2D Hexagonal Boron Nitride Research Articles

Memory effect of vertically stacked hBN/QDs/hBN structures based on quantum-dot monolayers sandwiched between hexagonal boron nitride layer

The characteristics of a flexible write-once-read-many-times (WORM) memory fabricated with monolayered 0-dimensional (0D) CdSe–ZnS quantum dots (QDs) layers sandwiched between two insulating 2-dimensional (2D) hexagonal boron nitride (hBN) multilayers were investigated by electrical measurement method. The hBN/QDs monolayer/hBN structure was fabricated in a vertical stacked structure using a technique which control the formation of the QDs monolayer. QDs monolayer was formed by electrostatic interaction between the negative charge group on the CdSe–ZnS QDs surface and the positive charge group on the hBN surface. The device has a WORM characteristic due to the presence of QDs in the current-voltage (I–V) measurement. When a bias is applied, carriers were initially trapped by tunneling due to the QDs and then a conductive filament was formed in the hBN, which were not detrapped and exhibit characteristics of write-once-read-many-times memory. The maximum ON/OFF ratio of the current for the devices was as large as 4 × 10, and the endurance was 5 × 10 4 cycles, and a retention time was larger than 1 × 10 5 s. In order to explain the carrier transport mechanism and conductive filament of the WORM memory device caused by QDs, it through various methods such as I–V fitting data, simulation, and conductive AFM. Unlike the conventional conductive filament mechanism, through random diffusion such as Ag filament, the Au/hBN/QD/hBN/ITO/PET structures implemented a consistent conductive filament using Au metal and QDs active layer.

Transferable room-temperature single-photon emitters in hexagonal boron nitride grown by molecular beam epitaxy

The solid-state single-photon source is the core of applications such as quantum cryptography, quantum sensing, and quantum computing. Recently, the point defects in two-dimensional (2D) hexagonal boron nitride (h-BN) have become excellent candidates for next-generation single-photon sources due to their chemical and physical stability and ultra-high brightness at room temperature. The 2D layered structure of h-BN allows the single-photon emitters (SPEs) in it to have high photon extraction efficiency and be integrated into photonic circuits easily. However, most of the SPEs found in h-BN flakes are present at the edges or wrinkles. Here, we report on the room-temperature SPEs in h-BN film grown by molecular beam epitaxy followed by a high-temperature post-annealing process and their deterministic transfer. Using the all-dry viscoelastic stamping method, the h-BN film grown on the Al2O3 substrate can be transferred to other substrates. The transferred SPEs are discretely distributed among the continuous h-BN flakes, and the SPE density is as high as ∼0.17 μm−2. After identification, the determined SPE can be deterministically transferred to other structures by the all-dry transfer method. The deterministic transfer of SPEs distributed on the h-BN flakes promises the potential to integrate SPEs into many quantum technology applications.

Massive enhancement in power output of BoPET-paper triboelectric nanogenerator using 2D-hexagonal boron nitride nanosheets

In the present era of the Internet of Things (IoT) and sensor networks, clean and sustainable power sources are in huge demand, and triboelectric nanogenerators (TENGs) are a hot cake in green energy production. Here, we have developed a contact-separation mode TENG using liquid-phase exfoliated 2D-hexagonal boron nitride nanosheets (BNNSs) coated on biaxially-oriented polyethylene terephthalate (BoPET) and paper as counter triboelectric materials, which showed an impressive 70 times higher power output than simple BoPET-paper TENG assembly. Even under a moderate finger tapping force (~3 N), the developed BNNSs/BoPET-paper TENG device could generate an open circuit output voltage of ~200 V and a short circuit current density of ∼0.48 mA/m2. While under load testing, the peak value of electric power density for the BNNSs/BoPET-paper TENG device reached ~0.14 W/m2 at 200 MΩ resistive load. The incorporation of BNNSs has significantly enhanced the electron-accepting capabilities of the BoPET film which is evident from the enhanced dielectric permittivity of the BNNSs/BoPET assembly, and thus resulted in the enhanced electrical output of TENG. Additionally, the fabricated BNNSs-TENG was successfully demonstrated for powering electronic gadgets such as LCD clock, digital thermometer, and LEDs through cyclic finger tapping force.

