J Ringnalda

Evidence for a Critical Amorphization Thickness Limit of Ga+ Ion Bombardment in Si

Focused ion beam (FIB) instruments which provide low energy (e.g., 2 keV) Ga ions offer a direct method for reducing conventional high energy (e.g., 30 keV) ion implantation damage for transmission electron microscopy (TEM) specimens [1], atom probe specimen preparation [2], and improvements in electron backscattered diffraction pattern quality [3]. As the ion energy is reduced, the ion range, and therefore the target surface damage, is also reduced [1]. However, there is a theoretical limit to the possible energy that can be used since the sputter yield (Y) also decreases as the ion energy decreases and a value Y less than 1 atom/ion implies that deposition of Ga rather than sputtering may occur. In this paper, we compare Ga ion implantation results into Si, Ta, and Au, from a FIB column operating at 2 keV and below.

Live Imaging of Reversible Domain Evolution in BaTiO3 on the Nanometer Scale Using In Situ STEM and TEM

1. Department of Physics and Astronomy, School of Mathematics and Physics, Queens University Belfast, UK, BT7 1NN 2. FEI Company, Europe NanoPort, Achtseweg Noord 5, 5651 GG Eindhoven, The Netherlands There is an increasing interest in novel ferroic materials, especially in device applications such as transistors, memory devices, tunneling barriers, etc.. The functionality of such materials is enabled by the reversible switching between equivalent states (or domains) that form to minimize the system’s free energy. This switching behavior depends strongly on the domain structure pattern and their mobility under external stimuli (electrical, mechanical, temperature, etc.). There is a strong need to study this switching in detail. Nanoscale domain structures and their specific switching behavior strongly influence the material responses and properties such as dielectric permittivity, piezoelectric coefficients and remnant polarization. Fortunately in-situ (scanning) transmission electron microscopy (S/TEM) represents a powerful technique for studying ferroic materials and their switching behavior with resolutions down to the atomic scale. Here, the domain pattern evolution in BaTiO

The Design and First Results of a Dedicated Corrector (S)TEM.

In all TEM imaging, the spatial resolution is predominantly limited by the spherical aberration and chromatic aberration of the objective lens [1, 2]. These aberrations cause the information in the image to be blurred. This information can be retrieved by through-focus series reconstruction or by holography. Alternatively, a more direct way is to correct the spherical aberration by incorporating a Cs corrector in the TEM column [3], thus making the point resolution equal to the information limit. For the situation where the aberrations are corrected on the image (Objective lens correction), a system shows enhancement of the resolution all the way down to the information limit. For the situation where the aberrations are corrected on the probe [4] (Condenser lens correction), the probe size can be improved however system stability starts to play a more and more important role in determining the final performance of the total system

Towards Quantitative EDX Results in 3 Dimensions

In principle, energy dispersive X-ray (EDX) mapping can be combined with electron tomography since the number of generated X-rays scales linearly with sample thickness. However, early attempts to perform 3D EDX experiments were complicated by the specimen-detector geometry [5]. Therefore, recent efforts lead to a novel design of the EDX detector system, which enables one to apply 3D EDX mapping to different structures [6]. An example of a 3D EDX reconstruction, obtained using 2D EDX maps that have been acquired using a probe corrected Titan, equipped with a Super-X system is presented in Figure 1. The reconstruction shows a Au@Ag nanocube of which the Au core yields an octahedral shape [7]. This example clearly illustrates the potential of 3D EDX mapping, but one needs to be careful when extracting quantitative information from such reconstructions. To reach this goal, the different steps of an EDX tomography experiment need to be optimized.

