Ultraviolet and electron radiation induced fragmentation of adsorbed ferrocene

Abstract

Welipitiya, Dulip; Green, A.; Woods, J.P.; Dowben, Peter A.; Robertson, Brian W.; Byun, Dongjin; and Zhang, Jiandi, "Ultraviolet and electron radiation induced fragmentation of adsorbed ferrocene" (1996) From thermal desorption spectroscopy we find that ferrocene, Fe͑C 5 H 5 ͒ 2 , adsorbs and desorbs associatively on Ag͑100͒. Photoemission results indicate that the initially adsorbed surface species closely resembles that of molecular ferrocene. The shift in photoemission binding energies relative to the gas phase is largely independent of the molecular orbital. We find that ultraviolet light does lead to partial fragmentation of the ferrocene and that the molecular fragments are much more strongly bound to the surface than the associatively adsorbed ferrocene. Since fragmentation occurs only in the presence of incident radiation, selective area deposition from this class of molecules is possible. Using a focused electron beam in a scanning transmission electron microscope, we show that selective area deposition of features with resolution of a few hundred angstroms is readily achieved.

Orientation of nickelocene on Ag(100)

“…Recently, there have been several studies of adsorbed metallocenes, primarily as a result of their potential use as source molecules for the selective area deposition of metals on surfaces ( [1][2][3][4][5][6][7]; D. Welipitiya, C. Waldfried, P. A. Dowben, I. Goblukoglu, B. Robertson, in preparation). Determination of the dominant interactions between a particular metallocene and the surface is essential for understanding how the metallocene decomposes and deposits metal on a surface.…”

Cobaltocene adsorption and dissociation on Cu(111)

“…1) at 9.0 ± 0.2 eV (peak B), 12.7 ± 0.2 eV (peak C), and 17.3 ± 0.2 eV (peak D) as well as the much weaker features at 0.9 ± 0.2 eV (peak A′) and 5.1 ± 0.2 eV (peak A″) are similar in relative intensities and binding energies to those assigned to cobaltocene adsorbed on cleaved graphite [32]. There is also a strong similarity between the gas phase photoemission spectra of cobaltocene [36][37], but with a shift of about 4 eV in the energy scale, as is typical of metallocenes [13][14][15], [17], [20][21][22][23], and [32], even though the moleculesubstrate as well as intermolecular interactions may shift, or broaden the molecular orbitals.…”

“…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]).…”

“…While induced decomposition of metallocenes certainly is possible, during photoemission [2], [3], [13][14], decomposition induced by absorption on the bare metal substrate is certainly more signifi cant. Very little decomposition of the multilayer molecular cobaltocene species is observed on the time scale of our photoemission measurements, with much of the multilayer molecular cobaltocene desorbing below 290 K.…”

“…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...…”