Central (Lumigen) Instrument Facility

Laboratory of Analytical Electron Microscopy Stephanie L. Brock, Professor Department of Chemistry Wayne State University Zhi “Mike” Mei, Ph.D. Laboratory of Analytical Electron Microscopy Lumigen Instrument Facility & Department of Chemistry Wayne State University Tel: 313-577-2604, Email: [email protected]

Lumigen Instrument Facility

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Why use an Electron Beam? Can we magnify an image taken by an optical microscope unlimitedly?

No!!!!!!!!!!!!!!!!

Resolution more important! Not magnification!!! The Laboratory of Analytical Electron Microscopy

Electron Microscopy Why use Electron Beam? The resolution is usually given by Rayleigh Criteria: Where, δ is the smallest distance resolved (resolution) λ is the wavelength of the light μ is the refractive index of the viewing medium, β is the semi-angle of the lens

δ=

0.61λ μ sin β d0

The limitation of visible light: Green light in the middle of the visible spectrum, λ is ~550 nm, δ is ~300 nm Electron beam: λ=0.251 nm (200kV), δ is ~0.2 nm M d0

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Why use an Electron Beam?

From JEOL-2200FS Brochure

SEM

EBSD

EDX

Contribute to background of EDX Diffraction TEM image STEM image TEM: SEM: STEM: EDX: EBSD: EELS:

EELS

Transmission electron microscope Scanning electron microscope Scanning transmission electron microscope Energy dispersive X-ray Spectrometer Electron Backscattering diffraction Electron energy-loss spectrum

Atomic energy levels

High Energy Electron beam Vacuum

EL3 EL2 EL1 EK Nucleus

L3 L L 21 K Characteristic X-rays Energy-loss electron

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Analytical Electron Microscopy (TEM/SEM) Lab at WSU Funded by National Science Foundation, Installed in 2004 (TEM), 2011 (SEM)

Transmission Electron Microscope (TEM) JEOL 2010 FasTEM operating at 200kV, two CCD cameras and one film camera Energy Dispersive X-Ray Spectrum (EDS) detector: Local chemical analysis Double tilt sample holder: Diffraction analysis Double tilt heating stage and cooling stage with precisely controllers: dynamic microstructure evolution

Scanning Electron Microscope (SEM) JEOL 7600F and 6510LV Energy dispersive X-ray Spectrum (EDS) detector: Local chemical analysis Backscattered electron detector (BSD): Composition distribution, electron channeling contrast image Electron backscattered diffraction detector (EBSD/Orientation Imaging Microscopy (OIM)): Orientation of grains, Texture analysis, Orientation Density Function (ODF)

Computer Simulation and Analysis on TEM Images Diffraction patterns indexing and simulations High resolution image simulation Crystal models for interface

Sample Preparations Capable of preparations for Metals & Alloys, Ceramics, Semiconductors, powders, nanoparticles Facilities include Gatan Ion-Beam Milling (Pips), Dimpler Grinder, Grinder/Polisher, Low Speed Diamond saw, Ultrasonic Cutter, Twin-Jet Electron Polisher, Gold Evaporator

The Laboratory of Analytical Electron Microscopy

Lumigen Instrument Facility JEOL 2010 TEM Electron Gun

Condenser lens system

Objective lens system Intermediate and Projector lens system

Camera Chamber

The Laboratory of Analytical Electron Microscopy

Electron Microscopy

TEM Sample Preparation Methods For the electron beam to pass through the sample, very thin specimens are needed (< 500 nm) Powders (including nano-particles) Use dropper to put the solution directly onto a carbon-coated copper grid

Metal and Alloys: • Make discs 3mm in diameter • Mechanically grind and polish down to 50-80μm • Electro-polish the sample until transparent to electron beam

Semiconductors and Ceramics: • Make discs 3mm in diameter • Mechanically grind and polish down to 50-80μm • Ion-beam mill The Laboratory of Analytical Electron Microscopy

Electron Microscopy

TEM Sample Preparation Methods Cross-section method: This method is suitable for any material that needs to be observed from the cross-section direction. These materials include semiconductor thin films, superlattices, multilayer structured materials, or materials with a coating layer, etc. Substrate

Thin film

A substrate coated with one layer of thin film

Grind the surface of the disk and glue it onto a copper ring to support the sample

Substrate

Thin film (Red color)

A layer of glue

Two pieces of substrate with thin film glued face to face using MBond 610 adhesive

Dimple grinder

A ~3mm disk obtained with an ultrasonic cutter

Ion-beam milling

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Bright Field / Dark Field Imaging Bright Field – imaging with the main transmitted beam (diffraction contrast and mass/thickness contrast)

Dark Field – imaging with electron beam scattered at some angle (diffraction contrast only)

http://www.microscopy.ethz.ch The Laboratory of Analytical Electron Microscopy

Electron Microscopy Bright Field / Dark Field Imaging

http://www.microscopy.ethz.ch BF (left) shows the contrast (dark) for entire specimen; we can’t distinguish between crystalline regions and non-crystalline regions DF (below) shows contrast (bright) only for crystalline regions

