SnS2/MoS2 van der Waals Heterostructure Photodetector with Ultrahigh Responsivity Realized by a Photogating Effect.

Photoresponsivity is a fundamental parameter used to quantify the ability of photoelectric conversion of a photodetector device. High-responsivity photodetectors are essential for numerous optoelectronic applications. Due to the strong light-matter interactions and the high carrier mobility, two-dimensional (2D) materials are promising candidates for the next-generation photodetectors. However, poor light absorption, lack of photoconductive gain, and the interfacial recombination lead to the relatively low responsivity of 2D photodetectors. The photogating effect, which extends the lifetime of photoexcited carriers, provides a simple approach to enhance responsivity in photodetector devices. Here, the O2 plasma treatment introduced surface traps on the SnS2 surface, leading to a gate-tunable photogating effect in SnS2/MoS2 heterojunctions. The heterojunction device exhibits an ultrahigh responsibility of up to 28 A/W. Moreover, the photodetector possesses a wide spectral photoresponse spanning from 300 to 1100 nm and a high specific detectivity (D*) of 4 × 1011 Jones under a 532 nm laser at VDS = 1 V. These results demonstrate that O2 plasma treatment is an efficient and simple avenue to achieve photogating effects, which can be employed to enhance the performance of van der Waals heterostructure photodetector devices and make them suitable for future integration into advanced electronic and optoelectronic systems.

[Nonlinear Regression Methods of Ethanol Raman Spectra Quantitative Analysis].

Ethanol concentration quantitative analysis of ethanol-water solution can be realized by measuring the ratio of Raman characteristic peak heights. The content of ethanol can be determined by linear relation between relative intensity ratio and ethanol concentration. However, this analytical method only applies to the ethanol solution at low concentration. Concerning this issue, relative intensity of characteristic peak of ethanol (asymmetric stretching vibration of CH2 2 924.0 cm-1) and peak background of water (3 350 cm-1) at different ethanol concentration is experimentally measured by using a self-developed laser Raman ethanol content detection system. According to the relationship between relative ratio of characteristic peak heights and ethanol concentration, the nonlinear regression analysis methods are proposed to apply in the measurement of ethanol concentration in a wide range. Adjacent region average method is utilized to remove mutational random noise in Raman spectra of ethanol solution. Combined with multi-point interpolation processing, the baseline of Raman spectra can be calibrated. The influences of mutational random noise and the strong fluorescence background can be effectively eliminated with baseline correction and normalization methods. Polynomial and exponential mathematical models are adopted for nonlinear regression analyses by the relation between ratio of characteristic peak heights and concentration of ethanol solution. The analysis results show that the correlation coefficient of linear fitting and nonlinear fitting is about 0.991 and higher than 0.997 respectively. The linear analytical method can be effectively applied when ethanol concentration range is 15%～60%. The nonlinear analytical method has higher measurement accuracy in a wider ethanol concentration range of 3%～97%. Nonlinear mathematical model will provide theoretical basis for analysis of ethanol concentration, which can be applied in laser Raman ethanol content detection system to calculate the relatively accurate ethanol concentration of ethanol-water solution. Rapid, real-time and accurate quantitative analysis of wide concentration range ethanol solution, which has mutational random noise and strong fluorescence background interference, can be achieved by these analytical methods.

Theoretical and experimental investigations on measuring underwater temperature by the coherent Brillouin scattering method.

In this paper, a new method of measuring a water-stimulated Brillouin scattering (SBS) frequency shift by optical coherent detection is presented, in order to remote-sense the underwater temperature of the ocean. A single longitudinal mode, passively Q-switched pulsed Nd:YAG laser is used as the light source, the water SBS beam is used as the signal beam, and a portion of the incident laser beam is used as the local oscillator. The heterodyne is detected by a high-speed photodetector, and the heterodyne frequency is the Brillouin frequency shift. Therefore, the underwater temperature can be determined according to the relationship between the Brillouin frequency shift and the water temperature. To test and verify its practicability, the heterodyne waveforms at different water temperatures are recorded in the laboratory with a wide-band oscilloscope, and the Brillouin frequency shifts are deduced by a Fourier transform. The experimental results are consistent with the theoretical analysis. This work provides the foundation for the development of a water temperature measurement system based on coherent Brillouin scattering.