Theory of elasticity and electric polarization effects in the group-III nitrides

In this work, the properties of strained tetrahedrally bonded materials are explored theoretically, with special focus on group-III nitrides. In order to do so, a multiscale approach is taken: accurate quantitative calculations of material properties are carried out in a quantum first-principles frame, for small systems. These properties are then extrapolated and empirical methods are employed to make predictions for larger systems, such as alloys or nanostructures. We focus our attention on elasticity and electric polarization in semiconductors. These quantities serve as input for the calculation of the optoelectronic properties of these systems. Regarding the methods employed, our first-principles calculations use highly- accurate density functional theory (DFT) within both standard Kohn-Sham and generalized (hybrid functional) Kohn-Sham approaches. We have developed our own empirical methods, including valence force field (VFF) and a point-dipole model for the calculation of local polarization and local polarization potential. Our local polarization model gives insight for the first time to local fluctuations of the electric polarization at an atomistic level. At the continuum level, we have studied composition-engineering optimization of nitride nanostructures for built-in electrostatic field reduction, and have developed a highly efficient hybrid analytical-numerical staggered-grid computational implementation of continuum elasticity theory, that is used to treat larger systems, such as quantum dots.

Accommodating interruptions: a grounded theory of young people with asthma

Background: Accommodating Interruptions is a theory that emerged in the context of young people who have asthma. A background to the prevalence and management of asthma in Ireland is given to situate the theory. Ireland has the fourth highest incidence of asthma in the world, with almost one in five Irish young people having asthma. Although national and international asthma management guidelines exist it is accepted that the symptom control of asthma among the young people population is poor. Aim: The aim of this research is to investigate the lives of young people who have asthma, to allow for a deeper understanding of the issues affecting them. Methods: This research was undertaken using a Classic Grounded Theory approach. It is a systematic approach to allowing conceptual emergence from data in generating a theory that explains behaviour in resolving the participant’s main concern. The data were collected through in-depth interviews with young people aged 11-16 years who had asthma for over one year. Data were also collected from participant diaries. Constant comparative analysis, theoretical coding and memo writing were used to develop the theory. Results: The theory explains how young people resolve their main concern of being restricted, by maximizing their participation and inclusion in activities, events and relationships in spite of their asthma. They achieve this by accommodating interruptions in their lives in minimizing the effects of asthma on their everyday lives. Conclusion: The theory of accommodating interruptions explains young people’s asthma management behaviours in a new way. It allows us to understand how and why young people behave the way they do in order minimise the effect of asthma on their lives. The theory adds to the body of knowledge on young people with asthma and challenges some viewpoints regarding their behaviours.

Anticipatory vigilance: A classic grounded theory of risk reduction and management in the perioperative setting

This research aimed to investigate the main concern facing nurses in minimising risk within the perioperative setting and to generate an explanatory substantive theory of how they resolve this through anticipatory vigilance. In the context of the perioperative setting, nurses encounter challenges in minimising risks for their patients on a continuous basis. Current explanations of minimising risk in the perioperative setting offers insights into how perioperative nurses undertake their work. Currently research in minimising risk is broadly related to dealing with errors as opposed to preventing them. To date, little is known about how perioperative nurses practice and maintain safety. This study was guided by the principles of classic grounded theory as described by Glaser (1978, 1998, 2001). Data was collected through individual unstructured interviews with thirty seven perioperative nurses (with varying lengths of experiences of working in the area) and thirty three hours of non-participant observation within eight different perioperative settings in the Republic of Ireland. Data was simultaneously collected and analysed. The theory of anticipatory vigilance emerged as the pattern of behaviour through which nurse’s deal with their main concern of minimising risk in a high risk setting. Anticipatory vigilance is enacted through orchestrating, routinising and momentary adapting within a spirit of trusting relations within the substantive area of the perioperative setting. This theory of offers an explanation on how nurses resolve their main concern of minimising risk within the perioperative setting. The theory of anticipatory vigilance will be useful to nurses in providing a comprehensive framework of explanation and understanding on how nurses deal with minimising risk in the perioperative setting. The theory links perioperative nursing, risk and vigilance together. Clinical improvements through understanding and awareness of the theory of anticipatory vigilance will result in an improved quality environment, leading to safe patient outcomes.

