P-Benzoquinone on Si(111)-7×7: [6 + 2]-like Cycloaddition

Abstract

The Covalent binding of p-benzoquinone (O═C6H4═O) and the formation of an aromatic ring (−O—C6H4—O−) on Si(111)-7×7 have been investigated by using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. For chemisorbed p-benzoquinone, the absence of v(C═O) at 1659 cm−1, the retention of sp2-v(C−H) at 3050 cm−1, the appearance of v(Si−O) at 824 cm−1, and aromatic v(C═C)/δip(C−H) at 1600/1505 cm−1 demonstrate that the molecule reacts with the surface in a [6+2]-like cycloaddition mode, which is further confirmed by XPS and density functional theory (DFT) vibrational calculations. DFT calculations indicate that the [6+2]-like cycloadduct (−O—C6H4—O−) bridging two nearest adatoms in neighboring half-unit cells is the most stable. This binding scheme may prove useful for chemical and electronic modification of the semiconductor surfaces.