NON-TECHNICAL DESCRIPTION: The principal objective of this work is the experimental fabrication of a new, technologically important, carbon-based nanostructured material referred to as mattressene. Structurally, mattressene consists of alternating single-layer graphene sheets connected to each other by parallel arrays of carbon nanotubes, and this regular, periodic arrangement of graphene and nanotubes enables mattressene to exhibit remarkable electronic, thermal and mechanical properties, making it applicable as a (i) high-speed, high-density semiconductor chip device, (ii) high-efficiency thermoelectric material capable of converting waste heat to electricity, (iii) thermal interface material for efficient and swift removal of heat in electronic devices and (iv) high-capacity reversible hydrogen storage in hydrogen fuel cells. TECHNICAL DETAILS: The experimental ability to synthesize a new, ordered, carbon-based nano-metamaterial- mattressene is being explored in this project. Mattressene consists of parallel sheets of graphene connected to each other by ordered, parallel arrays of same-length single-walled carbon nanotubes oriented orthogonal to the graphene sheets. The key elements of the chemical synthesis strategy, appropriately informed by high-accuracy density functional theory (DFT) calculations, consists of assembling a layered structure comprised of alternating graphene and functionalized-fullerene layers, followed by chemical attachment between graphene and fullerenes and conversion of the fullerenes to carbon nanotubes via cycloaddition reactions. The building blocks of mattressene consist of graphene and nanotubes, and that in combination with a 3-D periodic arrangement which can be suitably varied by adopting the layer by layer synthesis approach, enables mattressene to exhibit tunable electronic, thermal and thermoelectric properties. This tunability makes mattresene highly desirable and ideally suited for technological applications as semiconducting devices, efficient thermal transport materials and thermoelectric materials. Another significant impact of this project is the rigorous training of a graduate student in a multi-disciplinary environment spanning across many fields of science and engineering as well as allowing the student to get familiarized with advanced, cutting-edge experimental and theoretical research tools and techniques that are adopted in this work. A post-doctoral scholar and several undergraduate students are also engaged in this project.