Direct writing of hafnium diboride metallic nanostructures on silicon (100) surfaces using a UHV-STM

The patterning of metallic nanostructures on surfaces is of great interest in fabricating nanoelectronics and quantum devices. In this work, we deposited HfB$_{2}$ nanostructures on silicon surfaces from Hf(BH$_{4})_{4}$ by electron beam induced deposition (EBID). At positive sample bias, the electron beam from a STM probe initiates the local CVD by the decomposition of Hf(BH$_{4})_{4}$ under STM tip. By repeatedly scanning STM tip along a specific path, well-defined HfB$_{2 }$nanostructures can be directly written onto the surface. Scanning tunneling spectroscopy was used to characterize the electronic properties of the nanostructures. We have achieved 4 nm linewidths and complete selectivity relative to adjacent H-Si(100) regions. The thickness of the nanostructures is controlled by the exposing time to the electron beam from STM tip, while the width is controlled only by the geometry of the tip apex and the sample-tip separation. STS data confirm that the HfB$_{2}$ nanostructures deposited are pure metallic, indicating minimum contaminations in the nanostructures, which we attribute to the carbon-free nature of the CVD precursor. To our knowledge this is the first demonstration of sub-5 nm metallic nanostructures in a STM/CVD experiment.