Findings of an experimental study in a rabbit model on posterior capsule opacification after implantation of hydrophobic acrylic and hydrophilic acrylic intraocular lenses

Nikolaos Trakos1, Elli Ioachim2, Elena Tsanou2, Miltiadis Aspiotis1, Konstantinos Psilas1, Chris Kalogeropoulos11University Eye Clinic of Ioannina, Ioannina, Greece; 2Pathology Department, University of Ioannina, Ioannina, GreecePurpose: Study on cell growth on the posterior capsule after implantation of hydrophobic acrylic (Acrysof SA 60 AT) and hydrophilic acrylic (Akreos Disc) intraocular lenses (IOL) in a rabbit model and comparison of posterior capsule opacification (PCO).Methods: Phacoemulsification was performed in 22 rabbit eyes, and two different IOL types (Acrysof SA60 AT and Akreos Disc) were implanted. These IOLs had the same optic geometry (square edged) but different material and design. Central PCO (CPCO), peripheral PCO (PPCO), Sommering’s ring (SR) formation, type of growth, extension of PCO, cell type, inhibition, and fibrosis were evaluated three weeks after surgery. Histological sections of each globe were prepared to document the evaluation of PCO.Results: No statistically significant difference was observed between a hydrophobic acrylic IOL and a hydrophilic acrylic IOL in relation to the CPCO, PPCO, type of growth, extension, cell type, inhibition, and fibrosis. Statistically significant difference was observed in relation to the formation of SR with Acrysof SA 60 AT group presenting more SR than Akreos Disc group.Conclusion: PCO was not influenced by the material of the IOL or the design of the haptics of the IOLs we studied.Keywords: posterior capsule opacification, intraocular lenses, rabbit mode

Graphene-based fiber polarizer with PVB-enhanced light interaction

Graphene is a two-dimensional material which, as a result of its excellent photonic properties, has been investigated for a wide range of optical applications. In this paper, we propose and fabricate a commercial grade broadband graphene-based fiber polarizer using a low loss side-polished optical fiber platform. A high index polyvinyl butyral layer is used to enhance the light-graphene interaction of the evanescent field of the core guided mode to simultaneously obtain a high extinction ratio ~37.5 dB with a low device loss ~1 dB. Characterization of the optical properties reveals that the polarizer retains low transmission losses and high extinction ratios across an extended telecoms band. The results demonstrate that side-polished fibers are a useful platform for leveraging the unique properties of low-dimensional materials in a robust and compact device geometry

Chemical vapor deposition and Van der Waals epitaxy for wafer-scale emerging 2D transition metal di-chalcogenides

Transition metal di-chalcogenides (TMDCs) such as MoS2, MoSe2, WS2 and WSe2 have become promising complimentary materials to graphene sharing many of its attributes. They may however offer properties that are unattainable in graphene, in particular TMDCs offer a bandgap tunable through both composition and number of layers. This has led to use of TMDCs in applications such as transistors, photodetectors, electroluminescent and bio-sensing devices. The current challenge in this emerging research field is to provide a reliable process to fabricate large area of atomically thin 2D TMDCs on the desired substrate. Chemical vapor deposition (CVD) technology has the advantage of offering conformal, scalable, and controllable thin film growth on a variety of different substrates. In addition, Van der Waals epitaxy could provide the vapor phase epitaxy of these TMDCs on the substrates with mismatched lattice constants. In this talk we describe our recent development in TMDCs materials using CVD technology and Van der Waals epitaxy and discuss their properties and potential applications

Emerging CVD technology for functional chalcogenide materials

Chalcogenide materials, formed from metallic alloys of S, Se, and Te, have received considerable attention for applications in optoelectronic devices over the past two decades in part due to their unique properties such as high infrared transparency, strong photosensitivity, large nonlinearity, capability of high rare-earth doping, and ability to readily change phase. Thin amorphous chalcogenide films are of particular interest because their diverse active properties are easily exploited in integrated planar optical circuits, as well as for memory and other optoelectronic applications. More recently, transition metal dichalcogenides (TMDCs), two-dimensional (2D) layered materials, such as MoS2, MoSe2, WS2, and WSe2 have become a noteworthy complimentary material to field. Sharing many of the properties of graphene they also offer properties that are unattainable in 2D graphene including a tunable bandgap; easily modified through both composition and the number of layers. This has led to use of TMDCs in applications such as transistors, photodetectors, electroluminescent and bio-sensing devices. In this talk we describe our development of functional chalcogenide materials by the chemical vapour deposition technology and discuss their potential applications

Two dimensional materials synthesis for electronic and optoelectronic applications

