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Abstract. In this paper, we attempted to detect the effect of provided answers on those that succeed them, the “item proximity effect,” within a questionnaire with randomized item order for each respondent. In two studies, we administered personality inventories to two samples of mostly undergraduate students, consisting of 742 and 205 respondents, respectively. We expected to see a strong item proximity effect that quickly diminishes with higher item distances, but we found no evidence of such effect in the data. Thus, we failed to conceptually replicate the findings of previous studies. After discussing the probable causes for these discrepancies, we argue that a general item proximity effect does not need to be considered a major factor when employing and evaluating common psychological inventories with randomized item order for research purposes.

Microscopically visualizing the evolution of electronic structures at the interface between two electron-correlated domains shows fundamental importance in both material science and physics. Here, we report scanning tunneling microscopy and spectroscopy studies of the interfacial electronic structures evolution in a phase-engineered monolayer NbSe2 heterostructure. The H-NbSe2 metallic state penetrates the Mott insulating T-NbSe2 at the H/T phase interface, with a prominent 2D charge density wave (CDW) proximity effect. Moreover, an insulating Mott gap collapse with the disappearance of the upper Hubbard band is detected at the electronic phase transition region. Theoretical calculations reveal that such insulating Mott gap collapse can be attributed to the electron doping effect induced by the interface. Our findings promote a microscopical understanding of the interactions between different electron-correlated systems and provide an effective method for controlling the Mott insulating states with phase engineering.

Introduction: Consumption of snacks and food can be reduced by placing them further away from an individual, known as the Proximity Effect. This effect is generally thought to be robust, and observable between when snacks are presented at 20cm and 70cm. It is assumed that this effect occurs without conscious awareness or processing, but no study has experimentally tested whether the effect occurs via non-conscious processing. Method: A sample of 84 individuals is targeted, with each individual being assigned to one of four conditions via computerised random number sequence. A 2(Distance; 20cm, 70cm) x 2(Attention State; Distraction/Video, Control/No Video) between subjects design is implemented, with all individuals being presented with a bowl containing 250g of M&M’s. Individuals will either be asked to watch a 5-minute video clip, or sit quietly for 5 minutes. Snack consumption is measured at two levels: likelihood of consumption (any snack consumed vs none consumed), and actual consumption (continuous, measured in grams). Snacks will be removed after the 5 minute period, with individuals then being asked to complete a short questionnaire. Analysis: A binary logistic regression will be conducted to test for differences in likelihood of consumption. Actual consumption will be analysed through a 2x2 ANCOVA. Covariates of Perceived Effort and Visual Salience will be included in models for both analyses to assess the influence of these factors. Sensitivity analysis will be conducted for when outliers, those who were aware of the study intent, and those influenced by their environment are removed from analysis. All outcomes will be reported.Discussion: The proposed study will assess whether individuals consume more snacks when presented closer (proximity effect), as well as if consumption is higher when watching a short video clip, and the interaction between the two factors. Outcomes of the study will allow researchers to determine whether the proximity effect is likely to occur via non-conscious processing and without conscious awareness, or whether the effect occurs while individuals are aware of their behaviour. The results may influence future research and choice architects to ensure less-healthy snacks are placed further away if individuals are distracted with another stimulus to prevent mindless eating.

The development of stable and low-cost catalysts with high reactivity to replace Pt-based ones is the central focus but challenging for hydrogen evolution reaction (HER). The incorporation of single atoms into two-dimensional (2D) supports has been demonstrated as an effective strategy because of the highly active single atomic sites and extremely large surface area of two-dimensional materials. However, the doping of single atoms is normally performed on the surface suffering from low stability, especially in acidic media. Moreover, it is experimentally challenging to produce monolayered 2D materials with atomic doping. Here, we propose a strategy to incorporate single foreign Fe atoms to substitute W atoms in sandwiched two-dimensional WS2. Because of the charge transfer between the doped Fe atom and its neighboring S atoms on the surface, the proximate S atoms become active for HER. Our theoretical prediction is later verified experimentally, showing an enhanced catalytic reactivity of Fe-doped WS2 in HER with the Volmer-Heyrovsky mechanism involved. We refer to this strategy as proximity catalysis, which is expected to be extendable to more sandwiched two-dimensional materials as substrates and transition metals as dopants.

In a Fe/(Cd,Mg)Te/CdTe quantum well hybrid structure, short-range and long-range ferromagnetic proximity effects are found to coexist. The former is observed for conduction band electrons, while the latter is observed for holes bound to shallow acceptors in the CdTe quantum well. These effects arise from the interaction of charge carriers confined in the quantum well with different ferromagnets, where electrons interact with the Fe film and holes with an interfacial ferromagnet at the Fe/(Cd,Mg)Te interface. The two proximity effects originate from fundamentally different physical mechanisms. The short-range proximity effect for electrons is determined by the overlap of their wave functions with d-electrons of the Fe film. On the contrary, the long-range effect for holes bound to acceptors is not associated with overlapping wave functions and can be mediated by elliptically polarized phonons. The coexistence of the two ferromagnetic proximity effects reveals the presence of a nontrivial spin texture within the same heterostructure.

