Surface Energy Of Thin Films Research Articles

Isomeric acceptors incorporation enables 18.1% efficiency ternary organic solar cells with reduced trap-assisted charge recombination

The donor–acceptor miscibility is one of the most critical factors in controlling the active layer morphologies with multiple components. However, how to practically select the third component with the desired miscibility for efficient ternary organic solar cells remains unresolved. Herein, we demonstrate that the surface energy of thin films could be manipulated by altering the weight ratios of the isomeric acceptors in the blend films and, therefore, the regulation of donor–acceptor miscibility. When the acceptor weight ratio (M−Cl:O-Cl) is 1:0.3, low miscibility (χ = 5.43 × 10-2K) with PM6 is achieved, and the power conversion efficiency of organic solar cells composed of PM6:M−Cl (17.1%) is enhanced to 18.1% (PM6:M−Cl:O-Cl). The increased power conversion efficiency resulted from the surface energy-driven active layer morphology and donor–acceptor phase separations, associated with the significantly lower energetic disorder, trap density, and thus reduced free charge recombination. Our findings underline the significance of the isomeric approach to managing the blend film surface energy and, therefore, the donor–acceptor miscibility for improving the device performance, providing guidelines for the fabrication of high-performed ternary OSCs and material designs.

Water and oxygen environment induced surface cracks healing in solution processed gallium oxide thin films

Solution based low temperature gallium oxide (Ga2O3) films with high quality is present need for large area deposition, cracks and other parameters resist the use of these films in applications. We have tried to develop good quality crack free films of Ga2O3. Deposition of Ga2O3 thin films by spin coating method and investigation of removal of surface cracks by adding secondary solvent (water) under oxygen environment. The as-synthesized film (without water and oxygen) shows cracks all over the surface. Deionized (DI) water and oxygen atmosphere act as efficient medium that alter surface energy of thin films while undergoing heat treatment. During the heat treatment of the thin films, addition of water forms interparticulate system between the molecules, yielding better evaporation balance and the oxygen environment helps to seize the rate of molecule evaporation which improves the surface uniformity of the thin film. A significant variation in the surface morphology of the films is observed using high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) images. X-ray diffraction (XRD) and Raman spectroscopy are used for the structural confirmation of the thin films. Increase in surface roughness is observed (from 0.28 nm to 0.98 nm) with increase in annealing temperature. Improvement in the crystalline feature results into augmented current density value. The developed crack-free films can be utilized for various electronics and optoelectronics application.

The dependence of surface tension of solid nanoscale films on their thickness

This paper presents a theoretical method to calculate the surface energy dependence on thickness of nanofilms based on the Landau theory. For the first time, it is shown that the surface energy of thin films having free surfaces is greater than the surface energy of macroscopic objects. For nano-objects having free surfaces, it is stated that their interior order parameter is always less than that of macroscopic solids of the same composition. It is obtained that the surface energy of thin films increases with decrease in their thickness passing its maximum meaning. A further decrease in the solid film thickness leads to a monotonic decrease in the surface energy.

Structural and chemical characterization of fluorinated amorphous carbon films (a-C:F) as a liquid crystal alignment layer

a-C:F thin films with varying fluorine content were prepared by plasma CVD and the sputtering method as inorganic alignment layers for overcoming the disadvantages of conventional liquid crystal (LC) alignment layers. The material and structural properties were investigated by X-ray photoelectron spectroscopy, Fourier transform infrared absorption, and contact angle measurement. For elucidation of the liquid crystal alignment layers, LC cells with a-C:F films were fabricated, followed by examination of the textures of the LC and electro-optical characteristics. The fluorine concentrations of a-C:F films were controlled by changing the mixture gas ratio ( R G) in CVD and applied power ratio ( R P) in the sputter system. An increase in R G and R P led to increase fluorine incorporation, and the film microstructure changed from a diamond-like to a polymer-like structure. In addition, the sputtered a-C:F films showed a higher fluorination than the CVD sample since the PTFE target was only composed of CF 2 functional groups. Surface composition influenced the surface energy of thin films and an extremely hydrophobic property was obtained in the case of fluorine-rich a-C:F films. LC orientations were observed in various compositions of a-C:F films, and the vertically self-aligned LC textures confirmed that a sputtered a-C:F film is a good candidate for an alignment layer without any post-treatment.

Three-Dimensional Molecular Dynamics Analyses of Atomic-Scale Indentation and Cutting Process in AFM.

This paper describes the effect of tool materials on the mechanism of atomic-scale indentation and cutting process of thin films in an atomic force microscope (AFM) by molecular dynamics simulation. The interatomic force between tool and thin film is assumed to be derived from the two-body interatomic potential using parameters based on the ab-initio molecular orbital calculation for a (Cr, Ni)-(C, Si)6H9 atom cluster. Molecular dynamics simulated the atomic-scale indentation and cutting process of chromium and nickel thin films using diamond, silicon and diamond-like carbon (DLC) pin tools. The indentation was formed by diamond and DLC pin tools, but was not formed by a silicon pin tool. Load-penetration depth curves showed the yield behavior in the indentation using diamond and DLC pin tools, but did not show that using a silicon pin tool. Elastic moduli of chromium and nickel thin films calculated from load-penetration depth curves were larger than experimental values. These are resulted from the effect of the surface energy of thin films on the elastic modulus. The machinability of the cutting process of thin films using a diamond pin tool was better than that using a silicon pin tool. The surface of thin films in nano-scale cutting experiments with AFM was similar to that in atomic-scale cutting by molecular dynamics simulation.