The application of shadow nanosphere lithography for the preparation of large-area, two-dimensional, metallic nanostructures of different shape is described. Through changing the mask morphology by temperature processing and varying the evaporation conditions, particles with morphologies such as rings, rods, and dots have been produced. This process allows outstanding control of the size and morphology of the particles. The efficient technique is shown to scale down the size of metallic nanoparticles from 200 to 30 nm, while preserving the original nanosphere spacing and order. The 150-nm-diameter Fe rings produced by this method show ferromagnetic behavior, which was predicted by theoretical simulation. All the experimental results were confirmed by computer simulations, which also showed the possibility of creating periodic arrays of any other geometrical shape.

In this letter we describe the preparation of large-area, two-dimensional metallic structures using shadow nanosphere lithography. By varying the position of the substrate with respect to the evaporation source during the sample preparation, we make morphologies such as cups, rods, and wires, that are not accessible by the standard nanosphere lithography. This technique also allows for an encapsulation of the metallic structures, to prevent them from oxidation. Morphologies predicted by our computer simulations have been subsequently confirmed experimentally.

A fast and cheap, large-area (>1 cm(2)), high-coverage fabrication technique for periodic metallic split-ring resonator metamaterials is presented, which allows control of inner- and outer-ring diameters, gap angles, as well as thickness and periodicity. This method, based on shadow nanosphere lithography, uses tilted-angle-rotation thermal evaporation onto Langmuir-Blodgett-type monolayers of close-packed polystyrene nanospheres. Excellent agreement of the process parameters with a simplified model is demonstrated. Pronounced, tunable optical metamaterial resonances in the range of 100 THz are consistent with simulations.

Multiwall carbon nanotubes (CNTs) have been assembled on various types of colloidal templates using the well-known polyelectrolyte-assisted layer-by-layer (LBL) assembly technique. Dense mono-and multilayers of CNTs were successfully deposited on silica, polystyrene, and melamine spherical colloids of different size, showing that relatively short CNTs completely wrap the surface of the spheres, while long nanotubes stick out of the surface, allowing them to contact various spheres at the same time. Decomposition of the colloidal template leads to formation of hollow CNT spheres, which was demonstrated through treatment of melamine@CNT particles with HCl. The deposition was also carried out on ordered arrays of polystyrene particles, leading to nanostructured, conducting CNT assemblies. Rupture of the assemblies with ultrasound shows that the assembly only takes place on one-half of the colloid spheres, so that "Janus" particles with asymmetric functionalities can be easily prepared.

The cover image shows a scanning electron microscopy image of periodically arranged metallic split‐ring resonators, which are manufactured by tilted‐angle‐rotation thermal evaporation of gold onto Langmuir–Blodgett‐type monolayers of close‐packed polystyrene nanospheres. The split rings with dimensions smaller than the wavelength of light are deposited within the nanosphere gaps and form a metamaterial with pronounced, tunable optical resonances in the range of 100 THz. The presented technique allows control of the inner‐ and outer‐ring diameters, gap angles, as well as thickness and periodicity. Being a flexible and reliable alternative to electron‐beam lithography, this method should therefore pave the way towards cheap, large‐area metamaterials for applications such as perfect lenses and optical cloaking devices. For more information, please read the Full Paper “Periodic Large‐Area Metallic Split‐Ring Resonator Metamaterial Fabrication Based on Shadow Nanosphere Lithography” by H. Giessen et al. beginning . (Cover artwork by S. Hein.).

