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Abstract
The broadband nonlinear optical material towards the mid-infrared spectral range is highly needed for civil and military applications. Here, we have investigated the nonlinear optical response of the nickel ditelluride (NiTe2) single crystal prepared by the chemical vapor deposition (CVD) method, and found that the layered NiTe2 exhibits attractive broadband nonlinear optical absorption performance towards the mid-infrared regime. We further explored the nonlinear optical response of the layered NiTe2 in the erbium-doped fluoride fiber laser, and have realized the stable Q-switched fiber laser with a pulse width of 708 ns and a repetition rate of 81 kHz around 2.8 µm wavelength. The experimental results may not only make inroads towards the understanding the nonlinear optical response of the topological materials, but also explore their broadband applications in mid-infrared photonics.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The broadband nonlinear optical material towards mid-infrared spectral range is very important for civil and military applications. The mid-infrared spectrum region locates in the atmospheric window and the strong absorption band of some molecules (H2O, CO, NO2 …) [1–2]. These unique characteristics stimulate the potential application of mid-infrared laser in remote sensing, lidar, environmental monitoring, medicine, scientific research, etc. [3]. Encouraged by the versatile requirements in the mid-infrared regime, the broadband nonlinear optical materials are indispensable for the specific applications, such as nonlinear Q-switcher, mode-locker, the optical limiter, etc. [4].
The pulsed operation was usually accomplished by incorporating a Q-switcher into the fiber laser cavity [5–9]. The selection of Q-switcher is of great significance in scaling the performance of pulsed lasers, especially towards the mid-infrared spectral range. To date, different Q-switchers have been used in passively Q-switched Er3+-doped ZBLAN fiber lasers, such as Fe2+:ZnSe crystals [10,11], semiconductor saturable absorber mirrors [12], graphene [13] and graphene-like materials [14–24]. Topological insulators (TIs), such as Bi2Se3, Bi2Te3, Sb2Te3, have been proved to be excellent nonlinear optical material for the unique electronic band structure [25–27]. Similar to TIs, topological semimetals (TSs) is a topological material with topological non-trivial quantum state and Dirac band structure [28]. TSs can be divided into Dirac semimetal, Weyl semimetal, etc. TSs with point like fermi surface is called type-I TSs, such as Cd3As2, Na3Bi, TaAs, while TSs with Lorentz invariance breaking was called type-II TSs [29]. To date, some TMDs have been identified as type-II TSs, such as WTe2 [30], PdTe2 [31], PtTe2 [32], PtSe2 [33] and NiTe2 [30]. Broadband ultrafast optical response and controllable carrier dynamics experiments of type-I Dirac semimetal Cd3As2 have been reported [34,35], and the type-II Weyl semimetal candidate WTe2 has also been demonstrated in the mid-infrared ultrafast photonics application [36,37]. In contrast, NiTe2 would be an excellent candidate for studying the physical characteristics of type-II Dirac material because its Dirac nodes are closer to the Fermi energy [29]. NiTe2 was a layered metallic ditelluride with a CdI2 structure of triangular crystal system (space group: P$\overline{3}$m1) [38,39]. Layer-dependent electronic and optical properties endow NiTe2 compounds intriguing sparkle. B. Zhao et al. successfully prepared NiTe2 single crystals with precisely controllable layers by CVD method, and demonstrated that the layer numbers and lateral size of NiTe2 crystal could be controlled by adjusting the growth temperature [39]. Moreover, the electronic transport studies show that NiTe2 single crystals exhibit metal-like behavior [39,40]. NiTe2 crystals have exhibited some fascinating physical properties, such as ultrafast carrier dynamics, broadband response and good stability, which are expected to be an excellent candidate for optoelectronic devices [41]. However, the intensity-dependent broadband nonlinear optical response and applications of the layered NiTe2 has not been explored so far.
