Optical-constant metrology of VUV thin-film materials

Helmholtz-Building of the Berlin-Charlottenburg, Berlin, November 5th to 6th, 2015; http://www.euv2015.ptb.de/euv2015/euv2015-home.htmlAbstract comunicación oral: Optical constants of materials, when available, often lack consistency, which may be due to the use of data from different sources and/or to the use of inaccurate data. Consistency requires that n and k be connected with the Kramers-Krönig (KK) relations. GOLD has been obtaining self-consistent optical constants of several materials. Samples of the target material are measured in a wide range in order to minimize extrapolations in KK analysis. VUV transmittance and reflectance of thin films can be measured in GOLD¿s reflectometer, which enables in situ measurements of films before exposed to the atmosphere. The obtained n-k data set must fit all experimental data. When no data are available in some range, interpolations are performed with a physically meaningful model, such as Lorentz oscillators. The self-consistent n-k data so produced are tested with the use of two sum rules. We will display examples of optical constants obtained for materials among fluorides, oxides, and metals.Peer Reviewe

Empirical relations among scattering, roughness parameters, and thickness of aluminum films

Experimental measurements of the angular distribution of scattering and scanning electron microscopy pictures of thin aluminum films were used to relate the total integrated scattering and the statistical parameters of the surface roughness to the film thickness. © 1993 Optical Society of AmericaPeer Reviewe

Introduction of Zr in nanometric periodic Mg/Co multilayers

We study the introduction of a third material, namely Zr, within a nanometric periodic Mg/Co structure designed to work as optical component in the extreme UV (EUV) spectral 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 equal to 50% at 25.1 nm and 45deg of grazing incidence and reaches 51.3% upon annealing at 200deg C. Measured EUV reflectivity values of tri-layered systems are discussed in terms of material order within a period and compared to the predictions of the theoretical model of Larruquert. Possible applications are pointed out.Comment: 19 page

Optical coatings for the spectral range 50 – 200 nm

The development of efficient optical coatings in the spectral region between 50 and 200 nm (EUV-FUV) is an important challenge due to the great absortion and low reflectance that most of the materials present in this region. In addition, these coatings are an important element in the advance of many fields like astronomical abservations, plasma diagnosis and lithography. In this work we describe some of the optical coatings developed by the Research Group in Thin Film Coatings (GOLD), which operate in the EUV-FUV region of the spectrum. In GOLD we have an ultra high vacuum experimental system that permits the deposition and in situ measurement of the transmittance and reflectance of multilayers, as a function of the angle of incidence, and in the EUV-FUV spectral range. We prepare multilayers with up to six different materials, which can be deposited using three different techniques. In situ transmittance and reflectance measurements versus the angle of incidence permits the determination of the optical constants (n,k) of the materials, without being exposed to the atmosphere. Due to the great dependance between the optical properties of thin film layers in this spectral range, and the exposition to the atmosphere, our experimental system is a very adequate tool for the determination of those properties, and therefore for the design and fabrication of novel multilayers.El desarrollo de recubrimientos ópticos eficientes en la región espectral comprendida entre 50 y 200 nm (UVE-UVL) supone un reto debido a la gran absorción y baja reflectancia que presentan la mayoría de los materiales en este intervalo. Por otro lado estos recubrimientos son una pieza importante para el progreso de multitud de campos como las observaciones astronómicas, el diagnóstico de plasmas y la litografía. En este trabajo se describen algunos de los recubrimientos ópticos desarrollados hasta el momento por el Grupo de investigación en Óptica de Láminas Delgadas (GOLD), que operan en la región UVE-UVL del espectro. En GOLD disponemos de un equipo experimental de ultra-alto vacío que permite la deposición y medida in situ de la transmitancia y la reflectancia de multicapas en función del ángulo de incidencia y en el rango espectral UVL-UVE. Las multicapas están formadas por hasta seis materiales distintos, que pueden ser depositados mediante tres técnicas de preparación diferentes. Las medidas de transmitancia y reflectancia en función del ángulo de incidencia realizadas in situ permiten la determinación de las constantes ópticas (n, k) de los materiales sin que hayan sido expuestos a la atmósfera. Dada la gran dependencia existente entre las propiedades ópticas de las láminas delgadas y la exposición atmosférica en este rango espectral, nuestro equipo experimental constituye una herramienta muy adecuada para su determinación, y por lo tanto para el diseño y preparación de multicapas innovadoras.Mónica Fernández Perea agradece al Consejo Superior de Investigaciones Científicas la financiación a través del programa de becas predoctorales I3P.Peer reviewe

