472 research outputs found
Antimonene: a tuneable post-graphene material for advanced applications in optoelectronics, catalysis, energy and biomedicine.
The post-graphene era is undoubtedly marked by two-dimensional (2D) materials such as quasi-van der Waals antimonene. This emerging material has a fascinating structure, exhibits a pronounced chemical reactivity (in contrast to graphene), possesses outstanding electronic properties and has been postulated for a plethora of applications. However, chemistry and physics of antimonene remain in their infancy, but fortunately recent discoveries have shed light on its unmatched allotropy and rich chemical reactivity offering a myriad of unprecedented possibilities in terms of fundamental studies and applications. Indeed, antimonene can be considered as one of the most appealing post-graphene 2D materials reported to date, since its structure, properties and applications can be chemically engineered from the ground up (both using top-down and bottom-up approaches), offering an unprecedented level of control in the realm of 2D materials. In this review, we provide an in-depth analysis of the recent advances in the synthesis, characterization and applications of antimonene. First, we start with a general introduction to antimonene, and then we focus on its general chemistry, physical properties, characterization and synthetic strategies. We then perform a comprehensive study on the allotropy, the phase transition mechanisms, the oxidation behaviour and chemical functionalization. From a technological point of view, we further discuss the applications recently reported for antimonene in the fields of optoelectronics, catalysis, energy storage, cancer therapy and sensing. Finally, important aspects such as new scalable methodologies or the promising perspectives in biomedicine are discussed, pinpointing antimonene as a cutting-edge material of broad interest for researchers working in chemistry, physics, materials science and biomedicine
Topographic control of order-disorder phase transitions in a quasi-2D granular system
The focus of current research in two-dimensional phase transitions has shifted
towards non-equilibrium systems such as active matter and fluid dynamics.
However, unlike in equilibrium systems, we lack a complete framework to
describe their behaviour. Although previous work has shown that some basic
concepts from statistical mechanics can be applied to non-equilibrium systems,
the extent to which they can be applied remains unclear.
One intriguing problem in equilibrium systems is the two-dimensional hard-disc
liquid-to-crystal phase transition. The nature of this phase transition differs
from that in three-dimensions and was, until recently, a matter of much debate.
Extending this debate, two-dimensional granular systems have also been studied
to investigate the applicability of hard-disc model descriptions to non-equilibrium
systems. Granular systems are convenient for manipulation and offer easy
observations at the particle level and therefore represent an ideal test case for
these investigations.
In this thesis, I present an investigation of the order-disorder phase transition in
a 2D driven granular system. Previous research has shown that these systems
undergo a continuous two-step phase transition. We explore a mechanism for
changing the nature of this transition from continuous to first-order by introducing
a triangular lattice of dimples milled into the surface. The change in phase
transition behaviour, for the system we focus on for much of this thesis, enables
further study of other behaviours from equilibrium physics, such as hysteresis,
surface tension and wetting.
The phase behaviour of our system was studied on these dimpled surfaces for
three different spacings. One of these spacings produced first-order like behaviour
and was focussed on for much of the thesis.
We also investigated how changing the geometry and the inelasticity at the
boundary affects the wetting of different phases. This allowed us to spatially
control the coexisting liquid and solid phases. Our findings showed behaviour
similar to wetting in equilibrium systems. Furthermore, I present a quantitative
study confirming the first-order nature of the phase transition in this system.
While doing this, I demonstrate evidence of coexistence, hysteresis and surface
tension which are all ideas that are commonly associated with first-order phase
transitions in equilibrium systems.
Inspired by the hydrophobic effect observed in equilibrium systems, a similar
effect called the orderphobic effect was recently proposed. This is where disorder inducing
intruders placed in an ordered solid experience a force of attraction. The
authors suggest that this effect should be general to any system that experiences a
first-order order-disorder phase transition. Since our results showed the necessary
pre-prerequisites for observing such an effect, we investigated whether such a
force could be observed. Although our attempts to reproduce this effect in our
non-equilibrium system were inconclusive, we believe the results are promising
for future investigation.
