  By means of low-temperature scanning tunneling microscopy, we report on the
electronic structures of BiO and SrO planes of Bi2Sr2CuO6+{\delta} (Bi-2201)
superconductor prepared by argon-ion bombardment and annealing. Depending on
post annealing conditions, the BiO planes exhibit either pseudogap (PG) with
sharp coherence peaks and an anomalously large gap of 49 meV or van Hove
singularity (VHS) near the Fermi level, while the SrO is always characteristic
of a PG-like feature. This contrasts with Bi2Sr2CaCu2O8+{\delta} (Bi-2212)
superconductor where VHS occurs solely on the SrO plane. We disclose the
interstitial oxygen dopants ({\delta} in the formulas) as a primary cause for
the occurrence of VHS, which are located dominantly around the BiO and SrO
planes, respectively, in Bi-2201 and Bi-2212. This is supported by the
contrasting structural buckling amplitude of BiO and SrO planes in the two
superconductors. Our findings provide solid evidence for the irrelevance of PG
to the superconductivity in the two superconductors, as well as insights into
why Bi-2212 can achieve a higher superconducting transition temperature than
Bi-2201, and by implication, the mechanism of cuprate superconductivity.
