Taipei, November 22, 2011 F From STEM ‐ EELS to multi ‐ dimensional and STEM EELS t lti di i l d multi ‐ signal electron microscopy Christian Colliex Laboratoire de Physique des Solides, Bldg 510 L b i d h i d S lid ld 10 Université Paris Sud, 91405, Orsay, France christian colliex@u ‐ psud fr christian.colliex@u ‐ psud.fr
Outline Outline Signals, instrumentation and methods for STEM EELS Atomically resolved elemental and bonding maps Mapping plasmons and EM fields When electrons and photons team up
Electron Electron – Matter interactions Matter interactions Secondary Secondary Event vs. Primary Event Transmission Electron Microscopy ‐ A Textbook for Material Science David Williams and Barry Carter, Fig. 1.3, page 7.
Working modes for an transmission electron microscope Electron source (0.5 à 2eV) Diffractions EDX spectroscopy anode(s) d ( ) a few 100kV condensers object (gonio) object (gonio) HREM Nanolaboratory : Objective imaging Specific specimen lens holders and stages holders and stages Intermediate lenses Projector lens Hologram Hologram Electron Energy Loss Spectroscopy (EELS) Magnetic prism p Energy filtered imaging Energy filtered imaging
STEMs with EELS analysers at Orsay y 1980 20 1980 ‐ 20xx 2008 ‐ 2011 2011 ‐ 20xx VG HB 501 NION UltraSTEM 100 NION UltraSTEM 200
EELS spectrum ‐ image 20 nm EELS spectrum at Orsay y B A 300 350 400 450 SPECTRE LIGNE Energy Loss (eV) SPECTRUM LINE HADF image 0.5 to 0.8 eV Spectrum 1 ms to 5 s Magnetic spectrometer Magnetic spectrometer E o C amera CCD E E - o HADF A detectors Specimen Specimen 0- Probe (nm) (nm) Scanning coils • 0.1 to 1nA • in 0.5 to 1 nm 40- I I I I 2 0 250 300 300 3 0 350 400 400 B 100 keV Energy Loss (eV) Field emission gun
Multi ‐ dimensional microscopy in a composite space (x,y position, E energy and t time) (x,y position, E energy and t time) x x y E E 1D : EELS spectrum 1D EELS t 0D : bit of information x x 3D : spectrum image y data cube data cube E (or x) y y 2D 2D : spectrum line t li or E ‐ filtered image E
Use of C correctors to reduce Use of C s correctors to reduce probe size or to increase probe current : i) <1 Å probe size at 100 kV, <0.7 Å at 200 kV Å ii) 200 pA of current in a 1.4 Å probe iii) 1 nA current in a 2 3 Å probe iii) 1 nA current in a 2.3 Å probe Orsay Nion U ‐ STEM 100 acceptance tests
New UltraSTEM for aberration ‐ corrected nanoanalysis (delivered in Orsay in 2008) (delivered in Orsay in 008) The column is built from modules that all have the modules that all have the b a same mechanical interface and are 100% interchangeable. interchangeable. Each module has triple magnetic plus acoustic g p shielding. Emphasis is on small probe formation and efficient coupling into detectors. Everything including sample exchange can be operated remotely. t d t l
Nion UltraSTEM 200 performance at Orsay
Imaging molecules containing heavy atoms (b) (a) (c) 1 nm 1 nm 0. 5 nm 0. 5 nm (d) (d) 2 nm 2 nm 2 nm 2 nm polyoxometalate (POM; As 2 W 20 O 70 Co(H 2 O)) molecules grafted on C ‐ SWNT courtesy A. Gloter, Orsay (2011)
BN monolayer with impurities imaged by MAADF Result of DFT calculation overlaid on Matt Chisholm’s experimental MAADF image C ring is C ring is deformed N N Cx6 C C B B O O O O Longer Longer bonds C C Na adatom
Si substituting for C in monolayer graphene 2 Å Si Si Si Si Si N Si Si Si Si in topologically Si at and near Si at graphene’s correct graphene topological defects edge M di Medium angle annular dark field (MAADF) images. l l d k fi ld (MAADF) i Nion UltraSTEM100 at ORNL, 60 kV. Image courtesy Matt Chisholm, ORNL, sample courtesy Venna Krisnan and Gerd Duscher, U. of Tennessee.
