Improved cationic stoichiometry and insulating behavior at the interface of LaAlO
                    <sub>3</sub>
                    /SrTiO
                    <sub>3</sub>
                    formed at high oxygen pressure during pulsed-laser deposition

Kalabukhov, A.; Boikov, Yu. A.; Serenkov, I. T.; Сахаров, В. И.; Börjesson, Johan; Ljustina, Nikolina; Olsson, Eva; Winkler, Dag; Claeson, T.

doi:10.1209/0295-5075/93/37001

Cited by 47 publications

(61 citation statements)

References 17 publications

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“…29 Low growth pressures can not only cause oxygen vacancies in SrTiO 3 , but can also enhance bombardment effect due to energetic species that may lead to La-Sr intermixing at the interface. 27 At present, there is no consensus on the origin of the 2D electron gas at the LaAlO 3 /SrTiO 3 interface.…”

Section: Resultsmentioning

confidence: 99%

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr 1+x Ti 1-x O 3+δ , Ruddlesden-Popper phase La n+1 Ni n O 3n+1 (n = 4), and LaAl 1+y O 3(1+0.5y) /SrTiO 3 interfaces, that atomic layer-by-layer laser molecular-beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser molecular-beam epitaxy we have produced conducting LaAlO 3 /SrTiO 3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.npj Quantum Materials (2017) 2:10 ; doi:10.1038/s41535-017-0015-x INTRODUCTION 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. 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. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited. 5 Reactive MBE employing alternately-shuttered elemental sources (atomic layerby-layer MBE, or ALL-MBE) can control the cation stoichiometry precisely, thus producing oxide thin films of exceptional quality. [6][7][8] There are, however, limitations in both techniques. Reactive MBE can use only source elements whose vapor pressure is sufficiently high, excluding a large fraction of 4d and 5d metals. In addition, ozone is needed to create a highly oxidizing environment while maintaining low-pressure MBE conditions, which increases the system complexity. On the other hand, conventional PLD using a compound target often results in cation off-stoichiometry in the films. 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. 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. Stoichiometry for both the cations and oxygen in the oxide films can be controlled. 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

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Section: Resultsmentioning

confidence: 99%

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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“…This allows us to exclude lasting influences of the deposition on the substrate like induced cation defects or the creation of a chemically broad interface103940.…”

Section: Relevance For Low Pressure Depositionsmentioning

confidence: 99%

Unraveling the enhanced Oxygen Vacancy Formation in Complex Oxides during Annealing and Growth

Hensling

Gunkel

et al. 2017

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The reduction of oxides during annealing and growth in low pressure processes is a widely known problem. We hence investigate the influence of mere annealing and of growth in vacuum systems to shed light on the reasons behind the reduction of perovskites. When comparing the existing literature regarding the reduction of the perovskite model material SrTiO3 it is conspicuous that one finds different oxygen pressures required to achieve reduction for vacuum annealing and for chemically controlled reducing atmospheres. The unraveling of this discrepancy is of high interest for low pressure physical vapor depositions of thin films heterostructures to gain further understanding of the reduction of the SrTiO3. For thermal annealing, our results prove the attached measurement devices (mass spectrometer/ cold cathode gauge) to be primarily responsible for the reduction of SrTiO3 in the deposition chamber by shifting the thermodynamic equilibrium to a more reducing atmosphere. We investigated the impact of our findings on the pulsed laser deposition growth at low pressure for LaAlO3/SrTiO3. During deposition the reduction triggered by the presence of the laser plume dominates and the impact of the measurement devices plays a minor role. During post annealing a complete reoxidization of samples is inhibited by an insufficient supply of oxygen.

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“…[12][13][14][15] Here again, the P(O 2 ) should have a strong influence on interface formation, but only a few studies explored high P(O 2 ) growth of LAO/STO. [3,11,12] Furthermore, the subtle effects of P(O 2 ) on the chemical composition of the interface and its structure, as well as its influence on subsequent growth have not been studied systematically.Here, we show that P(O 2 ) plays a dramatic role in determining the properties of LAO/STO at the initial stage of the growth. While low P(O 2 ) growth resulted in a mostly relaxed LAO layer, inserting only a single monolayer (i.e., one unit cell, u.c.)…”