Self-consistent optical constants of MgF2,LaF3, and CeF3 films

18 pags., 11 figs., 3 tabs.Various fluorides are materials in nature that extend their transparency range to the shortest wavelengths in the far ultraviolet (FUV, 100nm<¿<200 nm). These are relevant materials to prepare multilayer coatings in the FUV for demanding applications such as space instrumentation for astrophysics, solar physics and atmosphere physics, as well as free electron lasers, plasma diagnostics, synchrotron radiation, lithography, spectroscopy, etc. Multilayer design requires the optical constants of the coating materials. Multilayers optimally alternate two transparent materials with contrasting refractive indices. The optical constants of a low-index material, MgF2, and of two high-index materials, LaF3 and CeF3, have been determined in a wide spectral range and are presented here. Thin films of MgF2, LaF3, and CeF3 were deposited by boat evaporation onto substrates at 523 K. Transmittance, reflectance, and ellipsometry measurements were performed in ranges jointly covering the 30- 950-nm spectral range. This range was extended with literature data and extrapolations to obtain self-consistent optical constants using the Kramers-Kronig (KK) analysis. An iterative, double KK analysis procedure (successive reflectance-phase and k-n KK analyses) was carried out to obtain a self-consistent set of optical constants per material. With the final data sets, the experimental measurements were satisfactorily reproduced. Global self-consistency of the data sets was successfully evaluated through sum rules; additionally, local selfconsistency at each photon energy range was also evaluated through a novel sum-rule method which involves window functions. The new sets of optical constant extend the data availability mainly to the FUV and beyond, particularly for CeF3, where few data had been reported.Spanish Programa Estatal de Investigación Científica y Técnica de Excelencia, Secretaría de Estado de Investigación, Desarrollo e Innovación (AYA2013-42590-P and ESP2016-76591-P).Peer Reviewe

Narrowband filters for the FUV range

10 págs.; 6 figs.; 4 tabs.We address the design, fabrication, and characterization of transmittance filters for the Ionosphere Photometer instrument (IP), developed by the Center for Space Science and Applied Research (CSSAR). IP, a payload of Feng-Yun 3D meteorological satellite, to be launched on 2016, is aimed to perform photometry measurements of Earth¿s ionosphere by the analysis of the OI (135.6 nm) spectral line and N2 Lyman-Birge-Hopfield (LBH, 140-180 nm) band, both of them in the far ultraviolet (FUV) range. The most convenient procedure to isolate a spectral band is the use of tunable transmittance filters. In many applications the intensity of the ultraviolet, visible and infrared background is higher than the intensity of the target FUV lines; therefore one of the most important requirements for transmittance filters is to reject (by reflecting and/or by absorbing) as efficiently as possible the visible and close ranges. In the FUV range, (Al/MgF2)n transmittance filters are the most common, and they are suitable to reject the visible and adjacent ranges. These materials present unique properties in this range: MgF2 is transparent down to ~115 nm and Al has a very low refractive index in the FUV that contrasts well with MgF2. Narrowband tunable filters with very low transmittance at long wavelengths are achievable. The main data on the preparation and characterization of IP filters by Grupo de Óptica de Láminas Delgadas (GOLD) is detailed. In this proceeding we present (Al/MgF2)3 filters peaked at either 135.6 nm or at the center of the LBH band (~160 nm). Filters were characterized in the 125-800 nm range (143-800 nm range for the LBH filter). After some storage in a desiccator, both coatings kept a transmittance of ~0.14 at their target wavelengths, with visible-topeak transmittance ratios of 1.2·10-4 (OI filter) and 1.3·10-4 (LBH filter). One filter tuned at each target wavelength was exposed to ~300 Gy 60Co gamma dose, with no significant transmittance change. Keywords: Coatings, Far Ultraviolet, Atmosphere Physics, Transmittance Filters, Space OpticsThis research was partly supported by the National Programme for Research, Subdirección General de Proyectos de Investigación, Ministerio de Ciencia e Innovación, project number AYA2010-22032 and AYA2013- 42590-P. The authors are gratefully acknowledged to Pedro Valdivieso (Instalación de irradiación Náyade, CIEMAT).Peer Reviewe

