Download Titan™ G2 with ChemiSTEM™ Technology A revolution in atomic

Application Note
Titan™ G2 with ChemiSTEM™ Technology
A revolution in atomic analytics
Application Note Atomic EDX
For many years now, analytical S/TEM systems (scanning/
transmission electron microscopes) have combined information
from high-resolution imaging with elemental composition maps
obtained from either energy dispersive X-ray spectroscopy (EDX)
or by electron energy loss spectroscopy (EELS), but only with
limited resolution in chemical mapping well above the atomic
length scale. These boundaries of performance in chemical
mapping applications are now overcome by revolutionary
improvements in the EDX system detection sensitivity and
sufficient probe currents in atomic-sized probes provided by
correction of the spherical aberration in electron optics (by probe
Cs-correction). In this application note, we describe application
results obtained on the Titan G2 series of Cs-corrected S/
TEM with the revolutionary ChemiSTEM™ Technology. This
new technology greatly enhances EDX detection sensitivity
due to a number of innovations in the system architecture,
including: the X-FEG (a high-brightness Schottky FEG source),
the Super-X EDX detector system (4 windowless silicon drift
detectors with shutters integrated deeply into the objective
lens), and a high-speed electronics capable of 100,000 spectra/
second readout. This new system architecture provides many
performance benefits, such as improved light element detection,
better sample tilt response, faster mapping, and especially
atomic chemical mapping capabilities on crystalline structures.
This atomic analytical performance was achieved only by EELS
mapping in the past, which limited the applications to suitable
elements for EELS and required ultrathin specimens to avoid
multiple scattering artifacts. Examples of the atomic chemical
mapping with ChemiSTEM Technology on Titan G2 are shown
in this brochure on single crystals, interfaces and multilayer
systems to exemplify the power of ChemiSTEM Technology
combined with the Titan G2 family of S/TEMs across the broadest
range of the periodic table that has ever been accessible.
Figure 1: A schematic of the ChemiSTEM™ design, showing the X-FEG
high-brightness, Schottky electron source, and the Super-X™ geometry
including 4 SDD detectors arranged symmetrically around the sample
and the objective lens pole pieces. This schematic is not to scale.
Page 2
Advantages of the ChemiSTEM Technology System
Architecture
Silicon Drift Detectors (SDDs) are rapidly replacing Si(Li)
detectors for EDX in SEMs, but they only recently began
entering the S/TEM world. One of the biggest advantages of
SDDs is their capability of handling very high count rates without
saturation. Although high count rates of over 100,000 counts
per second can easily be generated with bulk samples in an
SEM, this was traditionally less likely or even impossible with
thin specimens in the S/TEM. However, the advent of probecorrected S/TEMs and high brightness Schottky field emission
sources (X-FEGs) has led to a considerable increase in available
beam currents even in small atomic-sized electron probes, and
therefore much higher EDX count rates are achievable. Moreover,
SDDs can be designed in a very compact way allowing the
integration of multiple detectors inside the S/TEM column as
opposed to just attaching them to ports close to the objective
lens. ChemiSTEM Technology is now available on the Titan G2
series and incorporates 4 such SDD detectors symmetrically
placed around the optical axis close to the sample area (see
Figure 1) in combination with an ultra-stable X-FEG highbrightness electron source. The resulting total sensor area of
120 mm2 and its integration deep inside the electron-optical
column result in a solid angle of 0.7 steradian (sr) which allows
to obtain chemical information on the atomic scale on the Titan
G2 series. Clearly, a major advantage comes from the large
solid angle for X-ray collection provided by four X-ray detectors
symmetrically arranged around the specimen. Additionally
there is an important advantage related to specimen tilting. The
dependency of the detected X-ray count rate on the specimen
tilt is greatly improved since the EDX signal can be obtained
under all tilt conditions of the specimen. In contrast, a single
detector solution, whether Si(Li) or SDD, always suffers from its
asymmetrical geometrical placement of the single detector. In
this case, the count rate is maximized only when tilting towards
the (single) detector and strongly decreases when the orientation
of the sample requires negative tilt angles, for example, at
an interface or grain boundary. For negative tilt angles above
approximately -10°, the count rate even drops to zero in most
conventional EDX systems because the sample and/or specimen
holder completely shadows the single detector. Figure 2
shows (lower blue curve) an example of this single detector tilt
dependency on a conventional EDX system with a 0.3 sr solid
angle. The ability to acquire high EDX count rates irrespective
of sample tilt adds a new degree of flexibility. This is of great
importance if a crystal has to be oriented in the zone axis to
reveal the atomic chemical structure using STEM-EDX.
