Dynamical scaling behavior in two-dimensional ballistic deposition with shadowing

Controlling Film Thickness Distribution by Magnetron Sputtering with Rotation and Revolution

The laterally graded multilayer collimator is a vital part of a high-precision diffractometer. It is applied as condensing reflectors to convert divergent X-rays from laboratory X-ray sources into a parallel beam. The thickness of the multilayer film varies with the angle of incidence to guarantee every position on the mirror satisfies the Bragg reflection. In principle, the accuracy of the parameters of the sputtering conditions is essential for achieving a reliable result. In this paper, we proposed a precise method for the fabrication of the laterally graded multilayer based on a planetary motion magnetron sputtering system for film thickness control. This method uses the fast and slow particle model to obtain the particle transport process, and then combines it with the planetary motion magnetron sputtering system to establish the film thickness distribution model. Moreover, the parameters of the sputtering conditions in the model are derived from experimental inversion to improve accuracy. The revolution and rotation of the substrate holder during the final deposition process are achieved by the speed curve calculated according to the model. Measurement results from the X-ray reflection test (XRR) show that the thickness error of the laterally graded multilayer film, coated on a parabolic cylinder Si substrate, is less than 1%, demonstrating the effectiveness of the optimized method for obtaining accurate film thickness distribution.

An examination of scaling behavior in unstable epitaxial mound growth via kinetic Monte Carlo simulations

We investigate the scaling behavior for roughening and coarsening of mounds during unstable epitaxial growth. By using kinetic Monte Carlo (KMC) simulations of two lattice-gas models of crystal surfaces, we find scaling exponents that characterize roughening and coarsening at long times. Our simulation data show that these exponents have a complicated dependence on key model parameters that describe a step edge barrier and downward transport mechanisms. This behavior has not been fully described in previous works. In particular, we find that these scaling exponents vary continuously with parameters controlling the surface current. The kinetic processes of the KMC models that we employ include surface diffusion, edge diffusion, step-edge barriers, and also account for transient kinetics during deposition via downward funneling and transient mobility. Our extensive simulations make evident the salient interplay between step-edge barrier strength and transient kinetic processes.

A simple approach for the ultrasensitive detection of paraquat residue in adzuki beans by surface-enhanced Raman scattering

Paraquat (PQ), has been used in many countries for controlling weed growth in agriculture because of its quick-acting and nonselective contact with green plant tissue.

Coalescent models for developmental biology and the spatio-temporal dynamics of growing tissues

Development is a process that needs to be tightly coordinated in both space and time. Cell tracking and lineage tracing have become important experimental techniques in developmental biology and allow us to map the fate of cells and their progeny. A generic feature of developing and homeostatic tissues that these analyses have revealed is that relatively few cells give rise to the bulk of the cells in a tissue; the lineages of most cells come to an end quickly. Computational and theoretical biologists/physicists have, in response, developed a range of modelling approaches, most notably agent-based modelling. These models seem to capture features observed in experiments, but can also become computationally expensive. Here, we develop complementary genealogical models of tissue development that trace the ancestry of cells in a tissue back to their most recent common ancestors. We show that with both bounded and unbounded growth simple, but universal scaling relationships allow us to connect coalescent theory with the fractal growth models extensively used in developmental biology. Using our genealogical perspective, it is possible to study bulk statistical properties of the processes that give rise to tissues of cells, without the need for large-scale simulations.

Large artificial anisotropic growth rate in on-lattice simulation of obliquely deposited nanostructures

On-lattice particle simulation is one of the most common types of Monte Carlo simulations used in studying the dynamics of film growth. We report the observation of a large artificial anisotropic growth rate variation owing to the fixed arrangement of particles in an on-lattice simulation of oblique angle deposition. This unexpectedly large anisotropy is not reported in previous literatures and substantially affects the simulation outcomes such as column angle and porosity, two of the most essential quantities in obliquely deposited nanostructures. The result of our finding is of interest to all on-lattice simulations in obliquely deposited films or nanostructures.

