Tfy-125.4313 Microscopy of Nanomaterials P (5 cr) Prof. Janne Ruokolainen (nanotalo 107) Email:

[email protected]

~3 nm

First lecture 19.1. 2016 Tuesday 12.15 – 14, lecture hall nanotalo 228 Assistant: Johannes Haataja email: [email protected]

Course overview: The course gives basic knowledge of the microscopy of materials nanoscale structures - including soft and hard materials. Lectures will concentrate on transmission electron microscopy (TEM), cryo-electron microscopy, high resolution imaging, electron diffraction and analytical microscopy by using elemental analyses (EDX, EELS). Additionally scanning electron microscopy (SEM), atomic force microscopy (AFM) and methods to prepare samples are lectured.. Course Registration: WebOodi (or First Lecture if you do not have access to Oodi)

200 Å

Tfy-125.4314 Microscopy of Nanomaterials, laboratory course P (5 cr)

Assistants: Johannes Haataja (Tomography), Mededi Reza (TEM), Dr. Hua Jiang (HR-TEM), Dr. Krista Vajanto (SEM), Matti Toivonen (AFM)

As practical exercises nanostructured materials are studied with various microscopy methods. Course includes practical microscopy exercises by using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Number of students participating to the course will be limited. (max. 18 ) Based on applications… application form in Web: (Deadline 1st of February) http://dy.fi/bpx Assistant: Johannes Haataja email: [email protected]

Basic exercises – Demos: (3 groups 6 persons per group): 1) High resolution TEM (Jeol 2200FS Cs-corrected TEM) 2) 3D tomography data collection (Jeol 3200FSC liquid helium cryo TEM) + Tomography data processing (Computer room)

Small group exercises: (6 groups - 3 persons per group) 1) basic-TEM imaging (Tecnai 12 TEM) 2) SEM imaging 3) AFM imaging Independent Small group exercises (without supervision.. 3 person per group)

(2 exercises) 1) TEM imaging 2) SEM imaging 3) AFM imaging

Lecture 2: Transmission Electron Microscopy (TEM) Janne Ruokolainen

1) JEOL JEM-3200FSC 300 kV CryoTransmission Electron Microscope (EELS)

2) JEOL JEM-2200FS 200 kV Double Cs corrected Transmission Electron Microscope (EDX & EELS)

3) FEI Tecnai 120 kV Transmission Electron Microscope

1/2016: 4) JEOL JEM-2800 200 kV Transmission Electron Microscope (EDX)

Contents: • Definitions and some background.. * TEM lens systems and general operation principles briefly * Dark field vs. Bright field * Imaging, Diffraction, analytical TEM • Imaging: Contrast (mass-thickness, diffraction, phase contrast) • Electron interaction with matter: Particles... Coulomb interaction – threfore very strong... * Elastic Scattering: Imaging, Diffraction * Inelastic Scattering: Analytical microscopy, beam damage, EDX, EELS • Electron Sources

Transmission Electron Microscopy A Textbook for Materials Science David B. Williams, C. Barry Carter

Chapter 5: Electron Sources Chapter 6: Lenses, Apertures, and Resolution Chapter 7: ”How to see electrons” Chapter 8: Vacuum pumps and Holders Chapter 9: The Instrument Chapter 10: Specimen preparation Chapters 2-4: Scattering and Diffraction, beam damage

Transmission electron microscopy (TEM) vs. Optical microscope (Transmission mode) (TEM)

(OM)

0.61* λ δ = Resolution µ sin β

λ= 400 - 700 nm, Optical microscope numerical aperture µ sin β ~1  Resolution ~ 200 - 300 nm

Why use Electrons: • Higher resolution... But also • Diffraction • Elemental Analysis

Electron microscopy TEM vs. STEM Transmission electron microscopy TEM

Scanning Transmission electron microscopy STEM

Electron transparent Thin Specimen

CCD camera

Detector

Dark field vs. Bright field TEM and STEM STEM detectors

Literature exampl:e High resolution (ADF) STEM

FIG. 1 (color online). Atomic structures for threefold and fourfold coordinated Si impurities in monolayer graphene. [(a)-(c)] STEMADF images of individual Si impurity atoms in the most common defect configurations with threefold or fourfold coordination. [(d)-(f )] Schematics of the structure models, overlaid with the corresponding ADF images, for the defect structures shown in (a)-(c), respectively. The chemical identity of each atom was obtained from quantitative ADF image analysis. Scale bars: 0.2 nm. Wu Zhou et al. “Direct Determination of the Chemical Bonding of Individual Impurities in Graphene “ PHYSICAL REVIEW LETTERS, 2012, 109, 206803

Diffraction & Imaging (Direct beam and elastic scattering..) YBa2Cu3 O7-δ

200 kV e sample Obj. Lens

Back focal plane

diffraction

image

• An image represents the structure in real space at a certain resolution; • The diffraction is an reproduction of the structure in reciprocal space.

