Advanced Bandgap-Engineered Two-Dimensional Materials for Photonics Device Applications

Advanced two-dimensional materials including MoS2, MoSe2, and h-BCN has recently gain much importance in material and photonics research owing to their capabilities of tuning their electronic bandgap hence optical absorption spectra. This project focuses on the complete investigation of synthesis, transfer/deposition and characterizations of the 2D materials for practical photonics device applications.

Since the discovery of graphene, huge amount of work has been levied on understanding its basic properties and fundamental characteristics. Many useful applications have been proposed and demonstrated, which primarily leverage on the many outstanding properties of the material. For example, graphene has a very unique band structure and interesting semi-metallic electrical property which give rise to a variety of unique and unusual optical properties. Despite being only one atom thick, graphene is found to absorb a significant fraction of incident light due primarily to its unique electronic properties.

Moreover, due to the linear dispersion relation of graphene their absorption is also wavelength independent. Furthermore, the absorption increases proportionally to the number of layers, which indicates that the number of the layers can be found by observing the optical contrast in the sample. The wonderful properties of such 2D material allow for multiple functions of signal emitting, transmitting, modulating, and detection to be realized in one single class of material. Based on the advances of graphene, 2D composite materials such as MoS2, MoSe2, and h-BCN has recently gain much importance in 2D material research owing to their reported capabilities of further tuning their electronic bandgap via relatively simple mechanism. Together with their intrinsically superior properties makes these 2D materials extremely attractive for various applications. Combing the capabilities of engineering of bandgap thus the optical absorption spectrum, intrinsic ultra-fast optical response, and 2D atomic layer physical properties, these advanced 2D materials are known as the future materials of many photonics applications in our daily life. Examples include video imaging, optical communications, biomedical imaging, security, night vision, gas sensing, wearable health devices, and motion detection.

In particular, there is an ever-stronger demand for sensors or imaging systems that are having faster response and can cover specific spectral ranges ranging from visible light to infrared or even THz range. The capabilities of tailor-made optical absorption spectrum make such 2D materials extremely attractive for these applications. However, there still exist many obstacles, both fundamental and practical, towards practically applying these materials. Regarding synthesis of these 2D materials, some of them can be prepared by chemical exfoliation, chemical reduction of graphite oxide, CVD and epitaxial method.

To achieve very high quality materials for device application, typical state-of-the-art techniques include CVD and epitaxy/thermal decomposition. In these techniques, usually the substrates are heated to exceeding high temperatures of 600-800 OC. Obviously at these process temperatures, flexible, plastic and more delicate substrates cannot be used. In order to deposit these materials onto temperature sensitive substrates, investigation of post growth cold transfer techniques becomes emerging for practical device applications.

This project focuses on the investigation of a series of advanced 2D materials from their synthesis and applications. Specific aims include:

1. Development of bandgap engineered large area films of 2D materials for specific photonics applications in different wavelength ranges through both chemical vapour deposition (CVD) and plasma assisted method.

2. Development of cold transfer methods of the 2D materials such as spray coating or optical tweezers effect on targeted optical waveguides or substrates for device fabrications.

3. Characterization of the optical properties of the fabricated 2D material based devices for practical applications including sensing and light detection.

This project will comprise of challenging aspects both in terms of theoretical studies and experimentation. However, the gains we can achieve from here will be of importance to many in the scientific arena as well as the industry in general. Supported by the strong foundation of graphene and nano-material research at MMU, the supervisory team comprises of multi-disciplinary experts in the field of optics, nano-materials, as well as material analysis. As such we are confident of achieving the stated goals of our project and look forward to further external grant bidding ahead.