Substitutional Doping of MoS₂ for Superior Gas-Sensing Applications: A Proof of Concept

Abstract

Two-dimensional layered materials (like MoS 2 and WS 2 ) those are being used as sensing layers in chemoresistive gas sensors suffer from poor sensitivity and selectivity. Mere surface functionalization (decorating of material surface) with metal nanoparticles (NPs) might not improve the sensor performance significantly. In this respect, doping of the layered material can play a significant role. Here, we report a simple yet effective substitutional doping technique to dope MoS 2 with noble metals. Through various material characterization techniques like X-ray diffraction, scanning tunneling spectroscopy images, and selected area electron diffraction pattern, we were able to put forward the difference between surface decoration and substitutional doping by Au at S-vacancy sites of MoS 2 . Lattice strain was found to exist in the Au-doped MoS 2 samples, while being absent in the Au NPdecorated samples. Surface chemistry studies performed using X-ray photoelectron spectroscopy showed a shift of Mo 3d peaks to lower binding energies, thus realizing p-type doping due to Au. The blue shift of the peaks as observed in Raman spectroscopy further confirmed the p-type doping. We found that gold-doped MoS 2 was more sensitive and selective toward ammonia (with a response of 150% for 500 ppm of ammonia at 90 °C) as compared to gold NP-decorated MoS 2 . The advantages of substitutional doping and the gas-sensing mechanism were also explained by the density functional theory study. From the first principles study, it was found that the adsorption of Au atoms on the S-vacancy site of a monolayer of the MoS 2 sheet was thermodynamically favorable with the adsorption energy of 2.39 eV. We also successfully doped MoS 2 with Pt using the same technique. It was found that Ptdoped MoS 2 gives huge response toward humidity (60,000% at 80% relative humidity). Thus, various noble metal doping of MoS 2 selectively improved the sensing response toward specific analytes. From this work, we believe that this method could also be useful to dope other layered nanomaterials to design gas sensors with improved selectivity.

Selective N,N-Dimethylformamide Vapor Sensing Using MoSe2/Multiwalled Carbon Nanotube Composites at Room Temperature

“…These results indicated that, irrespective of the method of preparation of a monolayer or a few layers, the sensors so obtained have several drawbacks. These include slow charge transfer and poor performance under high-humidity conditions, which limit their gas detection performance. , Subsequent to that, methodologies for altering the physical or chemical properties of pure MoSe 2 , such as noble-metal doping and heterostructure fabrication, have been examined. ,,, Unfortunately, enhancing the reactivity of sensing materials toward gases or VOCs via noble-metal catalysis decoration does not really improve the sensing surface activities . Furthermore, the scarcity and higher cost of noble metals limit their widespread application .…”

Bidimensional Engineered Amorphous a-SnO2 Interfaces: Synthesis and Gas Sensing Response to H2S and Humidity

“… 1 − 4 Key advantages of these interfaces are represented by their high surface-to-volume ratios, 5 the direct-to-indirect band gap transition, 6 , 7 the occurrence of chemical terminations like edges, boundaries, and surface vacancies, 8 − 10 and the engineered functionalities by metal nanoparticle decoration or substitutional doping. 11 , 12 Despite these features, a substantial disadvantage of TMDs and MCs, adversely affecting sensors’ signal reproducibility, is represented by their intrinsic thermodynamic instability (Δ G < 0), leading to spontaneous oxidation in dry-/wet-air laboratory conditions. 13 , 14 In details, the displacement of sulfur, selenium, and tellurium atoms, operated by ambient O 2 in MoS 2 and WS 2 sulfides, 15 , 16 MoSe 2 , WSe 2 , InSe, GaSe, and SnSe 2 selenides, 17 − 20 and MoTe 2 and WTe 2 21 , 22 tellurides, stimulates the nucleation over step edges of amorphous oxidized states, which proceeds through basal planes, eventually passivating all the flake’s surface.…”

“…Two-dimensional (2D) layered transition metal dichalcogenide (TMD) and metal chalcogenide (MC) semiconductors, with near atomic-scale thickness, have been extensively proposed in the past decade as alternative materials for traditional nanocrystalline metal oxides (MO) for gas sensing applications. − Key advantages of these interfaces are represented by their high surface-to-volume ratios, the direct-to-indirect band gap transition, , the occurrence of chemical terminations like edges, boundaries, and surface vacancies, − and the engineered functionalities by metal nanoparticle decoration or substitutional doping. , Despite these features, a substantial disadvantage of TMDs and MCs, adversely affecting sensors’ signal reproducibility, is represented by their intrinsic thermodynamic instability (Δ G < 0), leading to spontaneous oxidation in dry-/wet-air laboratory conditions. , In details, the displacement of sulfur, selenium, and tellurium atoms, operated by ambient O 2 in MoS 2 and WS 2 sulfides, , MoSe 2 , WSe 2 , InSe, GaSe, and SnSe 2 selenides, − and MoTe 2 and WTe 2 , tellurides, stimulates the nucleation over step edges of amorphous oxidized states, which proceeds through basal planes, eventually passivating all the flake’s surface. This phenomenon is further enhanced when the sensor’s operating temperature (OT) is increased in the range of 25–150 °C to compensate for irreversible adsorption of gas molecules, as frequently experienced in metal oxide and 2D layered sensors. , …”

Efficient Sensing of Selected Amino Acids as Biomarker by Green Phosphorene Monolayers: Smart Diagnosis of Viruses

“…Significant improvement in sensing performance of various 2D dichalcogenides over surface functionalization with suitable metal nanoparticles has been reported elsewhere. [ 57 ] Following this, we have doped GPM with selected dopants (Ag, Cu, Zn) separately, which results into the formation of Ag@GPM, Cu@GPM, and Zn@GPM, respectively. The formation energies ( E f ) of these substitutions are calculated to be −2.6, −4.8, and −1.8 eV for Ag@GPM, Cu@GPM, and Zn@GPM, respectively.…”