Vahan R. Nikoghosyan

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.

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.

Simultaneous recording of two- and four-probe resistive transitions in laser-processed Sr-Ru-O

To confirm previously reported evidence of high-temperature superconductivity in laser processed Sr-Ru-O, we performed simultaneous two-probe and four-probe resistive measurements, using bar-geometry samples. A superconducting-type transition with an onset at about 250K was recorded in one of the samples, consistent with our previously reported measurements in the X-bridge geometry. Some new data on samples preparation are also presented.

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.

Modeling of kinetic processes in thermoelectric single photon detectors

The results of computer modeling of the thermoelectric single-photon detector are presented. We observe the processes of heat distribution after absorption of a photon of 0.1-1 keV energy in different parts of the absorber for different geometries of absorbers and thermoelectric sensors. The calculations were carried out by the matrix method for differential equations using parameters for the tungsten absorber and thermoelectric sensor made of (La, Ce)B6. The results of calculations show that it is realistic to detect photons about 0.1-1 keV and determine their energy with accuracy of not less than 1%. High count rates up to 200 GHz can be achieved.

Change in oxygen concentration in Sr2RuO4 single crystals after laser processing

In order to check the possibility of realization of high-temperature superconductivity in strontium ruthenate, we studied experimentally the influence of laser radiation on single-crystal samples of Sr2RuO4. Results obtained by the technique of electron-probe X-ray microanalysis showed an enhancement of the oxygen concentration in the near-surface layer of samples, which may most probably be caused by the change in the ruthenium valence as a result of laser treatment.