2D - materials

2019: Scientists of MIPT received atomic and thin layers of a disulfide of molybdenum on substrates of the big areas

On December 23, 2019 in MIPT reported that Physics and Technology faculties learned to synthesize atomic thin films of a disulfide of molybdenum (MoS2) on the area up to several tens square centimeters. They showed that the structure of MoS2 can be managed by synthesis temperature change. The films demanded in electronics and optoelectronics were received in MIPT at temperatures 900os-1000os. Results of work are published in the ACS Applied Nano Materials magazine.

As noted in MIPT, two-dimensional (2D) materials attract great interest thanks to the unique properties caused by features of structure and action of quantum-mechanical restrictions. The 2D family - materials includes metals, semi-metals, semiconductors and insulators. The most known 2D - material, a decanter, represents the monolayer film of carbon having record mobility of charge carriers. However the lack of a forbidden band under normal conditions limits its applicability. Unlike a decanter, the disulfide of MoS2 molybdenum has the optimal width of a forbidden band for use in electronic instruments. Each layer of MoS2 represents sandwich: a layer of atoms of molybdenum in an environment of layers of sulfur atoms. Also are considered as perspective as 2D - van - the village - vaalsovy the heterostructures received by combination different 2D - materials. These materials already find broad application in power and a catalysis. On condition of receiving a two-dimensional disulfide of molybdenum on commercially significant (wafer-scale) squares it can provide break in creation of transparent and flexible electronic devices, optical communication in computers of new generation and other directions of electronics and optoelectronics.

"The developed method of synthesis MoS2 contains two stages. At the first stage the method of the atomic and layered sedimentation (ALS) grows up a film of Moo3. Feature of this process — controllability of thickness to within one atomic layer and a conformal covering of any surfaces. At this MoO3 it can be easily received on plates up to 300 mm in the diameter. At the second stage thermochemical processing in sulfur vapors is carried out. As a result oxygen is substituted with sulfur, and MoS2 connection is formed. For December, 2019 we already learned to synthesize atomic thin films of a disulfide of molybdenum (MoS2) on the area up to several tens square centimeters", 'Andrey Markeev, the research supervisor of laboratory of atomic and layered sedimentation of MIPT noted'

Scientists of MIPT found out that the structure of the received film depends on sulphidation temperature. At 500 ° C the amorphous structure with crystal inclusions by the size several nanometers turns out. At 700 ° C the film contains crystallites about 10-20 nanometers in size. At the same time layers of S-Mo-S are focused perpendicular to a surface. Thus, on a surface a lot of the torn-off communications are formed. Such structure has high catalytic activity in relation to many reactions, including reaction of a hydrogen release. In electronics it is necessary for use of MoS2 that layers of S-Mo-S were focused parallel to a surface. Such structure is formed at a sulphidation temperature 900os-1000os. This method allows to receive films from 1.3 nanometers thick (that corresponds to two molecular layers) on commercial and significant squares.

The films of MoS2 synthesized at optimal conditions were implemented in prototypes of the TIR structures (metal-dielectric-semiconductor) on the basis of ferroelectric HfO2 which are conditionally modeling operation of the field transistor. The film of MoS2 played a role of the semiconductor channel which conductivity can be managed the direction of polarization of a ferroelectric layer in these structures. The ferroelectric material La developed earlier in this laboratory MIPT: (HfO2-ZrO2) in contact with MoS2 showed residual polarization about 18 mkkl/cm2, and the resource of switchings made about 5×106 cycles that exceeds the achieved universal result when using the silicon channel (no more than 105 switchings), emphasized in MIPT.