Auger Electron Research Articles

Growth of MnxAu1−x Films on Cu(001) and Ag(001) Single‐Crystal Substrates

The growth, morphology, and structure of films on Cu(001) and Ag(001) are studied by means of low‐energy electron diffraction (LEED), medium‐energy electron diffraction, Auger electron spectroscopy, and scanning tunnelling microscopy. Different concentrations x from about 0.5 to 1 and thicknesses from 0.2 to 12.9 ML of are examined. For several values of x, exhibits a c(2 2) superstructure pattern on Cu(001) when the total thickness is around or above 0.5 ML. Above 1 ML, LEED patterns of can be only observed on Ag(001), but not on Cu(001). LEED‐I(V) is employed to deduce the vertical interlayer distance for as‐grown and post‐annealed films on Ag(001). Above 500 K, Ag from the substrate segregates into the films.

Ultrasmall Gold Nanoparticles Radiolabeled with Iodine-125 as Potential New Radiopharmaceutical.

The relatively high linear energy transfer of Auger electrons, which can cause clustered DNA damage and hence efficient cell death, makes Auger emitters excellent candidates for attacking metastasized tumors. Moreover, gammas or positrons are usually emitted along with the Auger electrons, providing the possibility of theragnostic applications. Despite the promising properties of Auger electrons, only a few radiopharmaceuticals employing Auger emitters have been developed so far. This is most likely explained by the short ranges of these electrons, requiring the delivery of the Auger emitters to crucial cell parts such as the cell nucleus. In this work, we combined the Auger emitter 125I and ultrasmall gold nanoparticles to prepare a novel radiopharmaceutical. The 125I labeled gold nanoparticles were shown to accumulate at the cell nucleus, leading to a high tumor-killing efficiency in both 2D and 3D tumor cell models. The results from this work indicate that ultrasmall nanoparticles, which passively accumulate at the cell nucleus, have the potential to be applied in targeted radionuclide therapy. Even better tumor-killing efficiency can be expected if tumor-targeting moieties are conjugated to the nanoparticles.

High Separation Factor, High Molar Activity, and Inexpensive Purification Method for the Production of Pure 165Er.

Introduction: Auger electron-emitting radionuclides with low (0.001-1 keV) energy, short-range (2-500 nm), and high linear energy transfer (4-26 keV/μm) can play an important role in the targeted radionuclide therapy (TRT) of cancer. 165Er is a pure Auger electron-emitting radionuclide, making it a useful tool for the fundamental studies of the biological effects of Auger electrons. This work develops a simple, inexpensive, high separation factor, and high molar activity radiochemical isolation process for the production of 165Er (t1/2 10.36 h) suitable for TRT in vitro and in vivo studies using irradiated natHo solid targets. Methods: Small medical cyclotron proton-irradiation of natHo targets produced 165Er in GBq scale quantities. 165Er was isolated using cation exchange chromatographic resin (AG 50W-X8, 200-400 mesh, 20 mL, under atmospheric pressure) using α-hydroxyisobutyric acid (70 mM, pH 4.75) followed by extraction using TK212, TK211, and TK221 extraction chromatographic columns. Radio nuclidic and chemical purity of the final 165Er were confirmed using HPGe Gamma spectrometry and induction coupled plasma-mass spectrometry analysis, respectively. The purified 165Er was radiolabeled with two radiometal chelators (DOTA and Crown) and used to produce a new Auger electron-emitting radiopharmaceutical, [165Er]Er-Crown-TATE. Results: Irradiation of 200 mg natHo targets with 20-30 μA of 12.8 MeV protons produced 165Er at 25 ± 5 MBq·μA-1·h-1. The 4.5 ± 0.5 h radiochemical isolation yielded GBq scale of 165Er in 0.05 M HCl (2 mL) with a radiochemical yield of 78.0 ± 5.6% decay corrected to the end of bombardment (EoB) and a Ho/165Er separation factor of (1.14 ± 0.25) × 106. The product showed high radio nuclidic purity and chemical purity. Concentration-dependent radiolabeling experiments with Crown and DOTA were performed resulting in the successful labeling of 165Er with high (>90%) radiochemical yield. Radiolabeling experiments with Crown-TATE were performed 8 h after EoB and synthesized [165Er]Er-Crown-TATE at molar activities of 202.4 MBq·nmol-1 at the end of synthesis (EoS). Conclusions: A 3 h cyclotron irradiation and 4.5 h radiochemical separation produced GBq-scale 165Er suitable for producing radiopharmaceuticals at molar activities satisfactory for investigations of targeted radionuclide therapeutic effects of Auger electron emissions. This will enable future fundamental radiation biology experiments of pure Auger electron-emitting therapeutic radiopharmaceuticals, such as [165Er]Er-Crown-TATE, which will be used to understand the impact of Auger electrons in TRT.