The efforts toward the experimental realization of spin-polarized transports in ideal materials or platforms, such as the magnetized graphene or various quantum Hall states, is a research hotspot in spintronics. Magnetic van der Waals materials open the door for exploring various physical phenomena, technologies, and integrating novel spintronic devices seamlessly within the 2D limit. Here, we demonstrate magnetic proximity effect in chromium trichloride (CrCl3)/bilayer graphene (BLG) heterostructures by low-temperature transport measurements. An effective exchange field induced in BLG has been demonstrated by the Zeeman spin Hall effect via nonlocal measurements. Furthermore, the exchange field modulates the quantum Hall ground state of BLG and thus favors the formation of a canted antiferromagnetic (CAF) phase in an external perpendicular magnetic field (B⊥). Asymmetric nonlocal magneto-transport behaviors are also observed at opposite B⊥ directions, due to the asymmetric modulation on the exchange field by external B⊥ directions. Our work suggests that the 2D magnetic van der Waals materials and graphene hybrid systems offer a unique platform for quantum Hall ferromagnetism physics.

van der Waals ferromagnets have gained significant interest due to their unique ability to provide magnetic response even at the level of a few monolayers. Particularly in combination with 2D semiconductors, such as the transition metal dichalcogenide WSe2, one can create heterostructures that feature unique magneto-optical response in the exciton emission through the magnetic proximity effect. Here we use 0D quantum emitters in WSe2 to probe for the ferromagnetic response in heterostructures with Fe3GT and Fe5GT ferromagnets through an all-optical read-out technique that does not require electrodes. The spectrally narrow spin-doublet of the WSe2 quantum emitters allowed to fully resolve the hysteretic magneto-response in the exciton emission, revealing the characteristic signature of both ferro- and antiferromagnetic proximity coupling that originates from the interplay among Fe3GT or Fe5GT, a thin surface oxide, and the spin doublets of the quantum emitters. Our work highlights the utility of 0D quantum emitters for probing interface magnetic dipoles in vdW heterostructures with high precision. The observed hysteretic magneto response in the exciton emission of quantum emitters adds further new degrees of freedom for spin and g-factor manipulation of quantum states.

Recent advances in two-dimensional van der Waals (2D vdW) magnets provide new platforms to study their magnetism in reduced dimensions. However, most of the studies performed to date have been limited to low temperatures. Here, we report the proximity effect of a 2D vdW magnet Fe3GeTe2 (FGT) on nickel (Ni) films at room temperature. Ferromagnetic resonance measurements show that FGT can increase the perpendicular magnetic anisotropy (PMA) and magnetic damping of the adjacent Ni film. Such an interfacial effect is observed at room temperature, and becomes more pronounced as the temperature decreases. A similar effect is also achieved in another 2D heterostructure of Cr2Ge2Te6/Ni, implying its universality in a variety of 2D magnetic materials. Our work provides a new approach for utilizing 2D magnets in spintronics at room temperature.

The fluorescence of most organic chromophore is emitted from the ππ* state, whereas the nπ* state, as a dark state, plays an important role in quenching the fluorescence when its energy is close to the ππ* state. Herein, we report a theoretical study on the fluorescence quenching of 8-methoxy-4-methyl-2H-benzo[g]chromen-2-one by the nπ* state and propose a new mechanism for describing the vibronic coupling between the ππ* and nπ* states. By applying extended multistate complete-active-space second-order perturbation theory (XMS-CASPT2) to optimize the geometries, the geometry distortion of the ππ* state along the out-of-plane mode is observed. This geometry distortion causes the stretching vibration of the carbonyl group to be coupled with the C-C bonds of the pyran ring, which become a Franck-Condon active mode upon photoexcitation and provides a driving force for nonradiative decay from the nπ* state, even if it is energetically unfavorable. This mechanism is significantly different from the previously proposed "proximity effect" and cannot be captured by the popularly used time-dependent density functional theory (TDDFT) and complete-active-space self-consistent field (CASSCF) methods.

The presence of two-dimensional (2D) layer-stacking heterostructures that can efficiently tune the interface properties by stacking desirable materials provides a platform to investigate some physical phenomena, such as the proximity effect and magnetic exchange coupling. Here, we report the observation of antisymmetric magnetoresistance in a van der Waals (vdW) antiferromagnetic/ferromagnetic (AFM/FM) heterostructure of MnPS3/Fe3GeTe2 when the temperature is below the Neel temperature of MnPS3. Distinguished from two resistance states in conventional giant magnetoresistance, the magnetoresistance in the MnPS3/Fe3GeTe2 heterostructure exhibits three states, of high, intermediate, and low resistance. This antisymmetric magnetoresistance spike is determined by an unsynchronized magnetic switching between the AFM/FM interface layer and the bulk of Fe3GeTe2 during magnetization reversal. Our work highlights that the artificial vdW stacking structure holds potential to explore some physical phenomena and spintronic device applications.

Detection of the antiferromagnetic (AFM) state is an important issue for the application of two-dimensional (2D) antiferromagnets in spintronics, and interfacial exchange coupling is a highly efficient means to detect AFM order. However, there are no experimental reports of AFM state detection in van der Waals heterostructures, based on which 2D AFM spintronics can be developed. In this paper, we report a spin flop transition (SFT)-induced anomalous Hall effect in a heterostructure of MnPS3/graphite flake (GF) through van der Waals proximity coupling. The scaling behavior study and theoretical calculations confirm that the SFT in AFM MnPS3 can generate momentum-space nonzero Berry curvature integration in the adjacent GF. Our work opens a path for the realization of AFM state detection through the proximity effect in a stacking structure, thereby promoting the application of 2D antiferromagnets in future 2D spintronics.

External influence is essential for any change to occur in this world. Similarly, the reaction path of a chemical reaction can be changed with the addition of a catalyst from outside. Sometimes a catalyst performs better when it remains associated with an inert substance, which is called a support material (SM). Improved catalyst accomplishment arises from the 'proximity effect'. Even inert supports play a role in better product formulation or environmental remediation. In this review, it has been shown how the SM, as a nest, aids the catalyst particle synergistically to perform a good job in a chemical reaction. The structure-function relationship of SM helps in catalyst activation to some extent, and produces active centres that are difficult to fully ascertain. In the text, Langmuir-Hinshelwood (L-H), Mars-van Krevelen (MVK), and Eley-Rideal (E-R) mechanisms are highlighted for the adsorption processes as the case may be. Again, the importance of SM for both catalyst and substrates has been consolidated here in the text. Finally, the role of the initiator and the promoter is also discussed in this review.

