Multilayer Optics Research Articles

Transient Cooling of Ultrathin Epitaxial Bi(111)-Films on Si(111) Upon Femtosecond Laser Excitation Studied by Ultrafast Reflection High Energy Electron Diffraction

AbstractWith time resolved ultrafast electron diffraction the cooling process across the interface between a thin film and the underlying substrate was studied after excitation with short laser pulses. From the exponential decay of the surface temperature evolution a thermal boundary conductance of 1430 W/(cm2K) is determined for a 9.7 nm thin Bi(111) film on Si(111). A linear dependence between laser fluence and initial temperature rise was measured for film-thicknesses between 2.5 nm and 34.5 nm. The ratio of initial temperature rise and laser fluence for different film-thicknesses is compared to a model taking multilayer optics into account. The data agree well with this model.

An analytical approach to estimating aberrations in curved multilayer optics for hard x-rays: 2 Interpretation and application to focusing experiments

Aberration effects are studied in parabolic and elliptic multilayer mirrors for hard x-rays, basing on a simple analytical approach. The interpretation of the underlying equations provides insight into fundamental limitations of the focusing properties of curved multilayers. Using realistic values for the multilayer parameters the potential impact on the broadening of the focal spot is evaluated. Within the limits of this model, systematic contributions to the spot size can be described. The work is complemented by a comparison with experimental results obtained with a W/B(4)C curved multilayer mirror.

Total reflection and multilayer optics for synchrotrons and free-electron lasers

Total reflection and multilayer optics for synchrotrons and free-electron lasers

Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics

Cr/Sc and Ni/V multilayers, intended as normal incidence soft x-ray mirrors and Brewster angle polarizers, have been synthesized by employing a novel modulated low-energy and high-flux ion assistance as a means of engineering the interfaces between the subnanometer layers on an atomic scale during magnetron sputter deposition. To reduce both roughness and intermixing, the ion energy was modulated within each layer. The flat and abrupt interfaces yielded soft x-ray mirrors with near-normal incidence reflectances of R = 20.7% at the Sc 2p absorption edge and R = 2.7% at the V 2p absorption edge. Multilayers optimized for the Brewster angle showed a reflectance of R = 26.7% and an extinction ratio of R(s)/R(p)=5450 for Cr/Sc and R = 10% and R(s)/R(p)=4190 for Ni/V. Transmission electron microscopy investigations showed an amorphous Cr/Sc structure with an accumulating high spatial frequency roughness. For Ni/V the initial growth mode is amorphous and then turns crystalline after approximately 1/3 of the total thickness, with an accumulating low spatial frequency roughness as a consequence. Elastic recoil detection analyses showed that N was the major impurity in both Cr/Sc and Ni/V with concentrations of 15 at. % and 9 at. %, respectively, but also O (3 at. % and 1.3 at. %) and C (0.5 at. % and 1.9 at. %) were present. Simulations of the possible normal incidence reflective properties in the soft x-ray range of 100-600 eV are given, predicting that reflectivities of more than 31% for Cr/Sc and 5.8% for Ni/V can be achieved if better control of the impurities and the deposition process is employed. The simulations also show that Cr/Sc is a good candidate for mirrors for the photon energies between the absorption edges of B (E = 188 eV) and Sc (E = 398.8 eV).

Characterization and comparison of X-ray focusing optics for ultrafast X-ray diffraction experiments

We have characterized and compared the performance of different types of multi-layer optics for the focusing of femtosecond X-ray pulses. Using X-ray pulses at 8 keV, from a laser-driven plasma source we have measured the spatial distribution of the diffracted X-rays directly after and in the focal plane of the various X-ray optical devices. For a Montel optic with 7.3× magnification we obtained the largest number of focused X-ray photons per unit angle. The performance of this optic in the X-ray diffraction experiment on a thin germanium film is demonstrated.

An analytical approach to estimating aberrations in curved multilayer optics for hard x-rays: 1. Derivation of caustic shapes

An analytical approach has been developed to derive aberration effects in parabolic and elliptic multilayer optics with weak interaction between photons and matter. The method is based on geometrical ray tracing including refraction effects up to the first order of the refractive index decrement delta. In the parabolic case, the derivation leads to simple parametric equations for the caustic shape. In the elliptic case, the analytical results more involved, but can be well approximated by the parabolic solution. Both geometries are compared with regard to the fundamental impact on their focusing properties.

