Characterization Tools PDF

XING YI LING, CBC, NTU Chapter 3: Characterization tools 3.1 Optical probes 3.1 Optical Microscope 3.1.2 Optical Imaging Techniques beyond Diffraction Limit...

XING YI LING, CBC, NTU Chapter 3: Characterization tools 3.1 Optical probes 3.1 Optical Microscope 3.1.2 Optical Imaging Techniques beyond Diffraction Limit 3.2 Scanning Probe Microscope 3.2.1 Atomic Force Microscope (AFM) 3.2.2 Scanning Tunneling Microscope 3.3 Electron probes 3.3.1 Electron Interactions with Matter 3.3.2 Scanning Electron Microscopy 3.3.3 Transmission Electron Microscopy Based on Introduction to Nanoscience by Hornyak, Dutta, Tibbals, and Rao. CRC 1  XING YI LING, CBC, NTU 3.1 Optical probes Birth of the Light Microscope About 1590, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, while experimenting with several lenses in a tube, discovered that nearby objects appeared greatly enlarged. That was the forerunner of the compound microscope and of the telescope. In 1609, Galileo, father of modern physics and astronomy, heard of these early experiments, worked out the principles of lenses, and made a much better instrument with a focusing device. Zacharias Janssen Antony van Leeuwenhoek (1585-1632) (1632-1723) He was the first to see and describe bacteria, yeast plants, the teeming life in a droplet of water, and the circulation of blood 2 corpuscles in capillaries.  XING YI LING, CBC, NTU 3.1 Optical probes World’s first compound Today’s modern microscope compound microscope (~ 1595) 3  XING YI LING, CBC, NTU 3.1 Optical probes Modern compound microscope source -Add light Collinater weS mechinal 3 > - > - motorised (mm) > - piezo(umi Emargnity sample - Istage. 4 computerized https://www.youtube.com/watch?v=RKA8_mif6-E 4  XING YI LING, CBC, NTU 3.1 Optical probes The primary probe in optical methods is visible light of wavelength within the 400 – 800 nm. 5  XING YI LING, CBC, NTU 3.1 Optical probes The numerical aperture (N.A.) of a lens - a dimensionless number that characterizes the range of angles over which the system can accept or emit light. Show much light optical microscope accept/emit] - has significant influence over the resolution. N.A.  n sin in vacuum  > - speed of light ↑ V medium - n is the refractive index of the medium between the lens and the sample -  Is the half-angle that is subtended by the rays entering the objective lens. n4 ↑N A. , Of - The N.A. can reach about 1.4 in modern optics. 6  XING YI LING, CBC, NTU 3.1 Optical probes Example: Numerical aperture 1 2 3 n = 1.0 (air) 1 = 7o, N.A. = (1) Sin7° = 0 122. 2 = 20o, N.A. = 111 Sin 200 = 0 342. 3 = 60o, N.A. = (1) sin 600 = 0. 866 7 http://www.microscopyu.com/articles/formulas/formulasna.html  XING YI LING, CBC, NTU 3.1 Optical probes The resolving power (aka Abbe Resolutionx,y) of the lens - The ability to measure the angular separation of images that are close together. - is proportional to wavelength divided by the numerical aperture   I R  I N A. = Using + = 0. 61E N A 2 N. A. 2. ansing F refractive index · The resolution gets better (i.e. R gets smaller) when: ↓R = better 1. The wavelength of the impinging radiation gets shorter resolve ( close 2. The refractive index of the connecting medium gets larger objects- 3. N.A. gets larger Rw 44 , , 04 Ernst Karl Abbe– credited for discovering the resolution limit of the microscope, and the formula (published in 1873) 8  XING YI LING, CBC, NTU 3.1 Optical probes Airy disk Object A point object in a microscope, such as a fluorescent protein single molecule, generates an Image image at the intermediate plane that consists of a diffraction pattern created by the action of interference. When highly magnified, the diffraction pattern of the point object is observed to consist of a central spot (diffraction disk) surrounded by a series of diffraction rings. This point source diffraction pattern is referred to as an Airy disk. => - point object top view pinhole - Radius of disk I airy = 0 61 :. x N A - Swave-like - unte. * r as small as possible , why? & N AP/i sideview. , : 9 plane  XING YI LING, CBC, NTU 3.1 Optical probes Imaging Resolution Distance > /2 < /2 Object G O ⑮ ⑭ Image N l well. resolved for ↑ resolution Reno ↑ not resolved Due to the diffraction limit, the imaging resolution of optical systems is roughly /2. If two objects are separated by a distance shorter than /2, they will appear as a single object and we cannot distinguish them. 10  XING YI LING, CBC, NTU 3.1 Optical probes The diameter of the most intense (central) Airy disk is inversely proportional to the diameter of the aperture. Because each object in the image is capable of diffracting the impinging optical beam, each object is able to form its own Airy disk. If the point images seem to be merged (unfocused, unresolved), a disk of confusion is formed. N.A.  n sin  R 2 N. A. (a) small O , N. At R4 (lower resolution] Increase in N.A.;  Decrease in diameter of the central airy disk  Higher resolution! 