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In Intelligent Transportation Systems (ITS), vehicular networks are enabling technologies for onboard data services such as traffic safety, user infotainment, etc. Vehicular networks face many challenges when it comes to providing satisfactory quality of service, mainly because of issues that arise from unreliable communication in unfavorable propagation conditions. One prime example is Vehicle-to-Vehicle (V2V) communication in the presence of big vehicles that present obstacles in the communication path of smaller vehicles, where the signal strength decays drastically due to the big vehicle shadowing. As a result, the communication range is shortened, and the safety message dissemination capability is reduced. In this paper, we analyze the impact of big vehicle shadowing on V2V communications, taking into account Cellular Vehicle-to-Everything (C-V2X) networks. A geometric as well as a stochastic approach is employed to analyze the length of shadow regions for conventional cars and big vehicles on the road in different scenarios. This paper analyses the effect of large vehicles shadowing on a V2V communication link as a function of the shadow region length. A beamforming-based signal reception technique is proposed in order to mitigate packet collisions caused by hidden nodes. Considering relaying operation by big vehicles, three relaying schemes are proposed to improve the V2V message dissemination performance. Extensive simulations are conducted to demonstrate the effectiveness of the proposed schemes.

Defect sites present on the surface of catalysts serve a crucial role in different catalytic processes. Herein, we have investigated defect engineering within a hybrid system composed of “soft” polymer catalysts and “hard” metal nanoparticles, employing the disparity in their thermal expansions. Electron paramagnetic resonance, X-ray photoelectron spectroscopy, and mechanistic studies together reveal the formation of new abundant defects and their synergistic integrability with plasmonic enhancement within the hybrid catalyst. These active defects, co-localized with plasmonic Ag nanoparticles, promote the utilization efficiency of hot electrons generated by local plasmons, thereby enhancing the CO2photoreduction activity while maintaining the high catalytic selectivity.

Photoluminescence spectra have been measured at 80 K in Czochralski-grown silicon wafers annealed at 450 °C, causing thermal donor and oxygen-precipitate generation. Six subbandgap luminescence peaks were identified after the annealing. One peak, centered at 1206 nm, was found to increase with a similar time constant to the thermal donor concentration measured by changes in the resistivity. We propose that the other five peaks are related to the formation of oxygen precipitates (OPs), or their nuclei. These peaks remain after a thermal donor annihilation (TDA) step, while the 1206 nm peak disappeared. This is consistent with our previous observations that the growth of OPs occurs concurrently with the growth of thermal donors at low temperatures. The annihilation of the thermal donors leads to an incomplete recovery of the interstitial oxygen concentration, consistent with the formation of precipitates. Recombination-active ring-defects formed during the annealing also remain after TDA.

Human bone marrow‐derived mesenchymal stem/stromal cells (BM‐MSCs) represent promising stem cell therapy for the treatment of type 2 diabetes mellitus (T2DM), but the results of autologous BM‐MSC administration in T2DM patients are contradictory. The purpose of this study was to test the hypothesis that autologous BM‐MSC administration in T2DM patient is safe and that the efficacy of the treatment is dependant on the quality of the autologous BM‐MSC population and administration routes. T2DM patients were enrolled, randomly assigned (1:1) by a computer‐based system into the intravenous and dorsal pancreatic arterial groups. The safety was assessed in all the treated patients, and the efficacy was evaluated based on the absolute changes in the hemoglobin A1c, fasting blood glucose, and C‐peptide levels throughout the 12‐month follow‐up. Our data indicated that autologous BM‐MSC administration was well tolerated in 30 T2DM patients. Short‐term therapeutic effects were observed in patients with T2DM duration of <10 years and a body mass index <23, which is in line with the phenotypic analysis of the autologous BM‐MSC population. T2DM duration directly altered the proliferation rate of BM‐MSCs, abrogated the glycolysis and mitochondria respiration of BM‐MSCs, and induced the accumulation of mitochondria DNA mutation. Our data suggest that autologous administration of BM‐MSCs in the treatment of T2DM should be performed in patients with T2DM duration <10 years and no obesity. Prior to further confirming the effects of T2DM on BM‐MSC biology, future work with a larger cohort focusing on patients with different T2DM history is needed to understand the mechanism underlying our observation. Human bone marrow‐derived mesenchymal stem/stromal cells (BM‐MSCs) represent promising stem cell therapy for the treatment of type 2 diabetes, but the results of autologous BM‐MSC admniistration in T2DM patients are contradicted. Our data indicated that autologous BM‐MSC administration was well tolerated in 30 T2DM patients. The potential therapeutic effects of the treatments were observed in patients with less than 10 years of T2DM and a BMI<23, and this finding could be explained by reductions in autologous stem cell phenotypes, including prolonged cell proliferation, reduced metabolic functions, and alterations in mtDNA.

