Multilayer Optics Research Articles

Tuning of the surface plasmon resonance in TiO2/Au thin films grown by magnetron sputtering: The effect of thermal annealing

Nanocomposites consisting of a dielectric matrix, such as TiO2, with embedded noble metal nanoparticles (NPs) possess specific optical properties due to the surface plasmon resonance (SPR) effect, interesting for several applications. The aim of this work is to demonstrate that these properties are sensitive to the nanostructure of magnetron-sputtered TiO2/Au thin films, which can be tuned by annealing. We study the role of the shape and size distribution of the NPs, as well as the influence of the crystallinity and phase composition of the host matrix on the optical response of the films. All these characteristics can be modified by vacuum annealing treatments of the deposited films. A theoretical interpretation and modeling of the experimental results obtained is presented. The model involves a modified Maxwell-Garnett approach for the effective dielectric function of the composite (describing the SPR effect) and the transfer matrix formalism for multilayer optics. Input data are based on the experimental information obtained from the detailed structural characterization of the films. It is shown that the annealing treatments can be used for controlling the optical properties of the composite films, making them attractive for decorative coatings.

Optical Design and Fabrication of Fully Sputtered CdTe/CdS Solar Cells

A model is presented for optimising the integrated intensity of light passing into the absorber layers of thin-film solar cells. Dispersion data for each of the transparent layers in the cells was obtained from variable angle spectroscopic ellipsometry. This data was then used in a transfer matrix model of multi-layer optics to determine the intensity spectrum passing over the interface from the transparent to the absorbing parts of the cell. Application of the method to the case of CdTe/CdS/ZnO/ITO/glass solar cells is described in detail, including the fitting of oscillator models to extract the complex dielectric function from the ellipsometry data. It was found that light coupling into the absorber was particularly sensitive to the CdS thickness but that tuning the ZnO (highly resistive transparent) layer was also influential. All-sputtered cells of this type were demonstrated as having efficiencies of 12.5% for 5 × 5 mm2 contacts.

Reduction of interlayer thickness by low-temperature deposition of Mo/Si multilayer mirrors for X-ray reflection

Thin interlayers are essential for high-quality multilayer optics. We present the first investigation of reducing the interlayer thickness of Mo/Si multilayer structures by cooling the substrate with liquid nitrogen during the deposition. The structures were deposited by means of electron beam evaporation. Even after warming up to room temperature prior to analysis, the interlayers that formed upon cryogenic deposition were found to be approximately 60% thinner compared to room temperature deposition. The interlayer thickness reduction at low temperature and its preservation upon warming up are attributed to a lower mobility of adatoms, reduced surface segregation of Si during Mo-on-Si growth, and/or crystallization of Mo.

Aperiodic normal-incidence antimony-based multilayer mirrors in the 8 — 13-nm spectral range

The optical properties of several materials were analysed from the standpoint of fabrication of broadband normal-incidence multilayer mirrors possessing maximal uniform reflectivity in the 8–13-nm range. By solving the inverse problem of multilayer optics we show that aperiodic Sb/(B4C, Sc, Si) multilayer structures optimised for maximum uniform reflectivity in the 8–13-nm range are able to afford a normal-incidence reflectivity R∼10 % throughout this range. The best results are exhibited by the pair Sb/B4C, for which the average reflection coefficient amounts to about 13%. The dependence of optimisation result on the programmable limitation on the minimal layer thickness in the multilayer structure was numerically investigated. An empirical rule was established whereby setting the lower bound for a layer thickness at a level ∼λmin/4 (in this case, λmin = 8 nm) does not result in an appreciable lowering of attainable uniform reflectivity.

Particulars of studying the roughness of substrates for multilayer X-ray optics using small-angle X-ray reflectometry, atomic-force, and interference microscopy

The abilities of standard methods for rough surface investigation are analyzed in case of supersmooth substrates for multilayered X-ray optics. The X-ray specular reflection technique is shown to be the most adequate one. X-ray diffuse scattering and AFM can be applied only in a case of PSD-function calculation and approximation over the entire spectrum range of spatial frequencies.

用光导波方法确定扭曲向列相液晶盒指向矢剖面

Using the optical guided wave method,the full leaky waveguide mode assembled by prism,matching fluid of refractivity and twisted nematic liquid crystal cell is studied under different voltages.Some experimental data of reflected light corresponding to different external angles through the full leaky guided mode of twisted nematic liquid crystal are obtained.From Snell law,some experimental curves between the reflectivity and the internal angle are also obtained.By comparing these experimental curves with the theoretical curves obtained from multi-layer optics theory,with a greatly good accordance,the director profile of twisted nematic liquid crystal cell for different voltages is determined.

