Ar 3P2 Research Articles

Analysis of silver metal with a Thermo Scientific K-Alpha XPS instrument at 50 and 200 eV pass energies

Silver metal was analyzed by x-ray photoelectron spectroscopy using a Thermo Scientific K-Alpha instrument with an Al Kα x-ray source (1486.6 eV). The silver survey spectrum and high-resolution Ag 3d, Ag M4N45N45, Ag M5N45N45, Ag 3p, O 1s, C 1s, Ar 2p, Ag 4p, and Ag 4s narrow scans were obtained. The sample analyzed is the standard instrument calibration silver foil mounted inside the analysis chamber of the K-Alpha. Sputtering with monoatomic Ar+ was performed prior to analysis to remove surface contamination. Narrow and survey scans were collected at 50 and 200 eV pass energy, respectively.

Multi-sideband interference structures by high-order photon-induced continuum-continuum transitions in helium

Following up on a previous paper on two-color photoionization of Ar(3p) [D. Bharti , ], we present measurements and calculations for a modified three-sideband (3-SB) version of the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) configuration applied to He(1s). The 3-SB RABBITT approach allows us to explore interference effects between pathways involving different orders of transitions within the continuum. The relative differences in the retrieved oscillation phases of the three sidebands provide insights into the continuum-continuum transitions. The ground state of helium has zero orbital angular momentum, which simplifies the analysis of oscillation phases and their angle dependence within the three sidebands. We find qualitative agreement between our experimental results and the theoretical predictions for many cases but also observe some significant quantitative discrepancies. Published by the American Physical Society 2024

Analysis of copper metal with a K-Alpha instrument from Thermo Scientific by XPS at 60 and 200 eV pass energy

Copper metal was analyzed by x-ray photoelectron spectroscopy (XPS) using a K-Alpha instrument from Thermo Scientific that employed an Al K-alpha x-ray source (1486.6 eV). The sample was the copper standard on the instrument sample stage that was sputtered with Ar+ to remove its oxide layer and hydrocarbon contamination. Shown in this work are the survey spectrum and high-resolution Cu 2p, Cu L3M45M45, Cu 3s, Cu 3p, O 1s, C 1s, and Ar 2p narrow scans. Narrow and survey scans were collected at 60 and 200 eV pass energy, respectively.

XPS Al Kα and high energy x-ray photoelectron spectroscopy (HAXPES) Cr Kα measurement of bulk boron

Bulk boron was analyzed using both XPS and high-resolution high energy x-ray photoelectron spectroscopy. The spectra of boron obtained using monochromatic Al Kα radiation include survey scan and high-resolution spectra of B 1s, O 1s, N 1s, C 1s, and Ar 2p. The Cr Kα spectra with radiation at 5414.8 eV include survey scan and high-resolution spectra of B 1s, O 1s, N 1s, C 1s, Ar 2p, and Ar 1s.

2000-eV argon ion beam induced formation of multiple chemical states in titanium dioxide mesoporous film

Oxygen vacancies were created on the surface of TiO2 mesoporous film after exposure to a 2000 eV argon ion beam. Confirmation of the presence of the vacancies was conducted through x-ray photoelectron spectroscopy analysis which reveals Ti 2p, O 1s, C 1s, and Ar 2p chemical states at different binding energies. Ti 2p spectra show five distinct peaks corresponding to Ti2+ 2p1/2, Ti3+ 2p3/2, Ti4+ 2p3/2, Ti3+ 2p1/2, and Ti4+ 2p1/2 states while the Ti4+ continuously reduced to Ti3+ and Ti2+ as the irradiation time of Ar+ increases. The Ar+ irradiation leads to the lower binding energy of the Ti 2p state with an increase in irradiation time while the binding energy of O 1s becomes higher with irradiation time. The peaks correspond to lattice oxygen; oxygen vacancy and adsorbed oxygen were observed in high-resolution O 1s spectra while the peak area ratio of oxygen vacancy with lattice oxygen increases with irradiation time. The atomic percentage of C 1s decreases with irradiation time while that of Ti 2p, O 1s, and Ar 2p increases with irradiation time. An increase in irradiation time leads to insignificantly shifting of the valence band edge towards the conduction band. The observed response of the prepared nano-particle TiO2 after 2000 eV Ar+ exposure which conveniently creates oxygen vacancies in the crystallographic structure of the semiconductor could be a versatile approach to enhancing the photocatalytic activity of the semiconductor for various industrial and technological applications.

