Bruker AXS Microanalysis Revolutionizing EDS analysis on TEMs … · 2012-11-29 · Bruker AXS...

Bruker AXS Microanalysis

Revolutionizing EDS analysis on TEMs using silicon drift detectors

Panelists

Dr. Holm Kirmse, Senior Research Associate, Institute of Physics, Chair of Crystallography, Humboldt University, Berlin, Germany

Dr. Meiken Falke, Global Product Manager EDS / TEM, Bruker AXS Microanalysis GmbH, Berlin

Dr. Ralf Terborg, Methodology Specialist, Bruker AXS Microanalysis GmbH, Berlin

Topics

EDS with SDD for S/TEM• Introduction• Spectroscopic properties• Acquiring spectra, line scans and maps

Quantitative analysis of TEM spectra• Element identification• Background removal• Peak deconvolution• Quantification

TEM based EDX analysis of nano-structured materials using the XFlash® SD Detector• Characteristics of EDS analysis on TEMs• Application examples

EDS with SDD for S/TEM

Dr. Meiken Falke

SDD for EDS QUANTAX system

XFlash®5000Electronics

ESPRIT Software

PC

XFlash®5030 T

Available resolutions (Mn Kα)

Standard: 133 eVPremium: 129 eVPremium plus: 127 eV

Mn Kα

127 eVF Kα

64 eV

C Kα

54 eV

Detection of boron and beryllium

X-ray detectors for TEM / STEM

In S/TEM EDS gives element ID - complementary to EELS,

which provides information about the bonding environment as well.

Certain element combinations are unfortunate for EELS

(magnetic materials: Ta, Pt, Co; catalysts: Pt, Ru, Pa; doped

BaTiO3); EELS artefacts

If many elements at once have to be found

(biological, medical, environmental e.g.

electron dense material in the macro-

phages: Fe, Cd, Pb, Ni … ?).

Good fast overview of sample composition.

SDDs have better light element performance than Si(Li).

Why EDS for TEM?

Round 30mm2 SDD

drift field for the generated charge:

Strüder

L., et al. Microsc. Microanal.

4 (1999), 622–631.

Thickness of crystal

Si(Li): 3.5 mmXFlash: 0.45 mm

Quantum Efficiency of SDD on TEM

Output count rate vs Input count rate (OCR vs. ICR)

„Dead time“ (signal loss) of Bruker Hybrid electronics is significantly lower than that of the Si(Li) electronics > higher count through put

Quantum Efficiency of SDD on TEM

Output count rate vs Input count rate (OCR vs. ICR)

„Dead time“ (signal loss) of Bruker Hybrid electronics is significantly lower than that of the Si(Li) electronics > higher count through put

Quantum Efficiency of SDD on TEM

SDD: collection of lines higher than 20 kV is possibleSDD collection efficiency is partly compensated by better ICR-OCR ratioHeavier elements can be distinguished by L, M, N lines too

Thickness of crystal

Si(Li): 3.5 mmXFlash: 0.45 mm

Quantum Efficiency of SDD on TEM

Solid Angle for X-ray collection:

wikipedia

Ω = Asurf

/ r2

[sr]

ΩEDS-S/TEM

~ 0.1 –

0.3 sr

Increase solid angle through:

Area (small: less cooling, better energy resolution …)Distance (pole piece geometry)Multiple detectors

Courtesy

of: L. Allard, OakridgeNational Lab (ORNL)M&M 2009

Bruker SDD on JEOL 2200FS, Probe - CS -corrected

Bruker SDD on JEOL 2200FS, Probe - CS -corrected

Left side: Ronchigrams of carbon film with the SDD Out and Off (top)) vs In and On (bottom). No detectable change in the apparent aberration-corrected alignment was noted. Right side: HAADF images of SrTiO3 <100> normal, showing no detectable change in the image with the detector Out and Off vs In and On, respectively.

By

courtesy

of: L. Allard, ORNL,M&M 2009

RonchigramC -

film

HAADFSrTiO3

out/off:

in/on:

XFlash® 5030 T, Ag particles on C-film, Cu grid, CS -corrected STEM instrument

Courtesy: L. Allard (JEOL 2200FS)

Example of Light-Element Mapping

STEM ADF image of interface in an  Al‐B‐C ceramic, showing a thin Al‐

rich phase in high contrast between  a B4 C grain and an AlBxCy

grain; 

b)‐d) element maps as indicated.Scale bar: 500nm

a b

c dBy

courtesy

of:

L. Allard, ORNL,M&M 2009

This research at the Oak Ridge National Laboratory's High Temperature Materials Laboratory was sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.

