High-resolution Photoemission Spectroscopy Research Articles

Topological Quantum Well States in Pb/Sb Thin-Film Heterostructures.

Composite topological heterostructures, wherein topologically protected states are electronically tuned due to their proximity to other matter, are key avenues for exploring emergent physical phenomena. Particularly, pairing a topological material with a superconductor such as Pb is a promising means for generating a topological superconducting phase with exotic Majorana quasiparticles, but oft-neglected is the emergence of bulklike spin-polarized states that are quite relevant to applications. Using high-resolution photoemission spectroscopy and first-principles calculations, we report the emergence of bulk-like spin-polarized topological quantum well states with long coherence lengths in Pb films grown on the topological semimetal Sb. The results establish Pb/Sb heterostructures as topological superconductor candidates and advance the current understanding of topological coupling effects required for realizing emergent physics and for designing advanced spintronic device architectures.

Thermal- and air- stability of the compositional variants of van der Waals Pt-Telluride thin films probed by high resolution photoemission spectroscopy

The Pt-Te compositional phase diagram consists of at least three different compositional line phases (PtTe2, Pt3Te4, and Pt2Te2) that can be described as layered van der Waals materials. This presents challenges in controlling the composition of ultrathin Pt-telluride 2D materials by physical vapor deposition methods. Here we show by temperature programmed synchrotron photoemission spectroscopy that the different phases have varying thermal stability in vacuum. This enables the synthesis of these materials by preparation of PtTe2 films at low growth temperatures and subsequent vacuum annealing to ∼ 350 °C for Pt3Te4, or ∼ 400 °C for Pt2Te2. Such prepared phases are characterized by high resolution core level spectroscopy to provide reference spectra for these materials. Moreover, the chemical stability of these materials was tested by exposure to oxygen and air. Even after prolonged air exposure only the surface Te layer was modified by oxygen chemical bonds that caused a 3-eV shift to higher binding energy of the Te-3d core levels. However, these oxygen species could be desorbed by vacuum annealing at 280 °C and pristine Pt-telluride samples can be re-established. This shows the excellent chemical stability of these materials, important for practical applications.

Formation of germanene with free-standing lattice constant

Two-dimensional sheets of ultra-thin germanium with the lattice parameter of free-standing germanene, i.e., 0.41 nm, are formed by atomic segregation epitaxy on face-centered-cubic Ag0.9Al0.1(111) thin films grown on a Ge(111) template. Low-energy electron diffraction clearly shows a square-like (√13 × √13)R ± 46° superstructure, expressed as (4114) in Matrix form, whose 92° angle between the two vectors is clearly observed, as well as incommensurate (1.41 × 1.41)R ± 27° spots. Scanning tunneling microscopy (STM) images show the square-like superstructure and a defective honeycomb-like arrangement with this characteristic 0.41 nm lattice constant, corresponding to LEED patterns. Complimentary high-resolution synchrotron radiation photoemission spectroscopy measurements reveal the electronic structure of the honeycomb-like germanene sheet and further demonstrate that it overlays the surface of the Ag0.9Al0.1(111) alloy.

Adsorption behavior of furan at Ge(100) surface

The adsorption behavior of furan on the Ge(100) surface was studied using a combination of high-resolution photoemission spectroscopy (HRPES) and density functional theory (DFT) calculations. We identified the two adsorption species produced by the [4 + 2] cycloaddition and deoxygenation reactions of furan with the Ge(100) surface in a ratio of approximately 76:24 at the surveyed coverages, via an analysis of the binding energies and relative area proportions of all the peaks in the C 1s and O 1s core-level spectra. The DFT simulation results revealed that the [4 + 2] cycloaddition and deoxygenation adducts are thermodynamically preferred by the reaction of furan with the Ge(100) surface compared with others, which is consistent with the HRPES results. The findings will further our understanding of the surface reactions of five-membered heterocyclic molecules.

Valence fluctuation in Yb3Si5 probed by synchrotron X-ray photoemission spectroscopy

We report the direct evidence of valence fluctuation in the thermoelectric material Yb3Si5 by using synchrotron X-ray photoemission spectroscopy. The Yb 3d core level photoemission spectrum of a Yb3Si5 single crystal shows clear separation of the Yb2+ peak and Yb3+ multiplet peaks. From the spectral weight of each component, the mean valence of Yb ions is estimated to be +2.67 at 20 K. Furthermore, a Kondo resonance peak just below the Fermi energy is also observed by high-resolution soft X-ray photoemission spectroscopy, suggesting the valence fluctuating state in Yb3Si5.

