1 Layered Nanoassembly of Three-Dimensional Structures A. A. G. Requicha, S. Meltzer, R. Resch, D. Lewis, B. E. Koel and M. E. Thompson Laboratory for Molecular Robotics University of Southern California Abstract NEMS (nanoelectromechanical systems) loom beyond the MEMS horizon as the new frontier in miniaturization. Nanorobots and other NEMS are expected to find revolutionary applications in science, engineering and everyday life. Until now, nanostructures have been built primarily in two dimensions, because of the difficulties of three- dimensional (3-D) fabrication. This paper describes a promising approach to the construction of 3-D nanostructures by working in successive layers, much like the rapid prototyping techniques used in the macroscopic world. Each object nanolayer is built by nanomanipulation, or possibly by programmed self- assembly, and then surrounded by a sacrificial layer that planarizes the sample and serves as a substrate for the deposition of the next object nanolayer. Initial experimental results which show that the approach is feasible are presented. Introduction Rapid prototyping, also known as solid freeform fabrication and by other designations, was introduced at the macroscale more than a decade ago, and is widely used in industry. Conceptually, one slices the desired object and then builds each of its layers sequentially. The actual layer construction may use several physical processes, such as curing a polymer or sintering a powdered material—see e.g. [Sprow 1992] for an introduction, at the trade magazine level. Recently, the EDAM rapid prototyping process dveloped at USC was demonstrated at the microscale. At the nanoscale, however, layered fabrication has been impossible until now, and none of the macro or micro rapid prototyping techniques can be extended directly to the nanometer range. More generally, fabrication of 3-D nanostructures by any means has proven very difficult, and essentially all the nanofabrication techniques demonstrated to date have been 2-D. In the remainder of this paper we describe a novel process for 3-D nanofabrication that is based on the robotic assembly of nanoparticles in successive layers. Basic Process Much like in macroscale rapid prototyping, we approximate the object by a set of layers or slices, and build these sequentially. The process is illustrated schematically in Figure 1, and has the following steps. 1. Conceptually slice the nanoscale object to be fabricated by a set of parallel planes, thus defining a sequence of layers to be produced. 2. Construct the first layer of the desired material on a substrate surface. This layer, and others to be constructed sucessively, are called here nanoslices and have heights on the order of a few nm. 3. Level off, or planarize the result by constructing a layer that covers the substrate but not the previous nanoslice, and whose height equals the height of the previous nanoslice. This layer is called a sacrificial layer. The result of this step is a new surface that will serve as a substrate for the construction of the next nanoslice. 4. Repeat Steps 2 and 3 with the successive nanoslices required to construct the entire object. 5. Remove the sacrificial layers and fuse the nanoslices to produce a solid nanoscale object. Figure 1 –Layered nanofabrication principles In the following sections we describe in more detail Steps 2, 3, and 5. Substrate Substrate Surface 1st Sacrificial Layer 1st Nanolayer 2nd Nanolayer