Characterization of Nanomaterials PDF

Characterization of Nanomaterials Assoc. Prof. Dr. Serdar YILDIRIM Dokuz Eylul University, Dept. of Metallurgical and Materials Eng., Izmir, Turkey Phone: +90 (232) 301 74 57 (Dept. of Metallurgical) E-mail: serdar.yildirim@deu...

Characterization of Nanomaterials Assoc. Prof. Dr. Serdar YILDIRIM Dokuz Eylul University, Dept. of Metallurgical and Materials Eng., Izmir, Turkey Phone: +90 (232) 301 74 57 (Dept. of Metallurgical) E-mail: [email protected]  Introduction Nanomaterials, dispersed in the form of colloids in solutions, particles (dry powders) or thin films, are characterized by various techniques. Although the techniques to be used would depend upon the type of material and information one needs to know, usually one is interested in first knowing the size, crystalline type, composition, thermal, chemical state, and properties like optical or magnetic properties. A simple way of categorizing the characterization methods is to consider imaging and analytical techniques. Imaging involves some kind of microscopy, whereas analysis involves some type of spectroscopy. Introduction  Introduction Surface position Particle Surface Surface Surface size area composition structure (Topography) Surface Complexes Electron microscopy X-ray diffraction LEED Magnetic measurements AES SEM XPS TEM SIMS EXAFS EPMA EXAFS IR, UV-Vis, ESR, NMR, Raman  Introduction AFM : Atomic Force Microscope STM : Scanning Tunneling Microscope MFM : Magnetic Force Microscope SEM : Scanning Electron Microscope SPM : Scanning Probe Microscope TEM : Transmission Electron Microscope SNOM:Scanning Near-Field Optical Microscope LEED: Low Energy Electron Diffraction EPMA: Electron Micro Probe Analyzer EXAFS:Extended X-ray Absoption Fine Stracture AES : Auger Electron Spectroscopy SIMS : Secondary Ion Mass Spectroscopy ESR : Electron Spin Resonance EELS : Electron Energy Loss Spectroscopy XPS : X-Ray Photoelectron Spectroscopy  Introduction Microscopes Optical microscope, Confocal microscope, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Scanning Tunnelling Microscope (STM), Atomic Force Microscope (AFM), Scanning Near-Field Optical Microscope (SNOM). Microscopes are useful to investigate morphology, size, structure and even composition of solids depending upon the type of microscope. Some of the powerful microscopes are able to resolve structures up to atomic resolution. Diffraction Techniques X-ray Diffraction (XRD), Electron Diffraction, Neutron Diffraction, Small Angle X-ray Scattering (SAXS), Small Angle Neutron Scattering (SANS) and Dynamic Light Scattering (DLS). Scattering or diffraction techniques are often used in particle shape and average particle size analysis as well as structural determination.  Introduction Spectroscopies UV-Vis-IR absorption (transmission and reflection modes), Fourier Transform Infra Red (FTIR), Atomic Absorption Spectroscopy (AAS), Electron Spin (or Paramagnetic) Resonance (ESR or EPR), Nuclear Magnetic Resonance (NMR), Raman Spectroscopy, various luminescence spectroscopies, Electron Spectroscopy for Chemical Analysis (ESCA) or X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES). Spectroscopies are useful for chemical state analysis (bonding or charge transfer amongst the atoms), electronic structure (energy gaps, impurity levels, band formation and transition probabilities) and other properties of materials.  Introduction Electric and Magnetic Measurements Two or four probe measurements, Magnetoresistivity, Vibrating Sample Magnetometer (VSM), Superconducting Quantum Interference Device (SQUID), Magneto-Optical Measurements (Kerr and Faraday rotations). Measurement of resistivity is necessary for many applications. Magnetic and magneto-optical measurements throw light on the behaviour of the materials in presence of external magnetic fields. Mechanical Measurements Hardness, strength (Elastic moduli), Nanoindentation.  Microscopes Low dimensional materials such as quantum dots, quantum wires, quantum wells, self-assembled materials, interactions of small molecules with surfaces, multilayers etc. need special microscopes like Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Scanning Tunnelling Microscope (STM) and Atomic Force Microscope (AFM). Electron Microscopes Electron microscopes bear similarity with optical microscopes. In optical microscopes, electromagnetic waves of appropriate wavelength scattered from the specimen are detected using a system of focussing lenses. In electron microscopes, electrons are used in place of electromagnetic radiation and electrostatic or magnetic lenses are used instead of glass lenses. According to wave-particle duality, electrons can sometimes behave as particles and sometimes as waves. Therefore, just like electromagnetic radiation, which can be used to image the objects, electron waves can be used to image the objects. Electron Microscopes  Electron Microscopes There are two types of electron microscopes. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). Scanning electron microscope uses backscattered electrons from a sample for imaging and transmission electron microscope utilizes electrons transmitted through a sample. Obviously SEM can be used to image the surface of a thick sample but TEM needs to have a thin (maximum thickness ~300 nm) sample so that high energy electrons can transmit through the sample. Both the microscopes use electrons which need to reach the sample without getting scattered by air. Therefore, the electron microscopes need vacuum for their operation. Electron Microscopes  Scanning Electron Microscope (SEM) The SEM uses electrons to form an image. A beam of electrons is produced at the top of the microscope by heating of a metallic filament. The electron beam follows a vertical path through the column of the microscope. It makes its way through electromagnetic lenses which focus and direct the beam down towards the sample. Once it hits the sample, other electrons (backscattered or secondary ) are ejected from the sample. Detectors collect the secondary or backscattered electrons, and convert them to a signal that is sent to a viewing screen similar to the one in an ordinary television, producing an image.  Scanning Electron Microscope (SEM) The scanning electron microscope (SEM) uses a focused beam of high- energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, crystalline structure , and orientation.  Scanning Electron Microscope (SEM) Electrons Secondary Electrons: Imaging mode collects low-energy secondary electrons (