Preparation, characterization and magnetic properties of Sm0.95Ho0.05FeO3 nanoparticles and their application in the purification of water

Sm0.95Ho0.05FeO3 was successfully prepared in a single phase using the citrate combustion method. The investigated sample was characterized using X-ray diffraction (XRD), a high-resolution transmission electron microscope (HRTEM) and X-ray photoemission spectroscopy (XPS). XRD confirmed that the sample was synthesized in an orthorhombic phase with an average crystallite size of 12 nm. HRTEM indicated that the sample was prepared in the nanoscale with an average particle size of 18 nm. XPS was used to identify the chemical bonds, binding energies and core levels of Sm0.95Ho0.05FeO3. The magnetic properties were studied using a vibrating sample magnetometer and DC magnetic susceptibility using Faraday’s method. The sample has an antiferromagnetic behavior with weak ferromagnetic components. The presence of magnetic Ho3+ ions in the SmFeO3 sample causes the magnetic exchange interaction between the 2p orbital of Fe3+ and the 4d sub-shell of Ho3+ ions. The dependence of pH value on the removal efficiency of Pb2+ from water was studied. The maximum Pb2+ removal efficiency of the Ho-doped SmFeO3 nano perovskite is 26% at pH = 5 and 99% at pH = 8. The Freundlich, Langmuir and Temkin isotherms were studied to understand the adsorption mechanism. The Temkin adsorption isotherm best fitted with the experimental data.

Crystal Phase, Electronic Structure, and Surface Band Bending of (InxGa1–x)2O3 Alloy Wide-Band-Gap Semiconductors

Ga2O3 is emerging as a promising wide-band-gap semiconductor for high-power electronics and deep ultraviolet optoelectronics. Alloying Ga2O3 with In2O3 leads to the modulation of the band gaps and possible carrier confinement achieved at the heterointerface. In this work, we report a systematic study on the crystallographic phase, electronic structure, and surface band bending of (InxGa1–x)2O3 thin films over the whole composition range of 0 ≤ x ≤ 1 grown on α-Al2O3 (0001) substrates by pulsed laser deposition. It was found that with In content x < 0.2, a monoclinic β-phase of an (InxGa1–x)2O3 film is epitaxially grown on Al2O3 (0001), while a bixbyite phase of the (InxGa1–x)2O3 film grows when x ≥ 0.8. When 0.2 ≤ x < 0.8, a mixed β-phase and bixbyite phase coexist. The evolution of electronic structures of the (InxGa1–x)2O3 films was examined by high-resolution X-ray photoemission spectroscopy (XPS) and optical absorption spectroscopy. For the β-phase films, the optical band gaps decrease from 4.96 eV for Ga2O3 to 4.43 eV for x = 0.4, while for bixbyite (InxGa1–x)2O3, the optical band gaps slightly increase from 3.57 eV for In2O3 to 3.70 eV for x = 0.8. Detailed electronic structure study indicates that the decrease of band gaps of (InxGa1–x)2O3 with an increase of In content mainly results from the upper movement of the valence band edge because the shallow In 4d orbitals introduce a hybridized state with O 2p at the top of the valence band. In addition, the presence of surface electron accumulation (i.e., downward band bending) was identified at the surface region of the (InxGa1–x)2O3 films with x ≥ 0.6, which would provide an opportunity to modulate the surface electronic properties for device applications.