XFlash® for TEM: Tests at low magnification (Zeiss Libra TEM)

Effect at low magnification:

Electron beam hits copper grid (or thicker sample parts) thus generating excessive X-ray counts (high count rates)

Si(Li): 15 min recovery time when exposed to high count rates

SDD: withstands sudden change of count rates

Carbon Nano Tubes (CNT)

CNT with Ni-catalyst, raw data

EDS with SDD for TEM with nm Resolution Example: Quantum Well Structures

200kV, Jeol FS2200 FEG TEM/STEMXFlash 5030, solid angle 0.12sr512 x 512, dwell/pixel 0.512 μsMeasuring time [s] 182.93 (3 min)Life time [s] 173,13Take off angle 22.5°Spectrum 2.93kcpsProbe current: 210 pA

Sample: court. of FBH and Dr. Mogilatenko, Prof. Neumann,HU Berlin: Quantum well for laser diodes

AlGaAs5nm GaAsP7nm InGaAs5nm GaAsP

AlGaAs

EDS with SDD for TEM with nm-Resolution

Sample: Quantum well for laser diodes – element map244 by 342 pixel map was acquired in 6 minutes using 4 ms dwell time per pixel

Quantification:8 by 8 pixel binning,theoretical CL-factors

elemental profile: adding up 8x8 pixel dataperpendicular to layersas shown

AlGaAs5nm GaAsP7nm InGaAs5nm GaAsP

AlGaAs

Sample: Quantum well for laser diodes – element map244 by 342 pixel map was acquired in 6 minutes using 4 ms dwell time per pixel

EDS with SDD for TEM with nm-Resolution

Excellent energy resolution: 133 eV, 129, eV, 127 eV

Extreme count rate capabilities, immune to overload conditions

Minimum signal loss (lowest dead time in the market)

Optimized for large solid angle (positioning / multiple detectors)

No LN2 necessary, no heavy weight on column, no bubbling, no vibration, no detector icing / conditioning

Low temperature gradient due to -30° C Peltier cooling,

No disturbance of electron optics

Tailor-made system (special collimators to block spurious X-rays)

Hardware

Advantages of Bruker SDD in S/TEM

Transparent scientific tools for mapping and quantificationin TEM and STEM

Complete on- and off-line analysis provided

Quantification using theoretical and experimental Cliff-Lorimer-factors

Most modern database to separate N- and M-lines in the low energy region

Fast system calibration

Software

Advantages of Bruker SDD in S/TEM

Successful routine installation of XFlash® SDDsystems on conventional and aberrationcorrected S/TEMs

Reliable and stable measurement conditions

Hardware and software provide powerful and transparent tool for on-line and off-line EDS analysis

More than a dozen satisfied customers, several ofthem with CS-corrected instruments

Summary

EDS on S/TEM with XFlash® 5030 T Detector

Quantitative Analysis with SDDs on TEMs using Esprit

Ralf Terborg

Outline

Quantitative Analysis can be divided into:

Identification

Background calculation

Deconvolution

Quantification

Quantification steps

Ident BG

Deconv Quant

Quantification steps

Quantitative analysis steps

1. Identification: comparison between the peaks found in the spectrum and the atomic data (line energies and intensities)

2. Background: Calculation of the physical Bremsstrahlungbackground based on the assumed sample composition or mathematical filter

3. Deconvolution: the BG corrected peak intensities, especially at line overlaps, are attributed to the element lines

4. Quantification: element concentrations are calculated from deconvolved line intensities: Cliff-Lorimer-Quantification

Quantitative analysis steps

1. Identification: comparison between the peaks foundin the spectrum and the atomic data (line energies and intensities)

2. Background: Calculation of the physical Bremsstrahlung background based on the assumed sample composition ormathematical filter

3. Deconvolution: the BG corrected peak intensities, especiallyat line overlaps, are attributed to the element lines

4. Quantification: element concentrations are calculated from deconvolved line intensities: Cliff-Lorimer-Quantification

Identification

Automatic identification procedures consist of two parts:

1) peak search algorithm

2) comparison of found peaks with atomic data

Even with sophisticated peak search good and complete line energies and intensities are necessary

Because of high line density and likely overlaps accurate low energy line data (L,M) are important

Esprit atomic database was improved over the last years with focus on the low energy range:

0 – 2 keV : 100 additional lines compared to standard databases2 – 4 keV : 150 additional lines in total4 – 6 keV : 50 additional lines in total

Ident

Comparison with new and extended atomic database

Steel sample was supposed to contain BEtching with HCl →

peak at ~183eV

B-Kα

(183 eV)

Cl-Ll (182 eV),Cl-Lη

(184 eV)

Ident

Misidentification of L lines: Cl-Ll could be identified as B-Kα

Quantitative analysis steps

1. Identification: comparison between the peaks found in thespectrum and the atomic data (line energies and intensities)

2. Background: Calculation of the physicalbremsstrahlung background based on the assumedsample composition or mathematical filter

3. Deconvolution: the BG corrected peak intensities, especiallyat line overlaps, are attributed to the element lines

4. Quantification: element concentrations are calculated from deconvolved line intensities: Cliff-Lorimer-Quantification

Physical bremsstrahlung calculation for TEM and thin films

Shape different to SEM Bremsstrahlung

Maximum at lower energy for thin films

No significant absorption for thin films

BG

BaTiO3 :– TEM– SEM

Physical bremsstrahlung calculation for TEM and thin films

Physical TEM background calculationEfficiency according to detector design taken into accountAdditional fit regions possibleAlternatively: mathematical filter

BG

BaTiO3 :– TEM– SEM

Quantitative analysis steps

1. Identification: comparison between the peaks found in thespectrum and the atomic data (line energies and intensities)

2. Background: Calculation of the physical Bremsstrahlung background based on the assumed sample composition

3. Deconvolution: the BG corrected peak intensities, especially at line overlaps, are attributed to the elementlines

4. Quantification: element concentrations are calculated from deconvolved line intensities: Cliff-Lorimer-Quantification

Deconvolution

Deconvolution not necessary without line overlap

Accuracy of deconvolution results will improve with smaller line overlap → detector resolution important

Accuracy will improve with peak shape (Gaussian) →detector peak shape important

Bayes deconvolution: based on the Bayes theorem of inverse probabilities (widely used in computer science, e.g. Google or spam filters)

Least square: minimising χ² value

Deconv

Deconvolution example

Evaluation of MoS2 spectrum:Mo-Lα: 2.293keVS-Kα: 2.307keV→ large overlap, deconvolution complicated

Deconvolution can only be done by optimizing the whole line series

Optimize Mo-Lα+Mo-Lβ and S-Kα+S-Kβ

Deconv

MoS2 :– S– Mo– S+Mo – Exp

Quantitative analysis steps

1. Identification: comparison between the peaks found in the spectrum and the atomic data (line energies and intensities)

2. Background: Calculation of the physical Bremsstrahlungbackground based on the assumed sample composition

3. Deconvolution: the BG corrected peak intensities, especially at line overlaps, are attributed to the element lines

4. Quantification: element concentrations are calculated from deconvolved line intensities: Cliff-Lorimer-Quantification

Quantification for TEM + thin films: Cliff-Lorimer

CL Quant:Theoretical factorsExperimental factorsManual (CL factors editable)Can be used when absorption insignificant: high E0 and/or thin films

Quant

LaB6 spectrum was used as standard: B-K and La-L (~5 keV) line families used for determination of B CL-factorLaB6 was then quantified using B-K and La-K lineEfficiency of the La-K line at 34 keV has to be taken into account

Cliff-Lorimer quantification: LaB6

Sample: LaB6

standard

on holey

C-film

Theoretical values: 14.29% / 85.71% SDD efficiency is calculated / compensated by the quantification method for La-K (34 keV)

Sample: LaB6

standard

on holey

C-film

Cliff-Lorimer quantification using high energy lines

Summary

Quantification of S/TEM spectra in Esprit can be divided in four steps

For each step an intermediate result can be shown User can interact, make optimizations

Identification: benefits from improved atomic database

Background: Calculation of the physical TEM-Bremsstrahlungbackground taking detector parameters into account

Deconvolution: overlapping lines will be devonvolved and attributed to the element lines using Bayes deconvolution or least square fit

Analysis using Cliff-Lorimer quantification with theoretical or experimentally determined CL factors

Efficiency of detector is taken into account

TEM based EDX analysis of nanostructured materials

using the X-Flash® SD detector

H. Kirmse, A. Mogilatenko, I. Häusler, W. Neumann

Humboldt Universität

zu

Berlin, Institut

für

Physik,Newtonstraße

15, 12489 Berlin, Germany

Revolutionizing EDS analysis on TEMs using silicon drift detectorsWebinar: September 16th, 2009

