Theory for the XPS of Actinides

Two aspects of the electronic structure of actinide oxides that significantly affect the X-ray photoelectron spectroscopy (XPS) spectra are described; these aspects are also important for the materials properties of the oxides. The two aspects considered are: (1) The spin–orbit coupling of the open 5f shell electrons in actinide cations and how this coupling affects the electronic structure. And, (2) the covalent character of the metal oxygen interaction in actinide compounds. Because of this covalent character, there are strong departures from the nominal oxidation states that are significantly larger in core–hole states than in the ground state. The consequences of this covalent character for the XPS are examined. A proper understanding of the way in which they influence the XPS makes it possible to use the XPS to correctly characterize the electronic structure of the oxides.     

Spin Polarization in Single Spin Experiments on Defects in Diamond

Generation of pure spin states is an important step towards coherent control of single spin systems. Especially for nitrogen-vacancy defects in diamond, where readout of single spins using optical detection is available, fast initialization of spin is significant in the context of quantum computing applications. In this system the spin polarization is caused by an intersystem crossing process via the meta-stable singlet state ¹ . The slowest relaxation rate is the intersystem to the triplet ground-state ³ on a timescale of 400 ns. The intersystem crossing process mainly populates the ms = 0 spin sublevels of the paramagnetic ground state. Although no direct nuclear spin polarization is seen for low magnetic fields, frequency selective microwave pulses can be used to transfer electron spin polarization to ¹³C nuclear spin states.     

Optical spin polarization in the di-〈001〉-split interstitial (R1) centre in diamond

Irradiating diamond with electrons or neutrons produces the electron paramagnetic resonance (EPR) R1 centre which has been shown to be a di-〈001〉-split interstitial. We report that on cooling below a certain threshold temperature and illuminating with unpolarized light of energy greater than 1.7(1) eV, spin polarization within the S=1 multiplet of the ground state of the R1 centre is observed. The threshold temperature to observe this effect depends on the concentration of the defect in the diamond. For a type IIa stone irradiated to a dose of 7×10¹⁷ 2 MeV e⁻cm⁻² with an R1 concentration of 0.056(15) ppm the temperature is 67(2) K. The results of this study are consistent with a spin-selective, orientation-dependent optical transition, which changes the populations of the spin manifold and results in emissive EPR transitions. The spin polarization arises by selective excitation/repopulation of the ³B_u ground state of R1 mediated by spin–orbit coupling with a higher ¹B_u state. Optical activity in the EPR system has yielded information about the electronic energy levels, and provides a bridge between optical and magnetic resonance spectroscopy. This system might have use as a light-pumped microwave or millimetre-wave maser material.     

取代苄叉亚胺类化合物溶液电子光谱的研究

研究了二甲氨基苄叉亚胺类化合物溶液的电子光谱。结果表明一端为电子给体另一端为电子受体的共轭型取代苄叉对硝基苯胺3,在基态下发生了分子内电荷转移,其跃迁吸收波长比化合物1,2(315 nm)红移90 nm。以乙撑基联接的非共轭型苄叉亚胺奥化合物4,5,6未观察到基态时的电荷转移现象,但在激发条件下可明显的发生分子内的电荷转移而使荧光强度大大减弱。MMA等对1的荧光有明显的猝灭作用,表明其间发生了电荷转移。丙烯酸则因会引起西佛碱的水解,而使荧光减弱。     

新型卟啉及其金属配合物的合成与性能

通过琥珀酰基、马来酰基和邻苯二甲酰基对四-(4-氨基苯基)卟啉进行修饰改性,合成不同结构的新型卟啉及其铜配合物。对合成的新型结构卟啉配体进行核磁共振、质谱和红外表征,对其铜配合物进行质谱表征,结果表明,所合成的化合物是目标产物。通过紫外-可见、荧光发射、热重、循环伏安法进行性质测试,计算出HOMO和LUMO能级。结果表明,新型化合物具有良好的可见光区吸收和纯红光发射光谱,热稳定性高,可以作为红光材料的备选材料。     

Deformation Defects Supporting Quantum Readout of <Superscript>29</Superscript> Si Nuclear Spins in Si: P Deformed Crystals

High temperature (950 °C) plastic deformation of the ²⁹Si enriched silicon crystals generates ?10 ¹⁵ cm^?3 paramagnetic defects of the new type. The multiline spectrum of electron paramagnetic resonance (EPR) of the defects corresponds to S = 1 electronic spin of the clusters containing oxygen. Strong anisotropy and large linewidth of the EPR spectra (?1 kOe) were observed. The Pake doublet split by spin-spin nuclear dipole interaction was analyzed in the nuclear magnetic resonance (NMR) spectra of the crystals. Contribution of the electron-nuclear interaction to the EPR linewidth is negligibly small, while the NMR linewidth is controlled by the dipole-dipole nuclear relaxation.     

