In this work, we present a comprehensive theoretical and experimental study of quantum confinement in layered platinum diselenide (PtSe₂) 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 PtSe₂ 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 PtSe₂ energy gap. Large-area PtSe₂ 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/SiO₂ substrates. The PtSe₂ films exhibit p-type semiconducting behavior with hole mobility values up to 13 cm²/V·s. Metal-oxide-semiconductor field-effect transistors have been fabricated using the grown PtSe₂ 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 PtSe₂ film, while the ratio drops to <2 for 5–6.5 nm-thick PtSe₂ films, consistent with a semiconducting-to-semimetallic transition with increasing PtSe₂ film thickness. These experimental observations indicate that the low-temperature growth of semimetallic or semiconducting PtSe₂ could be integrated into the back-end-of-line of a silicon complementary metal-oxide-semiconductor process.

Platinum diselenide (PtSe₂) field‐effect transistors with ultrathin channel regions exhibit p‐type electrical conductivity that is sensitive to temperature and environmental pressure. Exposure to a supercontinuum white light source reveals that positive and negative photoconductivity coexists in the same device. The dominance of one type of photoconductivity over the other is controlled by environmental pressure. Indeed, positive photoconductivity observed in high vacuum converts to negative photoconductivity when the pressure is raised. Density functional theory calculations confirm that physisorbed oxygen molecules on the PtSe₂ surface act as acceptors. The desorption of oxygen molecules from the surface, caused by light irradiation, leads to decreased carrier concentration in the channel conductivity. The understanding of the charge transfer occurring between the physisorbed oxygen molecules and the PtSe₂ film provides an effective route for modulating the density of carriers and the optical properties of the material.

Inspired by recent experimental realizations and theoretical simulations of thin silicon nanowire-based devices, we perform proof-of-concept simulations of junctionless gated Si nanowire transistors. Based on first-principles, our primary predictions are that Si-based transistors are physically possible without major changes in design philosophy at scales of $\sim 1\text{nm}$ wire diameter and $\sim 3\text{nm}$ gate length, and that the junctionless transistor avoids potentially serious difficulties affecting junctioned channels at these length scales. We also present investigations into atomic-level design factors such as dopant positioning and concentration.

The properties and performance of two-dimensional (2D) materials can be greatly affected by point defects. PtTe₂, a 2D material that belongs to the group 10 transition metal dichalcogenides, is a type-II Dirac semimetal, which has gained a lot of attention recently due to its potential for applications in catalysis, photonics, and spintronics. Here, we provide an experimental and theoretical investigation of point defects on and near the surface of PtTe₂. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements, in combination with first-principle calculations, we identify and characterize five common surface and subsurface point defects. The influence of these defects on the electronic structure of PtTe₂ is explored in detail through grid STS measurements and complementary density functional theory calculations. We believe these findings will be of significance to future efforts to engineer point defects in PtTe₂, which is an interesting and enticing approach to tune the charge-carrier mobility and electron–hole recombination rates, as well as the site reactivity for catalysis.

Tailoring the electrical properties of transition metal dichalcogenides by doping is one of the biggest challenges for the application of 2D materials in future electronic devices. Here, we report on a straightforward approach to the n-type doping of molybdenum disulfide (MoS₂) films with rhenium (Re). High-Resolution Scanning Transmission Electron Microscopy and Energy-Dispersive X-ray spectroscopy are used to identify Re in interstitial and lattice sites of the MoS₂ structure. Hall-effect measurements confirm the electron donating influence of Re in MoS₂, while the nominally undoped films exhibit a net p-type doping. Density functional theory (DFT) modelling indicates that Re on Mo sites is the origin of the n-type doping, whereas S-vacancies have a p-type nature, providing an explanation for the p-type behaviour of nominally undoped MoS₂ films.