Density Functional Theory-based Simulations Research Articles

Carrier transport in bulk and two-dimensional Zn2(V,Nb,Ta)N3 ternary nitrides.

Density functional theory-based simulations are applied to study the electronic structures, carrier masses, carrier mobility and carrier relaxation times in bulk and two-dimensional (2D) Zn2(V,Nb,Ta)N3 ternary nitrides. Bulk Zn2(V,Nb,Ta)N3 possess moderate band gap sizes of 2.17 eV, 3.11 eV, and 3.40 eV, respectively. Two-dimensional Zn2(V,Nb,Ta)N3 have slightly higher band gap sizes of 2.77 eV, 3.33 eV, and 3.23 eV, respectively. Carrier mass, carrier mobility and carrier relaxation time are found to be anisotropic in all the studied structures. Bulk and 2D samples show an order of magnitude higher electron mobility compared to hole mobility. The highest electron mobility in bulk Zn2NbN3 and Zn2TaN3 is about ∼103 cm2 V-1 s-1. Importantly, for 2D Zn2NbN3, an abnormally high electron mobility of 1.67 × 104 cm2 V-1 s-1 is observed, which is not inferior to the highest known electron mobility values in 2D materials. Such a high electron mobility in 2D Zn2NbN3 can be attributed to a strong delocalization of the conduction band minimum, which is responsible for electron transport. Therefore, this work opens up new materials for high performance nanodevices, such as tandem solar cells and field-effect transistors. This study also provides deep physical insights into the nature of carrier transport mechanisms in bulk and 2D Zn2(V,Nb,Ta)N3 ternary nitrides.

Defect-Engineered 3D Nanostructured MoS2 for Detection of Ammonia Gas at Room Temperature

Recent studies on nanostructured MoS2 show promising performance in the detection of reducing gases like ammonia (NH3). However, this material in the pristine form possesses limitations in terms of response, recovery, and repeatability over a long duration of time. Several attempts have been made to overcome these shortcomings by modifying it chemically to make a hybrid form or direct doping with other atoms. In this work, we demonstrate that suitable defect engineering of 3D nanostructured MoS2 induced by a low energy ion beam can lead to a significantly improved performance of sensing NH3 compared to the as-prepared one. Significant decreases in response and recovery times have been demonstrated at room temperature for the modified MoS2 compared to its pristine form, which shows its best response only at a higher temperature of about 200 °C. A 3D nanoflower-like structure of MoS2 was synthesized hydrothermally, which was coated on substrates, and then irradiated with 5 keV argon ions at different doses. While the ion beam-induced morphological modifications are observed via electron microscopic study, the surface defects are apparent in X-ray diffraction, Raman scattering, and X-ray spectroscopic studies. The ion beam-modified MoS2 shows a higher electrical conductivity and water-repelling nature compared to the pristine one, which are complementary properties for better sensing performance. While Monte Carlo-based 3D ion-solid interaction simulation was used to support the morphological modifications and defect developments after ion irradiation, the sensing mechanism and change in conductivity were successfully explained using density functional theory-based simulations.

Helium electron beam rf plasma for low-k surface functionalization

A complex simulation approach is applied to determine optimal conditions for the functionalization of low-k materials in e-beam rf discharge generated by 1 keV electron beam in He. The possibility and mechanisms of methyl group elimination from low-k surfaces with low-energy He ions and fast He atoms are studied with ab initio dynamic density functional theory-based simulations. The effect of gas pressure, rf voltage, and rf frequencies on the ion energy and angle distribution functions is analyzed using a 1D Particle-in-Cell Monte Carlo model. The relative contribution of fast atoms in the surface functionalization is estimated. Ion fluxes on the 2D trench walls and bottom are calculated with the developed analytical approach.

