Graphene Analogues Research Articles

Epitaxial growth of Bi, Sb, and Sn

Graphene analogs composed of Bi, Sb, and Sn, respectively, are predicted to be great candidates to realize the quantum spin Hall effect at high temperatures and have attracted intensive research interest in recent years. However, their structural and electronic properties are greatly affected by substrates. Here, we epitaxially grow Bi, Sb, and Sn overlayers on various substrates. We observed the formation of Au–Bi alloy on Au(111) substrates, while α-Bi was formed on the TaIrTe4, TiSe2and Cr2Ge2Te6 substrates. Large-scale thin films of α-Bi, α-Sb and β-Sn can be prepared on the TiSe2 substrates due to the high quality of the substrates with very few defects. The lattice of the Sb films is slightly compressed on the TiSe2 substrates, due to the interfacial interaction. α-Sn transitions to β-Sn on the TiSe2 substrates with increasing Sn coverages. Our work is very helpful for tuning the structural and electronic properties of epitaxial Bi, Sb, and Sn films via proper substrates.

Observation of Zitterbewegung in photonic microcavities

We present and experimentally study the effects of the photonic spin–orbit coupling on the real space propagation of polariton wavepackets in planar semiconductor microcavities and polaritonic analogues of graphene. In particular, we demonstrate the appearance of an analogue Zitterbewegung effect, a term which translates as ‘trembling motion’ in English, which was originally proposed for relativistic Dirac electrons and consisted of the oscillations of the centre of mass of a wavepacket in the direction perpendicular to its propagation. For a planar microcavity, we observe regular Zitterbewegung oscillations whose amplitude and period depend on the wavevector of the polaritons. We then extend these results to a honeycomb lattice of coupled microcavity resonators. Compared to the planar cavity, such lattices are inherently more tuneable and versatile, allowing simulation of the Hamiltonians of a wide range of important physical systems. We observe an oscillation pattern related to the presence of the spin-split Dirac cones in the dispersion. In both cases, the experimentally observed oscillations are in good agreement with theoretical modelling and independently measured bandstructure parameters, providing strong evidence for the observation of Zitterbewegung.

Quantum Spin Hall Effect Seen in Graphene Analog

Quantum Spin Hall Effect Seen in Graphene Analog

Large-scale thallene film with emergent spin-polarized states mediated by tin intercalation for spintronics applications

The quantum effects confined in the ultimate two-dimensional limit are able to address the challenges and provide advances in high-performance spintronic devices. In the paper we show a successful strategy to enrich the electronic properties of thallene, a new honeycomb analogue of graphene, through the interface engineering, which opens a great potential of thallene as an advanced spintronics material. While the thallene has been experimentally realized recently on NiSi2/Si(111) substrate, there remains a lack of attractive electronic properties due to the strong thallene-substrate coupling. This challenge is addressed here through the decoration of thallene/NiSi2 interface by Sn interlayer, which allows to eliminate the thallene-substrate coupling and produce a high-quality large-scale thallene monolayer with exotic electron bands demonstrating colossal spin-polarization just above the Fermi level. It is demonstrated that appropriate electron doping or external electric field are enable the spin-transport regime. The discovered band structure regulation boosts the functionality of the 2D-Tl Xene and makes it a highly attractive material for spintronics applications.

Visualizing defect dynamics by assembling the colloidal graphene lattice

Graphene has been under intense scientific interest because of its remarkable optical, mechanical and electronic properties. Its honeycomb structure makes it an archetypical two-dimensional material exhibiting a photonic and phononic band gap with topologically protected states. Here, we assemble colloidal graphene, the analogue of atomic graphene using pseudo-trivalent patchy particles, allowing particle-scale insight into crystal growth and defect dynamics. We directly observe the formation and healing of common defects, like grain boundaries and vacancies using confocal microscopy. We identify a pentagonal defect motif that is kinetically favoured in the early stages of growth, and acts as seed for more extended defects in the later stages. We determine the conformational energy of the crystal from the bond saturation and bond angle distortions, and follow its evolution through the energy landscape upon defect rearrangement and healing. These direct observations reveal that the origins of the most common defects lie in the early stages of graphene assembly, where pentagons are kinetically favoured over the equilibrium hexagons of the honeycomb lattice, subsequently stabilized during further growth. Our results open the door to the assembly of complex 2D colloidal materials and investigation of their dynamical, mechanical and optical properties.

