Electron beam-assisted healing of nanopores in magnesium alloys

Abstract

Nanopore-based sensing has emerged as a promising candidate for affordable and powerful DNA sequencing technologies. Herein, we demonstrate that nanopores can be successfully fabricated in Mg alloys via focused electron beam (e-beam) technology. Employing in situ high-resolution transmission electron microscopy techniques, we obtained unambiguous evidence that layer-by-layer growth of atomic planes at the nanopore periphery occurs when the e-beam is spread out, leading to the shrinkage and eventual disappearance of nanopores. The proposed healing process was attributed to the e-beam-induced anisotropic diffusion of Mg atoms in the vicinity of nanopore edges. A plausible diffusion mechanism that describes the observed phenomena is discussed. Our results constitute the first experimental investigation of nanopores in Mg alloys. Direct evidence of the healing process has advanced our fundamental understanding of surface science, which is of great practical importance for many technological applications, including thin film deposition and surface nanopatterning.

Faceting oscillations in nano-ferroelectrics

“…We have no independent theoretical estimate of this time for our domain walls, but this comparison shows that it is similar to that in liquid crystals, which is plausible in view of the initial domain-wall topology comparison with nematics of Srolovitz and Scott. We know in the present work that the driving force for faceting is not thermal: Heating is only about 1 K. 23 The actual driving force is charging (Ahluwalia and Ng), and its effect upon surface tension. The surface tension in ferroelectric nanodomains has been analyzed by Lukyanchuk et al 24 and shown very recently by Scott 25 to fit quantitatively hoop stress (neglected in all previous models, such as that of Arlt 26 ).…”

Non-classical Crystallization

“…Irradiation Zheng et al (2013) fabricated nanopores in a Mg substrate using a focused e-beam inside the TEM and subsequently, observed that the nanopores were shrinking and eventually disappeared by defocused e-beam irradiation with the intensity of 10 1 -10 2 A cm −2 . Figure 1.8a-c schematically illustrates the healing of a nanopore under defocused electron beam irradiation.…”

“…It is believed that if electrically floating and grounded Mg substrates are compared, the pore elimination rate of the former would be much faster than that of the latter. (Zheng et al 2013) …”

Fabrication of faceted nanopores in magnesium

“…The nanopore size ranged from 3 nm to 8 nm. Details of nanopores fabricated along this direction can be found in our previous report, 23 which was mainly focused on the e-beam assisted shrinkage and final disappearance of nanopores along the 11 20 ½ zone axis, resulting from the anisotropic diffusion of Mg atoms at the vicinity of nanopore edges.…”

“…S2] exhibits the detailed real-time feedback of dynamics of faceted nanopore morphology, which is in accordance with the previous report about healing of nanopores in magnesium alloy. 23 It should be noted that the nanopore would retain its shape without the e-beam irradiation. Thus, it is suggested that such a convinient method can be applied to effectively fabricate the faceted nanopores and precisely tune their sizes.…”