A stable substrate is disclosed comprising one more nanopores coated with an adhesion layer of a stabilizing compound, covalently bound to the nanopore interior via at least one bonding site, and having at least one coupling site. The substrate further comprises a functional enhancement layer of coupling partner molecules bound to the adhesion layer with a bond between the stabilizing compound's coupling site and the coupling partner's coupling bonding site.

A process for producing a silicon nitride powder characterized by comprising a step of providing a starting material powder containing not less than 90% by mass of a silicon powder; the step of filling a heat-resistant reaction vessel with the starting material powder; a step of obtaining a massive product thereof by a combustion synthesis reaction by igniting the starting material powder filled in the reaction vessel in a nitrogen atmosphere and permitting a heat of nitriding combustion of silicon to propagate to the whole starting material powder; and a step of mechanically milling the massive product by a dry method.

A silicon nitride powder for sintering which, despite of its fine powdery form, shows a very small increase in the oxygen concentration with time and features excellent storage stability. The silicon nitride powder for sintering has a specific surface area of 5 to 30 m.sup.2/g, and is characterized by having a hydrophobicity (M value) of 30 or more and an increase in the oxygen concentration of 0.30% by mass or less after left to stand in the air of a humidity of 90% and 20 C. for 48 hours. The silicon nitride powder for sintering can be obtained by dry-pulverizing aggregated masses of the silicon nitride in an inert atmosphere in the presence of a silane coupling agent.