Local Spectroscopy and Atomic Imaging of Tunneling Current, Forces, and Dissipation on Graphite

Hembacher, Stefan; Giessibl, Franz J.; Mannhart, J.; Quate, C. F.

doi:10.1103/physrevlett.94.056101

Cited by 113 publications

(100 citation statements)

References 28 publications

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“…At closer distances, we enter the repulsive part of the interaction for the top site and a crossing between force curves takes place, leading to an inversion of the image contrast. These changes in the topography images (from honeycomb to hexagonal) with the tip-sample distance have been experimentally observed in graphite [7,19]. We expect the same contrast inversion on materials with similarly high surface atomic densities like closed-pack metallic surfaces [32].…”

Section: Prl 106 176101 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 72%

“…According to simulations using Lennard-Jones potentials to describe the van der Waals (vdW) interaction between the atoms in the Si tip and the sample, these attractive force maxima do not correspond to any of the atoms but to the hollow sites [4]. Graphite was later reexamined with a new approach to the FM-AFM that uses a metallic tip attached to one of the arms of a tuning fork as the sensing element [5,19]. The high stiffness (k $ 2000 N=m) makes it possible to operate the microscope with a small oscillation amplitude.…”

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confidence: 99%

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Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

et al. 2011

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First-principles calculations show that the rich variety of image patterns found in carbon nanostructures with the atomic force and scanning tunneling microscopes can be rationalized in terms of the chemical reactivity of the tip and the distance range explored in the experiments. For weakly reactive tips, the Pauli repulsion dominates the atomic contrast and force maxima are expected on low electronic density positions as the hollow site. With reactive tips, the interaction is strong enough to change locally the hybridization of the carbon atoms, making it possible to observe atomic resolution in both the attractive and the repulsive regime although with inverted contrast. Regarding STM images, we show that in the near-contact regime, due to current saturation, bright spots correspond to hollow positions instead of atomic sites, providing an explanation for the most common hexagonal pattern found in the experiments. Fullerenes, nanotubes, graphene, and carbon nanoribbons are among the most promising materials for nanotechnological applications due to their unique mechanical and electronic properties [1,2]. Turning these expectations into real-world devices requires tools like the STM and the atomic force microscope (AFM) with true atomic resolution (FM-AFM) [3] to visualize, characterize, and manipulate these materials at the atomic scale. However, in spite of the apparent simplicity of the common honeycomb structure and the long-standing experimental research effort, we do not know yet something as fundamental as whether the maxima in the scanning probe microscopy images correspond to atoms or to the hollow sites [4][5][6][7]. Here, we use first-principles calculations to show that the rich variety of AFM and STM image patterns found in carbon nanostructures can be rationalized in terms of the chemical reactivity of the tip and the distance range explored in the experiments.The first STM images of the graphite(0001) surface did not display the expected honeycomb pattern but a hexagonal arrangement of bright spots (topographic maxima; see Fig. 1 in [8]) [9][10][11]. The accepted interpretation relies on a subtle electronic effect [12]. The Bernal stacking makes the two surface atoms inequivalent. C atoms, with a nearest neighbor right below in the second layer, do not contribute significantly to the density of states close to the Fermi level, and only the C atoms are imaged as bright spots at low bias voltages. Although a honeycomb pattern should be recovered for larger biases, the experimental evidence accumulated over the past 25 years [9][10][11][12][13] shows that STM images with a hexagonal pattern are overwhelmingly recorded over a broad range of bias voltages and distance operation conditions. Nevertheless, several groups have reported honeycomb patterns even for small bias voltage [13][14][15][16][17].The FM-AFM, relying on the forces between the tip and surface, is expected not to be so sensitive to electronic effects and to reflect the real atomic structure of the surface. However, the first reported ...

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Section: Prl 106 176101 (2011) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 72%

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confidence: 99%

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

et al. 2011

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“…However, they fail to reproduce the moiré contrast in the attractive regime and the dissipation in the experiments. It has been proposed that in STM or AFM experiments on layered materials as graphite, the tips could detach large areas of the last layer from the underneath substrate [9,44,45]. This tip-induced detaching could explain our dissipation signal: during tip approach, G is attached to the substrate, but, upon tip retraction, G locally adheres to the tip temporally, inducing a large-scale deformation of the sheet.…”

