8 research outputs found
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Semiconductor Nanowires: A Platform for Exploring Limits and Concepts for Nano-Enabled Solar Cells
Over the past decade extensive studies of single semiconductor nanowire and nanowire array photovoltaic devices have explored the potential of these materials as platforms for a new generation of efficient and cost-effective solar cells. This feature review discusses strategies for implementation of semiconductor nanowires in solar energy applications, including advances in complex nanowire synthesis and characterization, fundamental insights from characterization of devices, utilization and control of the unique optical properties of nanowires, and new strategies for assembly and scaling of nanowires into diverse arrays that serve as a new paradigm for advanced solar cells.Chemistry and Chemical Biolog
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Facet-Selective Growth on Nanowires Yields Multi-Component Nanostructures and Photonic Devices
Enhanced synthetic control of the morphology, crystal structure, and composition of nanostructures can drive advances in nanoscale devices. Axial and radial semiconductor nanowires are examples of nanostructures with one and two structural degrees of freedom, respectively, and their synthetically tuned and modulated properties have led to advances in nanotransistor, nanophotonic, and thermoelectric devices. Similarly, developing methods that allow for synthetic control of greater than two degrees of freedom could enable new opportunities for functional nanostructures. Here we demonstrate the first regioselective nanowire shell synthesis in studies of Ge and Si growth on faceted Si nanowire surfaces. The selectively deposited Ge is crystalline, and its facet position can be synthetically controlled in situ. We use this synthesis to prepare electrically addressable nanocavities into which solution soluble species such as Au nanoparticles can be incorporated. The method furnishes multicomponent nanostructures with unique photonic properties and presents a more sophisticated nanodevice platform for future applications in catalysis and photodetection.Chemistry and Chemical Biolog
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Design of Nanowire Optical Cavities as Efficient Photon Absorbers
Chemistry and Chemical Biolog
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Tuning Light Absorption in Core/Shell Silicon Nanowire Photovoltaic Devices through Morphological Design
Subwavelength diameter semiconductor nanowires can support optical resonances with anomalously large absorption cross sections, and thus tailoring these resonances to specific frequencies could enable a number of nanophotonic applications. Here, we report the design and synthesis of core/shell p-type/intrinsic/n-type (p/i/n) Si nanowires (NWs) with different sizes and cross-sectional morphologies as well as measurement and simulation of photocurrent spectra from single-NW devices fabricated from these NW building blocks. Approximately hexagonal cross-section p/i/n coaxial NWs of various diameters (170–380 nm) were controllably synthesized by changing the Au catalyst diameter, which determines core diameter, as well as shell deposition time, which determines shell thickness. Measured polarization-resolved photocurrent spectra exhibit well-defined diameter-dependent peaks. The corresponding external quantum efficiency (EQE) spectra calculated from these data show good quantitative agreement with finite-difference time-domain (FDTD) simulations and allow assignment of the observed peaks to Fabry–Perot, whispering-gallery, and complex high-order resonant absorption modes. This comparison revealed a systematic red-shift of equivalent modes as a function of increasing NW diameter and a progressive increase in the number of resonances. In addition, tuning shell synthetic conditions to enable enhanced growth on select facets yielded NWs with approximately rectangular cross sections; analysis of transmission electron microscopy and scanning electron microscopy images demonstrate that growth of the n-type shell at in the presence of phosphine leads to enhanced relative Si growth rates on the four {113} facets. Notably, polarization-resolved photocurrent spectra demonstrate that at longer wavelengths the rectangular cross-section NWs have narrow and significantly larger amplitude peaks with respect to similar size hexagonal NWs. A rectangular NW with a diameter of 260 nm yields a dominant mode centered at 570 nm with near-unity EQE in the transverse-electric polarized spectrum. Quantitative comparisons with FDTD simulations demonstrate that these new peaks arise from cavity modes with high symmetry that conform to the cross-sectional morphology of the rectangular NW, resulting in low optical loss of the mode. The ability to modulate absorption with changes in nanoscale morphology by controlled synthesis represents a promising route for developing new photovoltaic and optoelectronic devices.Chemistry and Chemical Biolog
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Nanowire Architectures for Next-Generation Solar Cells and Photonic Devices
This thesis presents the design and synthesis of nanowires (NW) with targeted and tunable optical properties. Moreover, we show how single and assembled NW devices can enable new photovoltaic (PV) and photonic platforms. Beginning with an investigation of axially modulated p-i-n junction NWs, we established several fundamental parameters dictating solar cell performance at the nanoscale and demonstratred the first series integration of multiple solar cells on a single NW. Thereafter, implementation of the first silicon NW photovoltaic device with radially modulated p-n junctions showed that power conversion efficiencies of 3-4% are attainable from a nanoscale architecture, exceeding efficiencies for many organic and hybrid organic-inorganic solar cells. Despite these achievements, the poor electrical characteristics and insufficient control over absorption properties characterizing the aforementioned devices would limit the promise of silicon NWs for next generation solar cells. We overcome these limitations with a class of polymorphic core/multi-shell silicon NWs with highly-crystalline