11  XING YI LING, CBC, NTU 3.1 Optical probes for ↑ in t R = - resolution Insing Factors Affecting Resolution ↑ ↑   R  2( n  sin ) 2 NA Resolution improves ( r ↓) if  ↓, or n ↑, or ↑ M O Assume = 65º, so sin = 0.906 ↑ refractive index of medium (v) Wavelength Resolution in Air (n=1) Resolution using Oil Immersion (n=1.515) Red 650 nm 359 nm 237 um Green 550 nm 304 nm 200 nm Blue 475 nm 262 nm 173 nm The imaging resolution of conventional microscopes is a few hundred nanometers, still fairly large compared to most nanostructures or internal organelles of biological cells. 12  XING YI LING, CBC, NTU 3.1 Optical probes Optical images Red blood cells Fluorescent images of cells Snowflakes Bacteria 13  XING YI LING, CBC, NTU Summary of Optical Microscope Advantages: Direct imaging with no need of sample pre-treatment, the only microscopy for real color imaging. Fast, and adaptable to all kinds of sample systems, from gas, to liquid, to living cells, and to solid sample systems, in any shapes or geometries. Disadvantages: Low resolution, usually down to a few hundreds of nanometers, mainly due to the light diffraction limit. An excellent of overview of optical microscopy: 39 min! https://www.youtube.com/watch?v=sTa-Hn_eisw 14  XING YI LING, CBC, NTU 3.1.2 Optical Imaging Techniques beyond Diffraction Limit attach functionalized finorescence probes /molecules : > - on > - light : activation #1 > - computer activate tubule. = most intense spof - I com microtripules * Eit > repeat activation - > - superimpose mose intensive spots > - ↑ resolution 15 < 100-200mm  XING YI LING, CBC, NTU 3.2 Scanning Probe Microscope Scanning probe microscope (SPM) is a relatively new branch of microscopy that forms images of surfaces using a physical probe to scan the specimen. Basic principle: Using probe tip fastened to a cantilever, a scanning (motion mechanism), and a detector system. An three-dimensional image of the surface with atomic resolution is obtained by mechanically moving the probe in a raster scan of the specimen, line by line, and recording the probe-surface interaction as a function of position. > record - amt of current funneled through > - light sourceapplied from tip : light-matter interaction of localized area (fr tip) - atomic resolution - 16  XING YI LING, CBC, NTU 3.2 Scanning Probe Microscope Two major types of SPMs use valuum , X Scanning tunneling microscope (STM) very sensitive Atomic force microscope (AFM)> rtp - , ampient conditions. less resolved than Sin STM AFM Other scanning probe microscopes Magnetic force microscope (MFM) Near-field scanning optical microscope (NSOM) Nobel Prize for Physics (1986) Scanning voltage microscope (SVM) Gerd Binnig (left) & Heinrich Rohrer …… (right) of IBM Research, Zurich “for the invention of the scanning 17 tunneling microscope (STM).”  XING YI LING, CBC, NTU 3.2 Scanning Probe Microscope Component: Scanning probe tips ① tip must be sharp The tip is important to the feature-resolving ability of the SPM. For AFM – Si or Si3N4 tips For STM – Tungsten tips (must be conductive) The probe is sharpened to a fine tip to provide the best resolution. tip y #I scanning direction # metal Tip sharpness limits the ultimate resolution! 11 height Surface profile 18  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) laser reflected on & US photodiode based on how much cantilever deflected ↓ laser location deflected OS z surface on Piezoelectric Stage ↓ movement in u Scale * y , z · can measure in air/liquid samples A mechanical device capable of imaging atoms photodetector > computer - Feedback Can be performed at ambient environment and temperature, loop requires no expensive high-energy radiation or beam source. able to convert mechanical stress into electrical Stage lowers I · signals & vice versa point back to neutral 19 "force. to indent sample" piezoelectric components)  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) Principle: Rely on the mechanical deflection of a cantilever to relay information about the contour of a sample surface. An atomically sharpened probe tip (20 – 50 nm or less) descends perpendicularly from the distal end of a cantilever. The tip-to-distance