A spatially and temporally resolved transient absorption technique has been employed to investigate the dynamics of ground-state YO during 355 nm laser ablation of Y2O3. Time-of-flight (TOF) measurements of the expanding YO plume in vacuum and in Ar or O2 ambient are reported. During the initial expansion of YO in vacuum, the center-of-mass velocity and the expansion velocity increase with distance up to the boundary of the Knudsen layer. In the presence of oxygen, reactions of the ablated atomic species with oxygen take place, resulting in the formation of YO with broad velocity distribution. From the peak time of the observed TOF distributions, the most probable velocities of YO are found to be 2.6 km/s in vacuum, 2.2 km/s in 50 mTorr Ar, and 1.8 km/s in 50 mTorr O2, respectively. The dependence of the peak time on distance shows that the experimental data can be well fitted with a shock wave model at higher ambient gas pressure.

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Mass, velocity and angle distributions of the ablated species generated from 355 nm pulsed laser ablation of a LiMn 2 O 4 target were investigated with an angle-and time-resolved mass spectrometric technique. Both neutral and ionic species of Li, O, LiO, LiO 2 , Mn, Li 2 , Li 4 , Li 6 , LiMn, MnO and MnO 2 were observed at the laser fluence of 0.8 J·cm −2 . The yield and variety of the ablated species increase with increasing the laser fluence. The time-of-flight spectra of ablated species can be fitted by a Maxwell-Boltzmann distribution with a center-of-mass velocity. There exist laser fluence thresholds for the ablated LiMn, Li 2 O and LiO 2 species, and the fluence threshold of ionic species is higher than that of neutral species. The angular distributions of the ionic and neutral ablated species can be simulated by a cos n θ or a bicosine function α cosθ +(1− α)cos n θ. In addition, the ablation mechanism of LiMn 2 O 4 by a 355 nm pulsed laser is discussed.Recently, all-solid-state thin film rechargeable lithium batteries have been investigated extensively because of their high energy density, superior charge-discharge property and safety [1] . The study of novel cathode materials has been an important subject. In comparison with LiNiO 2 and LiCoO 2 , LiMn 2 O 4 is the most promising candidate due to its high theoretical energy density, low cost and less toxicity [2] . LiMn 2 O 4 thin films have been prepared by various methods including RF sputtering, electron beam deposition and pulsed laser deposition (PLD) [3] . The capability of depositing high quality films with nearly the original stoichiometry of a bulk target and high deposition rate make PLD technique an attractive method for the fabrication of thin films. LiMn 2 O 4 thin films have been prepared by PLD [4,5] , however, the previous studies usually focused on their fabrication process and electrochemical properties and rarely on the physico-chemical process of the laser ablation of LiMn 2 O 4 . In our laboratory, we have successfully prepared thin film electrodes for Li-ion batteries and electrochromic devices, high dielectric materials and photoluminescence films using PLD method. In order to extend our understanding of the thin film formation and the nature of the laser ablation process, we have carried out the identification of neutral and ionic ablated species as well as the determination of their kinetic energy and spatial distributions [6][7][8][9][10] , since the measurements of the angular distributions of the ablated species can provide important information on the expansion dynamics of the ablated plume as well as the chemical composition and thickness uniformity of the deposited film. In this paper, we measure No. 6 TIME-RESOLVED QUADRUPOLE MS STUDY 609

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