Showing papers on "Charge density published in 2019"

Charge order and broken rotational symmetry in magic-angle twisted bilayer graphene

Abstract: Bilayer graphene can be modified by rotating (twisting) one layer with respect to the other. The interlayer twist gives rise to a moire superlattice that affects the electronic motion and alters the band structure1–4. Near a ‘magic angle’ of twist2,4, where the emergence of a flat band causes the charge carriers to slow down3, correlated electronic phases including Mott-like insulators and superconductors were recently discovered5–8 by using electronic transport. These measurements revealed an intriguing similarity between magic-angle twisted bilayer graphene and high-temperature superconductors, which spurred intensive research into the underlying physical mechanism9–14. Essential clues to this puzzle, such as the symmetry and spatial distribution of the spectral function, can be accessed through scanning tunnelling spectroscopy. Here we use scanning tunnelling microscopy and spectroscopy to visualize the local density of states and charge distribution in magic-angle twisted bilayer graphene. Doping the sample to partially fill the flat band, we observe a pseudogap phase accompanied by a global stripe charge order that breaks the rotational symmetry of the moire superlattice. Both the pseudogap and the stripe charge order disappear when the band is either empty or full. The close resemblance to similar observations in high-temperature superconductors15–21 provides new evidence of a deeper link underlying the phenomenology of these systems. When scanning tunnelling spectroscopy is used to map the electronic structure of magic-angle twisted bilayer graphene, a pseudogap phase is found, accompanied by a global charge-ordered stripe phase.

Transferable Machine-Learning Model of the Electron Density

Abstract: The electronic charge density plays a central role in determining the behavior of matter at the atomic scale, but its computational evaluation requires demanding electronic-structure calculations We introduce an atom-centered, symmetry-adapted framework to machine-learn the valence charge density based on a small number of reference calculations The model is highly transferable, meaning it can be trained on electronic-structure data of small molecules and used to predict the charge density of larger compounds with low, linear-scaling cost Applications are shown for various hydrocarbon molecules of increasing complexity and flexibility, and demonstrate the accuracy of the model when predicting the density on octane and octatetraene after training exclusively on butane and butadiene This transferable, data-driven model can be used to interpret experiments, accelerate electronic structure calculations, and compute electrostatic interactions in molecules and condensed-phase systems

Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor.

Abstract: Charge density modulations have been observed in all families of high–critical temperature (Tc) superconducting cuprates. Although they are consistently found in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa2Cu3O7–δ and Nd1+xBa2–xCu3O7–δ for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudogap temperature T*, are characterized by energies of a few milli–electron volts, and pervade a large area of the phase diagram.

Superconductivity in the doped Hubbard model and its interplay with next-nearest hopping t′

Abstract: The Hubbard model is widely believed to contain the essential ingredients of high-temperature superconductivity. However, proving definitively that the model supports superconductivity is challenging. Here, we report a large-scale density matrix renormalization group study of the lightly doped Hubbard model on four-leg cylinders at hole doping concentration δ = 12.5%. We reveal a delicate interplay between superconductivity and charge density wave and spin density wave orders tunable via next-nearest neighbor hopping t'. For finite t', the ground state is consistent with a Luther-Emery liquid with power-law superconducting and charge density wave correlations associated with half-filled charge stripes. In contrast, for t' = 0, superconducting correlations fall off exponentially, whereas charge density and spin density modulations are dominant. Our results indicate that a route to robust long-range superconductivity involves destabilizing insulating charge stripes in the doped Hubbard model.

Real-space charge-density imaging with sub-ångström resolution by four-dimensional electron microscopy

Abstract: The distribution of charge density in materials dictates their chemical bonding, electronic transport, and optical and mechanical properties. Indirectly measuring the charge density of bulk materials is possible through X-ray or electron diffraction techniques by fitting their structure factors1-3, but only if the sample is perfectly homogeneous within the area illuminated by the beam. Meanwhile, scanning tunnelling microscopy and atomic force microscopy enable us to see chemical bonds, but only on the surface4-6. It remains a challenge to resolve charge density in nanostructures and functional materials with imperfect crystalline structures-such as those with defects, interfaces or boundaries at which new physics emerges. Here we describe the development of a real-space imaging technique that can directly map the local charge density of crystalline materials with sub-angstrom resolution, using scanning transmission electron microscopy alongside an angle-resolved pixellated fast-electron detector. Using this technique, we image the interfacial charge distribution and ferroelectric polarization in a SrTiO3/BiFeO3 heterojunction in four dimensions, and discover charge accumulation at the interface that is induced by the penetration of the polarization field of BiFeO3. We validate this finding through side-by-side comparison with density functional theory calculations. Our charge-density imaging method advances electron microscopy from detecting atoms to imaging electron distributions, providing a new way of studying local bonding in crystalline solids.