Application Note Atomic EDX
Sensitive Detection of Light Elements
The detection of light elements is not regarded as a traditional
strength of EDX as a technique, however the combination
of SDD technology with a windowless design considerably
enhances the sensitivity for light elements like oxygen and
nitrogen (figure 3). Figure 3 shows the loss in signal due to
both the Si support grid bars and the thin polymer windows
in a traditional EDX system. The benefits of this design are
illustrated in the example of atomic oxygen mapping in a SrTiO3
crystal investigated in [110] and [100] projection at 200 kV (see
figure 15-16).
Fast Mapping of Large Areas
Due to the capabilities of the revolutionary ChemiSTEM
Technology (including fast electronics), elemental maps can be
recorded with mapping speed enhancements of factors up to
~50 when benchmarked against the traditional 0.3 sr EDX Si(Li)
system. The new system software allows map sizes up to 1,000 x
1,000 pixels to be collected as spectrum images and still provide
for each individual point of the map a complete EDX spectrum.
This allows post acquisition searching for further elements in the
stored data cube. Since the EDX spectra are easy to analyze due
to the low background signal and the symmetric peak shapes
the elemental maps can be processed live during the acquisition.
This capability allows for direct feedback to check the quality
during the acquisition and the mapping result is immediately
obtained afterwards.
Page 3
-20 degrees
beam
Det. 3, 4
0 degrees
+20 degrees
Det. 1, 2
Sample
1.2
1.0
Normalized count rate
0.8
0.6
0.4
Super-X
0.2
Si(Li) 0.3 sr
-30
-20
-10
0
10
20
30
Alpha tilt angle (degrees)
-20 degrees
0 degrees
+20 degrees
Figure 2: Comparison of relative EDX count rates of the Super-X system
(on Tecnai Osiris with 0.9 sr collection angle) and a single Si(Li) detector
system with 0.3 sr nominal solid angle. Both S/TEMs were operated at 200
kV with the same (constant) beam current. NiOx films were used as samples
for both tilt series. Positive tilt angles represent specimen tilts towards the
single detector for the Si(Li) system. Diagrams above the graph show the
effects of detector shadowing for the 4 Super-X detectors, and diagrams
below show shadowing effects for the single detector system.
1
Si grid bar
Window
Transmission Efficiency
The four SSDs are cooled for optimum performance by a direct
connection to the cold trap of the Titan G2 and no additional
Dewar is required. The detector system and cold trap share the
same Dewar, which offers a capacity of more than 4 days of
liquid nitrogen supply for both. The windowless design of the
SDDs improves the sensitivity for light elements compared to
detectors with thin polymer windows, and mechanical shutters
protect the SDDs against high-energy electrons. Specially
designed front-end electronics and an ultrafast multi-channel
pulse processor are employed and the entire EDX system is
fully embedded in the system control of the Titan G2 S/TEM .
Pixel dwell times down to 10 μs can be used for fast mappings,
acquired and processed using Bruker’s ESPRIT software. The use
of a probe Cs-corrector allows atomic chemical maps to even be
acquired at lower acceleration voltages, such as 80 kV, in order
to reduce knock-on damage effects for the high electron doses
required for atomic chemical imaging.
0.8
0.6
Shadowing
0.4
Windowless SDD
0.2
SDD with ultra-thin
polymer window
0.1
2
3
4 5 6 7
1
2
3
4 5 6 7
10
2
3
4 5 6
X-ray Energy (keV)
Figure 3: X-ray transmission efficiency versus energy for a windowless
SDD detector (red curve) and an SDD detector with thin polymer window
(blue curve). Loss due to the both the Si grid bars and the polymer window
contributes to the lower efficiency across all energies of the detector with
window. The schematic (insert) is showing the loss due to the holder
shadowing and the detector window. The loss due to the window includes
total absorption by the Si support grid bars (at all energies) and selective
absorption by the polymer window (at energies below 1 keV).
