Nanostructured surfaces yield earlier: Molecular dynamics study of nanoindentation into adatom islands

Ziegenhain, Gerolf; Urbassek, Herbert M.

doi:10.1103/physrevb.81.155456

Cited by 11 publications

(6 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There are an increasing number of works showing the importance of surface defects in the mechanical properties, motivated by the subject of contact between rough surfaces. More specifically, several studies [7][8][9][10][11][12][13][14][15][16][17][18] have addressed the role of surface defects in reducing the yield stress compared to that of the flat, defect-free surface.…”

Section: Introductionmentioning

confidence: 99%

Surface defects and their influence on surface properties

Fuente

Barrio

Navarro

et al. 2013

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

Surface defects have a profound influence on many attributes of materials, therefore experimental techniques and specific studies focused on their controlled generation and properties are mandatory. We have carried out a thorough study of the role of surface defects on a variety of physico-chemical properties of metals and oxides, using different experimental techniques and molecular dynamics simulations. In particular, we have studied the defects formed upon bombardment with Ar+ ions in a reconstructed Au(100) surface at very low ion doses. At room temperature, the pristine defects are mainly single vacancies, which diffuse by collective atomic motions, then cluster and collapse, resulting in 2D dislocation dipoles. These dislocations exhibit an enhanced chemical reactivity due to the elastic stress of their cores. We have also performed indentation tests of flat and stepped Au(111) samples with an atomic force microscope, revealing noticeable differences in their mechanical behavior when probed at the nanoscale. Thus, the stepped sample has a 20% smaller Young's modulus, 40% smaller yield point and 50% smaller shear stress. These differences, as well as reversible, quasiplastic behavior of the stepped sample up to a critical load, are due to the active role of steps as dislocation nucleation centers. In contrast, a TiO2(110) surface, modified with ion bombardment, does not show noticeable changes in its nanomechanical properties, which is an indication of the very different mechanical responses of oxides compared to simple metals at the nanoscale. Finally, we show how surface defects affect the chemical activity of a Pt(111) surface when exposed to methanol. The nature of the adsorbed species and the dynamics of the surface reactions are modified in the presence of surface defects, rendering the defective surface into a more robust state against catalytic poisoning.

show abstract

Section: Introductionmentioning

confidence: 99%

Surface defects and their influence on surface properties

Fuente

Barrio

Navarro

et al. 2013

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

show abstract

“…2(a) shows, compressive stress along the ½001 B2 direction was applied by two parallel planar indenters. The indenter stiffness was set as 3 eV= A 3 [20,21]. The loading and unloading processes were performed by a stepwise adjustment of the distance between two indenters with a strain rate of 10 À5 ps À1 [21,22].…”

mentioning

confidence: 99%

Nonhysteretic Superelasticity of Shape Memory Alloys at the Nanoscale

et al. 2013

View full text Add to dashboard Cite

We perform molecular dynamics simulations to show that shape memory alloy nanoparticles below the critical size not only demonstrate superelasticity but also exhibit features such as absence of hysteresis, continuous nonlinear elastic distortion, and high blocking force. Atomic level investigations show that this nonhysteretic superelasticity results from a continuous transformation from the parent phase to martensite under external stress. This aspect of shape memory alloys is attributed to a surface effect; i.e., the surface locally retards the formation of martensite and then induces a critical-end-point-like behavior when the system is below the critical size. Our work potentially broadens the application of shape memory alloys to the nanoscale. It also suggests a method to achieve nonhysteretic superelasticity in conventional bulk shape memory alloys.

show abstract

“…We present in figure 6(b) a close-up view of the emerging plasticity showing developing shear loops and the enclosed stacking faults. Such a dislocation structure, with shear loops emitted near the crater surface in all available {111} planes, has many similarities to the structure produced by nanoindentation [44,45], and to void growth/collapse induced by tensile or compressive strain [46,47], including the presence of 'multi-planar' loops, as shown in figure 6(b).…”

Section: Plasticitymentioning

confidence: 87%

Crater formation by nanoparticle impact: contributions of gas, melt and plastic flow

Anders¹,

Ziegenhain²,

Ruestes³

et al. 2012

New J. Phys.

Self Cite

View full text Add to dashboard Cite

The processes underlying crater formation by energetic nanoparticle impact are investigated using molecular dynamics simulations. Both metallic and van-der-Waals-bonded targets are studied. We find a transition from crater formation by melt flow at small impact energies to an evaporation (gas flow) mechanism at higher energies. The transition occurs gradually at impact energies per atom of a few tens of the cohesive energy of the target. van-der-Waals-bonded solids do not exhibit the melt flow cratering regime, in agreement with the narrow liquid zone in their phase diagram. We find that the size of the target region heated above the critical temperature roughly corresponds to the crater volume. The transition shows up most clearly in the increase of the volume of ejected material relative to the crater volume. Finally, we demonstrate the punching of dislocations below the crater for high-velocity impact into ductile targets, leading to a contribution of plastic flow to the crater volume. Gesellschaft have considerably larger sizes. Typical velocities are in the range of 3-100 km s −1 ; this is conventionally called the hypervelocity impact regime. Further interest in such impacts can be found in applications of cluster-surface modification [7][8][9][10][11].The volume of the excavated crater scales in good approximation linearly with the total kinetic energy of the projectile. Such a linear dependence is found in experiments of µmand mm-sized metal dust particles or bullets on various materials [12][13][14]. Hydrocode simulations typically do not include an intrinsic length scale and also display this linear behavior. Molecular dynamics simulations of cluster impacts [15,16] have also found this linear scaling. In a recent publication [17], we could show that this linear scaling extends over a wide range of impact energies and cluster sizes. However, the question of which mechanisms lie beneath crater formation has not been satisfactorily answered until now. Undoubtedly, there is not a single mechanism responsible, but-depending on the projectile size, its energy and the nature of the target-several mechanisms may be involved.Molecular dynamics simulations may prove useful in studying nanoparticle impacts since they allow us to extract detailed (atomistic and thermodynamic) information on the crater formation mechanisms for these small projectiles. Here, we use these simulations to demonstrate that for a metallic target both melt flow, at lower energies, and gas flow, at higher energies, contribute to crater formation. For van-der-Waals-bonded materials, which exhibit only a narrow melting regime, the contribution of melt flow could not be identified. For ductile materials, such as the Cu target studied here, plastic flow by dislocation motion can also contribute to crater growth.

show abstract

Nanostructured surfaces yield earlier: Molecular dynamics study of nanoindentation into adatom islands

Cited by 11 publications

References 25 publications

Surface defects and their influence on surface properties

Surface defects and their influence on surface properties

Nonhysteretic Superelasticity of Shape Memory Alloys at the Nanoscale

Crater formation by nanoparticle impact: contributions of gas, melt and plastic flow

Contact Info

Product

Resources

About