Nanoscale coating on tip geometry by cryogenic focused ion beam deposition

Abstract

We report application of nanoscale in-situ cryo-condensation coating technique on needle-shaped specimens and frozen hydrated cells. By using a cryogenic focused ion beam/ scanning electron microscopy (cryo-FIB/SEM) instrument, phase transformation of the metal–organic precursor gas has been demonstrated to occur at the cryogenically cooled metal tip of 50 nm in radius, and the properties of the deposited layer can be tuned by the control parameters. Revealed surface morphologies on the needle tip include nanoscale columns using glancing angle deposition (GLAD). With deposition performed at multiple orientations, a continuous frozen shell as thin as 40 nm can be formed. The physical mechanisms of curing by ion beam/electron beam irradiation have been further investigated with characterization tools including transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS), and the results confirm the feasibility of constructing a platinum-rich conductive layer. The proposed approach is also demonstrated by depositing a thin conductive layer on frozen hydrated bacterial cells to facilitate sectioning and high-resolution electron imaging. The proposed approach opens a novel route to nanofabrication on tip geometry as well as site-specific conductive protection to facilitate nanocharacterisation.