Dynamic scaling study of vapor deposition polymerization: a Monte Carlo approach

The morphological scaling properties of linear polymer films grown by vapor deposition polymerization are studied by 1+1D Monte Carlo simulations. The model implements the basic processes of random angle ballistic deposition (F) , free-monomer diffusion (D) and monomer adsorption along with the dynamical processes of polymer chain initiation, extension, and merger. The ratio G=D/F is found to have a strong influence on the polymer film morphology. Spatial and temporal behavior of kinetic roughening has been extensively studied using finite-length scaling and height-height correlations H(r,t). The scaling analysis has been performed within the no-overhang approximation and the scaling behaviors at local and global length scales were found to be very different. The global and local scaling exponents for morphological evolution have been evaluated for varying free-monomer diffusion by growing the films at G=10 , 10(2), 10(3), and 10(4) and fixing the deposition flux F. With an increase in G from 10 to 10(4), the average growth exponent beta approximately 0.50 was found to be invariant, whereas the global roughness exponent alpha(g) decreased from 0.87 (1) to 0.73 (1) along with a corresponding decrease in the global dynamic exponent z(g) from 1.71(1) to 1.38(2). The global scaling exponents were observed to follow the dynamic scaling hypothesis, z(g)=alpha(g)/beta. With a similar increase in G however, the average local roughness exponent alpha(l) remained close to 0.46 and the anomalous growth exponent beta(*) decreased from 0.23(4) to 0.18(8). The interfaces display anomalous scaling and multiscaling in the relevant height-height correlations. The variation in H(r,t) with deposition time t indicates nonstationary growth. A comparison has been made between the simulational findings and the experiments wherever applicable.

Surface and bulk properties of deposits grown with a bidisperse ballistic deposition model

We study roughness scaling of the outer surface and the internal porous structure of deposits generated with the three-dimensional bidisperse ballistic deposition (BBD), in which particles of two sizes are randomly deposited. Systematic extrapolation of roughness and dynamical exponents and the comparison of roughness distributions indicate that the top surface has Kardar-Parisi-Zhang (KPZ) scaling for any ratio F of the flux between large and small particles. A scaling theory predicts the characteristic time of the crossover from random to correlated growth in BBD and provides relations between the amplitudes of roughness scaling and F in the KPZ regime. The porosity of the deposits monotonically increases with F and scales as F{12} for small F, which is also explained by the scaling approach and illustrates the possibility of connecting surface growth rules and bulk properties. The suppression of relaxation mechanisms in BBD enhances the connectivity of the deposits when compared to other ballisticlike models, so that they percolate down to F approximately 0.05. The fractal dimension of the internal surface of the percolating deposits is D{F} approximately 2.9, which is very close to the values in other ballistic-like models and suggests universality among these systems.

Aggregation in a mixture of Brownian and ballistic wandering particles

In this paper, we analyze the scaling properties of a model that has as limiting cases the diffusion-limited aggregation (DLA) and the ballistic aggregation (BA) models. This model allows us to control the radial and angular scaling of the patterns, as well as their gap distributions. The particles added to the cluster can follow either ballistic trajectories, with probability Pba, or random ones, with probability Prw=1-Pba. The patterns were characterized through several quantities, including those related to the radial and angular scaling. The fractal dimension as a function of Pba continuously increases from df approximately 1.72 (DLA dimensionality) for Pba=0 to df approximately 2 (BA dimensionality) for Pba. However, the lacunarity and the active zone width exhibit a distinct behavior: they are convex functions of Pba with a maximum at Pba approximately 1/2. Through the analysis of the angular correlation function, we found that the difference between the radial and angular exponents decreases continuously with increasing Pba and rapidly vanishes for Pba>1/2, in agreement with recent results concerning the asymptotic scaling of DLA clusters.