WSe2 Surface Research Articles

−DFT study of the adsorption of temozolamide anticancer drugs on the TM-adsorbed WSe2 nanocarriers: Applications to drug delivery systems

The interaction of temozolamide anticancer drugs with transition metal (TM) adsorbed WSe2 nanosheets was examined using the first principles approach. Main electronic and geometric parameters were systematically analyzed to comprehensively evaluate the drug nanocarrier characteristics of the modified WSe2 systems. Pt, Pd and Ag binding on the surface of WSe2 leads to the favorable structures for drug sensing process. Our results suggested a stronger interaction between temozolamide anticancer drugs and Pt-adsorbed WSe2 nanosheets, indicating the prospects for drug delivery systems based on modified WSe2. The oxygen atoms of temozolamide drug are found to be more interactive than other atoms when approaching the Pt-adsorbed WSe2 substrates. The moderate adsorption energy and recovery time reveal the potentials of Pt-adsorbed WSe2 for proper adsorbing of temozolamide drug. This research aims at giving theoretical insights into the prospective application of TM adsorbed WSe2 systems as effective nanocarriers for temozolamide drugs.

Theoretical study on the effect of shear deformation on WSe2 as a cathode material for calcium ion batteries

AbstractIn this paper, the first‐principles method is used to calculate the electronic structure of the intrinsic WSe2 system and the Ca adsorbed WSe2 system under shear deformation, and the diffusion barrier of Ca on WSe2 is studied in depth. The results show that shear deformation can effectively reduce the band gap of WSe2 system, and shear deformation can easily lead to the transition from semiconductor properties to metal properties. The adsorption of Ca leads to the change of the band structure of WSe2. The contribution of Ca‐d electrons leads to an increase in the peak in the range of 3–6 eV. The shear deformation reduces the diffusion barrier of Ca on the WSe2 surface. This paper provides an improvement method for the application of WSe2 in the field of battery.

Exploration of SF6 and its decomposed gases in adsorption and sensing (four modified WSe2 monolayers at quantum level)

As SF6 is the most widely used high-voltage insulating gas, the monitoring of its decomposition products to ensure the stable operation of GIS equipment and the treatment of leakage have been two important research topics. This work is based on the first principles of adsorption and sensing characterization of SF6 and its decomposed gases (HF, H2S, SO2, SOF2, SO2F2) using four modification strategies on the surface of WSe2. The energy parameters such as transfer charge, density of states, adsorption energy, band gap, and work function are calculated for each system. The results show that the electrical conductivity of the system is greatly enhanced when defect modification is employed, and the band gap is changed from 2.018 eV to 0.008 eV (W@WSe2) and 1.271 eV (Se@WSe2). The CoO and TiO2 doped WSe2 showed excellent adsorption of SF6 (−7.818 eV) and SOF2 (−14.263 eV), respectively, which is of great significance for SF6 gas leakage treatment. In addition, the results of work function calculations indicate that CoO-WSe2 has potential as a work function type sensor for these six gases. Finally, by calculating the desorption time (τ), we systematically explored whether the four modified materials have the characteristics to be used as recyclable resistive type sensors under different temperature environments. Our work will help to explore the adsorption performance and sensing characteristics of WSe2 monolayers with different modifications for SF6 and its decomposed gases, which is crucial for the protection of GIS equipment in power systems.

First-principles study on the effect of torsional deformation on WSe2 as an anode material for calcium ion batteries.

In this paper, the effects of torsional deformation on the electronic properties of intrinsic WSe2 system and Ca-adsorbed WSe2 system were systematically studied by first-principles method. The results show that Ca can be stably adsorbed on the vacancy (H site) of WSe2 surface in all deformation systems, and the adsorption energy of the system without deformation is the highest. Intrinsic WSe2 is a semiconductor with a direct band gap of 1.53 eV. The torsional deformation makes WSe2 change from a direct band gap semiconductor to an indirect band gap semiconductor and finally to a metal property. The adsorption of Ca makes the conduction band of WSe2 move down and increases the number of peaks in the conduction band region. The new density of state peaks are mainly derived from the contribution of W-d, Se-p, and d orbitals of adsorbed atoms in each adsorption system. Mulliken charge analysis shows that Ca transfers most of the valence electrons to the substrate, and the torsional deformation changes the amount of transferred charge. The twist deformation reduces the diffusion barrier of Ca on WSe2 surface from 0.20 to 0.14 eV. The above results provide a basis for the improved application of WSe2 in ion batteries. In this study, all the first-principles calculations are based on Materials Studio 8.0 software package. The generalized gradient approximation (GGA) functional Perdew-Burke-Ernzerhof (PBE) is used for the electron exchange correlation interactions in all systems. The optimization algorithm uses Broyden-Fletcher-Goldfarb-Shanno (BFGS) to optimize the model structure and calculate the energy. The measured cutoff energy is optimized to 450 eV, and the radius of the vacuum layer in the Z-axis direction is 20 Å. The K-point of 7 × 7 × 1 is selected by Monkhorst-Pack method. The structural optimization criterion is selected, the convergence radius of the force is 0.01 eV/Å, and the displacement radius between atoms is within 0.001 Å distance. The energy convergence radius of each atom is less than 1.0 × 10-6 eV/atom.

