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Effect of atom adsorption on the electronic, magnetic, and optical properties of the GeP monolayer: A first-principle study
摘要： First-principles calculations have been carried out to explore the effect of atom surface adsorption on the electronic, magnetic, and optical properties of the germanium phosphide (GeP) monolayer. It is shown that the GeP monolayer exhibits good adsorption capability to all the selected adatoms and can preserve the structural integrity upon the adsorption of most adatoms. The adatoms can bring out diverse electronic properties to the GeP monolayer. The H, Li, Na, K, and Al adatoms donate electrons to the GeP monolayer and result in its metallization. The other adatoms do not change the semiconducting nature of the GeP monolayer and will induce midgap states (Mg, Ca, Si, Ge, Ag, and Au) or reduce the bandgaps (Ni, Pd, and Pt). The B, N, P, As, V, Cr, Mn, Fe, and Co adatoms induce spin magnetic moments into the GeP monolayer. Especially, the spin magnetic moments are mainly located on the adatoms for the GeP decorated with the V, Cr, Mn, Fe, and Co atoms. As a result, the dilute magnetic semiconductor can be obtained. In addition, all the adatoms decrease the work function, except O. Thus, some effects on the optical properties are highly expected. The GeP monolayer exhibits a wide range of light absorption and the Mg, Si, Ge, Cu, Ag, Au, and Pt adatoms can further redshift the absorption edge of the GeP monolayer along the x and y directions. Our calculations provide an effective method to modulate the electronic, magnetic, and optical properties of the GeP monolayer for device applications.
关键词： and optical properties,GeP monolayer,magnetic,First-principles calculations,electronic,atom surface adsorption
更新于2025-09-23 15:23:52
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Optical Imaging of Charges with Atomically Thin Molybdenum Disulfide
摘要： Mapping local surface charge distribution is critical to the understanding of various surface processes and also allows the detection of molecules binding to the surface. We show here that the optical absorption of monolayer MoS2 is highly sensitive to charge and demonstrate optical imaging of local surface charge distribution with this atomically thin material. We validate the imaging principle and perform charge sensitivity calibration with an electrochemical gate. We further show that binding of charged molecules to the atomically thin material leads to a large change in the image contrast, allowing determination of the charge of the adsorbed molecules. This capability opens possibilities for characterizing impurities and defects in two dimensional materials and for label-free optical detection and charge analysis of molecules.
关键词： electrochemical gate,monolayer molybdenum disulfide,protein binding,local charge imaging,charged impurities
更新于2025-09-23 15:23:52
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Electrowetting on 2D dielectrics: a quantum molecular dynamics investigation
摘要： Electrowetting on dielectrics (EWOD) is widely used to manipulate the spreading of a conductive liquid on a dielectric surface by applying an electric field. 2D hydrophobic dielectrics are promising candidates for EWOD applications. In this study, extensive quantum molecular dynamics (MD) simulations are performed to investigate the electrowetting behavior of salty water on hexagonal boron nitride (h-BN) monolayer. The proximal adsorption of salt ions and the associated realignment of the dipole moments of interfacial water with the applied electric field are found to be the physical origin of the electrowetting behavior. At low salt concentration and low electric fields, the proximal adsorption and the realignment follow the applied electric field, and the cosine of the water contact angle (WCA) follows a quadratic dependence on the applied electric field. At high salt concentration and high electric fields, the proximal adsorption saturates, which restricts further realignment and causes a saturation of the WCA. This case study provides physical insights into the much debated mechanism that underlies the contact angle saturation (CAS) found in macroscopic electrowetting phenomena and also provides an avenue for further studies of electrowetting at the atomic scale.
