Observation of nonstandard Fickian diffusion at the interface of isotopically pure amorphousB11on

Abstract

As part of a larger study to investigate atomic-diffusion behavior in both elemental boron and refractory transition-metal borides, neutron reflectometry was used to examine the temperature-induced self-diffusion of isotopically enriched thin films of amorphous 11 B on 10 B deposited by electron-beam evaporation. The reflectometry studies were performed and model boron density profiles for samples annealed at various times and temperatures of 360 and 400°C were fit to the reflectivity data. Although the 10 B/ 11 B interface did not move relative to the air/boron interface upon annealing, the expected standard Fickian diffusion for the annealed samples was not observed. A pinned Fickian diffusion model, which imposes the boundary conditions of a fixed composition of 10 B to 11 B at the interface, fit the reflectivity data accurately and consistently. A typical equilibrium diffusion constant was determined to be ϳ10 Ϫ17 cm 2 s Ϫ1 , measured at an annealing temperature of 360°C. The measured diffusion constants are inconsistent with the high melting temperature of elemental boron, but are consistent with measured boron diffusion constants in other amorphous thin films. The presence of clusters in the boron film is proposed to explain the observed results.

Effect of dopants on thermal stability and self-diffusion in iron-nitride thin films

“…Since scattering length density (SLD) of neutrons is [43], B self-diffusion in amorphous boron [44], and N self-diffusion in Si 3 N 4 [45], Si-C-N [46], and iron monontrides (Nat. % ∼ 50) [47] compounds.…”

Molecular view of the isothermal transformation of a stable glass to a liquid

“…12 Figure 2 shows the specular NR of a multilayer TNB sample vapor deposited onto a silicon substrate held at 242 K. One can think of the multilayer protio/deuterio structure as a diffraction grating for neutrons. [13][14][15] Because the interfaces are sharp, many Bragg peaks are evident, extending out to the 17th harmonic. Only odd harmonics are prominent as expected for a sample in which every protio and deuterio layer has the same thickness.…”

Neutron reflectivity measurements of the translational motion of tris(naphthylbenzene) at the glass transition temperature

“…Practically, such samples give rise to strong diffraction peaks and the decay of these peaks with time provides direct information about translational motion at a well-defined wavelength. This type of experiment has previously been utilized to study translational motion in polymers, 33 metallic glass formers, 34,35 and other systems 34 ͑in these latter cases, isotopes such as 57 Fe and 10 B were used͒.…”