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-electron materials: Sn monolayer on a SiC(0001) surface
摘要： Materials with sp magnetism demonstrate strongly nonlocal Coulomb interactions, which opens a way to probe correlations in the regimes not achievable in transition metal compounds. By the example of Sn monolayer on a SiC(0001) surface, we show that such systems exhibit unusual but intriguing magnetic properties at the nanoscale. Physically, this is attributed to the presence of a significant ferromagnetic coupling, the so-called direct exchange, which fully compensates ubiquitous antiferromagnetic interactions of the superexchange origin. Having a nonlocal nature, the direct exchange was previously ignored because it cannot be captured within the conventional density functional methods and significantly challenges ground state models earlier proposed for Sn/SiC(0001). Furthermore, heavy adatoms induce strong spin-orbit coupling, which leads to a highly anisotropic form of the spin Hamiltonian, in which the Dzyaloshinskii-Moriya interaction (DMI) is dominant. The latter is suggested to be responsible for the formation of a nanoskyrmion state at realistic magnetic fields and temperatures.
关键词： Dzyaloshinskii-Moriya interaction,SiC(0001) surface,direct exchange,nonlocal Coulomb interactions,nanoskyrmion state,sp magnetism,Sn monolayer
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Reduced energy-angle dispersion of output electrons from a nanocrystalline Si emitter with a monolayergraphene surface electrode
摘要： It is shown that the angle dispersions of output electrons of nanocrystalline silicon (nc-Si) quasiballistic electron emitter are significantly reduced by using a monolayer graphene as the surface electrode. This is closely linked with a remarkable enhancement in the emission efficiency and a suppression of the electron energy dispersion. The angle distribution curves become more directional at lower temperatures. These results are attributed to high transparency of monolayer graphene for quasiballistic electrons generated in the nc-Si layer. The intrinsic multi-tunneling cascade mode through nc-Si dots can be utilized most effectively by monolayer graphene surface electrode.
关键词： quasiballistic emission,monolayer graphene,nanocrystalline silicon
更新于2025-09-23 15:21:21
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Efficient and selective sensing of nitrogen containing gases by Si2BN nanosheets under pristine and pre-oxidized conditions
摘要： Motivated by the promise of two-dimensional nanostructures in the field of gas sensing, we have employed van der Waals corrected density functional theory calculations to study the structural, electronic and gas sensing propensities of recently designed Si2BN monolayer. Our rigorous simulations reveal that the representative members of nitrogen containing gases (NCGs) such as NO, NO2 and NH3 binds extremely strongly on pristine Si2BN monolayer. However a strong dissociative adsorption in case of NO and NO2 would poison the Si2BN and ultimately reversibility of the monolayer would be compromised. Exploring the sensing mechanism in more realistic pre-oxidized conditions, the binding characteristics of O2@Si2BN changed dramatically, resulting into much lower adsorption in associative manner for all NO, NO2 and NH3. A visible change in work function indicates the variation in conductivity of O2@Si2BN upon the exposure of incident gases. Sustainable values of binding energies would also ensure a quick recovery time that makes O2@Si2BN an efficient nano sensor for pollutants like NCGs.
关键词： Conductivity,Adsorption,Work function,Recovery time,Monolayer
更新于2025-09-23 15:21:21
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Catalytic growth of large area monolayer molybdenum disulfide film by chemical vapor deposition
摘要： Large area monolayer molybdenum disulfide (MoS2) film grown on silica/silicon substrate was synthesized using a catalyst perylene-3, 4, 9, 10-tetracarboxylic acid tetrapotassium salt (PTAS) by the method of chemical vapor deposition. The properties of the monolayer MoS2 film were characterized using a number of techniques. The optical microscope images show the film is uniform and continuous on a large scale. The 0.7 nm film thickness measured by atomic force microscope, as well as the difference of 20 cm-1 between the two characteristic Raman peaks, all prove that the film is single layer. The strong photoluminescence spectrum and image as well as the x-ray diffraction indicate that the monolayer MoS2 film has a good quality. The MoS2 film synthesized under the same conditions without PTAS was also characterized as a comparison. The results show that the MoS2 film tends to thicker without using PTAS, suggesting that PTAS can not only promote the formation of the MoS2 seeding, but also induce horizontal growth of the MoS2 film on the substrate.
