Presentation on theme: "Lecture-2 Optical Microscopy"— Presentation transcript:
1 Lecture-2 Optical Microscopy IntroductionLens formula, Image formation and MagnificationResolution and lens defectsBasic components and their functionsCommon modes of analysisSpecialized Microscopy TechniquesTypical examples of applications
2 Basic components and their functions Microscope Review (simple, clear)(I) Parts and Function of a Microscope (details)(II)How to use a microscope
3 Basic components and their functions (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)
4 Functions of the Major Parts of a Optical Microscope Lamp and Condenser: project a parallel beam of light onto the sample for illuminationSample stage with X-Y movement: sample is placed on the stage and different part of the sample can be viewed due to the X-Y movement capabilityFocusing knobs: since the distance between objective and eyepiece is fixed, focusing is achieved by moving the sample relative to the objective lens
6 Condenser Light from the microscope light source -Condenser Alignment and Field Diaphragm Opening Size-Condenser Light Cones-Condenser Aperture Diaphragm - Control Of Specimen ContrastLight from the microscope light sourceCondenser gathers light and concentrates it into a cone of light that illuminates the specimen with uniform intensity over the entire viewfield
8 Functions of the Major Parts of a Optical Microscope Objective: does the main part of magnification and resolves the fine details on the samples (mo ~ 10 – 100)Eyepiece: forms a further magnified virtual image which can be observed directly with eyes (me ~ 10)Beam splitter and camera: allow a permanent record of the real image from the objective be made on film (for modern research microscope)
9 Olympus BX51 Research Microscope Cutaway Diagram cameraBeamsplitterOlympus BX51 Research Microscope Cutaway Diagram
10 Objective Lens dmin = 0.61l/NA Anatomy of an objective Objective specificationsricalture- Dry and oil immersion objective use in microscope-Specifications and Identification-Numerical Aperture Light ConesObjectives are the most important components of alight microscope: image formation, magnification, thequality of images and the resolution of the microscope
11 Eyepiece Lens M=(L/fo)(25/fe) (Diaphragm)M=(L/fo)(25/fe)Eyepieces (Oculars) work in combination with microscopeobjectives to further magnify the intermediate image
12 Common Modes of Analysis Depending on the nature of samples, different illumination methods must be usedTransmitted OM - transparent specimensthin section of rocks, minerals and single crystalsReflected OM - opaque specimensmost metals, ceramics, semiconductorsSpecialized Microscopy TechniquesPolarized LM - specimens with anisotropic opticalcharacterCharacteristics of materials can be determinedmorphology (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.
13 Anatomy of a modern OM Illumination System Reflected OM Transmitted OM Illumination SystemReflectedOMTransmitted light microscopy is the general term used for any type of microscopy where the light is transmitted from a source on the opposite side of the specimen from the objective. Usually the light is passed through a condenser to focus it on the specimen to get very high illumination. After the light passes through the specimen, the image of the specimen goes through the objective lens and to the oculars where the enlarged image is viewed.Reflected light microscopy is often referred to as incident light or metallurgical microscopy, and is the method of choice for imaging specimens that remain opaque even when ground to a thickness of 30 microns.TransmittedOMIllumination System
14 Polarized Light Microscopy 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 refractingPolarized light microscopy is a useful method to generate contrast in birefringent specimens and to determine qualitative and quantitative aspects of crystallographic axes present in various materials.
15 Polarization of LightWhen 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.~3:30min
16 Birefringence anisotropic Isotropic CaCO3 Birefringence is optical property of a material having a refractive index that depends on the polarization and propagation direction of light.IsotropicanisotropicCaCO3Double Refraction (Birefringence)Anisotropic
17 BirefringenceaCubicCrystals 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.tetragonalcAnisotropic 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.a
18 Olympus BX51 Research Microscope Cutaway Diagram cameraBeamsplitterOlympus BX51 Research Microscope Cutaway Diagram
19 Specialized OM Techniques Enhancement of ContrastDarkfield MicroscopyPhase contrast microscopyDifferential interference contrast microscopyFluorescence microscopy-medical & organic materialsScanning confocal optical microscopy (relatively new)Three-Dimensional Optical Microscopyinspect and measure submicrometer features in semiconductors and other materialsHot- and cold-stage microscopymelting, freezing points and eutectics, polymorphs, twin and domain dynamics, phase transformationsIn situ microscopyE-field, stress, etc.Special environmental stages-vacuum or gases
20 ContrastContrast 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 bySspecimen-Sbackgroud SC = =Sspecimen SASspecimen and 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.
21 Formation of ContrastContrast 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 microscopyDarkfield 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.When imaging specimens in the optical microscope, differences in intensity and/or color create image contrast, which allows individual features and details of the specimen to become visible.
