Band gap opening of graphene by doping small boron nitride domains

Enhancing the energetic and magnetic stability of atomic hydrogen chemisorbed on graphene using (non)compensated B-N pairs

In this pioneering study for identifying atomic scale magnetic moment, a single hydrogen atom chemisorbed on pristine graphene exhibits distinct spin polarization. Using first-principles calculations and analyses, we demonstrate that the binding between a H adsorbate and a C substrate is substantially enhanced via compensated B-N pairs embedded into graphene. Surprisingly, the interaction can be further enhanced via non-compensated B-N pair doping. Our established prototype of orbital intercoupling between H 1s and hybridized pz of gapped band edges gives an insight into the enhancing mechanism. For compensated B-N doping, the conduction band minimum (CBM) is pushed upward, which induces stronger interaction between the H 1s and hybridized pz orbitals of the CBM. For non-compensated B-N doping, the orbital interaction occurs between H 1s and hybridized pz orbitals of valence band maximum, thus further lowering the resulting bonding energy due to the enlarged gap. This significantly enhanced interaction between H and C atoms agrees well with the results of charge localization at the gapped band edges. More importantly, the corresponding magnetic moments can be well maintained or even enhanced in both doping; here, one more H atom is needed for non-compensated doping, where its electron occupies the empty CBM. Our findings might provide an effective and practical way to enhance the energetic and magnetic stability of atomic scale magnetic moment on graphene and extensively expand the conception of non-compensated doping.

Graphene materials in pollution trace detection and environmental improvement

Water scarcity is a pressing issue experienced in numerous countries and is expected to become increasingly critical in the future. Anthropogenic activities such as mining, agriculture, industries, and domestic waste discharge toxic contaminants into natural water bodies, causing pollution. Addressing these environmental crises requires tackling the challenge of removing pollutants from water. Graphene oxide (GO), a form of graphene functionalized with oxygen-containing chemical groups, has recently garnered renewed interest due to its exceptional properties. These properties include a large surface area, mechanical stability, and adjustable electrical and optical characteristics. Additionally, surface functional groups like hydroxyl, epoxy, and carboxyl groups make GO an outstanding candidate for interacting with other materials or molecules. Because of its expanded structural diversity and enhanced overall properties, GO and its composites hold significant promise for a wide range of applications in energy storage, conversion, and environmental protection. These applications encompass hydrogen storage materials, photocatalysts for water splitting, the removal of air pollutants, and water purification. Serving as electrode materials for various lithium batteries and supercapacitors. Graphene-based materials, including graphene, graphene oxide, reduced graphene oxide, graphene polymer nanocomposites, and graphene nanoparticle metal hybrids, have emerged as valuable tools in energy and environmental remediation technologies. This review article provides an overview of the significant impact of graphene-based materials in various areas. Regarding energy-related topics, this article explores the applications of graphene-based materials in supercapacitors, lithium-ion batteries, and catalysts for fuel cells. Additionally, the article investigates recent advancements in detecting and treating persistent organic pollutants (POPs) and heavy metals using nanomaterials. The article also discusses recent developments in creating innovative nanomaterials, nanostructures, and treatment methods for addressing POPs and heavy metals in water. It aims to present the field's current state and will be a valuable resource for individuals interested in nanomaterials and related materials.

Reversible Stacking of 2D ZnIn2 S4 Atomic Layers for Enhanced Photocatalytic Hydrogen Evolution

It is technically challenging to reversibly tune the layer number of 2D materials in the solution. Herein, a facile concentration modulation strategy is demonstrated to reversibly tailor the aggregation state of 2D ZnIn2 S4 (ZIS) atomic layers, and they are implemented for effective photocatalytic hydrogen (H2 ) evolution. By adjusting the colloidal concentration of ZIS (ZIS-X, X = 0.09, 0.25, or 3.0 mg mL-1 ), ZIS atomic layers exhibit the significant aggregation of (006) facet stacking in the solution, leading to the bandgap shift from 3.21 to 2.66 eV. The colloidal stacked layers are further assembled into hollow microsphere after freeze-drying the solution into solid powders, which can be redispersed into colloidal solution with reversibility. The photocatalytic hydrogen evolution of ZIS-X colloids is evaluated, and the slightly aggregated ZIS-0.25 displays the enhanced photocatalytic H2 evolution rates (1.11 µmol m-2 h-1 ). The charge-transfer/recombination dynamics are characterized by time-resolved photoluminescence (TRPL) spectroscopy, and ZIS-0.25 displays the longest lifetime (5.55 µs), consistent with the best photocatalytic performance. This work provides a facile, consecutive, and reversible strategy for regulating the photo-electrochemical properties of 2D ZIS, which is beneficial for efficient solar energy conversion.

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates

The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic structure of a pristine monolayer of h-BN is dependent on the type of substrate, as h-BN is decoupled electronically from the HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111) substrate, metallic-like behavior is predicted. These different film/substrate systems therefore show different reactivities and defect chemistries. The formation energies for substitutional defects are significantly lower than for intrinsic defects regardless of the substrate, and vacancies formed during film deposition are expected to be filled by either ambient oxygen or carbon from impurities. Significantly lower formation energies for intrinsic and oxygen and carbon substitutional defects were predicted for h-BN on Ni(111). In-plane h-BCN hybrid structures were predicted to be terminated by N-C bonding. Substitutional carbon on the boron site imposes n-type semiconductivity in h-BN, and the n-type character increases significantly for h-BN on HOPG. The h-BN film surface becomes electronically decoupled from the substrate when exceeding monolayer thickness, showing that the surface electronic properties and point defect chemistry for multilayer h-BN films should be comparable to those of a freestanding h-BN layer.

Lateral Heterostructures of Graphene and h-BN with Atomic Lattice Coherence and Tunable Rotational Order

In-plane heterostructures of graphene and hexagonal boron nitride (h-BN) exhibit exceptional properties, which are highly sensitive to the structure of the alternating domains. Nevertheless, achieving accurate control over their structural properties, while keeping a high perfection at the graphene-h-BN boundaries, still remains a challenge. Here, the growth of lateral heterostructures of graphene and h-BN on Rh(110) surfaces is reported. The choice of the 2D material, grown firstly, determines the structural properties of the whole heterostructure layer, allowing to have control over the rotational order of the domains. The atomic-scale observation of the boundaries demonstrates a perfect lateral matching. In-plane heterostructures floating over an oxygen layer have been successfully obtained, enabling to observe intervalley scattering processes in graphene regions. The high tuning capabilities of these heterostructures, along with their good structural quality, even around the boundaries, suggest their usage as test beds for fundamental studies aiming at the development of novel nanomaterials with tailored properties.