关键词： Molybdenum disulfide,Chemical vapor deposition,Monolayer
更新于2025-09-23 15:21:21
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Electrochemical Polishing of Two-Dimensional Materials
摘要： Two-dimensional (2D) layered materials demonstrate their exquisite properties such as high temperature superconductivity, superlubricity, charge density wave, piezotronics, flextronics, straintronics, spintronics, valleytronics, and optoelectronics, mostly, at the monolayer limit. Following initial breakthroughs based on micromechanically exfoliated 2D monolayers, significant progress has been made in recent years towards the bottom-up synthesis of large-area monolayer 2D materials such as MoS2 and WS2 using physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques in order to facilitate their transition into commercial technologies. However, the nucleation and subsequent growth of the secondary, tertiary, and greater numbers of vertical layers poses a significant challenge not only towards the realization of uniform monolayers, but also to maintain their consistent electronic and optoelectronic properties which change abruptly when transitioning from the monolayer to multilayer form. Chemical or physical techniques which can remove the unwarranted top layers without compromising the material quality will have tremendous consequence towards the development of atomically flat, large-area, uniform monolayers of 2D materials. Here, we report a simple, elegant, and self-limiting electrochemical polishing technique which can thin down any arbitrary thickness of 2D material, irrespective of whether these are obtained using powder vapor transport (PVT) or mechanical exfoliation, into their corresponding monolayer form at room temperature within a few seconds without compromising their atomistic integrity. The effectiveness of this electrochemical polishing technique is inherent to 2D transition metal dichalcogenides (TMDCs) owing to the stability of their basal planes, enhanced edge reactivity, and stronger-than-van der Waals (vdW) interaction with the substrate. Our study also reveals that 2D monolayers are chemically more robust and corrosion resistant compared to their bulk counterparts in similar oxidative environments which enables electrochemical polishing of such materials down to a monolayer.
关键词： physical vapor transport,MoS2,WS2,monolayer,corrosion,two-dimensional (2D) materials,electrochemical polishing,electro-ablation
更新于2025-09-23 15:21:21
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Performance enhancement of inverted perovskite solar cells through interface engineering by TPD based bidentate self-assembled monolayers
摘要： Perovskite solar cells (PSCs) have recently appeared as a promising photovoltaic technology and attracted great interest in both photovoltaic industry and academic community. Numerous active researches related to the material processing and operational aspects of device fabrication are under progress since PSCs have a great potential for attaining higher performance compared to that of other solar cell technologies. In particular, interfacial engineering is a crucial issue for obtaining high efficiency in solar cells where perovskite absorber layer is deposited between hole and electron transport layers. In inverted type architecture, PEDOT:PSS is used as both hole transport layer and surface modifier; but unfortunately, this material bears instability due to its acidic nature. Thus, self-assembled monolayers (SAMs) not only are considered as suitable alternative, but also their application is regarded as an efficient and cost effective method to modify electrode surface since it provides a robust and stable surface coverage. In this context, we have employed two novel N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) based SAM molecules to customize indium tin oxide (ITO) surface in inverted type PSCs. Furthermore, fine-tuning of spacer groups enables us to study device performance depending on molecular structure. This study proposes promising materials for anode interface engineering and provides a feasible approach for production of organic semiconductor based SAMs to achieve high performance PSCs.
关键词： Interface,ITO,TPD,Bidentate,Self-assembled monolayer,Perovskite solar cell
更新于2025-09-23 15:21:01
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Estimation of the lateral dimensions of epitaxial submonolayer CdSe/ZnSe quantum dots
摘要： CdSe fractional monolayer quantum dots (FMQDs) embedded in a ZnSe matrix were produced by atomic layer epitaxy with a nominal coverage of 0.5 monolayer. They have a thickness of a/2, where a is the strained perpendicular lattice constant of cubic CdSe. Their photoluminescence spectra at low temperature exhibit narrow and intense excitonic emission around 2.759 eV. Based on the experimental excitonic emission energy and applying the factorized-envelope approximation, we have estimated that the lateral dimensions of these FMQDs are around 4 - 5 nm and their density is ~ 3 × 1012 cm-2.
