2D Monoelements. Группа авторов
plasma, which induced simultaneously the condensation of Sb atoms to form multilayer antimonene. The band gap of multilayer antimonene was opened because of the quantum confinement effect and the turbostratic stacking, then producing the orange light emission (610 nm). Like other 2D materials, antimonene flakes can also be grown through the CVD on SiO2 substrates [39]. Sb powders were used as the Sb source, and Ar gas was the carrier gas. The growth of antimonene flakes began at 600°C and maintained for 10 min. The obtained flakes showed various shapes, including nanoribbon, hexagon, and trapezoid. The antimonene flakes were very stable in air even when heated by a hot plate below 250°C. Moreover, ultrathin Sb films were alternatively grown on the topological insulators (such as Bi2Te2Se and Bi2Se3) by a thermal effusion cell [40, 41].
2.4 Applications of Antimonene
2.4.1 Nonlinear Optics
As an excellent nonlinear absorption material, antimonene has broadband nonlinear optical response, high photothermal efficiency, strong Kerr nonlinearity, low saturable intensity, high two-photon absorption coefficient, and large cross-section, offering the potential nonlinear optical applications in all-solid-state lasers, fiber lasers, optical switchers, optical modulators, and optical thresholders [42–47].
Wang et al. first reported the passively Q-switched Nd3+ solid-state lasers using few-layer antimonene peeled off by the LPE as the saturable absorber (SA) [42]. With antimonene/quartz as the passively Q-switcher, the laser operations were realized at 946, 1,064 nm in Nd:YAG crystal with pulse widths of 209, 129 ns and peak powers of 1.48, 1.77 W, while the laser emission of Nd:YVO4 crystal generated at 1,342 nm with pulse width and peak power of 48 ns and 28.17 W, respectively. By fitting the saturable absorption results of nanosecond laser pulses, the saturable intensities of antimonene were obtained to be 0.43 MW/cm2 at 532 nm and 0.53 MW/cm2 at 1064 nm. In this work, the 1,342 nm Nd:YVO4 laser achieved the best results, including the shortest pulse width (48 ns), the highest peak power (28.17 W), and the largest single pulse energy (1.36 μJ). The following drawbacks often occurred in passive Q-switching, including the degradation, failed saturable absorber, and inaccurate modification of repetition rate. To overcome the drawbacks in passive Q-switching, Wang et al. devised an actively Q-switched fiber laser with an antimonene-based all-optical modulator (AOM) as a Q-switcher [43]. The antimonene nanosheets fabricated by the LPE were deposited onto a 10 μm microfiber, which was then employed to devise an AOM with a fiber-type Michelsom interferometer (MI) due to the obvious photothermal effect of antimonene. The antimonene-based AOM exhibited a large phase modulation capacity with a conversion efficiency of 0.049 π mW−1, and at the same time, it achieved the intensity modulation with large modulation depth of 25 dB. Also, this AOM showed a long-term stability with only 8.2% decline of phase conversion efficiency after 1 month (Figure 2.7a). The obtained active Q-switching pulses possessed a microsecond duration (the rise time constant of 3.2 ms) and tunable repetition rate ranging from 0.96 to 6.64 kHz (Figure 2.7b).
Using the strong Kerr nonlinearity of antimonene, Song et al. devised a new type of optical device based on few-layer antimonene (FLA)-decorated microfiber, which was operated both as an all-optical Kerr switcher and an all-optical wavelength converter [46]. The FLA-based Kerr switcher featured a high extinction ratio of 12 dB with a long-time stability, which could be used to realize the process of controlling light by light in optical communication systems (Figure 2.7c). In addition, by taking advantage of the four-wave mixing (FWM) effect, the designed FWM-based wavelength converter achieved a high conversion efficiency of 63 dB and converted efficiently the modulated radio frequency (RF) signals to the sidebands with a maximum frequency of ~18 GHz, which was a vital part in the optical signal processing (Figure 2.7d). In another work, Song et al. also employed FLA-decorated microfiber as an all-optical pulse thresholder to effectively suppress the noise in the transmission system, by which the signal to noise ratio (SNR) was largely improved (~10 dB) [47].
Figure 2.7 (a) Phase shift of the antimonene-based AOM as a function of pump power before and after 1 month. (b) Calculated active Q-switching pulse trains at different repetition rates (0.96, 2.02, 6.64 kHz). (c) The calculated extinction ratio of the FLA-based Kerr switcher. (d) FWM output spectra of the FLA-decorated microfiber with RF modulation (10 GHz). (a, b) Reproduced with permission [43]. Copyright 2019, Wiley-VCH. (c, d) Reproduced with permission [46]. Copyright 2018, Wiley-VCH.
2.4.2 Optoelectronic Device
For optoelectronic applications, materials are usually required to have proper band gaps in the visible region, high mobility, as well as excellent stability. By reducing bulk antimony to only one atomic layer, one can obtain a tunable band gap ranging from 0 to 2.28 eV together with high carrier mobility, which makes antimonene a suitable semiconductor in the field of optoelectronic device [11, 12].
Wang et al. first applied antimonene prepared by the modified LPE as a HTL in the perovskite solar cells (PVSCs) [21]. The small differences of the energy levels between antimonene and CH3NH3PbI3 perovskite provided a driving force for the hole extraction. As shown in Figures 2.8a, b, the antimonene-HTL device exhibited a higher power conversion efficiency (Jsc = 14.6 mA cm–2, EQE = 55%–60%) than the HTL-free device (Jsc = 11.2 mA cm–2, EQE < 45%). Besides, the EQE-based integrated Jsc in the antimonene-HTL device (14.8 mA cm–2) was also higher than that in the HTL-free device (10.1 mA cm–2). Afterwards, Zhang et al. also used LPE-exfoliated semiconductive antimonene nanosheets (SANs) as an ideal hole transfer and extraction layer to fabricate the planar inverted PVSCs [48]. In the constructed PVSCs, poly[bis(4-phenyl)(2,4,6-trimethylphenyl) amine] (PTAA) modified SANs were very compatible with CH3NH3PbI3 perovskite, meanwhile SANs increased the grain size of CH3NH3PbI3 and inhibited the ion migration. All the above factors indicated that SANs were expected to achieve efficient hole transfer from CH3NH3PbI3 to the HTL. Compared with the control devices (without SANs layer), the SANs devices obtained higher power conversion efficiencies (PCEs) of 20.05%, Voc of 1.115 V, Jsc of 23.46 mA cm−2, and fill factor (FF) of 0.767 in forward scan direction (Figures 2.8c, d). In addition, antimonene quantum dots and sheets were employed as an effective photoactive material in the solar cells and organic photovoltaics as well [49, 50].
Figure 2.8 (a) Current-density-voltage (J-V) curves of devices without (Device 1) and with (Device 2) antimonene HTL. (b) EQE spectra and EQE-based integrated Jsc for