Results

2020:
   Thin layers of VO₂ grown on Si (002) and TiO₂ (001) / (100) substrates were obtained by laser ablation. These layers epitaxially increased, with nanometric thicknesses, have been characterized structurally and morphologically.
   From a morphological point of view, it was found that as the number of applied laser pulses increases, the films become more granular, and the number and size of micron-sized particles present on the surface increases.
   From a structural point of view, it was observed that for deposition temperatures < 300°C, the films have an amorphous structure, while at temperatures ≥ 360°C, diffraction peaks corresponding to some secondary phases appear. The absence of other diffraction peaks, apart from those in the plane family {0 0 1}, shows that the films are textured along the c-axis.


2021:
   VO₂ films were deposited on TiO₂ and Si substrates heated to different temperatures. The dependence on the substrate temperature, the semiconductor-metal transition temperature, the electrical resistance and the crystallinity of the films were studied.
   The epitaxial nature of the films in the interface region was confirmed by SAED, which indicated the presence of two tetragonal crystal structures: R-TiO₂ and R-VO₂.
   For the samples deposited at 400°C and 500°C a type of column growth was observed, while the sample deposited at 300 ° C shows a pyramidal growth mode (Volmer-Weber). Conventional imaging showed the morphology of the film with a non-uniform appearance, locally being observed formations with the appearance of splashes of about 2 μm.
   For Ts ≤ 400°C, the parameter of the VO₂ network along the a-axis shows a linear increase; and for Ts> 400°C, the parameter of the network along the c-axis shows a linear increase, suggesting that above this temperature the unit cell of the epilayer cannot maintain the volume, because the parameter of the network along the a-axis has the same tendency as the thermal expansion of the substrate network of TiO₂. 



2022:
   During this period, VO₂ films were deposited on several substrates (LSAT, Si, quartz), under different conditions of substrate temperature, working partial pressure and number of pulses.
   The preparation conditions of the VO₂ films have been optimized, so that substantial MIT transitions can be observed, with resistance/resistivity variations of more than 3 orders of magnitude in the 300K-340K range, optimal for thermochromic window applications, in the climatic conditions of Romania.
   The most important conclusion that can be derived from this study is that both the position of the transition and its magnitude can be controlled by the preparation conditions of the VO₂ films.