Periodic Multilayers Research Articles

Tuning dielectric properties of sputtered BaTiO3 thin film capacitors via multilayering with SrTiO3

[Formula: see text]/[Formula: see text] (BTO/STO) multilayer films were successfully prepared on (La, Sr)[Formula: see text]-coated (100) [Formula: see text] substrates by using a radio-frequency (RF) magnetron sputtering process at [Formula: see text]C. Benefiting from the flexible deposition configuration of a multi-target sputtering system, we were able to tune the dielectric properties of the multilayer film by varying the number of multilayer periods [Formula: see text] and the individual layer thickness [Formula: see text]. It was found that, in a superlattice-like structure ([Formula: see text]=4 nm, [Formula: see text] 10 unit cells), the dielectric constant increased and the loss tangent decreased with an increasing [Formula: see text], especially in the high frequency range ([Formula: see text]Hz). This can be attributed to a reduced volumetric contribution to the dielectric property from the leaky interface capacitor layer, which lies between the multilayer film and the (La, Sr)[Formula: see text] electrode. On the other hand, as the individual layer thickness [Formula: see text] exceeds the superlattice limit ([Formula: see text]=8 nm, [Formula: see text] 20 unit cells), the superlattice strain effect disappeared and the dielectric constant value dropped by [Formula: see text]50%. However, owing to the reduced number of interfaces and associated defects, the dielectric loss of the multilayer film with a larger period was reduced significantly, as compared to its superlattice counterpart with the same thickness and more periods. The dielectric loss power density of the former was about one order of magnitude lower than that of the latter. These observations provide a solid foundation for using RF magnetron sputtering as an effective method to prepare various forms of multilayer film capacitors for integrated device applications.

Investigation of nanostructural and electronic properties of silicides intermetallic in Mo/Si interfaces of periodic multilayers and bilayer structures

Investigation of nanostructural and electronic properties of silicides intermetallic in Mo/Si interfaces of periodic multilayers and bilayer structures

Depth-resolved oxidational studies of Be/Al periodic multilayers investigated by X-ray photoelectron spectroscopy.

The quantification of surface and subsurface oxidation of Be/Al periodic multilayer mirrors due to exposure in the ambient atmosphere was investigated by depth-resolved X-ray photoelectron spectroscopy. The contribution of oxidation was lower for the thicker layer of Al in the periodic structures since the surface was less chemically reactive for the oxidation. This was investigated by finding the depth-resolved slope of the intensity ratio of metal/oxides (Be/BeOx and Al/AlOx) by analyzing the chemical shift of Al 1s and Be 1s photoelectrons. Furthermore, a well-resolved doublet chemical shift in the O 1s spectra indicated the formation of BeOx/AlOx and BeOH/AlOH oxides. The investigation showed that the subsurface and surface regions were dominated by metal-hydroxide (BeOH/AlOH) and metal-oxide (BeOx/AlOx) bonding, respectively, analyzed by the depth-resolved chemical shifts.

Microstructure and electrical transport properties of nanoscale [(CO40Fe40B20)34(SiO2)66/(In2O3)/C]46 multilayers

We investigated the role of microstructure and In2O3/C interlayer thickness on the electrical transport properties of [(Co40Fe40B20)34(SiO2)66/(In2O3)/C]46 multilayers prepared using ion-beam sputtering. These multilayers were characterized using an X-ray diffraction, X-ray reflectivity, impedance spectroscopy, and magnetoresistive measurements. The X-ray diffraction data showed that regardless of the layer thickness, all components of the multilayers are X-ray amorphous. Fitting X-ray reflectivity data, multilayer periodicities are extracted and layers thicknesses, densities and roughnesses are determined. Impedance spectroscopy has shown a resistive-capacitive coupling between electrically conductive ferromagnetic CoFeB clusters which corresponds to the model of a prepercolation composite. For the thinnest multilayer with nonmagnetic In2O3/C interlayer thickness of about 1.6 nm, we managed to achieve a magnetoresistance of about 0.8% at room temperature and 3.2% at cryogenic temperature.

Al/Mo/SiC multilayer diffraction gratings with broadband efficiency in the extreme ultraviolet.

