Comparison of the empty electronic states of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ (001) and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CuO}}_6$ (001) at 60 and 300 K

Inverse photoelectron spectroscopy has been used to study the unoccupied electronic states of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ (001) and ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_6$ (001) at 60 and 300 K. Both compounds exhibit low emission between ${\mathit{E}}_{\mathit{F}}$ and ${\mathit{E}}_{\mathit{F}}$+2 eV derived from Cu 3d–OR 2p and Bi 6p–O 2p hybrids and structure centered at ∼4 and 9.5 eV that can be attributed to empty Bi 6p and Sr 4d levels. Results for ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ show additional structure near ${\mathit{E}}_{\mathit{F}}$+10 eV because of contributions from Ca 3d levels. Plasmons are found for both compounds at 15 and 21.2 eV. Off-normal studies of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ (001) at 60 K showed O 2p holes with ${\mathit{p}}_{\mathit{x},}$y character. Results obtained at 300 K showed decreased O 2p hole emission and increased Cu 3${\mathit{d}}^{10}$ emission for both ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ and ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_6$ compared with the 60 K results.