Diffraction Methods & Electron Microscopy Lecture 2 Sandeep - - PowerPoint PPT Presentation

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Diffraction Methods & Electron Microscopy Lecture 2 Sandeep - - PowerPoint PPT Presentation

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FYS 4340/FYS 9340 Diffraction Methods & Electron Microscopy Lecture 2 Sandeep Gorantla 1 FYS 4340/9340 course Autumn 2016 Transmission Electron Microscopy Introduction and Basics Part- 1 Sandeep Gorantla 2 FYS 4340/9340 course

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FYS 4340/9340 course – Autumn 2016 1

Diffraction Methods & Electron Microscopy

Sandeep Gorantla

FYS 4340/FYS 9340

Lecture 2

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FYS 4340/9340 course – Autumn 2016 2

Transmission Electron Microscopy

Sandeep Gorantla

Introduction and Basics Part- 1

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Learning more about TEM!

Courtesy: WWW.amazon.com 3 FYS 4340/9340 course – Autumn 2016

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Learning more about TEM!

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http://www.matter.org.uk/tem/

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Learning more about TEM!

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FYS 4340/9340 course – Autumn 2016 6

Why learn about Transmission Electron Microscopy (TEM)?

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FYS 4340/9340 course – Autumn 2016 7

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Role of TEM in Materials Science Research and Development

Materials Science Paradigm

Courtesy: www.wikipedia.com

Solving Materials Science problems/mysteries by probing analytically and understanding structure-property relationships at atomic scale level

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FYS 4340/9340 course – Autumn 2016 9 graphite graphene nanotube fullerene

(Courtesy: The Royal Swedish Academy of Sciences)

Allotropes of carbon

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Courtesy: www.extremetech.com

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Courtesy: Knut Urban, Nature Materials 10, 165–166 (2011)

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1D nanomaterials modification in TEM

  • Irradiation of solids with energetic particles usually leads to damage
  • However, in the case of carbon nanostructures, electron irradiation was observed to have some

beneficial effects (a) Irradiation – mediated engineering (b) self-assembly or self-organization

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Courtesy: Krasheninnikov, A. V. et al., Nature Mater., 6, 723 (2007)

FYS 4340/9340 course – Autumn 2016

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FYS 4340/9340 course – Autumn 2016 13

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Interface: defects on outer-wall of a nanotube and fullerene

Courtesy: Gorantla, S. et al., Nanoscale, 2, 2077 (2010)

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FYS 4340/9340 course – Autumn 2016 16

Courtesy: Gorantla, S. et al., Nanoscale, 2, 2077 (2010)

Movie Settings:

  • Frame speed: 0.6 s
  • Total Frames: 48

Experimental conditions:

  • Acquisition time: 1 s
  • Time gap between

individual frames: 1s - 30s

  • Total time: 14 mins

Interface: defects on outer-wall of a nanotube and fullerene

Nanohump formation (Covalent interactions of fullerene fusion)

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FYS 4340/9340 course – Autumn 2016 17

Interface: defects on the outer-wall of a SWCNT and fullerene

Fullerene fusion with a nanohump (Covalent interactions of fullerene fusion) Movie Settings:

  • Frame speed: 0.6 s
  • Total Frames: 48

Experimental conditions:

  • Acquisition time: 1 s
  • Time gap between

individual frames: 1 s

Courtesy: Gorantla, S. et al., Nanoscale, 2, 2077 (2010)

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HETEROSOLAR PROJECT

The aim of the work

Develop new solar cell devices base on ZnO/Cu2O heterojunctions coupled with convetional Si based solar cells Si

* Theoretical eficiency ~20 % * Highest exp. eficiency 1-4 %

ZnO Cu2O

Properties determined by the structures, faults and interfaces. n-type 3.4 eV 2.17 eV p-type TCO Sub project : (S)TEM to characterize the thin films and their interfaces.

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FYS 4340/9340 course – Autumn 2016 19

ZnO Cu2O ???

ZnO Cu2O

50 nm

1 nm

ZnO Single Crystal Cu2O (sputtering, 300nm)

CuO

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FYS 4340/9340 course – Autumn 2016 20

ZnO CuO

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FYS 4340/9340 course – Autumn 2016

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Transmission Electron Microscope

Brief History

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Brief History: The first electron microscope

  • Knoll and Ruska, first TEM in 1931
  • Idea and first images published in 1932
  • By 1933 they had produced a TEM

with two magnetic lenses which gave 12 000 times magnification.

