Low-force spectroscopy on graphene membranes by scanning tunneling microscopy

Uder, B.; Gao, Hongze; Kunnas, Peter; Jonge, Niels de; Hartmann, Uwe

doi:10.1039/c7nr07300c

Cited by 12 publications

(11 citation statements)

References 30 publications

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“…Many studies [23][24][25][26] experimentally characterizing Y obtain it by measuring E 2D , then back-calculating Y using equation (1). One group [27] experimentally measured D of multi-layered graphene (  L 8 c ), and found that it obeys equation (2), when Y is obtained as above.…”

Section: Computational Techniques: Ce Modelmentioning

confidence: 99%

Shapes of Fe nanocrystals encapsulated at the graphite surface

et al. 2020

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We describe and analyze in detail the shapes of Fe islands encapsulated under the top graphene layers in graphite. Shapes are interrogated using scanning tunneling microscopy. The main outputs of the shape analysis are the slope of the graphene membrane around the perimeter of the island, and the aspect ratio of the central metal cluster. Modeling primarily uses a continuum elasticity (CE) model. As input to the CE model, we use density functional theory to calculate the surface energy of Fe, and the adhesion energies between Fe and graphene or graphite. We use the shaft-loaded blister test (SLBT) model to provide independent stretching and bending strain energies in the graphene membrane. We also introduce a model for the elastic strain in which stretching and bending are treated simultaneously. Measured side slopes agree very well with the CE model, both qualitatively and quantitatively. The fit is optimal for a graphene membrane consisting of 2-3 graphene monolayers, in agreement with experiment. Analysis of contributions to total energy shows that the side slope depends only on the properties of graphene/graphite. This reflects delamination of the graphene membrane from the underlying graphite, caused by upward pressure from the growing metal cluster. This insight leads us to evaluate the delamination geometry in the context of two related, classic models that give analytic results for the slope of a delaminated membrane. One of these, the point-loaded circular blister test model, reasonably predicts the delamination geometry at the edge of an Fe island. The aspect ratio also agrees well with the CE model in the limit of large island size, but not for small islands. Previously, we had speculated that this discrepancy was due to lack of coupling between bending and stretching in the SLBT model, but the new modeling shows that this explanation is not viable. metal. This is challenging, since 2D materials have intrinsically low surface energies, so metals tend to grow on top of them as 3D clusters [7]. It is therefore attractive to consider synthesis strategies wherein metal morphologies are kinetically-limited [8], or the metal morphology is constrained (and stabilized) by intercalation, to promote the 2D morphology.Elsewhere, we have reported that metal nanoclusters can be synthesized at the surface of the 3D van der Waals material, graphite, in an intercalated form if two conditions are met [9][10][11][12]. First, the graphite surface must be ion bombarded to introduce defects that can act as entry portals for the metal atoms. Second, the graphite must be held at relatively high temperature while the metal is deposited, so that portals do not become blocked by growing metal clusters. Under these two conditions, we observe stable metal nanoclusters that are encapsulated beneath the graphite surface. Depending on the metal, they are a few atomic layers to hundreds of atomic layers tall, and about ten to hundreds of nm wide. We have reported the growth conditions and characteristics of such clusters in detail fo...

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Section: Computational Techniques: Ce Modelmentioning

confidence: 99%

Shapes of Fe nanocrystals encapsulated at the graphite surface

et al. 2020

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“…16 For Y, a significant amount of variation is present among literature reports. Y has been characterized by a number of methods; 15,[20][21][22][23][24] of these, methods that use atomic force microscopy to deform a region of freestanding graphene most closely resemble the geometry and loading in the present work, pointing to Y ∼1 TPa. 15,21,22 One of these studies showed that Y increases and then decreases as a function of defect density in graphene.…”

Section: U-termmentioning

confidence: 99%

Squeezed nanocrystals: equilibrium configuration of metal clusters embedded beneath the surface of a layered material

et al. 2019

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“…AFM indentation measurements record values of k which reduce away from the edge of the void towards a minimum when suspended graphene is furthest from boundary clamping [31]. Our method lifts the graphene away from the surface and if the graphene-substrate forces which create the boundary clamping were reduced, we may measure lower values of k. If after deposition there is slack in the graphene layers, this too would reduce the apparent stiffness [8].…”

Section: Voltage-dependent Manipulationmentioning

confidence: 99%

“…Scanning tunneling microscopy (STM) is an ideal tool to both measure and manipulate graphene and other 2D materials by using the interaction of the probe to pull and push the graphene layers, simultaneously loading and measuring the electronic response [5][6][7]. As well as inducing and stretching ripples normal to the graphene plane, STM can also be used to perform stress-strain measurements on graphene, offering greater insights into its behavior when used in flexible electronics [8,9].…”

Section: Introductionmentioning

confidence: 99%

The voltage-dependent manipulation of few-layer graphene with a scanning tunneling microscopy tip

Alyobi

Barnett

Muratov

et al. 2020

Carbon

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Strain and deformation alter the electronic properties of graphene, offering the possibility to control its transport behavior. The tip of a scanning tunneling microscope is an ideal tool to mechanically perturb the system locally while simultaneously measuring the electronic response. Here we stretch few-and multi-layer graphene membranes supported on SiO2 substrates and suspended over voids. An automated approach-retraction method stably traces the graphene deflection hysteresis curve hundreds of times across four samples, measuring the voltage-dependent stretching, from which we extract the hysteresis width. Using a force-balance model, we are able to reproduce the voltage-dependent hysteretic graphene extension behavior. We directly observe a voltage-dependent interplay where electrostatic forces dominate at high voltage and van der Waals forces at low voltage. The relative contribution of each force is dependent on the graphene and tunneling resistance, giving rise to different observed voltage-dependent behavior between samples. Understanding the voltage dependence of these forces impacts scanning probe measurement of 2D materials and informs oscillating graphene device design where similar forces act from the side walls of cavities, leading towards strain engineering of layered 2D systems.

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Low-force spectroscopy on graphene membranes by scanning tunneling microscopy

Cited by 12 publications

References 30 publications

Shapes of Fe nanocrystals encapsulated at the graphite surface

Shapes of Fe nanocrystals encapsulated at the graphite surface

Squeezed nanocrystals: equilibrium configuration of metal clusters embedded beneath the surface of a layered material

The voltage-dependent manipulation of few-layer graphene with a scanning tunneling microscopy tip

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