Nanoindentation of model diamond nanocomposites: Hierarchical molecular dynamics and finite-element simulations

Pearson, James; Gao, Guangtu; Zikry, M. A.; Harrison, Jeffrey S.

doi:10.1016/j.commatsci.2009.06.007

Cited by 15 publications

(15 citation statements)

References 69 publications

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“…There is also evidence for noncontinuum behavior from atomistic simulations of other materials (besides soft metals). Simulations of small-radii diamond indenters showed that the contact area calculated from the simulation was consistently larger than that predicted by continuum contact mechanics models [102,107,113]. The difference between atomistic and continuum contact areas is typically attributed to the fact that the simulations violate the assumptions on which the continuum contact theories are based.…”

Section: Simulation Support For Atomisticmentioning

confidence: 91%

“…Some models explicitly include grain boundaries [89,113], which further improves the accuracy of the simulation for some materials. Other features that have been included in nanocontact simulations are near-surface material amorphization [103] and oxygen or hydrogen surface termination [106,107,[112][113][114]. Finally, in cases where the tip and/or substrate contain roughness, this too may affect nanocontact behavior.…”

Section: Defining Modelmentioning

confidence: 99%

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Measuring and Understanding Contact Area at the Nanoscale: A Review

Jacobs

Martini

2017

Applied Mechanics Reviews

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The size of the mechanical contact between nanoscale bodies that are pressed together under load has implications for adhesion, friction, and electrical and thermal transport at small scales. Yet, because the contact is buried between the two bodies, it is challenging to accurately measure the true contact area and to understand its dependence on load and material properties. Recent advancements in both experimental techniques and simulation methodologies have provided unprecedented insights into nanoscale contacts. This review provides a detailed look at the current understanding of nanocontacts. Experimental methods for determining contact area are discussed, including direct measurements using in situ electron microscopy, as well as indirect methods based on measurements of contact resistance, contact stiffness, lateral forces, and topography. Simulation techniques are also discussed, including the types of nanocontact modeling that have been performed and the various methods for extracting the magnitude of the contact area from a simulation. To describe and predict contact area, three different theories of nanoscale contact are reviewed: single-contact continuum mechanics, multiple-contact continuum mechanics, and atomistic accounting. Representative results from nanoscale experimental and simulation investigations are presented in the context of these theories. Finally, the critical challenges are described, as well as the opportunities, on the path to establishing a fundamental and actionable understanding of what it means to be “in contact” at the nanoscale.

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Section: Simulation Support For Atomisticmentioning

confidence: 91%

Section: Defining Modelmentioning

confidence: 99%

Measuring and Understanding Contact Area at the Nanoscale: A Review

Jacobs

Martini

2017

Applied Mechanics Reviews

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“…The amorphous carbon sample attached to C(001) is hydrogen-free and contains 80.6% sp 2 -hybridized carbon ( Table 1). The MDN surfaces were generated by inserting sixteen H-terminated diamond (111) and (110) grains into an amorphous carbon matrix [39]. Although the identity and number of each type of grain embedded in the matrix were the same, the location and tilt varied so that films of different roughnesses were created.…”

Section: Simulation Methodsmentioning

confidence: 99%

“…Although the identity and number of each type of grain embedded in the matrix were the same, the location and tilt varied so that films of different roughnesses were created. The average root-mean-square (RMS) roughness on MDN2 and MDN1 are given in Table 1 [39]. Snapshots of the samples are shown in Fig.…”

Section: Simulation Methodsmentioning

confidence: 99%

“…Nonetheless, it should be noted that because carbon and hydrogen have similar electronegativities, partial charges were not included in the REBO or the AIREBO potentials. Both the REBO and the AIREBO potentials have been used successfully to model mechanical properties of filled [41,42] and unfilled [43] nanotubes, properties of clusters [44], indentation and contact [15,16,22,39,45], the tribology of diamond [22,33,38,[46][47][48] and DLC [17,18,37,49], stress at grain boundaries [50], and friction and polymerization of model self-assembled monolayers [51][52][53][54][55].…”

Section: Simulation Methodsmentioning

confidence: 99%

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Atomistic Factors Governing Adhesion between Diamond, Amorphous Carbon and Model Diamond Nanocomposite Surfaces