Super-Planckian thermal radiation between 2D phononic hBN monolayers

Near-field radiation heat transfer (NFRHT) in two-dimensional (2D) hexagonal boron nitride (hBN) monolayer and its composite symmetric-based structure was investigated. Contrary to three-dimensional (3D) materials, the splitting of modes (in 2D materials) into the longitudinal optical (LO) and transverse optical (TO) phononic modes disappears at the Γ-point even in some polar materials. The conductivity of atomic thin hBN monolayer depends on the LO phonon frequency under the long wavelength limit. Exploiting such concept, the electromagnetic local density of states (EM-LDOS) accounting for the near-field radiation spectrum was evaluated in free-space close to an interface with the hBN monolayer as well as composite structures. An intense narrow peak of LDOS was found in the case of hBN monolayer caused by the surface phonon polariton (SPhP) resonance. This peak was modified in the case of hBN-graphene composite due to hybridization, which strongly depends on two factors – the distance of observer (in vacuum) from interface and graphene Fermi energy. It was found that the flux density between monolayer hBN gets 2.8-fold enhanced as compared to the monolayer graphene configuration under 0.11 eV Fermi energy applied at a vacuum gap of 15 nm. The possibility of tuning Fermi energy has great potentials in designing thermally controlled devices.

Quasi-Isotropically Thermal Conductive, Highly Transparent, Insulating and Super-Flexible Polymer Films Achieved by Cross Linked 2D Hexagonal Boron Nitride Nanosheets.

Polymer-based thermal management materials (TIMs) show great potentials as TIMs due to their excellent properties, such as high insulation, easy processing, and good flexibility. However, the limited thermal conductivity seriously hinders their practical applications in high heat generation devices. Herein, highly transparent, insulating, and super-flexible cellulose reinforced polyvinyl alcohol/nylon12 modified hexagonal boron nitride nanosheet (PVA/(CNC/PA-BNNS)) films with quasi-isotropic thermal conductivity are successfully fabricated through a vacuum filtration and subsequent self-assembly process. A special structure composed of horizontal stacked hexagonal boron nitride nanosheets (h-BNNSs) connected by their warping edges in longitudinal direction, which is strengthened by cellulose nanocrystals, is formed in PVA matrix during self-assembly process. This special structure makes the PVA/(CNC/PA-BNNS) films show excellent thermal conductivity with an in-plane thermal conductivity of 14.21 W m-1 K-1 and a through-plane thermal conductivity of 7.29 W m-1 K-1 . Additionally, the thermal conductive anisotropic constants of the as-obtained PVA/(CNC/PA-BNNS) films are in the range of 1 to 4 when the h-BNNS contents change from 0 to 60wt%, exhibiting quasi-isotropic thermal conductivity. More importantly, the PVA/(CNC/PA-BNNS) films exhibit excellent transparency, super flexibility, outstanding mechanical strength, and electric insulation, making them very promising as TIMs for highly efficient heat dissipation of diverse electronic devices.

Hexagonal Boron Nitride Meeting Metal: A New Opportunity and Territory in Heterogeneous Catalysis.

Two dimensional (2D) hexagonal boron nitride (h-BN) has been ignored for a long time in catalysis research because of its chemical inertness. Recently there has been a significant advance highlighting the role of metal/h-BN interfaces in catalytic applications. In this Perspective, we summarize state-of-the-art progress regarding h-BN-involved metal catalysts. Vacancy- and defect-rich h-BN sheets are able to anchor and modify supported metals, in which the interfacial metal-support interaction effect helps to enhance catalytic performance. Oxidative etching of h-BN sheets causes encapsulation of metal catalysts via boron oxide (BOx) species, which work synergistically with neighboring metal sites in catalysis. Covering a metal surface with ultrathin h-BN shells creates a 2D nanoreactor featuring confinement effect, providing a novel way to modulate metal-catalyzed reactions. Given all those fascinating combinations of metal catalyst and h-BN, the emerging opportunity when h-BN meets metal in heterogeneous catalysis is clearly underlined. The outlook, especially the challenges in the field, are discussed as well.

