Modelling silver thin film growth on zinc oxide

Ag thin film growth on ZnO substrates has been investigated theoretically using multi-timescale simulation methods. The models are based on an atomistic approach where the interactions between atoms are treated classically using a mixture of fixed and variable charge potential energy functions. After some preliminary tests it was found that existing fixed charge potential functions were unreliable for surface growth simulations. This resulted in the development of a ReaxFF variable charge potential fitted to Ag/ZnO surface interactions. Ab initio models of simple crystal structures and surface configurations were used for potential fitting and testing. The dynamic interaction of the Ag atoms with the ZnO surface was first investigated using single point depositions, via molecular dynamics, whereby the Ag impacted various points on an irreducible symmetry zone of the ZnO surface at a range of energies. This enabled the determination of the relative numbers of atoms that could penetrate, reflect or bond to the surface as a function of incident energy. The results showed that at an energy of up to 10 eV, most atoms deposited adsorbed on top of the surface layer. The second part of the dynamic interaction involved a multi-timescale technique whereby molecular dynamics (MD) was used in the initial stages followed by an adaptive kinetic Monte Carlo (AKMC) approach to model the diffusion over the surface between impacts. An impact energy of 3 eV was chosen for this investigation. Ag was grown on various ZnO surfaces including perfect polar, O-deficient and surfaces with step edges. Initial growth suggests that Ag prefers to be spread out across a perfect surface until large clusters are forced to form. After further first layer growth, subsequent Ag atoms begin to deposit on the existing Ag clusters and are unlikely to join the first layer. Ag island formation (as mentioned within the literature) can then occur via this growth mechanism. O-deficient regions of ZnO surfaces result in unfavourable Ag adsorption sites and cause cluster formation to occur away from O-vacancies. In contrast, ZnO step edges attract deposited Ag atoms and result in the migration of surface Ag atoms to under-coordinated O atoms in the step edge. Various improvements have been made to the existing methodology in which transitions are determined. A new method for determining defects within a system, by considering the coordination number of atoms, is shown to increase the number of transitions found during single ended search methods such as the relaxation and translation (RAT) algorithm. A super-basin approach based on the mean rate method is also introduced as a method of accelerating a simulation when small energy barriers dominate. This method effectively combines states connected by small energy barriers into a single large basin and calculates the mean time to escape such basin. To accelerate growth simulations further and allow larger systems to be considered, a lattice based adaptive kinetic Monte Carlo (LatAKMC) method is developed. As off-lattice AKMC and MD results suggest Ag resides in highly symmetric adsorption sites and that low energy deposition events lead to no penetrating Ag atoms or surface deformation, the on-lattice based approach is used to grow Ag on larger perfect polar ZnO surfaces. Results from the LatAKMC approach agree with off-lattice AKMC findings and predict Ag island formation. Critical island sizes of Ag on ZnO are also approximated using a mean rate approach. Single Ag atoms are placed above an existing Ag cluster and all transition states are treated as belonging to a single large super-basin . Results indicate that small Ag clusters on the perfect ZnO surface grow in the surface plane until a critical island size of around 500 atoms is reached. Once a critical island size is reached, multiple Ag ad-atoms will deposit on the island before existing Ag atoms join the cluster layer and hence islands will grow upwards. A marked difference is seen for second layer critical island sizes; second layer Ag islands are predicted to be two orders of magnitude smaller (< 7 atoms). This analysis suggests that Ag on ZnO (000 ̄1) may exhibit Stranski-Krastanov (layer plus island) growth

A Cabin in the Woods: A Former Statistician Responds to a Critique of the Bayesian Version of the Fine-Tuning Argument for God’s Existence

Many theists and atheists agree that the fine-tuning argument is the most compelling argument for the existence of God. However, there are many different versions of this argument and, as with most things in life, some versions are better than others. In this paper I will respond to Neil A. Manson’s recent critique of what I call the Bayesian Version of the Fine-Tuning Argument for God’s existence. I will argue that the Bayesian version is a relatively poor argument but that the Abductive Version of the Fine-Tuning Argument for God’s existence is quite compelling