is fixed by means of a feedback mechanism that maintains a constant force between them (i.e. constant height). A laser beam is focused on the top of the cantilever and is reflected into a photodiode detector. The differences in the reflected beam are recorded by a split photodiode and recorded as changes in topography. The photodetector is able to discriminate motion with accuracy imaging (contact/non-contact) - AFM Operation Modes mechanical > - - measure force 1. Contact mode: snarpl hard tip Tip is in continuous “contact” with sample. Detect deflection at a constant height, or use the feedback signal to keep the cantilever deflection constant. Preferably used for hard samples. Possess high resolution –provide quantitative information include topographic mapping, particle and pore size and morphology, surface roughness, texture, deflection and etc. lasen Fr. ↓ G - , http://www.youtube.com/watch?v=0juoPeGVCLY - - weight M piezostage & 21  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) AFM Operation Modes 2. Non-contact Mode Tip doesn’t touch sample. Instead, the cantilever is oscillated around its resonant frequency, and the amplitude of oscillation is typically a few nanometers or smaller. The van der Waals forces, which are strongest from 1 nm to 10 nm above the surface, or any other long-range force which extends above the surface acts to decrease the resonance frequency or amplitude of the cantilever. Doesn’t degrade or interfere with sample. Therefore it’s very useful for soft samples, e.g., biology sample and organic thin film. Imaging resolution is not very good. Animation: http://www.youtube.com/watch?v=Ha53tFTsmW8 22  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) Tip-Sample Interaction Force Interaction between a pair of neutral atoms or molecules:   12   6  ( r )  4        r   r   The r −12 term, which represents it contac approve the repulsive force at short ranges (< a few Å) due to overlapping electron orbitals; The r −6 term, which is the attractive long-range term, describes attractive van der Waals retract vowleecratic forces force. W Fd = 23  Force-Distance Curve picoNewton - XING YI LING, CBC, NTU Vertical tip movement during the approach and retract parts of a force spectroscopy experiment “snap-on” E F, G D D D A, B C Approach Contact Retract Approach A Tip far away No interaction (10 – 100 microns) B Tip approaching Electrostatic forces (few microns) C Tip close to surface Van der Waals (nm to atomic distances) Other possible short range forces: “Snap-on” Capillary forces (in air) touch surface LVO/screen electrostatics (in aq solutions) > - not yet Chemical potential Magnetic Solvation forces (water layers) Contact D Tip indenting sample Stiffness (Young’s modulus, elastic response) > measure mechanical forces - Viscoelastic response (variable rates or indentation depth) Measurement of active forces (such as generated by cells) 24 usa.jpk.com/index.download.c46f64176d66c310620d0c4bdf4be7ef  XING YI LING, CBC, NTU Force-Distance Curve (Cont’d) Vertical tip movement during the approach and retract parts of a force spectroscopy experiment “snap-on” E F, G D D D A, B C Approach Contact Retract Retract E Tip lifting off surface Adhesion, (few atomic distances to nm) e.g. non-specific binding (chemical affinity, surface coating), ligand-receptor interactions (antibody-antigen), cell surface interactions. F Tip further away Stretched molecules between tip and surface. (nm to hundreds of nm) e.g. protein unfolding, conformational changes in stretched molecules. G Tip far from surface Connections broken between tip and surface, (1 – 5 microns) no further interaction. 25 usa.jpk.com/index.download.c46f64176d66c310620d0c4bdf4be7ef  XING YI LING, CBC, NTU Force-Distance Curve “snap- on” E F, G D D D A, B C Approach Contact Retract D A, B C F, G D E 26  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) Phase image of a Polystyrene- Stained Chromosome block-polybutadiene diblock copolymer sample Ball and stick model of pentacene (above) and NC-AFM image of pentacene on a copper surface (below) Science, 2009, 324, 1428 27 Silver nanoparticles bundled collagen fibres.  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) Examples of AFM images Nature 2007,446,64 28 Single atom chemical identification of a Si-Sn-Pb surface alloy by AFM  XING YI LING, CBC, NTU 3.2.1 Atomic Force Microscope (AFM) Various Applications of AFM http://www.jpk.com/ http://www.asylumresearch.com/Gallery/G allery.shtml 29  3.2.1 Atomic Force Microscope (AFM) XING YI LING, CBC, NTU FAMARS (First AFM on Mars), Artistic sketch of the Phoenix Lander On July 9, 2008, Mars day 44 of the that has landed on Mars on May 25th Phoenix Mars Mission. 