Exploring Non-Toxic Lower Dimensional Perovskites for Next-Generation X-Ray Detectors.

Owing to their extraordinary photophysical properties, organometal halide perovskites are emerging as a new material class for X-ray detection. However, the existence of toxic lead makes their commercialization questionable and should readily be replaced. Accordingly, several lead alternatives have been introduced into the framework of conventional perovskites, resulting in various new perovskite dimensionalities. Among these, Pb-free lower dimensional perovskites (LPVKs) not only show promising X-ray detecting properties due to their higher ionic migration energy, wider and tunable energy bandgap, smaller dark currents, and structural versatility but also exhibit extended environmental stability. Herein, first, the structural organization of the PVKs (including LPVKs) is summarized. In the context of X-ray detectors (XDs), the outstanding properties of the LPVKs and active layer synthesis routes are elaborated afterward. Subsequently, their applications in direct XDs are extensively discussed and the device performance, in terms of the synthesis method, device architecture, active layer size, figure of merits, and device stability are tabulated. Finally, the review is concluded with an in-depth outlook, thoroughly exploring the present challenges to LPVKs XDs, proposing innovative solutions, and future directions. This review provides valuable insights into optimizing non-toxic Pb-free perovskite XDs, paving the way for future advancements in the field.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges.

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

Current crowding in graphene-silicon schottky diodes.

The performance of the Graphene/Si (Gr/Si) Schottky interface and its potential in future electronics strongly rely on the quality of interconnecting contacts with external circuitry. In this work, we investigate the dominating and limiting factors of Gr/Si interfaces designed for high light absorption, paying particular attention to the nature of the contact failure under high electrostatic discharge (ESD) conditions. Our findings indicate that severe current crowding at contact edges of the graphene is the dominating factor for the device breakdown. Material degradation and electrical breakdown are systematically analyzed by atomic force, Raman, scanning electron, and energy-dispersive x-ray spectroscopies. This work enlists the robustness and limitations of Gr/Si junction in photodiode architecture under high ESD conditions that can be used as general guidelines for 2D-3D electronic and optoelectronic devices.

Ultra-Narrow Linewidth Photo-Emitters in Polymorphic Selenium Nanoflakes.

Photoluminescence (PL) in state-of-the-art 2D materials suffers from narrow spectral coverage, relatively broad linewidths, and poor room-temperature (RT) functionality. The authors report ultra-narrow linewidth photo-emitters (ULPs) across the visible to near-infrared wavelength at RT in polymorphic selenium nanoflakes (SeNFs), synthesized via a hot-pressing strategy. Photo-emitters in NIR exhibit full width at half maximum (Γ) of 330 ± 90 µeV, an order of magnitude narrower than the reported ULPs in 2D materials at 300 K, and decrease to 82 ± 70 µeV at 100 K, with coherence time (τc ) of 21.3 ps. The capping substrate enforced spatial confinement during thermal expansion at 250 °C is believed to trigger a localized crystal symmetry breaking in SeNFs, causing a polymorphic transition from the semiconducting trigonal (t) to quasi-metallic orthorhombic (orth) phase. Fine structure splitting in orth-Se causes degeneracy in defect-associated bright excitons, resulting in ultra-sharp emission. Combined theoretical and experimental findings, an optimal biaxial compressive strain of -0.45% cm-1 in t-Se is uncovered, induced by the coefficient of thermal expansion mismatch at the selenium/sapphire interface, resulting in bandgap widening from 1.74 to 2.23 ± 0.1 eV. This report underpins the underlying correlation between crystal symmetry breaking induced polymorphism and RT ULPs in SeNFs, and their phase change characteristics.

Enhancement of lateral Casimir force on a rotating particle near hyperbolic metamaterial.

