Nion UltraSTEM 100 electron microscope

Nion UltraSTEM™ 100

The UltraSTEM 100 is a high-performance dedicated scanning-transmission electron microscope (STEM) with many unique features. Its flexible column provides < 1 Å resolution imaging as well as rapid nanoanalysis with an atom-sized electron probe containing >0.5 nA of current, and efficient coupling into a variety of detectors. It can also produce high-quality diffraction patterns and even CTEM images.

The UltraSTEM has produced atomic-resolution elemental maps in less than a minute (see news). This promises to lead to a new era in electron microscopy in which atomic-resolution elemental maps become a powerful addition to the range of available microscopy techniques.

The principal design elements of the UltraSTEM that have made this advance possible are:

• high-brightness cold field emission electron gun (CFEG)
• high-performance 3rd generation C3/C5 aberration corrector
• ultra-stable sample stage using detachable sample cartridges
• optimized EELS coupling optics
• UHV construction
• complete remote operability, including sample exchange

Many of these features are unique to the Nion microscope. A full description of the microscope has recently been published in Ultramicroscopy.

Nion UltraSTEM 200

This electron microscope extends the range of operating voltages to 200 kV. Its column is similar to the UltraSTEM 100. The higher operating voltage gives:

• higher resolution: < 0.8 A high angle dark field resolution (HAADF)
  
• higher probe current: > 1 nA in a 2 A probe
  
• greater sample penetration

The delivery of the first UltraSTEM 200 is scheduled to take place in spring of 2009.

Spherical aberration correctors

Nion was the first company in the world to deliver a commercial aberration corrector, for a 100 kV VG HB501. VG microscopes equipped with Nion Cs correctors have established many performance benchmarks by which other microscopes are now measured (see results section). They continue to provide hard-to-equal imaging and analytical performance, at a fraction of the cost of complete new systems.

The correctors are incorporated into the VG microscope at the customer site, without raising the height of the VG column. This is accomplished by replacing the VG scan coils by miniaturized scan coils which fit into the lower bore of the objective lens of the microscope. The corrector then simply occupies the space vacated by the VG scan coils. The corrector consists of four quadrupoles and three octupoles, numerous auxiliary alignment and adjustment coils, and power supplies and controlling software. The corrector is compatible with the UHV standards employed by the VG microscopes: it uses double O-rings with a guard vacuum, and can be baked to 140° C. The controlling software is able to analyze all axial aberrations of the microscope system up to fifth order in a few seconds, and adjusts them automatically for optimum performance.

The VG corrector package includes several major upgrades to the microscope: a bakeable, fiber-optically coupled 1k x 1k CCD camera for Ronchigram recording (for both 100 kV and 300 kV systems), a vacuum upgrade to all-dry construction using ion pumps and a turbo pump, and a quadrupole-octupole EELS coupling module (for 100 kV systems only). A useful further option is a 100 kV OL polepiece that allows standard VG tilt cartridges to be used but lowers the OL aberration coefficients to C_s ~ C_c ~ 1.7 mm.

Custom solutions

Nion is a small and responsive company whose scientists and engineers are deeply knowledgeable about electron microscopes and very interested in pursuing new applications. Our UltraSTEM microscopes are completely modular; all the modules of the microscope column use the same exact mating surface. They can therefore be stacked in almost any sequence and total number. The vacuum system, the electronics, and the detector column are also modular. This means that the column can be reconfigured in many different and unique configurations.

Examples of possible column variants include:

• a sample chamber reconfigured for in-situ electrical measurements and other experiments
  
• high-quality post-column optics. A second corrector can be placed after the objective lens to provide C₃/C₅ aberration-corrected CTEM imaging
  
• extra lenses for the post-sample column, to provide high-magnification CTEM imaging even with the objective lens off
  
• extra modules for the illumination column to provide new capabilities such as ultra-fast beam blanking
  
• new detectors, such as large-format CCDs
  
• back-scatter electron detector for imaging of bulk samples
• simplified column without an aberration corrector for biological STEM

Nion Service

The service of Nion microscopes is based on four principles:

• Remote diagnosis. The Nion microscope is completely remotely operable. If a problem appears, Nion personnel typically diagnose it by operating the microscope remotely, within 24 hours of the problem being reported.
  
• Modularity. Because the microscope is modular, the number of different types of spare parts (PCBs, cables, mechanical modules) is minimized. Nion is typically able to ship a replacement for a defective module that can be installed by the customer within 24 hours of the diagnosis becoming clear.
  
• Site Service. More challenging problems requiring an on-the-spot intervention are typically resolved with a visit by the Nion expert specializing in that particular subsystem. Customers therefore do not have to go through several visits by service engineers who are not sufficiently familiar with the full complexities of the microscope and end up passing the problem onto a higher level in the service organization.
  
• Update visits. As a part of the Nion service plan, Nion engineers visit the site at least once a year to carry out major software updates and customer training refreshers.