The analytical value of peaks arising by a proximity effect in the electron ionization mass spectra of benzanilides has been established by examining the spectra of numerous examples of general structure XC6H4NHCOC6H4Y. Significant [M-X]+ signals are observed only when X = Cl, Br, I or CH3O in the 2-position. The presence of strong [M-X]+ signals, but negligibly weak [M-Y]+ peaks, even when the C-Y bond would be expected to break more readily than the C-X bond, indicates that these diagnostically useful signals do not arise by simple cleavage. Similarly, the presence of an appreciable [M-Cl]+ signal, but no [M-Br]+ signal, in the spectra of representative examples of 4-Br-2ClC6H3NHCOC6H4Y, reveals that loss of a substituent from the 2-position occurs much more rapidly than fission of a weaker bond to a substituent in the 4-position. These trends are interpreted in terms of cyclization of the ionized 2-substituted benzanilide, followed by elimination of the substituent originally in the 2-position, to form a protonated 2-arylbenzoxazole.

Antimonene is a promising two-dimensional (2D) material that is calculated to have a significant fundamental bandgap usable for advanced applications such as field-effect transistors, photoelectric devices, and the quantum-spin Hall (QSH) state. Herein, we demonstrate a phenomenon termed topological proximity effect, which occurs between a 2D material and a three-dimensional (3D) topological insulator (TI). We provide strong evidence derived from hydrogen etching on Sb2Te3 that large-area and well-ordered antimonene presents a 2D topological state. Delicate analysis with a scanning tunneling microscope of the evolutionary intermediates reveals that hydrogen etching on Sb2Te3 resulted in the formation of a large area of antimonene with a buckled structure. A topological state formed in the antimonene/Sb2Te3 heterostructure was confirmed with angle-resolved photoemission spectra and density-functional theory calculations; in particular, the Dirac point was located almost at the Fermi level. The results reveal that Dirac fermions are indeed realized at the interface of a 2D normal insulator (NI) and a 3D TI as a result of strong hybridization between antimonene and Sb2Te3. Our work demonstrates that the position of the Dirac point and the shape of the Dirac surface state can be tuned by varying the energy position of the NI valence band, which modifies the direction of the spin texture of Sb-BL/Sb2Te3via varying the Fermi level. This topological phase in 2D-material engineering has generated a paradigm in that the topological proximity effect at the NI/TI interface has been realized, which demonstrates a way to create QSH systems in 2D-material TI heterostructures.

Most often, the substituent effects are described using rather troublesome Hammett constants. Quite recently, it has been proposed to use the so-called substituent energy, which is based on total energies of the X-substituted polycyclic aromatic hydrocarbon and phenyl. This article concerns the influence of the applied level of theory (i.e., both the basis set and the method) on the determined values of the substituent energies. For this purpose, the energies of the NH2 and NO2 groups in 16 unique positions of naphthalene, anthracene, tetracene, phenanthrene, and pyrene were calculated using 10 different basis sets and 23 various exchange-correlation functionals representing the entire Jacob's Ladder, from local, through gradient- and meta-gradient-corrected, to hybrid and double-hybrid ones. Additionally, using even larger 6-311++G(2df,2p) basis set, the energies of NH2 , NO2 , CN, and Cl were also computed. Both the basis set and the method used have little effect on the substituent energy if the substituent is in the benzene-like position. On the contrary, the effect of the level of theory is pronounced especially in the case of the most spatially crowded 4-substituted phenanthrene. Substituent energies have been shown to be very useful theoretical parameters describing the proximity effect in the substituted derivatives of polycyclic aromatic hydrocarbons.

The proximity of a transition-metal dichalcogenide (TMD) to graphene imprints a rich spin texture in graphene and complements its high-quality charge/spin transport by inducing spin-orbit coupling (SOC). Rashba and valley-Zeeman SOCs are the origin of charge-to-spin conversion mechanisms such as the Rashba-Edelstein effect (REE) and spin Hall effect (SHE). In this work, we experimentally demonstrate for the first time charge-to-spin conversion due to the REE in a monolayer WS2-graphene van der Waals heterostructure. We measure the current-induced spin polarization up to room temperature and control it by a gate electric field. Our observation of the REE and the inverse of the effect (IREE) is accompanied by the SHE, which we discriminate by symmetry-resolved spin precession under oblique magnetic fields. These measurements also allow for the quantification of the efficiencies of charge-to-spin conversion by each of the two effects. These findings are a clear indication of induced Rashba and valley-Zeeman SOC in graphene that lead to the generation of spin accumulation and spin current without using ferromagnetic electrodes. These realizations have considerable significance for spintronic applications, providing accessible routes toward all-electrical spin generation and manipulation in two-dimensional materials.

Recently, single-layer CrI3, a member of the chromium trihalides CrX3 (where X = Cl, Br, or I), has been exfoliated and experimentally demonstrated as an atomically thin material suitable for two-dimensional spintronics. Valley splitting due to the magnetic proximity effect has been demonstrated in a WSe2/CrI3 van der Waals heterojunction. However, the understanding of the mechanisms behind the favorable performance of CrI3 is still limited. Here, we systematically study the carrier mobility and the intrinsic point defects in CrX3 and assess their influence on valley splitting in WSe2/CrI3 by first-principles calculations. The flat-band nature induces extremely large carrier mass and ultralow carrier mobility. In addition, intrinsic point defects-localized states in the middle of the band gap-show deep transition energy levels and act as carrier recombination centers, further lowering the carrier mobility. Moreover, vacancies in CrI3 can enhance ferromagnetism and valley splitting in a WSe2/CrI3 heterojunction, proving that chromium trihalides are excellent ferromagnetic insulators for spintronic and valleytronic applications.

