Vanadium dioxide and tungsten-doped (W-doped) vanadium dioxide thin films deposited by aqueous Sol-Gel method were characterized with several different techniques (i.e. X-ray photoelectron spectroscope, atomic force microscope, X-ray diffraction), to determine their morphology and microstructure. Their metal-to-insulator (MIT) phase transition behavior in infrared spectral region (λ=4 μm) and terahertz (THz) spectral region (0.3–1.0 THz) were observed respectivele. The results demonstrate that the transmittance of W-doped VO 2 film at room temperature is visibly lower than that of undoped VO 2 film in both infrared and terahertz spectral region. The transition temperature of W-doped VO 2 film is also lower than that of undoped VO 2 film in the THz range. The MIT and structural phase transition (SPT) are observed during the phase transition of VO 2 and W-doped VO 2 , and an obvious change of peak position occurs in W-doped VO 2 film.

Study on Phase Transition Property of Tungsten-doped Vanadium Dioxide Thin Film at Terahertz Range

Vanadium dioxide (VO2) has attracted much interest in material field due to its unique semiconductor-metal phase transition properties. And now, the problem of stability has been highlighted and concerned for the practical application in VO2. In order to establish a relatively complete guide of stability study on VO2 which would contribute to deeply and systematically researches, the article made a review of the stability study on VO2 from thermal excitation, photo-excitation and electro-excitation. Moreover, the key aspects for future research on the stability study of VO2 was proposed.

The Stability Study on Vanadium Dioxide

Design and fabrication of frequency-responsive terahertz transmittance modulator based on vanadium dioxide spherical films

We demonstrate a photo-induced high modulation depth terahertz (THz) modulator based on a VO x /Si/VO x hybrid structure. The thickness of the embedded high resistance silicon substrate is 510 µm and two layers of VO x films are 100 nm, respectively. Compared with other THz modulators based on the phase transition of vanadium oxide which were fabricated by complex chemical vapor deposition and sputtering processes, the VO x film in this device is fabricated using a simple spin coating process of VO x solution. The sample is characterized using a THz time-domain-spectroscopy system. In the test experiment, the insulator–metal-transition of the VO x is induced by two oblique incident pump lasers with a central wavelength of 650 nm from two sides. The experimental results show that it can be optically modulated in a wide frequency range from 0.2 to 2.0 THz, and the maximum modulation depth of 93% is realized when the optical power is 120 mW. Film theory and Drude theory are introduced to interpret the mechanism of modulation. This modulator has broadband, a simple fabrication process and very low optical power, which are important for broadband THz communication and all-optical THz systems.

https://iopscience.iop.org/article/10.1088/1361-6463/ab046f/pdf

Photo-induced high modulation depth terahertz modulator based on VO x ─Si─VO x hybrid structure

Low terahertz-band scanning near-field microscope with 155-nm resolution

The photo-induced insulator-metal transition for silicon-based VO 2 nanofilm is studied by THz time-domain spectroscopy (THz-TDS). Obvious variations of THz ray transmittance are observed before and after the CW laser beam exciting, and the conductivity of metallic-phased VO 2 film in the THz region is calculated in the thin film approximation. According to the measured results, the metallic-phased VO 2 film is characterized equivalently with Drude’s model, and complex conductivity, dielectric function and refractive index are acquired by the model. As an examination on the equivalent Drude model, numerical simulation based on the finite integral method in time domain is carried out. The results show that they are in good agreement with the experimental results. This work provides a reference for the study on phase transition of VO 2 nanofilm and its application in the THz region.

Photo-induced insulator-metal transition of silicon-based VO 2 nanofilm by THz time domain spectroscopy

Recently, terahertz radiation has been a branch of cutting-edge science and technology involving many fields such as public security, military defense and national economy. In the past, far-field measurements were widely carried out based on terahertz time-domain spectroscopy. But the spatial resolution is limited by far-field diffraction effect. In order to break diffraction limit and gain sub-wavelength spatial resolution in terahertz frequency region, a series of near-field detection methods came into being, such as confocal microscopy, using an aperture, guided mode, scattering, direct detection in the near-field, etc. Each method has its own advantages and disadvantages. Using the photoconductive-antenna tip is one of the direct detection methods and it delivers the possibility of near-field measurements of terahertz waves. In this method, the photoconductive-antenna tip is a tapered photoconductive tip probe. So it can be close enough to the sample surface and receive the near-field signal on the basis of principle of photoconductivity. In this way, high spatial resolution can be gained. In this article, we introduce our recent progress of near-field and far- field scanning terahertz spectroscopy system with photoconductive-antenna in detail. Firstly, we analyze and summarize the near-field detection methods that have been developed in these years. And then, using the femtosecond laser whose center wavelength is 800 nm and the photoconductive-antenna tip detector coupled with fiber, we construct fiber near-field/ far-field scanning terahertz spectroscopy (N/F-STS). The frequency bandwidth is in a range from 0.2 THz to 1.5 THz and the terahertz spot is circular and uniform indicated by performance test. Also the amplitude and phase of the terahertz field are recorded simultaneously. It has the ability to perform three-dimension scan in various experiment conditions conveniently. Finally, we introduce the real applications in our laboratory. N/F-STS can be used to scan spatial electric distribution in three dimensions and test the spectral properties in terahertz range like other traditional far-field methods. Nevertheless, the most importantly, N/F-STS is used to scan the terahertz near-field of samples, such as terahertz surface plasmon polaritons, etc. The presented method thus is useful in some application areas, such as metamaterials, graphene, surface plasmons, waveguide transmission, near-field imaging, biological test, and chip inspection.

Near-field and far-field scanning terahertz spectroscopy based on photoconductive microprobe

ESG is a brand-new concept about how environmental, social and corporate governance supports sustainable development in enterprises. However, little research is done on how to reshape the internal mechanism by which data element embedding drives enterprise performance based on the brand-new sustainable concept. From the perspective of contingency theory and organizational agility, a conceptual model including ESG investment, data element embedding, organizational agility and environmental uncertainty is constructed to study the internal mechanism by which data element embedding affects enterprise performance. The model is empirically researched through the data obtained from the survey of 287 manufacturing enterprises in China. The results show that, ESG investment and external data element embedding impose no direct impact on enterprise performance, but create an indirect impact through organizational agility; environmental uncertainty negatively moderates the effect of ESG investment on organizational agility. Through the hierarchical analysis of ESG investment and data elements embedded in enterprise performance, the value creation mechanism of data elements is revealed, which enriches and expands the theory of data elements and organizational agility, and provides enlightenment for ESG investment to drive the value creation of data elements.

Gu Jianqiang

Papers

Photo-induced insulator-metal transition of silicon-based VO 2 nanofilm by THz time domain spectroscopy

Near-field and far-field scanning terahertz spectroscopy based on photoconductive microprobe

Data element embedding and firm performance: The influence of ESG investment