LS and QSZ contributed to the main ideas of AlN/GaN heterostructures design and drafted the manuscript. GPL and HJL carried out the measurement of X-rayphotoemission spectroscopy. XWZ, WM, and YH carried out the MOCVD growth. SYY, HYW, CMJ, SML, ZGW, and BS gave important advices to the paper. All authors read and approved the final manuscript.
When comparing the computational results with experimental photoemission data it is necessary to account for the effects of instrumental and phonon broadening. Gaussian convolution was applied to the calculated densities of states using a profile with a full width at half maximum (FWHM) of 0.8 eV. For states in the lower part of the valence band the contribution of lifetime broadening also becomes significant. This can be accounted for by additional convolution with a Lorentzian lineshape, whose FWHM scales with the square of the binding energy; in this case the best agreement was obtained when FWHM = 0.008 E 2 where E is expressed in electronvolts. The justification for the E 2 dependence of the inverse lifetime of the final state of the photoemission process arises as follows: whilst the Einstein coefficient for spontaneous emission scales as E 3 , this is offset by a decrease in the matrix elements connecting the states at the Fermi level and the hole state with increasing binding energy. Whilst exact E 2 scaling is only obtained in the case of Fermi liquid theory, as an approximation it seems to work well even in non-metallic systems. 40-43
The PEDOS contributions were weighted by the known x-ray photoionization cross section 41 of their respective atoms and were then summed, resulting in the total VB-DOS. The weighting was performed to accurately repre- sent the processes that contributed to the experimental XPS data. The raw VB-DOS was then convoluted with an instrument-specific spectrometer response function and the results were then fit to the leading edge of the XPS data. The spectrometer response function was determined for the Kratos instrument by measurement of the Au 4f doublet. The Au spectrum was fit to a Voigt function assuming Gaussian broadening and an inherent Lorentzian linewidth of 0.317 eV. The details of the convolution and fitting proce- dure have been described previously. 28
The synthesis of novel TM porphyrins has received great attention in the past few years [2, 4, 7-9], while spectroscopic characterization of their electronic structure remains a less well investigated area [10-15]. Experimental studies of TM porphyrins carried out recently have provided useful information about their electronic structure and physical-chemical properties [10-12, 15], but the lack of well reasoned explanations of the results leaves open questions about the nature of the chemical bonding in these compounds. The central part of these complexes (3d-atom and its nearest neighbours) is known to define their most important applications and reactivity. Thus it is evident that a detailed knowledge of the electronic structure and chemical bonding in these 3d TM macrocyclic rings is required for the realization of their full potential. Such information can be obtained with high-resolution X-ray absorption (XA) spectroscopy and X-rayphotoemission spectroscopy (XPS).
High-resolution x-rayphotoemission spectra were mea- sured in a Scienta ESCA 300 spectrometer. This incorporates a rotating anode Al K ␣ 共h = 1486.6 eV兲 x-ray source, a seven-crystal x-ray monochromator, and a 300 mm mean ra- dius spherical sector electron energy analyzer with parallel electron detection system. The x-ray source was ran with 200 mA emission current and 14 kV anode bias, while the ana- lyzer operated at 150 eV pass energy. Gaussian convolution of the analyzer resolution with a linewidth of 260 meV for the x-ray source gives an effective instrument resolution of 450 meV. Samples were cleaned in situ by annealing at 400 ° C. The C 1s to O 1s intensity ratio was reduced to below 1/100. Binding energies are referenced to the Fermi energy of a silver sample regularly used to calibrate the spec- trometer.
Goethe‟s quote “The history of science is science itself” could offer a simple chronological approach starting from the studies of crystal mor- phology marvelled by Pliny the Elder (AD 23 to 79) who described the faces of quartz crystals. These observations were followed by more com- plex discoveries. On a historical route, for instance, one would enjoy reading the interesting papers of Pierre Curie on crystallography and symmetry, as well as about physical properties of crystals such as piezoelectricity and magnetism. However, such an approach would be extensive and probably miss to point out the highlights that put forward the X- ray crystallography as a central method to many disciplines and different areas of science. To learn the history of crystallography, there is no need to strictly separate crystallography from mineralogy, chemistry, biology, physics; it should be under- stood in synergy with these sciences that change drastically the basic concepts through close inter- actions among them and opening new approaches. “After all, are there the true boundaries between sciences? May be the boundaries of a science, as they are established, represent only artificial con- structions adapted to current understanding” .