The natural J-coupling (NJC) method is applied to analyze the Fermi contact contribution of the NMR spin–spin coupling constant decomposing this contribution in terms of natural localized molecular orbitals. We investigated the influence of the basis set on the NJC analysis for the formyl group coupling constant (1JCHf) of benzaldehyde derivatives. NJC and other NBO analyses, like steric and natural Coulombic energy, were chosen to explain the influence of electron-donating and electron-withdrawing groups on 1JCHf for some substituted benzaldehydes (Me, OH, OMe, F, Cl, Br, I, and NO2). For the ortho derivatives, electronegative substituents near the C–Hf bond increase the 1JCHf coupling. This effect could be related to an increase in formyl carbon s character and changes in the carbon and hydrogen natural charges. This indicates that the substituents in ortho have a proximity effect on 1JCHf coupling mainly of electrostatic origin instead of the expected hyperconjugative interactions.

Van der Waals heterostructures composed of multiple few layer crystals allow the engineering of novel materials with predefined properties. As an example, coupling graphene weakly to materials with large spin–orbit coupling (SOC) allows to engineer a sizeable SOC in graphene via proximity effects. The strength of the proximity effect depends on the overlap of the atomic orbitals, therefore, changing the interlayer distance via hydrostatic pressure can be utilized to enhance the interlayer coupling between the layers. In this work, we report measurements on a graphene/WSe2 heterostructure exposed to increasing hydrostatic pressure. A clear transition from weak localization to weak antilocalization is visible as the pressure increases, demonstrating the increase of induced SOC in graphene.

Magnetocrystalline anisotropy, a key ingredient for establishing long-range order in a magnetic material down to the two-dimensional (2D) limit, is generally associated with spin-orbit interaction (SOI) involving a finite orbital angular momentum. Here we report strong out-of-plane magnetic anisotropy without orbital angular momentum, emerging at the interface between two different van der Waals (vdW) materials, an archetypal metallic vdW material NbSe2 possessing Zeeman-type SOI and an isotropic vdW ferromagnet V5Se8. We found that the Zeeman SOI in NbSe2 induces robust out-of-plane magnetic anisotropy in V5Se8 down to the 2D limit with a more than 2-fold enhancement of the transition temperature. We propose a simple model that takes into account the energy gain in NbSe2 in contact with a ferromagnet, which naturally explains our observations. Our results demonstrate a conceptually new magnetic proximity effect at the vdW interface, expanding the horizons of emergent phenomena achievable in vdW heterostructures.

Recently, a new class of 2D Dirac materials, spin–valley-coupled Dirac semimetals (svc-DSMs), was proposed in strained SbAsX2 monolayers (MLs) and transition metal dichalcogenide-supported graphene. Owing to the superb properties, including Dirac spin–valley Hall effect and dissipationless transport, svc-DSMs provide an ideal platform for exploring the integration of Dirac physics, spintronics and valleytronics. However, the predicted candidate materials are all extrinsic, requiring tensile strain or proximity effect. Using first-principles calculations, herein we identify that strain-free BrBiAsCl ML is an intrinsic svc-DSM that is located at the boundary between 2D trivial insulators and topological insulators owing to the balance between spin–orbit coupling (SOC) and the built-in polarized vertical electric field. Under inversion asymmetry, the strong SOC in BrBiAsCl ML induces giant spin-splittings in both the uppermost valence band and the lowermost conduction band, rendering a nearly closed bulk gap and the formation of a spin–valley-dependent Dirac cone. Remarkably, such an svc-DSM state can be well preserved in BrBiAsCl ML when supported on a proper substrate, which is indispensable for the application of svc-DSMs in devices.

Nitride-based van der Waals magnetic heterostructures can simultaneously utilize both charge and spin degrees of electrons, which are important materials for low-dimensional spintronic devices. In this work, we study the stabilities and the electronic and magnetic properties of GaN/VN and VN/GaN/VN van der Waals heterostructures via first-principles calculations. The GaN/VN van der Waals heterostructure is a half-metal with 100% spin polarization, which can be applied in a spin filter and spin injection. Although monolayer GaN is a nonmagnetic semiconductor, it can introduce half-metallic characters via the magnetic proximity effect in both GaN/VN and VN/GaN/VN van der Waals heterostructures. The easy magnetization axis of hexagonal VN transits from the out-of-plane to the in-plane direction after combining with hexagonal GaN due to the different orbital occupations. Moreover, the electronic properties of the VN/GaN/VN van der Waals heterostructure depend largely on the magnetic configurations of the VN layers. By applying parallel or antiparallel magnetic configurations, the VN/GaN/VN van der Waals heterostructure presents half-metallic and semiconducting characters. The transformation indicates that the VN/GaN/VN van der Waals heterostructure is a promising candidate for room-temperature van der Waals spin valve devices.

Constraints on the time-scales of quasar activity are key to understanding the formation and growth of supermassive black holes (SMBHs), quasar triggering mechanisms, and possible feedback effects on their host galaxies. However, observational estimates of this so-called quasar lifetime are highly uncertain (t_Q~10^4-10^9 yr), because most methods are indirect and involve many model-dependent assumptions. Direct evidence of earlier activity is gained from the higher ionization state of the intergalactic medium (IGM) in the quasar environs, observable as enhanced Ly$\alpha$ transmission in the so-called proximity zone. Due to the ~30 Myr equilibration time-scale of HeII in the z~3 IGM, the size of the HeII proximity zone depends on the time the quasar had been active before our observation t_on30 Myr that does not depend on quasar luminosity, black hole mass, or Eddington ratio. These results point to episodic quasar activity over a long duty cycle, but do not rule out substantial SMBH growth during phases of radiative inefficiency or obscuration., Comment: 20 pages, 14 figures; accepted for publication in MNRAS

Here, fluorescent molecular rotors are employed to develop a new type of high-performance FRET system with large Stokes shift, high photostability, and pH insensitivity, showing great promise for use in proximity-dependent DNA aptasensors. Two carboxylated benzothiazole-based molecular rotors are synthesized, displaying bright green and red fluorescence once labeled to DNA. In the proximity state, an efficient FRET occurs between the two dyes, comparable to that of the most commonly used Cy3/Cy5 pair. Similar phenomena are also observed if naphthothiazole-based analogues are adopted. Our developed FRET pair is then attached to the two parts of a split ATP aptamer in a dimeric DNA nanoscaffold controlled by a bimolecular i-motif. In this way, a pH-switched proximity-induced fluorescent ATP aptasensor is constructed, with good sensitivity, selectivity, and reconfiguration. Furthermore, by altering the linker length of the switching unit, the proximity effect is investigated systematically, providing new insight into DNA proximity reactions and their roles in some physiological processes.

