Interface structure in nanoscale multilayers near continuous-to-discontinuous regime

Abstract

Interfacial atomic diffusion, reaction, and formation of microstructure in nanoscale level are investigated in W/B4C multilayer (ML) system as functions of thickness in ultrathin limit. Hard x-ray reflectivity (XRR) and x-ray diffuse scattering in conjunction with x-ray absorption near edge spectroscopy (XANES) in soft x-ray and hard x-ray regimes and depth profiling x-ray photoelectron spectroscopy (XPS) have been used to precisely evaluate detailed interfacial structure by systematically varying the individual layer thickness from continuous-to-discontinuous regime. It is observed that the interfacial morphology undergoes an unexpected significant modification as the layer thickness varies from continuous-to-discontinuous regime. The interfacial atomic diffusion increases, the physical density of W layer decreases and that of B4C layer increases, and further more interestingly the in-plane correlation length decreases substantially as the layer thickness varies from continuous-to-discontinuous regime. This is corroborated using combined XRR and x-ray diffused scattering analysis. XANES and XPS results show formation of more and more tungsten compounds at the interfaces as the layer thickness decreases below the percolation threshold due to increase in the contact area between the elements. The formation of compound enhances to minimize certain degree of disorder at the interfaces in the discontinuous region that enables to maintain the periodic structure in ML. The degree of interfacial atomic diffusion, interlayer interaction, and microstructure is correlated as a function of layer thickness during early stage of film growth.

Sub-nanograin metal based high efficiency multilayer reflective optics for high energies

“…It is noted that in the discontinuous region of both the earlier two cases (ref. 28 and 29 ), as the thickness was decreased, minimization of a certain degree of interface width was observed, which is unlike the general increasing trend, due to minimization of surface free energy as a result of compound formation. Similarly, Vainer et al 30 observed an increase in roughness as period thickness decreases below the layer continuous limit of the ultra-short period ( d = 0.8–1.5 nm) W/B 4 C ML.…”

“… 28 Whereas, in the second case, the individual thickness was varied (∼2.45–0.87 nm) keeping the thickness of the other layer fixed above the continuous limit. 29 In the first case, as the period decreases from 4.94 nm to 1.34 nm, the density contrast ( ρ W − ρ B 4 C ) decreases from 14.2 g cm −3 to 11.1 g cm −3 . In addition, although the interface width of W layers decreases from 0.63 nm to 0.36 nm, the physical roughness of W layers increases from 0.05 nm to 0.13 nm.…”

Microstructure, Surface Plasmon, Magneto-Optic Surface Plasmon, and Sensitivity Properties of Magneto-Plasmonic Co/Au Multilayers

“…where v is the momentum transfer factor, and it is given as v = 4sin λ , and Ru is the reflectivity of an identical smooth surface, and  is the root mean square, rms, the roughness of the surface. The rms roughness value is quantitatively equal to interface width  for interfaces and it, in turn, equals the sum of the interfacial roughness and interfacial diffusion [39].…”