was sputtered with a power density of 7 8 w cm 2 to obtain an oxide film fourth layer having an atomic ratio of sn to si of 2 8 and a refractive index of about 1 6 in a thickness of 10 nm this film will be referred to as sto 2 by the same method and under the same conditions as in example 1 zno ag zno were formed in the same film thicknesses as in example 1 on a float glass substrate having a thickness of 2 mm by the same method and under the same conditions as in example 1 zno ag zno were formed in the same thicknesses as in example 1 on a float glass substrate having a thickness of 2 mm then a gas mixture of argon and oxygen flow rate of 1 1 was introduced into the chamber the pressure was adjusted to 2 u00d7 10 31 3 torr and the tin target was sputtered with a power density of 7 w cm 2 to form a sno 2 film fourth layer in a thickness of 10 nm by the same method and under the same conditions as in example 1 zno ag zno were formed on a float glass substrate having a thickness of 2 mm the film thicknesses were 40 nm.