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1. A Comprehensive Model of Nitrogen-Free Ordered Carbon Quantum Dots

Author

Boukhvalov, D. W., Osipov, V. Yu., Hogan, B. T., and Baldycheva, A.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science, Physics - Chemical Physics, Physics - Computational Physics
Abstract

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen content in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works., Comment: 32 pages, 6 figures, accepted to Nanoscale Research Letters

Published
2022
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2. Anisotropic Optical Properties of Hexagonal Boron Nitride Thin Films

Author

Kotova, L. V., Altynbaev, L. A., Zhukova, M. O., Hogan, B. T., Baldycheva, A., and Kochereshko, V. P.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Few-layer flakes of hexagonal boron nitride were prepared by ultrasonication of bulk crystals and agglomerated to form thin films. The transmission and reflection spectra of the thin films were measured. The spectral dependences of the linear and circular polarization revealed a hidden anisotropy of the films over the whole sample area which could not be explained by the anisotropy of the chaotically-oriented individual particles. Statistical analysis of optical microscopy images showed a macroscopic particle density distribution with ordering corresponding to the optical axis observed in the polarization data.

Published
2021
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3. Fluid-dispersed 2D material composites for integrated optoelectronic and photonic devices

Author

Hogan, B., Baldycheva, A., and Craciun, M.

Subjects
620
Abstract

In this thesis, fluid dispersed two-dimensional (2D) material composites with the potential for integration with optoelectronic and photonic devices are looked at. By considering the existing literature, three key areas that require further development are identified. Firstly, new materials with improved properties (faster switching, facile reconfigurability, etc.) are required to enable the development of new devices with improved performance over the state-of-the-art. Fluid dispersed 2D material composites are then synthesised by two routes: dispersing 2D materials in a nematic liquid crystal host, and using 2D materials dispersed in an organic solvent as the mesogens of a liquid crystal phase. By dispersing 2D materials such as graphene, graphene oxide, and transition metal dichalcogenides in a nematic liquid crystal, one can take advantage of the orientational reconfigurability of the liquid crystal to controllably reorient the dispersed 2D materials. The properties of the fluid composites are also investigated - namely the switching time, threshold voltage, critical temperature and dichroism properties. Switching times, threshold voltages, and critical temperatures were found to compare favourably to the pure liquid crystal independent of the dispersed 2D material. Dichroism measurements were inconclusive, but demonstrate possible suppression or enhancement of the dichroism of the pure liquid crystal under the correct 2D material doping conditions. Liquid crystals based on tungsten disulfide dispersed in organic solvents by a scalable liquid phase exfoliation method were also synthesised. The particle sizes were analysed by scanning electron microscopy, atomic force microscopy, optical microscopy, Raman spectroscopy, and dynamic light scattering. Dynamic light scattering results are particularly promising as this technique has not previously been successfully applied to the determination of sizes of high aspect ratio particles. The linear and circular dichroic properties of the tungsten disulfide liquid crystals were also considered. Particularly interesting is the emergence under applied magnetic field of circular dichroism, suggesting a helical alignment of the dispersed 2D material particles. Secondly, a new characterisation technique to analyse particle positions using Raman spectroscopy was developed. Microfluidic structures were designed to maximise the Raman signal intensity for the different Raman bands of 2D materials by numerically analysing the expected Raman intensity via a scattering matrix method. The enhancement was experimentally verified. It is then shown that integrated 2D material particles can be dynamically controlled through the application of electric field, or by the use of a laser. How the Raman signal varies as a function of the particle position within the microfluidic cavity is considered. It is demonstrated that this variation can be used, by combining numerical analysis with experimental data, to track particles first in one dimension and then in two dimensions. A discussion of how three-dimensional tracking would be achieved is also presented. Consideration of how the ii particle alignment angle could further affect the Raman signal is included. The effect of having arrays of multiple particles, rather than a single particle, is also considered. The laser focus position is shown to affect only the intensities of the Raman signal, rather than the ratios between the intensities of the different peaks. Further analysis shows how the shape and size of the particle can affect the Raman signal intensity. A technique is presented to extract the concentration of fluid dispersed particles from Raman spectra, by considering only the Raman bands of the fluid. Finally, the possible applications of 2D material fluid composites are looked at, focusing on optoelectronic and photonic devices. Highly uniform thin films are produced from tungsten disulfide liquid crystalline dispersions. These films are then transferred to a variety of substrates. The terahertz regime performance of the tungsten disulfide thin films shows great promise for their future use in terahertz generation and detection applications. Unstable Q-switched lasing operation can also be observed for thin films transferred to silver mirrors and used to form a laser cavity. Methods for how the thin films can be integrated with photonic structures such as waveguides and microring resonators are discussed. Analysis is presented for how the integration of graphene or transition metal dichalcogenides on top of the photonic structures can affect their resonance and absorption properties, depending on the film area and thickness. The future prospects for the application of these materials are also outlined.

