In-situ Spectroscopic Studies of Electronic Processes in Buckminsterfullerene Thin Films

This study attempts to develop an understanding of the electronic processes active within the solid state of C60. The emphasis throughout the work has been upon the generation and spectroscopic identification of any species, which could potentially contribute to electronic conduction in thin films of C60. The relative importance of these inter-and intramolecular processes in terms of their contribution to the electronic transport is discussed through the comparison of the properties of the molecule with the properties of the bulk solid Initially the low intensity optical properties of the C60 molecule in solution and in solid were assessed. Vibrational spectroscopy of C60 in the solid state indicated that C60 was predominantly molecular in character, however electronic spectroscopy revealed features, which were specific to the solid. These features have been attributed to an intermolecular charge transfer state, which can potentially contribute to the generation of photocarriers. Further optical analysis at higher intensities revealed that the excited state properties of molecular C60 were dominated by an extremely fast intersystem crossing rate (~1.2ns) to the first triplet state manifold. This was indicated by the rapid evolution of a triplet – triplet absorption at ~750nm in the transient absorption measurements. This molecular triplet was assigned the Raman signature 166cm-1 and was seen to play an integral part in the 2+2 –cycloaddition mechanism proposed for the photopolymerisation of C60 from solution. The molecular triplet was identified for the first time in the solid state using Raman spectroscopy and was seen to be positioned at 1466cm-1 as in solution. In addition to the molecular triplet a second excited state species positioned at 14663cm-1 was observed in the solid state. It was proposed that the species positioned at 1463cm-1 was an excited co-operative involving two or more molecules in the solid. A temperature dependence study of the excited state species in the solid indicated that the co-operative species was extremely non-linear and intrinsic to the material below the orientational phrase transition, which occurs at 249K in C60. Both the molecular triplet state and the excited states specific to the solid were seen to have active roles in the photopolymerisation and depolymerisation of C60. The Raman signature of the photopolymer of C60, seen at ~1458cm-1, completed the optical characterisation of all the photophysical states of C.60. This characterisation raised a number of questions regarding the triplet excited state and the role of excited state species in the conduction process. The electrical generation of ionic species that can contribute to the electronic transport process in solid state C60 were also examined using electron injection techniques. In solution it was seen that the C60-1 and C60-3 ionic species, which are analogues to the highly conducting and superconducting salts KC60 and K3C60 respectively, could be readily produced by the application of moderate voltages. Raman spectroscopy indicated that the C60-1 species was analogous to the aforementioned excited state co-operative observed in the solid. In the solid state structural arrangements and subsequent electronic interactions resulted in the formation of polymeric species. The formation of these polymeric species complicated the generation of anionic species and inhibited the conductivity of the solid state. The effect of this was evident from reported conductivity measurements on C60 drop cast films, and the current-voltage characteristics of vacuum evaporated C60 films incorporated into sandwich type structures. \u3c The effect of this structural rearrangements and electronic interactions was overcome for the sandwich type structure by cooling the arrangement down to 20K. At this low temperature a relatively stable, highly conducting film was produced. However the nature of the conducting species remains to be determined. It is speculated to be a reduced form of C60, which may resemble the excited states co-operative species, which is intrinsic to the material at these low temperatures It was proposed that the key to preserving the conducting species was the stabilisation of the C60 lattice against a polymeric breakdown, thereby shifting the phase transition at 249K to higher temperatures. This was done through the incorporation of neutral solvent molecules into the lattice, which then behave as ‘molecular spacers’, inhibiting the formation of polymeric bonds. The incorporation of the solvent molecules was seen to result in a change in the crystal packing with the emergence of a new phase as evident from X-ray diffraction data. This type of solvent inclusion compound is referred to as a clathrate. Alternatively structural enhancement was also achieved by thermal annealing. The annealing process also resulted in an apparent change in phase. This new phase in both techniques appears to be resistant to photodegradation indicating an enhanced lattice stability at room temperature. In the future this enhanced stability should allow a more detailed exploration of the highly conducting species for application in optical and electronic devices. A number novel thin film devices have been discussed as well as the potential of this excited material for non-linear optical applications

Assessing A National Nanotechnology Infrastructure For Enforcing Nanosafety In Consumer Food - Funding The Infrastructure

