Thursday /.TI4

CThH88

Neutral and ion number density mapping of laser ablated t i tanium plasma plumes using speclroscopic and electroSlatie probe techniques.

T. Williamson, A.H. El-Asial, G.W. Martin, L. Doy1e.A. Al-Khateeb,]. Weauci, U. Riley, M Lamb, T. Monuw, and CLS. Lcwis.

Thomas Williamson., School of Matheniatics and Physics. I'he Qucen's Llriwerstty ofBelFmt, BT7 INN, Northem Ireland. 'Tel. (01232) 273520 Far:(O1232) 418918 emai l . t willian,,,~l~qub.ac.uk

Summary: Devdopment of spectroscopic and electrostatic probe techniques fim the quantilative charactcriration of low tanperature laser ahlated plesma plumes me dcacribed. The ciianium plasma plume is formed hy KrF irradiation, incident on a rotating raigel at I s m fluences o i2 -6 Jcm ' with B spot size 1.4 mm x 1.4 mm A col l imaled. short pulsed, tunable dye lam &t L set delay time. between 5Wns - 2ps, i s urcd to s p t i a l l y and temporally prohe the plasma plume m a direction parallel to the rar$cl surface (i e. i n X-L plane) Fora plasma under-going self.similar expansion. the obscmcd ahsorhmce values ACA?.,, L! are relatcd to the corresponding absorher nembei dcnsilies N(x. zl within Ihs (x-zl plane by ( 1 ) where f is the absorption orcillutor strength, I is the probe drlar time and A?, is the dye laser detumng From lmc c m t x wwc len~ th h,, or the transtion

For mcilrured absarbmce values in l l i c range 0.05 - 2.00, typlcai number densities V ~ I L I C I m ~ m g fiom 10"cni' . I 0 ' " c d CBI be determined depending on the osci l ial i l r strength OF the absorption Ums~tmn. Dat.! oblained using a simple rlrctrostatic prohe technique, under trpical pulsed laser deposition ().e 2 J c d ) condirions. are validsred against dircct absorption nieasurenimts of ion numher density The evpclimenrill data abtmed iiom these diagnortic took is uscd to developcd m d validate computer simulations or lbe plasma processes within the

N(* , r )= [Zn YnlOii i t juil A(A&, z ) (1)

p1urnr.

CThH89

"Nanocrystalline Growth olHard Coatings by Palsod Laser Deposition" I. Zergioti, C. Fotakis

Foundauon fnr Research aud TechnolagyHellas, Institute of Electlonic Structure and h e r , P.0.Bnx 1527, Herakllon 711 I O , Greece.

G. N. Haidernenopoulos Depmien t of Mechmcal and Iridusmal Engioeenng, University of Thessaly,

Volos 38334, Greece.

The main objective of this research work war: the growlh of Titanium Carbide and T~taruum Dibofiddc hard coatings on bol steels w t h Pulsed Laser Deposition (PLD) m order fo improve their surface mechanical pmpertics. A pulsed KrF excimer laser was used with the dcposition chamber at a base pressure of 1 U 6 mbar. The morphology and the microstructure of the coatings were ermined using Scanning Elmnon hl icmxapy. X Ray Diihaction and Transmission Electron M ~ C C O S C O ~ ~ . High quality stoichiomenic and nanocqsralline thin fihs of refractory coatings, Tic and TiB,, were deposited at low substrate temperature bemeen 25°C and 600°C, using the Pulsed Laser Deposition technique. The microstructure of the TIC coatings was FCC with lattice parameter a-4.318k. The g~ov.6 of thc coatings vas pollycrystalline. and the ga in size decreased as the substrate temperature decreased. The grain sire varied between IO Lo 70 nm as this was measured b y the TEM. The growth of the p~llycrystall ine coatings possessed a wlumnar morphology with a

preferred mentation. The XRD examination showed that the diffractton pattern %'as depcndmt on the substrate tempmature. ShiRs on the XRD panern were obsemed as substrate temperature was decreased. The shifts werc amibuted to residual tensile Stresses in lhe coatings due to the nanocrystalliniry oFtheir stm~ture. The microstmch~re of the TiB, coatings was HCP with lattice pmmetm a=3.03A and c=3.23A. Thc gmwh of the coatings was pollycqrt.stalline and the grain size vaned between 10 and 50 m. The growth of the TiB, coatings had also a co l l l f nw m q h o l o a with a <0001> preferred mentation.

The hardness of Be coatings was determined to be 40 GPa and the elastic modulus 240FPa The elastic modulus in both materials, TIC and TiB,, 11'8s reduced up to 40% relat ive lo the bulk value due to nanaclystallinity The surface roughness measured with Ihr AFM was between 0.28 and 2.47 m. The electrical properties of the coatings confirmed their metallic nature. Mass spectroscopy and optical spectroscopy were applied as diagnostic methods for the constitution of the laser pllime. The ion formation due to Tic and TiB, excimer laser ablation wa detected using timc of flight ma56 spectroscopy. For the case ofTiC the detected inns were Ti and C with kinetic energies 0.5eV-3.7eV and 4.4eV-340eV respectively. For thc ease of the T B , the deterled m s u'm Ti, B and B, with energies 0.5eW2.2eV, 4.5eV and 260cV. and 9.6eV-153eV respeciively. The influence of different wavelenyh was also studied. The kinetic energy and the evolution of the plasma wils studied with a streak camera. The velocity of the plasma -2s ofthe older of IO'ccm/sec and was linearly dependenl on the energy fluence of the laser. Thc emission spectroscopy of Ihe plwma plume confirmed the atomic neutrsl and single ionised excited species of Ti. The above results indicate that coating growth OCCUIS basicillly by thc recombination of the ionic species at the surface of the suhsmfe.