Cost and Capability Compromises in STEM Instrumentation for Low-Voltage Imaging

Abstract

Low-voltage transmission electron microscopy (≤80 kV) has many applications in imaging beam-sensitive samples, such as metallic nanoparticles, which may become damaged at higher voltages. To improve resolution, spherical aberration can be corrected for in a scanning transmission electron microscope (STEM); however, chromatic aberration may then dominate, limiting the ultimate resolution of the microscope. Using image simulations, we examine how a chromatic aberration corrector, different objective lenses, and different beam energy spreads each affect the image quality of a gold nanoparticle imaged at low voltages in a spherical aberration-corrected STEM. A quantitative analysis of the simulated examples can inform the choice of instrumentation for low-voltage imaging. We here demonstrate a methodology whereby the optimum energy spread to operate a specific STEM can be deduced. This methodology can then be adapted to the specific sample and instrument of the reader, enabling them to make an informed economical choice as to what would be most beneficial for their STEM in the cost-conscious landscape of scientific infrastructure.

Retrofitting a Photoelectron Source: Improving Resolution & Functionality

“…The chromatic (defocus) blur can be reduced by decreasing the energy spread of the primary electrons. This usually involves an upgrade to a lower energy spread electron gun such as a cold FEG (∆E≈0.3eV) or installing an expensive electron monochromator which is not feasible for many global research laboratories [2].…”

The User Adjustable Pole-piece: Expanding TEM Functionality Without Compromise

“…A TEM column is a significant investment for any research institution due to both the high initial cost, followed by the running and cooling energy costs (leading to non-trivial carbon emissions), support staff costs, and maintenance contracts for perhaps another 15 years. If, to avoid performance compromises, multiple columns must be purchased, then this duplication of both up-front and running costs raises significant sustainability considerations [5].…”

Benchmarking the Performance of a New Photoelectron Source

“…Decreasing the energy spread of an instrument's beam could involve upgrading your electron gun to a lower energy spread electron source such as a cold field emission gun or investing in an expensive electron monochromator. Figure 1 is an graph adapted from [3] on the approximate cost of electron monochromators and different electron guns versus their electron energy spread. We see that there is a general trend that the lower the electron energy spread required the more expensive the equipment needed.…”

“…Figure 1.A representation of the general trend in the price/performance trade-off of a variety of electron guns and monochromators. Further details for all emitters are found in[3]. Information on the energy spread of the photoelectron gun can found in[4].…”