Synthesis of hexagonal boron nitrides by chemical vapor deposition and their use as single photon emitters

Two-dimensional (2D) hexagonal boron nitride (hBN), due to its extraordinary thermal, chemical, and optical properties, has arisen as an enticing material for the research community to explore for various applications, including the use of site defects in hBN as single photon emitters (SPEs). In this review, we systematically summarize recent advanced strategies towards the controllable synthesis of 2D hBN using chemical vapor deposition, towards a full control of the domain size, orientation, morphology, layer number, and stacking order, etc . Moreover, we review the underlying mechanisms for single photon emission (SPE) in hBN and methods to selectively generate and tune the SPEs. Defects ( e.g ., carbon substituted defects) are discussed for the potential use as emission sites. We finally give an outlook of future challenges and opportunities on desirable hBN synthesis and further investigation of SPEs in hBN, targeting to utilize hBN as single photon emitters in an industrial scale.

Enhanced Activation of CO2 on h-BN Nanosheets via Forming a Donor–Acceptor Heterostructure with 2D M2X Electrenes

The activation of CO2 is the first crucial step in the CO2 reduction reaction (CO2RR), but it faces the challenge of the ultrahigh chemical stability of the CO2 molecule. Two-dimensional (2D) hexagonal boron nitride (h-BN) has been considered as a promising electrocatalytic interface material due to its high specific surface area, N- and B-active sites, and adjustable chemical reactivity through interactions with other materials. Here we report a donor–acceptor heterostructure (DAH) containing 2D h-BN and M2N (M = Ca, Sr, and Ba) or Y2C electrene, single-layer electride materials, toward the activation of the CO2 molecule on the basis of first-principles calculations. Our results demonstrate that a considerable number of electrons (0.1 e per BN unit) transfer from M2X electrene to the h-BN sheet due to the strong electrostatic interaction between the cation boron in the h-BN sheet and the anion electron gas in M2X electrides, which significantly enhances the CO2 activation activity of the h-BN monolayer. The adsorption of CO2 on h-BN is exothermic, with a negligible energy barrier down to 0.013 eV. Meanwhile, the overpotential of the hydrogenation of CO2 to HCOOH is as low as 0.17 V on the h-BN/Y2C DAH, implying superior performance for the CO2 reduction on the h-BN/M2X DAH. This work provides a strategy for activating CO2 on the h-BN monolayer by building a DAH with 2D electride materials.

Spatially controlled epitaxial growth of 2D heterostructures via defect engineering using a focused He ion beam

The combination of two-dimensional (2D) materials into heterostructures enables the formation of atomically thin devices with designed properties. To achieve a high-density, bottom-up integration, the growth of these 2D heterostructures via van der Waals epitaxy (vdWE) is an attractive alternative to the currently mostly employed mechanical transfer, which is problematic in terms of scaling and reproducibility. Controlling the location of the nuclei formation remains a key challenge in vdWE. Here, a focused He ion beam is used to deterministically place defects in graphene substrates, which serve as preferential nucleation sites for the growth of insulating, 2D hexagonal boron nitride (h-BN). Therewith a mask-free, selective-area vdWE (SAvdWE) is demonstrated, in which nucleation yield and crystal quality of h-BN are controlled by the ion beam parameters used for defect formation. Moreover, h-BN grown via SAvdWE is shown to exhibit electron tunneling characteristics comparable to those of mechanically transferred layers, thereby lying the foundation for a reliable, high-density array fabrication of 2D heterostructures for device integration via defect engineering in 2D substrates.

The role of substrate on stabilizing new phases of two-dimensional tin

In this work, we investigate the role of substrates in determining the morphologies and electronic structures of two-dimensional (2D) Sn. We use Ir(111) and 2D hexagonal boron nitride (h-BN) predeposited on Ir(111) as substrates. The latter contains Moiré patterns with varying binding strength between h-BN and metal. Using scanning tunneling microscopy and first-principles calculations, we reveal the distinct morphologies of 2D Sn on different substrates. Of particular interest, we discover a new √7 × √7 Sn phase, originating from the local charge transfer with metal beneath the ‘decoupling’ h-BN monolayer at the strongly interacting Moiré region. To the best of our knowledge, this work demonstrates, for the first time via combined experimental and theoretical approach, that new 2D Sn phases can be achieved using Moiré patterns on h-BN/metal. This finding should be instrumental in the development of 2D-based topological materials.