Critical method evaluation refutes the Ar 2p signal of implanted Ar for referencing X-ray photoelectron spectra

Correct binding energy (BE) spectra referencing of insulating samples remains the major challenge in modern XPS analyses. Ar 2p signal of implanted Ar is sometimes used for this purpose. The method relies upon the assumption that chemically inert species such as noble gas atoms would be ideally suited as other factors affecting core level peak positions (such as chemical bonding) can be excluded. Here, we present a systematic study on the Ar 2p referencing method applied to a wide range of thin film sample materials of metals, nitrides, carbides, and borides. All specimens exhibit a well-defined Fermi edge, which serves as an independent internal reference for Ar 2p spectra of in-situ implanted Ar. Ar 2p3/2 binding energy is shown to vary by as much as 5.1 eV between samples. This is more than typical chemical shifts of interest, which obviously disqualifies Ar 2p referencing. The BE of the Ar 2p peaks shows a strong correlation to the number of valence electrons available for screening, implying that the polarization energy has a major role for the observed large spread of Ar 2p3/2 BE values. In several cases of single-phase films, an additional Ar 2p doublet is observed with the Ar 2p3/2 BE referenced to the vacuum level higher than the gas phase value of 248.6 eV, which is tentatively assigned to the formation of Ar-N and Ar-C complexes stabilized by Van der Waals forces. Ar implantation into two-phase samples, exemplified here by phase-segregated NiCrC/a-C:H and nanocomposite c-TiN/SiNx thin films, leads to complex Ar 2p spectra, which further demonstrates unreliability of the referencing method. The firm conclusion of the study is that the Ar 2p3/2 peak from implanted Ar is not a remedy for the charge referencing problem.

Ultra-fast development of Ar 2p relative densities in nanosecond-pulsed barrier discharge in argon

A time-correlated single photon counting based optical emission spectroscopy technique is applied for an investigation of the nanosecond-pulsed barrier discharge in atmospheric pressure argon gas. We record the development of the light intensities originating from all ten Ar 2p (Paschen notation) radiative states with high spatio-temporal resolution. We identify different stages of the discharge development: an early rapid electron avalanching, streamer propagation phase, generation of discharge channel and surface streamer propagation over the dielectric surface. The quantified relative 2p densities for identified discharge phases enable a well-resolved insight into the ultra-fast discharge kinetics and open a possibility for the development of future detailed diagnostics of the rapidly ionized argon plasmas. Moreover, the electrical characterization of the discharge is made using the simplest equivalent circuit and it reveals new findings for the application of such an approach for similar discharges.

Tuning the oxidation state of titanium dioxide mesoporous film by 1000 eV argon ion beam irradiation

This work proposes the creation of oxygen vacancies on the surface of TiO2 mesoporous film using a 1000 eV argon ion (Ar+) beam. After X-ray photoelectron spectroscopic characterization, the survey spectra of TiO2 nano-particles reveal the presence of oxygen (with chemical state O 1s), titanium (with chemical state Ti 2p), carbon (with chemical state C 1s) and argon (with chemical state Ar 2p) while the concentrations of each chemical states vary with an irradiation time of the Ar+ beam. The acquired Ti 2p spectra show five peaks at high resolution which correspond to Ti4+ 2p3/2, Ti4+ 2p1/2, Ti3+ 2p3/2, Ti3+ 2p1/2, and Ti2+ 2p1/2. The concentrations of Ti2+ and Ti3+ increase with irradiation time while the concentrations of Ti4+ decrease as the irradiation time increases. Three peaks characterize high-resolution spectra of O 1s which correspond to lattice oxygen, oxygen vacancy, and adsorbed oxygen. The peak area of lattice oxygen decreases with irradiation time while that of oxygen vacancies increases with irradiation time which shows the creation of oxygen vacancies at the expense of contaminant removal due to Ar+ exposure. Valence spectra analysis shows an insignificant effect on the valance band as the sample exposure to Ar+ increases. This proposed method of oxygen vacancy creation would facilitate the effective utilization of TiO2-based semiconductors in addressing many photo-catalytic challenges and widening the sunlight absorption capacity of the semiconductor.

