Outer-shell Electrons Research Articles

Statistical analyses of fluorometry data from chloroform filtrate of lamb feces

Accurately identifying the botanical composition of free-ranging animal diets remains a challenge. Currently accepted procedures are time consuming, many requiring painstaking sample preparation while none produce data useful for real-time management. Automated procedures focusing on detection of chemical and/or physical plant properties using specific molecules called fluorophores offers possibilities for determining the species composition of herbivore diets. This study was designed to evaluate fluorometry techniques in herbivore diet determinations using fecal samples obtained from 13 lambs fed a basal diet of tobosa hay (Pleuraphis mutica Buckley), and containing 4 different levels (0, 10, 20, and 30%) of tarbush (Flourensia cernua D C.) leaf material. Chloroform (CHCl3) filtrate obtained from the lamb's feces was exposed to UV light from a xenon arc lamp. This caused fluorophore molecules in the filtrate to have their outer shell electrons move to a higher energy state as a result of UV light excitation. After excitation by UV light at 310, 320, 330, 340, 350, and 355 nm, the fluorophores returned to their ground state giving off light (fluorescence). This fluorescence intensity (counts) varied and when captured using appropriate electronics, produced 1,024 pairs of light intensities (counts) and fluorescent wavelengths between 175 and 818 nm in 0.63 nm increments. Previous research indicated differences among diets could be determined using distinct peaks in the red and blue regions of the visible light spectrum and a univariate (1 variable at a time) analysis. This research demonstrates the entire fluorescence data set can be used to determine differences among diets using multivariate statistics. Sequences of 5 increasingly complex statistical techniques were used to distinguish among diets: 2-dimensional plots, polynomial regression models, confidence interval plots, discriminant analysis, and 3-dimensional plots. Two-dimensional plots indicated 2 spectral fluorescence peaks, 1 in the blue-green (420-600 nm) and 1 in the red (640-720 nm) region of the visible spectrum. Because of the asymmetrical nature of these peaks, fifth-order polynomials were developed to differentiate among the 4 diets. Statistical reliability was high when discriminating between diets containing no tarbush leaf and the diets containing 30% tarbush leaf; however, it was not possible to statistically separate diets containing intermediate (10 and 20%) amounts of tarbush leaf material from each other or from the 2 extremes (0 and 30% tarbush leaf). These results suggest spectral signatures arising from fluorometry data may be useful for differentiating among botanical composition diets that differ in plant form, but that a multivariate approach may require large sample sizes.

Synthesis, structures and magnetic properties of a series of polynuclear copper(II)‐lanthanide( III) complexes assembled with carboxylate and hydroxide ligands

AbstractHeterometallic copper(II)‐lanthanide(III) complexes have been made with a variety of exclusively O‐donor ligands including betaines (zwitterionic carboxylates) and chloroacetate, which are dinuclear CuLn, tetranuclear Cu2Ln2, pentanuclear Cu3Ln2, and octadecanuclear Cu12 complexes. The results show that subtle changes in both the carboxylates and acidity of the reaction solution can cause drastic changes in the structures of the products. Magnetic studies exhibit that shielding of the Ln3+ 4f electrons by the outer shell electrons is very effective to preclude significant coupling interaction between the Ln3+ 4f electrons and Cu2+ 3d electrons in either a mono‐atomic hydroxide‐bridged, or a carboxylate‐bridged system.

Many-electron and orientation effects in anomalouselastic scattering of an x-ray photon by a linearmolecule

A strong orientation effect is discovered theoretically upon thechange of the scheme of a suggested experiment on the anomalouselastic x-ray scattering of linearly polarized x-ray radiationby linear diatomics near the ionization thresholds of innermolecular orbitals. The effects on the shape oftheoretical scattering spectra of vibronic phenomena (for theHF and HCl molecules) are studied, as well as the additional excitation/ionizationof outer-shell electrons (the CO molecule). Within theone-centre approximation for the molecular orbitalwavefunctions the analytical structure of the linear molecule'sform factor is obtained. The calculation of one-electronwavefunctions is carried out with the inclusion of the effect ofcore relaxation in the field of the inner-shell vacancy withinthe one-centre method in the Hartree-Fock approximation. Thedipole transition matrix elements and photoabsorption crosssections are calculated by the methods of the theory ofnon-orthogonal orbitals.

