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Physical Optics - Facilities
Our Physical Optics research laboratory is well equipped to provide insightful characterisation of nano-gratings:
Our integrated Nonlinear Scanning Optical Microscope/Atomic Force Microscope (NSOM/AFM) by Nanonics, is equipped with a thermal probe that performs an electrical resistance scanning thermometry under DC. The instrument allows for the correlation of topological, refractive index, and thermal conductivity measurements of the laser processed regions with sub-50 nm resolution, thus providing crucial insight on the optical and electrical properties of each nano-layers.
Upon cleaving/polishing and/or chemical etching treatment to expose a cross-section of the laser affected regions, information on the quality, uniformity and morphology of the nanogratings will be obtained by Scanning Electron Microscopy (SEM). We have access to the Zeiss EVO SEM, which is equipped to image a wide variety of non-conducting materials including transparent dielectrics. The instrument has a resolution of 3nm at 30kV, 10nm at 3kV and 20nm at 1kV. Integrated X-ray functionality allows for Energy-Dissipative X-ray Spectroscopy (EDX/EDS) and X-ray Fluorescence Spectroscopy (XRF).
In addition, a new type of microscope that uses helium ions for surface imaging and analysis was recently installed in our faculty. The Zeiss Orion helium ion microscope has similar functionality to an electron microscope, but uses a focussed beam of helium ions in place of the electrons. The larger mass and therefore smaller de Broglie wavelength of helium ions compared to electrons means that the scanning helium ions microscope suffers less from diffraction effects than a scanning electron microscope (SEM). Since helium ions can be focused into a smaller probe size and provide a much smaller sample interaction compared to electrons, the Orion generates higher resolution images with better material contrast and 5 times improved depth of focus. The high resolution arises from the use of a finely sharpened needle and a process that strips individual atoms away from the source until an atomic pyramid is created with just three atoms at the very end of the source tip. The Orion achieves a resolution of less than 0.9nm at an energy of 25-30kV and can deliver beam currents between 1fA and 25pA. Analysis of material composition can also be performed using Rutherford backscattering.
Measurement of the retardance and of the orientation of the slow axis of birefringence provides us with information about the refractive index contrast between nano-layers and their orientation relative to the writing polarisation. For this characterisation we found quantitaitive birefringence measurements an invaluable tool. The Abrio system enables label-free and non-invasive observation and quantitative imaging of birefringent structures. The core optical components of the system include a Circular Polarizer and Interference Filter (CPIF) that fits into an open position in the condenser turret, a liquid crystal universal compensator that fits into the analyzer slot of the microscope. A scientific-grade megapixel CCD camera and powerful software complete the system. Furthermore a Digital Holographic Microscope (DHM T1000) by Lyncée Tec, providing quantitative phase measurements, is used to characterise the strength and sign of the refractive index change in the laser modified region.
Copyright University of Southampton 2006