High Density of Quantum-Sized Silicon Nanowires with Different Polytypes Grown with Bimetallic Catalysts

Abstract

When Si nanowires (NWs) have diameters below about 10 nm, their band gap increases as their diameter decreases; moreover, it can be direct if the material adopts the metastable diamond hexagonal structure. To prepare such wires, we have developed an original variant of the vapor−liquid−solid process based on the use of a bimetallic Cu−Sn catalyst in a plasmaenhanced chemical vapor deposition reactor, which allows us to prevent droplets from coalescing and favors the growth of a high density of NWs with a narrow diameter distribution. Controlling the deposited thickness of the catalyst materials at the subnanometer level allows us to get dense arrays (up to 6 × 10 10 cm −2 ) of very-small-diameter NWs of 6 nm on average (standard deviation of 1.6 nm) with crystalline cores of about 4 nm. The transmission electron microscopy analysis shows that both 3C and 2H polytypes are present, with the 2H hexagonal diamond structure appearing in 5−13% of the analyzed NWs per sample.

Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn‐Cu Bimetallic Seeds

“…They have diameters ranging from 4 to 9 nm with an average diameter of 6.3 nm (measured by TEM based on 89 SiNWs); the average diameter of their crystalline core is around 4 nm. [11] They have thus the size where the bandgap depends on wire diameter. TEM observation shows that these thin SiNWs systematically have a special structure with an amorphous NW separating the initial single-particle catalyst into several NPs.…”

“…This catalyst separation phenomenon along with the growth of the amorphous oxide has only been observed in the SiNWs synthesized with Sn-Cu-mixed catalysts, never in SiNWs synthesized with pure Sn or Au catalyst. [11] (Let us mention that SiNWs cannot be grown with pure Cu catalysts under the current PECVD conditions. [11] ) An example of a SiNW tip obtained with a pure Sn catalyst is shown in Figure S1, Supporting Information.…”

“…[11] (Let us mention that SiNWs cannot be grown with pure Cu catalysts under the current PECVD conditions. [11] ) An example of a SiNW tip obtained with a pure Sn catalyst is shown in Figure S1, Supporting Information.…”

“…We have achieved to grow very dense quantum wire arrays with average diameter around 6 nm using a plasma-enhanced chemical vapor deposition (PECVD) method with a novel Sn-Cu-mixed catalyst and a liquid-assisted vapor-solid-solid (LAVSS) mechanism. [11] However, these NWs systematically wear an amorphous cap, which can become an actual NW on top of the Si NWs. We show in this article that this amorphous cap or NW is the result of the oxidation of the SiNW, catalyzed by Cu in air, as indeed, Cu is a catalyst of Si oxidation.…”

Analytical description of nanowires III: regular cross sections for wurtzite structures

“…with sufficient spatial resolution) to match them with analytic number series. Several literature sources exist for irregularshaped w-NWire cross sections, consisting of CdS, CdSe (Duan & Lieber, 2000), GaN (Kuykendall et al, 2004), GaAs (Zardo et al, 2009;Harmand et al, 2018), core-shell GaAs-SiGe (de Matteis et al, 2020), InAs (Caroff et al, 2009), InP (Gao et al, 2014) and Si (Wang et al, 2021). Second, we received several requests to explain the underlying crystallographic geometry and number theory used to arrive at the equations we pub-lished previously.…”