Ultrahigh vacuum studies of the interaction of 514 nm radiation from a cw Ar ion laser and its second harmonic at 257 nm with mono- and multilayer coverages of Mo(CO)6, W(CO)6, and Fe(CO)5 adsorbed on Si(111)7×7 at 90 K using thermal desorption spectroscopy (TDS), laser induced desorption spectroscopy, high resolution electron energy loss spectroscopy (HREELS), and Auger electron spectroscopy were performed. A model for the temperature rise of the sample due to cw laser heating is developed. By directly measuring the substrate temperature, these experiments were able to distinguish between photoelectronic and thermal effects active in the decomposition and desorption mechanisms of the adsorbed carbonyls. Results from TDS and HREELS show that Mo(CO)6 and W(CO)6 are molecularly adsorbed, while Fe(CO)5 partially dissociates upon adsorption. The decomposition of adsorbed Mo(CO)6 is caused by electronic excitation due to direct absorption of the 257 nm radiation. Irradiation with 514 nm radiation results in no photochemistry. The same mechanism is dominant for adsorbed W(CO)6 and Fe(CO)5; however, new excitation mechanisms are available to these molecules that lead to bonding changes in W(CO)6 and Fe(CO)5 with 514 nm irradiation. The photodecomposition products of the adsorbed carbonyls are found to be different from the gas-phase decomposition products. The surface stabilizes the adsorbed carbonyls, preventing complete removal of all the CO ligands. Desorption of CO due to photoelectronic excitation is found to occur via sequential single photon absorption and extraction of CO ligands. Evidence of clustering of carbonyl fragments was observed after 257 nm irradiation.

Articles you may be interested inGrowth of metal oxide thin films by laserinduced metalorganic chemical vapor deposition We report the results of a series of experiments studying metal film growth by low-power UVlaser photolysis of metal carbonyls. Small-area Mo, W, and Cr films were grown on Si substrates by photolysis in a background pressure of 0.1-0.2 Torr of the carbonyl. The different metals exhibited vastly different deposit morphologies. Elemental depth profiling by Auger electron spectroscopy (AES) revealed the presence of large amounts of carbon and oxygen in the films. Ultrahigh vacuum studies of the interaction of 257-and 514-nm radiation with multilayer coverages of Moe CO)" and W (CO)/) adsorbed on SiC 111)7 X 7 using highresolution electron energy-loss spectroscopy, laser-induced desorption, and AES were performed to clarify the mechanisms of adsorbed metal carbonyl decomposition and impurity incorporation into the films. Decomposition of both the adsorbed and gas-phase carbonyls proceeds through direct electronic excitation of the molecule by absorption of the 257-nm radiation; however. the photodecomposition products of the adsorbed carbonyls are different from the gas-phase decomposition products. The evidence suggests that both the surface and the previously deposited photofragments stabilize the partially photolyzed carbonyls, preventing removal of all the CO ligands from the adsorbed species. 996

Laser-induced electronic excitation of adsorbed MoCCOe followed by CO desorption is observed to occur on Si(l 11) (7 x 7) irradiated with 257-nm (4.8 eV) laser radiation. The process is shown to be completely nonthermal in nature. In contrast, irradiation with 514-nm radiation is found to be identical to resistive heating of the crystal. Adsorption does not open up new excitation mechanisms that allow decomposition to occur in the visible region of the spectrum.

Chemisorption of silanes on the Si(111)(7×7) surface J. Vac. Sci. Technol. A 5, 628 (1987); 10.1116/1.574648 Mechanisms of laser interaction with metal carbonyls adsorbed on Si(111)7×7: Thermal vs photoelectronic effects Summary Abstract: Observation and properties of the Ge(111)7×7 surface from Si(111)/Ge structures J. Vac. Sci. Technol. A 3, 1633 (1985); 10.1116/1.573150 Summary Abstract: Transmission channeling studies of the Pd/Si(111)7×7 system J.