Perovskite material with a bandgap of 1.7–1.8 eV is highly desirable for the top cell in a tandem configuration with a lower bandgap bottom cell, such as a silicon cell. This can be achieved by alloying iodide and bromide anions, but light-induced phase-segregation phenomena are often observed in perovskite films of this kind, with implications for solar cell efficiency. Here, we investigate light-induced phase segregation inside quadruple-cation perovskite material in a complete cell structure and find that the magnitude of this phenomenon is dependent on the operating condition of the solar cell. Under short-circuit and even maximum power point conditions, phase segregation is found to be negligible compared to the magnitude of segregation under open-circuit conditions. In accordance with the finding, perovskite cells based on quadruple-cation perovskite with 1.73 eV bandgap retain 94% of the original efficiency after 12 h operation at the maximum power point, while the cell only retains 82% of the original efficiency after 12 h operation at the open-circuit condition. This result highlights the need to have standard methods including light/dark and bias condition for testing the stability of perovskite solar cells. Additionally, phase segregation is observed when the cell was forward biased at 1.2 V in the dark, which indicates that photoexcitation is not required to induce phase segregation.

Two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors exhibit many important structural and optoelectronic properties, such as strong light–matter interactions, direct bandgaps tunable from visible to near-infrared regions, flexibility and atomic thickness, quantum-confinement effects, valley polarization possibilities, and so on. Therefore, they are regarded as a very promising class of materials for next-generation state-of-the-art nano/micro optoelectronic devices. To explore different applications and device structures based on 2D TMDs, intrinsic material properties, their relationships, and evolutions with fabrication parameters need to be deeply understood, very often through a combination of various characterization techniques. Among them, steady-state photoluminescence (PL) spectroscopy has been extensively employed. This class of techniques is fast, contactless, and nondestructive and can provide very high spatial resolution. Therefore, it can be used to obtain optoelectronic properties from samples of various sizes (from microns to centimeters) during the fabrication process without complex sample preparation. In this article, the mechanism and applications of steady-state PL spectroscopy in 2D TMDs are reviewed. The first part of this review details the physics of PL phenomena in semiconductors and common techniques to acquire and analyze PL spectra. The second part introduces various applications of PL spectroscopy in 2D TMDs. Finally, a broader perspective is discussed to highlight some limitations and untapped opportunities of PL spectroscopy in characterizing 2D TMDs.

We examine correlations between the recombination lifetime and hydrogen content of hydrogenated amorphous silicon films (a-Si:H) and the surface passivation afforded by such films when deposited on crystalline silicon wafers, during annealing at 350–500 °C. Our results show that, as the annealing duration increases, both the a-Si:H recombination lifetime and the surface recombination velocity evolve at a similar rate to the hydrogen concentration. This suggests that the loss of hydrogen during annealing is the direct cause of the reduction in the a-Si:H film lifetime, and that the loss of hydrogen occurs both at the a-Si:H/c-Si interface as well as in the bulk of a-Si:H film. We calculated the activation energy of the surface depassivation reaction during annealing to be 0.62 ± 0.1 eV, which suggests that the depassivation reaction is limited by the migration of hydrogen within the film, without significant hydrogen trapping. Secondary-ion mass spectrometry further demonstrates the loss of hydrogen across the film thickness during annealing.