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confidence: 98%

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy

et al. 2016

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We show that noncontact atomic force microscopy (AFM) is sensitive to the local stiffness in the atomicscale limit on weakly coupled 2D materials, as graphene on metals. Our large amplitude AFM topography and dissipation images under ultrahigh vacuum and low temperature resolve the atomic and moiré patterns in graphene on Pt(111), despite its extremely low geometric corrugation. The imaging mechanisms are identified with a multiscale model based on density-functional theory calculations, where the energy cost of global and local deformations of graphene competes with short-range chemical and long-range van der Waals interactions. Atomic contrast is related with short-range tip-sample interactions, while the dissipation can be understood in terms of global deformations in the weakly coupled graphene layer. Remarkably, the observed moiré modulation is linked with the subtle variations of the local interplanar graphene-substrate interaction, opening a new route to explore the local mechanical properties of 2D materials at the atomic scale. DOI: 10.1103/PhysRevLett.116.245502 Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are tools of choice for characterizing the unique mechanical and electronic properties of graphene (G) and other 2D materials. Dynamic AFM [1] in the frequency modulation (FM) mode [2] has resolved the true geometric structure of a broad range of materials [3][4][5]. FM AFM experiments on carbon-based materials [6][7][8][9][10][11][12][13] show atomic contrast in Δf images and, depending on the setup, in the dissipation channel. While the origin of the dissipation is not well understood, the Δf contrast has been linked with the nature of the tip-sample interaction [14].G properties can be efficiently tuned by the interaction with metals [15,16]. The interaction strength varies widely from the strong coupling with Rh [17,18] and Ru [19] to the weak limit (Ir [20], Pt [21]), where G retains its unique electronic properties [22]. The different lattice parameters of G and the metal underneath are accommodated through the formation of commensurate structures known as moiré patterns, where C atoms become inequivalent due to their different bonding configuration with the metal. The resulting "true" topographic corrugation of G-the difference in height among the topmost and the bottom C atom-varies widely, even in the weakly interacting cases, where it ranges from ≈50 pm on Ir [23,24] to practically flat (≤ 3 pm) on Pt [21].While STM can easily resolve these moiré patterns, even in the G=Pt case [21,25], AFM experiments have only been reported in highly corrugated cases as Ru [26], Rh [27], and Ir [12,28]. Focusing on the most challenging case, G=Ir, experiments with a Kolibri sensor using a W tip clearly resolved the moiré in constant height (CH) AFM images [28]. Measurements with a tuning fork using both inert (CO-terminated) and reactive (Ir-terminated) tips [12] were able to identify the atoms with both tips at any tip-sample distance. This atomic-scale resolution allowed the ...

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“…The "qPlus sensor," a sensor built from a quartz tuning fork where one prong is fixed to some substrate and the other to which a tip is attached serves as a self-sensing cantilever, 1-4 has raised increased interest in the past years. While the first applications of qPlus showed an increased spatial resolution 5,6 and simultaneous scanning tunneling microscopy ͑STM͒ and atomic force microscopy ͑AFM͒ operation, 6,7 later applications demonstrated the capability to measure the forces that act in atomic manipulation on a piconewton scale, 8 the threedimensional distribution of short range chemical forces on graphite, 9 surface properties of oxides, 10 the measurement of single electronic charges on single atoms, 11 and the resolving of the full structure of an organic molecule that is weakly adsorbed to a surface. 12 While all these experiments were performed at the fundamental flexural eigenmode of the qPlus sensor, recently 300 kHz operation at the second flexural eigenmode on a modified qPlus sensor 13 was reported at Omicron Nanotechnology.…”

Section: Introductionmentioning

confidence: 99%

Higher-order eigenmodes of qPlus sensors for high resolution dynamic atomic force microscopy

Tung

Wutscher

Martínez-Martín

et al. 2010

Journal of Applied Physics

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The time response of tuning-fork based sensors can be improved by operating them at higher eigenmodes because a measurement takes at least one oscillation cycle in dynamic force microscopy and the oscillation period of the second eigenmode is only about one sixth of the fundamental mode. Here we study the higher-order eigenmodes of quartz qPlus sensors ͓Bettac et al., Nanotechnology 20, 264009 ͑2009͒; Giessibl and Reichling, Nanotechnology 16, S118 ͑2005͒; Giessibl, Appl. Phys. Lett. 76, 1470 ͑2000͒; and Giessibl, Appl. Phys. Lett. 73, 3956 ͑1998͔͒, their equivalent stiffness, and piezoelectric sensitivity, while paying special attention to the influence of the mass and rotary inertia of the sensing tip which is attached to the end of the qPlus quartz cantilever. A combination of theoretical modeling and scanning laser Doppler vibrometry is used to study the eigenmodes of qPlus sensors with tungsten tips. We find that the geometry of tungsten tips can greatly influence the shape, equivalent stiffness, and piezoelectric sensitivity of the second eigenmode of the quartz cantilever. At a critical tip length it is possible to theoretically achieve infinite equivalent stiffness and infinite piezoelectric sensitivity when the tip becomes a perfect node of vibration and beyond this critical tip length the second eigenmode loses its vibration node and the trajectory of the tip reverses with respect to the beam curvature. The findings have major implications for optimizing tip geometry for high-resolution imaging with qPlus sensors using higher eigenmodes.

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Local Spectroscopy and Atomic Imaging of Tunneling Current, Forces, and Dissipation on Graphite

Cited by 113 publications

References 28 publications

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

Forces and Currents in Carbon Nanostructures: Are We Imaging Atoms?

Atomic-Scale Variations of the Mechanical Response of 2D Materials Detected by Noncontact Atomic Force Microscopy

Higher-order eigenmodes of qPlus sensors for high resolution dynamic atomic force microscopy

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