Electron-beam current density found to be key when writing ferroelectric domains

Russian physicists took a back-to-basics approach to determine how electron-beam (EB) characteristics dictate the growth and quality of engineered ferroelectric domain patterns in lithium niobate (LN), the so-called silicon of optoelectronics. They report their findings in the Journal of Applied Physics.

According to paper co-author Tatyana Volk, their findings should help researchers to fine tune irradiation parameters as they seek to optimize the non-contact technique for creating arrangements of nano-scale domains in LN, its doped versions, and other ferroelectric crystals—a capability that could lead to vastly better technologies.

The researchers compared how EB characteristics affected domain growth in Y-cut slices of congruent LN (CLN), the most electrically resistant of ferroelectric crystals, and hydrogen-annealed, chemically reduced LN (RLN), which is significantly less resistant.

Differences between the two types of LN enabled examination of how conductivity affects electron-beam charging and, ultimately, domain formation—a neglected research topic, Volk said.

An SEM was used to write domains, point by point. The team used several microscopy methods to study how domains formed under two voltages and ranges of current and irradiation time. Comparisons revealed frontal growth was 20 times slower in RLN, resulting in much shorter domains. Irradiation-dose and space-charge thresholds for initiating domain formation were five to ten times greater in RLN, which, the researchers suggest, stems from an increase in leakage current.

The authors attribute dissimilarities to a fundamental change in charge transport in RLN – the result of reduction-caused changes in the structure of LN-intrinsic defects that create domain-wall pinning centers. In crystals with varying conductance, they write, the “only path” to achieve effective EB domain writing in a wide range of ferroelectrics is through adjustments of beam current.

Source: “Electron beam domain writing in reduced LiNbO3 crystals,” by L. S. Kokhanchik, Ya. V. Bodnarchuk, and T. R. Volk, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4991509 .