Twisted electron impact single ionization coincidence cross-sections for noble gas atoms

We present the angular profiles of the triple differential cross-section (TDCS) for the (e, 2e) process on the noble gas atoms, namely He (1s), Ne (2s and 2p), and Ar (3p), for the plane wave and the twisted electron impact. We develop the theoretical formalism in the first Born approximation (FBA). The present study compares the TDCS for different values of orbital angular momentum number m and opening angles θ p of the twisted electron beam with that of the plane wave beam in co-planar asymmetric geometry. In addition, we also investigate the TDCS for macroscopic targets to explore the influence of the opening angle θ p of the twisted electron beam on the TDCS. Our results show that the peaks in binary and recoil regions shift from the momentum transfer direction. The results also show that for larger opening angles, the peaks for p-type orbitals split into double-peak structures, which are not observed in the plane wave results for the given kinematics. The angular profiles for averaged cross-section show the dependence of TDCS on the opening angles, especially for the larger opening angles, which are significantly different from the plane wave TDCS.

A Composite Velocity Map Imaging Spectrometer for Ions and 1 keV Electrons at the Shanghai Soft X-ray Free-Electron Laser

Velocity map imaging (VMI) spectrometry is widely used to measure the momentum distribution of charged particles with the kinetic energy of a few tens of electronVolts. With the progress of femtosecond laser and X-ray free-electron laser, it becomes increasingly important to extend the electron kinetic energy to 1 keV. Here, we report on a recently built composite VMI spectrometer at the Shanghai soft X-ray free-electron laser, which can measure ion images and high-energy electron images simultaneously. In the SIMION simulation, we extended the electron kinetic energy to 1 keV with a resolution <2% while measuring the ions with the kinetic energy of 20 eV. The experimental performance is tested by measuring Ar 2p photoelectron spectra at Shanghai Synchrotron Radiation Facility, and O+ kinetic energy spectrum from dissociative ionization of O2 by 800 nm femtosecond laser. We reached a resolution of 1.5% at the electron kinetic energy of 500 eV. When the electron arm is set for 100 eV, a resolution of 4% is reached at the ion kinetic energy of 5.6 eV. This composite VMI spectrometer will support the experiment, such as X-ray multi-photon excitation/ionization, Auger electrons emission, attosecond streaking.

Twisted distorted wave Born approximation as a new tool to investigate collisional processes

In this work, we report on triply differential ionization cross sections (e,2e) for atomic and molecular targets, namely, Ar(3p), Kr(4p), Xe(5p) and H2 impacted by twisted electron beams. The calculations were performed within the distorted wave Born approximation by using twisted and distorted waves for describing the incident and outgoing electrons, respectively. We found that the triply differential cross sections were strongly influenced by both the opening angle θ p and the orbital angular momentum OAM number m. Comparisons with experiments as well as existing results were reported.

Nonstatistical behavior of the photoionization of spin–orbit doublets

The photoionization branching ratios of spin–orbit doublets are studied both experimentally and theoretically at energies several keV above threshold. The results show significant relativistic effects for Ar 2p in the autoionizing region below the 1s threshold, and large many-body effects for Xe 3d and 4d in the vicinity of the L-shell thresholds. The branching ratios in Xe are also found to vary significantly over very broad multi-keV energy regions both above and below the inner-shell thresholds. In addition, the Ar 2p study confirms experimentally the decades-old theoretical prediction that the nonresonant branching ratio does not approach the statistical (nonrelativistic) value, and, in fact, progressively diverges from statistical with increasing photon energy.

Electron and positron impact single ionization TDCS of argon atoms in the second Born approximation

We present triple-differential cross section results for the positron and electron induced single ionization of the Ar (3p) and Ar (3s) atoms at incident energy 1 keV. The triple-differential cross sections (TDCSs) have been calculated in the modified distorted wave formalism using the second Born approximation. The TDCSs have been calculated in coplanar asymmetric geometry for different kinematical conditions. The second Born term has been found to be significant in obtaining the TDCS for electron as well as positron impact at smaller values of momentum transfer and it produces better agreement with the recent available measurements for Ar (3p). With the increase of momentum transfer, the dominance of binary emission of electrons has been found to increase for the positron impact ionization of Ar (3s).

