The Centre for Extreme Performance Optical Coatings (EPOC) is pleased to share insights into a significant development in the field of optical coatings, stemming from a comprehensive study recently published. The research, focused on the intricate properties of hafnium oxide (HfO2) thin films, unveils a systematic exploration of the effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry, and optical properties of these films.
The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was employed to fabricate the films on JGS-3 fused silica substrates. The amorphous structure of HfO2 films was confirmed by X-ray Diffraction. The composition and stoichiometry were analyzed using Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry, indicating the formation of over-stoichiometric films. The O:Hf ratio in the ECR-IBD fabricated HfO2 films in this study ranged from 2.4 – 4.45 to 1.
Hafnium oxide, known for its high refractive index and excellent thermal and chemical stability, is widely used in optical coating applications. It is a common component in multilayer optical coatings, interference filters, anti-reflective coatings, and is integral in the construction of metal-oxide-semiconductor transistors and cameras for space applications. The wide bandgap and high laser-induced damage threshold of HfO2 make it a preferred choice for high-power laser systems.
The study reveals a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas. The refractive index and bandgap energy were found to be significantly influenced by variations in the reactive and sputtering oxygen partial pressure. This discovery opens new avenues for the customization of optical properties to meet specific application requirements, enhancing the performance and efficiency of optical devices.
The ECR-IBD technique has demonstrated its capability in fabricating high-quality thin films with properties akin to bulk materials. These films exhibit low scattering, high density, high refractive index, low absorption, excellent mechanical structural properties, and environmental stability. The purity, stoichiometric defects, and optical properties are of paramount importance for the preparation of high-quality coatings.
In this context, EPOC underscores the importance of ongoing research and development to advance the field of optical coatings. The Centre is committed to contributing to this body of knowledge, fostering innovations that will drive the next generation of optical technologies. The insights gained from this study are instrumental in enhancing our understanding and manipulation of hafnium oxide thin films, promising advancements in the performance and application of optical coatings.
Source: The paper can be accessed on ScienceDirect through the following link: Hafnium oxide (HfO2) thin films: Effects of reactive and sputtering oxygen partial pressure on their structure, stoichiometry, and optical properties
