tailieunhanh - Handbook of Analytical Methods for Materials Part 3

Tham khảo tài liệu 'handbook of analytical methods for materials part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | LIGHT MICROSCOPY DESCRIPTION OF TECHNIQUE Light microscopy in materials analysis generally refers to reflected light microscopy. In this method light is directed vertically through the microscope objective and reflected back through the objective to an eyepiece view screen or camera. Transmitted light is occasionally used for transparent and translucent materials. For some low-magnification work stereo microscopy external oblique illumination can be reflected offthe sample into the objective. Magnification ofthe sample image is obtained by light refraction through a combination of objective lenses and eyepieces. The minimum feature resolution is approximately pm. However smaller features - as small as about pm - can be detected by image contrast enhancement with polarized light interference contrast and dark field illuminations. The resulting images can be recorded either on traditional films or as digital files for computer display analysis and storage. Interference Contrast Image of IC ANALYTICAL INFORMATION Bright Field Light Microscopy - This method produces true color images at magnifications up to approximately 2000X. The sample surface is uniformly illuminated by incident light rays directed perpendicularly to the sample surface. Light reflected back toward the objective lens is collected and focused on the eyepieces to form the observed image. Surfaces that are reflective and perpendicular to the light rays appear bright. Alternatively nonreflective or oblique features reflect less light and appear darker. Polarized Light - This method produces enhanced contrast for features that have anisotropic refractive properties. Two polarizing lenses are inserted into the optical path - one in the incoming illumination and one between the sample and eyepieces. When these lenses are rotated 90 to one another the crossed polarizers result in the subtraction of a portion of the light spectrum by destructive interference. Contrast is obtained between sample .

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