Current trends seek to make TEM operation more routine and productive. One of these follows the lead made in scanning electron microscopy in which the spatial distribution of crystallographic data over a selected area of a sample surface is determined by automated recognition of Backscatter Kikuchi patterns (EBSD), Adams et al . This method has been extended to the TEM in a novel manner, Wright et al . Dark field images are collected sequentially from the area of interest for all possible incident beam directions over a solid cone of semi-apex angle up to 4 degrees, Figure 1. The images are recorded directly into a computer. Off line automated analysis follows in which all dark field images are searched to determine the beam conditions under which each pixel in the image brightens, i.e. when the corresponding point in the sample came into a diffraction condition. The measurement of three such non-coplanar conditions for a pixel leads to the determination of the corresponding crystallographic orientation. The accuracy of orientation measurement has been improved to 1 degree by the fitting of the determined diffraction vectors to the surface of the Ewald sphere. The analysis allows grain maps to be reconstructed from which grain size distribution can be automatically determined. Figure 2.

The movement towards a single platform concept for the operation of multi-functional analytical instruments has progressed over the past 10 years largely due to the availability of powerful computer technology combined with the need of ease of use to increase productivity. Other factors include the need to share data obtained from these increasingly complex instruments, and to transport these data in an easily managed format and the possibility of storing large amounts of data generated from projects.

Initial efforts in this field were generated by the need for computer control of complex instrumentation such as TEMs, EPMAs and dual beam instruments. Microprocessors enabled easy alignment, storage of stage parameters and digital image acquisition. with the boom in the semiconductor industry it was necessary to design tools that could be operated by individuals who did not possess the same amount of knowledge as the scientists and technologists of the previous generation. Early attempts at integration of techniques on a single platform were restricted, largely due to limitations in the capacity of the computers employed in controlling these tasks. Indeed, in some cases this actually increased the complexity of some instruments due to a profusion of microprocessors controlling the various analytical components of the larger analytical machines.

The resolution of state-of-the-art low-voltage scanning electron microscopes (LV SEM), which is currently limited by the chromatic and spherical aberrations of the objective lens, can be improved by incorporating an aberration correcting device. At present four different concepts are discussed in literature: Zach and Haider demonstrated that a quadrupole/octupole corrector can correct both chromatic and spherical aberration. Rose proposed a Wien filter for chromatic aberration correction, which has relaxed stability requirements. Recently, we reported a simplified version of this corrector and showed that a spherical aberration corrector can be integrated in a Wien filter. Henstra and co-workers suggested a purely electrostatic corrector that can correct both chromatic and spherical aberration.

For all these concepts problems may arise when the lens-to-sample (working) distance for an aligned corrector is to be changed. in general, the corrector settings depend on the ratio Cc/f2, where Cc and f denote the coefficient of the chromatic aberration and the focal length of the objective lens, respectively. When the working distance is changed, this ratio is no longer perfectly matched to the corrector settings. The tedious realignments and readjustments, which then seem necessary, can be avoided by using a doublet objective lens as illustrated schematically in Figure 1.

Past FE-SEM could obtain a high resolution image, however its probe current was not sufficiently strong enough for analytical purpose.

We have developed a multi-purpose thermal field emission scanning electron microscope (JSM- 6500F), in which a new designed “In-Lens Thermal FEG” is installed.

Fig. 1 shows a cross section images of the In-Lens Thermal FEG, comparing with the past FEG. The In-Lens Thermal FEG consists of the thermal FEG and the 1st condenser lens. The emitter is located in the magnetic field produced by the 1st condenser lens, so that electrons emitted from the emitter are condensed effectively to produced a high probe current. The maximum probe current of 200 nA is attainable at the accelerating voltage of 15 kV, ten times larger than the maximum probe current of ordinary FE-SEMs. Therefore the WDS analysis can be performed by this newly FE-SEM.

The “aperture angle control lens” has been installed in the electron optics system, for improving the resolution at a large probe current. The resolution of 3.0nm at the analytical condition (at probe current 5nA, accelerating voltage 15kV, WD 10mm: fig.2).

The ultimate resolution of the microscope is 1.5nm at 15kV and 5nm at lkV. The objective lens is not an immersion type and does not leak magnetic fields on the specimen surface, therefore this equipment was suitable for observing or analyzing magnetic materials, and also suitable for the EBSD analysis. Fig.3 shows an example of the EBSD analysis.

Electron beam - specimen interactions and SEM signals have been well understood and documented for many years. These interactions result in a variety of electron signals including the most common, secondary and backscattered electron. Each electron signal produces unique characteristic information about the sample surface, subsurface, and elemental composition. Important information can be gained by controlling and filtering electron signals collected by the electron detector system.

