Article pubs.acs.org/JPCC
Fabrication of Graphene−Alumina Heterostructured Films with Nanotube Morphology Arunas Jagminas,*,† Saulius Kaciulis,‡ Vaclovas Klimas,† Alfonsas Reż a,† Sigitas Mickevicius,† ̅ and Peiman Soltani‡ †
State Research Institute Center of Physical Sciences and Technology, Savanoriu 231, LT-02300, Vilnius, Lithuania Institute for the Study of Nanostructured Materials, ISMN-CNR, P.O. Box 10, Monterotondo Stazione, 00015 Roma, Italy
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S Supporting Information *
ABSTRACT: The search for highly scalable techniques for the fabrication of promising nanostructured materials is one of the key challenges in modern nanotechnology. Herein, we report on the formation of novel alumina−graphene composite films with an unprecedentedly low optical gap (1.53 eV) and an exciting chemical inertness via Al anodizing in a tartaric acid solution at extremely high current densities that exceed burning initiation. These properties were ascribed to the entrapping of a significant amount of graphene-based materials at the top and back sides of the film. Moreover, nanotube morphology and other properties untypical for alumina films were revealed using scanning electron microscopy, Xray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet photoemission spectroscopy, and reflectance spectroscopy techniques. Because of novel, exciting optical properties and chemical stability, aluminum anodic oxide films heterostructured with a high amount of graphene material open up opportunities for the fabrication of promising coatings, selective electrodes, and sensors.
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INTRODUCTION The anodizing of aluminum is a simple and cheap approach for creating a well-adhering oxide film with functional properties. This method has been known for half a century. Hundreds of papers reported on the peculiarities of aluminum anodizing in aqueous solutions containing di- and tribasic acids, their salts, and composites. It is commonly accepted that depending on the electrolyte solution, two types of films can be formed: (1) a compact and thin film with a thickness determined by the final anodizing voltage (the theoretical value is 1.4 nm V−1) and (2) a porous film with a thickness of up to several hundreds of microns.1,2 Further increases in the anodizing voltage usually lead to the plasma electrolytic oxidation phenomena.3 Porous anodic oxide films (AOFs) typically have a close-packed hexagonal morphology of cells, perpendicular to the substrate, with a pore in the central part. The diameter of cells depends on the bath voltage up to the film breaking value, which is characteristic for a given solution composition.4 Highly ordered honeycomb structure AOFs can be formed only under appropriate anodizing conditions in sulfuric,5 oxalic,6 and phosphoric7 acid solutions on pure and smooth substrates.8 It has been reported that self-ordered films with a 600 and 670 nm interpore spacing can also be formed in solutions of some organic acids (e.g., malonic, citric, and etidronic9,10) under the critical voltages just below burning. The composition of porous AOFs is complex. The inner part of the hexagons contains anions and water molecules entrapped from the anodizing solution. The content and the formula of entrapped species are © XXXX American Chemical Society
primarily determined by the acid type. For example, AOFs formed in the classical sulfuric, chromic, and oxalic acid baths contain 13 to 14% HSO4−,
