Nikola Radic | Ruder Boskovic Institute (original) (raw)

Papers by Nikola Radic

Metals and Materials International, Apr 22, 2019

Some of mechanical, electrical, and thermal properties of the Al-(Nb, Mo, Ta, W) binary thin film... more Some of mechanical, electrical, and thermal properties of the Al-(Nb, Mo, Ta, W) binary thin films which are important for the stability and usability of the amorphous alloys were examined. Samples were prepared by magnetron deposition technique in wide range of composition onto various substrates held at room temperature. Different experimental techniques were used for the characterization of samples. The results of structural relaxation and crystallization measurements under isochronal conditions are compared with the results of measurements of micro/nano hardness and strain in the films. From the micro/nano hardness measurement, the elastic deformation energy fraction is calculated. The elastic deformation energy fraction is correlated with the various results obtained from electrical resistivity measurements under isochronal conditions. Particular emphasis was placed on the Al-Mo amorphous alloys. It turns out that elastic deformation energy fraction becomes important indicator and phenomenological correlation parameter between various physical properties of examined films.

Solid State Communications, Feb 1, 2004

... Mater. Sci. Engng, 99 (1988), p. 187. [6] FM Mayeya and MA Howson. Phys. Rev. B, 49 (1994), p... more ... Mater. Sci. Engng, 99 (1988), p. 187. [6] FM Mayeya and MA Howson. Phys. Rev. B, 49 (1994), p. 3167. [7] FM Mayeya, BJ Hickey and MA Howson. Phys. Rev. B, 51 (1995), p. 15567. [8] U. Mizutani, S. Ohashi, T. Matsuda, K. Fukamichi and K. Tanaka. Phys. J.: Condens. ...

Journal of Non-crystalline Solids, May 1, 2003

The pronounced variation of the electrical resistivity of the amorphous Al-W thin films observed ... more The pronounced variation of the electrical resistivity of the amorphous Al-W thin films observed during initial heating above room temperature was examined. Both isochronal and isothermal treatments were performed in order to investigate the effects of the film composition, substrate material, and substrate temperature, on the magnitude of the relaxation phenomena. Regarding the isochronal heating, it was observed that the relaxation effects decreased with an increase of the heating rate, and decreased with the aluminum content in the film. The Al 78 W 22 amorphous thin films were subjected to isothermal annealing for 6 h at a temperature of 515°C. The effects of the substrate material (alumina ceramic, glass and sapphire), and the deposition temperature (LNT, RT, 200 and 400°C) were examined. The relaxation decreased in a sequence of: alumina ceramic-glass-sapphire substrates, as well as with an increase of the substrate temperature. An assumed dominant role of the aluminum in the effects observed, was tested by the corresponding investigation of Al-Ti and Cu-Ti amorphous thin films.

Vacuum, May 1, 2001

Thin films of Al–W alloys were prepared on sapphire substrates by magnetron co-sputtering. By X-r... more Thin films of Al–W alloys were prepared on sapphire substrates by magnetron co-sputtering. By X-ray diffraction, it was revealed that, within a composition range Al80W20 to Al67W33, the films were amorphous. The increase of tungsten content in the films (Al60W40 and Al50W50) resulted in the appearance in a mixture of two or three metastable crystalline phases. Apparently, the mixture of

Fizika A, 2006

Different methods of X-ray diffraction line profile analysis (XRDLPA) are used to study microstru... more Different methods of X-ray diffraction line profile analysis (XRDLPA) are used to study microstructural parameters such as crystallite size (diffracted domain size), microstrain and texture in tungsten thin films deposited on glass by DC magnetron sputtering at different substrate temperatures and at different working-gas pressures. The whole-pattern analysis within the Rietveld method, the "single-line" method and "double Voigt" method (equivalent to the Warren-Averbach method) are applied and mutually compared. In addition, the results obtained by the Scherrer method are also discussed. The line broadening has been found to be isotropic, supporting the reliability of usage of the Rietveld method in the size-microstrain extraction.

Corrosion Science, Feb 1, 2010

Pure aluminium corrodes readily in 1 M HCl solution while its supersaturated alloys with Mo, expl... more Pure aluminium corrodes readily in 1 M HCl solution while its supersaturated alloys with Mo, explored in this work, exhibit excellent corrosion properties due to the oxide barrier film formation on the alloy surface. The influence of Mo content in the alloy on the potential and charge distribution across the system alloy |oxide film| solution was studied in situ using dc and ac electrochemical methods. Passivity, a sudden change in electrode impedance, and the onset of secondary passivity and pitting were discussed in terms of the solute segregation, according to the solute-rich mechanism, change in the alumina structure and solid state processes connected with the transport of point defects and spatial distribution of surface charge.