We propose novel spin-valve-like van der Waals heterostructures, in where one nonmagnetic buckled honeycomb monolayer intercalates two insulating ferromagnets. By switching the relative orientation of magnetic moments in two ferromagnets from antiparallel to parallel arrangement, semiconductor-to-metal transition yields owing to a strong magnetic proximity effect. Based on first-principles calculations, we have tested the feasibility of this model. Twelve heterostructures are investigated and seven in them show the desired semiconductor-to-metal transition. Especially, the CrI3/Ge/CrI3 heterostructure exhibits the biggest opening gap on the value of 0.31 eV among all heterostructures. Using a simple tight-binding model and the perturbation theory, we have revealed that such magnetic-order-dependent semiconductor-to-metal transition originates from the spin splitting induced by the strong magnetic proximity effect. We find an appreciable strength of magnetic proximity is crucial for achieving the semiconductor-to-metal transition, via closing the bandgap only for the parallel arrangement but remaining the antiparallel arrangement to be semiconductive. The presented heterostructures enable reversible and nonvolatile control of semiconductor-to-metal transition and are of giant potential in low-consumption and nonvolatile logic and memory devices.

Intelligent stimulus–response (S/R) systems are the basis of natural process and machine control, which are intensively explored in biomimetic design and analytical/biological applications. However, nonmonotonic multi‐S/R systems are still rarely studied so far. In this work, a rational design strategy is proposed to achieve such a unique S/R system by integrating opposite luminescence behaviors in one molecule. When solvent polarity increases, many heterocyclic or carbonyl‐containing compounds often become more emissive due to the suppression of the proximity effect, whereas molecules with donor–acceptor (D–A) structures tend to be less emissive because of the twisted intramolecular charge transfer. Meanwhile, protonation on D/A moieties will weaken/strengthen the D–A interaction to result in blue/redshifted emissions. By combining a protonatable heterocyclic acceptor and a protonatable donor together in one molecule, nonmonotonic brightness responses to polarity stimuli and nonmonotonic color responses to pH stimuli can be achieved. The design strategy is successfully verified by a simple molecule named 4‐(dimethylamino)styryl)quinoxalin‐2(1H)‐one (ASQ). ASQ exhibits nonmonotonic responses to polarity and pH stimuli, and aggregation‐induced emission (AIE) with a nonmonotonic AIE curve. Meanwhile, ASQ can be adjusted to emit white light in an acidic environment, and it shows multivalent functionalities including albumin protein sensing, ratiometric pH sensing, and amine gas sensing., Nonmonotonic multistimuli responsive systems are rarely reported. Now, an intelligent AIEgen is developed to show a nonmonotonic brightness response to solvent polarity, and a nonmonotonic color response to solution acidity. Meanwhile, it can serve as a white‐light emitter and a sensor for the detection of albumin, amine gas, and pH.

The proximity effect opens ways to transfer properties from one material into another and is especially important in two-dimensional materials. In van der Waals heterostructures, transition metal dichalcogenides (TMD) can be used to enhance the spin-orbit coupling of graphene leading to the prediction of gate controllable spin-to-charge conversion (SCC). Here, we report for the first time and quantify the SHE in graphene proximitized with WSe$_2$ up to room temperature. Unlike in other graphene/TMD devices, the sole SCC mechanism is the spin Hall effect and no Rashba-Edelstein effect is observed. Importantly, we are able to control the SCC by applying a gate voltage. The SCC shows a high efficiency, measured with an unprecedented SCC length larger than 20 nm. These results show the capability of two-dimensional materials to advance towards the implementation of novel spin-based devices and future applications., Comment: 12 pages, 4 figures, 1 table, Supplementary Material

Two-dimensional (2D) van der Waals heterostructures serve as a promising platform to exploit various physical phenomena in a diverse range of novel spintronic device applications. The efficient spin injection is the prerequisite for these devices. The recent discovery of magnetic 2D materials leads to the possibility of fully 2D van der Waals spintronics devices by implementing spin injection through magnetic proximity effect (MPE). Here, the investigation of magnetic proximity effect in 2D graphene/CrBr3 van der Waals heterostructures is reported, which is probed by Zeeman spin Hall effect through non-local measurements. Quantitative estimation of Zeeman splitting field demonstrates a significant magnetic proximity exchange field even in a low magnetic field. Furthermore, the observed anomalous longitudinal resistance changes at the Dirac point R_(XX,D) with increasing magnetic field near ν= 0 may attribute to the MPE induced new ground state phases. This MPE revealed in our graphene/CrBr3 van der Waals heterostructures therefore provides a solid physics basis and key functionality for next generation 2D spin logic and memory devices. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was supported by Singapore NRF fellowship grant (NRF-NRFF2015-03) and NRF QEP grant, Singapore Ministry of Education (MOE2016-T2-2-077, MOE2016-T2-1-163 and MOE2016- T3-1-006 (S)), A*Star QTE programme.

The development of information processing device with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and 2D heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-oTbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) National Research Foundation (NRF) Accepted version We acknowledge the financial support from the Singapore National Research Foundation through its Competitive Research Program (CRP Award No. NRF-CRP21-2018-0007), Singapore Ministry of Education (MOE2016-T2-2-077, MOE2016-T2-1-163 and MOE2016-T3-1-006 (S)), A*Star QTE programme.

