Optical Transistor for an Amplification of Radiation in a Broadband THz Domain

We propose a new type of optical transistor for a broadband amplification of THz radiation. It is made of a graphene--superconductor hybrid, where electrons and Cooper pairs couple by Coulomb forces. The transistor operates via the propagation of surface plasmons in both layers, and the origin of amplification is the quantum capacitance of graphene. It leads to THz waves amplification, the negative power absorption, and as a result, the system yields positive gain, and the hybrid acts like an optical transistor, operating with the terahertz light. It can, in principle, amplify even a whole spectrum of chaotic signals (or noise), that is required for numerous biological applications.Comment: 7 pages, 3 figure

Pd-Decorated 2D MXene (2D Ti₃C₂Ti_x) as a High-Performance Electrocatalyst for Reduction of Carbon Dioxide into Fuels toward Climate Change Mitigation

Palladium nanoparticles (Pd NPs) have attracted considerable attention recently for their excellent catalytic properties in various catalysis reactions. However, Pd NPs have some drawbacks, including their high cost, susceptibility to deactivation, and the possibility of poisoning by intermediate products. Herein, Pd nanoparticles with an average diameter of 6.5 nm were successfully incorporated on electronically transparent 2D MXene (Ti3C2Tix) nanosheets (Pd-MXene) by microwave irradiation. Considering the synergetic effects of ultra-fine Pd NPs, together with the intrinsic properties of 2D MXene, the obtained Pd-MXene showed a specific surface area of 97.5 m2g−1 and multiple pore channels that enabled excellent electrocatalytic activity for the reduction of CO2. Further, the 2D Pd-MXene hybrid nanocatalyst enables selective electroreduction of CO2 into selective production of CH3OH in ambient conditions by multiple electron transfer. A detailed explanation of the CO2RR mechanism is presented, and the faradic efficiency (FE) of CH3OH is tuned by varying the cell potential. Recyclability studies were conducted to demonstrate the practical application of CO2 reduction into selective production of CH3OH. In this study, metal and MXene interfaces were created to achieve a highly selective electroreduction of CO2 into fuels and other value-added chemical products

Photon drag currents and terahertz generation in α-Sn/Ge quantum wells

We have fabricated α-Sn/Ge quantum well heterostructures by sandwiching nano-films of α-Sn between Ge nanolayers. The samples were grown via e-beam deposition and characterized by Raman spectroscopy, atomic force microscopy, temperature dependence of electrical resistivity and THz time-resolved spectroscopy. We have established the presence of α-Sn phase in the polycrystalline layers together with a high electron mobility μ = 2500 ± 100 cm2 V−1 s−1. Here, the temperature behavior of the resistivity in a magnetic field is distinct from the semiconducting films and three-dimensional Dirac semimetals, which is consistent with the presence of linear two-dimensional electronic dispersion arising from the mutually inverted band structure at the α-Sn/Ge interface. As a result, the α-Sn/Ge interfaces of the quantum wells have topologically non-trivial electronic states. From THz time-resolved spectroscopy, we have discovered unusual photocurrent and THz radiation generation. The mechanisms for this process are significantly different from ambipolar diffusion currents that are responsible for THz generation in semiconducting thin films, e.g., Ge. Moreover, the THz generation in α-Sn/Ge quantum wells is almost an order of magnitude greater than that found in Ge. The substantial strength of the THz radiation emission and its polarization dependence may be explained by the photon drag current. The large amplitude of this current is a clear signature of the formation of conducting channels with high electron mobility, which are topologically protected