Si substituting for C: 2 structures are possible 2 Å Si Si Si Si Si Si N Si Si Si in defect ‐ free graphene strains (and Si in defective, but less strained graphene is buckles) the foil. more stable. (15 images added together, no (courtesy Matt Chisholm) other processing, courtesy Juan ‐ Carlos Idrobo)
EELS spectroscopy : spectral domains Phonons Plasmons Absorption edges X IR UV visible 2.5 ) x 10 6 ) Low losses Low losses C Core losses l ts number) 2.0 CK 1.5 sity (count 1.0 Intens MnL 2,3 0.5 Energy loss (eV) x10 6 x50 0 0 600 700 100 200 300 400 500
EELS: Involved electron populations and associated transitions Energy (eV) 60 O ‐ K CB . 50 0^3 0^3 40 40 x 10 x 10 E F 30 VB. 20 Plasmons 120 IT IT 10 10 100 520 530 540 550 560 570 580 590 600 610 K L 2,3 eV eV 80 60 O 1s O 1 350 40 -530 eV TM L 2,3 TM L 2,3 300 20 250 -710 eV TM 2p 0 5 10 15 20 25 0^3 0^3 200 x 10 x 10 eV eV -725 eV 2 150 100 50 0 0 695 700 705 710 715 720 725 730 735 eV eV EELS gives informations on the electronic structure
EELS spectroscopy : spectral domains Low energy ‐ loss domain Low energy loss domain Core energy ‐ loss domain Core energy loss domain Plasmon modes CK CK MnL 2,3 0 10 20 30 40 250 250 300 300 350 350 400 400 630 650 670 690 Energy loss (eV) Energy loss (eV) Energy loss (eV) Map with high accuracy the nature, i h hi h h Map different physical the position and bonding parameters, electronic, of the atoms responsible for the optical or magnetic, structural properties structural properties which are especially important which are especially important of real materials for electronic industries (defects, interfaces, nanomaterials) Requires instruments adapted R Requires instruments with i i i h to measure the properties of interest best spatial and energy resolutions at the relevant scale (0.1 nm, 0.1 eV) In all cases, develop the theory for interpreting Towards the nanolaboratory Towards the nanolaboratory spectroscopical data i e spectroscopical data, i.e. a physics of excited states
Absorption Absorption edges Absorption Absorption edges edges domain edges domain domain : domain : : three three types of information types of information Identification of elements CK Elementary quantification 250 300 350 400 Energy loss (eV) Study of the unoccupied electron states distribution
Q Quantitative elemental analysis y Characteristic signal : proportional to the number of atoms per unit area for the element detected in area for the element detected in the analysed area BK S S = ct. I N CK Atomic concentration ratios: NK B N A S A sity = Intens A N B S B 200 300 400 Energy loss (eV)
EELS core ‐ level spectroscopy: EELS core level spectroscopy: elemental and bonding maps with atomic resolution resolution 1. Individual atoms 1. Individual atoms 2. Crystalline structures and interfaces 3. Application to Tunnel ElectroMagneto 3. Application to Tunnel ElectroMagneto Resistance – TEMR
Single atom identification (signal/noise criteria) Peapods : Gd@C 82 @SWCNT Element selective single ‐ atom imaging A HREM i A : HREM image B : Schematic presentation C : Superposed maps of the Gd N45 and C K signals extracted from a 32x128 pixels spectrum image (C in 32x128 pixels spectrum ‐ image (C in blue, Gd in red) K. Suenaga et al., Science (2000)
STEM imaging of peapods at 30 and 60 kV with Delta STEM imaging of peapods at 30 and 60 kV with Delta corrector 30kV 60kV Damage drastically reduced at 30kV Courtesy Suenaga, Sawada & Sasaki (2010)
Single atom imaging by STEM ‐ EELS at low voltage with the g g g y g delta corrector Endohedral fullerenes M@C82 (M= La, Ce, Er) Iizumi and Okazaki
Atom by atom labeling at 60kV y g Courtesy K. Suenaga (AIST, Tsukuba, 2010)
Valence state identification of individual atoms La 3+ Ce 3+ La 3+ in LaCl 3 Ce 3+ in CeCl 3 Ce 4+ in CeO 2 Courtesy K. Suenaga (AIST, Tsukuba, 2010)
EELS spectrum ‐ imaging across interfaces S See C. Colliex, Nature N&V (2007) C C lli N t N&V (2007) HAADF micrograph
Elemental maps recorded with NION UltraSTEM at Orsay ( (courtesy Laura Bocher, 2011) t L B h 2011)
Spectroscopic imaging of LMO down the pseudocubic <110> axis. The sketch shows the projected structure of LMO down this direction. In green, the O K edge image; in blue the simultaneously acquired Mn L2,3 image and in red the La M4,5 image. The RGB overlay of the three elemental maps is also shown. From M. Varela et al. to be published in MRS bulletin 01/2012
D. Muller et al. Science 319 (2008) 1073)
High resolution Z contrast image of a LCMO/YBCO/LCMO heterostructure The inset High resolution Z ‐ contrast image of a LCMO/YBCO/LCMO heterostructure. The inset marks the region where an EELS spectrum image was acquired, along with the simultaneous ADF signal. (b) O K, Mn L2,3, Ba M4,5 and La M4,5 atomic resolution images (c) RGB overlay of the Mn (red) La (green) and Ba (blue) images in (b) The images. (c) RGB overlay of the Mn (red), La (green) and Ba (blue) images in (b). The sketch shows the interface structure. From M. Varela et al. to be published in MRS bulletin 01/2012
Recommend
More recommend
