-metal interface

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

Patterns of Organics on Substrates with Metallic Surface States: Why?, So??

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