TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The magnesium salt is magnesium chloride hexahydrate, magnesium nitrate hexahydrate or magnesium sulfate. The calcium salt is calcium sulfate, calcium nitrate or calcium chloride tetrahydrate. The manganese salt is manganese chloride tetrahydrate, manganese acetate tetrahydrate or manganese sulfate monohydrate. The iron salt is iron nitrate nonahydrate, ferric chloride hexahydrate or ferric sulfate. The nickel salt is nickel sulfate heptahydrate, nickel nitrate hexahydrate, or nickel chloride hexahydrate. The copper salt is copper chloride dihydrate, copper sulfate pentahydrate or copper nitrate trihydrate. The zinc salt is zinc chloride, zinc sulfate heptahydrate or zinc nitrate hexahydrate. The yttrium salt is yttrium nitrate hexahydrate or yttrium chloride hexahydrate. The cadmium salt is cadmium chloride or cadmium nitrate tetrahydrate. The barium salt is barium nitrate or barium chloride dihydrate. Preferred Properties: The film has average fiber diameter of 10-500 nm, relative standard deviation of 1-5% and softness of 10-100 mN.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The molar ratio of tin source and salt of metal other than tin is 100:1-10. The molar ratio of tin source and solvent is 10 g:50-150 mL. The molar ratio of tin source and coupling agent is 1:0.05-0.25. The molar ratio of the tin source and surfactant is 1:0.05-0.2. The tin source is tin tetrachloride, tin sulfate, or tin oxalate. The metal other than tin or its salt is magnesium salt, aluminum salt, calcium salt, chromium salt manganese salt, iron salt, cobalt salt, nickel salt, copper salt, zinc salt, yttrium salt, zirconium salt, antimony salt, cadmium salt, titanium salt or barium salt. The aluminum salt is aluminum nitrate nonahydrate, aluminum chloride hexahydrate or aluminum isopropoxide. The chromium salt is chromium acetate, chromium trichloride or chromium nitrate. The zirconium salt is zirconium chloride or zirconium acetate. The antimony salt is antimony pentachloride, antimony trichloride or antimony acetate. The titanium salt is titanium tetrachloride, isopropyl titanate or tetrabutyl titanate. The solvent corresponding to tin tetrachloride is chosen from water, ethanol, toluene, carbon tetrachloride or acetone. The solvent corresponding to tin sulfate is chosen from water, alcohol, isobutyl alcohol or acetone. The cobalt salt is cobalt acetate, cobalt nitrate hexahydrate or cobalt sulfate heptahydrate. The solvent corresponding to tin oxalate is water, or hydrochloric acid. The coupling agent is gamma -aminopropylmethyldiethoxysilane, beta -aminoethyl- gamma -aminopropylmethyldimethoxysilane, methyltrimethoxysilane, vinyltrimethoxysilane or gamma -(methacryloyloxypropyl)methyldimethoxysilane. The surfactant is dodecyl dimethyl benzyl ammonium chloride, sodium dodecylbenzene sulfonate, dodecyl dimethyl amine oxide, N-dodecyl-N,N-dimethylglycine, N-(2-hydroxyethyl)dodecyl amide or glycerol ethoxylate. Preferred Properties: The precursor solution has dynamic viscosity of 0.1-5 Pa.second and conductivity of 10-50 mS/m.