关键词： hexagonal boron nitride monolayer,contact angle saturation,electrowetting on dielectrics,first-principles
更新于2025-09-23 15:23:52
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Night-Time Oxidation of a Monolayer Model for the Air–Water Interface of Marine Aerosols—A Study by Simultaneous Neutron Reflectometry and in Situ Infra-Red Reflection Absorption Spectroscopy (IRRAS)
摘要： This paper describes experiments on the ageing of a monolayer model for the air–water interface of marine aerosols composed of a typical glycolipid, galactocerebroside (GCB). Lipopolysaccharides have been observed in marine aerosols, and GCB is used as a proxy for these more complex lipopolysaccharides. GCB monolayers are investigated as pure films, as mixed films with palmitic acid, which is abundant in marine aerosols and forms a stable attractively mixed film with GCB, particularly with divalent salts present in the subphase, and as mixed films with palmitoleic acid, an unsaturated analogue of palmitic acid. Such mixed films are more realistic models of atmospheric aerosols than simpler single-component systems. Neutron reflectometry (NR) has been combined in situ with Fourier transform infra-red reflection absorption spectroscopy (IRRAS) in a pioneering analysis and reaction setup designed by us specifically to study mixed organic monolayers at the air–water interface. The two techniques in combination allow for more sophisticated observation of multi-component monolayers than has previously been possible. The structure at the air–water interface was also investigated by complementary Brewster angle microscopy (BAM). This study looks specifically at the oxidation of the organic films by nitrate radicals (NO3?), the key atmospheric oxidant present at night. We conclude that NO3? oxidation cannot fully remove a cerebroside monolayer from the surface on atmospherically relevant timescales, leaving its saturated tail at the interface. This is true for pure and salt water subphases, as well as for single- and two-component films. The behaviour of the unsaturated tail section of the molecule is more variable and is affected by interactions with co-deposited species. Most surprisingly, we found that the presence of CaCl2 in the subphase extends the lifetime of the unsaturated tail substantially—a new explanation for longer residence times of materials in the atmosphere compared to lifetimes based on laboratory studies of simplified model systems. It is thus likely that aerosols produced from the sea-surface microlayer at night will remain covered in surfactant molecules on atmospherically relevant timescales with impact on the droplet’s surface tension and on the transport of chemical species across the air–water interface.
关键词： palmitic acid,monolayer,neutron,nitrate radical,palmitoleic acid,reflectivity,aerosol,infra-red,cerebroside,Brewster angle microscopy
更新于2025-09-23 15:23:52
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Adsorption of hazardous gases in nuclear islands on monolayer MoS2 sheet
摘要： Monitoring and removing the hazardous gases (such as radioactive gases and hydrogen) in the nuclear islands are full with enormous challenges, although the two methods can improve the safety level of the nuclear power plant. Due to its excellent electronic and chemical properties, two dimensional materials are considered as the candidate for monitoring and removing the hazardous gases in the nuclear islands. In this paper, the adsorption of the hazardous gases on monolayer MoS2 sheet was investigated by using the first principles calculation method. The adsorption energy, total charge transfer, and density of states (DOS) were calculated to understand the adsorption mechanism and sensing performance of the monolayer MoS2 sheet to the hazardous gases. The results show that an attractive interaction exists between the hazardous gases and the monolayer MoS2 sheet. The magnitude of the adsorption energy demonstrates that physisorption dominates the adsorption of the hazardous gas molecules on the monolayer MoS2 sheet, but the adsorption of the dissociated H/I atom belongs to chemisorption. The DOS shows that the orbitals, H 1s and I 5p, play a crucial role in the adsorption, and the change of the electronic structure indicates that the monolayer MoS2 sheet might be a promising material which is used for monitoring the gaseous radioactive iodine in the nuclear islands.
关键词： Hydrogen,Hazardous gases,Radioactive gases,First principles calculation,Monolayer MoS2 sheet
更新于2025-09-23 15:23:52
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Hybrid bilayer gate dielectric-based organic thin film transistors
摘要： Organic thin film transistors (OTFTs) are key building blocks for flexible, low cost electronics systems. They provide a viable alternative for silicon-based electronics with added advantages of low cost and flexibility. However, few issues like high-operating voltage, low-switching speed, high-leakage current and reliability are still a challenge. The overall performance of an OTFT depends on organic semiconductors and gate dielectric interface. In this paper, we review the current status and trends in the choice of dielectric layer for OTFTs. As a starting point, the performance parameters of an OTFT and their dependence on the dielectric layer are briefly discussed. A variety of dielectric materials which includes high-k inorganic, organic, surface coated inorganics and nanocomposites are also presented. The advantages and drawbacks of each of these materials are discussed in detail. We reviewed the latest developments in the dielectric materials especially, self-assembled monolayers (SAMs), hybrid bilayers and nanocomposites. SAM-based OTFTs offer several advantages but shift in the threshold voltage remains a concern. Nanocomposites are a latest addition to the dielectric materials, which offer advantages like solution processing and improved dielectric constant but have a rough surface. A hybrid bilayer that incorporates the inorganic dielectric as a base layer and a thin polymer layer over it to improve the surface properties offers several desirable characteristics over the other choices. Hence, we propose that hybrid bilayer gate dielectrics shall play a pivotal role in improving the OTFT performance.
