Vertically aligned carbon nanotube (CNT) forests may be used as miniature springs, compliant thermal interfaces, and shock absorbers, and for these and other applications it is vital to understand how to engineer their mechanical properties. Herein is investigated how the diameter and packing density within CNT forests govern their deformation behavior, structural stiffness, and elastic energy absorption properties. The mechanical behavior of low‐density CNT forests grown by fixed catalyst CVD methods and high‐density CNT forests grown by a floating catalyst CVD method are studied by in situ SEM compression testing and tribometer measurements of force‐displacement relationships. Low‐density and small‐diameter CNT columns (fixed catalyst) exhibit large plastic deformation and can be pre‐deformed to act as springs within a specified elastic range, whereas high‐density and large‐diameter CNT columns (floating catalyst) exhibit significant elastic recovery after deformation. In this work the energy absorption capacity of CNT forests is tuned over three orders of magnitude and it is shown that CNT forest density can be tuned over a range of conventional foam materials, but corresponding stiffness is ∼10× higher. It is proposed that the elastic behavior of CNT forests is analogous to open‐cell foams and a simple model is presented. It is also shown that this model can be useful as a first‐order design tool to establish design guidelines for the mechanical properties of CNT forests and selection of the appropriate synthesis method.

We present a method for electromechanical characterization of carbon nanotube ͑CNT͒ films grown on silicon substrates as potential electrical contacts. The method includes measuring the sheet resistance of a tangled CNT film, measuring the contact resistance between two tangled CNT films, and investigating the dependence on applied force and postgrowth annealing. We also characterize Au-CNT film contact resistance by simultaneous measurement of applied force and resistance. We measure a contact resistance as low as 0.024 ⍀ /mm 2 between two films of tangled single-wall carbon nanotubes grown on a polished silicon substrate and observe an electromechanical behavior very similar to that predicted by classical contact theory.

Because of their outstanding electrical and mechanical properties, including high stiffness and mechanical resilience, ballistic electron transport at micrometer scales, and high current-carrying capacity, [1] carbon nanotubes (CNTs) could enable a new class of electrical elements ranging from transistors to interconnects. However, realizing the properties of individual CNTs in assemblies of CNTs has been a formidable challenge. Realistic applications of CNTs at the micrometer scale must employ thousands or millions of CNTs in a parallel fashion, yet, the understanding of the electromechanical behavior is still not mature enough. Most of the research so far has been either for sensing [2] or actuation applications, [3][4][5][6] whereas the potential benefits of CNTs in probing applications, where both mechanical integrity and electrical conduction is critical, have not been investigated as yet. Electromechanical probing applications continuously require smaller pitches, faster manufacturing, and lower electrical resistance. Achieving low-pitch structures without compromising elastic properties is a challenge with conventional techniques, such as in microelectromechanical systems (MEMS)-based structures. CNT-based structures present a scalable manufacturing approach, in which thousands of probes can be fabricated in very short production times and by means of a full wafer batch fabrication mode, reducing the fabrication steps currently necessary with conventional methods, all of which can have significant cost benefits.Growth of vertically aligned CNTs (VA-CNTs) by thermal chemical vapor deposition (CVD) [7,8] has created films and microstructures containing large numbers of CNTs aligned in parallel. Unfortunately, these high-temperature synthesis processes are typically optimized for growth from metal nanoclusters on silicon and ceramic substrates; whereas devices utilizing these CNTs will require a wider variety of substrates, including metals and plastics that cannot withstand the harsh processing conditions for high-yield CNT growth. To our knowledge, growth of VA-CNTs by thermal CVD with simultaneous ohmic contact on electrically conductive substrates has not yet been achieved and will remain a major challenge because of the apparent necessity of a buffer layer, such as Al 2 O 3 , SiO 2 , or MgO, for high-yield VA-CNT growth. Furthermore, weak mechanical adhesion to the substrate [7] and low bulk density [9] often prevent robust electrical and mechanical integration of CNTs under as-grown conditions. An emerging approach for device integration of VA-CNTs is to transfer the VA-CNTs from the growth substrate to a second "device" substrate. Full films of VA-CNTs have been transferred with a main emphasis on field-emission applications; however, the nature of interconnection to the CNTs and the lengthwise electrical and mechanical properties of the transferred films have not been assessed. CNTs have been previously embedded in an otherwise insulating matrix to form conducting composites, [10] but these are not al...

MEMS-fabricated electrical contacts are commonly used in MEMS relays. These electrical contacts can be as simple as two flat surfaces coming into contact [1]. Modeling their contact force/resistance relationship can be difficult because much of the theory on contact resistance was developed for macro-scale contacts [2], and contact properties for MEMS-scale contacts do not always agree with those predicted by this theory [3]. One contribution to this disagreement is that when the dimensions of the contact thickness are on the order of the a-spot dimensions, the spreading resistance is affected [4]. In order to determine the relationship between contact force and resistance for a wide range of parameters, we have developed a two-coupon test system which allows the properties of these contacts to be empirically determined. The design of the two-coupon system allows for the rapid fabrication of multiple contact materials and geometries. The two-coupon system was used to test the contact resistance properties of sputtered and electroplated Au films in thicknesses of 0.1 μm, 0.3 μm, and 0.5 μm. Contact force was measured using a custom flexural force gauge and the 4-point contact resistance was measured using an integrated Kelvin Structure [5]. The results are compared to traditional Holm theory to determine the effects of film thickness on spreading resistance.

Plating defects known as pores are unavoidable in most noble metal plating thicknesses used in separable electrical contact applications. Mixed flowing gas tests commonly used as accelerated life tests for connectors and sockets can attack these plating defects to create corroded pore sites on the electrical contact surface. To examine the effects of corroded pores on a gold contact finish, the chemical composition and physical appearance of the corroded pores was examined. The contact resistance at various positions on corroded pores was then measured to examine the effects normal force, geometry, wipe, and backwipe on the contact resistance. The pore sites were also examined under an electron microscope to see how the wipe mechanically displaces the corrosive film in different areas of the pore. Wipe onto the corroded pore site produced better results than landing on the pore site and wiping off, but the magnitude of the contact resistance values would be unacceptable in most dry circuit applications. The design parameters of normal force, geometry, wipe, or backwipe at the levels tested were not found to be able to produce a low and stable contact resistance when making contact to corrode pore sites on gold plated finishes.