Optical properties of Cu ions‐doped ZnSe quantum dots in silicate glasses

In order to alleviate the effect of the surface defects on the emission properties of quantum dots, copper ions‐doped ZnSe quantum dots (QDs) in the glasses are prepared using melt‐quenching and subsequent thermal annealing methods. For glasses without copper doping, tunable band‐edge emission from ZnSe QDs is achieved. For glasses with copper doping, efficient energy transfer from ZnSe QDs to copper ions is observed, and efficient broad band emission from copper ions is realized at the expense of the band‐edge emission of ZnSe QDs. Absorption spectra, size‐dependent broad‐band emission spectra and electron spin resonance spectra show the cupric ions are doped into the ZnSe QDs. Results reported here shows that doping of transition‐metal ions into semiconductor QDs in glasses is promising for development of high efficient luminescent glasses.     

Non-platinum oxygen reduction electrocatalysts based on pyrolyzed transition metal macrocycles

In this work pyrolyzed porphyrins were investigated for oxygen reduction electrocatalysis. Pyrolysis of non-supported cobalt and iron tetraphenylporphyrins in the temperature range of 500-800 °C generates high surface area catalysts with high degree of exposure of active sites to the reacting species. This is achieved through templating porphyrins on fumed amorphous silica that is removed after pyrolysis by etching with concentrated KOH.Detailed material characterization of the pyrolyzed materials is presented here. X-ray photoelectron spectroscopy (XPS) analysis of cobalt and iron porphyrins was used to elucidate the transformations of nitrogen, carbon, cobalt and iron species resulting from the heat treatment. Partial decomposition of the precursor material and formation of polymer-like network decorated by metal oxide particles are identified. Differences in the chemical composition of products of pyrolysis of FeTPP, CoTPP and Co/FeTPP are discussed. Transmission electron microscopy (TEM) imaging revealed the structure of the pyrolyzed porphyrins and was used to gain insight into the size of the metal crystals formed in the bulk. X-ray diffraction spectra (XRD) provided information about the type of crystals formed in the different formulations of the precursor porphyrins. Further, steady state polarization curves were obtained utilizing gas diffusion type electrodes in 0.5 M sulfuric acid and membrane electrode assembly (MEA) configurations under working PEM fuel cell conditions. This work revealed the necessity of the metal phases for the oxygen reduction process.     

The Structural Chemistry of Metallocorroles: Combined X-ray Crystallography and Quantum Chemistry Studies Afford Unique Insights

Although they share some superficial structural similarities with porphyrins, corroles, trianionic ligands with contracted cores, give rise to fundamentally different transition metal complexes in comparison with the dianionic porphyrins. Many metallocorroles are formally high-valent, although a good fraction of them are also noninnocent, with significant corrole radical character. These electronic-structural characteristics result in a variety of fascinating spectroscopic behavior, including highly characteristic, paramagnetically shifted NMR spectra and textbook cases of charge-transfer spectra. Although our early research on corroles focused on spectroscopy, we soon learned that the geometric structures of metallocorroles provide a fascinating window into their electronic-structural characteristics. Thus, we used X-ray structure determinations and quantum chemical studies, chiefly using DFT, to obtain a comprehensive understanding of metallocorrole geometric and electronic structures. This Account describes our studies of the structural chemistry of metallocorroles. At first blush, the planar or mildly domed structure of metallocorroles might appear somewhat uninteresting particularly when compared to metalloporphyrins. Metalloporphyrins, especially sterically hindered ones, are routinely ruffled or saddled, but the missing meso carbon apparently makes the corrole skeleton much more resistant to nonplanar distortions. Ruffling, where the pyrrole rings are alternately twisted about the M-N bonds, is energetically impossible for metallocorroles. Saddling is also uncommon; thus, a number of sterically hindered, fully substituted metallocorroles exhibit almost perfectly planar macrocycle cores. Against this backdrop, copper corroles stand out as an important exception. As a result of an energetically favorable Cu(d(x2-y2))-corrole(π) orbital interaction, copper corroles, even sterically unhindered ones, are inherently saddled. Sterically hindered substituents accentuate this effect, sometimes dramatically. Thus, a crystal structure of a copper β-octakis(trifluoromethyl)-meso-triarylcorrole complex exhibits nearly orthogonal, adjacent pyrrole rings. Intriguingly, the formally isoelectronic silver and gold corroles are much less saddled than their copper congeners because the high orbital energy of the valence d(x2-y2) orbital discourages overlap with the corrole π orbital. A crystal structure of a gold β-octakis(trifluoromethyl)-meso-triarylcorrole complex exhibits a perfectly planar corrole core, which translates to a difference of 85° in the saddling dihedral angles between analogous copper and gold complexes. Gratifyingly, electrochemical, spectroscopic, and quantum chemical studies provide a coherent, theoretical underpinning for these fascinating structural phenomena. With the development of facile one-pot syntheses of corrole macrocycles in the last 10-15 years, corroles are now almost as readily accessible as porphyrins. Like porphyrins, corroles are promising building blocks for supramolecular constructs such as liquid crystals and metal-organic frameworks. However, because of their symmetry properties, corrole-based supramolecular constructs will probably differ substantially from porphyrin-based ones. We are particularly interested in exploiting the inherently saddled, chiral architectures of copper corroles to create novel oriented materials such as chiral liquid crystals. We trust that the fundamental structural principles uncovered in this Account will prove useful as we explore these fascinating avenues.     