Graphene oxide:Fe2O3 nanocomposites for photodetector applications: experimental and ab initio density functional theory study

In this report, a GO:Fe₂O₃ nanocomposite was synthesized using a one-step covalent attachment approach using a sol-gel technique. The optical absorbance, photoconductive, photo-capacitive, and electrical properties were obtained using spectroscopy, and current-voltage (I-V) measurements. An enhanced optical absorbance with corresponding band gap reduction is observed when Fe₂O₃ nanoparticles are incorporated in GO. A corresponding enhanced photoconductance in the order of ×10¹ was observed due to the impact of band gap narrowing. The enhanced photoconductivity and photo-capacitance can be attributed to energy and charge transfer between GO and Fe atoms, leading to the generation of photo-induced excitons. Density function theory calculations indicate increased charge transfer when GO is doped with Fe-O atoms, which is consistent with experimental data. The observed results could potentially enable the use of GO:Fe₂O₃ nanocomposites for photodetectors and other optoelectronic applications.

Hexagonal-borocarbonitride (h-BCN) based heterostructure photocatalyst for energy and environmental applications: A review

Formulation of heterojunction with remarkable high efficiency by utilizing solar light is promising to synchronously overcome energy and environmental crises. In this concern, hexagonal-borocarbonitride (h-BCN) based Z-schemes have proved potential candidates due to their spatially separated oxidation and reduction sites, robust light-harvesting ability, high charge pair migration and separation, and strong redox ability. H-BCN has emerged as a hotspot in the research field as a metal-free photocatalyst with a tunable bandgap range of 0-5.5 eV. The BCN photocatalyst displayed synergistic benefits of both graphene and boron nitride. Herein, the review demonstrates the current state-of-the-art in the Z-scheme photocatalytic application with a special emphasis on the predominant features of their photoactivity. Initially, fundamental aspects and various synthesis techniques are discussed, including thermal polymerization, template-assisted, and template-free methods. Afterward, the reaction mechanism of direct Z-scheme photocatalysts and indirect Z-scheme (all-solid-state) are highlighted. Moreover, the emerging Step-scheme (S-scheme) systems are briefly deliberated to understand the charge transfer pathway mechanism with an induced internal electric field. This review critically aims to comprehensively summarize the photo-redox applications of various h-BCN-based heterojunction photocatalysts including CO₂ photoreduction, H₂ evolution, and pollutants degradation. Finally, some challenges and future direction of h-BCN-based Z-scheme photocatalyst in environmental remediation are also proposed.

In Situ Growth Dynamics of Uniform Bilayer Graphene with Different Twisted Angles Following Layer-by-Layer Mode

Synthesis of large-area uniform bilayer graphene (BLG) with different twisted angles has gathered extensive interest but remains a challenge, hindered by the ubiquitous layer-plus-island growth and the uncontrollable layer rotation. Herein, using real-time surface imaging, film uniformity and stacking structures in BLG were well controlled by a two-step carbon segregation on Ni(111) films following the layer-by-layer growth mode. The aligned first graphene layers formed at 850 °C through a thermodynamics-limit process, followed by decreasing temperatures to grow the second layers, eventually enabling the extremely uniform 15°-twisted BLG at 790 °C and AB-stacked BLG at 720 °C, respectively. Essentially, the growth dynamics is perceived to determine that for the different stacking structures, nonaligned second layers are more kinetically preferable than aligned ones at relatively high temperatures, but the case reverses at low temperatures. This work conveys a fundamental dynamic understanding of the controllable integration of uniform BLG and tuning stacking structures.

Atomically Precise Incorporation of BN-Doped Rubicene into Graphene Nanoribbons

Substituting heteroatoms and non-benzenoid carbons into nanographene structure offers a unique opportunity for atomic engineering of electronic properties. Here we show the bottom-up synthesis of graphene nanoribbons (GNRs) with embedded fused BN-doped rubicene components on a Au(111) surface using on-surface chemistry. Structural and electronic properties of the BN-GNRs are characterized by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with CO-terminated tips supported by numerical calculations. The periodic incorporation of BN heteroatoms in the GNR leads to an increase of the electronic band gap as compared to its undoped counterpart. This opens avenues for the rational design of semiconducting GNRs with optoelectronic properties.

Combined effect of stacking and magnetic field on the electrical conductivity and heat capacity of biased trilayer BP and BN

In this paper, the Kubo-Greenwood formula based on the tight-binding model is used to investigate the effects of the bias voltage and magnetic field on the electrical conductivity and heat capacity of the trilayer BP and BN with energy-stable stacking structures. The results show that electronic and thermal properties of the selected structures can be significantly modified by external fields. The position and intensity of DOS peaks and the band gap of selected structures are affected by the external fields. When external fields increases above critical value, the band gap decreases to zero and semiconductor-metallic transition occurs. The results show that the thermal properties of the BP and BN structures are zero in TZ temperature region and increase by temperature above TZ. The increasing rate for thermal properties depends on the stacking configuration and changes with the bias voltage and magnetic field. In the presence of the stronger field, the TZ region decreases below 100 K. Compared to the BP structures, the BN types with larger band gap has smaller electrical conductivity which can be increased in order to 3L-BP by applying the stronger magnetic field or bias voltage. These results are interesting for the future development of nanoelectronic devices.

Unveiling the Role of Charge Transfer in Enhanced Electrochemical Nitrogen Fixation at Single-Atom Catalysts on BX Sheets (X = As, P, Sb)

To tune single-atom catalysts (SACs) for effective nitrogen reduction reaction (NRR), we investigate various transition metals implanted on boron-arsenide (BAs), boron-phosphide (BP), and boron-antimony (BSb) using density functional theory (DFT). Interestingly, W-BAs shows high catalytic activity and excellent selectivity with an insignificant barrier of only 0.05 eV along the distal pathway and a surmountable kinetic barrier of 0.34 eV. The W-BSb and Mo-BSb exhibit high performances with limiting potentials of -0.19 and -0.34 V. The Bader-charge descriptor reveals that the charge transfers from substrate to *NNH in the first protonation step and from *NH₃ to substrate in the last protonation step, circumventing a big hurdle in NRR by achieving negative free energy change of *NH₂ to *NH₃. Furthermore, machine learning (ML) descriptors are introduced to reduce computational cost. Our rational design meets the three critical prerequisites of chemisorbing N₂ molecules, stabilizing *NNH, and destabilizing *NH₂ adsorbates for high-efficiency NRR.

