The ability to transform two-dimensional (2D) materials into a three-dimensional (3D) structure while preserving their unique inherent properties might offer great enticing opportunities in the development of diverse applications for next generation micro/nanodevices. Here, a self-assembly process is introduced for building free-standing 3D, micro/nanoscale, hollow, polyhedral structures configured with a few layers of graphene-based materials: graphene and graphene oxide. The 3D structures have been further modified with surface patterning, realized through the inclusion of metal patterns on their 3D surfaces. The 3D geometry leads to a nontrivial spatial distribution of strong electric fields (volumetric light confinement) induced by 3D plasmon hybridization on the surface of the graphene forming the 3D structures. Due to coupling in all directions, resulting in 3D plasmon hybridization, the 3D closed box graphene generates a highly confined electric field within as well as outside of the cubes. Moreover, since the uniform coupling reduces the decay of the field enhancement away from the surface, the confined electric field inside of the 3D structure shows two orders of magnitude higher than that of 2D graphene before transformation into the 3D structure. Therefore, these structures might be used for detection of target substances (not limited to only the graphene surfaces, but using the entire volume formed by the 3D graphene-based structure) in sensor applications.

tailored anisotropic optical, or magnetic responses; [11][12][13][14][15][16] ii) Metal and/or semiconductor material patterns on the 3D dielectric substrate can also be used for building 3D electric circuits ( Figure 1 ) including sensors, transistors, and memory devices; [17][18][19] and iii) free-standing hollow structures can be used as 3D containers (or encapsulation) for targeted drug delivery or used as scaffolds for artifi cial tissues. [20][21][22][23] In order to fully serve these functions, micro-and nanoscale surface patterning on the 3D dielectric structures plays a crucial role and, therefore, must be realized.Conventional 3D fabrications are typically built using layer-by-layer lithographic patterning methods, [ 20,24 ] 3D printing, [ 25,26 ] and/or self-aligned membrane projection lithography. [ 12,27 ] With these traditional methods, development of a 3D, hollow, polyhedral structure has been possible. In addition, limited surface patterning in microscale has been achieved. [ 28,29 ] However, since the conventional lithographic process is a top-down strategy, surface patterning on a free-standing enclosed hollow structure (i.e., 3D microcontainer) has not been realized. In this paper, we report on the realization of a 3D, free-standing, polyhedral, hollow structure with desired surface patterning on a dielectric material, i.e., aluminum oxide (Al 2 O 3 , 150 nm thick), in microscale to be used as a functionalized device (Figure 1 c). The 3D structure was realized with the combination of topdown (lithographic, Figure 1 a) and bottom-up (origami-inspired self-assembly, Figure 1 b) processes. The origami-inspired selfassembly approach combined with a top-down process is one of the few dependable approaches to realize 3D micro/nanoscale polyhedral structures with surface patterning. [ 4,10,[30][31][32] In this approach, 2D, lithographically patterned, planar features are connected with hinges at the joints which fold up the structure when they are heated to their melting temperature (Figure 1 ). This process not only offers easy control of size and shape, allowing for fabrication of free-standing, hollow systems, but also supports surface patterning with metal/semiconductor materials on each face of the 3D structure and large-scale production with a high yield. As a result, the technique allows heterogeneous integrations with various materials which can produce free-standing, 3D, multifunctional devices (Figure 1 c). In turn, diverse applications in electronic circuits, as well as optical and biomedical modules, can be achieved. In a previous study, a 3D structure has been made with desired surface patterning on dielectric materials using this self-assembly process. [ 10 ] However, the 3D structure was in nanoscale and showed low Multifunctional 3D microstructures have been extensively investigated for the development of new classes of electronic and optical devices. Here, functionalized, free-standing, hollow, 3D, dielectric (150 nm thick aluminum oxide) microcontainers with metal patterning on their...

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Thermal reflow of polymers is a well-established phenomenon that has been used in various microfabrication processes. However, present techniques have critical limitations in controlling the various attributes of polymer reflow, such as the position and extent of reflow, especially at the nanoscale. These challenges primarily result from the reflow heat source supplying heat energy to the entire substrate rather than a specific area. In this work, a focused ion beam (FIB) microscope is used to achieve controllable localized heat generation, leading to precise control over the nanoscale polymer reflow. Through the use of the patterning capability of FIB microscopy, dramatically different reflow performances within nanoscale distances of each other are demonstrated in both discrete periodic and continuous polymer structures. Further, we utilize a self-assembly process induced by nanoscale polymer reflow to realize 3D optical devices, specifically, vertically aligned nanoresonators and graphene-based nanocubes. HFSS and Comsol simulations have been carried out to analyze the advantages of the polymer-based 3D metamaterials as opposed to those fabricated with a metallic hinge. The simulation results clearly demonstrate that the polymer hinges have a dual advantage; first, the removal of any interference from the transmission spectrum leading to strong and distinct resonance peaks and, second, the elimination of parasitic leeching of the enhanced field by the metallic hinge resulting in stronger volumetric enhancement. Thus, the 2-fold advantages existing in 3D polymer-hinge optical metamaterials can open pathways for applications in 3D optoelectronic devices and sensors, vibrational molecular spectroscopy, and other nanoscale 3D plasmonic devices.

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