Ar Ion Irradiation Research Articles

The influence of structural defects on the electrical and infrared emission properties of VO2 thin films

Defect engineering is widely used in the modification of transition metal oxides. In this study, defects are introduced into the polycrystalline VO2 film by the energetic Ar ion irradiation, and the influence of structural defects on the electrical and infrared emission properties of VO2 thin films have been investigated. The decrease in electrical switching ratio with the increase of defect ratio (displacement per atom (dpa)) can be described as R10°C/R90°C=2.032×(dpa+0.005)−1.8069, while the infrared modulation performance is Δε=−0.119×ln(dpa+0.061). The dpa thresholds of the electrical switching ratio and the infrared modulation performance are ηdpaRR = 0.005/atom and ηdpaΔε = 0.0426/atom, respectively, indicating that the electrical switching ratio of VO2 films is more responsive to defects than the infrared modulation performance. The relationship between transition temperature and defect ratio has be determined. Concerning electrical properties, the heating phase transition temperature can be described as TMITHeating=25.88−10.93×ln(dpa+0.01); while for infrared emission modulation, the heating phase transition temperature is given by Tε−MITHeating=31.65−8.18×ln(dpa+0.01). While reducing the phase transition temperature, the VO2 thin films still exhibit an electrical switching ratio of more than two orders of magnitude and obvious infrared modulation performance. It not only offers a viable solution for broadening the application scope of VO2 but also contributes to understanding the role of defects in VO2 thin films for further research.

Effect of Ar-ion irradiation on electrical transport of WS2 monolayer

Two-dimensional transition metal dichalcogenides (2D-TMDs), such as WS2 and MoS2, have attracted exceptional attention as promising materials for future optoelectronic systems due to their unique properties, including a direct band gap, high quantum efficiency, and flexibility. However, exploiting these materials’ potential in their pristine state remains a key challenge because of limited tunability and control over their properties. The introduction of crystal defects, such as vacancies and dopants, induces localized mid-gap states in 2D materials, enhances electrical transport, and creates a platform for tuning and exploiting these materials for practical applications. Our study explores the effect of Ar-ion beam irradiation on monolayer WS2, resulting in enhanced electrical transport compared to the pristine sample. We regulated the Ar-ion bombardment energy to vary the defect concentration from 0.1 to 0.5 keV. Photoluminescence (PL) and Raman investigations, revealed the extent of damage to the material. At the same time, x-ray photoelectron spectroscopy showed changes in the oxidation state with increasing irradiation energy. Our results demonstrated that Ar-ion treatment at low-energy irradiation enhanced electrical transport by ∼12 fold compared to pristine till 0.2 keV of irradiation by incorporating defects. However, higher irradiation energies reduced electrical transport due to increased disorder in the WS2 monolayer. This investigation highlights the potential for controlled defect engineering to optimize the properties of 2D-TMDs for practical applications.

Ar-ion- and electron-irradiated ZrC layers in ZrC-SiC-coated surrogate TRISO fuel particles

Surrogate tristructural isotropic (TRISO) particles, including ZrC and SiC layers, were manufactured through fluidized-bed chemical vapor deposition and irradiated. ZrC layers exhibited C/Zr atomic ratio of 0.95 without distinct crevices at interfaces in microscopy, but underwent significant microstructural changes post-irradiation. Defects included black dots and Frank loops, with increasing irradiation doses augmenting their area fractions. Frank loop density reduced at 9.4dpa due to the formation of fewer, fully circular loops. The ZrC hardness and modulus rose by 25% and 26% following Ar-ion irradiation at 9.4dpa, linked to the formed defects and implanted Ar ions. Electron irradiation expanded the defect-prone zone up to 100nm from the ZrC grain boundary and led to ZrO2 formation. ZrC grains recrystallized post electron irradiation at 700 °C, causing initial grain decomposition, amorphization, and nanocrystal formation. These nanocrystals, formed at 3.3dpa, closely aligned with ZrC diffraction patterns with no preferred orientations.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