less. 18 However, the separation of the process of bremsstrahlung generation into two steps, electron penetration into a target and bremsstrahlung emission, can provide insight into the nature of beam transport in an x-ray target and the affect that this has on an emerging spectra. Examinations of the sufficiency of theoretical results for the differential bremsstrahlung cross-section are also readily made. This article, Part I, is 60
The 16ID-B beamline in APS is a dedicated high-pressure beamline for X-ray diffraction measurements. The source for 16ID-B is the dual undulator Type A, which provides X- ray in the energy region from 6 keV – 40 keV (normal) up to 60 keV – 70 keV. A Si double crystal was employed as monochromator. This beamline can provide a beam size of 4×5 μm 2 with the help of 200 mm KBr mirrors and produce a flux of 5 × 10 10 photons/s at the sample position. Such a small beam size and high energy at the sample position make it possible to conduct the XRD measurement on different sample spots in relatively short accumulation time. Besides, a MAR345 imaging plate detector is used to collect the diffraction patterns of the sample. In addition to the XRD technique, 16ID-B also provides many excellent technical supports such as the membrane and mechanical pressure control, online ruby and Raman system, and offline alignments and Ruby system.
In Table 4.3 we present the catalog of 1034 hard-band SEXSI sources – the table is published in its entirety in the electronic version of the Astrophysical Journal. Columns 1 – 7 present X-ray source information for easy reference, while the optical photometric data are presented in columns 8 – 15. Complete X-ray source information is presented in Chapter 3, Table 4. The X-ray source positions in Table 4.3 are corrected for mean optical to X-ray offsets. Note that since the source names (column 1), identical to the source names in Chapter 3, are derived from the hard-band X-ray images, the refined positions of columns 2 – 3 will not exactly match those of column 1 (though mean offsets are typically less than 1 00 ). Column 4 lists the off-axis angle (OAA, i.e., the angular distance, in arcmin, of the source position from the telescope aim point). The 2 – 10 keV flux (in units of 10 −15 erg cm −2 s −1 ) and detection SNR are shown in columns 5 – 6, while column 7 gives the hardness ratio, HR = (H − S)/(H + S), where H and S are the counts cm −2 in the 2 – 10 keV and 0.5 – 2 keV bands, respectively. Here, as distinct from Paper I, we record the hardness ratio derived from the net soft X-ray counts recorded at the hard-band source position when there was not a significant soft-band source detected (in Paper I these cases are reported as HR = 1.0). In addition, for a subset of these cases, when the soft-band counts recorded at the hard-band source position were less than twice the soft-band background counts, the HR is considered a lower limit, flagged as such in the catalog, and set to HR = (H − S limit )/(H + S limit ), where S limit = 2 × soft-band background counts.
The perspective projection calibration process involves ac- quisition of multiple X-ray views of an acrylic calibration ob- ject that can accept 14 point markers. The markers are based on those used in the Acustar Neurosurgical guidance system , and our version has previously been described by Edwards et al. . These markers have alternative caps for use in MR and X-ray imaging (containing a mixture of gadolinium and iodine contrast material), X-ray imaging alone (containing 3-mm-di- ameter steel ball bearings), and physical caps for use with a pointing device that is tracked with the Optotrak. The calibration object needed to be imaged with both MR imaging and X-ray imaging without being moved with respect to the sliding table top. Therefore, it was placed in the head coil that was firmly fixed to the sliding table top. A bottle containing copper sulphate solution was also placed within the head coil to give sufficient loading. Initially the table top was docked to the X-ray table and the physical markers were placed on the calibration object. Only 10 out of the 14 markers were used because four were inacces- sible in the head coil. The position of the markers was located in X-ray table space using the pointing device and the Optotrak. The positions were marked three times and averaged to reduce location error. These markers were then changed for the ball bearing markers. Twelve tracked X-ray images were acquired with the X-ray gantry being moved to cover the typical locations used for interventions [gantry angles 0 , 30 , 60 , and 90 from AP to lateral and translating parallel to the X-ray table by 0.00, 0.25, and 0.50 meters (m)]. Although three electronic magni- fication settings are allowed by the X-ray system, our current system only supports the largest field of view size (23 cm), so the calibration images and the subsequent patient images must be acquired using the same magnification setting. Fig. 3 shows one of the calibration images. Not all markers were visible in all views, therefore, the user had to interactively label each marker. In total the position of 48 markers was found in 2-D by manual marking followed by a local center of gravity approach. The cor- responding 3-D positions were calculated by transforming the previously determined marker positions in X-ray table space to C-arm space using the matrix for each X-ray image. Now