Role of hexagonal boron nitride configuration in gate-induced hysteresis of WSe2 field-effect transistors

Environmental sensitivity of layered materials necessitates investigating the impact of surrounding materials like hexagonal boron nitride (hBN) on their electrical properties. We investigate the effects of hBN on gate-induced hysteresis in multilayer WSe2 field-effect transistors (FETs) with four configurations: bare WSe2, WSe2 on bottom hBN (b-hBN), WSe2 under top hBN (t-hBN), and WSe2 encapsulated with hBN. The presence of b-hBN greatly improves the electrical properties of the two corresponding WSe2 FETs, leading to a more than tenfold increase in channel currents and a significant reduction in hysteresis. In contrast, the effect of t-hBN is weaker than that of b-hBN. When the environment changes from vacuum to atmospheric conditions, the hysteresis of the two WSe2 FETs without b-hBN increases substantially, while the change is small for those with b-hBN. Our observations support that pressure-dependent hysteresis originates from gas molecule adsorptions at the WSe2/SiO2 interface, not directly on the WSe2 surface.

Polarized X-ray diffraction anomalous near-edge structure study on the orbital physics of thin WSe2 layers

The electronic structures at band edges play an important role in the physical properties of few-layer and monolayer WSe2. In this study, polarization-dependent diffraction anomalous near-edge structure (DANES) is applied to measure and analyse the electronic orbitals of few-layer WSe2. By selecting diffraction geometries with the electric field perpendicular or parallel to the c axis of few-layer WSe2, this method can separately probe the in-plane and out-of-plane orbital components involved at the band edges. The WSe2 (00.8) surface normal was aligned and the preferred orientation of few-layer WSe2 grown on an Al2O3 (00.1) substrate was identified. DANES was then performed for Se K-edge WSe2 00.8 and 11.0 reflections to examine the W 5d orbitals hybridized with the Se 4p orbitals: these two DANES spectra exhibit fairly anisotropic valence orbital characteristics in few-layer WSe2. Coupled with first-principles calculations, these results allow the identification of the in-plane and out-of-plane orbital distribution and hybridization in WSe2. At the conduction band edge, the contributions of px and py orbitals are predominant over pz and the splitting of the p-orbital energy levels has been confirmed. Hence DANES is shown to be a useful synchrotron X-ray technique that can help identify the valence orbital structure of various 2D transition metal dichalcogenides.

Atomic insight into the effects of precursor clusters on monolayer WSe2.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been attracting much attention due to their rich physical and chemical properties. At the end of the chemical vapor deposition growth of 2D TMDCs, the adsorption of excess precursor clusters onto the sample is unavoidable, which will have significant effects on the properties of TMDCs. This is a concern to the academic community. However, the structures of the supported precursor clusters and their effects on the properties of the prepared 2D TMDCs are still poorly understood. Herein, taking monolayer WSe2 as the prototype, we investigated the structure and electronic properties of SeN, WN (N = 1-8), and W8-NSeN (N = 1-7) clusters adsorbed on monolayer WSe2 to gain atomic insight into the precursor cluster adsorption. In contrast to W clusters that tightly bind to the WSe2 surface, Se clusters except for Se1 and Se2 are weakly adsorbed onto WSe2. The interaction between W8-NSeN (N = 1-7) clusters and the WSe2 monolayer decreases with the increase in the Se/W ratio and eventually becomes van der Waals interaction for W1Se7. According to the phase diagram, increasing the Se/W ratio by changing the experimental conditions will increase the ratio of SeN and W1Se7 clusters in the precursor, which can be removed by proper annealing after growth. W clusters induce lots of defect energy levels in the band gap region, while the adsorption of W1Se7 and SeN clusters (N = 3-6, 8) promotes the spatial separation of photo generated carriers at the interface, which is important for optoelectronic applications. Our results indicate that by controlling the Se/W ratio, the interaction between the precursor clusters and WSe2 as well as the electronic properties of the prepared WSe2 monolayer can be effectively tuned, which is significant for the high-quality growth and applications of WSe2.