Moral shielding: A grounded theory of integrity maintenance in multidisciplinary teams

Using a classic grounded theory methodology (CGT), this study explores the phenomenon of moral shielding within mental health multidisciplinary teams (MDTS). The study was located within three catchment areas engaged in acute mental health service practice. The main concern identified was the maintenance of a sense of personal integrity during situational binds. Through theoretical sampling thirty two practitioners, including; doctors, nurses, social workers, occupational therapists, counsellors and psychologists, where interviewed face to face. In addition, emergent concepts were identified through observation of MDTs in clinical and research practice. Following a classic grounded theory methodology, data collection and analysis occurred simultaneously. A constant comparative approach was adopted and resulted in the immergence of three sub- core categories; moral abdication, moral hinting and pseudo-compliance. Moral abdication seeks to re-position within an event in order to avoid or deflect the initial obligation to act, it is a strategy used to remove or reduce moral ownership. Moral gauging represents the monitoring of an event with the goal of judging the congruence of personal principles and commitments with that of other practitioners. This strategy is enacted in a bid to seek allies for the support of a given moral position. Pseudo-compliance represents behaviour that hides desired principles and commitments in order to shield them from challenge. This strategy portrays agreement with the dominant position within the MDT, whilst holding a contrary position. It seeks to preserve a reservoir of emotional energy required to maintain a sense of personal integrity. Practitioners who were successful in enacting moral shielding were found to not experience significant emotional distress associated with the phenomenon of moral distress; suggesting that these practitioners had found mechanisms to manage situational binds that threatened their sense of personal integrity.

Theory of the electronic and optical properties of dilute bismide alloys

Dilute bismide alloys, containing small fractions of bismuth (Bi), have recently attracted interest due to their potential for applications in a range of semiconductor devices. Experiments have revealed that dilute bismide alloys such as GaBixAs1−x, in which a small fraction x of the atoms in the III-V semiconductor GaAs are replaced by Bi, exhibit a number of unusual and unique properties. For example, the band gap energy (E g) decreases rapidly with increasing Bi composition x, by up to 90 meV per % Bi replacing As in the alloy. This band gap reduction is accompanied by a strong increase in the spin-orbit-splitting energy (ΔSO) with increasing x, and both E g and ΔSO are characterised by strong, composition-dependent bowing. The existence of a ΔSO > E g regime in the GaBixAs1−x alloy has been demonstrated for x ≳10%, a band structure condition which is promising for the development of highly efficient, temperature stable semiconductor lasers that could lead to large energy savings in future optical communication networks. In addition to their potential for specific applications, dilute bismide alloys have also attracted interest from a fundamental perspective due to their unique properties. In this thesis we develop the theory of the electronic and optical properties of dilute bismide alloys. By adopting a multi-scale approach encompassing atomistic calculations of the electronic structure using the semi-empirical tight-binding method, as well as continuum calculations based on the k•p method, we develop a fundamental understanding of this unusual class of semiconductor alloys and identify general material properties which are promising for applications in semiconductor optoelectronic and photovoltaic devices. By performing detailed supercell calculations on both ordered and disordered alloys we explicitly demonstrate that Bi atoms act as isovalent impurities when incorporated in dilute quantities in III-V (In)GaAs(P) materials, strongly perturbing the electronic structure of the valence band. We identify and quantify the causes and consequences of the unusual electronic properties of GaBixAs1−x and related alloys, and our analysis is reinforced throughout by a series of detailed comparisons to the results of experimental measurements. Our k•p models of the band structure of GaBixAs1−x and related alloys, which we derive directly from detailed atomistic calculations, are ideally suited to the study of dilute bismide-based devices. We focus in the latter part of the thesis on calculations of the electronic and optical properties of dilute bismide quantum well lasers. In addition to developing an understanding of the effects of Bi incorporation on the operational characteristics of semiconductor lasers, we also present calculations which have been used explicitly in designing and optimising the first generation of GaBixAs1−x-based devices.