Coating material

The properties of the film system depend on the materials that make up the film system. For example, the oxide layer is generally much harder than the fluoride, sulfide or semiconductor layer and, therefore, the oxide layer is suitable for use on the outer surface. In the case of a wide temperature range, the filter should avoid the use of a semiconductor film layer because the optical constant of the semiconductor varies greatly with temperature. For some metal materials, because of the low strength, it is easy to cause damage, and it is easy to oxidize when exposed to the atmosphere. A protective layer is applied to such a film layer or glued between two transparent plates. For other materials, in order to ensure a good adhesion between the film and the substrate during coating, it is necessary to plate an adhesion layer on the substrate. For example, prior to plating a gold (Au) film on a glass substrate, a nickel (Ni) adhesion layer is often plated on the glass. Vacuum coating is suitable for various materials such as metal, resin, plastic (ABS, foamed plastic, recycled plastic), glass (crystal), ceramic, acrylic, wood, cement, phosphorus and magnesium. Can be widely used in automotive, electrical appliances, handicrafts, computer mobile phones, jewelry, high-end furniture and other surface decoration industry, which can give birth to a variety of new decorative industries. The non-conductive sample has large insulation resistance. Under the continuous scanning of electron beam, the surface of the sample gradually accumulates negative charge, forming a relatively high negative electric field, repels incident electrons, unstable secondary electron emission, and randomly deflects the secondary electron trajectory, affecting detection. Receiver, causing image sloshing, sudden change in brightness, and appearance of irregular light and dark stripes, this is the so-called "charge effect", also known as "charge effect." Usually, a conductive film is coated to improve the conductivity of the sample, and the negative charge on the surface is released into the ground through the conductive film to eliminate the charging phenomenon. The premise of charge release is that the film layer must be connected to the metal sample stage to form a conductive path. A continuous conductive film can also increase the thermal conductivity of the sample and reduce thermal damage. Currently, coating techniques commonly used in laboratories are vacuum evaporation and ion sputtering. The conductive film layer should have high secondary electron yield and good coverage, and the film layer is uniform and stable under an electron beam. This film faithfully reflects the microscopic details of the sample surface and effectively improves image quality. Commonly used coating materials are C, Al, Cr, Au, Pt, Au-Pd alloys. Among them, the Au film has high secondary electron yield, good coverage and easy coating. It is the most commonly used material, but the Au film particles are large, and an obvious "island structure" is observed under high magnification. This is a decorative illusion, see Figure 1-8a. Au plating is suitable for low to medium resolution and 20,000 times or less. The particles of the Pt and Au-Pd alloy films are much finer and suitable for high resolution images, see Figure 1-8b. The field emission electron microscopy is required to have a higher film layer, and it is required that the film layer cannot be visualized at least 200,000 times, and high vacuum plating of Cr can meet the requirements. The C film has good uniformity, high electrical and thermal conductivity, and is the most economical material, but the secondary electron yield of the C film is low, and it is not suitable for high-power images. Figure 1 shows the morphology of a plastic ball after coating, with a film thickness of 10 nm.