Organic–inorganic (O–I) heterostructures, consisting of atomically thin inorganic semiconductors and organic molecules, present synergistic and enhanced optoelectronic properties with a high tunability. Here, we develop a class of air-stable vertical O–I heterostructures comprising a monolayer of transition-metal dichalcogenides (TMDs), including WS2, WSe2, and MoSe2, on top of tetraphenylethylene (TPE) core-based aggregation-induced emission (AIE) molecular rotors. The created O–I heterostructures yields a photoluminescence (PL) enhancement of up to ∼950%, ∼500%, and ∼330% in the top monolayer WS2, MoSe2, and WSe2as compared to PL in their pristine monolayers, respectively. The strong PL enhancement is mainly attributed to the efficient photogenerated carrier process in the AIE luminogens (courtesy of their restricted intermolecular motions in the solid state) and the charge-transfer process in the created type I O–I heterostructures. Moreover, we observe an improvement in photovoltaic properties of the TMDs in the heterostructures including the quasi-Fermi level splitting, minority carrier lifetime, and light absorption. This work presents an inspiring example of combining stable, highly luminescent AIE-based molecules, with rich photochemistry and versatile applications, with atomically thin inorganic semiconductors for multifunctional and efficient optoelectronic devices.

Photocatalytic CO2transformation into value-added chemicals has enormous industrial importance, but is challenging to operate with multifaceted performances in activity, selectivity, stability and regenerability. We successfully achieved this goal by integrating plasmonic bismuth nanoparticles and non-plasmonic redox heterojunctions. This maximizes the product selectivity by directing the reaction paths via the electric field of localized surface plasmon resonances (LSPRs). We attach non-noble plasmonic Bi particles with a shell of BiOCl to self-assembled TiO2nanosheets, creating a transformative hybrid plasmonic nanostructure for CO2-to-methanol conversion. It exhibits high photoactivity (235.26 µmol g-1h-1), outstanding selectivity (∼90 % sole carbon/methanol product, ∼10 % H2) and is free of backward reactions, thanks to the synergistic effects of the hybrid nanostructure: complementary light absorption, strong local fields, and an adaptive redox heterojunction. Macro-to-micro experiments and simulations reveal that the BiOCl shell is responsible for stabilizing Bi to generate robust LSPRs, to induce 7–9 times local field enhancement, enabling efficient and selective CO2-to-methanol conversion at the TiO2-BiOCl heterointerfaces. This work demonstrates a durable and easily-regenerable photocatalyst with the capability to tune the CO2reduction pathway by plasmon fields. Moreover, it provides a unique paradigm to harvest hydrogen carriers (liquid methanol and hydrogen gas) from the greenhouse gas CO2.

ABSTRACTDimethyl sulfoxide (DMSO) is a dipolar aprotic solvent widely used in biological assays. Here, we observed that DMSO enhanced the hypo-osmotically induced increases in the concentration of Ca2+in cytosolic and nucleic compartments in the transgenic cell-lines of tobacco (BY-2) expressing aequorin.

We characterize and discuss the impact of hydrogenation on the performance of phosphorus-doped polycrystalline silicon (poly-Si) films for passivating contact solar cells. Combining various characterization techniques including transmission electron microscopy, energy-dispersive X-ray spectroscopy, low-temperature photoluminescence spectroscopy, quasi-steady-state photoconductance, and Fourier-transform infrared spectroscopy, we demonstrate that the hydrogen content inside the doped poly-Si layers can be manipulated to improve the quality of the passivating contact structures. After the hydrogenation process of poly-Si layers fabricated under different conditions, the effective lifetime and the implied open circuit voltage are improved for all investigated samples (up to 4.75 ms and 728 mV on 1 Ω cm n-type Si substrates). Notably, samples with very low initial passivation qualities show a dramatic improvement from 350 μs to 2.7 ms and from 668 to 722 mV.

We report on the characterization of heavily boron doped epitaxial silicon regions grown in a hot-wire chemical vapor deposition tool, using micro-Raman and photoluminescence spectroscopy. In particular, the use of this approach for emitter fabrication in an interdigitated back contact silicon solar cell is studied, by analyzing its suitability concerning selective growth, uniformity, anneal time, and luminescent defects. We show that by reducing the silane flow rate, both the required postanneal time and intensity of defect luminescence are reduced. Furthermore, we show that selective area growth does not affect either the quality of the films or the sharpness of the resulting lateral doping profile. The uniformity of the doping is shown to be better than that achieved using laser doping.