A number of techniques, including molecular-beam epitaxy (MBE), electron-beam evaporation (EBE), and chemical vapor deposition (CVD), have been used for depositing solid thin films with precision in the sub-nanometer range. [1] Through the combination of these techniques and the use of sacrificial template structures, nanoparticles can be synthesized with morphologies and compositions that would have been extremely difficult to prepare using standard colloid synthesis. As an example, Whitesides and co-workers [2] have recently deposited metallic thin films onto arrays of spherical colloids, subsequently producing metallic half-shells with nanometerscale dimensions through dissolution of the colloidal template.On the other hand, the bottom±up assembly of nanoparticles in solution within functional nanoscale architectures is a goal shared by researchers in many fields because of its relative simplicity and low cost, but still significant technological potential.[3] Despite recent progress, it remains the case that the structural diversity and functional complexity of nanoscale architectures assembled from solution do not fulfill all technological requirements. Spherical substrates have been patterned in various different ways, including seeding methods and/or electroless plating, [4] chemical surface functionalization, [5] surface reaction, [6] co-precipitation, [7] polyelectrolyte-mediated layer-by-layer (LbL) assembly, [8,9] or various combinations of such techniques.[10] The strategy presented here is based on the self-assembly of hexagonal closed-packed (hcp) monolayers of colloidal spheres, which have been widely used as masks for the deposition of various materials, typically by evaporation or sputtering. [11,12] The combination of EBE and LbL assembly allows the deposition of metallic thin films and nanoparticle monolayers onto different templates, providing a simple route for the preparation of asymmetric functional spheres, which would be very hard to obtain through other procedures. This paper describes a versatile and reproducible technique for fabricating asymmetric core±shell spheres with diameters ranging from several hundreds of nanometers to micrometers, showing different properties depending on the functionalities of the shell materials. Metallic hemispheres with different morphologies have been prepared in the past by means of different techniques, [2,13] turning a variety of colloids of different sizes into optically active core±shell structured particles. The metal halfshells provide the spheres with different properties depending on their composition and morphology. For the deposition of metals, we used EBE on self-assembled hcp monolayers of polystyrene (PS) spheres in a process identical to that previously used in our group for nanosphere lithography (NSL). [11] Regardless of the nature of the evaporated material, the half-coated particles show homogeneous half-shells, which can be easily identified using scanning electron microscopy (SEM). Examples are shown in Figure 1 for two...

Fullerenes [1] and single-(SWNT) and multiwalled (MWNT) carbon nanotubes [2] have created a field of research with possible uses in areas that could exploit their unique, structure-dependent electrical, mechanical, and optical properties. [3][4][5] New synthesis and fabrication techniques are being pioneered to obtain different carbon morphologies and their applications [6] in several fields including composites, electrochemical devices, field-emission and nanoscale electronic devices, and sensors, among others, have been recently demonstrated. [7][8][9][10][11] Synthetic routes where carbon nanotubes (CNTs) are useful for biological applications have been also reported. [12] The increasing number of reports on the preparation of CNT thin films, including the spraying of CNT dispersions onto substrates, [13] stretching polymer films loaded with CNTs, Langmuir-Blodgett deposition, [14] and layer-bylayer (LbL) assembly [15][16][17] offers high-quality systems on a macroscopic scale, a fundamental prerequisite for investigating their optical, optoelectronic, and electrical properties. Furthermore, the incorporation, redispersion, and alignment of CNTs into polymer composites [18] are desirable qualities, and in this way, petroleum pitch, [19] poly(methyl methacrylate) (PMMA), [20] poly(p-phenylene benzobisoxazole) (PBO), [21] and polypropylene [22] are examples of matrixes where CNTs have been dispersed successfully, improving the mechanical properties of the oriented composite fibers. However, limitations in the strategies for functionalizing, processing, and/or the assembly of CNTs are important barriers in the pursuit of potential applications and therefore, new experimental developments are required.In this perspective, exploiting the potential and feasibility of the layer-by-layer self-assembly technique, [23] which is based on the alternating adsorption of monolayers of individual components (typically including polyelectrolytes) at-tracted to each other by electrostatic and Van der Waals interactions, a simple and reproducible approach for the production of CNT-based polymeric thin films is reported. The flexibility of MWNTs allows their coiling around fairly small particles and the relatively low glass-transition temperature (T g ) of polystyrene (PS) particles facilitates their ability to be embedded inside a polymeric matrix. Patterning the resulting composite thin films with a concrete permanent distribution of carbon nanotubes and conductive properties can be achieved, as outlined in Scheme 1.Stable aqueous dispersions of oxidized MWNTs (which were used due to their low cost and better accessibility, compared to SWNTs), were obtained following a reported experimental process. [24] This method provides CNTs with mainly carboxyl groups on their walls by using an acidic solution (H 2 SO 4 /HNO 3 ; 3:1) that renders the CNTs negatively charged, and consequentially facilitates their dispersion in water. The usefulness of the LbL technique was again demonstrated by using a 2D hexagonally ordered array of PS sp...

No abstract