Enhancement of Optical Gain in Colloidal CdSe/CdS/ZnS Quantum Dots through Nanosecond Optical Pumping.

Optical gain and lasing in colloidal nanocrystals are often hindered by sub-nanosecond rapid Auger non-radiative recombination, especially under continuous wave optical or electrical excitation. This study demonstrates amplified spontaneous emission (ASE) from CdSe/CdS/ZnS quantum dot (QD) solids through prolonged pulsed optical pumping over 10 ns. The incorporation of CdS and ZnS double shells on CdSe QDs effectively decelerates the Auger process in multiexcitonic states by extending the electron wave function and enhancing dielectric screening. Furthermore, we engineer smooth, densely packed QD solid films that efficiently guide the optical mode, achieving substantial net gain values under nanosecond pumping. The proposed approach helps observe ASE with gain thresholds of 0.84 and 1.5 mJ/cm2 under optical pumping pulse widths of 6 and 15 ns, respectively. This advancement can promote continuous pumping in colloidal QD gain systems, opening new avenues for optoelectronic applications.

Coupled Electron-Nuclear Dynamics Induced and Monitored with Femtosecond Soft X-ray Pulses in the Amino Acid Glycine.

The coupling of electronic and nuclear motion in polyatomic molecules is at the heart of attochemistry. The molecular properties, transient structures, and reaction mechanism of these many-body quantum objects are defined on the level of electrons and ions by molecular wave functions and their coherent superposition, respectively. In the present contribution, we monitor nonadiabatic quantum wave packet dynamics during molecular charge motion by reconstructing both the oscillatory charge density distribution and the characteristic time-dependent nuclear configuration coordinate from time-resolved Auger electron spectroscopic data recorded in previous studies on glycine molecules [Schwickert et al. Sci. Adv. 2022, 8, eabn6848]. The electronic and nuclear motion on the femtosecond time scale was induced and probed in kinematically complete soft X-ray experiments at the FLASH free-electron laser facility. The detailed analysis of amplitude, instantaneous phase, and instantaneous frequency of the propagating many-body wave packet during its lifecycle provides unprecedented insight into dynamical processes beyond the Born-Oppenheimer approximation. We are confident that the refined experimental data evaluation helps to develop new theoretical tools to describe time-dependent molecular wave functions in complicated but ubiquitous non-Born-Oppenheimer photochemical conditions.

Passive Film Formed on Si-Mn Steel in Boric Acid-Borate Buffer at 6.5

Passivity-maintaining current of high-strength (Si-Mn) steel in boric acid-borate buffer at pH 6.5 was larger than that of ferrite/pearlite (F/P) steel. Charge transfer resistance of the Si-Mn steel surface passivated at 1.10 V vs SHE in pH 6.5 buffer was smaller than that of F/P steel surface. Nano-analyses using AES and STEM revealed the details of the structure and components of the passive film on the Si-Mn steel. The inferiorities of passivity of Si-Mn steel were suggested to be due to the alloying components and metallurgical structure to increase the strength of the steel.

Ultralow Auger-Assisted Interlayer Exciton Annihilation in WS2/WSe2 Moiré Heterobilayers.