Al/Mo/SiC periodic and aperiodic multilayers were optimized and deposited on high groove density gratings to achieve broadband efficiency in the extreme ultraviolet (EUV). Grating efficiencies were measured by monochromatic synchrotron radiation under 5° and 45° incident angles in the wavelength ranges 17-25 nm and 22-31 nm, respectively. We study the influence of the number of deposited periods on the initial trapezoidal profile and the EUV diffraction efficiency. We propose models of periodic and aperiodic coatings based on a combination of characterizations and compare rigorous coupled-wave analysis (RCWA) simulations with experimental data. We demonstrate the possibility to select the optimal balance between peak efficiency and bandwidth by adjusting the number of periods in the case of periodic multilayer grating. We also report unprecedented broadband diffraction efficiency with an Al/Mo/SiC aperiodic multilayer grating.

Narrowband aperiodic multilayers with flat spectral response for plasma diagnostics

Aperiodic W/Si multilayer mirrors with the narrow bandwidth and the flat spectral response are presented as X-ray reflectors operated at 8.05 keV for plasma diagnostics. In this manuscript, aperiodic W/Si samples with different periods and thickness ranges were prepared on ultra-smooth silicon (100) substrates by direct-current magnetron sputtering. Grazing incidence X-ray reflection measurements were conducted to characterize the thickness distribution and the interfacial width of multilayer samples. Depth profiles of major elements in a periodic multilayer were investigated using time-of-flight secondary ion mass spectrometry to qualitatively estimate the effect of impurities from the residual gas. Cross-sectional transmission electron microscope images of the aperiodic multilayer indicate the asymmetric interfaces with the increasing interfacial width. The cumulative roughness model and the diffusion layer model were employed to fit the thickness sequence, interfacial roughness and diffusion zone width from GIXRR curves for further optimization with the given interfacial effect. The reflection spectrum of the optimal W/Si sample was measured at the beamline BL09B of Shanghai Synchrotron Radiation Facility. The measured results of the aperiodic W/Si multilayer exhibit the (56.2 ± 1.3)% reflectivity, 936eV bandwidth and 581eV flat-band region.

Methods of Coupled Wave Thicknesses and Equivalent Substitutions for the Exact Analytical Solution of the Problems of Synthesis of Multilayer Periodic Structures with Specified Amplitude–Phase Characteristics ($$\pi$$-Structures)

Methods of Coupled Wave Thicknesses and Equivalent Substitutions for the Exact Analytical Solution of the Problems of Synthesis of Multilayer Periodic Structures with Specified Amplitude–Phase Characteristics ($$\pi$$-Structures)

A Multichannel Superconductor-Based Photonic Crystal Optical Filter Tunable in the Visible and Telecom Windows at Cryogenic Temperature

We design and evaluate the performance of a one-dimensional photonic crystal (PhC) optical filter that comprises the integration of alternating layers of a barium titanate ferroelectric (BaTiO3) and an yttrium oxide dielectric (Y2O3), with a critical high-temperature superconductor defect, yttrium–barium–copper oxide (YBa2Cu3O7−X), resulting in the (BTO/Y2O3)N/YBCO/(Y2O3/BTO)N multilayered nanostructure array. Here, we demonstrate that such a nanosystem allows for routing and switching optical signals at well-defined wavelengths, either in the visible or the near-infrared spectral regions—the latter as required in optical telecommunication channels. By tailoring the superconductor layer thickness, the multilayer period number N, the temperature and the direction of incident light, we provide a computational test-bed for the implementation of a PhC-optical filter that works for both wavelength-division multiplexing in the 300–800 nm region and for high-Q filtering in the 1300–1800 nm range. In particular, we show that the filter’s quality factor of resonances Q increases with the number of multilayers—it shows an exponential scaling with N (e.g., in the telecom C-band, Q≈470 for N=8). In the telecom region, the light transmission slightly shifts towards longer wavelengths with increasing temperature; this occurs at an average rate of 0.25 nm/K in the range from 20 to 80 K, for N=5 at normal incidence. This rate can be enhanced, and the filter can thus be used for temperature sensing in the NIR range. Moreover, the filter works at cryogenic temperature environments (e.g., in outer space conditions) and can be integrated into either photonic and optoelectronic circuits or in devices for the transmission of information.

