RESUMO
A highly sensitive room-temperature graphene photothermoelectric terahertz detector, with an efficient optical coupling structure of asymmetric logarithmic antenna, was fabricated by planar micro-nano processing technology and two-dimensional material transfer techniques. The designed logarithmic antenna acts as an optical coupling structure to effectively localize the incident terahertz waves at the source end, thus forming a temperature gradient in the device channel and inducing the thermoelectric terahertz response. At zero bias, the device has a high photoresponsivity of 1.54 A/W, a noise equivalent power of 19.8 pW/Hz1/2, and a response time of 900 ns at 105 GHz. Through qualitative analysis of the response mechanism of graphene PTE devices, we find that the electrode-induced doping of graphene channel near the metal-graphene contacts play a key role in the terahertz PTE response. This work provides an effective way to realize high sensitivity terahertz detectors at room temperature.
RESUMO
Objective: To study the chemical constituents from the fleshy stems of Cynomorium songaricum. Methods: The chemical constituents were isolated and purified by chromatography on MCI, silica gel, Sephadex LH-20 columns, etc. The structures of compounds were elucidated by physicochemical property and spectral analyses. Results: 15 compounds were isolated and identified as choerospondin( 1), isolariciresinol-4-O-ß-D-glucopyranoside( 2), lutelin-7-O-ß-D-glucopyranoside( 3), 3, 4-dihydroxyphenethylacetate( 4),maslinic acid( 5),catechin ( 6),ursolic acid( 7),gentisic acid( 8),mannitol( 9), phloroglucinol( 10), ß-sitosterol( 11), daucosterol( 12), rutin( 13), cetylic acid( 14) and epicatechin( 15). Conclusion: Compounds 4,5,8,9 and 10 are obtained from this plant for the first time.