Crystal Structure Investigation of PBO Thin Films Produced by Pulsed Laser Evaporation

Abstract

PbO exists in two polymorphic forms — the low-temperature tetragonal phase — α-PbO and the high-temeprature orthorhombic phase β-PbO. At 489° C and atmospheric pressure α-PbO undergoes phase transition to β-PbO. The interest in deposition of PbO thin films has been stimulated by the potential application as antireflection coatings of detectors operating in the atmospheric window 3–5 μm. These two phases of lead monoxide possess different optical properties and the establishment of the influence of technological conditions on the crystal structure of films deposited is of great importance. The aim of the present work is the investigation of the overall crystal structure of PbO thin films deposited by Pulsed Laser Evaporation (PLE). The PLE technique ensures high speed of evaporation leading to the stoichiometry reproduction which is the most important factor in the case of oxide thin film production. The crystal structure of PbO thin films deposited at different substrate temperatures in the range from 50° C to 300° on two type of substrates — monocrystal (101) quartz and amorphous glass is investigated by X-ray diffraction. The analysis of X-ray diffraction patterns demonstrates:

• 1. The films grow with β-PbO phase predominantely. The crystallization of the phase depends strongly on the substrate temperature. On elevating substrate temperature an oriented growth in (001) direction takes place. The oriented growth of the β-PbO phase depends on the substrate type. In the films deposited on quartz substrate (possesing periodical relief) it takes place at lower substrate temperatures.

• 2. The α-PbO phase is present in the films produced at substrate temepratures higher than 250° C being with preferred (001) direction of crystallization on monocrystal quartz substrates and polycrystal on glass substrates.