Here, the broadband nonlinear absorption behavior of the layered NiTe2 single crystal prepared by CVD method has been characterized. In addition, the prepared NiTe2 single crystal was introduced into the Er3+-doped ZBLAN fiber laser as a Q-switcher, and stable Q-switched pulse was achieved at 2795 nm with a repetition rate of 81 kHz and a corresponding pulse width of 708 ns. The experimental result confirms the nonlinear optical response and application of NiTe2 toward mid-infrared spectral range, which was expected to provide many practical and potential applications in mid-infrared photonics.
2. Material characterizations
Layered NiTe2 single crystals on quartz substrate have been synthesized by CVD method and characterized, as shown in Fig. 1. Figure 1(a) shows the SEM image of NiTe2 single crystals measured by scanning electron microscopy (SEM). Figures 1(b)–1(c) shows the image of optical microscopy (OM). From the figures, we can know the size, morphology and distribution of NiTe2 single crystals. In order to identify the crystallinity and absorption characteristics of the sample, we have further characterized the layered NiTe2 single crystals. The comparisons of the X-ray diffraction pattern (blue line) and the standard spectrum (red line) of NiTe2 single crystals sample are shown in Fig. 2(a). All the diffraction peaks of the NiTe2 sample can be indexed to NiTe2 (PDF#08-0004), and its diffraction peaks are consistent with previous reports [42], which indicating the high quality of the samples. The linear transmission spectrum of the NiTe2 single crystals show the broadband absorption characteristics of the sample from 800 nm to 3000 nm in Fig. 2(b), which are consistent with its semi-metallic nature. The electronic structure and Dirac nature of semimetal provide a robust platform for the interaction of light and optical material, which can lay the basis for the broadband ultrafast photonic applications [35].
Fig. 2. Characterization of NiTe2 single crystals measured, (a) XRD pattern; (b) Linear transmission spectrum from near-infrared to mid-infrared bands.
The broadband nonlinear absorption characterization of the layered NiTe2 was measured via the open aperture Z-scan technique with the help of four separate excitation sources operating ranging from 800 nm to ∼2 µm wavelength, as shown in Fig. 3 and Fig. 4. The incident pulse intensities at the focus of the four lasers with different parameters of 800 nm (100 fs, 1 kHz), 1064 nm (4 ns, 100 kHz), 1560 nm (100 fs, 80 MHz) and 1930 nm (2.8 ps, 32.3 MHz) are 70.5 GW/cm2, 33.3 kW/cm2, 9.95 MW/cm2 and 9.2 MW/cm2, respectively. The open aperture Z-scan experimental data can be fitted by the following equation:
where z0 was the Rayleigh length, and q0=βI0Leff, β was the nonlinear absorption coefficient, I0 was the incident pulse intensity at the focus, Leff was the sample’s effective length. By recording the transmission of NiTe2 single crystal at different incident pulse intensities, the measured data were fitted by a nonlinear absorption model, as shown in Fig. 4. The saturation intensity and modulation depth of NiTe2 single crystals were obtained by fitting experimental data using the following equation: where T(I) was the transmission, ΔT was the modulation depth, I, Is and Tns were incident pulse intensity, saturation intensity and non-saturation loss, respectively. By fitting the experimental results, the modulation depth and saturation intensity at 1930 nm were 17.7% and 112.45 kW/cm2, respectively. From the relatively flat linear transmittance spectra of the layered NiTe2, it is reasonable to conclude that the broadband saturation absorption of layered NiTe2 towards 3 µm spectral range. Considering the broadband nonlinear response, the Pauli blocking effect caused by band filling can be responsible for the saturable absorption signatures [36].Fig. 4. Characterization of saturable absorption of NiTe2 single crystal at 1930nm. (a) Z-scan curve; (b) Nonlinear transmission.
