A very high-resolution scanning nonlinear dielectric microscope was developed for the observation of ferroelectric polarization. We demonstrate that the resolution of the microscope is of a nanometer order by measurement of the c–c domain wall of a BaTiO3 single crystal, and that this microscope is very useful not only for the domain observation of ferroelectric bulk material but also for that of thin films.

A multi-layered MoS 2 film was formed on a SiO 2 film by high-temperature sputtering, which is one of the alternative methods of Si LSI technology. It was found that the carrier density of a sputter-deposited MoS 2 film is 1000 times smaller than that of an exfoliated one. By sputtering, two different orientations, namely a layer lateral to a SiO 2 /Si substrate and a layer perpendicular to the substrate, were formed. The lateral layer showed a lower carrier density than the perpendicular layer because of the decrease in the number of sulfur vacancies, as commonly discussed in several research studies. However, the vacancies are not sufficient for describing this significant reduction in carrier density. It is considered that a sodium ion functioning as an interface trapped charge is one of the main origins of carriers. Sputtering, which enables us to determine the sodium contamination level, can be seen as appropriate for reducing the carrier density; hence, this method is considered to be efficient in realizing enhancement-mode MoS 2 MOSFETs. In addition, sputtering also enable us to form large-scale MoS 2 films up to a wafer size. Therefore, a sputterdeposited MoS 2 film is a promising material for post-silicon devices.

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A sputtered MoS2 thin film is a candidate for realizing enhancement-mode MoS2 metal–oxide–semiconductor field-effect transistors (MOSFETs). However, there are some sulfur vacancies in the film, which degrade the device performance. In this study, we performed postdeposition sulfurization annealing (PSA) on a sputtered MoS2 thin film in order to complement sulfur vacancies, and we investigated the fundamental properties of the MoS2 film. As a result, a high-quality crystalline 10-layer MoS2 film with an ideal stoichiometric composition was obtained at a relatively low process temperature (500 °C). The MoS2 film had an indirect bandgap of 1.36 eV and a high Hall mobility compared with the as-deposited sputtered MoS2 film.

The fabrication of a high-quality single-layer MoS2 film was achieved at a sufficiently low temperature of 500 °C by the combination of sputtering deposition and post deposition sulfurization annealing. Fabrication only by sputtering produces unintentionally sulfur-deficient nonstoichiometric films with poor crystalline quality in nature, making it difficult to fabricate atomically thin sputtered MoS2 films, especially with a single layer. From the results of the sulfurization annealing, sulfur deficiencies in the film were fully complemented and the crystalline quality, especially in-plane symmetry, was dramatically improved. The quasi-layered structure of the sputtered-MoS2 film led to the success in achieving low-temperature sulfurization annealing. Moreover, the film had large area uniformity, accurate thickness controllability, a direct bandgap of 1.86 eV, and an extremely high visible transmittance of more than 97%. Therefore, we consider that the fabrication technique will contribute to realizing MoS2 display applications such as a low-power-consumption thin-film-transistor liquid crystal display.