Transparent conductive SnO2 thin films via resonant Ta doping

Transparent conductive oxide (TCO) thin films are highly desired as electrodes for modern flat-panel displays and solar cells. Alternative indium-free TCO materials are highly needed, because of the scarcity and the high price of indium. Based on the mechanism of resonant doping, Ta has been identified as an effective dopant for SnO2 to achieve highly conductive and transparent TCO. In this work, we fabricated a series of Ta-doped SnO2 thin films (Sn1−xTaxO2, x = 0.001, 0.01, 0.02, 0.03) with high conductivity and high optical transparency via a low-cost sol-gel spin coating method. The Sn0.98Ta0.02O2 film achieves the highest electrical conductivity of 855 S cm−1 with a carrier concentration of 2.3 × 1020 cm−3 and high mobility of 23 cm2 V−1 s−1. The films exhibit a very high optical transparency of 89.5% in the visible light region. High-resolution X-ray photoemission spectroscopy and optical spectroscopy were combined to gain insights into the electronic structure of the Sn1−xTaxO2 films. The optical bandgaps of the films are increased from 3.96 eV for the undoped SnO2 to 4.24 eV for the Sn0.98Ta0.02O2 film due to the occupation of the bottom of conduction band by free electrons, i.e., the Burstein-Moss effect. Interestingly, a bandgap shrinkage is also directly observed due to the bandgap renormalization arising from many-body interactions. The double guarantee of transparency and conductivity in Sn1−xTaxO2 films and the low-cost growth method provide a new platform for optoelectronic and solar cell applications.

(Invited) Thin Epitaxial Single-Crystal Si on Sige Followed By in-Situ Deposition of High-k Dielectrics – Novel Gate Stacks for Achieving Extremely Low Dit and Highly Reliable SiGe MOS

Silicon-germanium (SiGe) is replacing silicon (Si) as the channel layer for the p-type metal-oxide-semiconductor (pMOS) in the aggressively scaled complementary MOS (CMOS) technology. Many research efforts involving SiGe gate stacks have resulted in the attainment of low interfacial trap densities (Dits). Si-passivated SiGe gate stacks are the most promising method to achieve both low Dit and high device reliability. However, regardless of the growth methods, most publications reported the pileup of Ge atoms on top of the grown Si even after extensive treatments. The subsequent process in forming gate stacks, including oxidation, inevitably caused the segregated Ge to form GeOx, leading to degradation of the interfacial quality of the gate stacks.We have used molecular beam epitaxy (MBE) to grow thin single-crystal Si of 0.79nm thickness (six MLs) epitaxially on epi-Si1-xGex(001) under ultra-high vacuum (UHV). Different from its counterpart of chemical vapor deposition (CVD), MBE enables epi-Si growth on Ge at growth temperatures below 300 °C. The measurements using reflection high-energy electron diffraction (RHEED), high-resolution synchrotron radiation X-ray diffraction (HR-XRD), and the scanning transmission electron microscopy with high-angle annular-dark-field (STEM-HAADF) have revealed high crystallinity of the epi-Si, the Si1-xGex layers and abrupt interfaces of the high-k/epi-Si/Si1-xGex layers. Moreover, our unique capability of epi growth/analysis enabled the study of the electronic surface structures of epi-Si/epi-Ge using in-situ high-resolution synchrotron radiation photoemission spectroscopy (SRPES) via a portable sample transfer station under UHV. We have used SRPES to demonstrate that the as-grown Si1−xGex(001)-2×1 surfaces with Ge content ranging from 0.1 to 0.9 are all terminated with buckled Ge–Ge dimers, and the surface electronic structure is similar to that of epi-Ge(001)-2×1. The direct deposition of epi-Si on as-grown SiGe removed the top buckled Ge-Ge dimers, which diffused into the epi-Si and some segregated to the top of the Si. As a result, the topmost layer beneath the epi-Si was 1 ML of Ge, and the interfaces of high-k/epi-Si/Si1−xGex are similar to those of the high-k/epi-Si/Ge. Again, the hetero-interfaces of our gate dielectrics are different from those grown using CVD.The well-controlled interfaces have enabled the achievement of low interfacial trap densities (Dit) of (3 - 6) × 1011 eV-1cm-2 in these high-k/epi-Si/Si1-xGex samples. The minimum Dit values remained at 3 × 1011 eV-1cm-2 regardless of the Ge content, demonstrating the effective passivation of the low-temperature deposited epi-Si. The limited Ge segregation during the low-temperature growth of epi-Si may attribute to the attainment of the low Dit values. We have benchmarked the minimum Dit (Dit, min) of our work with other state-of-the-art SiGe gate stacks. The Dit,min values from the other efforts increased with increasing Ge content, which may be caused by the GeOx formation that was difficult to control in the high-Ge-content (HGC) Si1-xGex.The effective charge sheet densities for the Si1-xGex gate stacks were extracted via examination of capacitance-voltage (C-V) hysteresis with decreasing stress voltage in the accumulation region of the MOS capacitors. We have attained very high acceleration factors of 8-12, indicating high reliability of the HfO2/epi-Si/Si1-xGex pMOS gate stacks.Furthermore, we have used a scavenging method, consisting of a cyclic process of an O2 exposure followed by a UHV annealing, to eliminate the segregated and diffused Ge in epi-Si before high-k deposition. Upon O2 exposure at room temperature, both the Si and Ge surface atoms are simultaneously oxidized to give rise to four Si charge states and Ge suboxides, respectively. The subsequent in-situ annealing at 500 °C under UHV moved the oxygen atom in the Ge suboxides to bond with the nearby Si atom. The annealing also caused the diffused Ge inside the epi-Si to segregate to the surface. The processes of O2 exposure followed by annealing were repeated three times resulting in an oxidized Si/Ge surface having only the four Si oxidized states without GeOx, but with a minimal amount of segregated Ge.

