We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination ...dynamics we assess the exciton fine structure in these systems. In addition to the typical bright–dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (∼100 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright–dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures.
In condensed matter, scattering processes determine the transport of charge carriers. In case of heterostructures, interfaces determine many dynamic properties such as charge transfer and transport, ...and spin current dynamics. Here, we discuss optically excited electron dynamics and their propagation across a lattice-matched, metal-metal interface of single crystal quality. Using femtosecond time-resolved linear photoelectron spectroscopy upon optically pumping different constituents of the heterostructure, we establish a technique that probes the electron propagation and its energy relaxation simultaneously. In our approach, a near-infrared pump pulse excites electrons directly either in the Au layer or in the Fe layer of epitaxial Au/Fe/MgO(001) heterostructures while the transient photoemission spectrum is measured by an ultraviolet probe pulse on the Au surface. Upon femtosecond laser excitation, we analyze the relative changes in the electron distribution close to the Fermi energy and assign characteristic features of the time-dependent electron distribution to transport of hot and nonthermalized electrons from the Fe layer to the Au surface and vice versa. From the measured transient electron distribution, we determine the excess energy, which we compare with a calculation based on the two-temperature model that takes diffusive electron transport into account. On this basis, we identify a transition with increasing Au layer thickness from a superdiffusive to a diffusive transport regime at 20–30 nm.
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The transport of optically excited, hot electrons in heterostructures is analyzed by femtosecond, time-resolved two-photon photoelectron emission spectroscopy (2PPE) for epitaxial Au/Fe/MgO(001). We ...compare the temporal evolution of the 2PPE intensity upon optically pumping Fe or Au, while the probing occurs on the Au surface. In the case of Fe-side pumping, assuming independent relaxation in the Fe and Au layers, we determine the hot electron relaxation times in these individual layers by an analysis of the Au layer thickness dependence of the observed, effective electron lifetimes in the heterostructure. We show in addition that such a systematic analysis fails for the case of Au-side pumping due to the spatially distributed optical excitation density, which varies with the Au layer thickness. This work extends a previous study Beyazit et al., Phys. Rev. Lett. 125, 076803 (2020) by new data leading to reduced error bars in the determined lifetimes and by a non-linear term in the Au-thickness dependent data analysis which contributes for similar Fe and Au film thicknesses.
In condensed matter, scattering processes determine the transport of charge carriers. In case of heterostructures, interfaces determine many dynamic properties like charge transfer and transport and ...spin current dynamics. Here we discuss optically excited electron dynamics and their propagation across a lattice-matched, metal-metal interface of single crystal quality. Using femtosecond time-resolved linear photoelectron spectroscopy upon optically pumping different constituents of the heterostructure we establish a technique which probes the electron propagation and its energy relaxation simultaneously. In our approach a near-infrared pump pulse excites electrons directly either in the Au layer or in the Fe layer of epitaxial Au/Fe/MgO(001) heterostructures while the transient photoemission spectrum is measured by an ultraviolet probe pulse on the Au surface. Upon femtosecond laser excitation, we analyze the relative changes in the electron distribution close to the Fermi energy and assign characteristic features of the time-dependent electron distribution to transport of hot and non-thermalized electrons from the Fe layer to the Au surface and vice versa. From the measured transient electron distribution we determine the excess energy which we compare with a calculation based on the two-temperature model and takes diffusive electron transport into account. On this basis we identify a transition from a super-diffusive to a diffusive transport regime to occur for a Au layer thickness of 20-30~nm.
