List of Journal Publications
2014
4.
Zhang, Yunhe, Thijsse, Barend, Nicola, L.
Competition between dislocations and cracks in molecular dynamics simulations of metal nanoimprinting Journal Article
In: COMPUTATIONAL MATERIALS SCIENCE, vol. 94, no. C, pp. 95–105, 2014.
Abstract | BibTeX | Tags: Crack, Dislocations, Molecular dynamics simulations, Nanoimprinting, Thermal fluctuations | Links:
@article{Zhang2014,
title = {Competition between dislocations and cracks in molecular dynamics simulations of metal nanoimprinting},
author = {Yunhe Zhang and Barend Thijsse and L. Nicola},
doi = {10.1016/j.commatsci.2014.02.016},
year = {2014},
date = {2014-01-01},
journal = {COMPUTATIONAL MATERIALS SCIENCE},
volume = {94},
number = {C},
pages = {95–105},
publisher = {Elsevier B.V.},
abstract = {Direct metal nanoimprinting of a gold thin layer is studied by means of quasi-static molecular dynamics simulations. The aim of this study is to understand if it is possible to obtain a reproducible nanopattern with features of a few nanometers, that closely resembles the shape of the template. The majority of our simulations show an unexpected competition between crack formation and dislocation plasticity upon retraction of the template, which leads in some cases to an imprint and in other cases to a flat surface. These results are at odds with previous simulations of metal nanoimprinting, which always predicted formation of an imprint. The reason for this discrepancy lies in the much lower (and thus more realistic) imprinting velocity used in this work. The most interesting finding of this paper is that the competition between crack and dislocations for certain loading conditions and geometry of the crystals is driven by thermal fluctuations of the atomic velocities. Local events, namely atomic fluctuations and dislocation nucleation, determine the global mechanical response of the system, i.e. whether an imprint is obtained or not. The relevance of thermal fluctuations is confirmed by the fact that any of the simulations presented here, if repeated at 10 K, leads to a brittle material behavior.},
keywords = {Crack, Dislocations, Molecular dynamics simulations, Nanoimprinting, Thermal fluctuations},
pubstate = {published},
tppubtype = {article}
}
Direct metal nanoimprinting of a gold thin layer is studied by means of quasi-static molecular dynamics simulations. The aim of this study is to understand if it is possible to obtain a reproducible nanopattern with features of a few nanometers, that closely resembles the shape of the template. The majority of our simulations show an unexpected competition between crack formation and dislocation plasticity upon retraction of the template, which leads in some cases to an imprint and in other cases to a flat surface. These results are at odds with previous simulations of metal nanoimprinting, which always predicted formation of an imprint. The reason for this discrepancy lies in the much lower (and thus more realistic) imprinting velocity used in this work. The most interesting finding of this paper is that the competition between crack and dislocations for certain loading conditions and geometry of the crystals is driven by thermal fluctuations of the atomic velocities. Local events, namely atomic fluctuations and dislocation nucleation, determine the global mechanical response of the system, i.e. whether an imprint is obtained or not. The relevance of thermal fluctuations is confirmed by the fact that any of the simulations presented here, if repeated at 10 K, leads to a brittle material behavior.
3.
Zhang, J., Zhang, Y., Mara, N. A., Lou, J., Nicola, L.
Direct nanoimprinting of single crystalline gold: Experiments and dislocation dynamics simulations Journal Article
In: APPLIED SURFACE SCIENCE, vol. 290, pp. 301–307, 2014.
Abstract | BibTeX | Tags: Dislocation dynamics simulations, Experiments, Nanoimprinting | Links:
@article{Zhang2014b,
title = {Direct nanoimprinting of single crystalline gold: Experiments and dislocation dynamics simulations},
author = {J. Zhang and Y. Zhang and N. A. Mara and J. Lou and L. Nicola},
doi = {10.1016/j.apsusc.2013.11.072},
year = {2014},
date = {2014-01-01},
journal = {APPLIED SURFACE SCIENCE},
volume = {290},
pages = {301–307},
abstract = {This paper addresses the feasibility of direct nanoimprinting and highlights the challenges involved in this technique. Our study focuses on experimental work supported by dislocation dynamics simulations. A gold single crystal is imprinted by a tungsten indenter patterned with parallel lines of various spacings. Dedicated dislocation dynamics simulations give insight in the plastic deformation occurring into the crystal during imprinting. We find that good pattern transfer is achieved when the lines are sufficiently spaced such that dislocation activity can be effective in assisting deformation of the region underneath each line. Yet, the edges of the obtained imprints are not smooth, partly due to dislocation glide.},
keywords = {Dislocation dynamics simulations, Experiments, Nanoimprinting},
pubstate = {published},
tppubtype = {article}
}
This paper addresses the feasibility of direct nanoimprinting and highlights the challenges involved in this technique. Our study focuses on experimental work supported by dislocation dynamics simulations. A gold single crystal is imprinted by a tungsten indenter patterned with parallel lines of various spacings. Dedicated dislocation dynamics simulations give insight in the plastic deformation occurring into the crystal during imprinting. We find that good pattern transfer is achieved when the lines are sufficiently spaced such that dislocation activity can be effective in assisting deformation of the region underneath each line. Yet, the edges of the obtained imprints are not smooth, partly due to dislocation glide.
