All of the power, none of the space

The power of an electron microscope needn’t come at the cost of lab space says Mhairi Crawford of Hitachi High-Technologies

Figure 1: Starsand

Space is always at a premium in any laboratory, yet the most powerful analytical equipment usually comes at the cost of having the highest demand for space.
This has been especially true in the world of microscopy, where electron microscopes have traditionally required a room to themselves, not just for reasons of their size but because of ancillary demands for pipes and services. The simpler optical microscopes, of course, can happily occupy the bench-top, but because their performance is limited by the wavelength of light, their powers of magnification and resolution are inferior to that of the electron microscope. Therefore, where magnification is required in excess of 1000x, or a resolution of much better than 0.3μm is needed, the optical microscope is unable to deliver.

Simple alternative

Figure 2: Stent, used to open arteries

In April 2006, at Analytica in Munich, the European laboratory market had its first sight of a new tabletop microscope from Hitachi-High Technologies, which bridges the gap between the worlds of optical and electron microscopes. Available in Japan since April 2005, the TM-1000 has already found applications in industrial, academic and government laboratories, examining material as diverse as cosmetics, stone, fabrics, electronic parts and pharmaceuticals.
With a footprint of just 564mm x 478mm, the TM-1000 will sit comfortably on a bench top but offers magnification and resolution performances much closer to that of a standard SEM. Indeed, the TM-1000 can be properly described as a scanning electron microscope, but it is greatly simplified for easy set-up and ease of use. In terms of set-up the TM-1000 is virtually ready for use as soon as it’s delivered. No special facilities such as cooling water are required. It merely needs to be plugged in to a standard electrical supply. The ‘Autostart’ function turns on the beam, and automatically adjusts the magnification and focus, so that the specimen can be imaged immediately.
Whilst the tungsten filament used as the electron source is just the same as that used in a standard SEM, the accelerating voltage is set at a constant 15 keV. The rest of the instrument is optimised for this accelerating voltage, and so the TM-1000 is very stable.
The depth of field and resolution of images produced by the TM-1000 are superior to those offered by light microscopes as the high resolution image of star sand demonstrates (Figure 1). Moreover, it is capable of producing both topographical and elemental contrast detail. Figure 2 is that of a stent, used in medical applications for opening arteries, and the back scatter detector of the TM-1000 clearly exposes contamination on the surface.
Conducting samples, such as the PCB are readily observed because the entire chip can be put straight into the microscope with no sample preparation and the microscope itself is also easy to use. In fact, auto functions for focus, brightness and contrast, give the TM-1000 a ‘point and click’ functionality, such that anyone familiar with using a digital camera will be able to use the TM-1000 with very little training.

Non conductors
Non-conducting samples have always presented something of a challenge for the electron microscope, because the electron beam can cause charging on the surface of the specimen leading to damage and image distortion. The usual

Figure 4: Shirt during charge   reduction mode	Figure 5: Shirt during high-vacuum mode

approach taken in a standard SEM is to coat the specimen with a thin conducting layer (often gold, platinum or carbon), but no such preparation is required for imaging non-conducting samples in the TM-1000. The TM-1000 has a charge-reduction mode, which allows non-conducting samples to be observed directly, without any preparation. The examples shown here of shirt fabric (Figures 4 and 5) show the difference between images produced under high-vacuum and charge-reduction modes.
Similarly, the image of pollen grains on a bee’s-knee (Figure 6) clearly illustrates that the fine detail of biological specimens is maintained under this procedure and the resolution and depth of field again exceeds that of a light microscope. Very wet samples, such as cells and fully hydrated samples can also be imaged in the TM-1000.

High performance
As discussed above, the TM-1000 offers a 10x improvement in resolution and

Figure 6: This image is the Bee's knees. Literally.

magnification range as well as 100x improvement in depth of field compared to conventional optical microscopes. It therefore provides a real and high performance alternative to optical microscopes, stereo microscopes and confocal laser scanning microscopes. The remarkably powerful imaging capabilities reveal surface morphology in great detail, with the added benefit that the imaging detector shows contrast from different average atomic number composition in the sample.
Samples of up to 70mm in diameter and 20mm thickness can be accommodated, and the TM-1000 features a magnification range of 20 – 10,000x using standard imaging and up to 40,000x using digital zoom capabilities. A built-in measurement function allows dimensional information to be acquired quickly and easily.

Revolution or evolution
The dedicated microscopy laboratory will, of course, always find a place for a conventional SEM. The TM-1000 was never intended to replace the conventional

Figure 7: White blood cells

SEM, and experienced microscopists will continue to value the flexibility provided by a full range of accelerating voltages and detectors, and the higher resolution provided by such a system. Nonetheless, for routine observations, the TM-1000 could prove to be a useful addition to the laboratory. It will give microscopists a useful ‘first-look’ at samples, at the same time as freeing time on the conventional SEM for more detailed investigative work. Similarly, the general laboratory, which is perhaps frustrated by the limitations of their optical and stereoscopic microscopes, will undoubtedly find many reasons to welcome the greater magnification and resolution of this new SEM. And since it only occupies a modest space on the bench-top, they should also find many places where they can put it.

Hydrated samples In common with conventional Hitachi scanning electron microscopes the TM-1000 can accommodate Quantomix WETSEM technology, enabling hydrated or oily samples to be studied at atmospheric pressure and room temperature. It is equipped to accept a specially designed sample capsule, which fits in the standard stub holder of most instruments and was developed in the physics department at the Weizmann Institute of Science, Israel. Now commercialised by QuantomiX, the capsule is a single-use vacuum-tight container, whose upper surface consists of a grid covered in a unique electron-transparent and pressure resistant membrane.  The grid provides support for the membrane to withstand differential pressure. This ultra-thin membrane is robust enough to completely isolate the wet sample from the vacuum environment within the chamber of a standard SEM, yet allows the penetration and reflection of a scanning electron beam. In this way, the sample remains both at ambient temperature and atmospheric pressure, and allows the hydration process to be observed under completely natural conditions.

By Mhairi Crawford, Hitachi High-Technologies Corporation