In this work, we present a comprehensive theoretical and experimental study of quantum confinement in layered platinum diselenide (PtSe 2 ) films as a function of film thickness. Our electrical measurements, in combination with density functional theory calculations, show distinct layer-dependent semimetal-to-semiconductor evolution in PtSe 2 films, and highlight the importance of including van der Waals interactions, Green's function calibration, and screened Coulomb interactions in the determination of the thickness-dependent PtSe 2 energy gap. Large-area PtSe 2 films of varying thickness (2.5-6.5 nm) were formed at 400°C by thermally assisted conversion of ultra-thin platinum films on Si/SiO 2 substrates. The PtSe 2 films exhibit p-type semiconducting behavior with hole mobility values up to 13 cm 2 /V·s. Metal-oxide-semiconductor field-effect transistors have been fabricated using the grown PtSe 2 films and a gate field-controlled switching performance with an I ON /I OFF ratio of >230 has been measured at room temperature for a 2.5-3 nm PtSe 2 film, while the ratio drops to <2 for 5-6.5 nm-thick PtSe 2 films, consistent with a semiconductingto-semimetallic transition with increasing PtSe 2 film thickness. These experimental observations indicate that the low-temperature growth of semimetallic or semiconducting PtSe 2 could be integrated into the back-end-of-line of a silicon complementary metaloxide-semiconductor process.npj 2D Materials and Applications (2019) 3:33 ; https://doi.

Thin films of noble-metal-based transition metal dichalcogenides, such as PtSe2, have attracted increasing attention due to their interesting layer-number dependent properties and application potential. While it is difficult to cleave bulk crystals down to mono- and few-layers, a range of growth techniques have been established producing material of varying quality and layer number. However, to date, no reliable high-throughput characterization to assess layer number exists. Here, we use top-down liquid phase exfoliation (LPE) coupled with centrifugation to produce PtSe2 nanosheets of varying sizes and thicknesses with a low degree of basal plane defectiveness. Measurement of the dimensions by statistical atomic force microscopy allows us to quantitatively link information contained in optical spectra to the dimensions. For LPE nanosheets we establish metrics for lateral size and layer number based on extinction spectroscopy. Further, we compare the Raman spectroscopic response of LPE nanosheets with micromechanically exfoliated PtSe2, as well as thin films produced by a range of bottom up techniques. We demonstrate that the Eg 1 peak position and the intensity ratio of the Eg 1/A1g 1 peaks can serve as a robust metric for layer number across all sample types.This will be of importance in future benchmarking of PtSe2 films.

Molybdenum dioxide (MoO2) is a layered material which shows promise for a number of applications in the electrochemical energy storage arena. This work describes the production of molybdenum dioxide nanosheets by liquid phase exfoliation.

2D materials display very promising intrinsic material properties, with multiple applications in electronics, photonics, and sensing. In particular layered platinum diselenide has shown high potential due to its layer-dependent tunable bandgap, low-temperature growth, and high environmental stability. Here, the conformal and area selective (AS) low-temperature growth of layered PtSe 2 is presented defining a new paradigm for 2D material integration. The thermally-assisted conversion of platinum which is deposited by AS atomic layer deposition to PtSe 2 is demonstrated on various substrates with a distinct 3D topography. Further the viability of the approach is presented by successful on-chip integration of hybrid semiconductor devices, namely by the manufacture of a highly sensitive ammonia sensors channel with 3D topography and fully integrated infrared-photodetectors on silicon photonics waveguides. The presented methodologies of conformal and AS growth therefore lay the foundation for new design routes for the synthesis of more complex hybrid structures with 2D materials.

Two-dimensional (2D) molybdenum disulfide (MoS 2 )h olds great promise in electronic and optoelectronic applicationso wing to its unique structure and intriguing properties. The intrinsic defects such as sulfur vacancies (SVs) of MoS 2 nanosheets are found to be detrimental to the device efficiency.T om itigate this problem, functionalization of 2D MoS 2 using thiols has emerged as one of the key strategies for engineering defects. Herein,w ed emonstrate an approach to controllably engineer the SVs of chemically exfoliated MoS 2 nanosheets using as eries of substituted thio-phenols in solution. The degree of functionalization can be tuned by varying the electron-withdrawing strength of substituents in thiophenols. We find that the intensity of 2LA(M) peak normalized to A 1g peak strongly correlates to the degree of functionalization. Our resultsp rovide as pectroscopici ndicatort om onitora nd quantify the defecte ngineering process. This methodo fM oS 2 defectf unctionalization in solution also benefitst he further exploration of defect-free MoS 2 for aw ide range of applications.[a] Dr.