The image entered in 2021 in Guinnes World Record for the highest resolution ever achieved portrays a crystalline lattice of praseodymium orthoscandate (PrScO3) magnified well 100 million times with distinguishable details up to 0.02 nanometers (a nanometer is one millionth of a millimeter) and was created by a team of scientists from Cornell University thanks to a technique he calls electronic ptychography. Each “ball” seen in this image is a single atom: the close pairs are atoms of praseodymiumthe single, lighter ones are atoms of scandium and while the darker and more nuanced ones are atoms of oxygen. The crystalline nature of the material is evident from the almost perfectly regular distribution of the atoms it contains.
The electronic ptychography technique makes use of a electronic microscope. To “see,” electron microscopes do not use light (like a traditional optical microscope) but electrons. In general, the more energy the electrons have, the higher the resolution of the image. The problem is that too energetic electrons can alter the sample that we want to observe: this represents a resolution limitand for images via electron microscope.
The technique of electronic ptychography was invented precisely for get around this problem, increasing the resolution of the images while maintaining “acceptable” electron energy. To understand how it works, imagine having an unknown object completely immersed in darkness and having small balls (representing electrons) with you. If you throw the balls from a certain direction, these they will bounce on the walls based on the shape of the object in the space, thus creating a precise pattern of bounces on the walls. If you then throw them from a slightly different direction, the bounce pattern will also change accordingly. With enough balls and enough throwing directions, therefore, you can in principle – with a lot of patience! – reconstruct the shape of the object and then understand how it is done. This is in a nutshell the principle behind electronic ptychography, whose name derives from the Greek root ptych- which roughly means “to bend” (referring to the trajectories of the electrons).
That's exactly what researchers at Cornell University did to obtain this incredibly detailed image of an orthoscanned praseodymium lattice. They occur naturally extremely complex algorithms and a large amount of time for the 3D reconstruction of the image, but as you can see the method works. Think that the “blur” that you can see around the individual atoms is not due to a flaw in the method, but to thethermal agitation of the atoms themselves. Basically, atoms are not perfectly still: they “shake” slightly but continuously, since they have a certain energy. This means that the photo came out “shaky” not because the camera is defective but because the subject moved! We basically passed the technological limitations for resolving atomic images and achieved the physical limit.
This technique is not just an exercise in style. The possibility of observing even three-dimensional samples of material with a level of detail of hundredths of a nanometer can open up new avenues for the creation of chips or batteries with higher performance and at the same time more efficient, for example by identifying impurity in a material or allowing us to observe in an unprecedented way materials fundamental to electronics, such as semiconductors or materials for the creation of quantum computers. Other application possibilities are in medical fieldfor example for the study of synapses or the most diverse cellular tissues.
