The electronic and optical properties of (In x Ga1–x )2O3 alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ...ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ x ≤ 0.82) and three crystallographic phases (monoclinic, hexagonal, and bixbyite). The optical gaps over this composition range are determined, and only a weak optical gap bowing is found (b = 0.36 eV). The valence band edge evolution along with the change in the fundamental band gap over the composition gradient enables the surface space-charge properties to be probed. This is an important property when considering metal contact formation and heterojunctions for devices. A transition from surface electron accumulation to depletion occurs at x ∼ 0.35 as the film goes from the bixbyite In2O3 phase to the monoclinic β-Ga2O3 phase. The electronic structure of the different phases is investigated by using density functional theory calculations and compared to the valence band X-ray photoemission spectra. Finally, the properties of these alloys, such as the n-type dopability of In2O3 and use of Ga2O3 as a solar-blind UV detector, are understood with respect to other common-cation compound semiconductors in terms of simple chemical trends of the band edge positions and the hydrostatic volume deformation potential.
Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO2 is an earth abundant, cheaper alternative to In2O3 as a TCO. However, its performance in terms of mobilities ...and conductivities lags behind that of In2O3. On the basis of the recent discovery of mobility and conductivity enhancements in In2O3 from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy, and semiconductor statistics modeling to understand what is the optimal dopant to maximize performance of SnO2-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO2, as it is a resonant dopant which is readily incorporated into SnO2 with the Ta 5d states sitting ∼1.4 eV above the conduction band minimum. Experimentally, the band edge electron effective mass of Ta doped SnO2 was shown to be 0.23m 0, compared to 0.29m 0 seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.
The van der Waals material GeSe is a potential solar absorber, but its optoelectronic properties are not yet fully understood. Here, through a combined theoretical and experimental approach, the ...optoelectronic and structural properties of GeSe are determined. A fundamental absorption onset of 1.30 eV is found at room temperature, close to the optimum value according to the Shockley–Queisser detailed balance limit, in contrast to previous reports of an indirect fundamental transition of 1.10 eV. The measured absorption spectra and first-principles joint density of states are mutually consistent, both exhibiting an additional distinct onset ∼0.3 eV above the fundamental absorption edge. The band gap values obtained from first-principles calculations converge, as the level of theory and corresponding computational cost increases, to 1.33 eV from the quasiparticle self-consistent GW method, including the solution to the Bethe–Salpeter equation. This agrees with the 0 K value determined from temperature-dependent optical absorption measurements. Relaxed structures based on hybrid functionals reveal a direct fundamental transition in contrast to previous reports. The optoelectronic properties of GeSe are resolved with the system described as a direct semiconductor with a 1.30 eV room temperature band gap. The high level of agreement between experiment and theory encourages the application of this computational methodology to other van der Waals materials.
Abstract
The solid electrolyte interphase (SEI) that forms on Li-ion battery anodes is critical to their long-term performance, however observing SEI formation processes at the buried ...electrode-electrolyte interface is a significant challenge. Here we show that
operando
soft X-ray absorption spectroscopy in total electron yield mode can resolve the chemical evolution of the SEI during electrochemical formation in a Li-ion cell, with nm-scale interface sensitivity. O, F, and Si K-edge spectra, acquired as a function of potential, reveal when key reactions occur on high-capacity amorphous Si anodes cycled with and without fluoroethylene carbonate (FEC). The sequential formation of inorganic (LiF) and organic (-(C=O)O-) components is thereby revealed, and results in layering of the SEI. The addition of FEC leads to SEI formation at higher potentials which is implicated in the rapid healing of SEI defects and the improved cycling performance observed.
Operando
TEY-XAS offers new insights into the formation mechanisms of electrode-electrolyte interphases and their stability for a wide variety of electrode materials and electrolyte formulations.
The factors limiting the conductivity of fluorine‐doped tin dioxide (FTO) produced via atmospheric pressure chemical vapor deposition are investigated. Modeling of the transport properties indicates ...that the measured Hall effect mobilities are far below the theoretical ionized impurity scattering limit. Significant compensation of donors by acceptors is present with a compensation ratio of 0.5, indicating that for every two donors there is approximately one acceptor. Hybrid density functional theory calculations of defect and impurity formation energies indicate the most probable acceptor‐type defects. The fluorine interstitial defect has the lowest formation energy in the degenerate regime of FTO. Fluorine interstitials act as singly charged acceptors at the high Fermi levels corresponding to degenerately n‐type films. X‐ray photoemission spectroscopy of the fluorine impurities is consistent with the presence of substitutional FO donors and interstitial Fi in a roughly 2:1 ratio in agreement with the compensation ratio indicated by the transport modeling. Quantitative analysis through Hall effect, X‐ray photoemission spectroscopy, and calibrated secondary ion mass spectrometry further supports the presence of compensating fluorine‐related defects.
Compensating acceptor defects dramatically reduce electronic performance of F:SnO2 transparent conductor grown by chemical vapor deposition. Electron carrier mobilities are seen to be greatly diminished from the theoretically predicted optimum. Using hybrid density functional theory calculations and experimental methods, and analysis, the defect responsible for self‐compensation in F:SnO2 is determined to be the fluorine interstitial.
