Apparent self-absorption effect: anomalous anti-resonance in soft X-ray fluorescence spectroscopy

X-ray fluorescence yield (FY) is a useful mode to collect signals for soft X-ray absorption spectroscopy (XAS). Despite its bulk-sensitive nature, use of FY for L-edge XAS of 3d transition metal (TM) oxides (TMOs) is limited by a severe signal suppression or even anti-resonance at low-energy region. Although such abnormal decrease in intensity is often called a “self”-absorption or over-absorption effect, this paper provides experimental data and interpretation to support that such an anti-resonance concentrated at low-energy region originates from a combinational effect of a destructive interference of O fluorescence and the total angular momentum-dependent suppression of TM fluorescence emission channel.