Electron diffraction pattern (above): the spots indicate the presence of single microcrystals. The apertures (red circles) are localized around the direct beam for recording the bright field (BF) image and around a few diffracted beams for the dark field (DF) image. The intense direct beam is blocked by a metal rod (black shadow on the left center) to avoid overexposure. The Laboratory of Analytical Electron Microscopy

Electron Microscopy Electron Diffraction Electron Diffraction carries structure information of crystals: Show symmetry of crystals Measure the distance of crystal plane, the angle between different direction/plane Identify different phases in materials Determine unknown structure of materials (series tilting) Yields discrete spots (single crystals) or rings (polycrystalline or amorphous materials) Convergent-Beam Electron Diffraction (CBED): Measure point group, space group of crystals Measure local lattice parameter change/local strain in materials Measure specimen thickness Provides a “road map” in reciprocal space (Kikuchi lines) The Laboratory of Analytical Electron Microscopy

Electron Microscopy Electron Diffraction (a)

Condenser Lens

(b)

Condenser Lens Aperture The beam convergent on the surface of the sample

Condenser Mini-Lens

A parallel beam illuminates the surface of the sample

Objective Lens Specimen

Back Focal Plan

A convergent-beam electron diffraction

Field Limiting Aperture

An ordinary diffraction pattern

A convergent-beam electron diffraction pattern contains more information about the crystal structure. It can measure point group & space group, sample thickness, lattice parameter changes, etc. The Laboratory of Analytical Electron Microscopy

Electron Microscopy Convergent Beam Electron Diffraction 4-fold symmetry (square)

2-fold symmetry (rectangular)

(rounded)

Lattice distortion by the changes in chemical composition [001] CBED of Si and SiGe crystals John Mansfield, Lecture about TEM, EMAL lab at University of Michigan (Ann Arbor)

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Electron Diffraction & High Resolution Imaging

Diffraction pattern from Al-Ni-Co alloy showing 5-fold symmetry of quasicrystal. Quenched Al80Mn20 Alloy showing the lattice image of quasicrystal Daisuke Shindo & Kenji Hiraga, The High-Resolution Electron Photomicrograph Method of Judgment materials, 1996, Kyoritsu Shuppon Co., Ltd, Tokyo, Japan

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Imaging “real” samples at WSU

Fe3O4 nanoparticles on carbon film

The Laboratory of Analytical Electron Microscopy

Electron Microscopy High Resolution Imaging Lattice fringes due to diffraction off lattice planes within crystalline samples

Fe3O4 nanoparticles on carbon film

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Using the heating stage

Fig. 1: TEM micrographs of the Ni3(AsO4)2•H2O produced from the microemulsion based solvothermal reaction: a) as prepared; b) after water bath sonication for 60 minutes.

Fig. 3: In situ study of the transformation of arsenate nanoribbons to arsenide nanoparticles conducted at 420 ºC a) after 3 minutes of electron beam exposure; particle formation only at the ribbon edges, b) after 10 min of electron beam exposure; particle formation throughout the ribbon.

Fig. 2: TEM micrograph of the product of in situ carbothermal reduction of Ni3(AsO4)2•H2O at a) 400 ºC (30 minutes) and b) 420 ºC (10 minutes). The inset shows a high resolution image of a particle formed from coalescence of several adjacent smaller particles (65 minutes of heating, 420 ºC). Lattice fringes correspond to d = 0.317 nm.

Fig. 4: AFM height images analysis: a) Ni3(AsO4)2•H2O sonicated product before hydrogen annealing, b) after hydrogen annealing at 425 ºC for 3 h. P. Arumugam, S. S. Shinozaki, R. Wang, G. Mao, S. L. Brock “From Ribbons to Nanodot Arrays: Nanopattern Design through Reductive Annealing” Chemical Communications, 2006, 1121-1123.

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Selected Area Electron Diffraction vs. Powder X-ray Diffraction (SAED vs. PXRD) 250

____ Ni11As8 ____ Ni5As2

Intensity (arbitrary units)

200

____ NiAs 150

100

50

0 20

30

40

50

60

2θ, Degrees Fig. 2: The X-ray diffraction pattern of the product from hydrogen annealing of Ni-arsenate precursor conducted at 425 °C for an hour using an unsupported media (alumina boat).

Fig. 1: Selected area diffraction pattern of the product of in situ carbothermal reduction of the Ni arsenate precursor conducted at 420 ºC. Table 1: Measured d-spacing values from the electron diffraction pattern (Fig.1), as well as dspacing values for the metal-rich nickel arsenide phases and their respective (hkl) values

P. Arumugam, S. S. Shinozaki, R. Wang, G. Mao, S. L. Brock “From Ribbons to Nanodot Arrays: Nanopattern Design through Reductive Annealing” Chemical Communications, 2006, 1121-1123.

