Optical gaps and excitons in semiconducting transition metal carbides (MXenes)

Ketolainen, Tomi; Karlický, František

doi:10.1039/d2tc00246a

Cited by 24 publications

(36 citation statements)

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“…Carbide MXenes show high conductivity, high oxidation resistance, and easily tunable surface terminations, , which make them potential candidates for energy storage applications, supercapacitors, sensors, carbon capture technologies, , and heterogeneous catalysts. − Studies on MXenes suggest that most titanium-based MXenes without surface functionalization show metallic behavior, , and the electronic properties could be modulated by surface terminations. However, Ti 2 CO 2 shows semiconductor characteristics with an indirect band gap. − …”

Section: Introductionmentioning

confidence: 99%

“…Ti 2 C was shown to be a typical semiconductor system with an electronic band gap of about 0.2 eV . The A-AFM configuration was favored over FM, C-AFM, and G-AFM in a Ti 2 C system, where A-AFM means a ferromagnetic alignment between intralayer Tis and antiferromagnetic ordering among the top and bottom layers, while in the C-type (G-type) structure, spins are arranged antiferromagnetically within each Ti layer and ferromagnetically (antiferromagnetically) ordered between lines of the top and bottom layers. , Recently, Ketolainen et al showed that the ground state of Ti 2 C is an AFM semiconductor; the electronic band gap was calculated to be 0.18 and 0.32 eV using the Perdew–Burke–Ernzerhof (PBE) and the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional, respectively. However, the magnetic ground states can also have FM alignment.…”

Section: Introductionmentioning

confidence: 99%

“…From a theoretical point of view, density functional theory (DFT) calculations have been used to investigate the electronic structures of Ti n +1 C n terminated with F, O, and OH, respectively. Ti 2 CO 2 was predicted to be a semiconductor with an indirect band gap, − , high carrier mobility, ,, high thermodynamic stability, and strong excitonic effect. , Moreover, the pure carbide MXene monolayers are magnetic, while functionalization removes magnetism . In addition, surface functionalization is also a critical factor that modifies the fundamental properties of MXenes. , First-principles calculations of V 2 C showed a metallic character of bare V 2 C, which is preserved for all surface groups .…”

Section: Introductionmentioning

confidence: 99%

“…35 From a theoretical point of view, density functional theory (DFT) calculations have been used to investigate the electronic structures of Ti n+1 C n terminated with F, O, and OH, respectively. Ti 2 CO 2 was predicted to be a semiconductor with an indirect band gap, [25][26][27]36 high carrier mobility, 25,26,37 high thermodynamic stability, 38 and strong excitonic effect. 27,39 Moreover, the pure carbide MXene monolayers are magnetic, while functionalization removes magnetism.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Ti 2 CO 2 was predicted to be a semiconductor with an indirect band gap, [25][26][27]36 high carrier mobility, 25,26,37 high thermodynamic stability, 38 and strong excitonic effect. 27,39 Moreover, the pure carbide MXene monolayers are magnetic, while functionalization removes magnetism. 40 In addition, surface functionalization is also a critical factor that modifies the fundamental properties of MXenes.…”

Section: ■ Introductionmentioning

confidence: 99%

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Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study

Sakhraoui

Karlický

2022

ACS Omega

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The structural, electronic, and magnetic properties of vacancy defect in Ti 2 CO 2 MXene and the effect of strain have been investigated using the density functional tight-binding (DFTB) approach including spin-polarization with Hubbard onsite correction (DFTB + U). The band gap of pure Ti 2 CO 2 is ∼1.3 eV, which decreases to ∼0.4 and ∼1.1 eV in the case of C-and O-vacancies, respectively, i.e., the semiconducting behavior is retained. In contrast, Ti 2 CO 2 undergoes semiconductor-to-metal transition by the introduction of a single Ti-vacancy. This transition is the result of introduced localized states in the vicinity of the Fermi level by the vacancy. Both Ti-and O-vacancies have zero net magnetic moments. Interestingly, the nonmagnetic (NM) ground state of semiconducting Ti 2 CO 2 turns into a magnetic semiconductor by introducing a C-vacancy with a magnetization of ∼2 μ B /cell. Furthermore, we studied the effect of strain on the electronic structure and magnetic properties of Ti-, C-, and O-vacant Ti 2 CO 2 . The nature of the band gap in the presence of single O-vacancy remains indirect in both compression and tensile strain, and the size of the band gap decreases. Compression strain on Ti-vacant Ti 2 CO 2 changes metal into a direct semiconductor, and the metallic character remains under tensile biaxial strain. In opposition, a semiconductor-to-metal transition occurs by applying a compressive biaxial strain on C-vacant Ti 2 CO 2 . We also find that the magnetism is preserved under tensile strain and suppressed under compression strain on V C -Ti 2 CO 2 . Moreover, we show that double C-vacancies maintain magnetism. Our findings provide important characteristics for the application of the most frequent MXene material and should motivate further investigations because experimentally achieved MXenes always contain point defects.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study

