||~ 2.0 eV (indirect); ~ 1.2 eV (direct)
|Classification / Family
Transition metal dichalcogenides (TMDCs), 2D Semiconductor materials, Nano-electronics, Nano-photonics, Photovoltaic, Materials science
||Synthetic - chemical vapour transport (CVT)
||Dark brown powder
Like all other 2D materials (such as graphite), Hafnium disulfide (HfS2) powder has a layered structure. Each layer is bound by weak van der Waals forces. Ultra-thin films of HfS2 can be chemically-exfoliated from its layered bulk powder form. HfS2 crystallises with octahedral metal coordination in the 1T polytype.
1T-HfS2 is semiconducting in nature. Ultrathin HfS2 shows a higher, faster response and higher stability than most other two-dimensional materials. However, the 1T-HfS2 monolayer system undergoes a semiconductor-to-metal transition while compressive strain is applied.
Exfoliated ultra-thin films of HfS2 have an indirect bandgap of ~ 1.2 eV, with high stability against surface degradation. FET based on HfS2 nanosheets gave a high current on/off ratio over 10,000 at room temperature. Photodetectors based on HfS2 nanosheets provide high photosensitivity to 405 nm lasers, with a large on/off ratio of ca. 103 and ultrafast response performance (with rise and fall times of 24 ms).
2D-HfS2 can also be used as an efficient photocatalyst for water splitting, with a strong absorption mainly in the visible and ultraviolet regions.
Hafnium disulfide powder is obtained via the CVT method, with a purity in excess of 99.995% achieved.
Hafnium disulfide powder is suitable for liquid chemical exfoliation to prepare HfS2 nanosheets and nanoparticles down to few-layer films. HfS2 powder is also used to prepare mono-layer and few-layer films via chemical vapour deposition (CVD).
Literature and Reviews
High-yield synthesis and liquid-exfoliation of twodimensional belt-like hafnium disulphide, H. Kaur et al., Nano Res., 11(1): 343–353 (2018); doi: 10.1007/s12274-017-163.
Vertically oriented few-layered HfS2 nanosheets: growth mechanism and optical properties, B. Zheng et al., 2D Mater., 3, 035024 (2016); doi:10.1088/2053-1583/3/3/035024.
Efficient charge separation and visible-light response in bilayer HfS2-based van der Waals heterostructures, B. Wang et al., RSC Adv., 8, 18889 (2018); DOI: 10.1039/c8ra03047b.
Few-layer HfS2 transistors, T. Kanazawa et al., Sci. Rep., 6, 22277 (2015); DOI: 10.1038/srep22277.
Ultrasensitive Phototransistors Based on Few-Layered HfS2, K. Xu et al., Adv. Mater., 27, 7881–7887 (2015); DOI: 10.1002/adma.201503864.
Toward High-Performance Top-Gate Ultrathin HfS2 Field-Effect Transistors by Interface Engineering, K. Xu et al., small, 12 (23), 3106–3111 (2016); DOI: 10.1002/smll.201600521.
Space-Confined Chemical Vapor Deposition Synthesis of Ultrathin HfS2 Flakes for Optoelectronic Application, C. Yan et al., Adv. Funct. Mater., 27, 1702918 (2017); DOI: 10.1002/adfm.201702918.