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Note: Experimental observation of nano-channel pattern in light sheet laser interference nanolithography system

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Mohan, K., & Mondal, P. (2016). Note: Experimental observation of nano-channel pattern in light sheet laser interference nanolithography system. Review of Scientific Instruments, 87(6): 066107, pp. 1-3. doi:10.1063/1.4954198.

Cite as: https://hdl.handle.net/21.11116/0000-0007-B01C-3
We experimentally observed nano-channel-like pattern in a light-sheet based interference nanolithography system. The optical system created nano-channel-like patterned illumination. Coherent counter-propagating light sheets are made to interfere at and near geometrical focus along the propagation z-axis. This results in the formation of nano-channel-like pattern (of size ≈ 300 nm and inter-channel periodicity of ≈337.5 nm) inside the sample due to constructive and destructive interference. In addition, the technique has the ability to generate large area patterning using larger light-sheets. Exciting applications are in the broad field of nanotechnology (nano-electronics and nano-fluidics).
Generation of periodic nano-pattern has gained interest due to its vast applications ranging from nano-electronics to nano-fluidics. High density printing of nano-structures per chip has enabled miniaturization and substantially improved the cost-per function in IC technology. The other field that has emerged out of this technique is nano-fluidics that can function as protein analyzer1 and immunoassay devices.2 These emerging fields are progressing fast and finding new applications in Nanophysics and Nanotechnology.
Existing techniques such as, focussed ion-beam (FIB) lithography and laser interference lithography (LIL) are considered as state-of-the-art techniques that have the distinct ability of generating any complex arbitrary nano-structure.3,5,4 In FIB, a beam of accelerated ionic particles from a liquid metal ion source interacts with the substrate resulting in both milling and imaging the sample. This is due to the elastic and inelastic collisions that lead to sputtering of atoms and emission of secondary electrons. On the other hand, LIL is a simple and cost effective technique for generating periodic structures. In LIL, the intensity of the interference pattern produced by the coherent beams is recorded on the photoresist and is then developed by the well known chemical processes.6,7 In LIL, the spacing between two successive features is ≈λ/2nsinθ, θ being the inclination angle and n the refractive index of the substrate.9,8 Though LIL is widely used to generate periodic structures, it also has wide range of applications in photonic crystals,10 magnetic storage devices,11 biosensors,12 diffraction gratings,13 and broadband reflectors.14 However, the existing techniques require optical mask, suffer from slow speed, and are incapable of high-throughput fabrication. In this note, the development of optical system to create nano-channel-like patterned illumination is reported. It may however be noted that the laser power limitation especially in the visible range will strongly limit the fabrication capabilities of the system. Currently, challenging tasks for laser interference lithography include avoiding unwanted structures in photoresist layer15 and the ability to pattern user defined area. Proposed technique uses two phase-matched counter-propagating light-sheets to create nano-channel-like interference pattern that can be easily recorded on the photopolymer for nanofabrication. However no optical artifacts were observed, which may result in the creation of anomalous structures. This technique has the added advantage of selectively exposing any desired plane with a user-defined variable patterning area within the 3D sample. This can be achieved by optically enlarging the size of light-sheets by simply under-filling the back-aperture of illumination objective thereby resulting in low numerical aperture and consequent large light-sheets.