Application Note Atomic EDX
Atomic chemical mapping:
The benchmark on SrTiO3 versus EELS spectroscopy
By combining the sub-atomic resolution imaging capabilities
of the Titan G2 family with the record EDX detection sensitivity
of ChemiSTEM™ Technology, now routine atomic-level
spectroscopy is achievable for the first time. The images on
this page are chemical maps of a thin Strontium Titanate
(SrTiO3) crystal in which the individual atomic positions can be
distinguished by their unambiguous chemical signal (red is Sr,
green is Ti). Raw data of EDX and EELS is shown to compare the
results, with no post-processing. The individual atomic columns
are not only visible, but distinguished from their neighbors by
a very high contrast in EDX. The sampling of these chemical
maps was 0.075 Angstroms/pixel, representing the highest pixel
sampling obtained so far by any atomic spectroscopy
S/TEM technique while maintaining excellent signal-to-noise
quality. These images were obtained in just minutes due to
the unprecedented sensitivity of the ChemiSTEM Technology
detection system on the Titan G2 platform. The number of
elements in the periodic table accessible for chemical mapping
in EDX is much higher than EELS. Therefore EDX mapping
allows chemical information to be obtained on the atomic level
on complex multiphase materials, which were not previously
accessible via EELS measurements.
Figure 4: On the left side data
extracted from EELS are shown,
and on the right side the
corresponding chemical imaging
with the EDX signal is shown.
The top images are showing the
composite maps, while below
the elemental maps of the single
elements are presented. The
EDX maps for each element were
extracted using background
corrected integrated intensities
for the corresponding edges. No
post data acquisition processing
was applied other than colorization
of the elemental signals. The
sampling in EDX is 0.075
Angstroms/pixel and in the EELS
data is 0.32 Angstrom/pixel. The
EDX map has the highest sampling
ever obtained in an atomic level
chemical map. Both the EDX and
EELS results were obtained on a
Titan G2 at 200 kV acceleration
voltage using 10ms total dwell time
per pixel.
Page 4
Application Note Atomic EDX
Atomic chemical mapping:
The benchmark data with ChemiSTEM Technology on SrTiO3 versus
conventional EDX technology
SrTiO3 is a well understood perovskite structure and this
structure is a good benchmark to illustrate the recent progress
in atomic chemical mapping. The map obtained on a Titan G2
with ChemiSTEM Technology shows the breakthrough progress
in atomic spectroscopy and is superior not only in the chemical
ChemiSTEM Technology
Filtered
signal and contrast, but also in the mapping speed and map size
compared to the conventional technology. The raw data is of
such high signal-to-noise quality that noise filtering is not even
necessary to identify the positions of strontium and titanium in
the lattice.
Conventional Si(Li) Technology
Raw
HAADF
Raw
Figure 5: Comparison of atomic chemical mapping performance obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector compared
to a Titan with conventional Si(Li) EDX detector. The chemical map of SrTiO3 in the [100] direction is acquired with 128x128 pixels with 250 pA probe current
in 259 s exposure time. The map on a Titan G1 was acquired with 40x40 pixels with a probe current of 10-20pA with 800 s exposure time (see reference:
PRB 81 (2010) A.J. D’Alfonso, B. Freitag, D. Klenov, and L.J. Allen). The atomic structure of SrTiO3 is shown in the middle diagram.
Page 5
Application Note Atomic EDX
Atomic chemical mapping:
The benchmark data on SrTiO3 without Cs-correction at 300 kV
SrTiO3 has a reasonably large lattice spacing between the
atoms when looking along the [100] projection (~0.38 nm
Ti-Ti or Sr-Sr). Therefore, no probe Cs-corrector is required to
obtain the required probe diameters to resolve the atomic
structure. The proprietary FEI high-brightness X-FEG electron
source delivers the required probe current ( 250 pA, 0.2nm
probe size) to obtain chemical maps with high sampling and
speed for atomic chemical mapping of perovskite structures.