Electron density learning of non-covalent systems

Abstract: Chemists continuously harvest the power of non-covalent interactions to control phenomena in both the micro- and macroscopic worlds. From the quantum chemical perspective, the strategies essentially rely upon an in-depth understanding of the physical origin of these interactions, the quantification of their magnitude and their visualization in real-space. The total electron density ρ(r) represents the simplest yet most comprehensive piece of information available for fully characterizing bonding patterns and non-covalent interactions. The charge density of a molecule can be computed by solving the Schrodinger equation, but this approach becomes rapidly demanding if the electron density has to be evaluated for thousands of different molecules or very large chemical systems, such as peptides and proteins. Here we present a transferable and scalable machine-learning model capable of predicting the total electron density directly from the atomic coordinates. The regression model is used to access qualitative and quantitative insights beyond the underlying ρ(r) in a diverse ensemble of sidechain–sidechain dimers extracted from the BioFragment database (BFDb). The transferability of the model to more complex chemical systems is demonstrated by predicting and analyzing the electron density of a collection of 8 polypeptides.

Modeling the electrical double layer to understand the reaction environment in a CO2 electrocatalytic system

Abstract: The environment of a CO2 electroreduction (CO2ER) catalyst is intimately coupled with the surface reaction energetics and is therefore a critical aspect of the overall system performance. The immediate reaction environment of the electrocatalyst constitutes the electrical double layer (EDL) which extends a few nanometers into the electrolyte and screens the surface charge density. In this study, we resolve the species concentrations and potential profiles in the EDL of a CO2ER system by self-consistently solving the migration, diffusion and reaction phenomena using the generalized modified Poisson–Nernst–Planck (GMPNP) equations which include the effect of volume exclusion due to the solvated size of solution species. We demonstrate that the concentration of solvated cations builds at the outer Helmholtz plane (OHP) with increasing applied potential until the steric limit is reached. The formation of the EDL is expected to have important consequences for the transport of the CO2 molecule to the catalyst surface. The electric field in the EDL diminishes the pH in the first 5 nm from the OHP, with an accumulation of protons and a concomitant depletion of hydroxide ions. This is a considerable departure from the results obtained using reaction-diffusion models where migration is ignored. Finally, we use the GMPNP model to compare the nature of the EDL for different alkali metal cations to show the effect of solvated size and polarization of water on the resultant electric field. Our results establish the significance of the EDL and electrostatic forces in defining the local reaction environment of CO2 electrocatalysts.

Imaging the electronic Wigner crystal in one dimension.

Abstract: The quantum crystal of electrons, predicted more than 80 years ago by Eugene Wigner, remains one of the most elusive states of matter. In this study, we observed the one-dimensional Wigner crystal directly by imaging its charge density in real space. To image, with minimal invasiveness, the many-body electronic density of a carbon nanotube, we used another nanotube as a scanning-charge perturbation. The images we obtained of a few electrons confined in one dimension match the theoretical predictions for strongly interacting crystals. The quantum nature of the crystal emerges in the observed collective tunneling through a potential barrier. These experiments provide the direct evidence for the formation of small Wigner crystals and open the way for studying other fragile interacting states by imaging their many-body density in real space.

Optical generation of high carrier densities in 2D semiconductor heterobilayers

Abstract: Controlling charge density in two-dimensional (2D) materials is a powerful approach for engineering new electronic phases and properties. This control is traditionally realized by electrostatic gating. Here, we report an optical approach for generation of high carrier densities using transition metal dichalcogenide heterobilayers, WSe2/MoSe2, with type II band alignment. By tuning the optical excitation density above the Mott threshold, we realize the phase transition from interlayer excitons to charge-separated electron/hole plasmas, where photoexcited electrons and holes are localized to individual layers. High carrier densities up to 4 × 1014 cm−2 can be sustained under both pulsed and continuous wave excitation conditions. These findings open the door to optical control of electronic phases in 2D heterobilayers.

