分析电子显微镜AEMppt课件.ppt
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1、Part III Analytical Electron Microscopy in Materials Science1.Introduction2.Image mode in AEM3.Microanalysis in AEM 3.1 X-ray Energy Dispersive Spectroscopy (EDS) 3.2 Electron Energy Loss Spectroscopy (EELS) 3.3 Microdiffraction 3.4 Convergent beam diffraction 1、Introduction1.Signals generated in th
2、e interaction between the incident high energy electron beam and the thin crystalline specimen2.How to form a probe3.Relationship between TEM, SEM and AEM 3.1 TEM Image mode Diffraction mode 3.2 SEM Image mode: SE, BSE, X-Ray Mapping Microanalysis: WDS, EDS 3.3 AEM Imaging mode: TEM, STEM, SEM, Mapp
3、ing (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, micro-diffraction, convergent beam diffraction How to form a probe ?Detectors needed for an AEM3.Relationship between TEM, SEM and AEM 3.1 TEM Image mode Diffraction mode 3.2 SEM Image mode:
4、SE, BSE, X-Ray Mapping Microanalysis: WDS, EDS 3.3 AEM Imaging mode: TEM, STEM, SEM, Mapping (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, micro-diffraction, convergent beam diffraction3.2 SEM Image mode: SE, BSE, X-Ray Mapping Microanalysis
5、: WDS, EDS3.3 AEM Imaging mode: TEM, STEM, SEM, Mapping (X-Ray + EELS) Diffraction mode: Scanning probe Stationary diffraction pattern Microanalysis: EDS, EELS, Micro-diffraction, Convergent beam diffraction1. BF detectorIt is placed at the same site as the aperture in BF-TEM and detects the intensi
6、ty in the direct beam from a point on the specimen. 2. ADF detectorThe annular dark field (ADF) detector is a disk with a hole in its center where the BF detector is installed. The ADF detector uses scattered electrons for image formation, similar to the DF mode in TEM. The measured contrast mainly
7、results from electrons diffracted in crystalline areas but is superimposed by incoherent Rutherford scattering.3. HAADF detectorThe high-angle annular dark field detector is also a disk with a hole, but the disk diameter and the hole are much larger than in the ADF detector. Thus, it detects electro
8、ns that are scattered to higher angles and almost only incoherent Rutherford scattering contributes to the image. Thereby, Z contrast is achieved. 2、Imaging in AEM2.1.TEM2.2.STEM - Scanning transmission electron microscopy2.3.STEM/SEM imaging2.4.Signal mixing - Hybrid imaging2.5.X-Ray and EELS mappi
9、ng STEM images of Pt particles in SiO2 nanotubes In the BF-STEM image, the contrast is similar to that in BF-TEM images: Pt particles appear with dark contrast since they are crystalline and the heaviest scatterers in this system. In the ADF-STEM image, the Pt particles appear with bright contrast b
10、ecause of diffraction and incoherent scattering (cf., DF-TEM images). In the HAADF-STEM image, only the incoherently scattered electrons contribute to the image, which nonetheless appears to be very similar to the ADF-image.HAADF-STEM image of Au/Pt particles on Silica In the high-angle annular dark
11、 field (Z contrast) image, the metal particles, which have high atomic numbers Z compared to the SiO2 matrix, are imaged as bright dots. Thus, this method is a valuable tool to investigate catalysts and to determine the sizes of metal particles and the corresponding size distribution. High-Resolutio
12、n HAADF-STEM Fourier-filtered HAADF-STEM image of Nb4W13O47 oxidized at 1000C. Projection along the short axis This HAADF-STEM image shows WO3 segregations in a matrix of a TTB-type Nb-W oxide. The positions of the metal atom columns appear with bright contrast (c.f., HRTEM image of Nb4W13O47 3、Micr
13、oanalysis in AEM3.1 X-Ray quantitative microanalysis 3.1.1 X-Ray signal generation in TEM thin foil specimens 3.2.2 Identification and elimination of spurious signals 3.2.3 Optimization of the AEM for microanalysis 3.2.4 X-Ray microanalysis 3.2.5 Microanalysis limit3.2 EELS - Electron Energy Loss Sp
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