NCLA - Computational



Overview of NCLA Nanotechnology Activities
In a collaborative project with microbiologists in NCBES, we are following a top-down formalism and developing advance laser-based techniques to fabricate nanostructures on polymer surfaces and have succeeded in producing periodic features < 200 nm in width. Cell culture experiments on these materials have revealed that the cellular response is modified in the presence of the nanostructures. In addition to the obvious benefits of engineering cell response to a material, the ability to fabricate these structures could also have an important impact on a wide range of electronic and photonic devices. This will be particularly true in the case of materials that are not easily processed through photolithography.
Excimer laser generated surface nanostrucutres on PET. The periodicity of the ripples is 170 nm
In a project in collaboration with the University of Virginia and the Laser Zentrum Hannover, we are investigating the formation of laser induced “nanojets”. Nanojets appear to be self-organised structures of the order of 200 nm in diameter that are generated through the interaction of ultrafast (femtosecond) laser pulses with thin metallic materials coatings. At NCLA, we are generating computer models to analyse the molecular hydrodynamic effects at play during the formation of these structures with a view to understanding and controlling how they are formed. The structures are important in the creation of raised nanoscale features (in contrast to the normal material removal mode of operation for lasers) for biotech applications. The structures are important in the formation of novel low dimensional structures in ICT and in the fabrication and rapid prototyping of plasmonic devices.
Computer simulation of laser-generated nanojet in 20 nm Ni film on silica. The coloured areas represent regions of different crystalline phase.
Methods for producing sub-nanolitre droplets of liquid drug formulations are being investigated. Laser techniques are being used to drill specially shaped micro-holes in a thin membrane, which will be used to generate a monodisperse cloud of the droplets for pulmonary drug delivery applications. Cleanliness of nanostructured materials is obviously a key technological challenge. NCLA is currently undertaking an EI funded project to improve the removal of debris generated as a result of laser processing. In parallel with the fabrication activities, expertise and instrumentation is being developed for analysing materials on the nanoscale. Research is underway to build an instrument that will be capable of highly resolved, near-field optical studies of samples through fluorescence, Raman and time-resolved spectroscopies. Techniques are also being developed to resolve the chemical nature of the surface through chemical force microscopy (CFM). For the future, we intend to build on the foundations provided by the work described above to develop techniques for machining of features < 50 nm. These will include the utilisation of: High NA optics and fluid immersion techniques Near-field optical enhancement Multiphoton photopolymerisation Multibeam holographic machining utilising complex diffractive optical elements In addition to topographical structuring of materials, temporal control of the laser on the femtosecond scale enables, through non-equilibrium chemical dynamics, the controlled formation of multiphase surface domains on the sub-100 nm scale. Such processing will occur below the ablation threshold for the materials. We also see “cold” laser-ablative nanoparticle generation as an important technique going forward. In this technique the ability to control the temporal characteristics of the output on the femtosecond scale – a property unique to lasers – will facilitate completely non-thermal ablation of materials with subsequent agglomeration into nanoparticles from the vapour phase. This could be of great importance to the generation of nanoparticles of thermally sensitive compounds such as drugs. Furthermore, if the process is carried out in the correct atmosphere (e.g. SF₆ or a,b-cyclodextran) it is possible that an encapsulating layer can be deposited on the drug nanoparticles that can inhibit the breakdown of the drug in the stomach, allowing it to absorbed in the small intestine, thereby optimising the efficacy of the drug. These future areas are an indication of NCLA’s immediate interests in further developing its nanotechnology capability. However, it is not an exhaustive list of ways in which lasers can and will make an impact in the field.



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