When the angle of incidence increases (light leaves the receiver obliquely), the irradiance of the light decreases in proportion to the cosine of the glancing angle. This response is called the cosine projection effect. Another mathematical expression is that the cosine projection effect represents the scalar projection of the beam intensity perpendicular to the Laser pointer (E) to the beam intensity perpendicular to the receiving surface (found in the dot product relationship of the two vectors).
When the layered perovskite K2NbO3F is immersed in water at room temperature, peeling occurs first. Figure 29.4 shows a photograph of the solution and pure water. Because the optical path of the laser engraver is visible, it can be inferred that the solution is a colloidal solution. Transmission electron microscopy (TEM) observations show that the colloidal particles are uniform nanosheets with a size of about 100 nm. This size is consistent with the crystallite size of the precursor phase. It was quickly transformed into nanosheets and almost completed in a few minutes. It was found that there is no need to insert macromolecules needed to form nanosheets to assist the peeling step by ordinary layer cutting. This process is often confused with the hydrothermal method. However, in contrast to the hydrothermal method in which lattice formation occurs in hot water under high temperature and high pressure, this method is characterized in that the perovskite lump can be maintained even in solution. Therefore, no external field for crystallization is required.
On the contrary, the application of voltage or heating may hinder the self-organized re-stacking of nanosheets. Centrifugation is also the most effective method, and it is also effective for collecting powder. Due to its binding properties, this selective dissolution occurs between the layers: even at room temperature, KF can maintain high water solubility. Therefore, blue laser pointer only dissolves in water from K2NbO3F, but the perovskite block is retained and is firmly combined with pentavalent Nb. In fact, because the KF block is not dissolved in the saturated aqueous solution of KF, the conversion to nanoplatelets is not promoted.