Ernst Ruska: Nobel Prize in physics 1986 Electron Microscope Deutsches Museum, 1933 model 22

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Brief History: The state-of-art TEM

Electron Microscope Deutsches Museum, 1933 model 23 FEI Titan 60-300 TEM, NORTEM facility- UiO Installed: 2014

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FYS 4340/9340 course – Autumn 2016

Resolution limit

Year Resolution 1940s ~10nm 1950s ~0.5-2nm 1960s 0.3nm (transmission) ~15-20nm (scanning) 1970s 0.2nm (transmission) 7nm (standard scanning) 1980s 0.15nm (transmission) 5nm (scanning at 1kV) 1990s 0.1nm (transmission) 3nm (scanning at 1kV) 2000s <0.1 nm (Cs correctors)

Courtesy: http://www.sfc.fr/Material/hrst.mit.edu/hrs/materials/public/ElecMicr.htm

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Brief History: The state-of-art TEM

BIG LEAP: Introduction of Lens Aberration Correctors allowing atomic resolution at low accelerating voltages.

Core of the M100 galaxy seen through Hubble (source: NASA)

Before Cs correction After Cs correction

300 kV 200 kV 80 kV 60 kV Typical TEM operating voltages in Materials Science Research

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FYS 4340/9340 course – Autumn 2016 25

Transmission Electron Microscope

Fundamentals

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Electrons interaction with the specimen

26 300 kV 200 kV 80 kV 60 kV Typical TEM operating voltages in Materials Science Research

Courtesy: D.B. Williams & C.B. Carter, Transmission electron microscopy

Electrons have both wave and particle nature Typical specimen thickness ~ 100 nm or less FYS 4340/9340 course – Autumn 2016

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Electron lenses

  • Electrostatic

– Not used as imaging lenses, but are used in modern monochromators

  • ElectroMagnetic

– Can be made more accurately – Shorter focal length

F= -eE F= -e(v x B)

Any axially symmetrical electric or magnetic field have the properties

  • f an ideal lens for paraxial rays of charged particles.

Courtesy: http://www.matter.org.uk/tem/lenses/electromagnetic_lenses.htm

27 FYS 4340/9340 course – Autumn 2016

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TEM Lens Aberrations

  • Spherical aberration coefficient

ds = 0.5MCsα3

M: magnification Cs :Spherical aberration coefficient α: angular aperture/ angular deviation from optical axis

r1 r2 Disk of least confusion α v v - Δv

y-focus x-focus y x

Spherical aberration Chromatic aberration Astigmatism

28 FYS 4340/9340 course – Autumn 2016

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TEM Lens Aberrations

29 Schematic of spherical aberration correction

Courtesy: Knut W. Urban, Science 321, 506, 2008; CEOS gmbh, Germany; www.globalsino.com

FYS 4340/9340 course – Autumn 2016

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TEM Lens Aberrations

Why we need an aberration-corrected TEM at 80kV???

  • Correcting aberrations improves the TEM resolution at 80 kV

Uncorrected 80 kV ~ 0.3 nm Corrected 80 kV ~ 0.14 nm

  • Improved resolution enables the possibility of imaging carbon nanostructures at atomic level

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Uncorrected 80 kV

  • Aberr. corrected

80 kV

(Courtesy: NASA)

FYS 4340/9340 course – Autumn 2016

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FYS 4340/9340 course – Autumn 2016 31

Transmission Electron Microscope

Instrumentation – Part 1

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FEG gun Extraction Anode Gun lens Monochromator Monochromator Aperture Accelerator Gun Shift coils C1 aperture/mono energy slit C1 lens C2 lens C2 aperture Condenser alignment coils C3 lens C3 aperture Beam shift coils Mini condenser lens Objective lens upper Specimen Stage Objective lens upper Image Shift coils Objective aperture Cs Corrector SA Aperture Diffraction lens Intermediate lens Projector 1 lens Projector 2 lens HAADF detector Viewing Chamber Phosphorous Screen BF/CCD detectors GIF CCD detector EELS prism

Courtesy: David Rassouw, CCEM, Canada

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FYS 4340/9340 course – Autumn 2016 33 Electron gun Illumination system Imaging system Projection and Detection system Specimen stage

Courtesy: David Rassouw

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FYS 4340/9340 course – Autumn 2016 34 FEG Electron gun source