2010
2.
Zhang, Yun-He, Nicola, L.
Effect of template shape on metal nanoimprinting: A dislocation dynamics study Journal Article
In: JOURNAL OF ZHEJIANG UNIVERSITY. SCIENCE A, vol. 11, no. 10, pp. 722–726, 2010.
Abstract | BibTeX | Tags: dislocation dynamics, Nanoimprinting, Simulations | Links:
@article{Zhang2010,
title = {Effect of template shape on metal nanoimprinting: A dislocation dynamics study},
author = {Yun-He Zhang and L. Nicola},
doi = {10.1631/jzus.A1000175},
year = {2010},
date = {2010-01-01},
journal = {JOURNAL OF ZHEJIANG UNIVERSITY. SCIENCE A},
volume = {11},
number = {10},
pages = {722–726},
publisher = {ZHEJIANG UNIV},
abstract = {Dislocation dynamics simulations are performed to investigate the effect of template shape on the nanoimprinting of metal layers. To this end, metal thin films are imprinted by a rigid template made of an array of equispaced indenters of various shapes, i.e., rectangular, wedge, and circular. The geometry of the indenters is chosen such that the contact area is approximately the same at the final imprinting depth. Results show that, for all template shapes, the final patterns strongly depend on the dislocation activity, and that each imprint differs from the neighboring ones. Large material pile ups appear between the imprints, such that polishing of the metal layer is suggested for application of the patterns in electronics. Rectangular indenters require the lowest imprinting force and achieve the deepest retained imprints.},
keywords = {dislocation dynamics, Nanoimprinting, Simulations},
pubstate = {published},
tppubtype = {article}
}
Dislocation dynamics simulations are performed to investigate the effect of template shape on the nanoimprinting of metal layers. To this end, metal thin films are imprinted by a rigid template made of an array of equispaced indenters of various shapes, i.e., rectangular, wedge, and circular. The geometry of the indenters is chosen such that the contact area is approximately the same at the final imprinting depth. Results show that, for all template shapes, the final patterns strongly depend on the dislocation activity, and that each imprint differs from the neighboring ones. Large material pile ups appear between the imprints, such that polishing of the metal layer is suggested for application of the patterns in electronics. Rectangular indenters require the lowest imprinting force and achieve the deepest retained imprints.
1.
Zhang, Yunhe, Giessen, Erik Van Der, Nicola, L.
Discrete dislocation simulations of the flattening of nanoimprinted surfaces Journal Article
In: MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, vol. 18, no. 3, 2010.
Abstract | BibTeX | Tags: Discrete dislocation simulations, Nanoimprinting, rough surface flattening | Links:
@article{Zhang2010a,
title = {Discrete dislocation simulations of the flattening of nanoimprinted surfaces},
author = {Yunhe Zhang and Erik Van Der Giessen and L. Nicola},
doi = {10.1088/0965-0393/18/3/034006},
year = {2010},
date = {2010-01-01},
journal = {MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING},
volume = {18},
number = {3},
publisher = {IOP PUBLISHING LTD},
abstract = {Simulations of rough surface flattening are performed on thin metal films whose roughness is created by nanoimprinting flat single crystals. The imprinting is carried out by means of a rigid template with equal flat contacts at varying spacing. The imprinted surfaces are subsequently flattened by a rigid platen, while the change of roughness and surface profile is computed. Attention is focused mainly on comparing the response of the film surfaces with those of identical films cleared of the dislocations and residual stresses left by the imprinting process. The aim of these studies is to understand to what extent the loading history affects deformation and roughness during flattening. The limiting cases of sticking and frictionless contact between rough surface and platen are analyzed. Results show that when the asperities are flattened such that the contact area is up to about one third of the surface area, the loading history strongly affects the flattening. Specifically, the presence of initial dislocations facilitates the squeezing of asperities independently of the friction conditions of the contact. For larger contact areas, the initial conditions affect only sticking contacts, while frictionless contacts lead to a homogeneous flattening of the asperities due to yield of the metal film. In all cases studied the final surface profile obtained after flattening has little to no resemblance to the original imprinted surface.},
keywords = {Discrete dislocation simulations, Nanoimprinting, rough surface flattening},
pubstate = {published},
tppubtype = {article}
}
Simulations of rough surface flattening are performed on thin metal films whose roughness is created by nanoimprinting flat single crystals. The imprinting is carried out by means of a rigid template with equal flat contacts at varying spacing. The imprinted surfaces are subsequently flattened by a rigid platen, while the change of roughness and surface profile is computed. Attention is focused mainly on comparing the response of the film surfaces with those of identical films cleared of the dislocations and residual stresses left by the imprinting process. The aim of these studies is to understand to what extent the loading history affects deformation and roughness during flattening. The limiting cases of sticking and frictionless contact between rough surface and platen are analyzed. Results show that when the asperities are flattened such that the contact area is up to about one third of the surface area, the loading history strongly affects the flattening. Specifically, the presence of initial dislocations facilitates the squeezing of asperities independently of the friction conditions of the contact. For larger contact areas, the initial conditions affect only sticking contacts, while frictionless contacts lead to a homogeneous flattening of the asperities due to yield of the metal film. In all cases studied the final surface profile obtained after flattening has little to no resemblance to the original imprinted surface.
