Transistors and sensors based on molybdenum disulfide
Dimitrios N. Kouvatsos
Limitations in silicon technology make novel materials necessary for a variety of applications. Transition metal dichalcogenides in thin or two-dimensional films are a class of materials with unique electrical, optical and mechanical properties. The most important of these is molybdenum disulfide (MoS2). After initially attracting much interest because of its electrocatalytic activity for hydrogen production, its width-adjustable energy gap has lately invited intense research for electronic and photonic application impossible with the use of gapless graphene. In this project we will investigated MoS2 films, which we will deposit with a novel technique, and their applications in thin film transistor (TFTs) and sensors. We will utilize the method of hot-wire chemical vapor deposition (CVD) using a homemade reactor, adapted to control film thickness down to low values, possibly single molecular layers of MoS2. Our approach is compatible with substrates that can only be exposed to room temperature, suitable for flexible electronics.We will investigate the relation between the molecular structure and the properties of hot-wire CVD MoS2 films with the deposition conditions and the type of substrate. Subsequently, the relation of the structure, the morphology and the thickness of the films with the electrical properties and the degradation endurance of the transistors made in them will be
elucidated. Possible techniques for the neutralization of active defects of sulfur vacancies will be studied to improve the transistor electrical characteristics. While MoS2 monolayers have attracted most research effort, they are sensitive and limited to small surfaces. We will thus investigate how some of their properties can be preserved in multilayer deposited films. This will be particularly useful for sensors detecting hydrogen, carbon monoxide, moisture, ammonia and organic compounds, based on the adsorption of hydrogen or other molecules to MoS2 films, which we will develop. Film surface modifications and roughness variations will be studied to this end to increase, for the case of sensors, the film active defects capturing the molecules to be detected. Sensing techniques based on variations of the electrical resistance of the films will be used, while detection via parameter modification of TFTs specially made in them will also be considered.The project results will open the way to wider applications, such as smart microsystems of sensors actively controlled be TFTs in cheap flexible substrates, for which the excellent mechanical flexibility of MoS2 films will be useful. Properties of these films beyond the scope of the present project, such as thermoelectric effects in metallic film phases, will also provide the capability of energy harvesting and thus self-charging, leading to microsystems with almost limitless capabilities. In this way a much promising, yet not overly complex, technology will be developed, suitable for countries without a tradition of microelectronics and nanoelectronics industry.