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AP 5301/8301 Instrumental Methods of Analysis and Laboratory

AP 5301/8301 Instrumental Methods of Analysis and Laboratory. Zhengkui XU Office: G6760 Tel: 34429143 Email:apzkx@cityu.edu.hk. Course Objectives. Basic understanding of materials characterization techniques Physical basis – basic components and their functions

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AP 5301/8301 Instrumental Methods of Analysis and Laboratory

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  1. AP 5301/8301Instrumental Methods of Analysisand Laboratory Zhengkui XU Office: G6760 Tel: 34429143 Email:apzkx@cityu.edu.hk

  2. Course Objectives • Basic understanding of materials • characterization techniques • Physical basis – basic components and their functions • Common modes of analysis • Range of information provided by the techniques • Recent development of the techniques • Emphasis on applications • Typical examples and case studies • How to use different techniques to solve different problems in manufacturing and research

  3. Microscopy and Related Techniques • Light (optical) microscopy (LM) or (OM) • Scanning electron microscopy (SEM) • Energy dispersive X-ray spectroscopy (EDS) • & Wavelength dispersive X-ray spectroscopy • (WDS) • X-ray diffraction (XRD)/X-ray fluorescence • (XRF) • Transmission electron microscopy (TEM) • Surface Characterization Techniques • Scanning probe microscopy (AFM & STM) • Secondary ion mass spectroscopy (SIMS) • Auger electron spectroscopy (AES) • X-ray photoelectron spectroscopy (XPS) Non-Destructive Analysis

  4. Processing-structure-property Processingstructureproperty ) ( Chemical composition Crystal Structure (Characterization) Materials Processing Intrinsic Materials Selection Extrinsic Microstructure Properties (Characterization)

  5. Microstructure Nature, quantity and distribution of phases in the ceramics, e.g., crystals, glass, porosity, grain boundary and impurity (secondary) phase. Secondary (amorphous) phase impurity Grain Boundary phase Grain boundary Grain Grain boundary pore 50 m Pore within grain Phase- A homogeneous portion of a system that has uniform physical and chemical characteristics. http://en.wikipedia.org/wiki/Phase_(matter)

  6. Scale and Characterization Techniques XRD,TEM,STMSEM OM Valve Turbo charge Grain I Grain II atomic 1

  7. SiC turbine blades crack Grain 1 Intergranular amorphous phase Grain 2 2nm TEM image

  8. Effect of Microstructure on Mechanical Property f d-1/2 d-grain size 10m 50m a b OM images of two polycrystalline samples. Mechanical test: fa>fb Mechanical property Microscopic analysis: da< db Microstructure

  9. Identification of Fracture Mode Pores Cracks Cracks Grain boundary 4m 20m Intergranular fracture Intragranular fracture

  10. OM and SEM BaTiO3 Growthstep 50m OM - 2D 5m SEM – 3D

  11. High Resolution Z-contrast ImagingAtomic Ordering in Ba(Mg1/3Nb2/3)O3 http://www.youtube.com/watch?v=egPQZw0QkVw I a Z2 [110] (STEM) First Place Winner (TEM category) in the 1998 Ceramographic Contest at 100th Annual Meeting of Am. Ceram. Soc. Z. Xu et al.

  12. Aberration-corrected high-resolution transmission electron microscopy simulation Profile Profile 100% 60% 0.138 nm Simulation 100% 0 20 40 60 80 100 Occupancy (%) Sr Ti O SrTiO3 C.L. Jia, M. Lentzen & K. Urban, Science 299, 870 (2003)

  13. STM - Seeing Atoms STM image showing single-atom defect in iodine adsorbate lattice on platinum. 2.5nm scan Iron on copper (111)

  14. 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 http://micro.magnet.fsu.edu/primer http://www.doitpoms.ac.uk/tlplib/optical-microscopy/index.php

  15. Physics of http://micro.magnet.fsu.edu/primer http://www.doitpoms.ac.uk/vidlib/browse.php

  16. How Fine can You See? • Can you see a sugar cube? The thickness of a sewing needle? The thickness of a piece of paper? … • The resolution of human eyes is of the order of 0.1 mm. • However, something vital to human beings are of sizes smaller than 0.1mm, e.g. our cells, bacteria, microstructural details of materials, etc.