Nanoscale EELS analysis of dielectric function and bandgap properties in GaN and related materials

The low loss region of an EEL spectrum (<50 eV) contains information about excitations of outer shell electrons and thus the electronic structure of a specimen which determines its optical properties. In this work, dedicated electron energy loss spectroscopy (EELS) methods for the experimental acquisition and analysis of spectra are described, which give improved information about the electronic structure near the bandgap region at a spatial resolution in the range of nanometers. For this purpose, we made use of a cold field emission scanning transmission electron microscope (STEM) equipped with a dedicated EELS system. This device provides a subnanometer electron probe and offers an energy resolution of 0.35 eV. Application of suitable deconvolution routines for removal of the zero loss peak extracts information on the bandgap region while the Kramers–Kronig transformation deduces the dielectric properties from the measured energy loss function. These methods have been applied to characterize the optical properties of wide-bandgap materials for the case of III-nitride compounds, which are currently the most promising material for applications on optoelectronic devices working in the blue and ultraviolet spectral range. The obtained results are in excellent agreement with experimental measurements by synchrotron ellipsometry and theoretical studies. The potential of the superior spatial resolution of EELS in a STEM is demonstrated by the analysis of dielectric properties of individual layers of heterostructures and individual defects within wurtzite GaN.

Observation of satellite structures for TbLγx-ray emission in the presence ofM- andN-shell multiple vacancies

Multiple-vacancy states for outer-shell electrons created in heavy-ion--atom collision have been studied through high-resolution measurement of the $L\ensuremath{\gamma}$ x rays emitted from ${}_{65}\mathrm{Tb}$ induced by 15- and 30-MeV carbon ions. For the $L{\ensuremath{\gamma}}_{1}$ x-ray emission, it is found that the satellite structure due to N-shell multiple vacancies can be well resolved from the satellite structures due to M-shell multiple vacancies. The spectral features observed provide experimental evidence for the manifestation of the exchange interaction between the ${4d}_{3/2}$ hole and the unpaired $4f$ electrons in the presence of several N vacancies. An interpretation of the observed satellite structure for the complex $L{\ensuremath{\gamma}}_{2,3}$ x-ray emission is presented.

A Review of Accelerator-Based Techniques in Analytical Studies

Sensitive methods of elemental analysis have been developed using charged-particle beams. These techniques are usually insensitive to the effects of outer-shell electrons and provide little or no information on chemical bonding. The past 50 years has seen wide applications of various accelerator-based methods in different areas of analysis. This paper reviews the development and major advances of a variety of ion-beam techniques and their impact in analytical studies.

HOW CAN AN ATOM OR ION REMEMBER ITS INITIAL STATE?

The experiment has found that in order to form the thin film of certain compound by deposition, the same compound should be used for the target material. A stoichiometric mixture of components for forming the compound by solid reaction as the target material won't do the work. It seems that the particle emitted from the target remembers its initial state, the state when it is in the compound. By perturbation approximation, we estimated the life time of the initial state of the emitted particle, if the states of the particle are represented only by the states of outer shell electrons. To elucidate the experimental finding, other factors regarding the states of the emitted particle may have to take into consideration.

