Rolf Mitzner

Optical emission studies of laser desorbed C60

The optical emission spectra of laser desorbed C60 have been investigated as a function of laser fluence for desorption with a XeCl excimer laser (pulse length 20 ns). The observed spectra show close similarities to black‐body radiation and can be fitted with the Planck black body formula (modified for small particles) thus giving information on the temperature of the desorbed species. The temperatures obtained (2300–3000 K) are in good qualitative agreement with previous, indirect temperature estimates. Spatially and temporally resolved measurements provide additional insight into the desorption mechanisms. An estimate of cooling rates indicates that thermionic electron emission and C2 fragmentation dominate for temperatures above about 3000 K but below this value the dominant cooling mechanism is black‐body radiation.

Stability of photo-excited C60 chemisorbed on Ni(111)

Abstract A single monolayer of C60 on Ni(111) was subjected to nanosecond UV pulsed laser irradiation. Neither desorption nor decomposition of the ordered monolayer system could be observed up to laser fluences close to the nickel ablation threshold. This is indicative of a very efficient dissipation of the absorbed photon energy into the nickel substrate. At higher laser fluences, decomposition of the C60 monolayer occurs on the surface.

ON THE MECHANISM OF C60 THIN FILM LASER-INDUCED DESORPTION

The mechanism of thin film C60 laser desorption has been investigated using nanosecond and picosecond UV laser pulses. The desorption experiments were performed under ultrahigh‐vacuum conditions using reflectron time‐of‐flight mass spectroscopy from which the velocity distributions of the desorbed ions and the dependence of the ion yield on the laser fluence were obtained. A strong nonlinear dependence of the desorption yield on laser fluence in the threshold region, indicative of a thermal mechanism, was found for both ns and ps pulses. Typically, the C+60 velocity distributions were bimodal and could be fitted by modified Maxwell–Boltzmann distributions. The fits to the slow contributions gave translational temperatures consistent with surface temperatures due to laser heating with ns pulses as estimated by solving the one‐dimensional heat equation. In contrast, translational temperatures which are much too high to be consistent with purely thermal processes were obtained for the fast contributions. The...

Nanosecond and picosecond laser desorption of C60

Abstract Laser desorption of C 60 using nanosecond and picosecond laser pulses has been investigated. The velocity distributions of the desorbed ions were determined by means of time-of-flight mass spectrometry. Optical emission spectroscopy was used to determine the internal energy of the desorbed species. Typically, the C 60 + velocity distributions are bimodal, indicative of two distinct desorption mechanisms. The velocities and internal energies of the slow particles are consistent with a purely thermal desorption mechanism. The fast particles, which dominate for desorption with ps pulses, cannot be produced by a purely thermal mechanism. Different mechanisms are postulated for the production of the fast components in the two cases.

Reply to the comment on 'The dispersed laser induced fluorescence spectrum of gas phase C60 at 308 nm'

We reply to the comment made by Sassara A et al 1997 ( J. Phys. B: At. Mol. Opt. Phys. 30 4415 - 6) and agree with their conclusions.

The dispersed laser-induced fluorescence spectrum of gas-phase at 308 nm

We have recorded the dispersed laser-induced fluorescence spectrum of gas-phase ablated from a rotating copper cylinder by 308 nm radiation from a XeCl excimer laser. At vibrational energies below the spectrum consists of three progressions of transitions to the electronic ground state ending on the odd vibrational levels of the lowest frequency mode, with the lowest and modes as additional origins or on the vibrational levels of the third mode with two quanta of the lowest mode and the combination as the additional origins. At higher vibrational energies, the observed bands become more complex and have yet to be analysed.