RESUMEN
Terahertz frequency has promising applications in communication, security scanning, medical imaging, and industry. THz absorbers are one of the required components for future THz applications. However, nowadays, obtaining a high absorption, simple structure, and ultrathin absorber is a challenge. In this work, we present a thin THz absorber that can be easily tuned through the whole THz range (0.1-10 THz) by applying a low gate voltage (<1 V). The structure is based on cheap and abundant materials (MoS2/graphene). Nanoribbons of MoS2/graphene heterostructure are laid over a SiO2 substrate with an applied vertical gate voltage. The computational model shows that we can achieve an absorptance of approximately 50% of the incident light. The absorptance frequency can be tuned through varying the structure and the substrate dimensions, where the nanoribbon width can be varied approximately from 90 nm to 300 nm, while still covering the whole THz range. The structure performance is not affected by high temperatures (500 K and above), so it is thermally stable. The proposed structure represents a low-voltage, easily tunable, low-cost, and small-size THz absorber that can be used in imaging and detection. It is an alternative to expensive THz metamaterial-based absorbers.
RESUMEN
[This corrects the article DOI: 10.1002/advs.201901438.].
RESUMEN
The quantum well (QW) realizes new functionalities due to the discrete electronic energy levels formed in the well-shaped potential. Magnetic tunnel junctions (MTJs) combined with a quasi-QW structure of Cr/ultrathin-Fe/MgAl2O4(001)/Fe, in which the Cr quasi-barrier layer confines Δ 1 up-spin electrons to the Fe well, are prepared with perfectly lattice-matched interfaces and atomic layer number control. Resonant peaks are clearly observed in the differential conductance of the MTJs due to the formation of QWs. Furthermore, enhanced tunnel magnetoresistance (TMR) peaks at the resonant bias voltages are realized for the MTJs at room temperature, i.e., it is observed that TMR ratios at specific and even high bias-voltages (V bias) are larger than zero-bias TMR ratios for the MTJs with odd Fe atomic layers, in contrast to the earlier experimental studies. In addition, a new finding in this study is unique sign changes in the temperature coefficient of resistance (TCR) depending on the Fe thickness and V bias, which is interpreted as a signature of the QW formation of Δ1 symmetry electronic states. The present study suggests that the spin-dependent resonant tunneling via the QWs formed in Cr/ultrathin-Fe/MgAl2O4/Fe structures should open a new pathway to achieve a large TMR at practically high V bias.