Humboldt University of Berlin

Institute of PhysicsChair of Crystallography

Newtonstrasse

15D-12489 BerlinGermany

Bruker AXS

TEM instrumentation: JEOL JEM-2200FS

XFlash® Detector Field-emission gunIn-column energy filter

Energy dispersive X-ray detector (EDXS)

High angle annular dark- field (HAADF) detector

Electron biprism

Accelerating voltage:

200 kVEnergy resolution:

0.7 eV

Point resolution: 0.19 nmProbe size STEM:

0.14 nm

Humboldt University of Berlin, Institute of Physics, Chair of Crystallography

●

Small electron probe size for the EDXS analysis of nanostructures:

•

0.2 -

1.5 nm

(JEOL TEM/STEM 2200FS) •

Low EDXS intensity at small probe sizes!

→ Optimum probe size for EDXS: 0.7 nm

●

Thin specimens (20 -

500 nm) •

Low signal intensity → Long acquisition time

●

Specimen drift at high magnifications→ Wait for a proper conditions→ Drift correction software→ High stability of specimen stage

●

Artefacts of specimen preparation●

Projection artefacts

Several characteristics of TEM-based EDXS analysis of nanostructured materials

1. ZnTe / CdTe nanowires

2. AlN / AlGaN short period superlattices

3. III-V-based overgrown structures

Examples

1. ZnTe / CdTe nanowires

2. AlN / AlGaN short period superlattices

3. III-V-based overgrown structures

Examples

ZnTe CdTe

TEM bright-field image

[111]

Polish Academy of Science, Institute of Physics, Warsaw, Poland

Growth of NWs via vapour-liquid-solid mode realized in a molecular beam epitaxy chamber at T = 460°C

Objectives of investigation:→ Sharpness of ZnTe/CdTe interface→ Understanding of NW formation

catalyst

Example 1: ZnTe/CdTe nanowires

ZnTe CdTe

TEM bright-field image

[111]

High-resolution TEM

Polish Academy of Science, Institute of Physics, Warsaw, Poland

ZnTe CdTe

50 nm

catalyst

Example 1: ZnTe/CdTe nanowires

Quantitative high-resolution TEM imaging

70 nm

position

z (nm)

ZnTe

Zn0.4

Cd0.6

Te

GPA: M. Hytch

et al.,Ultramicroscopy

74(1998) 131

Relative displacement of the (111) lattice planes as revealed by geometric phase analysis of an HRTEM image.

50 nm

Example 1: ZnTe/CdTe nanowires

Energy dispersive X-ray spectroscopy

Zn

Au

Te

STEM dark-field

image

Cd

Zn Cd Au

Example 1: ZnTe/CdTe nanowires

Elemental mapping

Smeared interface

Energy dispersive X-ray spectroscopy

170 nm

EDXS line scan along the nanowire axis

Example 1: ZnTe/CdTe nanowires

Probe size: 0.7 nm, Spot distance: 3.6 nm

Energy dispersive X-ray spectroscopy

170 nm

EDXS line scan along the nanowire axis

Example 1: ZnTe/CdTe nanowires

Probe size: 0.7 nm, Spot distance: 3.6 nm

Strong intermixing (diffusion, segregation, …?)Smeared interface

CdTe

020 40 60 80

EDX

coun

ts

(a.u

.)

position (nm)

Energy dispersive X-ray spectroscopy

ZnZn

CdCd

ZnTe

Interface region

0

100200

300400

500600

position (nm)

EDXS line scans normal to the nanowire axis

Example 1: ZnTe/CdTe nanowires

Probe size: 0.7 nm, Spot distance: 3.3 nm

Energy dispersive X-ray spectroscopy

Example 1: ZnTe/CdTe nanowires

CdTe

020 40 60 80

EDX

coun

ts

(a.u

.)

position (nm)

ZnZn

CdCd

ZnTe

Interface region

0

100200

300400

500600

position (nm)

EDXS line scans normal to the nanowire axis

Probe size: 0.7 nm, Spot distance: 3.3 nmHomogeneous composition normal to the NW axis

1. ZnTe / CdTe nanowires

2. AlN / AlGaN short period superlattices

3. III-V-based overgrown structures

Examples

UV light

UV-LEDs:UV transparent smooth (Al,Ga)N buffer layers with low dislocation density

