Pressureeffectsduringexcimerlaserablation ofmagnesiumdiboridetargets S.Amoruso a,b,* ,M.Armenante c ,R.Bruzzese a,d ,N.Spinelli a,d , R.Velotta a,d ,M.Vitiello a,d ,X.Wang a,d a Coherentia-INFM, Via Cintia 26, I-80126 Napoli, Italy b Dipartimento di Ingegneria e Fisica, dell'Ambiente, Universita Á della Basilicata, C.da Macchia Romana, I-85100 Potenza, Italy c Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Via Cintia 26, I-80126 Napoli, Italy d Dipartimento di Scienze Fisiche, Universita Á degli Studi di Napoli Federico II, Via Cintia 26, I-80126 Napoli, Italy Abstract TheexpansiondynamicsandkineticsoftheplasmaproducedbyexcimerlaserirradiationofMgB 2 inArbackgroundgashas beenstudiedbyspace-andtime-resolvedopticalemissionspectroscopy.Theexperimentalresultsshowthatthereisadistance- relatedpressurethresholdabovewhichtheexpansiondynamicschangesfromafreeexpansiontoashockwaveregime,causing bothaconsiderableincreaseofthefractionofexcitedMgatomsandasimultaneousreductionoftheirkinetic¯uxenergy.The analysisoftheresultswithintheframeworkofamodeldescribingtheplumeexpansionintoanambientgasindicatesthatthe shockwaveformationleadstoplumeheating,thus,in¯uencingitsexcitation/ionisationkinetics.Theproductionofaplume whoseparticlesarecharacterisedbyalower¯uxkineticenergyandahigherdegreeofinternalenergycanbeparticularlyuseful forMgB 2 thin®lmdepositionatlowersubstratetemperature,duetothehighvolatilityofMg. # 2002ElsevierScienceB.V.Allrightsreserved. PACS: 52.50Jm;52.50Lp Keywords: Laserablation;Spectroscopy;Magnesiumdiboride 1. Introduction Therecentdiscoveryofsuperconductivityat 40K in the simple inter-metallic compound MgB 2 [1] has generated great scienti®c and practical interest. MgB 2 has the highest transition temperature among non-oxidematerials,andthefabricationofsupercon- ducting MgB 2 thin ®lms is considered of signi®cant importanceformanyelectronicapplications.Different reportsonMgB 2 thin®lmspreparationwithdifferent techniqueshavebeenwritten [2].Althoughdifferent methodshaveprovidedfairqualityMgB 2 thin®lms, as-grown superconducting thin ®lms are preferable for the fabrication of junctions and multilayers. The maindif®cultyinobtaining as-grown superconducting MgB 2 thin®lmsliesinthehighvolatilityofMg. Amongthedifferentdepositionmethods, as-grown MgB 2 thin®lmshavebeensuccessfullyobtainedby pulsedlaserdeposition(PLD)inArbuffergas [3,4]. Thecrucialfactortoobtainsuperconducting®lmsis AppliedSurfaceScience208±209(2003)39±44 * Correspondingauthor.Tel.: 39-97-1205-164; fax: 39-97-1205-160. E-mail address: amoruso@unibas.it(S.Amoruso). 0169-4332/02/$±seefrontmatter # 2002ElsevierScienceB.V.Allrightsreserved. PII:S0169-4332(02)01282-5