Auger Electron Research Articles

Development of a cylindrical mirror analyser electron spectrometer and associated data acquisition system to study inner shell electron emission following ion-atom collision

In this paper we report on the development and performance of a cylindrical mirror analyser electron spectrometer for ion atom collision experiments. A low cost data acquisition system using Arduino microcontroller has also been developed and tested. We have measured the Auger emission spectra for various gaseous targets in collision with 1 MeV proton beams. Relative total Auger emission cross sections have also been measured for N2 molecular target as a function of incident proton energy. The projectile energy dependence agrees well with earlier reported measurements.

Quantification of alloy atomic composition sites in 2D ternary MoS2(1-x)Se2x and their role in persistent photoconductivity, enhanced photoresponse and photo-electrocatalysis

Engineering transition metal dichalcogenides-based semiconducting two-dimensional (2D) layered materials for photo(electro)chemical (PEC) hydrogen evolution reaction (HER) by water splitting is an enduring challenge. Here, alloy-assisted photoconductivity and photoresponse from CVD-grown MoS2(1-x)Se2x (MSSE) 2D ternary atomic layered alloy-based photodetector device is presented for the realization of PEC HER. The explicit role of ‘S–Se’ and ‘Se2’ atomic alloy sites including chalcogen-induced vacancy defects on the photoconductivity/photoresponse and PEC HER performance of MSSE 2D alloy is investigated. Alloy formation, atomic site-by-site ‘Se’ composition and atomic structure are characterized using Raman/Photoluminescence (PL) spectroscopy, high-angle annular dark field (HAADF)- scanning transmission electron microscopy (STEM) extensively and supported with Auger Electron Spectroscopy (AES) mapping. Further, the local density and concentration of S–Se, Se2 atomic sites and defects were quantitatively estimated using HAADF-STEM image analysis in correlation with AES and it is found between the range of ∼15–20 % in MSSE alloy. A 10-fold high photoresponsivity in the case of MSSE concerning as-grown MS having fast photocurrent growth time and the prolonged decay time originates from the ‘Se’ and this alloy assisted states to enhance the PEC performance of MSSE alloy. The enhanced PEC HER activity of MSSE alloy was identified in terms of overpotential and current density. In addition, increased density of states as a function of ‘Se’ alloying, shifts in a p-band centre and lowers ΔGH* according to density functional theory calculations, which makes MSSE alloy an efficient HER activity. Further, the PEC stability and presence of the ‘S–Se’ and ‘Se2’ alloying and their role towards HER have been correlated by the spectral line shape analysis of PL and Raman spectra from post-PEC HER catalysts. These experimental and theoretical findings establish the role of chalcogen, and transition metal-based 2D alloy, leading to the design of new PECs of engineered 2D atomic layer interfaces.

An environmentally-friendly approach to monovalent Cu-doped ZnS: Physicochemical characterization and photocatalytic activity

Certain semiconducting species suffer from the lack of optical activity in the visible region of electromagnetic spectrum, due to large band gap. The integration of various dopants has been widely used in order to generate additional electron transitions and subsequently lead to red-shifted absorption spectrum and enhanced photon harvesting in the visible-NIR region. Herein, a facile two-step environmentally-friendly approach was employed to integrate monovalent Cu species onto ZnS lattice. The study was set to assess the effect of Cu doping in Zinc Sulfide lattice on optical and photocatalytic properties. The theoretical weight fraction of the dopant ranged between 0% and 50%. The physicochemical characterization of either neat semiconductors (ZnS and Cu2O) or Cu-doped ZnS hybrids was performed by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman, X-ray photoelectron spectroscopy (XPS), X-ray induced Auger electron spectroscopy (XAES) and Diffuse reflectance spectroscopy (DRS). XPS provided some enhanced understanding about the chemical speciation of the hybrid materials. This information was strongly supported by Raman analysis. The optimized Cu-doped ZnS hybrid demonstrated enhanced photocatalytic activity towards the degradation of Orange G dye, under UV irradiation.

Efficient, Color-Stable, Pure-Blue Light-Emitting Diodes Based on Aromatic Ligand-Engineered Perovskite Nanoplatelets.

