1：Experimental Design and Method Selection:

The IL-MPCVD process was used for the synthesis of BDD films from mixtures of methanol, ethanol, and boron trioxide. The methodology included monitoring optical emission spectra (OES) during the processes and estimating substrate temperatures from infrared emission in OES spectra.

2：Sample Selection and Data Sources:

A p-type Si substrate was used for diamond film growth. The boron concentration in the film was estimated using Raman spectroscopy.

3：List of Experimental Equipment and Materials:

A homemade IL-MPCVD machine consisting of a 2.45 GHz microwave generator, a reactor, a substrate holder, and a diaphragm pump was used. The substrate was a p-type Si (10 × 10 × 0.7 mm3).

4：45 GHz microwave generator, a reactor, a substrate holder, and a diaphragm pump was used. The substrate was a p-type Si (10 × 10 × 7 mm3). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The substrate was fixed to a substrate holder, and the substrate surface was adjusted to be 1.0 mm above a φ 3 mm tungsten electrode. A mixture of MeOH and EtOH was added to the reactor as a precursor for diamond, with B2O3 dissolved into this solution as the boron source for BDD growth. The pressure in the reactor was maintained at 60 kPa, and microwaves with a power of 500 W were irradiated to form a plasma in bubbles of vaporized solution.

5：0 mm above a φ 3 mm tungsten electrode. A mixture of MeOH and EtOH was added to the reactor as a precursor for diamond, with B2O3 dissolved into this solution as the boron source for BDD growth. The pressure in the reactor was maintained at 60 kPa, and microwaves with a power of 500 W were irradiated to form a plasma in bubbles of vaporized solution. Data Analysis Methods:

5. Data Analysis Methods: The boron concentration in the diamond film was estimated using Raman spectroscopy. The electrochemical properties of the BDD film were evaluated using cyclic voltammetry (CV) measurements.