Original Article

, Volume: 22( 11) DOI: 10.37532/0974-7419.2022.22(11).226

• View PDF
• Download PDF

Reactions: Surface science perspectives

*Correspondence:

Jackson Will* Managing Editor, Analytical Chemistry: An Indian Journal, New York, USA. , E-mail: will.jackson411@gmail.com

Abstract

Around ten years ago, basic research on the surface science elements of plasma-assisted etching was started in labs all over the world. This experimentally difficult problem has been approached in a number of ways, including using directed beams of energetic positive ions and thermally energetic reactive molecules/radicals in a UHV environment to simulate the reactive gas glow discharge environment; simulating the reactive gas glow discharge using a beam of reactive ions (reactive ion beam etching), and carefully ex-situ analyzing surfaces etched in reactive gas glow discharges without air exposure. This paper, which summarises the state of this mostly unknown area of surface chemistry, will solely evaluate the work that was reported using the first of these methodologies. Understanding the bulk, surface, and interfacial events that take place during TiO2 photocatalysis can be done in a special way thanks to the discipline of surface science. This review presents new research that offers a molecular-level understanding of photon-initiated phenomena occurring at TiO2 surfaces from the standpoint of surface science. The structure of this review identifies seven major scientific issues.

Keywords

Titanium oxidel; Scanning tunneling microscopy; Single-crystalline surfaces; Adhesion; Catalysis

Introduction

Plasma-assisted etching, which employs reactive gas glow discharges to etch solids, is a crucial step in the manufacture of very large-scale integrated circuits and is becoming more and more significant in other fields. The fundamental principle behind plasma-assisted etching is very straightforward: use a molecular gas glow discharge to split relatively stable molecules into highly reactive atoms and/or molecular radicals, then choose the chemistry so that these species react with the solid being etched to produce volatile products. The etching of silicon in a CF, glow discharge is the most well-known illustration of this method. When employed as a feed gas in a glow discharge, CF, a fairly stable, non-toxic, non-reactive, and easily handled gas, swiftly dissociates into F atoms and CF radicals.

Early plasma experiments led to the revelation that some implementations of this method can produce anisotropic or directed etching, which led to the discovery of the significance of plasma-assisted etching in the manufacture of integrated circuits. This enables the etching of incredibly minute details with minimal to no loss of dimensional control. Devices with feature sizes of the order of 2 pm-3 pm or fewer cannot be reliably fabricated using the isotropic etching accomplished using wet chemical techniques. Cleanliness, environmental effect (the disposal of huge amounts of poisonous liquids is avoided), and compatibility with other dry processes are further aspects that have prompted the usage of plasma-assisted etching technologies in manufacturing processes.

A photocatalytic reaction's photon absorption step is frequently thought of as a bulk, or subsurface, process. Two problems, though, make this subject pertinent to surfaces. First, the electronic structures of surfaces differ significantly from those of the bulk as a result of lattice truncation and the creation of surface "dangling" bond states. Surface states or surface charge transfer complexes are capable of producing unusual excitation events. Second, surface photon absorption activities can significantly boost a TiO₂ nanoparticle's overall photon absorption capability. For instance, a TiO₂ nanoparticle with a nominal radius of 3 nm to 4 nm has a surface-to-bulk atom ratio of about 1 to 10. In this instance, a TiO₂ nanoparticle material's surface area.

Conclusion

There are still many opportunities and difficulties. Researchers have found that the R TiO₂ (110) surface is essential for providing a platform for researching key mechanisms crucial to TiO₂ photocatalysis under carefully controlled conditions. The development of other clearly defined TiO₂ surfaces (such as significant R or A orientations) is proceeding. It is still to be seen whether researchers will be able to use single crystal surfaces to replicate indirect processes (such the creation and reactivity of OH). The effects of additives (such as dopants, cocatalysts, etc.) on TiO₂ photocatalysis have been the subject of numerous studies, but more research is still needed at the molecular level to understand how these additives affect processes like photon absorption, electron transfer, and thermal/non-thermal chemistry at TiO2 surfaces.