N-type and p-type molecular doping on monolayer MoS2 (original) (raw)
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N-type and p-type molecular doping on monolayer MoS2
RSC Advances, 2021
Monolayer MoS 2 has attracted much attention due to its high on/off current ratio, transparency, and suitability for optoelectronic devices. Surface doping by molecular adsorption has proven to be an effective method to facilitate the usage of MoS 2. However, there are no works available to systematically clarify the effects of the adsorption of F 4 TCNQ, PTCDA, and tetracene on the electronic and optical properties of the material. Therefore, this work elucidated the problem by using density functional theory calculations. We found that the adsorption of F 4 TCNQ and PTCDA turns MoS 2 into a p-type semiconductor, while the tetracene converts MoS 2 into an n-type semiconductor. The occurrence of a new energy level in the conduction band for F 4 TCNQ and PTCDA and the valence band for tetracene reduces the bandgap of the monolayer MoS 2. Besides, the MoS 2 /F 4 TCNQ and MoS 2 /PTCDA systems exhibit an auxiliary optical peak at the long wavelengths of 950 and 850 nm, respectively. Contrastingly, the MoS 2 /tetracene modifies the optical spectrum of the monolayer MoS 2 only in the ultraviolet region. The findings are in good agreement with the experiments.
RSC Advances, 2020
is one of the well-known transition metal dichalcogenides. The moderate bandgap of monolayer MoS 2 is fascinating for the new generation of optoelectronic devices. Unfortunately, MoS 2 is sensitive to gases in the environment causing its original electronic properties to be modified unexpectedly. This problem has been solved by coating MoS 2 with polymers such as polyethyleneimine (PEI). Furthermore, the application of pressure is also an effective method to modify the physical properties of MoS 2. However, the effects of polyethyleneimine and pressure on the electronic and optical properties of monolayer MoS 2 remain unknown. Therefore, we elucidated this matter by using density functional theory calculations. The results showed that the adsorption of the PEI molecule significantly reduces the width of the direct bandgap of the monolayer MoS 2 to 0.55 eV because of the occurrence of the new energy levels in the bandgap region due to the contribution of the N-2p z state of the PEI molecule. Remarkably, the transition from semiconductor to metal of the monolayer MoS 2 and the MoS 2 /PEI system occurs at the tensile pressure of 24.95 and 21.79 GPa, respectively. The bandgap of these systems approaches 0 eV at the corresponding pressures. Importantly, new peaks in the optical spectrum of the clean MoS 2 and MoS 2 /PEI appear in the ultraviolet region under compressive pressures and the infrared region under tensile strains.
Ab-initio study on the possible doping strategies for MoS2 monolayers
Density functional theory is used to systematically study the electronic and magnetic properties of doped MoS2 monolayers, where the dopants are incorporated both via S/Mo substitution or as adsorbates. Among the possible substitutional dopants at the Mo site, Nb is identified as suitable p-type dopant, while Re is the donor with the lowest activation energy. When dopants are simply adsorbed on a monolayer we find that alkali metals shift the Fermi energy into the MoS2 conduction band, making the system n-type. Finally, the adsorption of charged molecules is considered, mimicking an ionic liquid environment. We find that molecules adsorption can lead to both n-and p-type conductivity, depending on the charge polarity of the adsorbed species.
Nano Letters, 2013
Using first-principles calculations within density functional theory, we investigate the electronic and chemical properties of a single-layer MoS 2 adsorbed on Ir(111), Pd(111), or Ru(0001), three representative transition metal substrates having varying work functions but each with minimal lattice mismatch with the MoS 2 overlayer. We find that, for each of the metal substrates, the contact nature is of Schottky-barrier type, and the dependence of the barrier height on the work function exhibits a partial Fermi-level pinning picture. Using hydrogen adsorption as a testing example, we further demonstrate that the introduction of a metal substrate can substantially alter the chemical reactivity of the adsorbed MoS 2 layer. The enhanced binding of hydrogen, by as much as ∼0.4 eV, is attributed in part to a stronger H−S coupling enabled by the transferred charge from the substrate to the MoS 2 overlayer, and in part to a stronger MoS 2-metal interface by the hydrogen adsorption. These findings may prove to be instrumental in future design of MoS 2-based electronics, as well as in exploring novel catalysts for hydrogen production and related chemical processes.
Large Work Function Modulation of Monolayer MoS2 by Ambient Gases
ACS nano, 2016
Although two-dimensional monolayer transition metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS2 via ambient gases. The work function was measured by in situ Kelvin probe technique, further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O2 exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ~200 ...
