電子能量損失譜儀在材料科學(xué)中的應(yīng)用

1、電子能量損失譜儀電子能量損失譜儀在材料科學(xué)中的應(yīng)用在材料科學(xué)中的應(yīng)用段曉峰中國科學(xué)院電子顯微鏡重點實驗室中國科學(xué)院物理研究所凝聚態(tài)物理中心電子與樣品的相互作用電子與樣品的相互作用電子的非彈性散射電子與樣品的相互作用:原子散射截面dEdEd),(2Inelastic scattering透射電鏡和電子能量損失譜儀Project crossover掃描透射電鏡和電子能量損失譜儀調(diào)整 EELS位置的3種途徑1 磁棱鏡 energy shift 2 高壓 mapping3 Drift tube EELS像模式光路圖衍射模式光路圖EELS 的聚焦和AC雜散磁場補償聚焦和補償：0峰變高變窄和穩(wěn)定CCD的尺

2、寸：1K x 1K2K x 2K動態(tài)范圍： 14比特：016383 16比特：065535冷卻1小時以上避免使用強電子束照射:零損失峰，透射斑CCD結(jié)構(gòu)示意圖EELS包含的信息等離子激發(fā) The main exci-tation allowed for core elec-trons obeys the dipole selection rule:K-edge absorptionL1-edge absorptionL2,3-edge absorption1s2s3s2p3p3dM1-edge absorptionM2,3-edge absorptionS-likeP-likeD-likeEf

3、1l1, 0 lm內(nèi)殼層電子的激發(fā)和躍遷內(nèi)層電子激發(fā)和能帶結(jié)構(gòu)內(nèi)殼層電子的激發(fā)符號規(guī)定內(nèi)殼層電子的激發(fā)和周期表電子能量損失譜和X射線能譜EELS的優(yōu)點：靈敏度高，分辨率高會聚角和接收角的測量02EEEEEkq0EELS的特征角EELS的特征角E接收角=(2-4)E 不能E樣品厚度對EELS的影響樣品厚度對EELS的影響:多次散射樣品厚度的影響:非彈性散射平均自由程樣品厚度的影響:等離子損失譜樣品厚度的影響:電離損失峰樣品厚度的影響:最佳厚度退卷積退卷積: Fourier ratio方法消除譜儀的影響退卷積: Fourier log方法退卷積：Fourier ratio方法EELS的背底扣除：指

4、數(shù)定律rBAEIEELS的背底扣除:窗口位置的影響EELS的背底扣除: 指數(shù)定律失效1Im)(1),(222002EainnvmadEdEd等離子散射可以看作是多體散射問題，根據(jù)電磁場理論介質(zhì)的損失函數(shù)可以推導(dǎo)出了二階微分散射截面的表達(dá)形式：1Im被稱為損失函數(shù)， 為介質(zhì)的介電常數(shù) 在介電理論中， )()()(iri低能損失譜的應(yīng)用:損失函數(shù)),(1E根據(jù)Kramers-Kronig關(guān)系: 22),(1Im(),(1Re(),(1Im(),(1Re(),(),(),(EEEiEEiEEir求出相應(yīng)的實部),(1Re(E從電子能量損失譜可以得到 的虛部 ，得到材料的復(fù)介電常數(shù)Kramers-Kr

5、onig 分析220) (1Im21)(1ReEEdEEEE低能量損失的應(yīng)用：介電常數(shù)電離損失峰分析：峰位的確定拐點拐點二階微分：確定電離損失峰峰位拐點拐點拐點拐點二階微分：微量元素分析成分定量分析1 退卷積2 扣背底3 散射截面計算近邊精細(xì)結(jié)構(gòu)近邊精細(xì)結(jié)構(gòu):碳和碳化物近邊精細(xì)結(jié)構(gòu):過渡族金屬氧化物100200300400500600-200002000400060008000100001200014000NW BB2O3Pure BCounts (a.u.)energy loss (eV)近邊精細(xì)結(jié)構(gòu):硼化物近邊精細(xì)結(jié)構(gòu)：化學(xué)位移(離子鍵）近邊精細(xì)結(jié)構(gòu)：化學(xué)位移(共價鍵）近邊精細(xì)結(jié)構(gòu)(5)近

6、邊精細(xì)結(jié)構(gòu):分子軌道近邊精細(xì)結(jié)構(gòu):八面體結(jié)構(gòu)近邊精細(xì)結(jié)構(gòu)：八面體結(jié)構(gòu)和四面體結(jié)構(gòu)近邊精細(xì)結(jié)構(gòu):過渡族金屬L23近邊精細(xì)結(jié)構(gòu):氧化銅的L23600650700750800Mn-L2Mn-L3Photodiode Counts (a.u.)Energy loss (eV)1234234MnCO3MnOMn3O4Mn2O3MnO2Intensity ratio L3/L2Valence state of MnDipole rule: L3: 2p3/2 to 3d3/2,3d5/2 ; L2: 2p1/2 to 3d3/2近邊精細(xì)結(jié)構(gòu):確定錳元素的價態(tài)近邊精細(xì)結(jié)構(gòu):過渡族金屬的L3/L2EXELFS

7、模型EXELFS分析 取向效應(yīng):散射幾何取向效應(yīng):石墨的ELNES取向效應(yīng):石墨的 EXELFS取向效應(yīng)：ALCHEMI(改變s s)S0Fig. 11 projection of the wurtzite GaN structure model. The direction of the cation (Ga) to the anion (N) is defined as 0001 in the real space.0001GaN取向效應(yīng): ALCHEMI(改變g g)氮化鎵的極性Fig. 13 The calculated thickness-averaged electron curr

8、ent density across a unit cell at (0002) (a), and (000-2) (b) Bragg conditions for the impact parameter b= 0.0nm (without delocalization), 0.073nm, and 0.087nm.The sample thickness is 0.40002. 0 .00 .40 .81 .21 .62 .00 .00 .40 .81 .21 .62 .0(a ) g = 0 0 0 2 b = 0 .0 b = 0 .0 7 3 b = 0 .0 8 7TAECD(b

9、) NNG aG aG ag = 0 0 0 -2G aNG aNG a b = 0 .0 b = 0 .0 7 3 b = 0 .0 8 7TAECDA to m ic L o c a tio n取向效應(yīng):氮化鎵的極性 Fig. 12 Comparison of the EEL spectra acquired at (0002) and (000-2) Bragg conditions. The inset is the magnified N K-edge. 40060080010001200140001000002000003000004000005000006000003504004

10、505005500100000200000300000400000500000Ga-LN-K Counts (a.u.)Energy Loss (eV) (0002) (000-2)Energy Loss (eV) (0002) (000-2)取向效應(yīng):氮化鎵的極性Fig. 16 The difference of the calculated averaged-thickness electron current density vs. the sample thickness. The thickness is expressed in units of the two-beam exti

11、nction distance 0002.The difference of the calculated averaged-thickness electron current density does not change sign when the thickness changes. 0.00.51.01.52.00.00.20.40.60.81.01.21.41.61.8 b=0.0 b=0.073 b=0.087TAECD DifferenceThickness取向效應(yīng):氮化鎵的極性 GaAsEELSSpectrometerAnnular Detector1.4AsGaObjective LensForms a 1.3Probe I Z2 Z=31 Z=3319881998 Invented by Crewe in 1960s Incoherent imaging with electrons Atomic resolution spectroscopy Now standard on all commercial TEMsZ-Contrast Scanning Transmission Electron MicroscopySpatially resolv