Alloyed AuPt nanoframes loaded on h-BN nanosheets as an ingenious ultrasensitive near-infrared photoelectrochemical biosensor for accurate monitoring glucose in human tears

Photo-electro-chemical (PEC) glucose biosensor has recently attracted extensive attention due to the double advantages of both photocatalysis via photon energy utilization and electrocatalytic oxidation through extra electric field. Compared with previous shorter wavelength (violet-visible) light-induced PEC reaction, the anticipated near infrared (NIR, >~700 nm) excited PEC biosensor with multiple fascinating features should be more suitable for clinical diagnostic biology. Herein, we report an ingenious NIR-PEC biosensor by loading alloyed Au5Pt9 nanoframes on two dimensional (2D) hexagonal boron nitride (h-BN) nanosheets. The obtained h-BN/Au5Pt9 nanoframes exhibit a remarkable higher NIR-PEC activity in comparison with other as-prepared h-BN/AuPt references. The improved PEC performance is attributed to the enhanced synergetic coupling effect between Au5Pt9 nanoalloys and constitutionally stable h-BN that gives rise to a stronger absorbance capacity and pronounced localized surface plasmon resonance (LSPR) in visible-NIR region as well as high free-electron mobility of framework-like Au/Pt. Interestingly, the obtained h-BN/Au5Pt9 nanoframes excited by 808 nm NIR light provide superior PEC accuracy and sensitivity as compared to visible or other NIR light irradiation. Then, the novel 808 nm NIR-PEC biosensor was used for precise glucose monitoring in human tears with a detectable concentration of 0.03~100 μM and a low detection limit of 0.406 nM. Undoubtedly, the proposed h-BN/Au5Pt9 nanoframes as an appealing NIR-PEC glucose biosensor can possess greater potential values for practical glucose monitoring in biomedicine.

Half-metallic ferromagnetism induced by TM-TM atom pair co-doping in 2D hexagonal boron nitride monolayer: A first principle study

The wide band gap of graphitic 2D hexagonal boron nitride nanosheets (h-BNNS) has recently been extensively studied to engineer for next generation electronic devices. Here, we report a systematic theoretical investigation of the structural, electronics and magnetic properties for the vacancy defected and transition metal (TM) pair co-doped h-BNNSs. All of our calculations have been performed based on spin polarized first-principles calculation using density functional theory. We have investigated the structural stability of h-BNNSs monolayer due to TM-TM pair co-doping and describe their interesting magneto-electronic properties as evident from the spin polarized projected density of state. Although, pristine h-BNNS is a nonmagnetic insulator, our investigation shows that the addition of transition metal pair induced interesting magnetic ground state. The interaction of selective TM atom pairs transferred the h-BNNS from a spin non-polarized to spin polarized half-metal and semiconductor demonstrating an effective strategy to tune magneto-electronic properties of h-BNNS.

Mitigation of Electromigration in Metal Interconnects via Hexagonal Boron Nitride as an Ångström‐Thin Passivation Layer

AbstractElectromigration in metal interconnects remains a significant challenge in the continued scaling of integrated circuits towards ever‐smaller single‐nanometer nodes. Conventional damascene architectures of barrier/liner layers and conducting metal cause inevitable compromises between device performance and feature dimensions. In contrast to contemporary barrier/liner materials (e.g., Co, Ta, and Ru), an ultrathin passivation layer that can effectively mitigate electromigration is needed. At the ultimate atomically‐thin limit, 2D materials are promising candidates given their exceptional mechanical properties and impermeability. Here, a facile and effective approach is presented to mitigating electromigration in copper (Cu) interconnects via passivation with insulating monolayer 2D hexagonal boron nitride (hBN). The hBN‐passivated Cu interconnects, compared to otherwise identical but bare Cu interconnects, exhibit on average a >20% higher breakdown current density and a >2600% longer lifetime (at a high current density of 5.4 × 107 A cm−2). Post‐mortem metrology elucidates uniform conformal contact between the hBN‐passivated Cu interface and common failure features due to electromigration.

Characterization of 2D boron nitride nanosheets with hysteresis effect in the Schottky junctions

