1：Experimental Design and Method Selection:

The study employs two laser-assisted direct solid sampling methods, LA-ICP-MS and LIBS, for the determination of the stoichiometry of novel diboride based materials. Liquid standards are used to overcome the need for certified reference materials or matrix matched standards.

2：Sample Selection and Data Sources:

The ternary system W1-xTaxB2-z is used as a model. Thin films with varying stoichiometry are fabricated via magnetron sputtering. Reference compositions are obtained by liquid digestion of the samples and subsequent ICP-OES measurement.

3：List of Experimental Equipment and Materials:

Instruments include an ICP-OES iCAP 6500 RAD, a J200 Tandem system for LIBS, and a quadrupole ICP-MS iCAP Qc with a NWR213 laser ablation system for LA-ICP-MS.

4：Experimental Procedures and Operational Workflow:

For LIBS, dried droplet standards are prepared and measured. For LA-ICP-MS, microgroove standards are prepared and measured. Both methods are compared for accuracy and reproducibility.

5：Data Analysis Methods:

Data treatment methods include linear regression, internal standard-independent calibration strategy, multiple linear regression, and PLS for LA-ICP-MS. For LIBS, different calibration approaches such as simple linear regression and PLS are used.