Transport Properties of Monolayer MoS 2 Grown by Chemical Vapor Deposition
Nano Letters, 2014
Recent success in the growth of monolayer MoS2 via chemical vapor deposition (CVD) has opened up prospects for the implementation of these materials into thin film electronic and optoelectronic devices. Here, we investigate the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2. The devices show low temperature mobilities up to 500 cm 2 V −1 s −1 and a clear signature of metallic conduction at high doping densities. These characteristics are comparable to the electronic properties of the best mechanically exfoliated monolayers in literature, verifying the high electronic quality of the CVD-grown materials. We analyze the different scattering mechanisms and show, that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures. Additionally, the influence of phonons as a limiting factor of these devices is discussed. arXiv:1401.1063v1 [cond-mat.mes-hall]
Strain engineering of selective chemical adsorption on monolayer MoS2
Nanoscale, 2014
Nanomaterials are prone to influence by chemical adsorption because of their large surface to volume ratios. This enables sensitive detection of adsorbed chemical species which, in turn, can tune the property of the host material. Recent studies discovered that single and multi-layer molybdenum disulfide (MoS 2 ) films are ultra-sensitive to several important environmental molecules. Here we report new findings from ab inito calculations that reveal substantially enhanced adsorption of NO and NH 3 on strained monolayer MoS 2 with significant impact on the properties of the adsorbates and the MoS 2 layer. The magnetic moment of adsorbed NO can be tuned between 0 and 1 µ B ; strain also induces an electronic phase transition between half-metal and metal. Adsorption of NH 3 weakens the MoS 2 layer considerably, which explains the large discrepancy between the experimentally measured strength and breaking strain of MoS 2 films and previous theoretical predictions. On the other hand, adsorption of NO 2 , CO, and CO 2 is insensitive to the strain condition in the MoS 2 layer. This contrasting behavior allows sensitive strain engineering of selective chemical adsorption on MoS 2 with effective tuning of mechanical, electronic, and magnetic properties. These results suggest new design strategies for constructing MoS 2 -based ultrahigh-sensitivity nanoscale sensors and electromechanical devices.
Probing the Electronic Properties of Monolayer MoS2 via Interaction with Molecular Hydrogen
Advanced Electronic Materials, 2018
This work presents a detailed experimental investigation of the interaction between molecular hydrogen (H2) and monolayer MoS2 field effect transistors (MoS2 FET), aiming for sensing application. The MoS2 FET exhibit a response to H2 that covers a broad range of concentration (0.1-90 %) at a relatively low operating temperature range (300-473 K). Most important, H2 sensors based on MoS2 FETs show desirable properties such as full reversibility and absence of catalytic metal dopants (Pt or Pd). The experimental results indicate that the conductivity of MoS2 monotonically increases as a function of the H2 concentration due to a reversible charge transferring process. It is proposed that such process involves dissociative H2 adsorption driven by interaction with sulfur vacancies in the MoS2 surface (VS). This description is in agreement with related density functional theory studies about H2 adsorption on MoS2. Finally, measurements on partially defect-passivated MoS2 FETs using atomic layer deposited aluminum oxide consist of an experimental indication that the VS plays an important role in the H2 interaction with the MoS2. These findings provide insights for futures applications in catalytic process between monolayer MoS2 and H2 and also introduce MoS2 FETs as promising H2 sensors.
First-principles study of molecule adsorption on Ni-decorated monolayer MoS2
Journal of Computational Electronics, 2019
The interactions between four different gas molecules (methanol, o-xylene, p-xylene and m-xylene) and Ni-decorated monolayer MoS 2 were investigated by means of density functional computations to exploit its potential application as a gas sensor. The electronic properties of the Ni-decorated monolayer MoS 2 and gas molecule (adsorbent-adsorbate properties) strongly depend on the Ni-decorated monolayer MoS 2 structure and the molecular configuration of the adsorbate. The adsorption properties of volatile organic compound (VOC) molecules on Ni-decorated MoS 2 has been studied taking into account the parameters such as adsorption energy, energy bandgap, density of states, and Mulliken charge transfer. All three xylene isomers showed considerably stronger adsorption on the Ni-decorated monolayer MoS 2 than the methanol. Among them, p-xylene was found to have the highest adsorption energy and charge transfer value in interaction with the Ni-decorated monolayer MoS 2. The adsorption energy shows a significant improvement after nickel decoration for xylene adsorption. Therefore, the adsorption of xylene vapor on Ni-decorated monolayer MoS 2 was found to be favorable comparing to other VOC molecules.