Materials Lab Procedures
Materials Lab Procedures MSE 300
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Date Created: 10/26/15
Optical Microscopy Philip D Rack Assistant Professor University of Tennessee 603 Dougherty Hall prackutkedu Acknowledgement This lecture was generated by Professor James Fitz Gerald at the University of Virginia University or Tenne n mm M anineering Optical Microscopy 10 Introduction and Histor 11 Brief Review of Light Physics 12 Characteristic Information 20 Basic Principles 21 Ray Optics of the Optical Microscope 22 Summary 30 Instrumentation 31 Sample Prep 32 Measurement Systems and Types 40 Examples 50 Correct Presentation of Results 51 Publication 52 Presentation University or Tenne n mm M anineering 21 Ray Optics Converging Convex Lens f i f i Axis Focal plane Fncal plane The simplest magnifying lens foc curvature angle and lens materials N the larger N the shorterf lucite glass diamond N 147 151 242 University of Tenne no Dept nf Fnoinoprina Defects in Lenses El Spherical Aberration Peripheral rays and axial rays have different focal points This causes the image to appear hazy or blurred and slightly out of focus This is very important in terms of the resolution of the lens because it affects the coincident imaging of points along the optical axis and degrades the performance of the lens Spherical Aberration Monochromatic Light Foca F nin39ils r I 1 2 Defects in Lenses Chromatic Aberration llxial Blue light is reliautedtn the greatest extent followed by green and red light a phenomenon ennmnnty ideired to as dispersinn Lateral diromatr39c dl eraiae almagni izti39on thehlue image at a daail was slightly larger than the green image er the red image in white light thus using color ringing nl specimen daails at the outer ieginns vi the eld M View 539 liennverging lens can he ennhined w39nh a weaker diverging lens sn that the chromatic ahena nns heel for eerta39n wavelengths The cnmhinatinn aehinmatic dnuhla Chmmalln Anernllnn thmmal Dannie Defects in Lenses E Astigmatism The offaxis image of a specimen point appears as a disc or blurred lines instead of a point Depending on the angle of the offaxis rays entering the lens the line image may be oriented either tangentially or radially Astigmatism Geometrical Aberration Radial Line Image Oblen ve Vangenlial JIM Line Plan I39M Specimen Polnl Opllcal Axis Resolution RO6101 NA where 061 is a geometrical term based on the average 2020 eye x wavelength of illumination NA Numerical Aperture The NA is a measure of the light gathering capabilities of an objective lens NA n sin or where n index of refraction of medium or lt subtended by the lens Dept of Materials Scien Factors Affecting Resolution E Resolution dmin improves smaller dmin if M or n or ocT 9 Assuming that Sinoc 095 on 718 Wavelength Air n 1 Oil n 1515 linih i Violet 400 nm 027 pm 017 pm Resolution air Resolution 9 The eye is more sensitive to blue than violet Magnification The overall magnification is given as the product of the lenses and the distance over which the image is projected M DM1 M2 250mm where D projection tube length usually 250 mm M1 M2 magnification of objective and ocular 250 mm minimum distance of distinct vision for 2020 eyes University or Tenne n mm M anineering Depth of Focus We also need to consider the depth of focus vertical resolution This is the ability to produce a sharp image from a nonflat surface 130in NA Depth of Focus is increased by inserting the objective aperture just an iris that cuts down on light entering the objective lens However this decreases resolution University or Tenne n mm M anineering 22 Summary 1 All microscopes are similar in the way lenses work and they all suffer from the same limitations and problems 2 Magnification is a function of the number of lenses Resolution is a function of the ability of a lens to gather light 3 Apertures can be used to affect resolution and depth of field if you know how they affect the light that enters the lens University nf T n t 30 Instrumentation Several important features are visible Lenses Eyepieces oculars Lightsource Camera University nf T n t Anatomy of a modern LM Auanm mmquot r o a Cullnnnv 39 an University nf T n t Contrast and Illumination Brightness contrast arises from different degrees of absorption at different points in the specimen Color contrast can also arise from absorption when the degree of absorption depends on the wavelength and varies from point to point in the specimen Phase contrast arises from a shift in the phase of the light as a result of interaction with the specimen Polarizationdependent phase contrast arises when the phase