Molecular Evolution of Nitrogen Dioxide on a Nanostructured Gold Surface in the Atmosphere by In Situ Surface-Enhanced Raman Spectroscopy

It has generally been believed that the interaction between nitrogen dioxide (NO2) and Au can occur only under ultralow temperature (<200 K) and vacuum conditions. The evolution process of NO2 on the Au surface and its products are still seriously controversial. Here, the molecular evolution of NO2 on a nanostructured Au surface in the atmosphere is studied by time-dependent in situ surface-enhanced Raman spectroscopy. According to the spectral measurements and density functional theory-based simulations, it has been found that when NO2 contacts the Au surface in the air with enough relative humidity (≳20%), chemisorbed NO2 species would be produced quickly, and after a short induction period (about 1 min), would evolve into NO[Au(NO3)4], which subsequently decomposes into O2 and NO, and/or deliquesce into the adsorbed NO2 and −OH as well as HNO3, depending on the temperature and the relative humidity. Further experiments show that the presence of O2 and H2O molecules is crucial to such molecular evolution of NO2 on the Au surface in the atmosphere. Finally, a H2O and O2-assisted reaction mechanism is proposed and nicely describes the molecular evolution of NO2 on the Au surface. This work provides sufficient spectral evidences for the molecular evolution of NO2 on the Au surface in the atmosphere, and offers a new insight into the interaction between NO2 and the Au surface.

Nanosensors Based on a Single ZnO:Eu Nanowire for Hydrogen Gas Sensing.

Fast detection of hydrogen gas leakage or its release in different environments, especially in large electric vehicle batteries, is a major challenge for sensing applications. In this study, the morphological, structural, chemical, optical, and electronic characterizations of ZnO:Eu nanowire arrays are reported and discussed in detail. In particular, the influence of different Eu concentrations during electrochemical deposition was investigated together with the sensing properties and mechanism. Surprisingly, by using only 10 μM Eu ions during deposition, the value of the gas response increased by a factor of nearly 130 compared to an undoped ZnO nanowire and we found an H2 gas response of ∼7860 for a single ZnO:Eu nanowire device. Further, the synthesized nanowire sensors were tested with ultraviolet (UV) light and a range of test gases, showing a UV responsiveness of ∼12.8 and a good selectivity to 100 ppm H2 gas. A dual-mode nanosensor is shown to detect UV/H2 gas simultaneously for selective detection of H2 during UV irradiation and its effect on the sensing mechanism. The nanowire sensing approach here demonstrates the feasibility of using such small devices to detect hydrogen leaks in harsh, small-scale environments, for example, stacked battery packs in mobile applications. In addition, the results obtained are supported through density functional theory-based simulations, which highlight the importance of rare earth nanoparticles on the oxide surface for improved sensitivity and selectivity of gas sensors, even at room temperature, thereby allowing, for instance, lower power consumption and denser deployment.

Analysis of hydrogen embrittlement in palladium–copper alloys membrane from first principal method using density functional theory

Hydrogen embrittlement has significant effects on membrane properties, and it is vital to develop countermeasures to avoid this problem from the start. The impact of hydrogen on pure palladium and palladium-copper alloys used for hydrogen purification/separation was investigated in this study. It was discovered that the lattice parameter and crystalline structure of pure Pd change from 3.92 Å to 5.55 Å and from cubic structure to triclinic structure, respectively. The presence of hydrogen atoms in the crystalline structure is responsible for this alteration. The absorption enthalpy of Pure Pd and PdCu of −4.38eV and −4.86eV, respectively, showed that a PdCu membrane with a lower enthalpy value increased anti-hydrogen brittleness. Due to hydrogen exposure, the mechanical characteristics of pure palladium were considerably affected. This study demonstrates that the mean peak on EF of Pd–Cu (0.259eV) is lower than that of pure Pd (0.955eV) when exposed to hydrogen, indicating more stability and lower hydrogen embrittlement in Pd–Cu alloy than pure Pd. Density functional theory-based simulation is used to analyse what happened at the grain boundary, the causes of hydrogen embrittlement, and possible ways to prevent it.

Excited-state geometry relaxation of pyrene-modified cellulose nanocrystals under UV-light excitation for detecting Fe3+

Abstract Capturing and detecting Fe3+ ions in aqueous solution is of great significance in biological systems as well as the water treatment industry. Herein, pyrene-modified cellulose nanocrystal (CNC-1-Pyr) acting as a fluorescent probe was prepared by a one-step esterification reaction, which shows geometry relaxation under UV-light excitation. Experiments and density functional theory-based simulations revealed that the structural geometry relaxation is controlled by the electron excitation and fluorescence emission. The S1 state of CNC-1-Pyr provides a conformation match for coordination with Fe3+ under the excitation of UV light, facilitating the detecting and capturing of Fe3+ efficiently.