Enhancement of weak Casimir forces is extremely important for their practical detection and subsequent applications in variety of scientific and technological fields. We study the lateral Casimir forces acting on the rotating particles with small radius of 50 nm as well as that with large radius of 500 nm near the hyperbolic metamaterial made of silicon carbide (SiC) nanowires. It is found that the lateral Casimir force acting on the small particle of 50 nm near hyperbolic metamaterial with appropriate filling fraction can be enhanced nearly four times comparing with that acting on the same particle near SiC bulk in the previous study. Such enhancement is caused by the coupling between the resonance mode excited by nanoparticle and the hyperbolic mode supported by hyperbolic metamaterial. The results obtained in this study provide an efficient method to enhance the interaction of nanoscale objects.

Does air pollution upsurge in megacities after Covid-19 lockdown? A spatial approach.

The current coronavirus (COVID-19) pandemic has a high spreading and fatality rate. To control the rapid spreading of the COVID-19 virus, the government of India imposed lockdown policies, which creates a unique opportunity to analyze the impact of lockdown on air quality in the two most populous cities of India, i.e., Delhi and Mumbai. To do this, the study employed a spatial approach to examine the concentration of seven criteria pollutants, i.e., PM2.5, PM10, NH3, CO, NO2, O3, and SO2, before, during, and after a lockdown in Delhi and Mumbai. Overall, around 42%, 50%, 21%, 37%, 53%, and 41% declines in PM2.5, PM10, NH3, CO, NO2, and SO2 were observed during the lockdown period as compared to previous years. On the other hand, a 2% increase in O3 concentration was observed. However, the study analyzed the National Air Quality Index (NAQI) for Delhi and Mumbai and found that lockdown does not improve the air quality in the long term period. Our key findings provide essential information to the cities' administration to develop rules and regulations to enhance air quality.

COVID-19's disasters are perilous than Global Financial Crisis: A rumor or fact?

This investigation employed the Asymmetric Power GARCH model and found that COVID-19 substantially harms the US and Japan's market returns. Moreover, COVID-19 has influenced the variance of the US, Germany, and Italy's stock markets more than the Global Financial Crises (GFC). However, GFC indicated a more significant impact on the financial volatility of the Nikkei 225 index and SSEC than COVID-19. The study confirmed the leverage effect for the S&P 500, Nasdaq Composite Index, DAX 30, Nikkei 225, FTSE MIB, and SSEC. The analysis authenticated that the health crisis that befell due to COVID-19 have imperatively originated the financial crisis globally; however, the Asian markets still make available better prospects for portfolio optimization.

Facile Synthesis of γ-In2 Se3 Nanoflowers toward High Performance Self-Powered Broadband γ-In2 Se3 /Si Heterojunction Photodiode.

An effective colloidal process involving the hot-injection method is developed to synthesize uniform nanoflowers consisting of 2D γ-In2 Se3 nanosheets. By exploiting the narrow direct bandgap and high absorption coefficient in the visible light range of In2 Se3 , a high-quality γ-In2 Se3 /Si heterojunction photodiode is fabricated. This photodiode shows a high photoresponse under light illumination, short response/recovery times, and long-term durability. In addition, the γ-In2 Se3 /Si heterojunction photodiode is self-powered and displays a broadband spectral response ranging from UV to IR with a high responsivity and detectivity. These excellent performances make the γ-In2 Se3 /Si heterojunction very interesting as highly efficient photodetectors.

Three-dimensional macro-structures of two-dimensional nanomaterials.

If two-dimensional (2D) nanomaterials are ever to be utilized as components of practical, macroscopic devices on a large scale, there is a complementary need to controllably assemble these 2D building blocks into more sophisticated and hierarchical three-dimensional (3D) architectures. Such a capability is key to design and build complex, functional devices with tailored properties. This review provides a comprehensive overview of the various experimental strategies currently used to fabricate the 3D macro-structures of 2D nanomaterials. Additionally, various approaches for the decoration of the 3D macro-structures with organic molecules, polymers, and inorganic materials are reviewed. Finally, we discuss the applications of 3D macro-structures, especially in the areas of energy, environment, sensing, and electronics, and describe the existing challenges and the outlook for this fast emerging field.