Carbon doped two-dimensional (2D) hexagonal boron nitride nanosheets (BNNSs) are obtained through a CO2—pulsed laser deposition (CO2—PLD) technique on silicon dioxide (SiO2) or molybdenum (Mo) substrates, showing - stable hysteresis characteristics over a wide range of temperatures, which makes them a promising candidate for materials based on non-volatile memory devices. This innovative material with electronic properties of n-type characterized in the form of back-to-back Schottky diodes appears to have special features that can enhance the device performance and data retention due to its functional properties, thermal-mechanical stability, and its relation with resistive switching phenomena. It can also be used to eliminate sneak current in resistive random-access memory devices in a crossbar array. In this sense constitutes a good alternative to design two series of resistance-switching Schottky barrier models in the gold/BNNS/gold and gold/BNNS/molybdenum structures; thus, symmetrical and non-symmetrical characteristics are shown at low and high bias voltages as indicated by the electrical current-voltage (I–V) curves. On the one hand, the charge recombination caused by thermionic emission does not significantly change the rectification characteristics of the diode, only its hysteresis properties change due to the increase in external voltage in the Schottky junctions. The addition of carbon to BNNSs creates boron vacancies that exhibit partially ionic character, which also helps to enhance its electrical properties at the metal-BNNS-metal interface.

Strong catalyst support interactions in defect-rich γ-Mo2N nanoparticles loaded 2D-h-BN hybrid for highly selective nitrogen reduction reaction

Electrochemical ammonia synthesis by N2 fixation has proven to be a promising alternative to the energy-consuming, befouling Haber-Bosch process. Considering the low faradaic efficiency and sluggish kinetics of Nitrogen Reduction Reaction (NRR), it is significant to design a robust and selective catalyst. Herein, we demonstrate a single step in-situ nitridation method to grow cubic molybdenum nitride (γ-Mo2N) nanoparticles on a 2D hexagonal boron nitride (h-BN) sheets as a potential, cost-effective electrocatalyst for NRR, in which the selectivity for N2 was regulated by interfacially engineering the Mo2N-BN bridge. The maneuverability of h-BN sheets enabled the provocation of N-vacancies governed by the particle size, where the fine-tuning of their significance emanated the highest faradaic efficiency of 61.5 %. Moreover, such non-noble metal-based hybrids delivered a stable performance for 20 h. Therefore, our approach of designing the electronic structure of a catalyst by controlling the defects could be an effective practice for selective NRR.

Visible light sensitive hexagonal boron nitride (hBN) decorated Fe2O3 photocatalyst for the degradation of methylene blue

The role of the carbon-based two-dimensional (2D) structures such as graphene or graphene oxide on the properties of metal oxide/2D composites materials are extensively studied for the environmental applications like photocatalysis. However, the metal oxide/inorganic 2D structure-based composites are less explored. In this regard, we have explored the α-Fe2O3/inorganic 2D hexagonal boron nitride (hBN) composite as an efficient visible light photocatalyst for the degradation of methylene blue (MB). A systematic investigation on the role of varying the weight percent of hBN on the photocatalytic efficiency for MB degradation under visible light was studied. The α-Fe2O3/(x) hBN (x = 1, 5, 10 wt%) composites were characterized by various analytical and spectroscopic techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The bandgap tuning with varying compositions of α-Fe2O3/(x) hBN (x = 1, 5, 10 wt%) were investigated by UV–vis diffuse reflectance spectroscopy (UV DRS) and the bandgap values were found to decrease with addition of hBN (1.56 eV for 5 wt%) compared to bare α-Fe2O3 (2.02 eV). The composite α-Fe2O3 with 5 wt% of hBN (FB2) showed an enhanced methylene blue (MB) degradation of ~ 91% with a high rate constant value of 5.03 × 10–4 s−1. This was ~ 3.3 times higher than the rate constant observed for the MB degradation using bare hematite. The material after photocatalysis process was retrieved by simple sedimentation process and reused for four cycles with no loss in degradation efficiency. The as-prepared composite material may have application in recycling and reuse of water in textile industries.

A hexagonal boron nitride super self-collimator for optical asymmetric transmission in the visible region

The two-dimensional (2D) hexagonal boron nitride (hBN) has been considered as a promising platform for quantum computing and information processing, due to the possibility in the generation of optically stable, ultra-bright quantum emitters in the visible region. In the meantime, integrable optical asymmetric transmission devices are necessary for functional quantum computing chips. In this study, we theoretically demonstrate an optical asymmetric transmission device working in the visible region based on a monolith 2D hBN super self-collimator. To maximize the self-collimation effect on improving the efficiency of the forward transmission, we not only design the photonic crystal structure with strong self-collimation characteristic, but also engineer the shape of the device. It is shown that by combining the two factors, the super self-collimation effect allows achieving a forward transmittance of up to 0.77. In the meantime, the structure effectively suppresses the backward transmission (down to 0.05) based on the directional bandgap, which results in a contrast ratio of up to 0.95 in the visible wavelength range of 590 nm–632 nm. More importantly, it is shown that by using the super self-collimation effect, the propagation efficiency inside the structure can be as high as 0.99 with minimum loss. Our results open up new possibilities in designing new nanophotonic devices based on 2D hBN for quantum computing and information processing.

