TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The gas injector includes an elongated body, where the first set and the second set of gas orifices are disposed on a first surface of the elongated body. The elongated body comprises an injector plate coupled to a base plate, where the first and second sets of gas orifices are disposed in the injector plate. The base plate includes many plenums configured to receive process gases via respective inlets (208), where the first and second sets of gas orifices are separated into zones, each zone associated with one of the many plenums. The gas injector further comprises: a flow controller coupled to each zone such that gas injection via each of the zones can be modulated at least one of temporally or spatially by starting, stopping, or varying the flow rates of the first and second process gases; a first gas supply coupled to the first and second set of gas orifices such that the first and second process gases are a same species of gases; a first gas supply coupled to the first set of gas orifices, and a second gas supply coupled to the second set of gas orifices, such that the first and second process gases are different species of gases; and a third set of gas orifices surrounding the first and second set of gas orifices, where the third set of gas orifices is configured to provide a purge gas barrier into the process chamber. The gas injector is fabricated from transparent quartz or non-transparent quartz. The substrate processing tool is an indexed inline substrate processing tool that includes many substrate processing modules coupled to one another in a linear arrangement, where each substrate processing module of the many substrate processing modules comprises an enclosure having a first end (216), a second end (218), and a lower surface to support the substrate carrier and to provide a path for the substrate carrier to move linearly through many modules from a first module of the modules, through any intervening modules, to a last module of the modules. In the substrate processing tool, the gas injector further comprises a third set of gas orifices configured to provide a purge gas barrier around the substrate carrier proximate walls of the first substrate processing module, where the purge gas barrier substantially prevents cross-contamination or deposition between the substrate processing modules. The substrate processing tool further comprises: the flow controller coupled to each zone; and a third set of gas orifices surrounding the first and second set of gas orifices, where the third set of gas orifices is configured to provide a purge gas barrier into the process chamber proximate to at least one vertical wall of the process chamber.