Synthesis of a Self‐Assembled Hybrid of Ultrananocrystalline Diamond and Carbon Nanotubes

Abstract

Recent strong scientific and technological interest in nanostructured carbon materials (nanocarbons) has been motivated by the diverse range of physical properties these systems exhibit. These properties arise from the many different local bonding structures of carbon, as well as the long-range order. For example, carbon nanotubes (CNTs) are distinct from graphite, although both consist essentially of sp 2 -bonded carbon; [1] CNTs are the strongest known material and exhibit unique electronic transport properties, making them candidates for a wide range of applications. Similarly, nanocrystalline diamond films are distinct from single-crystal diamond, although both are mostly sp 3 -bonded carbon, and exhibit high hardness, exceptional chemical inertness, biocompatibility, [2] and negative electron affinity with proper treatment.[3]The unique mechanical and electrochemical properties of nanocrystalline diamond make it a promising candidate for use as a protective coating of machining tools; a hermetic, corrosion-resistant coating for biodevices; [4] a cold-cathode electron source; [5] and structural material in micro-and nanoelectromechanical systems (MEMS/NEMS).[6]It has been speculated that the synergistic combination of carbon nanotubes and nanocrystalline diamond could give rise to materials with novel properties that could be used advantageously in applications such as electronic devices [7] or MEMS/NEMS. [8] However, a synthesis pathway must be developed that would lead to the concurrent growth of different allotropes of carbon that are covalently bonded and organized at the nanometer-scale. In this work we demonstrate, for the first time, that the simultaneous synthesis of nanocrystalline diamond and carbon nanotubes to form a covalently bonded hybrid materialÐa nanocomposite of diamond and CNTsÐ can be achieved. One of the most commonly used processes for preparing nanostructured carbon materials is plasma-enhanced chemical vapor deposition (PECVD), in which chemically activated carbon-based molecules are produced. For instance, different carbon-rich combinations of C 2 H 2 /H 2 , [9] C 2 H 2 /NH 3 , [10,11] and CH 4 /Ar [12] have been employed for growing CNTs. In contrast, hydrogen-rich (~99 % H 2 ) CH 4 /H 2 plasmas are the most common mixtures used for growing microcrystalline diamond films, wherein large amounts of atomic hydrogen play a critical role in both the gas-phase and surface-growth chemistries. Importantly, atomic hydrogen is also needed to selectively etch the non-diamond carbon during growth. Over the past several years we have developed hydrogen-poor Ar/CH 4 (99 % Ar, 1 % CH 4 ) chemistries to grow ultrananocrystalline diamond (UNCD) films, which consist of diamond grains 3±5 nm in size, and atomically abrupt high-energy grain boundaries.[8] The special nanostructure of UNCD yields a unique combination of properties, such as low deposition temperatures, [13] excellent conformal growth on high-aspect ratio features, [8] and the highest room-temperature n-type electronic conductivity demons...

From Carbon Nanostructures to New Photoluminescence Sources: An Overview of New Perspectives and Emerging Applications of Low‐Pressure PECVD

“…Further work by Carlisle and co-workers [116] adding N 2 to CH 4 /Ar plasmas allowed the synthesis of highly conducting (five orders of magnitude above undoped samples), nitrogen-doped, ultrananocrystalline diamond films of interest for applications in electronic devices. Very recently, Carlisle and co-workers [117] have also reported the first successful result on the synthesis (by low-pressure PECVD) of self-assembled hybrids of ultrananocrystalline diamond and carbon nanotubes (see Fig. 8).…”

Investigation on Nanodiamond and Carbon Nanotube‐Diamond Nanocomposite Synthesized using RF‐PECVD

“…[3] The unique mechanical and electronic properties of CNTs and ND make both promising candidates for use in microelectronic devices. Recently, Xiao et al [1] have developed a synthesis pathway to realize the concurrent growth of various allotropes of carbon that are covalently bonded and organized at the nanometer scale, and a covalently bonded hybrid material/composite of CNTs and diamond has been achieved. However, although the hybrid material has been obtained, many nanocrystalline diamond grains form ''supergrains'' with a size 0.1-0.5 mm, which significantly damages the synergistic effect of the hybrid material.…”

“…These properties arise from the quite different local bonding structures of carbon, and the microstructures of the materials. [1,2] CNTs, consisting of dominant sp 2 -bonded carbon, form the strongest known material and exhibit unique electronic transport properties, while ND, containing predominant sp 3 -bonded carbon, exhibits high hardness, stable surface chemistry, and good biocompatibility. [3] The unique mechanical and electronic properties of CNTs and ND make both promising candidates for use in microelectronic devices.…”

Current-induced nanogap formation and graphitization in boron-doped diamond films

“…For instance, hybrid diamond/graphite structures can be relevant in molecular electronic applications because they benefit from both the robustness of sp 3 bonds and the flexibility of sp 2 hybridization for functionalizing with a large variety of molecules. Hybrid structures such as diamond/graphite nanowires, 4 diamond/graphite nanoflakes, 5 and diamond/CNTs 6 composites have been reported in recent years.…”

“…The results presented here offer a method to engineer diamond devices to incorporate hybrid diamond/graphitic structures and nanogaps which cannot be performed using alternative techniques. [4][5][6] B:NCD films were grown on a silicon oxide substrate in an ASTeX 6500 series using microwave plasma-enhanced CVD technique. Prior to the CVD, a silicon substrate was cleaned with nitric acid in an ultrasonic bath for 2-3 min and then rinsed with deionized water.…”