An interferometric-spatial-phase imaging (ISPI) system includes an
alignment mechanism for obtaining continuous six-axis control of a
scanning probe tip with respect to a coordinate system attached to a
substrate. A gap detection mechanism measures tip height above a
substrate and controls tip approach toward the substrate of one or more
tips, as well as measures tip deflection during surface contact of the
one or more tips. A plurality of complementary marks is provided for
attachment to the one or more tips. A plurality of grating marks is
provided to backdiffract a reflected beam from a flexible cantilever to
detect high-frequency tip deflection in a compact configuration of a
light source and a light detector.