Anomalies at the Dirac Point in Graphene and Its Hole-Doped Compositions

We study the properties of the Dirac states in SiC-graphene and its hole-doped compositions employing angle-resolved photoemission spectroscopy and density functional theory. The symmetry-selective measurements for the Dirac bands reveal their linearly dispersive behavior across the Dirac point which was termed as the anomalous region in earlier studies. No gap is observed even after boron substitution that reduced the carrier concentration significantly from 3.7×10^{13}  cm^{-2} in SiC-graphene to 0.8×10^{13}  cm^{-2} (5% doping). The anomalies at the Dirac point are attributed to the spectral width arising from the lifetime and momentum broadening in the experiments. The substitution of boron at the graphitic sites leads to a band renormalization and a shift of the Dirac point towards the Fermi level. The internal symmetries appear to be preserved in SiC-graphene even after significant boron substitutions. These results suggest that SiC-graphene is a good platform to realize exotic science as well as advanced technology where the carrier properties like concentration, mobility, etc., can be tuned keeping the Dirac fermionic properties protected.

First-Principles Study of Electronic Properties of Substitutionally Doped Monolayer SnP3

SnP3 has a great prospect in electronic and thermoelectric device applications due to its moderate band gap, high carrier mobility, absorption coefficients, and dynamical and chemical stability. Doping in two-dimensional semiconductors is likely to display various anomalous behaviors when compared to doping in bulk semiconductors due to the significant electron confinement effect. By introducing foreign atoms from group III to VI, we can successfully modify the electronic properties of two-dimensional SnP3. The interaction mechanism between the dopants and atoms nearby is also different from the type of doped atom. Both Sn7BP24 and Sn7NP24 systems are indirect bandgap semiconductors, while the Sn7AlP24, Sn7GaP24, Sn7PP24, and Sn7AsP24 systems are metallic due to the contribution of doped atoms intersecting the Fermi level. For all substitutionally doped 2D SnP3 systems considered here, all metallic systems are nonmagnetic states. In addition, monolayer Sn7XP24 and Sn8P23Y may have long-range and local magnetic moments, respectively, because of the degree of hybridization between the dopant and its adjacent atoms. The results complement theoretical knowledge and reveal prospective applications of SnP3-based electrical nanodevices for the future.

Permeability of boron- and nitrogen-doped graphene nanoflakes for protium/deuterium ions

Two-dimensional (2D) monolayer nanomaterials are the thinnest possible membranes with interesting selective permeation characteristics. Among two-dimensional materials, graphenes and hexagonal boron nitride (h-BN) are the most promising membrane materials, which can even allow the separation of proton isotopes. The current work aims at understanding the higher reported permeability of h-BN by sequential doping of B and N atoms in graphene nanoflakes. The kinetic barriers were calculated with two different models of graphenes; coronene and dodecabenzocoronene via zero-point energy calculations at the transition state for proton permeability. The lower barriers for h-BN are mainly due to boron atoms. The trends of kinetic barriers are B < BN < N-doped graphenes. The permeation selectivity of graphene models increases with doping. Our studies suggest that boron-doped graphene models show an energy barrier of 0.04 eV for the permeation of proton, much lower than that of the model graphene and h-BN sheet, while nitrogen-doped graphenes have a very high energy barrier up to 7.44 eV for permeation. Therefore, boron-doped graphene models are suitable candidates for proton permeation. Moreover, the presence of carbon atoms in the periphery of BN sheets has significant negative effects on the permeation of proton isotopes, an unexplored dimension of the remote neighboring effect in 2-D materials. This study illustrates the need for permeation study through other hetero-2D surfaces, where interesting hidden chemistry is still unexplored.

Two-dimensional (2D) monolayer nanomaterials are the thinnest possible membranes with interesting selective permeation characteristics.

Electron Transport of the Nanojunctions of (BN) n (n = 1-4) Linear Chains: A First-Principles Study

We applied the density functional theory and nonequilibrium Green's function method (DFT + NEGF) to investigate the relationship between the conductance and chain length in the stretching process, the asymmetric coupling of contact points, and the influence of positive and negative biases on the electron transport properties of the nanojunctions formed by the coupling of (BN) _n (n = 1-4) linear chains and Au(100)-3 × 3 semi-infinite electrodes. We find that the BN junction has the lowest stability and the (BN)₂ junction has the highest stability. Under zero bias, the equilibrium conductance decreases as the chain length increases; p_x and p_y orbitals play a leading role in electron transport. In the bias range of -1.6 to 1.6 V, the current of the (BN) _n (n = 1-4) linear chains increases linearly with increasing voltage. Under the same bias voltage, (BN)₁ has the largest current, so its electron transport property is the best. The rectification effect reflects the asymmetry of the structure of BN linear chains themselves and the asymmetry of coupling with the Au electrode surfaces at both ends. With the chain length increasing, the transmission spectrum near E _f is suppressed, the tunneling current decreases, and the rectification ratio increases. (BN)₄ molecular junctions have the largest rectification ratio, reaching 13.32 when the bias voltage is 1.6 V. Additionally, the Au-N strong coupling is more conducive to the electron transport of the molecular chain than the Au-B weak coupling. Our calculations provide an important theoretical reference for the design and development of BN linear-chain nanodevices.

Investigating size effects in graphene-BN hybrid monolayers: a combined density functional theory-molecular dynamics study

We combine Density Functional Theory (DFT) and classical Molecular Dynamics (MD) simulations to study graphene-boron nitride (BN) hybrid monolayers spanning a wide range of sizes (from 2 nm to 100 nm). Our simulations show that the elastic properties depend on the fraction of BN contained in the monolayer, with Young's modulus values decreasing as the BN concentration increases. Furthermore, our calculations reveal that the mechanical properties are weakly anisotropic. We also analyze the evolution of the stress distribution during our MD simulations. Curiously, we find that stress does not concentrate on the graphene-BN interface, even though fracture always starts in this region. Hence, we find that fracture is caused by the lower strength of C-N and C-B bonds, rather than by high local stress values. Still, in spite of the fact that the weaker bonds in the interface region become a lower fraction of the total as size increases, we find that the mechanical properties of the hybrid monolayers do not depend on the size of the structure, for constant graphene/BN concentrations. Our results indicate that the mechanical properties of the hybrid monolayers are independent of scale, so long as the graphene sheet and the h-BN nanodomain decrease or increase proportionately.

