Surface polymerization by ion-assisted deposition (SPIAD) is used here to grow novel polythiophene and polyphenyl thin films on a silicon surface by hyperthermal, mass-selected thiophene cations coincident with a thermal beam of alpha-terthiophene or p-terphenyl neutrals. X-ray photoelectron spectroscopy (XPS) observes a large enhancement in film growth for SPIAD compared with either thiophene ions or alpha-terthiophene exposure alone. Changes in S/Si and C/Si ratios from XPS, direct observation of higher polymerization products by mass spectrometry, characteristic vibrations in the Raman data, and enhanced stability in a vacuum all indicate that 200 eV SPIAD polythiophene films are most efficiently polymerized at a 1/150 ion/neutral ratio. Other ion/neutral ratios are less efficient at film growth, in the order 1/150 > 1/450 > 1/900 > direct ion deposition > 1/50. Changes in C/Si ratios and higher polymerization products indicate polymerization occurs in SPIAD polyphenyl films grown with a 1/100 ion/neutral ratio. Furthermore, thiophene ions are found to incorporate into some, but not all, of the polymerization products observed in mass spectrometry.