Giant optical birefringence of semiconductor nanowire metamaterials

Semiconductor nanowires exhibit large polarization anisotropy for the absorption and emission of light, making them ideal building blocks for novel photonic metamaterials. Here, we demonstrate that a high density of aligned nanowires exhibits giant optical birefringence, a collective phenomenon observable uniquely for collections of wires. The nanowire material was grown on gallium phosphide (GaP) (111) in the form of vertically standing GaP nanowires. We obtain the largest optical birefringence to date, with a difference between the in-plane and out-of-plane refractive indices of 0.80 and a relative birefringence of 43%. These values exceed by a factor of 75 the natural birefringence of quartz and a by more than a factor of two the highest values reported so far in other artificial materials. By exploiting the specific crystallographic growth directions of the nanowires on the substrate, we further demonstrate full control over the orientation of the optical birefringence effect in the metamaterial.Comment: 10 pages, 4 figure

Single quantum dot nanowire LEDs

We report reproducible fabrication of InP-InAsP nanowire light emitting diodes in which electron-hole recombination is restricted to a quantum-dot-sized InAsP section. The nanowire geometry naturally self-aligns the quantum dot with the n-InP and p-InP ends of the wire, making these devices promising candidates for electrically-driven quantum optics experiments. We have investigated the operation of these nano-LEDs with a consistent series of experiments at room temperature and at 10 K, demonstrating the potential of this system for single photon applications

'She doesn’t want to go to hospital. That’s one thing she hates’: Collective performativity in avoidable nursing home to hospital transfers

Older people who live with a combination of conditions experience fluctuations over time, which others may interpret as a need for medical attention. For some nursing home residents, this results in transitions in and out of hospital. Such transfers may be arranged without expectation ofimproved quality of life, can be associated with significant morbidity and mortality, and may preclude end-of-life preferences. Factors affecting avoidable hospitalisation for nursing home residents are not well understood. I aim to explore potential drivers, moving beyond deficit explanations relating to funding, training and resources. I use a framework of analysis that firstly considers medicalisation of frailty, as a state of vulnerability that provides focus for others’ action. I then draw on Judith Butler’s theory of performativity, to explore nursing homes as sites of identify work for staff, residents and families. I consider ways subjectivities can be effected through reiterative practice that is compelled by normative conventions. Trouble may arise when citational practice of healthcare staff, and performative acquiescence of residents and families, culminate in an inevitability of hospitalisation when navigating grey areas of assumed clinical risk. Principles of coproduction could present a disruptive opening, to rework power asymmetries and move toward aspirations for residents and their relatives to be at the centre of decisions about care

Learning from a crisis

Background: The enacted sensemaking of third-party logistics (TPL) providers during the pandemic crisis may present an opportunity to explore their strategic operations. Objectives: The aim is to understand the TPL strategic implications related to a crisis and specifically how TPL providers make sense of and respond to crises. The two research questions are as follows: How has the COVID-19 pandemic crisis affected the business operations of TPL providers? What have TPL providers learnt from enacting the crisis, and how has this experience affected their strategic development? Method: We conduct an abductive study using combined data from interviews and a targeted archive search. The data are focused on the Swedish context and on a period of the COVID-19 pandemic. Results: Three distinct groups of TPL providers have different sense and action processes impacting their business operations. This research shows how an understanding of servitisation is relevant for TPL theory. Finally, we develop the strategic perspective of TPL providers by defining TPL providers as value-cocreating relationships that can help manage the complexities of logistics services. Conclusion: This research shows that TPL providers play an important role in crises, as they contribute to solving customer problems. This role appears to be strengthened during crises, but it imposes great demands on TPL providers. Contribution: Third-party logistics providers work with their customers during crises. The sensemaking view emphasises the importance of personnel, organisational commitment, capacity and expectations during crises. This is an interplay that requires adaptation to shortterm changes in operational processes and adaptability in long-term operations.peerReviewe

UV exposure : A novel processing method to fabricate nanowire solar cells

We demonstrate a novel and rapid method for nanowire (NW) solar cell processing. NW arrays were embedded in photoresist. The strong absorption of light in the NWs leads to self-limited exposure of the resist, which enables selective removal of the exposed part of the resist, opening up for the tips of the NWs and further processing. The UV-exposure technology allows a fast and low-cost process compared to the conventional reactive ion etching method

Design study of a nanowire three-terminal heterojunction bipolar transistor solar cell

We present an optical design study on a nanowire heterojunction bipolar transistor solar cell. The simple structure of this novel architecture of double-junction solar cell, allows for independent power extraction from the two junctions and makes the nanowire growth easier than in current-matched double-junction solar cells as there is no need for tunnel junctions and only three main semiconductor regions must be grown. We show that the nanowire heterojunction bipolar transistor solar cell design results in an optical performance similar to comparable planar devices, with the nanowires only covering 1/3 of the substrate area. Furthermore, it allows for the growth of lattice-mismatched semiconductor combinations, which increases the detailed balance efficiency limit

Optoelectronic III-V nanowire implementation of a neural network in a shared waveguide

Neural node components consisting of III-V nanowire devices are introduced. This allows for the construction of a small footprint specialized neural network. A broadcasting strategy is developed which removes the need for inter-node wiring. As a model system, an insect brain navigational circuit is chosen and successfully emulated using the introduced nodes and network architecture. The results are based on electronic transport simulations in each device as well as finite-difference time-domain simulations for the broadcasting of optical signals