Sakhraoui

Karlický

2022

ACS Omega

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Optically Active MXenes in Van der Waals Heterostructures

Purbayanto,

Chandel,

Birowska

et al. 2023

Advanced Materials

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The vertical integration of distinct 2D materials in van der Waals (vdW) heterostructures provides the opportunity for interface engineering and modulation of electronic as well as optical properties. However, scarce experimental studies reveal many challenges for vdW heterostructures, hampering the fine‐tuning of their electronic and optical functionalities. Optically active MXenes, the most recent member of the 2D family, with excellent hydrophilicity, rich surface chemistry, and intriguing optical properties, are a novel 2D platform for optoelectronics applications. Coupling MXenes with various 2D materials into vdW heterostructures can open new avenues for the exploration of physical phenomena of novel quantum‐confined nanostructures and devices. Therefore, the fundamental basis and recent findings in vertical vdW heterostructures composed of MXenes as a primary component and other 2D materials as secondary components are examined. Their robust designs and synthesis approaches that can push the boundaries of light‐harvesting, transition, and utilization are discussed, since MXenes provide a unique playground for pursuing an extraordinary optical response or unusual light conversion features/functionalities. The recent findings are finally summarized, and a perspective for the future development of next‐generation vdW multifunctional materials enriched by MXenes is provided.

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2D Transition Metal Carbides (MXenes) for Third Order Nonlinear Optics: Status and Prospects

Wang

2023

Laser & Photonics Reviews

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The family of 2D transition metal carbides, nitrides, and carbonitrides (MXenes) has attracted an enormous amount of attention due to their tunable optical, electronic, electrochemical, and mechanical properties. Recently, a new branch of MXenes materials research has emerged that is exploring and engineering the intrinsic optical response of MXenes, resulting in compact nonlinear optical (NLO) devices. As a novel 2D materials system, MXenes not only exhibit common advantages of classical 2D materials for NLO applications but also demonstrate their unique superiority, such as high yield and scalable synthesis, good stability, switchable NLO response, etc. Here, a fundamental overview of MXenes nonlinear optics is provided, covering everything from MXenes synthesis to linear and NLO properties and NLO applications. The synthesis method and its influence on the MXenes structures and morphology are discussed, which dominated the linear optics of MXenes. Then, the third‐order NLO properties and carrier dynamics of MXenes, from basic theory to experimental results, are elaborated. Their NLO applications, including ultrashort laser pulse, single‐frequency laser generation, all‐optical phase modulation, wavelength modulation, and passive photonic diodes, are also highlighted. Finally, the current challenges and an outlook for future MXenes NLO research are proposed.

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Optical gaps and excitons in semiconducting transition metal carbides (MXenes)

Abstract: We use time-dependent density functional theory together with the HSE06 hybrid functional to investigate the optical and excitonic properties of two-dimensional transition metal carbides, MXenes. We determine reliable optical gaps,...

Cited by 24 publications

References 55 publications

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study

Optically Active MXenes in Van der Waals Heterostructures

2D Transition Metal Carbides (MXenes) for Third Order Nonlinear Optics: Status and Prospects

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Optical gaps and excitons in semiconducting transition metal carbides (MXenes)

Abstract: We use time-dependent density functional theory together with the HSE06 hybrid functional to investigate the optical and excitonic properties of two-dimensional transition metal carbides, MXenes. We determine reliable optical gaps,...

Cited by 24 publications

References 55 publications

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti2CO2 MXene under Biaxial Strain: A DFTB + U Study

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti2CO2 MXene under Biaxial Strain: A DFTB + U Study

Optically Active MXenes in Van der Waals Heterostructures

2D Transition Metal Carbides (MXenes) for Third Order Nonlinear Optics: Status and Prospects

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Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected Ti₂CO₂ MXene under Biaxial Strain: A DFTB + U Study