Electron Emission Spectra Research Articles

The stereo-dynamics of collisional autoionization of ammonia by helium and neon metastable excited atoms through molecular beam experiments.

A combined analysis of both new (energy spectra of emitted electrons) and previously published (ionization cross sections) experimental data, measured under the same conditions and concerning electronically excited lighter noble gas -NH3 collisional autoionization processes, is carried out. Such an analysis, performed by exploiting a formulation of the full potential energy surface both in the real and imaginary parts, provides direct information on energetics, structure, and lifetime of the intermediate collision complex over all the configuration space. The marked anisotropy in the attraction of the real part, driving the approach of reagents, and the selective role of the imaginary component, associated to the charge transfer coupling between entrance and exit channels, suggests that reactive events occur almost exclusively in the molecular hemisphere containing the nitrogen lone pair. Crucial details on the stereo-dynamics of elementary collisional autoionization processes are then obtained, in which the open shell nature of the disclosed ionic core of metastable atom plays a crucial role. The same analysis also suggests that the strength of the attraction and the anisotropy of the interaction increases regularly along the series Ne*((3)P), He*((3)S), He*((1)S)-NH3. These findings can be ascribed to the strong rise of the metastable atom electronic polarizability (deformability) along the series. The obtained results can stimulate state of the art ab initio calculations focused on specific features of the transition state (energetics, structure, lifetime, etc.) which can be crucial for a further improvement of the adopted treatment and to better understand the nature of the leading interaction components which are the same responsible for the formation of the intermolecular halogen and hydrogen bond.

Preparation and luminescence characteristics of monazite Eu3+:LaPO4 nanocrystals in NH4NO3 molten salt

Molten-salt method and NH4NO3 flux were developed to fabricate monoclinic monazite Eu3+:LaPO4 nanocrystals for the first time. The products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, excitation spectra, emission spectra and luminescence decay curves. The as-obtained products were quasihexagonal Eu3+:LaPO4 nanocrystals with the mean size of 30nm. The room temperature charge transfer bands (CTB) exhibited red-shift and spectral broadening in comparison with 10K CTB. The optimal Eu3+ concentration was determined to be 8mol% by a comparative study of the relative emission intensities for different Eu3+ doping concentrations. The higher concentration quenching could be caused by the possible nonradiative energy transfer (electric multipole–multipole interaction). The relationship between the FL lifetime of 5D0 energy level and Eu3+ concentration was investigated based on Auzel’s model. This work is important not only to understand the unique physical properties of Eu3+:LaPO4 nanocrystals but also to bring an opportunity for the development of the other nanocrystals via the molten salt synthesis in NH4NO3 flux.

The collisional relaxation of electrons in hot flaring plasma and inferring the properties of solar flare accelerated electrons from X-ray observations.

X-ray observations are a direct diagnostic of fast electrons produced in solar flares, energized during the energy release process and directed towards the Sun. Since the properties of accelerated electrons can be substantially changed during their transport and interaction with the background plasma, a model must ultimately be applied to X-ray observations in order to understand the mechanism responsible for their acceleration. A cold thick target model is ubiquitously used for this task, since it provides a simple analytic relationship between the accelerated electron spectrum and the emitting electron spectrum in the X-ray source, with the latter quantity readily obtained from X-ray observations. However, such a model is inappropriate for the majority of solar flares in which the electrons propagate in a hot megaKelvin plasma, because it does not take into account the physics of thermalization of fast electrons. The use of a more realistic model, properly accounting for the properties of the background plasma, and the collisional diffusion and thermalization of electrons, can alleviate or even remove many of the traditional problems associated with the cold thick target model and the deduction of the accelerated electron spectrum from X-ray spectroscopy, such as the number problem and the need to impose an ad hoc low energy cut-off.

Nanop: An x-ray to gold nanoparticle electron and photon emission software

Nanoparticles have been explored as radiosensitizers for cancer radiotherapy. While the nanoparticle radiotherapy improvement has been clearly observed, there is still a debate over the physical and biological mechanisms leading to this result. In particular, the role of electrons and photons emitted by nanoparticle after x-ray absorption is not well understood and their energies are not well known. Therefore, we developed in this paper a new model to determine the electron and photon emission spectra of nanoparticles irradiated by x-ray photons. This model is implemented, for a gold nanoparticle, in a newly available software called Nanop which allows anyone to determine gold nanoparticle photon and electron emissions.

