Continuous-flow helium cryostats

To understand the nature of the spins in the polymers, electron paramagnetic resonance (EPR) experiments were carried out using a Bruker ESP 300 spectrometer equipped with a TE102 rectangular cavity that resonates at 9.5 GHz (X band). An ESR-900 continuous flow helium cryostat from Oxford Instruments provided temperature control from 4 to 300 K. 

IR spectra were taken at room temperature (300 K) and liquid-helium temperatures (5-15 K), using a Bomem DAS Fourier transform infrared (FTIR) spectrometer and an InSb detector. For the low-temperature measurements, a Janis continuous-flow liquid-helium cryostat with wedged, IR-transparent windows was utilized. Hall-effect measurements, in the Van der Pauw geometry, were performed at room temperature using a system from MMR Technologies. Wires were attached to the ZnO using silver paint, which provided adequate Ohmic contacts for the electron concentrations (10 cm ) in these samples. 

Fig. 4.6. Cross-section of an optical continuous-flow cryostat (CF 204 of Oxford Instruments), with the extremity of the removable transfer tube inserted, but without sample holder. The evacuation valve at the top is masked by the sample port. The optional windows on the radiation shield can be replaced by metallic irises to reduce the field of view. This cryostat can be fitted with one or two more optical windows at 90° from the main optical axis for additional excitation, and also with a down-looking window. The arrows indicate the direction of the flow of liquid or gaseous helium. Reproduced with permission from Oxford Instruments...

The low temperature measurements used an helium continuous-flow cryostat, allowing work at fixed temperature down to 15 K. Most of the experiments were performed at 30 K + 5 K. 

Figure 7 Continuous-gas-flow cryostat of Ref. 86, with its special helium siphon installed on the Eulerian cradle of the neutron diffractometer DIO at the Institut Laue Langevin (Grenoble, France). The arrows indicate the two rotating Johnstons the circles indicate the corners with magnetic spacers.

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