Perovskite nanoplatelets (NPLs) show great potential for high-color-purity light-emitting diodes (LEDs) due to their narrow line width and high exciton binding energy. However, the performance of perovskite NPL LEDs lags far behind perovskite quantum dot-/film-based LEDs, owing to their material instability and poor carrier transport. Here, we achieved efficient and stable pure blue-emitting CsPbBr3 NPLs with outstanding optical and electrical properties by using an aromatic ligand, 4-bromothiophene-2-carboxaldehyde (BTC). The BTC ligands with thiophene groups can guide two-dimensional growth and inhibit out-of-plane ripening of CsPbBr3 NPLs, which, meanwhile, increases their structural stability via strongly interacting with PbBr64- octahedra. Moreover, aromatic structures with delocalized π-bonds facilitate charge transport, diminish band tail states, and suppress Auger processes in CsPbBr3 NPLs. Consequently, the LEDs demonstrate efficient and color-stable blue emissions at 465 nm with a narrow emission line width of 17 nm and a maximum external quantum efficiency (EQE) of 5.4%, representing the state-of-the-art CsPbBr3 NPL LEDs.

Lattice destabilization in electron-beam-irradiated antimony in TEM

This study investigates the effect of electron-beam heating in transmission electron microscopy (TEM) on the structure of antimony (Sb) thin films. TEM of Sb irradiated with 300 keV electrons reveals a significant deviation (2–3°) from the theoretical interplanar angle between certain planes within the irradiated region. We relate this anomaly to electron-beam heating under electron-beam irradiation. Our FEA simulations reveal localized heating within the irradiated region caused by Auger electron excitation. These simulations predict temperatures as high as 949 K, accompanied by ultrafast heating and quenching rates. This extreme thermal cycling likely induces significant thermal stress in localized regions, possibly exceeding their elastic limits. This stress is likely related to the observed structural anomalies. This work highlights the importance of considering beam heating, particularly when interpreting TEM data from nanoscale materials with reduced thermal conductivity due to surface scattering effects.

Epitaxial Fe/Rh bilayers for efficient spin-to-charge conversion

To address the spin pumping in the conventional ferromagnetic/“normal” metal systems, we fabricated 6 nm Fe/1–15 nm Rh epitaxial bilayers and determined the g-factor, magnetic anisotropy, and magnetization damping by combining both 0–40 GHz CPW-based frequency-dependent and cavity-based 9.56 GHz in-plane angular-dependent ferromagnetic resonance measurements at room temperature. Auger electron spectroscopy and low-energy electron diffraction show that Rh grows epitaxially on Fe. The epitaxial bilayers exhibit a high spin mixing conductance gmix↑↓=(2.9±0.2)×1019 m−2 and a spin diffusion length in Rhodium λsd=9.0±1.3 nm. This makes Rh comparable to Pt and Pd in terms of spin pumping and spin transport efficiency at room temperature.

Study of activation cross sections of double neutron capture reaction on 193Ir for the reactor production route of radiotherapeutic 195mPt

The radiotherapeutic 195mPt is among the most effective Auger electron emitters of the currently studied radionuclides that have a potential theranostic application in nuclear medicine. Production of 195mPt through double neuron capture of enriched 193Ir followed by β−-decay to the radioisotope of interest carried out at the research reactor IBR-2 is described. Because of the high radiation background, radiochemical purification procedure of 195mPt from bulk of iridium was needed to be developed and is detailed here as well. For the first time, cross section and resonance integral for the reaction 194Ir(n,γ)195mIr were determined. Resonance neutrons contribution was established to exceed that of thermal neutrons, and resonance integral for the reaction 194Ir(n,γ)195mIr is calculated to be 2900 b. Specific activity of 195mPt was estimated to reach a value of 38.7 GBq/(g Pt) at IBR-2 by the end of bombardment (EOB).

