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Phase change materials can enable temperature self-regulation due to their drastic changes in optical properties accompanying the phase transition. Significant reduction of the optical absorption after the transition is the key ingredient for an enhanced regulating performance. However, the absorptivity of unpatterned vanadium dioxide (VO2) thin films can hardly be reduced after phase transition at visual-to-infrared band. In this work, we combine the direct binary search (DBS) and particle swarm optimization (PSO) algorithms for an optimized design of temperature self-regulating nano-photonic devices on VO2 thin films. For a given incident wavelength, a pixelated structure is firstly inverse-designed by the DBS algorithm which maximizes the absorption contrast before and after the transition. To overcome fabrication challenges as pixel size is at deep sub-wavelength scale, the pixelated structure can then be replaced by geometric shapes which are more tractable in manufacturing processes. The geometrical parameters are optimized by the PSO algorithm where our optimized device brings the absorptivity down to 33% after the transition. These results provide an effective way for the inverse design of optimized nano-photonic structures based on phase change materials. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we studied the effect of NaCl electrolyte as a surface treatment on improving the uniformity and stability of field emission of screen-printed carbon nanotubes (CNTs). A short period of the electrolyte treatment of CNT films remarkably increase emission uniformity and stability. Furthermore, the field emission characteristics of screen-printed carbon nanotubes (CNTs) such as low turn-on field, high emission current density and strong adhesion of the CNT film on the substrate were also reinforced after post-treated. SEM, TEM and Raman spectrum study revealed that uniformity and stability of field emission is enhanced by two factors. Firstly, the electrolyte treatment appeared to render the CNT surfaces more actively by exposing more CNTs form the CNT paste, which dominates initial uniformity and stability of field emission. Secondly, the number of opened CNTs and defects CNTs of CNT film were increased by electrical current energy. [Copyright &y& Elsevier]

Abstract: Screen printing is undoubtedly the most cost-effective process for the fabrication of large-sized carbon nanotube field emission display (CNT-FED). A novel post-treatment method in NaCl electrolyte was presented to solve the problem of poor field emission characteristics of printed CNT films. Compared to those of untreated films, the turn-on electric field of the treated film decreased from 2.4 to 1.4V/μm and the total emission current of the treated film that has the same printing area as the untreated one increased from ∼100 to ∼1800μA. Scanning electron microscope (SEM) and Raman spectrum study revealed that field emission characteristics are enhanced by two factors. Firstly, the NaCl electrolyte treatment appeared to render the CNT surfaces more activey by exposing more CNTs from the CNT film. Secondly, the numerous defects of CNTs of the CNT film were increased by electrical current energy. [Copyright &y& Elsevier]

SnS2 films have been deposited on glass and alumina plate substrates by the reactions between an organotin precursor [tetrabuyltin, (CH2CH2CH2CH3)4Sn] and carbon disulfide in n-hexane at the temperature range 180–200 °C for 10–40 h. The reaction system was oxygen free and applied at a moderate temperature. The films so prepared were characterized by techniques of X-ray diffraction, Scanning electron microscopy, Raman and Mo¨ssbauer spectroscopies. The films deposited on glass as well as on alumina plate have an average thickness of 30 μm, but have different rose-like morphologies, which are influenced by both the anisotropic growths of crystals and the different substrate structures. Photoluminescence measurements show that the films have an emission peak at approximately 590 nm. [Copyright &y& Elsevier]

Highlights: [•] The high c-axis oriented AZO film possesses high quality in terms of optical and electrical properties. [•] The resistivity is as low as 4.973×10−4 Ωcm. [•] High photocurrent is obtained under a reverse bias for AZO/p-Si heterojunction. [ABSTRACT FROM AUTHOR]