shift depends on the plane of polarization of the incident light Fluorescence contrast arises when the incident light is absorbed and partially reemitted at a different wavelength Unlversity at Tennessee Dan at Materials Scimceaml Engineaing Bright Field Microscopy Principle Light from an incandescent source is aimed toward a lens beneath the stage called the condenser through the specimen through an objective lens and to the eye through a second magnifying lens the ocular or eyepiece The condenser is used to focus light on the specimen through an opening in the stage After passing through the specimen the light is displayed to the eye with an apparent field that is much larger than the area illuminated Typically used on thinly sectioned materials University or Tenne 9 mm M anineering Dark Field Viewing Principle To view a specimen in dark field an opaque disc is placed underneath the condenser lens so that only light that is scattered by objects on the slide can reach the eye Instead of coming up through the specimen the light is reflected by particles on the slide Everything is visible regardless of color usually bright white against a dark background University or Tenne 9 mm M anineering Dark Field Viewing Specialized LM Techniques Enhancement of Contrast Bright amp Dark field Microscopy Phase contrast microscopy Differential interference contrast microscopy Convert phase differences to amplitude differences Fluorescence microscopymainly organic materials Confocal scanning optical microscopy new ThreeDimensional Optical Microscopy inspect and measure submicrometer features in semiconductors and other materials Hot and coldstage microscopy melting freezing points and eutectics polymorphs twin and domain dynamics phase diagram In situ microscopy Efield stress etc Special environmental stagesvacuum or gases University of Tennessee Dun of Materials Scimceand Eng39nea39ing 31 Sample Preparation Before performing an experiment always consider the information that you want to obtain and the methods by which to obtain ALL of it Sample preparation methods vary widely Depends to some degree on the next phase of characterization Particulate It needs to be mounted in a refractive index liquid for determination of the optical properties OR Mounted on tape for size and shape analysis University or Tenne n mm M anineering 31 Sample Preparation gtm If the sample is metal embed in a polymer section and polish Organic samples may be sectioned processed with a cryomicrotome among other types to reduce sample prep damage L University or Tenne n mm M anineering Grain Size Examination Thermal Etching 7 1 A grain boundary intersecting a polished surface i um a At elevated temperatures b surface diffusion forms a grainboundary groove in order to balance the surface tension forces University urTennessee Dept uf Materials Science and Engineering Contrast Contrast is defined as the difference in light intensity between the specimen and the adjacent background relative to the overall background ens ty Image contrast C is defined by Sspecimen Sbackgraund Sb ackgraund Sspecimen and Sbackground are intensities measured from the specimen and background eg A and B in the scanned area wquot innnvin Grain Growth Reflected OM L a Polycrystalline CaF2 illustrating normal grain growth Better grain size distribution f 7 V 30pm t 1 hquot 7 L Large grains in polycrystalline spinel MgAl204 growing by secondary recrystallization from a finegrained matrix University of Tennessee Dept ol Materials Science and Engineering Effect of Microstructure on Mechanical Property cfoc d391 2 dgrain size 0M images of two polycrystalline samples Mechanical test ofa gt 6 Mechanical property It Microscopic analysis da lt db Microstructure University of Tennessee Dept ol Materials Science and Engineering Polarized Optical Microscopy POM Reflected POM Transmitted POM a Surface features of a microprocessor integrated circuit b Apollo 14 Moon rock Contrast Enhancement brighf eld a dar39kfield laidxix www cellsolive corn Hotstage POM Phase Transformations in PbMg13Nb23O3PbTi03 crystals a and b at 20 C strongly birefringent domains with extinction directions along lt100gtcube indicating a tetragonal symmetry c at 240 C phase transition from the tetragonal into cubic phase with increasing isotropic areas at the expense of vanishing strip domains University oiTennessee Dept oI Malerials Science and Engineering Optical Microscopy vs Scanning Electron Microscopy OM SEM Small depth of eld Large depth of eld Low resolution High resolution University nl39Tonno no Dom nl39 39 39 FnEinoorinE 50 Correct Presentation of Results University nf T n