Positive Energy Research Articles

Existence and blow up for viscoelastic hyperbolic equations with variable exponents

<p>In this article, we consider a nonlinear viscoelastic hyperbolic problem with variable exponents. By using the Faedo$ - $Galerkin method and the contraction mapping principle, we obtain the existence of weak solutions under suitable assumptions on the variable exponents $ m(x) $ and $ p(x) $. Then we prove that a solution blows up in finite time with positive initial energy as well as nonpositive initial energy.</p>

Research on the Tunneling Radiation of Bosons from the Kerr-Sen-like Black Hole by Einstein-Bumblebee Gravitational Theory

Lorentz-breaking theory not only affects the curved space-time background, but also modifies the dynamic equations of bosons and fermions in curved space-time to some extent. Therefore, we need to make appropriate corrections for the quantum tunneling radiation of bosons and fermions in different black hole spacetimes. New expressions of black hole Hawking temperature and other physical quantities modified by Lorentz-breaking theory and their physical meanings are obtained. In this paper, according to the Kerr-Sen-like (KSL) black hole spacetime metric obtained from Einstein-Bumblebee gravitational theory, by introducing the correction term of the aether-like field vector into the scalar field action and the d'Alembert operator in curved spacetime, and applying the variational principle in curved spacetime, the Lorentzbreaking correction term in the spacetime metric and the new form of the dynamic equation of the bosons with zero spin in KSL spacetime are studied. By correctly selecting the aether-like field vector corresponding to the KSL spacetime metric and solving the modified bosons dynamic equation, the modified quantum tunneling rate is obtained. On this basis, the Hawking temperature and Bekenstein- Hawking entropy of the black hole with Lorentz-breaking correction term are studied. The effects of Lorentz-breaking theory on the distribution of positive and negative energy levels of bosons and the maximum crossing of energy levels are also studied, and then the conditions of quantum non-thermal radiation in the black hole space-time is studied. At the end of this paper, the physical significance of a series of results obtained in this paper is discussed in depth. The results show that the modified form of the bosons dynamic equation in curved spacetime, taking into account Lorentz-breaking theory, is shown in equation (26) and equation (27). The new expressions of the quantum tunneling rate, Bekenstein-Hawking entropy, Hawking temperature and quantum non-thermal radiation energy range of KSL black hole are obtained by applying equation (26) to KSL black hole space-time. These results are useful for studying the quantum tunneling radiation characteristics of black holes. It should be noted that the above research results are obtained under the WKB theory and the semiclassical case. If the effects of different powers of Planck are to be considered, the above research methods and related results need to be used for further modified research by using beyond the semi-classical theory.

Novel nitrogen-doped carbon-coated SnSe2 based on a post-synthetically modified MOF as a high-performance anode material for LIBs and SIBs.

SnSe2 with high theoretical capacity has been identified as an emerging anode candidate for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, the rate performance and cycling performance of this material in practical applications are still limited by unavoidable volume expansion and low conductivity. In this work, we designed and synthesized nitrogen-doped carbon-coated SnSe2/C-N composites using 2-aminoterephthalic acid (C8H7NO4) as a nitrogen-containing compound for modification by hydrothermal and vacuum calcination methods to achieve efficient utilization of active sites and optimization of the electronic structure. The carbon skeleton inherited from the Sn-MOF precursor can effectively improve the electronic conduction properties of SnSe2. N-doping in the Sn-MOF can increase the positive and negative electrostatic potential energy regions on the molecular surface to further improve the electrical conductivity, and effectively reduce the binding energy with Li+/Na+ which was determined by Density Functional Theory (DFT) methods. In addition, the N-doped carbon skeleton also introduces a larger space for Li+/Na+ intercalation and enhances the mechanical properties. In particular, the post-synthetically modified MOF-derived SnSe2/C-N materials exhibit excellent cyclability, with a reversible capacity of 695 mA h g-1 for LIBs and 259 mA h g-1 for SIBs after 100 cycles at 100 mA g-1.