Reactive adsorption and catalytic oxidation of gaseous formaldehyde at room temperature by a synergistic copper-magnesium bimetal oxide biochar composite

Formaldehyde molecules are actively adsorbed over the copper (glowing blue sphere)-magnesium (glowing green sphere)/biochar (black surface with cracks) to produce formate and carbon dioxide species. The synergistic interaction between copper and magnesium (as depicted by lightning) leads to the enhancement of the overall performance. • Cu-Mg/RH550 oxidized FA into CHOO – and CO 2 through reactive adsorption and catalysis. • Cu-Mg/RH550 showed a maximum adsorption capacity of 10 mg g −1 against 100 ppm FA. • Cu-Mg interaction in bimetallic form lowered their crystallite sizes to enhance activity. • The oxidation of adsorbed FA is expedited via partial reduction of Cu 2+ to Cu + . • Metal oxides host H of FA to make the oxidation reaction thermodynamically feasible. The interactive hybridization of reactive adsorption and catalytic oxidation (RACO) was investigated for the removal of formaldehyde (FA) by fine-tuning the relative compositions of bimetallic oxides between copper (Cu) and magnesium (Mg) on biochar (RH550). The best performer against 100 ppm FA was 8%-Cu-8%-Mg/RH550 when assessed in terms of 10% breakthrough volume (3 L atm g −1 ). The corresponding values for reference materials (e.g., RH550, 16%-Cu/RH550, and 16%-Mg/RH550) were 0.4, 1.1, and 0.5 L atm g −1 , respectively. Adsorption kinetic models confirmed the synergistic roles of physicochemical interactions between the target (FA molecules) and composite material (both organic (RH550) and inorganic (metal oxides) phases). The characterization of the spent Cu-Mg/RH550 suggests that the adsorbed FA molecules were partially oxidized into dioxymethylene and formate. Remarkably, Cu-Mg/RH550 led to the complete room-temperature mineralization of FA into carbon dioxide (CO 2 ) for up to 50 h time-on-stream (artificially set maximum test duration) without any deactivation (gas hourly space velocity of 2,229 h −1 ). The oxidation reaction of FA is expedited by the partial reduction of copper(II) oxide (in Cu-Mg/RH550) to copper(I) oxide. According to the density functional theory-based simulations, the metal oxides make the oxidation reaction thermodynamically favorable by hosting hydrogen abstracted from the adsorbed FA molecules. The Cu-Mg synergy also enhances the capture and activation of molecular oxygen (O 2 ) to boost FA oxidation while sustaining the catalytic process. Overall, this study offers new insights into the synergistic role of RACO in the effective removal of FA under ambient conditions.

Exploring Mechanisms of Hydration and Carbonation of MgO and Mg(OH)2 in Reactive Magnesium Oxide-Based Cements.

Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H2O and CO2 molecules with MgO and brucite (Mg(OH)2) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH)2, (iv) hydration of Mg(OH)2, and (v) hydration of carbonated Mg(OH)2. A comparison of the energy barriers and reaction pathways of these mechanisms shows that the carbonation of MgO is hindered by the presence of H2O molecules, while the carbonation of Mg(OH)2 is hindered by the formation of initial carbonate and hydrate layers as well as presence of excessed H2O molecules. To compare these finding to bulk mineral surfaces, the interactions of the CO2 and H2O molecules with the MgO(001) and Mg(OH)2 (001) surfaces are studied. Therefore, this work presents deep insights into the physical nature of the reactions and the mechanisms involved in hydrated magnesium carbonates production that can be beneficial for its development.

Activation of CO2 on the Surfaces of Bare, Ti-Adsorbed and Ti-Doped C60

There is a growing interest in finding a suitable catalyst for the adsorption and activation of CO2 molecules to minimize the effect of global warming. In this study, density functional theory-based simulations are employed to examine the adsorption and activation of a CO2 molecule on the pure, Ti-supported and Ti-doped surfaces of C60. The adsorption on the pure surface is very week. Adsorption becomes significant on the Ti-supported C60 surface together with significant activation. Such strong adsorption is evidenced by the significant charge transfer between Ti and C60. The Ti-doped C60 surface adsorbs weakly, but the activation is not significant.

Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions

• The effects of Er micro-alloying on the mechanical properties and microstructural evolution of Al-Sc-Zr at different isothermal ageing temperatures were investigated. • The Er additions significantly improve the mechanical properties of Al-Sc-Zr alloy during elevated temperature ageing, especially at 400 °C. • The Er additions can increase the nucleation rate of precipitates and consequently enhance the age-hardening response of the Al-Sc-Zr alloy. • DFT calculations were conducted to rationalize the observed precipitate structure and the underlying formation mechanism in the Al-Sc-Zr(-Er) alloys. Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements, transmission electron microscopy, atom probe tomography and density functional theory-based simulations. The results demonstrate that the Er additions significantly improve the hardness during elevated temperature ageing, especially at 400 °C. This is mainly because Er additions increase the nucleation rate of the Al 3 (Er,Sc,Zr) precipitates, resulting in a higher density of fine and uniform dispersion of L1 2 structured nanoparticles. First-principles calculations demonstrate that the second nearest neighboring solute-solute interactions for the species Sc, Zr and Er are energetically favored – a key feature to rationalize the observed precipitate structure and the underlying formation mechanism. The sequential formation of the core/shell precipitates in the Er-free alloy and core/double-shell precipitates in the Er-containing alloy arises due to the different solute-solute and solute-vacancy interaction energies, and the relative diffusivities of the Er, Sc and Zr species in Al. These results shed light on the beneficial effects of Er additions on the age-hardening behavior of Al-Sc-Zr alloy and provide guidance for designing the ageing treatments for the Al-Sc-Zr(-Er) alloys.

Molecular Modelling of Optical Biosensor Phosphorene-Thioguanine for Optimal Drug Delivery in Leukemia Treatment.

Simple SummaryNanocarriers have been used to solve the problems associated with conventional antitumor drug delivery systems, including no specificity, severe side effects, burst release and damaging the normal cells. It improves the bioavailability and therapeutic efficiency of antitumor drugs, while providing preferential accumulation at the target site. Various 2D nanomaterials such as graphene, MoS2, and WSe2 have been used as nanocarrier. The recent discovery of phosphorene has introduced new possibilities in designing a sensible drug delivery system, due to low cytotoxicity, biocompatibility, high surface to volume ratio, which can increase its drug loading capacity. The biodegradation of phosphorene inside the human body produces non-toxic intermediates, like phosphate. Phosphate is necessary for the formation of bone and teeth. Phosphate is also used by the cell for energy, cell membranes, and DNA (deoxyribonucleic acid). Therefore, phosphorene nanocarrier is not harmful, especially for the treatment of cancer in vivo applications.Thioguanine is an anti-cancer drug used for the treatment of leukemia. However, thioguanine has weak aqueous solubility and low biocompatibility, which limits its performance in the treatment of cancer. In the present work, these inadequacies were targeted using density functional theory-based simulations. Three stable configurations were obtained for the adsorption of thioguanine molecules on the phosphorene surface, with adsorption energies in the range of −76.99 to −38.69 kJ/mol, indicating physisorption of the drug on the phosphorene surface. The calculated bandgap energies of the individual and combined geometries of phosphorene and thioguanine were 0.97 eV, 2.81 eV and 0.91 eV, respectively. Owing to the physisorption of the drug molecule on the phosphorene surface, the bandgap energy of the material had a direct impact on optical conductivity, which was significantly altered. All parameters that determine the potential ability for drug delivery were calculated, such as the dipole moment, chemical hardness, chemical softness, chemical potential, and electrophilicity index. The higher dipole moment (1.74 D) of the phosphorene–thioguanine complex reflects its higher biodegradability, with no adverse physiological effects.

Electrochemical Potential of the Metal Organic Framework MIL-101(Fe) as Cathode Material in Li-Ion Batteries

We discuss the characteristic factors that determine the electrochemical potentials in a metal-organic framework used as cathode for Li-ion batteries via density functional theory-based simulations. Our focus is on MIL-101(Fe) cathode material. Our study gives insight into the role of local atomic environment and structural deformations in generating electrochemical potential.

