Adsorption and thermal decomposition of 2-octylthieno[3,4-b]thiophene on Au(111)

Abstract

The adsorption and thermal stability of 2-octylthieno[3,4-b]thiophene (OTTP) on the Au(1 1 1) surfaces have been studied using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). UHV-STM studies revealed that the vapor-deposited OTTP on Au(1 1 1) generated disordered adlayers with monolayer thickness even at saturation coverage. XPS and TPD studies indicated that OTTP molecules on Au(1 1 1) are stable up to 4501< and further heating of the sample resulted in thermal decomposition to produce H-2 and H2S via C-S bond scission in the thieno-thiophene rings. Dehydrogenation continues to occur above 600 K and the molecules were ultimately transformed to carbon clusters at 900 K. Highly resolved air-STM images showed that OTTP adlayers on Au(1 1 1) prepared from solution are composed of a well-ordered and low-coverage phase where the molecules lie flat on the surface, which can be assigned as a (9 x 2 root 33)R5 degrees structure. Finally, based on analysis of STM, TPD, and XPS results, we propose a thermal decomposition mechanism of OTTP on Au(1 1 1) as a function of annealing temperature.