The Open Beam Interface Offers Digital Image Capture From Almost Any Scanning Electron Microscope

Electron microscope engineers Adam McCombs and Isabel Burgos have opened pre-orders for a small-run batch of the Open Beam Interface — billed as the first open source digital image capture device for scanning electron microscopes (SEMs).

"Bring your analog SEM into the digital world, all over one USB Type-C connection," McCombs writes of the device, which links to open source software capable of digitising images from a broad range of SEM devices at resolutions up to 16,384×16,384. "We are obsessive electron (and ion) microscope hackers and maintainers working to enable more people to truly own these systems. Through freely shared information and resourceful engineering we want to open the way for exploration by teaching old microscopes new tricks and microscope owners new skills."

Scanning electron microscopes go considerably beyond optical microscopes, peering down at scales where optical microscopy can't reach by bombarding a target with a focused beam of electrons that interact on an atomic level in a way that can be measured and decoded into an image. While traditionally the preserve of well-funded laboratories, older SEMs find their way into hackers' hands not-infrequently — and the Open Beam Interface aims to make it easier to get quality imagery out of them.

"We have crafted this board to support as many microscopes as possible," the pair write of the device and its software stack. "We do not know of a SEM or FIB [Focused Ion Beam] that specifically does not have these signals somewhere inside that can be tapped. Many microscopes have an existing dedicated connector for external scan inputs. This was in general originally for external beam control coming from EDS or other X-Ray mapping systems. For microscopes that do not have a dedicated external scan connector, the X and Y ramps that drive the scan coils exist somewhere."

Driven by a field-programmable gate array (FPGA) programmed in Amaranth HDL and building atop the Glasgow Interface Explorer, the Open Beam Interface offers two high-speed digital-to-analog converters (DACs) and a single high-speed analog-to-digital converter (ADC). Using this, the SEM's electron beam can be controlled and the resulting data captured for decoding into a high-resolution. There's a live view mode, for focusing the beam, and image capture at an impressive 16,384×16,384 resolution.

The board and its software have been tested with the JEOL 35C, 840, and 63/6400 SEMs, McCombs and Burgos note, while "partial support" is possible on FEI XP devices including the FIB 200, Expedia 830, and Expedia 1230. "Tapping into the signal path may require fabricating a custom cable," they warn of devices not yet tested.

Those with an SEM interested in ordering from an initial batch of six Open Beam Interface boards can contact McCombs on Mastodon for details; the hardware designs, meanwhile, are available on GitHub under the weakly reciprocal CERN Open Hardware License.