Figure 4 illustrates how CXL allows high-resolution im- aging of the local sub-surface microstructure in paintings in a non-invasive and non-destructive way. Results of feasibility tests on a painting mockup (consisting of an oak panel, a chalk ground superimposed with vermilion and lead white paint layers, see Figure 4AB) show that achieving lateral and depth resolutions of up to a few micrometres is possible. Based on absorption and phase contrast, the method can provide high-resolution 3D maps of the paint stratigraphy (Figure 4C), including the wooden substrate, and visualize small features, such as pigment particles, voids, cracks, cells in the wood support etc. (Figure 4D). In resulting virtual cross sec- tions (Figure 4EF) the local density and chemical com- position of the different paint layers are visible due to increased attenuation of X-rays by elements of higher atomic number. A typical CXL scan consists of 1000 to 3600 radiographs, each with a size of 2048 by 2048 pixels and a pixel size of 0.28 to 1.4 micrometers. While each
Cu with Al in weight ratio x= 10%, 20%, 30%, 40% and 50%. The high purity (99.9-99.99 %) fine powder of Al, Cu and Fe were obtained from Sigma Aldrich. The mixing has been done using ball milling (Planetary Ball Mill PM100) contained stainless steel container (volume about 75 cm3) and stainless steel ball having a diameter of 10 mm. We put the sample powder (Fe 100-x Al x and Cu 100-x Al x) separately in ball milling container
It is noticeable that systems with orbital periods shorter than 25 mins are concentrated in the lower left hand corner of the colour-colour plane, ie compared to other CVs they show either a low soft X-ray flux or a high UV flux. In contrast, systems with orbital periods longer than 25 mins, show a steadily increasing soft X-ray/UV ratio. We also show the position of the candidate system RX J0806+15, which is located in the far top right hand corner of the colour-colour plane. This is not unexpected since there is evidence that this system could be powered by a non-accretion mechanism and so therefore would be expected to show different X-ray/UV colours (eg Hakala, Ramsay & Byckling 2004). It is predicted that for sys- tems with shorter orbital periods the emission from an accretion disk will dominate the UV emission while for longer orbital periods the white dwarf will dominate (eg Bildsten et al 2006). This would naturally result in the ob- served trend in the AM CVn colours seen in Figure 3. To test this we determine the X-ray and UV luminosities in the next section: the UV luminosity should increase with decreasing orbital period.
Within the framework of hierarchical structure formation the properties of galaxy clus- ters are also expected to follow certain scaling relations and simulations have shown that scaled dark matter profiles look similar (e.g., Navarro et al. 1995). Despite the well estab- lished overall understanding of galaxy clusters, in detail deviations from this picture have been found from observationally accessible quantities, e.g., by the relation between X-ray luminosity and intracluster gas temperature (e.g., David et al. 1993), and the gas properties in the center of groups of galaxies (e.g., Ponman et al. 1999). A variety of models has been suggested to explain these deviations (Sect. 7.4). Tests of detailed predictions of these models unfortunately are still compromised by observational difficulties. For instance the observed gas mass fraction has been found in the recent literature to either stay constant, decrease, or increase as a function of cluster temperature (Sect. 7.4). The homogeneously selected and analyzed cluster sample presented here, comprising more than 100 galaxy groups and clusters, is therefore used to determine physical quantities like the X-ray luminosity, intracluster gas density distribution, temperature, and mass, as well as the gravitational mass over a wide temperature range from 0.7 to 13 keV. The relations between these quantities are analyzed and compared to predicted relations.
The single crystal X-ray diffraction analysis on Glycine doped Atenolol single crystals was recorded using X-ray diffractometer. The unit cell dimensions for doped Atenolol are compared with that of pure Atenolol and are given in the Table.2. Single crystal XRD reveals that in GATN, the host molecule increases the void altering the guest molecules included and trapped in the crystal structure and hence the crystal structure is monoclinic with decrease of a, b, c values and volume.
substrate at optimized preparative parameters. The sharp peaks reveal the polycrystalline nature with hexagonal crystal structure. The observed ‘d’ values are compared with JCPDS data  to determine the crystal structure. Observed ‘d’ values have been found to be in good agreement with standard ‘d’ values as shown in Table 1. The crystallite size was calculated from the full-width at half- maximum (FWHM) measurement for the prominent X-ray diffraction peaks using Scherrer formula,
technologies of vision might emerge that could exploit the rays for specifically intrusive ends. In 1896, it was reported that Assemblyman Reed of Somerset County New Jersey was introducing a bill to the New York legislature ‘prohibiting the use of x-rays in opera glasses in theatres.’ This seemed to respond to a prurient idea that x rays could be calibrated to see through clothes but stop at the skin rather than penetrating the body to the skeleton. It is an anxious concern that resurfaced in the twenty-first century with the development of ‘scatter back’ xray machines at airport security intended to reveal objects concealed under clothes.
where I hkl exp(cal) is the experimental (calculated) intensity of the corresponding Bragg peak. In Fig. 2(e), we show the experimental intensity ratios as a function of Fe concentration, together with the expected values in the case of excess Ga atoms in the 2b position. The good agreement between the simulation and the experimental data for S inter−plane confirms that Ga is confined to the 2a-2b positions. The ordering of Ga at the center of the unit cell is less marked but still present, and it increases with x. Due to the very similar atomic form factors of Mn and Fe, laboratory x-ray diffractometry is unable to discern the ordering among these two species.