Interfacial Modification of NiO_(x)by Self-assembled Monolayer for Efficient and Stable Inverted Perovskite Solar Cells

NiO_(x)as a hole transport material for inverted perovskite solar cells has received great attention owing to its high transparency,low fabrication temperature,and superior stability.However,the mismatched energy levels and possible redox reactions at the NiO_(x)/perovskite interface severely limit the performance of NiO_(x) based inverted perovskite solar cells.Herein,we introduce a p-type self-assembled monolayer between NiO_(x)and perovskite layers to modify the interface and block the undesirable redox reaction between perovskite and NiO_(x)The selfassembled monolayer molecules all contain phosphoric acid function groups,which can be anchored onto the NiOr surface and passivate the surface defect.Moreover,the introduction of self-assembled monolayers can regulate the energy level structure of NiO_(x),reduce the interfacial band energy offset,and hence promote the hole transport from perovskite to NiO_(x)layer.Consequently,the device performance is significantly enhanced in terms of both power conversion efficiency and stability.

High-Quality van der Waals Epitaxial CsPbBr_(3)Film Grown on Monolayer Graphene Covered TiO_(2)for High-Performance Solar Cells

Two-dimensional materials have been widely used to tune the growth and energy-level alignment of perovskites.However,their incomplete passivation and chaotic usage amounts are not conducive to the preparation of highquality perovskite films.Herein,we succeeded in obtaining higher-quality CsPbBr_(3)films by introducing large-area monolayer graphene as a stable physical overlay on top of TiO_(2)substrates.Benefiting from the inert and atomic smooth graphene surface,the CsPbBr_(3)film grown on top by the van der Waal epitaxy has higher crystallinity,improved(100)orientation,and an average domain size of up to 1.22μm.Meanwhile,a strong downward band bending is observed at the graphene/perovskite interface,improving the electron extraction to the electron transport layers(ETL).As a result,perovskite film grown on graphene has lower photoluminescence(PL)intensity,shorter carrier lifetime,and fewer defects.Finally,a photovoltaic device based on epitaxy CsPbBr_(3)film is fabricated,exhibiting power conversion efficiency(PCE)of up to 10.64%and stability over 2000 h in the air.

Morphology and Mechanical Characteristics of Monolayer and Multilayer Ir Coating by Double Glow Plasma

Multilayer iridium coating was manufactured on tungsten carbide substrates by a double glow plasma process.As comparison,monolayer was also produced.The microstructure and morphology were observed using scanning electron microscopy.Grain orientation and phase were determined using X-ray diffraction.The residual stress of the coating was studied by glancing incidence X-ray diffraction.The adhesive force of the coating was measured by a scratch tester.The results showed that both monolayer and multilayer had a polycrystalline phase with a strong（110） reflection.The coating had an excellent adhesion with no evidence of delamination.The adhesive force of the monolayer and multilayer was about 50 and 43 N,respectively.The interfacial reaction between the substrate and the layer occurred and a new WIr phase was found due to the high-temperature deposition process.The residual stress in the monolayer and multilayer was-1.6 and-1.1 GPa,respectively.

Size-Dependent Gold Nanoparticle Interaction at Nano–Micro Interface Using Both Monolayer and Multilayer(Tissue-Like) Cell Models

Gold nanoparticles(GNPs) are emerging as a novel tool to improve existing cancer therapeutics. GNPs are being used as radiation dose enhancers in radiation therapy as well as anticancer drugs carriers in chemotherapy. However,the success of GNP-based therapeutics depends on their ability to penetrate tumor tissue. GNPs of 20 and 50 nm diameters were used to elucidate the effects of size on the GNP interaction with tumor cells at monolayer and multilayer level. At monolayer cell level, smaller NPs had a lower uptake compared to larger NPs at monolayer cell level. However, the order was reversed at tissue-like multilayer level. The smaller NPs penetrated better compared to larger NPs in tissue-like materials.Based on our study using tissue-like materials, we can predict that the smaller NPs are better for future therapeutics due to their greater penetration in tumor tissue once leaving the leaky blood vessels. In this study, tissue-like multilayer cellular structures(MLCs) were grown to model the post-vascular tumor environment. The MLCs exhibited a much more extensive extracellular matrix than monolayer cell cultures. The MLC model can be used to optimize the nano–micro interface at tissue level before moving into animal models. This would accelerate the use of NPs in future cancer therapeutics.