  17. Microstructural Features which Concern Us • Grain size: from <m to the cm regime • Grain shapes • Precipitate size: mostly in the m regime • Volume fractions and distributions of various phases • Defects such as cracks and voids: <m to the cm regime • … …

  18. What is a Microscope? • A microscope is an instrument designed to make • fine details visible. The microscope must accomplish • three tasks: • To produce a magnified image of the specimen • (magnification). • 2. To separate the details in the image (resolution). • 3. To render the details visible to the eye, camera, or other imaging device (contrast).

  19. Introduction- Optical Microscopy • Use visible light as illumination source • Has a resolution of ~o.2m • Range of samples characterized - almost unlimited for solids and liquid crystals • Usually nondestructive; sample preparation may involve material removal • Main 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 http://www.youtube.com/watch?v=bGBgABLEV4g&feature=endscreen&NR=1

  20. http://www.youtube.com/watch?v=sCYX_XQgnSA&feature=related <2min Old and Modern Light Microscopes http://www.youtube.com/watch?annotation_id=annotation_100990&feature=iv&src_vid=L6d3zD2LtSI&v=ntPjuUMdXbg http://www.youtube.com/watch?v=X-w98KA8UqU&feature=related

  21. Simple Microscope Low-power magnifying glasses and hand lenses 2x 4x 10x A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy.

  22. Light path bends at interface between two transparent media of different indices of refraction (densities) Refraction of Light Incident angleq1 Normal Refracted angleq2 air Sinq1 V1 N2 = = Sinq2 V2 N1 Snell’s Law Materials N Air 1.0003 Water 1.33 Lucite 1.47 Immersion oil 1.515 Glass 1.52 Zircon 1.92 Diamond 2.42 N - Refractive index of material - Speed of light in vacuum • Velocity of light • in material N  1 http://micro.magnet.fsu.edu/primer/java/refraction/refractionangles/index.html

  23. Focusing Property of A Curved Surface In entering an optically more dense medium (N2>N1), rays are bent toward the normal to the interface at the point of incidence. Curved (converging) glass surface normal N1 N2 Air F Focal plane f F - focal point f – focal length

  24. Curvature of Lens and Focal Length Normal The larger curvature angle  The shorter focal length f 1 N1 N2 F Optical axis Bi-Convex Lens f1 1>2 2 N1 N2 F f2 Centerline of the lens f1<f2

  25. Converging (Convex) Lens f f F Focal plane The simplest magnifying lens fcurvature angle andlens materials (N) the larger N, the shorter f lucite glass diamond N: 1.47 1.51 2.42 http://www.youtube.com/watch?v=hDRb9HAK5s4 http://www.youtube.com/watch?v=K5LeAV0Ztkg

  26. Image Formation by a Converging Lens • Two fundamental properties of lenses: • Deviating a light beam parallel to its own axis, then making it to pass through the focus; • Leaving unaltered the path of the rays which pass through the lens center. The A ray (principal ray) passes through the lens center and is not deflected. The B ray comes to the lens moving parallel to the axis and passes through F1. The C ray which in a similar way passes through F2 and leaves the lens parallel to the optical axis. Any two of these three characteristic rays can be utilized to determine the size and placement of the image formed by the lens. http://www.youtube.com/watch?v=-k1NNIOzjFo&feature=related