3. Mid-infrared fiber laser modulated by layered NiTe2
We have validated the broadband nonlinear optical response of the layered NiTe2 towards mid-infrared spectral range by introducing it into the Er3+:ZBLAN fiber laser as a nonlinear modulator, as shown in Fig. 5. In the passively Q-switched Er3+:ZBLAN fiber laser, the pump source is a 976 nm laser diode with maximum output power 50 W, and the core diameter and numerical aperture of the pigtail are 105 µm and 0.15, respectively. The gain medium is double-cladding Er3+-doped ZBLAN fibers with core diameter of 15 µm and inner cladding diameter of 240×260 µm, respectively. The erbium ions doping concentration is 7 mol%, and the numerical aperture is 0.12. Both ends of the fibers were fixed on the fiber holder, the end facet of the optical fiber near the pump source was perpendicularly cleaved to realize the function of the output coupler, and the other side of the optical fiber was cleaved with an 8°angle to prevent parasitic oscillation. Finally, the resonator was composed of a perpendicularly cleaved fiber end and a mirror M2 (HR@2800 nm) to realize laser oscillation. Technically, the coupling of the pump light to the gain fiber requires a coupling system, which was composed of lens group L1 (N-BK7, f = 25.4 mm) and L2 (L2, CaF2, f = 50 mm). L3, L4 and L5 were three lenses, and the SA was placed at the minimum spot between L4 and L5. L3, L4, and L5 are CaF2 lenses with focal lengths of 20 mm, 20 mm, and 25.4 mm, respectively. M1 is a dichroic mirror (HT@976 nm, HR@2800 nm), which was placed between L1 and L2 at a 45° angle for the separation of pump light and laser. A monochromator with a scanning resolution of 0.1 nm (Princeton instrument Acton SP2300) was utilized to measure the laser spectrum. The signal-to-noise ratio (SNR) was analyzed by a radio-frequency spectral analyzer (Agilent, N9322C). The Newport 1919-R high-performance optical power meter is used for power measurement. The pulse train is monitored by using a real time oscilloscope with a bandwidth of 4 GHz together with a HgCdTe detector.
Fig. 5. Experimental setup of passively Q-switched Er3+:ZBLAN fiber laser based on NiTe2 single crystals.
With the increase of pump power, the Q-switched fiber laser experiences three stages: CW, unstable pulsed and Q-switched pulsed regimes. When the incident pump power was 0.26 W, the laser was in the CW operation stage. By increasing the incident pump power up to about 0.5 W, the laser was switched from an unstable pulse state to a stable Q-switched pulse state. The Q-switched regime remains stable until the incident pump power was increased to 1.93 W. Figure 6 shows the corresponding operation state of the laser measured by an oscilloscope when the incident pump power ranges from 0.97 W to 1.93 W. When the laser passes through the quartz substrate, there was no Q-switched pulse. It can be inferred that the Q-switched pulse was modulated by the layered NiTe2. When the incident pump power was 1.93 W and the output power was 62 mW, the variation of pulse width and repetition rate with incident pump power was shown in Fig. 7, and the variation trend of pulse width and repetition rate with incident pump power was opposite. When the incident pump power was 1.93 W, the minimum pulse width and maximum repetition rate were 708 ns and 81 kHz, respectively. Figure 8(a) depicts the optical spectrum of the passively Q-switched Er3+-doped ZBLAN fiber laser. The center wavelength of the optical spectrum was 2795 nm and the full width at half maximum (FWHM) was 0.8 nm. In addition, the RF spectrum of the Q-switched laser was also measured, as shown in Fig. 8(b). The signal-to-noise ratio (SNR) of the fiber laser was about 33 dB, which indicates the stable Q-switched operation. Table 1 have summarized the typical recent reports of 3 µm Q-switched fiber laser based on different SAs. From the table, we can see that Er3+:ZBLAN fiber laser modulated by layered NiTe2 has obtained pulses with narrower pulse duration, which is inseparable from the contribution of saturable absorber (SA).