Surface activated bonding (SAB) on wafer level is enabled by the EVG ComBond® system for irradiation with different ion species. In this process, the native oxide of 200 mm Si wafers is sputter-removed, and an amorphous layer is generated. After ion treatment, the wafers are bonded in ultra-high vacuum (UHV) at room temperature. The impact of Ar, Kr and Xe ion irradiation on the amorphous layer thickness (ALT) was investigated with the goal of optimizing the bonding process. This was i.a. motivated by the fact, that the presence of an amorphous layer reduces the electrical conductivity across the wafer interface [1].The ALT of unbonded wafers was evaluated via spectroscopic ellipsometry (SE) for varying ion species, ion energies and angles of incidence. The results show that heavier ions generate a thinner amorphous layer than light ions (see Fig. 1). This is most likely due to the higher scattering cross section of heavy ions resulting in a lower penetration depth. For each ion type there is a minimum in the ALT as a function of the ion energy which can be attributed to sputter-implantation dynamics. Furthermore, the ALT is decreasing with the angle of incidence as the incoming ions are projected into the material.Transmission electron microscopy (TEM) measurements were conducted on bonded wafer pairs and confirm the trend of heavy ions generating a thinner amorphous layer. Moreover, the TEM measurements show that post-bond annealing at 450°C for 5 h reduces the ALT due to recrystallization near the bonding interface.To ensure mechanical stability for further wafer processing and for the final device, bonding energy measurements were conducted via the Maszara method [2]. Although maximum bonding energy can be achieved for specific parameters with each ion species, Xe irradiated samples tend to have a higher overall bonding energy.[1] P.A. Stolk et al., “Contribution of defects to electronic, structural, and thermodynamic properties of amorphous silicon”, in Journal of Applied Physics, vol. 75, no. 11, pp. 7266-7286 (1994).[2] W.P. Maszara et al., “Bonding of silicon wafers for silicon-on-insulator”, in Journal of Applied Physics, vol. 64, no. 10, pp. 4943-4950 (1988). Figure 1

Collision Cascade in a Silicon-Based Device under Energetic Ar Ions Irradiation

Silicon, as the basic material of biochips and electronic devices, is often exposed to irradiation environments, and its radiation resistance has attracted much attention in recent decades. We calculated collision cascade in a silicon-based device under energetic Ar ions irradiation by using Monte Carlo and molecular dynamics simulations. The difference in vacancy probability density under different energetic incident ion irradiation is caused by the penetrating power and the straggling power of incident ions. The kinetic energy of an incident ion determines the size of local collision cascade density; a high energy incident ion can induce greater local collision cascade density. The efficiency of transferring energy from incident ions to target electrons at the silicon surface is more than in silicon, and the recoil atoms dissipate most of their energy at the lattice sites where they are stopping. These results provide more insight into the radiation resistance of silicon-based devices.

380-keV Ar+-irradiation effects on optical phonons in graphite studied with transient reflection measurement

In this work, we performed transient reflection measurements using the pump–probe protocol to investigate the influence of lattice defects induced by 380 keV argon (Ar) ions on the phonon dynamics of interlayer shearing (E2g1) and in-plane carbon stretching (E2g2) modes in highly oriented pyrolytic graphite (HOPG). The frequency and decay rate of E2g1- and E2g2-mode phonons were changed significantly at the fluence of 1×1014 ions/cm2. This indicated that significant structural changes in HOPG due to 380 keV Ar-ion irradiation were expressed as changes in the frequency and decay rate of phonons. In HOPG irradiated with 380 keV Ar+ at the fluence of 1×1014 ions/cm2, our measurement results indicated that compressive and tensile stresses contributed to in-plane and interlayer graphite structures, respectively.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

Surface activated bonding on wafer level is enabled by an advanced direct wafer bonding system for irradiation with different ion species. In this process, the native oxide of 200 mm Si wafers is sputter-removed and an amorphous layer is generated. After ion treatment, the wafers are bonded in ultra-high vacuum at room temperature. The impact of Ar, Kr and Xe ion irradiation on the amorphous layer thickness was investigated with the goal of optimizing the bonding process for establishing interfaces with electronic functionality. This was i.a. motivated by the fact, that the presence of an amorphous layer reduces the electrical conductivity across the wafer interface.

Shaping Perpendicular Magnetic Anisotropy of Co2MnGa Heusler Alloy Using Ion Irradiation for Magnetic Sensor Applications.