t Publication and Presentation Responsibilities of a Scientist Understand the technique your discussing presenting at the required level Have supporting characterization is possible How much information are you drawing off of in terms of numerical analysis Is the data supportive of measurements you are quoting How clear is the image I features that you are specifying in your talk or paper Are the magnification bars and text properly labeled and displayed 7 University nf T n t University at Tenne 99 mm M anineering The Polarizing Microscope Light from an incandescent source is passed through a polarizer so that all of the light getting through must vibrate in a single plane The beam is then passed through a prism that separates it into components that are separated by a very small distance equal to the resolution of the objective lens The beams pass through the condenser then the specimen In any part of the specimen in which adjacent regions differ in refractive index the two beams are delayed or refracted differently When they are recombined by a second prism in the objective lens there are differences in brightness corresponding to differences in refractive index or thickness in the specimen University at Tenne 99 mm M anineering Polarization of Light Light Passing nimugn crossed Paiarizers Polarizer 1 Venical incident Beam mummified y Light Wave When the electric field vectors orlight 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 ves vibrate in the same plane Polarized OM Configuration Dalila Recambined l is c lm ngmRIyi 1 Camera Syllem Aher lmerlerenc 6mm Ey pleces Exienlion H Tube 1 Epilf1mlniior or Analyzer A 5298 o a 15 Omlnyiry L i 4 lnvealgauons Birelvingenl S eclmen aim P gm Roiling SligE Polarlxar r Mlcmscop gm Slam From 5 Source Phase Contrast Microscopy Zernike Nomarski DIC Hoffman Modulation Contrast Phase Contrast Microscopy Phase contrast Introduced in the 1930 s by Zernike converts phase differences into amplitude differences Differential interference microscopy DIC requires several optical components therefore it can be very expensive to set up University or Tenne 9 mm M anineering 1m Adtlllmml plum llil39l bulween Ill m C and 1 Than I cunlruu l5 c II h k in 11 l thc mmmx microscopy works h lllerdUL39lll If and RI cn ulmg u dil lurcncc lll unplilmlc nl iiquot mulled Thu ph c Iul l i m1 d b pl lhc nbycunc n p n m M lhcl IL l In mu til 1 additional 917 l39cl nu In in Icmlhrnrdcr lercull butlm 39lm rcxull xx llml Ixquot I dircclcd w gt1u RH m m the whiml ul Image pnuu und gnu A mmnnum ul uucmil l lmzlgc lmml I R l rumm mmrdul I w in mpcm mm uml n Ilwn39l39nrc 2 mm may Phase contrast microscopy rst described in 1934 by 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IleKwumdpnnmnulhgurcthmlvhquot Mum m w lolhuln uullmlmUH y m umhlm u mm burHualvdlmmmch m Yuma umhlm cundmplvmc mummhmwmmm w mmquot m h mm BHHBV A A A E A C Al D Transpavem bat mm 5m 5 5y 5 7 i I BgHsg Ba By 50 m n 15quot th wwmnzn mm AVA NB NC AID Transparent bay lransparenl 501 equa ndex spam By A s o 5 Rga Aand mam mm ms nw mmlcl m phmv mner The Confocal Microscope In the confocal microscope all structures out of focus are suppressed at image formation This is obtained by an arrangement of diaphragms which at optically conjugated points of the path of rays act as a point of source and as a point detector respectively Rays from outof focus are suppressed by the detection pinhole The depth of the focal plane is besides the wavelength of light determined in particular by the numerical aperture of the objective used and the diameter of the diaphragm University of Tennessee Dept of Materials The Confocal Microscope ll At a wider detection pinhole the confocal effect can be reduced To obtain a full image the image point is moved across the specimen by mirror scanners The 39 quot quot 39 light 39 quot 39 the 39 pinhole is I u U transformed into electrical signals by a photomultiplier and displayed on a computer monitor screen Cerulean sin10 Enamswllkknr 7 obch Not m 20 Plant am an n Focal mane 3 not m ml Plane Unlverslty m 1 enn The Confocal Microscope lll Ivlajul 39 39 conventional microscope may be summarized as follows 1I39 39 39 planewill 2 H as u y 39rhm eventually disappear This feature is called optical sectioning dimensional data sets can be recorded 4 s a W axis allows viewing the objects from all sides 5 dimension or 39 39 39 light is minimized 639 quotY I 1 1 as i H 39 39 39 of the aperture and thus sacri cing resolution University nf T n quot r the object and Crystals GrowthInterference Contrast Microscopy Growth spiral on cadmium iodide crystals growing From water solution 1025x