Physical Self-Assembly and Nano-Patterning
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PHYSICAL SELF-ASSEMBLY AND NANO-PATTERNING* T.-M. Lu, D.-X. Ye, T. Karabacak, and G.-C. Wang, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180-3590 Abstract It is known that oblique angle deposition (or glancing angle deposition) can create 3D architectures that are otherwise difficult to produce using the conventional lithographic techniques. The technique relies on a self-assembly mechanism originated from a physical shadowing effect during deposition. In this paper we show examples of 3D nanostructures obtained by this oblique angle deposition on a templated substrate with regularly spaced pillar seeds. We show that common to this technique is the phenomenon of side-way growth on the seeds. The side-way growth leads to a fan-like structure at the initial stages of growth if the incident oblique angle is fixed during growth. Simulations based on a steering effect due to the attractive force between the incoming atom and the existing atoms on the surface produce a fanlike structure similar to that observed experimentally. We show that a two-phase substrate rotation scheme during deposition can dramatically reduce this fan-out effect and can lead to uniform and isolated columns. Introduction The morphology of thin film growth fronts formed by a physical vapor deposition technique is controlled by many factors including: surface diffusion, sticking coefficient, and shadowing. Instabilities of growth can occur if the shadowing is more dominant compared to other surface effects and can lead to many substrate diverse physically (a) (b) self-assembled 3D nanostructures. One motor θ way to create a dominant shadowing effect is by oblique angle deposition [1vapor 7]. In this technique, incident deposition (c) (d) flux arrives at the substrate at an angle θ with respect to the source surface normal. A variety of evaporation sources Fig. 1. Left: A schematic of the oblique angle deposition setup. Right: such as thermal examples of Si structures (amorphous) that we recently fabricated in our evaporation and lab on templated Si wafer (vertical rods (a), tilted beams (b), top view of sputter deposition helical springs (c), and side view of helical springs (d)) using oblique can be employed in angle deposition. The scale bars are one micron. 1 µm
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the oblique angle deposition configuration. The technique has been known for more than a century [8,9]. Only recently research activities using the oblique angle deposition has increased. This is perhaps due to the recognition that this technique allows one to produce diverse morphologies and microstructures that possess a wide range of interesting optical, electrical, and magnetic properties. Figure 1 (left) shows the deposition configuration during an oblique angle deposition. The flux strikes the substrate with an angle θ normal to the substrate surface. The substrate can be rotated around the substrate normal with an angular speed ω. If the substrate is templated with a seed pattern having periodic arrays of p
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