Magnetic sensors are key elements in many industrial, security, military, and biomedical applications. Heusler alloys are promising materials for magnetic sensor applications due to their high spin polarization and tunable magnetic properties. The dynamic field range of magnetic sensors is strongly related to the perpendicular magnetic anisotropy (PMA). By tuning the PMA, it is possible to modify the sensing direction, sensitivity and even the accuracy of the magnetic sensors. Here, we report the tuning of PMA in a Co2MnGa Heusler alloy film via argon (Ar) ion irradiation. MgO/Co2MnGa/Pd films with an initial PMA were irradiated with 30 keV 40Ar+ ions with fluences (ions·cm-2) between 1 × 1013 and 1 × 1015 Ar·cm-2, which corresponds to displacement per atom values between 0.17 and 17, estimated from Monte-Carlo-based simulations. The magneto optical and magnetization results showed that the effective anisotropy energy (Keff) decreased from ~153 kJ·m-3 for the un-irradiated film to ~14 kJ·m-3 for the 1 × 1014 Ar·cm-2 irradiated film. The reduced Keff and PMA are attributed to ion-irradiation-induced interface intermixing that decreased the interfacial anisotropy. These results demonstrate that ion irradiation is a promising technique for shaping the PMA of Co2MnGa Heusler alloy for magnetic sensor applications.

GaAs a model system to study the role of electron–phonon coupling on ionization stimulated damage recovery

The latent ion tracks observed in various materials after swift heavy ion (SHI) irradiation is often explained in the framework of thermal spike model (TSM). Dominantly, SHIs deposit most of their energy via intense ionization leading to a very high density of localized electronic excitations. The energy transfer from electrons to lattice, within a time of electronic cooling ∼100 fs, is governed by the ‘electron-phonon coupling’ parameter g. In this work, GaAs is used as a model system for studying ionization-stimulated damage recovery. Controlled damage is introduced using 300 KeV Ar ion irradiation, followed by successive irradiation using 100 MeV Ag ions at ∼80 K by varying the fluence (ions cm−2). The TSM is utilized to explain the observed recovery. Using the previously published value of 1012 W cm−3 K−1 for GaAs, the existing thermal spike code resulted in melting and quick quenching within ∼10 ps, suggesting the formation of SHI-induced tracks. However, experimental observations do not support the formation of tracks in pristine GaAs. Multiple simulation runs, for different g values, predict that for no melting in GaAs, g should be 1.4 × 1012 W cm−3 K−1. Finally, the 3D version of the TSM is used to simulate the temperature profiles after an impact of SHI irradiation on an amorphous nano-zone embedded in a crystalline GaAs matrix. Simulations predict that the thermal spike in this zone is confined, indicating melt-flow at the crystalline-amorphous interface that can promote recovery. This lattice recovery is further supported by both RBS/C and TEM results.

Mechanical behavior of ion-irradiated ODS RAF steels strengthened with different types of refractory oxides

One of the most promising candidates for constructing IV generation nuclear reactors is Oxide Dispersed Strengthening (ODS) Reduced Activation Ferritic (RAF) steel. It is known that introducing refractory oxides to the ferritic matrix makes it possible to obtain a brand-new kind of materials with an excellent set of properties. In the present work, the authors focused on verifying materials' structural and mechanical properties strengthened by three different types of refractory oxides submitted to ion-irradiation. Three materials with an elemental chemical composition of 12 %Cr, 2 %W, 0.3 %Ti, and strengthened with 0.3% Y2O3 or Al2O3 or ZrO2 were produced by mechanical alloying and subsequently consolidated by Spark Plasma Sintering technique. Manufactured materials have been submitted to high energy (500 keV) Ar-ion irradiation at room temperature with three fluences (up to 5x1015 ions/cm2). This procedure allowed to generate a thin, strongly damaged zone with approximate thickness of 230 nm. SEM/EBSD and TEM bservations, Grazing Incidence X-ray Diffraction analysis, and nanoindentation tests have been included in examination of modified layers. Implementation of these techniques allowed to reveal alteration of structural and mechanical features between unmodified material and radiation-affected layer. Obtained results showed a strong correlation between the strengthening oxide and materials' microstructural and mechanical behavior under radiation damage. It has been proved that below 1x1015 ions/cm2 mechanical properties in the modified layer of all materials are very similar. Reported behavior may be related to the efficient annealing of the radiation defect process. Above this limit, significant differences between the materials are visible. It is believed that described phenomenon is directly related to the presence of the structural features and their capacity to act as defect sinks. Consequently, type of dominant mechanisms occurring in modified layer is proposed.

