Domain formation by e-beam writing on metal-coated −<i>Z</i> cut of lithium niobate

Electron beam writing experiments of large regular arrays of domains on the −Z cut of congruent lithium niobate crystals covered with a grounded thin metal film have been performed. The written patterns contained micrometer-sized square regions placed at nodes of a rectangular grid with periods of 2–6 μm. Writing was performed at accelerating voltages of 5, 10, 15, and 25 kV. For all combinations of patterns and accelerating voltages used, regular 2D domain structures were formed near the sample surface. The writing conditions, shape, and formation regularities of these structures differed significantly from those previously observed in the absence of a metallic surface coating. The resulting domains have a structured top that deepens at about 200 nm. At a depth of approximately 1.7 μm, the domains merge into 1D structures. To explain the experimental results, a model is proposed based on the existence of a near-surface defect layer created during the fabrication of the samples. This layer is characterized by a high concentration of shallow and deep electron traps and the presence of centers where domain nucleation occurs under different conditions than in the sample bulk. The model assumes that when writing with the metallic surface coating, the electric field governing domain formation is generated by both the charge of primary electrons captured on deep traps in the sample bulk and the charges associated with secondary electrons captured on shallow and deep traps in the near-surface defect layer.