A resistance-driven H2 gas sensor : high-entropy alloy nanoparticles decorated 2D MoS2

The need to use hydrogen (H2) gas has increasingly become important due to the growing demand for carbon-free energy sources. However, the explosive nature of H2 gas has raised significant safety concerns, driving the development of efficient and reliable detection. Although 2D materials have emerged as promising materials for hydrogen gas sensing applications due to their relatively high sensitivity, the incorporation of other nanomaterials into 2D materials can drastically improve both the selectivity and the sensitivity of sensors. In this work, high-entropy alloy nanoparticles using non-noble metals were used to develop a sensor for H2 gas detection. This chemical sensor was realized by decorating 2D MoS2 surfaces with multicomponent body-centered cubic (BCC) equiatomic Ti–Zr–V–Nb–Hf high-entropy alloy (HEA) nanoparticles. It was selective towards H2, over NH3, H2S, CH4, and C4H10, demonstrating widespread applications of this sensor. To understand the mechanisms behind the abnormal selectivity and sensitivity, density functional theory (DFT) calculations were performed, showing that the HEA nanoparticles can act as a chemical hub for H2 adsorption and dissociation, ultimately improving the performance of 2D material-based gas sensors

MBE deposited scandium nitride (ScN) for thermoelectric applications

Resumen del trabajo presentado en el Virtual Conference on Thermoelectrics (VCT), celebrado online del 21 al 23 de julio de 2020Scandium nitride (ScN) is an emerging rocksalt III-nitride semiconductor and has attracted significant interests in recent years for its potential thermoelectric applications, as a substrate for high-quality epitaxial GaN growth and as a semiconducting component for epitaxial singlecrystalline metal/semiconductor superlattices for thermionic energy conversion. In this poster, we show high mobility and high thermoelectric power factor in epitaxial ScN thin films deposited on MgO substrates with plasma-assisted molecular beam epitaxy (PAMBE). Structural and microscopic characterization showed epitaxial 002 oriented ScN film growth on MgO (001) substrates and the presence of extended defects including dislocations and grain boundaries. Electrical measurement exhibited high room-temperature mobility of 127 cm2 /Vs and temperaturedependent mobility from 50-400 K temperature range that is dominated by dislocation and grain boundary scattering. Due to the high mobility and a moderately large carrier concentration (8.6×1019 cm-3 ), ScN films exhibit high Seebeck coefficients (180 µV/K at 950 K) and a large thermoelectric power factor (2.3 × 10-3 W/m K2 at 500K). The thermal conductivity measured with a time-domain thermoreflectance (TDTR) measurement system exhibit a value of 7.33 W/m K at 500 K that results in a maximum ZT of 0.2. Further research on alloy formation as well as nanostructuring is currently underway to reduce the thermal conductivity and improve the ZT.Peer reviewe

High mobility and high thermoelectric power factor in epitaxial ScN thin films deposited with plasma-assisted molecular beam epitaxy

Scandium nitride (ScN) is an emerging rock salt III-nitride semiconductor and has attracted significant interest in recent years for its potential thermoelectric applications as a substrate for high-quality epitaxial GaN growth and as a semiconducting component for epitaxial single-crystalline metal/semiconductor superlattices for thermionic energy conversion. Solid-solution alloys of ScN with traditional III-nitrides such as AlScN have demonstrated piezoelectric and ferroelectric properties and are actively researched for device applications. While most of these exciting developments in ScN research have employed films deposited using low-vacuum methods such as magnetron sputtering and physical and chemical vapor depositions for thermoelectric applications and Schottky barrier-based thermionic energy conversion, it is necessary and important to avoid impurities, tune the carrier concentrations, and achieve high-mobility in epitaxial films. Here, we report the high-mobility and high-thermoelectric power factor in epitaxial ScN thin films deposited on MgO substrates by plasma-assisted molecular beam epitaxy. Microstructural characterization shows epitaxial 002 oriented ScN film growth on MgO (001) substrates. Electrical measurements demonstrated a high room-temperature mobility of 127 cm/V s and temperature-dependent mobility in the temperature range of 50-400 K that is dominated by dislocation and grain boundary scattering. High mobility in ScN films leads to large Seebeck coefficients (-175 μV/K at 950 K) and, along with a moderately high electrical conductivity, a large thermoelectric power factor (2.3 × 10 W/m-K at 500 K) was achieved, which makes ScN a promising candidate for thermoelectric applications. The thermal conductivity of the films, however, was found to be a bit large, which resulted in a maximum figure-of-merit of 0.17 at 500 K.D.R., B.B., and B.S. acknowledge the International Center for Materials Science (ICMS) and Sheik Saqr Laboratory (SSL) in JNCASR for support. B.S. acknowledges the Science and Engineering Research Board (SERB) of the Government of India, Start-Up Research Grant No. SRG/2019/000613 for financial support. M.S.M.G. wants to acknowledge financial support from No. MAT2017-86450- C4-3-R and intramural CSIC Project No. 2D-MESES. M.G., V.B., and A.I.K.P acknowledge the facilities of Sydney Microscopy and Microanalysis at the University of Sydney. Y.R.K. and P.E.H. appreciate support from a MURI program through the Office of Naval Research, Grant No. N00014-18-1-2429

Magnetic Stress-Driven Metal-Insulator Transition in Strongly Correlated Antiferromagnetic CrN

Traditionally, the Coulomb repulsion or Peierls instability causes the metal-insulator phase transitions instrongly correlated quantum materials. In comparison, magnetic stress is predicted to drive the metalinsulator transition in materials exhibiting strong spin-lattice coupling. However, this mechanism lacksexperimental validation and an in-depth understanding. Here we demonstrate the existence of the magneticstress-driven metal-insulator transition in an archetypal material, chromium nitride. Structural, magnetic,electronic transport characterization, and first-principles modeling analysis show that the phase transitiontemperature in CrN is directly proportional to the strain-controlled anisotropic magnetic stress. Thecompressive strain increases the magnetic stress, leading to the much-coveted room-temperature transition.In contrast, tensile strain and the inclusion of nonmagnetic cations weaken the magnetic stress and reducethe transition temperature. This discovery of a new physical origin of metal-insulator phase transition thatunifies spin, charge, and lattice degrees of freedom in correlated materials marks a new paradigm and couldlead to novel device functionalities