Cryostat

Cryogenics We use several types of evacuated stainless steel cryostats of about 1 htre capacity to provide the 77 K cooling with hquid nitrogen. The simplest, best valued and easiest to handle one is a ordinary thermos flask available from the supermarket (see fig.3). It is sufficient for a measurement period of more than 12 hours. A specially designed stainless steel vessel gains cooling periods of 30 hours. 

Figure Bl.4.2. (A) Basic components of an astronomical heterodyne receiver. The photomicrograph in (B) presents the heart of a quasi-optical SIS mixer and its associated superconducting timing circuits, while the image in (C) shows the fiilly assembled mixer, as it would be incorporated into a low-temperature cryostat (J Zmuidzinas, private conmumication).

Bartelt A, Close J D, Federmann F, Quaas N and Toennies J P 1996 Cold metal clusters helium droplets as a nanoscale cryostat Phys. Rev. Lett. 77 3525... 

Durand Y, Woehl J C, Viellerobe B, Gdhde W and Orrit M 1999 New design of a cryostat-mounted scanning near-field optical microscope for single molecule spectroscopy Rev. Sc/. Instrum. 70 1318-25... 

Alternatively, the following liquids can be used, partially frozen, as cryostats, by adding solid CO2 from time to time to the material in a Dewar-type container and stirring to make a slush ... 

For semiconductor work, either whole wafers or small pieces are used, the latter often being necessary for insertion into a cryostat. Bulk solids may be analyzed in any form, but scattered light may be reduced and the signal increased if the emitting surface is specular. 

A sample holder, including optics for focusing the incident light and collecting the luminescence. Efficient light collection is important, and the sample holder may need to allow for a cryostat, pressure cell, magnet, or electrical contacts. 

Because Raman spectroscopy requires one only to guide a laser beam to the sample and extract a scattered beam, the technique is easily adaptable to measurements as a function of temperature and pressure. High temperatures can be achieved by using a small furnace built into the sample compartment. Low temperatures, easily to 78 K (liquid nitrogen) and with some diflSculty to 4.2 K (liquid helium), can be achieved with various commercially available cryostats. Chambers suitable for Raman spectroscopy to pressures of a few hundred MPa can be constructed using sapphire windows for the laser and scattered beams. However, Raman spectroscopy is the characterizadon tool of choice in diamond-anvil high-pressure cells, which produce pressures well in excess of 100 GPa. ... 

Fig. 7. The effect of Brj intercalation on the temperature dependence of the resistivity of a bulk SWCNT sample. Curve a, pristine material curve b, saturation-doped with Br2 curve c, after heating in the cryostat vacuum to 4. 0 K for several hours [3. ].

Somatostatin. Figure 1 Somatostatin-like im mu noreactivity in neurons of the periventricular hypothalamic nucleus of the rat. Coronal brain cryostat sections have been processed for im mu nohistochemistry and sequentially incubated with a primary monoclonal mouse anti human somatostatin antibody and secondary antimouse antibody conjugated with the fluorescence-dye Cy-3. Images have been taken with a Zeiss Axioplan fluorescence microscope. Scale bar, 100 pM. 

A method of rotating cryostate (15) is a promising technique for study of unstable radicals. 

In comparison with hydrocarbon and polymeric matrices, which have their own absorptions in the IR and can react chemically with the intermediates, inert gas matrices are free of these shortcomings. Neon, krypton and xenon have been used as matrix substances in some studies. However, only argon and nitrogen matrices are widely adopted because of the availability of the pure gases and the fact that there is a variety of cryostats that can provide the optimal temperature conditions for the formation of rigid and transparent matrices from these elements. 

Besides thermolysis, the photochemical decomposition of solid trihalo-methylmercury compounds RHgCCli, CF3HgOCOCF3 and Hg(OCOCF3)2 has been studied (Scheme 2). The irradiation of samples placed in an evacuated quartz tube, which was connected to a helium cryostat, was carried out at -50 to +10°C. Thus, a desorption into the gas phase of the primary products of the photolysis occurred, and consequent low-temperature matrix stabilization of them was made. As a result, the formation of only the radicals CCI3 (1 3 898 cm" ) and CF3 (vi 1084, V2 702, P2+ V4 1205, r>3 1249 cm ) or of products of their secondary reactions was observed (Mal tsev et al., 1974, 1975, 1977b). 

An important accessory in many applications of Mossbauer spectroscopy is a cryostat for low temperature and temperature-dependent measurements. This may be necessary to keep samples frozen or to overcome small Debye-Waller factors of the absorbers at room temperature in the case of an isotope with high y-energy. Paramagnetic samples are measured at liquid-helium temperatures to slow down... 

Figure 3.9 shows a schematic sectional drawing of a liquid-helium Mbssbauer cryostat with a superconducting magnet optionally included. The layout is kept generic to highlight a few issues that are essential for applications in transition metal chemistry ... 

Fig. 3.9 Schematic view of a Mbssbauer cryostat with a superconducting cryo-magnet for horizontal transmission experiments with the field parallel to the y-rays. Without a magnet the helium reservoir may end above the optical axis, such that the cryostat can have a narrow tail with much shorter window-to-window distance...

Fig. 9.19 Experimental NFS spectrum of Fe02(SCsHF4) (TPpjvP) at 4.2 K together with stainless steel (SS) at 300 K as reference scatterer, the latter placed 30 cm downstream and outside the cryostat. A lit with the CONUSS program [9,10] yields the value 5 = 0.30 mm s as isomer shift of the porphyrin relative to stainless steel [25]...

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