Fig. 8. Passively Q-switched Er3+-doped ZBLAN fiber laser based on NiTe2 single crystals, (a) Q-switched optical spectrum; (b) Radio frequency spectrum centered around 81 kHz of the Q-switched operation at the incident pump power of 1.93 W.
Table 1. Typical report on 3 µm Q-switched fiber laser with different SAs.
4. Conclusions
In summary, we have found that the layered NiTe2 prepared by CVD method presented attractive broadband nonlinear optical absorption performance. The broadband saturation absorption behavior of the layered NiTe2 towards the mid-infrared region has been observed and characterized. In addition, we demonstrated the passively Q-switched Er3+-doped ZBLAN fiber laser modulated by layered NiTe2 experimentally. The measured Q-switched 2795 nm pulse laser has pulse width of 708 ns and repetition rate of 81 kHz, which can manifest the potential application of the layered NiTe2. The experimental results may make inroads towards the understanding the nonlinear optical response of the exotic Dirac semimetal.
Funding
National Natural Science Foundation of China (61775056, 61975055); Natural Science Foundation of Hunan Province (2017JJ1013); Research Fund of Science and Technology on Plasma Physics Laboratory (6142A0403050717).
Disclosures
The authors declare no conflicts of interest.
References
1. T. Gabriele, “Extending opportunities,” Nat. Photonics 6(7), 407 (2012). [CrossRef]
2. C. Ziolek, H. Ernst, G. F. Will, H. Lubatschowski, H. Welling, and W. Ertmer, “High-repetition-rate, high-average-power, diode-pumped 2.94-µm Er:YAG laser,” Opt. Lett. 26(9), 599–601 (2001). [CrossRef]
3. S. D. Jackson, “Towards high-power mid-infrared emission from a fibre laser,” Nat. Photonics 6(7), 423–431 (2012). [CrossRef]
4. P. Yan, A. Liu, Y. Chen, H. Chen, S. Ruan, C. Guo, S. Chen, I. Li, H. Yang, J. Hu, and G. Cao, “Microfiber-based WS2-film saturable absorber for ultra-fast photonics,” Opt. Mater. Express 5(3), 479–489 (2015). [CrossRef]
5. Z. T. Wang, Y. Chen, C. J. Zhao, H. Zhang, and S. C. Wen, “Switchable dual-wavelength synchronously Q-switched erbium-doped fiber laser based on graphene saturable absorber,” IEEE Photonics J. 4(3), 869–876 (2012). [CrossRef]
6. J. Ma, S. Lu, Z. Guo, X. Xu, H. Zhang, D. Tang, and D. Fan, “Few-layer black phosphorus based saturable absorber mirror for pulsed solid-state lasers,” Opt. Express 23(17), 22643–22648 (2015). [CrossRef]
7. L. Zhao, D. Tang, X. Wu, and H. Zhang, “Dissipative soliton generation in Yb-fiber laser with an invisible intracavity bandpass filter,” Opt. Lett. 35(16), 2756–2758 (2010). [CrossRef]
8. Y. Chen, C. Zhao, S. Chen, J. Du, P. Tang, G. Jiang, H. Zhang, S. Wen, and D. Tang, “Large energy, wavelength widely tunable, topological insulator Q-switched erbium-doped fiber laser,” IEEE J. Sel. Top. Quantum Electron. 20(5), 315–322 (2014). [CrossRef]
