Elsevier

Applied Surface Science

Volume 571, 1 January 2022, 151176
Applied Surface Science

Full Length Article
Modulating the electron transfer and resistivity of Ag plasma implanted and assisted MoS2 nanosheets

https://doi.org/10.1016/j.apsusc.2021.151176Get rights and content

Highlights

  • The Ag plasma implanted and assisted MoS2 nanosheets are constructed by co-sputtering.

  • The growth mechanisms and bonding mode of the Ag-power/MoS2 nanosheets are illustrated.

  • The regulation of the acceptor impurity Ag on the Hall coefficient of the MoS2 is discussed.

  • The electronic excitation-relaxation mechanism of Ag-power/MoS2 nanosheets is explained.

Abstract

A simple and controllable technique has been proposed for single-step co-sputtering of homogeneous Ag-power/MoS2 film as excellent photoelectric materials. Interestingly, the binding mode of Ag plasma implanted and assisted MoS2 nanosheets are investigated by adjusting the sputtering power. The diffraction peaks of Ag2S/Ag and valence electronic structure of Ag0/Ag1+ have been studied by a combined analysis of X-ray diffraction and X-ray photoelectron spectroscopy measurements, which confirm the implantation of Ag on MoS2 nanosheets. More specifically, the slight shift of the Mo3d/S2p demonstrated that the electrons moved from the MoS2 band gap to the ground state energy level of the Ag NPs. The significantly excellent linear absorption characteristic has been demonstrated, which can be attribute to the synergetic effects of SPR and the lower energy barrier of internal defects in the more homogeneous film. The implantation and assistance of Ag plasmon not only increased the visible/near-infrared absorption and emission of MoS2 nanosheets, but also induced the high amplification of the local electric field intensity in MoS2 nanosheets. Our work provides an effective strategy for the preparation of plasmonic Ag implanted and assisted Few-Layers MoS2 nanosheets and prompts their wider applications in visible/near-infrared devices.

Introduction

Over the past decades, two-dimensional (2D) semiconductor materials have been concerned for their multiple functions and wide application, including optoelectronic devices and biodegradable catalysts [1], [2], [3], [4], [5], [6], [7]. In particular, the graphene and graphene-like has been discovered to be the typical 2D material with the excellent carrier mobility, which reveals its promising role in an electronic buffer and containment layer between various semiconductor–semiconductor materials and semiconductor–metal electrodes [8], [9], [10], [11], [12], [13], [14]. However, the zero-band gap feature of graphene has seriously limited its application in the field of linear-nonlinear optoelectronics [15], [16], [17]. As a “Star Material”, transition metal dichalcogenides (TMDs) have attracted the attention of researchers and become the ideal substitute of graphene in various fields. Unlike graphene, the optical band gap of the TMDs can be flexible modulated by the quantum size effect among different layers. This unique energy band feature results in some novel optoelectronic properties and a variety of different optical behaviors of TMDs, which undoubtedly broadens its application prospects [18], [19], [20], [21]. Among the TMDs, molybdenum disulfide (MoS2) has the excellent characteristics of stress resistance, easy to prepare, non-toxic, and thermal stability [22], [23], [24], [25], [26]. The relative movement can be easily caused by the unique Van der Waals force among the molecular layers, which enables its role as a solid lubricant in precision instruments. Furthermore, the accumulation method (AA or AB accumulation) between the inner layer of Mo and S atoms also results in different bulk phases of MoS2 (such as: 1 T, 2H, etc). The combination of the metallic and semiconducting properties leads to the application of MoS2 in different fields [27], [28], [29], [30], [31].