Electronic structure of a Kondo lattice system CeCuAs2

We study the electronic properties of a Ce-based Kondo material, CeCuAs2 employing high-resolution hard x-ray photoemission spectroscopy. The measurements were done with different photon energies to probe the surface-bulk differences of the electronic structure. Experimental results show significant difference in the hybridization physics for the surface and bulk electronic structures indicating different Ce valency at the surface compared to the bulk. Surface termination appears to play an important role in the correlation physics of this system. In addition, the experimental spectra show loss features due to plasmon excitations. These results bring out complexity of this novel Kondo lattice system that does not show magnetic order down to the lowest temperature studied and have significantly different surface-bulk properties.

Signatures of Weyl Fermion Annihilation in a Correlated Kagome Magnet.

The manipulation of topological states in quantum matter is an essential pursuit of fundamental physics and next-generation quantum technology. Here we report the magnetic manipulation of Weyl fermions in the kagome spin-orbit semimetal Co_{3}Sn_{2}S_{2}, observed by high-resolution photoemission spectroscopy. We demonstrate the exchange collapse of spin-orbit-gapped ferromagnetic Weyl loops into paramagnetic Dirac loops under suppression of the magnetic order. We further observe that topological Fermi arcs disappear in the paramagnetic phase, suggesting the annihilation of exchange-split Weyl points. Our findings indicate that magnetic exchange collapse naturally drives Weyl fermion annihilation, opening new opportunities for engineering topology under correlated order parameters.

Anomalies in the electronic structure of a 5d transition metal oxide, IrO2

Ir-based materials have drawn much attention due to the observation of insulating phase believed to be driven by spin-orbit coupling, while Ir $5d$ states are expected to be weakly correlated due to their large orbital extensions. ${\mathrm{IrO}}_{2}$, a simple binary material, shows a metallic ground state which seems to deviate from the behavior of most other Ir-based materials and varied predictions in this material class. We studied the electronic structure of ${\mathrm{IrO}}_{2}$ at different temperatures, employing high-resolution photoemission spectroscopy with photon energies spanning from ultraviolet to hard $x$-ray range. Experimental spectra exhibit a signature of enhancement of Ir-O covalency in the bulk compared to the surface electronic structure. The branching ratio of the spin-orbit split Ir core-level peaks is found to be larger than its atomic values and it enhances further in the bulk electronic structure. Such deviation from the atomic description of the core-level spectroscopy manifests the enhancement of the orbital moment due to the uncompensated electric field around Ir sites. The valence-band spectra could be captured well within the density functional theory. The photon energy dependence of the features in the valence-band spectra and their comparison with the calculated results show dominant Ir $5d$ character of the features near the Fermi level; O $2p$ peaks appear at higher binding energies. Interestingly, the O $2p$ contributions of the feature at the Fermi level are significant, and it enhances at low temperatures. This reveals an orbital selective enhancement of the covalency with cooling, which is an evidence against the purely spin-orbit coupling based scenario proposed for these systems.

