We present a novel approach for the simultaneous determination of the thermal conductivity κ and the total interface conductance g of supported 2D materials by the enhanced opto-thermal method. We harness the property of the Gaussian laser beam that acts as a heat source, whose size can easily and precisely be controlled. The experimental data for multi-layer graphene and MoS₂ flakes are supplemented using numerical simulations of the heat distribution in the Si/SiO2/2D material system. The procedure of κ and g extraction is tested in a statistical approach, demonstrating the high accuracy and repeatability of our method.

We propose a method for monitoring the large-scale homogeneity of the reduction process of graphene oxide. For this purpose, a Raman mapping technique is employed to probe the evolution of the phonon properties of two different graphene oxide (GO) thin films upon controllable thermal reduction. The reduction of GO is reflected by the upshift of the statistical distribution of the relative intensity ratio of the G and D peaks ( I _D / I _G ) of the Raman spectra and is consistent with the ratio obtained for chemically reduced GO. In addition, the shifts of the position distributions of the main Raman modes ( ω D , ω G ) and their cross-correlation with the I _D / I _G ratio provides evidence of a change of the doping level, demonstrating the influence of reduction processes on GO films.

In this work, we report the impact of the substrate type on the morphological and structural properties of molybdenum disulfide (MoS₂) grown by chemical vapor deposition (CVD). MoS₂ synthesized on a 3D substrate, that is SiO₂, in response to the change of the thermodynamic conditions yielded different grain morphologies, including triangles, truncated triangles, and circles. Simultaneously, MoS₂ on graphene is highly immune to the modifications of the growth conditions, forming triangular crystals only. We explain the differences between MoS₂ on SiO₂ and graphene by the different surface diffusion mechanisms, namely hopping and gas-molecule-collision-like, respectively. As a result, we observe the formation of thermodynamically favorable nuclei shapes on graphene, while on SiO₂ a full spectrum of domain shapes can be achieved. Additionally, graphene withstands the growth process well, with only slight changes in strain and doping. Furthermore, by the application of graphene as a growth substrate we realize van der Waals epitaxy, and achieve strain-free growth, as suggested by the photoluminescence (PL) studies. We indicate that PL, contrary to Raman spectroscopy, enables us to arbitrarily determine the strain levels in MoS₂.

One of the primary factors hindering the development of 2D material-based devices is the difficulty of overcoming fabrication processes, which pose a challenge in achieving low-resistance contacts. Widely used metal deposition methods lead to unfavorable Fermi level pinning effect (FLP), which prevents control over the Schottky barrier height at the metal/2D material junction. We propose to harness the FLP effect to lower contact resistance in field-effect transistors (FETs) by using an additional 2D interlayer at the conducting channel and metallic contact interface (under-contact interlayer). To do so, we developed a new approach using the gold-assisted transfer method, which enables the fabrication of heterostructures consisting of TMDs monolayers with complex shapes, prepatterned using e-beam lithography, with lateral dimensions even down to 100 nm. We designed and demonstrated tungsten disulfide (WS₂) monolayer-based devices in which the molybdenum disulfide (MoS₂) monolayer is placed only in the contact area of the FET, creating an Au/MoS₂/WS₂ junction, which effectively reduces contact resistance by over 60% and improves the I_on/I_off ratio 10 times in comparison to WS₂-based devices without MoS₂ under-contact interlayer. The enhancement in the device operation arises from the FLP effect occurring only at the interface between the metal and the first layer of the MoS₂/WS₂ heterostructure. This results in favorable band alignment, which enhances the current flow through the junction. To ensure the reproducibility of our devices, we systematically analyzed 160 FET devices fabricated with under-contact interlayer and without it. Statistical analysis shows a consistent improvement in the operation of the device and reveals the impact of contact resistance on key FET performance indicators.

We first report the temperature phonon properties of a large-area thin film (lateral size: ∼mm, thickness ∼50 nm) made from WS₂ mono and few layers deposited on the SiO₂/Si substrate. We show that temperature phonon properties probed by Raman spectroscopy significantly differ for bulk and thin-film systems in a temperature range of 90–450 K; however, both exhibit strong temperature-dependent phonon energy nonlinear behavior. Employing the optothermal Raman method, we also estimate thin-film thermal conductivity (κ = 4.3 W/(m K)) and thermal interface conductance (g = 5.5 MW/(m² K)) at room temperature. We find that the thermal properties of thin films (κ and g) are 1 order of magnitude lower than that for bulk or monolayer WS₂, which is caused by a reduction in flake size and an increase in boundary scattering. This finding is important for heat management in future applications of thin films made from two-dimensional (2D) nanoflakes.