Y Ba O Cu/O

Diffraction: Bragg’s law Bragg’s Law:

nλ = 2d sin θ

Example: Hexagonal structure

Elastic scattering and diffraction

2nd

1st

0th

Single crystal

Amorphous - disordered

Poly crystalline

Simple analysis based on Bragg’s Law:

nλ = 2d sin θ

Simple cupic 1 : 2 : 3 : 4 : 5 : 6 : .... = 1 : 1.41 : 1.73 : 2 : .. Face centered cubic

Body centered cubic

3 : 4 : 8 : 11 : 12 : 16 .... = 1 : 1.15 : 1.63 : ...

2 : 4 : 6 : 8 : 10 : 12 .... = 1 : 1.41 : 1.73 : 2 : ..

Hexagonal 1 : 3 : 4 : 7 : 9 : 12 : 13.... = 1 : 1.73 : 2 : ... Lamellar 1 : 4 : 9 : 16 : .. = 1 : 2 : 3 : 4 : 5 : 6 : 7 : ... Gyroid

6 : 8 : 14 : 16 : 20 : 22 :... = 1 : 1.15 : 1.53 : ...

More on electron diffraction See book II diffraction

EXAMPLE: X-ray diffraction, TEM (FFT), cryo-TEM ...

Effect of an Asymmetric Lipid Structure on Self-Assembly in Ionic Complexes With Helical Polypeptides

Sirkku Hanski Molecular Materials Group Aalto University, Department of Applied Physics

Polylysine-lipid(DMPE-EG7) complex SAXS

O O

O O H

O O P O O +

H N

O O O

H3N

O

H N

O

O

O

NH3+ R

O

NH N H

m

O

O

O

NH3+ R

O

O

SAXS

Bragg’s Law:

nλ = 2d sin θ lipid : Lamellar 1 : 4 : 9 : 16 : .. = 1 : 2 : 3 : 4 : 5 : 6 : 7 : ...

Cryo-TEM

γ

Image formation and contrast in TEM

Image formation and contrast 200 kV e -

200 kV e sample

sample

Obj. Lens

Obj. Lens

diffraction

Small Aperture

image No contrast when in focus – Note that when under/over focus then there is normally phase contrast

image 1) Bright field (BF) image Contrast: mass-tickness/Diffaction contrast Typical for soft materials which are selectively stained Or for low resolution imaging of crystalline materials (crystals oriented in the Bragg angle are black in the image)

No objective aperture

Diffraction

Objective aperture inserted

No objective aperture

Objective Aperture inserted to select the central direct unscattered beam

Image formation and contrast (Dark field) 200 kV e sample Obj. Lens

Small Aperture

image

2) Dark field (DF) image Contrast: Diffaction contrast Crystalline materials (crystals are white in the image)

Example: Bright field (BF) vs Dark field (DF) 200 kV e sample Obj. Lens

Small Aperture image

Bright field (BF) vs Dark field (DF) 200 kV e sample Obj. Lens

Small Aperture

image

3. Phase contrast

Intensity depends also from the electron wave phase:

For the phase contrast we need (in the image) two electron beams with different phases to form the image:

Electrons

Sample

Obj. Lens

(Back focal plane)

Typically 1) Non scattered electrons 2) Scattered (diffracted) electrons Similar princible in phase contrast Optical microscope:

Image

Image formation and contrast: Phase Contrast 200 kV e sample Obj. Lens

diffraction Large Aperture

3) High resolution lattice imaging: Phase contrast No contrast when in focus – But when under focusing there is a phase shift in difracted beams – therefore lattice image can be obtained

Under focus image

In reality: mass-thickness and phase contrast mechanism are present at the same time – esspecially for typical polymer nanostructures, which are quite large (1nm to 100 nm) and diffarction angle is propotional to ~1/size, therefore diffracted beams are so close to the direct beam that even the smallest aperture allows them to pass into image and contribute to the phase contrast

