Effects of current on early stages of focused ion beam nano-machining

In this report we investigate the effects of focused ion beam machining at low doses in the range of 1015–1016 ions cm-2 for currents below 300 pA on Si(100) substrates. The effects of similar doses with currents in the range 10–300 pA were compared. The topography of resulting structures has been characterized using atomic force microscope, while crystallinity of the Si was assessed by means of Raman spectroscopy. These machining parameters allow a controllable preparation of structures either protruding from, or recessed into, the surface with nanometre precision

Three-dimensional microstructured lattices for oil sensing

Monitoring of environmental contamination, including oil pollution, is important to protect marine ecosystems. A wide range of sensors are used in the petroleum industry to measure various parameters, such as viscosity, pressure, and flow. Here, we create an optical lattice mesh structure that can be used as an oil sensor integrated with optical fiber probing. The principle of operation of the sensor was based on light scattering, where the tested medium acted as a diffuser. Three different mesh-patterned structures were analyzed by optical imaging, light transmission, and scattering in the presence of supercut, diesel, and stroke oil types. The meshes were used as a medium for different types of oils, and the optical diffusion and transmission were studied in the visible spectrum. Angle-resolved measurements were carried out to characterize the light scattering behavior from the mesh structures. Different types of oils were identified on the basis of the optical behavior of the lattice structure. The fabricated mesh structures can be used as a low-cost measurement device in oil sensing

Light scattering and optical diffusion from willemite spherulites

This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.optmat.2015.12.025Willemite is a zinc silicate mineral used in modern day pottery as a decorative feature within glazes. It is produced by controlled heat treatment of zinc oxide-containing ceramic glazes. The heat-treated glazes devitrify, producing thin nanoscale needle-like willemite crystals growing in spherulitic morphologies through branching of the needles. We show here that this resulting morphology of willemite crystals in an inorganic glass matrix has a previously unreported strong interaction with light, displaying remarkable optical diffraction patterns. Thin sections of such spherulites act as optical diffusers, enabling light beams to be spread up to 160? in width. Analysis of the interaction between the willemite spherulites and light suggests that the high density of willemite crystals in the spherulites and the length scales associated with both the thickness of the needles and the spacings between branches are together responsible for this optical diffusion behaviour

Optical scattering from graphene foam for oil imaging/sensing

This work studied a new way of sensing oil leaks using graphene foam through an optical imaging and light scattering method.</p

Femtosecond laser directed fabrication of optical diffusers

Optical diffusers are widely used in filament lamps, imaging systems, display technologies, lasers, and Light Emitting Diodes (LEDs). Here, a method for the fabrication of optical diffusers through femtosecond laser machining is demonstrated. Float glass surfaces were ablated with femtosecond laser light to form nanoscale ripples with dimensions comparable to the wavelength of visible light. These structures produce highly efficient and wide field of view diffusers. The machined patterns altered the average surface roughness, with the majority of particles in the range of a few hundred nanometers. The optical diffusion characteristic and a maximum diffusion angle of near 172° was achieved with optimum machining parameters. The transmission performance of the diffusers was measured to be ∼30% across the visible spectrum. The demonstrated technique has potential for producing low-cost large area optical devices. The process benefits from the flexibility of the laser writing method and enables the production of custom optical diffusers

Nanofabrication by means of focused ion beam

Focused ion beam (FIB) systems have been used widely in micro/nano technology due to their unique capabilities. In this fabrication technique, ions are accelerated towards the sample surfaces and substrate atoms are removed. Despite the ubiquity of this method, several problems remain unsolved and are not fully understood. In this thesis, the effects of FIB machining and its halo effects on substrate are investigated. A novel detector which can perform measurements of the current density profile of the generated beam, was successfully demonstrated. The effect of ion solid interactions for 30keV Ga FIB are investigated through atomic force microscopy (AFM) and Raman spectroscopy, for various machining parameters such as current, dwell time and pixel spacing. The FIB implanted regions were also studied for use as a hard mask in plasma etching, and was found to be suitable for high speed patterning in large area fabrication of nano-featured surfaces for metamaterials. It was observed by controlling the implantation parameters, the ultra-thin structures could be made. These structures have wide range of applications such as nano-scale resonators with application of chemical and biological sensing, membranes with nano-pores for DNA translocation and fabrication of near field optical devices

Pixel spacing effects for nanofabrication using focused ion beam

Focused ion beam (FIB) systems are widely used as a versatile tool for nanofabrication prototyping, device modification and ion beam lithography. However, there are still many unexplored effects due to the different methods that ion implantation could perform during FIB milling using Ga as a liquid metal ion source. In this report we studied the effects of pixel spacing when FIB is used for direct milling of a substrate at different milling currents for constant implantation doses. The experiment consists of FIB milling of a Si substrate at 30 keV using currents of 50 pA and 100 pA for a dose of 5×1016 ions/cm2. The dwell time was set to be 1 μs and the pixel spacing varied from 6.2 nm to 34.2 nm. The surface topographies of machined regions were examined using the atomic force microscope and the quality is described by comparing the intensities of a crystal to amorphous peak of the recorded trace from Raman spectroscopy measurements. This method was introduced by Wagner. In order to more accurately consider the sputtering yield the effect of second order deposition was neglected. It was observed that by increasing the pixel spacing the sputtering yield starts to increase and then gradually decreases for both currents. Ion implantation breaks the crystal structure and the process involves displacement of the atoms from the atomic rows which consequently increases the effect of de-channeling in ion implantation. The increase in sputtering yield could be because of the enhanced de-channeling which is due to the changes of the substrate structure which increases the collisions between implanted ions and the substrate atoms. After a threshold, the sputtering yield gradually decreases, which is due to having less implanted ions per unit of volume for each scan and therefore less applied damage. Pixel spacing at different currents and dose rates can yield different behavior due to the concentration of implanted ions per pixel dwell time. In our study the maximum concentration of implanted ions per pixel dwell time is about 5×1017 ions/cm3 and 1018 ions/cm3 for currents of 50 pA and 100 pA respectively; this concentration is lower than 1019 ions/cm3 which is the saturation point of Ga solubility in Si. It was observed that increasing the pixel spacing leads to rougher surfaces. It was also found that the quality of Si is at its highest when the pixel spacing is 14.8 nm. This is consistent with the topography results which were described by the de-channeling effect. As the de-channeling increases, the depth of implanted ions is decreased, and therefore fewer layers of substrate are damaged. In this study, we investigated the effect of FIB milling pixel spacing on substrate physical and structural changes at a dose of 5×1016 ions/cm2. We observed the sputtering yield is first increased and then decreased, which is mainly due to structural changes in substrate. The quality of substrate was also studied, revealing less damage when the pixel spacing is 14.8 nm for both currents