Demonstration of Transmission Mode Soft X-ray NEXAFS Using Third- and Fifth-Order Harmonics of FEL Radiation at SACLA BL1

We demonstrate the applicability of third- and fifth-order harmonics of free-electron laser (FEL) radiation for soft X-ray absorption spectroscopy in the transmission mode at SACLA BL1, which covers a photon energy range of 20 to 150 eV in the fundamental FEL radiation. By using the third- and fifth-order harmonics of the FEL radiation, we successfully recorded near-edge X-ray absorption fine structure (NEXAFS) spectra for Ar 2p core ionization and CO2 C 1s and O 1s core ionizations. Our results show that the utilization of third- and fifth-order harmonics can significantly extend the available photon energies for NEXAFS spectroscopy using an FEL and opens the door to femtosecond pump-probe NEXAFS using a soft X-ray FEL.

Gas-phase endstation of electron, ion and coincidence spectroscopies for diluted samples at the FinEstBeAMS beamline of the MAX IV 1.5 GeV storage ring.

Since spring 2019 an experimental setup consisting of an electron spectrometer and an ion time-of-flight mass spectrometer for diluted samples has been available for users at the FinEstBeAMS beamline of the MAX IV Laboratory inLund, Sweden. The setup enables users to study the interaction of atoms, molecules, (molecular) microclusters and nanoparticles with short-wavelength (vacuum ultraviolet and X-ray) synchrotron radiation and to follow the electron and nuclear dynamics induced by this interaction. Test measurements of N2 and thiophene (C4H4S) molecules have demonstrated that the setup can be used formany-particle coincidence spectroscopy. The measurements of the Ar 3p photoelectron spectra by linear horizontal and vertical polarization show that angle-resolved experiments can also be performed. The possibility to compare the electron spectroscopic results of diluted samples with solid targets in the case of Co2O3 and Fe2O3 at the Co and Fe L2,3-absorption edges in the same experimental session is also demonstrated. Because the photon energy range of the FinEstBeAMS beamline extends from 4.4 eV up to 1000 eV, electron, ion and coincidence spectroscopy studies can be executed in a very broad photon energy range.

Conjugate photoelectron recapture peaks in the high resolution Auger electron spectra following near-threshold Ar 2p photoionization

We have observed formation of Rydberg series superimposed on the Ar (L3M2,3M2,3) Auger electron spectral profile with photoexcitation just above the 2p−13/2 photoionization threshold. This is due to the recapture of photoelectrons induced by post-collision interaction between the Auger electron and photoelectron: Ar+ 2p−13/2 + e− → Ar+ 3p−2ml + e−. The intensity distribution of the angular momentum state resolved Rydberg peaks revealed prominent conjugate peaks due to angular momentum exchange between photoelectrons and Auger electrons in the process. In addition, we measured the 2p−13/2nl → 3p−2ml + e− resonant Auger spectra with high resolution below the 2p−13/2 threshold. Our results showed that conjugate shake-up/down 2p−13/2nd → 3p−2mp + e− processes are stronger than the direct 2p−13/2nd → 3p−2ms, (m−1)d + e− processes in the spectator Auger processes, implying a strong angular momentum exchange effect between photoelectron and Auger electron.

Effect of Ar(3p54p; 2p)+M → Ar(3p54s; 1s)+M branching ratio on optically pumped rare gas laser performance

Optically pumped rare gas laser performance is analyzed as a function of the Ar(3p54p; 2p) + M → Ar(3p54s; 1s) + M branching ratios. Due to the uncertainty in the branching ratios, a sensitivity study is performed to determine the effect on output and absorbed pump laser intensities. The analysis is performed using a radio frequency dielectric barrier discharge as the source of metastable production for a variety of Argon in Helium mixtures over pressures ranging from 200 to 500 Torr. Peak output laser intensities show a factor of 7 increase as the branching ratio is increased from 0.25 to 1.00. The collection of Ar* in Ar(1s4) is inversely proportional to the branching ratio and decreases output laser intensity by reducing the density of species directly involved with lasing.

