Naslov
Epitaxial Growth of Aluminum-Tungsten Thin Films on Sapphire Substrates

Autori
Radić, Nikola ; Car, Tihomir ; Tonejc, Antun ; Tonejc, Anđelka ; Ivkov, Jovica

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Abstract Book / Ono, M. - Birmingham : International Convention Centre, 1998

Skup
14th Intrenational Vacuum Congress

Mjesto i datum
Birmingham, Ujedinjeno Kraljevstvo, 1998

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Al-W thin films; Epitaxial Growth

Sažetak
Binary Al-W amorphous alloys deposited onto alumina ceramic substrates exhibit high crystallization temperatures (520°C-620°C) within a whole compositional range of amorphicity (Al82W18-Al62W38). They are rather stable against prolonged annealing at temperatures slightly below crystallization temperature. However, amorphous films deposited at room temperature exhibit a strong/pronounced structural relaxation at temperatures between about 100°C and 500°C. In this work we report the effects of substrate temperature upon the structure of the as-deposited Al-W films. The films with nominal composition Al75W25 were prepared by a codeposition technique in a two-magnetron-source apparatus. The working gas was argon at 0,7 Pa in a continuos flow mode. The area-averaged current densities were 4 mA/cm2 for tungsten and 12 mA/cm2 for aluminum target. The film deposition rate onto surface at room temperature was about 0,4 nm/s, whereas/while its final thickness depended upon deposition time. A circular (1 cm dia) sapphire substrates rotated during the deposition to ensure a lateral compositional homogeneity of the film. During deposition the substrates were held at four, well below crystallization, temperatures: LN2, 100°C, 200° and 400°C, respectively. The structure of the films was examined by the X-ray diffraction method. The films deposited at LN2, 100°C and 200°C were completely amorphous. However, the films deposited onto substrate at 400°C to about 3 mm final thickness exhibit the XRD pattern indicating/corresponding to a two-phase structure: upon a broad amorphous-phase pattern a strong and simple three-line pattern (up to the 2q = 80°) is superimposed. The diffraction angles correspond to the first, second and third diffraction from a strongly/perfectly layered structure, with interplanar distance of about 0,383 nm. The films of/with 1,5 and 0,7 nm thickness, respectively, retain a two-phase XRD pattern. It seems that a two-layered structure is formed, a lower (close-to-the-substrate) layer being epitaxially grown and strongly oriented, while/whereas the upper amorphous layer resulted from weakening of the sapphire substrate influence at some distance from the substrate surface. Not aluminum, a- or b-tungsten, nor three established intermetallic compouns (Al12W, Al5W, Al4W) match the observed interplanar distance of 0,383 nm well. That left one or the other of the three tentative intermetallic phases (Al3W, Al7W3 or Al2W) which are considered stable at high temperature only, as a candidate for epitaxial layer material. The examination of the Al75W25 films by the SEM and HREM methods, which might resolve spatial distribution of the observed two phases , are in progress. The diffraction pattern imply an existanceof layered structure, with interplanar distance of about 0,383 nm. The films of/with 1,5 and 0,7 nm thickness, respectively, all show the two-phase XRD pattern. It seems that a two-layered structure is formed, a lower (close-to-the-substrate) layer being epitaxially grown and strongly oriented, while/whereas the upper amorphous layer resulted from weakening of the sapphire substrate influence at some distance from the substrate surface. At the present we cold not match the unknown pattern with any established intermetallic compouns (Al12W, Al5W, Al4W) or aluminum, a- or b-tungsten. We The examination of the Al75W25 films by the SEM and HREM methods, which might resolve spatial distribution of the observed two phases , are in progress.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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