Introduction of Near to Far Infrared Range Direct Band Gaps in Graphene: A First Principle Insight

Lack of band gaps hinders application of graphene in the fields like logic, optoelectronics, and sensing despite its various extraordinary properties. In this work, we have done systematic investigations on direct band gap opening in graphene by hydrogenation and fluorination of carbon vacancies using the density functional theory computational approach. We have seen that although a carbon vacancy (void) opens an indirect band gap in graphene, it also creates unwanted mid gap (trap) states, which is attributed to unbound orbitals of the nearest unsaturated carbon atoms at the vacant site. The unsaturated carbon atoms and corresponding trap states can degrade the stability of graphene and create band gaps particularly for large size vacancies. We have proposed that hydrogenation or fluorination of the unsaturated carbon atoms near the vacant site helps in disappearance of the trap states while contributing to promising direct band gaps in graphene. The opened band gap is tunable in the infrared regime and persists for different sizes and densities of hydrogenated or fluorinated patterns. In addition, we have also found that the proposed approach is thermodynamically favorable as well as stable. This keeps the planar nature of the graphene monolayer, despite creation of defects and subsequent functionalization, thereby making it useful for 2D material-based electronics, optoelectronics, and sensing applications.

Heterojunction of N/B/RGO and g-C3N4 anchored magnetic ZnFe2O4@ZnO for promoting UV/Vis-induced photo-catalysis and in vitro toxicity studies

To promote the low photocatalytic efficiency caused by the recombination of electron/hole pairs and widen the photo-response wavelength window, ZnFe₂O₄@ZnO-N/B/RGO and ZnFe₂O₄@ZnO-C₃N₄ ternary heterojunction nanophotocatalysts were designed and successfully prepared through a sol-gel technique. In comparison to bare ZnFe₂O₄ and ZnO, the ZnFe₂O₄-ZnO@N/B/RGO and ZnFe₂O₄@ZnO-C₃N₄ ternary products showed highly improved photocatalytic properties in the degradation of methyl orange (MO) under ultra-violet (UV) and visible light irradiation. Various physicochemical properties of the photocatalysts were evaluated through field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM) techniques. The observations indicated that the ternary heterojuncted ZnFe₂O₄@ZnO-N/B/RGO absorbs lower energy visible light wavelengths, which is an enhancement in the photocatalytic properties of ZnFe₂O₄@ZnO loaded on reduced graphene oxide (RGO) nanosheets and graphite-like carbon nitride (g-C₃N₄). This gives the catalyst photo-Fenton degradation properties.

Mechanical and electronic properties of boron nitride nanosheets with graphene domains under strain

Hybrid structures comprised of graphene domains embedded in larger hexagonal boron nitride (h-BN) nanosheets were first synthesized in 2013. However, the existing theoretical investigations on them have only considered relaxed structures. In this work, we use Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations to investigate the mechanical and electronic properties of this type of nanosheet under strain. Our results reveal that the Young's modulus of the hybrid sheets depends only on the relative concentration of graphene and h-BN in the structure, showing little dependence on the shape of the domain or the size of the structure for a given concentration. Regarding the tensile strength, we obtained higher values using triangular graphene domains. We find that the studied systems can withstand large strain values (between 15% and 22%) before fracture, which always begins at the weaker C–B bonds located at the interface between the two materials. Concerning the electronic properties, we find that by combining composition and strain, we can produce hybrid sheets with band gaps spanning an extensive range of values (between 1.0 eV and 3.5 eV). Our results also show that the band gap depends more on the composition than on the external strain, particularly for structures with low carbon concentration. The combination of atomic-scale thickness, high ultimate strain, and adjustable band gap suggests applications of h-BN nanosheets with graphene domains in wearable electronics.

We investigate the mechanical and electronic properties of hBN nanosheets with graphene domains under strain. We find that the structures withstand large strain values and present highly adjustable band gaps, ranging from 1.0 to 3.5 eV.

Two-dimensional blue phosphorene–BAs vdW heterostructure with optical and photocatalytic properties: a first-principles study

In this work, we investigated the electronic, optical and photocatalytic properties of a blue phosphorene–BAs (BlueP–BAs) vdW heterostructure using first-principles calculations.

Structural and electronic properties of a novel two-dimensional Janus Pd4S3Se3 monolayer controllable by electric field and strain engineering

In this work, we investigate the structural and electronic properties of a newly-discovered two-dimensional Janus Pd4S3Se3 monolayer, as well as its controllable structural and electronic properties under an electric field and strain engineering using first-principles calculations.

Boron Carbon Nitride Thin Films: From Disordered to Ordered Conjugated Ternary Materials

We present an innovative method for the synthesis of boron carbon nitride thin film materials in a simple furnace setup, using commonly available solid precursors and relatively low temperature compared to previous attempts. The as-prepared structural and optical properties of thin films are tuned via the precursor content, leading to a sp²-conjugated boron nitride–carbon nitride mixed material, instead of the commonly reported boron nitride–graphene phase segregation, with tunable optical properties such as band gap and fluorescence.

Boron-Doped Reduced Graphene Oxide with Tunable Bandgap and Enhanced Surface Plasmon Resonance

Graphene and its hybrids are being employed as potential materials in light-sensing devices due to their high optical and electronic properties. However, the absence of a bandgap in graphene limits the realization of devices with high performance. In this work, a boron-doped reduced graphene oxide (B-rGO) is proposed to overcome the above problems. Boron doping enhances the conductivity of graphene oxide and creates several defect sites during the reduction process, which can play a vital role in achieving high-sensing performance of light-sensing devices. Initially, the B-rGO is synthesized using a modified microwave-assisted hydrothermal method and later analyzed using standard FESEM, FTIR, XPS, Raman, and XRD techniques. The content of boron in doped rGO was found to be 6.51 at.%. The B-rGO showed a tunable optical bandgap from 2.91 to 3.05 eV in the visible spectrum with an electrical conductivity of 0.816 S/cm. The optical constants obtained from UV-Vis absorption spectra suggested an enhanced surface plasmon resonance (SPR) response for B-rGO in the theoretical study, which was further verified by experimental investigations. The B-rGO with tunable bandgap and enhanced SPR could open up the solution for future high-performance optoelectronic and sensing applications.