Electron production by noble metal nanoparticles in collision processes with photons and fast ions

SynopsisWe analyzed electron production by noble metal nanoparticles irradiated by photons and fast ions. For that, photoabsorption spectra of several gold clusters were calculated in a broad photon energy range by means of time-dependent density-functional theory (TDDFT). Two dominant peaks appearing in the spectra of electron emission of noble metal clusters were assigned to two distinct types of collective electron excitations. This study revealed that the decay of the collective excitations formed in the nanoparticles is an important mechanism of generation of low-energy electrons, which are known to act as important agents of biodamage.

Electron interferences in the ionization of the dimers by swift ion impact: Origin of high-order frequency

SynopsisWe report evidence for interference phenomena beyond Young-type in electron emission spectrum from the dimers by fast ions. Prior measurements for H2 have led to a wide discussion for which no definitive conclusions have been settled, whereas theoretical-side have failed to reproduce the phenomenon. The process under investigations is treated by using a nonperturbative semi-classical approach to solve the time-dependent Schrodinger equation. Our results are supported by an analytic model based on second- and third-order Born series.

Influence of the projectile charge state on electron emission spectra from a Cu(111) surface

SynopsisDouble differential electron emission distributions produced by grazing impact of fast dressed ions on a Cu(111) surface are investigated focusing on the effects of the electronic band structure. The process is described within the Band-Structure-Based (BSB) approximation, which is a perturbative method that incorporates information of the electronic band structure of the solid. Differences in the behavior of the emission spectra for He+q, Li+q, Be+q and C+q projectiles with different charge states q are explained by the combined effect of the projectile trajectory and the projectile charge distribution.

Spectroscopic Measurements in the Experiments of Gas Injection to the Divertor Simulation Experimental Module of GAMMA 10/PDX

In this paper, detailed results on spectral measurement are reported and the argument on impurity transport is presented from the comparison of the spectral measurements in the end-cell and the plug/barrier-cell. Spectroscopic measurement in the plug/barrier-cell was carried out for the first time. Ionization behavior in the plug/barrier-cell showed a significant difference from that in the end-cell. Discussion of detached plasma generation from the change of the electron temperature, density and emission spectrum by the gas injection conditions is also presented. In the case that the plenum pressure of noble gas was increased, the radiation of hydrogen neutrals decreased by 20~90% and the ion saturation current decreased by 90~95%, which indicated that electron density is reduced by recombination. It is suggested that the effect of molecular activated recombination may have appeared.

Electron emission spectra of U28+-ions colliding with gaseous targets

SynopsisThe electron-loss to continuum has been studied experimentally and theoretically for the collision systems U28+ + H2 at a collision energy of 50 MeV/u, U28+ + N2 at 30 MeV/u, and U28+ + Xe at 50 MeV/u.

Tb3+/Eu3+: YF3 nanophase embedded glass ceramics: Structural characterization, tunable luminescence and temperature sensing behavior

Tb3+/Eu3+ co-doped transparent bulk glass ceramics containing orthorhombic β-YF3 nanocrystals were successfully synthesized by melt-quenching and subsequent heating. The partition of the active centers into the YF3 crystalline lattice was confirmed by elemental mapping in the scanning transmission electron microscope, emission spectra and decay curves. As a consequence, Tb3+ → Eu3+ energy transfer was demonstrated to be more efficient in the glass ceramic than in the precursor glass, which resulted in color tunable luminescence by simply modifying Eu3+ content and induced the linearly temperature-dependent fluorescence intensity ratio between the Tb3+: 5D4 → 7F5 transition and the Eu3+: 5D0 → 7F4 one in the Tb3+/Eu3+ co-doped glass ceramic. It is expected that the investigated glass ceramic might be a promising candidate for solid-state lighting as well as optical temperature sensor.

