To increase the x-ray optical contrast of Mo/Si multilayers, we study low energy hydrogen ion implantation of amorphous Si layers. Using elastic recoil detection and Rutherford backscattering spectrometry, we measure the result of hydrogen implantation on Si atomic density. We find a lowering of Si atomic density, and, thus, an enhancement of x-ray optical contrast, as a result of H implantation. We find that the Si atomic density saturates at a minimum of 64±5% of the crystalline value. We have also observed a minor smoothing effect of H+ ion bombardment. Combined with Kr+ ion bombardment, causing a very much larger smoothing of the Si surface, the atomic density is found to saturate at a minimum of 77±5% of the crystalline value.
We report a significant increase of the reflectivity of a soft x-ray Mo/Si multilayer mirror after low energy hydrogen ion beam bombardment of each of the Si layers after deposition. Cross section transmission electron microscopy pictures indicate no significant qualitative difference in interface roughness between the two samples. Elastic recoil detection and Rutherford backscattering spectrometry reveal a concentration of 22 at. % of H in the ion beam bombarded Si layers and a 12% reduction of the Si atomic density. Calculations using the measured atomic density and a very simple roughness model agree with the measured reflectivities. This is the first report of the modification of atomic density of Si in order to change the x-ray optical constants of the Si layer.
We present low energy ion beam mixing as a tool for the fabrication of composite layers with smooth interfaces. Using this tool we make a stack of alternating layers of Si and MoxSiy. We measure composition and interfacial roughness (σ) and find x/y≊5/3 and σ≊4 Å. The method can be applied to reduce absorption losses in x-ray multilayer mirrors for high-resolution dispersive purposes, and to increase thermal stability of multilayers. The thickness of the mixed layers is found to be equal to the ion range.
Energetic ions penetrating a solid lose their energy by nuclear interaction with one or more target atoms as well as by electronic excitation of the target atoms. The energy loss by nuclear interaction can be described in the classical ballistic way. Target atoms, put into motion by a primary collision, can exchange momentum with surrounding target atoms. This results in implantation of primary ions and damage in the target structure. A part of the momentum exchange is reversed in the direction of the target surface. This can give rise to the release of surface atoms, which is known as sputtering. Momentum transfer at an interface of two different materials will give rise to intermixing as demonstrated by van der Weg1). Fundamental research2) revealed that ion beam mixing could not only be explained by ballistic effects, but that also thermodynamic and chemical effects play a role. These effects are expected to take place in the end of a cascade formation, when the average energy is smaller than 1 eV. Further experiments have shown the importance of radiation enhanced diffusion, which shows up as a temperature dependent effect for a temperature higher than a critical value. The physics of this effect is based on vacancy enhanced diffusion.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.