X-ray photoelectron spectroscopy of high-throughput mechanically exfoliated van der Waals materials

X-ray photoelectron spectroscopy (XPS) is a widely used and easy accessible characterisation technique for investigating the chemical composition of materials. However, investigating the composition of van der Waals (vdW) flakes by XPS is challenging due to the typical spot size of XPS setups compared to the dimensions of the flakes, which are usually one thousand times smaller than the spot size. In this work, we demonstrate the feasibility of quantitative elemental analysis of vdW materials by using high-throughput mechanical exfoliations, which favour the coverage of arbitrary substrates with flakes of areas of the order of the cm2 using minimal quantities of materials (about 10 mu g). We have analysed the chemical composition of MoS2, graphite, WSe2 and FePS3. The high-resolution measurement of their main core levels through XPS demonstrates the absence of significant contamination during the transfer method. In the case of air-sensitive FePS3, the glove box fabrication and its degradation in air are discussed. Overall, this research opens the possibility of evaluating the purity of commercial or lab-synthesized flakes and paves the way towards a more systematic comparison between the composition of vdW materials produced and used among different laboratories.Quantitative elemental analysis of van der Waals materials can be done by XPS by using high-throughput mechanical exfoliations, which favour the coverage of large area substrates with flakes using minimal quantities of starting materials.