Characterization of nanopartical

Characterization of nanopartical

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  Characterization of Nanoparticles Prepared by: Amany F. El-Hallaq Safia F. Salama Supervisor : Dr. Issa El-Nahal
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   CHARACTERIZATION OFNANOPARTICLES - Characterization refers to study of materials features such as its composition, structure, and various properties like physical, electrical, magnetic, etc.  Important characterization of nanoparticles -Nanoparticle properties vary significantly with size and shape. - Accurate measurement of nanoparticles size and shape is, therefore, critical to its applications.
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  General characterization method Microscopy 1- Scanning Electronic Microscopy ) SEM ( 2- Transmission Electron Microscopy ) TEM) 3- Scanning Tunneling Microscopy )STM) Spectroscopy 1- X-ray Diffraction (XRD) 2- Small Angle X-ray Scattering (SAXS) 3- X-ray Photoelectron Spectroscopy ( XPS ) 4- UV-vis spectroscopy 5- FT-IR spectroscopy 3
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  Microscopy : 1-Scanning Electronic Microscopy ) SEM ( 2- Transmission Electron Microscopy ) TEM) 3- Scanning Tunneling Microscopy )STM)
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  Scanning Electron Microscopy 5
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  Basic principle Whenthe beam of electrons strikes the surface of the specimen & interacts with the atoms of the sample, signals in the form of secondary electrons, back scattered electrons & characteristic X-rays are generated that contain information about the samples’ surface topography, composition etc.
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  What can yousee with an SEM? -Topography Texture/surface of a sample -Morphology Size, shape, order of particles -Composition Elemental composition of sample -Crystalline Structure Arrangement present within sample
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  Operation modes Thereare 3 modes -Primary: High resolution (1-5 nm); secondary electron imaging -Secondary: Characteristic X-rays; identification of elemental composition of sample by EDX technique -Tertiary: Back-scattered electronic images; clues to the elemental composition of sample
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  Electronic devices areused to detect & amplify the signals & display them as an image on a cathode ray tube in which the raster scanning is synchronized with that of the microscope.
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  In a typicalSEM, the beam passes through pairs of scanning coils or pairs of deflector plates in the electron column to the final lens, which deflect the beam horizontally & vertically. The image displayed is therefore a distribution map of the intensity of the signal being emitted from the scanned area of the specimen.
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  Scanning Electron Microscopy Holm Oak Leaf Mosquito Antennae Hibiscus Pollen Penicillin Spores Beetles Skin
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  Crystalline Latex ParticlesPolymer Hydrogel Surface
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  Wood Fibers
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   Advantages: 1-Bulk-samples can be observed and larger sample area can be viewed, 2- generates photo-like images, 3- very high-resolution images are possible 4- SEM can yield valuable information regarding the purity as well as degree of aggregation  Disadvantages: 1- Samples must have surface electrical conductivity 2- non- conductive samples need to be coated with a conductive Layer 3- Time consuming & expensive. 4- Sometimes it is not possible to clearly differentiate nanoparticle from the substrate. 5- SEM can’t resolve the internal structure of these domains.
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  Transmission Electron Microscopy
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   What canwe see with a TEM? -Morphology • Shape, size, order of particles in sample -Crystalline Structure • Arrangement of atoms in the sample • Defects in crystalline structure -Composition • Elemental composition of the sample
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  Basic principle Thecrystalline sample interacts with the electron beam mostly by diffraction rather than by absorption. The intensity of the diffraction depends on the orientation of the planes of atoms in a crystal relative to the electron beam. A high contrast image can be formed by blocking deflected electrons which produces a variation in the electron intensity that reveals information on the crystal structure. This can generate both ‘bright or light field’& ‘dark field’ images.
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  Transmission Electron Microscopy Paramyxovirus Collagen Fibres Herpes Virus Flu Virus
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  TEM comparison StandardTEM Standard TEM High resolution TEM High resolution TEM
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  Isotactic Polypropylene Particle TEM Micrographs
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  Large Ceria Nanoparticles Small Ceria Nanoparticles
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  * Advantages: 1-Additional analysis techniques like X-ray spectrometry are possible with the STEM. 2- high- resolution 3- ( 3-D) image construction possible but aberrant. 4- Changes in nanoparticle structure as a result of interactions with gas, liquid & solid-phase substrates can also be monitored. * Disadvantages : 1- Sample must be able to withstand the electron beam & also the high vacuum chamber. 2- sample preparation necessary, mostly used for 2-D images. 3- Time consuming.
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  SEM vs TEM
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  Synthesis and opticalcharacterization of copper oxide nanoparticles: SEM and TEM study -Figure 2 shows the SEM image of as prepared CuO nanoparticles. It shows that the CuO nanoparticles are in rectangular shape. -Figure 3 (a) shows the TEM image of as prepared nanoparticles. The size of particle observed in TEM image is in the range of 5-6 nm which is in good agreement with calculated by Scherrer formula using XRD. Figure 3 (b) shows the selected area diffraction pattern (SAED) of as prepared CuO nanoparticles. It shows that the particles are well crystallized. -The diffraction rings on SAED image matches with the peaks in XRD pattern which also proves the monoclinic structure of as prepared CuO nanoparticles [18]
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  Scanning Tunneling Microscopy
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  Basic principle Itis based on the concept of quantum tunneling. When a conducting tip is brought very near to a metallic or semi-conducting surface, a bias between the two can allow electrons to tunnel through the vacuum between them. Variations in tunneling current as the probe passes over the surface are translated into an image. They normally generate image by holding the current between the tip of the electrode & the specimen at some constant value by using a piezoelectric crystal to adjust the distance between the tip & the specimen surface.
