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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.


(a) SEM image of a multiwalled carbon nanotube film on silicon prior to brazing. (b) High magnification HeIM image of the CNTs. Optical microscope image of CNT films brazed to (c) Ti and (d) to Ni-metalized Ti (Ti/Ni) at 880 °C with the Cu–Sn–Ti–Zr filler alloy. (e) Raman spectra of the surface of the as-grown and brazed CNT films indicating a slight increase in graphitization after brazing.
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Figure 2: (a) SEM image of a multiwalled carbon nanotube film on silicon prior to brazing. (b) High magnification HeIM image of the CNTs. Optical microscope image of CNT films brazed to (c) Ti and (d) to Ni-metalized Ti (Ti/Ni) at 880 °C with the Cu–Sn–Ti–Zr filler alloy. (e) Raman spectra of the surface of the as-grown and brazed CNT films indicating a slight increase in graphitization after brazing.

Mentions: A typical CNT film with a density of 1010–1011 CNTs cm−2 grown on silicon is shown in figure 2(a). The vermicular nanotube diameters range from 2 to 20 nm as seen by HeIM in figure 2(b). Two representative CNT films brazed to Ti and Ti/Ni substrates with the Cu–Sn–Ti–Zr alloy at 880 °C are shown in figures 2(c) and 1(d) respectively. In both cases, the braze alloy has formed a fillet along the film’s edge which is indicative of a chemical reaction leading to wetting.


Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
(a) SEM image of a multiwalled carbon nanotube film on silicon prior to brazing. (b) High magnification HeIM image of the CNTs. Optical microscope image of CNT films brazed to (c) Ti and (d) to Ni-metalized Ti (Ti/Ni) at 880 °C with the Cu–Sn–Ti–Zr filler alloy. (e) Raman spectra of the surface of the as-grown and brazed CNT films indicating a slight increase in graphitization after brazing.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: (a) SEM image of a multiwalled carbon nanotube film on silicon prior to brazing. (b) High magnification HeIM image of the CNTs. Optical microscope image of CNT films brazed to (c) Ti and (d) to Ni-metalized Ti (Ti/Ni) at 880 °C with the Cu–Sn–Ti–Zr filler alloy. (e) Raman spectra of the surface of the as-grown and brazed CNT films indicating a slight increase in graphitization after brazing.
Mentions: A typical CNT film with a density of 1010–1011 CNTs cm−2 grown on silicon is shown in figure 2(a). The vermicular nanotube diameters range from 2 to 20 nm as seen by HeIM in figure 2(b). Two representative CNT films brazed to Ti and Ti/Ni substrates with the Cu–Sn–Ti–Zr alloy at 880 °C are shown in figures 2(c) and 1(d) respectively. In both cases, the braze alloy has formed a fillet along the film’s edge which is indicative of a chemical reaction leading to wetting.

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.