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We examined the spatial distribution of the velocity distribution function of Fe atoms in a conventional dc magnetron sputtering source by laser-induced fluorescence (LIF) imaging spectroscopy. By measuring the Doppler broadening of the excitation spectrum of LIF, we evaluated the velocity distribution function of Fe at many positions in the discharge space. By calculating the first- and second-order moments of the velocity distribution function, we obtained two-dimensional maps of the average velocity and the effective temperature in the r-z plane of the cylindrically symmetric magnetron discharge. The map of the average velocity clearly indicates that Fe atoms have fast velocity in the region adjacent to the target at a low discharge pressure such as 3 mTorr, while at a high gas pressure such as 20 mTorr, the average velocity of Fe atoms is almost zero in the entire discharge space. On the other hand, it has been found from the map of the effective temperature that the velocity distribution function observed at 3 mTorr has a broad width corresponding to approximately 8×104 K in the bright plasma near the target. [ABSTRACT FROM AUTHOR]

The synthetic characteristics of large carbon cluster ions by laser ablation of polymers in vacuum were investigated. Time-of-flight mass spectrometry was used for analyzing the masses of ionic species produced by laser ablation. We found that large carbon cluster ions C[sup +, sub n] with n up to 400 were synthesized in vacuum when copolymer of ethylene and tetrafluoroethylene, polyvinyliden fluoride, and chlorotrifluoroethylene were employed as the target material. Since the synthesis of large cluster ions in vacuum is a surprising phenomenon, we examined the synthesis efficiency in various experimental conditions. By comparing mass spectra obtained from various polymers containing hydrogen and/or halogen atoms, the existence of both hydrogen and halogen atoms in polymers do not directly contribute to enhance the synthesis efficiency of large carbon clusters. In addition, microscopic observations of surface morphologies of laser-ablated polymers revealed that the clustering reactions in eroded craters had little correlation with the synthesis efficiency of large carbon clusters. [ABSTRACT FROM AUTHOR]

Time-of-flight mass spectrometry was used for analyzing ionic species produced by Nd:YAG laser ablation of polymers [polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene] in vacuum. The temporal variation of the mass distribution after the laser irradiation was investigated. The target polymers were decomposed to almost atomic species by the laser irradiation. After the laser irradiation, significant temporal evolution of carbon cluster ions (C[sub n]H[sub m][sup +], C[sub n]H[sub m][sup -], and C[sub n]F[sub m][sup -]) was observed. This result indicates that the cluster ions are produced from atomic species via gas-phase reactions in the ablation plume with no ambient gases. The mass spectra of C[sub n][sup -] and C[sub n]H[sub m][sup -] obtained from the PP and PE targets suggest that even carbon clusters (C[sub 2k]) are hydrogenated more efficiently than odd ones (C[sub 2k+1]) to produce C[sub 2k]H[sub m]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [&z.sbnd;CH2&z.sbnd;CH2&z.sbnd;CF2&z.sbnd;CF2&z.sbnd;]n) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions Cn+ with n≥30 were observed in the mass spectra. The fractional abundance of heavy clusters in the mass spectrum decreased with the number of laser pulse. On the other hand, carbon became rich in the atomic composition of the laser-irradiated surface, and the eroded area on the surface increased with the number of laser pulse. From these results, it is suggested that the carbon-rich material surface results in the less efficient production of heavy carbon clusters. In addition, it is also suggested that clustering reactions in eroded craters do not contribute to the synthesis of heavy clusters. [Copyright &y& Elsevier]

We investigated the effect of the pre-irradiation of a polymer target in vacuum, using a low-fluence laser pulse, on the synthesis efficiency of carbon cluster ions ejected by laser ablation. A polymer target was irradiated by two laser pulses. The first laser was used for the pre-irradiation, and the second laser was used for ablation. The masses of the ions in the ablation plume were analyzed by time-of-flight mass spectrometry. It was found that the synthesis efficiency of carbon cluster ions was enhanced by the pre-irradiation. The effects of the fluence of the pre-irradiation, the wavelengths of the lasers, and the interval between the oscillations of the two laser pulses on the enhancement of the cluster synthesis are reported. [ABSTRACT FROM AUTHOR]

Abstract: We observed four experimental results which suggest the existence of unidentified species other than metal atoms and metal ions in magnetron sputtering discharges employing metal targets. The most probable species which are compatible with the experimental observations are clusters (mainly dimers and trimers) of metal atoms. According to the experimental results, it is speculated that the amount of clusters is comparable to that of metal atoms. In other words, the present experimental results suggest a possibility that dimers and trimers are major sputtering products from metal targets. [Copyright &y& Elsevier]