Emergence of well-screened states in a superconducting material of the CaFe2As2 family

Coupling among conduction electrons (e.g., Zhang-Rice singlet) are often manifested in the core level spectra of exotic materials such as cuprate superconductors, manganites, etc. These states are believed to play key roles in the ground state properties and appear as low binding energy features. To explore such possibilities in the Fe-based systems, we study the core level spectra of a superconductor $\mathrm{Ca}{\mathrm{Fe}}_{1.9}{\mathrm{Co}}_{0.1}{\mathrm{As}}_{2}$ (CaCo122) in the $\mathrm{Ca}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ (Ca122) family employing high-resolution hard x-ray photoemission spectroscopy. While As core levels show almost no change with doping and cooling, the Ca $2p$ peak of CaCo122 shows reduced surface contribution relative to Ca122 and a gradual shift of the peak position towards lower binding energies with cooling. In addition, we discover the emergence of a feature at the lower binding energy side of the well-screened Fe $2p$ signal in CaCo122. The intensity of this feature grows with cooling and indicates additional channels to screen the core holes. The evolution of this feature in the superconducting composition and its absence in the parent compound suggests relevance of the underlying interactions in the ground state properties of this class of materials. These results reveal another dimension in the studies of Fe-based superconductors and the importance of such states in the unconventional superconductivity in general.

Local excitons in Si/Ge inverted quantum huts (IQHs) embedded Si

We investigate the properties of excitons in the SiGe inverted quantum huts (IQHs) embedded in Si employing high-resolution x-ray photoemission spectroscopy. Ultra-small Si/Ge IQHs (13.3 nm × 6.6 nm) were grown on a Si buffer layer deposited on a Si (001) substrate using molecular beam epitaxy. We study the behavior of the excitons at different depths of the IQH structures by exposing the desired surfaces via controlled sputtering and annealing processes. The Si and Ge core level spectra show interesting properties at different surfaces; additionally, we discover distinct new features at the lower binding energy side of the Ge 3d peak. The emergence of these features is attributed to the final state effects arising from core hole screening by the excitons. The properties of these features in the spectra collected at different locations of the IQHs are found significantly different from each other, indicating the local character of the excitons. These results provide a pathway to study the properties of excitons in such quantum structures. The evidence of the local character of the excitons suggests a type I behavior of the system, which is important for the devices for optoelectronic applications, quantum communications, etc.

Reaction Behaviors of S‐, O‐, and N‐containing Aliphatic Molecules with a Propyl Moiety on Ge(100) Surface

The reaction pathways of 1-propanethiol, 1-propanol, and propylamine molecules, containing a propyl moiety, on a Ge(100) surface were investigated using high-resolution photoemission spectroscopy (HRPES) experiments and density functional theory (DFT) calculations. Upon analysis of the HRPES data, the adsorption of 1-propanethiol and 1-propanol was found to occur through a dissociation reaction, whereas that of propylamine took place via N dative bonding at room temperature. On the basis of our DFT results, adsorption geometries and transition states for each of these molecules on the Ge(100) surface were confirmed. Systematic studies of S-, O-, and N-containing molecules, composed of an identical propyl moiety, on the Ge(100) surface provide insight into the adsorption mechanism of aliphatic molecules containing alkyl chains on the Ge(100) surface.

In-plane strain-free stanene on a Pd2Sn(111) surface alloy

Here we report the growth of laterally strain-free stanene, that is a two-dimensional (2D) honeycomb structure of tin atoms, on a Pd(111) crystal terminated by a ${\mathrm{Pd}}_{2}\mathrm{Sn}$ surface alloy. The atomic geometry and the electronic structure have been thoroughly investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), Auger electron spectroscopy, high-resolution synchrotron radiation photoemission spectroscopy, and advanced first principles calculations. The STM images clearly reveal the epitaxial growth of honeycomb stanene on the preformed ${\mathrm{Pd}}_{2}\mathrm{Sn}$ surface alloy. LEED patterns clearly show commensurate (\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}3)R30\ifmmode^\circ\else\textdegree\fi{} spots, corresponding to a lattice constant of 0.47 nm, in perfect accord with the cell size of free-standing stanene. The measured very low buckling, within 20 pm, is derived from section profiles of atomic-scale STM images. This contrasts the significantly larger buckling of free-standing stanene, possibly due to a STM tip effect as well as a non-negligible interaction with the underlying surface alloy. The electronic structure exhibits a characteristic 2D band with parabolic dispersion, which is in good accordance with electronic structure calculations in density functional theory.

