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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.

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(a) Side view SEM image of the Cu–Sn–Ti–Zr fillet with labeled regions. (b) SEM image (55° tilt) of the top of region 2 after the removal of the CNT layer in region 1. (c) SEM image (55° tilt) of the bundles in region 2. (d) Side view HeIM image of the top of region 2 showing individual CNTs coated with metal. (e) Top view HeIM image of the fractured metal matrix composite bundles. (f) High magnification HeIM image of a composite bundle’s fracture surface.
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Figure 3: (a) Side view SEM image of the Cu–Sn–Ti–Zr fillet with labeled regions. (b) SEM image (55° tilt) of the top of region 2 after the removal of the CNT layer in region 1. (c) SEM image (55° tilt) of the bundles in region 2. (d) Side view HeIM image of the top of region 2 showing individual CNTs coated with metal. (e) Top view HeIM image of the fractured metal matrix composite bundles. (f) High magnification HeIM image of a composite bundle’s fracture surface.

Mentions: The side view SEM image of the Cu–Sn–Ti–Zr fillet, after Si lift-off, reveals three distinct regions as shown in figure 3(a). Region 1 at the top of the film consists of CNTs having retained more or less their vertical alignment after brazing. Region 2 contains metal-coated CNT bundles while the region closest to the brazing foil is characterized by larger bundles completely encased in metal; hereafter referred to as the metal matrix CNT composite region. The partially melted brazed foil is seen below this region and above the substrate.


Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance
(a) Side view SEM image of the Cu–Sn–Ti–Zr fillet with labeled regions. (b) SEM image (55° tilt) of the top of region 2 after the removal of the CNT layer in region 1. (c) SEM image (55° tilt) of the bundles in region 2. (d) Side view HeIM image of the top of region 2 showing individual CNTs coated with metal. (e) Top view HeIM image of the fractured metal matrix composite bundles. (f) High magnification HeIM image of a composite bundle’s fracture surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: (a) Side view SEM image of the Cu–Sn–Ti–Zr fillet with labeled regions. (b) SEM image (55° tilt) of the top of region 2 after the removal of the CNT layer in region 1. (c) SEM image (55° tilt) of the bundles in region 2. (d) Side view HeIM image of the top of region 2 showing individual CNTs coated with metal. (e) Top view HeIM image of the fractured metal matrix composite bundles. (f) High magnification HeIM image of a composite bundle’s fracture surface.
Mentions: The side view SEM image of the Cu–Sn–Ti–Zr fillet, after Si lift-off, reveals three distinct regions as shown in figure 3(a). Region 1 at the top of the film consists of CNTs having retained more or less their vertical alignment after brazing. Region 2 contains metal-coated CNT bundles while the region closest to the brazing foil is characterized by larger bundles completely encased in metal; hereafter referred to as the metal matrix CNT composite region. The partially melted brazed foil is seen below this region and above the substrate.

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.


Related in: MedlinePlus