Mechanistic Insight into Photocatalytic Pathways of MIL-100(Fe)/TiO2 Composites.

Abstract: The integration of metal-organic frameworks (MOFs) with semiconductors has attracted mounting attention for photocatalytic applications. However, more efforts are needed to unravel the interface structure in MOF/semiconductor composites and its role in charge transfer. Herein, a MIL-100(Fe)/TiO2 composite was synthesized as a prototypical photocatalyst and studied systematically to explore the interface structure and unravel the charge transfer pathways during the photocatalytic processes. The composite was fabricated by growing MIL-100(Fe) crystals on TiO2 using surface-coated FeOOH as the precursor. The as-prepared MIL-100(Fe)/TiO2 exhibited significantly improved photocatalytic performance over pristine TiO2, which was mainly because of the enhanced charge separation as confirmed by transient absorption spectroscopy analysis. This enhancement partially arose from the special chemical structure at the interface, where the Fe-O-Ti bond was formed. As verified by the density functional theory calculation, this distinct structure would create defect energy levels adjacent to the valence band maximum of TiO2. During the photocatalytic processes, the defect energy levels serve as sinks to capture excited charge carriers and retard the recombination, which subsequently leads to the increased charge density and promoted photocatalytic efficiency. Meanwhile, the intimate interactions between MIL-100(Fe) and TiO2 would also help to improve the charge separation by transferring photo-induced holes through the ligands to Fe-O clusters. These findings would advance the fundamental understanding of the interface structure and the charge transfer pathways in MOF/semiconductor composite photocatalysts.

Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS 2 Composites

Abstract: Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a method to effectively increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS2 composite. Specifically, by compositing bulk MoS2 flakes with both Nylon-11 and PVDF-TrFE, respectively, charge density of each triboelectric charging surface was significantly increased. In addition, proper polarization of both ferroelectric composite layers has also led to an additional increase in the charge density. A combination of them synergistically increases the surface charge density, generating huge output current and the power output density. By optimizing the fabrication process, the output voltage and current density up to ∼145 V and ∼350 μA/cm2 are achieved, respectively. Consequently, the TENG exhibits a recordable output power density of ∼50 mW/cm2, which is one of the highest output power densities reported to date. The method introduced in this work can greatly increase the output current density of TENGs, facilitating the development of high-performance triboelectric energy harvesting devices.

Deep learning and density-functional theory

Abstract: We show that deep neural networks can be integrated into, or fully replace, the Kohn-Sham density functional theory (DFT) scheme for multielectron systems in simple harmonic oscillator and random external potentials with no feature engineering. We first show that self-consistent charge densities calculated with different exchange-correlation functionals can be used as input to an extensive deep neural network to make predictions for correlation, exchange, external, kinetic, and total energies simultaneously. Additionally, we show that one can make all of the same predictions with the external potential rather than the self-consistent charge density, which allows one to circumvent the Kohn-Sham DFT scheme altogether. We then show that a self-consistent charge density found from a nonlocal exchange-correlation functional can be used to make energy predictions for a semilocal exchange-correlation functional. Lastly, we use a deep convolutional inverse graphics network to predict the charge density given an external potential for different exchange-correlation functionals and assess the viability of the predicted charge densities. This work shows that extensive deep neural networks are generalizable and transferable given the variability of the potentials (maximum total energy range $\ensuremath{\approx}100$ Ha) because they require no feature engineering and because they can scale to an arbitrary system size with an $O(N)$ computational cost.

Unraveling the Anomalous Surface-Charge-Dependent Osmotic Power Using a Single Funnel-Shaped Nanochannel.

Abstract: Nanofluidic osmotic power, which converts a difference in salinity between brine and fresh water into electricity with nanoscale channels, has received more and more attention in recent years. It is long believed that to gain high-performance osmotic power, highly charged channel materials should be exploited so as to enhance the ion selectivity. In this paper, we report counterintuitive surface-charge-density-dependent osmotic power in a single funnel-shaped nanochannel (FSN), violating the previous viewpoint. For the highly charged nanochannel, the performance of osmotic power decreases with a further increase in its surface charge density. With increasing pH (surface charge density), the FSN enables a local maximum power density as high as ∼3.5 kW/m2 in a 500 mM/1 mM KCl gradient. This observation is strongly supported by our rigorous model where the equilibrium chemical reaction between functional carboxylate ion groups on the channel wall and protons is taken into account. The modeling reveals that for a highly charged nanochannel, a significant increase in the surface charge density amplifies the ion concentration polarization effect, thus weakening the effective salinity ratio across the channel and undermining the osmotic power generated.

