NOVELTY - Fabricating copper nanoparticles (200) comprises: heating a copper salt solution comprising a copper salt, an N,N'-dialkylethylenediamine, and a 6-18C alkylamine in an organic solvent to 30-50 degrees C; heating a reducing agent solution comprising a reducing agent, N,N'-dialkylethylenediamine, and 6-18C alkylamine in an organic solvent to 30-50 degrees C; and adding the heated copper salt solution to the heated reducing agent solution to produce copper nanoparticles.    USE - The method is useful for fabricating and producing copper nanoparticles, which is useful: in a composition (claimed), nanoelectronic and photonic materials (e.g. micro-electro-mechanical systems and nanoelectromechanical systems), biomaterials, nanomaterials (e.g. in polymers, textiles, fuel cell layers, composites and solar energy materials), anti-microbial formulations, antibiotic and antifungal agents, copper diet supplements, in a formulation of ink for ink jet printing of conducting vias and thin film solar cell; and as biomarkers, diagnostics, sensors, and incorporation in coatings, plastics and textiles.    ADVANTAGE - The method provides copper nanoparticles, which: provide low cost flexible thin film solar cell; are formed in scalable quantities with very small diameters in a stabilized form; and exhibit fusion at temperatures as low as 100 degrees C, and hence provide a lead-free solder for electronics applications. the method: avoids uneven temperatures on mixing and allows for rapid addition of the two solutions while heating the substrate copper salt solution and the reducing agent solution; uses inexpensive copper halide salts; provides a stabilized copper nanoparticle; provides readily scalable copper nanoparticles; allows low cost mass production; and is performed at less reaction time.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a stabilized copper nanoparticle made by the method; and    (2) a composition comprising copper nanoparticles, the 6-18C alkylamine and the N,N'-dialkylethylenediamine ligand, where the copper nanoparticles have a fusion temperature of 100-200 degrees C; and    (3) a surfactant system for the stabilizing copper nanoparticles comprising the N,N'-dialkylethylenediamine and the 6-18C alkylamine.    DESCRIPTION OF DRAWING(S) - The figure shows the structure of a surfactant stabilized nanoparticle.    Nanoparticle (200)    Dense core (202)    Lower density shell (204)    Protective surfactant layer (206)