Lecture-2 Optical Microscopy. Introduction Lens formula, Image formation and Magnification Resolution and lens defects Basic components and their functions Common modes of analysis Specialized Microscopy Techniques Typical examples of applications. Basic components and their functions.
http://www.youtube.com/watch?v=PMIU1fkIPQsMicroscope Review (simple, clear)
http://www.youtube.com/watch?annotation_id=annotation_100990&feature=iv&src_vid=L6d3zD2LtSI&v=ntPjuUMdXbg (I)Parts and Function of a Microscope (details)
http://www.youtube.com/watch?v=X-w98KA8UqU&feature=relatedHow to use a microscope
(1) Eyepiece (ocular lens)
(2) Revolving nose piece (to hold multiple objective lenses)
(3) Objective lenses
(4) And (5) Focus knobs
(4) Coarse adjustment
(5) Fine adjustment
(6) Stage (to hold the specimen)
(7) Light source (lamp)
(8) Condenser lens and diaphragm
(9) Mechanical stage (move the specimen on two horizontal axes for positioning the specimen)
Light from the microscope light source
Condenser gathers light and concentrates it into a cone of light that illuminates the specimen with uniform intensity over the entire viewfield
dmin = 0.61l/NA
Anatomy of an objective
Objectives are the most important components of a
light microscope: image formation, magnification, the
quality of imagesand the resolutionof the microscope
Eyepieces (Oculars) work in combination with microscope
objectives to further magnify the intermediate image
Depending on the nature of samples, different illumination methods must be used
thin section of rocks, minerals and single crystals
most metals, ceramics, semiconductors
Specialized Microscopy Techniques
Characteristics of materials can be determined
morphology (shape and size), phase distribution (amorphous or crystalline), transparency or opacity, color, refractive indices, dispersion of refractive indices, crystal system, birefringence, degree of crystallinity, polymorphism and etc.
Polarized light microscope is designed to observe specimens that are visible primarily due to their optically anisotropic character (birefringent). The microscope must be equipped with both a polarizer, positioned in the light path somewhere before the specimen, and an analyzer (a second polarizer), placed in the optical pathway between the objective rear aperture and the observation tubes or camera port.
birefringent - doubly refracting
When the electric field vectors of light are restricted to a single plane by filtration, then the the light is said to be polarized with respect to the direction of propagation and all waves vibrate in the same plane.
Birefringence is optical property of a material having a refractive index that depends on the polarization and propagation direction of light.
Double Refraction (Birefringence)
Crystals are classified as being either isotropic or anisotropic depending upon their optical behavior and whether or not their crystallographic axes are equivalent. All isotropic crystals have equivalent axes that interact with light in a similar manner, regardless of the crystal orientation with respect to incident light waves. Light entering an isotropic crystal is refracted at a constant angle and passes through the crystal at a single velocity without being polarized by interaction with the electronic components of the crystalline lattice.
Anisotropic crystals have crystallographically distinct axes and interact with light in a manner that is dependent upon the orientation of the crystalline lattice with respect to the incident light. When light enters the optical axis(c) of anisotropic crystals, it acts in a manner similar to interaction with isotropic crystals and passes through at a single velocity. However, when light enters a non-equivalent axis (a), it is refracted into two rays each polarized with the vibration directions oriented at right angles to one another, and traveling at different velocities. This phenomenon is termed "double" or "bi"refraction and is seen to a greater or lesser degree in all anisotropic crystals.
Phase contrast microscopy
Differential interference contrast microscopy
Fluorescence microscopy-medical & organic materials
Three-Dimensional Optical Microscopy
inspect and measure submicrometer features in semiconductors and other materials
melting, freezing points and eutectics, polymorphs, twin and domain dynamics, phase transformations
E-field, stress, etc.
Contrast is defined as the difference in light intensity between the specimen and the adjacent background relative to the overall background intensity.
Image contrast, C is defined by
C = =
Sspecimenand Sbackgroud are intensities measured from specimen and backgroud, e.g., A and B, in the scanned area.
Cminimum~ 2% for human eye to distinguish differences between the specimen (image) and its background.
Formation of Contrast
Contrast produced in the specimen by the absorption of light (directly related to the chemical composition of the absorber) and the predominant source of contrast in the ordinary optical microscope, brightness, reflectance, birefringence, light scattering, diffraction, fluorescence, or color variations have been the classical means of imaging specimens in brightfield microscopy.
Enhancement of contrast by darkfield microscopy
Darkfield microscopy is a specialized illumination technique that capitalizes on oblique illumination to enhance contrast in specimens that are not imaged well under normal brightfield illumination conditions.
OM images of the green alga Micrasterias
Phase contrast microscopy is a contrast-enhancing optical technique that can be utilized to produce high-contrast images of transparent specimens, such as living cells, thin tissue slices, lithographic patterns, fibers, latex dispersions, glass fragments, and subcellular particles (including nuclei and other organelles).
Growth spiral on cadmium iodide crystals growing
From water solution (1025x).
Fluorescence microscopy - medical & organic materials
Three-Dimensional Optical Microscopy
Critical dimension measurements
in semiconductor metrology
Cross-sectional image with line scan at PR/Si interface of a sample containing 0.6m-wide lines and 1.0m-thick photoresist on silicon.
The bottom width, w, determining the area of the circuit that is protected from further processing, can be measured accurately by using SCOP.
Measurement of the patterned photoresist is important because it allows the process engineer to simultaneously monitor for defects, misalignment, or other artifacts that may affect the manufacturing line.
A grain boundary intersecting a polished surface is not in equilibrium (a). At elevated temperatures (b), surface diffusion forms a grain-boundary groove in order to balance the surface tension forces.
Polycrystalline CaF2 illustrating normal grain
growth. Better grain size distribution.
Large grains in polycrystalline
spinel (MgAl2O4) growing by
from a fine-grained matrix
Microstructure of MgO-2% kaolin body resulting
from reactive-liquid phase sintering.
Magnetic domains and walls on a (110)-oriented garnet crystal (Transmitted LM with oblique illumination). The domains structure is illustrated in (b).
Reflected POM Transmitted POM
YBa2Cu307-x superconductor material: (a) tetragonal phase and (b) orthorhombic phase with multiple twinning (arrowed) (100 x).
(a) and (b) at 20oC, strongly birefringent domains with extinction directions along <100>cubic, indicating a tetragonal symmetry; (c) at 240oC, phase transition from the tetragonal into cubic phase with increasing isotropic areas at the expense of vanishing strip domains.
Schematic diagram for
in situ domain observa-
Domain structures of PZN-PT
crystals as a function of E-field;
Rhombohedral at E=0 and
Tetragonal was induced at E>20kV/cm
Morphology (shape and size), phase distribution (amorphous or crystalline), transparency or opacity, color, refractive indices, dispersion of refractive indices, crystal system, birefringence, degree of crystallinity, polymorphism and etc.
Thin section or polished surface
Small depth of field
Large depth of field