Understanding the microscopic spatio-temporal dynamics of nonequilibrium charge carriers in heterosystems promises optimization of process and device design towards desired energy transfer. Hot ...electron transport is governed by scattering with other electrons, defects, and bosonic excitations. Analysis of the energy dependence of scattering pathways and identification of diffusive, super-diffusive, and ballistic transport regimes are current challenges. We determine in femtosecond time-resolved two-photon photoelectron emission spectroscopy the energy-dependent change of the electron propagation time through epitaxial Au/Fe(001) heteostructures as a function of Au layer thickness for energies of 0.5 to \unit2.0{eV} above the Fermi energy. We describe the laser-induced nonequilibrium electron excitation and injection across the Fe/Au interface using real-time time-dependent density functional theory and analyze the electron propagation through the Au layer by microscopic electron transport simulations. We identify ballistic transport of minority electrons at energies with a nascent, optically excited electron population which is determined by the combination of photon energy and the specific electronic structure of the material. At lower energy, super-diffusive transport with 1 to 4 scattering events dominates. The effective electron velocity accelerates from 0.3 to \unit1{nm/fs} with an increase in the Au layer thickness from 10 to 100~nm. This phenomenon is explained by electron transport that becomes preferentially aligned with the interface normal for thicker Au layers, which facilitates electron momentum / energy selection by choice of the propagation layer thickness.
Employing femtosecond laser pulses in front and back side pumping of Au/Fe/MgO(001) combined with detection in two-photon photoelectron emission spectroscopy we analyze local relaxation dynamics of ...excited electrons in buried Fe, injection into Au across the Fe-Au interface, and electron transport across the Au layer at 0.6 to 2.0 eV above the Fermi energy. By analysis as a function of Au film thickness we obtain the electron lifetimes of bulk Au and Fe and distinguish the relaxation in the heterostructure's constituents. We also show that the excited electrons propagate through Au in a superdiffusive regime and conclude further that electron injection across the epitaxial interface proceeds ballistically by electron wavepacket propagation.
Limited research has examined the clinical consequences of sarcopenia and myosteatosis in Crohn's disease. This study aimed to determine the prevalence, risk factors, and effects of sarcopenia and ...myosteatosis on prognostic outcomes in Crohn's disease patients who underwent magnetic resonance enterography.
This retrospective observational study included 116 Crohn's disease patients who underwent magnetic resonance enterography between January 2015 and August 2021. Skeletal muscle index was the ratio of the cross-sectional area of skeletal muscles at the L3 vertebral level to the square of the neck in cross-sectional imaging. Sarcopenia was defined as skeletal muscle index <38.5 cm2/m2 in women and <52.4 cm2/m2 in men. Myosteatosis was considered positive if the ratio of the mean signal intensity of the psoas muscle to the mean signal intensity of the cerebrospinal fluid was above 0.107.
Among the negative results in the post-procedure follow-up of the patients, a significant increase was observed in the sarcopenia group regarding abscess and the need for surgery (P < .05). Anti-tumor necrosis factor initiation was found to be significantly higher in the follow-up than in patients without myosteatosis (P = .029). In the multivariate model established with these variables, the presence of sarcopenia in the surgical follow-up was odds ratio = 5.34 (CI: 1.02-28.03, P = .047) and was found to be significantly associated with the increased risk.
The presence of myosteatosis and sarcopenia detected in magnetic resonance enterography may be a harbinger of negative outcomes in Crohn's disease patients. Nutritional support should be provided to these patients with the potential to alter the course of the disease.
Objective: To determine the anatomic and functional outcomes of macular hole surgery with the temporal inverted flap technique. Methods: In this retrospective study, 9 eyes of 9 patients, who were ...treated with pars plana vitrectomy using the temporal inverted flap technique and had at least 6 months of postoperative follow-up were enrolled. Best-corrected visual acuity and spectral-domain optical coherence tomography images were determined before and after surgery. Results: The primary disorders were idiopathic macular holes. The mean minimum macular hole diameter was 456.7 + or - 150.0 microm (221-622). In all patients, macular hole closure was performed successfully. The final U-shaped foveal contour type was achieved in 77.7% (7/9 eyes) of the patients and V-shape in 22.2% (2/9 eyes). None of the patients had W-shaped closures or fat/open-type contour. Mean best-corrected visual acuity increased from 1.47 + or - 0.40 logarithm of the minimal angle of resolution to 0.8 + or - 0.41 logarithm of the minimal angle of resolution at the last follow-up visit (P < .001). Conclusion: Temporal inverted flap technique may be an effective method for treating macular holes with different etiologies to minimize the microsurgical trauma. Further large-scale studies are required to assess the efficacy and safety of this technique. Keywords: Internal limiting membrane, inverted flap, macular hole, pars plana vitrectomy, temporal inverted flap
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