SU‐E‐T‐544: Microscopic Dose Enhancement of Gold Nanoparticles in Water for Proton Therapy: A Simulation Study

Purpose:To quantify the microscopic dose and linear energy transfer (LET) enhancement of gold nanoparticles (GNPs) in water for proton therapy.Methods:The GEANT4 toolkit (version 10) with low energy electromagnetic classes was used to create a series of simulations where three radii (r=5, 20, 100 nm) of gold nanoparticles (GNPs) were irradiated with 5 × 106 80 MeV protons. A cubic detector (10 × 10 × 10 um, divided in 25 × 25 × 25 voxels) were placed in a water phantom where the GNP rests in the center. The size of incident proton beam was set to be same as the GNPs and perpendicularly aiming to the target. Dose deposited to each voxel were recorded to calculate the overall deposited dose and the dose‐averaged LET. The emitted secondary electron spectra were also collected in a spherical customized scorer (radius = 150 nm).Results:The average dose from a single GNP in a cubic water phantom was increased by 0.12 %, 1.12% and 2.3% and the mean dose‐averaged LET was increased by 5.87% and 27.67% and 0.31% for GNP radius of 5 nm, 20 nm and 100 nm, respectively.Conclusion:The dose enhancement effect from the presence of a single GNP was qualified in a water phantom. A significant increase in the mean dose‐averaged LET was found for 20 nm GNP.

Influence of the projectile charge state on electron emission spectra from a Cu(111) surface

Abstract Double differential electron emission distributions produced by grazing impact of fast dressed ions on a Cu(111) surface are investigated focusing on the effects of the electronic band structure. The process is described within the Band-Structure-Based approximation, which is a perturbative method that includes an accurate representation of the electron–surface interaction, incorporating information of the electronic band structure of the solid. Differences in the behavior of the emission spectra for He + q , Li + q , Be + q and C + q projectiles with different charge states q are explained by the combined effect of the projectile trajectory and the projectile charge distribution.

Differential electron emission in the ionization of Ne and Xe atoms under fast bare carbon ion impact

Measurement of the energy and angular distributions of the double differential cross section (DDCS) of electron emission from Ne and Xe atoms in collision with 5 MeV u−1 bare carbon ions is reported. This study aimed to investigate the electron emission processes in the case of multi-electronic systems. In general, several clear differences between the electron emission spectra of Ne and Xe are found, which indicate the influence of the increasing number of electrons. For instance, the sharp peak due to the binary nature of collision is almost absent in the case of Xe, unlike Ne, which could be understood due to the increasing contribution from the strongly bound inner shell (such as ) electrons for the Xe atom. The forward–backward angular asymmetry has also been derived from the angular distributions. For Xe, the qualitative behaviour of the asymmetry parameter is seen to be quite different since it reveals structures due to Auger contributions. It is, in general, different and much lower than that for Ne, which shows the smooth behaviour that one finds for other lighter atoms like He. The single differential and total cross sections are also derived. The theoretical calculations based on the prior form of the continuum distorted wave-eikonal initial state (CDW-EIS) approximation have been provided for both the targets. Overall, it gives a very good agreement with the energy and the angular distributions of DDCS for Ne. For Xe, the agreement is not as good as for Ne. We also provide a detailed discussion on the DDCS obtained from different sub-shell ionization, estimated in this framework.

Luminescence properties of ZrW2O8:Eu3+ nanophosphors for white light emitting diodes

ZrW2O8:Eu3+ nanophosphors (ca. 60nm) with different Eu3+ doping concentrations were obtained using hydrothermal syntheses. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence excitation and emission spectra as well as decay curve measurements were used for the characterization. Under 466nm excitation, strong red emission at 616nm corresponding to 5D0–7F2 transition of Eu3+ was observed for ZrW2O8:Eu3+ (9mol%) phosphors. The values of intensity parameter Ω2 and Ω4 are 17.82×10−20cm2 and 1.092×10−20cm2, respectively. The high quantum efficiency of 83.5% of the ZrW2O8:Eu3+ (9mol%) suggests this material could be promising red phosphor for generating white light in phosphor-converted white light-emitting diodes (LED).