. Crucial to assessing any national risk assessment infrastructure is the development of keen insights into the funding landscape, the base skill set and expertise levels, risk prioritisation, and stakeholder determination. This paper presents an overview of the first of these criteria with respect to the Irish funding landscape for nanotechnology and nano-agri-food. It examines difficulties with policy enforcement due to a lack of clarity and varying interpretations of the EU definition of nanomaterials and how the funding landscape could potentially facilitate the necessary infrastructure, to underpin regulatory enforcement and risk assessment for nanotechnology in food. In 2008 an assessment of the potential risks associated with nanotechnologies was carried out in Ireland which resulted in a number of recommendations centred around the provision of funding. This study examines Exchequer/public investment over the last decade to develop research infrastructure and it identifies if such investment has helped enhance the enforcement of nano-food safety legislation in Ireland

Acute growth inhibition & toxicity analysis of nano-polystyrene spheres on Raphidocelis subcapitata

Micro/nano-plastics (MNPs) have been found within many environments and organisms including humans, making them a significant and growing concern. Initial research into the potential detrimental effects these MNPs both from acute and chronic exposure has been ongoing but still requires substantially more data to clarify. This research presents the response of nano-polystyrene (NPS) on Raphidocelis subcapitata, a freshwater alga, under an existing acute toxicity test along with additional analytical techniques to try identifying possible sources of toxicity. R. subcapitata cells were exposed for 72 h to a concentration range of 0–100 mg/l NPS. Growth Inhibition (GI) testing showed the R. subcapitata demonstrated statistically distinct reductions in growth over 72 h at all NPS exposure concentrations while not suffering culture collapse. By the 100 mg/l NPS exposure the R. subcapitata has suffered almost a 33.7% reduction in cell concentration after 72 h compared to control samples. Confocal imaging showed the NPS wasn\u27t permeating into the algal plasma membrane or individual organelles but agglomerated onto the algal cell wall. The agglomeration was irregular but increased in total surface area covered as NPS concentration increases. UV–Vis fluorimetry testing produced a linear response of emission intensities to algae exposed to the 0–100 mg/l range of NPS. However, comparisons of emission intensity values of algae exposed to NPS to emission intensities of pure NPS at identical concentrations showed consistent intensity reduction. This response further indicated NPS agglomerating within the media and onto the alga cells seen from confocal imaging. Finally, Raman spectroscopy on R. subcapitata attempted to distinguish the key 1001 cm−1 peak or other crucial identifier peaks of polystyrene from overall Raman spectra. This was not successful as emissions from algal component (e.g. phenylaniline) completely suppressed the signal region

Personal Food Computer: A new device for controlled-environment agriculture

Due to their interdisciplinary nature, devices for controlled-environment agriculture have the possibility to turn into ideal tools not only to conduct research on plant phenology but also to create curricula in a wide range of disciplines. Controlled-environment devices are increasing their functionalities as well as improving their accessibility. Traditionally, building one of these devices from scratch implies knowledge in fields such as mechanical engineering, digital electronics, programming, and energy management. However, the requirements of an effective controlled environment device for personal use brings new constraints and challenges. This paper presents the OpenAg Personal Food Computer (PFC); a low cost desktop size platform, which not only targets plant phenology researchers but also hobbyists, makers, and teachers from elementary to high-school levels (K-12). The PFC is completely open-source and it is intended to become a tool that can be used for collective data sharing and plant growth analysis. Thanks to its modular design, the PFC can be used in a large spectrum of activities.Comment: 9 pages, 11 figures, Accepted at the 2017 Future Technologies Conference (FTC

Interaction of Carbon Nanotubes with Sugar Complexes

The interaction of carbon nanotubes with soft organic molecules such as cyclodextrins and other saccarides has recently been shown to produce water soluble composites. Such systems offer considerable advantages over polymer based composites due to their biocompatibility and noncovalent coupling which can potentially preserve the unique properties of the tubes. The mechanism of interaction for such systems has been proposed to be dominated by hydrophobic and hydrophilic interactions along the surface of the tube. However efforts to characterise and rationalise such noncovalent interactions between the sugar-based materials and the carbon nanotubes have been slow to emerge. In this study a composite system has been formed using HiPco Single Walled Carbon Nanotubes (HCNT) and starch (extracted from rice). This composite was characterised using a range of spectroscopic techniques, which showed clear evidence of an intermolecular interaction between the HCNT and starch. The characterisation of these systems will be presented and evidence to support the notion of a noncovalent interaction is clear

Fictitious inhibitory differences: how skewness and slowing distort the estimation of stopping latencies.

