RESUMEN
Visible-light detection with high sensitivity and strong wavelength selectivity is highly desired in emerging applications. Here, we demonstrate a high-performance visible-light photodetector with an active region composed of a polarization induced barrier and single-carrier superlattices (SCSLs). The barrier at SCSLs/GaN heterointerface brings both a low dark current and a high gain originating from the photoinduced barrier reduction effect. Meanwhile, the designed InGaN/GaN SCSLs allow the photoelectrons in the quantum wells to escape, but photogenerated holes are weakly localized, thus generating the additional photoconductive gain. The resulting devices exhibited a super-high gain of 7.8 × 104, a large detectivity of 1.2 × 1016 jones, and a relatively fast response speed with rise/falling time of 2.5/89.6â ns. Also, a 400/500-nm rejection ratio greater than 3 × 105 was shown at 1â V, indicating excellent wavelength selectivity.
RESUMEN
Enhanced geothermal systems (EGSs) developed by hydraulic stimulation are promising for exploiting petrothermal heat by improving fluid pathways in low-permeable geothermal reservoir rocks. However, fluid injection into the subsurface can potentially cause large seismic events by reactivating pre-existing faults, which is a significant barrier to EGSs. The management of injection-induced seismicity is, therefore, essential for the success of EGSs. During the hydraulic stimulation of an EGS, fluid can be injected into a fault zone or into the rock matrix containing pre-existing faults adjacent to the injection well. The differences in hydromechanical responses between fluid injection into and adjacent to a fault have not been investigated in detail. Here, we performed triaxial fluid injection experiments involving injecting fluid directly and indirectly into a fault in granite rock samples to analyse the distinct hydromechanical responses and estimate the injection-induced seismicity in both cases. Our results suggest that in addition to directly injecting fluid into a critically stressed fault, injecting into nearly intact granite adjacent to the fault could also cause injection-induced seismic hazards owing to the high fluid pressure required to create new fractures in the granite matrix. It is, therefore, important to carefully identify pre-existing faults within tight reservoirs to avoid injecting fluid adjacent to them. Additionally, once prior unknown faults are delineated during hydraulic stimulation, appropriate shut-in strategies should be implemented immediately to mitigate seismic risks. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'.
RESUMEN
Equal channel angular pressing (ECAP) and multi-axial compression deformation (MAC) are severe plastic deformation (SPD) processes that produce bulk nanostructured materials with ultrafine grains. The grains could be observably refined by multi-pass of ECAP and MAC. This research proposed new routes of cyclic equal channel compression (CECC), which combines ECAP and MAC to increase the mechanical properties of 6061 aluminum alloy. The tests, which are conducted through electron backscattered diffraction (EBSD) and transmission electron microscope (TEM), were performed on the grain size, recrystallization distribution, misorientation distributions, dislocations, and secondary phase distributions of CECC-processed 6061 aluminum alloys on the purpose of exploring the mechanism of grain refinement. MEM is the short form for the CECC processing route of MAC + ECAP + MAC, which is one ECAP pass between two MAC passes. The tests results showed that the average grain size could reach to as much as 1.1 µm after two MEM deformation circles named MEM-MEM, with the non-annealing average grain size being 21 µm and recrystallization annealed average grain size being 28 µm. The dislocation cells, which could be transformed into sub-grains with the increase of the strain, were formed by the slip and the accumulation of dislocations. The secondary phase was Mg2Si, which could prevent the refined grains from growing up again by pinning at the grain boundaries. Above all, the dislocation proliferation and secondary phases will both lead to the grain refinement.
