Accent Optical Technologies Inc. of Bend, Ore., a supplier of process control and metrology systems for semiconductor manufacturing, is expected to be acquired by Nanometrics Inc. in a transaction valued at about $81 million. The latter company will issue 5 million shares of its stock for outstanding Accent stock. Nanometrics will own 73 percent of the merged company, which will operate at its headquarters in Milpitas, Calif., and John D. Heaton will remain as president and chief executive officer. A designer and manufacturer of process control metrology systems for the semiconductor industry, Nanometrics expects that the acquisition, to close by midyear, will strengthen its position in optical CD and nonmetal thin-film metrology.