Quantum Anomalous Hall Effect with Tunable Chern Numbers in High-Temperature 1T-PrN_(2) Monolayer

Quantum anomalous Hall(QAH) insulators have highly potential applications in spintronic device. However,available candidates with tunable Chern numbers and high working temperature are quite rare. Here, we predict a 1T-PrN_(2) monolayer as a stable QAH insulator with high magnetic transition temperature of above 600 K and tunable high Chern numbers of C = ±3 from first-principles calculations. Without spin-orbit coupling(SOC),the 1T-PrN_(2) monolayer is predicted to be a p-state Dirac half metal with high Fermi velocity. Rich topological phases depending on magnetization directions can be found when the SOC is considered. The QAH effect with periodical changes of Chern number(±1) can be produced when the magnetic moment breaks all twofold rotational symmetries in the xy plane. The critical state can be identified as Weyl half semimetals. When the magnetization direction is parallel to the z-axis, the system exhibits high Chern number QAH effect with C = ±3.Our work provides a new material for exploring novel QAH effect and developing high-performance topological devices.

Excitonic Instability in Ta_(2)Pd_(3)Te_(5) Monolayer

By systematic theoretical calculations,we reveal an excitonic insulator(EI)in the Ta_(2)Pd_(3)Te_(5)monolayer.The bulk Ta_(2)Pd_(3)Te_(5)is a van der Waals(vdW)layered compound,whereas the vdW layer can be obtained through exfoliation or molecular-beam epitaxy.First-principles calculations show that the monolayer is a nearly zero-gap semiconductor with the modified Becke–Johnson functional.Due to the same symmetry of the band-edge states,the two-dimensional polarization 2D would be finite as the band gap goes to zero,allowing for an EI state in the compound.Using the first-principles many-body perturbation theory,the GW plus Bethe–Salpeter equation calculation reveals that the exciton binding energy is larger than the single-particle band gap,indicating the excitonic instability.The computed phonon spectrum suggests that the monolayer is dynamically stable without lattice distortion.Our findings suggest that the Ta_(2)Pd_(3)Te_(5) monolayer is an excitonic insulator without structural distortion.

The Electrochemical Characteristics of Multilayer Assembly of Hemoglobin and Polystyrene Sulfonate at Self-assembled MonolayerSurface

A multilayer film of hemoglobin (Hb) molecules and polyelectrolyte sulfonate were fabricated on a thiol self-assembled monolayers (SAMs) by electrostatic force. The Hb maintains electroactive property in the multilayer film, methylene blue (MB) incorporated into the multilayer can enhance the electron transfer rate between the Hb and the electrode surface.

Orbital-Ordering Driven Simultaneous Tunability of Magnetism and Electric Polarization in Strained Monolayer VCl_(3)

Two-dimensional(2D)van der Waals magnetic materials have promising and versatile electronic and magnetic properties in the 2D limit,indicating a considerable potential to advance spintronic applications.Theoretical predictions thus far have not ascertained whether monolayer VCl_(3) is a ferromagnetic(FM)or anti-FM monolayer;this also remains to be experimentally verified.We theoretically investigate the influence of potential factors,including C_(3) symmetry breaking,orbital ordering,epitaxial strain,and charge doping,on the magnetic ground state.Utilizing first-principles calculations,we predict a collinear type-Ⅲ FM ground state in monolayer VCl_(3) with a broken C_(3) symmetry,wherein only the former two of three t_(2g)orbitals(a_(1g),e_(g2)^(π)and e_(g1)^(π))are occupied.The atomic layer thickness and bond angles of monolayer VCl_(3) undergo abrupt changes driven by an orbital ordering switch,resulting in concomitant structural and magnetic phase transitions.Introducing doping to the underlying Cl atoms of monolayer VCl_(3) without C_(3) symmetry simultaneously induces in-and out-of-plane polarizations.This can achieve a multiferroic phase transition if combined with the discovered adjustments of magnetic ground state and polarization magnitude under strain.The establishment of an orbital-ordering driven regulatory mechanism can facilitate deeper exploration and comprehension of magnetic properties of strongly correlated systems in monolayer VCl_(3).

