Simulated Adhesion between Realistic Hydrocarbon Materials: Effects of Composition, Roughness, and Contact Point

Ryan, Kathleen E.; Keating, Pamela L.; Jacobs, Tevis D. B.; Grierson, David S.; Turner, Kevin T.; Carpick, Robert W.; Harrison, Jeffrey S.

doi:10.1021/la404342d

Cited by 38 publications

(45 citation statements)

References 54 publications

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“…This results in a supplemental work of adhesion term, which includes the effects of topography as well as the contribution to adhesion from covalent bonds at the interface, both of which can change during loading or sliding. However, other studies showed that continuum contact mechanics may break down at the atomic scale [23][24][25][26][27]. Further, due to the discreteness of atoms at the contact interface, the definition of contact is ambiguous at the atomic scale, which complicates comparison to continuum mechanics predictions [20,28,29].…”

Section: Introductionmentioning

confidence: 99%

Matching Atomistic Simulations and In Situ Experiments to Investigate the Mechanics of Nanoscale Contact

et al. 2019

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Many emerging devices and technologies rely on contacts between nanoscale bodies. Recent analytical theories, experiments, and simulations of nanocontacts have made conflicting predictions about the mechanical response as these contacts are loaded and separated. The present investigation combined in situ transmission electron microscopy (TEM) and molecular dynamics (MD) simulation to study the contact between a flat diamond indenter and a nanoscale silicon tip. The TEM was used to pre-characterize the materials, such that an atomistic model tip could be created with identically matched materials, geometry, crystallographic orientation, loading conditions, and degree of amorphization. A large work of adhesion was measured in the experiment and attributed to unpassivated surfaces and a large compressive stress applied before separation, resulting in covalent bonding across the interface. The simulations modeled atomic interactions across the interface using a Buckingham potential in order to reproduce the experimental work of adhesion without explicitly modeling covalent bonds, thereby enabling larger time-and length-scale simulations than would be achievable with a reactive potential. Then, the experimental and simulation tips were loaded under similar conditions with real-time measurement of contact area and deformation, yielding three primary findings. First, the results demonstrated that significant variation in the value of contact area can be obtained from simulations, depending on the technique used to determine it. Therefore, care is required in comparing measured values of contact area between simulations and experiments. Second, the contact area and deformation demonstrated significant hysteresis, with larger values measured upon unloading as compared to loading. Therefore, continuum predictions, in the form of a Maugis-Dugdale contact model, could not be fit to full loading/unloading curves. Third, the loaddependent contact area could be accurately fit by allowing the work of adhesion in the continuum model to increase with applied force from 1.3 to 4.3 J/m 2. The most common mechanisms for hysteretic behavior-which are viscoelasticity, capillary interactions, and plasticity-can be ruled out using the TEM and atomistic characterization. Stress-dependent formation of covalent bonds is suggested as a physical mechanism to describe these findings, which is qualitatively consistent with trends in the areal density of in-contact atoms as measured in the simulation. The implications of these results for real-world nanoscale contacts are that significant hysteresis may cause significant and unexpected deviations in contact size, even for nominally elastic contacts.

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Section: Introductionmentioning

confidence: 99%

Matching Atomistic Simulations and In Situ Experiments to Investigate the Mechanics of Nanoscale Contact

et al. 2019

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“…Hydrogenated amorphous carbon contains a higher fraction of sp 2 carbon and therefore will behave differently from single-crystal diamond. With regard to dispersion forces specifi cally, [ 52 ] a-C:H has a lower number density of atoms as compared to singlecrystal diamond, but the electrical conductivity is much higher, as is the polarizability of atoms. The surface termination and amount of hydrogen on the surface have also been shown to have an effect on work of adhesion.…”

Section: Comparing Work Of Adhesion To Previously Proposed Valuesmentioning

confidence: 99%

Measurement of the Length and Strength of Adhesive Interactions in a Nanoscale Silicon–Diamond Interface

