Influence of molecular ordering on electrical and friction properties of ω-(trans-4-stilbene)alkylthiol self-assembled monolayers on Au(111).
The electrical and friction properties of ω-(trans-4-stilbene)alkylthiol self-assembled monolayers (SAMs) on Au(111) were investigated using atomic force microscopy (AFM) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The sample surface was uniformly covered with a molecular film consisting of very small grains. Well-ordered and flat monolayer islands were formed after the sample was heated in nitrogen at 120 °C for 1 h. While lattice resolved AFM images revealed a crystalline phase in the islands, the area between islands showed no order. The islands exhibit substantial reduction (50%) in friction, supporting the existence of good ordering. NEXAFS measurements revealed an average upright molecular orientation in the film, both before and after heating, with a narrower tilt-angle distribution for the heated fim. Conductance-AFM measurements revealed a 2 orders of magnitude higher conductivity on the ordered islands than on the disordered phase. We propose that the conductance enhancement is a result of a better π-π stacking between the trans-stilbene molecular units as a result of improved ordering in islands.
Qi
Yabing
Y
Applied Science and Technology Graduate Group, University of California, Berkeley, California 94720, USA.
Liu
Xiaosong
X
Hendriksen
B L M
BL
Navarro
V
V
Park
Jeong Y
JY
Ratera
Imma
I
Klopp
J M
JM
Edder
C
C
Himpsel
Franz J
FJ
Fréchet
J M J
JM
Haller
Eugene E
EE
Salmeron
Miquel
M
D004583:Electrons; D006046:Gold / Q000737:chemistry*; D008567:Membranes, Artificial; D010316:Particle Size; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
D008567:Membranes, Artificial; D013438:Sulfhydryl Compounds; D006046:Gold