胡椒醛缩合卟啉化合物的合成及其光谱性能

以胡椒醛及羟基芳香醛为原料与吡咯在丙酸中回流,合成了6种卟啉化合物,其结构用1HNMR,IR,UV-V is和ESI-MS确定。与四苯基卟啉(TPP)相比,胡椒醛的引入增大了卟啉环的共轭性,使几种化合物的光学吸收波长均发生不同程度的红移,其中,Soret带最大红移11 nm;同时,胡椒醛的引入缩小了基态与激发态之间的能极差,化合物荧光发射波长发生1~5 nm的红移。     

卤化铜光致变色玻璃变色机理研究

本文报道了卤化铜光致变色玻璃中光色相物相分析方法和玻璃中铜胶体理论吸收光谱的计算方法。测定了玻璃的顺磁共振谱(ESR)和可见吸收光谱。证明了卤化铜光致变色玻璃的变色机理是CuX自身氧化还原的胶体暗化过程。     

Multiangle Polarimetry of Thermal Emission and Light Scattering by Individual Particles in Airflow

The generalized Kirchhoff's law predicts that the polarization state of thermal emission from an individual small particle depends on the particle shape. We show for the first time experimental evidence confirming this prediction for particles smaller than the wavelength by using a newly developed laser-induced incandescence instrument and a theoretical model that can predict the signals of thermal emission and light scattering for an ellipsoid under the dipole approximation (Rayleigh ellipsoid). We use single-sphere (singlet) and two-sphere clusters (doublet) of polystyrene latex spheres as primary test particles. These are currently available, well-characterized spherical and nonspherical particles, respectively. The polarization states of thermal emission and scattered light of graphite particles smaller than the wavelength show a good agreement with model calculations for plate-like Rayleigh-spheroids, consistent with their plate-like shapes observed by a transmission electron microscope. We propose that the measurement of the polarization state of thermal emission may be applicable to real-time analysis of the shape of light-absorbing particles in air.     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.     

New sulfonated aramide nanoparticles and their copper complexes with anomalous dielectric behavior

We report the preparation of thermally stable spherical sulfonated aramides nanoparticles and their copper(II) complexes. Metal chelation with copper ions furnished polymeric complexes in a 1 : 2 ratio with square planar geometries as judged by their IR, UV, electron spin resonance, and elemental analysis data. The direct‐current electrical conductivities demonstrated the semiconducting nature of the polymeric particles and their copper complexes. Dielectric loss analysis studies showed spectral peaks appearing at characteristic frequencies, which suggested the presence of relaxing dipoles in all of the polymers. All loss peaks were shown on a linear frequency scale and appeared in the range of 1 decade, and no overlap was observed in any of the samples, whereas in the normal polymer's dielectric loss behavior, each peak covered more than 1 decade. Moreover, the peak positions did not change with increasing temperature; this indicated a nonactivated process. The reported dielectric results revealed anomalous behavior, which has not been reported before for such polymeric analogues, as the polarization in these cases was limited by nonthermal forces, and a steady‐state constant polarization was produced by an applied field. A simple method for the formation of a microporous semiconducting thin film of a polymer derived from isophthalic acid and diaminodiphenylsulfone is described. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Spin excitations of bitumens