Mechanical properties of nickel-graphene composites synthesized by electrochemical deposition.

Graphene (Gr) nanosheets with multilayer structures were dispersed in a nickel (Ni) plating solution by using a surfactant with a magnetic stirring method. Gr nanosheets were incorporated into a Ni matrix through a plating process to form Ni-Gr composites on a target substrate. Gr nanosheets were uniformly dispersed in the Ni matrix, and the oxygen radicals present in the Gr were reduced during the electro-deposition process. The incorporation of Gr in the Ni matrix increases both the inter-planar spacing and the degree of preferred orientation of crystalline Ni. With the addition of Gr content as low as 0.05 g L(-1), the elastic modulus and hardness of the Ni-Gr composites reach 240 GPa and 4.6 GPa, respectively, which are about 1.7 and 1.2 times that of the pure Ni deposited under the same condition. The enhancement in mechanical properties of the composites is attributed to the preferred formation of the Ni crystalline phases in its (111) plane, the high interaction between Ni and Gr and the prevention of the dislocation sliding in the Ni matrix by the Gr. The results suggest that the method of using Gr directly instead of graphene oxide (GO) is efficient and scalable.

Developing imprinted polymer nanoparticles for the selective separation of antidiabetic drugs.

In this study, new molecularly imprinted polymer (MIP) nanoparticles are designed for selective recognition of different drugs used for the treatment of type 2 diabetes mellitus, i.e. sitagliptin (SG) and metformin (MF). The SG- and MF-imprinted polymer nanoparticles are synthesized by free-radical initiated polymerization of the functional monomers: methacrylic acid and methyl methacrylate; and the crosslinker: ethylene glycol dimethacrylate. The surface morphology of resultant MIP nanoparticles is studied by atomic force microscopy. Fourier transform infrared spectra of MIP nanoparticles suggest the presence of reversible, non-covalent interactions between the template and the polymer. The effect of pH on the rebinding of antidiabetic drugs with SG- and MF-imprinted polymers is investigated to determine the optimal experimental conditions. The molecular recognition characteristics of SG- and MF-imprinted polymers for the respective drug targets are determined at low concentrations of SG (50-150 ppm) and MF (5-100 ppm). In both cases, the MIP nanoparticles exhibit higher binding response compared to non-imprinted polymers. Furthermore, the MIPs demonstrate high selectivity with four fold higher responses toward imprinted drugs targets, respectively. Recycled MIP nanoparticles retain 90% of their drug-binding efficiency, which makes them suitable for successive analyses with significantly preserved recognition features.

Investigating the role of smart technologies, financial, and environmental innovations in tackling the ecological sustainability: a global pathway toward low carbon energy transition.

Since the beginning of the twenty-first century, the rapid development of modern technologies has brought unprecedented social prosperity to mankind as technologies penetrate every sector of the economy. These technologies have given a new dimension to the energy sector. The key purpose of this study is to investigate the crucial impact of technological revolutions, namely, smart grids, smart devices, financial innovations, and environmental innovations, on greenhouse gas emissions (GHGs). To this end, the study utilized data from European, Asian, Middle Eastern, and African countries and employed first- and second-generation methods, such as DOLS, FMOLS, and CS-ARDL models. The research shows that smart grids are the only factor in reducing GHGs, regardless of geographic division. Hence, linking smart grid resources to climate change goals requires short-term deployment strategies with a clear long-term vision and the fundamental goal of transforming the power structure into a net zero-emission system. The study also demonstrates that the emergence of ICT in electricity consumption has not yet reached a level that can promote environmental excellence. The study documented the critical role of financial innovation and environmental innovation in addressing environmental degradation.