The S-4700 Cold Field Emission SEM incorporates a set of electrodes and plates positioned in the objective lens upper pole piece in close proximity to the upper secondary detector (figure 1). When a positive voltage is applied to the electrode plates, a high yield of secondary and backscattered electrons spiral up the column of the objective lens. The backscattered electrons are filtered with the ExB producing a SE rich signal. The information from this type of signal provides absolute detail from the sample surface, but can be prone to charging with some highly nonconductive samples. Figure 2a shows the effect of charging while observing uncoated Teflon ™. The image becomes distorted with bright intermittent horizontal lines. Surface detail is enhanced due to the high contribution of SEs from the sample surface.

When the electrode voltage is set negative, through the instrument GUI, the low energy secondary electrons are repelled providing a signal rich in backscattered electrons. The information from this type of signal provides compositional information and inherently reduces charging. The uncoated Teflon ™ sample in figure 2b shows all charging affects have been eliminated.

To examine non conductive samples in their natural state (i.e. without significant sample preparation) at high resolution in the SEM the technique of low voltage field emission scanning electron microscopy (LVFESEM) is used. Due to the limitation in accelerating voltage (U<1kV) this technique is limited in respect of chemical analysis. Furthermore it is not possible to examine humid and outgassing samples in high vacuum. in recent years the application of variable pressure scanning electron microscopes (VPSEM) became an important technique in materials science as well as in life science. Due to the capability of maintaining a high chamber pressure humid, outgassing and non-conductive samples, can be examined in their natural state without significant sample modification or preparation. Especially compound materials with different electron yields can be imaged without any charging effects (Fig. 2), [2]. This paper describes a high resolution field emission electron microscope, that combines low voltage and variable pressure capabilities.

The high pressure capabilities of the instrument are realized by eliminating the high vacuum requirements of SEM in the microscope chamber. This is done by separating the vacuum environment in the chamber from the ultra high vacuum environment in the gun area.

The use of variable pressure SEMs (VP-SEMs) is increasing in various fields of science and industry, allowing microscopy in a variable pressure environment of 1 ∼ 270 Pa utilizing backscattered electrons for imaging. The VP-SEM allows microscopy of insulated samples without the need for sample preparation. Charging artifacts can be minimized as well. When the VP-SEM is operated with a cooling stage, which allows cooling of samples at −20° and above, vaporization of water from samples is reduced. This permits microscopy of wet samples at close to the natural state for extended periods of time.

Poor S/N ratio and deterioration of resolution, both of which are due to collisions among residual gas molecules and primary/backscattered electrons, have limited the performance of VP-SEMs. For resolving these limitations, we have completed the development of a new field emission VP-SEM which operates with a stable Schottky field emission source, a new environmental secondary electron detector (ESED), and a multi-stage differential pumping system. Fig. 1 shows a sectional view of the column with the differential pumping system. This design allows stable gun vacuum conditions with variable specimen chamber pressure 10 through 3,000 Pa, permitting a pressure difference from the gun by 1011 Pa without problems.

RÖNTEC’s UHV Dewar detectors have established new standards for high resolution, lowmaintenance, low operating cost, and reliability in Si(Li) X-ray detectors. Now, the recently introduced XFlash® series X-ray detectors are enabling new methodologies for microanalysis and element imaging in the SEM. These detectors are compact, liquid-nitrogen-free semiconductor Xray detectors that are based on Silicon Drift Diode (SDD) technology. XFlash detectors produce extraordinarily high count rates with excellent energy resolution and have introduced ultra-fast microanalysis and element mapping to the SEM world. The addition of color to SEM images enables easy visualization of element distributions and allows the microstructural features and compositional variations of different materials to be more readily identified. Persons unfamiliar with electron microscopy can more readily interpret color images than black and white or gray scale images. This new technology has great potential to revolutionize electron microscopy.

RÖNTEC’s UHV Dewar Detector offers the highest long-term stability and best energy resolution ever specified for a commercial Si(Li) detector (less than 129 eV). The UHV design leads to small size and weight (for reduced column loading) along with extremely low nitrogen consumption and low susceptibility to microphonics. The UHV detector never ices up and thus never requires defrosting or warm-ups. It is available with a variety of entrance windows for light element analysis.