3. Phase contrast

No objective aperture and in-focus

No objective aperture and under focus

Example (phase contrast): Polymer-amphiphile nanostructures

+ CH2

CH

n

+

HO

N

300 nm

30 nm

Image formation and contrast: Phase Contrast FFT from TEM Image or Diffraction would look the same

Real TEM Image

2x10 7 1x10 7

3x10 6

For the phase contrast imaging – we would like to have aperture so that also diffracted beams contribute the image and then defocusing the Objective lens to get optimum contrast

2x10 6 1x10 6

3x10 5 2x10 5 1x10 5 4x10 4 0.00

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1D Intergrated intensity from FFT

Example: Phase contrast Poly(4-vinylpyridin)+nonadekylfenol, I2 staining

“under focus”

“in focus”

Macromolecules 1998, 31, 3532

“over focus”

Phase Plate technology in TEM’s: The Ultimate in Contrast – JEM-2200FS with Phase Plate! Zernike phase plate in TEM: Thin carbon film with small hole in the center placed in the back focal plane (BFP) of objective lens – commercially available since ~ 2010-11

Ultramicroscopy, Volume 109, 2009, Pages 312–325

The 300 kV cryo-TEM images of a sample from negatively stained horse spleen ferritin [from Fig. 6 of ref. 14]. (a) ZPC-TEM image acquired using a Zernike phase plate. (b–d) Conventional TEM images at a defocus of 2550, 540 and 130 nm, respectively (underfocus). The insets show the diffractogram for each image. The scale bars in the insets correspond to 1 nm−1.

Kuniaki Nagayama, Journal of Electron Microscopy 60(Supplement 1): S43–S62 (2011) “Another 60 years in electron microscopy: development of phase-plate electron microscopy and biological applications”

Boersch phase plate: phase shift of unscattered electrons by an electrostatic potential in a microscaled electrostatic lens. (not commercial yet..)

Electron microscopy signals SEM signals

Most important in TEM

Analytical Microscopy (Elemental analysis)

Chapter 2 Scattering and Diffraction:

•What is the probability that an electron will be scattered when it passes near an atom? • If the electron is scattered, what is the angle through which it is deviated? • What is the average distance an electron travels between scattering events? • Does the scattering event cause the electron to lose energy or not?

Interaction of electrons with matter (Chapters 2,3,4)

Scattering Elastic Scattering (Chapter 3)

Inelastic Scattering (Chapter 4)

Electron energy is conserved

Electron energy is not conserved 

Most common scattering mechanism and largest contribution to the contrast

X-ray scattering, secondary electrons, auger electrons, plasmons, phonons etc.  Beam damage, but also analytical microscopy

Elektronit e Electrons

Näyte

Sample

Obj. Linssi Objective

lens Obj. Apertuuri Back focal (Back focal plane)

plane

Ensimmäinen Image kuva

Scattering cross section and elastic scattering (Chapters 2 and 3)

2

N  Ze  ~ 0 *π   * ρt A  Vθ 

Notice : Z (atom number), V (Voltage) and θ (scattering angle) relation. And ρt relation

Conclusion: Elastic scattering is increased when: ρ, t, Z are higher and decreasing when V is increased

Book: more detailed formulas for scattering... Not required in this course... differential cross section for high-angle scattering by the nucleus alone

After adding screening and relativity corrections is that

we can integrate this expression to obtain the total cross section over specific angular ranges.

Propability for the elestic scattering

2

NA  Ze  ~ *π   * ρt M  Vθ 

Conclusion: Elastic scattering is increased when: ρ, t, Z are higher and decreasing when V is increased

... Not either required in this course....

Interaction of electrons with matter (Chapters 2,3,4)

Scattering Elastic Scattering (Chapter 3)

Inelastic Scattering (Chapter 4)

Electron energy is conserved

Electron energy is not conserved 

Most common scattering mechanism and largest contribution to the contrast

X-ray scattering, secondary electrons, auger electrons, plasmons, phonons etc.  Beam damage, but also analytical microcopy

Elektronit e Electrons

Näyte

Sample

Obj. Linssi Objective

lens Obj. Apertuuri Back focal (Back focal plane)

plane

Ensimmäinen Image kuva

Inelastic scattering (chapter 4) + Possibility for the analytical microscopy - Beam damage

In the Book inelastic processes are separated into three components

Characteristic X-rays and energy loss electrons

EDX -signal

EELS-signal

Characteristic X-rays

Can you tell what the materials are they in the image?

