• MXene exhibits significant electric conductive variation relying on surface states. • Complete elimination of surface termination boosts up MXene’s electric conductance. • Surface termination coverage predictably determines MXene’s conductive degree. • The largest electric resistance is obtained at ∼ 50 % of surface termination coverage. Two-dimensional (2D) transition metal carbides (MXenes) are promising electron conducting materials. Noticeably, they intrinsically have surface functionality and the control of surface termination has proven robust and efficient for modulating MXenes’ mechanical and optical properties. However, its effects to MXenes’ electronic conduction have rarely been studied. Using nonequilibrium quantum mechanical simulations, here we showed that surface termination engineering can be powerful means of regulating the electric conductance of Ti 3 C 2 T x MXenes. Two extreme fully oxygen-terminated (Ti 3 C 2 O 2 ) and bare (Ti 3 C 2 ) surfaces were considered since oxygen is one of dominant surface terminations of MXenes. We revealed that Ti 3 C 2 are superior electric conductors compared to Ti 3 C 2 O 2 , showing five-times high performance in our system. We further explored this issue by gradually increasing the surface oxygen-terminated degree of the scattering region of Ti 3 C 2 . The conductance underwent an S-like variation, representing significant 7.5-times tunability showing minimum at the oxygen-termination portion of 50%. Ti 3 C 2 O 2 with various surface bareness also exhibited significant and dynamic conduction variation with minimum around 40%, but in a quantitatively different manner due to the use of oxygen-terminated electrodes.

Abstract Large optical nonlinearity at short‐wavelength‐infrared (SWIR) has enabled 2D MXene to be used explosively in ultrafast nonlinear photonics and optoelectronics. Despite the high technological interest in V 4 C 3 MXene in electrochemistry, investigations from a nonlinear photonics perspective have yet to be conducted. Here, the nonlinear optical characteristics of V 4 C 3 MXene at SWIR wavelengths are systemically investigated. First, Z‐scan measurements are performed and the saturated absorption and self‐defocusing properties of V 4 C 3 MXene at both wavelengths of 1560 and 1910 nm are observed. Density functional theory calculation shows metallic characteristics of V 4 C 3 MXene. Based on the saturable absorption properties of V 4 C 3 MXene, a single saturable absorber (SA) operating at both wavelengths of 1560 and 1910 nm is experimentally implemented. Stable mode‐locked pulses of 638 fs pulse duration at 1559.9 nm are produced instantaneously from an erbium‐doped fiber ring cavity using SA. The same SA generates 1.08 ps mode‐locked pulses at 1911.9 nm from the thulium holmium co‐doped fiber ring cavity. This indicates that the operating bandwidth of this realized V 4 C 3 MXene‐based SA could be at least 350 nm. This work strongly suggests that V 4 C 3 MXene can serve as an ultra‐broadband and high‐performance nonlinear optical material platform in the SWIR regions.

• MXene exhibits significant electric conductive variation relying on surface states. • Complete elimination of surface termination boosts up MXene’s electric conductance. • Surface termination coverage predictably determines MXene’s conductive degree. • The largest electric resistance is obtained at ∼ 50 % of surface termination coverage. Two-dimensional (2D) transition metal carbides (MXenes) are promising electron conducting materials. Noticeably, they intrinsically have surface functionality and the control of surface termination has proven robust and efficient for modulating MXenes’ mechanical and optical properties. However, its effects to MXenes’ electronic conduction have rarely been studied. Using nonequilibrium quantum mechanical simulations, here we showed that surface termination engineering can be powerful means of regulating the electric conductance of Ti 3 C 2 T x MXenes. Two extreme fully oxygen-terminated (Ti 3 C 2 O 2 ) and bare (Ti 3 C 2 ) surfaces were considered since oxygen is one of dominant surface terminations of MXenes. We revealed that Ti 3 C 2 are superior electric conductors compared to Ti 3 C 2 O 2 , showing five-times high performance in our system. We further explored this issue by gradually increasing the surface oxygen-terminated degree of the scattering region of Ti 3 C 2 . The conductance underwent an S-like variation, representing significant 7.5-times tunability showing minimum at the oxygen-termination portion of 50%. Ti 3 C 2 O 2 with various surface bareness also exhibited significant and dynamic conduction variation with minimum around 40%, but in a quantitatively different manner due to the use of oxygen-terminated electrodes.