First-Principles Study of 3d Transition-Metal-Atom Adsorption onto Graphene Embedded with the Extended Line Defect

A type of line defect (LD) composed of alternate squares and octagons (4-8) as the basic unit is currently an experimentally available topological defect in the graphene lattice, which brings some interesting modifications to the magnetic and electronic properties of graphene. The transitional-metal (TM) atoms adsorb on graphene with a line defect (4-8), and they show interesting and attractive structural, magnetic, and electronic properties. For different TMs such as Fe, Co, Mn, Ni, and V, the complex systems show different magnetic and electronic properties. The TM atoms can spontaneously adsorb at quadrangular sites, forming a metallic atomic chain along LD on graphene. The most stable configuration is the hollow site of a regular tangle. The TMs (TM = Co, Fe, Mn, Ni, V) tend to form extended metal lines, showing a ferromagnetic (FM) ground state. For the Co, Fe, and V atoms, the system is half-metal. The spin-α electron is insulating, while the spin-β electron is conductive. For the Mn and Ni atoms, Mn-LD and Ni-LD present a spin-polarized metal; for the Fe atom, Fe-LD shows a semimetal with Dirac cones. For Fe and V atoms, both Fe-LD and V-LD show spin-polarized half-metallic properties. And its spin-α electron is conducting, while the spin-β electron is insulating. Different TMs adsorbing on a graphene nanoribbon forming the same stable configurations of metal lines show different electronic properties. The adsorption of TMs induces magnetism and spin polarization. These metal lines have potential applications in spintronic devices and work as a quasi-one-dimensional metallic wire, which may form building blocks for atomic-scale electrons with well-controlled contacts at the atomic level.

Recent progress of TMD nanomaterials: phase transitions and applications

Transition metal dichalcogenides (TMDs) show wide ranges of electronic properties ranging from semiconducting, semi-metallic to metallic due to their remarkable structural differences. To obtain 2D TMDs with specific properties, it is extremely important to develop particular strategies to obtain specific phase structures. Phase engineering is a traditional method to achieve transformation from one phase to another controllably. Control of such transformations enables the control of properties and access to a range of properties, otherwise inaccessible. Then extraordinary structural, electronic and optical properties lead to a broad range of potential applications. In this review, we introduce the various electronic properties of 2D TMDs and their polymorphs, and strategies and mechanisms for phase transitions, and phase transition kinetics. Moreover, the potential applications of 2D TMDs in energy storage and conversion, including electro/photocatalysts, batteries/supercapacitors and electronic devices, are also discussed. Finally, opportunities and challenges are highlighted. This review may further promote the development of TMD phase engineering and shed light on other two-dimensional materials of fundamental interest and with potential ranges of applications.

Investigation on the mechanical properties and fracture phenomenon of silicon doped graphene by molecular dynamics simulation

Silicon doping is an effective way to modulate the bandgap of graphene that might open the door for graphene to the semiconductor industries. However, the mechanical properties of silicon doped graphene (SiG) also plays an important role to realize its full potential application in the electronics industry. Electronic and optical properties of silicon doped graphene are well studied, but, our understanding of mechanical and fracture properties of the doped structure is still in its infancy. In this study, molecular dynamics (MD) simulations are conducted to investigate the tensile properties of SiG by varying the concentration of silicon. It is found that as the concentration of silicon increases, both fracture stress and strain of graphene reduces substantially. Our MD results also suggest that only 5% of silicon doping can reduce the Young's modulus of graphene by ∼15.5% along the armchair direction and ∼13.5% along the zigzag direction. Tensile properties of silicon doped graphene have been compared with boron and nitrogen doped graphene. The effect of temperature, defects and crack length on the stress–strain behavior of SiG has also been investigated. Temperature studies reveal that SiG is less sensitive to temperature compared to free stranding graphene, additionally, increasing temperature causes deterioration of both fracture stress and strain of SiG. Both defects and cracks reduce the fracture stress and fracture strain of SiG remarkably, but the sensitivity to defects and cracks for SiG is larger compared to graphene. Fracture toughness of pre-cracked SiG has been investigated and results from MD simulations are compared with Griffith's theory. It has been found that for nano-cracks, SiG with larger crack length deviates more from Griffith's criterion and the degree of deviation is larger compared to graphene. Fracture phenomenon of pre-cracked SiG and the effect of strain rate on the tensile properties of SiG have been reported as well. These results will aid the design of SiG based semiconducting nanodevices.

Variations of fracture stress and Young’s modulus of graphene with the concentration of silicon doping.

Defect-enriched tunability of electronic and charge-carrier transport characteristics of 2D borocarbonitride (BCN) monolayers from ab initio calculations

Development of inexpensive and efficient photo- and electro-catalysts is vital for clean energy applications. Electronic and structural properties can be tuned by the introduction of defects to achieve the desirable electrocatalytic activity. Using first-principles molecular dynamics simulations, the structural, dynamical, and electronic properties of 2D borocarbonitride (h-BCN) sheets have been investigated, highlighting how anti-site defects in B and N doped graphene significantly influence the bandgap, and thereby open up new avenues to tune the chemical behavior of the 2D sheets. In the present work, all of the monolayers investigated display direct bandgaps, which reduce from 0.99 eV to 0.24 eV with increasing number of anti-site defects. The present results for the electronic structure and findings for bandgap engineering open up applications of BCN monolayers in optoelectronic devices and solar cells. The influence of the anti-site distribution of B and N atoms on the ultra-high hole/electron mobility and conductivity is discussed based on density functional theory coupled with the Boltzmann transport equation. The BCN defect monolayer is predicted to have carrier mobilities three times higher than that of the pristine sheet. The present results demonstrate that BN doped graphene monolayers are likely to be useful in the next-generation 2D field-effect transistors.

Defective graphene domains in boron nitride sheets

Novel two-dimensional materials have emerged as hybrid structures that combine graphene and hexagonal boron nitride (h-BN) domains. During their growth process, structural defects such as vacancies and change of atoms connectivity are unavoidable. In the present study, we use first-principle calculations to investigate the electronic structure of graphene domains endowed with a single carbon atom vacancy or Stone-Wales defects in h-BN sheets. The results show that both kinds of defects yield localized states within the bandgap. Alongside this change in the bandgap configuration, it occurs a splitting of the spin channels in such a way that electrons with up and down spins populate different energy levels above and below the Fermi level, respectively. Such a spin arrangement is associated to lattice magnetization. Stone-Wales defects solely point to the appearance of new intragap levels. These results demonstrated that vacancies could significantly affect the electronic properties of hybrid graphene/h-BN sheets. Graphical Abstract A Boron-Nitride sheet doped with a vacancy endowed Carbon domain.

