Amplitude mask for generating 2D periodic nano-structures

Introduction: Periodic nanostructures have gained lot of significance because of its wide range of applications ranging from nano-electronics to nano-fluidics. Laser interference lithography has emerged as a powerful, cost... [ view full abstract ]

Introduction:
Periodic nanostructures have gained lot of significance because of its wide range of applications ranging from nano-electronics to nano-fluidics. Laser interference lithography has emerged as a powerful, cost effective and simpler tool to generate periodic patterns over a large area. In Multi-beam interference lithography, amplitude and polarization angle of the individual beam and the angle between the beams control the interference pattern [1] [2]. Choosing the right set of parameters for the individual beam is highly challenging. Phase mask holography involves a 2D or 3D mask. Using a single laser source, phase mask creates beams with required properties but designing a proper mask and its fabrication processes are exigent.

We propose a new technique to generate 2D periodic nano structures. We have integrated light-sheet illumination technique with a spatial filtering technique in a 2π system to enable the generation of 2D periodic nano-structures. Selective plane illumination property of light sheets can be exploited to produce nanostructures with fewer defects.

Methods:
The schematic diagram of the proposed optical setup is as shown in Image 1. The electric field distribution at and near the focal region of the two opposing cylindrical lens C1 and C2 having semi-aperture angle alpha , are given in Image 2.,

So the intensity of the field distribution at and near the common focal region is given by

I=|E_x |^2+|E_y |^2+|E_z |^2 ------------------------------------------(2)

Results:
Computational techniques are adopted to study the nature of the intensity of the field distribution over a predefined 3D grid. A monochromatic wavelength of 364nm is chosen to evaluate equation (2). Image 3 shows the intensity cross sections for different values of stop angle β. Periodicity along z axis is found to be 180nm where as feature size is 80nm. Image 3 also shows the possibility of uniform patterning over a large area.

Conclusions:
The proposed technique is hoped to find immediate applications in the field of nano-waveguides and optical microscopy.

Reference:

1. J.-H. Jang, C. K.Ullal, M. Maldovan, T.Gorishnyy, S.Kooi, C.Koh, and E. L. Thomas, Adv. Funct. Mater.17, 30273041,2007.

2. G.v.Freymann, A.Ledermann, M.Thie,I.Staude,S. Essig, K.Busch, M. Wegener, Adv.Funct.Mater . 20, 1038, 2010.