Low-cost and simple fabrication of micro-mask/micro-channels on different substrates based on water-soluble fiber poly (vinyl alcohol) (PVA)

Here we report an approach to fabricate micro-mask/micro-channels using water-soluble fiber poly (vinyl alcohol) (PVA). The scheme is a simple, environmentally friendly, and low-cost technology, that can realize the preparation of micro-mask/micro-channels on different substrates. Scanning electron microscope (SEM) and optical microscope (OM) are used to observe surface morphology and measured fiber diameter. We showed that a variety of micro-mask/micro-channels can be easily controlled by changing the swelling temperature and time of the PVA fiber. The swelling temperature was varied from 25 °C to 50 °C, the diameter of the fiber increased by 9.5 μm, and the diameter and volume swelling rates reached 59.38% and 154%, respectively. Meanwhile, with the increase in swelling time, the diameter and volume swelling rate showed the same increasing trend. Additionally, we used the PVA fiber as a micro-mask to prepare the micro-channel on the WSe2 surface and verified the feasibility of the PVA fiber to prepare micro-mask/micro-channels by testing the electrical properties of the WSe2 sample. Finally, we also verified the feasibility of the above methods to fabricate micro-mask/micro-channels on different substrates such as conductive fibers, PDMS, and WSe2/SiO2Si, and proposed to realize nano-scale patterning through direct electrospinning. Therefore, it is expected to be more widely promoted in the future.

Effects of atmospheric UV-O3 exposure of WSe2 on the properties of the HfO2/WSe2 interface

Transition metal dichalcogenides (TMDCs), such as semiconducting WSe2, are typically interfaced with a high-quality dielectric layer in device applications. The unreactive basal plane of TMDCs makes the standard technique for deposition of dielectric oxides, atomic layer deposition (ALD), challenging on TMDC surfaces. In this work, we make use of atmospheric ultraviolet–ozone (UV-O3) exposure of WSe2 to functionalize its surface and promote uniform ALD of HfO2. We report two classifications depending on the UV-O3 exposure time. Low exposures do not result in detectable WSe2 surface oxidation, while high exposures result in a self-limiting and amorphous tungsten oxyselenide top layer. Following ALD of HfO2, low exposure samples have an abrupt HfO2/WSe2 interface with no interfacial oxide, while high exposure results in an interfacial WO3 layer between the HfO2 and the WSe2, as well as evidence of two doping states observed in the underlying WSe2. Despite differences in the interface chemistry, both low and high exposures result in uniform and smooth HfO2 films directly deposited by ALD and a reduction in gate leakage through this HfO2 layer. We report that our atmospheric UV-O3 exposure technique on WSe2 is an avenue for allowing direct ALD of thin uniform oxide films on WSe2, and the UV-O3 exposure time provides unique tunability and flexibility in interface design within devices.

Controllable synthesis of monolayer WSe2 crystals by Copper-Assisted chemical vapor deposition

In this work, we demonstrate the controllable synthesis of high-quality WSe2 monolayers via a copper-assisted chemical vapor deposition method. The structure characterizations confirm that the as-grown WSe2 crystals by introducing Cu powder exhibit monolayer thickness and high crystalline quality. Most importantly, theoretical calculation reveals that Cu atoms could easily occupy the active sites above the monolayer WSe2 surface, consequently forming a self-limited growth. The Cu-assisted growth method broadens the scope of the 2D growth of other TMD materials, and also provides more application potential in 2D electronics.