Published
2019

10. Observations of Relativistic Electron Enhancement and Butterfly Pitch Angle Distributions at Low L (<3).

Author

O'Brien, D., Li, X., Khoo, L., Selesnick, R. S., Hogan, B., Zhao, H., Mei, Y., Hoxie, V., Baker, D. N., and Kanekal, S. G.

Subjects
MAGNETIC storms, RADIATION belts, BUTTERFLIES, RELATIVISTIC electrons, PENETRATION mechanics, ELECTRONIC probes, ANGLES
Abstract

Electrons in Earth's outer radiation belt are highly dynamic, with fluxes changing by up to orders of magnitude. The penetration of electrons from the outer belt to the inner belt is one such change observed during geomagnetic storms and was previously observed in electrons up to 1 MeV for some strong storms observed by the Van Allen Probes. We analyze pulse height analysis data from the Relativistic Electric and Proton Telescope (REPT) on the Van Allen Probes to produce electron flux measurements with lower minimum energy and significantly improved resolution compared to the standard REPT data and show that electron penetrations into the inner belt (L ≤ 2) extend to at least 1.3 MeV and penetrations into the slot region (2 < L < 2.8) extend to at least 1.5 MeV during certain geomagnetic storms. We also demonstrate that these penetrations are associated with butterfly pitch angle distributions from 1 to 1.3 MeV. Plain Language Summary: Electrons in Earth's outer radiation belt are highly dynamic with the amount and energy of them changing drastically, especially during geomagnetic storms. The penetration of electrons from the outer belt to the inner radiation belt is one such change and was previously observed in electrons with energies ≤1 MeV during some of the strongest storms during the Van Allen Probes mission. Electrons in the radiation belts also have a pitch angle that describes what portion of their motion is along or perpendicular to the direction of the magnetic field. Pitch angle distributions (PAD) are often used to gain information on the dynamics of the electrons, as unstable distributions can be caused by and indicative of wave activity that cannot always be measured directly. PADs with a minimum at 90°, called butterfly PADs, are one such unstable distribution that have previously been observed in penetrating electrons with energies ∼100–900 keV. We use instrument simulation to analyze data from the Van Allen Probes that could not previously be analyzed to show that the maximum energy of these penetrations is higher than previously observed, up to 1.3 MeV, and that these penetrations are associated with butterfly PADs at 1–1.3 MeV. Key Points: REPT PHA data can be used to produce high energy resolution flux spectra of >1 MeV electronsElectron penetrations below L = 2 during strong geomagnetic storms extend in energy up to 1.3 MeVElectron penetrations below L = 2 at energies 1–1.3 MeV are associated with butterfly pitch angle distributions [ABSTRACT FROM AUTHOR]

Published
2024
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12. A comprehensive model of nitrogen-free ordered carbon quantum dots

Author

Boukhvalov, D. W. (Danil W.), Osipov, V. Y. (Vladimir Yu.), Hogan, B. T. (Benjamin Thomas), Baldycheva, A. (Anna), Boukhvalov, D. W. (Danil W.), Osipov, V. Y. (Vladimir Yu.), Hogan, B. T. (Benjamin Thomas), and Baldycheva, A. (Anna)

Abstract

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp²-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp²-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp²-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.

Published
2023

15. Boron nitride thin films with anisotropic optical properties from microscale particle density distributions

Author

Kotova, L. V. (Lyubov V.), Altynbaev, L. A. (Linar A.), Zhukova, M. O. (Maria O.), Borodin, B. R. (Bogdan R.), Kochereshko, V. P. (Vladimir P.), Baldycheva, A. (Anna), Hogan, B. T. (Benjamin T.), Kotova, L. V. (Lyubov V.), Altynbaev, L. A. (Linar A.), Zhukova, M. O. (Maria O.), Borodin, B. R. (Bogdan R.), Kochereshko, V. P. (Vladimir P.), Baldycheva, A. (Anna), and Hogan, B. T. (Benjamin T.)

