# Electrical and Optical Properties of Laser-Induced Structural Modifications in PbSe Films
## 3 Results and Discussion  
### Laser Modification of the Structure  
Optical characterization was carried out and the structure of untreated PbSe films, as well as films subjected to heat treatment, was studied. According to the results of optical microscopy, the untreated sample has an unstructured surface (Figure 3a,b), and the film itself contains light-scattering inhomogeneities with a size of about 1.0 \(\upmu\)m--dark for transmission and bright for reflection. The untreated sample is not transparent (transmission is about 0.1) and has a high reflection in the UV region of the spectrum (reflection at a wavelength of 405 nm corresponds to 52%). According to the results of optical microscopy (Figure 3a,b), the sample has a denser structure after activation in the furnace. Island formations (the second phase) with a size of more than 1.0 \(\upmu\)m appear, which are transparent in transmitted light and randomly arranged. The film matrix itself becomes opaque. However, the spectral transmission of the sample increases compared with the transmission of the untreated sample. This feature is due to the properties of the second phase, an oxide that is transparent in the optical wavelength range. The high concentration of the second phase provides a significant increase in the transmission of the entire film (by 30 times). The film matrix in reflection becomes lighter. The second phase is dark in reflected light. Therefore, its reflection is less than the reflection of the film matrix, which ensures a decrease in the reflection of the entire sample. According to the SEM results (Figure 3c,d), it can be seen that for the films after heat treatment, uncompensated stresses arise in the matrix due to the growth of the second phase. The second phase, being a material with a less dense structure, grows during the oxidation process. It increases in volume while maintaining mass, so compressive stresses arise, leading to the formation of cracks over the entire surface. The reflection spectra of the untreated film and the film that has undergone activation are presented below (Figure 4). Figure 3: Image of PbSe film obtained using an optical microscope in a bright field of reflected light: (**a**) untreated, (**b**) after heat treatment. Image of PbSe film obtained using the SEM secondary electron detector: (**c**) untreated, (**d**) after heat treatment. Based on the results obtained, it is possible to make an assumption about the mechanism of modification of the film's optical properties during heat treatment in an oven. During the heating of the film and its annealing, the phase transformation of the film matrix occurs: the inhomogeneities become centers for the nucleation of the second phase (lead oxide (Pb\({}_{3}\)O\({}_{4}\))), and the matrix itself becomes denser, which leads to a decrease in its transmission. Since the oxide is transparent and the size of the regions is commensurate with the film thickness, the film becomes clear at a high concentration in the second phase. The reduction in the reflection of the acting laser radiation can be used to control the quality of film processing in the implementation of feedback. During the formation of a structure with suitable optical characteristics, an increase in transmission at the wavelength of laser radiation is observed. In this case, the sample is clarified as a result of the formation of a transparent oxide and an increase in the concentration of the second phase, which affects the decrease in reflection to 1-2% with a subsequent increase to 5-7% at a constantly low transmission, approximately equal to 0.1. The effect of continuous laser radiation on the structure and optical properties of PbSe chalcogenide films was studied under conditions of scanning with a focused beam. First, the laser treatment mode was found (Figure 5b), in which the material was observed to become photobleached and melted, followed by its destruction, leading to the formation of microcracks. PbSe films that were not subjected to heat treatment in an oven were used as reference samples.