Use Electrons Sparingly but Efficiently, the Battle to get All the Required Information Needed While Minimizing Dose and Maximizing Data Collection at the Highest Resolution

Since aberration correction has been applied on modern electron microscope systems, there has been a need to demonstrate the benefits of this capability and in some respect, to justify the cost of these complex systems. Sometimes the justification of such a system is by the presentation of a colorful elemental map which correlates with the atomic periodicity in the sample. This type of visualization, while artistic, may not be sufficient to characterize materials at the levels proclaimed, since there are many events happening which are difficult to place with atomic certainty. There are many benefits of the correctors on the imaging side of the sample by removing delocalization and improving the image interpretability for phase contrast imaging, however there is a strict requirement on the sample both in terms of cleanliness, thickness and damage layers. In the case of correctors on the condenser or probe forming part of the microscope, this requirement is only amplified especially when the imaging techniques are combined with various spectroscopies.

High Performance in Low Voltage HR-STEM Applications Enabled By Fast Automatic Tuning of the Combination of a Monochromator and Probe Cs-Corrector

High tension flexibility in scanning transmission electron microscopy (STEM) enables versatility in the investigation of a broad variety of materials, which formally did not deliver the right contrast or were too beam sensitive at high acceleration voltages. By the introduction of spherical aberration (Cs) correction low voltage STEM has become the major imaging and spectroscopy technique for atomic resolution observation [1,2]. When reducing the acceleration voltage and correcting the Cs of the objective lens, the chromatic aberration (Cc) of the electron source becomes resolution limiting and needs to be addressed. This can be achieved by full correction or minimizing its effect on the image resolution [3]. The use of the monochromator to minimize the effect of Cc is beneficial in STEM application due to the fact that it improves the performance of EELS applications. To obtain reproducible results during daily operation the handling of a monochromized Cs corrected tool at low voltage needs simplification. In this contribution a Wien filter monochromator [4] and a probe Cs corrector [5] combination on a cubed Titan Themis is used to maintain the atomic resolution in low voltage STEM applications. State of the art low voltage images require both the monochromator and the Cs-corrector to be tuned optimally at the same time in an easy and reproducible way. Therefore we developed fast automatic routines to tune the monochromator and the Cs corrector to give easy access to high performance in LV S/TEM. These routines are quick and deliver within minutes a completely tuned tool. We demonstrate with videos the performance of the tuning and level of automation. The automatic tuning of the monochromator requires no sample and uses the flucam of the Titan cubed as a feedback detector. For optimum Cs correction mainly the lower order aberrations vary in operation and need daily retuning. For this reason a correction routine using a series of HRSTEM images is developed to correct the lower order aberration of the Cs-corrector (focus, 2-fold astigmatism, 3-fold astigmatism, coma) This routine can run on a crystalline sample, even on the area of interest in the zone axis of the crystal to ensure best result and fastest time-to-data. An example of the automatic routine is demonstrated in figure 1, where the images of silicon [110] and GaN [211] before and after autotuning of focus and 2-fold astigmatism on the crystalline material are shown. The negative effect of a large energy spread of the non-monochromized source is illustrated in figure 2 by looking at calculations of the transfer function in STEM with different energy resolution The calculated results are compared to images taken with different energy resolution, high tensions and beam currents, set-up via the above described automatic routines. The combination of XFEG gun with monochromator delivers even at low voltages high probe currents for analytical work. We discuss the influence of the energy resolution on the image quality. Therefore HR-STEM analytical and imaging results of various materials are presented to prove the robustness of the alignment procedures and the performance of the Wien filter/Cs corrector combination at low voltages down to 30kV. (Figure 3)

