Strain‐tunable electronic properties and optical properties of Hf₂CO₂ MXene

Abstract

Two-dimensional materials have been extensively applied because of their unusual electronic, mechanical, and optical properties. In this paper, the electronic structure and optical properties of Hf 2 CO 2 MXene under biaxial and uniaxial strains are investigated by the Heys-Scuseria-Ernzerhof (HSE06) method. Monolayer Hf 2 CO 2 can sustain stress up to 6.453 N/M for biaxial strain and 3.072 N/M for uniaxial strain. Monolayer Hf 2 CO 2 undergoes the transition from semiconductor to metal under −12% strain whether it is under biaxial or uniaxial strain. With the increasing biaxial compressive strain, the blue shift of Hf-d, O-p, and C-p orbitals in valence band maximum results in the metallization of monolayer Hf 2 CO 2 , while the red shift of Hf-d and O-p orbitals in conduction band minimum results in the metallization of monolayer Hf 2 CO 2 with increasing uniaxial compressive strain. The analysis of optical properties indicates that uniaxial strain weakens the reflectivity and refractive index of monolayer Hf 2 CO 2 in the visible-light range. In addition, the effective mass and the charge distribution under biaxial and uniaxial strains are also explored.

Optically Active MXenes in Van der Waals Heterostructures

“…[ 98 ] Interestingly, a similar effect upon applying strain was observed for the key absorption coefficient peak of Hf 2 CO 2 , located at 3.9 eV. [ 96 ] This peak experienced a blueshift when subjected to uniaxial compressive or tensile strain. In contrast, biaxial compressive or tensile strain caused a redshift.…”

“…[9] In this context, Li et al investigated the influence of strain on the optical properties of Hf 2 CO 2 monolayers, which are known to be semiconducting with an indirect bandgap. [96] The bandgap of unstrained Hf 2 CO 2 underwent an indirect-to-direct transition from 1.75 to 2.24 eV upon applying 13% of biaxial tensile strain. However, Hf 2 CO 2 transformed from a semiconductor to a metal when applying 12% of biaxial or uniaxial compressive strain (Figure 2g).…”

Band alignment type I, II transformations in Hf2CO2/MoS2 heterostructures using biaxial strain, external electric field, and interlayer coupling: a first principal investigation

“…From previous theoretical investigations, it is known that under applied biaxial compressive strain the band gap of Hf 2 CO 2 decreases while under tensile strain it increases in the case of small deformation values. 38 On the contrary, in the case of applied biaxial compressive strain, the band gap of MoS 2 firstly increases but after crossing the value of 2% the band gap value decreases due to restructuring of the band structure, while in the case of biaxial tensile strain, the band gap gradually decreases. 67 The same tendencies are observed in the case of the heterostructure (see Fig.…”

“…Some representatives from the MXene family have been successfully synthesized, [33][34][35] but the fabrication of Hf 2 CO 2 has not been reported yet; however, theoretical calculations show the possibility of exfoliation from its parent phases. 36 The electronic and optical properties of the Hf 2 CO 2 monolayer were shown to be significantly dependent on the applied strain 37,38 making this monolayer a promising candidate for straintronics elements. At the same time, MoS 2 monolayer has already proven itself as a promising element in different nanoelectronic devices, from elements of wearable electronics to energy storage applications, 39 due to many strikingly highlighted properties.…”

Electronic and Optical Properties of Atomic-Scale Heterostructure Based on MXene and MN (M = Al, Ga): A DFT Investigation

“…In particular, the Cr 2 TiC 2 monolayer behaves as a novel bipolar antiferromagnetic semiconductor showing opposite spin directions, which can be used as antiferromagnetic spin field effect transistor [61]. Hf 2 CO 2 possesses excellent electronic and thermoelectric properties and carrier mobility (about 1531.48 cm 2 /V•s for electrons), suggesting an efficient photocatalyst for water splitting and nano-electronic devices [62][63][64][65][66], and this novel electronic characteristic can even be tuned by external strain [67]. Hf 2 CO 2 is also sensitive to NH 3 , which can sharply enhance electronic conductivity [68].…”