Nanomaterials, defined as particles ranging from 1 to 100 nm diameter, have become widely utilized because of their unique physicochemical properties. Among those nanoparticles, titanium dioxide (TiO2) is frequently used in the production of paints, paper, plastics, welding rod-coating material, cosmetics, etc. TiO2 is the most commonly used semiconductor photocatalyst. Among the different nanomaterials, it is the most studied. Activated by UV-A irradiation, its photocatalytic properties have been utilized in various applications. A wealth of information on TiO2 photocatalytic in activation of bacteria has been acquired over the last 20 years. Hence, in this review article we have described synthesis methods mainly sol–gel type method like sol–gel method, ultrasonic-assisted sol–gel method, microemulsion method, colloidal synthesis, and also other method are discussed like solvo-thermal method, thermal plasma process, supersonically expanded plasma jet method, induction plasma torch, reactive plasma processing, plasma electrolytic oxidation, hydrolysis method, thermohydrolysis method, coprecipitation method, citrate–nitrate autocombustion method, etc. Also applications of TiO2 like medical applications, environmental application, sensor application, photocatalytic applications, and also its health impact for long-term exposure are discussed.

A review on nano-TiO2 sol–gel type syntheses and its applications

Van der Waals heterostructure based on layered two-dimensional (2D) materials offers unprecedented opportunities to create materials with atomic precision by design. By combining superior properties of each component, such heterostructure also provides possible solutions to address various challenges of the electronic devices, especially those with vertical multilayered structures. Here, we report the realization of robust memristors for the first time based on van der Waals heterostructure of fully layered 2D materials (graphene/MoS2-xOx/graphene) and demonstrate a good thermal stability lacking in traditional memristors. Such devices have shown excellent switching performance with endurance up to 107 and a record-high operating temperature up to 340oC. By combining in situ high-resolution TEM and STEM studies, we have shown that the MoS2-xOx switching layer, together with the graphene electrodes and their atomically sharp interfaces, are responsible for the observed thermal stability at elevated temperatures. A well-defined conduction channel and a switching mechanism based on the migration of oxygen ions were also revealed. In addition, the fully layered 2D materials offer a good mechanical flexibility for flexible electronic applications, manifested by our experimental demonstration of a good endurance against over 1000 bending cycles. Our results showcase a general and encouraging pathway toward engineering desired device properties by using 2D van der Waals heterostructures.

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Robust memristors based on layered two-dimensional materials

Photocatalytic TiO2 thin film deposited onto glass by DC magnetron sputtering

Influence of substrate temperature on atomic layer growth and properties of HfO2 thin films

Van der Waals heterostructures are formed by stacking layers of different two-dimensional materials and offer the possibility to design new materials with atomic-level precision. By combining the valuable properties of different 2D systems, such heterostructures could potentially be used to address existing challenges in the development of electronic devices, particularly those that require vertical multi-layered structures. Here we show that robust memristors with good thermal stability, which is lacking in traditional memristors, can be created from a van der Waals heterostructure composed of graphene/MoS2–xO
 x
 /graphene. The devices exhibit excellent switching performance with an endurance of up to 107 and a high operating temperature of up to 340 °C. With the help of in situ electron microscopy, we show that the thermal stability is due to the MoS2–xO
 x
 switching layer, as well as the graphene electrodes and the atomically sharp interface between the electrodes and the switching layer. We also show that the devices have a well-defined conduction channel and a switching mechanism that is based on the migration of oxygen ions. Finally, we demonstrate that the memristor devices can be fabricated on a polyimide substrate and exhibit good endurance against over 1,000 bending cycles, illustrating their potential for flexible electronic applications. Memristors that offer good thermal stability, which is lacking in traditional memristors, can be created from a van der Waals heterostructure composed of graphene/MoS2–xO
 x
 /graphene.

/pdf/robust-memristors-based-on-layered-two-dimensional-materials-4jut0qw14p.pdf

Daniel Rondot

Papers

Microstructure modification of amorphous titanium oxide thin films during annealing treatment