Controlled fabrication of freestanding monolayer SiC by electron irradiation

The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications.Electron irradiation has been demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise.It features the advantages of precise control over the patterning of such new materials and their integration with other materials with different functionalities.Here,we present a new strategy for fabricating freestanding monolayer SiC within nanopores of a graphene membrane.By regulating the energy of the incident electron beam and the in-situ heating temperature in a scanning transmission electron microscope(STEM),we can effectively control the patterning of nanopores and subsequent growth of monolayer SiC within the graphene lattice.The resultant SiC monolayers seamlessly connect with the graphene lattice,forming a planar structure distinct by a wide direct bandgap.Our in-situ STEM observations further uncover that the growth of monolayer SiC within the graphene nanopore is driven by a combination of bond rotation and atom extrusion,providing new insights into the atom-by-atom self-assembly of freestanding two-dimensional(2D)monolayers.

Highly enhanced UV absorption and light emission of monolayer WS_(2)through hybridization with Ti_(2)N MXene quantum dots and g-C_(3)N_(4)quantum dots

Two-dimensional(2D)transition metal dichalcogenides(TMD)are atomically thin semiconductors with promising optoelectronic applications across the visible spectrum.However,their intrinsically weak light absorption and the low photoluminescence quantum yield(PLQY)restrict their performance and potential use,especially in ultraviolet(UV)wavelength light ranges.Quantum dots(QD)derived from 2D materials(2D/QD)provide efficient light absorption and emission of which energy can be tuned for desirable light wavelength.In this study,we greatly enhanced the photon absorption and PLQY of monolayer(1L)tungsten disulfide(WS_(2))in the UV range via hybridization with 2D/QD,particularly titanium nitride MXene QD(Ti_(2)N MQD)and graphitic carbon nitride QD(GCNQD).With the hybridization of MQD or GCNQD,1LWS_(2)showed a maximum PL enhancement by 15 times with 300 nm wavelength excitation,while no noticeable enhancement was observed when the excitation photon energy was less than the bandgap of the QD,indicating that UV absorption by the QD played a crucial role in enhancing the light emission of 1L-WS_(2)in our 0D/2D hybrid system.Our findings present a convenient method for enhancing the photo-response of 1L-WS_(2)to UV light and offer exciting possibilities for harvesting UV energy using 1L-TMD.

Factors resisting protein adsorption on hydrophilic/hydrophobic self-assembled monolayers terminated with hydrophilic hydroxyl groups

The hydroxyl-terminated self-assembled monolayer(OH-SAM),as a surface resistant to protein adsorption,exhibits substantial potential in applications such as ship navigation and medical implants,and the appropriate strategies for designing anti-fouling surfaces are crucial.Here,we employ molecular dynamics simulations and alchemical free energy calculations to systematically analyze the factors influencing resistance to protein adsorption on the SAMs terminated with single or double OH groups at three packing densities(∑=2.0 nm^(-2),4.5 nm^(-2),and 6.5 nm^(-2)),respectively.For the first time,we observed that the compactness and order of interfacial water enhance its physical barrier effect,subsequently enhancing the resistance of SAM to protein adsorption.Notably,the spatial hindrance effect of SAM leads to the embedding of protein into SAM,resulting in a lack of resistance of SAM towards protein.Furthermore,the number of hydroxyl groups per unit area of double OH-terminated SAM at ∑=6.5 nm^(-2) is approximately 2 to 3 times that of single OH-terminated SAM at ∑=6.5 nm^(-2) and 4.5 nm^(-2),consequently yielding a weaker resistance of double OH-terminated SAM towards protein.Meanwhile,due to the structure of SAM itself,i.e.,the formation of a nearly perfect ice-like hydrogen bond structure,the SAM exhibits the weakest resistance towards protein.This study will complement and improve the mechanism of OH-SAM resistance to protein adsorption,especially the traditional barrier effect of interfacial water.