Atomic Resolution Cs-Corrected HR-S/TEM from 80-300kV

B. Freitag, M. Stekelenburg, J. Ringnalda, and D. Hubert FEI Company, Building AAE, Achtseweg Noord 5, Eindhoven, The Netherlands The latest generation of high-resolution Cs-corrected HR-S/TEM electron microscopes allows material scientists and nanotechnologists to cross a critical threshold in their efforts to understand the properties of materials down to the most fundamental level - the atomic level. Nanotechnology research involves a wide variety of sample classes, calling for microscopy that ensures flexibility towards optimization of analytical and imaging techniques while delivering atomic resolution. With high tension flexibility, the interaction of the electrons with the sample can be tuned to the needs of the sample and the information required: contrast, resolution, stability or analysis. The optimum choice is related to the characteristic elastic and inelastic scattering processes of the electrons with the very materials. Thick samples or extremely dense materials need high acceleration voltage simply due to the fact that penetration power is needed to obtain interpretable images. Thinner specimens or some classes of delicate ultra light materials which suffer from knock-on damage mechanisms or weak contrast prefer lower voltage. In other cases, e.g. cryo-microscopy, higher voltages are preferred to minimize bond breaking damage. The Titan 80-300 high-resolution transmission electron microscope was introduced recently as a dedicated platform for aberration correctors. One of the key features of its design is the flexibility in acceleration voltage (80-300kV) to permit imaging and analysis that are tuned for the application and the sample. The stability of the Titan 80-300 column in combination with the new Cs-corrector enables working with atomic resolution across the entire acceleration voltage range. Young’s fringe experiments show that the stability of the column: information better than 0.1nm is transferred, not only at 300kV, but even at 80kV. This is the result of the constant power design, the electronic power supply stability and the stability of the column and the new integrated Cs-correctors. In this contribution, the optimum parameters for different materials classes are discussed and application results in corrected HR-TEM are given on various material classes at acceleration voltages between 80 and 300 kV. Atomic imaging of silicon devices, metals, nanoparticles, and carbon nanotubes (CNTs) will be presented. Moreover, a focus series reconstruction of a DW- CNT acquired at 80 kV acceleration voltage will be discussed (Figure 1). This data was only possible due to the extended life time of CNTs at 80kV [1-2]. With this contribution we demonstrate that quantitative atomic HR-TEM of delicate structures is possible with an ultra stable Cs-corrected S/TEM and by a smart choice of the acceleration voltage: optimizing for technique and sample. References [1] V.E.Cosslett, Electron Microscopy and Analysis 1979, T.Mulvey, Institute of Physics, London, 1979, p. 177 [2] B.W. Smith et al., Journal of Applied Physics 90 (2001) 3509.

Comparison of Different Sample Preparation Techniques in TEM Observation of Microstructure of INCONEL Alloy 783 Subjeted to Prolonged Isothermal Exposure

INCONEL alloy 783 was annealed and aged following the standard heat treatment procedure. One set of specimens was then isothermally exposed at 500 8C for 3000 h. Mechanical properties were measured at room temperature and 650 8C, and the results showed the prolonged exposure increased the strength and decreased elongation of alloy 783. The microstructures of as-produced and exposed material were examined using optical microscope, SEM and TEM, respectively. Three techniques, jet electro-polishing, ion milling, and focused ion beam, were employed to prepare the TEM samples to observe the variation of microstructure of alloy 783 due to isothermal exposure. TEM images of samples prepared by different methods were analyzed and compared. The results indicate that the jet electro-polishing technique allows the detail microstructure of alloy 783 subjected to different treatments to be well revealed, and thereby the TEM images can be used to explain the enhancement of strength of alloy 783 caused by isothermal exposure. q 2004 Elsevier Ltd. All rights reserved.

Further Applications of Energy Filtered TEM in semiconductor Devices

Energy filtered TEM (EFTEM) imaging has been used extensively for material characterization. One of its major uses is to enhance image contrast from an area with difficult contrast phenomena due either to little density difference or large thickness variation. The projection nature of a TEM also generates difficult contrast if the structure is curved in the direction vertical to sample. In these cases, EFTEM provides a unique method to expand the spectrum of image contrast by carefully selecting an energy that provides excellent contrast in the area of interest. We will use the term “Energy Contrast” to describe this type of contrast, which has been used extensively. The other major advantage of EFTEM is the ability to provide high spatial resolution elemental maps very rapidly. These maps are obtained by acquiring three images at different energies (e.g. the three-window-mapping technique), followed by a calculation of elemental contribution vs thickness profile by characterizing the background.