However, the poor quantum yields and ultraviolet light absorption ability have become the major demerit of MoS2 due to the higher carrier recombination and narrow band gap, which greatly limit its application in the optical field [32], [33], [34], [35], [36]. To improve and regulate its electrical and optical properties, MoS2 has been doped or combined with various elements/compounds. Among them, the interesting optical effects were demonstrated by the strategy of using semiconductor compounds materials to composite MoS2 [37], [38], [39], [40], [41], [42], [43], [44]. The surface plasmon resonance effect (SPRE) of noble metals results in an higher transfer efficiency of the electrons and catalytic ability of MoS2, and has been successfully applied to explore the surface-enhanced Raman scattering (SERS) devices and photoelectrochemical catalysis [13], [20], [45], [46], [47], [48], [49], [50], [51], [52], [53]. J. Wu et al [46] studied the SERS effect of Ag2S/Ag@MoS2 composite system and theoretically calculated the relative positions of the conduction bands (CB). A.J. Cheah et al [47] demonstrated that the Ag/MoS2 composite system with higher reaction activity may be an ideal alternative material in the field of photocatalytic hydrogen evolution. K.G. Sun et al [52] studied the reduction characteristics of Ag-MoS2 under dark or light irradiation conditions. In dark conditions, MoS2 serves as an electron supply area to complete the reduction reaction of Cr4+. On the contrary, under light conditions, photo-generated electrons become the main participating component, and exert an obviously impact on the photocatalytic reaction. In fact, metal particles can better confine the photon energy in the band gap of the 2D material to manipulate the electromagnetic field distribution of materials. J. Li et al [50] studied the SERS effect of metal Ag NP dimers modified 1L-MoS2. The results show that the metal dimers can confine the photon energy in the band gap of MoS2 NP, which in turn changes the electromagnetic field of MoS2 and results in a stronger Raman scattering peak. In addition, noble metals will cause stronger visible light absorption through SPRE characteristics and generate a non-uniform electric field on the surface of the semiconductor. Plasma energy is used as an additional energy to suppress the charge recombination, generate a plasmon heating zone and promote photocatalytic chemical conversion. P. Miao et al [51] reported the crystallinity of MoS2 can greatly promote the electron transfer process, thus improving the SERS activity and reaction efficiency. In summary, the higher carrier recombination rate and resistivity of pure MoS2 nanosheets may reduce the quantum yield, which severely limits its application in the field of optoelectronic engineering. The binding mode and electron transfer mechanism of Ag-assisted MoS2 film prepared by co-sputtering method have not been fully discussed in detail. The effect of noble metal doping amount on the linear optical behavior of MoS2 has not been reported. Meanwhile, this research also provides an important reference for subsequent multi-dimensional modified semiconductor materials.

In this paper, the Ag-power/MoS2 film was prepared by a simple “one-step” co-sputtering method. When the DC sputtering power increases, the relative content of Ag NP in the Ag-power MoS2 film significantly increases and a large amount of Ag2S is produced. It means that the deposited Ag NPs form a bonding mode with a large number of external S atoms in the MoS2 during the co-sputtering process. Ag plasma can reduce the resistivity of the MoS2 film by 103-104 orders of magnitude, and obviously enhance the absorption/luminescence ability of MoS2 in the visible wavelength range. The implanted and assisted Ag plasmon not only increased visible/near-infrared absorption and emission of MoS2 nanosheets, but also induced highly amplified entire carrier mobility in MoS2 nanosheets. Considering that the binding mode and electron transfer characteristic may have a greater impact on the linear optical behavior of the Ag-power/MoS2 film, the discussion of this issue is of tremendous importance. The Ag-power/MoS2 film displays many characteristics that are desirable for the field of optoelectronic engineering devices.

Section snippets

Experimental

The MoS2 and Ag-power/MoS2 films were uniformly deposited on quartz substrates by co-sputtering method. Schematic diagram of the experimental device was illustrated in Fig. 1 (a). In the preparation stage, the substrate was washed with deionized water and absolute ethanol (concentration 99.99%) for 10–15 min and placed in the air to dry. This operation can prevent organic/inorganic impurities after introducing greater internal strain on the substrate surface during the particle deposition

Result and discussion

The SEM images of the Ag-power/MoS2 film along with their corresponding XRD results are presented in Fig. 2. According to Fig. 2 (a), the pure MoS2 film exhibits a nanosheet morphology with length of only 159 nm. The vertically aligned MoS2 nanosheets exhibit a larger specific surface area, which implies that the contact surface with Ag NPs is expanded. Furthermore, from the SEM image of the Ag-power/MoS2 film, it can be clearly seen that Ag NPs are uniformly attached to the MoS2 nanosheets and

Conclusions

Herein, the Ag-power/MoS2 film with excellent electrical conductivity and linear absorption capability has been uniformly deposited on the quartz substrates by single-step co-sputtering method. SEM and mapping results showed that Ag plasma implanted and assisted MoS2 nanosheets were successfully obtained. The peak positions of E12g/A1g and Mo3d/S2p shifted slightly, which is attributed to the stress and spontaneous/non-spontaneous electron transfer effect in Ag assisted MoS2 nanosheets. In

CRediT authorship contribution statement

Hai-Quan Liu: Conceptualization, Data curation, Investigation, Methodology, Software, Writing – original draft. Cheng-Bao Yao: Formal analysis, Funding acquisition, Supervision, Validation, Visualization, Writing – review & editing. Jin Li: Project administration, Resources. Wen-Jun Sun: Investigation, Software. Cai-Hong Jiang: Resources, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Natural Science Foundation of Heilongjiang Province under Grant No. LH2021A016 and LH2020F032. And the subject of Harbin Normal University under Grant No. 2020-KYYWF352 and HSDSSCX2021-28.

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