  Scanning tunneling microscopy and spectroscopy have been performed on
superconducting La$_{2-x}$Sr$_{x}$CuO$_{4}$ ($x=0.06, 0.12, 0.16$, and 0.21) at
4.2 K. Atomically resolved surface topography has been observed on the $ab$
surface, which exhibits a one-dimensional structure corresponding to the
buckling pattern of the orthorhombic phase. The tunneling spectra of all
samples exhibit kinks at about $\pm 5$ meV in addition to the energy gap,
indicating the existence of two energy scales. While the gap magnitude varies
on the length scale of a few nm and steadily increases upon underdoping, the
kink energy is spatially uniform on the surface and almost independent of the
doping level.
