Nature of Optical Transitions in Copper and Cu:Ni Alloys

The direct $L_{2^{\prime }}\to L_1$ transition is very apparent in photoemission data from pure Cu; however, as might be expected, there is no evidence for this transition in 87% Cu-13% Ni alloys. In contrast, structure in ${\epsilon }_2$ for $h\nu >~2.1$ eV for the alloy and pure Cu is qualitatively similar. These observations support the assignment of major structure in ${\epsilon }_2$ of pure Cu to nondirect transitions from the $d$ states and argue against the 5.0 eV peak being due principally to the $L_{2^{\prime }}\to L_1$ transition.