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Understanding the atomic bonding properties at the interface between thin films is crucial to a number of key modern technical devices, including semiconductor integrated circuits, magnetic recording media, batteries, and even solar cells. Semiconducting materials such as titanium nitride (TiNx) are widely used in the manufacturing of modern electronic devices, requiring a wealth of information about its electronic structure. We present data from soft x-ray emission, soft x-ray absorption, and Rutherford backscattering spectroscopy experiments involving a sample consisting of a 40 nm TiN layer on top of an aluminum film 600 nm thick. Soft x-ray emission spectroscopy and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy are tools that provide a nondestructive, atomic site-specific probe of the interface, where the electronic structure of the material can be mapped out element by element. Rutherford backscattering spectroscopy (RBS) measurements supply data on the elemental composition and dep...

The VUV ring at the National Synchrotron Light Source (NSLS, Brookhaven national Laboratory) is a source of nanosecond-duration, high-brightness, broadband IR pulses. The authors are developing several measurement techniques for characterizing Hg1-xCdxTe and other IR detector materials using this source. For example, the broadband IR pulses can be used to study transient photoconductive decay at various photon energies near the bandgap. A particularly novel technique they have developed is far-infrared photoinduced nanosecond spectroscopy (FIR-PINS). In this all-optical (contactless) measurement, a short laser pulse generates photocarriers which are subsequently sensed by a far-infrared pulse from the synchrotron. Spectroscopic analysis of the far-infrared yields the free carrier plasma frequency, providing information on the photocarrier density. By varying the delay time of the far-infrared pulse (relative to the laser pulse), the photocarrier relaxation is determined with nanosecond resolution. In addition to being contactless, the technique offers other potential advantages over electrical measurements. Results for MBE-grown Hg1-xCdxTe are presented.

Photon-excited soft x-ray emission spectra for CuO, Cu{sub 2}O, and bismuth cuprate in the region of the Cu 3{ital d}{r arrow}3{ital p} transitions were measured to obtain bulk-sensitive electronic partial density-of-states information. For CuO and Cu{sub 2}O transitions from the valence levels into the {ital M}{sub II} and {ital M}{sub III} levels were clearly resolved. The emission features were separated by the 2.3-eV spin-orbit interaction of the copper 3{ital p}{sub 1/2} and 3{ital p}{sub 3/2} states and appeared in the statistical intensity ratio. The copper {ital M}{sub III} emission spectrum of the superconductor is broader than the spectra of CuO and Cu{sub 2}O. For all three compounds the shape of the {ital M}{sub III} emission spectrum extracted from the data is qualitatively similar to calculations of the copper single-particle local density of states. No evidence of multiplet structure was observed in the emission spectrum of CuO in spite of the open {ital d} shell in the ground state. The measurements are compared with published copper {ital L} emission data and photoemission results.

Bulk iron silicides and implanted iron silicides have been studied by soft-x-ray emission (SXE) spectroscopy. The Si {ital L}{sub 2,3} emission spectra of these materials are measured. For bulk silicides, these spectra provide a measure of {ital s}- and {ital d}-type partial density of states (PDOS) localized on the Si sites. We compare them with available band-structure calculations and also with photoemission measurements. For implanted systems, the Si {ital L}{sub 2,3} emission spectra provide useful information about the silicide formation process with the variation of implant doses.

We present temperature-dependent soft-x-ray emission and soft-x-ray absorption measurements on MgO, \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$. The measurements show in detail the final-state effect on phonon broadening for transitions involving the Mg 2P core state in MgO. In addition, we report the temperature dependence of emission and absorption features for MgO, \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$. The temperature dependence of the transitions involving the valence- and conduction-band states should be an important check on band-structure calculations. These results are compared to published temperature-dependent optical-reflectivity measurements.

The Si L2,3 emission spectra of silicon crystals implanted with Co at doses of (1–8) × 1017 Co/cm2 have been examined using soft‐x‐ray‐emission (SXE) spectroscopy. At the lowest dose, the spectra are little modified from that of crystalline Si, indicating that only a small fraction of Si is in the form of silicides within the probe depth of SXE spectroscopy. For higher doses and implant profiles with Co extending to the surface, there is clear evidence for ordered CoSi2 combined with richer Co phases, but little evidence for pure Si or for ordered regions of CoSi.