Transition metal dichalcogenide (TMD) heterobilayers have emerged as a promising platform for exploring solid-state quantum simulators and many-body quantum phenomena. Their type II band alignment, combined with the moiré superlattice, inevitably leads to nontrivial exciton interactions and dynamics. Here, we unveil the distinct Auger annihilation processes for delocalized interlayer excitons in WS2/WSe2 moiré heterobilayers. By fitting the characteristic efficiency droop and bimolecular recombination rate, we quantitatively determine an ultralow Auger coefficient of 1.3 × 10-5 cm2 s-1, which is >100-fold smaller than that of excitons in TMD monolayers. In addition, we reveal selective exciton upconversion into the WSe2 layer, which highlights the significance of intralayer electron Coulomb interactions in dictating the microscopic scattering pathways. The distinct Auger processes arising from spatial electron-hole separation have important implications for TMD heterobilayers while endowing interlayer excitons and their strongly correlated states with unique layer degrees of freedom.

Assessing DNA damage and relative biological effectiveness of the secondary electrons in gadolinium neutron capture therapy using an adapted Geant4-DNA

The aim of this study is to assess the impact of internal conversion (IC) and Auger electrons released during gadolinium neutron capture therapy (157GdNCT) on the amount of DNA damage induced and the relative biological effectiveness (RBE) across varying cellular structures and types. We developed cell models that featured simplified chromosome geometries with diverse shapes and base pair densities, utilizing the Geant4-DNA package. The RBE values of these secondary electrons were determined based on the DNA double-strand breaks (DNA-DSBs) endpoint. The findings revealed that the more the distribution of gadolinium is concentrated in the nucleus, the greater the degree of DNA damage. In the cytoplasm, the influence of secondary electrons on DNA damage were not related to cell shape. However, when the secondary electrons were distributed in the nuclear membrane, the RBE of the secondary electrons was affected by the cell shape. When there is a greater difference in base pair density, more pronounced discrepancies in the yield of DSBs are evident. As the base pair density decreased, the yield of DSBs increased. Furthermore, the yield of DSBs exceeded 8.63 ± 0.33 DSBs/Gy/Gbp under different influencing factors. The RBE range of IC electrons and Auger electrons released from 157GdNCT based on DNA-DSBs endpoints was found to be between 0.8 and 1.6.

Using Temperature-Programmed Photoelectron Emission (TPPE) to Analyze Electron Transfer on Metallic Copper and Its Relation to the Essential Role of the Surface Hydroxyl Radical

Surface processes such as coatings, corrosion, photocatalysis, and tribology are greatly diversified by acid–base interactions at the surface overlayer. This study focuses on the action of a metallic copper surface as an electron donor/acceptor related to the inactivation of viruses. It was found that regarding Cu2O or Cu materials, electrostatic interaction plays a major role in virus inactivation. We applied the TPPE method to clarify the mechanism of electron transfer (ET) occurring at light-irradiated copper surfaces. The TPPE characteristics were strongly influenced by the environments, which correspond to the temperature and environment dependence of the total count of emitted electrons in the incident light wavelength scan (PE total count, NT), the photothreshold, and further the activation energy (ΔE) analyzed from the Arrhenius plot of NT values obtained in the temperature increase and subsequent temperature decrease processes. In this study, we re-examined the dependence of the TPPE data from two types of Cu metal surfaces: sample A, which was mechanically abraded in alcohols, water, and air, and sample C, which was only ultrasonically cleaned in these liquids. The NT for both samples slowly increased with increasing temperature, reached a maximum (NTmax) at 250 °C (maximum temperature, Tmax), and after that, decreased. For sample A, the NTmax value decreased in the order H2O > CH3OH > C2H5OH > (CH3)2CHOH > C3H7OH, although the last alcohol gave Tmax = 100 °C, while with sample C, the NTmax value decreased in the order C3H7OH > (CH3)2CHOH > C2H5OH > CH3OH > H2O. Interestingly, both orders of the liquids were completely opposite; this means that a Cu surface can possess a two-way character. The NT intensity was found to be strongly associated with the change from the hydroxyl group (–Cu–OH) to the oxide oxygen (O2−) in the O1s spectra in the XPS measurement. The difference between the above orders was explained by the acid–base interaction mode of the –Cu–OH group with the adsorbed molecule on the surfaces. The H2O adsorbed on sample A produces the electric dipole –CuOδ−Hδ+ ⋅⋅⋅ :OH2 (⋅⋅⋅ hydrogen bond), while the C3H7OH and (CH3)2CHOH adsorbed on sample C produce RO−δHδ+ ⋅⋅⋅ :O(H)–Cu− (R = alkyl groups). Gutmann’s acceptor number (AN) representing the basicity of the liquid molecules was found to be related to the TPPE characteristics: (CH3)2CHOH (33.5), C2H5OH (37.1), CH3OH (41.3), and H2O (54.8) (the AN of C3H7OH could not be confirmed). With sample A, the values of NTmaxa and ΔEaUp1 both increased with increasing AN (Up1 means the first temperature increase process). On the other hand, with sample C, the values of NTmaxc and ΔEcUp1 both decreased with increasing AN. These findings suggest that sample A acts as an acid, while sample C functions as a base. However, in the case of both types of samples, A and C, the NTmax values were found to increase with increasing ΔEUp1. It was explained that the ΔEUp1 values, depending on the liquids, originate from the difference in the energy level of the hydroxyl group radical at the surface denoted. This is able to attract electrons in the neighborhood of the Fermi level of the base metal through tunnelling. After that, Auger emission electrons are released, contributing to the ET in the overlayer. These electrons are considered to have a strong ability of reducibility.