Use of waste to wealth process derived sustainable silica-rich graphene analogues to provide enhanced corrosion resistance properties for coatings on carbon steel, exposed to marine environments

Here, we have demonstrated the effects of the application of silica-rich green-graphene analogues (SRGA) mixed epoxy coating on carbon steel in terms of corrosion resistance and other properties. The anticorrosion performance of SRGA/EP coatings with various concentrations (0.05 wt%, 0.1 wt%, and 0.5 wt% SRGA) on carbon steel in 3.5 wt% NaCl was investigated using the potentiodynamic polarization technique (PDP) and electrochemical impedance spectroscopy (EIS). The surface morphologies of pure epoxy (EP) and SRGA/EP-coated specimens were investigated by scanning electron microscopy (SEM). Incorporating the SRGA/EP coating approach on carbon steel pipes can improve the thermal stability, hydrophobicity, and surface finish of the produced composite coatings. The corrosion inhibition efficiency of 0.1 wt% SRGA/EP-coated carbon steel specimens was 99 % higher than uncoated carbon steel specimens. The thermal stability of 0.1 wt% SRGA/EP coating was improved by 5–7 % compared to pure EP coating. The synthesized SRGA/EP coating showed acceptable uniform distribution on the carbon steel. The average roughness (Ra) of SRGA/EP-coated carbon steel was 67.8 % lower compared to the uncoated ones and 37.3 % lower than the pure EP-coated carbon steel specimens. These materials, derived from green processes can be suitable replacements for traditional toxic chemicals employed for corrosion-resistant coating in carbon steel surfaces of water pipes. Apart from the benefits of use in performance, SRGA application can help environmental -social-governance (ESG) compliance for the paints and coatings industry.

Chemical Sensors Based on Graphene and 2D Graphene Analogs

AbstractThe outbreak of the global pandemic has aroused significant attention from the public for healthy living environments. From this point of view, chemical sensors are crucial since these devices or actuators have diverse applications, such as environmental monitoring, food safety, industry, and healthcare. The development of chemical sensors may substitute human senses and precisely identify unspecified substances or discriminate materials accurately. For the implementation of chemical sensors utilized in daily life, there are requirements such as portability, low cost, low power consumption, high selectivity, and sensitivity. The most adequate materials are 2D materials that exactly agree with the described conditions. 2D materials have been studied for sensor applications owing to their unique material characteristics specialized for detecting particular substances. High surface to volume ratio or numerous reaction sites are representative physical properties of 2D materials. Furthermore, high carrier mobility is a typical feature of these substances appropriate for manufacturing advanced chemical sensors. Herein, the history and recent advances of 2D material‐based chemical sensors along with a description of perspectives and future challenges are introduced. This review provides a guideline for preparing chemical sensors based on 2D materials as next‐generation sensing devices.

Frequency-dependent surface wave suppression at the Dirac point of an acoustic graphene analog

The dispersion of bound acoustic surface waves over hexagonal lattices of resonant cavities has been shown to be analogous to the dispersion of charge transport in carbon graphene. Of particular interest is the frequency range close to the acoustic Dirac point where novel physics is predicted to occur. In this study, we measure the dispersion curves of a single-layer acoustic graphene analogue with high resolution one-dimensional spatial scansand show how the curves can be suppressed (near and at the Dirac point) by strong variations in the impedance boundary conditions between the free field and surface wave regimes under certain experimental conditions. By systematically varying these impedance boundary conditions using different surface wave excitation techniques, we demonstrate that increased Rayleigh scattering and diffractive excitation can increase the dispersed surface wave pressure amplitude to an extent that the impedance-based wave suppression is circumvented. The improved conditions for observing acoustic Dirac points for two samples with two distinct operational frequency ranges are reported. The single-layer acoustic graphene analogue results discussed here are important for advancing the field of acoustic twistronics.

Two-dimensional-Ti3C2 magnetic nanocomposite for targeted cancer chemotherapy.