22 Angle of IlluminationBright filed illumination – The normal method of illumination, light comes from above (for reflected OM)Oblique illumination – light is not projected along the optical axis of the objective lens; better contrast for detail featuresDark field illumination – The light is projected onto specimen surface through a special mirror block and attachment in the objective – the most effective way to improve contrast.Light stopContrast 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 transmitted optical microscope. Different phases or variations in thickness absorb light to differing extends which causes them to differ in brightness in specimens of uniform thickness in the former and in specimens with different thickness in the latter. Furthermore, in some cases selective absorption of a particular wavelength or wavelengths of light occurs causing the phases to appear coloured.), brightness, reflectance (light from the surfaces that are perpendicular to the incident beam is reflected back into the objective, while light from tilted areas of the surfaces or grain boundaries is reflected away from the objective, so that they appear dark. Conversely with DF illumination, light reflected from grain surfaces which are almost perpendicular to the optical axis of the microscope is reflected away from the objective, while light from grain boundaries and tilted surfaces is reflected into it. Mainly for opaque specimens.), birefringence, light scattering, diffraction, fluorescence, or color variations has been the classical means of imaging specimens in brightfield microscopy.Imax-IminImaxC=IminImaxC-contrast
23 Transmitted Dark Field Illumination Oblique raysspecimenNo zeroth order light reaches the specimen, only light that has been diffracted, refracted and reflected from the surface of the specimen is able to enter the front lens of the objective to form an image. In the absence of a specimen, the viewfield appears totally back, because no light is reflected or diffracted into the objective.IIdistancedistance
24 Contrast EnhancementOM images of the green alga Micrasterias
25 Phase Contrast Microscopy 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).
26 Crystals Growth by Differential Interference contrast microscopy Growth spiral on cadmium iodide crystals growingFrom water solution (1025x).Fluorescence microscopy - medical & organic materials
27 Scanning Confocal Optical Microscopy Three-Dimensional Optical MicroscopyCritical dimension measurementsin semiconductor metrologywCross-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.Confocal microscopy offers several advantages over conventional optical microscopy, including controllable depth of field, the elimination of image degrading out-of-focus information, and the ability to collect serial optical sections from thick specimens. The key to the confocal approach is the use of spatial filtering to eliminate out-of-focus light or flare in specimens that are thicker than the plane of focus.
29 Grain Size Examination 1200C/30minThermal Etchinga1200C/2h20mbA 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.
31 Grain Growth - Reflected OM 5mm30mmPolycrystalline CaF2 illustrating normal graingrowth. Better grain size distribution.Large grains in polycrystallinespinel (MgAl2O4) growing bysecondary recrystallizationfrom a fine-grained matrix
32 Liquid Phase Sintering – Reflective OM Amorphousphase40mmMicrostructure of MgO-2% kaolin body resultingfrom reactive-liquid phase sintering.
33 Image of Magnetic Domains Magnetic domains and walls on a (110)-oriented garnet crystal (Transmitted LM with oblique illumination). The domains structure is illustrated in (b).
34 Polarized Optical Microscopy (POM) Reflected POM Transmitted POMSurface features of a microprocessor integrated circuitApollo 14 Moon rock
35 Phase Identification by Reflected Polarized Optical Microscopy YBa2Cu307-x superconductor material: (a) tetragonal phase and (b) orthorhombic phase with multiple twinning (arrowed) (100 x).Under plane-polarized light, i.e., only analyzer was used and incident beam is unpolarized. The color is due to anisotropic absorption.
36 Hot-stage POM of Phase Transformations in Pb(Mg1/3Nb2/3)O3-PbTiO3 Crystals (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.nT(oC)
37 E-field Induced Phase Transition in Pb(Zn1/3Nb2/3)O3-PbTiO3 Crystals Single domainSchematic diagram forin situ domain observa-tions.Domain structures of PZN-PTcrystals as a function of E-field;E=20kV/cm, (b) e=23.5kV/cm(c) E=27kV/cmRhombohedral at E=0 andTetragonal was induced at E>20kV/cm
38 Review - Optical Microscopy Use visible light as illumination sourceHas a resolution of ~o.2mRange of samples characterized - almost unlimited for solids and liquid crystalsUsually nondestructive; sample preparation may involve material removalMain use – direct visual observation; preliminary observation for final charac-terization with applications in geology, medicine, materials research and engineering, industries, and etc.Cost - $15,000-$390,000 or more
39 Characteristics of Materials Can be determined By OM: 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.
40 Limits of Optical Microscopy Small depth of field <15.5mmRough surfaceLow resolution ~0.2mmShape of specimenThin section or polished surfaceCover glassspecimenGlass slideresin20mmLack of compositional and crystallographic information
41 Optical Microscopy vs Scanning Electron Microscopy 25mmradiolarianOMSEMSmall depth of fieldLow resolutionLarge depth of fieldHigh resolution
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