No abstract

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.

The serial detectors traditionally used in Electron Energy Loss Spectroscopy (EELS) have mostly been replaced by parallel detection systems, for reasons of efficiency and ease of use. So far most parallel detection systems have been based on fiber or lens coupled Photo Diode Array (PDA). Although these systems have proven satisfactory they have some limitations: 1) high readout noise, 2) limited correction for gain variations and 3) point spread function or cross talk between channels all of which effects the ultimate sensitivity and resolution. This paper discusses a newly developed parallel detector for EELS based on a CCD and a new type of scintillator and fiber technology. The new detector shows large improvements in all areas of performance.The sensitivity of a detector is limited by the readout noise at low incident electron dose and the gain correction at high dose. Both these areas have been addressed in the new design. The readout noise is equivalent to approximately 1/2 a primary electron, about 40 times better than a typical PDA.

No abstract

Last year we discussed the performance of a new parallel EELS spectrometer, the ENFINA™. The spectrometer optics have been considerably improved over past designs and the detector changed from a photodiode to a charge coupled device that was designed specifically for spectroscopy. in this work we present application examples that demonstrate some of the capabilities of the ENFINA™.STEM spectrum imaging requires a spectrometer of high speed and sensitivity if useful data is to be collected in a short period of time. The ENFINA™ spectrometer achieves both of these through a radically improved point spread function, increased sensitivity, and fast detector readout. Useful spectrum images can be acquired in a few minutes. Figure 1 shows a dark-field STEM image of a typical semiconductor. A spectrum image containing 190 x 150 spectra was acquired from within the marked area.

No abstract

Post-column imaging filters on TEMs are powerful analytical tools for the purpose of elemental and chemical mapping, image resolution and contrast enhancement through zero-loss filtering [1], high resolution quantitative analysis through EELS spectroscopy and EELS spectrum imaging [2].We present a new post-column filter designed for TEMs up to 400 keV equipped with an electron source of energy spread greater than 0.3 eV. The chief advantages of the new design include a superior high-speed, high-resolution 2k x 2k CCD imaging system and improved electron optics which simplify the energy-filter operation and increase the field of view by a factor of almost 3.

We have designed and built a next generation high-voltage imaging filter (HV-GIF) which has several significant improvements with respect to the previous model.Most present day TEMs work with acceleration voltages between 100 and 400 kV, but for some applications it is advantageous to use an electron beam with higher energy. Previously, Gubbens et al. [1] reported on the design and testing of a post-column imaging filter suitable for use with electron-energies up to 1.25 MeV. Three of those filters were built and are still being used.The mechanical design has been improved to make the system more rigid, reduce the number of vacuum seals, and optimize reliability. The original system consisted of a single magnetic prism with curved entrance and exit faces, 6 strong quadrupoles and 5 strong sextupoles after the prism and several weak lenses before the prism. The new filter includes additional multipole lenses to correct for non-symmetrical chromatic and geometric aberrations introduced by mechanical imperfections. Chromatic aberration correction is useful especially when the filter is operated at lower voltages. Typically, a high-voltage TEM is operated at several voltages with the lowest in the 400 kV range.The filter is equipped with three cameras. First, a 676 off-axis intensified TV-rate camera is located near the entrance of the filter. This camera can be operated independently from the filter itself. Second, a 692 retractable TV-rate camera with a phosphor scintillator is at the end of the imaging filter. This camera is mainly used to quickly find areas of interest in the specimen, or for alignment purposes. Third, a specially designed high-voltage MultiScan camera is installed behind the 692 TV-rate camera. This camera is used for the final acquisition of images and spectra. To prevent Xrays generated by the electron beam from hitting the CCD the image on the scintillator is reflected upwards using a mirror at an angle of 45°, and projected on the 1k x 1k CCD with a custom-built projection system. [2] The CCD can be adjusted with three degrees of freedom to focus the image. This filter will be installed on a JEOL ARM1300S microscope, but can in principle be used with any high-voltage microscope.