Global existence of weak solutions to a class of higher-order nonlinear evolution equations

<p>This paper deals with the initial boundary value problem for a class of <italic>n</italic>-dimensional higher-order nonlinear evolution equations that come from the viscoelastic mechanics and have no positive definite energy. Through the analysis of functionals containing higher-order energy of motion, a modified potential well with positive depth is constructed. Then, using the potential well method, and Galerkin method, it has been shown that when the initial data starts from the stable set, there exists a global weak solution to such an evolution problem.</p>

Regulation of magnetic moment and magnetic anisotropy of magnetite by doping transition metal elements

Magnetic Fe<sub>3</sub>O<sub>4</sub> nanoparticles show promising applications in nanomedicine. The saturation magnetization (<i>M</i><sub>S</sub>) and magnetic anisotropy are critical for the applications of Fe<sub>3</sub>O<sub>4</sub> nanoparticles in drug delivery and magnetic hyperthermia. Here, by density functional computation, the doping effects of 3d and 4d transition metal elements (including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd) on the magnetic properties of Fe<sub>3</sub>O<sub>4</sub> are investigated in-depth. A conventional cell of Fe<sub>3</sub>O<sub>4</sub>, containing 24 Fe atoms and 32 O atoms, has been used to investigate the doping of group III elements. One 3d or 4d atom is doped in one conventional cell of Fe<sub>3</sub>O<sub>4</sub>, resulting in the formation of X<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> where X represents the dopant. The results show that the doping of most 3d and 4d transition metal elements will reduce the total magnetic moment, while the doping of Ag, Zn and Cd in Fe<sub>3</sub>O<sub>4</sub> will increase the total magnetic moment by 19%–22%. However, it is hard to dope Ag into Fe<sub>3</sub>O<sub>4</sub> according to the positive formation energy. Therefore, Zn and Cd are good candidates to improve the <i>M</i><sub>S</sub> of Fe<sub>3</sub>O<sub>4</sub>. The doping of Zn and Cd has also an influence on the magnetic anisotropy of Fe<sub>3</sub>O<sub>4</sub>. For Zn<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub>, the magnetic anisotropy energy is about 0.25 meV per cell, which is slightly larger than that of intrinsic Fe<sub>3</sub>O<sub>4</sub> (0.2 meV per cell). Interestingly, the doping of Cd (Cd<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub>) will greatly increase the magnetic anisotropy energy to 0.8 meV per cell, which is significant for the specific absorption rate in the magnetic hyperthermia application. In addition, the doping of Zn and Cd will not induce any defect states in the band gap according to the density of states. Zn<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> and Cd<sub>0.125</sub>Fe<sub>2.875</sub>O<sub>4</sub> are both semiconducting and both the top of valence band and the bottom of conduction band originate from octahedral Fe. This is because the impurity states are very deep in energy. Our research results show that doping Cd is a feasible way to improve the performance of Fe<sub>3</sub>O<sub>4</sub> as a material for drug delivery and magnetic hyperthermia.

Study and development of diagnostic systems to characterise the extraction region in SPIDER

