Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing large-scale monolayer TMDCs on the SiO 2 /Si substrate is crucial for practical applications, however, it remains a big challenge. In this work, a method which combines chemical vapor deposition (CVD) and thermal evaporation was employed to grow monolayer tungsten disulfide (WS 2 ) crystals. Through controlling the density and the distribution of W precursors, a wafer-scale continuous uniform WS 2 film was achieved, with the structural and spectral characterizations confirming a monolayer configuration and a high crystalline quality. Wafer-scale field-effect transistor arrays based on the monolayer WS 2 were fabricated. The devices show superior electrical performances, and the maximal mobility is almost 1 order of magnitude higher than those of CVD-grown large-scale TMDC devices reported so far.

Among large numbers of transition metal dichalcogenides (TMDCs), monolayer rhenium disulfide (ReS2) is of particular interest due to its unique structural anisotropy, which opens up unprecedented opportunities in dichroic atomical electronics. Understanding the domain structure and controlling the anisotropic evolution of ReS2 during the growth is considered critical for increasing the domain size toward a large-scale growth of monolayer ReS2. Herein, by employing angle-resolved Raman spectroscopy, we reveal that the hexagonal ReS2 domain is constructed by six well-defined subdomains with each b-axis parallel to the diagonal of the hexagon. By further combining the first-principles calculations and the transmission electron microscopy (TEM) characterization, a dislocation-involved anisotropic evolution is proposed to explain the formation of the domain structures and understand the limitation of the domain size. Based on these findings, growth rates of different crystal planes are well controlled to enlarge the domain size, and moreover, single-crystal domains with a triangle shape are obtained. With the improved domain size, large-scale uniform, strictly monolayer ReS2 films are grown further. Scalable field-effect transistor (FET) arrays are constructed, which show good electrical performances comparable or even superior to that of the single domains reported at room temperature. This work not only sheds light on comprehending the novel growth mechanism of ReS2 but also offers a robust and controllable strategy for the synthesis of large-area and high-quality two-dimensional materials with low structural symmetry.

Two-dimensional (2D) ferroelectric materials have attracted intensive attention in recent years for academic research. However, the synthesis of large-scale 2D ferroelectric materials for electronic applications is still challenging. Here, we report the successful synthesis of centimeter-scale ferroelectric In2Se3 films by selenization of In2O3 in a confined space chemical vapor deposition method. The as-grown homogeneous thin film has a uniform thickness of 5 nm with robust out-of-plane ferroelectricity at room temperature. Scanning transmission electron microscopy and Raman spectroscopy reveal that the thin film is 2H stacking α-In2Se3 with excellent crystalline quality. Electronic transport measurements of In2Se3 highlight the current–voltage hysteresis and polarization modulated diode effect due to the switchable Schottky barrier height (SBH). First-principles calculations reveal that the polarization modulated SBH is originated from the competition between interface charge transfer and polarized charge. The large area growth of epitaxial In2Se3 opens up potential applications of In2Se3 in novel nanoelectronics.

The van der Waals (vdW)-layered material In2Se3, known for exhibiting spontaneous ferroelectricity at room temperature, has promising applications in nonvolatile memory and advanced optoelectronics. In this work, we report on a strong coupling between strain, ferroelectricity, and optical absorption in the monolayer FEβ-In2Se3. Based on the density functional theory calculations, the monolayer FEβ-In2Se3 has an in-plane spontaneous polarization of 2.109 × 10–10 C/m, seven times larger than that of the reported α-In2Se3. It is found that the external strain can be used as an effective method to modulate the direction and magnitude of ferroelectric polarization. Moreover, our calculations indicate that in-plane polarization will further influence the light absorption anisotropy and absorbance of FEβ-In2Se3. The tunability of strain on the optic properties enables us to design FEβ-In2Se3-based logic devices where the information is read by the light absorption signal. These studies are not only of scientific interest in the interplay between strain and ferroelectric polarization in FEβ-In2Se3 but also open a new path to explore the electronic application of the ferroelectric vdW materials.

Hexagonal boron nitride (h-BN) has emerged as one of the most promising candidates for two-dimensional (2D) materials due to its exciting optoelectrical properties and a broad range of applications. In this work, we explore the potential applications of h-BN nanosheets and nanoribbons as wide band gap semiconductors in terms of carrier mobility. Based on the first-principles calculations and deformation potential (DP) theory, the phonon-limited carrier mobility of monolayer h-BN and nanoribbons at room temperature is predicted. We find that the hole mobility of armchair-edge h-BN nanoribbons (ABNNRs) oscillates regularly with the ribbon width N ac in 1–3 nm. The ABNNRs in the N ac = 3p + 1 family have larger hole mobility with the highest value of 1.9 × 104 cm2 V–1 s–1 in the narrow nanoribbons. Molecular orbital analyses reveal that the large hole mobility originates from the delocalization of the occupied orbitals of valence electrons in the transport direction. By studying the effect of ribbon width on mobility, we identify the role of quantum confinement in tuning the transport properties of h-BN nanoribbons. The potential technological application of h-BN nanostructures as a P-channel material in wide band gap 2D field effect transistors (FETs) is discussed.