9. X. Jiang, S. Liu, W. Liang, S. Luo, Z. He, Y. Ge, H. Wang, R. Cao, F. Zhang, Q. Wen, J. Li, Q. Bao, D. Fan, and H. Zhang, “Broadband Nonlinear Photonics in Few-Layer MXene Ti3C2Tx (T = F, O, or OH),” Laser Photonics Rev. 12(2), 1870013 (2018). [CrossRef]
10. A. A. Voronov, V. I. Kozlovskii, Y. V. Korostelin, A. I. Landman, Y. P. Podmar’kov, V. G. Polushkin, and M. P. Frolov, “Passive Fe2+:ZnSe single-crystal Q-switch for 3-µm lasers,” Quantum Electron. 36(1), 1–2 (2006). [CrossRef]
11. H. Luo, J. Yang, J. Li, and Y. Liu, “Widely tunable passively Q-switched Er3+-doped ZrF4 fiber laser in the range of 3.4–3.7 µm based on a Fe2+: ZnSe crystal,” Photon. Res. 7(9), 1106–1111 (2019). [CrossRef]
12. J. Li, H. Luo, Y. He, Y. Liu, L. Zhang, K. Zhou, A. Rozhin, and S. Turistyn, “Semiconductor saturable absorber mirror passively Q-switched 2.97 µm fluoride fiber laser,” Laser Phys. Lett. 9135(6), 065102 (2014). [CrossRef]
13. C. Wei, X. Zhu, F. Wang, Y. Xu, K. Balakrishnan, F. Song, R. A. Norwood, and N. Peyghambarian, “Graphene Q-switched 2.78 µm Er3+-doped fluoride fiber laser,” Opt. Lett. 38(17), 3233–3236 (2013). [CrossRef]
14. Z. Qin, T. Hai, G. Xie, J. Ma, P. Yuan, L. Qian, L. Li, L. Zhao, and D. Shen, “Black phosphorus Q-switched and mode-locked mid-infrared Er:ZBLAN fiber laser at 3.5 µm wavelength,” Opt. Express 26(7), 8224–8231 (2018). [CrossRef]
15. Y. Chen, G. Jiang, S. Chen, Z. Guo, X. Yu, C. Zhao, H. Zhang, Q. Bao, S. Wen, D. Tang, and D. Fan, “Mechanically exfoliated black phosphorus as a new saturable absorber for both Q-switching and mode-locking laser operation,” Opt. Express 23(10), 12823–12833 (2015). [CrossRef]
16. C. Wei, H. Luo, H. Zhang, C. Li, J. Xie, J. Li, and Y. Liu, “Passively Q-switched mid-infrared fluoride fiber laser around 3 µm using a tungsten disulfide WS2 saturable absorber,” Laser Phys. Lett. 13(10), 105108 (2016). [CrossRef]
17. B. Huang, Z. Kang, J. Li, M. Liu, P. Tang, L. Miao, C. Zhao, G. Qin, W. Qin, S. Wen, and P. N. Prasad, “Broadband mid-infrared nonlinear optical modulator enabled by gold nanorods: towards the mid-infrared regime,” Photon. Res. 7(6), 699–704 (2019). [CrossRef]
18. H. Luo, Z. Kang, Y. Gao, H. Peng, J. Li, G. Qin, and Y. Liu, “Large aspect ratio gold nanorods (LAR-GNRs) for mid-infrared pulse generation with a tunable wavelength near 3 µm,” Opt. Express 27(4), 4886–4896 (2019). [CrossRef]
19. L. Yang, Z. Kang, B. Huang, J. Li, L. Miao, P. Tang, C. Zhao, G. Qin, and S. Wen, “Gold nanostars as a Q-switcher for the mid-infrared erbium-doped fluoride fiber laser,” Opt. Lett. 43(21), 5459–5462 (2018). [CrossRef]
20. H. Luo, X. Tian, Y. Gao, R. Wei, J. Li, J. Qiu, and Y. Liu, “Antimonene: a long-term stable two-dimensional saturable absorption material under ambient conditions for the mid-infrared spectral region,” Photon. Res. 6(9), 900–907 (2018). [CrossRef]
