High field ESR measurements of spin gap system MCu2(PO4)2

Submillimeter and millimeter wave ESR measurements of spin gap systems SrCu₂(PO₄)₂ and PbCu₂(PO₄)₂, which have four kinds of dimers, have been performed to investigate the magnetic properties of spin gap systems using the pulsed magnetic field up to 35T. The observed ESR spectra of powder sample SrCu₂(PO₄)₂ show sharp and single peak in the temperature range from 4.2 to 80 K. The anisotropy of the g-values turned out to be very small compared to the usual anisotropic powder spectra of copper compounds. The dynamical properties will be discussed from the temperature dependence measurements.     

电子陷获型红外上转换材料的光谱测试

本文通过对电子陷获型红外上转换材料的激发光谱和发光光谱特性曲线的测试,论证该材料与一般红外器件相比,具有响应光谱范围广(0.8～1.6μm)等优点,为该材料的推广应用提供了可靠的依据。     

Solid-state NMR and EPR study of fluorinated carbon nanofibers

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF₄ during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)_n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C₂F)_n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O₂), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.     

Multi-channel Heterodyne Radiometer on HT-7 Tokamak

The incoherent radiation emanating out of the tokamak plasmas gives vital information about the electron temperature. Electron cyclotron emission (ECE) is a powerful diagnostic tool for the measurement of electron temperature due to many advantages such as the high spatial and temporal resolutions. This paper presents the sixteen channel superheterodyne radiometer as an electron cyclotron emission diagnostic to measure the electron temperature on HT-7 tokamak.     

VO(Ⅱ)-邻菲啰啉络合物的ESR波谱研究

该文考察了VOSO₄与1,10-邻菲啰啉(Phen)和3,4,7,8-四甲基-1,10-邻菲啰啉(TMP)在不同酸度(pH=1-14)的乙二醇/水(1:1)溶液中,在-100℃下的ESR波谱.发现在pH<1.0和pH>11范围内,二种配体均不能与VO(Ⅱ)生成络合物,当pH<1.0时,A=118×10^-4T归属于[VO(H₂O)₅]²⁺;当pH>11时,A=90×10^-4T归属于[VO(OCH₂CH₂O)₂]^2-.在1.4 < pH < 6之间,VO(Ⅱ)与phen生成三种不同络合物,在1.0 < pH < 7之间,VO(Ⅱ)则可与TMP生成四种络合物.本文推测了它们的可能结构.利用测得的波谱参数,计算了键参数和电子能级.利用电子光谱数据计算了晶体场参数.     

Adsorption of CO on a pseudomorphic palladium monolayer on Mo(110)

Adsorption of CO on a Pd monolayer (ML) supported on Mo(110) has been studied using low energy electron diffraction (LEED), temperature programmed desorption (TPD), and high resolution electron energy loss spectroscopy (HREELS). Three ordered CO substructures denoted as are observed with LEED. The binding energy of C0 on the 1.0 ML Pd/Mo(110) surface is reduced by 12 kcal/mol relative to the Pd(111) surface, consistent with previous results for supported palladium monolayers on other substrates. Two vibrational states of C0 are observed near 1950 and 2050 cm⁻¹, with the feature at the lower wavenumber having the smaller binding energy.     

Application of the Π theorem of dimensional analysis to electron scattering in multi-component systems

Summary Monte Carlo simulation of electron scattering in solids is considered and an extremely simplified picture of the process is demonstrated by a semi-empirical application of the Π theorem of dimensional analysis. The case of electron beam lithography is presented as an example. A set of parameters fully characterising the process is derived, and their dependence is investigated on electron energy, substrate thickness and the material physical constants, for a great number of single- and multi-component substrates. A single generalised argument is shown to be able to effectively describe the properties of forward and backward scattering of any substrate, in the elastic regime. The physical laws governing the process are approximated through analytical functions of this argument. These functions are theoretically deduced from very simple models and empirically demonstrated by fitting the numerical data. The efficacy of the proposed method, applicable to all elemental and composite substrate materials, is shown in the 5 to 150 keV energy range, with substrate thickness varying from 0.002 to 8 μm. The leading role of diamond as substrate material, emerging from such an analysis, is finally emphasised.     

Determination of transition curves of high-Tc superconductors by phase contrast microscopy

A new method which allows the detection of the superconducting phase transition of high-T_c superconductors (HTSC) on a microscopic scale is reported. Micro-size holes in thin foils of superconducting material are examined in a transmission electron microscope at varying temperatures. The superconducting transition induces small changes in the image intensity within the holes, which can be detected by using electronic image analysis. Superconducting transition curves are then obtained for various types of high-T_c superconductors and for given values of the applied magnetic field.     

Electronic and geometric structure of doped rare-gas clusters: surface, site and size effects studied with luminescence spectroscopy

The electronic and geometric structure of rare gas clusters doped with rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation spectroscopy in the VUV spectral range. Several absorption bands are observed in the region of the first electronic excitations of the impurity atoms, which are related to the lowest spin-orbit split atomic ³P₁ and ¹P₁ states. Due to influence of surrounding atoms of the cluster, the atomic lines are shifted to the blue and broadened (“electronical cage effect”). From the known interaction potentials and the measured spectral shifts the coordination of the impurity atom in Ar_N, Kr_N, Ne_N and He_N could be studied in great detail. In the interior of Kr_N and Ar_N the Xe atoms are located in substitutional sites with 12 nearest neighbours and internuclear distances comparable to that of the host matrix. In Ne_N and He_N the cluster atoms (18 and 22, respectively) arrange themselves around the Xe impurity with a bondlength comparable to that of the heteronuclear dimer. The results confirm that He clusters are liquid while Ne clusters are solid for N≥ 300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is strong, small Rg_m-clusters (Rg = Xe, Kr, Ar, m≤10 ²) are formed in the interior sites of the host cluster made of Ne or He. Specific electronically excited states, assigned to interface excitons are observed. Their absorption bands appear and shift towards lower energy when the cluster size m increases, according to the Frenkel exciton model. The characteristic bulk excitons appear in the spectra, only when the cluster radius exceeds the penetration depth of the interface exciton, which can be considerably larger than that in free Rg_m clusters. This effect is sensitive to electron affinities of the guest and the host cluster.     

The use of highly organized molecular films as electron scattering targets: spectroscopic and desorption measurements of selective bond rupture in organic films

In-situ FT-IR spectroscopic and desorption detection schemes have been used to observe, characterize and quantify electron-induced modifications of self-assembled monolayers (SAMs) of organic molecules chemisorbed to highly ordered metal surfaces. In the case of n-alkanethiol SAMs/Au(111) surfaces, the cross-sections for C---H bond rupture at the terminal methyl groups have onsets with incident energies near E_i7 eV and well-resolved maxima at E_i10 eV, indicating that dissociative electron attachment is the primary step of the excitation-dissociation process. The systematic differences between the depletion of the ---CH₃ and ---CH₂-functional groups on the surface, detected using infrared spectroscopy, show that molecular desorption of entire n-alkane chains is not a significant process, despite the S---Au(111) bond being the weakest of the system. The dissociation cross-sections increase with increasing chain length, indicating that the dissociation dynamics are strongly affected by the distance to the metal substrate, presumably via a dipole-damping process; we have used this behaviour to estimate that the excited state lifetimes for these systems are 2–10 fs. Chemisorption of “target” species to stable metal substrates appears to be a general approach for the study of electron-molecule interactions and condensed phase processes in molecular systems at ambient temperatures.