hexagonally-faceted shells and embedded coaxial p/i/n junctions. NW PV devices 200-300 nm in diameter exhibit open-circuit voltages of 0.5 V and fill-factors of 73% under one-sun solar illumination. Single-NW wavelength-dependent photocurrent measurements agree quantitatively with FDTD simulations. Synthetic manipulation of NW size and morphology drives tuning of optical resonances such that optimized structures can yield current densities double those for films of comparable thickness. Further optimized NW devices achieve current densities of 17 mA/cm2 and power conversion efficiencies of 6%. We also present steps toward rational assembly of larger-scale NW PV arrays. Parallel integration of NWs preserves PV metrics while assembly of vertically-stacked NWs yields current densities of and projected efficiencies of ~15% for thick assemblies. Finally, we present the first ever NW material possessing 3 degrees of structural freedom, thus expanding the NW "structome." Such NWs were achieved through the first demonstration of facet selective growth of silicon and germanium in the gas phase. Photonic devices based on this new material present intriguing optical properties, including selective attenuation, enhancement, and wavelength tunability of resonant cavity modes.Chemistry and Chemical Biolog
Risk factors for long-term invasive mechanical ventilation: a longitudinal study using German health claims data
Abstract Background Long-term invasive mechanical ventilation (IMV) is a major burden for those affected and causes high costs for the health care system. Early risk assessment is a prerequisite for the best possible support of high-risk patients during the weaning process. We aimed to identify risk factors for long-term IMV within 96 h (h) after the onset of IMV. Methods The analysis was based on data from one of Germany's largest statutory health insurance funds; patients who received IMV ≥ 96 h and were admitted in January 2015 at the earliest and discharged in December 2017 at the latest were analysed. OPS and ICD codes of IMV patients were considered, including the 365 days before intubation and 30 days after discharge. Long-term IMV was defined as evidence of invasive home mechanical ventilation (HMV), IMV ≥ 500 h, or readmission with (re)prolonged ventilation. Results In the analysis of 7758 hospitalisations, criteria for long-term IMV were met in 38.3% of cases, of which 13.9% had evidence of HMV, 73.1% received IMV ≥ 500 h and/or 40.3% were re-hospitalised with IMV. Several independent risk factors were identified (p < 0.005 each), including pre-diagnoses such as pneumothorax (OR 2.10), acute pancreatitis (OR 2.64), eating disorders (OR 1.99) or rheumatic mitral valve disease (OR 1.89). Among ICU admissions, previous dependence on an aspirator or respirator (OR 5.13), and previous tracheostomy (OR 2.17) were particularly important, while neurosurgery (OR 2.61), early tracheostomy (OR 3.97) and treatment for severe respiratory failure such as positioning treatment (OR 2.31) and extracorporeal lung support (OR 1.80) were relevant procedures in the first 96 h after intubation. Conclusion This comprehensive analysis of health claims has identified several risk factors for the risk of long-term ventilation. In addition to the known clinical risks, the information obtained may help to identify patients at risk at an early stage. Trial registration The PRiVENT study was retrospectively registered at ClinicalTrials.gov (NCT05260853). Registered at March 2, 2022
LifeTime and improving European healthcare through cell-based interceptive medicine
AUTEURS : LifeTime Community Working GroupsInternational audienceHere we describe the LifeTime Initiative, which aims to track, understand and target human cells during the onset and progression of complex diseases, and to analyse their response to therapy at single-cell resolution. This mission will be implemented through the development, integration and application of single-cell multi-omics and imaging, artificial intelligence and patient-derived experimental disease models during the progression from health to disease. The analysis of large molecular and clinical datasets will identify molecular mechanisms, create predictive computational models of disease progression, and reveal new drug targets and therapies. The timely detection and interception of disease embedded in an ethical and patient-centred vision will be achieved through interactions across academia, hospitals, patient associations, health data management systems and industry. The application of this strategy to key medical challenges in cancer, neurological and neuropsychiatric disorders, and infectious, chronic inflammatory and cardiovascular diseases at the single-cell level will usher in cell-based interceptive medicine in Europe over the next decade
LifeTime and improving European healthcare through cell-based interceptive medicine
LifeTime aims to track, understand and target human cells during the onset and progression of complex diseases and their response to therapy at single-cell resolution. This mission will be implemented through the development and integration of single-cell multi-omics and imaging, artificial intelligence and patient-derived experimental disease models during progression from health to disease. Analysis of such large molecular and clinical datasets will discover molecular mechanisms, create predictive computational models of disease progression, and reveal new drug targets and therapies. Timely detection and interception of disease embedded in an ethical and patient-centered vision will be achieved through interactions across academia, hospitals, patient-associations, health data management systems and industry. Applying this strategy to key medical challenges in cancer, neurological, infectious, chronic inflammatory and cardiovascular diseases at the single-cell level will usher in cell-based interceptive medicine in Europe over the next decade.We would like to acknowledge all participants that have attended and contributed to LifeTime meetings and workshops through many exciting presentations and discussions. We thank Johannes Richers for artwork. LifeTime has received funding from the European Unionʼs Horizon 2020 research and innovation framework programme under Grant agreement 820431