  We investigate vortices in LiFeAs using scanning tunneling
microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting
gaps without detectable spectral weight near the Fermi energy, evidencing
fully-gapped multi-band superconductivity. We image vortices in a wide field
range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi
energy. A quasi-hexagonal vortex lattice at low field contains domain
boundaries which consist of alternating vortices with unusual coordination
numbers of 5 and 7. With increasing field, the domain boundaries become
ill-defined, resulting in a uniformly disordered vortex matter. Tunneling
spectra taken at the vortex center are characterized by a sharp peak just below
the Fermi energy, apparently violating particlehole symmetry. The image of each
vortex shows energy-dependent 4-fold anisotropy which may be associated with
the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing
temperature and becomes smaller than the coherence length estimated from the
upper critical field. This is direct evidence of the Kramer-Pesch effect
expected in a clean superconductor.
