Surface Nanostructure of Layers from Water Solutions after Sedimentation

Authors L.A. Bulavin, Yu.F. Zabashta, L.Yu. Vergun, O.S. Svechnikova, S.R. Bobrovnik

T. Shevchenko National University of Kyiv, Faculty of Physics, 64/13, Volodymyrska St., 01601 Kyiv, Ukraine

Issue Volume 11, Year 2019, Number 4
Dates Received 12 April 2019; revised manuscript received 06 August 2019; published online 22 August 2019
Citation L.A. Bulavin, Yu.F. Zabashta, L.Yu. Vergun, et al., J. Nano- Electron. Phys. 11 No 4, 04012 (2019)
PACS Number(s) 81.15.Lm
Keywords Epitaxial growth of crystals, Atomic force microscopy (9) , Hydrogen bonds.

The question of mechanisms of sedimentation on a substrate of a substance from water solutions is considered. The surface structure of layers obtained by sedimentation of water solutions of two types is investigated. For the first type (an aqueous solution of glucose with a concentration of 40 %), the formation of hydrogen bonds of the dissolved substance with water molecules is characteristic. In the formation of the second type of crystals (aqueous NaCl solution with a concentration of 0.9 %), such bonds are not formed. An analysis of the images obtained using the Integra atomic force microscope revealed the difference between the surface structure of the layers obtained for these types of solutions. Using the histogram of the distribution of surface relief, a method for processing experimental data is proposed. According to this method, the surface is described using a traditional continuum model. When applying this model, the vertical displacement of the points of the surface from the plane is described by a random field. In addition, it is assumed that the projections on the surface are of the same shape and are arranged at the same distance from each other. For the averaged model, the density function is a deterministic periodic function. It is established that for the first type of aqueous solution, the smoothed histogram contains maxima, and for the second type – the absence of minima is observed in the smoothed histogram.It is taken into account that in the aqueous solution of the first type there are clusters containing both the particles of the dissolved substance and the molecules, and in the solution of the second type in the direction of the substrate, not the clusters but separate particles of the dissolved substance (ions) diffuse. It is shown that in the solution of the first type, the clusters diffuse to the substrate and deposit on it, forming an epitaxial layer consisting of areas with a horizontal surface separated by projections with substantially vertical walls and a depth of about the thickness of the layer. At the same time, the process of subsidence is realized, which is accompanied by the greatest decrease in the energy of the system. This process is achieved in the case when the largest contact area between the cluster and the substrate is ensured, if possible. In the second case, the layer is formed as a result of settling on the substrate of particles of the dissolved substance, which creates conditions for smoothing out the protrusions inherent in the substrate and smoothly changing the angle of inclination of the surface of the layer.

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