title: Operational Regimes in Picosecond and Femtosecond Pulse-Excited Ultrahigh Vacuum SERS.
abstract: We report a systematic study performed in ultrahigh vacuum designed to identify the laser excitation regimes in which plasmonically enhanced ultrashort pulses may be used to nondestructively probe surface-bound molecules. A nondestructive, continuous-wave spectroscopic probe is used to monitor the effects of four different femtosecond- and picosecond-pulsed beams on the SER signals emanating from molecular analytes residing within plasmonically enhanced fields. We identify the roles of plasmonic amplification and alignment with a molecular electronic transition on the observed changes in the SER signals. Our results indicate that overlap of the laser wavelength with the plasmon resonance is the dominant contributor to signal degradation. In addition, signal loss for a given irradiation condition is observed only for molecules residing in hot spots above a threshold enhancement. Identification of suitable laser energy density ranges demonstrates the importance of considering these parameters when implementing SERS in the presence of pulsed irradiation.
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Pozzi
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Natalie L
authors.initials: NL
authors.lastname: Gruenke
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Naihao
authors.initials: N
authors.lastname: Chiang
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Zhdanov
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Nan
authors.initials: N
authors.lastname: Jiang
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Tamar
authors.initials: T
authors.lastname: Seideman
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: George C
authors.initials: GC
authors.lastname: Schatz
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.affiliation: Department of Chemistry, ‡Department of Materials Science and Engineering, and §Applied Physics Program, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Van Duyne