  We observe a subharmonic gap sturucture (SGS) and the Josephson effect in
superconducting scanning tunneling microscope junctions with resistances below
100 kOhm. The magnitude of the n=2 SGS is shown to scale with the square of the
junction normal state conductance, in agreement with theory. We show by
analyzing the Josephson effect in these junctions that the superconducting
phase dynamics are strongly affected by thermal fluctuations. We estimate the
linewidth of the Josephson oscillations due to phase fluctuations, a quantity
that may be important in modern theories of the subgap structure. While phase
fluctuations may smear the SGS current onsets, we conclude that the sharpness
of these onsets in our data is not limited by fluctuations.
