Low Temperature Scanning Tunneling Spectroscopy of isolated Mn$_{12}$-Ph Single Molecule Magnets*

We study Mn$_{12}$O$_{12}$(C$_6$H$_5$COO)$_{16}$(H$_2$O)$_4$ (Mn$_{12}$-Ph) single-molecule magnets on a Cu(111) surface using scanning tunneling microscopy and scanning tunneling spectroscopy at cryogenic temperatures (T $<$ 6K). We report the observation of Mn$_{12}$-Ph in isolation and in thin films, deposited through $in\,situ$ vacuum spray deposition onto clean Cu(111). The tunneling current of isolated Mn$_{12}$-Ph, normalized with respect to the Cu background, shows a strong bias voltage dependence within the molecular interior. The qualitative features of these I vs.V curves differ by spatial location in several intriguing ways (e.g. fixed junction impedance with increasing bias voltages). We explore these normalized I vs. V curves and present a phenomenological explanation for the observed behaviors, corresponding to the physical and electronic structure within the molecule.