Controlling the Morphology of Carbon Nanotube Films by Varying the Areal Density of Catalyst Nanoclusters Using Block‐Copolymer Micellar Thin Films

Abstract

In spite of much research progress in the science and synthesis of carbon nanotubes (CNTs), [1] control over the location and orientation of CNTs on substrates remains a major challenge. A key breakthrough was the synthesis of vertically aligned CNT (VA-CNT) arrays using thermal chemical vapor deposition (CVD) [2][3][4][5][6][7] and plasma-enhanced CVD, [8] where the CNTs self-orient perpendicular to the substrate surface due to initial crowding and continue to grow upward in this direction. These CNT arrays have wide-ranging applications, including membranes, heat dissipation, electrical interconnects, and nanoelectronics. [9][10][11][12][13] The catalysts for synthesis of VACNTs are commonly prepared by sputtering or evaporating a thin metal film onto a substrate, [14,15] which dewets to form catalyst nanoparticles at an elevated temperature prior to growth. [16][17][18] While these catalysts are easily prepared and patterned by shadow masking or lithography, [7,14] these approaches are not easily able to create nanocluster catalysts that have monodisperse diameters and quantifiable areal densities. In thin metal films, both the nanocluster size and areal density are coupled to the film thickness, and the annealing procedure affects the size, density, and the chemical state of the nanoclusters. Recently, Huh et al. [19] demonstrated a route for controlling the density of CNT growth using varying densities of colloidal cobalt nanoparticles; however, due to nanoparticle coalescence their route does not enable precise quantification of nanocluster areal density and leads to a broad distribution of CNT diameters. Zhang et al. [20] also recently demonstrated the control of CNT growth by varying the density of Co-Mo nanoparticles, although their route is unable to independently vary the diameter and the areal density of nanoparticles.We employ a methodology for synthesizing iron oxide nanoclusters that utilizes micelles formed by the amphiphilic block copolymer, polystyrene-b-poly(acrylic acid) (PS-b-PAA). [21,22] This catalyst system has significant value because it enables the creation of nanocluster arrays of a chosen metal species, with independent control of the nanocluster diameter and areal density. [22] In previous work, nanocluster diameters were varied between 5 and 16 nm and the areal density was varied from 6.0 × 10 10 to 1 × 10 9 cm -2 , although variation outside of these ranges is easily accessible. At higher areal densities the nanoclusters are hexagonally ordered. Further, as we have presented separately, the nanocluster arrays can be patterned on the micrometer length scale using microcontact printing.[23]Here, we utilize this system to create arrays of uniform-diameter iron oxide nanoclusters, with quantifiable areal densities that can be varied over more than an order of magnitude. We achieve vertical CNT growth from our catalyst system through appropriate selection of the substrate, catalyst preparation procedure, and reaction conditions. To the best of our knowledge, our work is the first exampl...

Versatile Carbon Hybrid Films Composed of Vertical Carbon Nanotubes Grown on Mechanically Compliant Graphene Films

“…Nanopatterned iron catalyst particles were deposited on this film surface by means of self-assembled block-copolymer nanoporous templates. [2][3][4]11,[27][28][29][30][31][32][33][34] Figure 1b shows scanning electron microscopy (SEM) images of the uniformly sized catalyst islands upon the graphene film. The electron diffraction pattern of catalyst particles obtained by transmission electron microscopy (TEM) matches that of a face-centered cubic (fcc) iron crystal.…”

Implications of catalyst control for carbon nanotube based thermal interface materials

“…As an alternative, other authors have indirectly calculated the CNT number density by performing mass difference measurements via thermogravimetric analysis 24,29 or macroscopic weight gain measurements. 1͑d͒-1͑f͒, where CNT bundling and imperfect alignment make it impossible to count all individual CNTs.…”

“…23,24 A block copolymer ͓poly͑styrene-blockacrylic acid͒ ͑PS16500-PAA4500͔͒ was dissolved in toluene with different concentrations to form reverse micelles and then loaded with FeCl 3 . 23,24 A block copolymer ͓poly͑styrene-blockacrylic acid͒ ͑PS16500-PAA4500͔͒ was dissolved in toluene with different concentrations to form reverse micelles and then loaded with FeCl 3 .…”

Arrays of carbon nanoscrolls as deep subwavelength magnetic metamaterials

“…One of the possible routes to realize an array of carbon nanoscrolls is by self-folding of a single layer of graphene around a carbon nanotube, ordered arrays of which have already been realized in the laboratory. 27,28 …”