Either on Account of Sex or Color : Policing the Boundaries of the Medical Profession During Reconstruction

In 1868, the American Medical Association (AMA) was asked to permit consultation with female physicians and admit them as delegates. In 1870, a delegation of Black doctors sought entrance to an Annual AMA meeting. The AMA refused entrance to both female and Black physicians. This paper argues that these meetings, and the question of inclusion for Black and female practitioners, arose out of the political climate that Reconstruction created. Expanding from previous scholarship, this paper further analyzes the role of Chicago doctor Nathan Smith Davis in the perpetuation of a white medical profession

Mapping the Shores of the Brown Dwarf Desert. I. Upper Scorpius

We present the results of a survey for stellar and substellar companions to 82 young stars in the nearby OB association Upper Scorpius. This survey used nonredundant aperture mask interferometry to achieve typical contrast limits of ΔK ~5-6 at the diffraction limit, revealing 12 new binary companions that lay below the detection limits of traditional high-resolution imaging; we also summarize a complementary snapshot imaging survey that discovered seven directly resolved companions. The overall frequency of binary companions (~35 +5 -4% at separations of 6-435 AU) appears to be equivalent to field stars of similar mass, but companions could be more common among lower mass stars than for the field. The companion mass function has statistically significant differences compared to several suggested mass functions for the field, and we suggest an alternate lognormal parameterization of the mass function. Our survey limits encompass the entire brown dwarf mass range, but we only detected a single companion that might be a brown dwarf; this deficit resembles the so-called brown dwarf desert that has been observed by radial velocity planet searches. Finally, our survey’s deep detection limits extend into the top of the planetary mass function, reaching 8-12 MJup for half of our sample. We have not identified any planetary companions at high confidence (≳99.5%), but we have identified four candidate companions at lower confidence (≳97.5%) that merit additional follow-up to confirm or disprove their existence

“Either on Account of Sex or Color”: Policing the Boundaries of the Medical Profession During Reconstruction

In 1868, the American Medical Association (AMA) was asked to permit consultation with female physicians and admit them as delegates. In 1870, a delegation of Black doctors sought entrance to an Annual AMA meeting. The AMA refused entrance to both female and Black physicians. This paper argues that these meetings, and the question of inclusion for Black and female practitioners, arose out of the political climate that Reconstruction created. Expanding from previous scholarship, this paper further analyzes the role of Chicago doctor Nathan Smith Davis in the perpetuation of a white medical profession

Biomimetic Promotion and Inhibition of Crystal Growth in Calcium Carbonate

Living organisms have evolved effective mechanisms to control the growth of inorganic crystalline materials as structural elements. Previous research has shown that proteins rich in aspartic acid play a pivotal role in driving crystalline orientation, structure, and morphology of calcium carbonate biominerals in the formation of shells in marine bivalves (mussels, clams, abalone). In our research, we examine the effect of aspartic acid on the growth of calcium carbonate by a novel vapor diffusion-based growth technique. The vapor diffusion approach uses a gas-permeable membrane as a barrier to control the physical location of crystal growth. In this way, we are able to directly observe the crystal nucleation and growth using optical microscopy and record changes in growth rates and crystal orientation as we add peptide or polyelectrolyte-based modifiers to the growing crystals. Raman spectroscopy was employed to characterize the resulting crystals and provide insight into the actions of the growth modifiers. Our work is directed towards understanding how molecular modifiers interact with inorganic materials. Developing controls for the growth of calcium carbonate materials could have impacts in many industries which rely on the materials (including pharmaceutical development, household products, and paper, rubber, and paint manufacturing)

Combined visible and near-infrared OPA for wavelength scaling experiments in strong-field physics

