title: Quantum mechanics calculations of the thermodynamically controlled coverage and structure of alkyl monolayers on Si(111) surfaces.
abstract: The heat of formation, Delta E, for silicon (111) surfaces terminated with increasing densities of the alkyl groups CH3- (methyl), C2H5- (ethyl), (CH3)2CH- (isopropyl), (CH3)3C- (tert-butyl), CH3(CH2)5- (hexyl), CH3(CH2)7- (octyl), and C6H5- (phenyl) was calculated using quantum mechanics (QM) methods, with unalkylated sites being H-terminated. The free energy, Delta G, for the formation of both Si-C and Si-H bonds from Si-Cl model compounds was also calculated using QM, with four separate Si-H formation mechanisms proposed, to give overall Delta G(S) values for the formation of alkylated Si(111) surfaces through a two step chlorination/alkylation method. The data are in good agreement with measurements of the packing densities for alkylated surfaces formed through this technique, for Si-H free energies of formation, Delta G(H), corresponding to a reaction mechanism including the elimination of two H atoms and the formation of a C=C double bond in either unreacted alkyl Grignard groups or tetrahydrofuran solvent.
authors.affiliation: Division of Chemistry and Chemical Engineering, Kavli Nanoscience Institute and Beckman Institute, 127-72, Noyes Laboratory, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: E Joseph
authors.initials: EJ
authors.lastname: Nemanick
authors.forename: Santiago D
authors.initials: SD
authors.lastname: Solares
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Lewis