Monoelectronic and dielectronic processes producingK-shell vacancies in slowNeq++CH4collisions(q=3–9)

Cross sections for Auger emission following the creation of a K-shell vacancy in C have been measured in slow collisions of ${\mathrm{Ne}}^{q+}$ with ${\mathrm{CH}}_{4}(q=3--9).$ Projectile energies ranging from 30 to 180 keV were investigated. For projectile charges lower than 7, the transfer of a K electron from C into the projectile is attributed to monoelectronic $2p\ensuremath{\sigma}\ensuremath{-}2p\ensuremath{\pi}$ transitions induced by rotational coupling at small internuclear distances. For higher charge states, the measured cross sections are found to be significantly larger at the lowest projectile energies than predicted cross sections for $2p\ensuremath{\sigma}\ensuremath{-}2p\ensuremath{\pi}$ transitions. It is shown that other mechanisms must be invoked, such as dielectronic excitation due to electron-electron interaction. Dielectronic excitation gives rise to a simultaneous transfer of inner- and outer-shell electrons of ${\mathrm{CH}}_{4}$ into a $2\mathcal{l}$ shell of Ne.

Lasing in Rare-Earth-Doped Semiconductors: Hopes and Facts

Semiconductors doped with rare-earth (RE) elements have attracted a lot of attention as alternative materials for producing electrically pumpe d semiconductor lasers whose emission wavelength is very weakly dependent on temperature. This prospect is especially attractive in the case of indirect-gap Silicon, whose photonic applications as the material for light emitters still remain more of a hope than a reality. In view of a desirable emission wavelength at 1.5 μm, a lot of research has concentrated on Si:Er (see Coffa et al. for a recent review). It is generally recognized that doping with Er ions presents one of the most promising approaches to Silicon photonics. However, despiteintensive investigations, stimulated emission has not been conclusively demonstrated for Si.Er or for any other RE-doped semiconductor. This is in striking contrast to optical amplifiers and lasers based on various erbium-doped glasses. In this article, which builds on recent articles in MRS Bulletin on Silicon photonics, we will address the issues relevant to efficient light generation by semiconductors doped with RE elements in general, and specifically by Si:Er-based structures.The intraimpurity electronic structure of RE ions is dominate d by electron-electron and spin-orbit interactions within the 4f shell. In the case of Er3+, they produce separated J-multiplets with 4I15/2 and 4I13/2 as the ground and the lowest-lying excited states, respectively. Due to the effective Screening of 4f electrons by the outer electron Shells, the host has a very limited influence and changes only slightly the relative positions of the levels. Depending on a particular site symmetry, the even terms of the crystal field split the free-ion J-multiplets into the Stark components typically by several meV for the ground State. The energy-level diagram of an Er3+ ion in a cubic crystal field is shown in Figure 1, where the energy transfer paths relevant for Si:Er are also schematically indicated. The odd terms of the crystal field potential admix the states of opposite parity to the 4f11 configuration of the Er3+ ion, thereby introducing a certain degree of electric-dipole strength into the otherwise forbidden intra-4f-shell transitions. This effect enhance s slightly the magnetic-dipole strength of the 4I15/2 ↔ 4I13/2 transition and is host- and site-dependent. There-fore, Er-related center s of different microstructure can be fairly easily identified.

Beam capillary spectroscopy

In this short article, several recent findings on the interaction of slow highly charged ions with surfaces studied with thin microcapillary foils are discussed, which enables for the first time to extract atoms (ions) in highly and multiply excited states into vacuum, and to study the intrinsic nature of hollow atoms (ions) formed above a surface (HAA). It was found that observed charge-changed fractions were consistent with the prediction of the classical over barrier model. X-ray measurements revealed that a considerable fraction of charge changed ions are in metastable states though keeping multiple electrons in outershells and at the same time keeping innershell hole(s), i.e. metastable multiply excited Rydberg states are formed, which have lifetimes of ∼1 ns or longer. Spin-aligned states with less than half-filled shells and/or a highly excited high angular momentum state are possible first order models that explain such an extreme metastability. Visible light measurements, on the other hand, provide detailed information on electrons in highly excited states, e.g. Δ n = 1 transitions from states with n ∼ q ( n is the principal quantum number of the active electrons, and q the incident charge state) were observed, which proves that electrons on HAA are in high Rydberg states having principal quantum numbers around those predicted by the classical over barrier model, and further, the angular momentum quantum numbers are very high, which is again qualitatively explained with a classical picture. It is emphasized that the combination of slow highly charged ions and capillary foils provides a unique chance to study spectroscopic natures of HAA.