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confidence: 99%

“…[1,7,21] It should be further noted that the energetic process of PLD -i.e., species are transported from the target to the substrate with a high kinetic energy -may substantially influence the formation of cation off-stoichiomety, resulting in a chemically broadened interface. [12][13][14][15] Here again, the P(O 2 ) should have a strong influence on interface formation, but only a few studies explored high P(O 2 ) growth of LAO/STO. [3,11,12] Furthermore, the subtle effects of P(O 2 ) on the chemical composition of the interface and its structure, as well as its influence on subsequent growth have not been studied systematically.…”

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confidence: 99%

“…While the polar catastrophe model at the interface between a polar (LAO) and a non-polar (STO) oxide provides an appealing explanation for the characteristics of this system, [7] the role of extrinsic factors such as oxygen vacancies and/or cation intermixing in producing similar behavior cannot be ruled out. [8][9][10][11][12][13][14][15] Pulsed laser deposition (PLD) is the most frequently used method for fabricating LAO/STO heterostructures. It is generally understood that, among the various growth parameters, the background gas pressure and the substrate temperature have the greatest influence on the film quality.…”

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Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

et al. 2012

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Keywords: perovskite oxide interface, pulsed laser deposition, LaAlO 3 /SrTiO 3 , atomic layer engineering, epitaxial strain 2 The two-dimensional (2D) conducting interface between LaAlO 3 (LAO) and SrTiO 3 (STO) -both perovskite oxide band insulators -has attracted immense attention since its discovery by Ohtomo and Hwang. [1] Several unexpected physical properties have been experimentally observed, [2,3] which stimulated numerous theoretical investigations. [4][5][6] However, despite intense research, the exact origin of such remarkable behavior remains to be understood. While the polar catastrophe model at the interface between a polar (LAO) and a non-polar (STO) oxide provides an appealing explanation for the characteristics of this system, [7] the role of extrinsic factors such as oxygen vacancies and/or cation intermixing in producing similar behavior cannot be ruled out. [8][9][10][11][12][13][14][15] Pulsed laser deposition (PLD) is the most frequently used method for fabricating LAO/STO heterostructures. It is generally understood that, among the various growth parameters, the background gas pressure and the substrate temperature have the greatest influence on the film quality. Under optimal conditions -i.e., when the oxygen partial pressure P(O 2 ) is used to tune the kinetic energy of growth species in the laser-induced plume -single crystal thin films with atomically smooth surfaces can be grown. [16] However, at less than optimal growth conditions, the highly energetic plume-substrate interactions can produce undesirable departures from stoichiometry. [17,18] As summarized in Table 1 of Supporting Information, the PLD growth conditions used in published reports on the LAO/STO interface formation were not uniform, suggesting that the differences in the growth parameters might contribute to inconsistent observations and/or interpretations of interface conductivity. Most importantly, compared to conventional PLD growth conditions for typical perovskite oxides, [19,20] many LAO/STO heterostructures were grown at unusually low P(O 2 ) and rather high temperatures. 3The selective use of low P(O 2 ) in the early stage of LAO/STO growth raises an intriguing question: what if instead very high P(O 2 ) was used to grow the LAO film? It was shown that LAO/STO growth at low P(O 2 ) easily generates a high concentration of oxygen vacancies, [8][9][10][11] and post-annealing in a high-pressure oxygen ambient was found to reduce their number. [3,8,9] Interestingly, some previous work reported good metallic conduction even after post-annealing, suggesting that the contribution of oxygen vacancies to the electronic conduction is negligible. [1,7,21] It should be further noted that the energetic process of PLD -i.e., species are transported from the target to the substrate with a high kinetic energy -may substantially influence the formation of cation off-stoichiomety, resulting in a chemically broadened interface. [12][13][14][15] Here again, the P(O 2 ) should have a strong influence on interface formation, but onl...

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Improved cationic stoichiometry and insulating behavior at the interface of LaAlO ₃ /SrTiO ₃ formed at high oxygen pressure during pulsed-laser deposition

Cited by 47 publications

References 17 publications

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Unraveling the enhanced Oxygen Vacancy Formation in Complex Oxides during Annealing and Growth

Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

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Improved cationic stoichiometry and insulating behavior at the interface of LaAlO 3 /SrTiO 3 formed at high oxygen pressure during pulsed-laser deposition

Cited by 47 publications

References 17 publications

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

Unraveling the enhanced Oxygen Vacancy Formation in Complex Oxides during Annealing and Growth

Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

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Improved cationic stoichiometry and insulating behavior at the interface of LaAlO ₃ /SrTiO ₃ formed at high oxygen pressure during pulsed-laser deposition