Abstract

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed statistical analysis of optical microscopy images and atomic force microscopy to reveal an ordered particle density distribution at the microscopic level corresponding to the optical axis observed in the polarisation data. The direction of the observed ordering matched the axis of anisotropy. Hence, we attribute the measured optical anisotropy of the thin films to microscopic variations in the particle density distribution.

Published
2022

16. Anisotropic optical properties of hexagonal boron nitride films

Author

Kotova, L. V. (L. V.), Altynbaev, L. A. (L. A.), Zhukova, M. O. (M. O.), Hogan, B. T. (B. T.), Baldycheva, A. (A.), Kaliteevski, M. A. (M. A.), Kochereshko, V. P. (V. P.), Kotova, L. V. (L. V.), Altynbaev, L. A. (L. A.), Zhukova, M. O. (M. O.), Hogan, B. T. (B. T.), Baldycheva, A. (A.), Kaliteevski, M. A. (M. A.), and Kochereshko, V. P. (V. P.)

Abstract

A study is performed of the transmission, reflection, and photoluminescence spectra of films of hexagonal boron nitride with the thickness of several mono-atomic layers prepared by splitting bulk samples in an ultrasonic bath. The homogeneity of the obtained samples is established via scanning electron microscopy. Spectral dependences of the linear and circular polarizations of light transmitted through a sample are measured. Studying the Stokes parameters of light transmitted through a sample allows latent anisotropy in the optical properties of boron nitride films to be identified. Statistical analysis of optical microscope images reveals a macroscopic particle density distribution with ordering that corresponds to the optical axis observed in polarization.

Published
2022

17. OC-09: Rivaroxaban compared to no treatment in early breast cancer patients (the TIP Trial): initial findings for a phase II preoperative window-of-opportunity randomised controlled trial

Author

Kirwan, C.C., primary, Castle, J., additional, Pritchard, S.A., additional, Bundred, N.J., additional, Thachill, J., additional, Harvey, J.R., additional, Roy, P.G., additional, Volleamere, A., additional, Blower, E.L., additional, Palmieri, C., additional, Hogan, B., additional, Vinayagam, R., additional, Cox, K., additional, Marshall, A., additional, Turner, L., additional, Gibson, G., additional, Scott, H., additional, and Holcombe, C., additional

Published
2022
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18. On the Challenges of Measuring Energetic Particles in the Inner Belt: A Geant4 Simulation of an Energetic Particle Detector Instrument, REPTile‐2

Author

Khoo, L.‐Y., primary, Li, X., additional, Selesnick, R. S., additional, Schiller, Q., additional, Zhang, K., additional, Zhao, H., additional, Hogan, B., additional, Cantilina, J. T., additional, Sims, A., additional, Bauch, E., additional, Valade, T., additional, Boyajian, S., additional, and Kohnert, R., additional

Published
2022
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25. Embossed topographic depolarisation maps of biological tissues with different morphological structures

Author

Ushenko, V. A. (Volodimir A.), Hogan, B. T. (Benjamin T.), Dubolazov, A. (Alexander), Grechina, A. V. (Anastasiia V.), Gorsky, M. (Mikhailo), Ushenko, A. G. (Alexander G.), Ushenko, Y. O. (Yurii O.), Bykov, A. (Alexander), and Meglinski, I. (Igor)

Abstract

Layered topographic maps of the depolarisation due to diffuse biological tissues are produced using a polarisation-holographic Mueller matrix method approach. Histological sections of myocardial tissue with a spatially structured optically anisotropic fibrillar network, and parenchymal liver tissue with a polycrystalline island structure are successfully mapped. The topography of the myocardium maps relates to the scattering multiplicity within the volume and the specific morphological structures of the biological crystallite networks. The overall depolarisation map is a convolution of the effects of these two factors. Parenchymal liver tissues behave broadly similarly, but the different biological structures present cause the degree of scattering multiplicity to increase more rapidly with increasing phase. Through statistical analysis, the dependences of the magnitudes of the first to fourth order statistical moments are determined. These moments characterise the changing distributions of the depolarisation values through the volume of biological tissues with different morphological structures. Parenchymal liver tissue depolarisation maps are characterised by larger mean and variance, and less skewness and kurtosis, compared to the distributions for the myocardium. This work demonstrates that a polarisation-holographic Mueller matrix method can be applied to the assessment of the 3D morphology of biological tissues, with applications in disease diagnosis.