SPIDER, an RF-driven negative ion source in the Neutral Beam Test Facility (NBTF), serves as the prototype for ITER's neutral beam injector (NBI). It is composed of 8 drivers powered by 4 RF generators, aiming to accelerate 50 A of negative hydrogen ions to 100 KeV with a beam uniformity target of 10%. The experiment, launched in 2018, tested negative ion production using caesium. Results match those of similar facilities, but SPIDER faces challenges due to its size, multiple drivers, and non-uniform plasma expansion. These issues impact beam uniformity, preventing the machine from reaching expected performance. To address this, SPIDER initiated a significant shutdown at the end of 2021 for improvements.One the most important aspects studied during the first experimental campaign is source uniformity, addressed both in terms of plasma and of caesium distribution. The latter is particularly relevant since its quality is directly related to the beam uniformity and divergence. To have more insight about these issues, monitoring the plasma properties in the extraction region is crucial, hence in the present contribution, the design and development of two new diagnostic systems are described: a movable Langmuir probe and a Retarding Field Energy Analyser (RFEA).The first can provide a vertical scan of the main plasma parameters close to the plasma grid. The spatial resolution would improve with respect to the already installed set of fixed Langmuir probes embedded in the grid system, and the newly installed diagnostic could interact with other sensors to produce complementary measurements (namely, electron photo-detachment).The latter, instead, allows the monitoring of the positive ion energy distribution: positive ions, in fact, can be precursors of the negative ones produced at the caesiated surface, but also influence the energy of negative ion and their extraction probability and thus collecting information about their energy distribution allows inferring details about the extracted negative ion beam.The two diagnostics are designed focusing on the experimental constraint of integrating the diagnostics in a harsh and complex environment such as SPIDER plasma: a preliminary study of the placement inside the source is carried out, then the electrode of the movable probe and the RFEA sensor are sized according to the spatial and energy resolution requested by the system.

Broadband maps of eROSITA and their comparison with the ROSAT survey

By June of 2020, the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Spectrum Roentgen Gamma observatory had completed its first of the planned eight X-ray all-sky survey (eRASS1). The large effective area of the X-ray telescope makes it ideal for a survey of the faint X-ray diffuse emission over half of the sky with an unprecedented energy resolution and position accuracy. In this work, we produce the X-ray diffuse emission maps of the eRASS1 data with a current calibration, covering the energy range from 0.2 to 8.0 keV. We validated these maps by comparison with X-ray background maps derived from the ROSAT All Sky Survey (RASS). We generated X-ray images with a pixel area of 9 arcmin2 using the observations available to the German eROSITA consortium. The contribution of the particle background to the photons was subtracted from the final maps. We also subtracted all the point sources above a flux threshold dependent on the goal of the subtraction, exploiting the eRASS1 catalog that will soon be available. The accuracy of the eRASS1 maps is shown by a flux match to the RASS X-ray maps, obtained by converting the eROSITA rates into equivalent ROSAT count rates in the standard ROSAT energy bands R4–R7, within 1.25σ. We find small residual deviations in the R4–R6 bands, where eROSITA tends to observe lower flux than ROSAT (~11%), while a better agreement is achieved in the R7 band (~1%) The eRASS maps exhibit lower noise levels than RASS maps at the same resolution above 0.3 keV. We report the average surface brightness and total flux of different large sky regions as a reference. The detection of faint emission from diffuse hot gas in the Milky Way is corroborated by the consistency of the eRASS1 and RASS maps shown in this paper and by their comparable flux dynamic range.

A Market Strategy for Joint Profitability of Electric Vehicle Charging Stations and Retailers: Considering Electricity Price Fluctuations and Users’ Service Fee Response

With the introduction of the “carbon peaking and carbon neutralizing” initiative, China is undergoing a positive energy transition, emphasizing the replacement of traditional fossil fuels with clean energy sources. As part of this transition, numerous megacities are progressively endorsing electric vehicles (EVs) as substitutes for traditional fuel‐based vehicles. The expanding use of EVs, however, has presented challenges related to the randomness and volatility of EV charging. In response to this, many regions in China have mandated the implementation of the time‐of‐use (ToU) scheme. This scheme divides the day into distinct periods such as “valley,” “flat,” “peak,” and “critical peak,” each associated with varying charging prices. According to the management regulations, the fees collected from vehicle owners at the charging station are divided into two parts: ToU electricity value and service fees. The former is jointly determined by the power company and the government, while the latter is set by the charging station operator. To overcome the limitation on profitability, this paper proposes a scheme enabling charging stations and retailers to participate in the day‐ahead (DA) market. The proposed approach involves a two‐stage decision‐making method. By analyzing the charging habits of local residents, the paper constructs a quadratic curve for dynamic service fees and charging rates. The objective function is then utilized to adjust the anticipated charging load curve. Prior to the DA‐bidding process, an uncertain set of scenarios for electricity prices and charging loads is generated. The conditional value‐at‐risk (C‐VaR) method is employed to balance expected benefits and risks amid uncertain scenarios.