This is a postprint of an article published in Psychological Science © 2013 copyright SAGE Publications. Psychological Science is available online at: http://pss.sagepub.com/content/by/yearThe stop-signal paradigm is a popular method for examining response inhibition and impulse control in psychology, cognitive neuroscience, and clinical domains because it allows the estimation of the covert latency of the stop process: the stop-signal reaction time (SSRT). In three sets of simulations, we examined to what extent SSRTs that were estimated with the popular mean and integration methods were influenced by the skew of the reaction time distribution and the gradual slowing of the response latencies. We found that the mean method consistently overestimated SSRT. The integration method tended to underestimate SSRT when response latencies gradually increased. This underestimation bias was absent when SSRTs were estimated with the integration method for smaller blocks of trials. Thus, skewing and response slowing can lead to spurious inhibitory differences. We recommend that the mean method of estimating SSRT be abandoned in favor of the integration method

Relevance for Food Safety of Applications of Nanotechnology in the Food and Feed Industry

The application of nanotechnology in the food and feed industry offers many potential benefits for both consumers and manufacturers.The ultrafine dimensions of nanoparticles, and consequently their very large surface area, enable them to function more effectively than conventional macro-scale structures in many applications. Nanotechnology is however a relatively new area of science and the benefits and risks associated with its use in the food and feed industry are not fully understood at this time.This brings with it new challenges in ensuring the safety of food and feed that has been produced with the aid of nanotechnology. This report provides an overview of current and potential applications of nanotechnology in the food industry, which may equally be applied in the feed industry. The possible risks of nanotechnology, together with the adequacy of the existing EU regulatory framework in the control of any potential risks, are also examined with a view to determining what further legislative measures, if any, may be necessary to safeguard food safet

Occupational Noise Exposure of Nightclub Bar Employees in Ireland

Due to the transposition of the EU Directive 2003/10/EC into Irish Law, the entertainment sector was obligated to comply with the requirements of the Safety, Health and Welfare at Work (General Application) Regulations 2007, Chapter 1 Part 5: Control of Noise at Work since February 2008. Compliance with the Noise Regulations was examined in 9 nightclubs in Ireland. The typical daily noise exposure of 19 bar employees was measured using 2 logging dosimeters and a Type 1 fixed position sound level meter. Physical site inspections identified nightclub noise control measures. Interviews and questionnaires were used to assess the managers and employees awareness of the noise legislation. The average bar employee daily noise exposure (LEX, 8h) was 92 dBA, almost 4 times more than the accepted legal limit. None of the venues examined were fully compliant with the requirements of the 2007 Noise Regulations, and awareness of this legislation was limited

Comparative in Vitro Cytotoxicity Study of Silver Nanoparticle on Two Mammalian Cell Lines

In this study the cytotoxic effect of commercially available silver (Ag) nanoparticle was evaluated using human dermal and cervical cancer cell lines. Prior to the cellular studies a full particle size characterisation was carried out using Dynamic Light Scattering (DLS), Transmission Electron Microscopy and Scanning Electron Microscopy in distilled water and cell culture media. The Zeta Potential (ZP)associated with the Ag nanoparticle was also determined in order to assess its stability in the solutions and its possible interaction with the media. The DLS and ZP study have suggested interaction of Ag nanoparticles with the media, which can lead to secondary toxicity. The toxic effects of Ag nanoparticles were then evaluated using different cytotoxic endpoints namely the lysosomal activity, mitochondrial metabolism, basic cellular metabolism, cellular protein content and cellular proliferative capacity. The cytotoxic effect of Ag nanoparticle was dependant on dose, exposure time and on the cell line tested. Further investigation was carried out on HeLa and HaCaT cell lines to elucidate the mechanism of its cytotoxicity. The Ag nanoparticle was noted to induce elevated levels of oxidative stress, glutathione depletion and damage to the cell membrane as found from the adenylate kinase assay and that leads to the apoptosis. Overall, significant differences were observed between the sensitivity of the two cell lines which can be understood in terms of their natural antioxidant levels

Linear Electronic and Optical Processes in Fullerene Thin Films

The electrical properties of C60 have been extensively studied in both the solid and solution phases. The vibrational spectroscopy of C60 is predominantly molecular in character. However electronic spectroscopy reveals features, which are specific to the solid. These features have been attributed to intermolecular charge transfer states. The relative importance of these inter – and intramolecular processes in terms of their contribution to the electronic transport is discussed. Cyclic voltammetry is employed to generate charged molecular species, which also contribute to the conduction process and comparisons to optical excited states species are drawn. The cyclic voltammetry was monitored in situ with vibrational spectroscopy so as to observe any shifts in the C60 spectrum due to charging. The current voltage characteristics of thin film sandwich structures fabricated by vacuum are then presented and discussed. A strongly non-linear behaviour is observed, a sharp increase in the device conductance being observed at relatively low voltages at both room temperature and at 20K. The room temperature IV curves confirm a lattice collapse upon charging. The high conductivity state is however observed to be stable at low temperature