The thermal and electrical properties of the promising semiconductor MXene Hf2CO2

Abstract: In this work, we investigate the thermal and electrical properties of oxygen-functionalized M2CO2 (M = Ti, Zr, Hf) MXenes using first-principles calculations. Hf2CO2 is found to exhibit a thermal conductivity better than MoS2 and phosphorene. The room temperature thermal conductivity along the armchair direction is determined to be 86.25-131.2 Wm-1K-1 with a flake length of 5-100 um, and the corresponding value in the zigzag direction is approximately 42% of that in the armchair direction. Other important thermal properties of M2CO2 are also considered, including their specific heat and thermal expansion coefficients. The theoretical room temperature thermal expansion coefficient of Hf2CO2 is 6.094x10-6 K-1, which is lower than that of most metals. Moreover, Hf2CO2 is determined to be a semiconductor with a band gap of 1.657 eV and to have high and anisotropic carrier mobility. At room temperature, the Hf2CO2 hole mobility in the armchair direction (in the zigzag direction) is determined to be as high as 13.5x103 cm2V-1s-1 (17.6x103 cm2V-1s-1), which is comparable to that of phosphorene. Broader utilization of Hf2CO2 as a material for nanoelectronics is likely because of its moderate band gap, satisfactory thermal conductivity, low thermal expansion coefficient, and excellent carrier mobility. The corresponding thermal and electrical properties of Ti2CO2 and Zr2CO2 are also provided here for comparison. Notably, Ti2CO2 presents relatively low thermal conductivity and much higher carrier mobility than Hf2CO2, which is an indication that Ti2CO2 may be used as an efficient thermoelectric material.

Thermal and Electrical Properties of Semiconductor MXene Hf$_2$CO$_2$: An In-Depth Analysis

The research paper provides a detailed study focusing on the thermal and electrical properties of oxygen-functionalized MXenes, particularly Hf$_2$CO$_2$. The analysis utilizes first-principles calculations to predict these properties and examines the potential of Hf$_2$CO$_2$ in nanoelectronics applications.

MXenes, known for their versatile transition-metal carbide structure, have attracted considerable interest for their diverse applications in fields such as energy storage and electronics. Despite the broad applicability, there has been limited exploration of their thermal and electrical characteristics until now. This study fills this gap by offering comprehensive insights into Hf$_2$CO$_2$, Ti$_2$CO$_2$, and Zr$_2$CO$_2$, each with unique electronic and thermal profiles.

Key Findings

The critical findings from this work revolve around the superior properties of Hf$_2$CO$_2$, which demonstrate significant advantages for nanoelectronics:

• Thermal Conductivity: Hf$_2$CO$_2$ presents remarkable anisotropic thermal conductivity, surpassing materials like MoS$_2$ and phosphorene. Its thermal conductivity along the armchair direction is calculated at 86.25~131.2 W/m·K at room temperature, while the zigzag direction exhibits a conductivity approximately 42% lower. This property could prove beneficial for efficient heat dissipation in compact electronic devices.

• Thermal Expansion: The material displays a low thermal expansion coefficient of 6.094×10$^{-6}$ K$^{-1}$, contributing to structural stability under temperature variations.

• Band Gap and Carrier Mobility: Hf$_2$CO$_2$ exhibits a moderate band gap of 1.657 eV, aligning with the requirements for semiconductor applications. Furthermore, the carrier mobility is notably high and anisotropic, comparable to phosphorene. The hole mobility in the armchair and zigzag directions are calculated as 13.5×10$^3$ cm$^2$/V·s and 17.6×10$^3$ cm$^2$/V·s, respectively.

Comparative Analysis

Contrastive data on Ti$_2$CO$_2$ reveals a lower thermal conductivity yet higher carrier mobility, hinting at its potential as a thermoelectric material. These distinctions highlight Ti$_2$CO$_2$’s advantages where heat conduction is of lesser importance, such as electronic components where thermoelectric efficiency is crucial.

Implications and Future Directions

The findings underscore the promise of Hf$_2$CO$_2$ for next-generation electronic devices, especially given its balanced band gap, satisfactory thermal conductivity, and high carrier mobility. The anisotropic thermal properties facilitate its integration into devices requiring precise thermal management. However, further experimental validation is essential to consolidate the theoretical predictions and explore synthesis techniques for these MXene materials. The synthesis of M$_2$CO$_2$ MXenes appears feasible considering existing methodologies involving etching MAX phases and functionalizing MXenes.

The conclusions also propose potential directions for continued research into MXenes, specifically the pursuit of experimental measurements of their intrinsic properties. With successful synthesis, these materials could profoundly impact nanoelectronic advancements and thermoelectric applications.

Conclusion

In summary, this paper reveals significant insights into the properties of Hf$_2$CO$_2$ MXenes, with implications for their application in electronic and thermoelectric devices. The detailed analysis presents a foundation for future experimental studies and suggests a promising course for exploiting MXenes in various technological arenas.