Principal investigation on the surface chemistry of phosphated zinc coatings treated by hot active plasma

The effect of hot active plasma (HAP) on phosphated zinc coated steel was studied in detail with x-ray photoelectron (XPS) and scanning Auger electron spectroscopy (AES) combined with electron microscopy. In order to extend the scope of the methods from the surface down to the bulk of the coating, Ar+ ion sputter depth profiling coupled with XPS was utilized. While a mild surface cleaning effect was observed for weak treatments, increased HAP intensity caused significant chemical and structural changes on the coating surface. Initially, a partial decomposition of zinc orthophosphate (Zn3(PO4)2), as the sole surface constituent of the untreated coating, led to a mixed zinc metaphosphate (Zn(PO3)x) and zinc oxide (ZnO) phase, highly localized in randomly distributed micrometer sized spots on the treated surface. Finally, the most intensive HAP treatment, leading to a temperature rise of the treated sample up to 700 °C as revealed by in-situ temperature measurements, caused a complete transformation of the zinc phosphate material into a porous and rough ZnO layer. Moreover, the heat contribution of the HAP treatment induced remarkable modifications within the bulk of the coating – mixing of zinc with the underlying steel substrate – an effect mimicking a galvannealing process.

Experimental Realization of Auger Decay in the Field of a Positive Elementary Charge.

Auger electron spectroscopy is an omnipresent experimental tool in many fields of fundamental research and applied science. The determination of the kinetic energies of the Auger electrons yields information about the element emitting the electron and its chemical environment at the time of emission. Here, we present an experimental approach to determine Auger spectra for emitter sites in the vicinity of a positive elementary charge based on electron-electron-electron and electron-electron-photon coincidence spectroscopy. We observe a characteristic redshift of the Auger spectrum caused by the Coulomb interaction with the charged environment. Our results are relevant for the interpretation of Auger spectra of extended systems like large molecules, clusters, liquids, and solids, in particular in high-intensity radiation fields which are nowadays routinely available, e.g., at x-ray free-electron laser facilities. The effect has been widely ignored in the literature so far, and some interpretations of Auger spectra from clusters might need to be revisited.

Radiationless decay spectrum of O 1s double core holes in liquid water.

We present a combined experimental and theoretical investigation of the radiationless decay spectrum of an O 1s double core hole in liquid water. Our experiments were carried out using liquid-jet electron spectroscopy from cylindrical microjets of normal and deuterated water. The signal of the double-core-hole spectral fingerprints (hypersatellites) of liquid water is clearly identified, with an intensity ratio to Auger decay of singly charged O 1s of 0.0014(5). We observe a significant isotope effect between liquid H2O and D2O. For theoretical modeling, the Auger electron spectrum of the central water molecule in a water pentamer was calculated using an electronic-structure toolkit combined with molecular-dynamics simulations to capture the influence of molecular rearrangement within the ultrashort lifetime of the double core hole. We obtained the static and dynamic Auger spectra for H2O, (H2O)5, D2O, and (D2O)5, instantaneous Auger spectra at selected times after core-level ionization, and the symmetrized oxygen-hydrogen distance as a function of time after double core ionization for all four prototypical systems. We consider this observation of liquid-water double core holes as a new tool to study ultrafast nuclear dynamics.

Ab Initio Computation of Auger Decay in Heavy Metals: Zinc about It.

We report the first coupled-cluster study of Auger decay in heavy metals. The zinc atom is used as a case study due to its relevance to the Auger emission properties of the 67Ga radionuclide. Coupled-cluster theory combined with complex basis functions is used to describe the transient nature of the core-ionized zinc atom. We also introduce second-order Møller-Plesset perturbation theory as an alternative method for computing partial Auger decay widths. Scalar-relativistic effects are included in our approach for computing Auger electron energies by means of the spin-free exact two-component one-electron Hamiltonian, while spin-orbit coupling is treated by means of perturbation theory. We center our attention on the K-edge Auger decay of zinc dividing the spectrum into three parts (K-LL, K-LM, and K-MM) according to the shells involved in the decay. The computed Auger spectra are in good agreement with experimental results. The most intense peak is found at an Auger electron energy of 7432 eV, which corresponds to a 1D2 final state arising from K-L2L3 transitions. Our results highlight the importance of relativistic effects for describing Auger decay in heavier nuclei. Furthermore, the effect of a first solvation shell is studied by modeling Auger decay in the hexaaqua-zinc(II) complex. We find that K-edge Auger decay is slightly enhanced by the presence of the water molecules as compared to the bare atom.

