Core-level spectra of metallic lanthanides: Dysprosium (Dy)

The rare earth metal dysprosium (Dy) is found in the lanthanide series and has the ground state electronic configuration [Xe] 4f¹⁰ 6s². Since the metallic state of lanthanides is of little use, their surface chemistry is not greatly explored and to date, the published data on heavier lanthanide elements are mostly limited to non-monochromatic sources (Ref. 1). Given that photoemission of low-lying 4d orbitals will result in a final state of the form 4d⁹4fⁿ, complex multiplet splitting is observed through the coupling of the 4d core-hole and the partly filled 4f shell and are excellent materials to understand the complex spectra resulting from this phenomenon.

The lanthanide series is a highly distinctive class of elements, with notable electrophilicity and magnetic and electronic properties. However, despite being an uncommon element presented to surface analysts, dysprosium finds many uses in alloys for technological applications such as laser materials (Ref. 2), infrared sources (Ref. 3), and to aid coercivity in neodymium-based magnets in harsh environments (Ref. 4).

Given that lanthanides are electropositive, they have a high affinity for oxygen and halides. Keeping them clean to record core-level spectra is difficult as noted previously (Ref. 5). Within this reference, the spectra for clean Dy are presented, which were obtained by light argon etching (20 s) between acquisitions.

Specimen: Dysprosium, Dy

CAS Registry #: 7429-91-6

Specimen Characteristics: Homogeneous; solid; polycrystalline; conductor; metal; other

Chemical Name: Dysprosium

Source: Alfa Aesar

Composition: Dy

Form: Solid dendrite, approximately 20 × 10 mm²

Structure: Dy

History and Significance: Distilled dendrites of 99.9% grade material obtained from Alfa Aesar under an argon atmosphere.

As Received Condition: Received as distilled metallic dendrites packaged in an argon atmosphere.

Analyzed Region: Elliptical region within the approximate center of the etched area.

Ex Situ Preparation/Mounting: A suitably sized fragment was wet polished to form a visually flat and smooth surface using isopropyl alcohol and SiC paper (grit size 7 μm). After polishing, the sample was again washed with isopropyl alcohol and dried under a stream of nitrogen. The dry sample was then attached to a conducting sample plate using copper clips. Initial survey scans (not shown) of the polished sample revealed small amounts of Si and Zn and significant amounts of carbon and oxygen.

In Situ Preparation: Argon ion sputtering

Charge Control: None

Temp. During Analysis: 298 K

Pressure During Analysis: 1.33 × 10⁻⁶ Pa

Pre-analysis Beam Exposure: 30 s

Manufacturer and Model: Thermo Fisher Scientific K-Alpha+

Analyzer Type: Spherical sector

Detector: Multichannel resistive plate

Number of Detector Elements: 128

Analyzer Mode: Constant pass energy

Throughput (T = E^N): Calculated from a polynomial fit to a plot of log [peak area/(PE*XSF)] versus log(KE/PE), where PE is the pass energy, KE is the kinetic energy, and XSF is the relative sensitivity factor.

Excitation Source Window: No window

Excitation Source: Al K_α monochromatic

Source Energy: 1486.6 eV

Source Strength: 72 W

Source Beam Size: 600 × 400 μm²

Signal Mode: Multichannel direct

Incident Angle: 60°

Source-to-Analyzer Angle: 60°

Emission Angle: 0°

Specimen Azimuthal Angle: 0°

Acceptance Angle from Analyzer Axis: 0°

Analyzer Angular Acceptance Width: 30° × 30°

Manufacturer and Model: Thermo Scientific MAGCIS

Energy: 4000 eV

Current: 6 mA

Current Measurement Method: Faraday cup

Sputtering Species and Charge: Ar⁺

Spot Size (unrastered): 50 μm

Raster Size: 2000 × 1000 μm²

Incident Angle: 58°

Polar Angle: 58°

Azimuthal Angle: 90°

Comment: The ion gun was used to clean the as introduced sample for 300 s and then for 20 s between each region to minimize any adsorption of background gases, which readily oxidize the material during analysis.

Energy Scale Correction: The sample is conductive and mounted on a conductive sample holder using clips, hence no calibration is required.

Recommended Energy Scale Shift: 0

Peak Shape and Background Method: For Dy 4d, 3d_5/2, and Dy 4p_3/2 regions, a Shirley background is used. For Dy 4s and Dy 3d_3/2 peaks, a linear background is employed. Recommend background start and end points are (±0.2 eV) as follows:

Dy 4d: 147–196 eV

Dy 4p_3/2: 283–316 eV

Dy 4s: 404.5–429.5 eV

Dy 3d_5/2: 1286.5–1319 eV

Dy 3d_3/2: 1329.5–1348 eV

Quantitation Method: Data analysis was performed using casaxps performed in casaxps V2.3.26 rev1.0N, using a Shirley background unless otherwise specified. Electron escape depth correction was performed using the TPP-2M equation within casaxps and peak areas were corrected using Scofield sensitivity factors. Modified sensitivity factors were used for 4p and 4s levels as noted in the comments on the spectral features table.

This work was performed through the support of the EPSRC National Facility for photoelectron spectroscopy (‘HarwellXPS’), operated by Cardiff University and University College London, under Contract No. PR16195.

The author has no conflicts to disclose.

David Morgan: Conceptualization (lead); Data curation (lead); Formal analysis (lead); Investigation (lead); Methodology (lead); Project administration (lead); Writing – original draft (lead); Writing – review & editing (lead).

The data that support the findings of this study are available within the article and its supplementary material.