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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!