Abstract Large optical nonlinearity at short‐wavelength‐infrared (SWIR) has enabled 2D MXene to be used explosively in ultrafast nonlinear photonics and optoelectronics. Despite the high technological interest in V 4 C 3 MXene in electrochemistry, investigations from a nonlinear photonics perspective have yet to be conducted. Here, the nonlinear optical characteristics of V 4 C 3 MXene at SWIR wavelengths are systemically investigated. First, Z‐scan measurements are performed and the saturated absorption and self‐defocusing properties of V 4 C 3 MXene at both wavelengths of 1560 and 1910 nm are observed. Density functional theory calculation shows metallic characteristics of V 4 C 3 MXene. Based on the saturable absorption properties of V 4 C 3 MXene, a single saturable absorber (SA) operating at both wavelengths of 1560 and 1910 nm is experimentally implemented. Stable mode‐locked pulses of 638 fs pulse duration at 1559.9 nm are produced instantaneously from an erbium‐doped fiber ring cavity using SA. The same SA generates 1.08 ps mode‐locked pulses at 1911.9 nm from the thulium holmium co‐doped fiber ring cavity. This indicates that the operating bandwidth of this realized V 4 C 3 MXene‐based SA could be at least 350 nm. This work strongly suggests that V 4 C 3 MXene can serve as an ultra‐broadband and high‐performance nonlinear optical material platform in the SWIR regions.

Two-dimensional (2D) materials have exceptional mechanical properties that are absent in conventional bulk materials due to their ultra-thin structure with ultra-high surface-to-volume ratio. Despite their great potential both for basic research and applications, however, deep understanding of fundamentally important orientation-dependent mechanical responses of 2D materials have rarely been achieved. In this work, for the first time, we investigate the tensile mechanical response of 2D transition-metal carbides (MXenes) as gradually varying tensile direction by using reactive molecular dynamics simulations. Despite its highly bonded multi-atom-thick structure, MXene proves significantly stretchable (11–17%) for all directions with isotropic stiffness desirable for flexible/wearable applications, while exhibiting unusual characteristic fracture anisotropy. Noticeably, these mechanical features remained qualitatively the same regardless of presence/absence of surface termination. We discover that MXene has always fractured into zigzag-atomic edged fragments regardless of tensile direction and/or surface termination. We reveal the detailed fracture mechanism and propose its generalization to other hexagonal 2D materials with validation for both pristine and surface-hydrogenated graphene nanosheets. Based on these findings, we finally present a physically robust, computationally efficient framework for fast and reliable prediction of MXenes’ unique fracture anisotropy, showing excellent agreement with time-consuming simulation results and suggesting broad applicability to 2D material mechanics.

This study theoretically investigates the optimal filter configuration for separating a quantum key distribution (QKD) channel from classical C-band communication channels in a discrete-variable (DV) QKD-over-dense wavelength division multiplexing (DWDM) communication system with an O-band QKD channel. Three filter configurations are analyzed and compared in terms of quantum bit error rate (QBER), secret key rate (SKR), and fiber link distance: two cascaded 1310-nm bandpass filters, a 1310-nm uniform fiber Bragg grating (FBG) with a 1310-nm circulator, and a 1310-nm apodized FBG with a 1310-nm circulator. The findings reveal that the optical filter configuration incorporating a Gaussian apodized FBG exhibits the best performance with an isolation of ~ 93 dB between 1310 nm and 1550 nm wavelengths. This optimal performance can be attributed to the Gaussian apodization profile, which effectively suppresses spectral side-lobes to enhance channel isolation while maintaining a lower insertion loss compared to the cascaded bandpass filter configuration. For 50 classical WDM channels, the QKD fiber link distance is 35.4 km with a Gaussian apodized FBG, while a configuration incorporating two cascaded 1310-nm bandpass filters yields only 18.3 km. Finally, the impact of adopting a raised-cosine apodized FBG to further increase filter channel isolation is examined. Despite a substantial increase in channel isolation by using a raised-cosine apodized FBG filter, QKD fiber link distance yields negligible improvement for this system with a QKD channel in O-band, although this filter may be highly useful for QKD channels in C- or L-bands.

We demonstrate a polarization maintaining (PM) cladding light striper (CLS) with ultra-low backscattering, which can handle a residual pump power of 100 W. Using our previously proposed a periodically grooved CLS structure with multiple unetched sections of a suitable length, a CLS based on a 20/400 um PM large mode area (LMA), double clad fiber (DCF) was designed and fabricated. A hydrogen fluoride (HF)-free chemical etching technique was used for the fabrication considering fabrication and environmental safety. The pump stripping efficiency was ~98.7% and the backscattering level was ~0.13%. The degradation of the polarization extinction ratio at the CLS output was ~0.2 dB. The degradation of the polarization extinction ratio at the CLS output was only ~0.2 dB.