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FYS 4340/9340 course – Autumn 2016 35 Specimen Stage

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TEM Specimen Holder

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FYS 4340/9340 course – Autumn 2016 37

TEM Specimens

  • Typically 3 mm in diameter

Courtesy: http://asummerinscience.blogspot.no

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FYS 4340/9340 course – Autumn 2016 38 TEM Viewing Chamber – Phosphorous Screen

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FYS 4340/9340 course – Autumn 2016 39 TEM Image recording CCDs and EELS Spectrometer

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FYS 4340/9340 course – Autumn 2016 40

Transmission Electron Microscopy

Introduction and Basics Part-2

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TEM in Materials Science

The interesting objects for TEM is not the average structure or

homogenous materials but local structure and inhomogeneities

Defects Precipitates Interfaces

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Atomic Structure Chemical bonding Electronic Structure Chemical composition

FYS 4340/9340 course – Autumn 2016

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FYS 4340/9340 course – Autumn 2016 42

Imaging

Conventional TEM Bright/Dark-Field TEM High Resolution TEM (HRTEM) Scanning TEM (STEM) Energy Filtered TEM (EFTEM)

Diffraction

Selected Area Electron Diffraction Convergent Beam Electron Diffraction

Spectroscopy

Electron Dispersive X-ray Spectroscopy (EDS) Electron Energy Loss Spectroscopy (EELS)

TEM techniques

Main Constrast phenomena in TEM

  • Mass thickness Contrast
  • Diffraction contrast
  • Phase Contrast
  • Z-contrast

Chemical composition, electronic states, nature

  • f chemical bonding (EDS and EELS).

Spatial and energy resolution down to the atomic level and ~0.1 eV. Phase identification, defects, orientation relationship between different phases, nature of crystal structure (amorphous, polycrystalline, single crystal)

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Objective aperture: Contrast enhancement

All electrons contributes to the image. A small aperture allows only electrons in the central beam in the back focal plane to contribute to the image. Intensity: Thickness and density dependence

Mass-thickness contrast

Si Ag and Pb glue

(light elements)

hole 50 nm One grain seen along a low index zone axis.

Diffraction contrast

(Amplitude contrast) 43 FYS 4340/9340 course – Autumn 2016

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FYS 4340/9340 course – Autumn 2016 44

Imaging

Conventional TEM Bright/Dark-Field TEM High Resolution TEM (HRTEM) Scanning TEM (STEM)

Energy Filtered TEM (EFTEM)

Diffraction

Selected Area Electron Diffraction

Convergent Beam Electron Diffraction

Spectroscopy

Electron Dispersive Spectroscopy (EDS)

Electron Energy Loss Spectroscopy (EELS)

TEM techniques

200 nm Simplified ray diagram of conventional TEM

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FYS 4340/9340 course – Autumn 2016 45

Imaging

Courtesy: http://www.ifam.fraunhofer.de; I.MacLauren et al, International Materials Review, 59, 115 (2004)

Bright Field ADF ADF specimen Incident E-beam scattered E-beam (α = 22 mrad)

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FYS 4340/9340 course – Autumn 2016 46

Imaging

TEM STEM

Mass thickness and diffraction contrast Mass thickness and Z- contrast Gd-Hf-Co-Al quaternary alloys

Z

Gd 64 Hf 72 Co 27 Al 13

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FYS 4340/9340 course – Autumn 2016 47

Imaging

HRTEM STEM

Phase contrast Z- contrast

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FYS 4340/9340 course – Autumn 2016 48

Raw HAADF-STEM, ABF-STEM and HRTEM image of Si in the [110] zone axis by FEI Titan 60-300 with spatial resolutions of 0.8 Å for STEM and 2.0 Å for TEM. 1.36 Å HAADF-STEM ABF-STEM HRTEM

Courtesy: Wei Zhan, Øystein Prytz, et al. (2015), SMN, UiO

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FYS 4340/9340 course – Autumn 2016 49

Electron Diffraction in TEM

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Simplified ray diagram

Objective lense Diffraction plane (back focal plane) Image plane Sample Parallel incoming electron beam Si

1,1 nm 3,8 Å

Objective aperture Selected area aperture 50 FYS 4340/9340 course – Autumn 2016

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Elastic scattered electrons

Only the direction of v is changing. (Bragg scattering) Elastic scattering is due to Coulomb interaction between the incident electrons and the electric charge of the electron clouds and the nucleus. (Rutherford scattering). The elastic scattering is due to the average position of the atoms in the lattice. Reflections satisfying Braggs law:

2dsinθ=nλ Inelastic scattered electrons

Direction and magnitude of v change. Energy is transferred to electrons and atoms in the sample.

