Ion beam microscopy has recently attracted intense interest from the scientific communities in both physical and life sciences. Among the chief reasons for the rejuvenated interest is the capability to obtain sub 0.5 nm helium beam sizes using the high-brightness Gas-Field Ion Source (GFIS). In this proposed research project, we intend to expand the repertoire of characterization modalities. Specifically, we will explore and evaluate the scientific and technological opportunities available in the Transmission Mode of Helium Ion Microscopy, investigating both classical and quantum phenomena. The de Broglie wavelength of He+ ion is much smaller than that of electrons for the same energy. For instance, the wavelength of 30 keV He+ is just 83 fm which suggests that high-resolution imaging should be possible. As He+ has larger penetration depth than any other ion for a given energy except protons, there is an attractive and untapped potential to use transmitted He+ ions for materials characterization. Preliminary experiments indicate the feasibility of Scanning Transmission Helium Ion Microscopy (STHIM) for the simple cases of Bright-Field (BF) and Dark-Field (DF) imaging. Furthermore, advanced theoretical considerations suggest that STHIM with energy as low as 40 keV He+ would be capable of high-resolution magnetic moment imaging down to even atomic resolution. This will be investigated. To complement our sub-50 keV He+ investigations, we have partnered with other leading researchers at the Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf in Germany to benefit from their expertise in simulations (Wolfhard Möller) and high energy experiments (Gregor Hlawacek). Based on our comprehensive approach outlined here, we plan to explore, develop and demonstrate the proof-of-concept of advanced characterization modalities in STHIM.