1：Experimental Design and Method Selection:

A two-step synthesis procedure involving sol–gel spin-coating followed by solvothermal methods was used to prepare ZnO thin films with nanorod morphology. Factors such as metal precursors, solvent, stabilizing agents, structure directing agents, drying-coating cycles, and post-thermal annealing were optimized for homogeneity and quality.

2：Sample Selection and Data Sources:

Quartz glass substrates were used for deposition. Materials included zinc acetate dehydrate, zinc nitrate hexahydrate, monoethanolamine, hexamethylenetetramine, NaOH, ethanol, and LPG gas.

3：List of Experimental Equipment and Materials:

Field-emission scanning electron microscope (FESEM, Hitachi S-4160), x-ray diffractometer (Philips Xpert MPD), UV–Vis spectrophotometer (+T80, PG Instruments), Raman spectrometer (Nicolet Almega XR, Thermo Scientific), photoluminescence spectrometer (Avaspec 2048 TEC, Avantes Co.), home-made gas sensor setup, digital flow controller, digital multimeter, electric tube furnace, Te?on-lined stainless-steel autoclave, hot plate, ultrasonic cleaner.

4：Experimental Procedures and Operational Workflow:

Substrates were cleaned ultrasonically. Sol–gel spin-coating was performed with precursor solutions, followed by drying and annealing. Solvothermal growth of nanorods was conducted, with post-annealing. Characterization involved FESEM, XRD, EDX, UV–Vis, Raman, and PL measurements. Gas sensing tests were done at various temperatures and LPG concentrations, measuring electrical resistance.

5：Data Analysis Methods:

Crystallite size was calculated using the Debye–Scherrer equation. Sensor sensitivity was calculated as (Ra - Rg)/Ra * 100. LPG concentration was calculated based on volume ratios. Data were analyzed for morphological, structural, optical, and sensing properties.