Silicon/germanium nanoparticles and inks having low metal contamination

Abstract

Laser pyrolysis reactor designs and corresponding reactant inlet nozzles are described to provide desirable particle quenching that is particularly suitable for the synthesis of elemental silicon particles. In particular, the nozzles can have a design to encourage nucleation and quenching with inert gas based on a significant flow of inert gas surrounding the reactant precursor flow and with a large inert entrainment flow effectively surrounding the reactant precursor and quench gas flows. Improved silicon nanoparticle inks are described that has silicon nanoparticles without any surface modification with organic compounds. The silicon ink properties can be engineered for particular printing applications, such as inkjet printing, gravure printing or screen printing. Appropriate processing methods are described to provide flexibility for ink designs without surface modifying the silicon nanoparticles.

What is claimed is: 
     
         1 . A method for forming a high purity dispersion comprising silicon nanoparticles and a liquid, the method comprising:
 centrifuging an initial dispersion of silicon nanoparticles and the liquid, and   separating the high purity dispersion from settled contaminants.   
     
     
         2 . The method of  claim 1  wherein the silicon nanoparticles were formed by laser pyrolysis with a silane precursor. 
     
     
         3 . The method of  claim 1  wherein the silicon nanoparticles have an average primary particle size of no more than about 100 nm. 
     
     
         4 . The method of  claim 1  wherein the silicon nanoparticles have an average primary particle size of no more than about 50 nm and a z-average secondary particle size of no more than about 250 nm. 
     
     
         5 . The method of  claim 4  wherein the primary particles have a distribution in diameters such that at least about 95 percent of the particles have a diameter greater than about 35 percent of the average diameter and less than about 280 percent of the average diameter. 
     
     
         6 . The method of  claim 1  wherein the initial dispersion has a silicon nanoparticle concentration of at least about 0.05 weight percent. 
     
     
         7 . The method of  claim 1  wherein the initial dispersion has a silicon nanoparticle concentration of at least about 0.5 weight percent. 
     
     
         8 . The method of  claim 1  wherein the silicon nanoparticles are doped. 
     
     
         9 . The method of  claim 8  wherein the silicon nanoparticles have a dopant concentration from about 0.25 atomic percent to about 15 atomic percent. 
     
     
         10 . The method of  claim 1  further comprising performing sonication to form the initial dispersion. 
     
     
         11 . The method of  claim 10  wherein mixing with shear is performed in addition to sonication to form the initial dispersion. 
     
     
         12 . The method of  claim 1  wherein the decontaminated silicon nanoparticle dispersion is stable without visible settling for at least a week. 
     
     
         13 . The method of  claim 1  wherein the liquid comprises terpineol. 
     
     
         14 . The method of  claim 13  wherein the liquid further comprises a second solvent. 
     
     
         15 . The method of  claim 1  wherein the liquid comprises alcohol. 
     
     
         16 . The method of  claim 1  wherein the decontaminated dispersion has a viscosity that depends on shear rate. 
     
     
         17 . The method of  claim 1  wherein the decontaminated dispersion has a viscosity from about 10 Pa·s to about 300 Pa·s. 
     
     
         18 . The method of  claim 1  wherein the level of total metal contamination is no more than about 5 parts per million. 
     
     
         19 . The method of  claim 1  wherein the nanoparticles comprise no more than about 200 parts per billion of iron by weight.