Remote plasma chemical vapor deposition of silicon oxycarbide film with a styrene-containing precursor and in situ O2 plasma treatment

In this paper, a study was conducted on silicon oxycarbide thin-film deposition using remote plasma chemical vapor deposition. A di-methyldimethoxysilane)2styrene (MDMS)2styrene precursor and CH4 plasma were used in the deposition process, and in situ oxygen plasma treatment was performed to control the carbon content and properties of the thin film. During the deposition process, the thin-film growth rate was found to be almost constant regardless of in situ plasma treatment. This means that in situ oxygen plasma treatment had no significant effect on thin-film growth itself. Auger electron spectroscopy analysis revealed that the carbon content of the deposited thin film was 43 % when only deposition was performed, but could be lowered to 3 % by in situ oxygen plasma treatment, which demonstrated that the carbon content can be controlled in a relatively wide range. X-ray photoelectron spectroscopy showed that it was possible to preserve SiC bonds even as the oxygen content increased with the number of in situ plasma treatments. The refractive index increased from 1.33 to 1.49, indicating a decrease in the number of pores and an increase in density. Meanwhile, the dielectric constant increased with the oxygen content, but did not exceed 3.9 due to the SiC bond structure. As the pore size decreased, the leakage current tended to decrease to 9.51 × 10−9 A/cm2 in an electric field of 1 MV/cm, and the breakdown voltage increased. Finally, it was possible to improve the etching characteristic through plasma treatment by lowering the wet etch rate from 78 to 19 Å/min.

Electron-induced deposition using Fe(CO)4MA and Fe(CO)5 - effect of MA ligand and process conditions.

The electron-induced decomposition of Fe(CO)4MA (MA = methyl acrylate), which is a potential new precursor for focused electron beam-induced deposition (FEBID), was investigated by surface science experiments under UHV conditions. Auger electron spectroscopy was used to monitor deposit formation. The comparison between Fe(CO)4MA and Fe(CO)5 revealed the effect of the modified ligand architecture on the deposit formation in electron irradiation experiments that mimic FEBID and cryo-FEBID processes. Electron-stimulated desorption and post-irradiation thermal desorption spectrometry were used to obtain insight into the fate of the ligands upon electron irradiation. As a key finding, the deposits obtained from Fe(CO)4MA and Fe(CO)5 were surprisingly similar, and the relative amount of carbon in deposits prepared from Fe(CO)4MA was considerably less than the amount of carbon in the MA ligand. This demonstrates that electron irradiation efficiently cleaves the neutral MA ligand from the precursor. In addition to deposit formation by electron irradiation, the thermal decomposition of Fe(CO)4MA and Fe(CO)5 on an Fe seed layer prepared by EBID was compared. While Fe(CO)5 sustains autocatalytic growth of the deposit, the MA ligand hinders the thermal decomposition in the case of Fe(CO)4MA. The heteroleptic precursor Fe(CO)4MA, thus, offers the possibility to suppress contributions of thermal reactions, which can compromise control over the deposit shape and size in FEBID processes.

State-selective dissociative double ionization of CH3I and CH2I2 via I 4d core-hole states studied by multi-electron-ion coincidence spectroscopy.

The dissociative double ionization of CH3I and CH2I2 irradiated with extreme ultraviolet light at hv = 100eV is investigated by multi-electron-ion coincidence spectroscopy using a magnetic bottle type electron spectrometer. The spin-orbit state-resolved Auger electron spectra for the I 4d core-hole states, (I 4d3/2)-1 and (I 4d5/2)-1, provide clear identifications of electronic states of CH3I2+ and CH2I22+. The dominant ion species produced after the double ionization correlate with the Auger electron energy, showing that different fragmentation pathways are open depending on the electronic states populated by the Auger decay. Theoretical calculations are performed to understand the fragmentation from the doubly charged states and the observed spin-orbit specificity in the Auger decay.

Resonant Auger decay of iodobenzene below the I 4d edge.

