were obtained by keeping the power for the Nb deposition constant at 0.85 W/cm 2 (deposition rate of 1.7 nm/min) and changing the power for the Si deposition from 2 W/cm 2 (2.7 nm/min) to 5.1 W/cm 2 (6.7 nm/min). Per cycle about one monolayer NbSi is deposited. Series A contains 70% Nb and 30 % Si, and series B contains 42% Nb and 58% Si. The compositions are determined with microprobe analysis on thick films. The deposition time was varied to obtain films of different thicknesses.
X-ray diffraction shows no indications for the formation of multi-layers. Further, the films are analyzed with high resolution TEM. In a fJ.lm of 3 nm thickness no ordering at all was found, in a thicker fllm of 10 nm only some weak short range order on a scale less than I nm was observed. From this, we conclude that our fllms are amorphous. A similar result has been reported by Johnson et al.,4 who fmd that NbSi fllms which consist of 10% or more Si, are amorphous.
In Fig. I, the room temperature sheet resistance Rsqr,295, measured shortly after removal from the vacuum chamber, is plotted logarithmically as a function of the nominal thickness d for series A. For the thickest films the sheet resistance is proportional to lid. In this region the resistivity p for these fIlms is almost constant and equals 2.2 /lOrn. We estimate the pI product, with I the mean free path, to be 10-15 nm 2 . With this 10 1
We h~ve fabric~ted co-sputtered niobium-silicon mms with thicknesses ranging from I nm to 200 nm. Analysis by X-ray diffraction and high resolunon TEM shows that the films are amorphous. Due to their stability, the films are suited for the fabrication of reliable devices. The resistive transitions of the mms have been studied. The onset for superconductivity takes place at sheet resistances lower than the 'universal' value of h/4e 2 .