Published
2021

26. 3D Mueller matrix reconstruction of the optical anisotropy parameters of myocardial histopathology tissue samples

Author

Hogan, B. T. (Benjamin T.), Ushenko, V. A. (Volodimyr A.), Syvokorovskaya, A.-V. (Anastasia-Vira), Dubolazov, A. V. (Alexander V.), Vanchulyak, O. Y. (Oleg Ya.), Ushenko, A. G. (Alexander G.), Ushenko, Y. A. (Yuriy A.), Gorsky, M. P. (Mykhailo P.), Tomka, Y. (Yuriy), Kuznetsov, S. L. (Sergey L.), Bykov, A. (Alexander), and Meglinski, I. (Igor)

Subjects
Mueller matrix, histopathology, optical diagnosis, polarized light, optical anisotropy
Abstract

Diseases affecting myocardial tissues are currently a leading cause of death in developed nations. Fast and reliable techniques for analysing and understanding how tissues are affected by disease and respond to treatment are fundamental to combating the effects of heart disease. A 3D Mueller matrix method that reconstructs the linear and circular birefringence and dichroism parameters has been developed to image the biological structures in myocardial tissues. The required optical data is gathered using a Stokes polarimeter and then processed mathematically to recover the individual optical anisotropy parameters, expanding on existing 2D Mueller matrix implementations by combining with a digital holography approach. Changes in the different optical anisotropy parameters are rationalised with reference to the general tissue structure, such that the structures can be identified from the anisotropy distributions. The first to fourth order statistical moments characterising the distribution of the parameters of the optical anisotropy of the polycrystalline structure of the partially depolarising layer of tissues in different phase sections of their volumes are investigated and analysed. The third and fourth order statistical moments are found to be the most sensitive to changes in the phase and amplitude anisotropy. The possibility of forensic medical differentiation of death in cases of acute coronary insufficiency (ACI) and coronary heart disease (CHD) is considered as a diagnostic application. The optimal phase plane (θ∗ = 0.7rad) has been found, in which excellent differentiation accuracy is achieved ACI and CHD -Ac(ΔZ₄(θ∗,ΦL,ΔL))=93.05%÷95.8%. A comparative analysis of the accuracy of the Mueller-matrix reconstruction of the parameters of the optical anisotropy of the myocardium in different phase planes (θ = 0.9rad and θ = 1.2rad), as well as the 2D Mueller-matrix reconstruction method was carried out. This work demonstrates that a 3D Mueller matrix method can be used to effectively analyse the optical anisotropy parameters of myocardial tissues with potential for definitive diagnostics in forensic medicine.

Published
2021

28. 3D Mueller matrix mapping of layered distributions of depolarisation degree for analysis of prostate adenoma and carcinoma diffuse tissues

Author

Ushenko, V. A. (Volodymyr A.), Hogan, B. T. (Benjamin T.), Dubolazov, A. (Alexander), Piavchenko, G. (Gennadii), Kuznetsov, S. L. (Sergey L.), Ushenko, A. G. (Alexander G.), Ushenko, Y. O. (Yuriy O.), Gorsky, M. (Mykhailo), Bykov, A. (Alexander), and Meglinski, I. (Igor)