关键词： low-k organic,high-k inorganic,Organic thin film transistor,self-assembled monolayer,gate dielectric,hybrid bilayer
更新于2025-09-23 15:23:52
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Monolayer transition metal dichalcogenides in strong magnetic fields: Validating the Wannier model using a microscopic calculation
摘要： Using an equation of motion (EOM) approach, we calculate excitonic properties of monolayer transition metal dichalcogenides perturbed by an external magnetic field. We compare our findings to the widely used Wannier model for excitons in two-dimensional materials and to recent experimental results. We find good agreement between the calculated excitonic transition energies and the experimental results. In addition, we find that the exciton energies calculated using the EOM approach are slightly lower than the ones calculated using the Wannier model. Finally, we also show that the effect of the dielectric environment on the magnetoexciton transition energy is minimal due to counteracting changes in the exciton energy and the exchange self-energy correction.
关键词： monolayer transition metal dichalcogenides,magnetic field,Wannier model,excitons,magnetoexcitons,equation of motion
更新于2025-09-23 15:23:52
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Homogeneous Large-area Quasi-freestanding Monolayer and Bilayer Graphene on SiC
摘要： In this study, we first show that the argon flow during epitaxial graphene growth is an important parameter to control the quality of the buffer and the graphene layer. Atomic force microscopy (AFM) and low-energy electron diffraction (LEED) measurements reveal that the decomposition of the SiC substrate strongly depends on the Ar mass flow rate while pressure and temperature are kept constant. Our data are interpreted by a model based on the competition of the SiC decomposition rate, controlled by the Ar flow, with a uniform graphene buffer layer formation under the equilibrium process at the SiC surface. The proper choice of a set of growth parameters allows the growth of defect-free, ultra-smooth and coherent graphene-free buffer layer and bilayer-free monolayer graphene sheets which can be transformed into large-area high-quality quasi-freestanding monolayer and bilayer graphene by hydrogen intercalation. AFM, scanning tunneling microscopy, Raman spectroscopy and electronic transport measurements underline the excellent homogeneity of the resulting quasi-freestanding layers. Electronic transport measurements in four-point probe configuration reveal a homogeneous low resistance anisotropy on both μm- and mm scales.
关键词： SiC terrace steps,polymer assisted sublimation growth,Epitaxial graphene,freestanding bilayer graphene,argon gas flow,graphene buffer layer,monolayer graphene,resistance anisotropy,large-scale graphene growth,freestanding monolayer graphene
更新于2025-09-23 15:22:29
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Monolayer MoS? Strained to 1.3% With a Microelectromechanical System
摘要： We report on a modified transfer technique for atomically thin materials integrated into microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS while still providing precise positioning and crack-free transfer of flakes. Furthermore, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time and increases the yield, and allowed us to exploit the strong mechanical coupling between the 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating 2D materials with MEMS. We used the established strain response of MoS2 Raman and photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and the literature.
关键词： photoluminescence,Raman,strain,monolayer MoS2,MEMS
更新于2025-09-23 15:22:29
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Purcell Effect and Nonlinear Behavior of the Emission in a Periodic Structure Composed of InAs Monolayers Embedded in a GaAs Matrix
摘要： Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time-resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super-radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near-quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non-monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures.
关键词： Purcell effect,Bragg conditions,monolayer-thick InAs quantum wells,super-radiance
更新于2025-09-23 15:22:29