Brookhaven Science Associates U.S. Department of Energy JEOL TEM/STEM course 2010F FasTEM University of Michigan 27 – 29 June 2006 Robert Klie Center for Functional Nanomaterials Brookhaven National Laboratory

Brookhaven Science Associates U.S. Department of Energy n Day 2: TEM/STEM n Imaging and Diffraction: Lecture before lunch, demo before lunch n a. Koehler n 1) Skewed thoughts on Parallelism – measuring and understanding beam convergence n 2) High Contrast Aperture n Measurement of Convergence n Positional accuracy of diffraction and shadow image. n Camera length variation with focused patterns n L U N C H n STEM: Lecture after lunch, Hands-on lab after lunch STEM conditions/camera lengths Gun Conditions: finding the optimum values Ultra high resolution -A2 – change value -Objective lens angle – underfocus to overexcite n Condenser 3 lens n Sample: Si/SiO 2 /SrTiO 3 Syllabus:

Brookhaven Science Associates U.S. Department of Energy Syllabus (contd) n Day 3: FasTEM/STEM: n EDS 1. Aperture selection 2. Analytical measurements –A. Hole Counts –B. P/B –C. Film Count –D. NiK and NiL ratio: detector test and specimen stage position n EELS 1. Effect of gun 2. Collection angle 3. STEM Diffraction/TEM Diffraction 4. PL Crossover n Sample: Si/SiO 2 /SrTiO 3 n Sample: NiO x on Carbon on Mo grid

Brookhaven Science Associates U.S. Department of Energy Parallel illumination: Parallel illumination is needed for: SAD: to minimize the spot diameter Diffraction contrast: Since illumination angle differs by (β(r) 2 +Φ(r) 2 ) 1/2, shifting illumination would mean changing incident illumination angle. CBD: α changes resolution in CBD pattern HRTEM: α affects the quality of HRTEM images

Brookhaven Science Associates U.S. Department of Energy Obtaining parallel illumination The effect of changing C3: Condenser 3 lens changes the convergence angle off the illumination, but this is only 1/3 of the story.

Brookhaven Science Associates U.S. Department of Energy Convergence angles in a TEM: Convergence angles α and β Convergence angles Φ All three angles have to minimized for truly parallel illumination!

Brookhaven Science Associates U.S. Department of Energy Convergence angle α β α

Brookhaven Science Associates U.S. Department of Energy Convergence angle α  α is the semi-angle subtended by the electron source.  α gives rise to the finite size of diffraction spots for β=0.  by de-magnifying the electron source and CA, α can be reduced.  α is proportional to 1/illuminated area. Measuring K: 1) Parallel Illumination, measure half-angle of focused diffraction spots. K is product of divergence and radius of divergence. 2) Focused Illumination, measure half-angle of diffraction spots and FHWM of focused spot. K

Brookhaven Science Associates U.S. Department of Energy Reducing electron source size: Demagnification of electron source: Changing the spot size will reduce the effective source size by demagnifying the source image.

Brookhaven Science Associates U.S. Department of Energy Convergence angle β Underfocus, β < 0 Overfocus, β > 0 Overfocus, β > 0 Overfocus, β = 0 CL must be focused on OL FFP!

Brookhaven Science Associates U.S. Department of Energy Convergence angle β β β G is typically mm, CA of μm to get β~ 1mrad G c/o is 1/100 of G, so 2-3 μm required for similar β in conventional OL c/o

Brookhaven Science Associates U.S. Department of Energy Convergence angle Φ Φ for β=0 In a magn. field electrons spiral around field lines with: For small angles:

Brookhaven Science Associates U.S. Department of Energy Parallel Illumination mode α α α β

Brookhaven Science Associates U.S. Department of Energy Obtaining parallel illumination Bragg line rotation method: Focused probe:β = 0

Brookhaven Science Associates U.S. Department of Energy Obtaining parallel illumination Wobble OL, and change CL3 If illumination is not parallel, probe will change size when wobbling OL! Convergent Probe: If illumination is parallel, probe-size will remain some when wobbling OL! Convergent Probe:

Brookhaven Science Associates U.S. Department of Energy Diffraction Focus: Focusing of Kikuchi lines: Kikuchi line are sharp if diffraction lens images OL BFP, and illumination is focused. Parallel illumination by changing CL3 to minimize diffraction spots.

Brookhaven Science Associates U.S. Department of Energy Obtaining parallel illumination NBD mode: CM on CBD mode: CM off Different illumination modes:

Brookhaven Science Associates U.S. Department of Energy Measuring convergence angles For 200 keV instrument with B z =3 T: Φ/r=1.7 mrad/μm

Brookhaven Science Associates U.S. Department of Energy Measuring convergence angles F = Structure factor E = envelope functions N = noise function G SC = spatial coherence G TC = temporal coherence

Brookhaven Science Associates U.S. Department of Energy Measuring convergence angles Determine Noise:Fitting of the CTF:

Brookhaven Science Associates U.S. Department of Energy Measuring convergence angles

Brookhaven Science Associates U.S. Department of Energy Measuring convergence angles

Brookhaven Science Associates U.S. Department of Energy Parallel Illumination for EELS: To EELS Image modes for EELS:Convergence angle: PL focus has to be fixed to maintain focus of EELS spectrometer. Convergence angle is determined by SEA and imaging mode.

Brookhaven Science Associates U.S. Department of Energy INCIDENT BEAM C-AXIS q k k 1 0      APERTURE Can enhance or reduce orientation effects with C3 and projector lenses Browning, Yuan & Brown, Phil Mag A 67, 261 (1993) Collection conditions:

Brookhaven Science Associates U.S. Department of Energy B Mg Bulk [001] Bulk [100] B K-edge Introduction R. F. Klie, J. C. Idrobo, N. D. Browning, K.A. Regan, N.S. Rogado, and R. J. Cava, Appl. Phys. Let., 79 (12), 2001

Brookhaven Science Associates U.S. Department of Energy Position of the SAD aperture SAD aperture position The SAD aperture has to be in the image plane of the OL to obtain diffraction pattern from same area as image. In SAM mode, use DiffFocus to adjust position of SAD.

Brookhaven Science Associates U.S. Department of Energy Keeping the Diffraction Focus constant:

Brookhaven Science Associates U.S. Department of Energy