The complete and accurate identification of all of the phases present in a sample is the ultimate goal of any materials investigator. The identification should include compositional as well as crystalline measurements for unique characterization. in an SEM, the composition of individual regions can be routinely determined via EDS or WDS analysis. The main limitation is the need to visually identify the individual regions from the images alone. A method to limit this restriction is to collect x-ray maps of the field-of-view. This technique has the benefit of providing the spatial distribution of the elemental species, but requires knowledge of all of the elements of interest before the start of the analysis and composition quantification cannot be performed with data only from the maps. Another disadvantage is the possibility that materials may have similar compositional analyses but may be different phases only manifested by crystallographic means.

A better method of complete phase identification involves the collection and analysis of spectral images and the subsequent crystallographic phase identification via EBSD. Spectral imaging consists of the collection of complete EDS spectra at each location within a field-of-view. From this 3-D data set, a series of elemental maps may be extracted for visualizing the spatial distribution of any elements of interest. This data set is especially useful because elements, and even characteristic x-ray lines, can be fully analyzed after the data collection with total flexibility.

The EVACTRON is a new device (US Patent 6,105,589) designed to remove hydrocarbons from SEM specimens and SEM chambers to prevent contamination artifacts. The device uses a lowpowered RF plasma to make oxygen radicals from air. These radicals oxidize hydrocarbons to make CO, H2O, and CO2 that can be removed by the vacuum pump. The use of air as an oxygen source is convenient to the SEM operator but limits the cleaning effectiveness of the system to easily oxidized carbon species. The system does remove high percentages of the usual contamination problems of vacuum pump oil and skin oil hydrocarbons from surfaces in a relatively short time.

The EVACTRON SEM-CLEAN™ system provides a safe method for plasma cleaning inside the SEM. Air as a diluted oxygen gas mixture is chosen as the plasma reactant gas. Air is passed through a low-power RF glow-discharge to create oxygen radicals inside a generator mounted on a specimen chamber port. The generator chamber is subject to the same vacuum as the specimen chamber, and the vacuum pressure and gas flow are controlled by the EVACTRON SEM-CLEAN controller. The radicals are carried out of the plasma into the whole of the specimen chamber by convection. in the chamber they react with all exposed surfaces including the specimen if present. The plasma itself is confined to the generator chamber, which prevents ion and electron bombardment damage to the instrument or specimen.

Secondary Ion Mass Spectrometry (SIMS) has unique features that makes this technique a very attractive candidate for sub-micron analysis: high elemental sensitivity (ppm or better) if reactive primary ions are used ; isotopic analysis capability ; possible insulator analysis ; no sample preparation needed ; small probed depth (a few run) and small interaction volume (cascade collision dia. < 10 nm).

Similar to a SEM microscope, a beam of Cs+ or O− primary ions is focused and rastered on the surface of the sample. The ions sputtered by this primary beam are collected, and this secondary ion beam is shaped in order to be mass filtered by a magnetic sector mass analyzer. Five mass selected images can be simultaneously recorded, originating from the exact same sputtered volume, ensuring reliable isotopic ratio and perfect image registration.

Based on Pr. Slodzian and al. [1, 2] original design, the commercial version of the NANOSIMS 50 ion microprobe incorporates several new developments in order to improve performances:

With the advent of field emission gun equipped SEMs and TEMs with clean vacuum systems, it has been shown repeatedly that the surface cleanliness of samples exposed to the small, high current density electron beam available in these instruments is critical with respect to controlling hydrocarbon contamination under the electron beam. in previous studies of dedicated plasma cleaners for TEM samples by one of the authors (SDW), it was shown that surface analytical techniques are the best methods for determining the effectiveness of such cleaners in removing hydrocarbons from the samples’ surfaces. in the current study, some of the experiments that were used in these previous studies were repeated using the XEI Evactron® system in order to compare the relative effectiveness of this system for surface cleaning of EM samples.

Figure 1 shows a picture of the sample introduction chamber of a VG Scientific ESCALAB Mkll system (XPS) with the Evactron® in place. The Evactron® system consists of an RF head unit that attaches to the vacuum chamber with an adaptable flange, an RF impedance matching unit, and an RF generator/vacuum controller. Although a 100% O2 system can be used and is recommended, for safety reasons, a 20%O2/80%Ar by volume gas mixture was selected because of the hydrocarbon oil used in the mechanical pump. Cleaning was also performed using laboratory air. The major difference between the dedicated plasma cleaners and the Evactron® configuration is that the sample is not immersed in the plasma but is exposed to the activated oxygen species in the downstream flow.