The performance is shown in the maps below, and even in the
raw unprocessed data the sublattices of Sr and Ti can be clearly
resolved. An additional benefit of EDX analysis is by having
access to multiple edges of the same element. This is illustrated
by showing the atomic map of not only the Sr L-edge but also
the high energy Sr K-edge.
Figure 6: Atomic chemical mapping with ChemiSTEM Technology on the Titan G2 without probe Cs-corrector (via only the high analytical current of the
X-FEG high-brightness source). The chemical map of SrTiO3 in [100] direction is acquired with 256x256 pixel with 140 pA probe current in 300 s exposure
time. The top row of images shows the raw data, with no post-processing applied. The bottom row of images are filtered images using an average filter in
real space. This data was obtained at 300 kV acceleration voltage. The atomic structure of SrTiO3 is show on the right side.
Page 6
Application Note Atomic EDX
Atomic chemical mapping:
Quantitative atomic chemical mapping on different perovskites
Colorized elemental maps are difficult to analyze quantitatively
since the underlying statistics of the spectra are not directly
accessible. For a quantitative study of the signal the spectra
have to be analyzed carefully. Therefore the spectra of the two
different atomic positions of different perovskites are shown
here. The high quality of the spectra with statistics of up to
200 counts in peak heights is remarkable. In all perovskite
sturctures atomic chemical mapping is possible despite the
fact that the elements of the A and B site of the ABO3 structure
is exchanged from Sr to La to Dy on the A site, and Ti to Al to
Sc, on the B site. This shows the unique capability of energy
dispersive X-ray analysis to allow access to the majority of
the elements of the periodic table. All spectra of pure atomic
columns of an element show signals from the neighboring
column with different elements, which is not visible in the
composite images. The understanding of this behavior
requires theoretical calculations describing the scattering of
the electrons in the material and their redistribution in the
material.
Figure 7: Atomic chemical mapping on different perovskites obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector at 200 kV
acceleration voltage. The maps are acquired with 64x64 pixels using 50 pA of probe current. The spectra in different colors shown on the left are extracted
on the 2 atomic positions marked in the composite images on the right. No post data acquisition processing was applied to the composite images other
than colorization of the elemental signals.
Page 7
Application Note Atomic EDX
High lateral resolution in chemical mapping:
the L-edges. The contrast is calculated by dividing the difference
of maximum and minimum by the sum of the two. This result
indicates that higher energy loss x-rays have higher localization
than lower energy loss x-rays. Theoretical calculations can
reproduce this result, but further examinations are required[1].
This suggests that the ability of atomic EDX to access higher
energy loss peaks can be an advantage in obtaining the highest
possible spatial resolution in chemical mapping.
GaAs dumbbells in [110] direction at 80 & 200 kV using the
K and L edges
The GaAs dumbbell of 0.14 nm can be clearly resolved by
chemical mapping using energy dispersive x-ray analysis. Both
elements - the Ga and the As - can be resolved by using not
only the low energy L- peak but also the high energy K-peak,
as shown in figure 5. In energy dispersive x-ray analysis all
x-rays with different energies are acquired simultaneously up
to very high energy losses (40 keV). This allows comparison of
the performance in atomic chemical mapping using different
characteristic edges of the same element with perfect correlation
of the results. In figure 5 the contrast of Ga/As-K and Ga/As-L
peaks are compared and differences in contrast can be observed.
The contrast at the higher energy loss K-edges is better than for
K-line at 200 kV
Raw
filtered
The use of the probe corrector allows atomic sized probes to be
maintained at lower voltages, such as 80 kV. Therefore the GaAs
dumbbell of 0.14 nm can be resolved in chemical mapping even
at 80 kV (upper right image of figure 8).
[1] Chemical mapping on the atomic level using energy dispersive x-ray
spectroscopy, D.O. Klenov, H.S. von Harrach, B. Freitag, A.J. D’Alfonso, and
L.J. Allen, M&M2011, Nashville, USA,MC Kiel, 2011, Germany.
