New monolayer phases of n-alkane thiols self-assembled on Au(111): Preparation, surface characterization, and imaging

Abstract

We report the observation by scanning tunneling microscopy (STM) and low energy atom diffraction, of new, striped, structures at the surface of monolayers of n-alkane thiols [CH3 (CH2)n−1 SH with n=8,10,12] self-assembled on the (111) face of single crystal gold. These structures can be prepared by slow (room temperature) or thermally accelerated treatment of the well known c(4√3×2√3)R 30° phase formed by self-assembly in solution, or can be accessed directly by molecular beam deposition. With respect to the unit mesh of the gold substrate, the new striped structures can be described as p×√3 overlayers where 7.5≤p≤13. The discovery of these phases has implications for the understanding of the growth mechanisms and the pursuit of applications of this widely studied class of materials.

Nanopatterned self-assembled monolayers

“…Second, thiols desorb upon heating even to moderate temperatures [33,34], which is a significant problem if an annealing step has to be applied at some time during processing. Third, thiols bleed along gold grain boundaries, which tends to blur the nanopatterns.…”

n-alkyl thiol head-group interactions with the Au(111) surface

“…Their simplicity, highly ordered structures, and chemical stability make these systems ideal for study with a variety of techniques including atomic force microscopy, 5,6 infrared spectroscopy, 7,8 high-resolution electron-energy-loss spectroscopy, 9 grazing X-ray diffraction, 10 scanning tunneling microscopy (STM), 11-17 scanning probe microscopy, 18 lowenergy electron diffraction (LEED), [19][20][21] He atom diffraction, 22,23 and theory. 25-31 Despite 1…”

“…Alkanethiolates occupy three-fold hollow sites of the Au (111) surface with S-S spacings of 4.99Å, and the molecular axes are tilted by 30 • -35 • with respect to the surface normal. [13][14][15][16][17][18][19][20][21][22][23][30][31][32][33][34][35] The sulfur-pairing model involves a c(4 × 2) superlattice of the hexagonal lattice, where alkanethiolates form sulfur head group dimers with S-S spacings of 2.2Å. [9][10][11][12][24][25][26] Furthermore, other structural models have been reported, including n × √ 3 unit cells (8 ≤ n ≤ 10).…”

Copper Electrodeposition on Alkanethiolate Covered Gold Electrodes*

“…4 [10,[52][53][54][55]. At lower coverage (attainable by vapour phase dosing of thiols [56] or by heating above 370 [57,58]) and for short chain thiolates we detected striped structures [58] (see also [56,57,59,60]). All these structures can exist in different domains separated by domain walls.…”