Abstract
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.
Highlights
The increasing demand for elemental 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), emerged for applications in sensors[1,2,3], optoelectronics[4,5], flexible displays[6], and photovoltaics[7,8]
Based on the X-ray diffractometer (XRD) data, we found that our black phosphorus (BP) samples have an orthorhombic structure with lattice constants of a = 3.32 Å, b = 4.38 Å and c = 10.48 Å, which agrees with the previous studies for BP38
The peak for each vibration mode of our BP sample deviates from that of bulk BP in the literature: 365 cm−1 for A1g, 442 cm−1 for B2g, and 470 cm−1 for A2g39. The positions of these peaks are consistent with the Raman shift values of BP multilayers by Lu et al.[41], which implies that BP prepared by liquid exfoliation exhibits the crystalline thin-film phase
Summary
The increasing demand for elemental 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), emerged for applications in sensors[1,2,3], optoelectronics[4,5], flexible displays[6], and photovoltaics[7,8]. None of them showed well-defined crystalline thin films covering whole substrates They appear to be inappropriate for thin-film based electronic applications. It can be challenging to design uniform thin films using BP flakes with random shapes because high coverage of BP is needed to uniformly cover the whole substrate, which results in thick stacked BP layers close to bulk BP. Triangular BP layers can effectively cover the whole substrate with low coverage, which facilitates the fabrication of uniform thin films. This makes the liquid-exfoliated BP a perfect candidate for large-area applications in electronic devices
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