2008. test grid The particle is rounded, and about one micrometer, or one millionth of a meter, across. It is a speck of the dust that cloaks Mars. Such dust particlets color the Martian sky pink, feed storms that regularly envelop the planet and produce Mars’ distinctive red soil. 3-D image of a dust grain from 30 Phoenix's Atomic Force Microscope.  XING YI LING, CBC, NTU 3.2.2 Scanning Tunneling Microscope tipa sample muse be conductive -dist very small ① ultra high valuum , witly & , low Basic components: empt conductiva e & Metal tip (probe) Piezoelectric scanner Current amplifier (nA) i) Feedback loop Data processing and display & if tip far fo- sample is , ↓ cument founded through (IN) Feedback loop Source: Wikipedia tip closer surface It computer to , S m current T u 31  XING YI LING, CBC, NTU 3.2.2 Scanning Tunneling Microscope STM relies on an electronic signal to relay information about a sample – the strength of a tunneling current potential between the probe tip and the substrate surface. Small changes in the distance between the probe tip and substrate translate into large changes in tunneling current. By this phenomenon, atomic scale resolution by STM is possible in x, y, and z direction. The density of state (DoS) of solid-state materials can also be mapped by scanning tunneling spectroscopy. Chemical reactions induced and oriented by STM probe are also possible. 32  XING YI LING, CBC, NTU 3.2.2 Scanning Tunneling Microscope Electron tunneling Occurs between the conducting sample and the tip. The tip is very close to the substrate, but not in actual physical contact. Electron tunnelling current, I, between two flat plates separated by vacuum is dependent on the voltage applied, mass of electron, energy of electron. 33  XING YI LING, CBC, NTU 3.2.2 Scanning Tunneling Microscope Operation Modes ) - redox rxn. Summary of SPM Advantages: Can achieve three-dimensional topographic information with ~1 Å lateral resolution and ~0.1 Å vertical resolution. (z7 Truly local interaction on the atomic scale rather than the averaged properties of the bulk phase or of a large area. Work perfectly well in different environment, such as vacuum (for STM), ambient air or even a liquid (for AFM). Suitable for in-situ electrochemical studies, biological studies and the evolution of specimen. Can be used for the modification of a surface and for the manipulation of atoms and molecules through tip-sample interaction. Sim. Disadvantages: Need to scan samples, so the speed is slow, and typically the imaging Zot area is small. representative of entire The lateral resolution strongly relies on the properties of the probe surface (sharpness, materials). 40  XING YI LING, CBC, NTU 3.3.1 Electron Interactions with Matter Aurora Borealis interaction of electrons (from solar wind) with oxygen and molecular nitrogen electron-metal Aurora australis captured Colorful Aurora Borealis interactions by NASA’s IMAGE e- dejector ↓ detector satellite and overlaid onto e-metal interaction I My NASA’s satellite-based Scanning SE BSE backscattere ↓ e microscope interaction vol inter interacite Blue Marble image. er > Voltage density surfaced - , dependent e- - transmission ↓ e microscope E 45  XING YI LING, CBC, NTU 3.3.1 Electron Interactions with Matter Electrons are able to interact with matter in many different ways. Electrons serve as the primary probe (1o), impinging on a solid surface may scattered once, several times, or not at all. lose energy) > nackscattered (never - The scattering may be elastic or inelastic, forward or backward, including ↳ lose energy (x-ray.] etc secondary electrons, backscattered electrons, X-rays, and many other phenomena. When a high-energy beam of electron is incident upon a specimen, a pear- shaped region known as the interaction volume (excitation volume) is formed. The interaction volume increases with increasing beam voltage, and decreases with increasing specimen density. ↑ volume E voltagelet 44  XING YI LING, CBC, NTU 3.3 Electron probes High voltage Electrons have higher energy and no diffraction electron beam limit, hence can give better resolution. Once electrons interact with a specimen, secondary effects are detected and transformed into images or spectra. One of the most important characterization tool for nanoscience due to their capability to analyze nano-structures. Among which, scanning electron microscope (SEM) and transmission electron microscope (TEM) are the most significant. Electron TEM image of Ebola virus. corona a stable subatomic particle with a negative charge of 125nm Filamentous 970 nm long; 1.6022 × 10-19 C, with mass of 9.1094 × 10-31 kg. Diameter 80nm. 41 Zika : 40nm).  