Damage mechanisms of MoN/SiN multilayer optics for next-generation pulsed XUV light sources

We investigated the damage mechanism of MoN/SiN multilayer XUV optics under two extreme conditions: thermal annealing and irradiation with single shot intense XUV pulses from the free-electron laser facility in Hamburg - FLASH. The damage was studied "post-mortem" by means of X-ray diffraction, interference-polarizing optical microscopy, atomic force microscopy, and scanning transmission electron microscopy. Although the timescale of the damage processes and the damage threshold temperatures were different (in the case of annealing it was the dissociation temperature of Mo2N and in the case of XUV irradiation it was the melting temperature of MoN) the main damage mechanism is very similar: molecular dissociation and the formation of N2, leading to bubbles inside the multilayer structure.

Atomic Layer Deposition and Characterization of Aluminum Silicate Thin Films for Optical Applications

Optical multilayer interference coatings rely on the refractive index differences and specific thicknesses of the low and high refractive index materials used in optical multilayer structures. An accurate control of important parameters such as film thicknesses, uniformities, and refractive indexes is demanding. Atomic layer deposition (ALD) inherently possesses many characteristics beneficial for obtaining fully conformal and uniform films of specific thicknesses with excellent repeatability. Additionally, the layer-by-layer deposition of the films allows tuning of the film stack properties, such as refractive index, which is an advantage when designing optical filters. By now, has been most often used as a low refractive index material in ALD made interference filters because of a lack of suitable ALD processes. To lower the refractive index from that of , we have developed and examined various ALD processes of aluminum silicate thin films. We concentrate on reporting the refractive indexes, growth rates, and compositions of the films as these parameters are vital for screening suitable ALD processes for optical applications. By varying the amount of silicon in the thin films, the refractive indexes between 1.47 and 1.59 were obtained in this study.

The XIPHOS diffraction facility for extreme sample conditions

XIPHOS has been developed to expand home laboratory facilities closer to those found at central facilities, offering extremes of sample environment and flux densities far greater than standard laboratory sources. The system has a minimum operating temperature of 1.9 K, and has a direct-drive molybdenum rotating-anode generator coupled with the latest multilayer optics. XIPHOS has been specifically designed to accommodate various sample environments and is now operational. Furthermore, it has been calibrated with structural phase transitions from 14 to 148 K. Results are also presented from a full low-temperature data collection ofm-nitroaniline to demonstrate the quality of results attainable from XIPHOS.

Recent development and new ideas in the field of dispersive multilayer optics

A dispersive-mirror-based laser permits a dramatic simplification of high-power femtosecond and attosecond systems and affords promise for their further development toward shorter pulse durations, higher peak powers, and higher average powers with user-friendly systems. The result of the continuous development of dispersive mirrors permits pulse compression down to almost single cycle pulses of 3 fs duration. These design approaches together with the existing modern deposition technology pave the way for the manufacture of dielectric multilayer coatings able to compress pulses of tens of picoseconds duration down to a few femtoseconds.

EUV soft X-ray characterization of a FEL multilayer optics damaged by multiple shot laser beam

We have investigated the damaging effects of a femtosecond pulsed laser beam with 400 nm wavelength on a Mo/Si EUV multilayer. The exposures have been done in vacuum with multiple pulses (5 pulses/mm 2) of 120 fs varying the laser fluence in the 38–195 mJ/cm 2 range. The analysis of the different irradiated regions has been performed ex-situ by means of different techniques, including specular and diffuse reflectivity, X-ray photoemission spectroscopy (XPS) and total electron yield (TEY) in the EUV and soft X-ray range. Surface images have been acquired by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results clearly indicate a progressive degradation of the EUV multilayer performances with the increase of the laser fluence. Spectroscopic analysis allowed to correlate the decrease of reflectivity with the degradation of the multilayer stacking, ascribed to Mo–Si intermixing at the Mo/Si interfaces of the first layers, close to the surface of the mirror.

Multilayer optics to be used as FEL fundamental suppressors for harmonics selection

Pump and probe experiments are one of the most attractive and powerful tools offered by a free electron laser facility. In these experiments it is fundamental to pump the system with a particular wavelength (usually the fundamental one) and to probe it with a second wavelength (e.g. higher emitted harmonics). Radiation emitted at the fundamental wavelength is 100 or more times the number of photons emitted in higher harmonics; selection of higher harmonics can be therefore critical. Multilayer (ML) mirrors that are able to provide high reflectivity peak at the desired harmonic wavelength while rejecting the fundamental have been designed and their application is foreseen to the FERMI@Elettra FEL beam transport system. The photon beam will be split into two and one of these will pass through a set of ML mirrors optimized for third harmonics selection; this scheme is also useable to realize a delay line in which the few nanosecond time delay will be controlled by changing the mirrors distance. A set of target wavelengths has been considered and multilayer structure materials have been selected. The MLs have been designed using a method based on the control of standing wave distribution at the fundamental and third harmonics wavelength, using a capping layer as a key element to achieve the willing rejection. Fabrication and test of such structures are foreseen.