Problem:Lattice misfit between AlN

and

(Al,Ga)N

Idea: Stress management by

Short Period SuperLattices

5x3n

m In

AlG

aNM

QW

s

n-contact

2”, c-plane Sapphire

20 nm p-AlGaN

0.7 μm AlN buffer

180 nm p-AlGaN

n-AlGaN

barriers: InAlGaN

p-contact

SPSL

Example 2: AlN/AlGaN-short period superlattices

300 nm

AlGaN

AlN

~15 nm

HAADFposition (nm)

20 40 6010 30 50 70

Intermixing at the interface between AlN and SPSL

30 x 8 nm (Al,Ga)N / 2 nm AlNSPSL

AlN

ADF Quantified EDXS line scan Probe size: 0.7 nm

Spot distance: 0.5 nmCalibrated at AlN

Example 2: AlN/AlGaN-short period SPSL

300 nm

AlGaN

AlNHAADF 2 nm

Intermixing at the interface between AlN and SPSLDetection of 2 nm thin layers

position (nm)20 40 6010 30 50 70

AlN

30 x 8 nm (Al,Ga)N / 2 nm AlNSPSL

ADF Quantified EDXS line scan Probe size: 0.7 nm

Spot distance: 0.5 nmCalibrated at AlN

Example 2: AlN/AlGaN-short period SPSL

1. ZnTe / CdTe nanowires

2. AlN / AlGaN short period superlattices

3. III-V-based overgrown structures

Examples

STEM HAADF: Z-contrast

III: Ga-In-Al V: P-As Question: segregation of P?

AlGaAs

InGaP

GaAs

InGaP

AlGaAs

20 nm

AlGaAs

GaAs3 nm

??

Structure I

Example 3: III-V-based overgrown structures

Ga AsInPAl

Sum spectrum with energy intervals for the EDXS line scan

Example 3: III-V-based overgrown structures

Inte

nsity

(a.u

.)

(Al,Ga)As

(In,Ga)P

GaAs (Al,Ga)As

position (nm)20 40 6010 30 50 70 80 90

Dark region

P enrichmentIn enrichment

Structure I STEM probe size: 0.7 nm, Spot distance: 0.5 nm

As depletion

HAADF

Example 3: III-V-based overgrown structures

Elemental map:probe size 0.7nm

AlGa

III: Ga-In-Al V: P-As

Structure I

GaAs

InGaP

AlGaAs

InGaPHAADF In As

P

Example 3: III-V-based overgrown structures

STEM HAADF image: Z-contrast

Question: segregation of In?

GaAsP

InGaP

AlGaAs

InGaP

3 nm

GaAsP

InGaP

100 nm

III: Ga-In-Al V: P-As

??

Structure II

InGaP

AlGaAs

AlGaAs

Example 3: III-V-based overgrown structures

~4 nm

Elemental map:Probe size 0.7nm

InGaP

AlGaAs

GaAsPInGaP

AlGaAs

As

Ga Al

PIn

III: Ga-In-Al V: P-As

Structure II

HAADFExample 3: III-V-based overgrown structures

STEM HAADF image: Z-contrast

GaAsP

InGaP

AlGaAs

InGaP

3 nm

GaAsP

InGaP

100 nm

III: Ga-In-Al V: P-As

Structure II

InGaP

AlGaAs

AlGaAs

Question: segregation of In?

??

Example 3: III-V-based overgrown structures

Inte

nsity

(a.u

.)

InGaP AlGaAs

Bright region

position (nm)20 40 6010 30 50 70

P depletionIn depletion

As enrichment

Structure II

Ga(In)As(P)

STEM probe size: 0.7 nm, Spot distance: 0.5 nm

HAADF

Example 3: III-V-based overgrown structures

TEM based EDXS analysis with high spatial resolution is possible using the

XFlash® SD Detector !

Analysis of nanometre-sized features like nanowires (1d), quantum wells (2d), and overgrown 3-dimensional structures

High sensitivity and energy resolution for the detection of light elements

Additional information for the interpretation of signals from other detectors as, e.g., the STEM HAADF detector

Summary

Provision of samples:

Nanowires:

T. Wojtowicz (Institute of Physics, Polish Academy of Science, Warsaw, Poland)

Quantum wells and overgrown 3d structures:

M. Weiers, G. Tränkle(Ferdinand-Braun-Institut für Höchstfrequenztechnik, Berlin, Germany)

Bruker AXS for provision of the EDXS detector and continuing support

Acknowledgments

Prof. W. NeumannH. Kirmse

I. Häusler

A. Mogilatenko

AG Kristallographie, HU Berlin

Thank you for your attention!