Photoactive Heterostructures: How They Are Made and Explored

Abstract

In our review we consider the results on the development and exploration of heterostructured photoactive materials with major attention focused on what are the better ways to form this type of materials and how to explore them correctly. Regardless of what type of heterostructure, metal–semiconductor or semiconductor–semiconductor, is formed, its functionality strongly depends on the quality of heterojunction. In turn, it depends on the selection of the heterostructure components (their chemical and physical properties) and on the proper choice of the synthesis method. Several examples of the different approaches such as in situ and ex situ, bottom-up and top-down, are reviewed. At the same time, even if the synthesis of heterostructured photoactive materials seems to be successful, strong experimental physical evidence demonstrating true heterojunction formation are required. A possibility for obtaining such evidence using different physical techniques is discussed. Particularly, it is demonstrated that the ability of optical spectroscopy to study heterostructured materials is in fact very limited. At the same time, such experimental techniques as high-resolution transmission electron microscopy (HRTEM) and electrophysical methods (work function measurements and impedance spectroscopy) present a true signature of heterojunction formation. Therefore, whatever the purpose of heterostructure formation and studies is, the application of HRTEM and electrophysical methods is necessary to confirm that formation of the heterojunction was successful.

The Composite TiO2–CuOx Layers Formed by Electrophoretic Method for CO2 Gas Photoreduction

“…We used n = 2, which is typical for the indirect allowed transition [ 24 ]. The optical band gap values were obtained from the linear fits to (F(R d ) · hν) 1/2 versus hν (frequently called Tauc plot) [ 29 , 30 , 31 , 32 ].…”

Formation and Electrochemical Properties of Heterostructured Electrodes Based on Cu2O and CuCo2O4

“…The formation of heterostructured materials results in the formation of the interfaces [7], where contact resistance arises, depending on the nature of the interaction between the component compounds, and is determined by the synthesis route of the layer formation. There are many different methods of synthesis and formation of heterostructured electrode systems possessing their advantages and disadvantages [8,9]. In the case of a component layer deposition from a suspension, the contact area of the two phases is limited by the particle size, while the coating formation via sol-gel technology promotes the formation of a uniform coating.…”

Photoactive Heterostructures Based on α-Fe2O3 and CuO Thin Films for the Removal of Pollutants from Aqueous Solutions

“…Finally, 3D heterostructures expand in all three directions and involve multiple and rare shapes, the most common considering nanoparticle components. Frequently, these heterostructures are conformed by agglomerates of crystallites of different components, the more popular is the core-shell structure [14]. There is a growing interest in the research for nanofilms (2D) materials with novel properties that permit stacking and combination of thin layer-layer reaching unexpected features such as technological goals [15].…”