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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 Learn more at FEI.com World Headquarters Phone: +1.503.726.7500 FEI Europe Phone: +31.40.23.56000 FEI Japan Phone: +81.3.3740.0970 FEI Asia Phone: +65.6272.0050 FEI Australia Phone: +61. 7.3512.9100 AN0032 07-2011 TÜV Certification for design, manufacture, installation and support of focused ion- and electron-beam microscopes for the Electronics, Life Sciences, Research and Natural Resources markets. © 2011. We are constantly improving the performance of our products, so all specifications are subject to change without notice. Titan, ChemiSTEM and the FEI logo are trademarks of FEI Company, and FEI is a registered trademark of FEI Company. All other trademarks belong to their respective owners.