XING YI LING, CBC, NTU 3.3 Electron probes How powerful is electron probes as compared to optical probes? De Broglie Equation relates momentum of the electron to wavelength h p Where p is momentum (mv)  h is Planck’s constant (6.6262 × 10-34 J.s) h  is the wavelength  p If electron is accelerated through a potential eV, it gains kinetic energy 1 Kinetic energy  me v 2  eV 2 mev  2meeV Hence, the wavelength of an electron can be calculated by: h p  mv  be vacity  h h    me v 2me eV 42  XING YI LING, CBC, NTU Example: Calculate the wavelength of an electron under an accelerating potential of 500 V. Given that electron has a negative charge of 1.6022 × 10-19 C, and mass of 9.1094 × 10-31 kg. mer - M = = Mel. 626x18 34 J S 6 X109m -. = - 1094x10-3)(1 6022x10-19)(500V) ↓ a (9.. M = 0. 0548 nm = 0. 055nm sum = 0. 055 "election michoscope wavelength smaller - 43  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy source -f illumination e-gun & ↓↓L -> anode : accelerate Spin af er JOEL JSM 7610F condenser> - align. focus # objective http://www.jeol.co.jp/en/products/detail/JSM-7610F.html lens > - magnify same y -effects 46 http://virtual.itg.uiuc.edu/training/EM_tutorial/ secondary  XING YI LING, CBC, NTU dissipate e- 3.3.2 Scanning Electron Microscopy ↑ conductive surface. coated W sample on Principle: Q raster scale side > - conductivity tape on + carbon The electron gun at the top of the column produces electron beam. The beam is focused to a diameter of ~50 Å at the foot of the column by a Inm series of magnetic lenses. - The electron beam is raster-scanned across the surface of the specimen. collected of individual points - ~ Various 2o effects emitted from the interactions of the electron beam with the surface of the specimen, including secondary electrons, backscattered electrons, x-rays or photons, are detected and the signals are amplified and displayed. faster than AFM , > - sat The most immediate result of observation in the scanning electron A microscope is that it displays the topology and morphology of the sample. LG-D/pseudo 3-D Sample requirement: Must be conductive, and the sample is fixed to a metal stage with a conducting tape. ↳ onto sample heating e ↳ polymers : An/pt on surface -> e- can be dissipated 47  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy Components: Electron Guns [ produce e7 1. Thermionic emission A heated filament made from the metal tungsten. Much in the way that an incandescent light bulb works, the high current that is fed through the filament generates heat, and causes electron to be thermally excited out of the metal. The temperature is normally higher than 1000K. 2. Field emission gun > more - long-lasting Field emission guns utilize extremely sharp probes (such as LaB6 single crystal) to generate very high local field. A point of radius 100 nm held at potential of 1000 V experience a field at its surface of 1010 V/m, which is high enough to expel electrons and let them tunnel to vacuum.  XING YI LING, CBC, NTU Scanning Electron Microscopy Component: Condenser Collimate a divergent beam into a parallel or converging beam, focus it down the column, and regulate the amount of current. Component: Objective lens Magnify the specimen to hundreds to hundreds of thousands times its original size. Note that in electron microscopes, both these lenses are not made of a solid material, but rather controlled by a magnetic field. 49  3.3.2 Scanning Electron Microscopy XING YI LING, CBC, NTU Image Generation Image is generated by rastering the electron beam across the sample surface. A reconstructed image is sent to detector and viewed. There is a “dwell time” at which point the beam is paused, where numerous types of secondary electron effects are expressed. The lifetime of the secondary effects are shorter than the dwell time. Before the beam moves to the next segment, the secondary effects have been detected, recorded and dissipated. Topology affects secondary electron emission, therefore we have bright/dark contrast in SEM SE images. Edges appear bright, because more secondary electrons can escape. Element effects. Metals appear brighter than insulators in SEM images, because it can backscatter more electrons. backscattere compositional diff : = 2 e ' topology - - 50  XING YI LING, CBC, NTU Secondary Electrons Image