We investigate the light trapping in Si wafers that are textured with conventional random pyramids on their front surface and rounded random pyramids on their rear. It is well established that rounding the pyramids leads to better surface passivation, but whether or not it improves light trapping depends on the cell structure. In this paper, we apply ray tracing, spectrophotometry, and photoluminescence spectroscopy (PLS) to understand and quantify how rounding the rear pyramids might affect the light trapping in back-contact solar cells. We describe how rounding the pyramids leads to two competing optical effects: 1) reduced absorption in the rear films and 2) reduced scattering from the rear texture. The first effect improves light trapping whereas the latter degrades it. We show how the influence of each effect depends on wavelength and how they can be discerned (but not easily quantified) in reflectance curves. With PLS measurements, we conclude that for our sample structure and etch solution, the generation current is approximately constant for etch durations less than ~60 s, and decreases significantly as the etch duration increases. Thus, by limiting the duration of the rounding etch, superior surface passivation can be attained without degrading the light trapping.

Low temperature microphotoluminescence spectroscopy (μ-PLS) is employed to determine the inhomogeneous doping profiles for heavily boron-doped regions on silicon wafers. Samples having various Gaussian function doping profiles, in terms of surface dopant density and depth factor, are prepared via two-step thermal boron diffusion on high resistivity n-type silicon wafers. Measured PL spectra are normalized to the Si band-band luminescence peak, and PL components of undiffused Si are subtracted to resolve the doping peak. We show that the wavelength of the doping peak has a reliable and simple linear relationship with the measured surface dopant density on a semilog plot, and so establish a calibration curve which can be applied to estimate the surface dopant density. A second calibration curve for estimating the depth factor is also established after correcting the measured doping peak intensity to account for incomplete dopant ionization. We show the effectiveness of this method by reconstructing independently measured doping profiles using the surface dopant density and depth factors estimated from the PL spectra. Furthermore, by performing two-dimensional mapping, with μ-PLS measurements at 2 μm spatial resolution, we are able to map the surface dopant density and diffusion depth factor of micron-scale, locally diffused features.

Raman spectroscopy (RS) has shown great potential in noninvasive cancer screening. Statistically based algorithms, such as principal component analysis, are commonly employed to provide tissue classification; however, they are difficult to relate to the chemical and morphological basis of the spectroscopic features and underlying disease. As a result, we propose the first Raman biophysical model applied to in vivo skin cancer screening data. We expand upon previous models by utilizing in situ skin constituents as the building blocks, and validate the model using previous clinical screening data collected from a Raman optical fiber probe. We built an 830nm confocal Raman microscope integrated with a confocal laser-scanning microscope. Raman imaging was performed on skin sections spanning various disease states, and multivariate curve resolution (MCR) analysis was used to resolve the Raman spectra of individual in situ skin constituents. The basis spectra of the most relevant skin constituents were combined linearly to fit in vivo human skin spectra. Our results suggest collagen, elastin, keratin, cell nucleus, triolein, ceramide, melanin and water are the most important model components. We make available for download (see supplemental information) a database of Raman spectra for these eight components for others to use as a reference. Our model reveals the biochemical and structural makeup of normal, nonmelanoma and melanoma skin cancers, and precancers and paves the way for future development of this approach to noninvasive skin cancer diagnosis.

We investigate the microscopic distributions of sub-band-gap luminescence emission (the so-called D-lines D1/D2/D3/D4) and the band-to-band luminescence intensity, near recombination-active subgrain boundaries in multicrystalline silicon wafers for solar cells. We find that the sub-band-gap luminescence from decorating defects/impurities (D1/D2) and from intrinsic dislocations (D3/D4) has distinctly different spatial distributions, and is asymmetric across the subgrain boundaries. The presence of D1/D2 is correlated with a strong reduction in the band-to-band luminescence, indicating a higher recombination activity. In contrast, D3/D4 emissions are not strongly correlated with the band-to-band intensity. Based on spatially resolved, synchrotron-based micro-X-ray fluorescence measurements of metal impurities, we confirm that high densities of metal impurities are present at locations with strong D1/D2 emission but low D3/D4 emission. Finally, we show that the observed asymmetry of the sub-band-gap luminescence across the subgrain boundaries is due to its inclination below the wafer surface. Based on the luminescence asymmetries, the subgrain boundaries are shown to share a common inclination locally, rather than being orientated randomly.