L-lines at 200 kV
K-line at 80 kV
Raw
Raw
filtered
GaAs (110)
filtered
0.14 nm
Figure 8: Atomic chemical mapping GaAs in [110] projection using ChemiSTEM with probe Cs-corrector at 80&200 kV acceleration voltage. The upper
images (left and middle) of Ga and As are acquired at 200 kV using 200 pA probe current per pixel. In the upper right corner the GaAs map acquired at
80kV with 50 pA Probe current and 50 μs dwell time is shown. The atomic structure is shown on the lower right side of the figure. An intensity profile of the
Ga/As-K peaks and the Ga/As-L peaks reveals differences in contrast between the K&L signals.
Page 8
Application Note Atomic EDX
High lateral resolution in chemical mapping:
Seeing and identifying light elements in atomic EDX
on InP in [110] projection at 80 & 200 kV
HAADF
The dumbbell structure of In and P can be resolved using atomic
chemical mapping with ChemiSTEM Technology. The low atomic
number of phosphorous provides insufficient scattering power
to see the phosphorous in the z-contrast HAADF-STEM image.
However, both the In and P position can be clearly identified
and the dumbbell of InP is resolved in the ChemiSTEM maps.
Therefore the polarity of the atomic structure can be identified
in the chemical map, which is impossible in the atomic HAADF
STEM image. This enables the determination of the chemical
termination on interfaces or crystal defects, which was not
possible in the past.
Figure 9: Atomic chemical mapping of InP in [110] projection obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector at 80 & 200 kV
acceleration voltage. The background image is an HAADF STEM image of InP. Atomic resolution maps of In and P are shown, acquired at 200 kV(left) and
80 kV (right). Both the raw and the filtered data is presented in pairs. An overlay of the atomic structure indicates the positions of the different atomic
species. The maps size is 64x64 pixels, the dwell time is 173 s and 143 s with 50 pA probe current in both cases ( 80 & 200 kV).
Seeing mixed occupancies in atomic columns:
Atomic EDX on In0.53Ga0.47As in [110] projection at 200 kV
Not only can the dumbbell structure of InGaAs be resolved
using atomic chemical mapping with ChemiSTEM Technology,
but it also permits distinguishing between a mixed (In,Ga)
atomic column and pure atomic column (As), as shown in
figure 10. This application is even more demanding in the
In-L As-K
Ga-K As-K
Page 9
required sensitivity than atomic chemical imaging of pure
atomic columns - and the data below demonstrates the excellent
sensitivity of the ChemiSTEM Technology detector system of
4 SDD detectors. Since the signal in EDX is proportional to the
chemical concentration illuminated with the beam, the signal
is intrinsically more weak in case of mixed atomic columns due
to the small volume excited and the smaller concentrations
compared to pure atomic columns.
Figure 10: Atomic
chemical mapping
of In0.53 Ga0.47 As
in [110] projection
obtained with
ChemiSTEM
Technology on a
Titan G2 with probe
Cs-corrector at
200 kV acceleration
voltage. The raw
data (left) and
filtered data is
shown as pairs. The
atomic structure is
shown in the middle
of the figure. The
map size is 64x64
pixels, recorded for
174 s with 50 pA
beam current.
Application Note Atomic EDX
Atomic chemical analysis at interfaces:
Interface of SrTiO3 / PbTiO3 in [100] projection
In figures 4-10 perfect crystals were examined, and their
sub-lattices were imaged using EDX spectroscopy. This is an
important application, but the study of chemical variations
on interfaces, surfaces and defects is an even more exciting
application in atomic chemical analysis. Therefore the interface
of SrTiO3 / PbTiO3 has been studied with atomic EDX. The
positions of the Sr, Ti and Pb atomic columns can clearly be
visualized in the x-ray maps revealing the chemical change at
the interface. No change in contrast over the field of view shows
that the titanium concentration is stable across the interface.
The chemical maps of lead and strontium reveal a change at
the interface through the thickness of the sample. Simulations
(shown and referenced below) of atomic resolution EDX maps
of a SrTiO3/PbTiO3 interface have been made where the 200 keV
probe was assumed to be aberration free with a convergence
semi-angle of 21.5 mrad. The specimen was assumed to be
50 nm thick, and under these conditions agreement with the
experimental data is found.
