Thermoelectric cooling

Peltier coolers can be stacked so that the hot plate of the first cooler is cooled by the second cooler and so on. This type of stack is useful for making a small area, such as the focal plane of an irrfrared imager, very cold in order to reduce thermal noise in the image. 

Classical thermod)mamics using the equipartition of energy principle predicts that the lattice molar heat capacity will be given by 1/2R for each of the six degrees of freedom in a solid (three kinetic and three potential energy) for a total of 3R. As the temperature is increased, the observed heat capacity of materials approaches this value, which is known as the Dulong-Petit limit. However, at low temperatures, the observed heat capacity approaches zero as 7.  

Using the Planck distribution, Debye constructed a model in which the lattice heat capacity goes to zero as 7. The Debye model assumes a linear dispersion relation characteristic of a continuous medium rather than a chain of discrete atoms and cuts off the distribution at a frequency such that the number of normal modes is equal to 3 x the number of atoms. This frequency, knovm as the Debye frequency, is given by w-d = Vo 67t N/V), where Vq is the velocity of sound in the medium and N/V is the atoms per unit volume. A Debye temperature d is defined in terms of the Debye frequency d = hco-o/k. For T D, the Debye model approaches the classical Dulong-Petit limit. 

Even though the Debye model uses an unrealistic assumption for the dispersion relation, its primary justification comes from its excellent agreement with the observed heat capacity, especially at the lower temperatures. Apparently, the heat capacity is not particularly sensitive to the exact form of the dispersion relationship. 

The small electronic contribution to the heat capacity of metals can be imderstood by applying Fermi-Dirac statistics to the free electron gas. Since the groimd state energy is much higher than ambient thermal energy, only those electrons at the top of the Fermi sea can be thermally excited. As a result the electronic heat capacity is given by C = (tt /2)/ (KT/Tp) instead of the classical value of 3/2R. At very low temperatures, the electronic contribution, which has a linear temperature dependence, can exceed the lattice contribution to heat capacity, which has a temperature dependence. 

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In thermoelectric cooling appHcations, extensive use has been made of cascaded systems to attain very low temperatures, but because the final stage is so small compared to the others, the thermal flux is limited (Eig. 3). The relative sizes of the stages ate adjusted to obtain the maximum AT. Thus, for higher cooling capacity, the size of each stage is increased while the area ratios ate maintained. 

A. F. Joffe, Semiconductor Thermoelements and Thermoelectric Cooling, Infosearch Limited, London, 1957. 

Antimony is also used as a dopant in n-ty e semiconductors. It is a common additive in dopants for siHcon crystals with impurities, to alter the electrical conductivity. Interesting semiconductor properties have been reported for cadmium antimonide [12050-27-0] CdSb, and zinc antimonide [12039-35-9] ZnSb. The latter has good thermoelectric properties. Antimony with a purity as low as 99.9+% is an important alloying ingredient in the bismuth teUuride [1304-82-17, Bi Te, class of alloys which are used for thermoelectric cooling. 

Thermoelectrical cooling of the photomultiplier tube at about — 30°C reduces the dark noise current to a very low level. However, as the quantum efficiency of the S-20 type decreases as rapidly as the dark current in the red region, cooling brings only modest increases in the signal-to-noise ratio 23). 

Among all semiconductor NPs, metal selenides have been the focus of great attention due to their importance in various applications such as thermoelectric cooling materials, optical filters and sensors, optical recording materials, solar cells, superionic materials, laser materials and biological labels. Many synthetic methods have been developed for the preparation of relatively monodispersed selenide nanopartides (Murray et al., 1993 Korgel... 

Energy-dispersive spectrometry (EDS) is a technique of X-ray spectroscopy that is based on the simultaneous collection and energy dispersion of characteristic X-rays. Typical ED detectors are thermoelectrically cooled semiconductors (usually operated at 77 K), PIN diodes,... 

Uses. Semiconductors thermoelectric cooling power generation application for commercial use, Bi2Te3 is doped with selenium sulfide to alter its conductivity. 

IR spectra of starch can be obtained with an IR spectrometer such as a Digilab FTS 7000 spectrometer, Digilab USA, Randolph, MA, equipped with a thermoelectrically cooled deuterated tri-glycine sulfate (DTGS) detector using an attenuated total reflectance (ATR) accessory at a resolution of 4 cm by 128 scans. Spectra are baseline-corrected, and then deconvoluted between wavenumbers 1200 to 800 cm . A half-band width of 15 cm and a resolution enhancement factor of 1.5 with Bessel apodization are employed. Intensity measurements are performed on the deconvoluted spectra by recording the height of the absorbance bands from the baseline. 

Measurements between zero and 100° C can be done in this way temperatures below that of the surroundings can be reached by blowing air over solid C02 or a thermoelectrically cooled couple. At the higher temperatures, simple resistance heating and a fan to blow warmed air into the bath is satisfactory. 

The light-weight Elva-X energy dispersive XRF spectrometer employed for this study has an air-cooled rhodium target anode X-ray tube with 140 micron Be window and a thermoelectrically cooled Si-PIN diode detector. The detector... 

The slow-scan CCD, also called the scientific CCD, or in the spectroscopy literature simply CCD, is the detector of choice for most applications of Raman spectroscopy. A well-designed CCD has essentially zero dark current, very low readout noise, and high quantum efficiency (peak 45—70% near 700 nm) in the visible region of the spectrum. However, the response drops quickly above 800 nm and there is no photon response above 1.05 J m. For routine spectroscopy or process control, thermoelectrically cooled (to about —40° C) CCDs are adequate. Although these detectors are somewhat noisier than detectors operated at —100° C or lower, the former do not require liquid nitrogen cooling. The general properties and spectroscopic applications of the CCD have been reviewed (22). 

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