Van der Waals Materials for Atomically-Thin Photovoltaics: Promise and Outlook

Two-dimensional (2D) semiconductors provide a unique opportunity for optoelectronics due to their layered atomic structure, electronic and optical properties. To date, a majority of the application-oriented research in this field has been focused on field-effect electronics as well as photodetectors and light emitting diodes. Here we present a perspective on the use of 2D semiconductors for photovoltaic applications. We discuss photonic device designs that enable light trapping in nanometer-thickness absorber layers, and we also outline schemes for efficient carrier transport and collection. We further provide theoretical estimates of efficiency indicating that 2D semiconductors can indeed be competitive with and complementary to conventional photovoltaics, based on favorable energy bandgap, absorption, external radiative efficiency, along with recent experimental demonstrations. Photonic and electronic design of 2D semiconductor photovoltaics represents a new direction for realizing ultrathin, efficient solar cells with applications ranging from conventional power generation to portable and ultralight solar power.Comment: 4 figure

High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures

We report experimental measurements for ultrathin (< 15 nm) van der Waals heterostructures exhibiting external quantum efficiencies exceeding 50%, and show that these structures can achieve experimental absorbance > 90%. By coupling electromagnetic simulations and experimental measurements, we show that pn WSe2/MoS2 heterojunctions with vertical carrier collection can have internal photocarrier collection efficiencies exceeding 70%.Comment: ACS Nano, 2017. Manuscript (25 pages, 7 figures) plus supporting information (7 pages, 4 figures

Electrical Control of Linear Dichroism in Black Phosphorus from the Visible to Mid-Infrared

The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic control of light propagation by an applied potential. While many materials have been shown to exhibit electrically tunable permittivity and dispersion, including transparent conducting oxides (TCOs) and III-V semiconductors and quantum wells, these materials are all optically isotropic in the propagation plane. In this work, we report the first known example of electrically tunable linear dichroism, observed here in few-layer black phosphorus (BP), which is a promising candidate for multi-functional, broadband, tunable photonic elements. We measure active modulation of the linear dichroism from the mid-infrared to visible frequency range, which is driven by anisotropic quantum-confined Stark and Burstein-Moss effects, and field-induced forbidden-to-allowed optical transitions. Moreover, we observe high BP absorption modulation strengths, approaching unity for certain thicknesses and photon energies

Cruciate Retaining compared with Posterior Stabilised Nexgen total knee arthroplasty:results at 10 years in a matched cohort

Introduction: Debate has persisted for many years about whether to sacrifice or replace the posterior cruciate ligament when performing total knee arthroplasty. A paucity of long-term follow-up studies comparing outcomes between cruciate-retaining and posterior-stabilised knees exist. We aimed to compare results at ten-year follow-up.Methods: A matched paired study comparing a cohort of 107 Zimmer Nexgen® Cruciate Retaining (CR) patients with a cohort of 107 Nexgen Posterior-Stabilised (PS) knees matched for age, sex, body mass index and preoperative American Knee Society score was undertaken. All patients underwent independent clinical assessment and knee society scoring preoperatively and at 1, 3, 5, 7 and 10 years postoperatively.Results: Fifty-three patients (49.5%) in the CR group and 44 patients (41.1%) in the PS group were alive at 10-year follow-up. There were no significant differences between the CR and PS groups with regards to functional assessment (P = 0.95), overall range of movement (P = 0.46) or patient satisfaction (P = 1.0) at 10 years. However, there was a significantly better score improvement in range of movement in PS knees compared with CR knees (P = 0.027). There were six revisions (5.6%) in the PS group and 1 (0.93%) in the CR group (P = 0.12). Both CR and PS knees showed excellent survivorship with no significant difference at 10 years (P = 0.068).Conclusions: There were no significant differences in functional score, overall range of motion or patient satisfaction between the Nexgen cruciate retaining and posterior stabilised total knee arthroplasty at 10-year follow-up. However, PS knees had a greater score improvement in range of motion compared with CR knees.</p

Intrinsic Decoherence in Mesoscopic Systems

We present measurements of the phase coherence time $\tau_\phi$ in six quasi-1D Au wires and clearly show that $\tau_\phi$ is temperature independent at low temperatures. We suggest that zero-point fluctuations of the intrinsic electromagnetic environment are responsible for the observed saturation of $\tau_\phi$. We introduce a new functional form for the temperature dependence and present the results of a calculation for the saturation value of $\tau_\phi$. This explains the observed temperature dependence of our samples as well as many 1D and 2D systems reported to date.Comment: 4 pages, 4 figures & 1 tabl

Preparation and Characterization of Antimony Doped Tin Oxide Thin Films Synthesized by Co-Evaporation of Sn and Sb using Plasma Assisted Thermal Evaporation

