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

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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.


Schematic, different stages of the fabrication of active brazed CNT–metal joints.
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Figure 1: Schematic, different stages of the fabrication of active brazed CNT–metal joints.

Mentions: The as-grown nanotube films were brazed facedown to 4 × 4 × 0.6 mm3 Ni-metalized grade 2 titanium (Ti/Ni 2 μm) and to 4 × 4 × 0.95 mm3 grade 2 titanium substrates in a vacuum furnace (Cambridge Vacuum Engineering) at 10−6 mbar. The heating rate was 10 °C min−1, the dwell time was 5 min and the dwell temperature was 820 °C when using 100 μm thick foils having a composition of Ag 63.25–Cu 35–Ti 1.75 wt% (Wesgo Metals, Hayward USA) and was 880 °C with 60 μm thick foils having a composition of Cu 73.9–Sn 14.4–Ti 10.2–Zr 1.5 wt% (Sulzer Metco Germany). The solidus and liquidus temperatures for the silver alloy are 780 and 815 °C, respectively. The copper alloy has a solidus temperature of 868 °C and a liquidus temperature of 925 °C [17]. The brazing foils were made by mixing a metal alloy powder (325 mesh: particle size <44 μm) with an organic binder. The resulting paste was manually printed on a flat surface, dried in air and compressed into a foil to the desired thickness. The braze foil, substrate and inverted CNT film are assembled in a jig and held in place with an adjustable screw during brazing. Once the brazing step was completed, the Si substrate was removed with tweezers. For inspection, the joints were manually cleaved transversely and longitudinally with a steel blade. The different stages of the process are sketched in figure 1.


Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
Schematic, different stages of the fabrication of active brazed CNT–metal joints.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Schematic, different stages of the fabrication of active brazed CNT–metal joints.
Mentions: The as-grown nanotube films were brazed facedown to 4 × 4 × 0.6 mm3 Ni-metalized grade 2 titanium (Ti/Ni 2 μm) and to 4 × 4 × 0.95 mm3 grade 2 titanium substrates in a vacuum furnace (Cambridge Vacuum Engineering) at 10−6 mbar. The heating rate was 10 °C min−1, the dwell time was 5 min and the dwell temperature was 820 °C when using 100 μm thick foils having a composition of Ag 63.25–Cu 35–Ti 1.75 wt% (Wesgo Metals, Hayward USA) and was 880 °C with 60 μm thick foils having a composition of Cu 73.9–Sn 14.4–Ti 10.2–Zr 1.5 wt% (Sulzer Metco Germany). The solidus and liquidus temperatures for the silver alloy are 780 and 815 °C, respectively. The copper alloy has a solidus temperature of 868 °C and a liquidus temperature of 925 °C [17]. The brazing foils were made by mixing a metal alloy powder (325 mesh: particle size <44 μm) with an organic binder. The resulting paste was manually printed on a flat surface, dried in air and compressed into a foil to the desired thickness. The braze foil, substrate and inverted CNT film are assembled in a jig and held in place with an adjustable screw during brazing. Once the brazing step was completed, the Si substrate was removed with tweezers. For inspection, the joints were manually cleaved transversely and longitudinally with a steel blade. The different stages of the process are sketched in figure 1.

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 &deg;C with a Ag&ndash;Cu&ndash;Ti alloy and at 880 &deg;C with a Cu&ndash;Sn&ndash;Ti&ndash;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 &Omega;. 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 &mu;A was drawn from the brazed nanotubes at an applied electric field of 0.6 V &mu;m&minus;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.