Combined TPD and XPS Study of Ligation and Decomposition of 1,6-Hexanedithiol on Size-Selected Copper Clusters Supported on HOPG

Abstract

Ligation and decomposition of 1,6-hexanedithiol on copper clusters have been studied by means of temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Copper cluster anions were first made via magnetron sputtering, then size selected and soft landed into a frozen matrix of 1,6-hexandithiol on highly ordered pyrolytic graphite (HOPG) maintained at 100 K. After warming up to 298 K, a combination of TPD and XPS were performed to characterize the newly deposited sample. TPD data shed light upon the adsorption and decomposition pathways of 1,6-hexanedithiol molecules on copper clusters. Based on the TPD data, two different binding motifs are proposed: the dangling motif is with one sulfur atom binding to a copper cluster, and the bidentate motif is with both sulfur atoms binding to a copper cluster. Different decomposition products were observed for each binding motif. A series of hydrogen atom titration experiments were designed to provide further evidence for the proposed decomposition mechanism. XPS measurements at varied temperatures agree well with the TPD profile by confirming the formation of dithiol ligated copper clusters through Cu–S bond formation, and the decomposition of them via C–S bond scission. How well the dithiol ligand can protect the copper clusters from being oxidized is discussed, and the ligand number per cluster is estimated.

Thermal Decomposition of Dimethyl Methylphosphonate on Size-Selected Clusters: A Comparative Study between Copper Metal and Cupric Oxide Clusters

“…It should be mentioned that Cu 2+ in bare (CuO) 80 clusters can be reduced completely to Cu 1+ upon annealing to 200 °C under UHV (Figure b). Moreover, multiple studies have shown that lattice oxygen in CuO can participate in dissociative adsorption and oxidative decomposition processes at room temperature and elevated temperatures for many organic molecules such as DMMP, methanol, , and alkanethiols. , Therefore, the disappearance of low binding energy feature can be ascribed to the oxidative effects on potential atomic phosphorus from the activated lattice oxygen within (CuO) 80 as well as the loss of satellite feature of Cu 3s due to reduction of Cu 2+ into Cu 1+ upon heating to 200 °C.…”

“…TPD can offer evidence on the evolution of gaseous products during the temperature ramping, while XPS acquired after heating the sample to several critical temperatures can elucidate residual species on the surface. Our group has successfully applied this method to shed light on the decomposition mechanism of several organic molecules, including DMMP, on size-selected metal and metal oxide clusters. , Similarly, the decomposition process of DMMP on Cu 100 and (CuO) 80 clusters has been analyzed and compared via combined XPS and TPD in this study. As is shown in Scheme , a plausible DMMP decomposition scheme is presented with all the surface species and gaseous products described in the previous sections.…”

“…42 In our lab, the LNMD method was successfully implemented in order to probe the ligation and decomposition process of 1,6-hexanedithiol on size-selected Cu 100 clusters. 43 Prior to cluster deposition, the HOPG substrate was cleaved under ambient conditions right before being transported into a load-lock chamber and then into a UHV chamber. The substrate was then annealed at 500 °C for 30 min.…”

“…It was then adopted to probe the activities of metals or metal oxides toward a reactive matrix . In our lab, the LNMD method was successfully implemented in order to probe the ligation and decomposition process of 1,6-hexanedithiol on size-selected Cu 100 clusters …”

Exploring the materials space in the smallest particle size range: from heterogeneous catalysis to electrocatalysis and photocatalysis

“…1b). The size-selected Pt n (n = 4, 7-10, 15) clusters on TiO 2 (110) surfaces were scanned using an ultrahigh-vacuum STM with a carbon nanotube tip. The clusters smaller than Pt 7 laid flat on the surface with a planar structure.…”