Application of Taoist Principles and Feng Shui in Urban Spaces (Landscaping and Garden Design)

The Taoist school emphasizes concepts such as "Yin and Yang" and "Tehya." Taoism has had a profound influence on architecture, painting, landscaping, home decoration, and lifestyle, extending beyond the borders of China to impact the entire modern world. The application of Far Eastern worldviews based on Taoist thought and its arrangement techniques, such as Feng Shui and its unique interior decoration in homes, urban spaces, garden design, and landscaping, deeply enhances and elevates the quality of life. Relying on ancient knowledge and experience, it can be stated that Tao is a spiritual way of life that enables humans to channel the positive energies of nature into themselves. The present study poses the question of how Taoist philosophical concepts influence urban space design. Taoism, one of the oldest philosophical schools in China, has significantly impacted the art of that region, with its ultimate goal being the harmony and consonance of humans with the natural order in life. Given that the practical art of Feng Shui is a derivative of this philosophy, the aim of this research is to identify and apply the fundamental elements of this mystical philosophy in urban planning and landscaping, and to bridge the gap between theory and practice in the philosophy and art of interior and exterior design. In this study, which presents its findings in an analytical-descriptive manner, we first analyze and examine Feng Shui's influence on the mystical and ontological foundations of Taoism and the manifestation of this approach in design and landscaping principles. It is then demonstrated that the application of these elements in urban spaces can bring not only visual beauty but also peace, balance, and harmony to the modern urban dweller.

Co-creation Processes and Urban Digital Twins in Sustainable and Smart Urban District Development - Case Kera District in Espoo, Finland.

In the context of climate change mitigation, calls for methods that can facilitate co-creative practices and processes between different stakeholders in the development of sustainable and climate-neutral urban districts have been increasingly expressed in recent years. This has included calls for collaborative, accessible, transparent and open tools that can facilitate urban development processes and engage different stakeholders in the different phases and stages of an urban district development process towards shared targets on sustainability and emission reduction. In this paper, we present and examine two practical tools, 1) a co-creation model for developing positive energy district (PED) solutions, and 2) a digital twin tool for shared data sharing and collaboration, which were developed and utilized recently in two development projects focusing on Kera district, Espoo, Finland. The Kera district is a current brownfield area, which, since the early 2020s, has been undergoing a transformation from a former industrial and mass logistics area into a future mixed-use urban district with significant emphasis on sustainability and circular economy targets. We utilize actor-network theory (ANT) to explore the human and the non-human actors and their interrelations related to the district's development. Additionally, we seek to understand the networks that emerge within both the co-creation process and the virtual urban digital twin environment and the role these tools have in supporting the formation and facilitation of multi-stakeholder co-creation networks. Finally, we aim to examine the advantages and disadvantages of integrating a regional urban digital twin and the urban co-creation process to enhance sustainability in urban development projects.

High-Speed Rail and Energy Productivity: Evidence from China

Using the difference-in-differences method combined with the propensity score matching, this study identifies the causal relationship between high-speed rail (HSR) and energy productivity in China. Furthermore, we investigate the mechanism through which HSR affects energy productivity, as well as the heterogeneity of the impact across quantiles and distances. The results show that HSR connection contributes to the improvement of energy productivity. This finding is consolidated after a potential endogeneity problem is addressed using the instrumental variable method and a variety of potential confounders are controlled through a series of robustness checks. On average, the marginal impact of HSR on energy productivity is approximately 9%. Moreover, HSR connection cannot be completely substituted by traditional railway and aviation in improving energy productivity. The heterogeneity analysis suggests that the positive energy productivity effect of HSR gradually decreases with an increasing distance to the nearest HSR station. In addition, HSR network accessibility has a significant positive effect on energy productivity, while technological innovation mediates the relationship between HSR development and energy productivity. We propose that to achieve the long-term improvement of energy productivity, policymakers should comprehensively consider both transit-oriented development and ecology-oriented development modes.