Mo_(2)P Monolayer as a Superior Electrocatalyst for Urea Synthesis from Nitrogen and Carbon Dioxide Fixation:A Computational Study

Urea synthesis through the simultaneous electrocatalytic reduction of N_(2)and CO_(2)molecules under ambient conditions holds great promises as a sustainable alternative to its industrial production,in which the development of stable,highly efficient,and highly selective catalysts to boost the chemisorption,activation,and coupling of inert N_(2)and CO_(2)molecules remains rather challenging.Herein,by means of density functional theory computations,we proposed a new class of two-dimensional nanomaterials,namely,transition-metal phosphide monolayers(TM_(2)P,TM=Ti,Fe,Zr,Mo,and W),as the potential electrocatalysts for urea production.Our results showed that these TM_(2)P materials exhibit outstanding stability and excellent metallic properties.Interestingly,the Mo_(2)P monolayer was screened out as the best catalyst for urea synthesis due to its small kinetic energy barrier(0.35 eV)for C-N coupling,low limiting potential(-0.39 V),and significant suppressing effects on the competing side reactions.The outstanding catalytic activity of the Mo_(2)P monolayer can be ascribed to its optimal adsorption strength with the key^(*)NCON species due to its moderate positive charges on the Mo active sites.Our findings not only propose a novel catalyst with high-efficiency and high-selectivity for urea production but also further widen the potential applications of metal phosphides in electrocatalysis.

The Hydraulic Fracturing Optimization for Stacked Tight Gas Reservoirs Using Multilayers and Multiwells Fracturing Strategies

Based on a geology-engineering sweet spot evaluation,the high-quality reservoir zones and horizontal well landing points were determined.Subsequently,fracture propagation and production were simulated with a multilayer fracturing scenario.The optimal hydraulic fracturing strategy for themultilayer fracturing networkwas determined by introducing a vertical asymmetry factor.This strategy aimed to minimize stress shadowing effects in the vertical direction while maximizing the stimulated reservoir volume(SRV).The study found that the small vertical layer spacing of high-quality reservoirs and the presence of stress-masking layers(with a stress difference of approximately 3∼8 MPa)indicate that interlayer stress interference from multilayers and multiwells fracturing between neighboring developed formations could affect the longitudinal propagation of the reservoirs.In addition,this study investigated well spacing optimization by comparing uniformly spaced wells(100–300 m)with asymmetric spaced wells(200 m upper layer,250 m lower layer).Numerical results indicated that asymmetric spaced well placement yielded the largest stimulated reservoir volume(SRV)of 73,082 m^(3),representing a 65.42%increase compared to 100 m spaced wells.Furthermore,four different hydraulic fracturing sequences(interlayer,up-down,down-up,and center-edge)were compared for multilayer and multiwell networks.The center-edge sequence exhibited the lowest vertical asymmetry factor(0.71)and the least stress shadowing effects compared to the other sequences(0.78 for interlayer,0.75 for up-down,and 0.76 for down-up).This sequence also achieved the largest SRV(486,194m^(3)),representing an 11.87%increase compared to the down-up sequence.Therefore,the center-edge fracturing sequence is recommended formultilayer development in this block.These results offer valuable insights for optimizing well placement and fracturing sequence design in multilayer well networks,ultimately advancing the development of multilayer fracturing technology in the region.

