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Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

View Article: PubMed Central - PubMed

ABSTRACT

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm−1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

No MeSH data available.


(a) HeIM images of different regions along the joint’s transverse cross-section: (1) nanoparticles on CNTs (region 1), (2) metal-coated CNT (top of region 2), (3) partially encased bundles (bottom of region 2), (4) metal matrix composite (region 3) (b).
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Figure 4: (a) HeIM images of different regions along the joint’s transverse cross-section: (1) nanoparticles on CNTs (region 1), (2) metal-coated CNT (top of region 2), (3) partially encased bundles (bottom of region 2), (4) metal matrix composite (region 3) (b).

Mentions: High magnification HeIM images of the different regions along the joint’s transverse cross-section, obtained by mechanical cleaving, are also shown in figure 4(a). These images confirm that the different regions observed along the fillet are also distinguishable in the interior of the film. Nanoparticles are seen on the aligned CNTs in region 1 far from the joint line. Individual CNTs and small bundles thereof are coated with metal at the top of region 2. Partially encased bundles are identified in the lower part of region 2. The fracture here is due to shear forces during cleaving. The metal matrix composite containing flat hexagonal crystals is seen in region 3. The qualitative results of an EDX elemental mapping of a selected area between regions 1, 2 and 3 are shown in figure 4(b). While Cu and Ti are clearly enriched in the lower part (i.e. in the composite region), a slight Ti enrichment can be also seen in the CNT region in the upper part. This indicates the strong tendency of Ti to interact with the CNTs.


Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
(a) HeIM images of different regions along the joint’s transverse cross-section: (1) nanoparticles on CNTs (region 1), (2) metal-coated CNT (top of region 2), (3) partially encased bundles (bottom of region 2), (4) metal matrix composite (region 3) (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036490&req=5

Figure 4: (a) HeIM images of different regions along the joint’s transverse cross-section: (1) nanoparticles on CNTs (region 1), (2) metal-coated CNT (top of region 2), (3) partially encased bundles (bottom of region 2), (4) metal matrix composite (region 3) (b).
Mentions: High magnification HeIM images of the different regions along the joint’s transverse cross-section, obtained by mechanical cleaving, are also shown in figure 4(a). These images confirm that the different regions observed along the fillet are also distinguishable in the interior of the film. Nanoparticles are seen on the aligned CNTs in region 1 far from the joint line. Individual CNTs and small bundles thereof are coated with metal at the top of region 2. Partially encased bundles are identified in the lower part of region 2. The fracture here is due to shear forces during cleaving. The metal matrix composite containing flat hexagonal crystals is seen in region 3. The qualitative results of an EDX elemental mapping of a selected area between regions 1, 2 and 3 are shown in figure 4(b). While Cu and Ti are clearly enriched in the lower part (i.e. in the composite region), a slight Ti enrichment can be also seen in the CNT region in the upper part. This indicates the strong tendency of Ti to interact with the CNTs.

View Article: PubMed Central - PubMed

ABSTRACT

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 °C with a Ag–Cu–Ti alloy and at 880 °C with a Cu–Sn–Ti–Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Ω. The improved interfacial transport properties in the brazed films lead to superior electron field-emission properties when compared to the as-grown films. An emission current of 150 μA was drawn from the brazed nanotubes at an applied electric field of 0.6 V μm−1. The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

No MeSH data available.