Locally advanced nasopharyngeal carcinoma in adolescents treated with tomotherapy: Experience at King Faisal Specialist Hospital and Research Centre.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is a rare disease worldwide; To the best of our knowledge, there is no established standard of care specifically tailored for the adolescent population. The majority of existing research relies on retrospective data analysis. OBJECTIVE: Evaluate clinical features, treatment results, prognostic factors and late toxicities of locally advanced NPC patients treated with tomotherapy. DESIGN: Retrospective. SETTINGS: Tertiary care hospital. PATIENTS AND METHODS: Between January 2007 and January 2020, we treated patients with NPC, aged between 14 and 21 years, with concomitant chemoradiotherapy using tomotherapy at our institution. We prospectively collected details of clinical characteristics, treatment modalities, outcomes and prognostic factors of these patients and then analysed them retrospectively. MAIN OUTCOME MEASURES: 3-5 years overall survival (OS), 3-5 years locoregional control rate, 3-5 years disease-free survival (DFS), prognostic factors. SAMPLE SIZE: 51 patients. RESULTS: There were 26 male and 25 female patients included in our study. The mean age was 16.5 years, 5 (9.8%) patients with stage III, and 46 (90.2%) with stage IVa according to the American Joint Committee on Cancer, 8th edition staging system. Most patients (98%) received two or more cycles of induction chemotherapy. All patients received concomitant chemoradiotherapy. The median total dose of radiotherapy delivered was 6600 cGy (range 4800-7000). With a median follow-up of 73 months (range 9-168 months), a 5-year locoregional control rate, 5-year OS and 5-year DFS rates were 100%, 86.8% and 71.7%, respectively. Five years later, disease control was 71.7%. Ten (19.6%) patients had disease recurrence in the form of distant metastases during the follow up. CONCLUSIONS: Helical tomotherapy has an excellent late toxicity profile without compromising clinical outcome for patients with NPC. Radiotherapy remains the mainstay of treatment of nasopharyngeal carcinoma to achieve remarkable local control rates. LIMITATIONS: Single institution experience, small number of patients, and retrospective design.

Extreme flood in Pakistan: Is Pakistan paying the cost of climate change? A short communication.

Global warming is one of the foremost causes of changes in climate patterns around the world. Pakistan is among the top ten countries affected by global warming. Today, Pakistan is facing severe consequences of global warming in the form of an extreme flood. It affected 33 million people, destroyed 1.5 million homes, and caused $2.3 billion in crop damage. It has also damaged more than 2000 km of roads, cutting off connectivity to provinces and major cities. Thus, inflation in Pakistan has reached its highest level, i.e. 26 % - 27 %, and a severe food crisis is not far away. Recently, Pakistan noted a record temperature of 40 °C in several territories, notably 51 °C in Jacobabad. The study reported that high temperatures, melting glaciers, heavy monsoon rains, government inattention, and poor governance are the key reasons of this severe flood. Moreover, in 2080, the average temperature in Pakistan is predicted to increase by 4.38 degrees Celsius. The study suggested that Supply of cheap seeds and fertilizers to farmers, maintenance of water supply infrastructure, availability of food and medicines through domestic and foreign assistance, and reduction of electricity rates and taxes in flood-affected areas can be the solution to stop this crisis. Similarly, building dams, investing in technology and training, and educating the general public about environmental change should be included in the long-term goals to avoid future disasters.

Exploring the impact of public funds and eco-friendly innovations on reducing carbon pollution in North Africa.