We report on the electronic and magnetic properties of superconductor-ferromagnet heterostructures fabricated by electron beam evaporation on to unheated thermally oxidised Si substrates. ...Polycrystalline Nb thin films (5 to 50 nm thick) were shown to possess reliably high superconducting critical temperatures (Formula: see text), which correlate well with the residual resistivity ratio (RRR) of the film. These properties improved during ex-situ annealing, resulting in Formula: see text and Formula: see textRRR increases of up 2.2 K (Formula: see text 40% of the pre-annealed Formula: see text) and 0.8 (Formula: see text 60% of the pre-annealed RRR) respectively. Nb/Pt/Co/Pt heterostructures showed substantial perpendicular anisotropy in the ultrathin limit (≤ 2.5 nm), even in the extreme limit of Pt(0.8 nm)/Co(1 nm)/Pt(0.6 nm). These results point to the use of electron beam evaporation as route to line-of-sight deposited, low-thickness, high quality Nb-based superspintronic multilayers.
Systemic proinflammatory cytokines and oxidative stress have been described in association with peripheral muscle wasting and weakness of patients with severe chronic obstructive pulmonary disease ...(COPD), but their expression in skeletal muscle is unknown. The objectives of the present study were to determine muscle protein levels of selected cytokines in patients with COPD and to study their relationships with protein carbonylation as a marker of oxidative stress, quadriceps function and exercise capacity.
We conducted a cross sectional study in which 36 cytokines were detected using a human antibody array in quadriceps specimens obtained from 19 patients with severe COPD and seven healthy controls. Subsequently, selected cytokines (tumour necrosis factor (TNF)alpha, TNFalpha receptors I and II, interleukin (IL) 6, interferon gamma, transforming growth factor (TGF) beta and vascular endothelial growth factor (VEGF)), as well as protein carbonylation (oxidative stress index) were determined using an enzyme linked immunosorbent assay (ELISA) in all muscles.
Compared with controls, the vastus lateralis of patients with COPD showed significantly lower protein ELISA levels of TNFalpha, which positively correlated with their quadriceps function, TNFalpha receptor II and VEGF. Protein ELISA levels of IL6, interferon gamma and TGFbeta did not differ between patients and controls. Quadriceps protein carbonylation was greater in patients and inversely correlated with quadriceps strength among them.
These findings do not support the presence of a proinflammatory environment within the quadriceps muscles of clinically and weight stable patients with severe COPD, despite evidence for increased oxidative stress and the presence of muscle weakness.
Summary
Interventions that alter PTH levels in an animal model of chronic kidney disease have effects on the perfusion of bone and bone marrow.
Introduction
Patients with chronic kidney disease (CKD) ...have accelerated bone loss, vascular calcification, and abnormal biochemistries, together contributing to an increased risk of cardiovascular disease and fracture-associated mortality. Despite evidence of vascular pathologies and dysfunction in CKD, our group has shown that cortical bone tissue perfusion is higher in a rat model of high-turnover CKD. The goal of the present study was to test the hypothesis that parathyroid hormone (PTH) suppressive interventions would normalize cortical bone vascular perfusion in the setting of CKD.
Methods
In two separate experiments, 35-week-old CKD animals and their normal littermates underwent intra-cardiac fluorescent microsphere injection to assess the effect of 10 weeks of PTH suppression (Experiment 1: calcium supplementation, Experiment 2: calcimimetic treatment) on alterations in bone tissue perfusion.
Results
In Experiment 1, CKD animals had serum blood urea nitrogen (BUN) and PTH levels significantly higher than NL (+ 182% and + 958%;
p
< 0.05). CKD+Ca animals had BUN levels that were similar to CKD, while PTH levels were significantly lower and comparable to NL. Both femoral cortex (+ 220%,
p
= 0.003) and tibial cortex (+ 336,
p
= 0.005) tissue perfusion were significantly higher in CKD animals when compared to NL; perfusion was normalized to those of NL in CKD+Ca animals. MicroCT analysis of the proximal tibia cortical porosity showed a trend toward higher values in CKD (+ 401%;
p
= 0.017) but not CKD+Ca (+ 111%;
p
= 0.38) compared to NL. Experiment 2, using an alternative method of PTH suppression, showed similar results as those of Experiment 1.
Conclusions
These data demonstrate that PTH suppression-based interventions normalize cortical bone perfusion in the setting of CKD.
Summary
This work examines the skeletal accumulation of fluorescently tagged zoledronate in an animal model of chronic kidney disease. The results show higher accumulation in 24-h post-dose animals ...with lower kidney function due to greater amounts of binding at individual surfaces.
Introduction
Chronic kidney disease (CKD) patients suffer from increased rates of skeletal-related mortality from changes driven by biochemical abnormalities. Bisphosphonates are commonly used in reducing fracture risk in a variety of diseases, yet their use is not recommended in advanced stages of CKD. This study aimed to characterize the accumulation of a single dose of fluorescently tagged zoledronate (FAM-ZOL) in the setting of reduced kidney function.
Methods
At 25 weeks of age, FAM-ZOL was administered to normal and CKD rats. Twenty-four hours later, multiple bones were collected and assessed using bulk fluorescence imaging, two-photon imaging, and dynamic histomorphometry.
Results
CKD animals had significantly higher levels of FAM-ZOL accumulation in the proximal tibia, radius, and ulna, but not in lumbar vertebral body or mandible, based on multiple measurement modalities. Although a majority of trabecular bone surfaces were covered with FAM-ZOL in both normal and CKD animals, the latter had significantly higher levels of fluorescence per unit bone surface in the proximal tibia.
Conclusions
These results provide new data regarding how reduced kidney function affects drug accumulation in rat bone.
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