14800
J. Phys. Chem. B 2006, 110, 14800-14808
Chemical and Electrical Passivation of Silicon (111) Surfaces through Functionalization with Sterically Hindered Alkyl Groups E. Joseph Nemanick, Patrick T. Hurley, Bruce S. Brunschwig, and Nathan S. Lewis* 210 Noyes Laboratory, 127-72, DiVision of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 ReceiVed: December 5, 2005; In Final Form: May 10, 2006
Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using sterically bulky alkyl groups such as (CH3)2CH- (iso-propyl), (CH3)3C- (tert-butyl), and C6H5- (phenyl) moieties. X-ray photoelectron spectroscopic (XPS) data in the C 1s region of such surfaces exhibited a low energy emission at 283.9 binding eV, consistent with carbon bonded to Si. The C 1s XPS data indicated that the alkyls were present at lower coverages than methyl groups on CH3-terminated Si(111) surfaces. Despite the lower alkyl group coverage, no Cl was detected after alkylation. Functionalization with the bulky alkyl groups effectively inhibited the oxidation of Si(111) surfaces in air and produced low (4000 Ω cm), n-type, phosphorus-doped silicon was used. Prior to alkylation, samples were cut into sections ∼1 cm2 in area. The pieces were cleaned by sonication for 5 s in a series of organic solvents (VWR Scientific Products, West Chester, PA): methanol, acetone, dichloromethane, 1,1,1-trichloroethane, dichloromethane, acetone, and methanol, and then 18-MΩ·cm resistivity H2O. To produce a H-terminated surface, the samples were then etched for 30 s in buffered HF(aq). Samples were then etched, with occasional agitation to remove bubbles forming on the edges, for 10 min in 40% NH4F(aq) (Transene, Danvers, MA). After etching, the samples were dried under a stream of N2(g) and passed into a glovebox for functionalization. To chlorinate the surfaces, samples were immersed in 2 mL of anhydrous chlorobenzene (99.8% under argon, Aldrich) saturated with PCl5 (99.995%, Strem, Newburyport, MA) for 1 h at 95-100 °C. Benzoyl peroxide (97%, Aldrich) was added (
