Laser-assisted deposition of iron on Si(111)-(7×7): The mechanism and energetics of Fe(CO)5 decomposition

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Abstract
The adsorption and decomposition of Fe(CO)5 on the Si(111)‐(7×7) surface has been investigated using multiple internal reflection Fourier transform‐infrared, Auger electron, and temperature programmed desorption spectroscopies and low energy electron diffraction under ultrahigh vacuum conditions at 120 K. Resonant decomposition of adsorbed Fe(CO)5 via a multiphoton electronic excitation of the molecule was observed using laser photolysis. Iron deposition was induced efficiently by ultraviolet but not visible photons with high cross sections, in other words, only in the wavelength region where excitation of metal–ligand charge transfer bands and d–d transitions occur. In addition, Fe(CO)5 decomposition was induced using 1.6 keV electrons. No thermal reaction was apparent in temperature programmed desorption experiments. Only molecular Fe(CO)5 desorption was observed at temperatures of 150 and 170 K. Significant amounts of carbon were deposited from the electron induced decomposition while no residual oxygen or carbon were detected in the photodeposited Fe. No partially decarbonylated Fe(CO)x, xx, x5 decomposition based on the fluence dependence of the photodecomposition yield. These data are consistent with gas phase photodecomposition energetics. The two mechanisms proposed are rapid sequential ejection of CO into the gas phase with loss of the first CO being rate limiting or simultaneous ejection of all CO. An unresolved low frequency shoulder did appear in the infrared spectrum after exposing the Fe(CO)5 covered Si(111)‐(7×7) crystal to the electron beam, possibly due to formation of a distribution of surface stable Fe(CO)x, x5 had been photolytically decomposed and annealed to 300 or 1000 K, further evidence that isolated iron is not formed in the laser deposition process.