Finally, I present a more detailed investigation into how changing the spacing of
the dimpled lattice changes the nature of the transitions for a broader range of
spacings. Our results indicate that different phases form depending on the lattice
spacing. We also discuss how the equilibrium ideas of stability can be applied to
the system using spacings that display a combination of different phases
Scanning Probe Microscopy Studies of Petroleum Chemistry: Substrate-Dependent Catalytic Properties of MoS2 and Automating Scanning Probe Microscopy with Machine Learning
With the growth of the population, society’s energy demands are mostly reliant on petroleum products that come from the refining of crude oil. Most of these refining reactions have been developed through averaging spectroscopic techniques, but scientists do not know exactly what is happening in these processes at the nano and atomic levels. This information is crucial when designing an efficient refining process that produces petroleum products that emit fewer harmful gases when combusting. Scanning probe microscopy techniques have become a powerful tool to look into the chemical structures found in petroleum products, to understand catalytic reactions in refining processes, and to find new non-combustible uses for these products. In this dissertation, I show how scanning probe microscopy (SPM) techniques, especially non-contact atomic force microscopy (NC-AFM) can provide an atomic-level understanding of the chemical structures and active catalytic sites that play a role in these refining processes. First, I studied hydrodesulfurization reactions that use molybdenum disulfide as a main catalyst to explore the effect of layer thickness, strain, and underlying substrates on its electronic and catalytic properties. Here, I present the first NC-AFM experiments investigating the active catalytic sites of molybdenum disulfide on industrially relevant substrates. Through these experiments, I found how NC-AFM techniques on insulators need to be improved to achieve high-resolution images that are comparable to those collected on metal substrates. Second, I created Auto-HR-AFM, a machine-learning script that collects optimal high-resolution NC-AFM images. Auto-HR-AFM is a modular and open-source script that provides an initial framework for a fully automated SPM. Expanding on this framework will widen the use of scanning probe microscopy techniques to non-experts and the automation will increase the time the system is kept running to collect large optimal datasets. Ultimately, these studies will broaden the use of high-resolution SPM techniques and help create more efficient catalysts and refining processes to produce cleaner and more efficient petroleum products
Fundamental Study of Photoluminescence-Shape Relationship of Fluorescent Nanodiamonds using Machine Learning Assisted Correlative Transmission Electron Microscopy and Photoluminescence Microscopy Method
Luminescent nanoparticles have shown wide applications ranging from lighting, display, sensors, and biomedical diagnostics and imaging. Among these, fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) color centers are posed as emerging materials particularly in biomedical and biological imaging applications due to their room-temperature emission, excellent photo- and chemical- stability, high bio-compatibility, and versatile functionalization potentials. The shape variation of nanoparticles has a decisive influence on their fluorescence. However, current relative studies are limited by the lack of reliable statistical analysis of nanoparticle shape and the difficulty of achieving a precise correlation between shape/structure and optical measurements of large numbers of individual nanoparticles. Therefore, new methods are urgently needed to overcome these challenges to assist in nanoparticle synthesis control and fluorescence performance optimization.
In this thesis a new correlative TEM and photoluminescence (PL) microscopy (TEMPL) method has been developed that combines the measurements of the optical properties and the materials structure at the exact same particle and sample area, so that accurate correlation can be established to statistically study the FND morphology/structure and PL properties, at the single nanoparticle level. Moreover, machine learning based methods have been developed for categorizing the 2D and 3D shapes of a large number of nanoparticles generated in TEMPL method.
This ML-assisted TEMPL method has been applied to understand the PL correlation with the size and shape of FNDs at the single particle level. In this thesis, a strong correlation between particle morphology and NV fluorescence in FND particles has been revealed: thin, flake-like particles produce enhanced fluorescence. The robustness of this trend is proven in FND with different surface oxidation treatments. This finding offers guidance for fluorescence-optimized sensing applications of FND, by controlling the shape of the particles in fabrication.
Overall the TEMPL methodology developed in the thesis provides a versatile and general way to study the shape and fluorescence relationship of various nanoparticles and opens up the possibility of correlation methods between other characterisation techniques
Yielding Transitions in Amorphous Materials
Amorphous materials form a part of a wide array of common materials, including foams, emulsions, colloidal and metallic glasses and polymeric systems. Many amorphous materials exhibit yielding transitions from a solid-like to a fluid-like state under shear, and characterising and predicting these transitions is of key importance in a variety of industrial and biological applications. We study the yielding of amorphous materials in three separate studies.
First, we use a thermal fluidity model to explore the yielding transitions of an amorphous material under a shear startup protocol and categorise the yielding transitions as either brittle or ductile. We find that ductile and brittle yielding both occur in systems with a stress overshoot as a function of strain, with no need for an overhang, in contrast to recent claims in the literature.
Second, we use the Soft Glassy Rheology (SGR) model and a thermal elastoplastic model (EPM) to study slow fatigue followed by sudden catastrophic failure of amorphous materials subjected to a large amplitude oscillatory shear strain protocol. We find that both models display delayed yielding, in which there is a significant stress drop after many cycles. We fit the number of cycles before yielding to functions of the relevant physical parameters. In the SGR model, we find a critical amplitude below which the yielding is delayed but insignificant, and in the EPM we find a temperature-dependant critical amplitude at which the yielding cycle diverges.
