Note: Observation of the angular distribution of an x-ray characteristic emission through a periodic multilayer.

We present the observation of the angular distribution of a characteristic x-ray emission through a periodic multilayer. The emission coming from the substrate on which the multilayer is deposited is used for this purpose. It is generated upon proton irradiation through the multilayer and detected with an energy sensitive CCD camera. The observed distribution in the low detection angle range presents a clear dip at a position characteristic of the emitting element. Thus, such a device can be envisaged as a spectrometer without mechanical displacement and using various ionizing sources (electrons, x-rays, and ions), their incident direction being irrelevant.

EUV stimulated emission from MgO pumped by FEL pulses.

Stimulated emission is a fundamental process in nature that deserves to be investigated and understood in the extreme ultra-violet (EUV) and x-ray regimes. Today, this is definitely possible through high energy density free electron laser (FEL) beams. In this context, we give evidence for soft-x-ray stimulated emission from a magnesium oxide solid target pumped by EUV FEL pulses formed in the regime of travelling-wave amplified spontaneous emission in backward geometry. Our results combine two effects separately reported in previous works: emission in a privileged direction and existence of a material-dependent threshold for the stimulated emission. We develop a novel theoretical framework, based on coupled rate and transport equations taking into account the solid-density plasma state of the target. Our model accounts for both observed mechanisms that are the privileged direction for the stimulated emission of the Mg L2,3 characteristic emission and the pumping threshold.

X-ray fluorescence induced by standing waves in the grazing-incidence and grazing-exit modes: study of the Mg-Co-Zr system.

The characterization of Mg-Co-Zr tri-layer stacks using X-ray fluorescence induced by X-ray standing waves, in both the grazing-incidence (GI) and the grazing-exit (GE) modes, is presented. The introduction of a slit in the direction of the detector improves the angular resolution by a factor of two and significantly improves the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kα and Co Lα characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, it is shown that the interfaces of the Si/[Mg/Co/Zr] × 30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] × 30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. An explanation of this opposite behavior of the Co-on-Zr and Zr-on-Co interfaces is given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents a negative value and the other two systems present positive values. Together with the difference of the surface free energies of Zr and Co, this leads to the Mg/Zr/Co system being considered as a Mg/CoxZry bi-layer stack, with x/y estimated around 3.5.

Enhancement of the reflectivity of Al/Zr multilayers by a novel structure.

The reflectivity of Al/Zr multilayers is enhanced by the use of a novel structure. The Al layers are divided by insertion of Si layers. In addition, Si barrier layers are inserted at the Al/Zr interfaces (Zr-on-Al and Al-on-Zr). As a result, crystallization of the Al layer is inhibited and that of Zr is enhanced. In grazing incidence x-ray reflectometry, x-ray diffraction, and extreme ultraviolet measurements, the novel multilayers exhibit lower interfacial roughness compared with traditional multilayer structures, and their reflectivity is increased from 48.2% to 50.0% at a 5° angle of incidence. These novel multilayers also have potential applications in other multilayer systems and the semiconductor industry.

Optical and structural performance of the Al(1%wtSi)/Zr reflection multilayers in the 17-19nm region.

Two kinds of Al/Zr (Al(1%wtSi)/Zr and Al(Pure)/Zr) multilayers for extreme ultraviolet (EUV) optics were deposited on fluorine doped tin oxide coated glass by using direct-current magnetron sputtering technology. The comparison of the two systems shows that the Al(1%wtSi)/Zr multilayers have the lowest interfacial roughness and highest reflectivity. Based on the X-ray diffraction, the performance of the two systems is determined by the crystallization of Al layer. To fully understand the Al(1%wtSi)/Zr multilayer, we built up a two-layer model to fit situation of the AFM images, and simulate the grazing incident x-ray reflection-measurements of multilayers with various periods (N = 10, 40, 60, 80). Below 40 periods, the roughness components are lowered. After 40 periods, both surface and interfacial roughness increase with the period number, and decrease the reflectance. According to transmission electron microscope images, the model can represent the variable structure of the system.

Thermal stability of Mg/Co multilayer with B4C, Mo or Zr diffusion barrier layers.