Fabrication and Characterization of Self-Aligned WSe2 p-Type Field-Effect Transistor

Semiconducting transition metal dichalcogenides (TMDCs) have been growing interests as channel materials in field effect transistors (FET) for next generation low power digital electronics. [1]. Since a complementary metal oxide-semiconductor (CMOS) inverter constructed from pairs of n-type and p-type FETs is a fundamental building blocks in modern digital electronics [2], implementation of both n-type and p-type FETs with semiconducting TMDCs is of particular importance [3]. Among various semiconducting TMDCs, tungsten diselenide (WSe2) is a promising candidate for constructing a CMOS inverter because of its high mobility, symmetric electron and hole effective mass and ambipolar transport [4]. These prominent features of WSe2 is suitable for an application to CMOS inverter.One of the significant challenges is to develop a top gate and top contact FET structure with WSe2 for CMOS device integration on the same wafer. In addition, it is desirable to minimize the access region between channel and S/D contact because this access region served as a series resistance to channel resistance, resulting in the lower drain current in FET. This study reports a self-aligned process to fabricate top gate and top contact WSe2 p-type FET. In this self-aligned structure, the gate electrode and source/drain contact edges are automatically positioned and hence there are no overlap or access region between the gate and source/drain. The feature of this proposed method is that the gate stacks was utilized as a mask for self-aligned formation of WOx, which is source/drain contact for efficient hole injection [5]. The focus on this study is the impact of self-aligned structure of p-type WSe2 FET on the electrical characteristics. The effectiveness of proposed process was experimentally demonstrated by the fabrication and characterization of device.Figures 1 shows the self-aligned fabrication process of p-type WSe2 FET. 20 nm-thick SiO2 was formed by dry oxidation of p+-Si substrate. The mechanically exfoliated multi-layer WSe2 was transferred by PDMS stamp. Next, 15 nm-thick Al2O3 was prepared by ALD at 200 oC with H2O. Then, Nickel (Ni) metal was deposited by RF sputtering on Al2O3. Ni metal was patterned for gate electrode with conventional lithography process. After that, A2O3 layer was removed by wet etching. Subsequently, substrate was exposed to oxygen radicals to form WOx used as source/drain contact at surface of WSe2. Second layer of Al2O3 was deposited as an encapsulating passivation layer. After the contact hole opening, the electrical contact pad was fabricated. Finally, forming gas (N2 : H2 = 97 % : 3 %) annealing was performed at 200 oC for 30 min. The top gate length was 5 μm. The gate width was estimated to be 40 μm by optical microscope. The electrical characteristics were measured with a manual probe station in an atmospheric pressure without inert gas purge at room temperature using a precision semiconductor parameter analyzer (Agilent 4156 C).Figures 2 shows the Id–Vg characteristics of fabricated FETs for (a) back gate operation and (b) top gate operation. Representative Id–Vg characteristics of p-type FETs were observed irrespective of back gate and top gate operation. The on/off ratio of about 106 ~ 107 order were obtained for both back gate and top gate operation. Furthermore, the threshold voltage and sub-threshold slope were modulated by varying the substrate bias during gate sweep.This study opens up interesting directions for the research and development of TMDC-based devices.AcknowledgmentsThis study was supported by a JSPS Grant-in-Aid for Scientific Research (C) (Grant No. 20K04616), a research grant for Tokyo Tech Challenging Research Award, the Samco Foundation and a research grant for Suematsu Award.

Nanostructured doping of WSe2via block copolymer patterns and its self-powered photodetector application.

Transition metal dichalcogenides (TMDs), e.g., MoS2, MoSe2, ReS2, and WSe2, are effective materials for advanced optoelectronics owing to their intriguing optical, structural, and electrical properties. Various approaches for manipulating the surface of the TMDs have been suggested to unleash the optoelectronic potential of the TMDs. Herein, we employed the self-assembly of the poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer (BCP) to prepare a nanoporous pattern and generate nanostructured charge-transfer p-doping on the WSe2 surface, maximizing the depletion region in the absorber layer. After the spin coating and thermal annealing of PS-b-PMMA, followed by the selective etching of PMMA cylindrical microdomains using oxygen reactive-ion plasma, nanopatterned WOx with high electron affinity was grown on the WSe2 surface, forming a three-dimensional homojunction. The nanopatterned WOx significantly expanded the depletion region in the WSe2 layer, thus enhancing optoelectronic performance and self-powered photodetection. The proposed approach based on the nanostructured doping of the TMDs via BCP nanolithography can help create a promising platform for highly functional optoelectrical devices.