Simulation
Figure 11: Atomic chemical mapping of the interface of SrTiO3 / PbTiO3 obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector at
200 kV acceleration voltage. The underlaying image shows the HAADF STEM image of the interface. The composite image of the Pb and Sr signals is shown
in the bottom center and the maps of the individual elements are shown in raw and filtered on the left and right sides. The mapping size is 200×200 pixels
with a total mapping time of ~300 s. In the insert we show theoretical calculations in a color composite map constructed from the Pb L2,3 signal (cyan),
the Sr K signal (magenta) and the Ti K signal (yellow) (L.Allen et al., Melbourne, Australia). Sample courtesy M. Kurasawa, Y. Chen and P.C. McIntyre, Stanford
University.
Page 10
Application Note Atomic EDX
Atomic chemical analysis at interfaces:
La1-xSrxMnO3/SrRuO3 multilayer systems in [100] projection
In multilayer systems the physical properties strongly depend
on the layer thickness, termination and the roughness of the
interface between the different layers. In the dataset below,
hardly any differences in the layer thickness are observable in the
Z-contrast image, which indicates that the growth is perfect. In
the chemical maps, however, the picture is different. A difference
in the Ru layer thicknesses of 2 versus 3 atomic layers is clearly
visible (yellow). The Mn layers show homogeneous signals across
the structure, while the Sr and La signals show more variation
in signal across the interface (see as well intensity profile of Sr
and La on the right).This example shows strikingly the additional
information that can be obtained by atomic resolution EDX.
Nevertheless, quantification of unknown mixed layers still
requires image simulations.
Raw Intensity profile
Filtered
Sample courtesy of Ionela Vrejoiu and Eckhard Pippel, Max Planck
Institute of Microstructure Physics, Halle/Saale, Germany.
Figure 12: Atomic chemical mapping of La1-xSrxMnO3/SrRuO3 multilayer systems obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector
at 200kV acceleration voltage. The maps have a size of 256x128 pixels with a dwell time of 25 μs per pixel. A probe current of 150 pA was used. Pairs of maps
of Sr, La, Mn and Ru of raw data (left) and filtered data (right) using averaging over 3 pixels are shown above. An intensity profile of the elements across the
multilayers is shown on the right.
Page 11
Application Note Atomic EDX
Seeing mixed occupancies :
Atomic EDX on mixed and pure atomic columns in Y2Ti2O7
In the [110] projection of Y2Ti2O7 the concentration of Y,Ti is
changing in the atomic columns depending on the position
in the unit cell. Three different columns are present in this
projection. A pure Y, pure Ti and a mixed (50:50) Y,Ti column
(See structural model below). The different occupancies of the
structure can be clearly seen in the atomic EDX maps. Since the
concentration is known in this case a sensitivity in mixed column
detection of 50% for atomic resolution can be established.
This is the first time in EDX analysis that a 50% occupied column
can be resolved in an atomic chemical map. Hence atomic
chemical mapping using Chemistem Technology is not only
suitable to obtain atomic maps of pure columns, but also is
suitable to visualize mixed columns in complex structures.
HAADF-STEM
Figure 13: Atomic chemical mapping of Y2Ti2O7 in [110] projection obtained with ChemiSTEM Technology on the Titan G2 with probe Cs-corrector at 200 kV
acceleration voltage. The maps have a size of 64x64 pixels with a mapping time of 306 s. A probe current of 76 pA was used. EDX maps of filtered data using
averaging over 3 pixels are shown. A model of the structure in [110] projection indicates that in this projection three different occupancies are present. Pure Y,
pure Ti and 50:50 mixed Y/Ti columns.
Page 12
Application Note Atomic EDX
Seeing mixed occupancies :
Atomic EDX on mixed and pure atomic columns in Y2Ti2O7
For a quantitative understanding of the contrast differences of
figure 13 in the pure and mixed columns intensity profiles can
provide an answer to the question of how strong is the relative
difference in contrast. For this purpose, intensity profiles in two
directions have been extracted from the raw elemental maps.
One profile is taken in the direction of only pure atomic columns.