With the increasingly close relations between cities in China, it is of great significance to explore the regular characteristics of the intercity connection. Through Tencent’s population migration heat and Baidu map big data, this paper analyzes the regular characteristics of the relations between complex cities based on such index as the rich node propensity index, preference level index, and relative heat index and also investigates the influence of geographical proximity factors on the external relations of different cities. The research has the following results. Firstly, the relations between cities have obvious club characteristics. The rich nodes tend to connect with the rich nodes, while the nonrich nodes tend to connect with the nonrich nodes. Secondly, the connection between cities has the effect of hierarchical proximity, and cities mainly establish spatial connections with cities of the same level and adjacent level. Thirdly, the relations between cities also have the effect of geographical proximity, and the degree of influence of geographical proximity in low-level cities is greater than that in high-level cities. Fourthly, the external connection mode of high-level cities is to establish close contact with high-level cities adjacent to the level, with strong attraction to low-level cities adjacent to the location at the same time. The low-level cities are closely related to the high-level cities adjacent to the location and other cities of geographical proximity or adjacent level. This study helps to further understand the complex characteristics and laws of intercity connections and urban networks.

Electron transport through the quantum-dot system with ferromagnetic leads is theoretically investigated, by introducing one Majorana bound state (MBS) to be side-coupled with the dot. It is shown that even for the ferromagnetic leads, the zero-bias conductance is manifested as a peak. However, its magnitude becomes more adjustable, especially when the dot suffers from the external magnetic field and superconducting proximity effect. The other notable result is that the magnetoresistance displays interesting characteristics in this system, which is related to the interplay between the magnetization direction of the MBS and other structural parameters. We believe that this work can be helpful in presenting the MBS-assisted transport behaviors in quantum-dot systems.

Possessing a valley degree of freedom and potential in information processing by manipulating valley features (such as valley splitting), group-VI monolayer transition metal dichalcogenides have attracted enormous interest. This valley splitting can be measured based on the difference between the peak energies of σ+ and σ− polarized emissions for excitons or trions in direct band gap monolayer transition metal dichalcogenides under perpendicular magnetic fields. In this work, a well-prepared heterostructure is formed by transferring exfoliated WSe2 onto a EuS substrate. Circular-polarization-resolved photoluminescence spectroscopy, one of the most facile and intuitive methods, is used to probe the difference of the gap energy in two valleys under an applied out-of-plane external magnetic field. Our results indicate that valley splitting can be enhanced when using a EuS substrate, as compared to a SiO2/Si substrate. The enhanced valley splitting of the WSe2/EuS heterostructure can be understood as a result of an interfacial magnetic exchange field originating from the magnetic proximity effect. The value of this magnetic exchange field, based on our estimation, is approximately 9 T. Our findings will stimulate further studies on the magnetic exchange field at the interface of similar heterostructures. MOE (Min. of Education, S’pore)

The newly two-dimensional layered materials MA2Z4 (M = Ti/Cr/Mo, A = Si/Ge, Z = N/P/As) possess excellent stability, strong valley-dependent properties, and novel electronic structures. Motivated by recent experimental advances, we have constructed a van der Waals heterostructure consisting of MoSi2N4 and ferromagnetic CrCl3 monolayer and performed first principles calculations to investigate the spin-valley coupling and valley splitting properties. The MoSi2N4/CrCl3 heterostructure is thermally stable at room temperature. Our calculations have shown an enhancement of both valley splitting and valley-contrasting transport properties due to the magnetic proximity effect. Most importantly, the valley-related properties of the MoSi2N4 monolayer are predicated to be rather robust resulting from the protection of the outermost N–Si sublayers. These findings could be helpful to the understanding of the ferromagnetic substrate effect on the valley-dependent properties of MA2Z4-based heterostructures.

The vicinity to a two-dimensional magnetic material provides a simple and effective way to break the valley degeneracy of transition-metal dichalcogenides because of the magnetic proximity effect. Based on first-principles calculations, we study the band structure of a MoS2/CrI3 van der Waals heterostructure and its manipulation by vertical electric fields. A huge valley splitting of about 19.60 meV, equivalent to an external magnetic fields of about 89.0 T can be generated by an electric field of 0.115 V Å−1. The electric field causes discontinuous changes in the valley splitting. The electric field drives the bands of MoS2 across those of CrI3. At the critical electric fields, the interlayer orbital hybridization leads to the energy level repulsion and an abrupt exchange of the band index. We also study the effect of interlayer distance on the valley splitting and observe a more significant electric field modulation. This work deepens our understanding on the interfacial magnetic proximity effect as a result of the orbital hybridization across the van der Waals gap.

The proximity effect induced by the adsorption of butyl xanthate on the galena (1 0 0) surface and its influence with other butyl xanthate and methyl xanthate have been investigated based on DFT method. The finding shows that the bidentate coordination of butyl xanthate on the galena (1 0 0) surface can cause perturbations of the surrounding atoms. The Pb atoms on the surface are more sensitive than that of the S atoms, and their movements along the z-axis are much greater than the latter atoms; besides, the relaxation of the Pb atoms and single-S atoms decreases with the adsorption distance. The surface atomic charges are also redistributed after the adsorption of butyl xanthate, and the potential energy of Pb atoms increases with the closer distance of the adsorption site, i.e., Pb2 atoms are more stable than Pb3 and Pb4 atoms. Further studies prove that the adsorbed butyl xanthate ligand does have an effect on the re-adsorption of neighboring Pb atoms, and the Pb2 atoms are more obvious than the Pb3 atoms.

Two-dimensional (2D) magnetic materials have aroused tremendous interest due to the 2D confinement of magnetism and potential applications in spintronic and valleytronic devices. However, most of the currently 2D magnetic materials are achieved by the exfoliation from their bulks, of which the thickness and domain size are difficult to control, limiting the practical device applications. Here, we demonstrate the realization of thickness-tunable rhombohedral Cr2Se3 nanosheets on different substrates via the chemical vapor deposition route. The magnetic transition temperature at about 75 K is observed. Furthermore, van der Waals heterostructures consisting of Cr2Se3 nanosheets and monolayer WS2 are constructed. We observe the magnetic proximity effect in the heterostructures, which manifests the manipulation of the valley polarization in monolayer WS2. Our work contributes to the vapor growth and applications of 2D magnetic materials.

