Helium microscope non-destructive imaging
Paint this picture. You’re out and see something nice. You take a photo. And just like that, whatever was the focus of that camera is now destroyed...
Despite how it sounds, this is not an episode of Doctor Who, it is actually a real-life issue plaguing microscope imagery.
Thankfully, there is a solution, and it is called the Scanning Helium Microscope, or SHeM for short. Developed by scientists from the University of Newcastle in Australia and the Cavendish Laboratory in Cambridge, the microscope uses a beam of low energy, neutral helium atoms to create super-detailed images on microscopic scales without damaging the sample. “What we see now here for the first time is an imaging technique that is guaranteed not to damage what we look at,” comments Dr. Paul Dastoor, the project's lead scientist at the University of Newcastle.
The root of post-image damage stems from energy accumulation. Electron and light microscopes shoot their sample with a lot of energy, which is measured in a unit called electron volts. Altering chemical bonds in a material only takes about 1 electron volt. On this same scale, light has 2 of these units, which is why the sun can strip your favourite shirt of its rich colours. Electrons are in a league of their own, with a staggering 100,000 units, usually resulting in a slightly crispy sample. Helium atoms, however, carry only half a unit, which leaves a sample so undercooked Ramsey couldn’t dream of sleeping easy. “There is no chance of the helium atoms damaging the surface at all,” says Dastoor.
SHeM's superb sample safety is not its only key benefit. Light’s theoretical maximum resolution is half a micron - 0.0000005m - while helium's maximum resolution is 0.6 Angstroms at room temperature; that's 0.00000000006m. This means that images taken with SHeM can be roughly 8,000 times more detailed than anything light microscopes could theoretically offer. This resolution will be possible only once the detectors used in SHeM become more sensitive in detecting a larger number of reflected helium atoms. “The key here, the thing that is limiting us, is all around the detection, how sensitive can we make these detectors,” explains Dastoor. The resolution of SHeM at the moment is limited to about a micron, but this will soon be increased to 15 nanometres, thanks to another device that is being built right now in the Cavendish Laboratory.
As for the present model, the microscope itself is huge: about the size of a sofa. First, the helium gas is pumped up to a high pressure before being expanded into a vacuum through a small hole just 10 microns across. This produces a "beam" of helium atoms, which travels down a long pipe where it collides with the sample. Helium atoms that bounce off the sample are registered by a very sensitive helium atom detector. With the help of complex software that processes the flux, or flow, of force from the atoms through a finite surface area, an image can be created with the addition of position data from the reflected helium atoms. The leftover helium gas is then pumped up through the ceiling of the lab into a balloon. The gas isn’t being used for flashy party decorations though, it is actually separated from other gases and recycled for future images.
As the imaging technology gets better and more fields of science start to depend on SHeM, future ambitions for the team include making a desktop-sized model of the microscope. “In fact, we know that we can do that, there’s lots of empty space here,” Dastoor cheerfully acknowledges.
The team dreams of making SHeM’s benefits in microscopic imaging available for everyone around the world, hopefully allowing for more undercooked and not so crispy photos for everyone!