  V3Si, a classical silicide superconductor with relatively high TC (~16 K), is
promising for constructing silicon-based superconducting devices and
hetero-structures. However, real space characterization on its surfaces and
superconducting properties are still limited. Here we report the first
low-temperature scanning tunnelling microscopy (STM) study on cleaned V3Si
(111) single crystal surface. We observed a r3 by r3 superstructure which
displays mirror symmetry between adjacent terraces, indicating the surface is
V-terminated and reconstructed. The tunneling spectrum shows full
superconducting gap with double pairs of coherence peaks, but has a relatively
small gap size with comparing to bulk TC. Impurity induced in-gap state is
absent on surface defects but present on introduced magnetic adatoms. Upon
applying magnetic field, a hexagonal vortex lattice is visualized.
Interestingly, the vortex size is found to be field dependent, and the
coherence length measured from single vortex at low field is significantly
larger than estimated value from bulk H_c2. These results reflect V3Si is a
multi-band, s- wave superconductor.
