TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The compound containing a group 1B element or a group 3A element is a salt. The compound containing a group 1B element is a copper salt compound. The compound containing group 1B-6A elements is copper selenide. The copper salt compound is copper nitrate, copper sulfate, copper chloride, copper bromide, copper iodide, or copper hydroxide. The compound containing a group 3A element is an indium salt compound. The compound containing group 3A-6A elements is indium selenide. The indium salt compound is indium nitrate, indium sulfate, indium chloride, indium bromide, indium iodide, or indium hydroxide. The compound containing group 1B-6A elements, the compound containing group 3A-6A elements, and the compound containing group 1B-3A-6A elements are prepared in the form of particles. The particle containing group 1B-3A-6A elements is a reaction composite formed using a particle containing group 1B-6A elements and the particle containing group 3A-6A elements as a seed and bringing the remainder into contact with parts on a surface of the seed reactant. The reaction composite has a core-shell structure, where the seed reactant is coated with the remainder. The reaction composite has a dendrite structure, where the remainder is partially grown on a surface of the seed reactant. The reductant is sodium borohydride, or lithium aluminum hydride. The reductant is 1-100 equivalent weights of group 3A element or group 1B element. Preferred Method: The reaction is conducted at room temperature.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The reductant is hydrazine, sodium triacetoxyborohydride, diisobutylaluminum hydride, phenyl hydrazine, ascorbic acid, cysteine, fructose, ribose, galactose, tocopherol, and/or triethanolamine. The solvent is water, alcohol, ether, ketone, or amine based solvents. The solvent is water, ethanol, isopropanol, polyethylene glycol, ethylene glycol, diethylene glycol, or 1,4-butanediol; or two polar solvents selected including N-methyl-2-pyrrolidinone, dimethyl formamide, dimethyl sulfoxide, or dimethyl acetate. EXAMPLE - About 10 mmol aqueous indium nitrate solution and 10 mmol selenious acid were dissolved in ethylene glycol, mixed, and heated to 150 degrees C to proceed a reaction. A solution of (mmol) copper (II) nitrate (10), and selenious acid (20) was added to the reacted mixture, and hydrazine (100) as a reductant at room temperature. After reacting for 1 hour, the reaction product was centrifuged and purified to prepare a reaction composite in a core-shell form having a size of 50-100 nm, where an indium selenide particle was coated with copper selenide.