laboratory of analytical electron microscopynanocenter.eng.wayne.edu/nano workshop...

$: Laboratory of Analytical Electron Microscopynanocenter.eng.wayne.edu/Nano workshop Presentations/EM...Double tilt sample holder: Diffraction analysis Double tilt heating stage and$
The Laboratory of Analytical Electron MicroscopyThe Laboratory of Analytical Electron Microscopy

Central (Central (LumigenLumigen) Instrument Facility) Instrument Facility

Laboratory of Laboratory of Analytical Electron MicroscopAnalytical Electron Microscopyy

Stephanie L. Brock, ProfessorDepartment of ChemistryWayne State University

Zhi “Mike” Mei, Ph.D.Laboratory of Analytical Electron Microscopy

Lumigen Instrument Facility & Department of ChemistryWayne State University

Tel: 313-577-2604, Email: [email protected]

LumigenLumigen Instrument FacilityInstrument Facility

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

Electron MicroscopyElectron Microscopy

Resolution more important!Not magnification!!!

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


Why use Electron Beam?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 lightμ is the refractive index of the viewing medium, β is the semi-angle of the lens

0.61sin

λδμ β

=

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


d0

M d0


TEM: Transmission electron microscopeSEM: Scanning electron microscopeSTEM: Scanning transmission electron microscopeEDX: Energy dispersive X-ray SpectrometerEBSD: Electron Backscattering diffractionEELS: Electron energy-loss spectrum

TEM imageTEM imageSTEM imageSTEM image

SEMSEMEBSDEBSD

DiffractionDiffraction

EDXEDX

Contribute to Contribute to background of background of EDXEDX

EELS EELS

Why use an Electron Beam?Why use an Electron Beam?

CharacteristicX-rays

Ato

mic

ene

rgy

leve

ls Vacuum

EL3EL2EL1

EK KL1

L2

L3

Energy-loss electron

High EnergyElectron beam

Nucleus

From JEOL-2200FS Brochure



Analytical Electron Microscopy (TEM/SEM) Lab at WSUFunded 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 cameraEnergy Dispersive X-Ray Spectrum (EDS) detector: Local chemical analysisDouble tilt sample holder: Diffraction analysisDouble tilt heating stage and cooling stage with precisely controllers: dynamic microstructure evolution Scanning Electron Microscope (SEM)JEOL 7600F and 6510LVEnergy dispersive X-ray Spectrum (EDS) detector: Local chemical analysisBackscattered electron detector (BSD): Composition distribution, electron channeling contrast imageElectron backscattered diffraction detector (EBSD/Orientation Imaging Microscopy (OIM)): Orientation of grains, Texture analysis, Orientation Density Function (ODF)Computer Simulation and Analysis on TEM ImagesDiffraction patterns indexing and simulationsHigh resolution image simulationCrystal models for interfaceSample PreparationsCapable of preparations for Metals & Alloys, Ceramics, Semiconductors, powders, nanoparticlesFacilities include Gatan Ion-Beam Milling (Pips), Dimpler Grinder, Grinder/Polisher, Low Speed Diamond saw, Ultrasonic Cutter, Twin-Jet Electron Polisher, Gold Evaporator



Electron Gun

Condenser lens system

Objective lens system

Intermediate and Projector lens system

Camera Chamber

LumigenLumigen Instrument Facility JEOL 2010 TEMInstrument Facility JEOL 2010 TEM


Powders (including nanoPowders (including nano--particles)particles)Use dropper to put the solution directly onto a carbon-coated copper grid

TEM Sample Preparation MethodsTEM Sample Preparation Methods

Metal and Alloys: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:Semiconductors and Ceramics:• Make discs 3mm in diameter• Mechanically grind and polish down to 50-80μm• Ion-beam mill



For the electron beam to pass through the sample, very thin specFor the electron beam to pass through the sample, very thin specimens imens are needed (< 500 nm)are needed (< 500 nm)

CrossCross--section method: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.

A substrate coated with one layer of thin film

Substrate

Thin film

Substrate

Thin film(Red color) A layer of glue

Two pieces of substrate with thin film glued face to face using M-Bond 610 adhesive

A ~3mm disk obtained with an ultrasonic cutter

Grind the surface of the disk and glue it onto a copper ring to support the sample Dimple grinder Ion-beam milling

TEM Sample Preparation MethodsTEM Sample Preparation MethodsElectron MicroscopyElectron Microscopy


Bright Field / Dark Field Imaging



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

http://www.microscopy.ethz.ch

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

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.

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


Bright Field / Dark Field Imaging


http://www.microscopy.ethz.ch

Electron DiffractionElectron Diffraction

Electron Diffraction carries structure information of crystals:Show symmetry of crystalsMeasure the distance of crystal plane, the angle between different direction/planeIdentify different phases in materialsDetermine 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 crystalsMeasure local lattice parameter change/local strain in materialsMeasure specimen thickness

Provides a “road map” in reciprocal space (Kikuchi lines)



Electron DiffractionElectron DiffractionCondenser Lens

Condenser Lens Aperture

Condenser Mini-Lens

Objective Lens

Specimen

Back Focal Plan

Field Limiting Aperture

(a) (b)

A convergent-beam electron diffraction An ordinary diffraction pattern

The beam convergent on the surface of the sample

A parallel beam illuminates the surface of the sample

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.