Enhancing the Energy‐Storage Density and Breakdown Strength in PbZrO3/Pb0.9La0.1Zr0.52Ti0.48O3‐Derived Antiferroelectric/Relaxor‐Ferroelectric Multilayers

AbstractMultilayer thin‐film dielectric capacitors with high energy‐storage performance and fast charge/discharge speed have significantly affected the development of miniaturized pulsed‐power devices. Here, the interfacial strain in epitaxial multilayers of antiferroelectric PbZrO3 and relaxor‐ferroelectric Pb0.9La0.1Zr0.52Ti0.48O3 is shown to significantly enhance the maximum polarization of the multilayer thin‐film capacitors, beyond that of the composing individual layers. Insights obtained from atomically resolved energy‐dispersive X‐ray spectroscopy and high‐resolution X‐ray diffraction analysis of the interface and domain structure are used to develop phenomenological models that explain the observed trends in breakdown strength and energy‐storage density as a function of multilayer period number. The underlying mechanism is the mechanical coupling between the layers that depends on the individual layer thicknesses. These factors result in a strongly enhanced recoverable energy‐storage density (increased by a factor of 4 to ≈128.4 J cm−3) with high efficiency (≈81.2%). Moreover, the multilayer films show almost fatigue‐free energy‐storage performance after 1010 switching cycles, even at elevated temperatures up to 220 °C, demonstrating their robustness. The outstanding properties show the great potential of epitaxial multilayers for energy‐storage applications, due to the well‐defined separate layers and coupling of properties across the interfaces, not present in ceramic composites.

New Constraints on Dark Photon Dark Matter with Superconducting Nanowire Detectors in an Optical Haloscope.

Uncovering the nature of dark matter is one of the most important goals of particle physics. Light bosonic particles, such as the dark photon, are well-motivated candidates: they are generally long-lived, weakly interacting, and naturally produced in the early universe. In this work, we report on Light A^{'} Multilayer Periodic Optical SNSPD Target, a proof-of-concept experiment searching for dark photon dark matter in the eV mass range, via coherent absorption in a multilayer dielectric haloscope. Using a superconducting nanowire single-photon detector (SNSPD), we achieve efficient photon detection with a dark count rate of ∼6×10^{-6} counts/s. We find no evidence for dark photon dark matter in the mass range of ∼0.7-0.8 eV with kinetic mixing ε≳10^{-12}, improving existing limits in ε by up to a factor of 2. With future improvements to SNSPDs, our architecture could probe significant new parameter space for dark photon and axion dark matter in the meV to 10eV mass range.

Laser MBE growth of cobalt-platinum multilayers with perpendicular magnetic anisotropy

Periodic multilayers with perpendicular magnetic anisotropy (PMA) attract a lot of attention nowadays being fundamentally interesting from the point of view of interface magnetism. They also provide a suitable test bench for the studies of spatially resolved magnetization dynamics at picosecond time scale conducted at x-ray free electron laser (XFEL) facilities. In the present paper we have developed a novel laser molecular beam epitaxy (LMBE) approach to grow Co/Pt multilayers on crystalline Al2O3 (0001) substrates. By applying Kerr-effect magnetometry to the samples fabricated at different conditions, we have found it essential for the appearance of PMA, to perform metal deposition in 0.03 mbar of argon and to keep Co layer thickness below 4 Å. Along with magnetic studies, we have investigated crystal structure and depth resolved layer composition of the fabricated Co/Pt multilayers by applying electron diffraction, x-ray diffraction and x-ray reflectometry. The combined atomic-force/magnetic-force microscopy studies have revealed a very low surface roughness of down to 1 Å (for the samples grown at properly optimized growth conditions) and a pronounced labyrinth pattern of magnetic domains with a periodicity of 250 nm appropriate for XFEL studies of ultrafast optical magnetization. The presented LMBE approach to fabricate magnetically ordered heterostructures with a pronounced PMA is supposed to be an important milestone on the way of facilitating future design of nanomaterials for applications in magnetic memories and for fundamental studies of ultrafast magnetization dynamics.

Cross-sectional high-resolution transmission electron microscopy at Mo/Si multilayer stacks

Abstract Using a Mo/Si multilayer stack, capabilities and limits of high-resolution transmission electron microscopy with respect to thin film analysis are pointed out. Image processing is shown to provide non-subjective criteria for the determination of layer thicknesses. In comparison to measurements by X-ray reflectometry, an integrating method capable of determining multilayer periodicities, preparation and observation artefacts in transmission electron microscopy is discussed. Special emphasis is placed on cleavage as a powerful method for TEM sample preparation, its advantages and disadvantages.

