## 3 Results  
The RAIR spectra of Leu were first acquired at a low coverage of \(\sim\)0.20 ML on the Cu(110) surface at a relatively low coverage, as shown in Figure 1a. For molecules in general, their adsorption geometries can only be predicted by assigning the vibrational absorption bands associated with each of the main functional groups in the tested molecules (e.g., the COO-, -NH\({}_{2}\), -CH\({}_{3}\), and -CH- groups) as shown in Scheme 1. If all the bands in an RAIR spectrum can be analyzed to the functional groups of the molecule, then one can conclude that the molecule is adsorbed intact. The RAIR spectrum of Leu clearly showed a band at 1653 cm\({}^{-1}\), which was because of the asymmetric deformation mode of the NH\({}_{2}\) group. Therefore, it is suggested that the amine group participated in the adsorption on the Cu(110) surface at low coverage. However, an NH\({}_{2}\)+ peak was not observed, because the plane of the NH\({}_{2}\)+ group was, according to previous work, lying parallel to the surface [18]. Generally, the carboxylate group will give rise to two vibrational absorption features corresponding to the asymmetric and symmetric COO- stretching modes occurring at 1620-1540 cm\({}^{-1}\) and 1420-1300 cm\({}^{-1}\), respectively. However, in the obtained RAIR spectrum of the Cu(110) surface at low coverage of Leu, only the band at 1419 cm\({}^{-1}\) assigned to symmetric COO- stretching mode was observed. This result indicated that the two oxygen atoms in the carboxylate group are equidistant to the surface, which may be involved in the binding on the surface, resulting in making the stretch dipole of COO- to be inactive. A band at 2915 cm\({}^{-1}\) was also observed, and it may have been caused by the CH stretching modes--in particular, because these groups were slightly tilted from the normal position to the Cu(110) surface. Taken together, these RAIRS observations could support the adoption of the O-H dissociation bonded structure by Leu at low coverage on the Cu(110) surface. Figure 1: Reflection–absorption infrared (RAIR) spectra of (**a**) Leu and (**b**) Tyr on the Cu(110) surface at room temperature. Following the same method, RAIR spectra of Tyr on the Cu(110) surface at low coverage were obtained, as displayed in Figure 1b. Here, vibrations arose from the carboxylate (COO-) and amino (NH\({}_{2}\)) groups. However, a peak at 1592 cm\({}^{-1}\), corresponding to the asymmetric deformation mode of the NH\({}_{2}\) group, did not appear. Additionally, while the COO- stretching mode at 1439 cm\({}^{-1}\) was observed, the asymmetric vas (COO-) stretch was not found, and these results are similar to those for Leu, suggesting that the two carboxylate oxygen atoms of Tyr also bound equidistantly to the Cu(110) surface. These differential observations taken together were consistent with the appearance of the O-H dissociated-N dative bonded structure for Tyr at low coverage on the Cu(110) surface. To determine the electronic structures of the two adsorbed amino acids and, hence, the most favorable adsorption structures, high-resolution core-level spectra were obtained for Leu and Tyr adsorbed on the Cu(110) surface at a low coverage of \(\sim\)0.20 ML (Figure 2). Their C 1s, N 1s, and O 1s core-level spectra were specifically acquired and analyzed using HRPES. Four chemically distinct types of carbon were determined to be present on the Cu(110) surface exposed to \(\sim\)0.20 ML Leu, according to its C 1s core-level spectrum, as seen in Figure 2a. Considering the relationship between electronegativity and binding energy, the peaks at 284.5, 283.7, 285.6, and 287.9 eV, labeled as C1, C2, C3, and C4, were assigned to \(\sim\)CH(CH\({}_{3}\))\({}_{2}\), \(\sim\)CH\({}_{2}\), \(\sim\)CH-NH\({}_{2}\), and a deprotonated carboxyl carbon (-COO-), respectively. Figure 2d displays the deconvoluted spectrum of the C 1s core-level region after adsorption of \(\sim\)0.20 ML Tyr on the Cu(110) surface. As seen, we observed the presence of five chemically distinct types of carbon on the Cu(110) surface.