Tin oxide (SnO2) thin films are having promising properties such as high visible transmittance and low electric resistivity, makes them very important transparent conductor in a variety of optoelectronics devices. Further, doping with pentavalent impurity such as Antimony (Sb) enhances its conductivity considerably. In order to study the effect of Antimony doping, Antimony doped tin oxide (SnO2 : Sb) thin films have been prepared by the co-evaporation of Sn and Sb using Plasma Assisted Thermal Evaporation (PATE) in oxygen (O2) partial pressure at various doping level from 4% to 25%. The influence of various Sb doping levels on the compositional, electrical, optical and structural properties have been investigated using Energy Dispersive X-ray (EDX) spectroscopy, Ultraviolet-Visible (UV-VIS) transmission spectroscopy, four-probe resistivity measurement and X-ray Diffraction (XRD), respectively. EDX studies confirmed the different Sb doping levels in the grown films from 4 % to 25 %, while electrical resistivity is obtained in range of 0.36 to 9.5 Ohmcm using four-probe setup for 4 % to 25 % Sb doping levels. Transmittance spectra measured in UV-VIS range for Sb doped films show reduction in an average transmittance in respect to increase in Sb doping levels in the grown films. Whereas, XRD analysis reveals that higher Sb doping of 25 % induce the precipitation of antimony oxide (Sb2O3) phase and its precipitation suppressed the growth of SnO2 peaks as well as responsible for reduction in conductivity and transparency. The best electrical resistivity of optimized SnO2 : Sb (5 %) is 0.36 Ohmcm without deteriorating the high (~ 80 %) average transmittance in the wavelength region 300-800 nm in comparison to undoped SnO2 film (6.57 Ohmcm) , confirm the usefulness of SnO2 : Sb (5 %) films for device applications. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3102

Near-Unity Absorption in van der Waals Semiconductors for Ultrathin Optoelectronics

We demonstrate near-unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as van der Waals semiconductor active layers. Specifically, we report that near-unity light absorption is possible in extremely thin (<15 nm) van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency

Aligning everyday life priorities with people's self-management support networks: an exploration of the work and implementation of a needs-led telephone support system

Background: Recent initiatives to target the personal, social and clinical needs of people with long-term health conditions have had limited impact within primary care. Evidence of the importance of social networks to support people with long-term conditions points to the need for self-management approaches which align personal circumstances with valued activities. The Patient-Led Assessment for Network Support (PLANS) intervention is a needs-led assessment for patients to prioritise their health and social needs and provide access to local community services and activities. Exploring the work and practices of patients and telephone workers are important for understanding and evaluating the workability and implementation of new interventions. Methods: Qualitative methods (interviews, focus group, observations) were used to explore the experience of PLANS from the perspectives of participants and the telephone support workers who delivered it (as part of an RCT) and the reasons why the intervention worked or not. Normalisation Process Theory (NPT) was used as a sensitising tool to evaluate: the relevance of PLANS to patients (coherence); the processes of engagement (cognitive participation); the work done for PLANS to happen (collective action); the perceived benefits and costs of PLANS (reflexive monitoring). 20 patients in the intervention arm of a clinical trial were interviewed and their telephone support calls were recorded and a focus group with 3 telephone support workers was conducted. Results: Analysis of the interviews, support calls and focus group identified three themes in relation to the delivery and experience of PLANS. These are: formulation of ‘health’ in the context of everyday life; trajectories and tipping points: disrupting everyday routines; precarious trust in networks. The relevance of these themes are considered using NPT constructs in terms of the work that is entailed in engaging with PLANS, taking action, and who is implicated this process. Conclusions: PLANS gives scope to align long-term condition management to everyday life priorities and valued aspects of life. This approach can improve engagement with health-relevant practices by situating them within everyday contexts. This has potential to increase utilisation of local resources with potential cost-saving benefits for the NH

Growth of carbon nanotubes on quasicrystalline alloys

We report on the synthesis of carbon nanotubes on quasicrystalline alloys. Aligned multiwalled carbon nanotubes (MWNTs) on the conducting faces of decagonal quasicrystals were synthesized using floating catalyst chemical vapor deposition. The alignment of the nanotubes was found perpendicular to the decagonal faces of the quasicrystals. A comparison between the growth and tube quality has also been made between tubes grown on various quasicrystalline and SiO2 substrates. While a significant MWNT growth was observed on decagonal quasicrystalline substrate, there was no significant growth observed on icosahedral quasicrystalline substrate. Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) results show high crystalline nature of the nanotubes. Presence of continuous iron filled core in the nanotubes grown on these substrates was also observed, which is typically not seen in MWNTs grown using similar process on silicon and/or silicon dioxide substrates. The study has important implications for understanding the growth mechanism of MWNTs on conducting substrates which have potential applications as heat sinks