Tetragonal distortion modified magnetism and anomalous Hall effect of Mn2CoAl Heusler alloys through Ar ion irradiation

Tetragonal Heusler alloys have attracted increasing interest due to their great scientific and technological applications in spintronics. However, the crystal structures of most Heusler alloys are cubic. One feasible method to obtain tetragonal Heusler alloy is to manipulate the out-of-plane (OOP) distortion of cubic Heusler alloys. In this work, we report the ion irradiation-induced tetragonal distortion in Mn2CoAl Heusler films. The OOP lattice constant continuously increases from 5.84 to 6.09 Å, while the in-plane lattice constant remains nearly unchanged. Magnetic measurements show that saturation magnetization at 50 K decreases from 258 emu cc−1 to 167 emu cc−1 under Ar ion irradiation. Transport measurements show that the longitudinal resistivity decreases with increasing irradiation doses, and the anomalous Hall resistivity changes from negative to positive. Moreover, it is found that hump-like anomalies can be observed in the Hall resistivity loops at the irradiation dose of 1 and 1 cm−2, which are attributed to the irradiation-induced inhomogeneous magnetism in the surface and interface parts. This work demonstrates the considerable tunability of the structure, magnetism and transport properties of Mn2CoAl Heusler alloys by Ar ion irradiation.

Comprehensive effects of heavy-ion beam irradiation on sweet potato (Ipomoea batatas [L.] Lam.).

Sweet potato is a major root crop with nutritious tuberous roots. The mechanism of tuberous root development has not yet been adequately elucidated. Genetic resources are required to develop the molecular understanding of sweet potato. Heavy-ion beams were applied to hexaploid sweet potato for an increase in genetic variation, after which the comprehensive effects of heavy-ion beam irradiation were investigated. In vitro cultured shoots with an axillary bud of 'Beniharuka' were irradiated with Ar-ions at a dose of 1-5 Gy and C-ions at a dose of 5-20 Gy, and three irradiated lines were separated from each irradiated shoot. The shoot regeneration was inhibited at high doses of each ion irradiation. Ar-ion irradiation had an especially high biological effect on shoot regeneration. A total of 335 lines were obtained, consisting of 104 and 231 lines derived from Ar- and C-ion irradiation, respectively. The change in the DNA content of the lines was analyzed by flow cytometry to evaluate the irradiation-induced damage to the DNA. The two lines demonstrated significant differences in the DNA content and changes at the chromosome level. The screening for the morphological mutants was conducted in the field. Some irradiated lines showed inhibited or no tuberous root phenotype as mutant candidates. Additionally, the high-yield mutant candidates were dominated by Ar-ion irradiation. It was indicated that heavy-ion beam mutagenesis is effective in broadening the range of the phenotypes corresponding to tuberous root formation in hexaploid sweet potato.

Disorder-induced crossover of Mott insulator to weak Anderson localized regime in an argon-irradiated NdNiO3 film

We show that an introduction of disorder in a controlled way using 1 MeV argon (Ar) ion irradiation, suppresses the correlation driven metal-insulator transition (MIT) in $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{3}$ films. The films make a crossover to a heavily disordered conductor governed by weak localization (WL) and at even higher disorder, an Anderson localized state. The disorder (atomic displacement up to 2% of the total atoms) in the $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{3}$ films was created using 1 MeV ${\mathrm{Ar}}^{4+}$ ion irradiation. We show that the pristine films of $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{3}$ exhibit an MIT with the conduction process being governed by variable range hopping (VRH). For disorder up to 1% of the displaced atoms or lower, the insulating state arising from a gap in the density of states (DOS) at the Fermi level (${E}_{F}$) as in a Mott insulator is suppressed and the conduction in the film shows a WL behavior with finite conductivity at temperature $T\ensuremath{\rightarrow}0$. This behavior is expected in a disordered conductor that does not have a gap in DOS at ${E}_{F}$. At higher fluences the conductivity reduces substantially but the electrical conduction shows a power-law temperature dependence with a small but finite zero temperature conductivity $\ensuremath{\sigma}(T=0)$ which is expected in a solid with electrons that are Anderson localized. A similar experiment was performed on the La substituted $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{3}$ films (${\text{Nd}}_{1\ensuremath{-}x}{\text{La}}_{x}{\text{NiO}}_{3}$) with $x=0.3$ that are grown in the same way. La substitution in $\mathrm{Nd}\mathrm{Ni}{\mathrm{O}}_{3}$ suppresses the temperature driven transition and leads to a metallic state with critical composition at $x\ensuremath{\approx}0.3$. The pristine as well as films irradiated with lowest fluence shows metallic or marginally metallic behavior grown on $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ and $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrates, respectively. However, at higher fluences they too exhibit a convergence in electronic transport and $\ensuremath{\sigma}$ shows a power-law temperature dependence at low $T$ with $\ensuremath{\sigma}(T=0)\ensuremath{\ne}0$. Evidence of suppression of correlated behavior can also be seen in the irradiated films where the non-Gaussian nature of resistance fluctuation at $T\ensuremath{\approx}{T}_{\text{MI}}$, a signature of correlated electron systems, is suppressed on irradiation that leads to collapse of the MIT. Evidence for progressing disordering of the films on irradiation were observed in Raman spectroscopy as well as x-ray studies that show the basic integrity of the ${\text{NiO}}_{6}$ octahedra is preserved and the structure retains its crystallinity.