The Ni and Co monosilicides and disilicides are studied by soft-x-ray-emission spectroscopy. The Si {ital L}{sub 2,3} spectra, which provide a measure of the partial densities of states of {ital s} and {ital d} angular momentum symmetry (({ital s}+{ital d}) PDOS) localized on the Si site, are compared with available theoretical calculations, and discussed in terms of the contribution of {ital s} electrons to the bonding. The Ni and Co {ital M}{sub 2,3} emission spectra are also obtained, and analyzed to provide information about the {ital d} PDOS localized at the metal site. These spectra are discussed in terms of {ital p}-{ital d} bonding in the silicides.

Using site-specific soft x-ray emission and absorption spectroscopy in conjunction with site-specific x-ray photoelectron spectroscopy, we present measurements of the valence and conduction band states of NiO. Significant hybridization between the Ni and the O electronic states near the Fermi energy is observed throughout both the valence and conduction bands, in accordance with density-functional theory calculations also presented. The relationship between our emission and absorption measurements also shows direct similarities to other techniques used to measure the non-dipole-allowed $d\text{\penalty1000-\hskip0pt}d$ transitions within NiO, addressing questions concerning the character of the insulating band gap of this system. NiO has previously been described as a large-gap, charge-transfer insulator, while our data show the valence and conduction states at the Fermi energy to be primarily of Ni $d$--character hybridized with a small amount of O $p$--character states, suggesting a mixture of charge-transfer and Mott-Hubbard character as described by the Zaanen-Sawatzky-Allen model.

Si L 2.3 x-ray emission stimulated with narrow-band synchrotron radiation has been studied as a function of excitation energy. In strong contrast to crystalline silicon, amorphous silicon yields emission spectra that are independent of the excitation energy, thereby demonstrating that long-range order plays a necessary role in the excitation-energy dependence of the crystalline emission

Understanding the atomic bonding properties at the interface between thin films is crucial to a number of key modern technical devices, including integrated circuits, magnetic disk read/write heads, batteries, and solar cells. Semi-conducting materials such as titanium nitride (TiNx) are widely used in the manufacturing of modern electronics, requiring a wealth of information about its electronic structure. We present data from soft x-ray emission and absorption experiments involving a sample consisting of a 40 nm TiN layer on top of an aluminum film 550 nm thick. Soft x-ray emission spectroscopy (XES) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy are tools that provide a non-destructive, atomic site-specific probe of the interface, where the electronic structure of the material can be mapped out element by element. From these measurements, we show that the Ti and the N diffuse into the Al film to form an equivalent material depth of about 4.5 nm, and the NEXAF structure reveals that...

The results of x-ray fluorescence measurements of the molecular superconductors (ET)[(HO)Fe(CO) ]·CHCN (T = 8.5 K) and (ET)[(HO)Cr(CO) ]·CHCN (T ∼ 6 K) and molecular conductor (ET)[(HO)Fe(CO) ]·CHN containing paramagnetic 3d ions are presented. The following transition of the x-ray emission valence spectra are monitored: C K α, N K α (2p→1s transition) and Fe L, Cr L (3d4s→2p transition). It is found that the electronic structure of the solvents (benzonitrile, pyridine) that occupy the hexagonal cavities formed by the anionic layer is close to that of the neutral molecule. The ratio of the emission intensities of the peaks L to L for Fe and Cr is found to be 2.8-3.1 times higher for (ET)[(HO)Fe(CO) ]·CHCN and (ET)[(HO)Cr(CO) ]·CHCN than for pure metals. This indicates that the paramagnetic 3d ions are situated in highly insulating anionic layers. We did not find any changes in the C K α emission for different solvent molecules.

We investigate the excitation energy dependence of the boron [ital K] soft-x-ray emission of B[sub 2]O[sub 3] and hexagonal-BN using synchrotron radiation. When exciting into the core exciton state the spectra are shifted to lower energy by 1.5 and 1.8 eV, respectively. This shift is found to be a result of phonon relaxation and differences in initial-and final-state electronic screening.

