  Free-standing nanoribbons of InAs quantum membranes (QMs) transferred onto a
(Si/Mo) multilayer mirror substrate are characterized by hard x-ray
photoemission spectroscopy (HXPS), and by standing-wave HXPS (SW-HXPS).
Information on the chemical composition and on the chemical states of the
elements within the nanoribbons was obtained by HXPS and on the quantitative
depth profiles by SW-HXPS. By comparing the experimental SW-HXPS rocking curves
to x-ray optical calculations, the chemical depth profile of the InAs(QM) and
its interfaces were quantitatively derived with angstrom precision. We
determined that: i) the exposure to air induced the formation of an InAsO$_4$
layer on top of the stoichiometric InAs(QM); ii) the top interface between the
air-side InAsO$_4$ and the InAs(QM) is not sharp, indicating that
interdiffusion occurs between these two layers; iii) the bottom interface
between the InAs(QM) and the native oxide SiO$_2$ on top of the (Si/Mo)
substrate is abrupt. In addition, the valence band offset (VBO) between the
InAs(QM) and the SiO$_2$/(Si/Mo) substrate was determined by HXPS. The value of
$VBO = 0.2 \pm 0.04$ eV is in good agreement with literature results obtained
by electrical characterization, giving a clear indication of the formation of a
well-defined and abrupt InAs/SiO$_2$ heterojunction. We have demonstrated that
HXPS and SW-HXPS are non-destructive, powerful methods for characterizing
interfaces and for providing chemical depth profiles of nanostructures, quantum
membranes, and 2D layered materials.
