Raman Characterization on Two-Dimensional Materials-Based Thermoelectricity.

The emergence and development of two-dimensional (2D) materials has provided a new direction for enhancing the thermoelectric (TE) performance due to their unique structural, physical and chemical properties. However, the TE performance measurement of 2D materials is a long-standing challenge owing to the experimental difficulties of precise control in samples and high demand in apparatus. Until now, there is no universal methodology for measuring the dimensionless TE figure of merit (ZT) (the core parameter for evaluating TE performance) of 2D materials systematically in experiments. Raman spectroscopy, with its rapid and nondestructive properties for probing samples, is undoubtedly a powerful tool for characterizing 2D materials as it is known as a spectroscopic 'Swiss-Army Knife'. Raman spectroscopy can be employed to measure the thermal conductivity of 2D materials and expected to be a systematic method in evaluating TE performance, boosting the development of thermoelectricity. In this review, thermoelectricity, 2D materials, and Raman techniques, as well as thermal conductivity measurements of 2D materials by Raman spectroscopy are introduced. The prospects of obtaining ZT and testing the TE performance of 2D materials by Raman spectroscopy in the future are also discussed.

Tailoring the phase transition of silver selenide at the atomistic scale.

Thermoelectric materials provide promising solutions for energy harvesting from the environment. Silver selenide (Ag2Se) material attracts much attention due to its excellent thermoelectric properties under superionic phase transition. However, the optimal thermoelectric figure of merit occurs during the phase transition at high temperatures, making low-temperature devices unable to benefit from their best thermoelectric performance. Here, we tailored the phase transition process of Ag2Se materials with various sizes, and probed the phase transition temperature by in situ transmission electron microscopy. By tuning the motion of the atoms near the surface using size-dependent surface energy, the phase transition-induced process is tailored towards low temperatures. This work paves the way for future phase transition engineering to enhance thermoelectric performance.

The Trend of 2D Transistors toward Integrated Circuits: Scaling Down and New Mechanisms.

2D transition metal chalcogenide (TMDC) materials, such as MoS2 , have recently attracted considerable research interest in the context of their use in ultrascaled devices owing to their excellent electronic properties. Microprocessors and neural network circuits based on MoS2 have been developed at a large scale but still do not have an advantage over silicon in terms of their integrated density. In this study, the current structures, contact engineering, and doping methods for 2D TMDC materials for the scaling-down process and performance optimization are reviewed. Devices are introduced according to a new mechanism to provide the comprehensive prospects for the use of MoS2 beyond the traditional complementary-metal-oxide semiconductor in order to summarize obstacles to the goal of developing high-density and low-power integrated circuits (ICs). Finally, prospects for the use of MoS2 in large-scale ICs from the perspectives of the material, system performance, and application to nonlogic functionalities such as sensor circuits and analogous circuits, are briefly analyzed. The latter issue is along the direction of "more than Moore" research.