than the liner fig6 illustrates in greater detail the point where distortion of the gas injector is initiated at point 69 where the diameter of the highly thermally conductive sic liner 64 has narrowed the relatively more thermally expansive liner comes into close proximity or contact with injector 62 as the injector is contacted it may pivot slightly allowing it to be misaligned in the direction of the boat and wafers in the simplest of cases any contact during thermal excursions abrades the surfaces and results in particulate contamination of the wafers the contamination increases with each thermal excursion injectors 62 are inserted into the furnace assembly with the vertical portion aligned parallel with the inner surface of the most narrow portion the liner 64 but with thermal excursions spacing between the unsupported injector tube and the liner may change in particular distortion of long injectors becomes more pronounced as a result of the thermal expansion mismatch between liner and injector and with increasing thermal excursions a solution to the problem of distortion of the long injectors and liner contact is provided by the injector design and construction of this invention in fig7 the improved injector 72 includes a standoff 75 attached to the quartz injector near the onset of vertical rise the standoff of the same material composition as the injector preferably quartz is fused or otherwise permanently joined to the injector during fabrication standoff 75 has precisely defined thickness which allows contact and alignment of the injector to be made near the.