Armen S. Kuzanyan

Thermoelectric cooling at cryogenic temperatures

Experimental results demonstrating Peltier cooling below 10 K are reported, using crystals of the thermoelectric cerium hexaboride (CeB6). Direct measurements of the Peltier cooling showed δT up to ∼0.2 K in magnitude at T∼4–5 K. All three kinetic parameters: resistivity (ρ), heat conductivity (k), and Seebeck coefficient (S), characterizing the thermoelectric figure of merit ZT=S2T/ρk, were measured, giving high-confidence results.

Thermoelectric single-photon detectors for x-ray/UV radiation

A feasibility study of megapixel microcalorimeter arrays, based on thermoelectric energy to voltage conversion and digital superconducting readout, is presented. The design concept originated from the philosophy of employing the simplest principles at the single-pixel level to enable large arrays without sacrificing energy resolution, fast operation speed, and quantum efficiency. Initial experimental tests confirm the basic predictions of theory, and show no major obstacle in achieving the desired characteristics.

Imaging detectors based on anisotropic thermoelectricity

Abstract Transient voltage pulses spontaneously occur in anisotropic films following the absorption of photons. Experiments on normal state YBCO unambiguously confirm that the pulses sensed between the sample ends arise from the thermoelectric response to the heat flux propagating through the film, perpendicular to the voltage measurement axis. Good agreement is found between the measured voltage characteristics and a macroscopic model based on the Seebeck tensor of the material. The applicability of such materials to single-photon detectors is discussed. A class of materials with sufficiently large low-temperature Seebeck tensor to construct a high resolution detector has been identified but not yet optimized for this use.

Three simple methods to obtain large area thin films by pulsed laser deposition

Three new relatively simple methods of laser deposition of large area thin films are proposed. The thickness uniformity of films obtained with these methods was preserved within the limits of /spl plusmn/3.5% on 100 mm diameter substrates. The first method employs controlled tilting of the target around the axis parallel with the substrate plane, with the respective positions of the laser beam, focal spot, and substrate being kept constant. The peculiarity of the second and third methods is laser deposition of the compound upon a substrate through a mask. The possibilities of different configurations of the slit in the mask are considered. One method uses a mask with a slit in the form of a sector, which is symmetrical with regard to the substrate radius, with various angular dimensions at different distances from the rotation center of the substrate. Another method uses a mask with two slits in the form of a bent sector, the symmetry axis of which coincides with the line of equal velocity of mass transfer of the deposited compound onto the substrate.

Thermoelectric single-photon detector

The ability to detect a single photon is the ultimate level of sensitivity in the measurement of optical radiation. Sensors capable of detecting single photons and determining their energy have many scientific and technological applications. Kondo-enhanced Seebeck effect cryogenic detectors are based on thermoelectric heat-to-voltage conversion and voltage readout. We evaluate the prospects of CeB6 and (La,Ce)B6 hexaboride crystals for their application as a sensitive element in this type of detectors. We conclude that such detectors can register a single UV photon, have a fast count rate (up to 45 MHz) and a high spectral resolution of 0.1 eV. We calculate the electric potential generated along the thermoelectric sensor upon registering a UV single photon.

Laser-powered thermoelectric generators operating at cryogenic temperatures

A thermoelectric generator, operating in a cryostat at liquid helium temperatures, is described. Energy to the generator is supplied via an external laser beam. For this prototype device the associated heat load at permanent operation is comparable with the heat load associated with power delivery via metallic wires. Estimates indicate that still better performance can be enabled with existing thermoelectric materials, thereby far exceeding efficiency of traditional cryostat wiring. We used a prototype generator to produce electric power for measuring critical currents in Nb3Sn-films at 4K.

PLD of large area films onto substrate undergoing translational motion by mask method

The simple method of laser deposition of large area uniform-thickness films onto a moving ribbon of width up to 100 mm is proposed. The peculiarity of the method is the laser deposition of compound upon a substrate through a mask placed in immediate proximity of the substrate. Various configurations of mask slits that provide thickness uniformity of deposited films are considered. The precise sizes of slits in the masks are calculated using the data of an angular distribution of mass transfer of a deposited compound in a plasma plume. Given the advantage of laser deposition, the offered method should find practical uses, in particular, in the manufacture of superconducting ribbons.

Some peculiarities of pulsed laser deposition of large area thin films

The fabrication of large area Y-Ba-Cu-O thin films by pulsed laser deposition is discussed. The influence of laser spot dimension, laser fluence and the target topography on the plasma plume angular distribution has been investigated. A film-based method was used for determining angular distribution. The primary factors affecting the form of the plume have been determined. The spatial distribution of laser-generated particulates has also been investigated. A simple method to obtain large area thin films by deposition through a mask has been examined for reducing the number of particulates.

High-Z Lanthanum-Cerium Hexaborate Thin Films for Low-Temperature Applications

In order to find the next generation thermoelectric (TE) material, we are focussing on the parameter N v , the degeneracy of the band extrema in semiconductors near the Fermi energy. We attempt to synthesize ‘multivalley’ semiconductors by incorporating tetrahedral anions to introduce structural complexity while maintaining high crystallographic symmetry. The synthesis and crystal structures of two new compounds that partially fulfill our requirements for potential TE materials are reported. Pb 3 (PS 4 )Br 3 is monoclinic, space group P2 1 /m with a=9.1531(1)A, b=10.9508(3)A, c=12.7953(1)A and β=111.024(2)°. Pb 3 (PS 4 )I 1.75 Te 0.625 crystallizes in the space group R 3 with a=9.4876(4)A, c=46.189(3)A. Both structures are built from alternating layers of lead halide and the thiophosphate ion (PS 4 ) 3- .

An ultra-fast thermoelectric sensor for single-photon detection in a wide range of the electromagnetic spectrum

The results of computer simulation of heat distribution processes taking place after the absorption of single photons of 1-1000 eV energy in the three-layer detection pixel of the thermoelectric detector are presented. We considered different geometries of the detection pixel in which (La,Ce)B6 hexaboride is used as a thermoelectric layer and superconducting absorber and heat sink layers are of Nb, Pb and YBCO. The calculations are based on the heat conduction equation and are carried out by the matrix method for differential equations. It is shown, that by changing materials and sizes of the detection pixel’s layers it is possible to obtain transducers for the registration of photons within the given spectral range with the required energy resolution and count rate. It is demonstrated that such detector has a number of advantages, as well as improved characteristics, which give ground to consider the thermoelectric detector as a real alternative to superconducting nanowire single-photon detectors.