WhatisanEELSspectrum电子能量损失谱信息非弹性散射过程.ppt

M.S. Varela, et al., Phy. Rev. Lett. 92 (2004) 095502 STEM-EELS Atomic-Resolution Electron Energy Loss Spectroscopy La-doped CaTiO3 * 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 * Atomic-scale view of electron energy loss in TEM Incident beam electron E0 (100 to 1000 keV) Excited specimen electron EB + E Scattered beam electron E0 - E K L Zero loss Electron energy loss (eV) Electrons count 0 1 eV 290 C K Inelastic scattering K L Elastic scattering Carbon atom What is an EELS spectrum? 电子能量损失谱信息 非弹性散射过程: 声子激发 (0.1eV) 等离子激发 (30eV) 内壳层电子激发 (＞13eV) 自由电子激发 (二次电子) (50eV) (背底) 韧致辐射 (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 Specimen thickness measurement Rough estimate of λ : λ ~ 0.8Eo nm so for 100-keV electrons λ is 80-120 nm various materials λ 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 偶极跃迁：Δl = ±1 内壳层电子激发 * Correlation between EELS and specimen feature Magnetic prism spectrometer EELS spectrometer * Optical configuration at entrance Dispersion and focusing section Projection section Spectrum plane In-column omega-filter Energy-filter imaging and electron diffraction, CBED Inserted in the imaging lens system Post-column imaging filter Gatan (Tridiem) imaging filter (GIF). Attached to the TEM column below the viewing chamber Energy-loss spectroscopy (EELS - low loss) * Spectrum is enlarged and optimally coupled to detector Final EELS readout EELS spectrum projected onto CCD Energy-loss spectroscopy (EELS - core loss) * Final EELS readout O K edge Mn L edge The spectrum is shifted Best to do by changing prism current preserve probe focus Spectrum offset via prism current EELS spectrum projected onto CCD EFTEM: Energy Filtered TEM: GIF only * Projection sect