透射电子显微学课件

1、电子能量损失谱电子能量损失谱张 庶 元Electron Energy Loss Spectroscopy (EELS)入射高能电子与样品的相互作用入射高能电子与样品的相互作用Incident beam electronE0 (100 to 1000 keV)Excited specimen electronEB + EScattered beam electronE0 - EKLZero lossElectron energy loss (eV)Electrons count01 eV290C KInelastic scatteringKLElastic scatteringCarbonato

2、m电子能量损失谱信息电子能量损失谱信息非弹性散射过程非弹性散射过程:声子激发声子激发 (0.1eV)等离子激发等离子激发 (30eV)内壳层电子激发内壳层电子激发 (13eV)自由电子激发自由电子激发(二次电子二次电子) (50eV) (背底背底)韧致辐射韧致辐射 (背底背底) 根据等离子激发能量的大小，即谱峰的位置，可以确定物质的根据等离子激发能量的大小，即谱峰的位置，可以确定物质的种类和他的组成。种类和他的组成。Na： 5.70ev(一次激发) 11.4ev(二次激发) 随试样厚度的增加，电子在试样中可能产生二次，甚至多次等离子激随试样厚度的增加，电子在试样中可能产生二次，甚至多次等离子激

3、发，其峰位出现在第一次激发峰的两倍或多倍能量的位置。发，其峰位出现在第一次激发峰的两倍或多倍能量的位置。Al: 14.95ev 29.9ev 44.35ev 59.8ev 表中列出了几种物质的等离子激发峰的理论值和实测值表中列出了几种物质的等离子激发峰的理论值和实测值Specimen thickness measurementtlnITIoRough estimate of : 0.8Eo nmso for 100-keV electrons is 80-120 nm various materials 为电子非弹性散射的平均自由程 IT 为第一个等离激发峰的强度 Io 为零损失峰的强度偶极跃

4、迁：l = 1内壳层电子激发内壳层电子激发Correlation between EELS and specimen featureMagnetic prism spectrometerOptical configuration at entranceDispersion and focusing sectionProjection sectionSpectrum planeIn-column omega-filterEnergy-filter imaging and electron diffraction, CBEDInserted in the imaging lens systemPo

5、st-column imaging filterGatan (Tridiem) imaging filter (GIF).Attached to the TEM column below the viewing chamberEnergy-loss spectroscopy (EELS - low loss) Spectrum is enlarged and optimally coupled to detector Final EELS readoutEELS spectrum projected onto CCDFinal EELS readoutO K edgeMn L edgeThe

6、spectrum is shifted Best to do by changing prism current preserve probe focusSpectrum offset via prism currentEELS spectrum projected onto CCDProjection section operates in imaging modeSpectrum is projected back to an image Just like forming an image from a diffraction pattern in TEMUnfiltered image

7、 projected onto CCD detectorCore-loss image projected onto CCD detectorimage modeSpectrum offset via high tensionThe spectrum is shifted relative to the slit openingBest to do by increasing beam energy to preserve image focusSpectrum Imaging EFTEM modeCollects detailed spatial and spectroscopy infor

8、mationAllows processing decisions after acquisitionSpectrum imaging can create quantitative images / profiles Can confidently locate artifacts & understand image contrastDx, Dyspatial dimensionsDEenergy-loss dimensionDyDxDEimage at DE1image at DE2image at DEi.spectrum at Dxi ,DyiElemental Mappin

9、g Using Energy Filtered ImagingSiC/Si3N4Atomic Resolved EELS of GaAs in the bulkHAADF survey image Analysis was carried out using the facilities at Florida State University System: ARM200 with cold FEG equipped with GIF Quantum heavily upgraded Sample was provided by Glasgow University and Sample wa

10、s observed along the 110 direction Sample is 4 years old and shows some oxidationAtomic Resolved EELS of GaAs in the bulkEELS SIEELS spectrum extracted from the region in the red box in the EELS SIGa L2,3-edgesAs L2,3-edges Convergence angle: 25mrad Collection angle120mrad EELS data was acquired in

11、single range mode Exposure time per pixel: 50ms Dataset size: 26x25x2048 Total number of pixels: 650 Total acquisition time: 51secondsAs elemental mapGa elemental mapEELS colorized elemental mapGa: GreenAs: Red The GaAs dumbbell is clearly resolved with high contrastAtomic Resolved EELS of GaAs in t

12、he bulk The EELS elemental map for the Pd looks much sharper and shows higher contrast than the same map obtained using EDS. This can be directly attributed to the strong forward scattering of the EELS signal and the nearly 100% collection efficiency of detector. The high signal to noise ratio in th

13、e data is evident from intensity line profiles extracted from the region indicated in the box in the EDS and EELS Pd elemental maps. Intensity line profiles extracted from the region in the blue in the Pd mapsElemental mapsEDS PdEELS Pd Mean signalStd. Dev.SNRAu M EELS Map1446885617:1Au M EDS Map79.

14、910.17.9:1 The signal intensity was analyzed from a uniform region of a Au particle. This 16x16 pixel region is show by the red box in the Au elemental maps The SNR for the EELS data is 17 while that for the EDS data is 8 giving about a 2x improvement for the EELS data. the EELS signal is more than

15、twice as sensitive than the EDS dataElemental mapsAu EDSAu EELSEDSEELS Red: Pd Green: Au Despite the presence of heavy elements involved in the analysis, EELS maps show better contrast Some details in the maps can be observed only in the EELS elemental mapsColorized Elemental MapsState of the Art SrTiO3 Example LaMnO3/SrMnO3 superlattice grown on SrTiO3 NION UltraSTEM with Enfinium ER 2msec/pixel 250pA 8GB of data!2008(64x64)Acknowledgements: Jul