Abstract: The nanocrystalline VO2 thin films, which surface has a flake grain structure, are achieved by DC sputtering deposition at different sputtering powers. It is found that the hysteresis loop of metal-insulator phase transition (MIT) is almost superposition, and the hysteresis width is only 0.4°C for the surface flake grain structure that obtained at 132W DC sputtering power. Moreover, it is shown that the phase transition is very steep, and the film displays 3–4 orders of the change of sheet resistance at MIT. The characterizations of SEM, AFM and four-point probe methods show that the hysteresis width, the orders of the change of sheet resistance and the phase transition become narrower, higher and steeper at MIT, respectively when the surface shapes of the nanocrystalline VO2 thin films change from nanoparticle structures to flake structures with the DC sputtering powers increased from 66W to 132W and the surface flake grain sizes reduced gradually to minimum at 132W. Meanwhile, the surface roughness also changes into minimum. However, with the powers further increased from 132W to 176W, the surface flake grain sizes become bigger, and then the surface roughness changes poor. At 176W, the surface flake structures begin to turn into nanoparticle structures. The hysteresis width, the orders of the change of sheet resistance and the phase transition become wider, lower and poorly steeper at MIT, separately. The results reveal that the nanocrystalline shapes and the surface roughness can affect the hysteresis width and the sheet resistance steepness in MIT. Our analysis shows that the mechanism of the narrowed hysteresis width mainly depends on the strain imbalance of the nanocrystalline VO2 thin film of the flake structures at MIT. [Copyright &y& Elsevier]

• VO 2 and TiO 2 thin films were synthesized on Si substrates by a simple and controllable method. • The almost coincident hysteresis loops of VO 2 thin films including a TiO 2 buffer layer was realized on Si substrates. • The reasons for the narrowing of hysteresis loops width of VO 2 were analyzed and summarized from three aspects. The overlapped degree of hysteresis loops is critically important for the accurate response of vanadium dioxide (VO 2)-based optoelectronics devices. Generally, the hysteresis loops width is not less than 10 ℃ for VO 2 thin films deposited on amorphous SiO 2 /Si or Si substrates. In this work, the almost coincident hysteresis loops of VO 2 thin films including a TiO 2 buffer layer was synthesized successfully on Si substrate by a simple and controllable method. Here, the thickness of VO 2 and TiO 2 were 60 nm and 100 nm, respectively. XRD patterns show that the peak of rutile phase TiO 2 begin to appear while the thickness of buffer layer increases to about 65 nm, which is more compatible with the lattice structure of VO 2. Combined with the XPS spectra, it is found that the VO 2 thin films formed on different substrates include quite a few V5+ and relatively few V3+ impurity phases. In addition, theoretical analysis indicates that an inversely proportional relationship exists between the hysteresis loops width and the average grain size of VO 2 thin film, The SEM images confirm this point well revealing the average grain size of VO 2 thin film does increase with the thickness increase of TiO 2 buffer layer. ga1 The overlapped degree of hysteresis loops is critically important for the accurate response of vanadium dioxide (VO 2)-based optoelectronics devices. Generally, the hysteresis loops width is not less than 10 ℃ for VO 2 thin films deposited on amorphous SiO 2 /Si or Si substrates. In this work, the almost coincident hysteresis loops of VO 2 thin films including a TiO 2 buffer layer was synthesized successfully on Si substrate by a simple and controllable method. Here, the thickness of VO 2 and TiO 2 were 60 nm and 100 nm, respectively. XRD patterns show that the peak of rutile phase TiO 2 begin to appear while the thickness of buffer layer increases to about 65 nm, which is more compatible with the lattice structure of VO 2. Combined with the XPS spectra, it is found that the VO 2 thin films formed on different substrates include quite a few V5+ and relatively few V3+ impurity phases. In addition, theoretical analysis indicates that an inversely proportional relationship exists between the hysteresis loops width and the average grain size of VO 2 thin film, The SEM images confirm this point well revealing the average grain size of VO 2 thin film does increase with the thickness increase of TiO 2 buffer layer. [ABSTRACT FROM AUTHOR]