Comparing the net-energy balance of standalone photovoltaic-coupled electrolysis and photoelectrochemical hydrogen production.

Photovoltaic-coupled electrolysis (PV-E) and photoelectrochemical (PEC) water splitting are two options for storing solar energy as hydrogen. Understanding the requirements for achieving a positive energy balance over the lifetime of facilities using these technologies is important for ensuring sustainability. While neither technology has yet reached full commercialisation, they are also at very different technology readiness levels and scales of development. Here, we model the energy balance of standalone large-scale facilities to evaluate their energy return on energy invested (ERoEI) over time and energy payback time (EPBT). We find that for average input parameters based on present commercialised modules, a PV-E facility shows an EPBT of 6.2 years and ERoEI after 20 years of 2.1, which rises to approximately 3.7 with an EPBT of 2.7 years for favourable parameters using the best metrics amongst large-scale modules. The energy balance of PV-E facilities is influenced most strongly by the upfront embodied energy costs of the photovoltaic component. In contrast, the simulated ERoEI for a PEC facility made with earth abundant materials only peaks at 0.42 after 11 years and about 0.71 after 20 years for facilities with higher-performance active materials. Doubling the conversion efficiency to 10% and halving the degradation rate to 2% for a 10-year device lifetime can allow PEC facilities to achieve an ERoEI after 20 years of 2.1 for optimistic future parameters. We also estimate that recycling the materials used in hydrogen production technologies improves the energy balance by 28% and 14% for favourable-case PV-E and PEC water splitting facilities, respectively.

Interacting dark energy: clarifying the cosmological implications and viability conditions

In this study, cosmological models are considered, where dark matter and dark energy are coupled and may exchange energy through non-gravitational interactions with one other. These interacting dark energy (IDE) models have previously been introduced to address problems with the standard ΛCDM model of cosmology (which include the coincidence problem, Hubble tension and S_8 discrepancy). However, conditions ensuring positive energy densities have often been overlooked. Assuming two different linear dark energy couplings, Q = δ H ρ_de and Q = δ H ρ_dm, we find that negative energy densities are inevitable if energy flows from dark matter to dark energy (iDMDE regime) and that consequently, we should only seriously consider models where energy flows from dark energy to dark matter (iDEDM regime). To additionally ensure that these models are free from early time instabilities, we need to require that dark energy is in the `phantom' (ω<-1) regime. This has the consequence that model Q=δ H ρ_dm will end with a future big rip singularity, while Q = δ H ρ_de may avoid this fate with the right choice of cosmological parameters.

Life-cycle assessment of microalgae liquid biofuel production in biofilm cultivation system via conversion technologies of transesterification, hydrothermal liquefaction and pyrolysis

Biofilm seems to be an ideal cultivation system for microalgae liquid biofuel conversion technologies due to the advantage of high biomass concentration. However, research on the biofilm cultivation system for microalgae liquid biofuel producing were limited. In this study, a life-cycle assessment was conducted for microalgae liquid biofuel production in this system via three conversion technologies: transesterification, hydrothermal liquefaction and pyrolysis. The result shows that scenario hydrothermal liquefaction seems to be the most feasible technology to produce liquid biofuel in biofilm system because only hydrothermal liquefaction achieved positive energy and environment benefits with a net energy ratio of 0.87 and Greenhouse gas emissions of −39.91 g CO2-eq MJ−1. For transesterification and pyrolysis, the net energy ratio (2.18 and 2.06) were larger than 1, while Greenhouse gas emissions (3.28 and 59.25 g CO2-eq) were greater than 0. This indicated that these scenarios exhibited negative energy and environment benefits due to heavy use of chemicals and high energy consumption during biomass drying process, respectively. Additionally, according to the sensitivity analysis, bio-crude mass yield exhibited a more significant impact on the energy and environment loads for scenario hydrothermal liquefaction than the other factors.

