Theoretical model for deposition of superconducting thin films using pulsed laser evaporation technique

Abstract

Normal metal-superconductor decoupling as a source of thermal fluctuation noise in transition-edge sensors J. Appl. Phys. 112, 034515 (2012) Transport critical-current density of superconducting films with hysteretic ferromagnetic dots AIP Advances 2, 022166 (2012) Pressure effects on strained FeSe0.5Te0.5 thin films J. Appl. Phys. 111, 112610 (2012) Magnetoresistance and transistor-like behavior of a double quantum-dot via crossed Andreev reflections J. Appl. Phys. 111, 113905 (2012) What are the internal field and the vortex density along the edges of a coated conductor or a superconducting bridge carrying current?We have theoretically and experimentally analyzed the laser-induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos () thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward-directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu30, targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three-dimensional expansion of the laser-generated plasma, initially at high temperature and pressure. The forward-directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma. The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is non thermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin fi1ms. The effects of the various beam and substrate parameters induding energy density and substrate-target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon su...

Dynamics of laser produced silver plasma under film deposition conditions studied using optical emission spectroscopy

“…Recombination is more probable in regions where plasma temperature is low, i.e., away from the target. The linear increase in the velocity is in agreement with the widely accepted theory of adiabatic plasma expansion [28,29]. During adiabatic expansion, the x-component of the velocity u, is given by the relation x dX(t)…”

“…Singh and Narayan [28,29]. The species velocities will be maximum in the direction having smaller initial dimensions.…”

Spectroscopic characterization of laser-induced tin plasma

“…The decay of the density is much faster at shorter distances from the target surface, especially Ͻ3 mm after which it levels off. The variation of density with distance ͑z͒ approximately follows a 1 / z law, which indicates that the initial expansion of the plume is one dimensional, and is in good agreement with the predictions of the plume expansion model given by Singh et al 27 The time-integrated temperature variation with distance from the target surface is given in Fig. 9.…”

Time evolution of the electron density and temperature in laser-produced plasmas from YBa2Cu3O7

“…Pulsed laser ablation has become a very successful method for the deposition of high-quality superconducting YBa 2 Cu 3 O 7 thin films [1][2][3][4]. Because of this and other technological applications, considerable efforts have been made to understand the dynamics of the laser-ablated material.…”

“…Line broadening of the Ba I emission line at 553.5 nm was monitored as a function of time elapsed after the incidence of a laser pulse on the target. Measured line profiles of barium species were used to infer the electron density and temperature, and the time evolution of these important plasma parameters has been worked out.PACS: 52.50Jm; 52.70 kz Pulsed laser ablation has become a very successful method for the deposition of high-quality superconducting YBa 2 Cu 3 O 7 thin films [1][2][3][4]. Because of this and other technological applications, considerable efforts have been made to understand the dynamics of the laser-ablated material.…”