Jacobs¹,

Lefever²,

Carpick³

2015

Adv Materials Inter

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the interaction (characterized by the range of adhesion z 0 ).The intrinsic work of adhesion W adh is the energy per unit area required to separate two planar surfaces from equilibrium contact to infi nite separation. In terms of surface energy (γ i of surface i ) and interfacial energy (γ ij between surfaces i and j ), the work of adhesion is calculated as follows:In accordance with prior literature on adhesion and roughness, [ 9 ] the intrinsic work of adhesion W adh,int is defi ned as the work of adhesion between two perfectly fl at, planar surfaces. While W adh,int is a continuum concept, it can be robustly mapped onto an atomistic description of two atomically fl at, single-crystal surfaces in contact. The effective work of adhesion, W adh,eff , is defi ned as the work of adhesion for the same material pair and the same global geometry (planar), but with the addition of local surface roughness on one or both surfaces. The distinction between W adh,int and W adh,eff is shown schematically in Figure 1 . The W adh,int is determined by the identity of the materials in contact, and the environment, whereas W adh,eff is a function of W adh,int and the local surface topography. For hard, non-conforming materials, W adh,eff is typically much smaller than W adh,int . The primary reason for this is that the roughness increases the effective separation between the two materials, and therefore signifi cantly increases γ ij between the materials as they can no longer make intimate contact. Roughness can also increase the surface energies γ i and γ j , but this effect is typically overwhelmed by the change in γ ij . This distinction is drawn because many experimental techniques exist to measure W adh,eff (for example, using microfabricated beam tests [ 10 ] ), but generally applicable techniques to deduce from this the W adh,int are not well established.Physically, z 0 describes the equilibrium separation distance between perfectly fl at surfaces, i.e., the separation distance at which their interaction force is zero. However, in many mathematical descriptions of adhesion (for instance, refs. [ 5,7,8,11 ] ) z 0 also scales the distance over which adhesion acts for a particular material. Therefore, the parameter z 0 is referred to in this paper as the "range of adhesion," (in accordance with Greenwood, [ 5 ] who calls it the "range of action of the surface forces").The adhesive interactions between nanoscale silicon atomic force microscope (AFM) probes and a diamond substrate are characterized using in situ adhesion tests inside of a transmission electron microscope (TEM). In particular, measurements are presented both for the strength of the adhesion acting between the two materials (characterized by the intrinsic work of adhesion W adh,int ) and for the length scale of the interaction (described by the range of adhesion z 0 ). These values are calculated using a novel analysis technique that requires measurement of the AFM probe geometry, the adhesive force, and the position where the snap-in instability occurs. Values ...

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“…It was reported that the adhesion hysteresis took place with the occurrence of plastic deformation when the yield point was passed during loading . The hysteresis could originate from the formation of the covalent bonds between the flat plate and asperities during contact process, and larger forces are required to separate the atoms forming the covalent bonds . Representative snapshots for the simulated systems when the plate is brought into contact and pulled back from the substrate with six asperities (shielded by the front ones three asperities cannot be seen; asperity height: 10 Å) are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Nano‐adhesion and friction of multi‐asperity contact: a molecular dynamics simulation study

Wang

Xie

et al. 2015

Surface & Interface Analysis

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aIn our study, the contact and sliding processes between a flat plate and a substrate with multiple asperities are studied by molecular dynamics (MD) simulations, and how the number of asperities and asperity height influence the adhesion force and friction force are investigated thoroughly. The normal force versus the separation distance curve during contact processes is analyzed completely and from which the van der Waals (vdW) force (F vdW ) and the adhesion force (F adh ) are obtained and compared with the Katainen model. The adhesion force and the friction force increase linearly as the increase of the number of asperities (i.e. real contact area) with same asperity height. With the identical number of asperities, the adhesion force and the friction force decrease with the increase of the asperity height at first. However the reductions of the adhesion force and the friction force become less obvious, when the asperity height is larger than a critical value (20 Å for our simulation parameters).

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Simulated Adhesion between Realistic Hydrocarbon Materials: Effects of Composition, Roughness, and Contact Point

Cited by 38 publications

References 54 publications

Matching Atomistic Simulations and In Situ Experiments to Investigate the Mechanics of Nanoscale Contact

Matching Atomistic Simulations and In Situ Experiments to Investigate the Mechanics of Nanoscale Contact

Measurement of the Length and Strength of Adhesive Interactions in a Nanoscale Silicon–Diamond Interface

Nano‐adhesion and friction of multi‐asperity contact: a molecular dynamics simulation study

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