Very often, the performance of modern electron microscopes is limited by the poor quality of the laboratory rather than by the specifications of the microscope. Therefore, with microscopes aiming at subangstrom resolution microscopy and highest performing holography methods, special measures have to be taken to reach the needed low level of AC-stray fields, vibrations, and acoustic noise. in an ”organically“ grown institute, this is very difficult to realize, if possible at all.

• The Triebenberg Lab is newly built well outside the city of Dresden, in an area essentially free from disturbances, i.e. free from power lines, away from roads, trains and airplanes; fortunately, the site is shielded from wind by means of a dense belt of trees. The lab houses six microscope units each consisting of a microscope room, a room for peripheral devices (power supply, cooling units, computers, etc), and an office for up to three scientists. in view of the nearly ideal environment, the main challenge is to avoid any self-made disturbances which might arise by the operation of the lab. Therefore, without any compromise using the best art of engineering, we designed a special lab virtually free from disturbances. in the following, the main guidelines for the construction are sketched.

Surprising as it may seem, aberration correction for the scanning transmission electron microscope (STEM) is now a practical proposition. The first-ever commercial spherical aberration corrector for a STEM was delivered by Nion to IBM Research Center in June 2000, and other deliveries have taken place since or are imminent. At the same time, the development of corrector hardware and software is still proceeding at full speed, and our understanding of what are the most important factors for the successful operation of a corrector is deepening continuously.

Fig. 1 shows two high-angle dark field (HADF) images of [110] Si obtained with the IBM VG HB501 STEM operating at 120 kV, about 2 weeks after we fitted a quadrupole-octupole corrector into it. Fig. 1(a) shows the best HADF image that could be obtained with the corrector's quadrupoles on but its octupoles off. Sample structures were captured down to about 2.5 Å detail, easily possible in a STEM with a high resolution objective lens with a spherical aberration coefficient (Cs) of 1.3 mm. Fig. 1(b) shows a HADF image obtained after the Cs-correcting octupoles were turned on and the corrector tuned up. The resolution has now improved to 1.36 Å. This is sufficient to resolve the correct separation of the closely-spaced Si columns.

Sub-Ångstrom TEM to a resolution of 0.78Å has been demonstrated by the one-Ångstrom microscope (OÅM) project at the National Center for Electron Microscopy. The OÅM combines a modified CM300FEG-UT with computer software able to generate sub-Angstrom images from experimental image series.

Sub-Ångstrom HREM is gaining in importance as researchers design and build artificially-structured nanomaterials such as semiconductor devices, ceramic coatings, and nanomachines. Commonly, such nanostructures include atoms with bond lengths shorter in projection than the point resolution of a mid-voltage HREM. in addition, image simulations have shown that structure determinations of defects such as dislocation cores require sub-Angstrom resolution, as will hold true for grain boundaries and other interfaces.

Sub-Ångstrom microscopy with a transmission electron microscope requires meticulous attention to detail. As resolution is improved, resolution-limiting parameters need to be reduced. in particular, aberrations must be minimized, power supplies must be stabilized, and the microscope environment optimized to reduce acoustic and electromagnetic noise in addition to vibration.

One of the most striking problems in electron optics, the correction of resolution limiting aberrations by means of a corrector incorporated into the electron microscope column, has been solved during the last six years by demonstrating the improvement of resolution beyond the theoretical limit of the uncorrected Electron Microscope (EM). At first, in 1995 [1] with the correction of spherical and chromatic aberration of a dedicated Low Voltage Scanning Electron Microscope (LVSEM) and later, in 1997, with the correction of only spherical aberration of a commercially available 200 kV TEM [2]. The correction of spherical aberration of a dedicated Scanning Transmission Electron Microscope (STEM) at 100 keV primary energy has been demonstrated [3] and further improvements can be anticipated within the near future.

These achievements could only be obtained due to the emergence of new computer technology and especially CCD-cameras in the case of TEM correctors. These two developments made it possible first to calculate the electron optical components more precisely and hence, to achieve a better understanding of the requirements on the hardware and second, to have a better computer control of the electron microscope and the corrector itself. The combination of these two new technologies made it possible to go towards an automatisation of the alignment. This simplification of the alignment of an even more complex system is achieved by means of a proper combination of image acquisition and dedicated software in order to analyze and measure the aberrations of an electron optical system on one side and on the other to have appropriate tools to compensate these aberrations by computer controlled power supplies [4,5].