Abstract

Prostate cancer is the second most common cancer globally in men, and in some countries is now the most diagnosed form of cancer. It is necessary to differentiate between benign and malignant prostate conditions to give accurate diagnoses. We aim to demonstrate the use of a 3D Mueller matrix method to allow quick and easy clinical differentiation between prostate adenoma and carcinoma tissues with different grades and Gleason scores. Histological sections of benign and malignant prostate tumours, obtained by radical prostatectomy, were investigated. We map the degree of depolarisation in the different prostate tumour tissues using a Mueller matrix polarimeter set-up, based on the superposition of a reference laser beam with the interference pattern of the sample in the image plane. The depolarisation distributions can be directly related to the morphology of the biological tissues. The dependences of the magnitude of the 1st to 4th order statistical moments of the depolarisation distribution are determined, which characterise the distributions of the depolarisation values. To determine the diagnostic potential of the method three groups of histological sections of prostate tumour biopsies were formed. The first group contained 36 adenoma tissue samples, while the second contained 36 carcinoma tissue samples of a high grade (grade 4: poorly differentiated—4 + 4 Gleason score), and the third group contained 36 carcinoma tissue samples of a low grade (grade 1: moderately differentiated—3 + 3 Gleason score). Using the calculated values of the statistical moments, tumour tissues are categorised as either adenoma or carcinoma. A high level (> 90%) accuracy of differentiation between adenoma and carcinoma samples was achieved for each group. Differentiation between the high-grade and low-grade carcinoma samples was achieved with an accuracy of 87.5%. The results demonstrate that Mueller matrix mapping of the depolarisation distribution of prostate tumour tissues can accurately differentiate between adenoma and carcinoma, and between different grades of carcinoma. This represents a first step towards the implementation of 3D Mueller matrix mapping for clinical analysis and diagnosis of prostate tumours.

Published
2021

29. The Enhanced Liver Fibrosis test maintains its diagnostic and prognostic performance in alcohol-related liver disease: a cohort study.

Author

Connoley D., Patel P.J., Hogan B., Tanwar S., Rhodes F., Parkes J., Burt A., Watkins J., Sievert W., Rosenberg W., Connoley D., Patel P.J., Hogan B., Tanwar S., Rhodes F., Parkes J., Burt A., Watkins J., Sievert W., and Rosenberg W.

Abstract

Background: Alcohol is the main cause of chronic liver disease. The Enhanced Liver Fibrosis (ELF) test is a serological biomarker for fibrosis staging in chronic liver disease, however its utility in alcohol-related liver disease warrants further validation. We assessed the diagnostic and prognostic performance of ELF in alcohol-related liver disease. Method(s): Observational cohort study assessing paired ELF and histology from 786 tertiary care patients with chronic liver disease due to alcohol (n = 81) and non-alcohol aetiologies (n = 705). Prognostic data were available for 64 alcohol patients for a median of 6.4 years. Multiple ELF cut-offs were assessed to determine diagnostic utility in moderate fibrosis and cirrhosis. Survival data were assessed to determine the ability of ELF to predict liver related events and all-cause mortality. Result(s): ELF identified cirrhosis and moderate fibrosis in alcohol-related liver disease independently of aminotransferase levels with areas under receiver operating characteristic curves of 0.895 (95% CI 0.823-0.968) and 0.923 (95% CI 0.866-0.981) respectively, which were non-inferior to non-alcohol aetiologies. The overall performance of ELF was assessed using the Obuchowski method: in alcohol = 0.934 (95% CI 0.908-0.960); non-alcohol = 0.907 (95% CI 0.895-0.919). Using ELF < 9.8 to exclude and 10.5 to diagnose cirrhosis, 87.7% of alcohol cases could have avoided biopsy, with sensitivity of 91% and specificity of 85%. A one-unit increase in ELF was associated with a 2.6 (95% CI 1.55-4.31, p < 0.001) fold greater odds of cirrhosis at baseline and 2.0-fold greater risk of a liver related event within 6 years (95% CI 1.39-2.99, p < 0.001). Conclusion(s): ELF accurately stages liver fibrosis independently of transaminase elevations as a marker of inflammation and has superior prognostic performance to biopsy in alcohol-related liver disease.Copyright © 2021, The Author(s).

Published
2021

30. Anisotropy of optical properties of hexagonal boron nitride films

Author

Kotova, L. V. (L. V.), Altynbaev, L. A. (L. A.), Zhukova, M. O. (M. O.), Hogan, B. T. (B. T.), Baldycheva, A. (A.), Kurbatov, D. M. (D. M.), Kochereshko, V. P. (V. P.), Kotova, L. V. (L. V.), Altynbaev, L. A. (L. A.), Zhukova, M. O. (M. O.), Hogan, B. T. (B. T.), Baldycheva, A. (A.), Kurbatov, D. M. (D. M.), and Kochereshko, V. P. (V. P.)