  27. http://www.youtube.com/watch?v=lBKGP6Fh9vs Magnifier – A Converging Lens If o’-o’ is ~0.07mm, o=0.016o NDDV-ability to distin-guish as separate points which are ~0.07mm apart. o - visual angle subtended at the eye by two points o’-o’ at NDDV. retina I’ I’ nearest distance of distinct vision (NDDV) o” o-object distance Magnification I-I o”-o” A m= = cornea B o h  I’-I’ o’-o’ o” Virtual image o f m = /o -i 25cm Real inverted image Ray diagram to show the principle of a single lens http://www.youtube.com/watch?v=_5dEO-LRV-g

  28. Lens formula and magnification Objective lens ho f f hi O i -Inverted image I1 1 1 1 _ = _ + _ Lens Formula f-focal length (distance) O-distance of object from lens i-distance of image from lens f Oi i Magnification by objective hi mo = = ho O http://micro.magnet.fsu.edu/primer/java/lenses/converginglenses/index.html

  29. Maximum Magnification of a Lens 1/f = 1/O + 1/i • Angular magnification is maximum when virtual image is at “near point” of the eye, i.e. 25 cm (i = -25 cm) • Using the lens formula, o = 25f/(25+f ) • 0  h/25 and   h/o f in cm

  30. Magnification when the Eyes are Relaxed 1/f = 1/O + 1/i • The eyes can focus at points from infinity to the “near point” but is most relaxed while focus at infinity. • When o = f, i =  • For this case, 0  h/25 and   h/f

  31. Limitations of a Single Lens • From the formula, larger magnificationrequires smaller focal length • The focal length of a lens with magnification 10 is approximately 2.5cm while that of a 100 lens is 2.5mm. • Lens with such a short focal length (~2.5mm) is very difficult to make • Must combine lenses to achieve high magnifications

  32. Image Formation in Compound Microscope Compound microscope consists of two converging lenses, the objective and the eyepiece (ocular). • Object (O) placed just outside focal point of objective lens • A real inverted (intermediate) image (I1) forms at or close to focal point of eyepiece. • The eyepiece produces a further magnified virtual inverted image (I2). • L – Optical tube length 25cm http://www.youtube.com/watch?v=RKA8_mif6-E

  33. Magnification of Compound Microscope • Magnification by the objective m0 = s’1/s1 • Since s’1 L and s1  f0, therefore magnification of objective mo  L/fo • Magnification of eyepiece me = 25/fe (assuming the final image forms at ) • Overall magnification M = mome =

  34. How Fine can You See with an Optical Microscope? • Magnification M = 25L/fofeIf we can make lenses with extremely short focal length, can we design an optical microscope for seeing atoms? • Can you tell the difference between magnification and resolution? • Imagine printing a JPEG file of resolution 320240 to a A4 size print!!

  35. Empty Magnification Higher resolution Lower resolution

  36. Diffraction of Light Light waves interfere constructively and destructively. Sin=/d Distribution 1st 2nd 3rd film http://micro.magnet.fsu.edu/primer/java/diffraction/basicdiffraction/index.html http://www.youtube.com/watch?v=-mNQW5OShMA

  37. Resolution of an Optical Microscope – Physical Limit • Owing to diffraction, the image of a point is no longer a point but an airy disc after passing through a lens with finite aperture! • The disc images (diffraction patterns) of two adjacent points may overlap if the two points are close together. • The two points can no longer be distinguished if the discs overlap too much

  38. Resolution of Microscope – Rayleigh Criteria Rayleigh Criteria: Angular separation of the two points is such that the central maximum of one image falls on the first diffraction minimum of the other =m  1.22/d

  39. Resolution of Microscope – Rayleigh Criteria Image 1 Image 2 http://micro.magnet.fsu.edu/primer/java/imageformation/rayleighdisks/index.html

  40. Resolution of Microscope – in terms of Linear separation • To express the resolution in terms of a linear separation r, have to consider the Abbe’s theory • Path difference between the two beams passing the two slits is • Assuming that the two beams are just collected by the objective, then i =  and dmin = /2sin I II I II