High-brilliance home-lab X-ray sources: status and future

Introduction Modern microfocus X-ray sources define the state-of-the-art for a number of applications such as protein crystallography and smallangle scattering in the home lab. These sources have anode spot sizes of 100 μm or smaller. They are usually combined with Montel multilayer optics as beam-shaping devices that image the source spot onto the position of the sample, magnifiying the beam to a suitable size. Multilayer optics deliver a parallel or focused monochromatic beam. Below results of three different microfocus sources are shown: a sealed tube source, a rotating anode source, and a liquid metal jet X-ray source. The power densities of these three X-ray sources range from several kW/mm2 for the sealed tube source, to about 20 kW/mm2 for the rotating anode source, and to more than 500 kW/mm2 for the liquid metal jet X-ray source.

New developments in low-power beam-delivery systems with aspheric multilayer optics

New developments in low-power beam-delivery systems with aspheric multilayer optics

Secondary electron yield measurements of carbon covered multilayer optics

Carbon contamination on extreme ultraviolet (EUV) optics has been observed in EUV lithography. In this paper, we performed in situ monitoring of the build-up and removal of carbon contamination on Mo/Si EUV multilayers by measuring the secondary electron yield as a function of primary electron energy. An electron beam with an energy of 2keV was used to simulate the EUV radiation induced carbon contamination. For a clean EUV multilayer, the maximum secondary electron yield is about 1.5 electrons per primary electron at a primary electron energy of 467eV. The maximum yield reduced to about 1.05 at a primary electron energy of 322eV when the surface was covered by a non-uniform carbon layer with a maximum thickness of 7.7nm. By analyzing the change in the maximum secondary electron yield with the final carbon layer thickness, the limit of detection was estimated to be less than 0.1nm.

Soft X-ray imaging of thick carbon-based materials using the normal incidence multilayer optics

The high transparency of carbon-containing materials in the spectral region of “carbon window” ( λ ∼ 4.5–5 nm) introduces new opportunities for various soft X-ray microscopy applications. The development of efficient multilayer coated X-ray optics operating at the wavelengths of about 4.5 nm has stimulated a series of our imaging experiments to study thick biological and synthetic objects. Our experimental set-up consisted of a laser plasma X-ray source generated with the 2nd harmonics of Nd–glass laser, scandium-based thin-film filters, Co/C multilayer mirror and X-ray film UF-4. All soft X-ray images were produced with a single nanosecond exposure and demonstrated appropriate absorption contrast and detector-limited spatial resolution. A special attention was paid to the 3D imaging of thick low-density foam materials to be used in design of laser fusion targets.

Nitridation and contrast of B 4C/La interfaces and X-ray multilayer optics

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices such as nano-electronics, magneto-optical storage and multilayer X-ray optics. We show that with the nitridation of reactive B 4C/La interfaces, both the chemical and optical contrast can be greatly enhanced. Although interaction and diffusion of N 2 from the substrate towards the adlayer does occur, this surfactant mediated growth contributes to chemical and optical interface properties that enable major reflectivity improvements of multilayer optics for 6.7 < λ < 7.0 nm.

High throughput and wide field of view EUV microscope for blur-free one-shot imaging of living organisms

We present and demonstrate the use of an extreme ultraviolet (EUV) microscope that was developed in-house. Images are acquired using Bragg reflection multilayer optics and a laser-produced plasma light source. The upper-limit spatial resolution of the EUV microscope is 130 nm with a 10 ns exposure time and 250 x 250 microm(2) field of view. Resolution is superior to that of visible microscopes with the same size of field of view, and the exposure time is short enough to observe fine structures in-vivo. Observation of the cerebral cortex of a mouse is demonstrated.

One analytic form for four branches of the ABCD matrix

It is not always possible to diagonalize the optical ABCD matrix, but it can be brought into one of the four Wigner matrices by a similarity transformation. It is shown that the four Wigner matrices can be combined into one matrix with four branches. This result is illustrated in terms of optical activities, laser cavities, and multilayer optics.

Deposition and characterization of titania–silica optical multilayers by asymmetric bipolar pulsed dc sputtering of oxide targets

Titania–silica (TiO2/SiO2) optical multilayer structures have been conventionally deposited by reactive sputtering of metallic targets. In order to overcome the problems of arcing, target poisoning and low deposition rates encountered there, the application of oxide targets was investigated in this work with asymmetric bipolar pulsed dc magnetron sputtering. In order to evaluate the usefulness of this deposition methodology, an electric field optimized Fabry Perot mirror for He–Cd laser (λ = 441.6 nm) spectroscopy was deposited and characterized. For comparison, this mirror was also deposited by the reactive electron beam (EB) evaporation technique. The mirrors developed by the two complementary techniques were investigated for their microstructural and optical reflection properties invoking atomic force microscopy, ellipsometry, grazing incidence reflectometry and spectrophotometry. From these measurements the layer geometry, optical constants, mass density, topography, surface and interface roughness and disorder parameters were evaluated. The microstructural properties and spectral functional characteristics of the pulsed dc sputtered multilayer mirror were found to be distinctively superior to the EB deposited mirror. The knowledge gathered during this study has been utilized to develop a 21-layer high-pass edge filter for radio photoluminescence dosimetry.