We present L2 and L3 x-ray absorption spectroscopy measurements on all of the 5d transitionmetal (T) elements and selected TAIS intermetallic compounds. For the 5d elements we discuss the general trends in the strength of the near-edge "white-line" (WL) feature, the manifestations of the spin-orbit effects, and the dearth of WL strength for Pt and Au. The changes in the intensity of the L-edge WL s in the intermetallic compounds TA12 (T =Au and Pt) are discussed in terms of strong T-Al chemical bonding. Interestingly, our results for this bonding in AuA12 are in good agreement with the arguments presented by Pauling lThe Nature of the Chemical Bond (Cornell Univ. Press, Ithaca, NY, 1960), pp. 431-435].The transition metals are the largest and most diverse group of the periodic table. As such, transition-metal compounds are at the forefront of much of the new materials work in both applied and fundamental solid-state physics. In this paper, we illustrate how x-ray-absorption near-edge spectroscopy (XANES) can provide a sensitive, atom-specific probe of electronic structure around the atom (transition metals in our case) whose core level is being excited. ' Specifically, we present synchrotronradiation studies of the 2p Sd (L2 and L3 edge) transitions of the elements and selected compounds of the Sd transition metals. As we shall see, these studies provide direct and in some cases dramatic evidence of Sd occupancy and chemical-bonding effects in the solid state.The XANES measurements were made both in transmission mode (on 2-6-pm foils and powders) and in the total-electron-yield mode (where only a 2000 A depth is probed). From these measurements sample-thickness effects contribute less than 5% excursions from the whiteline (WL) areas discussed here. In the simplest interpretation, XANES spectra are discussed in a single-particle picture where the energy dependence of the photon absorption coefficient provides a profile of the unoccupied-electron-state density (projected with the dipole selection rule). 'In such an approximation, the strength of the WL at the L2 and L3 edges of the Sd transition metals would be proportional to the groundstate Sd-band hole population (one-hole count nd) convoluted with the average transition-matrix element. Our transition-metal results are discussed quantitatively in terms of such single-particle ideas; however, we qualitatively indicate where we believe many-particle effects become important. Specifically, the many-particle question of final-state changes in nd to screen the photoexcited core hole is of concern.Theoretical calculations by Horsley indicate that many-body-induced final-state shifts in nd are comparable in different compounds for a given atom. Thus for a given atom one would expect Sd-orbital-occupancy changes in different materials to be reflected in their respective Ledge absorption spectra. It is in an extension of this spirit of identifying changes in Sd occupancy in elements and compounds that we address our XANES results. In fact, although we will calibrate ou...
A high precision and high resolution time-to-digital converter (TDC) based on multichain measurements averaging method is implemented in a 40 nm fabrication process Virtex-6 FPGA. The results of the detailed theoretical analysis and the simulation with the MATLAB tool based on a complete TDC module show that the resolution limitation determined by the intrinsic cell delay of plain tapped-delay chain can be overcame, which results in an improvement on both resolution and precision without increasing the dead time. The test results agree with the simulation results quite well. In such a TDC, the input signal is connected to multiple tapped-delay chains simultaneously (the number of the chains is M), and each chain is just a plain TDC and generates a timestamp for a hit signal. Therefore, M timestamps should be obtained in total, which, after averaging, give the final timestamp. A TDC with 1.7 ps equivalent bin size, 1.5 ps averaged bin size and 4.2 ps RMS has been implemented with M being 16, which performs much better than the plain TDC constructed of a single tapped delay chain having 42.3 ps equivalent bin size, 24.0 ps averaged bin size resolution and 13.2 ps RMS precision. The comparisons of equivalent bin size and averaged bin size show that the nonlinearity is improved with a larger M. Due to the real time integral nonlinearity (INL) calibration and averaging calculation, the multichain TDC is almost insensitive to the process voltage and temperature (PVT) variations.Index Terms-Field programmable gate array (FPGA), multichain averaging, time domain measurements, time to digital converters (TDCs).
In intermetallic compounds of Ce involving late 3d, 4d, and 5d row transition metals (T), the Ce valence state increases with decreasing T-d-band electron count. Neifeld, et al. [Phys. Rev. B 32, 6928 (1985)] have recently shown (using extensive Ce-L3-edge measurements) that this trend is reversed for the Ce-3d row compounds earlier than Co. This somewhat striking behavior is nowhere more apparent than in the ThCr2Si2 crystal structure series CeT2Si2 with T=Cu, Ni, Co, Fe, Mn, and (MnxCr1−x). In this paper, we will discuss the following: (1) the extension of this crystal structure to its stability limit in the T=(Mn,Cr) substituted system; (2), how this extension permits restoration of the Ce-valence state to the Kondo local-moment regime; (3) low-temperature electrical resistivity measurements which support first the Kondo to mixed valent followed by mixed valent to Kondo regime passage with decreasing 3d electron count in this series; and (4) finally the apparent compatibility of the Ce-Kondo effect with strong 3d antiferromagnetism for some of these materials.
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