Comparative studies of compact kHz and MHz driven low pressure plasmas by emission and laser spectroscopy

The temporal evolution of a low pressure argon plasma driven by a combination of radio frequency and kilohertz frequency power sources was characterized by phase resolved optical emission and laser absorption spectroscopy. The compact, low pressure plasma was formed in a hybrid surface/jet geometry and powered by a high voltage power supply operating at 31 kHz and by a lower voltage RF supply operating at 13.56 MHz. An accurate evaluation of the 1s state density dynamics was performed by means of laser absorption measurements of the 1s5 and 1s4 sublevels. The emission spectra were recorded with a submicrosecond temporal resolution and evaluated using an extended Corona model. In comparison with the modeling results, the phase dependent ratio of different Ar(2p) → Ar(1s) emission lines was used to determine temporal profiles of electron temperature and relative electron density. The results were compared with the results from time averaged emission measurements by performing an identical analysis. Strong spatial and temporal variations of plasma parameters were observed when the plasma was driven solely by the 31 kHz source, resulting in nonequilibrium conditions for long living states. Inconsistent observations in the reconstructed temporal development of plasma energy and density were further investigated by illustrating full spatiotemporal reconstruction of plasma parameters. These results permit clear identification of strong spatial gradients through the tube.

Multi-scale investigation in the frequency domain of Ar/HMDSO dusty plasma with pulsed injection of HMDSO

A combination of time-resolved optical emission spectroscopy measurements and collisional–radiative modeling is used to investigate the phenomena occurring over multiple time scales in the frequency domain of a low-pressure, axially asymmetric, capacitively coupled radio-frequency (RF) argon plasma with pulsed injection of hexamethyldisiloxane (HMDSO, Si2O(CH3)6). The collisional–radiative model developed here considers the population of argon 1s and all ten 2p levels (in Paschen’s notation). The presence of HMDSO in the plasma is accounted for in the model by quenching of the argon 1s states by species generated by plasma processing of HMDSO, including HMDSO-15 (Si2O(CH3)5), acetylene (C2H2) and methane (CH4). Detailed analysis of the relative populations of Ar 2p states reveals cyclic evolutions of the electron temperature, electron density and quenching frequency that are shown to be linked to the kinetics of dust formation in Ar/HMDSO plasmas. Penning ionization of HMDSO and its fragments is found to be an important source of electrons for the plasma maintenance. It is at the origin of the cyclic formation/disappearance of the dust cloud, without attenuation of the phenomenon, as long as the pulsed injection of HMDSO is sustained. The multi-scale approach used in this study further reveals the straightforward relation of the frequency of HMDSO pulsed injection, in particular the HMDSO duty cycle, with the frequency of dust formation/disappearance cycle.

Depth profiling of noble gas atoms implanted in Al matrix: A photoelectron energy loss spectroscopy study

A non-destructive spectroscopic method based on core level photoelectron energy loss spectra (PEELS) measured at variable emission angle is proposed for depth profiling of implanted atoms in a solid matrix. Extrinsic plasmon excitation during the photoelectron path to the solid surface being the dominant loss mechanism and neglecting elastic scattering, analytic relations are obtained for several depth profiles (Gaussian, triangular, square) between calculated relative intensities of first-order and second-order plasmon excitation peaks and the distribution characteristics (average depth and width). This method is illustrated by PEELS analysis of a model system, namely shallow implantation of argon ions (EION = 2.0 keV, 35° incidence, 3 ML) into Al(001) matrix. The average depth (dPEELS = 2.0 ± 0.1 nm) of subsurface Ar bubbles obtained from energy loss spectra of Ar 2p photoelectrons (inelastic mean free path IMFP = 2.15 nm at EKIN = 1011 eV) is significantly smaller than the average depth of the distribution calculated from SRIM code (dSRIM = 3.8 nm). This discrepancy, found for all model depth profiles, is attributed to significant sputtered thickness (≈1.7 nm) of Al, as well as some possible diffusion of argon-vacancy complexes towards the surface during Ar ion implantation.