Photonic Applications of Rare-Earth-Doped Materials

The elements of the lanthanide series, from Ce (atomic number 58) to Yb (atomic number 70), form a group of chemically similar elements that have in common a partially filled 4f shell. These so-called “rare earth” (RE) elements usually take on a 3+ ionic state (RE3+). Because the 4f electronic-energy levels of each lanthanide ion are shielded from external fields by 5s2 and 5p6 outer-shell electrons, RE3+ energy levels are predominantly independent of their surroundings.The characteristic energy levels of 4f electrons of the trivalent RE elements have been investigated in detail by Gerhard Heinrich Dieke and co-workers and were reported approximately 30 years ago. The Dieke diagram showing RE3+ energy levels is a familiar tool of scientists and engineers working with RE elements. However, the history of RE elements goes back to the year 1787 in the small Swedish town of Ytterby near Stockholm and to the gifted amateur mineralogist and military man Lt. Carl Axel Arrhenius. Arrhenius discovered an unusual black mineral in Ytterby (perceived initially as much rarer in occurrence and in concentration than the common ores or earths of aluminum, calcium, etc.). Many new elements were discovered by various chemists upon analysis of this black stone and others like it. The names given to these elements are variations of the location where the first discovery was made: yttrium, ytterbium, terbium, and erbium. The history of RE elements is fascinating and involves many other famous names in science: Berzelius, Gadolin, Bunsen.The properties of these elements and their multifaceted applications to science and industry are equally fascinating and have remained important to this day. Commercial applications of RE elements began after World War II, when their available quantity and purity were greatly enhanced by improved separation techniques developed as a part of the Manhattan Project. Until fairly recently, the main industrial application of RE elements has been in permanent magnets. The unpaired 4f electrons result in some RE elements having the highest magnetic moments of any element. The development and applications of RE magnets are reviewed in a very interesting article by Livingston3 in a previous MRS Bulletin issue. In this issue of MRS Bulletin, we have taken as our aim to review some of the properties and applications of RE elements relevant to photonics.

Observing the Chemical State of Elements With Z=21 To 28 From L Alpha1 To L L Ratios With Energy Dispersive Spectroscopy (EDS)

Abstract It is well known that chemical bonding affects elemental x-ray emission spectra. The spectra of low atomic number elements show energy shifts which depend on the bonding of the element. To observe these shifts, a high resolution wavelength dispersive (WDS) x-ray spectrometer is required. Intensity variations of the L series can be observed with an EDS system which also show chemical effects. The L Alphal and the L L radiations are produced from a vacancy in the L III shell. Normally the L L line is about 5 to 6% of the intensity of the L Alphal line. However, in the atomic number range of Z=21 to 28, it is easily observed that the L L line becomes more intense. The L Alphal is no longer present at Z=20. These intensity changes are due to the outer electron shells of these atoms being unfilled. The L Alphal comes from the L3-M5 transition, while the L L comes from L3-M1 transition. The M5 (3d level) of the M shell is partially filled for Z=21 to 28; empty for Z&amp;lt;21and full for Z&amp;gt; 28. Holliday observed a Ti LL which was 17% greater than the Ti L Alphal.

EELS Characterization of Electronic Structure in Group III - Nitrides Compared With Synchrotron Ellipsometry Results

Abstract EELS in the low loss region of the spectra (&amp;lt; 50eV) provides information on excitations of outer shell electrons and thus the electronic structure of a specimen material which determines its optical properties. In this work dedicated EELS methods for the experimental acquisition and analysis of spectra are described which give improved information about the electronic structure near the bandgap region at a spatial resolution in the range of nanometers. For this purpose we made use of a cold field emission STEM equipped with a dedicated EELS system. This device provides a subnanometer electron probe and offers an energy resolution of 0.35 eV. Application of suitable deconvolution routines for removal of the zero loss peak extracts information on the closest bandgap region while Kramers-Kronig transformation deduces the dielectric properties from the measured energy loss function. These methods have been applied to characterize the optical properties of wide-bandgap materials for the case of group Ill-nitride compounds which are currently the most promising material for applications on optoelectronic devices working in the blue and ultraviolet spectral range.

