Figure 3

N K-edge NEXAFS spectra of the unhybridized A _n T ₁₅ films. Left: Spectra acquired at an X-ray incidence angle of 55°. The positions of the most pronounced, π*-like absorption resonances of thymine (T) and adenine (A) are marked by the thin vertical blue (T) and red (A) dotted lines. Right: Difference of the spectra acquired at X-ray incidence angles of 90° and 20°. Adenine and thymine contributions are indicated by the red or blue fill (respectively), with an upward or downward orientation indicating a mostly horizontal or vertical orientation (respectively) of the nucleotides relative to the surface. Horizontal dashed lines correspond to zero for the individual difference spectra.