关键词： quantum dots size,fractional monolayer quantum dots,epitaxial quantum dots,submonolayer quantum dots,ultra-thin quantum dots,CdSe quantum dots
更新于2025-09-23 15:21:01
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Effect of the Interface Improved by Self-Assembled Aromatic Organic Semiconductor Molecules on Performance of OLED
摘要： This work focuses on characterization the performance of enhanced interface of organic light emitting diode (OLED) device by Self-assembled Monolayer (SAM) technique. SAM technique is popular in order to overcome the weak bonding at the organic/inorganic interface in OLED. New generation of SAM molecules, phenyl-benzoic-acid (PBA, 4-(9H-carbazol-9-il) benzoic acid (MZ39), 4-(2,5-di-2thienyl-1H-pyrrol-1-il) benzoic acid (MZ25) were coated on between Indium Tin Oxide (ITO). The two con?guration of ITO/SAM/TPD/Al and ITO/TPD/Al diode were fabricated as hole-only device to show the contribution of SAM layer on the hole mobility calculated by Space Charge Limited Current (SCLC) technique. The optical characterization of OLED devices with con?guration ITO/TPD/Alq3/Al and ITO/SAM/TPD/Alq3/Al was performed to see the effect of aromatic SAM molecules on the luminance and quantum ef?ciency. Especially, the SAM modi?ed OLED has a maximum luminance of 397 cd m?2. All devices containing SAM layer showed better performance than reference one.
关键词： Indium Tin Oxide (ITO),quantum efficiency,OLED,luminance,Space Charge Limited Current (SCLC),Self-assembled Monolayer (SAM)
更新于2025-09-23 15:21:01
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Choline Chloride-modified SnO2 Achieving High Output Voltage in MAPbI3 Perovskite Solar Cells
摘要： Choline chloride as a photosynthesis promoter is important for increasing plant yield, and we have found that it has a similar effect in perovskite solar cells (PSCs). Here, we propose the innovation of using molecular self-assembly methods to produce a choline chloride monolayer on the surface of the SnO2; this monolayer works as a passivation layer that reduces the surface oxygen vacancies and improves the performance of CH3NH3PbI3 (MAPbI3) PSCs. The MAPbI3 PSC based on SnO2 modified by choline chloride (Chol-SnO2) electron transport layer (ETL) achieves an optimal power conversion efficiency (PCE) of 18.90% under one solar illumination. The PCE is increased by 10% ~ 25% compared to the device without modification, and hysteresis is significantly reduced by eliminating the charge accumulation between the interface of the perovskite and ETL. More importantly, the MAPbI3 PSC based on Chol-SnO2 ETL exhibits a higher open-circuit voltage (VOC) of 1.145 V compared to the control device (1.071 V). This work provides a very simple and effective way to improve PSC performance, which has long-term significance for the sustainable development of energy.
关键词： self-assembled monolayer,choline chloride,SnO2,electron transporting layer,perovskite solar cells
更新于2025-09-23 15:21:01
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Laser-Induced Dissociation of the Monolayer of Adsorbed Methanol Molecules
摘要： Astronomical observations indicate a high abundance of methanol molecules in the gas phase of molecular-cloud dense cores, which cannot be explained by gas-phase chemical reactions only. A significant contribution to the methanol abundance should be provided by chemical reactions on the dust particle surface with subsequent desorption of the produced molecules into the gas phase. For the development and refinement of models involving these processes, laboratory studies of photo-induced processes occurring in the adsorbed material are necessary. In this paper, the experiment results of adsorbed methanol molecules are presented. A methanol molecule monolayer, physically adsorbed on fused silica surface cooled by liquid nitrogen (Т ～ 100 K), was irradiated in high vacuum by nanosecond pulses of an excimer KrF laser with a fixed wavelength λ = 248 nm. The photodissociation products of three-photon laser excitation were recorded by a quadrupole mass spectrometer. Relative yields of photofragments H, OH, and CH3 were determined. Photolysis of partially deuterated CH3OH molecules has shown that hydrogen atoms can be ejected both from hydroxyl and methyl groups. In contrast to the isolated molecule photolysis in the gas phase and dissociation of the multilayer molecular coatings, photoexcitation of adsorbed methanol monolayer even in the energy region of 10 eV does not cause noticeable chemical transformations and does not lead to the formation of molecular components H2 and CH4. Due to existing astrochemical modeling problems, possible application methods of the obtained laboratory results are considered.
关键词： chemical reactions,astronomical observations,adsorbed monolayer,mass spectrometry,photo-induced processes,gas phase,dust particle surface,KrF laser,photodissociation,methanol
更新于2025-09-23 15:21:01