About 2500 years ago, Mozi had paid attention to a series of phenomena caused by the magical "light"; Chairman Mao praised the infinite mystery of iris with poems, because Mozi's attention to "light travels in a straight line" met the solar spectrum scattered and restored by "tiny raindrops" with the function of "Newton prism". Light is everywhere, and spectral analysis has penetrated into various important fields of industry and research. Through the characterization of optical properties by spectrometers, people can obtain information about the "fingerprint" of substances, so that they can infer the composition and structural characteristics of substances. With the demand for portability and "on-site", "in vivo" measurement, the miniaturization of spectrometer is imminent: for example, integrated in smartphone photo taking and biosensor functions, fluorescence and Raman analysis of molecules and quantum dots on chip, UAV carrying outdoor measurement, close space laboratory to analyze "light" from distant stars In recent 20 years, the research of micro spectrometer has made great progress, especially the advanced micro nano processing technology has given birth to rich and fine spectroscopic technology, and high detection rate is one of the most important factors to realize the real chip integration test.
Wang Xiaomu's team and collaborators from the school of Electronic Science and engineering of Nanjing University put forward a spectrometer integrating optical analysis and detection into a single nanowire. Based on the energy band engineering, the cdsxse1 – x nanowire with energy band gradient was prepared. The nanowire has excellent absorption rate for incident light, and the continuously changing energy band has selective absorption effect for incident light. These photo generated carriers are detected by Schottky diode detector array prepared along the nanowire, and the unique spectral response spectrum of each device can be obtained. Combined with the actual measurement of the photocurrent of each device, the inverse problem can be solved by regularization method The spectral reconstruction of the light source to be measured. For commonly used spectral analysis chips, the weak interaction between light and light is the bottleneck problem. The research team of Nanjing University solved this core difficulty through two solutions: first, photoelectric detection generally has two types of photoconductivity and diode. Through the design of metal / semiconductor interface, the researchers compared the detection rate of these two types of devices and found that the detection rate of diode detector is as high as 1013jones, which is more than two orders of magnitude higher than the photoconductivity type. On the other hand, the high-quality crystal nanowires themselves support the propagation of waveguide mode, and the light to be measured is incident from the broadband gap end through the coupler, and is absorbed and detected continuously during the propagation along the nanowires. Within a certain range, the photoelectric response spectrum in this mode is consistent with the normal incidence mode, which provides an optimized scheme for on-chip measurement and avoids the need for on-chip measurement Filter induced luminescence and spectral change of light source to be measured due to back incidence. Finally, we successfully demonstrated the advantages of using the nanowire spectrometer to test the photoluminescence spectrum of the materials on the chip, which fully affirmed the high detection rate and the waveguide working mode of the on-chip test. Relevant results were published in adv. optical mater (DOI: 10.1002 / Adom. 202000191). The nanowire spectrometer is called "Mozi" in the spectrometer mainly because of its three characteristics: 1. This is a landmark work related to "light". After careful design by "craftsmen", it will promote the wide application of on-chip spectrometer; 2. The spectrometer is a micro instrument related to "quantum". Based on the "quantum" theory, it is modified by components The size of the single nanowire spectrometer is less than 100 μ m, while the thickness of the industrial nanowire is less than 1% of the hair. 3. The strong light and material interaction and the advantages of high detection rate make the nanowire spectrometer have the potential of detecting weak light in space on chip. It is worth mentioning that this method provides a platform for the preparation of on-chip spectrometers. At present, the CDs xse1 – x nanowires are mainly used to detect the visible light band. Any nanowire with gradual band can replace the nanowire as the working material, and the detection spectrum range is expected to be further expanded. At that time, the on-chip laboratory will become a reality. The on-chip spectrometer will be integrated into the smart phone. People can use the mobile phone to scan and know whether the fruit has pesticide pollution and maturity, and can monitor environmental health. The UAV can carry the on-chip spectrometer to carry out spectral analysis, and even implant it into the human body for disease diagnosis
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