Bright Nonblinking Photoluminescence with Blinking Lifetime from a Nanocavity-Coupled Quantum Dot.

Colloidal quantum dots (QDs) are excellent luminescent nanomaterials for many optoelectronic applications. However, photoluminescence blinking has limited their practical use. Coupling QDs to plasmonic nanostructures shows potential in suppressing blinking. However, the underlying mechanism remains unclear and debated, hampering the development of bright nonblinking dots. Here, by deterministically coupling a QD to a plasmonic nanocavity, we clarify the mechanism and demonstrate unprecedented single-QD brightness. In particular, we report for the first time that a blinking QD could obtain nonblinking photoluminescence with a blinking lifetime through coupling to the nanocavity. We show that the plasmon-enhanced radiative decay outcompetes the nonradiative Auger process, enabling similar quantum yields for charged and neutral excitons in the same dot. Meanwhile, we demonstrate a record photon detection rate of 17 MHz from a colloidal QD, indicating an experimental photon generation rate of more than 500 MHz. These findings pave the way for ultrabright nonblinking QDs, benefiting diverse QD-based applications.

Co-deposition of bismuth-nitrogen films on MgO (001) by molecular beam epitaxy

We attempted to grow a thin film of BiN by co-deposition of bismuth and nitrogen on rock-salt structure MgO (001) substrates. Furthermore, we studied the effect of variation of the growth temperature and the nitrogen to bismuth flux ratios on sample growth. For the samples grown and conditions used, we do not find strong evidence for the formation of a bulk Bi-N alloy. Even for very high nitrogen to bismuth flux ratio, we observed only bismuth and no nitrogen using bulk Rutherford back-scattering spectroscopy measurements, and only 1%–2% nitrogen was seen through surface Auger electron spectroscopy measurements. The in-plane lattice measurements show that the resulting Bi (110) samples are strained, which is presumably caused by lattice mismatch between the sample and the substrate when grown without any buffer layer. The use of a high-temperature buffer layer helps to release strain in the sample but only along one axis. Measurements of the atomic layer spacing using x-ray diffraction and also scanning tunneling microscopy confirm the Bi (110) thin film sample structure.

Dissociation following the Auger decay of xenon difluoride molecules.

This study investigated the dissociation after the Xe 4d Auger decay of weak-bonding XeF2 molecules by multielectron-ion coincidence spectroscopy using a magnetic bottle electron spectrometer. Fragmentations from the XeF22+ states were clarified in the Auger spectra coincident with individual ion species. It was observed that the two-hole population led by the Auger decay was not directly inherited during the fragmentation of XeF22+. Furthermore, the dissociations of XeF23+ states produced by the double Auger decay were investigated.