Nanoscaled Multilayer Coatings for X‐Ray Optics

Incoatec develops and produces multilayer X-ray optics with single layers of a few nanometers thickness. These optics are used in X-ray diffractometers (XRD), X-ray fluorescence spectrometers (XRF), single crystal diffraction (SCD) applications and at synchrotron sources. In this contribution, details of the production of multilayer X-ray optics with sputter deposition methods are described.

EUV Sources for Lithographic Applications

AbstractSemiconductor device manufacturing is currently using excimer lasers as the light source for lithographic structuring. The wavelength of these ArF lasers is 193 nm and the high volume manufacturing of structures with 45 nm has started already. To further shrink the structure size to 32 nm and beyond, a reduction of the used wavelength is required for physical reasons. The next technology will be the extreme ultraviolet (EUV) lithography using light with 13.5 nm wavelength. Efficient optical elements like multi layer optics were developed in the last years using improvements in thin film technology on large area substrates with roughness in the sub­nanometer range. Sources for such light are plasma based sources in which the plasmas are generated either by electrical gas discharges or by pulsed laser radiation. In this paper we describe the discharge produced plasma (DPP) sources only because of their advantages concerning efficiency, simplicity, reliability and maturity.

Tuneable Fabry–Perot etalon for terahertz radiation

An indium tin oxide-clad liquid crystal filled Fabry–Perot etalon structure has been shown to act as an effective narrow-band filter at terahertz frequencies. An applied voltage, which controls the alignment of the nematic liquid crystal allows the refractive index of the core to be tuned. Transmission spectra show well-defined resonant peaks which shift in position when the alignment is changed from planar to homeotropic. The measured transmission spectra agree well with the results of a multilayer optics model and the birefringence of the liquid crystals over this frequency range are determined as Δn = 0.15(± 0.01) and Δn = 0.08(± 0.01) for E7 and ZLI 2293, respectively.

Application of Single and Dual Multilayer Optics for Powder X‐Ray Diffraction

The performance of parallel beam multilayer optics, including a parabolic multilayer Osmic MaxFlux GO‐13N and a flat custom multilayer, was evaluated experimentally and compared to Bragg‐Brentano and traditional ‘‘parallel beam’’ or ‘‘thin film’’ optical geometries. A novel arrangement of a parabolic multilayer in the incident beam with a flat multilayer in the diffracted beam functioning as an analyzer crystal was proven effective for powder diffraction applications. The dual‐optic configuration improves resolution while eliminating sample displacement and transparency errors as expected for a configuration with equatorial divergence below 100 arcseconds. Fundamental parameters fitting showed that the parabolic multilayer can be accurately modeled using a constant Gaussian function, while a long parallel‐plate soller collimator requires a constant hat function. No additional convolutions are necessary for the diffracted‐beam flat multilayer because of the lower acceptance angle.

Development of Optical Multilayer Thin Films and Their Application to Solar Cells

Increasing use of clean photovoltaic energy generation is being looked as a key measure to prevent global warming, but with a conversion efficiency of about 15%, solar cells are not yet up to the task. Moreover, the conversion efficiency of solar cells decreases with temperature rise caused by solar infrared radiation, and necessary visible radiation is reduced by 8% with the solar cell's cover glass. In this study we developed and evaluated optical multilayer thin films to reduce the infrared-caused temperature rise and to improve the transmission of visible light to solar cells. The optical multilayer thin films were designed using Essential Macleod simulation software, prepared with radio frequency (RF) sputtering equipment, and their transmission characteristics were evaluated. The in-operation temperature change and the current-voltage (I-V) characteristic curves of solar cells were measured with and without the optical multilayer thin films, and the results show that they suppressed the temperature rise and improved efficiency of solar cells.

Modern status and prospects of the development of methods of designing multilayer optical coatings

This paper discusses modern approaches to the design of multilayer optical coatings, based on the use of various modifications of the method of needle synthesis. The great possibilities of this method and the power of modern computer facilities make it possible to obtain practicable designs of the elements of multilayer optics with any complexity.