Introduction: Cervical cancer is the leading cause of cancer-related death in women, so novel therapeutic approaches are needed to improve the effectiveness of current therapies or extend their activity. In recent decades, graphene analogs, such as Mxene, an emerging class of two-dimensional (2D) graphene analogs, have been drawing considerable attention based on their intrinsic physicochemical properties and performance as potential candidates for tumor therapy, particularly for therapeutic purposes. Here we explored the targeted drug delivery in cervical cancer in in vivo model. Mxene-based nanocarriers are not able to be precisely controlled in cancer treatment. Method: To solve this problem, the titanium carbide-magnetic core-shell nanocarrier (Ti3C2-Fe3O4@SiO2-FA) is also developed to provide synergetic anticancer with magnetic controlling ability along with pH-responsive drug release. A xenograft model of the cervix was used to investigate the effects of Cisplatin alone, or in combination with Ti3C2@FA and Ti3C2@ Fe3O4@SiO2-FA, on tumor growth following histological staining for evaluation of necrosis. Result and Discussion: A significant tumor-growth suppression effect is shown when the Ti3C2-Fe3O4@SiO2-FA nanocarrier is magnetically controlled Cisplatin drug release. It reveals a synergistic therapeutic efficacy used in conjunction with pharmaceuticals (p < .001). According to the in vivo study, the Ti3C2@FA@Cisplatin nanocomposite exhibits less tumor growth than the drug alone or Ti3C2@FA@Cisplatin via increasing necrosis effect (p < .001). Through this study, Mxene nanosheets are expanded for biomedical applications, not only through the fabrication of biocompatible magnetic Mxene nanocomposite but also through the development of functionalization strategies that enable the magnetic Ti3C2 nanocomposite to load high levels of Cisplatin for cervical cancer treatment (242.5%). Hence, Ti3C2-Fe3O4@SiO2-FA nanocarriers would be promising candidates to improve cancer treatment efficiency.

Effect of different exfoliation solvents on the saturable absorption properties of germanene and silicene nanosheets prepared by the liquid-phase exfoliation

Germanene and silicene, as graphene analogs of germanium and silicon, have similar structures and properties to graphene, exhibiting exciting nonlinear optical absorption properties. Herein, 2D germanium nanosheets and 2D silicon nanosheets were successfully prepared by liquid-phase exfoliation method using ethanol, isopropanol, and N-methylpyrrolidone as exfoliation solvents, respectively. The dual-arm detection technique was used to systematically research the saturable absorption properties of the nanosheets prepared with different exfoliation solvents from the same material under the excitation of a picosecond pulsed laser. The nonlinear experiment results show that the saturable absorption properties of 2D germanium nanosheets and 2D silicon nanosheets are affected by different exfoliation solvents, and these influences from different exfoliation solvents have their advantages and disadvantages. In addition, the difference in saturable absorption properties of germanium nanosheets and silicon nanosheets under the same experimental conditions is compared. The saturable absorption behavior of germanium nanosheets in the near-infrared band is better than that in the visible band, while the silicon nanosheets have stronger saturable absorption behavior in the visible band. Both germanium nanosheets and silicon nanosheets exhibit superior SA properties, which have a wide range of application prospects in generating ultrashort pulses in ultrafast lasers as saturable absorbers. Our work provides a new idea for the study of nonlinear absorption properties of 2D materials and provides a reference and basis for further optimization and improvement of the properties parameters of saturable absorbers. Additionally, it inspires further research on the nonlinear absorption properties of semiconductor materials.

2D boron nitride supported Cu2O promotes photocatalytic nitrogen fixation at normal temperature and pressure

Boron nitride (BN) semiconductors, as graphene analogues, have attracted extensive attention in the field of photocatalysis due to their unique physical and chemical properties.

Few-monolayer Ga film on Si(111): illusive gallenene formation and localization instead of superconductivity

Si(111) substrates crucially affect the superconducting properties of few-atomic-layer Ga films and formation of the gallenene analogue of graphene.

Metallene-related materials for electrocatalysis and energy conversion.