Rebuilding the vibrational wavepacket in TRAS using attosecond X-ray pulses

Time-resolved X-ray photoelectron spectroscopy (TXPS) is a well-established technique to probe coherent nuclear wavepacket dynamics using both table-top and free-electron-based ultrafast X-ray lasers. Energy resolution, however, becomes compromised for a very short pulse duration in the sub-femtosecond range. By resonantly tuning the X-ray pulse to core-excited states undergoing Auger decay, this drawback of TXPS can be mitigated. While resonant Auger-electron spectroscopy (RAS) can recover the vibrational structures not hidden by broadband excitation, the full reconstruction of the wavepacket is a standing challenge. Here, we theoretically demonstrate how the complete information of a nuclear wavepacket, i.e., the populations and relative phases of the vibrational states constituting the wavepacket, can be retrieved from time-resolved RAS (TRAS) measurements. Thus, TRAS offers key insights into coupled nuclear and electronic dynamics in complex systems on ultrashort timescales, providing an alternative to leverage femtosecond and attosecond X-ray probe pulses.

Palladium-103 (103Pd/103mRh), a promising Auger-electron emitter for targeted radionuclide therapy of disseminated tumor cells - absorbed doses in single cells and clusters, with comparison to 177Lu and 161Tb.

Early use of targeted radionuclide therapy (TRT) to eradicate disseminated tumor cells (DTCs) might offer cure. Selection of appropriate radionuclides is required. This work highlights the potential of 103Pd (T1/2 = 16.991 d) which decays to 103mRh (T1/2 = 56.12 min) then to stable 103Rh with emission of Auger and conversion electrons. Methods: The Monte Carlo track structure code CELLDOSE was used to assess absorbed doses in single cells (14-μm diameter; 10-μm nucleus) and clusters of 19 cells. The radionuclide was distributed on the cell surface, within the cytoplasm, or in the nucleus. Absorbed doses from 103Pd, 177Lu and 161Tb were compared after energy normalization. The impact of non-uniform cell targeting, and the potential benefit from dual-targeting was investigated. Additional results related to 103mRh, if used directly, are provided. Results: In the single cell, and depending on radionuclide distribution, 103Pd delivered 7- to 10-fold higher nuclear absorbed dose and 9- to 25-fold higher membrane dose than 177Lu. In the 19-cell clusters, 103Pd absorbed doses also largely exceeded 177Lu. In both situations, 161Tb stood in-between 103Pd and 177Lu. Non-uniform targeting, considering four unlabeled cells within the cluster, resulted in moderate-to-severe dose heterogeneity. For example, with intranuclear 103Pd, unlabeled cells received only 14% of the expected nuclear dose. Targeting with two 103Pd-labeled radiopharmaceuticals minimized dose heterogeneity. Conclusion: 103Pd, a next-generation Auger emitter, can deliver substantially higher absorbed doses than 177Lu to single tumor cells and cell clusters. This may open new horizons for the use of TRT in adjuvant or neoadjuvant settings, or for targeting minimal residual disease.

Synthesis and properties of phosphorus nanostructures on Au(110).

Phosphorene, a semiconducting two-dimensional material, has recently attracted huge interest due to its potential applications in opto-electronics. The first attempts to synthesize phosphorene were based mainly on mechanical and chemical exfoliations. A few years later, different groups reported the synthesis of phosphorene using the molecular beam epitaxy process, which opened the way for research on physical properties. In this article, we report phosphorus growth on an Au(110) substrate via molecular beam epitaxy. The atomically resolved scanning tunneling microscopy images exhibit a self-assembled phosphorus-dimer structure, which is converted into phosphorus chains when increasing the phosphorus coverage. The chemical composition of the obtained structures is determined via Auger electron and X-ray photoelectron spectroscopies. Density functional theory calculations support the experimental findings.

Spectroscopic properties of yellow and red InP/ZnSe/ZnS quantum dots

The spectroscopic properties of yellow and red InP/ZnSe/ZnS quantum dots (QDs) were comparatively investigated. The red QDs exhibit a less serious Auger effect, a longer hot carrier cooling time and stronger multiphoton absorption cross-sections.

161Tb]Tb-PSMA-617 radioligand therapy in patients with mCRPC: preliminary dosimetry results and intra-individual head-to-head comparison to [177Lu]Lu-PSMA-617.