Optical constants of magnetron-sputtered magnesium films in the 25-1300 eV energy range

The transmittance of dc magnetron-sputtered Mg thin films was measured in the 25-1300 eV spectral range. Freestanding Mg films protected with Al layers were characterized ex situ. Transmittance measurements were used to obtain the extinction coefficient k of Mg films. The obtained k values along with the data available in the literature, and with interpolations and extrapolations for the rest of the spectrum, were used to obtain the real part of the index of refraction n by the Kramers-Krönig analysis. Sum-rule tests indicated a good consistency of the data. © 2010 American Institute of Physics.Peer Reviewe

Electron-beam deposited boron coatings for the extreme ultraviolet

Boron films deposited by evaporation with an electron-beam were found to have a relatively high reflectance in the extreme ultraviolet with values similar to those of ion-beam-sputtered (IBS) SiC and IBS B4C . The largest reflectance was measured for an 11¿nm thick boron film. Some reflectance degradation was observed for boron films stored in a desiccator. Reflectance degradation varied from sample to sample and was found to be either similar to that of IBS SiC and IBS B4C or larger. © 2008 Optical Society of AmericaThis work was supported by the National Programme for Space Research, Subdirección General de Proyectos de Investigación, Ministerio de Ciencia y Tecnología, project number ESP2005-02650. M. Fernández-Perea is thankful to Consejo Superior de Investigaciones Científicas (Spain) for funding under the Programa I3P (Ref. I3P-BPD2004) partially supported by the European Social Fund. We acknowledge the technical assistance of José M. Sánchez-Orejuela. M. Vidal-Dasilva is thankful to Ministerio de Educación y Ciencia for funding under the FPI BES-2006- 14047 fellowship.Peer Reviewe

Determination of reflectance and transmittance of multi-layer of InGaAs and theoretical methods for obtaining of optical constants

5 páginas, 3 figuras, 2 tablas.-- Trabajo presentado al 1st International Congress on Instrumentation and Applied Sciences celebrado en Cancún (México) del 26 al 29 de Octubre de 2010.The theoretical concepts are necessary to obtain the optical constants of several materials in InGaAs Photodiode and are possible to obtain from experimental dates of reflectance and transmittance and several optical coverings can be designed. In this work we will show how to calculate the reflectance of photodiode for all the wavelengths (each 50 nm, according to the data of refractive index), as well as changing to the angle of incidence and polarization s and p, besides the calculation of the transmittance of a multi-layer ones of InGaAs. A multi-layer is constituted by a series of piled up laminae some on others and in this work we will suppose that they are homogenous, isotropic and plane-parallel, the structure is in the first case we have a transparent layer of NSi, late second layer of InP (Zn), soon a third layer of InGaAs and finally a later of InP (S). These multilayers are destined for optical applications, in our case will be case of study in the case of the photodiodes, the thicknesses of the layers will be of the order of the wavelength of incident radiation, which in the case of radiation IR/NIR is translated in thicknesses of approximately between 1y 100 nm. For the determination of optical constants they are possible to be done of different ways in our case we will concentrate in 1) Measured of reflectance in normal incidence. These measures only provide the value of n in the case of means transparents.2) Measured of reflectance in two angles of incidence. It allows to the use of natural light or polarized.3) Two measures of R p R s in two angles of incidence outside the normal one. 4) Rs and Rp in a single angle of incidence outside the normal one.Peer reviewe