Surface diffusion of n-alkanes on Ru(001)

Abstract

The surface diffusion of n-alkanes on Ru(OOI) was measured using laser-induced thermal desorption (LITD) techniques. The surface diffusion coefficients for propane, n-butane, npentane, and n-hexane all displayed Arrhenius behavior. The surface diffusion activation energies increased linearly with carbon chain length from Edif = 3.0 ± 0.1 kcallmol for propane to Edif = 4.8 ± 0.2 kcallmol for n-hexane. In contrast, the surface diffusion preexponentials remained nearly constant at Do =0.15 cm 2 Is. Measurements performed at different coverages also revealed that the surface diffusion coefficients were coverageindependent for all the n-alkanes on Ru(OOI). The surface corrugation ratio 0 was defined as the ratio of the diffusion activation energy to the desorption activation energy, 0 = Edif IE des ' The surface corrugation ratio was observed to be remarkably constant at 0=0.3 for all the nalkanes. This constant corrugation ratio indicated a linear scaling between the diffusion activation energy and the desorption activation energy. This behavior also suggested that the nalkanes move with a rigid configuration parallel to the Ru(OOI) surface.5136

Two-Dimensional Crystals of Alkanes Formed on Au(111) Surface in Neat Liquid: Structural Investigation by Scanning Tunneling Microscopy

“…[6][7][8][9][10][11][12] The desorption energy was proportional to numbers of the methylene, ca. 6.5 kJ/mol per methylene unit.…”

“…Firment and Somorjai showed that the alkanes formed ordered monolayers on Pt(111) 4 and Ag(111) 5 under UHV conditions by low-energy electron diffraction (LEED). In addition, the physisorption of alkanes has been studied on Au(111), 6 Pt(111), 7,8 Pt(110), 9 Ir(110), 10 Cu(100), 11 Ru(001), 12 and Cu(111), 13 under UHV conditions. However, the local arrangement of the alkanes on a metal surface has not been investigated in contrast to numerous reports of alkane adlayers on graphite at the solid/liquid interface, [14][15][16][17][18][19][20][21] although studies using molecular dynamics 12,[22][23][24][25][26][27] and infrared spectroscopy [28][29][30][31][32] under UHV conditions have been carried out after the reports by Firment and Somorjai.…”

Desorption energies of linear and cyclic alkanes on surfaces: anomalous scaling with length

“…Desorption kinetics for linear alkanes on Cu(1 1 1) and Pt(1 1 1) surfaces have been measured in this work and on the Au(1 1 1), Cu(1 0 0), Ru(0 0 1) surfaces and the basal plane of graphite in other work [1][2][3][4][5][6][7][8]. These data were used to estimate values of DE z des as a function of chain length.…”

“…As mentioned, Wetterer et al [1] report that the intercepts of their Arrhenius plots indicate a value of v % 10 13 s À1 that is independent of chain length. The exception is the study of alkane desorption from the Ru(0 0 1) surface which showed that the pre-exponential factor decreased with increasing chain length [4]. In contrast, models for alkane desorption from both Au (1 1 1) and graphite indicate that the pre-exponent should increase with increasing chain length at least for short chain lengths (N < 20) [9,12].…”

Kinetics and Energetics of Oligomer Desorption from Surfaces

“…Since the desorbed state has no segments interacting with the surface one might predict that the DE z des should be linear in the chain length. There have been several prior sets of measurements which observe the effects of alkyl chain length on the desorption kinetics of species such as alkyl alcohols and simple alkanes adsorbed on metal surfaces [6][7][8][9]. In these cases the range of alkyl chain lengths has been limited to n # 12.…”