A convenient method for large-scale STM mapping of freestanding atomically thin conductive membranes

Uder, B.; Hartmann, Uwe

doi:10.1063/1.4985003

Cited by 3 publications

(1 citation statement)

References 21 publications

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“…Both the ECT and MCT experiments confirm that the observed trace in an AFM scan of a suspended membrane does not show the static configuration of the membrane (as it would be without the probe), but rather, a trace of how far the membrane can be displaced at each point. A membrane can be pulled by long range electrostatic forces or pushed by short range repulsive forces acting between the tip and the sample 20,25,27,[37][38][39] , depending in the case of STM on the tunneling parameters, and in the case of the AFM on the force setpoint (contact mode) or damping setpoint (tapping mode). During an AFM or STM scan, these forces deflect the membrane as far as it is possible without the introduction of significant in-plane strain (for the estimate of strain see supplementary information).…”

Section: Discussionmentioning

confidence: 99%

New imaging modes for analyzing suspended ultra-thin membranes by double-tip scanning probe microscopy

Elibol

Hummel

Bayer

et al. 2020

Sci Rep

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Scanning probe microscopy (SpM) techniques are amongst the most important and versatile experimental methods in surface-and nanoscience. Although their measurement principles on rigid surfaces are well understood and steady progress on the instrumentation has been made, SPM imaging on suspended, flexible membranes remains difficult to interpret. Due to the interaction between the SPM tip and the flexible membrane, morphological changes caused by the tip can lead to deformations of the membrane during scanning and hence significantly influence measurement results. On the other hand, gaining control over such modifications can allow to explore unknown physical properties and functionalities of such membranes. Here, we demonstrate new types of measurements that become possible with two SPM instruments (atomic force microscopy, AFM, and scanning tunneling microscopy, STM) that are situated on opposite sides of a suspended two-dimensional (2D) material membrane and thus allow to bring both SPM tips arbitrarily close to each other. One of the probes is held stationary on one point of the membrane, within the scan area of the other probe, while the other probe is scanned. This way new imaging modes can be obtained by recording a signal on the stationary probe as a function of the position of the other tip. The first example, which we term electrical crosstalk imaging (ECT), shows the possibility of performing electrical measurements across the membrane, potentially in combination with control over the forces applied to the membrane. Using ECT, we measure the deformation of the 2D membrane around the indentation from the AFM tip. In the second example, which we term mechanical cross-talk imaging (MCT), we disentangle the mechanical influence of a scanning probe tip (e.g. AFM) on a freestanding membrane by means of independently recording the response of the opposing tip. In this way we are able to separate the tip-induced membrane deformation topography from the (material-dependent) force between the tip and the membrane. Overall, the results indicate that probing simultaneously both surfaces of ultra-thin membranes, such as suspended 2D materials, could provide novel insights into the electronic properties of the materials.Scanning probe microscopes (SPMs) using small physical probes have become highly versatile tools for imaging and manipulation on rigid surfaces due to the many different types of interaction between the probe and the object that can be exploited. SPMs are typically able to map different types of forces, electric fields, currents, thermo power, and many other features of the sample, depending on the structure and materials of the tips and operation and feedback mode during the scan 1,2 . SPMs are also often used for nanoscale manipulation 3,4 , scanning probe lithography 5 and electric contacting on very small areas 6 . Especially for the latter two purposes, multi-probe SPMs have become popular 7 . In this way, transport over very short length scales has been achieved 8-13 , however, the distance betw...

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Section: Discussionmentioning

confidence: 99%

New imaging modes for analyzing suspended ultra-thin membranes by double-tip scanning probe microscopy

Elibol

Hummel

Bayer

et al. 2020

Sci Rep

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Low-force spectroscopy on graphene membranes by scanning tunneling microscopy

et al. 2018

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Two-dimensional atomically flat sheets with a high mechanical flexibility are very attractive as ultrathin membranes but are also inherently challenging for microscopic investigations. We report on a method using Scanning Tunneling Microscopy (STM) under ultra-high vacuum conditions for non-indenting low-force spectroscopy on micrometer-sized freestanding graphene membranes. The method is based on applying quasi-static voltage ramps with active feedback at low tunneling currents and ultimately relies on the attractive electrostatic force between the tip and the membrane. As a result a bulge-test scenario can be established. The convenience and simplicity of the method relies on the fact that the loading force and the membrane deflection detection are both provided simultaneously by the STM. This permits the continuous measurement of the stress-strain relation. Electrostatic forces applied are typically below 1 nN and the membrane deflection is detected at sub-nanometer resolution. Experiments on single-layer graphene membranes with a strain of 0.1% reveal a two-dimensional elastic modulus E = 220 N m.

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