This invention relates to a stack of well-aligned small holes to be used in ion and electron microscopy, and in particular to a method for fabricating apertures making up a lens system. 
One of the problems in ion or electron microscopy is the alignment of the ion or electron source with the apertures of the lens system, considering the fact that the dimensions of the sources as well as those of the lenses are extremely small. 
An obvious and generally practiced method in the fabrication of lenses, though with a much larger inner diameter, involves the electron-optical machining and simultaneous observation of the alignment process.  This method is, however, not applicable in the manufacture of apertures having a diameter in the nanometer range.