the ring structure 252 via suitable apertures 282 283 and 284 formed through the outer ring body 264 in this way the conductive wires 286 288 and 290 of the thermocouples 268 270 and 272 respectively extend out of the hostile environment of the susceptor 20 and ring structure 252 the electric signals produced by the thermocouples 120 268 270 and 272 are coupled to a suitable temperature control device not shown which forms no part of the substrate supporting mechanism 20 of this invention reference is now made in fig1 11 and 12 wherein a modified form of the rotatable substrate supporting mechanism is shown and is indicated generally by the reference numeral 20a the mechanism 20a is essentially the same as the previously described mechanism and has a modified form of gas restrictor housing 294 mounted in the bore 111 of the bearing seal mounting plate 110 the gas restrictor housing 294 has an inverted cup shaped body 296 with the annular groove 298 and injection ports 299 for receiving the purge gas from the passage 176 of the seal mounting plate 110 the purge gas is directed into the downwardly opening cavity 300 of the gas restrictor housing 294 for movement downwardly and then upwardly into the bore 52 of the rotation shaft 51 in the manner hereinbefore fully described with reference to the mechanism 20 the modified gas restrictor housing 294 of the mechanism 20a has an elongated tube 302 extending axially upwardly therefrom the rotation shaft 51 extends axially through the tube 302 which is sized to provide an annular gap 304 between the outside diameter of the rotation.