In-situ Quasi-Instantaneous e-beam Driven Catalyst-Free Formation Of Crystalline Aluminum Borate Nanowires

Abstract

The catalyst-assisted nucleation and growth mechanisms for many kinds of nanowires and nanotubes are pretty well understood. At times, though, 1D nanostructures form without a catalyst and the argued growth modes have inconsistencies. One such example is the catalyst-free growth of aluminium borate nanowires. Here we develop an in-situ catalyst-free room temperature growth route for aluminium nanowires using the electron beam in a transmission electron microscope. We provide strong experimental evidence that supports a formation process that can be viewed as a phase transition in which the generation of free-volume induced by the electron beam irradiation enhances the atomic mobility within the precursor material. The enhanced atomic mobility and specific features of the crystal structure of Al5BO9 drive the atomic rearrangement that results in the large scale formation of highly crystalline aluminium borate nanowires. The whole formation process can be completed within fractions of a second. Our developed growth mechanism might also be extended to describe the catalyst-free formation of other nanowires.

Electron-beam induced synthesis of nanostructures: a review

“…50,51 Gonzalez-Martinez et al performed a similar experiment to that of Sood et al but irradiating precursors that did not contained tunsgten. 119 In this case the precursors were composed by round amorphous micron-sized particles containing Al, B and O. The precursors quasi-instantaneously transformed into bundles of Al 5 BO 9 NWs sticking out from an amorphous scaffold remnant from the original precursors, a structure that resembles a sea urchin (see Fig.…”

Hybrid tungsten–carbon 2D nanostructures via in situ gasification of carbon substrates driven by ebeam irradiation of WO2.9 microparticles

“…The catalogue of nanostructures synthesized inside the TEM without the need of especially customized holders has expanded greatly [1] since the first reported production of Au nanoparticles over 23 years ago [2]. Up to date, nanostructures of all three dimensionalities have been produced inside the TEM, among which we have zero-dimensional (0D) of pure metals [2][3][4][5][6][7][8][9][10], metallic alloys [11,12] and metal oxides [13]; one-dimensional (1D) nanowires made of Ag [14,15], Cu [16,17], Te [18], Cu-Ag [19], Al 5 BO 9 [20], B/BO X [21], WO X [22][23][24] and SiO 2 [25] nanorods; and finally, two-dimensional (2D) Fe [26], ZnO [27], CuO [28] and Cr [29] membranes and free-standing graphene flakes have also been obtained [30]. Still, this catalogue pales in comparison to that of the nanostructures manufactured by more conventional techniques such as chemical vapor deposition (CVD) [31,32].…”

“…Except for the Fe, ZnO, CuO and Cr membranes [26][27][28][29] all the nanostructures listed above were produced following essentially the same protocol in the TEM. The method consists of making the microscope's e-beam converge gradually over a micron-sized precursor particle supported on the C substrate of the TEM grid (we have described this method in more detail elsewhere) [20,21,30]. What generally occurs is that the precursor particle begins to disintegrate after a certain current density threshold J T is reached by making the beam gradually converge upon it (this generic protocol can be labeled as 'convergent beam protocol' or CBP).…”

“…The first report of this phenomenon attributed it to charging [2]; however, later on the scientific community heavily favored beam-induced heating as a better explanation for it [3,6,8,9,11,12,17]. In recent times, mainly thanks to theoretical considerations, the charging-based hypothesis regained attention [7,20,21,30,[34][35][36][37][38]. Here we advocate for a charging-based mechanism, thus, we agree with regarding bea,-iduced fragemtnation as a form of beaminduced Coulomb explosion' as it has been suggested in previous works [7,8,37,38].…”

Considerable knock-on displacement of metal atoms under a low energy electron beam

“…In general, radiation damage of electron beam is undesirable, however, recent experiments have demonstrated that it can have beneficial effects 6 , 7 , 9 – 12 . Examples are precise cutting of single-walled carbon nanotubes using electron beam 13 , electron-beam-assisted coalescence or joining of single-walled carbon nanotubes 14 – 16 and metallic nanowires 17 , interesting phenomena due to electron beam irradiation such as phase transformation in graphite 18 , 19 , α-FeSi 2 20 , and Sn-based nanowires 21 , controlled growth-reversal of catalytic carbon nanotubes 22 , and extreme pressure inside carbon nanotubes 23 , 24 , electron-beam-induced formation of nanostructures like carbon onions 25 , double-walled nanotubes 26 , nanopores 27 , alumina nanocapsules 28 , silicon nanocrystals 29 , 30 , and crystalline aluminum borate nanowires 31 , restructuring of NaREF 4 nanocrystals under electron beam irradiation 32 , just to mention a few. In these examples, the applied electron energies are all equal to or greater than 200 keV and even up to MeV, which makes possible the atomic displacement.…”