Convergent Beam Electron DiffractionConvergent Beam Electron Diffraction

John Mansfield, Lecture about TEM, EMAL lab at University of Michigan (Ann Arbor)

Lattice distortion by the changes in chemical composition

4-fold symmetry (square)

2-fold symmetry(rectangular)

[001] CBED of Si and SiGe crystals



(rounded)

Electron Diffraction & High Resolution ImagingElectron 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



Fe3O4 nanoparticles on carbon film

Imaging Imaging ““realreal”” samples at WSUsamples at WSU



Fe3O4 nanoparticles on carbon film

High Resolution ImagingHigh Resolution Imaging



Lattice fringes due to diffraction off lattice planes within crystalline samples

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. 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. 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. 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.



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

Measured d-spacing

(Å)

Ni11As8 Ni5As2 NiAs

d-spacing (Å)

(h k l) d-spacing (Å)

(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)

20 30 40 50 600

50

100

150

200

250

Inte

nsity

(arb

itrar

y un

its)

2θ, Degrees

____ Ni11As8

____ Ni5As2

____ NiAs

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 situcarbothermal 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 d-spacing 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 NanodotArrays: Nanopattern Design through Reductive Annealing” Chemical Communications, 2006, 1121-1123.



In situ temperature control & SAEDThe heating (cooling) stage enables physical changes to be monitored

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 (ribbons dots) that could be monitored.

The electron beam can play a role: The electron beam can result in local heating as well chemical changes in sensitive samples.

You are operating under high vacuum: volatile materials can sublime upon heating or from beam damage.

Electron diffraction enables structural changes to be monitoredSAED 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)

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.



Size Distributions and Chemical Analysis via EDS

20 nm

5 nm

(a)10.2 ± 0.9 nm

20 nm

(b) 26.8 ± 1.9 nm

0 200 400 600 800 10000

4000

8000

12000

16000Ni (Κα)

P (Κα)

P: Ni = 0.37

C

oun

ts

eV

(b)

22 24 26 28 30 32 340

20

40

6026.8 ± 1.9 nm

Cou

nts

Size-Diameter (nm)

(a)

TEM images of (a) Ni2P nanoparticles with solid morphology (inset: HRTEM indicating the high degree of crystallinity and the absence of voids) and (b) Ni12P5nanoparticles with hollow morphology.

0 200 400 600 800 10000

2500

5000

7500

10000 P:Ni = 0.71

P (Kα)Ni (Kα)

eV

Cou

nts

(b)

7 8 9 10 11 12 13 140

20

40

60

80

100 10.2 ± 0.9 nm

Cou

nts

Size-Diameter (nm)

(a)

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.



Size Distributions and EDSStatistics on size distributions for nanomaterials can be achieved by measuring a suitable number.

Software enables rapid identification of particle sizes.

Depending on the degree of polydispersity, more or fewer measurements must be made to get a representative size and standard deviation.

Data should be acquired from multiple random places on the TEM grid to ensure it is representative of the sample dispersity.

Energy dispersive spectroscopy can give semi-quantitative chemical analysis for elements heavier than Li

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).

Semi-quantitative measurement relies on instrument factors (no calibration standards); need good signal and good peak and background fits. Watch out for overlapping lines.





SEM’s main componentsElectron column To accelerates and focuses a beam of electrons onto the sample surfaceSample chamberThe place where the electron beam interacts with the sampleDetectorsTo monitor a variety of signals resulting from the beam-sample interactionsViewing systemTo construct an image from the signal

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

Scanning Electron Microscopy (SEM)

Electron Beam's Path through the Column



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


Electron MicroscopyElectron MicroscopyPrincipal signals used in SEM

Secondary Electrons (SE): Topographical InformationThey 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 (<10nm) can exit the sample and be examined. As a result, contrast in a secondary electron image comes primarily from sample topography. Backscattered Electrons (BSE): Atomic Number and Topographic InformationThese are primarily beam electrons that have been scattered back out of the sample by elastic collisions with the nuclei of sample atoms. Their higher energy results in a larger specific volume of interaction and degrades the resolution of backscattered electron images. Contrast in backscattered images comes primarily from point to point differences in the average atomic number of the sample. High atomic number nuclei backscatter more electrons and create bright areas in the image. The origin of EBSD (Electron Backscattered Diffraction) patterns is also related to the interaction between the backscattered electron beam and the primary electron beam, with a highly tilted specimen illuminated with a stationary electron beam. Characteristic X-rays: Through Thickness Composition InformationThey are caused by the de-energization of the specimen atom after a secondary electron is produced. Since a lower (usually K-shell) electron was emitted from the atom during the secondary electron process an inner (lower energy) shell now has a vacancy. A higher energy electron can "fall" into the lower energy shell, filling the vacancy. As the electron "falls" it emits energy, usually X-rays, to balance the total energy of the atom. X-rays emitted from the atom will have a characteristic energy which is unique to the element from which it originated. These signals are collected and sorted according to energy to yield composition.

