Imaging Pauli Repulsion in Scanning Tunneling Microscopy

Weiss, Christian; Wagner, Christian; Kleimann, Christoph; Rohlfing, Michael; Tautz, F. Stefan; Temirov, Ruslan

doi:10.1103/physrevlett.105.086103

Cited by 151 publications

(180 citation statements)

References 23 publications

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“…Ef, 68.37.Ps, 68.43.Fg One of the most exciting and significant breakthroughs in field of scanning probe microscopy (SPM) in last years is undoubtedly the achievement of high-resolution STM [1] and AFM [2] images of molecular structures with functionalized tips [3,4]. In general, the high-resolution images, being typically acquired in the regime where the tip-surface interaction becomes repulsive, are characterized by a presence of sharp features in both intra and intermolecular regions.…”

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confidence: 99%

Origin of High-Resolution IETS-STM Images of Organic Molecules with Functionalized Tips

et al. 2014

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Recently, the family of high-resolution scanning probe imaging techniques using decorated tips has been complimented by a method based on inelastic electron tunneling spectroscopy (IETS). The new technique resolves the inner structure of organic molecules by mapping the vibrational energy of a single carbonmonoxide (CO) molecule positioned at the apex of a scanning tunnelling microscope (STM) tip. Here, we explain high-resolution IETS imaging by extending the model developed earlier for STM and atomic force microscopy (AFM) imaging with decorated tips. In particular, we show that the tip decorated with CO acts as a nanoscale sensor that changes the energy of the CO frustrated translation in response to the change of the local curvature of the surface potential. In addition, we show that high resolution AFM, STM and IETS-STM images can deliver information about intramolecular charge transfer for molecules deposited on a surface. To demonstrate this, we extended our numerical model by taking into the account the electrostatic force acting between the decorated tip and surface Hartree potential.PACS numbers: 68.37. Ef, 68.37.Ps, 68.43.Fg One of the most exciting and significant breakthroughs in field of scanning probe microscopy (SPM) in last years is undoubtedly the achievement of high-resolution STM [1] and AFM [2] images of molecular structures with functionalized tips [3,4]. In general, the high-resolution images, being typically acquired in the regime where the tip-surface interaction becomes repulsive, are characterized by a presence of sharp features in both intra and intermolecular regions. The sharp ridges observed in the intramolecular region often mimics the internal molecular structure [5], with only few exceptions [6,7]. The capability of AFM/STM to resolve internal atomic and chemical structure in real space opened new horizons for the characterization of molecules and surfaces [5,[8][9][10][11][12][13][14][15] at atomic scale.The origin of high resolution of molecular structures in AFM has been attributed to Pauli repulsion [2,16] and the bending of the functionalized tip apex [5]. Recently, we introduced a numerical model [7] which provides a unified insight into the detailed mechanism of the high resolution imaging with decorated tips in both AFM and STM. According to the model, the decorated tip apex acts as an atomistic force sensor that responds with significant relaxations of the decorating particle (probe particle) towards local minima of the tip-sample interaction potential at close distances. The relaxations cause discontinuities in both the frequency shift and the tunneling current signals and thus become observable in AFM and STM images as sharp contrast features. Although the model was originally used to confirm the decisive role of Pauli repulsion in the high-resolution STM and AFM imaging of molecular structures done with functionalized tips, it must be noted that imaging of other types of interactions (e.g. electrostatic) should also be possible [5]. Namely, the influence of intramo...

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Origin of High-Resolution IETS-STM Images of Organic Molecules with Functionalized Tips

et al. 2014

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“…2 shows that dosing 1 L H 2 at 10 K leads to a drop of the adsorbates apparent height from (330 ± 16) in (a) to (110 ± 20) pm in (b), clearly identifying the latter as the hydrogenated species. In addition to the Ti adsorbates, the STM images show h-BN point defects (one has been labeled d) that exhibit a marked contrast inversion upon hydrogen adsorption, presumably due to a H atom in the tunnel junction [5,6]. The line defect in Fig.…”

Section: Hydrogen Dosagementioning

confidence: 99%

“…Examples are the coverage dependent inelastic excitations detected in the differential conductance (dI/dV) of physisorbed hydrogen on a copper surface [2], the emergence of vibrational excitations in dI/dV for hydrogenated La, Cr, and Ce adatoms on Ag(100) [3], as well as the alteration of the magnetic characteristics (Kondo effect) of Co adatoms on Pt(111) upon hydrogen uptake [4]. Furthermore, molecular hydrogen was also studied for its role in providing ultra-high geometrical resolution in STM topographs [5,6].…”

Section: Introductionmentioning

confidence: 99%

Quantifying residual hydrogen adsorption in low-temperature STMs

2013

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We report on low-temperature scanning tunneling microscopy observations demonstrating that individual Ti atoms on hexagonal boron nitride dissociate and adsorb hydrogen without measurable reaction barrier. The clean and hydrogenated states of the adatoms are clearly discerned by their apparent height and their differential conductance revealing the Kondo effect upon hydrogenation. Measurements at 50 K and 5 × 10 −11 mbar indicate a sizable hydrogenation within only 1 h originating from the residual gas pressure, whereas measurements at 4.7 K can be carried out for days without H 2 contamination problems. However, heating up a low-T STM to operate it at variable temperature results in very sudden hydrogenation at around 17 K that correlates with a sharp peak in the total chamber pressure. From a quantitative analysis we derive the desorption energies of H 2 on the cryostat walls. We find evidence for hydrogen contamination also during Ti evaporation and propose a strategy on how to dose transition metal atoms in the cleanliest fashion. The present contribution raises awareness of hydrogenation under seemingly ideal ultra-high vacuum conditions, it quantifies the H 2 uptake by isolated transition metal atoms and its thermal desorption from the gold plated cryostat walls.

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“…This idea has been already picked up successfully for scanning probe techniques by using functionalized tips for high resolution experiments on molecules. [7][8][9] .…”

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Local transport measurements on epitaxial graphene

Baringhaus

Edler

Neumann

et al. 2013

Applied Physics Letters

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Growth of large-scale graphene is still accompanied by imperfections. By means of a four-tip STM/SEM the local structure of graphene grown on SiC(0001) was correlated with scanning electron microscope images and spatially resolved transport measurements. The systematic variation of probe spacings and substrate temperature has clearly revealed two-dimensional transport regimes of Anderson localization as well as of diffusive transport. The detailed analysis of the temperature dependent data demonstrates that the local on-top nano-sized contacts do not induce significant strain to the epitaxial graphene films.

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Imaging Pauli Repulsion in Scanning Tunneling Microscopy

Cited by 151 publications

References 23 publications

Origin of High-Resolution IETS-STM Images of Organic Molecules with Functionalized Tips

Origin of High-Resolution IETS-STM Images of Organic Molecules with Functionalized Tips

Quantifying residual hydrogen adsorption in low-temperature STMs

Local transport measurements on epitaxial graphene

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