We report the operation of an optical parametric amplifier (OPA) capable of producing gigawatt peak-power laser pulses with tunable wavelength in either the visible or near-infrared spectrum. The OPA has two distinct operation modes (i) generation of >350 uJ, sub 100 fs pulses, tunable between 1250 - 1550 nm; (ii) generation of >190 uJ, sub 150 fs pulses tunable between 490 - 530 nm. We have recorded high-order harmonic spectra over a wide range of driving wavelengths. This flexible source of femtosecond pulses presents a useful tool for exploring the wavelength-dependence of strong-field phenomena, in both the multi-photon and tunnel ionization regimes.Comment: 14 pages, 9 figures, This paper was published in Proceedings of SPIE 10088, Nonlinear Frequency Generation and Conversion: Materials and Devices XVI, doi 10.1117/12.225077

The Scottish Approach: A case study of the Out-Of-Hospital Cardiac Arrest Strategy

This report sets out the findings from a series of interviews with partner organisations involved in the design and delivery of Scotland’s first national Out-of-Hospital Cardiac Arrest (OHCA) Strategy, published in 2015. Staff were interviewed about the development of the Strategy, the on-going delivery, the strengths and challenges, as well as the main features of the policy-making process. By canvassing the views of those involved throughout this process it has been possible to assess to what extent the Strategy embodies what is known as the ‘Scottish Approach’ to policy.The Scottish Approach, put simply, “encapsulates a move within public services from top-down, service-led, reactive delivery, towards more personalised, preventative and collaborative ways of working” (Cook 2017, p 1). This Research Internship project serves as a ‘case study’ of the OHCA Strategy, and qualitatively measures whether this policy can be considered as the Scottish Approach in practice.Findings from the interviews point towards several key messages:1) The OHCA Strategy represents the core principles of the Scottish Approach – it has hallmarks of public service collaboration, cross-sectoral working, a focus on outcomes, co-production (at an organisational level), using and sharing assets (primarily organisational assets) and it adopts a system-wide approach.2) Partners have expressed that aspects of this strategy are best practice – if the potential of a distinctive Scottish Approach is to be realised, future policy can be informed by what stakeholders perceive as best practice in this case study.3) Looking forward, the Scottish Approach should be critically studied – the concept is still in its infancy and has received modest external scrutiny. Future studies should investigate the distinction between the Scottish Approach as a set of ideals – ‘what the approach is’ – and as an empirical practice – ‘what the Government does’

The Scottish Approach: A case study of the Out-Of-Hospital Cardiac Arrest Strategy

This report sets out the findings from a series of interviews with partner organisations involved in the design and delivery of Scotland’s first national Out-of-Hospital Cardiac Arrest (OHCA) Strategy, published in 2015. Staff were interviewed about the development of the Strategy, the on-going delivery, the strengths and challenges, as well as the main features of the policy-making process. By canvassing the views of those involved throughout this process it has been possible to assess to what extent the Strategy embodies what is known as the ‘Scottish Approach’ to policy.The Scottish Approach, put simply, “encapsulates a move within public services from top-down, service-led, reactive delivery, towards more personalised, preventative and collaborative ways of working” (Cook 2017, p 1). This Research Internship project serves as a ‘case study’ of the OHCA Strategy, and qualitatively measures whether this policy can be considered as the Scottish Approach in practice.Findings from the interviews point towards several key messages:1) The OHCA Strategy represents the core principles of the Scottish Approach – it has hallmarks of public service collaboration, cross-sectoral working, a focus on outcomes, co-production (at an organisational level), using and sharing assets (primarily organisational assets) and it adopts a system-wide approach.2) Partners have expressed that aspects of this strategy are best practice – if the potential of a distinctive Scottish Approach is to be realised, future policy can be informed by what stakeholders perceive as best practice in this case study.3) Looking forward, the Scottish Approach should be critically studied – the concept is still in its infancy and has received modest external scrutiny. Future studies should investigate the distinction between the Scottish Approach as a set of ideals – ‘what the approach is’ – and as an empirical practice – ‘what the Government does’