H2S Dissociation on Defective or Strained Fe (110) and Subsequent Formation of Iron Sulfides: A Density Functional Theory Study

In this paper, spin-polarized periodic density functional theory-based simulations were performed to investigate H2S adsorption and dissociation on the defective and strained Fe (110) surfaces which exist in real oil exploitation and transport. It was found that the defective surface facilitates H2S adsorption and dissociation with respect to the perfect surface, while the homogeneous external stresses, giving rise to uniform lattice expansion, show negligible effects for the strain estimated from experiment. More interestingly, the simulations predicted a correct order of phase transition at the Fe (110) surface by using the chemical potential based thermodynamic model, that is, from the elementary Fe crystal to the FeS crystal to the FeS2 crystal to the elementary S crystal with the S coverage on the Fe (110) surface increasing.

Doping of ultra-thin Si films: Combined first-principles calculations and experimental study

This paper presents comprehensive density functional theory-based simulations to understand the characteristics of dopant atoms in the core and on the surface of ultra-thin sub-5 nm Si films. Quantum confinement-induced bandgap widening has been investigated for doped Si films considering two different doping concentrations. Thickness-dependent evolution of dopant formation energy is also extracted for the thin films. It is evident from the results that doping thinner films is more difficult and that dopant location at the surface is energetically more favorable compared to core dopants. However, the core dopant generates a higher density of states than the surface dopant. Projecting the carrier states in the doped Si film onto those of a reference intrinsic film reveals dopant-induced states above the conduction band edge, as well as perturbations of the intrinsic film states. Furthermore, to experimentally evaluate the ab initio predictions, we have produced ex situ phosphorus-doped ultra-thin-Si-on-oxide with a thickness of 4.5 nm by the beam-line ion implantation technique. High-resolution transmission electron microscopy has confirmed the thickness of the Si film on oxide. Transfer length method test structures are fabricated, and the temperature-dependent electrical characterization has revealed the effective dopant activation energy of the ion-implanted phosphorus dopant to be ≤ 13.5 meV, which is consistent with our theoretical predictions for comparable film thickness. Ultra-thin Si films are essential in the next generation of Si-based electronic devices, and this study paves the way toward achieving that technology.

Strategies for Controlling Through-Space Charge Transport in Metal-Organic Frameworks via Structural Modifications.

In recent years, charge transport in metal-organic frameworks (MOFs) has shifted into the focus of scientific research. In this context, systems with efficient through-space charge transport pathways resulting from π-stacked conjugated linkers are of particular interest. In the current manuscript, we use density functional theory-based simulations to provide a detailed understanding of such MOFs, which, in the present case, are derived from the prototypical Zn2(TTFTB) system (with TTFTB4− corresponding to tetrathiafulvalene tetrabenzoate). In particular, we show that factors such as the relative arrangement of neighboring linkers and the details of the structural conformations of the individual building blocks have a profound impact on bandwidths and charge transfer. Considering the helical stacking of individual tetrathiafulvalene (TTF) molecules around a screw axis as the dominant symmetry element in Zn2(TTFTB)-derived materials, the focus, here, is primarily on the impact of the relative rotation of neighboring molecules. Not unexpectedly, changing the stacking distance in the helix also plays a distinct role, especially for structures which display large electronic couplings to start with. The presented results provide guidelines for achieving structures with improved electronic couplings. It is, however, also shown that structural defects (especially missing linkers) provide major obstacles to charge transport in the studied, essentially one-dimensional systems. This suggests that especially the sample quality is a decisive factor for ensuring efficient through-space charge transport in MOFs comprising stacked π-systems.

Adsorption behavior of tin phthalocyanine onto the (110) face of rutile TiO2.

The adsorption behavior of tin phthalocyanine (SnPc) molecules on rutile TiO2(110) was studied by scanning tunneling microscopy (STM). Low-temperature STM measurements of single molecules reveal the coexistence of two conformations of molecules on the TiO2 surface. Density functional theory-based simulations (DFT) indicate that the difference originates from the position of the tin atom protruding from the molecule plane. The irreversible switching of Sn-up molecules into the Sn-down conformation was observed either after sample annealing at 200 °C or as a result of tip-induced manipulation. Room-temperature measurements conducted for a coverage of close to a monolayer showed no tendency for molecular arrangement.

