11 on a first surface 12 of substrate 10 by any conventional method so as to produce a predetermined pattern of exposed substrate 10 and non reactive material substrate surface 12 is then etched using conventional orientation dependent etching techniques to form a hole 18 having a sharp apex 20 the resultant structure is shown in fig1 in this first embodiment the distance from the sharp apex 20 to a second surface 21 of substrate 10 is about 1 micrometer u03bcm as will be appreciated by those skilled in the art orientation dependent etching refers to etching in one crystal direction but not in another crystal direction for example an etch such as h 2 so 4 h 2 o 2 h 2 o may be used to preferentially attack the lt 100 gt planes of the substrate material the etchant will attack the crystal structure at a rapid rate until lt 111 gt planes are encountered at which time etching stops or proceeds at a significantly reduced rate this etching action produces a pyramidally shaped hole 18 the lt 111 gt sides of which intersect at an apex 20 which is crystallographically sharp the orientation dependent etching process results in uniformly sharp pieces 20 even though the etching time may vary from one hole 18 to another hole 18 in a plurality of such holes 18 other orientation dependent etching etchants can be used without departing from the.