High vacuum conditions are required in the electron gas and High vacuum conditions are required in the electron gas and throughout the column, where gas molecules can scatter throughout the column, where gas molecules can scatter electrons and degrade the beam. Instead of using a single electrons and degrade the beam. Instead of using a single pressure limiting aperture in conventional SEM, ESEM uses pressure limiting aperture in conventional SEM, ESEM uses multiple Pressure Limiting Aperture (multiple Pressure Limiting Aperture (PLAPLA’’ss) to separate the ) to separate the sample chamber from the column. The column is still high sample chamber from the column. The column is still high vacuum, but the chamber may sustain pressures as high as vacuum, but the chamber may sustain pressures as high as 50 50 TorrTorr. . The fact that it is not strictly necessary to use conventional The fact that it is not strictly necessary to use conventional methods in the preparation of biological samples methods in the preparation of biological samples (dehydration, critical point, conductive coatings) has allowed (dehydration, critical point, conductive coatings) has allowed improved, shorter time scales and lower costs in imaging improved, shorter time scales and lower costs in imaging biomaterials. biomaterials.

Environmental SEM (ESEM) Environmental SEM (ESEM)



SEM Instruments in the LIF



JSM – 6510LV SEMAccelerating voltage: 500V – 30 kVResolution: 3.0 nm at 30 kVMagnification: 5 to 300,000xEquipped with EDS and BSEWayne State University-LIF

This Tungsten filament SEM is configured to operate as both a high vacuum & low vacuum system. The low vacuum SEM mode enables one to observe and analyze non-conductive, wet, non-high vacuum compatible samples. Operating pressure is 1Pa to 270 Pa.



JSM – 7600F Thermal FEG SEMAccelerating voltage: 100V – 30 kVResolution: 0.8 nm at 30 kVMagnification: 25 to 1,000,000xSample stage: 5 axis motor driveWayne State University-LIF

Functions:Secondary electron (SE) detectorEDS detectorBSE detectorEBSD DetectorE-Beam LithographySTEM DetectorCRYOTRANSFER SYSTEM

SEM Instruments in the LIF

Two basic types of Two basic types of SEM'sSEM's: : • Regular SEM which requires a conductive sample. • Environmental SEM (ESEM) which can examine a non-conductive sample.

SEM Sample Preparation SEM Sample Preparation

Three requirements for preparing samples for a Three requirements for preparing samples for a regular SEM:regular SEM:

• Remove all water, solvents, or other materials that could vaporize while in the vacuum.

• Firmly mount all the samples.• Non-metallic samples, such as bugs, plants, fingernails, and ceramics,

should be coated so they are electrically conductive (an Au coater is available in the LIF). Metallic samples can be placed directly into the SEM.





The ALTO 2500 Cryo transfer will allow preparation of biological and other hydrated samples for imaging in the FE SEM. Liquids, suspensions, emulsions, polymers and other beam- or vacuum-sensitive specimens may also be easily prepared and examined.

Butterfly wing

Mammalian small intestine

http://www.gatan.com/products/sem_products/products/alto_2500.php

A comparison between secondary electron image A comparison between secondary electron image (SEI) and back(SEI) and back--scattered electron image (BSEI)scattered electron image (BSEI)



BSEI

SEI

A comparison between secondary electron image A comparison between secondary electron image (SEI) and back(SEI) and back--scattered electron image (BSEI)scattered electron image (BSEI)



By BSE detector, phases with different chemical composition show different contrast, confirmed by EDS.

Local Composition MeasurementLocal Composition Measurement

From JEOL-2010 Brochure



SEMSEM--EBSD/OIMEBSD/OIM

EBSD Detector

Pole piece

Sample



EBSD Detector

Pole piece

Sample

Lattice Planes

Diffracted beam


Ni3V2O8. Space group: Cmca. Lattice parameters are a=0.5936 nm; b= 1.142nm; and c= 0.824nm. Deposited on silicon wafer.






15 x 15 nm x 5nm deep pixel for evaluation of crystal orientation

TEM & SEM Billable Resource Price Structure (by tier)TEM & SEM Billable Resource Price Structure (by tier)

Billable ResourceBillable Resource Tier 1(wsu)Tier 1(wsu) Tier 2(edu)Tier 2(edu) Tier3(ind) Tier3(ind) TEMTEM 3535 4545 125 125

Tungsten SEMTungsten SEM 2424 3030 75 75 FE SEMFE SEM 3535 4545 125 125

Z. Mei (Mike)Z. Mei (Mike) 4545 6565 100 100


Lumigen Instrument Facility: Laboratory of Analytical Electron Microscopy

Tiers are billed on per hr basisTiers are billed on per hr basisTier 1Tier 1 ((wsuwsu) ) -- Wayne State UsersWayne State UsersTier 2Tier 2 ((eduedu) ) -- Other Educational Institutions (non WSU)Other Educational Institutions (non WSU)Tier 3Tier 3 ((indind) ) -- Industry Industry


laboratory of analytical electron microscopynanocenter.eng.wayne.edu/nano workshop...

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