Hybrid magnetron sputtering of ceramic superlattices for application in a next generation of combustion engines

A hybrid magnetron sputtering process (dcMS/HiPIMS) was developed to manufacture nanostructured CrN/Cr1-xAlxN multilayers, motivated by improving the low-emission efficiency when applied on gas-nitrided diesel piston rings of a next-generation of combustion engines. In order to improve the mechanical, tribological, and corrosion behavior of the multilayers, the hybrid dcMS/HiPIMS process was designed by selecting the optimal sputtering procedure applied to AISI 440 base steel. The effect of substrate bias and carousel rotational speed on the phase composition, crystallographic texture, residual stresses, surface roughness, coating periodicity and densification, instrumented hardness, elastic modulus, as well as wear and corrosion resistance was determined. The results have demonstrated that hybrid magnetron sputtering produces multilayers with a superlattice structure, which outperforms commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation. Also, multilayer periodicities in the range of 5 to 10 nm yield the best tribological performance under bench tests for the piston ring/cylinder liner system.

A volume plasmon blueshift in thin silicon films embedded within Be/Si periodic multilayer mirrors.

Microstructural properties of the beryllium (Be) and silicon (Si) in periodic multilayer mirrors Be/Si with the variation of film thickness were comprehensively determined by Raman scattering. For the thinner films, the structure of Be evolved in the amorphous phase, and it was transformed into the polycrystalline phase for thicker films. The Si films in the periodic structure were condensed into the amorphous phase. The small fraction of nanocrystalline Si particles was distributed within the amorphous phase. A shake-up satellite peak of Si 2s photoelectrons was observed in X-ray photoelectron spectroscopy which suggested the excitation of a plasmon in Si films embedded within Be/Si periodic multilayers. The energy of plasmons was sensitive to the film thickness of Si in the periods which directly corresponds to the particle size. The binding energy of the satellite peak of Si 2s photoelectrons was blueshifted (higher energy) with a decrease in the particle size. This was explained by size dependent quantum confinement of particles.

Pulse interactions in periodic and genetic-algorithm-optimized aperiodic epsilon-near-zero multilayers

The epsilon-near-zero (ENZ) multilayer with a vanishing real part of effective permittivity has been proven to have a reflective cutoff effect and an enhanced nonlinear optical response in its ENZ region, making the pulse propagation attract great interest. Here, with the introduction of genetic algorithms (GAs) as a tool to obtain the target spectra, the pulse interactions in A g − S i O 2 alternating stacked multilayers under the ENZ wavelength are numerically studied. It is found that in the original periodic ENZ multilayer, the temporal shapes and spectra first experience a significant attenuation, mainly because of the absorption loss. Afterward, a second peak appears along the propagation path because of localizations and resonances between the layers together with the combined effect of dispersion and nonlinearity. The presented pulse interaction dynamics can provide an insight into the interaction patterns in a periodic ENZ multilayer sample. We use the GAs to obtain a new ENZ multilayer with the same total thicknesses, aperiodic structure, and enhanced reflective properties. The pulse propagation is presented as the physical evidence to further ensure that the optimization has worked well. In this aperiodic sample, the normalized intensity rapidly decreases and the energy is mostly localized near the surface, which indicates the pulse achieves nearly total reflection. Thus, the effect of GA optimization has been confirmed; that is, under extremely high reflection, the pulse can barely propagate through the sample. This optimization toward the reflection spectra of ENZ multilayers could pave the way for a possible design of experimental schemes in a laser cavity, and the cutoff effect of that also could lead to potential applications of pulse shapers and micro/nano Fabry–Perot resonators.

Investigation of microstructure and reflectivity of thermally annealed Mo/Be and W/Be multilayer mirrors

Periodic multilayers of Mo/Be and W/Be are important classes of mirrors operating in extreme ultraviolet and soft X-ray region. The phase and microstructural stability of these mirrors upon thermal annealing were investigated by Raman scattering and X-ray diffraction. Both the absorbers (Mo and W) and spacer (Be) layers in the periodic multilayers existed in the polycrystalline phase, which remains stable upon thermal annealing of temperature up to 573 K. The reflectivity value of the thermally annealed mirrors was fairly stable and similar as compared to as-deposited multilayer mirrors. This was explained by the phase and microstructural stability of multilayer mirrors upon thermal annealing.