Atomic electrostatic maps of 1D channels in 2D semiconductors using 4D scanning transmission electron microscopy

Abstract: Defects in materials give rise to fluctuations in electrostatic fields that reflect the local charge density, but imaging this with single atom sensitivity is challenging. However, if possible, this provides information about the energetics of adatom binding, localized conduction channels, molecular functionality and their relationship to individual bonds. Here, ultrastable electron-optics are combined with a high-speed 2D electron detector to map electrostatic fields around individual atoms in 2D monolayers using 4D scanning transmission electron microscopy. Simultaneous imaging of the electric field, phase, annular dark field and the total charge in 2D MoS2 and WS2 is demonstrated for pristine areas and regions with 1D wires. The in-gap states in sulphur line vacancies cause 1D electron-rich channels that are mapped experimentally and confirmed using density functional theory calculations. We show how electrostatic fields are sensitive in defective areas to changes of atomic bonding and structural determination beyond conventional imaging.

Electric field modulation of magnetic exchange in molecular helices

Abstract: The possibility to operate on magnetic materials through the application of electric rather than magnetic fields—promising faster, more compact and energy efficient circuits—continues to spur the investigation of magnetoelectric effects. Symmetry considerations, in particular the lack of an inversion centre, characterize the magnetoelectric effect. In addition, spin–orbit coupling is generally considered necessary to make a spin system sensitive to a charge distribution. However, a magnetoelectric effect not relying on spin–orbit coupling is appealing for spin-based quantum technologies. Here, we report the detection of a magnetoelectric effect that we attribute to an electric field modulation of the magnetic exchange interaction without atomic displacement. The effect is visible in electron paramagnetic resonance absorption of molecular helices under electric field modulation and confirmed by specific symmetry properties and spectral simulation. A modulation of the magnetic exchange interaction using an electric field, in the absence of atomic displacement and not relying on spin–orbit coupling, is reported.

Interface Engineering V 2 O 5 Nanofibers for High‐Energy and Durable Supercapacitors

Abstract: A local electric field is induced to engineer the interface of vanadium pentoxide nanofibers (V2 O5 -NF) to manipulate the charge transport behavior and obtain high-energy and durable supercapacitors. The interface of V2 O5 -NF is modified with oxygen vacancies (Vo) in a one-step polymerization process of polyaniline (PANI). In the charge storage process, the local electric field deriving from the lopsided charge distribution around Vo will provide Coulombic forces to promote the charge transport in the resultant Vo-V2 O5 /PANI nanocable electrode. Furthermore, an ≈7 nm porous PANI coating serves as the external percolated charge transport pathway. As the charge transfer kinetics are synergistically enhanced by the dual modifications, Vo-V2 O5 /PANI-based supercapacitors exhibit an excellent specific capacitance (523 F g-1 ) as well as a long cycling lifespan (110% of capacitance remained after 20 000 cycles). This work paves an effective way to promote the charge transfer kinetics of electrode materials for next-generation energy storage systems.

An ab initio study of sensing applications of MoB2 monolayer: a potential gas sensor.

Abstract: Using first principles density functional theory, we have studied the interaction mechanism of NO2 and SO2 gas molecules on an MoB2 monolayer, for gas sensing applications. The selectivity for a particular gas by the sensor has been analyzed through electronic structure calculations and adsorption studies. The calculations have been performed by considering the fact that the MoB2 monolayer as a sensing material encounters a change in its electrical properties, when gas molecules with different orientations get adsorbed on the surface. From the density of states study, we find better selectivity for NO2 as compared to SO2, as the latter leaves the electronic structure of the sensing material unaffected. Further, the adsorption curves support the above fact as the larger value of adsorption energy (Ead ∼ −1 eV) for NO2 indicates stronger adsorption. The chemisorptive nature for NO2, in contrast with the relatively weaker physisorption for SO2, additionally supports the fact that NO2 gas has a better perspective for MoB2 sensor application. Charge density plots for each case are in good agreement with the above conclusions. The faster recovery time attributes the MoB2 monolayer better as a sensor material for NO2 interaction.

