Nickelocene adsorption on single-crystal surfaces

Abstract

Nickelocene adsorption onto Ag͑100͒, Ni͑100͒, and NiO͑100͒/Ni͑100͒ surfaces was studied with x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy at 135 K for monolayer and multilayer coverages of NiCp 2 . On the relatively inert Ag͑100͒ surface, nickelocene physisorbs molecularly, with its molecular axis perpendicular to the surface plane. Exposure to the reactive Ni͑100͒ surface results in the decomposition of nickelocene into acetylene and acetylene-like fragments and, when this surface is warmed to 273 K, carbide contamination is observed. There is evidence for double-bond carbon on nickelocene-exposed NiO͑100͒, and vinyl and propenyl fragments are the most likely decomposition products on this surface. At very large exposures, adsorbed nickelocene is molecularly condensed and, therefore, produces similar thin films on all three surfaces.

Cobaltocene adsorption and dissociation on Cu(111)

“…Nonetheless, initial nickelocene adsorption on Ni(1 0 0) [25] and NiO(1 0 0) [25] is dissociative even for substrate temperatures of 135 K. We might expect that cobaltocene adsorption, like that observed for other metallocenes, would also be molecular on substrates well below room temperature, but in this work, we show that (perhaps surprisingly) this is not the case, even for the relatively inert Cu(1 1 1) surface.…”

“…On more reactive surfaces such as Ni(1 0 0), it is perhaps signifi cant that the unpaired nickelocene shows dissociative adsorption behavior, even at substrate temperatures of 135 K [25], that resembles the dissociative adsorption behavior observed for cobaltocene on Cu (1 1 1), discussed here. More reactive surfaces, like Ni(1 0 0), may promote partial "ionosorption" to a greater extent (that is to say adsorption with very signifi cant charge transfer with the substrate), so that the adsorbed metallocene has a greater tendency to adopt an "oxidized" confi guration [M(Cp) 2 ] + .…”

“…When comparing initial cobaltocene adsorption on graphite [32] and Cu(1 1 1) (the work presented here) with other metallocenes, it seems fairly clear that cobaltocene is far less stable as a molecule on surfaces than ferrocene (Z − 1) [13][14][15][16][17][18][19][20][21][22] or nickelocene (Z + 1) [20], [23][24][25][26][27]. The big difference among these three metallocenes appears to be that the "nineteen electron" cobaltocene has a single unpaired electron resulting in a low ionization potential [32] of 5.56 eV [37] when compared to ferrocene (6.88 eV [37]) and nickelocene (6.51 eV [37]).…”

“…Of the many studies of molecular ferrocene [13][14][15][16][17][18][19][20][21][22], nickelocene [20][21][22][23][24][25][26][27][28][29][30][31] and cobaltocene [32] adsorption, the initial adsorption is associated (molecular) on most surfaces, when the adsorption is undertaken at substrate temperatures in the region of 100-200 K. Molecular metallocene adsorption has been observed on Ag(1 0 0) [13][14][15], [21], [22], [26], and [27], Cu(1 0 0) [15], [19], [21][22][23][24][25], Mo(1 1 2) [17] and [22], graphite [16], [18], and [32] and Si(1 1 1)-2 × 1 [20]. Nonetheless, initial nickelocene adsorption on Ni(1 0 0) [25] and NiO(1 0 0) [25] is dissociative even for substrate temperatures of 135 K. We might expect that cobaltocene adsorption, like that observed for other metallocenes, would also be molecular on substrates well below r...…”

Adsorption and decomposition of nickelocene on Ag(100): a high-resolution electron energy loss spectroscopy and temperature programmed desorption study

“…While a number of studies has been reported on metal deposition using metallocenes as precursors, very little is known about the surface chemistry of metallocenes at the molecular level [2,6,7,[17][18][19][20][21][22]. Furthermore, only a handful of studies have focused on nickelocene [7,[17][18][19].…”