Spontaneous self-assembly into chiral well-ordered two-dimensional molecular film at room temperature has been evidenced using the scanning tunneling microscopy for the growth of two enantiomerically pure L- and D-methionine on Au(111) surface. From the x-ray photoelectron spectroscopy measurements, the growth of methionine occurs through the formation of zwitterionic species. Our results demonstrate that this self-assembly mechanism is crucially driven by the interchain interactions via zwitterionic hydrogen bonding between neighboring negatively charged carboxylate groups and positively charged amino groups. Moreover, the molecular pair formation is incidental and results from the optimization of the interchain interactions, at least two chains are required for stability. (C) 2010 American Institute of Physics. [doi:10.1063/1.3524229]