The structural, electrical, and optical properties of monolayer ruthenium oxide (RuO₂) nanosheets (NSs) fabricated by chemical exfoliation of a layered three-dimensional form of K-intercalated RuO₂ are studied systematically via experimental and computational methods. Monolayer RuO₂ NS is identified as having a distorted h-MX₂ structure. This is the first observation of a RuO₂ NS structure that is unlike the t-MX₂ structure of the RuO₂ layers in the parent material and does not have hexagonal symmetry. The distorted h-MX₂ RuO₂ NSs are shown to have optical transparency superior to that of graphene, thereby predicting the feasibility of applying RuO₂ NSs to flexible transparent electrodes. In addition, it is demonstrated that the semiconducting band structures of RuO₂ NSs can be manipulated to be semi-metallic by adjusting the crystal structure, which is related to band-gap engineering. This finding indicates that RuO₂ NSs can be used in a variety of applications, such as flexible transparent electrodes, atomic-layer devices, and optoelectronic devices.

This comprehensive review of (K,Na)NbO ₃ -based perovskites explores design strategies, mechanisms, and applications in piezocatalysis and photo-piezocatalysis for sustainable environmental and energy solutions.

We investigate thermoelectric properties of Cu-doped Bi₂Te_2.7Se_0.3 fabricated using a simple doping process and spark plasma sintering. Through precise control of Cu doping, it is found that Cu atoms preferentially occupied Bi sites and then intercalated into the van der Waals gap with an increasing Cu content. Electrical transport properties of Cu-doped samples were systemically controlled using this mechanism. At the same time, thermal conductivities of the Cu-doped samples were reduced by the enhancement of point defect phonon scattering due to the Cu atoms. Compared to that of pristine samples, the dimensionless thermoelectric figure of merit (“ZT”) of 0.98 at 323 K for the Cu-doped sample was increased by more than 92% owing to these synergetic effects. Furthermore, the shift of maximum ZT to room temperature provides advantages for enlarging the applications of thermoelectric effects at room temperature.

To develop highly efficient thermoelectric materials, the generation of homogeneous heterostructures in a matrix is considered to mitigate the interdependency of the thermoelectric compartments. In this study, Cu₂Te nanoparticles were introduced onto Bi₂Te_2.7Se_0.3 n-type materials and their thermoelectric properties were investigated in terms of the amount of Cu₂Te nanoparticles. A homogeneous dispersion of Cu₂Te nanoparticles was obtained up to 0.4 wt.% Cu₂Te, whereas the Cu₂Te nanoparticles tended to agglomerate with each other at greater than 0.6 wt.% Cu₂Te. The highest power factor was obtained under the optimal dispersion conditions (0.4 wt.% Cu₂Te incorporation), which was considered to originate from the potential barrier on the interface between Cu₂Te and Bi₂Te_2.7Se_0.3. The Cu₂Te incorporation also reduced the lattice thermal conductivity, and the dimensionless figure of merit ZT was increased to 0.75 at 374 K for 0.4 wt.% Cu₂Te incorporation compared with that of 0.65 at 425 K for pristine Bi₂Te_2.7Se_0.3. This approach could also be an effective means of controlling the temperature dependence of ZT, which could be modulated against target applications.