New data are presented on the resonant Auger decay of iodobenzene (C6H5I) in the region of the I 4d-1 ionization threshold. The excited molecules decay by participator and spectator processes to populate single-hole valence states and two-hole, one-particle excited states of the cation, providing new information on the structure of C6H5I+. Excitation of dissociative C6H5I (I 4d5/2,3/2-1)σ* resonances can, in principle, result in ultrafast dissociation to C6H5 + I** and the subsequent autoionization of I**, but no evidence for this process is observed. The results are compared with our recent study of the resonant Auger decay of methyl iodide (CH3I).

In Vitro and Preclinical Systematic Dose-Effect Studies of Auger Electron- and β Particle-Emitting Radionuclides and External Beam Radiation for Cancer Treatment

Despite a rise in clinical use of radiopharmaceutical therapies, the biological effects of radionuclides and their relationship with absorbed radiation dose are poorly understood. Here, we set out to define this relationship for Auger electron emitters [99mTc]TcO4- and [123I]I- and β--particle emitter [188Re]ReO4-. Studies were carried out using genetically modified cells that permitted direct radionuclide comparisons. Triple-negative MDA-MB-231 breast cancer cells expressing the human sodium iodide symporter (hNIS) and green fluorescent protein (GFP; MDA-MB-231.hNIS-GFP) were used. In vitro radiotoxicity of [99mTc]TcO4-, [123I]I-, and [188Re]ReO4- was determined using clonogenic assays. Radionuclide uptake, efflux, and subcellular location were used to calculate nuclear absorbed doses using the Medical Internal Radiation Dose (MIRD) formalism. In vivo studies were performed using female NSG mice bearing orthotopic MDA-MB-231.hNIS-GFP tumors and compared with X-ray-treated (12.6-15 Gy) and untreated cohorts. Absorbed dose per unit activity in tumors and sodium iodide symporter-expressing organs was extrapolated to reference human adult models using OLINDA/EXM. [99mTc]TcO4- and [123I]I- reduced the survival fraction only in hNIS-expressing cells, whereas [188Re]ReO4- reduced survival fraction in hNIS-expressing and parental cells. [123I]I- required 2.4- and 1.5-fold lower decays/cell to achieve 37% survival compared with [99mTc]TcO4- and [188Re]ReO4-, respectively, after 72 hours of incubation. Additionally, [99mTc]TcO4-, [123I]I-, and [188Re]ReO4- had superior cell killing effectiveness in vitro compared with X-rays. In vivo, X-ray led to a greater median survival compared with [188Re]ReO4- and [123I]I- (54 days vs 45 and 43 days, respectively). Unlike the X-ray cohort, no metastases were visualized in the radionuclide-treated cohorts. Extrapolated human absorbed doses of [188Re]ReO4- to a 1 g tumor were 13.8- and 11.2-fold greater than for [123I]I- in female and male models, respectively. This work reports reference dose-effect data using cell and tumor models for [99mTc]TcO4-, [123I]I-, and [188Re]ReO4- for the first time. We further demonstrate the tumor-controlling effects of [123I]I- and [188Re]ReO4- in comparison with external beam radiation therapy.

Development of Novel Bimodal Agents Based on Near-Infrared BODIPY-Conjugated Hoechst Derivatives for Combined Use in Auger Electron and Photodynamic Cancer Therapy.

Auger electron therapy and photodynamic therapy (PDT) have attracted attention as powerful anticancer modalities. Herein, we report the development of novel bimodal agents for Auger electron therapy and PDT, and their application to combination therapy. [125I]NBH-1/NBH-1 and [125I]NBH-2/NBH-2, composing Hoechst and iodostyryl-BODIPY, were synthesized and evaluated regarding their usefulness as bimodal agents. [125I]NBH-1 showed significantly higher nuclear uptake than [125I]NBH-2 and radioactivity-dependent cytotoxicity induced by Auger electrons. In addition, NBH-1 exhibited photoinduced cytotoxicity. Combination therapy using [125I]NBH-1 and NBH-1 with light irradiation induced a superior cytotoxicity to these treatments alone. In tumor-bearing mice injected with NBH-1 or [125I]NBH-1/NBH-1 under light irradiation, significant tumor growth inhibition was observed compared with that of the control group. Especially, [125I]NBH-1/NBH-1 under light irradiation showed the strongest therapeutic effects among all treatments. These results suggest that [125I]NBH-1/NBH-1 is a potent bimodal agent for Auger therapy and PDT and that combination therapy using [125I]NBH-1 and NBH-1 shows enhanced therapeutic efficacy.