Analysis of pseudo jahn-teller distortion based on natural bond orbital theory: Case study for silicene

Ground state (GS) instability of nondegenerate molecules in high symmetric structures is understood through Pseudo Jahn-Teller mixing of the electronic states through the vibronic coupling. The general approach involves setting up of a Pseudo Jahn-Teller (PJT) problem wherein one or more symmetry allowed excited states couple to the GS to create vibrational instability along a normal mode. This faces two major complications namely (1) estimating the adiabatic potential energy surfaces for the excited states which are often difficult to describe in case the excited states have charge-transfer or multi-excitonic (ME) character and (2) finding out how many such excited states (all satisfying the symmetry requirements for vibronic coupling) of increasing energies need to be coupled with the GS for a particular PJT problem. An analogous alternative approach presented here for the well-known case of symmetry breaking of planar (D_6h ) hexasilabenzene (Si₆ H₆ ) to the buckled (D_3d ) structure involves identifying the second-order donor-acceptor, hyperconjugative interactions (E² _i → j ) that stabilize the distorted structure. Following the recent work of Nori-Shargh and Weinhold, one observes that the orbitals involved in the vibronic coupling between the S₀ /S_n states and those for the donor (filled)-acceptor (empty) interactions are identical. In fact, deletion of any particular pair of E² _i → j interaction creates vibrational instability in the buckled structure and as a corollary, deleting it for the planar structure removes its instability. The one-to-one correlation between the natural bond orbital theory and PJT theory assists in an intuitive identification of the relevant (few) excited states from a manifold of computed ones that cause symmetry breaking by vibronic coupling. © 2019 Wiley Periodicals, Inc.

Stacking stability of C2N bilayer nanosheet

In recent years, a 2D graphene-like sheet: monolayer C₂N was synthesized via a simple wet-chemical reaction. Here, we studied the stability and electronic properties of bilayer C₂N. According to a previous study, a bilayer may exist in one of three highly symmetric stacking configurations, namely as AA, AB and AB′-stacking. For the AA-stacking, the top layer is directly stacked on the bottom layer. Furthermore, AB- and AB′-stacking can be obtained by shifting the top layer of AA-stacking by a/3-b/3 along zigzag direction and by a/2 along armchair direction, respectively, where a and b are translation vectors of the unit cell. By using first-principles calculations, we calculated the stability of AA, AB and AB′-stacking C₂N and their electronic band structure. We found that the AB-stacking is the most favorable structure and has the highest band gap, which appeared to agree with previous study. Nevertheless, we furthermore examine the energy landscape and translation sliding barriers between stacking layers. From energy profiles, we interestingly found that the most stable positions are shifted from the high symmetry AB-stacking. In electronic band structure details, band characteristic can be modified according to the shift. The interlayer shear mode close to local minimum point was determined to be roughly 2.02 × 10¹² rad/s.

DFT study of CO adsorption on nitrogen/boron doped-graphene for sensor applications

We have performed a Density Functional study of the CO adsorption in B-doped, N-doped and BN-co-doped graphene considering a coronene based model in order to estimate the applications of this systems as CO-sensor. Different monosubstituted, disubstituted and trisubstituted alternatives of combining these two heteroatoms in a substitutional chemical doping and the influence of the relative positions of the heteroatoms are analyzed. In this study, the stability selectivity for CO adsorption and the change in the electric properties for the presence of this molecule, have been evaluated through the calculation of binding energy, CO-adsorption's energy and the gap HOMO-LUMO change due to CO adsorption. The results indicated that, even though all the configurations were stables and was confirmed a CO physical adsorption in all of them, the relative positions of Nitrogen and Boron gave different stabilities and different responses to the CO adsorption. Since monosubstituted Boron-coronene was the second in stability respect to pristine coronene, showed the highest CO adsorption energy and was also the second highest ∆(∆_HOMO-LUMO) value, this structure could be potentially a good CO-sensor.

Borocarbonitrides as Metal-Free Catalysts for the Hydrogen Evolution Reaction

Hydrogen generation by water splitting is clearly a predominant and essential strategy to tackle the problems related to renewable energy. In this context, the discovery of proper catalysts for electrochemical and photochemical water splitting assumes great importance. There is also a serious intent to eliminate platinum and other noble metal catalysts. To replace Pt by a non-metallic catalyst with desirable characteristics is a challenge. Borocarbonitrides, (B_x C_y N_z ) which constitutes a new class of 2D material, offer great promise as non-metallic catalysts because of the easy tunability of bandgap, surface area, and other electronic properties with variation in composition. Recently, B_x C_y N_z composites with excellent electrochemical and photochemical hydrogen generation activities have been found, especially noteworthy being the observation that B_x C_y N_z with a carbon-rich composition or its nanocomposites with MoS₂ come close to Pt in electrocatalytic properties, showing equally good photochemical activity.

Tunable, Multifunctional Ceramic Composites via Intercalation of Fused Graphene Boron Nitride Nanosheets

Ternary two-dimensional (2D) materials such as fused graphene-boron nitride (GBN) nanosheets exhibit attractive physical and tunable properties far beyond their parent structures. Although these features impart several multifunctional properties in various matrices, a fundamental understanding on the nature of the interfacial interactions of these ternary 2D materials with host matrices and the role of their individual components has been elusive. Herein, we focus on intercalated GBN/ceramic composites as a model system and perform a series of density functional theory calculations to fill this knowledge gap. Propelled by more polarity and negative Gibbs free energy, our results demonstrate that GBN is more water-soluble than graphene and hexagonal boron nitride (h-BN), making it a preferred choice for slurry preparation and resultant intercalations. Further, a chief attribute of the intercalated GBN/ceramic is the formation of covalent C-O and B-O bonds between the two structures, changing the hybridization of GBN from sp² to sp³. This change, combined with the electron release in the vicinity of the interfacial regions, leads to several nonintuitive mechanical and electrical alterations of the composite such as exhibiting higher young's modulus, strength, and ductility as well as sharp decline in the band gap. As a limiting case, though both tobermorite ceramic and h-BN are wide band gap materials, their intercalated composite becomes a p-type semiconductor, contrary to intuition. These multifunctional features, along with our fundamental electronic descriptions of the origin of property change, provide key guidelines for synthesizing next generation of multifunctional bilayer ceramics with remarkable properties on demand.

Recent progress in synthesis, properties, and applications of hexagonal boron nitride-based heterostructures

Featuring an absence of dangling bonds, large band gap, low dielectric constant, and excellent chemical inertness, atomically thin hexagonal boron nitride (h-BN) is considered an ideal candidate for integration with graphene and other 2D materials. During the past years, great efforts have been devoted to the research of h-BN-based heterostructures, from fundamental study to practical applications. In this review we summarize the recent progress in the synthesis, novel properties, and potential applications of h-BN-based heterostructures, especially the synthesis technique. Firstly, various approaches to the preparation of both in-plane and vertically stacked h-BN-based heterostructures are introduced in detail, including top-down strategies associated with exfoliation transfer processes and bottom-up strategies such as chemical vapor deposition (CVD)-based growth. Secondly, we discuss some novel properties arising in these heterostructures. Several promising applications in electronic and optoelectronic devices are also reviewed. Finally, we discuss the main challenges and possible research directions in this field.