Anisotropic Transport on Monolayer and Multilayer Phosphorene in the Presence of an Electric Field

We demonstrate theoretically the anisotropic quantum transport of electrons through an electric field on monolayer and multilayer phosphorene. Using the long-wavelength Hamiltonian with continuum approximation, we find that the transmission probability for transport through an electric field is an oscillating function of incident angle, electric field intensity, as well as the incident energy of electrons. By tuning the electric field intensity and incident angle, the channels can be transited from opaque to transparent. The conductance through the quantum waveguides depends sensitively on the transport direction because of the anisotropic effective mass, and the anisotropy of the conductance can be tuned by the electric field intensity and the number of layers. These behaviors provide us an efficient way to control the transport of phosphorene-based microstructures.

Dimethyl acridine-based self-assembled monolayer as a hole transport layer for highly efficient inverted perovskite solar cells

Self-assembled monolayers(SAMs)have recently emerged as excellent hole transport materials in inverted perovskite solar cells(PSCs)owing to their ability to minimize parasitic absorption,regulate energy level alignment,and passivate perovskite defects.Herein,we design and synthesize a novel dimethyl acridinebased SAM,[2-(9,10-dihydro-9,9-dimethylacridine-10-yl)ethyl]phosphonic acid(2PADmA),and employ it as a hole-transporting layer in inverted PSCs.Experimental results show that the 2PADmA SAM can modulate perovskite crystallization,facilitate carrier transport,passivate perovskite defects,and reduce nonradiative recombination.Consequently,the 2PADmA-based device achieves an enhanced power conversion efficiency(PCE)of 24.01%and an improved fill factor(FF)of 83.92%compared to the commonly reported[2-(9H-carbazol-9-yl)ethyl]phosphonic acid(2PACz)-based control device with a PCE of 22.32%and FF of 78.42%,while both devices exhibit comparable open-circuit voltage and short-circuit current density.In addition,2PADmA-based devices exhibit outstanding dark storage and thermal stabilities,retaining approximately~98%and 87%of their initial PCEs after 1080 h of dark storage and 400 h of heating at 85°C,respectively,both considerably superior to the control device.

Ozonolysis-oxidation-driven top-down strategy for the target preparation of ultrathin 2D metalorganic framework monolayers

Two-dimensional metal–organic-framework(2D MOF)nanosheets with a modular nature and tunable structures exhibit a bright future for sensors,separation,and catalysis.Developing ultrathin 2D MOF nanosheets with unique physical and chemical properties is urgently required but very challenging.Although the chemical exfoliation strategy has been regarded as a promising way to exfoliate large amounts of three-dimensional(3D)pillar-layered MOFs,this method still faces many problems and remains insufficient.In this study,a novel chemical exfoliation method is developed for the target preparation of 2D MOF monolayers from the 3D pillar-layered MOFs.The Co/Zn/Cu-MOFs with a pillar ligand of trans-1,2-bis(4-pyridyl)ethylene(bipyen)are subjected to be broken by the cleavage of CC bonds in the bipyen ligands via an ozone oxidation reaction.As chemical exfoliation is processed via the oxidation of the pillar ligand by ozone,the thickness of the 2D MOFs can be tuned by the control of oxidation time and the obtained 2D Co/Zn/Cu-MOF monolayers are functionalized with a–COOH group.This study provides an effective and general chemical exfoliation method to prepare monolayer MOFs from the 3D pillar-layered MOFs with bipyen as the pillar ligand.

