Oxford Applied Research recently opened a new US subsidiary in Newark, N.J., and said it has expanded its sales and marketing efforts to increase its share of the MBE and surface science market. Steven M. Rothstein was appointed US sales/marketing manager, and James P. Vance as Western regional sales manager.   . . .   Alpine Research Optics recently bought a five-acre site on which to build manufacturing and research facilities, in the Gunbarrel Technical Center in Boulder, Colo.