One of the limiting parameters in high-resolution transmission electron microscopy (HRTEM) are the high values for the spherical aberration Cs of the objective lens, which are the reason, that for TEM's with field-emitter the point resolution at Scherzer defocus is about two times lower than the information limit. Another effect of Cs-values of about one mm is the rather large disc of least confusion, which contributes to a high amount of contrast derealization. Furthermore the images are very sensitive towards beam tilt. These disadvantages contribute to a difficult interpretation of HRTEM-images especially at interfaces and defects. In-situ applications as well as diffraction contrast experiments require a gap of at least ten mm between the pole pieces. For the present TEM's this degrades the resolution at an acceleration voltage of 200 kV to approximately 0.27 nm. Cs-correction offers the ability to combine high resolution with a large space for the sample, which can be used for in-situ experiments.

Recently, we have constructed a lens system for Cs-correction based on hexapole lenses for a commercial 200 kV instrument equipped with a field emission gun. This system allows choosing the Cs-value between +2.0 mm and -0.05 mm. The objective lens of the microscope has a Cs value of 1.2 mm resulting in a point resolution of 0.24 nm.

In electron microscopy high-resolution imaging of finest object structures is generally hampered by the influence of aberrations of the lens system, especially the high spherical aberration of the objective lens. The delocalization of contrast details induced by aberrations is especially strong for microscopes equipped with a field emission gun providing a high spatial coherence. in recent years a prototype of an aberration correction system has been constructed by Haider et al., following a suggestion by Rose, consisting of two hexapole elements and four additional round lenses. The correction system was adapted to a Philips CM 200 FEG ST microscope with an information limit of 0.13 nm. The alignment is carried out using aberration measurements deduced from Zemlin tableaus. By appropriately exciting the hexapole elements it is possible to reduce or even fully compensate the spherical aberration of the objective lens.

With the freedom of a variable spherical aberration Cs new operation modes can be accessed that are not available in standard microscopes. with Cs = 0 and defocus Z = 0 pure amplitude contrast occurs, together with a vanishing contrast delocalization; phase contrast with a single, narrow pass-band up to the information limit can still be achieved by Z = ±7 nm, which introduces a delocalization of R = 0.13 nm. with Cs = 97 μm and Z = −18 nm the broad Scherzer pass-band for phase contrast can be extended to the information limit, with R = 0.35 nm. For the CM 200 Cs = 43 fim and Z = −12 nm still produces a high level of phase contrast, comparable with the extended Scherzer pass-band, but with R = 0.08 nm only. in the latter mode Scherzer’s defocus equals Lichte's defocus of least confusion.

Field emission electron microscopes operating at 200kV or 300kV and incorporating aberration correctors for either the incident electron probe or for the primary aberrations of the objective lens (OL) are currently under development for several laboratories in the world. OL-corrected instruments require monochromators for the electron beam, built into the electron gun prior to the accelerating stages, in order to optimize the contrast transfer characteristics of the objective lens to push the instrumental resolution limit to well beyond 0.1nm. This will allow the point resolution limit as controlled by the correction of spherical aberration Cs to potentially extend to the instrumental limit of better than 0.1nm. Figure 1 shows the contrast transfer characteristics of a Cs-corrected 200kV TEM, both without and with a beam monochromator.

Dedicated STEM instruments such as the 300kV VG-603 and lOOkV VG-501 at Oak Ridge National Laboratory, and other VG instruments at Cornell University and IBM Co. are also being adapted (by Nion Co., Kirkland, WA) to incorporate aberration correctors for the incident probe. The aim is to improve the resolution of the VG-603 instrument in dark-field imaging mode, for example, from 0.13nm to 0.05nm. in another ORNL project, the High Temperature Materials Laboratory has contracted JEOL Ltd. to construct a STEM-TEM instrument with a probe corrector designed and built by CEOS GmbH (Heidelberg, Germany).

A new type of electron energy loss spectrometer for use with monochromated microscopes is presented. The energy resolution of the spectrometer is better than 0.100 eV. A completely new electron optical design with a number of extra optical elements and advanced tuning software makes it possible to correct spectrum aberrations to 4th order, which increases sensitivity and collection angles. New high-stability electronics make it possible to maintain energy resolution over a period of several minutes in a practical laboratory environment.

The energy resolution of Transmission Electron Microscopes (TEMs) equipped with electron energy loss spectrometers is determined by a combination of the energy spread of the electron source, the stability of the microscope’s high voltage power supply, and the energy resolution of the spectrometer. Commercial microscopes usually employ electron sources with an energy distributions of around 0.5 eV or more (FWHM), limiting the energy ultimate energy resolution that can be achieved. Recently FEI constructed a special 200 kV TEM with a built-in monochromator which makes it possible to monochromize the electron source to better than 0.100 eV. A prototype of the presented spectrometer has been installed on this microscope.