Millimeters long super flexible Mn5Si3@SiO2 electrical nanocables applicable in harsh environments

Providing high performance electrical nano-interconnects for micro-nano electronics that are robust in harsh environments is highly demanded. Today, electrical nano-interconnects based on metallic nanowires, e.g. Ag and Cu, are limited by their positive physicochemical reactivity and ductility under large strain (i.e. irreversible dislocations and local necking-down elongation) at high temperatures or in strong oxidizing and acidic environments. Herein, to overcome these limitations, high-quality millimetre-sized soft manganese-based silicide (Mn5Si3@SiO2) nanowire nanocables are designed via a glassy Si–Mn–O matrix assisted growth. The proposed nanocables exhibit good electrical performance (resistivity of 1.28 to 3.84×10-6 Ωm and maximum current density 1.22 to 3.54×107 A cm−2) at temperatures higher than 317°C in air atmosphere, strongly acidic (HCl, PH=1.0) and oxidizing (H2O2, 10%) ambient, and under complex electric field. The proposed Mn5Si3@SiO2 nanocables, which withstand a strain of 16.7% free of failure, could be exploited for diverse applications in flexible electronics and complex wiring configurations.

(e-f) The nanocable was cut off and moved the maximally strained segments to carved region of the Si 3 N 4 film.

Supplementary Note 1 Growth mechanism of Mn 5 Si 3 @SiO 2 nanocables
The growth of high quality Mn 5 Si 3 nanocables was achieved via a two-stage experiment rationally designed (Procedure A and B). Procedure A was applied to create suitable growth atmosphere condition (glassy Mn-Si-O composite rich environment) and procedure B resulted in nanowires, as shown in Supplementary   Figure 1.
In detail, Mn and SiO powder with molar ratio of 6:1 was grinded in a mortar, until they were mixed homogeneously, which was applied as the sole reacting precursor  Figure 4(a-d)). Benefiting from the high quality of the nanowires, they could be uprooted mechanically from the substrate. Supplementary Figure 5 shows the residue fracture surface as marked using brown dash circles.
As soon as the nanowire grew out from the vapor-liquid interface, they would be wrapped by SiO 2 , which originates from the reaction of SiO→Si+SiO 2 and Si+MnO→Mn+SiO 2 . Noticeably, although the dimensions of the nuclei and resulted Mn-Si crystals display a wide range, only a small part of them could evolve into ultra-long nanowires, while others failed to grow in a considerable aspect-ratio.
Smooth and continuous supplement of source in the molten matrix were important.

Supplementary Note 2 The structural characterization of Mn 5 Si 3 @SiO 2 nanocables
The SAED pattern and HRTEM corresponding to four different regions in a long nanocable was acquired, as marked in Supplementary Figure 8. The upper panel of Supplementary Figure 9(a) is the TEM image of region 1# in low magjification, and below are corresponding to SAED pattern and HETEM image. The nanocable grows along c-axis as marked. For the other three regions, the similar operation was done, as shown in Supplementary Figure 9(b-d). It is obvious that the four sets of data point to the same lattice, which is to say the nanocable is in single crystal. All the nanocables exhibit the same feature.
In Supplementary Figure 10, it is shown that the nanocable display a very good diameter distribution, including the electrical core and the insulate shell.

Mn 5 Si 3 @SiO 2 nanocable
We employed combined bending experiments upon single nanocables and then examined their integrality using TEM. Supplementary Figure 11(a) shows the two nanocables chosen to be characterized (NO. 1 and NO. 2). Supplementary Figure   11(b) correspond to the NO. 1 nanocable in bended state with strain of 11.52% (circle diameter is 1.85um and diameter of the nanocable is 213nm). the image of it after the tungsten probe retracted was shown in Supplementary Figure 11(c). Afterwards, it was characterized by TEM. As in Supplementary Figure 11(d-i), the all parts of the nanocable segments that experienced maximum bended strain display excellent integrity, with no fracture behavior detected. The operation upon the other nanocable was recorded in Supplementary Figure 12(a-c). Supplementary Figure 12(d) shows its recovered configuration. Considering that the maximally bended region locates on the Si 3 N 4 film, we cut it off mechanically and then moved the targeted segment to the carved position using a tungsten probe (Supplementary Figure   12(e-f)). Supplementary Figure 12(g-i) correspond to the TEM examination of the bended region, which indicates that the nanocable can withstand the bended strain of 13.02% without fracture.

Mn 5 Si 3 @SiO 2 nanocable largely bended
As in Supplementary Figure 14 For all the configurations, the I-V characteristics were acquired, as shown in Supplementary Figure 14(h). It is obvious that the electrical property displays no degeneration during the repeated bended process. Noticeably, in (d), the end close to the tungsten tip was bended into a circle, whose radius decreased as the nanocable was stretched forward, until the circle almost wrapped the tip, as in (f-g). These operations indicate that the nanocable exhibits robust electrical property even under large bending deformation, without structural fracture and distinguished electrical performance degeneration.

Supplementary Note 5 The electrical performance and structural change of Mn 5 Si 3 @SiO 2 nanocables at elevated temperatures
In order to investigate the temperature dependent resistance of a single nanocable, a heating panel was used to raise the temperature. A thermal imager was applied to check the precise device temperature,as shown in Supplementary Figure 16. The emissivity of the substrate was firstly calibrated using Al 2 O 3 sheet and plastic as references, whose value are ~0.92. As in Supplementary Figure 16(b), they display almost the same surface temperature distribution, implying the same emissivity value.
Then, the exact temperatures of the substrate were determined as the hot plate heated.
At the meanwhile, resistances were recorded.
Supplementary Figure 17 shows the change of Au electrodes after the heating process. It is obvious that some degree of melting behavior occurred. Therefore, a higher temperature is not applicable to this experiment, although the nanocable can withstand a much higher temperature.
Supplementary Figure 18(a-b) shows the SEM images of the nanocables after annealing procedure at 500℃ for 2 hours. It is obvious that no visible change found.
In Supplementary Figure 18(e-f), SEM images of the nanocables after annealing process at 600℃ for 2 hours are shown. Noticeably, fatal change began to occur, i.e.
the Mn 5 Si 3 core degenerated followed by Mn-O composite separate out. In