Vacuum, Dec 1, 2013

Structural relaxation and crystallization of Al-(Nb, Mo, Ta, W) amorphous thin films under isochr... more Structural relaxation and crystallization of Al-(Nb, Mo, Ta, W) amorphous thin films under isochronal condition were examined by continuous in situ electrical resistance measurements in vacuum. The amorphous Al-early transition metals (TE) thin films were prepared by simultaneous sputtering from two independently controlled DC magnetron sources in the CMS 18 deposition device. The structure of the as-deposited, heat-treated, and crystallized films was investigated by the XRD method. The dynamical crystallization temperature was estimated from the rapid change of the derivative of resistivity vs. temperature curve (dr/dT). For the isochronal heating, it was observed that the relaxation effects decreased with an increase of the heating rate and decreased with the content of early transition metal in the film. Assuming the linear dependence of resistivity with temperature (Dr/r RT ¼ aDT) in the observed temperature interval the linear r(T) dependence is extracted from the relaxation effects. Adopted experimental function of r(T) is fitted to a modified BlocheGrüneisen formula. Excellent agreement of experimental data and fitting function is obtained.

Thin Solid Films, 1997

The 2D thickness distributions of Cu andAl planar thin films prepared by a home-made cylindrical ... more The 2D thickness distributions of Cu andAl planar thin films prepared by a home-made cylindrical magnetron with rectangular exit window were examined. The experimental results were compared with several models of sputtered particle transport. It has been shown that in the azimuthal direction the best agreement with experimental results was achieved with the free flight model. Due 10 an uneven target erosion, theagreement with the model calculations proved to be somewhat less satisfactory in the axial direction. An overall similarity of thickness distributions inthe case of AI deposition at PA1::::0.7 Paand Cu deposition at PAr:::: 2.25 Paworking gas pressure has been found. However. iI hasbeen found that the portion of backscattcred flux was greater inthecase of AI than it was for Cusputtering.

Strojarstvo : časopis za teoriju i praksu u strojarstvu, 2011

Tanki filmovi AlxNb1-x (95  x  20) dobiveni su magnetronskom depozicijom na sobnoj temperaturi ... more Tanki filmovi AlxNb1-x (95  x  20) dobiveni su magnetronskom depozicijom na sobnoj temperaturi koristenjem uređaja za depoziciju CMS 18. Struktura tek deponiranih filmova ispitana je rentgentskim zracenjem, i ustanovljeno je da su filmovi AlNb amorfni u podrucju od 30% do 85% udjela aluminija, dok izvan tog podrucja dobivamo nanokristalne strukture. Termicka stabilnost i fazne transformacije ispitvane su kontinuiranim in situ mjerenjem elektricnog otpora pod ne-izotermnim (izokronim) uvjetima pri brzini grijanja od 2 K/min. Svaka promjena u ponasanju otpora koja može znaciti i faznu transformaciju sukcesivno je ispitana rendgentskim zracenjem. Analize rentgenograma pokazuju da se kao konacni produkti transformacija amorfnih Al-Nb filmova javljaju intermetalni spojevi Al3Nb odnosno AlNb3, ovisno o sastavu amorfne faze. Brzina izlucivanja intermetalne faze ovisna je o blizini stehiometrijskog omjera aluminija i niobija u sastavu amorfne faze. Promjena otpornosti s temperaturom kod Al-Nb amorfnih tankih filmova pokazuje analogno ponasanje sa sistemima Al-Ta i Al-Mo osobito u kombinacijama sa velikim udjelom aluminija.

