title: UHV STM I(V) and XPS studies of aryl diazonium molecules assembled on Si(111).
abstract: Molecular layers formed from 4-trifluoromethylbenzenediazonium tetrafluoroborate and 4-Methylbenzenediazonium tetrafluoroborate have been assembled on H-passivated Si(111) and studied by UHV STM and XPS. STM imaging shows well-developed Si(111) step edges and terraces both on Si(111):H and Si(111) substrates covered with a molecular layer. STM I(V) data acquired at different tip-substrate separations reveals a factor of approximately 10 enhancement in current for positive bias voltage when current flows through the 4-trifluoromethyl molecule when compared to the 4-methyl variant. The observed current enhancement in I(V) can be understood by comparing the projected density of states of the two molecule-Si systems calculated using a density functional theory local density approximation after geometry optimization was performed via the conjugate gradient method. XPS data independently confirm that H-passivated Si(111) remains oxygen free for short exposures to ambient conditions and provide evidence that the molecules chemically react with the silicon surface.
authors: Department of Physics, Birck Nanotechnology Center, and School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA. dpandey@purdue.edu
authors: Deepak
authors: D
authors: Pandey
authors: Dmitry Y
authors: DY
authors: Zemlyanov
authors: Kirk
authors: K
authors: Bevan
authors: Ronald G
authors: RG
authors: Reifenberger
authors: Shawn M
authors: SM
authors: Dirk
authors: Steve W
authors: SW
authors: Howell
authors: D R
authors: DR
authors: Wheeler
mesh_terms: D003979:Diazonium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D016252:Microscopy, Scanning Tunneling / Q000379:methods*; D008956:Models, Chemical; D015394:Molecular Structure; D012825:Silicon / Q000737:chemistry*; D013053:Spectrophotometry; D013499:Surface Properties; D014965:X-Rays
chemical_list: D003979:Diazonium Compounds; D006859:Hydrogen; D012825:Silicon