Metal halide perovskites are a leading contender to disrupt not only terrestrial photovoltaic (PV) markets, but also the proliferating space PV markets. This is due to their impressive power conversion efficiencies, potentially low cost, and adaptability to flexible architectures. Here we assess the stability of three perovskite systems; a mixed Pb-Sn perovskite, and two mixed cation-triple halide systems. In all cases high tolerance to proton irradiation was observed. However, in the case of the mixed Pb-Sn system, irreversible decomposition of the perovskite along with the increased prevalence of defects was observed with thermal cycling. In the case of the mixed cation triple halides remarkable stability was demonstrated, in addition to self-healing, the results of which will be described here.
Fluorescent nanodiamonds (NDs) are new and emerging nanomaterials that have potential to be used as fluorescence imaging agents and also as a highly versatile platform for the controlled functionalization and delivery of a wide spectrum of therapeutic agents. We will utilize two experimental methods, TIRF, a relatively simple method based on total internal reflection fluorescence and SPRF, fluorescence enhanced by resonance coupling with surface plasmons. We estimate that the SPRF method will be 100 times sensitive than currently available similar detectors based on detectors. The ultimate goal of this research is to develop microarray platforms that could be used for sensitive, fast and inexpensive gene sequencing and protein detection.
We report the direct etching of Al2O3 and SiO2 using 900-keV Au+ ions. 2000-mesh Cu grids were employed as masks using two different configurations: (1) the Cu mesh was placed on top of each insulator separately and independent irradiations were performed, and (2) the Al2O3 and SiO2 substrates were positioned in an edge-to-edge configuration with a single Cu grid providing a common mask to both insulators. Scanning electron microscopy (SEM) analysis revealed quite different patterns resulting from the two irradiation configurations. While the irradiation using individual masks resulted in mirror-image patterns of the Cu mask in the substrates, the use of a common mask led to single line structures approximately normal to the edges of the substrates. The role of charge buildup and sputtering in relation to relative dielectric properties of the substrates and close proximity of the samples during irradiation is discussed.
High Energy Focused Ion Beam (HEFIB) direct writing is proving to be an attractive and powerful maskless lithography technique for production of high aspect ratio 3-D microstructures in polymer resists and semiconductors. HEFIB with Proton beam (P-beam writing) offers several unique advantages for microfabrication applications: (a) the focused beam is scanned directly across the sample (no mask), (b) the range of the beam in the sample is well defined with minimal lateral straggling than any other techniques, (c) use of different energies allows different exposure depths, (d) complex shapes are possible and (e) patterns can be made within short exposure time. These characteristics allow P-beam writing to be applied in several areas of microfabrication including (a) rapid (and cheaper) prototyping of 3-D microstructures, (b) custom built structures for basic research, (c) mask production and (d) stamp and mold manufacturing. Recently we have implemented high energy P-beam direct writing with a nuclear microprobe at the Louisiana Accelerator Center (LAC). We are presenting some of the modular structures illustrating the capabilities of this maskless micromachining technique and possible application into Micro-Electro-Mechanical Systems (MEMS) devices.
Ion beam implantation using 2.4 MeV H+ ions was used to fabricate long period gratings in multimode optical fibres. The Bragg peak from the ion beam was located in the centre of the core of the fiber. The ion beam was implanted through a mask on the fibre with a period of 1.1 mm to produce a periodic a refractive index modulation, of up to 1%, along the axis of the core of the fibre. The mode scrambling, from the established fundamental mode, was monitored in situ as the implantation was done by observation of the light transmitted through the fibre. This paper describes the experimental method used to achieve this and describes the results. Significant mode scrambling was observed to occur when 3 grating periods were written into the fibre.
We describe a novel technique for the fabrication of nanoscale structures, based on the development of localized chemical modification caused in a PMMA resist by the implantation of single ions. The implantation of 2 MeV He ions through a thin layer of PMMA into an underlying silicon substrate causes latent damage in the resist. On development of the resist we demonstrate the formation within the PMMA layer of clearly defined etched holes, of typical diameter 30 nm, observed using an atomic force microscope employing a carbon nanotube SPM probe in intermittent-contact mode. This technique has significant potential applications. Used purely to register the passage of an ion, it may be a useful verification of the impact sites in an ion-beam modification process operating at the single-ion level. Furthermore, making use of the hole in the PMMA layer to perform subsequent fabrication steps, it may be applied to the fabrication of self-aligned structures in which surface features are fabricated directly above regions of an underlying substrate that are locally doped by the implanted ion. Our primary interest in single-ion resists relates to the development of a solid-state quantum computer based on an array of 31P atoms (which act as qubits) embedded with nanoscale precision in a silicon matrix. One proposal for the fabrication of such an array is by phosphorous-ion implantation. A single-ion resist would permit an accurate verification of 31P implantation sites. Subsequent metalisation of the latent damage may allow the fabrication of self-aligned metal gates above buried phosphorous atoms.
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