The main objective of this study is to examine the impacts of green energy and public investment on the CO2 emissions in North Africa. Moreover, the study also tests the existence of the N-shaped Environmental Kuznets Curve (EKC) hypothesis for North African countries between 1995 and 2018. These factors were analyzed using the Dynamic Ordinary Least Squares (DOLS), Fully Modified Ordinary Least Squares (FMOLS), and Pooled Mean Group (PMG) estimators to obtain estimations of heterogeneous parameters. The outcome of these tests and examinations showed that the N-shaped curve was confirmed. Secondly, The results of the study also demonstrate the effectiveness of renewable energy as an eco-friendly innovation in reducing carbon emissions. This finding highlights the positive impact that renewable energy sources can have in terms of emitting fewer carbon emissions compared to traditional energy sources. Moreover, public investment, which interprets government expenditure, and urbanization contribute to environmental degradation by increasing CO2 emissions in the case of North African countries. Furthermore, the findings also indicated a trade-off effect resulting from the correlation between CO2 emissions and economic development. Based on these findings, the study recommends that economic policymakers in North African countries prioritize transforming the structure of government expenditures to improve environmental quality, optimize the utilization of revenues from non-environmentally friendly energy resources to accelerate the energy transition, increase the exploitation of renewable energy, and promote environmental awareness in society. By implementing these recommendations, North African countries can balance economic growth and environmental quality while reducing their carbon footprint.

Dynamic correlations and portfolio implications across stock and commodity markets before and during the COVID-19 era: A key role of gold.

Novel Coronavirus (COVID-19) has affected stock markets around the globe, adding serious challenges to asset allocations and hedging strategies. This investigation analyses the dynamic correlations and portfolio implications among the S&P 500 index and various commodities (gold, WTI crude oil, Brent oil, beverages, and wheat) before and during the COVID-19 era. Using multivariate asymmetric GARCH models, the results show weak correlations during the standard period. However, the correlations intensify and become more complicated during the COVID-19 era, especially between gold and S&P 500. Similarly, bidirectional return and volatility spillovers across stock-commodity markets are more pronounced during the COVID-19 outbreak. Analysis involving the optimal portfolio weights and time-varying hedge ratios indicates that a $1long position in the S&P 500 can be hedged for 15 cents in crude oil during the standard period and for 33 cents in gold during the COVID-19 era. A portfolio of S&P 500 - beverages displays the highest VaR, while a portfolio of S&P 500 - gold displays the lowest VaR, especially during the COVID-19 era. This finding suggests that gold offers better portfolio diversification benefits and downside risk reductions, which are useful in determining strategies for portfolio investors during the COVID-19 outbreak.

Revisiting the EKC hypothesis by assessing the complementarities between fiscal, monetary, and environmental development policies in China.

Recently, China has declared its national objective of becoming carbon neutral by 2060. Hence, mitigating carbon dioxide emissions has become an important agenda of the Chinese government. Against this backdrop, this paper aims to evaluate the effectiveness of pursuing expansionary fiscal and monetary policies on China's carbon dioxide emission figures by using annual frequency data from 1980 to 2018. Accordingly, this study considers the levels of government expenditure and broad money supply as fiscal and monetary policy instruments, respectively. Besides accounting for structural break concerns in the data, the findings from the empirical analysis reveal that there are long-run associations between carbon dioxide emissions, economic growth, and fiscal and monetary expansion in China. Moreover, the results also show that in both the short- and long-run expansionary fiscal policy trigger higher carbon dioxide emissions while expansionary monetary policy inhibits the carbon dioxide emission figures of China. Furthermore, the results invalidate the existence of the Environmental Kuznets Curve hypothesis since the relationship between China's economic growth and carbon dioxide emissions is evidenced to portray an N-shape. In line with these findings, it is recommended that China achieve environmentally sustainable economic growth by aligning the national fiscal and monetary policies with the 2060 carbon-neutrality objective.

Polymerization kinetics of bicyclic olefins and mechanism with symmetrical ansa-metallocene catalysts associated with active center count: relationship between their activities and structure and activation path.

