Aydin Sabouri

Printable Nanophotonic Devices via Holographic Laser Ablation.

Holography plays a significant role in applications such as data storage, light trapping, security, and biosensors. However, conventional fabrication methods remain time-consuming, costly, and complex, limiting the fabrication of holograms and their extensive use. Here, we demonstrate a single-pulse laser ablation technique to write parallel surface gratings and Fresnel zone plates. We utilized a 6 ns high-energy green laser pulse to form interference patterns to record a surface grating with 820 nm periodicity and asymmetric zone plate holograms on 4.5 nm gold-coated substrates. The holographic recording process was completed within seconds. The optical characteristics of the interference patterns have been computationally modeled, and well-ordered polychromatic diffraction was observed from the fabricated holograms. The zone plate showed a significant diffraction angle of 32° from the normal incident for the focal point. The nanosecond laser interference ablation for rapid hologram fabrication holds great potential in a vast range of optical devices.

Nanosecond pulsed laser texturing of optical diffusers

High-quality optical glass diffusers have applications in aerospace, displays, imaging systems, medical devices, and optical sensors. The development of rapid and accurate fabrication techniques is highly desirable for their production. Here, a micropatterning method for the fast fabrication of optical diffusers by means of nanosecond pulsed laser ablation is demonstrated (λ=1064 nm, power=7.02, 9.36 and 11.7 W and scanning speed=200 and 800 mm s-1). The experiments were carried out by point-to-point texturing of a glass surface in spiral shape. The laser machining parameters, the number of pulses and their power had significant effect on surface features. The optical characteristics of the diffusers were characterized at different scattering angles. The features of the microscale structures influenced average roughness from 0.8 μm to 1.97 μm. The glass diffusers scattered light at angles up to 20° and their transmission efficiency were measured up to ∼97% across the visible spectrum. The produced optical...

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.

Optical scattering from graphene foam for oil imaging/sensing

Oil spill detection is crucial, from an environmental perspective and in view of the associated economic losses. Current optical oil sensing techniques, such as underwater microscopy and light scattering methods, mainly focus on detecting the properties of particles or organisms in water and often require costly equipment and sophisticated data processing. Recent studies on graphitic foam show its extraordinary pollutant absorbing properties, with high absorption weight ratios. Here we propose to produce a graphene foam based ultra-light material that changes its optical properties on absorbing oil species. The results demonstrate clear changes in optical transmission and scattering properties of graphene foam when exposed to various oils. The effective graphene foam sorbent can be easily integrated with optical fiber systems to detect the optical property variations and also to monitor oil presence/spillages remotely. Such sensors can also be used for underground oil exploration.

Laser additive manufacturing of 3D meshes for optical applications

Selective laser melting (SLM) is a widely used additive manufacturing process that can be used for printing of intricate three dimensional (3D) metallic structures. Here we demonstrate the fabrication of titanium alloy Ti–6Al–4V alloy based 3D meshes with nodally-connected diamond like unit cells, with lattice spacing varying from 400 to 1000 microns. A Concept Laser M2 system equipped with laser that has a wavelength of 1075 nm, a constant beam spot size of 50μm and maximum power of 400W was used to manufacture the 3D meshes. These meshes act as optical shutters / directional transmitters and display interesting optical properties. A detailed optical characterisation was carried out and it was found that these structures can be optimised to act as scalable rotational shutters with high efficiencies and as angle selective transmission screens for protection against unwanted and dangerous radiations. The efficiency of fabricated lattice structures can be increased by enlarging the meshing size.

Mechanical Characterization of Torsional Micropaddles Using Atomic Force Microscopy

The reference cantilever method is shown to act as a direct and simple method for determination of torsional spring constant. It has been applied to the characterization of micropaddle structures similar to those proposed for resonant functionalized chemical sensors and resonant thermal detectors. It is shown that this method can be used as an effective procedure to characterize a key parameter of these devices and would be applicable to characterization of other similar MEMS/NEMS devices such as micromirrors. In this study, two sets of micropaddles are manufactured (beams at centre and offset by 2.5 μm) by using LPCVD silicon nitride as a substrate. The patterning is made by direct milling using focused ion beam. The torsional spring constant is achieved through micromechanical analysis via atomic force microscopy. To obtain the gradient of force curve, the area of the micropaddle is scanned and the behaviour of each pixel is investigated through an automated developed code. The experimental results are in a good agreement with theoretical results.

Room temperature thermally evaporated thin Au film on Si suitable for application of thiol self-assembled monolayers in micro/nano-electro-mechanical-systems sensors

Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness and be highly orientated. These requirements are normally achieved by either heating during Au deposition or postdeposition Au surface annealing. This paper shows that room temperature deposited gold can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. This paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 to 0.14 nm s−1 the gold surface root-mean-square roughness decreases, whereas the grain size of the deposited gold is seen to follow a step function decreasing suddenly between 0.06 and 0.10 nm s−1. The x-ray diffraction intensity of the preferentially [111] orientated gold crystallites is also seen to increase as the deposition rate increases up to a deposition rate of 0.14 nm s−1. The formation and characterization of 1-dodecanethiol on these Au coated samples is also studied using the contact angle. It is shown that by increasing the Au deposition rate, the contact angle hysteresis (CAH) decreases until it plateaus, for a deposition rate greater than 0.14 nm s−1, where the CAH is smaller than 9° which is an indication of homogeneous SAM formation, on a smooth surface.Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness and be highly orientated. These requirements are normally achieved by either heating during Au deposition or postdeposition Au surface annealing. This paper shows that room temperature deposited gold can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. This paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 to ...

Design and analysis of a rotary motion controller

Abstract This paper presents the design of a rotary motion controller based on the peritrochoid geometry of the rotary (Wankle) engine. It uses an orifice limited flow of incompressible fluid between the chambers of the Wankle-type geometry to control the rotation of the rotor. The paper develops the theory of operation and then implements the design as a Matlab model to simulate the motion control under various conditions. It is found that the time to reach stabilised motion is determined by the orifice size and fluid density. When stabilised motion is achieved, the motion dependence on material and geometry factors is determined by the orifice flow equation. The angular velocity is also found to have a square root dependence on the applied torque when in the stabilised regime.

Characterisation of nanoporous materials using Focused Ion Beam milling method

Focused Ion Beam (FIB) is generally used for machining of solid and bulk materials. However, new applications such as FIB nanotomography of nanoporous surfaces require sputtering yield characterisation. This paper presents the study of the FIB sputtering yield of Ga+ on nanoporous catalyst layers (CL) of a polymer electrolyte fuel cell (PEFC) based on analytical calculations and SEM stereo imaging experiments. It is shown that a porosity of around 50% has a significant effect (approximately 400%) on the sputtering yield of materials.