Materials Science and Engineering, 99 (1988) 201 205 201 Superconductivity in Crystalline and Amorphous Nb-Zr Thin Films* A. CAVALLER1, M. DAPOR, F. GIACOMOZZI and L. GUZMAN Materials Science Division, Istituto per la Ricerca Scientifica e Tecnologica, 38050 Povo (Trento) (Italy) P. M. OSSI lstituto di Ingegneria Nucleate, CESNEF, Politecnico di Milano, 20133 Milan (Italy) M. SCOTON1 Dipartimento di Fisica, Universita' di Trento, Trento (Italy) Abstract Alloy as well as multilayer Nb-Zr thin films have been prepared by r.f. magnetron sputtering at different substrate temperatures. The overall sample thickness was about 150 nm and the composition was chosen to be near NbsoZr2o. Some multilayers were ion implanted at room temperature, using either N + or Kr + ions. The structures, microstructures and compositions of the films were studied by the following techniques: X-ray diffraction, scanning electron microscopy, Auger elec- tron microscopy and secondary ion mass spectrometry. Alloy films deposited at room temperature always dis- play a crystalline structure, while those prepared at liquid nitrogen temperature can be crystalline or amor- phous depending on the deposition parameters. Also Kr +-ion-mixed multilavers are partially amorphous while N+-implanted samples are crystalline. Both for crystalline and.for amorphous alloys, Tc values were resistively determined and compared with those re- ported for bulk alloys of similar stoiehiometry. The present work seems to be the first experimental investigation on the physical properties of thin films of Nb Zr which is being considered also for technological applications. 1. Introduction Much work on metal glasses have been directed towards the identification of good glass-forming sys- tems. Several preparation techniques are used, includ- ing vacuum techniques such as ion mixing and sputter deposition. In the first case, the penetration of en- ergetic ions through multilayer thin films can lead to the formation of a wide variety of structures (equi- librium or metastable; amorphous or crystalline) *Paper presented at the Sixth International Conference on Rapidly Quenched Metals, Montr6al, August 3 7, 1987. depending on the elements deposited and the overall composition of the layers. In contrast, sputter deposi- tion techniques can be well adapted to the preparation of thin films of any metal or alloy with a predeter- mined composition. Nevertheless the attainment of an amorphous film is influenced by several parameters pertaining to the vacuum process and the thermody- namics of the system. Niobium and zirconium form a continuous series of disordered solid solutions with a composition-de- pendent superconducting transition temperature Tc which may be as high as 10.7 K for NbTsZr25 [1]. Moreover, both the presence of a miscibility gap in the alloy phase diagram [2] and the preferential diffu- sivity of zirconium in niobium [3] are factors indicat- ing that the system may be a good candidate for the attainment of glassy phases. In this work, we report on the structure of super- conducting properties of NI~Zr thin films prepared either by sputter codeposition or by ion beam mixing. 2. Experimental procedures All the samples used in this investigation are shown schematically in Fig. 1. Nb-Zr alloy films 150 nm thick were deposited on glass and single-crystal Si(11 I) substrates by using r.f. co-sputtering from a niobium target partially cov- ered with zirconium, in order to obtain an NbsoZr2o composition. The base pressure was typically lx 10 Spa and the argon working pressure was 0.5 Pa (in some cases, nitrogen at 10 -2 Pa was also supplied). With a power of 150 W the deposition rate was 13 nm/min- ~. The sample holder was earthed and could be cooled with liquid nitrogen. Nb/Zr multilay- ers on the same substrates were also obtained by r.f. sputtering at the same power and working pressure. For niobium the deposition rate was 12.5 nm min 1 while for zirconium it was 17.6 nm min-~. In order to 0025-5416/88/$3.50 © Elsevier Sequoia/Printed in The Netherlands