  The traveling waves for surface diffusion of plane curves are studied. We
consider an evolving plane curve with two endpoints, which can move freely on
the x-axis with generating constant contact angles. For the evolution of this
plane curve governed by surface diffusion, we discuss the existence, the
uniqueness and the convexity of traveling waves. The main results show that the
uniqueness and the convexity can be lost in depending on the conditions of the
contact angles, although the existence holds for any contact angles in the
interval $(0,\pi/2)$.