Manipulation of valley polarization in low-dimensional systems is desirable for future applications in information process and storage. Here, we design two-dimensional (2D) WSSe/CrN van der Waals (vdW) heterostructures and control the valley degree of freedom based on the first-principles calculations. Combining the internal electric field and magnetic proximity effect, the interfacial interaction and the valley splitting are efficiently modulated in the system. Intrinsic enormous valley splitting of 103 meV and 144 meV are generated in S- and Se-terminated WSSe/CrN heterostructures, which corresponds to the effective Zeeman magnetic field of 1280 and 1574 T, respectively. A prominent anomalous Hall conductivity at K valley is induced by time-reversal symmetry breaking and sizable Berry curvature. Furthermore, valley splitting can be manipulated continually by the in-plane strain and interlayer distance. The largest valley splitting of 272 (240) meV and the effective Zeeman magnetic field of 2560 (2275) T are achieved for S (Se)-terminated WSSe/CrN heterostructures, respectively, under the compressive interlayer distance. It is found that the changes of induced spin charges around S and W atom are responsible for the modulated valley splitting. This work opens new vistas for the design of valleytronic devices.

Superconducting proximity effect in the heterostructures opens up access to engineer superconductivity at the interface, and has inspired substantial research interest in the past decade. Here, we fabricate the van der Waals 2H-TaS2/NbSe2 heterostructure through the mechanical exfoliation and dry transfer technique. Enhanced superconductivity in 2H-TaS2 flakes with increased superconducting transition temperature by about 0.8 K is observed. Such enhancement is believed to be related to the leakage of the Cooper pairs from NbSe2 flakes to 2H-TaS2 flakes. In addition, the critical current of the superconducting transition of NbSe2 flakes is also increased in the heterostructures, which is related to the strengthened pairing strength of Cooper pairs in NbSe2 flakes arising from the interfacial coupling between NbSe2 flakes and 2H-TaS2 flakes. Our findings will open perspectives for insight into the superconducting proximity effect in the van der Waals heterostructures.

The evolution of low-dimensional materials has frequently revolutionized new intriguing physical standards and suggests a unique approach to scientifically design a novel device. However, scaling down of spin-electronic devices entails in-depth knowledge and precise control on engineering interfacial structures, which unveils the exciting opportunity. To reveal exotic quantum phases, atomically thin two-dimensional van der Waals material, embraces control and tuning of various physical states by coupling with peripheral perturbation such as pressure, photon, gating, Moire pattern and proximity effect. Herein, we discuss the physical property of a pristine material which can be converted via proximity effects to attain intrinsic spin-dependent properties from its adjacent material like magnetic, topological or spin–orbit phenomena. Realizing magnetic proximity effect in atomically thin vdW heterostructure not only balance the traditional techniques of designing quality spin interface by doping, defects or surface modification, but also can overcome their restrictions for modelling and fabricate novel spin-related devices in nanoscale phases. The proximitized van der Waals heterostructure systems unveil properties, which cannot be realized in any integral component of considered heterostructure system. These proximitized van der Waals material provide an ideal platform for exploring new physical phenomena, which delivers a broader framework for employing novel materials and investigate nanoscale phases in spintronics and valleytronics.

This study aimed to unpack the dynamic proximity effects of a park on residential values in the urban regeneration context: first by the development phase of the park, and second, by specific characteristics of the residential units. The study site is the Dream Forest in Seoul, South Korea, and the study period is from 2006 to 2015. The two-fold multilevel regression analysis suggests that the Dream Forest began exerting proximity effects from the time of site acquisition by the city, which peaked at a 3.7% price increment per 100-meter distance to the park from a prototypical housing unit, soon after the public announcement of the park procurement plan. During construction, inauguration and stabilization, the effect has remained at around 3.0%. The analysis also suggests that the proximity effect applies unevenly to housing units: apartment type or older housing units are more sensitive to the externality effects than their counterparts – multifamily type or newer housing units.

Understanding the structure–activity relation of nanostructured electrocatalysts is crucial for advances in emerging electrochemical energy systems, most prominently polymer electrolyte fuel cells and electrolyzers. In this realm, the surface-specific activity of platinum is a peculiar function of particle size and interparticle spacing. Previous attempts to rationalize the particle size and proximity effects focused on geometric and electronic factors and they largely ignored the role of the support. The present study focuses on a consistent treatment of electrostatic reaction conditions around Pt nanoparticles, taking into consideration the specific surface charging properties of Pt and the support material. The model reveals a double-layer overlap regime in which the surface-specific activity is significantly enhanced by decreasing the interparticle spacing. Relevance of the model in explaining the particle proximity effect is demonstrated.

Proximity effects in two-dimensional (2D) van der Waals heterostructures offer controllable ways to tailor the electronic band structure of adjacent materials. Proximity exchange in particular is important for making materials magnetic without hosting magnetic ions. Such synthetic magnets could be used for studying magnetotransport in high-mobility 2D materials, or magneto-optics in highly absorptive nominally nonmagnetic semiconductors. Using first-principles calculations, we show that the proximity exchange in monolayer MoSe2 and WSe2 due to ferromagnetic monolayer CrI3 can be tuned (even qualitatively) by twisting and gating. Remarkably, the proximity exchange remains the same when using antiferromagnetic CrI3 bilayer, paving the way for optical and electrical detection of layered antiferromagnets. Interestingly, the proximity exchange is opposite to the exchange of the adjacent antiferromagnetic layer. Finally, we show that the proximity exchange is confined to the layer adjacent to CrI3, and that adding a separating hBN barrier drastically reduces the proximity effect. We complement our ab initio results with tight-binding modeling and solve the Bethe-Salpeter equation to provide experimentally verifiable optical signatures (in the exciton spectra) of the proximity exchange effects.