  • It is due to the movements of the atoms

around their average position in the lattice.

  • It give rise to a diffuse background in the

diffraction patterns.

Electrons interacts 100-1000 times stronger with matter than X-rays

  • more absorption (need thin samples)
  • can detect weak reflections not observed with XRD technique

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Electron Diffraction in TEM

Courtesy: Dr. Jürgen Thomas, IFW-Dresden, Germany

FYS 4340/9340 course – Autumn 2016

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Selected area diffraction(SAD)

  • Parallel incoming electron beam and a

selection aperture in the image plane.

  • Diffraction from a single crystal in a

polycrystalline sample if the SAD aperture is small enough/crystal large enough.

  • Orientation relationships between grains or

different phases can be determined.

  • ~2% accuracy of lattice parameters

– Convergent electron beam better Image plane 52 FYS 4340/9340 course – Autumn 2016

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Camera constant

R=L tan2θB ~ 2LsinθB 2dsinθB =λ ↓ R=Lλ/d Camera constant: K=λL Film plate 53 FYS 4340/9340 course – Autumn 2016

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Indexing diffraction patterns

The g vector to a reflection is normal to the corresponding (h k l) plane and IgI=1/dnh nk nl

  • Measure Ri and the angles between

the reflections

  • Calculate di , i=1,2,3 (=K/Ri)
  • Compare with tabulated/theoretical

calculated d-values of possible phases

  • Compare Ri/Rj with tabulated values for

cubic structure.

  • g1,hkl+ g2,hkl=g3,hkl (vector sum must be ok)
  • Perpendicular vectors: gi ● gj = 0
  • Zone axis: gi x gj =[HKL]z
  • All indexed g must satisfy: g ● [HKL]z=0

(h2k2l2) Orientations of corresponding planes in the real space 54 FYS 4340/9340 course – Autumn 2016

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Poly crystalline sample

The orientation relationship between the phases can be determined with ED.

55 Single Crystals Interface between two different phases epitaxially grown

Electron Diffraction in TEM

Amorphous phase FYS 4340/9340 course – Autumn 2016

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56 FYS 4340/9340 course – Autumn 2016

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FYS 4340/9340 course – Autumn 2016 57

Spectroscopy

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FYS 4340/9340 course – Autumn 2016

Quartz (1mm) AZO (sputtering, ~200 nm) Cu2O (sputtering, 600nm) TiO2 (ALD, 10 nm)

X-ray Energy Dispersive Spectroscopy

We detect the X-rays generated by the sample on a spectrometer Each element has a unique atomic structure and hence a characteristic X-ray energy

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FYS 4340/9340 course – Autumn 2016

Quartz (1mm) AZO (sputtering, ~200 nm) Cu2O (sputtering, 600nm) TiO2 (ALD, 10 nm)

Energy Dispersive X-ray Spectroscopy

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Electron Energy Loss Spectroscopy (EELS)

Courtesy: William & Carter, Transmission Electron Microscopy; EM group, Univ. of Nevada, Reno.

Inelastically interacted incident electron suffers energy loss after passing through the specimen

  • Phonon Excitations
  • Inter and Intraband Transitions
  • Plasmon Excitations
  • Inner Shell Ionizations
  • Cherenkov radiation

Each element has characteristic ionization energy

  • wing to its unique atomic structure

FYS 4340/9340 course – Autumn 2016 60

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EELS of the Oxygen K edge

The reference spectra of Cu2O and CuO are from online EELS database1. The reference spectra were shifted in energy to match the first O K peak in our experimental, and scaled by the total counts in the energy-loss 560-590 eV.

1Ngantcha, Gerland, Kihn & Riviere, Eur. Phys. J. Appl. Phys. 29, (2005) 83.

ZnO CuO Cu2O

Electron Energy Loss Spectroscopy (EELS)

Courtesy: Cecilie Granerod, SMN, UiO

61 FYS 4340/9340 course – Autumn 2016

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Next Lecture

62

  • TEM Instrumentation – Part 2

(Text book Chapters: 5 – 9)

  • TEM Specimen Preparation

(Text book Chapters: 10)

FYS 4340/9340 course – Autumn 2016