A soft X-ray monochromator with a normal incidence transmission grating has been designed and installed on beamline U-10A at NSLS. The design uses the e-beam of the synchrotron light source as its input slit and provides high throughput and moderate resolution for photon energies from 20 to 1000 eV. Scanning is accomplished by the linear motion of a plane mirror. The monochromator is described and test results are presented.

An angle resolved photoelectron spectrometer has been constructed and coupled to the high throughout 2 m normal incidence monochromator now in operation at SURF-II. The electron analyzer whose design has been previously reported [2] scans the angular distribution of the ejected photoelectrons in a plane perpendicular to the partially polarized exit beam from the monochromator. The intensity of the photon beam from the monochromator is monitored by measuring the photocurrent from a screen in front of a three mirror polarization analyzer which is used to determine the degree of polarization of the photon beam. The function of the spectrometer is under computer control which is also acquires and processes the data output from the apparatus. Two novel features are employed to make the system highly effective: one is a capillary which channels the monochromatized output photon beam to the gas-photon-interaction zone and isolates the 10−4 vacuum int the spectrometer chamber from the 10−9 vacuum in the monochromator; the second feature is a high speed cryopump which permits a high density gas jet to interact with the photon beam while maintaining a high enough vacuum to minimize electron scattering and permit operation of the channeltron electron detector. These features combined with output fluxes of 5 × 1010 photons/s−1 A−1 permit vibrationally resolved photoelectron spectra of N2 and CO to be obtained in about 15 min.

We have begun a program to measure oscillator strengths of autoionizing resonances that result from a transition in the VUV between a laser excited initial state and a final state in which a core electron is promoted. These measurements demonstrate a new technique to combine synchrotron radiation, laser pumping, and photoelectron spectroscopy.Measurements of the energy positions of autoionizing resonances have been honed to a fine art over the past 50 years. Total cross section measurements and the parameters that describe autoionizing resonances have been determined. Most of these studies have been made from the dipole allowed ground state. Recently autoionizing resonances have been observed from excited initial states and from ion initial states. We have heard several talks, at this meeting which described some of this type of research. In the measurements to be described in this paper, laser radiation is combined with synchrotron radiation, as shown schematicaly in Figure 1, to study the photoionization from excited initial states to continuum final states or to autoionizing final states. Continuum radiation from the Aneau de Collisions d’Orsay (ACO), which is installed at the Universite de Paris-Sud, in Orsay France, is monochromatized by a toroidal grating monochromator (TGM) and is focused by a toroidal output mirror on to a weakly collimated sodium beam emanating from a furnace mounted on the axis of a cylinderical mirror analyzer (CMA). This electron spectrometer is used to study the kinetic energy distribution of the ejected photoelectrons produced by the interaction of the photon beam with the focused synchrotron radiation.

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10-17 cm2 and a Penning ionization cross section for the 5s state of 1.1 X 10-12 cm2 were found (within 50% uncertainty) for an oven temperature of 520 K.

The soft x-ray emission spectra of single-crystal LiF excited with synchrotron radiation are presented. The radiative decay of the lithium 1s core exciton is observed. Radiative transitions between the valence band and the core hole are also observed in undamaged samples. Spectra obtained with broadband synchrotron-light excitation are shown to be dominated by diffuse scattering from damaged sample surfaces. Excitation with photon energies between 100 and 150 eV generates true emission spectra. An important result is that electrons excited into the conduction band are frequently trapped in an exciton state before recombining with the core hole.

The high intrinsic brightness of the circulating electron beam at SURF-II is used as the entrance slit for a two-meter normal incidence monochromator. A typical beam size for the electron beam is 100 μ high by 2 mm wide yielding an observed resolution of 0.4 A with a 200 μm exit slit and a 2400 lines/mm grating. The instrument accepts a beam with a 65 mrad horizontal divergence and a 10 mrad vertical divergence. A plane pre-mirror used near normal incidence reflects the incoming radiation onto the 2 m grating; this combination provides a horizontal exit beam, and enables the experiment to be located three meters from the orbit tangent point. With magnesium fluoride coated aluminum optics a flux of 2×10″ photons/s·A at 1200 A is observed with a 10 mA circulating current. A flux of 5×10 10 photons/sdA at 600 A is observed with an osmium coated grating and a 10 mA circulating current. Sample spectra of the angle-resolved photoelectron spectrum of CO are presented.

