Electronic characterization of Si(100)-bound alkyl monolayers using kelvin probe force microscopy

Hydrogen-terminated and alkyl-chain (C₁₈H₃₇)- terminated Si(100) surfaces with different doping levels have been characterized using Kelvin probe force microscopy. n- and p-doped Si(100) and lateral p ⁺⁺n and n⁺⁺p silicon junctions were hydrogenated in dilute HF solution, followed with a self-assembly deposition of organic molecules by thermally activated free-radical reaction between C=C and Si - H. The surface band bending following the two different chemical treatments was almost identical for both p-type silicon (∼0.7 eV, with a surface charge of 9.4 ± 0.5 × 10¹¹cm²) and n-type silicon (0.6 eV, with a surface charge of 8.7 ± 0.5 × 10¹¹/cm ²). These results indicate that the self-assembly of the C ₁₈.H₃₇ monolayer on a Si (100) surface results in electrical properties similar to those of a hydrogenated Si surface, with the advantage of longer stability in an ambient environment. The hydrogen-terminated and alkyl-chain-terminated surface do differ, however, in the surface dipole, which is lower by ∼0.6 eV for the latter, a value deduced from both the measurements and independent first principles electronic structure calculations. This dipole change is essentially due to the change in bond dipole associated with the replacement of Si - H bonds by Si - C bonds and the dipole associated with the methyl group.