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  Fig. Highly orientedpyrolytic graphite sheet under STM Lateral resolution ~ 0.1 nm Depth resolution ~ 0.01 nm
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  STM Images
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  Advantages: 1- Veryhigh image resolution (capable of „seeing‟ and manipulating atoms). 2- STM can be used not only in ultra high vacuum but also in air & various other liquid or gas, at ambient & wide range of temperature. Disadvantages : 1- Again 2- radius of curvature of tip 3- extremely sensitive to ambient vibrations 4- STM can be a challenging technique, as it requires extremely clean surfaces & sharp tips.
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  Spectroscopy 1- X-rayDiffraction (XRD) 2- Small Angle X-ray Scattering (SAXS) 3- X-ray Photoelectron Spectroscopy ( XPS ) 4- UV-vis spectroscopy 5- FT-IR spectroscopy
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  Optical Spectroscopy Opticalspectroscopy uses the interaction of light with matter as a function of wavelength or energy in order to obtain information about the material. Typical penetration depth is of the order of 50 nm. Optical spectroscopy is attractive for materials characterization because it is fast, nondestructive and of high resolution.
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  X-ray Diffraction XRDcan be used to look at various characteristics of the single crystal or polycrystalline materials using Bragg’s Law , nλ = 2d sinθ
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  X-ray Diffraction XRD “Smaller crystals produce broader XRD peaks” Scherrer’s Formula t- thickness of crystallite K- shape constant λ- wavelength B- FWHM ϴ- Bragg Angle Characterizations 1.Lattice constant 2.d-spacing 3. crystal structure 4. Thickness (films) 5.sample orientation 6.Particle Size (grains) XRD is time consuming and requires a large volume of sample.
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  X-ray interactions dependson the number of atom on a plane. This is why only specific planes would cause diffraction.
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  Example of ZnO:
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  Example : HfO2
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  Small Angle X-rayScattering SAXS “SAXS is the scattering due to the existence of inhomogeneity regions of sizes of several nanometers to several tens nanometers.” Characterization 1.Particle Size 2. Specific Surface Area 3.Morphology 4.Porosity Fluctuations in electron density over lengths on the order of 10nm or larger can be sufficient to produce an appreciable scattered X-ray densities at angles 2ϴ < 50 It is capable of delivering structural information of molecules between 5 and 25 nm. Of repeated distances in partially ordered systems of up to 150 nm.
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  Example : SAXSdata from a titania nanopowder, before and after background correction, together with the background measurement. In this comparison, the data are already corrected for absorption by the sample .
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  X-ray Photoelectron SpectroscopyXPS
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  1200 1000 800 600 400 200 0 300 295 290 285 280 275 Counts / s C(1s) Binding Energy (eV) Peak Position Area % C1s Carbon- ID 1 285.50 1457.1 52% Pristine C60 2 287.45 489.75 18% Mono-oxidized C 3 289.73 836.67 30% Di-oxidized C
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  Analysis of carbonfiber – polymer composite material by XPS
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  UV-vis spectroscopy Thistechnique involves the absorption of near-UV or visible light. One measures both intensity and wavelength. It is usually applied to molecules and inorganic ions in solution. Broad features makes it not ideal for sample identification. However, one can determine the analyte concentration from absorbance at one wavelength and using the Beer-Lambert law: .where a = absorbance, b = path length, and c = concentration
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  EXAMPLE GOLD : 52
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  Infrared Spectroscopy FT-IR What is the principle behind IR spectroscopy? Firstly, molecules and crystals can be thought of as systems of balls (atoms or ions) connected by springs (chemical bonds). These systems can be set into vibration, and vibrate with frequencies determined by the mass of the balls (atomic weight) and by the stiffness of the springs (bond strength). With these oscillations of the system, a impinging beam of infrared EMR could couple with it and be absorbed. These absorption frequencies represent excitations of vibrations of the chemical bonds and, thus, are specific to the type of bond and the group of atoms involved in the vibration. In an infrared experiment, the intensity of a beam of IR is measured before and after it interacts with the sample as a function of light frequency.
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  Infrared Spectroscopy FT-IR Characterization: 1.Compositional 2.Concentration 3.Atomic Structure 4. surrounding environmentsor atomic arrangement The mechanical molecular and crystal vibrations are at very high frequencies ranging from 1012 to 1014 Hz (3-300μm wavelength), which is in the infrared (IR) regions of the electromagnetic spectrum. The oscillations induced by certain vibrational frequencies provide a means for matter to couple with an impinging beam of infrared electromagnetic radiation and to exchange energy with it when frequencies are in resonance.