Continuous-flow cryostat

Mossbauer spectra were collected as a function of temperature at room pressure, and as a function of pressure at room temperature. This was accomplished using a continuous flow cryostat for temperatures from 4.2 to 293 K, a vacuum furnace for temperatures... 

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. 

For measuring the resistivity of the films as a function of temperature, a continuous flow cryostat (Oxford Inst. Model CF-1204) with a temperature controller was used. The details of the sample preparation and measurement have been described previously (3). A temperature controlled silicon diode ( 0.1 K) was mounted next to the sample for accurate temperature measurement. X-ray powder diffraction patterns were obtained using a computerized Phillips powder diffractometer (Type AFD 3520) with Ni-filtered CuKa radiaticm. 

A standard six-circle diffractometer for diffraction experiments in horizontal and vertical scattering geometries at ambient conditions is operational in the first experimental hutch (EH I). In addition, it can accommodate a furnace (300-1200K) and continuous flow cryostat (10-300K) allowing for NRS experiments in a large temperature range. 

It is more convenient to use the enthalpy of the cold gas evaporating from the LHe in a continuous gas flow cryostat (Fig. 5.4). The flux and hence the temperature of the experiment can be regulated by a heater or a needle valve. 

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.

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. 4.7. Schematic of a stress apparatus of the compressing-spring type devised by C. Naud to be inserted in a continuous-flow optical cryostat for measuring the absorption of a sample under uniaxial stress. Extra optical apertures are indicated. The height adjustment system to the top of the cryostat is not shown (after [6])...

Pressure was generated with a diamond anvil cell (DAC) employing beveled anvils with central flats ranging from 20 to 100 jim and flat diamonds with 200-500 pm culets. Two types of DAC were used modified (to match a continuous flow He cryostat) Mao-Bell cell for operations at room and low temperatures [41] and a Mao-Bell high-T external heating cell [42]. The latter one is equipped with two heaters and thermocouples. Four experiments were performed at RT aiming to highest pressure and the final pressures varied from 180 to 268 GPa. For low-temperature measurements we used a continuous-flow He cryostat, which allowed infrared and in situ Raman/ fluorescence measurements. More details about our IR/Raman/fluorescence setup at the NSLS are published elsewhere [41]. 

For EL, the devices were driven under constant forward bias (Ca negative with respect to PEDOT PSS / ITO) and their emission was recorded using an Oriel InstaSpec IV spectrograph. The temperature was varied using a continuous-flow He cryostat (Oxford Instruments OptistatCF). For PL, the devices were optically excited through the ITO anode using a 407-nm pulsed diode laser (Pico-Quant LDH400). 

Time-resolved PL measurements were also performed using time-correlated single-photon counting (TCSPC) and photoluminescence upconversion (PLUC) spectroscopies. Descriptions of the setups can be found in refs. [14, 65], respectively. All measurements were taken in continuous-flow He cryostats (Oxford Instruments OptistatCF) under inert conditions. Finally, PL efficiency measurements were performed on simple polymer thin films spin coated on Spectrosil substrates using an integrating sphere coupled to an Oriel InstaSpec IV spectrograph and excitation with the same Ar+ laser as above. 

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 rectangular cavity that has a TE102 mode fi-equency of 9.5 GHz (X band). An ESR-900 continuous flow He cryostat from Oxford Instruments provided temperature control from 4 to 300 K. 

We probed by continuous wave (CW) PL a sample containing one (11-20) QD array (Figure 13.8). The experiment was made by exciting the sample at 244 nm with a doubled Argon laser on a 50-gm diameter spot, the sample being placed in a He-flow cryostat. 

An improved cryostat with more precise instrumentation and control was used to collect experimental data in the present investigation. The schematic diagram of the experimental apparatus is shown in Fig. 1. A flow system was employed as in the previous investigation, this method permitting a continuous gas-phase analysis. 

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