Molybdenum dioxide (MoO 2) a kind of semi-metal material shows many unique properties, such as high melting point, good thermal stability, large surface area-to-volume ratio, high-density surface unsaturated atoms, and excellent conductivity. There is a strong connection between structural type and optoelectronic properties of 2D nanosheet. Herein, the rectangular and hexagonal types of thin and thick MoO 2 2D nanosheets were successfully prepared from MoO 3 powder using two-zone chemical vapor deposition (CVD) with changing the experimental parameters, and these fabricated nanosheets displayed different colors under bright-field microscope, possess margins and smooth surface. The thickness of the blue hexagonal and rectangular MoO 2 nanosheets are~25 nm and~30 nm, respectively, while typical thickness of orange-colored nanosheet is around~100 nm. Comparative analysis and investigations were carried out, and mix-crystal phases were indentified in thick MoO 2 as main matrix through Raman spectroscopy. For the first time, the emission bands obtained in thick MoO 2 nanosheets via a Cathodoluminescence (CL) system exhibiting special properties of semi-metallic and semiconductors ; however, no CL emission detected in case of thin nanosheets. The electrical properties of thin MoO 2 nanosheets with different morphologies were compared, and both of them demonstrated varying metallic properties. The resistance of thin rectangular nanosheet was~25 Ω at ± 0.05 V while 64 Ω at ± 0.05 V was reported for hexagonal nanosheet, and observed lesser resistance by rectangular nanosheet than hexagonal nanosheet.
Determination of macroscale detonation parameters of energetic materials (EMs) in a safe and rapid way is highly desirable. However, traditional experimental methods suffer from tedious operation, safety hazards and high cost. Herein, we present a micro-scale approach for high-precision diagnosis of explosion parameters based on radiation spectra and dynamic analysis during the interaction between laser and EMs. The intrinsic natures of micro-explosion dynamics covering nanosecond to millisecond and chemical reactions in laser-induced plasma are revealed, which reveal a tight correlation between micro-detonation and macroscopic detonation based on laser-induced plasma spectra and dynamics combined with statistic ways. As hundreds to thousands of laser pulses ablate on seven typical tetrazole-based high-nitrogen compounds and ten single-compound explosives, macroscale detonation performance can be well estimated with a high-speed and high-accuracy way. Thereby, the detonation pressure and enthalpies of formation can be quantitatively determined by the laser ablation processes for the first time to our knowledge. These results enable us to diagnose the performance of EMs in macroscale domain from microscale domain with small-dose, low-cost and multiple parameters.
A variety of two-dimensional (2D) nanodevices with diverse optoelectronic properties have been successfully fabricated. A strategy for engineering 2D heterostructures high-performance devices rich in functions and adaptable for specific applications must be developed. Herein, two types of photodetectors fabricated through van der Waals interactions from vertically stacked MoSe 2 / MoO 2 heterostructures with the thickness of MoO 2 flakes at 25 and 105 nm, respectively, which exhibits metallic and semiconductor characteristics on elevation at thickness from 25 to 105 nm. A higher photoresponse can be obtained from the thin MoO 2 flake vertically stacked MoSe 2 /MoO 2 heterostructure with the merits of a photoresponsivity of 100.86 mA•W −1 and a detectivity of 23.4 × 10 9 Jones. The external quantum efficiency reaches 23.5% at bias of 3 V under the illumination of a monochromatic light at 532 nm, which is better than thick MoO 2 flake heterostructure (thickness ∼ 105 nm). The enhanced mechanism originates from high absorption efficiency, high carrier conductivity, and better contact of thin metallic MoO 2 flakes compared to the thick MoO 2 flakes heterostructure, which relates to various Fermi energy levels of the two different MoO 2 flakes photodetector. This work can provide an interesting route for engineering optoelectronic high-performance devices and developing a diverse photodetector on the basis of transition metal dichalcogenides (TMDs)/transition metal oxides (TMOs) heterojunction.
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