E-beam Characterization:

a primer Part 1

Matthew J Kramer225 Wilhelm

mjkramer@ameslab.gov

October 30,2009

Why and Which Method•

E-beam characterization–

IT IS

the only reliable means for microstructural

and microchemical

analysis!•

E-beam Instruments–

Surface•

SEI –

From mm to nm, surface information only

•

BSE–

Surface Z distribution–

Topography

–

Transmission•

Diffraction contrast–

Microns to atoms•

Crystallography•

Both types can utilize the various spectroscopes

Forest or the Leaves

What do you need to know?•

Surface scanning–

Loose powders to polished surfaces

•

Large depth of field

–

Morphology will effect spectroscopy

•

Transmission Microscopy–

Region of interest needs to be electron transparent

•

~10 –

100 nm, depending on Z

•

How you thin can matter–

Significantly higher resolution

•

Very different imaging contrast used

The SEM•

E beam is accelerated by a large voltage

•

Lens forms a fine probe

•

Rastered

across the sample–

SEI

–

BSE

Imaging•

Secondary Electrons–

Very near surface

•

Backscattered Electrons–

Strongly Z dependent

–

Interactions at a depth 0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70 80 90

Z

e(BS

)/e(in

cide

nt)

Co-Sm-Fe alloy

CrystallographyBSE can be induced to channel along

crystallographic planesElectron Backscattered Diffraction (EBSD)

Si dendrites in Al matrix10 mm10 mm

1 mm(a)

e interactions–

Auger electrons

•

Two views of the Auger process. (a) illustrates sequentially the steps involved in Auger deexcitation. An incident electron creates a core hole in the 1s level. An electron from the 2s level fills in the 1s hole and the transition energy is imparted to a 2p electron which is emitted. The final atomic state thus has two holes, one in the 2s orbital and the other in the 2p orbital. (b) illustrates the same process using spectroscopic notation, KL1

L2,3

.

e interactions•

C and higher Z

•

E-beam energy must exceed the binding energy

Auger e’s

vs

X-rays•

Counter yield

•

Auger e’s

low energy–

Require a high vacuum

–

Very near surface

0.01 x 0.01 x 0.002 μ(10 x 10 x 2 nm )200 x 200 μ

Sample being analyzed

1 μ3

XPS AES

EDS

Depth: 0.002 -

0.01 μ (2-10 nm) 5-20 atom layers

NOTE: Scaling is only approximate

Detecting and Quantifying X-rays•

Solid State detectors–

Energy Dispersive Spectroscopy (EDS)

Detecting and Quantifying X-rays•

Wavelength Dispersive Spectroscopy–

Much higher energy resolution

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

2.15 2.20 2.25 2.30 2.35 2.40 2.45 2.50E [keV]

coun

ts (a

rbitr

ary

units

)

S (WDS)Mo (WDS)S (EDS)

S eparatio no f M o Lαfrom S Kα14.3 eV

E D S en erg y reso lu tion

120eV FW H M

WDS energyresolution

3.45eV FWHM

0

25

50

75

100

0.6 0.7 0.8 0.9 1.0

distance (µm)

at %

AlGe

Quantification and Spatial Resolution

0

25

50

75

100

0 1 2

distance (µm)

at %

AlGe

1 µm

•

Average Z and E dependent

•

Requires stable e-beam source

•

Requires standardization

•

Requires known geometry–

i.e., flat, parallel surface

Al-K Ge-L

EDSAugerGe

Al20

15

10

5

KV

JEOL 5910lv •

Resolution (SEI) –

3.0 nm @30kv, 8 mmwd

•

Magnification –

18-300,000 x•

Probe Current–

1pa

1 microamp•

Image modes:–

SEI–

3 Backscatter•

Topo•

Compo•

Shadow•

EDS–

Line scans–

mapping

JEOL 5910lv•

Poor Vacuum mode:–

Resolution 4.5 nm @30kv, 5 mmwd–

Backscattered mode only in the poor vac

mode–

Adjustable chamber pressure 10-270 Pa

•

Tungsten filament with automatic adjustments

Beam Blanked in “Freeze”

mode

•

Alignments and conditions automatically and individually saved for each user

•

Specimen Chamber and Stage:–

5 axes (X 125mm range, Y 100mm range, Z 43mm range, T 10 to 90 range, R 360 endless)–

Maximum specimen size 7”

with full coverage–

Specimen position graphical indicator as well as chamber camera–

Absorbed current ( Specimen current ) measured

•

Image memory selectable to 1,280 x 960 x 8 bits

Can frame average

up to 255 frames

Image storage formats BMP, TIFF or JPEG.

–

We recommend BMP with merged text.