Abstract

Thin hexagonal boron nitride films with a thickness of several monoatomic layers have been manufactured by splitting of bulk samples in an ultrasonic bath. The transmission, reflection, and photoluminescence spectra of such films are studied. The spectral dependences of linear and circular polarization of light passing through the sample are measured. Scanning electron microscopy investigation demonstrates homogeneity of the obtained samples. However, investigation of Stokes parameters of light passing through the sample makes it possible to reveal hidden anisotropy of optical properties of these films.

Published
2021

39. High-quality green-emitting nanodiamonds fabricated by HPHT sintering of polycrystalline shockwave diamonds

Author

Osipov, V. Y. (Vladimir Yu.), Shakhov, F. M. (Fedor M.), Bogdanov, K. V. (Kirill V.), Takai, K. (Kazuyuki), Hayashi, T. (Takuya), Treussart, F. (François), Baldycheva, A. (Anna), Hogan, B. T. (Benjamin T.), and Jentgens, C. (Christian)

Abstract

We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3–4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

Published
2020

40. Transmission properties of van der Waals materials for terahertz time-domain spectroscopy applications

Author

Shaban, P. (Polina), Oparin, E. (Egor), Zhukova, M. (Maria), Hogan, B. (Benjamin), Kovalska, E. (Evgeniya), Baldycheva, A. (Anna), Tsypkin, A. (Anton), Shaban, P. (Polina), Oparin, E. (Egor), Zhukova, M. (Maria), Hogan, B. (Benjamin), Kovalska, E. (Evgeniya), Baldycheva, A. (Anna), and Tsypkin, A. (Anton)

Abstract

This work contains results from studying the electro-optical properties of bulk and few-layered Van der Waals materials including intercalated graphene, phosphorene, and tungsten disulfide thin films. Different production methods and substrates are considered. The objective of the research is to assess the relevance of application of these materials in terahertz (THz) time-domain spectroscopy (TDS). Therefore, the study is conducted in the visible, NIR (near-infrared) and THz frequency ranges as the most critically in need of research when searching for effective materials for TDS.

Published
2020

41. Spatial tracking of individual fluid dispersed particles via Raman spectroscopy

Author

Hogan, B. T. (Benjamin Thomas), O’Dowd, J. (Jennifer), Ruedas, J. F. (Joaquin Faneca), Baranov, A. (Alexander), Baldycheva, A. (Anna), Hogan, B. T. (Benjamin Thomas), O’Dowd, J. (Jennifer), Ruedas, J. F. (Joaquin Faneca), Baranov, A. (Alexander), and Baldycheva, A. (Anna)

Abstract

We demonstrate a method for the spatial tracking of individual particles, dispersed in a fluid host, via Raman spectroscopy. The effect of moving a particle upon the intensity of different bands within its Raman spectrum is first established computationally through a scattering matrix method. By comparing an experimental spectrum to the computational analysis, we show that the position of the particle can be obtained. We apply this method to the specific cases of molybdenum disulfide and graphene oxide particles, dispersed in a nematic liquid crystal, and contained within a microfluidic channel. By considering the ratio and difference between the intensities of the two Raman bands of molybdenum disulfide and graphene oxide, we demonstrate that an accurate position can be obtained in two dimensions.

Published
2020

47. Using platform signals for distinguishing discourses: The case of men's rights and men's liberation on Reddit

Author

Laviolette, J and Hogan, B

Abstract

Reddit’s men’s rights community (/r/MensRights) has been criticized for the promotion of misogynistic language, toxic masculinity and discourses that reinforce alt-right ideologies. Conversely, the men’s liberation (/r/MensLib) community integrates inclusive politics, intersectionality and masculinity within a broad umbrella of self-reflection that suggests toxic masculinity harms men as well as women. We use machine learning text classifiers, keyword frequencies, and qualitative approaches first to distinguish these two subreddits, and second to interpret the differences ideologically rather than topically. We further integrate platform metadata (referred to as ‘platform signals’) to distinguish the subreddits. These signals help us understand how similar terms can be used to arrive at different interpretations of gender and discrimination. Where /r/MensLib tends to see masculinity as an adjective and women as peers, /r/MensRights views being a man as an essential quality, men as the target of discrimination, and women as sources of personalized grievances.

Published
2019

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