Scanning Electron Microscopy for Your Lab

Source: Dr. Cameron Chai and Dr. Kamran Khajehpour

Scanning Electron Microscopy or SEM is no longer a technique found solely in central analytical facilities within universities. Systems like the TESCAN VEGA bring SEM capabilities well within the realms of possibility for smaller testing labs, quality control labs and companies involved in R&D. They can also prove their worth in short timeframes in onsite labs eliminating the need to send samples off-site for testing.

There was a time many years ago when SEMs required highly skilled operators who sat in dark rooms peering at small black and white screens, backed up by clever maintenance engineers who were regularly called on to fix all manner of problems. These days are all well behind us, with the latest crop of instruments from TESCAN providing unrivaled reliability and ease of use. TESCAN’s generation 4 SEMs come standard with their revolutionary Essence software. This allows the user interface to be customised to your own specific workflow requirements. With a host of automated operations and other innovations such a wide field optics which streamlines sample navigation and live chamber view camera, and a super-smart collision model, accidents become almost impossible. These features also make systems like the TESCAN VEGA an ideal teaching or workhorse instrument with even novice operators able to generate high-quality images with very little training. Essence EDS is fully integrated into the user interface and provides real-time chemical analysis via Energy Dispersive Spectroscopy (EDS). EDS is the most common analytical addition for SEMs. EDS mapping can provide valuable information about chemical distributions and inhomogeneities. Systems like the TESCAN VEGA are also highly affordable, especially when compared with other analytical instruments and smaller benchtop SEMs. As an entry-level system, the TESCAN VEGA Compact benefits from many years of evolution and other developments common to its more sophisticated stablemates. Furthermore, it is actually cheaper than many benchtop systems and offers superior performance and versatility with a larger chamber size and the ability to add additional detectors either at the time of purchase or down the track. Should you need to analyse even larger samples, this is possible at very little extra cost using similar systems with larger chamber sizes. While many things such as electronics can be successfully miniaturised while still bringing performance gains, this does not translate to everything, such as electron optics. Smaller electron optics i.e. SEM column typically translates into lower magnification and resolution power from benchtop SEMs. Benchtop SEMs often only offer low vacuum imaging capabilities. This means they rely on BSE detectors which do not reveal as much detail as SE detectors. Furthermore, benchtop SEMs typically have lower accelerating voltages and extremely lower probe currents. These make EDS analysis (qualitative and quantitative especially) much more challenging. With SEMs, there are often consequences to small and cheap. Imaging of most insulating and beamsensitive materials is fast and easy using the standard SingleVac mode. For the most challenging samples TESCAN offers the MultiVac option. TESCAN MultiVac enables low vacuum and extended variable pressure on TESCAN SEMs. MultiVac operates in both Nc and H2O atmospheres, and MultiVac’s extended variable pressure (up to 500 Pa) mode allows controlled fine-tuning of vacuum to achieve the best charge compensation for any insulating sample. MultiVac also includes TESCAN’s proprietary gaseous secondary electron detector (GSD) which, when used in H2O atmospheres, enables high resolution imaging at low keV and low beam currents for topography characterisation on beam sensitive samples. The ability to characterise a sample’s topography at low keV is essential, because lower beam penetration depth will enhance topographical contrast and reveal surface details. MultiVac seamlessly integrates with TESCAN SEMs and is controlled directly from TESCAN’s

Essence™ software, making high quality characterisation of insulating, beam sensitive and outgassing samples effortless and accessible to all users.