AFM Analysis of Micron and Sub-Micron Sized Bridges Fabricated Using the Femtosecond Laser on YBCO Thin Films

Abstract

The research arose as a result of the need to use the femtosecond laser to fabricate sub-micron and nano-sized bridges that could be analyzed for the Josephson effect. The femtosecond laser has a low pulse duration of 130 femtoseconds. Hence in an optical setup it was assumed that it could prevent the thermal degradation of the superconductive material during fabrication. In this paper a series of micron and sub-micron sized bridges where fabricated on superconductive yttrium barium copper oxide (YBCO) thin film using the femtosecond laser, a spherical convex lens of focal length 30 mm and the G-code control programming language applied to a translation stage. The dimensions of the bridges fabricated where analyzed using the atomic force microscope (AFM). As a result, micron sized superconductive bridges of width 1.68 μm, 1.39 μm, 1.23 μm and sub-micron sized bridges of width 858 nm, 732 nm where fabricated. The length of this bridges ranged from 9.6 μm to 12.8 μm. The femtosecond laser technique and the spherical convex lens can be used to fabricate bridges in the sub-micron dimension.

Keywords: YBCO thin film; atomic force microscope; laser ablation diameter; separation distance (SW); sub-micron bridges.

Figure 1

Block diagram of the overall laser optical experimental set up used to machine the bridges [21].

Figure 2

(a) topography line fit shows the width of the bridge at 1.68 $\mathsf{\mu }\mathrm{m}$ and (b) topography line fit shows the length of the bridge at 12.79 $\mathsf{\mu }\mathrm{m}$.

Figure 3

(a) topography line fit shows the width of the bridge at 1.39 $\mathsf{\mu }\mathrm{m}$ and (b) topography line fit shows the length of the bridge at 12.26 $\mathsf{\mu }\mathrm{m}$.

Figure 4

Topography line fit shows the width of the bridge at 1.23 $\mathsf{\mu }\mathrm{m}$.

Figure 5

(a) topography line fit shows the width of the bridge at $858\mathrm{nm}$ and (b) topography line fit shows the length of the bridge at 9.66 $\mathsf{\mu }\mathrm{m}$.

Figure 6

Topography line fit shows the width of the bridge at $732\mathrm{nm}$.

Figure 7

(a) I-V curve for Micro-A bridge and (b) I-V curve for Micro-B bridge.