“The possibility of looking inside silicon chips to see their tiny working parts, without damaging the chips, is a step closer thanks to an international team led by scientists at UCL. The group at UCL, led by Dr Neil Curson (UCL London Centre for Nanotechnology), have shown they can generate pictures of tiny three-dimensional components, made from phosphorus atoms, that are completely invisible to all other imaging technologies. Remarkably, the pictures of these components were obtained despite the fact that the components were the size of only a few tens of atoms, were atomically thin and were buried under the surface of the chip. An accurate quantitative determination of the location of the buried components was obtained, along with certain electrical properties. This breakthrough is published in Science Advances. The components that were studied, including a three-dimensional criss-cross of metallic phosphorus stripes, were designed and manufactured by UCL PhD student Alex Kölker. He used a super-sharp metal needle to write patterns in a single layer of hydrogen atoms that lay on the surface of a silicon chip, creating a template of a desired shape. By causing a chemical reaction to happen between the surface of the chip and phosphine gas, phosphorus atoms were written into the surface, in the shape of the template. The phosphorus structures were then buried with more silicon to complete the device. A recently developed scanning microwave microscope was used to take pictures of the components, obtained with our collaborators at Johannes Kepler University, led by Georg Gramse, and by Keysight Technologies (Austria), Paul Scherrer Institut, ETH Zürich and EPF Lausanne (Switzerland). The microscope works by focussing microwaves (like those from a microwave oven), to the end of a metal tip which is pushed against the surface of the chip. The microwaves are fired into chip, subsequently bouncing back from the buried components, measured, and used to construct a picture.”