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 report a model for the description of a room temperature photocurrent temporal response in devices made of a chemical vapor deposition grown molybdenum disulfide monolayer. The proposed model distinguishes three components of a photoresponse that may be attributed to photoconductance and a photogating effect, where photogating involves environmental and intrinsic material contribution. We showed that each time constant obtained from the model differed by an order of magnitude and remained unaffected by changes of the environment, whereas the amplitudes behaved according to the attributed effects. Notably, the rising photocurrent signal was a useful source of information regarding the persistent photoconductivity effect. Finally, we demonstrated the versatility of our model by applying it to some previous reports on time-resolved photocurrent. Our results help to determine the optoelectronic properties of MoS 2 monolayers and future photosensitive devices operating at ambient room temperature.

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 /I) 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 ([Formula: see text], [Formula: see text]) and their cross-correlation with the I /I 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 substrate type on the morphological and structural properties of molybdenum disulfide (MoS 2 ) grown by chemical vapor deposition (CVD). MoS 2 synthesized on a three-dimensional (3D) substrate, that is, SiO 2 , in response to the change of the thermodynamic conditions yielded different grain morphologies, including triangles, truncated triangles, and circles. Simultaneously, MoS 2 on graphene is highly immune to the modifications of the growth conditions, forming triangular crystals only. We explain the differences between MoS 2 on SiO 2 and graphene by the different surface diffusion mechanisms, namely, hopping and gas-molecule-collision-like mechanisms, respectively. As a result, we observe the formation of thermodynamically favorable nuclei shapes on graphene, while on SiO 2 , 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 MoS 2 .

A deep understanding of the thermal properties of 2D materials is crucial to their implementation in electronic and optoelectronic devices. In this study, we investigated the macroscopic in-plane thermal conductivity (κ) and thermal interface conductance (g) of large-area (mm2) thin film made from MoS2 nanoflakes via liquid exfoliation and deposited on Si/SiO2 substrate. We found κ and g to be 1.5 W/mK and 0.23 MW/m2K, respectively. These values are much lower than those of single flakes. This difference shows the effects of interconnections between individual flakes on macroscopic thin film parameters. The properties of a Gaussian laser beam and statistical optothermal Raman mapping were used to obtain sample parameters and significantly improve measurement accuracy. This work demonstrates how to address crucial stability issues in light-sensitive materials and can be used to understand heat management in MoS2 and other 2D flake-based thin films.