The Application and Management of University WeChat Official Accounts in College Student Ideological Education A Exploration Based on the “BIFT Art Sea Studio” WeChat Official Account

In the contemporary digital era, the utilization of university WeChat Official Accounts has become a pivotal tool in college student ideological education. This study delves into the application and management of such accounts, with a particular focus on the exploration of the “BIFT Art Sea Studio” WeChat Official Account. Grounded in the distinctive characteristics of the Beijing Institute of Fashion Technology (BIFT) — “Art as the Core, Fashion as the Guide, Integration of Art and Engineering,” this Official Account features sections such as “Famous Paintings in ‘Spring and Autumn’,” “Wearing Philosophy,” and “Red ‘Time Machine’.” The overarching goal is to transform individuals through art, refine morality, and concentrate positive energy. The study highlights the effective alignment of content with school characteristics, the use of multimedia content to capture student attention, and the positive impact on ideological education. It also acknowledges challenges in audience engagement and proposes future research directions to optimize the potential of WeChat Official Accounts in shaping the ideological landscape of college students.

Estimating the interfacial permeability for flow into a poroelastic medium.

Boundary conditions between a porous solid and a fluid has been a long-standing problem in modeling porous media. For deformable poroelastic materials such as hydrogels, the question is further complicated by the elastic stress from the solid network. Recently, an interfacial permeability condition has been developed from the principle of positive energy dissipation on the hydrogel-fluid interface. Although this boundary condition has been used in flow computations and yielded reasonable predictions, it contains an interfacial permeability η as a phenomenological parameter. In this work, we use pore-scale models of flow into a periodic array of solid cylinders or parallel holes to determine η as a function of the pore size and porosity. This provides a means to evaluate the interfacial permeability for a wide range of poroelastic materials, including hydrogels, foams and biological tissues, to enable realistic flow simulations.

Directional dependence of the electronic and transport properties of biphenylene under strain conditions.

In this study, we investigated the electronic and electronic transport properties of biphenylene (BPN) using first-principles density functional theory (DFT) calculations combined with the non-equilibrium Green's function (NEGF) formalism. We have focused on understanding the electronic properties of BPN, and the anisotropic behavior of electronic transport upon external strain. We found the emergence of electronic stripes (ESs) on the BPN surface and the formation of type-II Dirac cone near the Fermi level. In the sequence, the electronic transport results reveal that such ESs dictate the anisotropic behavior of the transmission function. Finally, we show that the tuning of the (anisotropic) electronic current, mediated by external mechanical strain, is ruled by the energy position of the lowest unoccupied states with wave-vectors perpedicular to the ESs. This control could be advantageous for applications in nanoelectronic devices that require precise control of current direction.

Quantum interference and spin transport in M-OPE molecular devices controlled by N or B atom substitution