Third, we attempt to derive a continuum model of epithelial tissue rheology. We present several model variants, and compare them to published Self-Propelled Voronoi (SPV) model simulations of epithelial rheology. While we are unable to derive a model that fully captures all of the features seen in the SPV Model, we do identify several necessary ingredients of an eventual successful model
Edoardo Benvenuto Prize. Collection of papers
The promotion of studies and research on the science and art of building in their historical development constitutes the objective that the Edoardo Benvenuto Association has set itself, since its establishment, in order to honor the memory of Edoardo Benvenuto (1940-1998). The Association in recent years has achieved interesting results by developing various activities such as: organization of national and international meetings, conferences, study days; collaborations with national and foreign research institutions; promotion of the editorial series “Between Mechanics and Architecture"; activation of the portal Bibliotheca Mechanica Architectonica, first “open source” digitized library dedicated to historical research on mechanical and architectural texts. But perhaps the most qualifying initiative was the institution of the Edoardo Benvenuto Prize, arrived in 2019 in its twelfth edition, reserved for young researchers in the field of historical studies on science and the art of building. The awarding of the Prize takes place after an in-depth examination of the texts received by the Association by an international commission of experts. The purpose of this book is to collect and present the most recent studies and publications produced by the winners of the various editions of the Edoardo Benvenuto Prize
Zooming in on the Universe: In Search of Quantum Spacetime
This thesis investigates low-dimensional models of nonperturbative quantum
gravity, with a special focus on Causal Dynamical Triangulations (CDT). We
define the so-called curvature profile, a new quantum gravitational observable
based on the quantum Ricci curvature. We subsequently study its coarse-graining
capabilities on a class of regular, two-dimensional polygons with isolated
curvature singularities, and we determine the curvature profile of
(1+1)-dimensional CDT with toroidal topology. Next, we focus on CDT in 2+1
dimensions, intvestigating the behavior of the two-dimensional spatial slice
geometries. We then turn our attention to matrix models, exploring a
differential reformulation of the integrals over one- and two-matrix ensembles.
Finally, we provide a hands-on introduction to computer simulations of CDT
quantum gravity.Comment: Ph.D. thesi
Mouldable Solids: Exploring Organisational Grid Strategies to Enhance Mud Architecture
Mud is a material with deep origins in human ecology and vernacular architecture. Despite housing one-third of the world’s population and almost half in developing countries, the application of mud as a building material has diminished over the years, perhaps due to a worldwide application of industrialised building materials and practices, as well as the perception of mud as a primitive material. On the contrary, mud is cheap, reusable and sustainable yet critical challenges relate to material behaviour and performance. The researcher takes the standpoint that mud architecture is a material practice and explores organisational grids consisting of skin and skeleton to enhance structural performance.
Three areas of interest combine to demonstrate how mud as a material operates in a contemporary context: (1) The Natural Philosophy of Aristotle and ibn Sina to understand the transitional state of matter and force-form relations; (2) Isaac Newton’s Laws of Motion and Hooke’s Law to understand force-displacement relationships; (3) Information theory to represent parameters and conditions as information in organisational strategies. While mud is of interest, other materials explored include plastic, concrete, clay, and adobe as they categorise as mouldable solids due to their transitional states. Where a careful focus on mud regarding material, form, motion and force, the research deploys the technical with the philosophical to negotiate the capacities of this particular mouldable solid. The hypothesis is that the greater the variance in the skin and skeleton grid, the better the resilience and adaptability a body has due to the complex interconnections between the parts that make up a whole, organising and re-organising to withstand forces.
The dissertation celebrates mud as a reconfigurable architectural material rather than static and outdated, allowing for a multi-approach solution to contemporary and standardised materials in the current industrialised context
Tidal Energy and Coastal Models: Improved Turbine Simulation
Marine renewable energy is a continually growing topic of both commercial and academic research sectors. While not as developed as other renewable technologies such as those deployed within the wind sector, there is substantial technological crossover coupled with the inherent high energy density of water, that has helped push marine renewables into the wider renewable agenda. Thus, an ever expanding range of projects are in various stages of development.As with all technological developments, there are a range of factors that can con-tribute to the rate of development or eventual success. One of the main difficulties, when looking at marine renewable technologies in a comparative view to other en-ergy generation technologies, is that the operational environment is physically more complex: Energy must be supplied in diverse physical conditions, that temporally fluctuate with a range of time scales. The constant questions to the iteration to the local ecology. The increased operational fatigue of deployed devices. The financial risk associated within a recent sector.This work presents the continual research related to the computational research development of different marine renewable technologies that were under develop-ment of several institutional bodies at the time of writing this document.The scope has a wide envelopment as the nature of novel projects means that the project failure rate is high. Thus, forced through a combination of reasons related to financial, useful purpose and intellectual property, the research covers distinct projects
- …