TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Sheet: The sheet comprises 1-100 boron-nitrogen layers. The sheet comprises hexagonal boron nitride with a purity of greater than or equal to 70%, when determined by Raman spectroscopy. The sheet has a peak at 1367 inverse cm with a full width at half maximum of less than or equal to 17 inverse cm in a Raman spectrum. The sheet has a length of greater than or equal to 1 mm. Preferred Method: In the method, a mean grain area of the metal catalyst in sheet form after the first thermal treatment has a mean increase of at least greater than or equal to 100% than a mean grain area of the metal catalyst before the first thermal treatment. The metal catalyst in sheet form after the first thermal treatment has a mean grain area of greater than or equal to 1 mu m2; and has a root mean square surface roughness of less than or equal to 7 nm. The first thermal treatment is performed at a temperature of lower temperature to an upper temperature, where the lower temperature satisfies the equation i.e. the lower temperature is equal to melting point of the metal catalystx 0.60, and the upper temperature satisfies the equation i.e. the upper temperature is equal to (melting point of the metal catalystx 0.97) degrees C. The metal catalyst in sheet form after the first thermal treatment has a mean grain area of 100-5000 mu m2; or 10000-100000 mu m2. The method further involves polishing a surface of the metal catalyst in sheet form after the first thermal treatment, where the polishing comprises at least one of chemical polishing, physical polishing, chemical mechanical polishing, and electrolytic polishing. In the method, the metal catalyst in sheet form after the polishing has a root mean square surface roughness of less than or equal to 5 nm, preferably less than or equal to 1.5 nm. The second thermal treatment is performed in the presence of inert gas and hydrogen gas. Preferred Components: The nitrogen source and the boron source are each a vapor. The nitrogen source comprises NH3 and N2. The boron source comprises at least one of BH3, BF3, BCl3, B2H6, (CH3CH2)3B, (CH3)3B, and diborane. The nitrogen source and the boron source comprise at least one of H3NBH3 and (BH)3(NH)3.    TECHNOLOGY FOCUS - METALLURGY - Preferred Components: The metal catalyst is at least one metal selected from nickel, cobalt, iron, platinum, palladium, gold, aluminum, chromium, copper, magnesium, manganese, molybdenum, rhodium, silicon, tantalum, titanium, tungsten, uranium, vanadium, and zirconium, and its alloy. EXAMPLE - No suitable example given.