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http://hdl.handle.net/10985/7175
Legitimate domain of a Newtonian behavior for thermal nanoimprint lithography
TEYSSEDRE, Hubert; GILORMINI, Pierre; LANDIS, Stefan; REGNIER, Gilles
Nanoimprint lithography is an efficient way to reproduce nanostructures down to 20 nanometers in sub-micrometer polymeric films. To optimize this process, simulation using a Newtonian behavior is a cheap and efficient way to predict the polymer flow in micro and nano size cavities. This behavior is nevertheless limited to flows with shear rates below a critical value that can be determined with standard rheology measurements. We have investigated the validity domain of this behavior to simulate thermal NIL. This domain of validity is composed of two uncoupled functions, one for the material properties and the mean pressure applied to the pattern, and one for the geometry considered. The latter function has been determined with numerical simulations using the natural element method. It is demonstrated that knowing the mean applied pressure, the critical shear rate, and the viscosity of the material we are able to determine, depending on stamp geometry, if shear-thinning may or may not occur during an imprinting process.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/71752013-01-01T00:00:00ZTEYSSEDRE, HubertGILORMINI, PierreLANDIS, StefanREGNIER, GillesNanoimprint lithography is an efficient way to reproduce nanostructures down to 20 nanometers in sub-micrometer polymeric films. To optimize this process, simulation using a Newtonian behavior is a cheap and efficient way to predict the polymer flow in micro and nano size cavities. This behavior is nevertheless limited to flows with shear rates below a critical value that can be determined with standard rheology measurements. We have investigated the validity domain of this behavior to simulate thermal NIL. This domain of validity is composed of two uncoupled functions, one for the material properties and the mean pressure applied to the pattern, and one for the geometry considered. The latter function has been determined with numerical simulations using the natural element method. It is demonstrated that knowing the mean applied pressure, the critical shear rate, and the viscosity of the material we are able to determine, depending on stamp geometry, if shear-thinning may or may not occur during an imprinting process.Influence of thermal diffusion and shear-thinning during the leveling of nanoimprinted patterns in a polystyrene thin film
http://hdl.handle.net/10985/9845
Influence of thermal diffusion and shear-thinning during the leveling of nanoimprinted patterns in a polystyrene thin film
TEYSSEDRE, Hubert; LANDIS, Stefan; GILORMINI, Pierre; REGNIER, Gilles
When capillary forces prevail, the leveling of the free surface of a fluid film is a natural phenomenon that has already found applicative interest either with brushmarks for paint coatings or for rheology on polymeric thin films. Among many parameters, the material behavior influences notably this phenomenon and its characterization still arouses curiosity at the nanoscale. In this article the nanoscale properties of a polystyrene film are derived from the leveling rate of nanoimprinted patterns and are compared to bulk values obtained with a parallel plate rheometer. In particular the focus is made on the isothermal assumption during the process and the consequences of an anisothermal state on the material behavior. Both points are investigated by using numerical simulations based on the natural element method. First we demonstrate experimentally that the leveling rate is influenced by the heat exchange at the air-polymer interface and that thermal diffusion should be taken into account within the film and its underlying substrate. Then we numerically investigate the influence of thermal diffusion and shear-thinning on the leveling rate. Finally we show that the bulk properties can represent particularly closely the behavior of the polymer at the nanoscale if adequate thermal boundary conditions are used and if shear-thinning is taken into account. This agreement postulates a decrease by 7◦C of the mean temperature of the polystyrene film coated on silicon when experiments are carried out on a hotplate at 100◦C in a cleanroom environment.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/98452015-01-01T00:00:00ZTEYSSEDRE, HubertLANDIS, StefanGILORMINI, PierreREGNIER, GillesWhen capillary forces prevail, the leveling of the free surface of a fluid film is a natural phenomenon that has already found applicative interest either with brushmarks for paint coatings or for rheology on polymeric thin films. Among many parameters, the material behavior influences notably this phenomenon and its characterization still arouses curiosity at the nanoscale. In this article the nanoscale properties of a polystyrene film are derived from the leveling rate of nanoimprinted patterns and are compared to bulk values obtained with a parallel plate rheometer. In particular the focus is made on the isothermal assumption during the process and the consequences of an anisothermal state on the material behavior. Both points are investigated by using numerical simulations based on the natural element method. First we demonstrate experimentally that the leveling rate is influenced by the heat exchange at the air-polymer interface and that thermal diffusion should be taken into account within the film and its underlying substrate. Then we numerically investigate the influence of thermal diffusion and shear-thinning on the leveling rate. Finally we show that the bulk properties can represent particularly closely the behavior of the polymer at the nanoscale if adequate thermal boundary conditions are used and if shear-thinning is taken into account. This agreement postulates a decrease by 7◦C of the mean temperature of the polystyrene film coated on silicon when experiments are carried out on a hotplate at 100◦C in a cleanroom environment.Extension of the natural element method to surface tension and wettability for the simulation of polymer flows at the micro and nano scales
http://hdl.handle.net/10985/7294
Extension of the natural element method to surface tension and wettability for the simulation of polymer flows at the micro and nano scales
TEYSSEDRE, Hubert; GILORMINI, Pierre
