Local Diffusion Induced Roughening in Cobalt Phthalocyanine Thin Film Growth

Abstract

We have studied the kinetic roughening in the growth of cobalt phthalocyanine (CoPc) thin films grown on SiO2/Si(001) surfaces as a function of the deposition time and the growth temperature using atomic force microscopy (AFM). We have observed that the growth exhibits the formation of irregular islands, which grow laterally as well as vertically with coverage of CoPc molecules, resulting rough film formation. Our analysis further disclosed that such formation is due to an instability in the growth induced by local diffusion of the molecules following an anomalous scaling behavior. The instability relates the (ln(t))(1/2), with t as deposition time, dependence of the local surface slope as described in nonequilibrium film growth. The roughening has been characterized by calculating different scaling exponents α, β, and 1/z determined from the height fluctuations obtained from AFM images. We obtained an average roughness exponent α = 0.78 ± 0.04. The interface width (W) increases following a power law as W ∼ t(β), with growth exponent β = 0.37 ± 0.05 and lateral correlation length (ξ) grows as ξ ∼ t(1/z) with dynamic exponent 1/z = 0.23 ± 0.06. The exponents revealed that the growth belongs to a different class of universality.

Roughness and Correlations in the Transition from Island to Film Growth: Simulations and Application to CdTe Deposition

“…Those authors proposed a mechanistic model in which the gaps between the islands remain after their coalescence. In a work with a molecular beam deposition setup, Gedda et al [22] grew cobalt phthalocyanine films on a SiO 2 /Si(001) substrate whose roughness was ≈ 0.3 nm. Their AFM images illustrate the transition from island to film growth at substrate temperature 120 o C. The roughness in this regime varies as W ∼ d 0.37 , but the slope of the log W ×log d plot increases after the continuous film is formed.…”

“…This approach helps to infer the main physical pro-cesses that control the growth and was already applied to deposits of various materials [15][16][17]. Several works have also investigated the scaling of surface fluctuations and correlations in the initial stages of heteroepitaxial film deposition [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Their results cannot be interpreted in the light of kinetic roughening theories because the deposits are mostly formed by isolated islands, so that height fluctuations and correlations are related to island widths, heights, and surface density.…”

Morphological stabilization and KPZ scaling by electrochemically induced co-deposition of nanostructured NiW alloy films

“…Hence, the analysis of the surface morphology evolution with growth time within the framework of kinetic roughening and associated scaling concepts has proved adequate to determine the main physical mechanisms controlling the films surface morphology when it is strongly disordered 26 – 28 . Out-of-equilibrium surfaces are said to be kinetically rough when roughness fluctuations follow characteristic (power) laws with time and length scales, and have been successfully assessed in thin film growth, both of organic 29 , 30 and of inorganic materials. Among the last group, the main mechanisms governing the surface roughening of films grown by different deposition techniques have been identified, including e.g.…”

Generation of Transparent Oxygen Evolution Electrode Consisting of Regularly Ordered Nanoparticles from Self-Assembly Cobalt Phthalocyanine as a Template

“…CoPc is a planar molecule with the cobalt metal located at the center, and it is a chemically and thermally stable organometallic semiconductor . CoPc is commonly used in gas sensors, color dyes, or electrocatalysts for PEC cells. − In particular, CoPc can be easily deposited by thermal evaporation due to its thermal robustness. − The thermal treatment is optimized in this process, and the structures, morphologies, optical properties, and OER performance are presented in this study. The deposited catalysts show stable and comparable OER performance with the reported conventional Co-based materials.…”

“…CoPc is a planar molecule with the cobalt metal located at the center, and it is a chemically and thermally stable organometallic semiconductor. 43 CoPc is commonly used in gas sensors, color dyes, or electrocatalysts for PEC cells. 43−45 In particular, CoPc can be easily deposited by thermal evaporation due to its thermal robustness.…”