EDX can! Al

O

O

Cl

Al2O3

Si

Si

Si 5 nm

Other Example: TiO2 and CaO pigment particles EDX mapping

STEM image and X-ray EDS mapping

Spectroscopy ---- EELS (Electron Energy loss..)

Zero loss

ELNES

Plasmons

EXELFS

as far as 3 kV

EELS collects electrons that experience energy losses after "inelastic" interaction with the specimen, then display their energy distribution.

Example: Jeol 3200FSC cryo-TEM lens system

In colum omega type Energy filter

Electron Energy loss spectra (EELS) 9000 8500 8000 7500 7000 6500 6000 5500

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Normal imaging we select: Zero loss imaging

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EELS recongnizes different members in CARBON family Carbon family C

EDS

EELS

100 nm

A bight-field TEM iamge http://eels.kuicr.kyoto-u.ac.jp/eels.en.html

Bremsstrahlung X-ray ”Braking radiation”

Secondary electron emission and Auger-electrons

Note that also SE imaging in STEM is approaching the 1 Å resolution, see Y. Zhu et al. Nature Materials October 2009, Vol 8 number 10, p. 808.

Fluorescence yield

Example: Carbon Z = 6, ω = 0.001, Germanium Ge, Z = 32 ω = 0.5  one needs to ionize 1000 carbon atom before you get single X-ray, but only 2 atoms for germanium ..

Plasmons

- Mostly in metals

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Phonons = lattice vibrations

Causes sample heating  Beam damage

Electron-hole pairs and cathodoluminescence

•semiconductors

Interaction of electrons with matter (Chapters 2,3,4)

Scattering Elastic Scattering (Chapters 2,3)

Inelastic Scattering (Chapter 4)

Electron energy is conserved

Electron energy is not conserved 

Most common scattering mechanism and largest contribution to the contrast

X-ray scattering, secondary electrons, auger electrons, plasmons, phonons etc.  Beam damage, but also analytical microcopy

Beam damage I) Radiolysis: Inelastic scattering (mainly electron-electron interactions such as ionization) breaks the chemical bonds of certain materials such as polymers and alkali halides. Polymers: Chain scission (produce low molecular weight compounds) or Crosslinking. II) Knock-on damage (direct displacement of atoms..) Knock-on damage or sputtering: Knock-on damage is the displacement of atoms from the crystal lattice and creates point defects. If atoms are ejected from the specimen surface we call it sputtering. These processes are ubiquitous if the beam energy (E0) is high enough. III) Heating: Phonons heat your specimen and heat is a major source of damage to polymers and biological tissue. •If thermal conduction is very high, heating is negligible. • If thermal conduction is poor, heating can be quite substantial So, beam heating for metals is usually minimal but small ceramic particles may be heated by the beam to temperatures of 1700oC.

How to minimize… 1. Low dose TEM: - As small intensity as possible Small spot size, small apertures, spread the beam, low magnification Focusing etc. in the adjacent area or the specimen - Automatic low dose software

2. High voltage TEM + Electron mean free path longer when V increased  less inelastic scattering  less damage - However knock-on damage is increased above 200 - 300kV – however e.g. carbon nanotubes quite low voltage 80kV is a good option.. - Less contrast in high voltages

3. Cryo microscopy At low temperatures degradation slower (either liquid nitrogen or liquid Helium cooling) (Dose typically ~10 electrons/Å^2 or some polymers even much less –but then the signal to noise ratio is a problem…)

4. Sample coating (thin film of carbon film), Replica …

Electron sources Thermionic Sources Electrons emitted by heating Richardson’s law

J = AT 2 e − Φ / kT

 High emission current either at high temperature or materials with low work function Tungsten hairpin

Field Emission - electrons emitted by high electric field Electric field at the sharp point with radius r

V E= r radius typically < 0.1µm

Lanthanium Hexaborade single crystal LaB6

Field emission (Tungsten single crystal)

Thermionic Sources: Electrons are emitted by heating

Field Emission Source: electrons are emitted by high electric field

V1 E= r

For FE to occur, the surface has to be pristine, i.e., it must be free of contaminants and oxide. We can achieve this by operating in ultra-high vacuum (UHV) conditions (