CHARACTERIZATION of NANOMATERIALS KHP

Transcription

1 CHARACTERIZATION of NANOMATERIALS

2 Overview of the most common nanocharacterization techniques MAIN CHARACTERIZATION TECHNIQUES: 1.Transmission Electron Microscope (TEM) 2. Scanning Electron Microscope (SEM) 3. Scanning Probe Microscope (SPM) 4. Elemental Analysis (EDS, XPS, ICP) 5. X-ray Powder Diffractometer (XRD) General Techniques NMR, IR, UV, CV, etc.,

3 1.Transmission Electron Microscope (TEM)

4 Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera. The first TEM was built by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolution greater than that of light in 1933 and the first commercial TEM in

5 High Voltage TEM(HVEM) Field Emission TEM(FE-TEM) Energy Filtering TEM(EF-TEM)

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7 Field emission Gun High voltage Tank Specimen Holder

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12 Different contrast of sample

13 SAED Electron diffraction is most frequently used in solid state physics and chemistry to study the crystal structure of solids. Experiments are usually performed in a transmission electron microscope (TEM), or a scanning electron microscope (SEM ). Selected area (electron) diffraction (abbreviated as SAD or SAED), is a crystallographic experimental technique that can be performed inside a transmissi on electron microscope (TEM). In a TEM, a thin crystalline specimen is subjected to a parallel beam of high energy electrons. As TEM specimens are typically ~100 nm thick, and the electrons typically have an energy of kiloelectron volts, the electrons pass through the sample easily. In this case, electrons are treated as wave-like, rather than particle-like. Because the wavelength of high-energy electrons is a few thousandths of a nanometer, and the spacing between atoms in a solid is about a hundred times larger, the atoms act as a diffraction grating to the electrons, which are diffracted. That is, some fraction of them will be scattered to particular angles, determined by the crystal structure of the sample, while others continue to pass through the sample without deflection. As a result, the image on the screen of the TEM will be a series of spots the selected area diffraction pattern, SADP, each spot corresponding to a satisfied diffraction condition of the sample's crystal structure. If the sample is tilted, the same crystal will stay under illumination, but different diffraction conditions will be activated, and different diffraction spots will appear or disappear. 14

14 Example

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16 HVEM

17 2. Scanning Electron Microscope (SEM) A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that can be detected and that contain information about the sample's surface topography and composition. The electron beam is generally scanned in a raster scan pattern, and the beam's position is combined with the detected signal to produce an image. SEM can achieve resolution better than 1 nanometer. Specimens can be observed in high vacuum, in low vacuum, in dry conditions (in environmental SEM), and at a wide range of cryogenic or elevated temperatures. The most common mode of detection is by secondary electrons emitted by atoms excited by the electron beam. On a flat surface, the plume of secondary electrons is mostly contained by the sample, but on a tilted surface, the plume is partially exposed and more electrons are emitted. By scanning the sample and detecting the secondary electrons, an image displaying the topography of the surface is created. Since the detector is not a camera, there is no diffraction limit for resolution as in optical microscopes and telescopes.

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20 3. Scanning Probe Microscope (SPM) Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded with the invention of the scanning tunneling microscope in Many scanning probe microscopes can image several interactions simultaneously. The manner of using these interactions to obtain an image is generally called a mode.

21 SPM (Scanning Probe Microscope) AFM (Atomic Force Microscope, SFM) (Scanning Force Microsccope) STM (Scanning Tunneling Microscope)

22 Atomic force microscopy Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit. The precursor to the AFM, the scanning tunneling microscope (STM), was developed by Gerd Binnig and Heinrich Rohrer in the early 1980s at IBM Research - Zurich, a development that earned them the Nobel Prize for Physics in The AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact force, van der Waals forces, capillary forces, chemical bonding, electrostatic forces, magnetic forces, etc. Along with force, additional quantities may simultaneously be measured through the use of specialized types of probes. Typically, the deflection is measured using a laser spot reflected from the top surface of the cantilever into an array of photodiodes. 27

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25 4. Elemental Analysis (EDS, XPS, ICP)

26 1) X-ray photoelectron spectroscopy (XPS) ESCA(Electron Spectroscopy for Chemical Analysis) XPS is also known as ESCA (Electron Spectroscopy for Chemical Analysis), an abbreviation introduced by Kai Siegbahn's research group to emphasize the chemical (rather than merely elemental) information that the technique provides. X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top 0 to 10 nm of the material being analyzed.

27 XPS is used to measure: elemental composition of the surface (top 0 10 nm usually) empirical formula of pure materials elements that contaminate a surface chemical or electronic state of each element in the surface uniformity of elemental composition across the top surface (or line profiling or mapping) uniformity of elemental composition as a function of ion beam etching (or depth profiling) 36

28 2) Energy Dispersive Spectrometer(EDS) Energy Dispersive X-ray Analysis(EDX, EDXS, XEDS, etc.) Energy-dispersive X-ray spectroscopy (EDS, EDX, or XEDS), sometimes called energy dispersive X-ray analysis (EDXA) or energy dispersive X-ray microanalysis (EDXMA), is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on an interaction of some source of X-ray excitation and a sample. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing unique set of peaks on its X-ray emission spectrum. 37

29 To stimulate the emission of characteristic X-rays from a specimen, a high-energy beam of charged particles such as electrons or protons (see PIXE), or a beam of X-rays, is focused into the sample being studied. At rest, an atom within the sample contains ground state (or unexcited) electrons in discrete energy levels or electron shells bound to the nucleus. The incident beam may excite an electron in an inner shell, ejecting it from the shell while creating an electron hole where the electron was. An electron from an outer, higher-energy shell then fills the hole, and the difference in energy between the higher-energy shell and the lower energy shell may be released in the form of an X-ray. The number and energy of the X-rays emitted from a specimen can be measured by an energy-dispersive spectrometer. As the energy of the X-rays are characteristic of the difference in energy between the two shells, and of the atomic structure of the element from which they were emitted, this allows the elemental composition of the specimen to be measured 38

30 3) Inductively Coupled Plasma (ICP) Emission Spectroscopy Inductively coupled plasma atomic emission spectroscopy (ICP-AES), also referred to as inductively coupled plasma optical emission spectrometry (ICP- OES), is an analytical technique used for the detection of trace metals. It is a type of emission spectroscopy that uses the inductively coupled plasma to produce excited atoms and ions that emit electromagnetic radiation at wavelengths characteristic of a particular element. The intensity of this emission is indicative of the concentration of the element within the sample. 39

31 5. X-ray Powder Diffractometer (XRD) Powder diffraction is a scientific technique using X-ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials

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34 Bragg's law (equation) nl = 2d hkl sinq

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36 JCPDS : Joint Committee on Powder Diffraction Standards ICDD : International Center for Diffraction Data Program: EVA, ICSD, Pcpdfwin. Powder Diffraction File (PDF) #

37 PCPDFWIN: JCPDS No. or PDF No.

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41 Example 4 Hexagonal In 2 S 3 Cubic InSe

42 B is the full-width at half maximum