Bitumen free radicals are located within the planar polynuclear aromatic ring systems of bituminous crystallites in such a manner as to optimize their stabilization by the resonance of delocalized π-electrons. The states of spin multiplicity exhibited by these substances are revealed by the observed transitions under thermal excitations. Experimental ESR intensity-temperature dependence data from several asphaltic bitumens, a model compound (phthalocyanine), and a few charge-transfer complexes were collected. Curves containing both exponential (singlet-triplet) and Curie-Weiss (doublet) components were then calculated from the curves and found to be consistent with published results. This spin correlation indicates that both singlet-triplet transitions and doublet states exist within the bituminous aromatic sheets. This and other forms of thermal excitation (e.g., Russell effect), may be attributed to the propagation of Wannier excitons. The predominance of doublet concentrations in high vanadium samples (e.g., Mara asphaltene) indicates that spins are localized by nuclei-spin interactions.     

Spin polarization of single-layer graphene epitaxially grown on Ni(1 1 1) thin film

The spin-resolved electronic structure of graphene on Ni(1 1 1) was investigated using spin-polarized metastable deexcitation spectroscopy (SPMDS). Graphene was grown epitaxially on a Ni(1 1 1) single-crystalline surface using the ultra high vacuum chemical vapor deposition technique with benzene vapor as a precursor. At 50 L (5 × 10⁻⁵ Torr s), a single epitaxial layer of graphene was formed, but no further growth was observed at higher exposure. The spin-summed spectrum of graphene/Ni(1 1 1) had a new peak at the Fermi level and three weak features corresponding to the molecular orbitals of graphene. Spin asymmetry analysis of the SPMDS spectra revealed that the spin polarization of the electronic states shown by the new peak was parallel to the majority spin of the Ni substrate. The appearance and spin polarization of the new electronic states are discussed in terms of the hybridization of graphene π orbitals and Ni d orbitals.     

Bipolar magnetic semiconductors: a new class of spintronics materials

Electrical control of spin polarization is very desirable in spintronics, since electric fields can be easily applied locally, in contrast to magnetic fields. Here, we propose a new concept of bipolar magnetic semiconductors (BMS) in which completely spin-polarized currents with reversible spin polarization can be created and controlled simply by applying a gate voltage. This is a result of the unique electronic structure of BMS, where the valence and conduction bands possess opposite spin polarization when approaching the Fermi level. BMS is thus expected to have potential for various applications. Our band structure and spin-polarized electronic transport calculations on semi-hydrogenated single-walled carbon nanotubes confirm the existence of BMS materials and demonstrate the electrical control of spin-polarization in them.     

Magnetic and electric properties,ESR, XPS and NEXAFS spectroscopy of CaCu3Ti4O12 ceramics

ESR, XPS and NEXAFS spectra, as well as magnetic and electric properties of CaCu₃Ti₄O₁₂ synthesized by the solid-phase method within 6,12,24,48 and 60 h were studied. The analysis of magnetic susceptibility of CaCu₃Ti₄O₁₂ and magnesium-containing solid solutions of CaCu_3-3xMg_3xTi₄O₁₂ revealed antiferromagnetic exchange interactions between Cu paramagnetic atoms, while the effective magnetic moment of copper atoms corresponds to the electronic state of Cu(II). In CaCu₃Ti_4-4хMg_4хO_12-δ samples within the whole concentration range the impurity phase MgTiO₃ was observed. The magnetic properties of calcium copper titanate were found to be inconsistent depending on the synthesis duration. The extreme point of magnetic susceptibility was found among samples synthesized within 48 h. Modelling and interpretation of the XPS spectra of CaCu₃Ti₄O₁₂ were performed. Based on the NEXAFS and XPS spectroscopy data, copper and calcium atoms in ceramics display oxidation state +2, while titanium atoms – Ti(IV). ESR spectra of CaCu₃Ti₄O₁₂ samples show an exchange-narrowing signal from copper (II) atoms at g = 2.15. In the ESR spectra of CaCu_3-3xMg_3xTi₄O₁₂ the only intense exchange-narrowed line of Lorentzian form of Cu²⁺ ions is observed. The impedance spectroscopy study of electric properties of CaCu₃Ti₄O₁₂ found the media to feature temperature-dependent reach-through conductivity with activation energy of 0.79–0.71 eV. At 255–300°С, the dominant polarization process is in line with the Gerischer model. It indicates the formation of anionic-cationic associates accompanied by decreased low-frequency capacitance of the samples. With temperatures of over 300°С the samples start displaying ion-migrating polarization which contributes to higher capacitance and dielectric loss at low frequencies. As the temperature grows further to 400°С, the ion migration process gets to dominate within the whole frequency range under study. Based on the study, a conclusion was made on movable cations of copper participating in the polarization process at room temperature.