The natural element method is used to simulate two-dimensional viscous flows where interfacial effects must be taken into account, for application to polymer melts at the micro and nano scales. The variational formulation includes surface tension on the free surfaces, a net wetting force is applied at the contact line where the fluid reaches a solid surface, and the Navier-slip condition is used along fluid-solid interfaces. No dynamic wetting angle is prescribed, and the contact angle obtained results from the other material parameters and from overall flow conditions. A comparison with an analytical solution in a simple surface tension-driven flow is given, and contact with a rigid solid is involved in the transient spreading of a droplet and in the steady movement of a meniscus between two plates.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/72942013-01-01T00:00:00ZTEYSSEDRE, HubertGILORMINI, PierreThe natural element method is used to simulate two-dimensional viscous flows where interfacial effects must be taken into account, for application to polymer melts at the micro and nano scales. The variational formulation includes surface tension on the free surfaces, a net wetting force is applied at the contact line where the fluid reaches a solid surface, and the Navier-slip condition is used along fluid-solid interfaces. No dynamic wetting angle is prescribed, and the contact angle obtained results from the other material parameters and from overall flow conditions. A comparison with an analytical solution in a simple surface tension-driven flow is given, and contact with a rigid solid is involved in the transient spreading of a droplet and in the steady movement of a meniscus between two plates.On using the leveling of the free surface of a Newtonian fluid to measure viscosity and Navier slip length
http://hdl.handle.net/10985/7394
On using the leveling of the free surface of a Newtonian fluid to measure viscosity and Navier slip length
GILORMINI, Pierre; TEYSSEDRE, Hubert
Measuring the relaxation time involved in the leveling of the free surface of a Newtonian fluid laid on a substrate can give access to material parameters. It is shown here how most favorable pattern geometries of the free surface and film thicknesses can be defined for the measures of viscosity and Navier slip length at the fluid-solid interface, respectively. Moreover, special emphasis is put on the conditions required to avoid shear-thinning by controling the maximum shear rate. For initially sinusoidal patterns with infinitesimal amplitudes, an analytical solution including slip at the fluid-solid interface is used, and numerical simulations based on the natural element method allow to discuss the effect of finite amplitudes. This leads to the definition of a relevance domain for the analytical solution that avoids the need for numerical simulations in practical applications. It is also shown how these results can be applied to crenelated profiles, where Fourier series expansion can be used, but with caution.
Version éditeur : http://rspa.royalsocietypublishing.org/content/469/2160/20130457.short
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/73942013-01-01T00:00:00ZGILORMINI, PierreTEYSSEDRE, HubertMeasuring the relaxation time involved in the leveling of the free surface of a Newtonian fluid laid on a substrate can give access to material parameters. It is shown here how most favorable pattern geometries of the free surface and film thicknesses can be defined for the measures of viscosity and Navier slip length at the fluid-solid interface, respectively. Moreover, special emphasis is put on the conditions required to avoid shear-thinning by controling the maximum shear rate. For initially sinusoidal patterns with infinitesimal amplitudes, an analytical solution including slip at the fluid-solid interface is used, and numerical simulations based on the natural element method allow to discuss the effect of finite amplitudes. This leads to the definition of a relevance domain for the analytical solution that avoids the need for numerical simulations in practical applications. It is also shown how these results can be applied to crenelated profiles, where Fourier series expansion can be used, but with caution.Limitations of simple flow models for the simulation of nanoimprint
http://hdl.handle.net/10985/6860
Limitations of simple flow models for the simulation of nanoimprint
TEYSSEDRE, Hubert; GILORMINI, Pierre; REGNIER, Gilles
A quick evaluation of the forces involved in nanoimprint would be very helpful in the prevention of mold deflection. Unfortunately, it is shown here that assuming simplified flows may lead to quite incorrect evaluations of these forces, even for simple periodic patterns and a Newtonian behavior. The mere use of the classical result of the lubrica- tion theory does not account for the range of thickness-to-width ratios that may be involved, especially at the beginning of the process. An improved squeeze model includes this effect, but still underestimates the imprint force. Moreover, finite element simulations demonstrate limitations of two more elaborate models that are found in the literature. These simulations also show that two flow modes can be defined, according to whether or not the polymer touches the mold sidewalls. A deeper analysis of these two modes may help the definition of a more appropriate simplified model in the future.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/68602013-01-01T00:00:00ZTEYSSEDRE, HubertGILORMINI, PierreREGNIER, GillesA quick evaluation of the forces involved in nanoimprint would be very helpful in the prevention of mold deflection. Unfortunately, it is shown here that assuming simplified flows may lead to quite incorrect evaluations of these forces, even for simple periodic patterns and a Newtonian behavior. The mere use of the classical result of the lubrica- tion theory does not account for the range of thickness-to-width ratios that may be involved, especially at the beginning of the process. An improved squeeze model includes this effect, but still underestimates the imprint force. Moreover, finite element simulations demonstrate limitations of two more elaborate models that are found in the literature. These simulations also show that two flow modes can be defined, according to whether or not the polymer touches the mold sidewalls. A deeper analysis of these two modes may help the definition of a more appropriate simplified model in the future.