Detecting Decompositions of Sulfur Hexafluoride Using MoS 2 Monolayer as Gas Sensor

Abstract: The adsorption and gas sensing properties of monolayer MoS2 to five kinds of sulfur hexafluoride decompositions (SO2, SOF2, SO2F2, H2S, HF) were explored using the density functional theory combined with the nonequilibrium Green’s function. The adsorption energy, electron transfer, charge density difference configurations, current–voltage ( $I$ – $V$ ) character using a two-electrode based device and transmission coefficient have been discussed. The results show that the adsorption of SO2 brings the largest adsorption energy as well as electron transfer. According to the simulated device, the unique negative conductance phenomenon was found for SO2. The MoS2 monolayer-based sensor has the highest response to SO2 when the bias voltage is 1.2 V, reaching 7.74 and has the largest response to H2S when 1.8 V. The transmission spectrum analysis shows that after introducing different gas molecules, the transmission coefficient has different changes in different energy ranges. This paper can provide a theoretical basis for designing MoS2 monolayer-based gas sensing device to detect the decompositions of sulfur hexafluoride or other specific gases.

Ligand-Induced Surface Charge Density Modulation Generates Local Type-II Band Alignment in Reduced-Dimensional Perovskites

Abstract: Two-dimensional (2D) and quasi-2D perovskite materials have enabled advances in device performance and stability relevant to a number of optoelectronic applications. However, the alignment among the bands of these variably quantum confined materials remains a controversial topic: there exist multiple experimental reports supporting type-I, and also others supporting type-II, band alignment among the reduced-dimensional grains. Here we report a combined computational and experimental study showing that variable ligand concentration on grain surfaces modulates the surface charge density among neighboring quantum wells. Density functional theory calculations and ultraviolet photoelectron spectroscopy reveal that the effective work function of a given quantum well can be varied by modulating the density of ligands at the interface. These induce type-II interfaces in otherwise type-I aligned materials. By treating 2D perovskite films, we find that the effective work function can indeed be shifted down by up to 1 eV. We corroborate the model via a suite of pump-probe transient absorption experiments: these manifest charge transfer consistent with a modulation in band alignment of at least 200 meV among neighboring grains. The findings shed light on perovskite 2D band alignment and explain contrasting behavior of quasi-2D materials in light-emitting diodes (LEDs) and photovoltaics (PV) in the literature, where materials can exhibit either type-I or type-II interfaces depending on the ligand concentration at neighboring surfaces.

Dissolved Gas Analysis in Transformer Oil Using Pt-Doped WSe 2 Monolayer Based on First Principles Method

Abstract: The composition and content of dissolved gases in transformer oil are closely related to the type of faults in the transformer and the severity of potential hazards. Dissolved gas analysis (DGA) in insulating oil is an important way to monitor the state of transformer equipment. CO, CH 4 , and C 2 H 2 are one of the dissolved gases in the transformer oil. Based on the density functional theory, the optimal adsorption site of the transition metal atom Pt on the surface of WSe 2 , one of the typical layered transition metal disulfides (LTMDs), is determined in the beginning. Attaining the adsorption behavior of these three gases on the surface of Pt-WSe 2 . The optimal structure of gas adsorption, charge transfer, adsorption energy, electronic density of states (DOS), deformation charge density (DCD), and frontier orbital are analyzed. As an electron acceptor, Pt-WSe 2 attracts electrons from all three gas molecules. The adsorption type of CO and C 2 H 2 molecules is chemisorption, whose adsorption effect is strong. The CH 4 adsorption is physical adsorption, whose adsorption effect is weak. The adsorption of all the three gas molecules leads to an increase in the bandgap of the Pt-WSe 2 , that is, the increase in the resistivity.

Measuring the Berry phase of graphene from wavefront dislocations in Friedel oscillations