Passivation of InP solar cells using large area hexagonal-BN layers

Surface passivation is crucial for many high-performance solid-state devices, especially solar cells. It has been proposed that 2D hexagonal boron nitride (hBN) films can provide near-ideal passivation due to their wide bandgap, lack of dangling bonds, high dielectric constant, and easy transferability to a range of substrates without disturbing their bulk properties. However, so far, the passivation of hBN has been studied for small areas, mainly because of its small sizes. Here, we report the passivation characteristics of wafer-scale, few monolayers thick, hBN grown by metalorganic chemical vapor deposition. Using a recently reported ITO/i-InP/p+-InP solar cell structure, we show a significant improvement in solar cell performance utilizing a few monolayers of hBN as the passivation layer. Interface defect density (at the hBN/i-InP) calculated using C–V measurement was 2 × 1012 eV−1cm−2 and was found comparable to several previously reported passivation layers. Thus, hBN may, in the future, be a possible candidate to achieve high-quality passivation. hBN-based passivation layers can mainly be useful in cases where the growth of lattice-matched passivation layers is complicated, as in the case of thin-film vapor–liquid–solid and close-spaced vapor transport-based III–V semiconductor growth techniques.

Line-defect orientation- and length-dependent strength and toughness in hBN

Applying classical molecular dynamics simulations, we report the effects of length (λ) and orientation (θ) of a line-defect on strength and toughness in defective 2D hexagonal boron nitride. Results reveal the existence of a “transition angle,” θt=2.47°, at which both toughness and strength are insensitive to the finite length of the defect in an infinite domain. For θ<θt, both toughness and strength increase with an increase in defect-length; whereas, for θ>θt, they show the opposite behavior. Examination of the stress-fields shows that θ-dependent variation in stress-localization at the edges of the line-defect and symmetry-breaking of the stress-fields with respect to the defect-axis govern the disparate θ-dependent behavior. For θ<θt, the intensity of elastic fields at the edges of the line-defect is substantially weakened by the elastic interactions originating from the atoms on the sides of the line-defect. For θ>θt, the stress-intensity at the edges is strongly localized at the opposite sides of the line-defect. The stress-intensity increases asymptotically with the increasing defect-length and reduces the strength and toughness of the defective lattice. The stress-localization, however, saturates at a “saturation angle” of around 60° for strength and 30° for toughness. Additionally, there exists a critical defect-length λc=60 Å, below which there is a strong θ-dependent variation in elastic interactions between the edges, affecting strength and toughness substantially. For λ>λc, the elastic interactions saturate and make both strength and toughness insensitive to the change in the length of the defect.

Syngas molecules as probes for defects in 2D hexagonal boron nitride: their adsorption and vibrations.

Single-layer, defect-laden hexagonal boron nitride (dh-BN) is attracting a great deal of attention for its diverse applications: catalysis on the one hand, and single photon emission on the other. As possible probes for identifying some common defects in single-layer h-BN, we present results of ab initio calculations for the adsorption and vibrational characteristics of syngas molecules (H2, CO, CO2) on dh-BN containing one of four types of defects: nitrogen vacancy (VN), boron vacancy (VB), Stone-Wales defect (SW), and nitrogen substituted by boron (BN). Through a comparative examination of adsorption features, charge transfer, electronic structure, and vibrational spectrum, we obtain a deep understanding of the interaction of these molecules with dh-BN and the role of the defect states. We find that while CO, CO2 and atomic hydrogen chemisorb, molecular H2 physisorbs on dh-BN with the four considered defect types. VN and VB show strong affinity for CO and CO2 since the defect states induced by them lie close to the Fermi level. SW does not favor adsorption of these small molecules, as the process for each is endothermic. In the case of BN, CO adsorbs strongly but CO2 only weakly. Vibrational frequencies of notable modes localized at the adsorbed molecules are analyzed and suggested as measures for identification of the defect type. Through a simple comparison of adsorption characteristics of the molecules on these defects, we propose dh-BN with VN to be a good catalyst candidate for CO2 hydrogenation.