21. J. Yi, L. Du, J. Li, L. Yang, L. Hu, S. Huang, Y. Dong, L. Miao, S. Wen, V. Mochalin, C. Zhao, and A. M. Rao, “Unleashing the potential of Ti2CTx MXene as a pulse modulator for mid-infrared fiber lasers,” 2D Mater. 6(4), 045038 (2019). [CrossRef]
22. P. Tang, M. Wu, Q. Wang, L. Miao, B. Huang, J. Liu, C. Zhao, and S. Wen, “2.8-µm Pulsed Er3+: ZBLAN Fiber Laser Modulated by Topological Insulator,” IEEE Photonics Technol. Lett. 28(14), 1573–1576 (2016). [CrossRef]
23. R. I. Woodward, M. R. Majewski, N. Macadam, G. Hu, T. Albrow-Owen, T. Hasan, and S. D. Jackson, “Q-switched Dy: ZBLAN fiber lasers beyond 3 µm: comparison of pulse generation using acousto-optic modulation and inkjet-printed black phosphorus,” Opt. Express 27(10), 15032–15045 (2019). [CrossRef]
24. H. Luo, J. Li, Y. Gao, Y. Xu, X. Li, and Y. Liu, “Tunable passively Q-switched Dy 3+-doped fiber laser from 2.71 to 3.08 µm using PbS nanoparticles,” Opt. Lett. 44(9), 2322–2325 (2019). [CrossRef]
25. C. Zhao, Y. Zou, Y. Chen, Z. Wang, S. Lu, H. Zhang, S. Wen, and D. Tang, “Wavelength-tunable picosecond soliton fiber laser with Topological Insulator: Bi2Se3 as a mode locker: erratum,” Opt. Express 21(1), 444 (2013). [CrossRef]
26. C. Zhao, H. Zhang, X. Qi, Y. Chen, Z. Wang, S. Wen, and D. Tang, “Ultra-short pulse generation by a topological insulator based saturable absorber,” Appl. Phys. Lett. 101(21), 211106 (2012). [CrossRef]
27. J. Li, H. Luo, L. Wang, C. Zhao, H. Zhang, H. Li, and Y. Liu, “3-µm mid-infrared pulse generation using topological insulator as the saturable absorber,” Opt. Lett. 40(15), 3659–3662 (2015). [CrossRef]
28. C. Xu, B. Li, W. Jiao, W. Zhou, B. Qian, R. Sankar, N. D. Zhigadlo, Y. Qi, D. Qian, F. C. Chou, and X. Xu, “Topological Type-II Dirac Fermions Approaching the Fermi Level in a Transition Metal Dichalcogenide NiTe2,” Chem. Mater. 30(14), 4823–4830 (2018). [CrossRef]
29. Q. Liu, B. Chen, B. Wei, S. Zhang, M. Zhang, F. Xie, M. Naveed, F. Fei, B. Wang, and F. Song, “Non-topological Origin of the Planar Hall Effect in Type-II Dirac Semimetal NiTe2,” Phys. Rev. B 99(15), 155119 (2019). [CrossRef]
30. M. N. Ali, J. Xiong, S. Flynn, J. Tao, Q. D. Gibson, L. M. Schoop, T. Liang, N. Haldolaarachchige, M. Hirschberger, N. P. Ong, and R. J. Cava, “Large, non-saturating magnetoresistance in WTe2,” Nature 514(7521), 205–208 (2014). [CrossRef]
31. Y. Wang, J. Zhang, W. Zhu, Y. Zou, C. Xi, L. Ma, T. Han, J. Yang, J. Wang, J. Xu, L. Zhang, L. Pi, C. Zhang, and Y. Zhang, “De Hass-van Alphen and magnetoresistance reveal predominantly single-band transport behavior in PdTe2,” Sci. Rep. 6(1), 31554 (2016). [CrossRef]