Rationale: Evaluation of alternative radionuclides for use in prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is currently focusing on 161Tb, which may provide advantages by emitting additional Auger and conversion electrons. In this pilot study, we present preliminary dosimetry data for [161Tb]Tb-PSMA-617 RLT in a direct comparison with [177Lu]Lu-PSMA-617. Method: Six patients with metastatic castration-resistant prostate cancer (mCRPC) underwent treatment with [177Lu]Lu-PSMA-617 and subsequently - after inadequate response - with [161Tb]Tb-PSMA-617. Whole-body planar and SPECT imaging-based dosimetry of organs at risk (kidneys and salivary glands) and tumor lesions were calculated using IDAC for 177Lu and OLINDA/EXM for 161Tb. The therapeutic index (TI) of mean tumor-absorbed doses over relevant organs at risk was calculated. Results: Mean absorbed doses to organs at risk of PSMA-RLT were slightly higher for [161Tb]Tb-PSMA-617 compared to [177Lu]Lu-PSMA-617 (kidneys: 0.643 ± 0.247 vs. 0.545 ± 0.231 Gy/GBq, factor 1.18; parotid gland: 0.367 ± 0.198 vs. 0.329 ± 0.180 Gy/GBq, factor 1.10), but markedly higher regarding tumor lesions (6.10 ± 6.59 vs 2.59 ± 3.30 Gy/GBq, factor 2.40, p < 0.001). Consequently, the mean TI was higher for [161Tb]Tb-PSMA-617 compared to [177Lu]Lu-PSMA-617 for both, the kidneys (11.54 ± 9.74 vs. 5.28 ± 5.13, p = 0.002) and the parotid gland (16.77 ± 13.10 vs. 12.51 ± 18.09, p = 0.008). Conclusion: In this intra-individual head-to-head pilot study, [161Tb]Tb-PSMA-617 delivered higher tumor-absorbed doses and resulted in superior TI compared to [177Lu]Lu-PSMA-617. This preliminary data support 161Tb as a promising radionuclide for PSMA-RLT in mCRPC.

Electronic Structure of Thin MoS2 Films

The valence electron structure of exfoliated monolayer MoS2 deposited onto SiO2 was determined by UV photoelectron spectroscopy through component analysis in combination with Auger electron microscopy. The valence electron cut-off...

Effect of Hf and Ta on Ni-based superalloy powders

The effect of Hf and Ta modifying on the microstructure and composition of Ni-based superalloy powders was investigated. The element concentrations on the powder surface and subsurface were quantitatively characterized by the Auger electron spectroscopy, and cross sections of powders were observed by the electron probe microanalysis. The results show that Hf and Ta hardly change the morphology of powders, but significantly change the powder surface and subsurface composition. Hf and Ta enhance the volume fraction of MC carbides in powders, thereby reducing the concentrations of C, Ti, and Nb on the powder surface and subsurface, which effectively inhibits the formation of the prior particle boundary during HIP. It reduces crack sources and thus improves the mechanical properties of the alloy.

Ab initio treatment of molecular Coster-Kronig decay using complex-scaled equation-of-motion coupled-cluster theory.

Vacancies in the L1 shell of atoms and molecules can decay non-radiatively via Coster-Kronig decay whereby the vacancy is filled by an electron from the L2,3 shell while a second electron is emitted into the ionization continuum. This process is akin to Auger decay, but in contrast to Auger electrons, Coster-Kronig electrons have rather low kinetic energies of less than 50 eV. In the present work, we extend recently introduced methods for the construction of molecular Auger spectra that are based on complex-scaled equation-of-motion coupled-cluster theory to Coster-Kronig decay. We compute ionization energies as well as total and partial decay widths for the 2s-1 states of argon and hydrogen sulfide and construct the L1L2,3M Coster-Kronig and L1MM Auger spectra of these species. Whereas our final spectra are in good agreement with the available experimental and theoretical data, substantial disagreements are found for various branching ratios suggesting that spin-orbit coupling makes a major impact on Coster-Kronig decay already in the third period of the periodic table.