Candidate Materials as Gain Media in Organic, Triplet-Based, Room-Temperature masers Targeting the ISM Bands

While lasers have enjoyed greater popularity, masers—which emit coherent radiation in the microwave spectrum—are also of critical importance to a variety of applications. Recently, an organic gain medium has been developed, which allows emission at room temperature without the traditional encumbrances of cryogenic cooling or an externally applied magnetic field, at vastly improved power efficiency. This discovery opens up new avenues for applications that were previously impractical. However, further investigation is still required for frequency tuning of the device, through the selection of alternate gain media beyond the original choice of pentacene-doped p-terphenyl and some linear acenes similar to the pentacene prototype. This chapter outlines some of the essential criteria necessary to achieve masing with an organic semiconductor gain medium, including zero-field splitting (ZFS), triplet sublevel division, and metastable population inversion. Three tables of possible candidate materials are presented based on this roster of criteria, particularly targeting emission in one of the industrial, scientific, and medical (ISM) bands. A selection of preferred guest molecules is recommended for in-situ testing as room-temperature masers gain media candidates

Solution-processed LiF for work function tuning in electrode bilayers

Although ambient processing is the key to low-cost organic solar cell production, high vacuum thermal evaporation of LiF is often a limiting step, motivating the exploration of solution processing of LiF as an alternative electrode interlayer. Sub-monolayer films are realized with the assistance of polymeric micelle reactors that enable LiF particle deposition with controlled nanoscale surface coverage. Scanning Kelvin probe reveals a work function tunable with nanoparticle coverage, with higher values than that of bare tin-doped indium oxide

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Cathode interface structure in organic semiconductor devices

As organic semiconductor technology matures, enhancement requires understanding/engineering of the cathode/organic interface. In this work, using X-ray photoelectron spectroscopy (XPS) and common materials for organic light emitting diodes (OLEDs), the expected interfacial structure in conventionally fabricated devices has been described and some simple predictive methods developed. The buried electrode/active layer interface was examined by analysing: (1) both sides of the interface in conventionally fabricated devices under high vacuum with the unique peel-off technique, and (2) monolayers of one material grown atop another. Connections were drawn between the interfacial structures in devices, those observed during traditional surface science investigations, and the device behaviour. A critical insight is that no one metal or metal/interlayer combination may be used as a universal cathode. Rather, certain criteria for interfacial structure and stability must be confirmed to ensure adequate performance. This can be determined through simple material property information, such as lattice constants, or with inorganic analogues for organic molecules. For combinations of metals and 8-tris(hydroxyquinoline aluminum) (Alq 3 ), interfacial reactions can be predicted by assuming Al2 O 3 as an inorganic analogue. Using this analogue, molecular fragmentation may be described as a simple metal-exchange oxidation-reduction reaction. As cathode complexity increases, such simple descriptions lose validity. This work shows that all three components (organic/LiF/metal) are required to adequately describe the interfacial structure of bi-layer cathodes. The major conclusions regarding the role of LiF are: (1) that 5-10Å LiF changes the cathode oxidation behaviour, predicted by the lattice mismatch of the interlayer with the metal. Oxidation is suppressed for Al, which is well matched to LiF; for Mg, which has poor matching, preferential formation of carbonates occurs. Device behaviour is related to the metal oxidation, such that Al/LiF cathodes are superior to Mg/LiF ones. (2) that near the interface, LiF forms charge transfer complexes with electron transporting molecules. (3) that the cathode should be considered a metal-insulator-metal capacitor with the organic layer acting as the bottom electrode. The usable thickness of LiF is dependent on the conductivity of the layer. These insights indicate some of the conditions necessary for adequate device performance and longevity, useful for future device optimization.Ph.D

LiF Nanoparticles Enhance Targeted Degradation of Organic Material under Low Dose X-ray Irradiation

The targeted irradiation of structures by X-rays has seen application in a variety of fields. Herein, the use of 5–10 nm LiF nanoparticles to locally enhance the degradation of an organic thin film, diindenoperylene, under hard X-ray irradiation, at relatively low ionizing radiation doses, is shown. X-ray reflectivity analysis indicated that the film thickness increased 12.04 Å in air and 11.34 Å in a helium atmosphere, under a radiation dose of ∼65 J/cm2 for 3 h illumination with a bi-layer structure that contained submonolayer coverage of thermally evaporated LiF. This was accompanied by significant modification of the surface topography for the organic film, which initially formed large flat islands. Accelerated aging experiments suggested that localized heating was not a major mechanism for the observed changes, suggesting a photochemical mechanism due to the formation of reactive species from LiF under irradiation. As LiF has a tendency to form active defects under radiation across the energy spectrum, this could could open a new direction to explore the efficacy of LiF or similar optically active materials that form electrically active defects under irradiation in various applications that could benefit from enhanced activity, such as radiography or targeted X-ray irradiation therapies

Solution processed LiF anode modification for polymer solar cells

The indium-tin-oxide/active layer interface is critical to the performance of organic solar cell devices. In this study, submonolayer films of LiF nanoparticles are deposited on the electrode surface with the assistance of polymeric micelle reactors, with controlled nanoscale surface coverage. Incorporation of the solution-processed bi-layer electrodes into a conventional poly(3-hexyl-thiophene): [6,6]-phenyl C61-butyric acid methyl ester device shows significant improvement in device performance, especially when used in combination with a poly(3,4-ethylenedioxythiophene: poly(styrene sulfonate) layer. The nearly 5x improvement in the short circuit current and decrease in the contact resistance is mostly likely related to the increase in surface work function from the use of LiF nanoparticles. The results strongly indicate that engineering of the interfaces is a useful tool for future device optimization