http://hdl.handle.net/10362/3984 Tue, 21 May 2013 07:34:28 GMT 2013-05-21T07:34:28Z http://hdl.handle.net/10362/4129 Title: Neutral C60 effusive source for atomic collisions with fullerene Authors: Lobo, R. F. M.; Silva, N. T. Abstract: A neutral C60 effusive source was assembled in a crossed molecular-beam apparatus in order to perform atom–molecule electron transfer collisions and its calibration by time-of-flight mass spectrometry. This source consists of a stainless-steel oven where the C60 sublimation takes place. Typical operation temperatures are in the range of 723 up to 888 K. Through this setup the study of the ion pair formation process K C60→K C60 where K is a potassium atom can be performed in a wide range of collision energies 10 up to 500 eV . The results show evidence of negative ion formation being the ratio of intensities between the parent ion and fragment ions clearly dependent on the collision energy used. Description: Review of scientific instruments, Vol.72, Nº9 Wed, 01 Aug 2001 00:00:00 GMT http://hdl.handle.net/10362/4129 2001-08-01T00:00:00Z http://hdl.handle.net/10362/4128 Title: Non-volatile analysis in fruits by laser resonant ionization spectrometry: application to resveratrol (3,5,4 -trihydroxystilbene) in grapes Authors: Lobo, R. F. M.; Montero, C.; Orea, J. M.; González Ureña, A.; Soledad Muñoz, M. Abstract: A laser desorption (LD) coupled with resonanceenhanced multiphoton ionisation (REMPI) and time-of-flight mass spectrometry (TOFMS) technique for non-volatile trace analysis compounds is presented. Essential features are: (a)an enhanced desorption yield due to the mixing of metal powder with the analyte in the sample preparation, (b) a high resolution, great sensitivity and low detection limit due to laser resonant ionisation and mass spectrometry detection. Application to resveratrol content in grapes demonstrated the capability of the analytical method with a sensitivity of 0.2 pg per single laser shot and a detection limit of 5 ppb. Description: Applied Physics B Lasers and Optics, vol.71 Mon, 01 May 2000 00:00:00 GMT http://hdl.handle.net/10362/4128 2000-05-01T00:00:00Z http://hdl.handle.net/10362/4125 Title: Fluorescence in nanostructured fulleride films Authors: Lobo, R. F. M.; Costa, M. S.; Ribeiro, J. H. F.; Sequeira, C. A. C.; Pereira, P. Abstract: Nanostructuring of fullerene C60 beam deposited films is achieved by electrochemical reduction in a potassium hydroxide aqueous solution. Alkali fulleride clusters are formed at the electrode, as it is illustrated by cyclic voltammetry, x-ray diffraction, and scanning tunneling microscopy. Fluorescence emission from fluorophore doped fullerene reduced films was investigated by fluorescence spectroscopy and scanning near-field optical microscopy. These techniques lead to results which also fit such nanometer-sized fulleride cluster interpretation. In particular, the fluorophore fluorescence lifetime decreases as long as aggregation in the film is more effective,which occurs with the increase of film thickness. Description: Applied Physics Letters, 89 Wed, 01 Nov 2006 00:00:00 GMT http://hdl.handle.net/10362/4125 2006-11-01T00:00:00Z http://hdl.handle.net/10362/4124 Title: Kinetic measurements during transient film growth on zinc Authors: Lobo, R. F. M.; Santos, Diogo M. F.; Sequeira, César A. C.; Yun, Chen Abstract: The electrochemical behaviour of zinc has been extensively studied in alkaline and acid media, but only a few studies have been reported in neutral solutions, particularly in deaerated media. Zinc passivation in neutral medium and the effect of the ClO4- ion on the nucleation and growth of the passive layer is studied in this paper by a transient technique at different electrolyte concentrations and applied potentials. ZnO growth rate was shown to decrease with increasing electrolyte concentration. Moreover, passive layer growth occurred followed by pitting nucleation and growth. Film growth and pit nucleation are explained by means of the Macdonald and Engell-Stolica models. Description: Quimica Nova, Vol. 32, Nº2 Thu, 01 Jan 2009 00:00:00 GMT http://hdl.handle.net/10362/4124 2009-01-01T00:00:00Z