Production and relaxation pathways of multiply excited states in slow highly charged ion-atom collisions

When a slow multiply charged projectile ion moving at a velocity below that of typical outer-shell atomic electrons collides with a many-electron neutral target, a large number of electrons can become active during the collision. Such collisions are dominated by the transfer of a number of target electrons to the projectile, resulting in the formation of projectile multiply excited states. Substantial progress has been made toward understanding one- and two-electron processes in slow ion-atom collisions during the past three decades ~see, e.g., Ref. @1#, and references therein!. Although slow collisions involving more than two active electrons have also been investigated for over two decades as well, our understanding of multielectron processes is by no means comparable to that of one- and two-electron processes. The vast majority of experimental studies of multielectron processes involved measurements of cross sections for projectile charge-change and recoil-ion production, both in a singles’ and in coincidence modes, and a limited number involved energy gain and visible photon spectroscopy ~see, e.g., @2‐5#, and references therein!. Moreover, since autoionization is a main decay mode of multiply excited states, Augerelectron spectroscopy has been employed in a singles’ mode @6,7# to study such collisions. While such measurements have played a significant role in understanding two-electron processes ~see, e.g., Ref. @8#, and references therein!, the situation is drastically different when many electrons are involved. For example, Benoit-Cattin et al. @6# obtained a singles’ electron spectrum for the 70-keV N 71 1Ar collision system. The analysis of the spectrum was rather difficult since it contained contributions from doubly, triply, quadruply, and quintuply excited states that rendered the interpretation nontrivial. During the last six years, however, Morgenstern and co-workers have made significant contributions @9‐12# toward understanding Auger-electron spectra obtained in multiple-electron capture processes by means of the coincident detection of Auger electrons and target ions. They obtained partial Auger spectra corresponding to the different target ion charge states that are much more informative than singles’ spectra. These spectra can provide further information if the final projectile charge state is also determined. From a theoretical point of view, understanding multielectron processes is a twofold problem. First, the different mechanisms involved in the collision process that lead to the production of the multiply excited states must be recognized and described. Second, the radiative and nonradiative properties of the resulting multiply excited states must be known. Concerning the first problem, quantum-mechanical or semiclassical treatment of collisions involving more than two electrons is prohibitively difficult due to the large number of channels involved. Therefore, extended classical overbarrier ~ECB! models have been developed @13,14# to account for multiple-electron capture processes. These models are limited to giving the capture state distribution on the projectile and possible simultaneous target excitation. There has been, until recently @15‐17#, a severe lack of theoretical work on the radiative and nonradiative properties of multiply excited states, due in part to the extremely large number of states that need to be taken into account, and in part to the lack of experimental data to which the calculations can be directly compared. Therefore, relaxation schemes @6,12# based on simple arguments, such as autoionization to the nearest continuum limits and minimum electron rearrangement ~twoelectron transitions!, have been invoked. This Rapid Communication reports triple-coincidence measurements of Auger electrons, scattered projectile, and target recoil ions in slow multiply charged ion-atom collisions. The measurements provide insights into the relaxation pathways of multiply excited states populated in such collisions.

Electronic band structure of metallic lithium in the field of external excitation

A procedure is developed that allows for exact calculations of the band energy of a solid in the Hartree–Fock approximation. The starting point is a self-consistent calculation that employs a Gaussian basis of functions. The method is used to establish the energy structure of the electrons in metallic lithium as a function of temperature. The calculated density of states, optical conductivity, the K-edge of the X-ray emission spectrum, and other properties of the electrons agree with the experimental data. Small variations in the band energies for lithium are discovered. The most important ones are the broadening of the core electron states and the transition of outer-shell electrons from s-symmetry stats to p-symmetry states as the temperature grows. Influence of vacancies and s-, p-, d-impurities on the electronic band structure is investigated. The influence of d-impurities is the most significant.