Abstract: Electronic band structures dictate the mechanical, optical and electrical properties of crystalline solids. Their experimental determination is therefore crucial for technological applications. Although the spectral distribution in energy bands is routinely measured by various techniques1, it is more difficult to access the topological properties of band structures such as the quantized Berry phase, γ, which is a gauge-invariant geometrical phase accumulated by the wavefunction along an adiabatic cycle2. In graphene, the quantized Berry phase γ = π accumulated by massless relativistic electrons along cyclotron orbits is evidenced by the anomalous quantum Hall effect4,5. It is usually thought that measuring the Berry phase requires the application of external electromagnetic fields to force the charged particles along closed trajectories3. Contradicting this belief, here we demonstrate that the Berry phase of graphene can be measured in the absence of any external magnetic field. We observe edge dislocations in oscillations of the charge density ρ (Friedel oscillations) that are formed at hydrogen atoms chemisorbed on graphene. Following Nye and Berry6 in describing these topological defects as phase singularities of complex fields, we show that the number of additional wavefronts in the dislocation is a real-space measure of the Berry phase of graphene. Because the electronic dispersion relation can also be determined from Friedel oscillations7, our study establishes the charge density as a powerful observable with which to determine both the dispersion relation and topological properties of wavefunctions. This could have profound consequences for the study of the band-structure topology of relativistic and gapped phases in solids. The Berry phase of graphene is measured in the absence of an applied magnetic field by observing dislocations in the Friedel oscillations formed at a hydrogen atom adsorbed on graphene.

Strong Charge Transfer at 2H–1T Phase Boundary of MoS2 for Superb High‐Performance Energy Storage

Abstract: Transition metal dichalcogenides exhibit several different phases (e.g., semiconducting 2H, metallic 1T, 1T') arising from the collective and sluggish atomic displacements rooted in the charge-lattice interaction. The coexistence of multiphase in a single sheet enables ubiquitous heterophase and inhomogeneous charge distribution. Herein, by combining the first-principles calculations and experimental investigations, a strong charge transfer ability at the heterophase boundary of molybdenum disulfide (MoS2 ) assembled together with graphene is reported. By modulating the phase composition in MoS2 , the performance of the nanohybrid for energy storage can be modulated, whereby remarkable gravimetric and volumetric capacitances of 272 F g-1 and 685 F cm-3 are demonstrated. As a proof of concept for energy application, a flexible solid-state asymmetric supercapacitor is constructed with the MoS2 -graphene heterolayers, which shows superb energy and power densities (46.3 mWh cm-3 and 3.013 W cm-3 , respectively). The present work demonstrates a new pathway for efficient charge flow and application in energy storage by engineering the phase boundary and interface in 2D materials of transition metal dichalcogenides.

Vertical ferroelectric switching by in-plane sliding of two-dimensional bilayer WTe2.

Abstract: Based on first-principles calculations, we studied the ferroelectric properties of bilayer 1T′-WTe2. In this work, we discovered that the polarization stems from uncompensated out-of-plane interlayer charge transfer, which can be switched upon interlayer sliding of an in-plane translation. Our differential charge density results also confirmed that such ferroelectricity in the bilayer WTe2 is derived from interlayer charge transfer. The ferroelectric polarization directions further control the spin texture of the bilayer WTe2, which may have important applications in spintronics. Therefore, we propose a spin field effect transistor (spin-FET) design that may effectively improve the spin-polarized injection rate. In addition, the lattice strain has been found to have an important influence on the ferroelectric properties of the bilayer WTe2. One can effectively increase the polarization with a maximum at 3% tensile strain, whereas a 3% compressive strain can transform the bilayer WTe2 from the ferroelectric to paraelectric phase.

Single-layer stanane as potential gas sensor for NO2, SO2, CO2 and NH3 under DFT investigation

Abstract: The monolayer stanane in chair form is reported to be a novel sensor for environmentally toxic and non-toxic gas molecules for the first time. The structure, electronic and vibrational properties of all three possible conformations (chair, stirrup and boat) of stanane are studied in detail using density functional theory (DFT) based on an ab-initio technique. The interactions and charge transfer of environmentally toxic (NO 2, SO2 and NH3) and non-toxic (CO2) gas molecules on the dynamically most stable hexagonal chair type hydrogenated stanene, viz. stanane has been investigated in detail. The most stable configuration, electronic properties, adsorption energies and charge transfer of these gases on stanane are systematically studied and discussed. The band gap of the pure stanane (0.52 eV) is noticed to be changed after interaction with gases. Moreover, the changes in the energy band gap and charge density is observed upon adsorption of NO2, SO2, NH3 and CO2 gases on p -type stanane based material. The results show that the selectivity of hydrogenated stanene based gas sensors is very important to enhance their sensitivity. It is found that all the gas molecules act as charge donors in which NO 2 gas shows maximum adsorption on the stanane surface along with the maximum charge transfer. The nontrivial affectability and selectivity of stanane demonstrate its potential application in the field of gas sensors and superior impetuses.