We present oxygen K soft x-ray emission spectra for the YBa/sub 2/Cu/sub 3/O/sub x/ compounds with x nominally equal to 6, 6.5, and 7 and compare them with x-ray emission spectra determined from recent band-structure calculations. The K emission spectrum of O provides a measure of the p-type local partial density of states to (p-LPDOS) at the oxygen sites. As x decreases from 7-delta about 6.5, a chemical shift of the entire spectrum to lower energy indicates that screening is modified for all oxygen sites. The integrated intensity of the spectra is nearly unchanged by oxygen removal, indicating an increase in p-LPDOS per oxygen site. These results and changes in the spectral shape suggest that itinerant electron density near the O atoms is reduced and bound electron density is increased as oxygen is removed.

The National Bureau of Standards (NBS) Synchrotron Ultraviolet Radiation Facility (SURF-II) is used in conjunction with a high flux normal incidence monochromator for angle resolved wavelength dependent photoelectron studies. The recent work has concentrated on studies of the effect of shape resonances on molecular vibrational intensity distributions as well as the effects of autoionization upon the vibrational intensity distributions over narrow wavelength regions. Results for CO, N2, Ar and Xe will be discussed.

The Al L/sub 2,3/ spectrum for dilute alloys of Al in Mg, and the Mg L satellite spectrum produced by transitions in atoms with doubly ionized 2p core levels have been measured. The two spectra contain similar features associated with screening of the extra core hole, but are otherwise dissimilar, which suggests that the equivalent-core approximation is not valid. The threshold peak is broadened in both spectra. The Al-impurity spectrum is found to be about 1 eV wider than that of the Mg host. The L/sub 3/-L/sub 1/ intercore transition in doubly ionized Mg is observed. Finally, a second, weak, high-energy satellite of Mg is observed that may be produced by transitions from the /sup 1/S/sub 0/ state of the doubly ionized core levels. These results provide important new data for comparison with theories of the electronic states of impurity atoms in metals.

Measurements of the K X-ray absorption and emission edges of Li are reported. They were made with the same spectrometer at the NBS storage ring and serve to establish a 0.1 eV separation between the edges with no possibility of instrument calibration error. These results are compared with recent theories of Almbladh and Mahan describing the effects of incomplete phonon relaxation about the core hole. It is concluded that these theories give a satisfactory explanation of the data.

Physical review / B 37(4), 2293 - 2296 (1988). doi:10.1103/PhysRevB.37.2293, We present e-beam-excited soft-x-ray emission spectra and total-photoelectron-yield spectra in the 20–600 eV photon energy range for $Ba_2YCu_3O_{7−x}$. In soft x-ray emission, the N4,5 structure of Ba, the M4,5 spectrum of Y, and the K spectrum of O provide a direct measure of the p-type partial density of states (p-PDOS) localized on the respective atomic sites. In each case the p-PDOS is very small at the Fermi energy ɛF. The maximum in the O K spectrum is 2.6±0.5 eV below ɛF. This result provides direct confirmation that the shoulder previously found at ɛ$_F$-2.3 eV in photoelectron emission spectra is associated with O p orbitals. No changes are observed between spectra taken above and below Tc. .AE, Published by Inst., Woodbury, NY

Aluminum L/sub 2,3/ soft-x-ray emission spectra have been observed for several aluminum-manganese alloys exhibiting icosahedral, decagonal, and the normal crystalline symmetries. The spectra of all the alloys are qualitatively similar and are slightly narrower (approx.0.2 eV) than the width observed for metallic aluminum. Compared to the sample with crystalline symmetry, the quasicrystals show no chemical shift and a decrease in the partial density of states of s and d symmetry at the Fermi energy, contradicting the predictions of several calculations

The first reported study of a fluorescence spectrum of a metal vapor resonantly excited by vacuum-ultraviolet radiation has been made in Ba ii. Seven Ba ii fluorescent transitions have been identified for Ba vapor excited by 584-A radiation. The intensities of these transitions are consistent with the population distribution of excited Ba ii observed by using photoelectron spectroscopy. No detectable Ba ii fluorescence was observed when 736–742-A excitation was used.