JEOL JXA-8200 Superprobe combined WDS/EDS

•

5 wavelength-dispersive spectrometers, 10 crystals

–

B through U–

four 140 mm Rowland circle

–

one 100mm Rowland circle

•

EDS, 10 mm2

Si(Li) crystal, Be window

–

Na through U•

Software –

quantitative analysis –

compositional mapping –

phase analysis–

integrated WDS/EDS operation.

Crystal K lines L lines

LIF (140mm) Ca – Rb Sn – U

LIF (100mm) Ca – Ge Sb – Hg

PET (140mm) Si – Fe Rb – Tb

PET (100mm) Si – Ti Rb – Ba

TAP O – P Cr – Nb

LDE1 (2d=60Å) C, N, O, F •

LDE2 (2d=90Å) B, C, N, O •

Overall Capabilities•

Electron Optical and Vacuum Systems–

W or LaB6 electron source–

Acceleration voltage 0.2-30kV–

Useable beam current 10-12 to 10-5A–

Pneumatically driven Faraday cup for beam current measurement (serves as beam blanking)–

Turbomolecular

vacuum pump–

All functions controlled through central computer system•

Imaging Capabilities–

Secondary electron detector–

Backscattered electron detector with composition/topography mode–

10 user selectable scan speeds–

Magnification 40x to 300,000x–

Optimal imaging resolution 6nm–

Dedicated 18 inch flat panel display for electronic images–

Optical microscope for reflected light observation of sample–

Optical system coaxial with electron beam–

High resolution color video mini camera–

Automatic optical focus device

Sample Preparation•

Maximum sample size–

150 x 150 x 50mm–

4 x 1in. diameter samples

•

Stage travel –

x = 100mm, y = 90mm, z = 3mm

•

Stage tracking–

< ±1μm

•

Requires flat, well polished surface

•

Standardization–

Elemental or line compounds

Element Mapping

JAMP7830F Auger Microprobe

•

Schottky

field emission gun•

0.5 to 25kV beam voltage•

10-11

to 1x10-7

A current•

Minimum probe size: –

4 nm in SEM mode, –

10 nm in Auger mode•

Chamber pressure–

5 x 10-8

Pa (3 x 10-10

torr)•

Stage movement: –

X,Y + -

10mm, Z + -

6mm•

Normal sample size: –

12mm dia. 5mm thick

JEOL 7830F AES Advantages & Capabilities ( HSA vs CMA, and FE vs LaB6 )

Key Components

that produce

High Energy

Resolution and Reliable

KE Values

JEOL 7830F Schematic View

Elemental Mapping

•

Nb-Cu metal-

metal composit

e

High Energy Resolution AES Chemical State Map:

SEM

Cu2 OCuo

Red = Cuo

Green = Cu2 O

•

Cuo

vs

Cu2

O (Δ E = 0.9 eV)

Chemical Shifts

O

CrOx

Cro

CrOx

Cro

This sample was ion etched to remove all

contamination and left in UHV at 3 x 10-10 torr

14 hr.

This reveals the reactive nature of “clean”

surfaces.

O hr -

start

14 hr -

end Gas Capture Study

•

Reactive Nature of the Clean Surface of a Co-Ni-Cr Alloy

Limitations of Auger Electron Spectroscopy•

Cannot detect hydrogen or helium

•

Destructive depth profiles.•

Samples must be small and compatible with high vacuum.

•

Elemental quantization depends on instrumental, chemical, and sample related factors.

•

Chemical information is depended on quantity and element

•

Most sample surfaces are contaminated—must be cleaned by ion etching

Sample Preparation•

Best if sample is parallel polished

•

Best sample size:–

< 10 mm dia.

–

< 3 mm thick•

Please no potting of sample in plastic matrix

•

For very small samples consult with us first•

Samples that are used in some type of process, need to be in proper form before processing

•

Remember ----

do not touch the samples with your hands!

Conclusions•

1st

determine what you need to know–

i.e., grain size or just average chemistry–

How precise do your measurements need to be?•

Will dictate sample preparation, obtaining standards etc.•

WDS vs

EDS or is BSE good enough–

What elements are possibly present, including impurities?•

Are there overlaps? WDS vs

EDS–

Chemistry of the surface or of the bulk?•

XPS and SAM vs

SEM•

Decide which instrument(s) will be needed–

Discus techniques and sample preparation first with staff•

Not with your classmates (unless they are an expert)!•

Keep an open mind–

It is not unusual that your preconceived notions are wrong–

But artifacts are possible•

How does grinding and polishing affect the composition and possibly microsctucture•

Is your sample sensitive to air, moisture etc.•

How do these results mesh with other bulk measurements?–

Microscopy is a powerful tool, but one of many tools, it should be complimented with other techniques when appropriate.

•

XRD, SQUID etc.