Effects of surface wettability on (001)-WO[formula omitted] and (100)-WSe[formula omitted]: A spin-polarized DFT-MD study

An extensive understanding of WO3 and WSe2 bulk crystalline structures and explicit solvent effects on (001)-WO3 and (100)-WSe2 facets are essential for design of efficient (photo) electrocatalysts. The atomistic level understanding of both WO3 and WSe2 bulk solids and how water solvation processes occur on WO3 and WSe2 facets are nowadays characterized by a noticeable lack of knowledge.Herein, forefront Density Functional Theory-based molecular dynamics have been conducted for assessing the role of an explicit water environment in the characterization of solid surfaces. Water at the interface and H-bonds environment, as well as WO3 and WSe2 surface activity, will be described in terms of surface wettability and interfacial water dynamics, revealing the relevance of treating explicitly liquid water and its dynamics in assessing catalytic features. We provide pieces of evidence of the hydrophobic character shown by (001)-WO3 and (100)-WSe2 facets. A preferential in-plane hydration structure of the first water layer has been detected at both (001)-WO3 and (100)-WSe2 water interface, in which the electric dipole moment of water molecules is re-oriented in a sort of 2-dimensional H-bond network. Bulk property calculations of WO3 and WSe2 are also provided.

Gold nanoparticles decorated 2D-WSe2 as a SERS substrate

Developing well-defined surface enhanced Raman scattering (SERS)-active substrates with superior performance is potentially attractive for many areas of research such as new generation sensing and analysis. Here, a nanohybrid SERS platform has been developed by decorating two-dimensional (2D) tungsten diselenide (WSe2) flakes with zero-dimensional (0D) plasmonic gold nanoparticles (Au NPs). The morphology studies showed that under optimal conditions densely populated Au NPs were formed on the WSe2 surface. Here, we report the utility of the Au NPs/WSe2 nanohybrid structure as an efficient SERS substrate by performing concentration-dependent SERS measurements of a highly fluorescent molecule (Rhodamine 6G, R6G). The hybrid substrate displays promising SERS activity with the detection limit as low as 1 × 10–9 M, which is several orders of magnitude higher than the bare WSe2 on its own (10-3 M). The substrate also exhibits reliable signal stability and reproducibility. These results indicate that the nanohybrid structure has great potential in SERS applications.

Nanometer-thick copper films with low resistivity grown on 2D material surfaces

Thin Copper (Cu) films (15 nm) are deposited on different 2D material surfaces through e-beam deposition. With the assist of van der Waals epitaxy growth mode on 2D material surfaces, preferential planar growth is observed for Cu films on both MoS2 and WSe2 surfaces at room temperature, which will induce a polycrystalline and continuous Cu film formation. Relative low resistivity values 6.07 (MoS2) and 6.66 (WSe2) μΩ-cm are observed for the thin Cu films. At higher growth temperature 200 °C, Cu diffusion into the MoS2 layers is observed while the non-sulfur 2D material WSe2 can prevent Cu diffusion at the same growth temperature. By further increasing the deposition rates, a record-low resistivity value 4.62 μΩ-cm for thin Cu films is observed for the sample grown on the WSe2 surface. The low resistivity values and the continuous Cu films suggest a good wettability of Cu films on 2D material surfaces. The thin body nature, the capability to prevent Cu diffusion and the unique van der Waals epitaxy growth mode of 2D materials will make non-sulfur 2D materials such as WSe2 a promising candidate to replace the liner/barrier stack in interconnects with reducing linewidths.

Molecular Dopant-Dependent Charge Transport in Surface-Charge-Transfer-Doped Tungsten Diselenide Field Effect Transistors.

The controllability of carrier density and major carrier type of transition metal dichalcogenides(TMDCs) is critical for electronic and optoelectronic device applications. To utilize doping in TMDC devices, it is important to understand the role of dopants in charge transport properties of TMDCs. Here, the effects of molecular doping on the charge transport properties of tungsten diselenide (WSe2 ) are investigated using three p-type molecular dopants, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 -TCNQ), tris(4-bromophenyl)ammoniumyl hexachloroantimonate (magic blue), and molybdenum tris(1,2-bis(trifluoromethyl)ethane-1,2-dithiolene) (Mo(tfd-COCF3 )3 ). The temperature-dependent transport measurements show that the dopant counterions on WSe2 surface can induce Coulomb scattering in WSe2 channel and the degree of scattering is significantly dependent on the dopant. Furthermore, the quantitative analysis revealed that the amount of charge transfer between WSe2 and dopants is related to not only doping density, but also the contribution of each dopant ion toward Coulomb scattering. The first-principles density functional theory calculations show that the amount of charge transfer is mainly determined by intrinsic properties of the dopant molecules such as relative frontier orbital positions and their spin configurations. The authors' systematic investigation of the charge transport of doped TMDCs will be directly relevant for pursuing molecular routes for efficient and controllable doping in TMDC nanoelectronic devices.