As a member of graphene analogs, metallenes are a class of two-dimensional materials with atomic thickness and well-controlled surface atomic arrangement made of metals or alloys. When utilized as catalysts, metallenes exhibit distinctive physicochemical properties endowed from the under-coordinated metal atoms on the surface, making them highly competitive candidates for energy-related electrocatalysis and energy conversion systems. Significantly, their catalytic activity can be precisely tuned through the chemical modification of their surface and subsurface atoms for efficient catalyst engineering. This minireview summarizes the recent progress in the synthesis and characterization of metallenes, together with their use as electrocatalysts toward reactions for energy conversion. In the Synthesis section, we pay particular attention to the strategies designed to tune their exposed facets, composition, and surface strain, as well as the porosity/cavity, defects, and crystallinity on the surface. We then discuss the electrocatalytic properties of metallenes in terms of oxygen reduction, hydrogen evolution, alcohol and acid oxidation, carbon dioxide reduction, and nitrogen reduction reaction, with a small extension regarding photocatalysis. At the end, we offer perspectives on the challenges and opportunities with respect to the synthesis, characterization, modeling, and application of metallenes.

First-principles study of surface modification of CuSe

Original bulk phases of two-dimensional atomic crystal materials are layered. However, a few relevant researches show that some of two-dimensional material crystals have non-layered bulk phases. In this work we investigate monolayer CuSe which is non-layered, belonging in a new kind of honeycomb graphene analogue. Monolayer CuSe is not suitable for application in electronic devices because of its metallic nature. In order to find new two-dimensional atomic crystal materials with excellent performance suitable for application in electronic devices, we change CuSe from metal to semiconductor through external atom modification. The first principles study of density functional theory is conducted to ascertain the energy band structure of monolayer CuSe after second periodic atoms have been added to the top, center and bridge sites. The characteristics of monolayer CuSe with addition of Li or B atoms are studied, including energy band structure, the density of states, differential charge density, and crystal orbital Hamiltonian population. The results show that after adding Li atoms to CuSe, the CuSe transforms from metallic to semiconductive property at all three positions, and Li atom is more easily to be modified in the hexagonal center of CuSe, with band gap being about 1.77 eV, the Fermi level biased towards the top of the valence band. The CuSe with addition of Li atoms exhibits a p-type semiconductor property, so it is a direct bandgap semiconductor. Adding B atom to the top of Cu atom can also make CuSe semiconductive, with a band gap of about 1.2 eV, the conduction band minimum at the &lt;i&gt;K&lt;/i&gt; point, and the valence band maximum at the &lt;i&gt;Γ&lt;/i&gt; point. The CuSe with addition of B atoms belongs in an indirect band gap semiconductor, and the Fermi energy level is biased towards the conduction band minimum, exhibiting the characteristics of an n-type semiconductor. According to the results of differential charge density and crystal orbital Hamiltonian population, the B atom is bound to the top of the monolayer CuSe with the B-Se polar covalent bond. The first principle study reveals the realization of metal-to-semiconductor transition from monolayer CuSe to Cu&lt;i&gt;X&lt;/i&gt;Se (&lt;i&gt;X&lt;/i&gt; = Li, B), and the calculation results also show that CuSe with addition of Li atoms or B atoms is likely to be used in future electronic devices.

2D Functionalized Germananes: Synthesis and Applications.

In the realm of 2D layered materials, the monoelemental group 14 Xene, germanene, as the germanium analog of graphene, has emerged as the next prospective candidate. Preceded by silicon, germanium is widely used in the semiconductor industry; thus, germanene is deemed compatible with existing semiconductor technologies. Germanene consists of mixed sp2 -sp3 -hybridized networks in a buckled hexagonal honeycomb structure. Chemical exfoliation of Zintl phases, such as CaGe2 , specifically the topotactical deintercalation in acidic media, removes the alkaline earth metal ions Ca2+ , giving rise to layered germanane (germanene with the Ge centers covalently saturated with terminal hydrogen atoms). Diverse variants of functionalized germananes (with covalent group(s) termination) can be obtained by varying the topotactical deintercalation precursors, elevating the game with limitless functionalization possibilities for customizable properties or new functionalities. The preparation of Zintl phases to the details of functionalized and modified germananes and their properties, and the additional exfoliation step to achieve mono- or few-layer germananes, are comprehensively covered. The progress and challenges of 2D functionalized germananes in optoelectronics, catalysis, energy conversion and storage, sensors, and biomedical areas are reviewed. This review provides insight into designing and exploring this class of atomically thin semiconductors in realizing future nanoarchitectonics.