Microdosimetry of the Auger electron emitting 123I radionuclide using Geant4-DNA simulations

Microdosimetric calculations of the Auger electron emitter 123I were done in liquid water spheres using the Geant4 toolkit. The electron emission spectrum of 123I produced by Geant4 is presented. Energy deposition and corresponding S-values were calculated to investigate the influence of the sub-cellular localization of the Auger emitter. It was found that S-values calculated by the Geant4 toolkit are generally lower than the values calculated by other Monte Carlo codes for the 123I radionuclide. The differences in the compared S-values are mainly due to the different particle emission spectra employed by the respective computational codes and emphasizes the influence of the spectra on dosimetry calculations.

Electron and photon emissions from gold nanoparticles irradiated by X-ray photons

In this paper, we develop a totally new probabilistic model for the electron and photon emission of gold nanoparticles irradiated by X-ray photons. This model allows direct applications to recent researches about the radiotherapy enhancement by gold nanoparticles in the context of cancer treatment. Our model uses, in a complete original way, simulated Auger cascade and stopping power to compute electron emission spectra, photon emission spectra and released energy inside the material of gold nanoparticles. It allows us to present new results about the electron and photon emission of gold nanoparticle irradiated by hard X-rays.

High-density Au nanorod optical field-emitter arrays

We demonstrate the design, fabrication, characterization, and operation of high-density arrays of Au nanorod electron emitters, fabricated by high-resolution electron beam lithography, and excited by ultrafast femtosecond near-infrared radiation. Electron emission characteristic of multiphoton absorption has been observed at low laser fluence, as indicated by the power-law scaling of emission current with applied optical power. The onset of space-charge-limited current and strong optical field emission has been investigated so as to determine the mechanism of electron emission at high incident laser fluence. Laser-induced structural damage has been observed at applied optical fields above 5 GV m−1, and energy spectra of emitted electrons have been measured using an electron time-of-flight spectrometer.

Radiation emission by electrons channeling in bent silicon crystals

Results of numerical simulations of electron channeling and emission spectra are reported for straight and uniformly bent silicon crystals. The projectile trajectories are computed using the newly developed module [G.B. Sushko, V.G. Bezchastnov, I.A. Solov’yov, A.V. Korol, W. Greiner, A.V. Solov’yov, J. Comput. Phys. 252, 404 (2013)] of the MBN Explorer packageb [I.A. Solov’yov, A.V. Yakubovich, P.V. Nikolaev, I. Volkovets, A.V. Solov’yov, J. Comput. Chem. 33, 2412 (2013)]. The electron channeling along Si(110) crystallographic planes is studied for the projectile energy 855 MeV.

Comparison of the efficiency of 63Ni beta-radiation detectors made from silicon and wide-gap semiconductors

The current induced by the radiation from a 63Ni film of variable thickness is simulated taking into account the real spectrum of emitted electrons and their angular distribution for GaN. The efficiency of β-radiation detectors made from Si and SiC is estimated based on the results obtained in this paper and previously. Using a scanning electron microscope the efficiency of β-radiation detectors made from Si and SiC under conditions corresponding to β radiation from a Ni film with a thickness of 3 μm and activity of 10 mCi/cm2 is analyzed. It is shown that the efficiency of real Si-based structures is virtually as good as the efficiency of SiC-based structures.

Crystal structure, energy band and optical properties of dysprosium monophosphate DyPO4

A rare earth monophosphate crystal of DyPO4 has been synthesized by high temperature solid-state reaction method and was structurally characterized by single crystal X-ray diffraction. Atomic arrangement of DyPO4 structure is based on corner and edge sharing PO4 tetrahedra and DyO8 polyhedra. The FTIR, Raman, Scanning electron microscopy, diffuse reflectance and emission spectra of the compound have been investigated. Density functional calculation using a Generalized Gradient Approximation was used to determine the electronic structure and optical properties. The calculated total and partial densities of states indicate that the top of valance band is mainly built upon O-2p states with P-3p states via σ (P–O) interactions, and the low conduction bands mostly originates from Dy-5d. The results show that the monophosphate DyPO4 is an insulator with a calculated band gap (5.8eV) closer to the experimental value (6.38eV).