The efficiency of B(4)C, Mo and Zr barrier layers to improve thermal stability of Mg/Co multilayer up to 400 °C is investigated. Multilayers were deposited by direct current magnetron sputtering and characterized using X-ray and extreme ultraviolet reflection. The results suggest that B(4)C barrier layer is not effective due to drastic diffusion at Mg-B(4)C interface. Although introducing Mo barriers improves the thermal stability from 200 to 300 °C, it increases the interface roughness and thus degrades the optical performances. On the contrary, Zr barriers can significantly increase the thermal stability of Mg/Co up to 400 °C without optical performance degradation. Thus, Mg/Zr/Co/Zr is suitable for EUV applications requiring both optimal optical performances and heat resistance.

Structural properties of Al/Mo/SiC multilayers with high reflectivity for extreme ultraviolet light.

We present the results of an optical and chemical, depth and surface study of Al/Mo/SiC periodic multilayers, designed as high reflectivity coatings for the extreme ultra-violet (EUV) range. In comparison to the previously studied Al/SiC system, the introduction of Mo as a third material in the multilayer structure allows us to decrease In comparison to the previously studied Al/SiC system with a reflectance of 37% at near normal incidence around 17 nm, the introduction of Mo as a third material in the multilayer structure allows us to decrease the interfacial roughness and achieve an EUV reflectivity of 53.4%, measured with synchrotron radiation. This is the first report of a reflectivity higher than 50% around 17 nm. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) measurements are performed on the Al/Mo/SiC system in order to analyze the individual layers within the stack. ToF-SIMS and XPS results give evidence that the first SiC layer is partially oxidized, but the O atoms do not reach the first Mo and Al layers. We use these results to properly describe the multilayer stack and discuss the possible reasons for the difference between the measured and simulated EUV reflectivity values.

Comparison of Mg-based multilayers for solar He II radiation at 30.4 nm wavelength.

Mg-based multilayers, including SiC/Mg, Co/Mg, B(4)C/Mg, and Si/Mg, are investigated for solar imaging and a He II calibration lamp at a 30.4 nm wavelength. These multilayers were fabricated by a magnetron sputtering method and characterized by x-ray reflection. The reflectivities of these multilayers were measured by synchrotron radiation. Near-normal-incidence reflectivities of Co/Mg and SiC/Mg multilayer mirrors are as high as 40.3% and 44.6%, respectively, while those of B(4)C/Mg and Si/Mg mirrors are too low for application. The measured results suggest that SiC/Mg, Co/Mg multilayers are promising for a 30.4 nm wavelength.

Characterization of Al and Mg alloys from their X-ray emission bands.

The valence states of Mg-Al alloys are compared to those of reference materials (pure Mg and Al metals, and intermetallics). Two methods based on X-ray emission spectroscopy are proposed to determine the phases and their proportion: first, by analyzing the Al valence spectra of the Mg-rich alloys and the Mg valence spectra of the Al-rich alloys; second, by fitting with a linear combination of the reference spectra the Al spectra of the Al-rich alloys and the Mg spectra of the Mg-rich alloys. This enables us to determine that Al and Al3Mg2 are present in the 0-43.9 wt% Al composition range and Mg and Al12Mg17 are present in the 62.5-100 wt% Al composition range. In the 43.9-62.5% Al range, the alloy is single phase and an underestimation of the Al content of the alloy can be estimated from the comparison of the bandwidth of the alloy spectrum to the bandwidths of the reference spectra.

Surface reactions of 3-butenenitrile on the Si(001)-2 x 1 surface at room temperature.

Using a combination of local -- scanning tunneling microscopy -- and spatially integrated, but chemically sensitive probes -- X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy -- we have examined how 3-butenenitrile reacts with the Si(001)-2 x 1 surface at room temperature. Electron spectroscopies indicate three different nitrogen chemical bonds: a Si-C=N-Si bond, a C=C=N cumulative double bond, and a CN moiety datively bonded to a silicon atom. All molecular imprints detected by scanning tunneling microscopy (STM) involve two adjacent silicon dimers in the same row. The three geometries we propose -- a double di-sigma bonding via the CN and the C=C, a cumulative double bond formation associated with alphaC-H bond dissociation, and a di-sigma vinyl bonding plus a CN datively bonded to a silicon atom -- are all compatible with electron spectroscopies and data. Real-time Auger yield kinetic measurements show that the double di-sigma bonding geometry is unstable when exposed to a continuous flux of 3-butenenitrile molecules, as the Si-C=N-Si unit transforms into a CN moiety. A model is proposed to explain this observation.