Oxidation of titanium through Nd:YAG laser irradiation A.Pe ÂrezdelPino * ,P.Serra,J.L.Morenza Departament de Fõ Âsica Aplicada i O Á ptica, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona, Spain Abstract Surface oxidation of titanium was performed by irradiation in air with a Nd:YAG (l  1:064 mm) laser operating in pulsedmode.Differentoxidecoatingsofapparentlyuniformcolorswereobtainedbychangingtheaccumulated¯uenceon thematerial.However,detailedviewofthesurfacesthroughanopticalmicroscopeshowedmicron-sizedzonesofdifferent colors.CompositionalstudiesperformedbyX-raydiffraction(XRD)showedthatthecoatingsweremainlycomposedof Ti 2 O and TiO. Micro-Raman spectroscopy of the small colored zones revealed the presence of Ti 2 O 3 and TiO 2 with differentratioscharacteristicofeachcolor.Theseresultsevidencethatexistssomecorrelationinthecoatingsbetween compositionandcolor,althoughonlythecompositionalchangesdetectedbyRamandonotfullyaccountfortheobserved differencesincolor. # 2002ElsevierScienceB.V.Allrightsreserved. Keywords: Laser; Surface treatment; Titanium; Titanium oxide; Color 1. Introduction Titanium oxide coatings exhibit a wide variety of physical properties that allow them to be useful in manyapplicationssuchasphotocatalysis,gassensors, medical implants and optical coatings. They also presentarangeofcolorsthatmakethemveryattrac- tiveinjewelryanddecorativeapplications [1±5].They can be obtained on titanium by surface oxidation, beingthelasertreatmentinairaninterestingtechnique experimented by some authors [3±5] because of its high spatial resolution, velocity and versatility. The aim of this work, is the study of the coloring of titanium by surface oxidation in air with a pulsed Nd:YAGlaseroperatingathighrepetitionrate. 2. Experimental The surface oxidation treatments were performed with a Baasel Lasertech Nd:YAG (l  1:064 mm) laser system operating in pulsed mode at 30kHz repetition rate. The pulse energy and duration were about1.9mJand300ns,respectivelyandtheaverage powerwas57W.Thelaserbeamwasfocusedthrough a160mmfocallengthlensinacircularspotwitha diameterofabout350 mm;leadingtoapulse¯uence of7MW/cm 2 , well below the ablation threshold. Five high purity titanium targets (10mm  10mm  1mm),about1.5 mmrough,werecarefully cleaned with ethanol and glued to a copper plate. Afterwards, they were irradiated in air scanning the samplesurfacelinebylinewithparallellasertracesat controlled scan velocity. Adjacent traces were sepa- rated200 mm,whichresultedinpartialoverlapping.A delaytimeof500msbetweenconsecutivetraceswas Applied Surface Science 197±198 (2002) 887±890 * Correspondingauthor.Tel.: 34-934021134; fax: 34-934021138. E-mail address: angel@fao.ub.es (A. Pe ÂrezdelPino). 0169-4332/02/$ ± see front matter # 2002ElsevierScienceB.V.Allrightsreserved. PII:S0169-4332(02)00447-6