Electrochemical Surface Nanostructuring of Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 Metallic Glass for Improved Pitting Corrosion Resistance

Ti‐based bulk metallic glasses are envisioned for human implant applications. Yet, while their elevated Cu content is essential for a high glass‐forming ability, it poses biocompatibility issues, necessitating a reduction in near‐surface regions. To address this, surface treatments that simultaneously generate protective and bioactive states, based on nanostructured Ti and Zr‐oxide layers are proposed. An electrochemical pseudo‐dealloying process using the bulk glass‐forming Ti47Cu38Fe2.5Zr7.5Sn2Si1Ag2 alloy is defined. Melt‐spun ribbons are immersed in hot concentrated nitric acid solution, monitoring the anodic polarization behavior. From the current density transient measurements, together with surface studies (field‐emission scanning electron microscopy, transmission electron microscopy, and Auger electron spectroscopy), the surface reactions are described. This nanostructuring process is divided into three stages: passivation, Cu dissolution, and slow oxide growth, leading to homogenous nanoporous and ligament structures. By tuning the applied potential, the pore and ligament sizes, and thickness values are adjusted. According to X‐ray photoelectron spectroscopy, these nanoporous structures are Ti and Zr‐oxides rich in hydrous and nonhydrous states. In a simulated physiological solution, for those treated glassy alloy samples, complete suppression of chloride‐induced pitting corrosion in the anodic regime of water stability is achieved. This high corrosion resistance is similar to that of clinically used cp‐Ti.

A Novel Method for Preparation of Al–Ni Reactive Coatings by Incorporation of Ni Nanoparticles into an Al Matrix Fabricated by Electrodeposition in AlCl3:1‐Eethyl‐3‐Methylimidazolium Chloride (1.5:1) Ionic Liquid Containing Ni Nanoparticles

Al/Ni reactive coatings are fabricated via electrochemical deposition (ECD) at different applied voltages for reactive bonding application. :1‐ethyl‐3‐methylimidazolium chloride ([EMIm]Cl) (1.5:1) ionic liquid electrolyte is used as source of Al, whereas Ni is in the bath and incorporated into final coatings as nanoparticles (NPs). Scanning electron microscopy and Auger electron spectroscopy reveal a homogeneous Ni particle dispersion, as well as a high amount of particle incorporation into the Al matrix. A maximum of 37 wt% (22 at%) of Ni is detected via atomic absorption spectroscopy in the Al/Ni coating deposited at −0.1 V from an electrolyte containing 20 g L−1 of Ni NPs. Previous literature show that for bonding application an ideal concentration is around 50 at% of Ni and 50 at% Al. However, this is achieved using high vacuum, time‐consuming processes, and costly techniques like evaporation and magnetron sputtering. The ECD used in this work represents a more cost‐efficient approach which is not reported up to date for the aforementioned application. The reactivity of the coatings is confirmed by Differential scanning calorimetry. Herein, an exothermic reaction is detected upon the mixing of Al and Ni occurring at high temperatures.

Failure analysis of heavy ion-irradiated silicon carbide junction barrier Schottky diodes

An analysis of damage, including single event burnout (SEB) and single event leakage current (SELC) caused by heavy ion irradiation in silicon carbide (SiC) junction barrier Schottky diodes (JBSDs), was performed using Auger electron spectroscopy (AES), emission microscope (EMMI), focused ion beam (FIB), transmission electron microscopy (TEM) and other methods. The damage of SEB extending from the Schottky contact through the epitaxial layer to the SiC substrate was observed. The damage causing SELC was related to the micro-burnout of the Schottky contact. It was concluded that the damage of Schottky contact was induced by incident high-energy particles under a large electric field, forming a leakage current path, resulting in SEB and SELC in the SiC device.