The surface morphology of a material can change when dopant atoms are introduced due to a number of reasons, including:

Overall, the specific reason for a more uniform surface morphology after the doping of atoms will depend on the specific material, dopant, and processing conditions. However, the factors mentioned above are some of the common reasons why doping can result in a more uniform surface morphology.

Nowadays, smart electronic devices have become ubiquitous. These devices require power for their functioning. The conventional energy resources are limited in nature, and their consumption produces unwanted byproducts, which cause the greenhouse effect. (1,2) Therefore, there is a need for alternative energy sources that are clean, green, and renewable in nature. The existing renewable energy resources can generate a huge amount of energy, but they are intermittent in nature. Efficient storage of energy to meet the energy demand as and when needed is still a challenge. (3,4)

There are basically two mechanisms of energy storage: one is through batteries, while the other is using electrochemical capacitors/supercapacitors (SCs). (5,6) Both batteries and supercapacitors have fundamental differences due to their materials, structures, and charge-storage mechanisms. Batteries yield a high energy density because of their storing charges in a bulk of electrodes, while SCs may provide high power density via surface charge-storage mechanisms. (1,5−7) SCs have many applications in the field of uninterrupted power supplies (UPS), automobiles, and power backup to protect, enhance, and/or replace batteries. (1,2,7−9) SCs can broadly be classified into two categories on the basis of the charge-storage mechanism: (i) electrical double-layer capacitors (EDLCs) and (ii) pseudocapacitors. (2) In EDLCs, the electrical charge is stored at the electrode–electrolyte interface, while in pseudocapacitors, the charge is stored through redox reactions occurring at the surface of an appropriate electrode. (1) Charge storage via the pseudocapacitance mechanism exhibits some interesting properties as compared to the EDLC mechanism. (1,2,10) For this reason, a lot of work has been done for the storage of charge via the pseudomechanism for the fabrication of high-performance supercapacitive electrodes. (2) Many researchers have suggested that the transition metal oxides can be a potential candidate for supercapacitive electrodes due to the high surface area of the material. (2,9−12) Graphene has also been exploited for supercapacitor applications. (5,13,14) Currently, materials such as NiO, TiO2, Co3O4, RuO2, Ni(OH)2, Sr(OH)2, MnO2, Co3O4, Bi2O, In2O3, and Fe3O4 are being investigated as supercapacitors keeping in view their cost-effectiveness, high capacity, and environment-friendly nature. (1,7,8,15)

Thin-film-based devices have attracted lots of attention, as thin films exhibit physical and chemical properties different from those of the same material in bulk. (16−22) In the case of thin-film and nanostructure devices, the surface to volume ratio is large compared to bulk material. (22,23) The surface morphology of thin films (nanostructure) influences the functional properties of SCs, which play a major role in energy storages. Therefore, a detailed knowledge of the surface morphology is important for the fabrication of devices having the desired properties. (24) Generally, surfaces can be studied using classical parameters (average roughness and interface width), which are highly dependent on the scale resolution of the measuring instruments. However, these traditional parameters are not able to give deeper, nanolevel insights such as the correlation, roughness exponent, height fluctuations, and complex structure of a surface. (24−30) Therefore, we require a technique that is scale invariant. This scale invariance can be achieved by employing fractal geometry. (9,24−30) Fractal objects show a self-affine nature, which can be seen by rescaling the surfaces along horizontal as well as vertical directions with different ratios. (24,25) Recently, Yadav et al. reported a close correlation between the fractal dimension and wettability of a surface. (30) Ţălu et al. have suggested a relationship between the electrical resistivity and fractal dimension. (31) Guisbiers et al. explored the relationship between residual stress and fractal dimension. (32) Wang et al. reported a relationship between the fatigue threshold value and fractal dimension. (33) Foadi et al. studied the roughness-dependent wettability of vapor-deposited metallic thin films. (34,35)

Surface morphology plays an essential role in governing the supercapacitive behavior of the material. An enhanced surface area increases the reactivity. Recently, a fractal study of a Cu-doped Sr(OH)2 thin film as a supercapacitive electrode reported that the supercapacitive value enhances with increase in fractal dimension. (9) This suggests that surface engineering can be an efficient tool to adjust the surface area of electrodes with fractal porosity/granularity for further improvements in the performance of devices. (1,36) It is interesting to note that the electrode–electrolyte interface with fractal geometry offers an improved electrode–electrolyte interface. (1,9,36,37) Fractal objects have a higher surface area as compared to the substrates. (9,38,39)

Many researchers have reported that the performance of a supercapacitor is enhanced with metal doping as well as the formation of nanocomposites. (9−11,36,40,41) Recently, our group reported a high specific capacity (∼413 C g–1), energy density (∼45.95 Wh kg–1), and power density (∼2.6 kW kg–1) in an Sr(OH)2-based supercapacitive electrode. The natural abundance, low cost, electrochemical performance, and environment-friendly nature of this material has made it an efficient candidate that has attracted the researchers to use it as a new electrode for supercapacitors. The supercapacitive properties can be further enhanced by suitable doping of metals such as Cu and Fe. (9,11)

In this work, fractal concepts have been applied to explore the irregularity and fragmentation of the samples. As a test case, we have taken Fe-doped Sr(OH)2 samples fabricated using the SILAR technique. A detailed experimental characterization of the surface morphology, structural analysis, and electrochemical characterization can be found elsewhere. (11) Here, we have focused on their theoretical investigations using fractal characterization. Our study suggests that the Fe doping affects the roughness exponent and fractal dimension. The fractal model will maximize the electrochemically active surface area and minimize the energy loss during the transport of ions inside the fractal networks.

Please check this DOI for more DATA : Article Effect of Fe Doping on the Surface Morphology and Supercapac...

When certain atoms are doped into a material, they can alter the crystal structure or affect the way the material grows. This can lead to a more uniform surface morphology due to the creation of defects that act as nucleation sites, more controlled growth, or changes in the material's chemical properties that affect its interactions with the environment. The specific mechanism by which dopants affect the surface morphology depends on factors such as dopant concentration, material composition, and growth conditions.