Nicola Mahne

The BEAR Beamline at Elettra

The BEAR (Bending Magnet for Emission Absorption and Reflectivity) beamline is installed at the right exit of the 8.1 bending magnet at ELETTRA. The beamline — in operation since January 2003 — delivers linear and circularly polarized radiation in the 5 – 1600 eV energy range. The experimental station is composed of a UHV chamber for reflectivity, absorption, fluorescence and angle resolved photoemission measurements and a UHV chamber for in‐situ sample preparation.

Electronic properties of tetrakis(pentafluorophenyl)porphyrin

We studied in detail the electronic properties of C44H10F20N4 (tetrakis(pentafluorophenyl)porphyrin, hereafter H2TPP(F)) via a combined study by photoelectron spectroscopy (PES) and density functional (DF) calculations, shedding new light on the role of the halide in this very interesting molecule for organic electronics. Valence and core levels have been investigated by means of PES on H2TPP(F) thin films deposited on the SiO2/Si(100) native oxide surface by supersonic molecular beam deposition (SuMBD). These experiments have been carefully interpreted on the basis of DF results pertaining to the isolated H2TPP(F). Non-relativistic calculations have been run to investigate valence states, whereas a two component relativistic approach within the zeroth-order regular approximation has been adopted to study core levels. The present results, in conjunction with those obtained previously on the H2TPP parent compound [M. Nardi, R. Verucchi, C. Corradi, M. Pola, M. Casarin, A. Vittadini and S. Iannotta, Phys. Chem. Chem. Phys., 2010, 12, 871], pave the way towards designing fully organic p–n junctions by using these macrocycles.

Chemistry at air/water interface versus reaction in a flask: tuning molecular conformation in thin films.

Atomic force microscopy and X-ray reflectivity studies of cobalt stearate Langmuir-Blodgett (LB) films (CoStp) deposited from a preformed bulk sample on quartz substrates showed formation of a Volmer-Weber type monolayer but no multilayers as compared to the excellent multilayers of cobalt stearate films (CoStn) deposited at the air/water interface by the usual LB technique, in spite of both showing bidentate bridging type coordination of cobalt ions with the carboxylate group. The difference is attributed to existence of different headgroup conformers, observed from Fourier transform infrared (FTIR) studies. The CoStp films had a higher energy boat conformation with linear O-Co-O linkage, whereas CoStn formed a low energy conformer with a bent O-Co-O configuration (bond angle of 105 degrees). Present results support the necessity of bidentate bridging coordination in multilayer deposition, but rejects its sufficiency by bringing out the crucial role played by air/water interface. Differences in surface pressure-molecular area isotherms and hydrocarbon tail-tail interactions (evident from FTIR spectra) of the films support the above statement. Methyl-methyl interactions observed in CoStn samples suggest hierarchy of supramolecular chemistry at the air/water interface in tuning the C-O-Co bond angle essential to satisfy the wetting condition with the substrate and subsequently form LB multilayers.

Efficiency of gratings in the conical diffraction mounting for an EUV time-compensated monochromator

Recent measurements of the absolute diffraction efficiency of plane gratings in the conical diffraction mounting (in which the light approaches the grating in the plane parallel to the direction of the grooves) are presented. Three gratings have been tested at the beamline BEAR (Elettra Synchrotron, Trieste) in the 10-130 nm region, showing a peak efficiency as high as 70%. The aim of these measurements is the use of two gratings in the conical diffraction mounting for the realization of a high-throughput time-compensated monochromator for the spectral selection of high-order harmonic radiation produced by the interaction between an ultrashort laser pulse (less than 100 fs) and a gas jet. The monochromatic and ultrashort pulse at the monochromator exit can be used for the injection of a Free Electron Laser. The theory of the time-compensation with gratings will be briefly resumed, the design of the monochromator will be presented, and the results of the measurements at BEAR will be discussed.

Transmittance and optical constants of Sr films in the 6–1220 eV spectral range

Strontium (Sr) is a material with low-absorption bands in the extreme ultraviolet (EUV), which makes it a potential candidate for band pass filters and multilayer coatings. Yet, a better knowledge of the optical properties of Sr is required for these developments. The optical constants n and k of Sr thin films have been obtained in the 6–1220u2009eV range from transmittance measurements performed at room temperature. These are the first experimental optical constant data of Sr in most of the range. Thin films of Sr with various thicknesses were deposited by evaporation in ultrahigh vacuum conditions, and their transmittance was measured in situ. Sr films were deposited onto grids coated with a thin C support film. Transmittance measurements were used to directly obtain the extinction coefficient k of Sr films. The refractive index n of Sr was calculated with Kramers-Kronig analysis. For this, k data were extrapolated both on the high- and on the low-energy sides by using experimental and calculated k data ava...

Compression of attosecond pulses with multilayer mirrors

We present the design, fabrication and characterization of non-periodic multilayer mirrors for the compression of attosecond pulses in the XUV domain. We demonstrate that time domain optimization allows pulse compression down to sub-50 as duration.

Introduction of Zr in Mg/Co nanometric periodic multilayers

We study the introduction of Zr as a third material within a nanometric periodic Mg/Co structure designed to work as optical component in the EUV range. Mg/Co, Mg/Zr/Co, Mg/Co/Zr and Mg/Zr/Co/Zr multilayers are designed, then characterized in terms of structural quality and optical performances through X-ray and EUV reflectometry measurements respectively. For the Mg/Co/Zr structure, the reflectance value is reported to be 50% at 25.1 nm and 45° of grazing incidence. Nuclear Magnetic Resonance (NMR) measurements are performed to study the nearest neighbour local environment around the Co atoms.

EUV polarimetry with single multilayer optical element

A polarimetric measurement technique based on the analysis of the reflection data given by a single mirror rotated around the incidence beam axis is presented. In the extreme ultraviolet spectral region, a multilayer coated mirror must be used. The multilayer mirror must be fully characterized before the experiment. Theory demonstrates how this method allows complete determination of Stokes parameters in case of a totally polarized beam. A simulation code has been developed in order to model the experiment in case of synchrotron radiation propagating in a bending magnet beamline and impinging a multilayer mirror. The simulation is useful to verify each time the effectiveness of the method in the different experimental conditions considered. Finally an experimental application is presented.

Quantitative modelization of particle emission from excited solids: application to spectroscopic diagnostics of buried interfaces in multilayer

The performance of multilayer optics depends on the quality of interfaces between spacer and absorber materials. Intermixing at the interfaces affects the optical behavior. An experimental method is presented here to obtain the amount of intermixing at the buried interfaces of multilayer structures. The method is based on the combined use of photoemission and a rocking scan through the Bragg peak. The possibility of obtaining quantitative information - through a phenomenological model - on the width of the intermixing region is presented and discussed.

The beam position monitor of the BEAR beamline

This article describes the photon beam position monitor installed at the BEAR beamline at Elettra, Trieste. The device, based on four Mo photoemitting plates, is installed upstream of the beamline optics. Two modes of operation are possible, including single-plate operation (integral mode) and two-plate operation (differential mode). The integral mode allows beam height determination in the laboratory frame of reference with an overall accuracy of about 0.1mm, while the differential mode features a sensitivity of the order of about 1μm. A quantitative model connecting the device output with beam height was deduced. A satisfactory agreement was found between model predictions and experimental results. The quantitative performance opens the possibility to implement a feedback procedure to stabilize or automatically numerically correct the delivered photon energy.