Molecular dynamics simulations of ion beam irradiation on graphene/MoS2 heterostructure

The interaction between ion irradiation and two-dimensional (2D) heterostructures is important for the performance modulation and application realization, while few studies have been reported. This paper investigates the influence of Ar ion irradiation on graphene/MoS2 heterostructure by using molecular dynamics (MD) simulations. The generation of defects is studied at first by considering the influence factors (i.e., irradiation energy, dose, stacking order, and substrate). Then uniaxial tensile test simulations are conducted to uncover the evolution of the mechanical performance of graphene/MoS2 heterostructure after being irradiated by ions. At last, the control rule of interlayer distance in graphene/MoS2 heterostructure by ion irradiation is illustrated for the actual applications. This study could provide important guidance for future application in tuning the performance of graphene/MoS2 heterostructure-based devices by ion beam irradiation.

HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY STUDY OF CRYSTALLOGRAPHY AND MORPHOLOGY OF TiC PRECIPITATES IN ARGON IRRADIATED 18Cr10NiTi STEEL

This work encompasses identification of the crystal structure and analysis of the TiC precipitates in 18Cr-10Ni-Ti austenitic stainless steel under Ar-ions irradiation. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) are used. Orientation relationship of TiC particles in surrounding matrix are indicated by HRTEM and diffraction patterns. The size of the precipitates is found to be critical: the coherency of TiC is kept at the interfaces when the precipitate is in the stage of nucleation, whereas the growth of precipitate up to 10 nm can lead to the loss of coherency in the austenitic steel. The findings suggest that the incoherent precipitate-matrix interface is an important point defect sink and contributes to inert gas bubble formation at elevated irradiation temperatures.

Toward a systematic discovery of artificial functional magnetic materials

Although ferromagnets are found in all kinds of technological applications, only few substances are known to be intrinsically ferromagnetic at room temperature. In the past twenty years, a plethora of new artificial ferromagnetic materials have been found by introducing defects into non-magnetic host materials. In contrast to the intrinsic ferromagnetic materials, they offer an outstanding degree of material engineering freedom, provided one finds a type of defect to functionalize every possible host material to add magnetism to its intrinsic properties. Still, one controversial question remains: Are these materials really technologically relevant ferromagnets? To answer this question, in this work the emergence of a ferromagnetic phase upon ion irradiation is systematically investigated both theoretically and experimentally. Quantitative predictions are validated against experimental data from the literature of SiC hosts irradiated with high energy Ne ions and own experiments on low energy Ar ion irradiation of TiO$_2$ hosts. In the high energy regime, a bulk magnetic phase emerges, which is limited by host lattice amorphization, whereas at low ion energies an ultrathin magnetic layer forms at the surface and evolves into full magnetic percolation. Lowering the ion energy, the magnetic layer thickness reduces down to a bilayer, where a perpendicular magnetic anisotropy appears due to magnetic surface states.