Atomically thin materials offer unique optical, electronic and physical properties due to quantum connement effects. Graphene has been the material that has primed the extensive research interest in the field. The lack of an energy bandgap in graphene helped to expand the research of 2D materials beyond graphene, in search for application tailored properties. The strongest overall candidate for electronic applications has since been Transition Metal Dichalcogenides (TMDCs). The metal-chalcogen bonds are strong covalent bonds that form stacked layers together by weak Van der Waals forces and can hence be easily separated to form individual layers. The significance of this ability lies in the fact that although TMDCs have an indirect bandgap in their bulk form, they transition to a direct bandgap in single layer form. This property is important for optoelectronic applications as it results in an enhanced photoluminescence quantum yield. A monolayer of such a material offers very high effective mobility that would otherwise require three times thicker single crystal silicon layer to reach. Transistors made of TMDCs have also been shown to reach the thermal transport limit achieving a subthreshold swing of as low as 60 mV/dec and on/off ratios of 108. Those attributes make TMDCs an ideal candidate for next generation electronic and optoelectronic applications potentially replacing current material technologies. Due to the weak Van der Waals forces between layers one of the first methods explored to obtain single layers of graphene and TMDCs has been exfoliation and transfer techniques involving tape, chemical or mechanical methods. Those techniques viii have been providing very high quality single crystal layers with excellent electronic and optoelectronic properties. A direct drawback of these methods is the lack of scalability. For this reason, there has been a collective research effort in the community towards the development of direct growth methods for TMDCs that are scalable and can be used in traditional top-down fabrication processes. Scalable techniques have recently included RF sputtering, CVD and ALD techniques that use solid, metal halide or organic precursors. Most of those studies rely on the transfer of the TMDC after it has been grown in order to form electronic devices such as field effect transistors. The main reason for this is that during the growth process the dielectric integrity of the underlying SiO2, on which the films are commonly grown, is compromised. This work aims to tackle the scalability of 2D materials by devising methods directly applicable to wafer scale production. In particular, for TMDCs a combination of Atomic Layer deposition and Thermal reaction is used to form a few layer MoS2 on a SiO2 substrate without the need for transfer to perform as an FET device. Using ALD, a thin layer of MoO3 is first formed on the SiO2 and then annealed in a CVD reactor in presence of H2S. As the wafers are already coated with MoO3 during the high temperature anneal in H2S the SiO2 quality is preserved removing the need to transfer to a fresh substrate and therefore enabling the practical upscale of the technology. This thesis discusses the methods developed by the author for growing 2D films of graphene, MoS2 and HfS2. The results from the characterization of the films at a variety of growing conditions provide a comprehensive guide to optimizing the film growth for optoelectronic and electronic applications. Moreover new fabrication protocols have been designed in order to accommodate the fragile nature of 2D materials while making high performance devices. This work provides an array of devices as performance demonstrators such as FET, fiber modulator, mechanochromic metamaterial and graphene photodetector. The most significant achievement of this work is the design of the full fabrication protocol for high performance FET devices and the resulting performance of these devices. It was demonstrated that a subthreshold slope of under 180 mV/dec and an on/off ratio of more than 104 can be achieved with directly grown transistors in a readily scalable process

Advanced CVD technology for emerging transition metal di-chalcogenides

Transition metal di-chalcogenides (TMDCs) such as MoS2, MoSe2, WS2 and WSe2 have become a noteworthy complimentary material to graphene sharing many of its properties. They may however offer properties that are unattainable in graphene since TMDCs offer a tunable bandgap through both composition and number of layers. This has led to use of TMDCs in applications such as transistors, photodetectors, electroluminescent and bio-sensing devices. In addition, chalcogenide thin films such as CuInGaSe2 and CdTe have been commercialized for photovoltaic application, however the search for low cost, non-toxic and earth abundant high efficiency absorbing materials remains under investigation. Sn-S, a p-type semiconductor with a band gap of ~1.3 eV and the sort after aforementioned properties, has attracted great interest recently. Chemical vapour deposition (CVD) technology has the advantage of offering conformal, scalable, and controllable thin film growth on a variety of different substrates. In this talk we describe our recent development in TMDCs materials using CVD technology and discuss their potential applications

Wafer scale pre-patterned ALD MoS2 FETs

Currently, 2D Transition metal dichalcogenides are emerging as the next generation semiconductor materials as they offer a direct bangap and therefore high on/off ratios, relatively high mobility, short-channel effects immunity, and near ideal subthreshold swings.In this work we present a simplified wafer scale processing of MoS2 transistors that alleviates lithography and etching issues. The first step of the process is to grow a 90 nm dry thermal oxide on 6 inch wafers. The wafers are then immersed in a HCl solution to ensure the hydrophilicity of the surface. Atomic layer deposition (ALD) is used to grow MoO3 on the wafer. For this we use the metal organic precursor Bis(tert-butylimido)bis(dimethylamido)Mo and Ozone at 250 C. The wafers are then patterned in a conventional lithography process using the positive tone resist S1813. After the resist development the wafers are rinsed in deionised water and washed thoroughly. This step not only removes the remaining developer but also etches away the exposed MoO3. The photoresist is then removed by Acetone and finally rinsed with IPA. The wafers are further cleaned and oxidised in an asher by O2 plasma.The patterned MoO3 wafers are then transferred in a furnace where they are annealed in H2S in two steps and at a low pressure. The first step is at substantially lower temperature than the melting point of MoO3 at 250C to eliminate vaporization of the material and for 1h whereas the second step is at 900C for 10 minutes to improve the crystallinity of the material. The pressure during the annealing is set at 4 Torr. After the H2S treatment the films are converted to MoS2 and since they are pre - patterned they are ready for metal deposition.For metal contacts we use sputtering of 5nm of Ti and 150 nm of Au on top. For the top gate dielectric we use 40nm ALD deposited HfO2 which is deposited at the entire wafer. After the deposition of the top dielectric we open metal window contacts to the metal pads of the transistors using traditional lithography and a 20:1 BHF solution. Finally, top metal gate is deposited by sputtering and patterned by lift-off.The novelty of this process lies within the pattern formation on MoO3 early in the process. This eliminates the issues involved with cross-linking of photoresist during MoS2 etching therefore simplifying and de-risking photoresist removal and reducing contamination. More importantly though as the patterns have already been formed before the high temperature conversion to MoS2 the layer stress has been released prior to the conversion. This results in higher quality films, free of pin holes, with fewer defects and of higher crystallinity, yielding superior electrical properties.Devices are currently at the electrical characterisation stage from which results will reveal the performance of the MoS2 FETs made by this method. Ultimate goal of this work is to create a robust wafer scale process with high quality transistors for biosensing applications