Dynamic control of visible radiation by a liquid crystal filled Fabry-Pérot etalon

A liquid crystal filled Fabry-Pérot etalon has been constructed to control the resonant transmission of electromagnetic radiation over the visible range of the spectrum. This has been achieved through the use of a 1.5μm thick homogeneously aligned liquid crystal layer in the core of a silver-clad etalon structure. Applying an electric field across the core reorientates the liquid crystal director and changes the refractive index for incident light polarized parallel to the rubbing direction. By measuring the transmitted intensity as a function of wavelength for a variety of applied voltages shifts in the positions of the resonant transmission modes of up to 80nm have been observed. In addition, these results have been compared to model data generated using a multilayer optics model to obtain the dispersion of the liquid crystal over the visible range of the electromagnetic spectrum.

Optical measurement of thermal deformation of multilayer optics under synchrotron radiation

An in situ optical technique to visualize surface distortions of the first monochromator crystal under synchrotron beam heat loading has been developed and applied to measure surface profiles of multilayer optics under white wiggler beam at the CHESS A2 beamline. Two identical multilayer structures deposited on Si and SiC substrates have been tested. Comparison of the reconstructed 3D heatbump profiles showed the surface distortions of the multilayer on SiC a factor of two smaller than the same multilayer on a Si substrate.

Correction to: "Study of Signal Processing for Optical Multi-Layer Disk" [Feb 07 840-844

In the above titled paper (ibid., vol 43, no. 2, pp. 840-844, Feb 07), portions of Tables I-IV were omitted. The correct tables are presented here.

Powerful 170-attosecond XUV pulses generated with few-cycle laser pulses and broadband multilayer optics

Single 170-as extreme ultraviolet (XUV) pulses delivering more than 106 photons/pulse at ∼100 eV at a repetition rate of 3 kHz are produced by ionizing neon with waveform-controlled sub-5 fs near-infrared (NIR) laser pulses and spectrally filtering the emerging near-cutoff high-harmonic continuum with a broadband, chirped multilayer molybdenum–silicon (Mo/Si) mirror.

D-10 Microfocusing X-ray Equipment for the Lab Diffractometer

Results of a new stationary microfocusing sealed tube X-ray source are presented. Measurements with the new low-maintenance, high-brilliance microfocus source IµS equipped with different two-dimensional beam shaping multilayer optics are shown. The comparison of IµS with typical sealed tube fine focus systems shows data of outstanding quality in diffractometry applications using a two-dimensional detector. A huge improvement in intensity and resolution by a factor of about 16 was observed. The IµS delivers very promising results especially for measurements of powders in transmission geometry. The focusing on the detector enables better crystallite statistics and better resolution. For some applications there are even intensity gain factors in the range of 100 achievable. For small angle scattering a factor of 5 in comparison to a typical sealed tube instrument was observed when using an IµS with optics for a parallel beam.

High resolution x-ray microscope

The authors present x-ray images of grid meshes and biological material obtained using a microspot x-ray tube with a multilayer optic and a 92-element parabolic compound refractive lens (CRL) made of a plastic containing only hydrogen and carbon. Images obtained using this apparatus are compared with those using an area source with a spherical lens and a spherical lens with multilayer condenser. The authors found the best image quality using the multilayer condenser with a parabolic lens, compared to images with a spherical lens and without the multilayer optics. The resolution was measured using a 155-element parabolic CRL and a multilayer condenser with the microspot tube. The experiment demonstrates about 1.1μm resolution.

Optimizing 13.5nm laser-produced tin plasma emission as a function of laser wavelength

Extreme ultraviolet lithography requires a light source at 13.5nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO2 lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO2 laser. The influence of reduced electron density in the CO2 laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.

The role of energetic ions in the development of multilayered X-ray reflection optics: An overview

Multilayer systems at nanometre scale have been applied as spectroscopic elements for wavelengths >1 nm and optical reflection systems in the short-wavelength region (<100 nm). Main requirements are a high optical contrast for the multilayer components in the wavelength region of application and a density profile with sharp interfaces between the components. Two sources are responsible for interface roughness, the development of surface roughness during deposition of the multilayer components and intermixing of these components at the interfaces. Etching a freshly deposited layer by low-energy ions has demonstrated to be successful in reducing the surface roughness of W on C, Ni on C and Si on Mo. Implantation of low-energy N + ions into Si has been applied to reduce the chemical reactivity at the interface with Ni. Formation of a carbide interlayer by implantation of Si with C + ions successfully prevented intermixing of the Mo on Si interfaces, improving the thermal stability of Mo/Si multilayers. Finally, a combination of implantation and annealing was applied to form Si/SiC multilayers.