Backscattered Electrons Image 51  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy 2º electron effect: Secondary Electrons (SE) Generated from the collision between the incoming electrons and the loosely bonded outer electrons of atoms. This is an inelastic scattering process, in which 2 surface - e-ouf atim the primary electrons lose energy, while the energy goes to the secondary electrons. Secondary electrons have low energy (~10-50 eV). Excitation depth 1 – 50 nm. 1 e-hit interact surface (2) Due to their low energy, the secondary electrons 2 >- kick out surface e originate within a few nanometers from the sample > - Ie lose every surface. Therefore, topographic information can be obtained from secondary electrons. * G' inelastic scattering : * surface info "topology" 52  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy 2º electron effect: Backscattered Electrons (BSE) Backscattered electrons consist of high-energy electrons originating in the electron beam, that are reflected or back- scattered by elastic scattering interactions with specimen = atoms. Heavy elements (high atomic number) backscatter electrons more strongly than light elements (low atomic number), and thus heavy elements appear brighter in the image. ↑ e-hit atom core , Excitation depth < 400 nm. bounce back BSE are used to detect contrast between areas with ①totally elastic scattering effect different chemical compositions. qualitative comparison of et , 4 mass of atom (heavier on atomic weight of element) require higher energy to hit , & core elements - bounce ① ↑ intensity/brighter image 53 on detector  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy 2º electron effect: Charateristic X-rays Incident high-energy electrons kick out inner-shell electrons. Outer-shell electrons fill the vacancy, and X-rays (photons) are emitted. Characteristic X-rays provide information of chemical elements. The wavelength of the x-rays emitted is inversely proportional to the square of the atomic number of an element: ↑ inner shell es outer e- e-hits fills in vacancy (flower energy) 1 exits  , 2 energy as X-ray z 54  XING YI LING, CBC, NTU ↳ separate identitdemecomposit t emission Characteristic X-rays provide information of chemical elements ~ alloy ? Dimetallic NP. 55  XING YI LING, CBC, NTU 3.3.2 Scanning Electron Microscopy Examples of SEM Images 10 m aligned carbon nanotube twisted PbS nanowire “pine-tree” Science 320, 5879 (2008) chemical analysis of battery electrode 200 nm surfaces GaAs/GaInP nanowires (MRS)  XING YI LING, CBC, NTU 3.2.2 Scanning Electron Microscopy These pollen grains taken Green Ant - SEM Coccolithophore, on an SEM show the Emiliania huxleyi characteristic depth of (photosynthetic plankton) field of SEM micrographs. This is an SEM image (color enhanced by Photoshop) of high aspect ratio 250nm thick epoxy bristles 57  XING YI LING, CBC, NTU Summary of SEM Advantages: Various samples from conducting, and non-conducting (metal coating normally needed). Based on surface interaction --- no requirement of electron- transparent sample. Very good topology and depth of field. Very Good imaging resolution of a few tens of nanometers at least. Disadvantages: Has to be in vacuum, and thus applications to living specimen or liquid are limited Non-conducting materials usually require surface stain-coating with metals for electron conductions, otherwise the surface accumulates charges and influences the image resolution. 58  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Principle: The Tem functions by the same principles as the SEM, except that the detector is a phosphor plate that is able to capture images formed by transmitted electrons. Electrons pass through specimen in TEM, while electrons scatter from specimen in SEM. Ernst Ruska (Nobel Prize in Physic 1986) The accelerating voltage in TEM is 40-1200 kV, higher than that in SEM that is about 0.5-30 kV. Hence TEM generally has a better resolution down to 1Å. org stringicas. T samples SEM - scatter > Better resolution Transmittede = Eincident - Escattering - Eabs ↑ 21 ) % ar more lower in everby require higher voltage Le-gun) pasthy ele 59 > -. > -  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Working principle: An image is formed from the interaction of the electrons transmitted through the specimen. Sample has to be transparent. TEM image contrast is due to absorption of electrons in the material, due to the thickness and composition of the material. TEM Images 60  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope anodes to accelerate > more