| abstract |
A graded material wherein the rate of etching by a specific chemical is changed continuously or stepwise from the uppermost surface to an inner part thereof; the above graded material which comprises a main material and an additive capable of changing the rate of etching the material wherein the concentration of the additive is changed continuously or stepwise; the above graded material which comprises, as the main material, a glass material having SiO2 as a primary component, and fluorine as the additive, which is a graded material exhibiting the rate of etching by hydrofluoric acid being changed gradually in the direction of depth. The graded material allows the solution of the problem associated with a conventional, isotropic or anisotropic, homogeneous material, that the etching characteristics of a material depends completely on the property inherent in the material and thus it is frequently difficult or impossible to realize a desired shape. |