All Precursors Are Not Equal: Morphology Control via Distinct Precursor–Facet Interactions in Eu3+-Doped NaLa(WO4)2

Morphology of lanthanide (Ln3+)-doped nanostructures plays a crucial role in determining the crystal-field-dependent luminescent properties as that modulates the surface-to-bulk ratio of Ln3+ ions. In this work, we demonstrate a systematic morphology control in Eu3+-doped sodium lanthanum tungstate NaLa0.95Eu0.05(WO4)2 by varying lanthanide precursor salts and report variation in its photoluminescence properties. Chloride and nitrate salts of lanthanide produce nanoneedles and -cuboids, respectively, whereas acetate and carbonate salts produce rugby ball-like morphology. Density functional theory-based simulations have been performed to study the effect of growth hindering species (Na salts of precursor anions, i.e., Cl–, NO3–, CO3–2) in controlling the evolution of low index (100) and (001) facets of NaLa0.95Eu0.05(WO4)2. The changes in morphology are correlated with the preferential development of low index (100) and (001) facets caused by differential adsorption of growth hindering species. Accordingly, they attach with La-sites of (100) rather than an O-terminated (001) facet; binding selectivity order being chloride > nitrate > carbonate. Strong adsorption of chloride salts on (l00) causes anisotropic growth along [001] direction and leads to needle morphology due to vast stacking of basal planes. The minor binding difference in adsorption of nitrate salts observed on (100) and (001) facets is responsible for overall growth and evolution of cuboid morphology. The binding of carbonate (or acetate) salts on (100) is weak, and combined evolution of (001), (011), and (100) facets leads to rugby ball morphology. Further, the needle, cuboidal, and rugby shape particles produce different UV sensitized emission with the Commission Internationale de I’ Eclairage (CIE) chromaticity coordinates as (0.44, 0.25), (0.48, 0.26), and (0.59, 0.32), respectively.

Electronic transport in metal-molecular nanoelectronic networks: A density functional theory study

Electronic transport properties of nanoscale networks composed of interconnected molecules/gold nanoclusters are examined via first-principles plane wave scattering density functional theory-based simulations. Au-molecular (benzene/alkanedithiol) junctions and networks, connected in linear chains and Y-, H- and ring-shaped networks were studied. Molecular orbital calculations show HOMO (highest-occupied-molecular-orbital)-LUMO (lowest-unoccupied-molecular-orbital) gaps of chains decreased with length, indicating decreased barrier to electron transport. Orbitals near the gap of benzenedithiol networks show good delocalization whereas those of alkanedithiol molecules were more localized the metallic clusters. The transmission spectra of benzenedithiol-based networks showed increase in number/width of peaks near the Fermi energy as structures were extended due to increased orbital overlapping (spatially/energetically) with each other leading to formation of transmission pathways and electronic energy band-like properties. In contrast, lower transmission was observed for networks having localized orbitals (alkanedithiol molecular networks) with less overlap near the Fermi energy. Transmission spectra were also in good agreement with associated peaks in electronic density of states. In the case of multi-terminal networks, the location of delocalized orbitals can also shift from one branch to another, indicating potential ON/OFF switching behavior is possible. Switching elements and molecular-scale circuits (e.g., logic gates or inverters) based on Y- and H-shaped networks are proposed in analogy to electron waveguide devices and our simulations indicated that low-energy switching operation on the order of 10-50 meV may be possible. These nanoscale molecular electronic networks linked via metallic clusters provide an avenue for engineering electronics at the molecular level by using superstructures of different organic molecules and topologies.

Rapid communication: Permeability of hydrogen in two-dimensional graphene and hexagonal boron nitride sheets

We study the permeability of atomic hydrogen in monolayer hexagonal boron nitride (h-BN) and graphene using first-principles density functional theory-based simulations. For the specific cases of physisorption and chemisorption, barrier heights are calculated using the nudged elastic band approach. We find that the barrier potential for physisorption through the ring is lower for graphene than for h-BN. In the case of chemisorption, we have studied three specific cases where the H atom passes through by making bonds with the atoms at different sites in the ring. The chemisorption barrier height for graphene is found to be, in general, higher than that of h-BN. We conclude that the dominant mechanism of tunnelling through the graphene sheet and h-BN sheets would be physisorption and chemisorption, respectively.