Measured d-spacing (Å)

Ni11As8 d-spacing (Å)

Ni5As2 (h k l)

d-spacing (Å)

NiAs (h k l)

d-spacing (Å)

(h k l)

2.189

2.370

(1 1 8)

2.190

(2 1 1)

2.520

(0 0 2)

1.922

1.899

(1 0 11)

1.960

(1 0 6)

1.961

(1 0 2)

1.602

1.621

(3 2 7)

1.660

(2 1 5)

1.568

(2 0 0)

1.441

1.449

(4 0 8)

1.403

(2 2 5)

1.471

(1 1 2)

1.017

1.023

(6 2 7)

1.054

(3 0 10)

1.033

(1 1 4)

The Laboratory of Analytical Electron Microscopy

Electron Microscopy In situ temperature control & SAED ¾ The heating (cooling) stage enables physical changes to be monitored ¾ The support matters: carbon supports can result in a chemical transformation upon heating due to carbothermal reduction; for nickel arsenate, the reduction to nickel arsenide resulted in a physical contraction (ribbonsÆ dots) that could be monitored. ¾ The electron beam can play a role: The electron beam can result in local heating as well chemical changes in sensitive samples. ¾ You are operating under high vacuum: volatile materials can sublime upon heating or from beam damage.

¾ Electron diffraction enables structural changes to be monitored ¾ SAED gives local structural information in a region defined by the aperature size and can be used to distinguish between different structures (arsenate vs. arsenide, in this case) ¾ In practice, we see fewer diffraction lines than by PXRD, and measurements are less precise; it can be very difficult to distinguish between similar structures using regular SAED. The Laboratory of Analytical Electron Microscopy

Electron Microscopy Size Distributions and Chemical Analysis via EDS (a)10.2 ± 0.9 nm

(b) 26.8 ± 1.9 nm

TEM images of (a) Ni2P nanoparticles with solid morphology (inset: HRTEM indicating the high degree of crystallinity and the absence of voids) and (b) Ni12P5 nanoparticles with hollow morphology.

5 nm

20 nm

20 nm

10000

Counts

Counts

80 60

(b)

P:Ni = 0.71

7500

60

Ni (Kα)

P (Kα)

5000

40

0

7

8

9

10

11

12

Size-Diameter (nm)

13

14

0

26.8 ± 1.9 nm

16000

40

20

2500

20

(a)

Counts

10.2 ± 0.9 nm

Counts

(a)

100

0

0

200

400

eV

600

800

1000

(b)

P: Ni = 0.37

Ni (Κα)

12000 P (Κα)

8000 4000

22

24

26

28

30

Size-Diameter (nm)

32

34

0

0

200

400

eV

600

800

1000

E. Muthuswamy, G. H. L. Savithra, S. L. Brock “Synthetic Levers Enabling Independent Control of Phase, Size, and Morphology in Nickel Phosphide Nanoparticles” ACS Nano, 2011, 5, 2402-2411.

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Size Distributions and EDS ¾ Statistics on size distributions for nanomaterials can be achieved by measuring a suitable number. ¾ Software enables rapid identification of particle sizes. ¾ Depending on the degree of polydispersity, more or fewer measurements must be made to get a representative size and standard deviation. ¾ Data should be acquired from multiple random places on the TEM grid to ensure it is representative of the sample dispersity.

¾ Energy dispersive spectroscopy can give semi-quantitative chemical analysis for elements heavier than Li ¾ If you are using a standard carbon coated copper grid, expect to see these signals (Cu and C). If you are analyzing for copper, use a nickel grid; for best analysis, Be grids can be purchased (expensive). ¾ Semi-quantitative measurement relies on instrument factors (no calibration standards); need good signal and good peak and background fits. Watch out for overlapping lines. The Laboratory of Analytical Electron Microscopy

Electron Microscopy Scanning Electron Microscopy (SEM) Advantages of the SEM -Large depth of field -High resolution -Ease of sample preparation (does not require thin samples)

SEM’s main components Electron column To accelerates and focuses a beam of electrons onto the sample surface

Sample chamber The place where the electron beam interacts with the sample

Detectors To monitor a variety of signals resulting from the beam-sample interactions

Viewing system To construct an image from the signal The Laboratory of Analytical Electron Microscopy

Electron Microscopy Electron Beam's Path through the Column

Iowa State University, Materials Science and Engineering, SEM Web Site. http://www.mse.iastate.edu/microscopy/

The Laboratory of Analytical Electron Microscopy

Electron Microscopy Principal signals used in SEM Secondary Electrons (SE): Topographical Information They are caused by an incident electron passing "near" an atom in the specimen, imparting some of its energy to a lower energy electron (usually in the K-shell). This causes a slight energy loss and path change in the incident electron and the ionization of the electron in the specimen atom. This ionized electron then leaves the atom with a very small kinetic energy (5eV) and is then termed a "secondary electron". Due to their low energy, only secondary electrons that are very near the surface (