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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) Four-probe current versus voltage curves of the (a) Si/CNT interface and (b) across the Cu–Sn–Ti–Zr and Ag–Cu–Ti joints.
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Figure 6: (a) Four-probe current versus voltage curves of the (a) Si/CNT interface and (b) across the Cu–Sn–Ti–Zr and Ag–Cu–Ti joints.

Mentions: It was demonstrated that both alloys can be used to join CNT films to titanium substrates. The joint properties were measured to confirm the applicability of such assemblies. The electrical resistances across the joints were determined by four-probe electrical measurements. Two gold contact pads were produced on the side of the CNT film (region 1) while the other two were on the substrate. Two probes were used to supply current while the other two measured the voltage drop across the joint. The results are shown in figure 6 with schematic representations of each measurement. The current versus voltage (I–V) curve across the Si/CNT interface for the as-grown film is provided in figure 6(a). The nonlinearity of the I–V curve in combination with the polarity of the applied bias is consistent with a Schottky diode-like junction consisting of a p-doped Si substrate and metallic CNTs. Fitting the linear portion of the curve yield a resistance of 40 Ω with a positive voltage and 125 Ω with a negative voltage. The I–V curves for the brazed films are shown in figure 6(b). The linearity indicates an ohmic contact with the substrate across both joints. The Ag–Cu–Ti joint shows slightly lower resistance of 0.35 Ω than the Cu–Sn–Ti–Zr joint with 0.86 Ω. The electrical conductivity for the Ag–Cu–Ti alloy is 23×106Ω−1 m−1 according to the supplier while conductivity values of ~7×106Ω−1 m−1 are typical for bronzes with 11 wt% Sn [29]. It is clear that the presence of the braze alloy significantly reduces the contact resistance between the nanotubes and the substrate when compared to when they are grown on Si.


Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
(a) Four-probe current versus voltage curves of the (a) Si/CNT interface and (b) across the Cu–Sn–Ti–Zr and Ag–Cu–Ti joints.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: (a) Four-probe current versus voltage curves of the (a) Si/CNT interface and (b) across the Cu–Sn–Ti–Zr and Ag–Cu–Ti joints.
Mentions: It was demonstrated that both alloys can be used to join CNT films to titanium substrates. The joint properties were measured to confirm the applicability of such assemblies. The electrical resistances across the joints were determined by four-probe electrical measurements. Two gold contact pads were produced on the side of the CNT film (region 1) while the other two were on the substrate. Two probes were used to supply current while the other two measured the voltage drop across the joint. The results are shown in figure 6 with schematic representations of each measurement. The current versus voltage (I–V) curve across the Si/CNT interface for the as-grown film is provided in figure 6(a). The nonlinearity of the I–V curve in combination with the polarity of the applied bias is consistent with a Schottky diode-like junction consisting of a p-doped Si substrate and metallic CNTs. Fitting the linear portion of the curve yield a resistance of 40 Ω with a positive voltage and 125 Ω with a negative voltage. The I–V curves for the brazed films are shown in figure 6(b). The linearity indicates an ohmic contact with the substrate across both joints. The Ag–Cu–Ti joint shows slightly lower resistance of 0.35 Ω than the Cu–Sn–Ti–Zr joint with 0.86 Ω. The electrical conductivity for the Ag–Cu–Ti alloy is 23×106Ω−1 m−1 according to the supplier while conductivity values of ~7×106Ω−1 m−1 are typical for bronzes with 11 wt% Sn [29]. It is clear that the presence of the braze alloy significantly reduces the contact resistance between the nanotubes and the substrate when compared to when they are grown on Si.

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.