Magnetic proximity effects are crucial ingredients for engineering spintronic, superconducting, and topological phenomena in heterostructures. Such effects are highly sensitive to the interfacial electronic properties, such as electron wave function overlap and band alignment. The recent emergence of van der Waals (vdW) magnets enables the possibility of tuning proximity effects via designing heterostructures with atomically clean interfaces. In particular, atomically thin CrI3 exhibits layered antiferromagnetism, where adjacent ferromagnetic monolayers are antiferromagnetically coupled. Exploiting this magnetic structure, we uncovered a layer-resolved magnetic proximity effect in heterostructures formed by monolayer WSe2 and bi/trilayer CrI3. By controlling the individual layer magnetization in CrI3 with a magnetic field, we found that the spin-dependent charge transfer between WSe2 and CrI3 is dominated by the interfacial CrI3 layer, while the proximity exchange field is highly sensitive to the layered magnetic structure as a whole. These properties enabled us to use monolayer WSe2 as a spatially sensitive magnetic sensor to map out layered antiferromagnetic domain structures at zero magnetic field as well as antiferromagnetic/ferromagnetic domains near the spin-flip transition in bilayer CrI3. Our work reveals a new way to control proximity effects and probe interfacial magnetic order via vdW engineering., Comment: to appear in Nature Nanotechnology

It has been shown that singlet Cooper pairs can be converted into triplet ones and diffuse into a ferromagnet over a long distance in a phenomenon known as the long-range proximity effect (LRPE). This happens in materials with inhomogeneous magnetism or spin-orbit coupling (SOC). Most of the previous studies focus on the cases with small SOC and exchange field. However, the physics was not clear when SOC and exchange field strength are both much greater than the disorder strength. In this work, we consider a two dimensional system with a large Rashba-type SOC and exchange field in the case where only one band is partially occupied. We develop a generalized quasiclassical theory by projecting the Green function onto the partially occupied band (POB). We find that when the SOC energy scale is comparable with the exchange field, there is no LRPE. The reason is that the nonmagnetic impurities together with the large SOC and exchange field can effectively generate spin-flip scattering, which suppresses the proximity effect. We also show that when increasing either SOC or exchange field, the decay length of superconducting correlations can be significantly increased due to an approximately restored time reversal symmetry or spin rotation symmetry around the $z$ (out-of-plane) axis., 10 pages, 5 figures

A study protocol outlining the procedure and analysis methods is presented to explore incentive salience, visual salience, and visibility, amongst other factors, in relation to chocolate consumption where the distances of the chocolate relative to the consumer is manipulated.

Using first principles theory, we investigated the behavior of the one-dimensional (1D) topological edge states of high temperature superconductiviing FeSe/SrTiO3 films with Te atoms substitution to Se atoms in the bottom (top) layer in single-layer FeSe, as a function of strain. It was discovered that the 1D topological edge states are present in single-unit-cell FeSe film on SrTiO3, but are absent when more than 50% Se atoms are replaced by Te atoms. Stress induced displacive phase transformation exists in FeSe/SrTiO3 film when Te atoms substitute Se atoms in the bottom (top) layer in single-layer FeSe under 3% strain respectively. The 1D topological edge states are present under 3% (1.8%) strain in FeSe/SrTiO3 films with Te substitution Se in the bottom (top) layer in single-layer FeSe, even up to 5%, respectively. This indicates that the bonding angle of Se-Fe-Se (Te) and the distance of Te (or Se) atoms to the Fe plane are correlated with the topological edge states. Our findings provide an effective interface system that provides both superconducting and topological states, opening a new route for realizing 2D topological superconductors with proximity effect.

Inspired by recent experiments on many-body localized systems coupled to an environment, we apply a Flow Equation method to study the problem of a disorder chain of spinless fermions, coupled via density-density interactions to a second clean chain of spinless fermions. In particular, we focus on the conditions for the onset of a many-body localized phase in the clean sector of our model by proximity to the dirty one. We find that a many-body localization proximity effect in the clean component is established when the density of dirty fermions exceeds a threshold value. From the flow equation method we find that, similar to many-body localization in a single chain, the many-body localization proximity effect is also described by an extensive set of local integrals of motion. Furthermore, by tuning the geometry of the inter-chain couplings, we show that the dynamics of the model is ruled, on intermediate time scales, by an emergent set of quasi-conserved charges., 22 pages, 7 figures

Spin orbit coupling (SOC) is the key to realizing time-reversal invariant topological phases of matter. Famously, SOC was predicted by Kane and Mele to stabilize a quantum spin Hall insulator; however, the weak intrinsic SOC in monolayer graphene has precluded experimental observation. Here, we exploit a layer-selective proximity effect---achieved via van der Waals contact to a semiconducting transition metal dichalcogenide--to engineer Kane-Mele SOC in ultra-clean \textit{bilayer} graphene. Using high-resolution capacitance measurements to probe the bulk electronic compressibility, we find that SOC leads to the formation of a distinct incompressible, gapped phase at charge neutrality. The experimental data agrees quantitatively with a simple theoretical model in which the new phase results from SOC-driven band inversion. In contrast to Kane-Mele SOC in monolayer graphene, the inverted phase is not expected to be a time reversal invariant topological insulator, despite being separated from conventional band insulators by electric field tuned phase transitions where crystal symmetry mandates that the bulk gap must close. Electrical transport measurements, conspicuously, reveal that the inverted phase has a conductivity $\sim e^2/h$, which is suppressed by exceptionally small in-plane magnetic fields. The high conductivity and anomalous magnetoresistance are consistent with theoretical models that predict helical edge states within the inversted phase, that are protected from backscattering by an emergent spin symmetry that remains robust even for large Rashba SOC. Our results pave the way for proximity engineering of strong topological insulators as well as correlated quantum phases in the strong spin-orbit regime in graphene heterostructures., 7 pages of main text + 13 pages supplementary material and figures. More information available at http://www.afylab.com/publications/