Interfacial Doping Effects in Fluoropolymer-Tungsten Diselenide Composites Providing High-Performance P-Type Transistors.

In this study, we investigated the p-doping effects of a fluoropolymer, Cytop, on tungsten diselenides (WSe2). The hole current of the Cytop–WSe2 field-effect transistor (FET) was boosted by the C–F bonds of Cytop having a strong dipole moment, enabling increased hole accumulation. Analysis of the observed p-doping effects using atomic force microscopy (AFM) and Raman spectroscopy shed light on the doping mechanism. Moreover, Cytop reduces the electrical instability by preventing the adsorption of ambient molecules on the WSe2 surface. Annealing Cytop deposited on WSe2 eliminated the possible impurities associated with adsorbates (i.e., moisture and oxygen) that act as traps on the surface of WSe2. After thermal annealing, the Cytop–WSe2 FET afforded higher p-type conductivity and reduced hysteresis. The combination of the Cytop–WSe2 FET with annealing provides a promising method for obtaining high-performance WSe2 p-type transistors.

Two-dimensional iodine-monofluoride epitaxy on WSe2

Interhalogen compounds (IHCs) are extremely reactive molecules used for halogenation, catalyst, selective etchant, and surface modification. Most of the IHCs are unstable at room temperature especially for the iodine-monofluoride (IF) whose structure is still unknown. Here we demonstrate an unambiguous observation of two-dimensional (2D) IF bilayer grown on the surface of WSe2 by using scanning transmission electron microscopy and electron energy loss spectroscopy. The bilayer IF shows a clear hexagonal lattice and robust epitaxial relationship with the WSe2 substrate. Despite the IF is known to sublimate at −14 °C and has never found as a solid form in the ambient condition, but surprisingly it is found stabilized on a suitable substrate and the stabilized structure is supported by a density functional theory. This 2D form of IHC is actually a byproduct during a chemical vapor deposition growth of WSe2 in the presence of alkali metal halides as a growth promoter and requires immediate surface passivation to sustain. This work points out a great possibility to produce 2D structures that are unexpected to be crystallized or cannot be obtained by a simple exfoliation but can be grown only on a certain substrate.

Synthesis of Colloidal WSe2 Nanocrystals: Polymorphism Control by Precursor-Ligand Chemistry

Syntheses of transition-metal dichalcogenides (TMDs) using colloidal-chemistry approaches are gaining significant interest in recent years, as these methods enable the morphology and properties of the nanocrystals to be tuned for targeted applications. In this work, by only varying the ligand used during synthesis, we synthesized nanoflowers with oleic acid (OA) and 1T' phase dominated WSe2 nanosheets with oleylamine (OLA). WSe2 nanocrystals show slower rate of formation for the metastable 1T' phase. Surface chemistry analyses of the synthesized nanocrystals by solution NMR establish that neither of the ligands bind strongly to the surface of nanocrystals but are in a dynamic coordination with the WSe2 surface. A further examination of the coordination of tungsten hexacarbonyl (W(CO)(6)) with the respective ligands confirms that W(CO)(6) decomposes in OA, losing its octahedral symmetry, which leads to fast reactivity in the flask. In contrast to this, W(CO)(6) reacts with OLA to form a new complex, which leads to slower reactivity and crystallization of the synthesized nanocrystals in the octahedral 1T' phase. These insights into the influence of precursor-ligand chemistry on reaction outcome and the peculiar surface chemistry of colloidal TMD nanocrystals will be instrumental in developing future colloidal TMD nanocrystals.

First-principle study for influence of normal strain on the magnetic properties of nonmetal adsorbed WSe2 monolayer

In this work, the magnetic properties of the WSe2 monolayer with different nonmetals (B, C, F, N, and O) are studied by the ab initio calculations. Different behavior shows up by applying the normal strain. Under the normal strain, the magnetism becomes tunable except for the B and O adatoms. Then, the magnetic coupling between two nonmetals has been checked. A transformation from ferromagnetic (FM) to nonmagnetic (NM) has been observed in two F-adsorbed systems, which could be explained by the p–p hybridization mechanism. Our results provide a theoretical reference for the adsorption on the WSe2 surfaces.