Ring-Opening Reaction of Tetrahydrofuran on Ge(100) Surface

The adsorption structures and reaction mechanism of tetrahydrofuran on a Ge(100) surface were investigated through high-resolution photoemission spectroscopy (HRPES) and density functional theory (DFT) calculations. On the basis of our analysis of the HRPES spectra, two adsorption species consisting of a major Ge–(CH2)4–O–Ge structure formed via a ring-opening reaction and a minor molecularly adsorbed structure formed via O dative bonding were identified. Our DFT results provided not only the optimized adsorption structures and their corresponding adsorption energies but also the level of the transition state for the pathway from the molecularly adsorbed species to the major adsorption structure. The results confirmed that the adsorption of tetrahydrofuran on the Ge(100) surface is under both kinetic and thermodynamic controls. Our discovery of the ring-opening reaction is an unprecedented result in the field of Ge(100) surface chemistry.

Electronic structure studies on single crystalline Nd2PdSi3, an exotic Nd-based intermetallic: evidence for Nd 4f hybridization

In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagnetic order unlike other members in this family. The magnetic ordering temperature is also unusually high compared to the expected value for a Nd-based system, assuming 4f localization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Theoretical results obtained for the effective on-site Coulomb energy of 6 eV corroborate well with the experimental valence band spectra. While there is significant Pd 4d–Nd 4f hybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f–Si 3p states, which is possibly responsible for the ferromagnetism in Nd compound. Nd 3d core level spectrum exhibits multiple features manifesting strong final state effects due to electron correlation, charge transfer and collective excitations. These results serve as one of the rare demonstrations of hybridization of Nd 4f states with the conduction electrons possibly responsible for the exoticity of this compound.

In situ investigation of interfacial properties of Sb2Se3 heterojunctions

Antimony selenide (Sb2Se3), emerging as a promising photovoltaic material, has achieved over 9% efficiency within only 6 years. Various kinds of buffer materials are employed for Sb2Se3 solar cells to construct heterojunctions with distinctive device performance. Herein, we introduce in situ high resolution photoemission spectroscopy (HRPES) to investigate the interfacial properties between Sb2Se3 and three types of widely adopted buffer layers: CdS, ZnO, and TiO2. HRPES results and theoretical thermodynamic calculations reveal that in the initial stage, the deposited Sb2Se3 reacts with buffer materials in terms of activity in the following order: CdS ≥ ZnO &amp;gt; TiO2. Distinct transition layers are formed at CdS/Sb2Se3 and ZnO/Sb2Se3 interfaces, whereas it is nearly absent at TiO2/Sb2Se3. Our results suggest that the CdS/Sb2Se3 heterojunction shows spike-like conduction band offsets (CBOs), whereas ZnO/Sb2Se3 demonstrates a cliff-like CBO, and TiO2/Sb2Se3 is almost flat. The transition layers and band alignments at the interface could be the reasons for the stability and performance of Sb2Se3 photovoltaic devices with different buffer materials. Our investigation deepens the understanding of Sb2Se3 heterojunction formation and can benefit further development of Sb2Se3 thin-film solar cells.

Synchrotron-based high-resolution photoemission spectroscopy study of ZIRLO cladding with H2O adsorption: Coverage and temperature dependence

The coverage and temperature dependence of ZIRLO cladding with H2O adsorption are studied using synchrotron-based high-resolution photoemission spectroscopy (HRPES). Based on the analytical results of the Zr 3d, O 1 s, C 1 s, and Sn 3d HRPES profiles prior to H2O adsorption, we determine the surface compositions of O2−, hydroxyl OH−, chemisorbed H2O, zirconium carbide, adventitious carbon, Sn metal, and SnO2 in ZIRLO. When ZIRLO is exposed to H2O molecules, the relative proportion of zirconium metal decreases, whereas that of the total zirconium oxides increases, suggesting the reaction between H2O and the zirconium metal in ZIRLO. On annealing a sample with 1000 L H2O on ZIRLO at 300 °C, Zr2O3 and ZrO2 decompose, and oxygen diffuses into the bulk, thereby reducing the oxidation states of zirconium on the surface. Moreover, at this temperature, the excess H2O molecules on ZIRLO are thoroughly desorbed and tin element is diffused into the bulk in ZIRLO.