Ion-assisted deposition of amorphous PbO layers

Abstract

Lead oxide (PbO) is one of the most promising materials for application in direct conversion medical imaging X-ray detectors. Despite its high potential, conventional polycrystalline PbO layers deposited with the basic thermal evaporation method are not yet mature for practical use in x-ray imaging; indeed, they are highly porous, unstable at ambient conditions, and sub-stoichiometric. In order to combat the above issues with PbO, we advance the basic evaporation process with simultaneous energetic ion bombardment of the growing film. We show that tuning the ion-assisted thermal deposition not only solves the structural problems of poly-PbO, but also enables the growth of a new non-crystalline polymorphic form of the material-amorphous PbO (a-PbO). In contrast to poly-PbO, novel a-PbO layers grown by ion-assisted thermal deposition are stable at ambient conditions. Structural and morphological analysis confirms that a-PbO is stoichiometric and free of detectable voids, which suggests higher bulk X-ray stopping power than porous poly-PbO.

A Probe of Valence and Conduction Band Electronic Structure of Lead Oxide Films for Photodetectors

“…PbO layers are deposited with the ion assisted thermal evaporation technique where molecular oxygen is supplied to the chamber through the commercial ion source, ionizing the oxygen and accelerating the ions. This presence of energetic oxygen ions during the deposition process is initially responsible for the amorphous nature of these materials …”

“…While the elimination of signal lag represents a breakthrough in PbO technology, more comprehensive research is needed to optimize a‐PbO technology and to grow detector‐grade a‐PbO layers. We recently reported a detailed structural characterization by Raman spectroscopy, X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), and morphological examinations with scanning electron microscopy (SEM) of both, amorphous and poly‐PbO . Furthermore, a study on the electronic structure of amorphous and polycrystalline PbO films was recently published by us .…”

“…When the amorphous sample is exposed to a sufficiently high temperature, it undergoes gradual recrystallization. Firstly, this is another proof of the existence of amorphous Lead oxide, which was only recently synthetized . Secondly, understanding of the recrystallization kinetics and associated changes in electronic properties is important for applications where elevated temperatures will be involved during the manufacturing or utilization.…”

“…We recently reported a detailed structural characterization by Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and morphological examinations with scanning electron microscopy (SEM) of both, amorphous and poly-PbO. [15] Furthermore, a study on the electronic structure of amorphous and polycrystalline PbO films was recently published by us. [16] The work presented here is a characterization the electronic properties of a-PbO and analysis of its fundamental metastability at elevated temperatures with respect to its polycrystalline counterpart.…”

“…Firstly, this is another proof of the existence of amorphous Lead oxide, which was only recently synthetized. [15] Secondly, understanding of the recrystallization kinetics and associated changes in electronic properties is important for applications where elevated temperatures will be involved during the manufacturing or utilization. The density of states near the Fermi level is probed using synchrotron-based resonant X-ray emission (RXES), nonresonant X-ray emission (NXES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) methods.…”