ABSTRACT
For specific application to an uncooled infrared detector, VO2 thin films should have a series of characteristics including purposefully chosen polymorphs, accurate stoichiometry, phase stabilization, a high temperature-coefficient of resistance (TCR), and suitable square-resistance. This work reports controllable preparation of high-performance VO2 films via post annealing of a sandwich-structured V2O5/metal (V, W)/V2O5 multilayer precursor, which was deposited by RF magnetron sputtering. This sandwich structure can dynamically regulate oxygen contents and doping element levels in the films, enabling us to achieve accurate regulation of stoichiometry and polymorphs. The precursor films undergo a B to M phase transition depending on the quantity of the metal layers. At the thickness of the metal layer below a limitation, the resulting film after heat treatment was VO2 (B), and above the limitation, the product was VO2 (M). The optical modulation of the VO2 (M) in the near-infrared region can be tuned from 1.2 to 39.8% (ΔT2000 nm). TCR values can range from -1.89 to -4.29%/K and the square-resistances at room temperature (R0) from 69.68 to 12.63 kΩ. The simplicity in phase regulation of the present method and the superior optical and electrical properties of the films may allow its wide applications in thermo-opto-electro sensing devices.
ABSTRACT
OBJECTIVE: To classify and grade the environments with Oncomelania hupensis snails inside embankment in marshland and lake areas, so as to improve the work efficiency and realize the systematic management. METHODS: The schistosomiasis endemic area Liaodi and Xiongdi villages in Jiangling County, Hubei Province were selected as the experiment villages, and the environments with snails in the two villages were divided into sections with a length of 500 m, then the snail situation were surveyed by the systematic sampling method with 10 m and 50 m a frame respectively. The environments were classified according to the discovery of infected snails and wild fecal contamination, and the numbers of sites with snails and their areas in different classes were recorded. Meanwhile, the data of sites with infected snails in Jingzhou City during the recent 5 years were collected and graded according to the average density of snails, so as to discuss the correlativity between the grades of environments with snails and the numbers of sites with infected snails and the occurrence rate of frames with snails. RESULTS: There were 1 967 sites with infected snails in Jingzhou City during the recent 5 years, and there was a positive correlation between the grades of environments with snails and the occurrence rate of frames with snails (r(s) = 0.77, P < 0.01), when the grade was 5, the constituent ratio of numbers of sites with infected snails was 3.1%, and when the grade was 2-3, the ratio raised to 56.3%. There were 39 sites with snails in the two villages, the Class 1, 2 and 3 environments included 1, 18 and 20 sites, with the areas of 1080, 51,640 m2 and 41,220 m2, respectively. There were no statistically significant difference between the grades divided by snail survey with 10 m and 50 m a frame ( chi2 = 4.667, P > 0.05), but the time-consuming of the former was 3 times of the latter. CONCLUSIONS: The classification and grading of the environments with snails inside embankment in marshland and lake areas can master the key point of the snail survey. The subsection and setting frames at a suitable distance can save time and manpower, improve work efficiency, as well as understand the distribution of snail status of the environment with snails, which can realize the sort management of the snail environments inside embankment.
