A study of the reactivity of elemental Cr/Se/Te thin multilayers using X-ray reflectometry, in situ X-ray diffraction and X-ray absorption spectroscopy

The reactivity of [Cr/Se/Te] multilayers under annealing was investigated using X-ray reflectometry, in situ X-ray diffraction, X-ray absorption fine structure (XAFS) measurements and transmission electron microscopy. For all samples, interdiffusion was complete at temperatures between 100 and 300 °C, depending on the repeating tri-layer thickness. A crystalline phase nucleated approximately 20 °C above the temperature where interdiffusion was finished. The first crystalline phase in a binary Cr/Te sample was layered CrTe 3 nucleating at 230 °C. In ternary samples (Se:Te=0.6–1.2), the low-temperature nucleation of such a layered Cr Q 3 ( Q=Se, Te) phase is suppressed and instead the phase Cr 2 Q 3 nucleates first. Interestingly, this phase decomposes around 500 °C into layered Cr Q 3. In contrast, binary Cr/Se samples form stable amorphous alloys after interdiffusion and Cr 3Se 4 nucleates around 500 °C as the only crystalline phase. Evaluation of the XAFS data of annealed samples yield Se–Cr distances of 2.568(1) and 2.552(1) Å for Cr 2 Q 3 and Cr Q 3, respectively. In the latter sample, higher coordination shells around Se are seen accounting for the Se–Te contacts in the structure. The first step of the reaction of elemental Cr/Te/Se-multilayers is the interdiffusion of the elements as evidenced by the decay of the modulation peaks in the low-angle region of the X-ray diffraction patterns. The subsequent growth of Bragg peaks at higher scattering angles indicates crystallization of chromium chalcogenide Cr 2Te 3− x Se x .