We have investigated a quasi-one-dimensional structure of Si(1 1 1)-8 x 2-In surface using reflection high-energy positron diffraction (RHEPD) and scanning tunneling microscopy (STM). From the RHEPD rocking curve analyses, we confirmed the formation of the In hexagon structure proposed by Gonzalez et al. [C. Gonzalez, F. Flores, J. Ortega, Phys. Rev. Lett. 96 (2006) 136101]. Furthermore, we found that the empty-state STM image at 44 K is consistent with that calculated with the optimum hexagon structure by the RHEPD analyses. (C) 2008 Elsevier B.V. All rights reserved.