The other profile is taken in a direction of both pure and mixed
columns. In the case of pure columns an extremely high contrast
of ~60% is obtained, which is calculated by the difference
Counts
Intensity Profile of across pure columns
Position (nm)
Counts
Intensity Profile of across pure & mixed columns
Position (nm)
Page 13
between minimum and maximum divided by the sum of both.
The profile of the mixed and pure columns (profile in the bottom
of figure 14) shows a clear contrast difference proportional to the
concentration change in the columns. The high quality of the
maps provides vital input for detailed image simulations in order
to provide a deeper and more quantitative understanding of the
interplay between chemical variation and sample/electron beam
interactions on the atomic level.
Figure 14: Atomic chemical
mapping Y2Ti2O7 in [110] projection
obtained with ChemiSTEM
technology on a Titan G2 with
probe Cs-corrector at 200 kV
acceleration voltage. The maps
have a size of 64x64 pixels with a
mapping time of 306 s. A probe
current of 76 pA was used. Intensity
profiles with a vertical binning of
4 are extracted in the direction of
pure atomic columns (left) and in
the direction of pure (yttrium )and
mixed columns (right). The plots
are shown below the maps and the
direction of the intensity profile is
indicated on top of the Y and Ti
maps.
Application Note Atomic EDX
Detection of light elements:
Oxygen mapping in SrTiO3 in [100] projection
Since ChemiSTEM Technology employs windowless detectors,
the sensitivity for light elements is higher than on detector
systems with polymer windows that absorb x-rays at lower
energies. The benefit of this design feature is illustrated by the
detection of single oxygen columns in atomic chemical mapping.
The oxygen edge has a very low energy loss of 532 eV.
Nevertheless, in the example of SrTiO3 the high performance
is shown by the visualization of the oxygen sub lattice in [100]
projection where the oxygen distribution is imaged clearly.
The composite image of Sr,Ti,O reveals the position of the pure
oxygen columns and mixed Ti/O columns.
Composite image: Sr + Ti
Composite image (filtered): Sr + Ti + O
Figure 15: Atomic chemical mapping SrTiO3 in [100] projection obtained with ChemiSTEM Technology on a Titan G2 with probe Cs-corrector at 200 kV
acceleration voltage. The maps have a size of 64x64 pixels with a mapping time of 306 s. The atomic structure is plotted on the right side. Two composite
images are shown. The left one shows only the Sr and Ti signal and consists of raw data. The upper right one shows the composite of Sr,Ti and O, and
shows filtered data.
Page 14
Application Note Atomic EDX
Detection of light elements:
Oxygen mapping of SrTiO3 in [110] projection
In the [100] projection of SrTiO3 the pure oxygen, strontium
and mixed Ti/O columns can be visualized in atomic chemical
mapping as shown in figure 15 on the facing page. Here the
distance between the Sr columns and Ti columns is 0.38 nm. By
tilting the crystal into the [110] direction the atomic columns of
the structure consist of pure titanium and oxygen columns and
a mixed Sr/O column in this projection. The spacing of Ti and Sr
shrinks in the [110] direction to 0.19 nm (horizontal direction in
the images). In the chemical maps of Sr, Ti and O this spacing
below 0.2 nm can be resolved. In this case the composite image
of Sr+Ti+O reveals the position of the pure oxygen and titanium
columns and mixed Sr/O columns. By using the two different
projections of SrTiO3, as shown on this page plus the facing page,
the complete sub lattices of oxygen, titanium and strontium can
be mapped in three dimensions, which illustrates the power of
chemical mapping using this technology.
Composite
image (filtered):
Sr + Ti + O
Figure 16: Atomic chemical mapping of SrTiO3 in [110] projection obtained with ChemiSTEM technology on a Titan G2 with probe Cs-corrector at 200 kV
acceleration voltage. The maps have a size of 64x64 pixels with a mapping time of 322 s. The atomic STEM imaging using HAADF and ABF (Annular Bright
Field) is shown on the left side of the figure. The Sr and Ti chemical mapping data presented are raw data obtained by only extracting the intensities of the
characteristic absorption edge of the elements, and the O and composite images shown above are filtered data.
Page 15
Application Note Atomic EDX
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