Interfacial engineering in graphene bandgap

Graphene exhibits superior mechanical strength, high thermal conductivity, strong light-matter interactions, and, in particular, exceptional electronic properties. These merits make graphene an outstanding material for numerous potential applications. However, a graphene-based high-performance transistor, which is the most appealing application, has not yet been produced, which is mainly due to the absence of an intrinsic electronic bandgap in this material. Therefore, bandgap opening in graphene is urgently needed, and great efforts have been made regarding this topic over the past decade. In this review article, we summarise recent theoretical and experimental advances in interfacial engineering to achieve bandgap opening. These developments are divided into two categories: chemical engineering and physical engineering. Chemical engineering is usually destructive to the pristine graphene lattice via chemical functionalization, the introduction of defects, doping, chemical bonds with substrates, and quantum confinement; the latter largely maintains the atomic structure of graphene intact and includes the application of an external field, interactions with substrates, physical adsorption, strain, electron many-body effects and spin-orbit coupling. Although these pioneering works have not met all the requirements for electronic applications of graphene at once, they hold great promise in this direction and may eventually lead to future applications of graphene in semiconductor electronics and beyond.

Realization of a half-metallic state on bilayer WSe2 using doping transition metals (Cr, Mn, Fe, Co, Ni) in its interlayer

The structural, electronic and magnetic properties of Cr, Mn, Fe, Co and Ni-doped bilayer WSe₂ are predicted by using first principles calculations. The doped transition-metal (TM) atoms show a covalent-binding with the nearest Se atoms. The calculated electronic structures reveal that the TM Cr, Mn, Fe and Co-doped bilayer WSe₂ exhibits a half-metallic character with a 100% spin polarization at the Fermi level, and the reason is ascribed to the strong hybridization peak between the transition metals and the parent W and Se atoms. The Ni-doped bilayer WSe₂ is still a semiconductor with nonmagnetism. The Fe-doped system has a robust stability of half-metallicity because there are three connected states peak spanning the Fermi level. The doping of Cr, Mn, Fe and Co atoms leads to a prominent total magnetism (0.93-3.65 [Formula: see text] moment per unit cell), and an induced ∼0.3 [Formula: see text] moment in parent W atoms is found in addition to the main contribution of TM atomic magnetism (0.71-3.33 [Formula: see text] moment per atom). The predicted Cr, Mn, Fe and Co-doped bilayer WSe₂ should be the candidate materials for spintronic devices due to their magnetic and half-metallic nature.

Band gap opening in stanene induced by patterned B-N doping

Stanene is a quantum spin Hall insulator and a promising material for electronic and optoelectronic devices. Density functional theory (DFT) calculations are performed to study the band gap opening in stanene by elemental mono-doping (B, N) and co-doping (B-N). Different patterned B-N co-doping is studied to change the electronic properties of stanene. A patterned B-N co-doping opens the band gap in stanene and its semiconducting nature persists under strain. Molecular dynamics (MD) simulations are performed to confirm the thermal stability of such a doped system. The stress-strain study indicates that such a doped system is as stable as pure stanene. Our work function calculations show that stanene and doped stanene have a lower work function than graphene and thus are promising materials for photocatalysts and electronic devices.

The unique Raman fingerprint of boron nitride substitution patterns in graphene

Boron nitride-substituted graphene (BNsG) two-dimensional structures are new materials of wide technological interest due to the rich variety of electronic structures and properties they can exploit. The ability to accurately characterize them is key to their future success. Here we show, by means of ab initio simulations, that the vibrational Raman spectra of such compounds are extremely sensitive to substitution motifs and concentration, and that each structure has unique and distinct features. This result can be useful as a guide for the optimization of production processes.

Electronic and thermoelectric properties of atomically thin C3Si3/C and C3Ge3/C superlattices

The nanostructuring of graphene into superlattices offers the possibility of tuning both the electronic and thermal properties of graphene. Using classical and quantum mechanical calculations, we have investigated the electronic and thermoelectric properties of the atomically thin superlattice of C₃Si₃/C (C₃Ge₃/C) formed by the incorporation of Si (Ge) atoms into graphene. The bandgap and phonon thermal conductivity of C₃Si₃/C (C₃Ge₃/C) are 0.54 (0.51) eV and 15.48 (12.64) W m^-1 K^-1, respectively, while the carrier mobility of C₃Si₃/C (C₃Ge₃/C) is 1.285 × 10⁵ (1.311 × 10⁵) cm² V^-1 s^-1 at 300 K. The thermoelectric figure of merit for C₃Si₃/C (C₃Ge₃/C) can be optimized via the tuning of carrier concentration to obtain the prominent ZT value of 1.95 (2.72).

Germanium quantum dot/nitrogen-doped graphene nanocomposite for high-performance bulk heterojunction solar cells

This study presents the successful synthesis of a novel nanocomposite, namely a germanium quantum dot/nitrogen-doped graphene nanocomposite (GeQD/NGr), and its use in the modification of the photoactive medium of bulk heterojunction solar cells (BHJ-SCs). The nanocomposite was prepared in two sequential steps. Firstly, a reduced graphene oxide-germanium oxide nanocomposite (rGO-GeO₂) was synthesized by microwave-assisted solvothermal reaction. The second step involved simultaneous N-doping of graphene and reduction of GeO₂ to obtain the GeQD/NGr nanocomposite by thermal treatment. The nanocomposite consists of highly crystalline, spherical shaped GeQDs with a mean diameter of 4.4 nm affixed on the basal planes of NGr sheets. Poly-3-hexylthiophene (P3HT), (6-6)phenyl-C60-butyric acid methyl ester (PCBM) and GeQD/NGr were used as the photoactive layer blend in the fabrication of BHJ-SCs. Enhanced short-circuit current density (J_sc) and fill factor (FF) is derived from the incorporation of the GeQD/NGr nanocomposite in the active layer. The nanocomposite in the active layer blend serves to ensure effective charge separation and transportation to the respective electrodes. Consequently, an improvement of up to 183% in the power conversion efficiency is achieved in the BHJ-SCs by the GeQD/NGr modification.

Germanium quantum dot/nitrogen-doped graphene, a novel nanocomposite, is successfully synthesized and utilized in the photoactive medium of organic solar cells.