Structural and Optical Properties of a Hybrid Material Based on Tin Oxides and Multilayer Periodic Structures with Pseudomorphic GeSiSn Layers

Structural and Optical Properties of a Hybrid Material Based on Tin Oxides and Multilayer Periodic Structures with Pseudomorphic GeSiSn Layers

Singular optical characteristics generated by Fibonacci multilayers composed of [formula omitted]-symmetric elements

In this paper, a class of one-dimensional (1D) Fibonacci quasi-periodic multilayers composed of two parity-time-symmetric (PT-symmetric) elements are designed. Their scattering spectra, transparencies, invisibilities, and other singular optical properties are investigated in detail. It is found that three types of new systematic phases, ten types of new unidirectional transparencies, two types of new bidirectional transparencies and one type of new bidirectional invisibility are created by this class of interesting systems, which possess more types compared with the PT-symmetric periodic multilayers and the Thue–Morse multilayers composed of PT-symmetric elements. It can be seen that although the order degree of the Fibonacci multilayers is lower than that of the other two systems, their types of systematic phases, transparencies, and invisibilities are obtained, their types of systematic phases, transparencies, and invisibilities are more abundant. This proves that, as the order degree of the PT-symmetric system decreases, its types of singular optical properties become more abundant. This work sheds some light on the PT-symmetric optical structures and Fibonacci sequence, offering the possibility to widen their application field. Moreover, it provides a theoretical basis to design new optical devices.

Microstructure and properties of Ti2AlN thin film synthesized by vacuum annealing of high power pulsed magnetron sputtering deposited Ti/AlN multilayers

The (002) texture, compactness, and smoothness Ti 2 AlN thin films render them promising for many potential applications, especially in the surface modification of wear-resistant components. In this study, Ti 2 AlN thin films were fabricated by the vacuum annealing of Ti/AlN multilayers deposited by high power pulsed magnetron sputtering (HPPMS). The influence of the multilayer modulation ratio and modulation period of Ti/AlN on the microstructure and properties of the Ti 2 AlN thin film were explored. The results indicate that a Ti/AlN modulation ratio close to 6:4 and period less than 30 nm are appropriate for yielding high-quality crystallized Ti 2 AlN thin films. The microstructure of the Ti 2 AlN thin film is (002) textured, nanocrystalline, smooth, and compact, which benefits from the HPPMS technique. The Ti 2 AlN thin film adheres well to the substrate and has a hardness of 32.5 ± 2.1 GPa and has a friction coefficient of 0.15 while tested with a Si 3 N 4 friction pair. • The modulation ratio and period are critical for Ti 2 AlN thin film synthesis. • HPPMS improves the (002) texture and compactness of the Ti 2 AlN thin film. • HPPMS enhances the adhesion, hardness and wear resistance of the Ti 2 AlN thin film.

Multilayer Reflective Coatings for BEUV Lithography: A Review.

The development of microelectronics is always driven by reducing transistor size and increasing integration, from the initial micron-scale to the current few nanometers. The photolithography technique for manufacturing the transistor needs to reduce the wavelength of the optical wave, from ultraviolet to the extreme ultraviolet radiation. One approach toward decreasing the working wavelength is using lithography based on beyond extreme ultraviolet radiation (BEUV) with a wavelength around 7 nm. The BEUV lithography relies on advanced reflective optics such as periodic multilayer film X-ray mirrors (PMMs). PMMs are artificial Bragg crystals having alternate layers of “light” and “heavy” materials. The periodicity of such a structure is relatively half of the working wavelength. Because a BEUV lithographical system contains at least 10 mirrors, the optics’ reflectivity becomes a crucial point. The increasing of a single mirror’s reflectivity by 10% will increase the system’s overall throughput six-fold. In this work, the properties and development status of PMMs, particularly for BEUV lithography, were reviewed to gain a better understanding of their advantages and limitations. Emphasis was given to materials, design concepts, structure, deposition method, and optical characteristics of these coatings.