Guiding Chart for Initial Layer Choice with Nanoimprint Lithography

When nanoimprint serves as a lithography process, it is most attractive for the ability to overcome the typical residual layer remaining without the need for etching. Then, ‘partial cavity filling’ is an efficient strategy to provide a negligible residual layer. However, this strategy requires an adequate choice of the initial layer thickness to work without defects. To promote the application of this strategy we provide a ‘guiding chart’ for initial layer choice. Due to volume conservation of the imprint polymer this guiding chart has to consider the geometric parameters of the stamp, where the polymer fills the cavities only up to a certain height, building a meniscus at its top. Furthermore, defects that may develop during the imprint due to some instability of the polymer within the cavity have to be avoided; with nanoimprint, the main instabilities are caused by van der Waals forces, temperature gradients, and electrostatic fields. Moreover, practical aspects such as a minimum polymer height required for a subsequent etching of the substrate come into play. With periodic stamp structures the guiding chart provided will indicate a window for defect-free processing considering all these limitations. As some of the relevant factors are system-specific, the user has to construct his own guiding chart in praxis, tailor-made to his particular imprint situation. To facilitate this task, all theoretical results required are presented in a graphical form, so that the quantities required can simply be read from these graphs. By means of examples, the implications of the guiding chart with respect to the choice of the initial layer are discussed with typical imprint scenarios, nanoimprint at room temperature, at elevated temperature, and under electrostatic forces. With periodic structures, the guiding chart represents a powerful and straightforward tool to avoid defects in praxis, without in-depth knowledge of the underlying physics.

Evolution of Ag nanostructures created from thin films: UV–vis absorption and its theoretical predictions

Ag-based plasmonic nanostructures were manufactured by thermal annealing of thin metallic films. Structure and morphology were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). SEM images show that the formation of nanostructures is influenced by the initial layer thickness as well as the temperature and the time of annealing. The Ag 3d and Ag 4d XPS spectra are characteristic of nanostructures. The quality of the nanostructures, in terms of their use as plasmonic platforms, is reflected in the UV–vis absorption spectra. The absorption spectrum is dominated by a maximum in the range of 450–500 nm associated with the plasmon resonance. As the initial layer thickness increases, an additional peak appears around 350 nm, which probably corresponds to the quadrupole resonance. For calculations leading to a better illustration of absorption, scattering and overall absorption of light in Ag nanoparticles, the Mie theory is employed. Absorbance and the distribution of the electromagnetic field around the nanostructures are calculated by finite-difference time-domain (FDTD) simulations. For calculations a novel approach based on modelling the whole sample with a realistic shape of the nanoparticles, instead of full spheres, was used. This led to a very good agreement with the experiment.

Reproductive qualities of meat chickens of the parent flock when using automatic nests

The aim of the study presented in this paper was to compare the reproductive qualities of laying hens of the parent flock of the ROSS 308 cross when using manual and automatic egg collection. The experimental part was carried out in the production conditions of a separate subdivision “Novosafonovskaya poultry farm” of Kuzbass Broiler LLC on laying hens of the parent flock of the ROSS 308 cross at the age of 155-435 days. The use of automatic nests for collecting hatching eggs did not affect the intensity of egg production, but contributed to an increase in the yield of hatching eggs due to a decrease in the culled eggs because of egg contamination, breakage, cracked shell and others. A decrease in the number of cleaned eggs among the hatching eggs contributed to an increase in the hatching of chicks and, as a consequence, an increase in the yield of day old chicks per initial layer by 11.9 heads or 8.5%.

Parametric Study of Metal 3D Printing Process Using Finite Element Simulation

Metal additive manufacturing (AM), also known as metal 3D printing, is a challenging process to be controlled for desirable outcome due to its many process parameters. Residual stresses or deformations may occur in an AM manufactured part because of rapid heating and cooling cycles in the layers. The effect of process-controlled parameters in laser powder bed fusion (L-PBF) on deformations of a manufactured part has not been well examined and reported only sparely in literature. The objectives of this paper are: to study deformation behavior of a L-PBF printed part using finite element method, to perform parametric study of process input variables by changing few selected process parameters in the simulations, and to attempt identifying optimal values within the studied range of selected parameters to minimize part distortion. In this study, the material used for the heat sink finite element model was Inconel 718 which is commonly found in AM manufactured parts. ANSYS finite element program was employed to simulate a heat sink fabrication. The finished dimensions of the heat sink model were 12 mm in height, 26 mm in width, and 26 mm in depth. Thermal-mechanical sequential coupling approach was employed to simulate layer-by-layer built up process. The resulting deformations was evaluated by varying laser travel speed, base plate temperature, and initial layer angle. The maximum deformation (distortion) was observed at the corners of the heat sink model upon release from the base plate and found to be approximately 0.115 mm. Based on this study, the relative optimal simulation results for minimum distortion for selected parameters were 600 °K base plate temperature, 600 mm/sec speed of laser, and 0° initial layer angle. These results can be served as foundation for further study of varying other L-PBF process parameters.

Initial layer and incompressible limit for Euler–Poisson equation in nonthermal plasma

The singular limit from compressible Euler–Poisson equation in nonthermal plasma to incompressible Euler equation with an ill-prepared initial data is investigated in this paper by constructing approximate solutions of the appropriate order via an asymptotic expansion. Nonlinear asymptotic stability of initial layer approximation is established with the convergence rate.

Retrogressive failure of a static granular layer on an inclined plane

When a layer of static grains on a sufficiently steep slope is disturbed, an upslope-propagating erosion wave, or retrogressive failure, may form that separates the initially static material from a downslope region of flowing grains. This paper shows that a relatively simple depth-averaged avalanche model with frictional hysteresis is sufficient to capture a planar retrogressive failure that is independent of the cross-slope coordinate. The hysteresis is modelled with a non-monotonic effective basal friction law that has static, intermediate (velocity decreasing) and dynamic (velocity increasing) regimes. Both experiments and time-dependent numerical simulations show that steadily travelling retrogressive waves rapidly form in this system and a travelling wave ansatz is therefore used to derive a one-dimensional depth-averaged exact solution. The speed of the wave is determined by a critical point in the ordinary differential equation for the thickness. The critical point lies in the intermediate frictional regime, at the point where the friction exactly balances the downslope component of gravity. The retrogressive wave is therefore a sensitive test of the functional form of the friction law in this regime, where steady uniform flows are unstable and so cannot be used to determine the friction law directly. Upper and lower bounds for the existence of retrogressive waves in terms of the initial layer depth and the slope inclination are found and shown to be in good agreement with the experimentally determined phase diagram. For the friction law proposed by Edwardset al.(J. Fluid. Mech., vol. 823, 2017, pp. 278–315,J. Fluid. Mech., 2019, (submitted)) the magnitude of the wave speed is slightly under-predicted, but, for a given initial layer thickness, the exact solution accurately predicts an increase in the wave speed with higher inclinations. The model also captures the finite wave speed at the onset of retrogressive failure observed in experiments.