A Simulation of Electron Scattering in Magnetic Materials

A new simulation model is proposed to calculate the electron scattering in magnetic materials. It takes into account not only the three-dimensional electron trajectory, but also the electron spin transport along the trajectory. The mechanisms considered in the magnetic materials are the Lorentz force, the spin-orbit interaction, and the secondary electron generation. The band structure of the outer-shell electrons in the material is considered in the cascade process of low-energy secondary electron generation. The calculated energy dependence of the spin-polarization shows a reasonable agreement with the experimental value.

Spin fluctuations in YBa2Cu3O6.6

An important feature of the high-transition-temperature (high-T-c) copper oxide superconductors is the magnetism that results from the spins associated with the incomplete outer electronic shells (3d(9)) of the copper ions. Fluctuations of these spins give rise to magnetic excitations of the material, and might mediate the electron pairing that leads to superconductivity. If the mechanism for high-T-c superconductivity is the same for all copper oxide systems, their spin fluctuations should be universal. But so far, the opposite has seemed to be the case: neutron scattering data reveal clear differences between the spin fluctuations for two major classes of high-T-c materials, La2-xSrxCuO4 (refs 1-3) and YBa2Cu3O7-x (refs 4-6), whose respective building blocks are CuO2 layers and bilayers. Here we report two-dimensional neutron-scattering imaging of YBa2Cu3O6.6, which reveals that the low-frequency magnetic excitations are virtually identical to those of similarly doped La2-xSrxCuO4. Thus, the high-temperature (T-c less than or similar to 92 K) superconductivity of the former materials may be related to spatially coherent low-frequency spin excitations that were previously thought to be unique to the lower-T-c (<40 K) single-layer La2-xSrxCuO4 family.

Inversion relations for exclusive and inclusive cross sections within the independent electron approximation

Inversion relations expressing inclusive cross sections as linear combinations of exclusive cross sections are derived within the independent electron approximation without exchange. Both binomial and multinomial probability distributions are used. No particular model is used for $P(\stackrel{\ensuremath{\rightarrow}}{b}).$ A criterion for applicability of the multinomial probability distribution to describe second-order transitions for the different collision channels, also independent of $P(\stackrel{\ensuremath{\rightarrow}}{b}),$ is presented. The coupling of ionization and capture of outer-shell electrons is discussed and the inversion relations derived are applied to the analysis of coincidence measurements of projectile and target charge states. Parametrization and scaling laws for single and double ionization of outer-shell electrons of many-electron atoms are considered by studying the influence of the electron capture channel.

Magnetic properties and magnetic Compton scattering for amorphous Cu 100− XGd X ( X = 30, 50 and 60) alloys

Saturation magnetization M s and Curie temperature T c for amorphous CuGd alloys are investigated in order to understand the role of electrons which contribute to magnetic properties. The magnetic moment per Gd atom is nearly equal to 7μ B assuming that Cu is nonmagnetic and the enhancement of M S through outer-shell electrons is found to be suppressed. The values of exchange interactions between Gd and Gd atoms are found to be nearly equal to that for a-FeGd system.

Stabilized Hollow Ions Extracted in Vacuum

K x rays emitted from 2.1 keV/uN{sup 6+} ions passed through a thin Ni microcapillary foil were measured in coincidence with the exit charge states. Ions with a K hole but with several electrons in outershells, i.e., hollow ions formed above a surface (in the first generation), were successfully extracted in vacuum. It was found that a considerable fraction of extracted hollow ions had extremely long lifetimes of the order of ns. {copyright} {ital 1997} {ital The American Physical Society}