The impact of oxygen precipitates and dislocations on carrier recombination is investigated on thick silicon slabs cut vertically from a Czochralski-grown silicon ingot. Using a combination of photoluminescence imaging, photoluminescence spectroscopy, and Fourier transform infrared spectroscopy, we investigate the impact of pre-anneal on their recombination activity. We show that the vacancy concentration during precipitate growth affects the recombination activity of oxygen precipitates. Finally, we demonstrate the impact of nonequilibrium point defect concentrations on precipitate and dislocation growth.

Employing microphotoluminescence spectroscopy at low temperatures, we are able to detect dopant diffusion enhancement along various grain boundaries and subgrain boundaries in multicrystalline silicon wafers. We find an enhancement of phosphorus diffusion at all investigated grain boundary types. In addition, the subgrain boundaries are demonstrated to contain a relatively high density of defects and impurities, suggesting that their presence does not significantly hinder the preferential diffusion of dopant atoms along the subgrain boundaries. Finally, we demonstrate that the technique can be applied to different diffused layers for solar cell applications, even at room temperature if an appropriate excitation wavelength is used. The results are validated with secondary electron dopant contrast images, which confirm the higher dopant concentration along the grain boundaries and subgrain boundaries.

Photoluminescence (PL) spectra from moderately doped, compensated silicon with boron and phosphorus concentrations on the order of 1016 - 1017 cm - 3, which is representative of the low-cost upgraded metallurgical grade silicon potentially used for photovoltaics, are presented and explained. At 79 K, the captured PL spectra from the compensated silicon reveal the presence of the following radiative recombination channels in the material: band-to-band recombination, recombination through a single neutral dopant (phosphorus or boron), and recombination from the neutral donors (phosphorus) to the neutral acceptors (boron), i.e., the D°-A° pair recombination. The D°-A° pair luminescence peaks are found to appear as rather broad in the measured PL spectra from compensated silicon at 79 K. The relative PL intensity of the broad dopant features is shown to increase with increasing dopant concentrations. The dopant-related luminescence of the compensated silicon demonstrates strong excitation dependence, as a result of the D°-A° recombination channel in compensated silicon. The dopant features become increasingly suppressed at higher excitations due to the increasing dominance of the band-to-band recombination channel. With increasing temperature, the dopant-related luminescence features diminish and become undistinguishable at around 200 K, due to the increased ionization of dopants and the broadening of the band-to-band recombination peaks at higher temperatures.

The highest efficiency perovskite solar cells reported so far are based on mixtures of formamidinium lead triiodide (FAPbI3) and methylammonium lead tribromide (MAPbBr3), where MAPbBr3acts as a stabilizer to improve the formation of the black perovskite phase. In this work, we dope the perovskite precursor mixture with rubidium iodide (RbI) and study the interplay between the doping substituent and the PbI2excess on the perovskite phase formation and film morphology. The addition of 5% RbI in combination with excess PbI2eliminates the formation of yellow non-perovskite phase and enhances the crystallinity of the films. However, the addition of more than 10% RbI results in the formation of a Rb-rich phase, which is detrimental for the cell performance. The findings are confirmed by cathodoluminescence measurements, which also reveal the spatial distribution of different phases on the perovskite films. The performance of RbI-doped perovskite cell is reported for the first time with the highest efficiency of 18.8% and improved thermal/photo stability compared to the undoped cells. The study demonstrates the potential of Rb as an alternative cation for use in high efficiency perovskite cells.

Photoluminescence spectroscopy at 79 K is shown to provide an alternative, non‐destructive characterisation method for quantifying the boron and phosphorous dopant concentrations in silicon. The dopant concentrations are revealed by the photoluminescence intensity ratios of the dopant‐related features to the band‐to‐band recombination peaks. The intensity ratio is found to be insensitive to the excitation power in a wide range of 0.3 W cm−2–100 kW cm−2. Calibration curves for boron and phosphorous in silicon are presented for [B] below 5 × 1017cm−3and [P] below 8 × 1016cm−3.