A Soft X-Ray Undulator Beamline at the Advanced Light Source  With Circular and Variable Linear Polarization for the Spectroscopy and  Microscopy of Magnetic Materials

Young, A. T.; Arenholz, Elke; Feng, Jun; Padmore, H. A.; Marks, S.; Schlueter, R.; Hoyer, E.; Kelez, Nicholas; Steier, C.

doi:10.1142/s0218625x02002622

Cited by 22 publications

(12 citation statements)

References 6 publications

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“…45 Samples were cryogenically cooled to 13 K. Average probing depth in the total electron yield XAS detection mode was estimated to be approximately 5 nm, providing interface-sensitive information with minimal contribution from surface adsorbates. Measurements were carried out in near-grazing (30°) incidence geometry, enabling selective alignment of the X-ray electric field parallel to the ab-plane of the film for vertically-polarized light (E║ab), and almost parallel to the c-axis of the film for vertically polarized light (E║c).…”

Section: Methodsmentioning

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: Methodsmentioning

confidence: 99%

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

et al. 2017

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“…This beamline uses a variable included angle grating monochromator and a vertical focusing mirror as detailed elsewhere [23]. Samples were mounted on a liquid helium cooled cold finger (Janis Research, Wilmington, MA) in UHV vacuum chamber.…”

Section: Methodsmentioning

confidence: 99%

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

George

Drury

et al. 2009

Journal of Inorganic Biochemistry

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We have surveyed the chemical utility of the near-edge structure of molybdenum x-ray absorption edges from the hard x-ray K-edge at 20,000 eV down to the soft x-ray M 4,5 -edges at ~230 eV. We compared, for each edge, the spectra of two tetrahedral anions, MoO 4 and MoS 4 2-. We used three criteria for assessing near-edge structure of each edge: (i) the ratio of the observed chemical shift between MoO 4 2-and MoS 4 2-and the linewidth, (ii) the chemical information from analysis of the near-edge structure and (iii) the ease of measurement using fluorescence detection. Not surprisingly, the K-edge was by far the easiest to measure, but it contained the least information. The L 2,3 -edges, although harder to measure, had benefits with regard to selection rules and chemical speciation in that they had both a greater chemical shift as well as detailed lineshapes which could be theoretically analyzed in terms of Mo ligand field, symmetry, and covalency. The soft x-ray M 2,3 -edges were perhaps the least useful, in that they were difficult to measure using fluorescence detection and had very similar information content to the corresponding L 2,3 -edges.Interestingly, the soft x-ray, low energy (~230 eV) M 4,5 -edges had greatest potential chemical sensitivity and using our high resolution superconducting tunnel junction (STJ) fluorescence detector they appear to be straightforward to measure. The spectra were amenable to analysis using both the TT-multiplet approach and FEFF. The results using FEFF indicate that the sharp near-edge peaks arise from 3d → 5p transitions, while the broad edge structure has predominately 3d → 4f character. A proper understanding of the dependence of these soft x-ray spectra on ligand field and site geometry is necessary before a complete assessment of the utility of the Mo M 4,5 -* Corresponding author: sjgeorge@lbl.gov, +1 510 486 6094, FAX +1 510 486 5664. Supporting Information(1) Crystallographic data of Na 2 MoS 4 in CIF format.

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“…In addition, an exhaustive characterization of such coherently-strained CaMnO3 films via XRD, x-ray reflectivity and atomic force microscopy was carried out by us in a prior study 20 , confirming crystallinity, tensile strain values, phase purity and coherence. Soft x-ray XAS measurements at the Mn L2,3 and O K absorption thresholds were carried out at the elliptically polarized undulator beamline 4.0.2 of the Advanced Light Source using the Vector Magnet endstation 21 . The average probing depth in the total electron yield XAS detection mode was estimated to be approximately 5 nm, providing optimal bulk-sensitivity to probe the buried CaMnO3 layer underneath the 3 nm-thick Pt cap.…”

Section: Textmentioning

confidence: 99%

Strain-Engineered Oxygen Vacancies in CaMnO₃ Thin Films

et al. 2017

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We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality singlecrystalline CaMnO 3 films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO 3 as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES). The relevant defect states in the densities of states are identified and the vacancy content in the films quantified using the combination of first-principles theory and core−hole multiplet calculations with holistic fitting. Our findings open up a promising avenue for designing and controlling new ionically active properties and functionalities of complex transition-metal oxides via strain-induced oxygen-vacancy formation and ordering.

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A Soft X-Ray Undulator Beamline at the Advanced Light Source With Circular and Variable Linear Polarization for the Spectroscopy and Microscopy of Magnetic Materials

Cited by 22 publications

References 6 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

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

Strain-Engineered Oxygen Vacancies in CaMnO₃ Thin Films

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A Soft X-Ray Undulator Beamline at the Advanced Light Source With Circular and Variable Linear Polarization for the Spectroscopy and Microscopy of Magnetic Materials

Cited by 22 publications

References 6 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

Molybdenum X-ray absorption edges from 200 to 20,000eV: The benefits of soft X-ray spectroscopy for chemical speciation

Strain-Engineered Oxygen Vacancies in CaMnO3 Thin Films

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Strain-Engineered Oxygen Vacancies in CaMnO₃ Thin Films