In this paper, the first-principles method based on density functional theory and non-equilibrium Green’s function is used to investigate the modulation of quantum interference and spin transport in N and B atom substituted meta-phenylene (M-OPE) molecular devices. The zero bias spin transmission spectrum of M-OPE molecular device shows that highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are located at higher energy positions on both sides of the Fermi level, and there is a clear transmission spectrum valley (anti resonance peak) on the right side of the Fermi level. This indicates that M-OPE molecules are typical destructive quantum interference molecular systems. Research has found that N and B atoms replace carbon atoms at positions 1, 2, and 3 on the central ring of the molecule, which suppress the original destructive quantum interference of M-OPE molecular device to different extents. The substitution of N and B atoms at position 1 has no effect on the original destructive quantum interference of M-OPE molecular device, while the substitution of N and B atoms at positions 2 and 3 significantly suppresses the original destructive quantum interference of M-OPE molecular device. Therefore, there is a significant difference in the electrical conductivity of devices with N and B atoms at different positions, with the order of electrical conductivity values being N2 &gt; N3 &gt; N1 and B2 &gt; B3 &gt; B1. In this study, it is also found that the spin current value of device with B atom substitution is significantly higher than that of device with N atom substitution. After the substitution of B atom at position 2, the spin current value of the device under negative bias is significantly greater than that under positive bias, exhibiting a significant spin rectification effect. Based on the extended curled arrow rule proposed by O’Driscoll et al. to predict the behavior of quantum interference effects, we explain the physical mechanism by which N and B protons at different positions have different effects on the suppression of quantum interference in M-OPE molecular device. The results of the quantum interference and spin transport regulation of molecular systems by the substitution of B and N atoms can provide theoretical guidance for realizing the further application of heterocyclic aromatic hydrocarbons in molecular electronics.

Allotropic Ga2Se3/GaSe nanostructures grown by van der Waals epitaxy: narrow exciton lines and single-photon emission.

The ability to emit narrow exciton lines, preferably with a clearly defined polarization, is one of the key conditions for the use of nanostructures based on III-VI monochalcogenides and other layered crystals in quantum technology to create non-classical light. Currently, the main method of their formation is exfoliation followed by strain and defect engineering. A factor limiting the use of epitaxy is the presence of different phases in the grown films. In this work, we show that control over their formation makes it possible to create structures with the desired properties. We propose Ga2Se3/GaSe nanostructures grown by van der Waals epitaxy with a high VI/III flux ratio as a source of narrow exciton lines. Actually, these nanostructures are a combination of allotropes: GaSe and Ga2Se3, consisting of the same atoms in different arrangements. The energy positions of the narrow lines are determined by the quantum confinement in Ga2Se3 inclusions of different sizes in the GaSe matrix, similar to quantum dots, and their linear polarization is due to the ordering of Ga vacancies in a certain crystalline direction in Ga2Se3. Such nanostructures exhibit single-photon emission with second-order correlation function g(2)(0) ∼ 0.10 at 10 K that makes them promising for quantum technologies.

Disentangling doping and strain effects at defects of grown MoS2 monolayers with nano-optical spectroscopy.

The role of defects in two-dimensional semiconductors and how they affect the intrinsic properties of these materials have been a widely researched topic over the past few decades. Optical characterization techniques such as photoluminescence and Raman spectroscopies are important tools to probe the physical properties of semiconductors and the impact of defects. However, confocal optical techniques present a spatial resolution limitation lying in a μm-scale, which can be overcome by the use of near-field optical measurements. Here, we use tip-enhanced photoluminescence and Raman spectroscopies to unveil the nanoscale optical properties of grown MoS2 monolayers, revealing that the impact of doping and strain can be disentangled by the combination of both techniques. A noticeable enhancement of the exciton peak intensity corresponding to trion emission quenching is observed at narrow regions down to a width of 47 nm at grain boundaries related to doping effects. Besides, localized strain fields inside the sample lead to non-uniformities in the intensity and energy position of photoluminescence peaks. Finally, two distinct MoS2 samples present different nano-optical responses at their edges associated with opposite strains. The edge of the first sample shows a photoluminescence intensity enhancement and energy blueshift corresponding to a frequency blueshift for E2g and 2LA Raman modes. In contrast, the other sample displays a photoluminescence energy redshift and frequency red shifts for E2g and 2LA Raman modes at their edges. Our work highlights the potential of combining tip-enhanced photoluminescence and Raman spectroscopies to probe localized strain fields and doping effects related to defects in two-dimensional materials.