  41. Resolution of Microscope – Numerical Aperture • If the space between the specimen and the objective is filled with a medium of refractive index n, then wavelength in medium n = /n • The dmin = /2n sin = /2(N.A.) • For circular aperture dmin= 1.22/2(N.A.)=0.61/(N.A.)where N.A. = n sin is called numerical aperture Immersion oil n=1.515 http://micro.magnet.fsu.edu/primer/java/imageformation/rayleighdisks/index.html

  42. Numerical Aperture (NA) NA=1 - theoretical maximum numerical aperture of a lens operating with air as the imaging medium Angular aperture (72 degrees)  One half of A-A NA of an objective is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance. NA = n(sin ) n: refractive index of the imaging medium between the front lens of objective and specimen cover glass http://micro.magnet.fsu.edu/primer/java/microscopy/immersion/index.html

  43. Factors Affecting Resolution • Resolution = dmin = 0.61/(N.A.) • Resolution improves (smaller dmin) if  or n or  • Assuming that sin = 0.95 ( = 71.8°) • (The eye is more sensitive to blue than violet)

  44. Resolution of a Microscope (lateral) The smallest distance between two specimen points that can still be distinguished as two separate entities dmin = 0.61l/NA NA=nsin() l – illumination wavelength (light) NA – numerical aperture -one half of the objective angular aperture n-imaging medium refractive index dmin ~ 0.3m for a midspectrum l of 0.55m

  45. Optical Aberrations Reduce the resolution of microscope Aberrationin optical systems (lenses intended to produce a sharp image) generally leads to blurring of the image. It occurs when light from one point of an object after transmission through the system does not converge into a single point. • Spherical (geometrical) aberration – related to the spherical nature of the lens • Chromatic aberration – arise from variations in the refractive indices of the wide range of frequencies in visible light Two primary causes of non-ideal lens action: Astigmatism, field curvature and comatic aberrations are easily corrected with proper lens fabrication. http://www.youtube.com/watch?v=XGjg64rayfM Aberration of microscope

  46. Defects in Lens • Spherical Aberration – Peripheral rays and axial rays have different focal points (caused by spherical shape of the lens surfaces). • causes the image to appear hazy or blurred and slightly out of focus. • very important in terms of the resolution of the lens because it affects the coincident imaging of points along the optical axis and degrade the performance of the lens. http://micro.magnet.fsu.edu/primer/java/aberrations/spherical/index.html

  47. Defects in Lens • Chromatic Aberration • Axial - Blue light is refracted to the greatest extent followed by green and red light, a phenomenon commonly referred to as dispersion • Lateral - chromatic difference of magnification: the blue image of a detail was slightly larger than the green image or the red image in white light, thus causing color ringing of specimen details at the outer regions of the field of view A converging lens can be combined with a weaker diverging lens, so that the chromatic aberrations cancel for certain wavelengths: The combination – achromatic doublet weaker diverging lens http://micro.magnet.fsu.edu/primer/java/aberrations/chromatic/index.html

  48. Defects in Lens • Astigmatism - The off-axis image of a specimen point appears as a disc or blurred lines instead of a point. • Depending on the angle of the off-axis rays entering the lens, the line image may be oriented either tangentially or radially A o http://micro.magnet.fsu.edu/primer/java/aberrations/astigmatism/index.html http://www.youtube.com/watch?NR=1&v=6YxffFmi4Eo&feature=endscreen

  49. Defects in Lens • Curvature of Field - When visible light is focused through a curved lens, the image plane produced by the lens will be curved • The image appears sharp and crisp either in the center or on the edges of the viewfield but not both http://micro.magnet.fsu.edu/primer/java/aberrations/curvatureoffield/index.html

  50. Defects in Lens • Coma - Comatic aberrations are similar to spherical aberrations, but they are mainly encountered with off-axis objects and are most severe when the microscope is out of alignment. Coma causes the image of a non-axial point to be reproduced as an elongated comet shape, lying in a direction perpendicular to the optical axis. http://micro.magnet.fsu.edu/primer/java/aberrations/coma/index.html

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