Temporal evolution study of the plasma induced by CO 2 pulsed laser on targets of titanium oxides L. Diaz a, ⁎, J.J. Camacho b , M. Sanz c , M. Hernández a , V. Jandova d , M. Castillejo c a Instituto de Estructura de la Materia, CFMAC, CSIC, Serrano 121, 28006-Madrid, Spain b Departamento de Química-Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain c Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006-Madrid, Spain d Laboratory of Laser Chemistry, Institute of Chemical Process Fundamentals, ASCR, 16502 Prague, Czech Republic abstract article info Article history: Received 11 January 2013 Accepted 1 June 2013 Available online 7 June 2013 Keywords: Laser induced breakdown spectroscopy Time-resolved optical emission spectroscopy High-power IR CO 2 pulsed laser Time of flight measurement Titanium oxides This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO 2 (anatase). LIBS excitation was performed using a CO 2 laser. The laser-induced plasma was found strongly ionized yielding Ti + ,O + , Ti 2+ ,O 2+ , Ti 3+ , and Ti 4+ species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti + , Ti 2+ and Ti 3+ was characterized. The results show a faster decay of Ti 3+ and Ti 2+ ionic species than that of Ti + and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO 2 -anatase induces on the surface sample the polymorphic transformation to TiO 2 -rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The study and characterization of the plasma produced by the in- teraction of a high-power laser with matter is an important tool for many technological applications such as control of properties of films grown by pulsed laser deposition (PLD), material processing and chemical analysis [1]. Characterization of the plasma plume is a good tool for controlling the properties of the deposits produced by PLD. In the past two decades, considerable effort was devoted to the solution of basic questions concerning the dynamics of the laser-induced expanding plasmas. Titanium dioxide (TiO 2 ) has generat- ed a lot of interest due to its versatile properties of application in optics, photovoltaics, gas sensing, photocatalysis. TiO 2 is also used as a pig- ment, for food coloring and as a high compressive strength material. Generally TiO 2 presents two polymorphic forms, anatase and rutile. On the other side, titanium monoxide (TiO) is non-stoichiometric in the range from TiO 0,7 to TiO 1.3 caused by vacancies of either Ti or O in the defect rock salt structure. Titanium oxides films can be produced by evaporation of a target by the action of a high-power laser [2–11]. The dynamics of materials ablated from surfaces by pulsed-laser irradi- ation is of fundamental technological and physical interest. Because of the transient characteristics of the plasma plume created by laser-induced breakdown (LIB), optical emission spectroscopy (OES) technique with time and space resolution is especially appropriate to obtain information about the behavior of the formed species as well as to study the dynamics of the plasma expansion. Temporally resolved LIB studies in titanium oxides has been reported by several researchers [12–23] using high-power lasers yielding interesting results. Recent time-resolved LIBS studies on different samples were carried out in our laboratory [24–28]. In this paper, we present a complete analysis of the plasma initiated on titanium oxides TiO and TiO 2 targets by nanosecond laser pulses at air pressures around 3 Pa. Our ultimate goal is to clarify the processes and the mechanism responsible for the observed emissions. The emis- sions generated by the plasma are mainly due to electronic relaxation of excited Ti, O, Ti + ,O + , Ti 2+ ,O 2+ , Ti 3+ , and Ti 4+ fragments. New re- sults, obtained from a time-resolved spectroscopic analysis, are shown. The intensities and the Stark-broadened profiles of several lines from Ti + were used to estimate both excitation temperature and electron den- sity. The temporal behavior of line intensities of Ti + , Ti 2+ and Ti 3+ was employed for the estimation of the three-body electron-ion recombina- tion rate constants for these species. Laser irradiation of TiO 2 -anatase produces on the surface sample a polymorphic transformation to TiO 2 - rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy. 2. Experimental procedure The experimental setup used in this study was described else- where [25]. The experiments were carried out with a transversely excited atmospheric (TEA) CO 2 pulsed-laser (Lumonics, model Spectrochimica Acta Part B 86 (2013) 88–93 ⁎ Corresponding author. E-mail address: luis.diaz@csic.es (L. Diaz). 0584-8547/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sab.2013.06.002 Contents lists available at ScienceDirect Spectrochimica Acta Part B journal homepage: www.elsevier.com/locate/sab