C-doping into h-BN at low annealing temperature by alkaline earth metal borate for photoredox activity

BCN (boron carbon nitride) nanosheets are promising photocatalyst materials for solar fuel production by visible light-driven water splitting and CO₂ reduction due to their tunable band gap and unique properties. C-doping into h-BN by thermal annealing makes possible the preparation of BCN nanosheets with photocatalytic activity under visible light irradiation, but it generally requires a very high temperature (>1250 °C) from the thermodynamic viewpoint. Here, we report a new method to prepare BCN nanosheets with visible light-photocatalytic activity at lower annealing temperature (1000 °C) than equilibrium by adding alkaline earth metal compounds. BCN nanosheets formed in borate melt show a clear layered structure, tunable bandgap and photocatalytic activity for water splitting and CO₂ reduction under visible light illumination. This provides a direction for doping other elements into h-BN at low annealing temperature by alkaline earth metal borates.

The alkaline earth metal borates promote the formation of C-doped h-BN nanosheets at low annealing temperature towards robust photocatalytic activity.

NanoVelcro: Theory of Guided Folding in Atomically Thin Sheets with Regions of Complementary Doping

Folding has been commonly observed in two-dimensional materials such as graphene and monolayer transition metal dichalcogenides. Although interlayer coupling stabilizes these folds, it provides no control over the placement of the fold, let alone the final folded shape. Lacking nanoscale "fingers" to externally guide folding, control requires interactions engineered into the sheets that guide them toward a desired final folded structure. Here we provide a theoretical framework for a general methodology toward this end: atomically thin 2D sheets are doped with patterns of complementary n-type and p-type regions whose preferential adhesion favors folding into desired shapes. The two-colorable theorem in flat-foldable origami ensures that arbitrary folding patterns are in principle accessible to this method. This complementary doping method can be combined with nanoscale crumpling (by, for example, passage of 2D sheets through holes) to obtain not only control over fold placements but also the ability to distinguish between degenerate folded states, thus attaining nontrivial shapes inaccessible to sequential folding.

Synthesis of High-Quality Graphene and Hexagonal Boron Nitride Monolayer In-Plane Heterostructure on Cu-Ni Alloy

Graphene/hexagonal boron nitride (h-BN) monolayer in-plane heterostructure offers a novel material platform for both fundamental research and device applications. To obtain such a heterostructure in high quality via controllable synthetic approaches is still challenging. In this work, in-plane epitaxy of graphene/h-BN heterostructure is demonstrated on Cu-Ni substrates. The introduction of nickel to copper substrate not only enhances the capability of decomposing polyaminoborane residues but also promotes graphene growth via isothermal segregation. On the alloy surface partially covered by h-BN, graphene is found to nucleate at the corners of the as-formed h-BN grains, and the high growth rate for graphene minimizes the damage of graphene-growth process on h-BN lattice. As a result, high-quality graphene/h-BN in-plane heterostructure with epitaxial relationship can be formed, which is supported by extensive characterizations. Photodetector device applications are demonstrated based on the in-plane heterostructure. The success will have important impact on future research and applications based on this unique material platform.

Borocarbonitrides, BxCyNz: Synthesis, Characterization, and Properties with Potential Applications

Borocarbonitrides, B_xC_yN_z, constitute a new family of layered two-dimensional materials and can be considered to be derived from graphene. They can be simple composites containing graphene and BN domains or more complex materials possessing B-C and C-N bonds besides B-N and C-C bonds. Properties of these materials depend on the composition, and the method of synthesis, wherein one can traverse from the insulating end (BN) to the conducting end (graphene). In this article, we present an up-to-date review of the various aspects of borocarbonitrides including synthesis, characterization and properties. Some of the properties have potential applications, typical of them being in gas adsorption and energy devices such as supercapacitors, fuel cells and batteries. Performance of borocarbonitrides as catalysts in the electrochemical hydrogen evolution reaction is impressive. It is noteworthy that with certain compositions on borocarbonitrides, field-effect transistors can be fabricated.

Piezoresistive Effect in Plasma-Doping of Graphene Sheet for High-Performance Flexible Pressure Sensing Application

This paper presents a straightforward plasma treatment modification of graphene with an enhanced piezoresistive effect for the realization of a high-performance pressure sensor. The changes in the graphene in terms of its morphology, structure, chemical composition, and electrical properties after the NH₃/Ar plasma treatment were investigated in detail. Through a sufficient plasma treatment condition, our studies demonstrated that plasma-treated graphene sheet exhibits a significant increase in sensitivity by one order of magnitude compared to that of the unmodified graphene sheet. The plasma-doping introduced nitrogen (N) atoms inside the graphene structure and was found to play a significant role in enhancing the pressure sensing performance due to the tunneling behavior from the localized defects. The high sensitivity and good robustness demonstrated by the plasma-treated graphene sensor suggest a promising route for simple, low-cost, and ultrahigh resolution flexible sensors.

Atomistic understanding of the lateral growth of graphene from the edge of an h-BN domain: towards a sharp in-plane junction

The in-plane combination of graphene (G) and hexagonal-boron nitride (h-BN) leads to lateral h-BN/G heterostructures, which are promising candidates for novel two-dimensional electronics. The quality of the interface between G and h-BN domains is crucial for the device performance. By comprehensive first-principles calculations, we explore the heteroepitaxial growth of graphene along the edge of an h-BN domain on a Cu(111) surface and compare it with that on a Cu(111) terrace. We find that the graphene nucleation site strongly depends on the chemical potential of carbon and predeposited h-BN coverage. Under the suitable carbon concentration and coverage of h-BN, graphene mainly grows along the h-BN edge, leading to a sharp and straight h-BN/G interface. Our results provide insightful knowledge to synthesize well-defined h-BN/G and other lateral heterostructures.

A DFT study on the central-ring doped HBC nanographenes

Nanographenes (NGs) are a segment of graphene whose dangling bonds are saturated with hydrogen atoms, introducing different properties and promising applications. Here we investigate the electronic, thermodynamic, optical, and structural properties of four C₃₆X₃Y₃H₁₈ NGs (X=B, and Al; and Y=N, and P) based on the density functional theory calculations. It was mainly found that 1) BN-NG is planar molecule and the others are buckybowl-shaped ones, 2) The bowl-to-bowl inversion Gibbs free energies (ΔG^#) of buckybowl shaped NGs are very huge and the rate constant is very small, hindering the inversion, 3) The relative energetic stability order based on the standard enthalpy of formation (ΔH_f^°) is as BN>AlN>BP>AlP, which the BN, and AlN doped NGs are stable at room temperature but the BP and AlP doped ones are instable, 4) The electrical conductivity order of magnitude is inverse of that of stability, 5) An exciton binding energy is predicted in the range of 0.57-0.75eV for the NGs which corresponds to Frenkel exciton type, 6) the NGs are not soluble in organic solvent in agreement with the experimental results and is partially soluble in water solvent with Gibbs free energy of solvation (ΔG_solv) in the range of -6.1 to -10.1kcal/mol.