Investigating the Influence of Ion Species on the Irradiation-Induced Mechanical Properties of Borosilicate Glass

Investigating the irradiation effects on borosilicate glass is of great significance for understanding the long-term evolutions of this substance in radioactive environments. In the present study, the hardness and modulus of conventional and ion-irradiated borosilicate glass were investigated through nanoindentation measurements. The obtained results show that the maximum decrease of the mean hardness after He and Ar ion irradiation was 8.4% and 17.0%, respectively, when the fluence reached 1.1 × 1015. It was found that the hardness reduction had a significant ionic correlation. Meanwhile, it was observed that the mean modulus increased by less than 5.0%, while there was no meaningful ionic correlation. The variation in hardness and modulus were primarily the consequence of nuclear energy deposition. The hardness recovery was observed under Ar-irradiated and He-irradiated Ar pre-damaged samples. It was concluded that the hardness recovery mainly originates from electronic energy deposition induced by ion irradiation.

Microstructure and Hardening Behavior of Argon-Ion Irradiated Steels 18Cr10NiTi and 18Cr10NiTi-ODS

Microstructure and nanohardness evolution in 18Cr10NiTi and 18Cr10NiTi-ODS steels after exposure to argon ion irradiation has been studied by combination of nanoindentation tests, XRD analysis, TEM and SEM observation. ODS-modified alloy was produced on the basis of conventional 18Cr10NiTi austenitic steel by mechanical alloying of steel powder with Y(Zr)-nanooxides followed by mechanical-thermal treatment. XRD analysis has showed no significant changes in the structure of 18Cr10NiTi steel after irradiation at room and elevated temperatures (873 K) and in ODS-steel after irradiation at 873 K, whereas the evidences of domains refinement and microstrain appearance were revealed after irradiation of 18Cr10NiTi-ODS steel at room temperature (RT). Layer-by-layer TEM analysis was performed to investigate the microstructure of alloys along the damage profile. The higher displacement per atom (dpa) and Ar concentration clearly lead to increased cavities size and their number density in both steels. The swelling was estimated to be almost half for 18Cr10NiT-ODS (4.8%) compared to 18Cr10NiTi (9.4%) indicating improved swelling resistance of ODS-steel. The role of oxide/matrix interface as a sink for radiation-induced point defects and inert gas atoms is discussed. The fine dispersed oxide particles are considered as effective factor in suppressing of cavity coarsening and limiting defect clusters to small size. The hardness behavior was investigated in both non-irradiated and irradiated specimens and compared to those at RT and elevated temperature of irradiation. The hardness increase of unirradiated ODS-steel is associated mainly with grain refinement and yttrium oxides particles addition. The hardening of 18Cr10NiTi-ODS after Ar ion irradiation at RT was found to be much lower than 18Cr10NiTi. Black dots and dislocation loops are observed for both steels in the near-surface area; however, the main hardening effect is caused by the cavities. Oxide dispersion strengthened steel was found to be less susceptible to radiation hardening/embrittlement compared with a conventional austenitic steel.

Defects assisted structural and electrical properties of Ar ion irradiated TiO2/SrTiO3 bilayer

The present study focuses on the effect of 1 MeV Ar ion irradiation on pulsed laser deposited TiO2/SrTiO3 bilayer thin films on Si (100) and SrTiO3 (STO) substrates. Irradiation results in the reduction of crystallinity and the bilayer film on Si exhibits higher electrical conductivity compared to film on STO with the Seebeck coefficient ~175 µV/K and the power factor ~0.13 mW.m−1K−2 at 420 K. The X-ray absorption spectra at Ti L and O K-edges reveal the reduction of the ion valence of Ti and the presence of oxygen vacancies. This study evidences that Ar ion irradiation enhances the electrical and thermoelectric properties in heterostructure oxides due to oxygen vacancies.

Oxygen Vacancy‐induced Electron Density Tuning of Fe3O4 for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction (OER) catalysts, there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts. Herein, Fe3O4 with oxygen vacancies (Fe3O4‐Vac) was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms. The electron density of Fe3O4‐Vac around Fe atoms increased compared to that of Fe3O4 according to the characterization of synchrotron‐based X‐ray absorption near‐edge structure (XANES), extended X‐ray absorption fine structure (EXAFS) spectra, and density functional theory (DFT) calculation. Moreover, the DFT results indicate the enhancement of the desorption of HOO* groups which significantly reduced the OER reaction barrier. Fe3O4‐Vac catalyst shows an overpotential of 353 mV, lower than that of FeOOH (853 mV) and Fe3O4 (415 mV) at 10 mA cm−2, and a low Tafel slope of 50 mV dec−1 in 1 M KOH, which was even better than commercial RuO2 at high potential. This modulation approach provides us with valuable insights for exploring efficient and robust water‐splitting electrocatalysts.