Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NanoStencil (Nanoscale self-assembled epitaxial nucleation controlled by interference lithography)

Teaser

The Nanostencil project seeks to utilise laser interference lithography to pattern surfaces in-situ during the materials synthesis phase. It seeks to use this novel method to produce dense arrays of identical nanostructures of precise size, shape and composition and to apply...

Summary

The Nanostencil project seeks to utilise laser interference lithography to pattern surfaces in-situ during the materials synthesis phase. It seeks to use this novel method to produce dense arrays of identical nanostructures of precise size, shape and composition and to apply this to diverse materials systems and reaction methods. In the approach, laser interference patterning is applied by means of splitting and combining ultrashort pulses to produce an interference pattern on the reacting surface. The pattern of laser fluence acts to modify local reaction processes providing energetically favourable sites for surface reactions which can nucleate self-assembly. The technique is applied to three materials systems; the MBE growth of III-V nanostructures, the CVD growth of zinc oxide and the surface reaction of metal films with supercritical CO2. To achieve this, in the first year, we have designed and built new optical interference systems and custom materials reactors, which are now under evaluation. We have also developed predictive models for the interference patterning and the interaction of the light with surfaces under typical reactor conditions. The technique combines the simplicity of patterning with light with the ability to form new structures through surface reactions and can provide a versatile and cost-effective next generation nanopatterning methodology. The new classes of nanostructure we will develop will have applications within the fields of electronic, photonics, sensing and bioengineering

Work performed

Workpackages WP1 (Surface interactions with pulsed laser interference patterns) and WP2 (Design and prototyping of laser interference systems for in-situ application) have been active during this period. In WP1 we have modelled the laser interference process and studied theoretically the interaction of pulsed laser light with known surface processes. In the case of the MBE application we have developed a 3D theoretical model that predicts the thermal response of a GaAs wafer after nanosecond pulsed laser irradiation by four-beam laser interference patterning and have simulated the effect on the desorption and diffusion of an indium layer. In the CVD cases, we have modelled the rather different thermal response of low thermal conduction substrates such as alumina and have developed an improved understanding of the properties and potential of the reaction of ScCO2.
The optical interference systems for each approach have been built, tested and verified. Three novel growth reactors have also been designed and built by the project partners. At CEIT, a CVD system which uses a novel aerosol generator is currently under test. At TUT, a high-pressure system for ScCO2 is currently under final build. At USFD, a custom MBE system designed for 4 beam interference is to be delivered within the next month. At Innolas, a new pulsed laser system has been built and delivered to the project at the end of September. The design of this laser incorporates elements of beam control which given a considerable improvement on previous designs.
The results have so far generated 2 publications (1 accepted, 1 under review) and around 10 conference presentations. An invited talk was given at the 2018 IEEE-3M Nano conference and a special session was organised which created strong interest. We have developed an exploitation plan and seek to implement this within the two remaining years.

Final results

We have developed a new thermal model for laser interference patterning. The results show laser interference patterning is feasible within the range of pulse energies available. From the MBE simulation, we determine the most likely mechanism to achieve nanopatterning is the surface diffusion of mobile species (eg: In on GaAs) and that this is achievable in a single pulse. For the CVD processes the reaction is directly initiated by the thermal or photochemical interaction with the laser pulse and the thermal response is somewhat slower. From the modelling of the thermal behaviour, we have determined two different laser protypes are needed, with a key difference in the pulse duration.
To address previous concerns over the shape and stability of the laser profile, a novel configuration of a VRM Resonator with an external pinhole for laser1. This laser has demonstrated a homogenous noise-free beam profile in near field. However, as part of this assessment, wave‐front aberrations have been identified as a critical risk and will be studied over the next few months
We have reviewed all the options for the interference lithography systems and have designed and tested prototype optical systems. The MBE system at USFD uses a system of beam splitters and mirrors and is based on a novel optical layout developed by BED. The more compact reactors at CEIT and TUT use a diffractive optical element arrangement in a custom configuration. All the optical systems contain significant novelty in design, component sourcing and mounting.
Three reaction chambers for in-situ laser interference patterning studies have been designed, built and in some cases are now operational. Each system has been specially designed to provide state of the art materials capability whilst allowing appropriate optical access. The CEIT approach of laser chemical vapour deposition (LCVD) using aerosol microdroplets is significantly novel in itself and ZnO nanoparticle growth has already been demonstrated using this process. The USFD uses a custom designed commercial MBE reactor, which has been adapted to allow optical access and reduced sensitivity to vibration. The TUT system studies the reaction of SCCo2 , injected up to 300bar and reacted with metal films in a laser assisted decomposition process. This is an emerging process which has already shown great potential. Patterning the surface using laser interference during this reaction is an entirely novel development

Potential impact
New optical systems and new reactor vessels have been developed and evaluated. Impact will be achieved from academic publication and potential technology transfer to industry
New patterned nanomaterials are expected to have significant impact within the fields of electronics, photonics, sensing and bio-engineering. Demonstration of methods and devices over the next year are expected to lead to opportunities for high quality scientific publications and potential uptake from industry
The build and evaluation of laser 1 has led to significant improvements which are marketable by Innolas and would be expected to generate future sales

Website & more info

More info: http://nanostencil.eu/.