Preparation of Aryldiazonium Salt Monolayers on Si（100） Surface by Chemomechanical Method

Functionalizing and patterning of the silicon surface can be realized simultaneously by the chemomechanical method. The oxide-coated crystalline silicon （100） surface is scratched with a diamond tool in the presence of aryldiazonium salt （C6H5N2BF4）. Scratching activates the silicon surface by removing the passivation oxide layer to expose fresh Si atoms. The sur- face morphologies before and after chemomechanical reaction are characterized with atomic force microscopy. Time-of-flight secondary ion mass spectroscopy confirms the presence of C6H5 and provides evidence for the formation of self-assembled monolayer （SAM） on silicon surface via Si-C covalent bonds by scratching the silicon in the presence of C6H5N2BF4. C6H5 groups further bond with surface Si atoms via Si-C covalent bonds as confirmed from infrared spectroscopy results. We propose that chemomechanical reaction, which occurred during scratching the silicon surface, produce C6H5 groups from aryldiazonium salt. The relevant adhesion of SAM is measured. It is found that SAM can reduce the adhesion of silicon. The monolayer can be used as anti-adhesion monolayer for micro/nanoelectromechanical systems components under different environments and operating conditions.

MICROSTRUCTURE AND MAGNETISM OF Co/Ti and Co/Cu(Ni) MULTILAYERS

The multilayers in the forms of glass/Cu(Ni)(5.0 nm)/[Co(2.0 nm)/Cu(Ni)(0.5～3.7 nm)] 30 and glass/Ti(5.0 nm)/[Co(2.0 nm)/Ti(0.4～3.5 nm)] 30 ,prepared by dual facing target sputtering at room temperature,exhibit a soft magnetic property.The structural and magnetic properties of Co/Cu(Ni) and Co/Ti multilayers were examined as a function of the spacer layer thickness (d Ti and d Cu(Ni) ) by low angle X ray diffraction (LAXRD) and VSM measurements.The saturation magnetization M s of the Co/Ti multilayers was found to decrease with d Ti and approached to a constant value when d Ti was thick enough.But in the Co/Cu(Ni) multilayers,the M s was found to oscillate with d Cu(Ni) when d Cu(Ni) was less than 3.0 nm,and the oscillation period was about 1.0 nm.This arose from the different interlayer magnetic coupling effects.We interpret these two different kinds of interlayer magnetic couplings as the consequence of the competition between the RKKY like and superexchange couplings.

Dielectric Properties of Self-assembled Monolayers of Dithiols

Dielectric properties of dithiol self-assemble monolayers （SAMs） under ac electric field were presented, Using a Hg-SAM/SAM-Ⅱg junction, the ac impedances of dithiol SAMs were measured using a sinusoidal perturbation of 30 mV （peak to-peak） with the frequency ranging from 1 Hz to 1 MHz at zero bias. The contributions from dithiol SAMs and solvent interlayers were separated due to their different behaviors at ac impedance. The peak position in the loss spectra （the plot; of tgδ vs. frequency） moves to low frequcney with the incrcase of chain length of dithiols. Using a correlation of peak position with the chain length, the active energies of 23-39 meV for dithiol SAMs of C6-C10 under an ac electric field were derived,

Enhanced Performance of a Monolayer MoS_2/WSe_2 Heterojunction as a Photoelectrochemical Cathode

Transition-metal dichalcogenide(TMD) semiconductors have attracted interest as photoelectrochemical(PEC) electrodes due to their novel band-gap structures,optoelectronic properties, and photocatalytic activities.However, the photo-harvesting efficiency still requires improvement. In this study, A TMD stacked heterojunction structure was adopted to further enhance the performance of the PEC cathode. A P-type WSe_2 and an N-type Mo S_2 monolayer were stacked layer-by-layer to build a ultrathin vertical heterojunction using a micro-fabrication method.In situ measurement was employed to characterize the intrinsic PEC performance on a single-sheet heterostructure.Benefitting from its built-in electric field and type II band alignment, the MoS_2/WSe_2 bilayer heterojunction exhibited exceptional photocatalytic activity and a high incident photo-to-current conversion efficiency(IPCE). Comparing with the monolayer WSe_2 cathode, the PEC current and the IPCE of the bilayer heterojunction increased by a factor of 5.6 and enhanced 50%, respectively. The intriguing performance renders the MoS_2/WSe_2 heterojunction attractive for application in high-performance PEC water splitting.