NOVELTY - Paste comprises: a solvent; and elemental silicon/germanium nanoparticles having an average primary particle diameter of no more than 75 nm at a concentration of 1-20 wt.%. The paste has a viscosity, at a shear rate of 2 s-1, of 2-450 Pa.s, a viscosity at a shear rate of 1000 s-1 of no more than 1 Pa.s, and a ratio of the viscosity at a shear rate of 2 s-1 to the viscosity at a shear rate of 1000 s-1 of at least 20.    USE - The paste is useful as a silicon/germanium ink (claimed), spin coating inks and screen printing pastes for printed electronics, solar cell component formation and other semiconductor applications.    ADVANTAGE - The paste or silicon/germanium ink has: no more than 500 parts per billion by weight metal contamination; a synergistic improvement to the quality of some of the inks; flexibility without surface modifying the silicon/germanium nanoparticles; improved stability, shelf life and improved deposition properties preferably rheological properties and printing properties; and increased smoothness and uniformity. The paste can be produced at high yield with good quality in a cost effective manner.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a silicon/germanium ink comprising a solvent and 0.25-10 wt.% elemental silicon/germanium nanoparticles having an average primary particle size of no more than 75 nm with a viscosity of 5-75 cP, where the solvent comprises at least 95 wt.% alcohol;    (2) a silicon/germanium ink comprising a solvent, 0.25-20 wt.% elemental silicon/germanium nanoparticles having an average primary particle size of no more than 100 nm and at least 1 wt.% silica etching composition;    (3) applying a silicon ink deposit to a silicon substrate (100) having a silica (silicon oxide) overcoat, comprising depositing an ink comprising silicon nanoparticles and a silica etchant to form ink deposits (108, 110) over at least a portion of the silica overcoat to etch through the silica overcoat and drying the ink deposits to remove solvent and silica etchant and to form a silicon nanoparticle deposit in contact with the silicon substrate;    (4) an ink comprising a solvent, 0.25-20 wt.% elemental silicon/germanium nanoparticles having an average primary particle size of no more than 100 nm and 0.25-15 wt.% silica/germania nanoparticles having an average primary particle size of no more than 100 nm; and    (5) producing silicon/germanium nanoparticle inks, comprising centrifuging an initial well mixed dispersion comprising silicon/germanium nanoparticles in a solvent, to separate a supernatant silicon/germanium nanoparticle dispersion from residue and further centrifuging the supernatant solution comprising the silicon/germanium nanoparticle dispersion to separate a multiply centrifuged supernatant as a stable silicon/germanium nanoparticle ink.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic top perspective view of a printed substrate.    Substrate (100)    Optional surface coating (102)    Windows (104, 106)    Deposits (108, 110)    Coating (112)