32. M. Yan, H. Huang, K. Zhang, E. Wang, Y. Wei, D. Ke, G. Wan, H. Zhang, M. Arita, and H. Yang, “Lorentz-violating type-II Dirac fermions in transition metal dichalcogenide PtTe2,” Nat. Commun. 8(1), 257 (2017). [CrossRef]
33. K. Zhang, M. Yan, H. Zhang, H. Huang, M. Arita, Z. Sun, W. H. Duan, Y. Wu, and S. Zhou, “Experimental evidence for type-II Dirac semimetal in PtSe2,” Phys. Rev. B 96(12), 125102 (2017). [CrossRef]
34. Y. Sun, Y. Meng, H. Jiang, S. Qin, Y. Yang, F. Xiu, Y. Shi, S. Zhu, and F. Wang, “Dirac semimetal saturable absorber with actively tunable modulation depth,” Opt. Lett. 44(3), 582–585 (2019). [CrossRef]
35. C. Zhu, F. Wang, Y. Meng, X. Yuan, F. Xiu, H. Luo, Y. Wang, J. Li, X. Lv, L. He, Y. Xu, J. Liu, C. Zhang, Y. Shi, R. Zhang, and S. Zhu, “A robust and tuneable mid-infrared optical switch enabled by bulk Dirac fermions,” Nat. Commun. 8(1), 14111 (2017). [CrossRef]
36. W. Gao, L. Huang, J. Xu, Y. Chen, C. Zhu, Z. Nie, Y. Li, X. Wang, Z. Xie, S. Zhu, J. Xu, X. Wan, C. Zhang, Y. Xu, Y. Shi, and F. Wang, “Broadband photocarrier dynamics and nonlinear absorption of PLD-grown WTe2 semimetal films,” Appl. Phys. Lett. 112(17), 171112 (2018). [CrossRef]
37. Y. Liu, C. Liu, X. Wang, L. He, X. Wan, Y. Xu, Y. Shi, R. Zhang, and F. Wang, “Photoresponsivity of an all-semimetal heterostructure based on graphene and WTe2,” Sci. Rep. 8(1), 12840 (2018). [CrossRef]
38. J. F. H. L. Monteiro, M. B. Marciniak, A. R. Jurelo, E. C. Siqueira, F. T. Dias, and J. L. Pimentel Júnior, “Synthesis and microstructure of NiTe2,” J. Cryst. Growth 478(15), 129–133 (2017). [CrossRef]
39. B. Zhao, W. Dang, Y. Liu, B. Li, J. Li, J. Luo, Z. Zhang, R. Wu, H. Ma, G. Sun, Y. Huang, X. Duan, and X. Duan, “Synthetic Control of Two-Dimensional NiTe2 Single Crystals with Highly Uniform Thickness Distributions,” J. Am. Chem. Soc. 140(43), 14217–14223 (2018). [CrossRef]
40. B. S. de Lima, R. R. de Cassia, F. B. Santos, L. E. Correa, T. W. Grant, A. L. R. Manesco, G. W. Martins, L. T. F. Eleno, M. S. Torikachvili, and A. J. S. Machado, “Properties and superconductivity in Ti-doped NiTe2 single crystals,” Solid State Commun. 283, 27–31 (2018). [CrossRef]
41. C. Xu, B. Li, W. Jiao, W. Zhou, B. Qian, R. Sankar, N. D. Zhigadlo, Y. Qi, D. Qian, F. C. Chou, and X. Xu, “Topological Type-II Dirac Fermions Approaching the Fermi Level in a Transition Metal Dichalcogenide NiTe2,” Chem. Mater. 30(14), 4823–4830 (2018). [CrossRef]
42. J. Guo, Y. Shi, Y. Chu, and T. Ma, “Highly efficient telluride electrocatalysts for use as Pt-free counter electrodes in dye-sensitized solar cells,” Chem. Commun. 49(86), 10157–10159 (2013). [CrossRef]
43. J. Li, H. Luo, B. Zhai, R. Lu, Z. Guo, H. Zhang, and Y. Liu, “Black phosphorus: a two-dimension saturable absorption material for mid-infrared Q-switched and mode-locked fiber lasers,” Sci. Rep. 6(1), 30361 (2016). [CrossRef]
