Optical Second Harmonic Generation from Periodic Steps on Rutile TiO2(110)

Abstract

We have succeeded in observing optical second harmonic generation (SHG) from steps on the TiO2 surfaces adsorbed with HCOOH. The samples were single crystals of rutile TiO2 with (110), (15 15 4), (13 9 0), and (671) faces. These samples underwent annealing in O2 gas, HF etching, and immersion into HCOOH aqueous solution to adsorb HCOOH molecules on their surfaces. Their surfaces were characterized by reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM), and were confirmed to have regularly aligned steps created by the miscut of the samples. SH intensity as a function of the sample rotation angle was measured in air with the incident angle of 2° at the SH photon energy of 2ω = 4.66 eV. The SH intensity from the surfaces with steps were 2 to 3 orders of magnitude stronger than that from the (110) surface. The SH intensity patterns from these stepped surfaces were anisotropic. The result indicates that the contribution of the surface steps was observed selectively. [DOI: 10.1380/ejssnt.2010.84]