Comparison and Verification of Coherent Doppler Wind Lidar and Radiosonde Data in the Beijing Urban Area

As a new type of wind field detection equipment, coherent Doppler wind lidar(CDWL) still needs more relevant observation experiments to compare and verify whether it can achieve the accuracy and precision of traditional observation equipment in urban areas. In this experiment, a self-developed CDWL provided four months of observations in the southern Beijing area. After the data acquisition time and height match, the wind profile data obtained based on a Doppler beam swinging(DBS) five-beam inversion algorithm were compared with radiosonde data released from the same location. The standard deviation(SD) of wind speed is 0.8 m s^(–1), and the coefficient of determination R~2 is 0.95. The SD of the wind direction is 17.7° with an R~2 of 0.96. Below the height of the roughness sublayer(about 400 m), the error in wind speed and wind direction is significantly greater than the error above the height of the boundary layer(about 1500 m). For the case of wind speeds less than 4 m s^(–1), the error of wind direction is more significant and is affected by the distribution of surrounding buildings. Averaging at different height levels using suitable time windows can effectively reduce the effects of turbulence and thus reduce the error caused by the different measurement methods of the two devices.

Binary-ternary transition metal chalcogenides interlayer coupling in van der Waals type-II heterostructure for visible-infrared photodetector with efficient suppression dark currents

Ternary two-dimentional(2D)materials exhibit diverse physical properties depending on their composition,structure,and thickness.Through forming heterostructures with other binary materials that show similar structure,there can be numerous potential applications of these ternary 2D materials.In this work,we reported the structure of few-layer CrPS_(4)by X-ray diffraction,transmission electron microscope,and electron-density distribution calculation.We also demonstrated a new application of the CrPS_(4)/MoS_(2)heterobilayer:visible-infrared photodetectors with type-II staggered band alignment at room temperature.The response of the heterostructure to infrared light results from a strong interlayer coupling that reduces the energy interval in the junction area.Since the intrinsic bandgap of individual components determines wavelengths,the decrease in energy interval allows better detection of light that has a longer wavelength.We used photoluminescence(PL)spectroscopy,Kelvin probe force microscopy(KPFM)under illumination,and electrical transport measurements to verify the photoinduced charge separation between the CrPS_(4)/MoS_(2)heterostructures.At forward bias,the device functioned as a highly sensitive photodetector,as the wavelength-dependent photocurrent measurement achieved the observation of optical excitation from 532 to 1,450 nm wavelength.Moreover,the photocurrent caused by interlayer exciton reached around 1.2 nA at 1,095 nm wavelength.Our demonstration of the strong interlayer coupling in the CrPS_(4)/MoS_(2)heterostructure may further the understanding of the essential physics behind binary-ternary transition metal chalcogenides heterostructure and pave a way for their potential applications in visible-infrared devices.