In a method, an aluminum body is chemically treated with at least one of an alkaline solution and an acid solution. Anode-oxidization is performed on the chemically treated aluminum body to form an aluminum oxide layer. The aluminum oxide layer is treated with hot water at a temperature more than 75° C. or steam. The aluminum oxide layer after being treated with hot water or steam includes plural columnar grains, and an average width of the columnar grains is in a range from 10 nm to 100 nm.