Piotrowski

Cannara

Gao

et al. 2010

Journal of Adhesion Science and Technology

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Complementary atomic force microscopy (AFM) measurements and molecular dynamics (MD) simulations were conducted to determine the work of adhesion for diamond (C)(111)(1 × 1) and C(001)(2 × 1) surfaces paired with carbon-based materials. While the works of adhesion from experiments and simulations are in reasonable agreement, some differences were identified. Experimentally, the work of adhesion between an amorphous carbon tip and individual C(001)(2 × 1)-H and C(111)(1 × 1)-H surfaces yielded adhesion values that were larger on the C(001)(2 × 1)-H surface. The simulations revealed that the average adhesion between self-mated C(001)(2×1) surfaces was smaller than for self-mated C(111)(1×1) contacts. Adhesion was reduced when amorphous carbon counterfaces were paired with both types of diamond surfaces. Pairing model diamond nanocomposite surfaces with the C(111)(1 × 1)-H sample resulted in even larger reductions in adhesion. These results point to the importance of atomic-scale roughness for adhesion. The simulated adhesion also shows a modest dependence on hydrogen coverage. Density functional theory calculations revealed small, C-H bond dipoles on both diamond samples, with the C(001)(2 × 1)-H surface having the larger dipole, but having a smaller dipole moment per unit area. Thus, charge separation at the surface is another possible source of the difference between the measured and calculated works of adhesion. of hydrogen into DLC films was shown to reduce friction in self-mated DLC-DLC contacts [18].By definition, the work of adhesion (W ) is the energy per unit area required to separate two semi-infinite surfaces from their equilibrium separation to infinity. For two dissimilar materials, this quantity is equivalent to a sum of the surface energies, γ 1 and γ 2 , of the two surfaces (because, effectively, the separation process creates the two surfaces), minus the interfacial energy, γ 12 . Hence, W = γ 1 + γ 2 − γ 12 , where W is also known as the Dupré energy of adhesion. To control adhesion forces between two materials, the work of adhesion can be varied by changing the surface termination. However, this assumes that the two surfaces are perfectly flat. If one or both of the surfaces is rough, then the actual area of contact will be less than the apparent contact area [19], even at the atomic scale [20][21][22]. Taller asperities (or protruding atoms) at the interface will prevent some of the smaller features (or other atoms) from closely approaching each other, increasing the separation between different regions of the surface and, therefore, reducing the energy of interaction. While the extent to which nano-or even atomic-scale roughness affects adhesion measurements is not fully understood [23], recent MD simulations indicate that the effects could be dramatic [20,21].At present, both modeling and experiment have been used to investigate adhesion at the nanometer scale. In an AFM experiment, adhesion is measured by recording pull-off forces (L C ) between an AFM tip and a sample surface in a controlled...

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Defining Contact at the Atomic Scale

Cheng

Robbins

2010

Tribol Lett

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Molecular dynamics simulations are used to study different definitions of contact at the atomic scale. The roles of temperature, adhesive interactions and atomic structure are studied for simple geometries. An elastic, crystalline substrate contacts a rigid, atomically flat surface or a spherical tip. The rigid surface is formed from a commensurate or incommensurate crystal or an amorphous solid. Spherical tips are made by bending crystalline planes or removing material outside a sphere. In continuum theory the fraction of atomically flat surfaces that is in contact rises sharply from zero to unity when a load is applied. This simple behavior is surprisingly difficult to reproduce with atomic scale definitions of contact. Due to thermal fluctuations, the number of atoms making contact at any instant rises linearly with load over a wide range of loads. Pressures comparable to the ideal hardness are needed to achieve full contact at typical temperatures. A simple harmonic meanfield theory provides a quantitative description of this behavior and explains why the instantaneous forces on atoms have a universal exponential form. Contact areas are also obtained by counting the number of atoms with a time-averaged repulsive force. For adhesive interactions, the resulting area is nearly independent of temperature and averaging interval, but usually rises from zero to unity over a range of pressures that is comparable to the ideal hardness. The only exception is the case of two identical commensurate surfaces. For nonadhesive surfaces, the mean pressure is repulsive if there is any contact during the averaging interval ∆t. The associated area is very sensitive to ∆t and grows monotonically. Similar complications are encountered in defining contact areas for spherical tips. Even for the adhesive case, the area based on time-averaged forces can not be described by continuum theory.

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Nanoindentation of model diamond nanocomposites: Hierarchical molecular dynamics and finite-element simulations

Cited by 15 publications

References 69 publications

Measuring and Understanding Contact Area at the Nanoscale: A Review

Measuring and Understanding Contact Area at the Nanoscale: A Review

Atomistic Factors Governing Adhesion between Diamond, Amorphous Carbon and Model Diamond Nanocomposite Surfaces

Defining Contact at the Atomic Scale

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