Synthesis and characterization of mesoporous vanadium sulfides as environmental catalysts for the cycloaddition of CO2 with 2-(phenoxymethyl)oxirane) and oxidation reactions

Metal sulfide is a vital species of compound semiconductor materials, whose metallic ions are in mono-, bi-, or maybe in multi-form. Considering such materials, layered transition metal sulfide (LTMS) including layered transition metal dichalcogenides (LTMDs) like VS2 and VS4 (also called patronite mineral) has attracted growing interest. Moreover, it can be regarded as graphene analogs due to its large interlayer spacing and high theoretical specific capacity, enabling such materials to be applied in different fields i.e. photoelectric staffs, electro-catalysis phenomena, Li-containing batteries, and energy storage usages. Herein, a practical synthetic protocol is designated to construct mesoporous vanadium sulfides (VS2 and VS4) with controlled morphologies from VS2 (Flower-like), VS4 (Urchin-like), VS4 (Microsphere), and VS2 (Nanosheet assemblies) via adjusting the molar ratio of vanadium acetylacetonate and L-cysteine using a one-step solvothermal method. The catalytic activity of vanadium sulfides as an environmental catalyst has been considered for cycloaddition reaction of CO2 and 2-(phenoxymethyl)oxirane), oxidation of dibenzyl sulfide, and 1-phenylethan-1-ol. The prepared mesoporous vanadium sulfides have a higher surface area than the previously reported ones. The results and analysis revealed that the catalytic behavior of vanadium sulfides significantly depends on physical features such as morphology and specific surface area. The structure of the prepared materials was studied using a variety of characterization techniques: FTIR, XRD, TGA, BET, FE-SEM, EDX, and X-ray mapping

The Covalent Functionalization of Surface‐Supported Graphene: An Update

AbstractIn the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high‐performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

The Covalent Functionalization of Surface-Supported Graphene: An Update.

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

Advances in low dimensional and 2D materials

This special issue is focused on the advances in low-dimensional and 2D materials. 2D materials have gained much consideration recently due to their extraordinary properties. Since the isolation of single-layer graphene in Novoselov et al. [Science 306, 666–669 (2004)], the work on graphene analogs of 2D materials has progressed rapidly across the scientific and engineering fields. Over the last ten years, several 2D materials have been widely explored for technological applications. Moreover, the existence in nature of layered crystallographic structures where exotic properties emerge when the thickness is reduced to a few monolayers has enlarged the field of low-dimensional (i.e., quasi-2D) materials. The special topic aims to collect the recent advances in technologically relevant low-dimensional and 2D materials, such as graphene, layered semiconductors (e.g., MoS2, WS2, WSe2, PtSe2, MoTe2, Black-P, etc.), MXenes, and topological insulators, such as Bi2Te3, Sb2Te3, etc.). There is an urgent need for material innovations for the rapid development of the next technologies based on these materials. The scope of this special topic is to address recent trends in 2D materials and hybrid structures and their widespread applications in device technology and measurement.

Exchange Bias State at the Crossover to 2D Ferromagnetism.

The inherent malleability of 2D magnetism provides access to unconventional quantum phases, in particular those with coexisting magnetic orders. Incidentally, in a number of materials, the magnetic state in the bulk undergoes a fundamental change when the system is pushed to the monolayer limit. Therefore, a competition of magnetic states can be expected in the crossover region. Here, an exchange bias state is observed at the crossover from 3D antiferromagnetism to 2D ferromagnetism driven by the number of monolayers in the metalloxene GdSi2. The material constitutes a stack of alternating monolayers of Gd and silicene, the Si analogue of graphene. The exchange bias manifests itself as a shift of the hysteresis loop signifying coupling of magnetic systems, as evidenced by magnetization studies. Two features distinguish the phenomenon: (i) it is intrinsic, i.e. it is detected in an individual compound; (ii) the exchange bias field, 1.5 kOe, is unusually high, which is conducive to applications. The results suggest magnetic derivatives of 2D-Xenes to be prospective materials for ultracompact spintronics.