Amorfne binarne slitine volframa i aluminija u obliku tankih filmova zanimljive su kao antikorozi... more Amorfne binarne slitine volframa i aluminija u obliku tankih filmova zanimljive su kao antikorozijske zastitne prevlake te protudifuzijske barijere na povisenim temperaturama. Postupkom magnetronske kodepozicije pripravljeni su tanki filmovi slitina aluminija i volframa u rasponu sastava od Al82W18 do Al50W50 na razlicitim podlogama [1, 3]. Filmovi u rasponu sastava Al82W18-Al62W38 su redovito potpuno amorfni, a pri daljnjem povecanju udjela volframa struktura filma je smjesa amorfne faze i kristalne cvrste otopine. Mjerenjem ovisnosti elektricnog otpora o temperaturi, uz određivanje strukture rentgenskom difrakcijom na odabranim temperaturama, pracene su promjene strukture do 1000 K. Od 400 K do 800 K procesi strukturne relaksacije u amorfnim filmovima imaju za posljedicu znatan porast el. otpora uz zadržavanje amorfnosti. Pritome je uocljiv utjecaj vrste podloge i temperature depozicije, a usporedbom sa ponasanjem slitina Al-Ti te Cu-Ti, cini se da osjetljivost el. otpora o relaksacciji amorfne strukture dolazi od aluminija. Temperatura kristalizacije (određena naglom promjenom el. otpora i temperaturnog koeficijenta el. otpora) amorfnih Al-W slitina opcenito je visoka i ovisi o sastavu: od 800 K za Al80W20 do 900 K za Al65W35. Glavni produkt kristalizacije u svim slucajevima je intermetalni spoj Al4W [2]. Kinetika fazne transformacije interpretirana je pomocu Johnson-Mehl-Avrami teorije modificirane za neizotermne uvjete [5]. Dobra termicka stabilnost amorfnih Al-W filmova potvrđena je dugotrajnim izotermnim napustanjem na visokim subkristalizacijskim temperaturama pri cemu amorfni filmovi samo djelomicno kristaliziraju. Mikrotvrdoca amorfnih filmova je oko 7, 5 GPa i slabo ovisi o sastavu, dok sa porastom udjela volframa u podrucju dvofazne strukture znacajno raste i dosiže oko 20 GPa za Al50W50. Elektricna otpornost amorfnih Al-W slitina je u rasponu 200-400 mikroomcm, a temperaturni koeficijent el. otpora ima visoke negativne vrijednosti: od -5, 5 x 10(-4) K(-1) za Al80W20 i postepeno opada do nule za Al50W50 slitinu. Analizom funkcionalne ovisnosti el. otpora o temperaturi procijenjena je Debyeova temperatura amorfnih slitina sastava oko Al70W30 na 450 K [4]. Elektrokemijska mjerenja korozije u tehnoloskim i fizioloskim otopinama ukazuju na visoku korozijsku otpornost amorfnih Al-W slitina: u 1 M HCl brzina korozije amorfnih filmova je dva reda velicine manja nego cistog aluminija i približava se cistom volframu [6]. Ukupni dobiveni rezultati cine amorfne tanke filmove Al-W slitina zanimljivim za primjenu. Literatura [1] T.Car, N.Radic: Thin Solid Films, 293 (1997) 78 [2] N.Radic, J.Ivkov, A.Tonejc, T.Car: JVC 7, Debrecen, 1997, Extended Abstracts p.167 [3] N.Radic, A.Tonejc, M.Milun, P.Pervan, J.Ivkov, M.Stubicar: Thin Solid Films, 317(1998) 96 [4] J.Ivkov, N.Radic: Solid State Comm., 106(1998) 273 [5] T.Car, N.Radic, J.Ivkov, E.Babic, A.Tonejc: Appl. Phys. A, 68(1999) 69 [6] M.Metikos-Hukovic, N.Radic, Z.Grubac, A.Tonejc: Eurocorr'99, Aachen, Proceedings, Topic 2, p. 65

Amorfne slitine aluminija i volframa imaju dobra elektricna i korozijska svojstva, te visoku otpo... more Amorfne slitine aluminija i volframa imaju dobra elektricna i korozijska svojstva, te visoku otpornost prema kristalizaciji. Mogu se upotrijebiti kao zastitne prevlake manje kvalitetnih podloga u kemijski agresivnoj okolini i na povisenoj temperaturi. Tanki filmovi Al-W pripravljeni su simultanom depozicijom cistih metala rasprasenih u dva neovisno kontrolirana cilindricna magnetronska izvora. Izbor uvjeta depozicije omogucio je pripravu filmova sirokog raspona kemijskog sastava, od Al80W20 do Al67W33, dok je konacna debljina filma bila reda 1 mikro metar. Korozijska otpornost pripravljenih amorfnih Al-W filmova i pojedinacnih komponenata slitine studirana je u otopini HCl koncentracije 1 M. Korozijski kineticki parametri određeni su iz DC polarizacijskih mjerenja, dok su elektricka i dielektricka svojstva određena iz AC mjerenja. Na osnovi rezultata elektrokemijske impedancijske spektroskopije predložen je model međufazne granice kruto/kapljevina. Korozijska svojstva korelirana su direktno s kemijskim sastavom slitine i njezinom strukturom. Utvrđeno je da korozijska stabilnost ispitivanih amorfnih slitina raste s povecanjem sadržaja volframa. Prije i nakon izlaganja korozivnoj sredini, struktura i morfologija pripravljenih filmova ispitane su metodom rentgenske difrakcije i opticke mikroskopije. Filmovi pripravljeni u rasponu sastava od Al80W20 do Al67W33 u pravilu su bili potpuno amorfni.

Corrosion behavior of sputter-deposited amorphous Al-W alloys in hydrochloric acid was compared t... more Corrosion behavior of sputter-deposited amorphous Al-W alloys in hydrochloric acid was compared to that of pure aluminum and tungsten metals. Both d.c. polarization and a.c. impedance studies clearly show that an increase of tungsten content in the alloy lowers the overall rate of corrosion and increases the critical pitting potential. The corrosion rate of amorphous Al-W films is about two orders of magnitude lower than that of aluminum, and the corrosion potential, E_corr, is about 500 mV higher than that of aluminum. Before and after exposure to corrosive environment, the structure of prepared films was investigated using X-ray diffraction method. The films prepared in the range of compositions from Al_80W_20 to Al_67W_33 were completely amorphous.