energy - Principle: A thermionic or field emission gun is used to accelerate electrons between 100 – 400 kV. The electron beam is accelerated by the anode plate and then collimated via an aperture. The electrons pass through a double condenser lens system and focus upon a anode sample. ~ In order to be transparent to the electron I beam, the thickness of specimens are 0.17 nm kV) TEM Resolution: >0.10 nm 62 http://www.jeol.co.jp/en/products/detail/JEM-1000.html  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope microtiuse /it diamond knife slice ↑ hand/soft sample Sample Preparation for TEM ~ epoxy polymer Cresin For transmission electron microscopy, specimens must be very thin (< 100 nanometers), i.e., electron transparent. For soft sample, the sample can be embedded in a polymeric resin, and sectioning with a microtome by the action of a diamond knife. Biological species can be frozen into a thin layer of ice and exposed to tiny doses of electrons. sample grid to hold samples 63  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Examples of TEM images single multi Discovery of the carbon nanotube S. Iijima, Nature 354, 56 (1991). Pt nanoparticles T 64  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Examples of High-Resolution TEM images HR 500kV lattice fringe image of ‘as grown’ silicon on sapphire showing complex twinning and stacking defects Structure image of tilt grain boundary in nickel oxide. Images from ‘HRTEM and associated techniques –Buseck, Cowley and Eyring – Oxford science pub 65  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Examples of High-Resolution TEM images 66  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Examples of High-Resolution TEM images Where these two gold crystals meet they are joined by a complex arrangement of atoms, forming a nanobridge that accommodates their different orientations. The gold atoms are 2.3 angstroms apart. TEAM 0.5's unprecedented signal- to-noise ratio makes it possible to distinguish individual atoms and, at the edges of the two crystals, deduce their position in three dimensions. ↑ heavier element appears CSEM) : brighten I SE Ar transmitted e darker ↓ appear - m 67 http://www.lbl.gov/Science-Articles/Archive/MSD-NCEM-TEAM05.html > - a lot of into w sample  XING YI LING, CBC, NTU 3.3.3 Transmission Electron Microscope Electron Diffraction in TEM Diffraction patterns give crystallographic information about a material from site specific small volumes, unlike XRD which is a bulk analysis technique. Can determine if a material is amorphous, polycrystalline or crystalline quickly and effectively. Amorphous polycrystalline crystalline 68  XING YI LING, CBC, NTU Summary of TEM Advantages: High resolution, as small as 0.1 nm. Direct imaging of crystalline lattice and defects inside the sample. No metallic stain-coating needed, thus convenient for structural imaging of organic materials. Electron diffraction technique: phase identification, structure and symmetry determination, lattice parameter measurement, disorder and defect identification Disadvantages: Has to be in vacuum, and thus applications to living specimen or liquid are limited. To prepare a thin, electron-transparent sample from the bulk is difficult. The field of view is relatively small. Hence, the section under analysis may not be representative of the sample as a whole. Sample structure and morphology have been known to change drastically under long exposure of electrons with extremely high energy, and damage to biological samples. 69  XING YI LING, CBC, NTU SEM TEM 70  XING YI LING, CBC, NTU Optical Microscope v.s. Electron Microscopes Electron gun Condenser Condenser lens lens Objective lens Optical Scanning Transmission Microscope Electron Electron Microscope Microscope 71  XING YI LING, CBC, NTU Optical Microscope v.s. SEM Optical microscope image SEM image image Copyright 1992, Plenum Publishing A comparison of the skeleton of a radiolarian—a one-celled animal common in plankton—examined with a optical microscope and a SEM. It is clear that SEM enables higher resolution (~ 1nm) and greater depth of field. 72  XING YI LING, CBC, NTU Optical Microscope Electron Microscope 73  XING YI LING, CBC, NTU Exercise – Chapter 3 Q3.1 The most important methods to determine the size of nanoparticles are TEM and AFM. What are the advantages and disadvantages of the two methods? Q3.2 Convert a 850-nm wavelength into unit of frequency, electron volts (eV), wavenumbers, and joules. Q3.3 Compare the differences of atomic force microscopy and scanning tunneling microscopy. 74