Time-resolved SFG study of the vibrational excitation of adsorbed CO on Ni(111) and NiO(111) surfaces under the irradiation of UV and visible photons

• Published in: Surface science Vol. 427; pp. 331 - 336
• Main Authors: Bandara, Athula, Kubota, Jun, Onda, Ken, Wada, Akihide, Kano, Satoru S., Domen, Kanzunari, Hirose, Chiaki
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01.06.1999; Amsterdam Elsevier Science; New York, NY
• Subjects: CO on Ni and NiO; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Hot electrons; Physics; Solid surfaces and solid-solid interfaces; Sum-frequency generation (SFG); Surface and interface dynamics and vibrations; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); v=2←1 hot band; Vibrational excitation by UV and visible photons; Vibrational excitation by UV and visible photons; CO on Ni and NiO; Sum-frequency generation (SFG); Hot electrons; v=2←1 hot band; Nickel oxides; Physical radiation effects; Transition element compounds; Sum frequency; Experimental study; Time resolution; Ultraviolet radiation; Adsorption; Transition elements; Adsorbed state; Vibrational modes; Visible radiation; Nickel; Carbon monoxide
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/S0039-6028(99)00298-8

The effects of irradiation by picosecond ultraviolet (266 nm) and visible (532 nm) pulses of CO-covered Ni(111) and NiO(111)/Ni(111) surfaces were investigated by infrared-visible sum-frequency generation (SFG) spectroscopy. As a result of the irradiation of UV pulses, the SFG signal by the v=1←0 bands of the CO stretching mode weakened and transient peaks tentatively assigned to the v=2←1 hot band transition appeared with a downshift by 18 and 14 cm −1 from v=1←0 bands on the metal and oxide-layered surfaces, respectively. The time profile of the weakening and that of the transient signal were coincident with the same rise and fall times of less than ∼10 ps. The irradiation of visible pulses also induced a weakening of the v=1←0 bands and transient peaks, but the decay time on the metal surface was longer than 100 ps. The temporal and spectral features imply that the persistent v=1←0 band and the transient band originated from the same CO molecule. Short decay times observed on irradiating UV pulses on to the Ni(111) and NiO(111) surfaces and that of the visible pulses on to the NiO(111) surface suggest that the photo-generated hot electrons induced the observed spectral changes. The long decay time observed on irradiating visible pulses on to the Ni(111) surface suggests the occurrence of a thermally driven process. Participation of the negative ion state was considered to be one of the possible mechanisms for the rapidly decaying features.