The technique is effective for both non-polar (such as SrTiO 3) and polar materials, such as the Ruddlesden–Popper (RP) phase La n+1Ni nO 3 n+1 with n = 4. Although the idea of depositing atomic layers by PLD has been explored since the early days of laser MBE, 11, 12 we show that levels of stoichiometry control and crystalline perfection rivaling those of reactive MBE can be achieved by ALL-Laser MBE. Stoichiometry for both the cations and oxygen in the oxide films can be controlled. Ablating alternately the targets of constituent oxides, for example SrO and TiO 2, a SrTiO 3 film can be grown one atomic layer at a time. 9, 10 In this paper we present an approach that combines the strengths of reactive MBE and PLD: atomic layer-by-layer laser MBE (ALL-Laser MBE) using separate oxide targets. On the other hand, conventional PLD using a compound target often results in cation off-stoichiometry in the films. In addition, ozone is needed to create a highly oxidizing environment while maintaining low-pressure MBE conditions, which increases the system complexity. Reactive MBE can use only source elements whose vapor pressure is sufficiently high, excluding a large fraction of 4 d and 5 d metals. 6, 7, 8 There are, however, limitations in both techniques. 5 Reactive MBE employing alternately-shuttered elemental sources (atomic layer-by-layer MBE, or ALL-MBE) can control the cation stoichiometry precisely, thus producing oxide thin films of exceptional quality. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited. 3, 4 Reactive molecular-beam epitaxy (MBE) and pulsed-laser deposition (PLD) are the two most successful growth techniques for epitaxial heterostructures of complex oxides. Technological advances in atomic-layer control during oxide film growth have enabled the discoveries of new phenomena and new functional materials, such as the two-dimensional (2D) electron gas at the LaAlO 3/SrTiO 3 interface, 1, 2 and asymmetric three-component ferroelectric superlattices.
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