Copolymerization of ethylene (E) with 5-vinyl-2-norbornene (VNB) catalyzed by ansa-metallocenes allows the precise control of essential polymeric properties such as comonomer incorporation, molecular weight (M w), and polydispersity (D). Significant efforts have been devoted to synthesizing and developing novel catalysts, cocatalysts, and activators, although the fundamental elements of catalytic processes remain unclear. For example, it is questionable how polymeric catalysts are divided across dormant and active sites and how this distribution affects the order of monomers for the propagation rate, which widely vary in the literature. Furthermore, although the empirical correlation between the monomers and average M w has been established in many systems, the fundamental processes of chain termination remain unknown. Furthermore, the involvement of ion-pairing in metallocene-catalyzed polymerization and the termination mechanisms are also contentious issues. In this study, we describe the use of a quenched-labeling technique based on acyl chloride to selectively quench the zirconium metal-polymeric bond, which can be used to study the kinetics, active site [Zr][C*] counting, copolymer microstructure, and molecular weight distribution (MWD) to determine the rate laws for chain initiation, chain propagation rate (R p), propagation rate constant (k p) and chain termination. In addition, we also predict previously unknown chemical characteristics of E/bicyclic copolymerization processes, where either a cis-endocyclic double bond with steric properties or a vinyl exocyclic double bond affects the activity, i.e., [Zr]/[*C], (R p) and (k p). All these properties require the implementation of a particular kinetic mechanism that assumes the low activity of the building copolymer chains incorporating a single ethylene/VNB unit, i.e., the Cp2Zr-C2H5 group, in the ethylene addition process in the Cp2Zr-C bond. Due to ß-agostic stabilization, the Cp2Zr-C2H5 group exhibits a distinct feature. These effects were confirmed experimentally, such as the E/VNB co-polymer activity and VNB mol%, propagation rate decrease in the polymerization time (t p) of 120 s to 1800 s, crystalline properties, and significant increase in molecular weight. The active center [Zr]/[*C] fraction considerably increased in the initial (t p) 840 s, and subsequently tended to the steady stage of 33%, which is lower than previously reported E homo- and E/P copolymerization. The lower [C*]/[Zr] in both the early and stable stages, decrease in VNB mol%, and R p with t p can be associated with the more significant fraction of Cp2Zr-CH2CH3-type dormant site by the ß-agostic hydrogen interaction with the Cp2Zr metal. The t p versus R pE, R pVNB, k pE, k pVNB, and [Zr]/[C*] count could be fitted to a model that invokes deactivation of the growing polymer chains. In the case of the thermal behavior of the copolymers (melting temperature (T m) and crystalline temperature (ΔH m)), T m varied from 101 °C to 121 °C, while ΔH m varied from 9 to 16 (J g-1).

Ceramic-reinforced HEA matrix composites exhibiting an excellent combination of mechanical properties.

CoCrFeNi is a well-studied face centered cubic (fcc) high entropy alloy (HEA) that exhibits excellent ductility but only limited strength. The present study focusses on improving the strength-ductility balance of this HEA by addition of varying amounts of SiC using an arc melting route. Chromium present in the base HEA is found to result in decomposition of SiC during melting. Consequently, interaction of free carbon with chromium results in the in-situ formation of chromium carbide, while free silicon remains in solution in the base HEA and/or interacts with the constituent elements of the base HEA to form silicides. The changes in microstructural phases with increasing amount of SiC are found to follow the sequence: fcc → fcc + eutectic → fcc + chromium carbide platelets → fcc + chromium carbide platelets + silicides → fcc + chromium carbide platelets + silicides + graphite globules/flakes. In comparison to both conventional and high entropy alloys, the resulting composites were found to exhibit a very wide range of mechanical properties (yield strength from 277 MPa with more than 60% elongation to 2522 MPa with 6% elongation). Some of the developed high entropy composites showed an outstanding combination of mechanical properties (yield strength 1200 MPa with 37% elongation) and occupied previously unattainable regions in a yield strength versus elongation map. In addition to their significant elongation, the hardness and yield strength of the HEA composites are found to lie in the same range as those of bulk metallic glasses. It is therefore believed that development of high entropy composites can help in obtaining outstanding combinations of mechanical properties for advanced structural applications.