Thin-film Resonators Research Articles

Attenuation of Spin Precession in Manganite/Normal Metal Heterostructures

Abstract—Temperature dependence of attenuation of magnetic spin precession in two-layer structures with a Pt top layer based on a La0.7Sr0.3MnO3 (LSMO) epitaxial manganite film is studied by measuring the width of a ferromagnetic resonance (FMR) line. Ferromagnetic resonance in thin ferromagnetic manganite films is used for the creation of a spin current at the interface between the metallic and ferromagnetic layers. A significant increase in a width of a line in FMR spectrum in two-layer structures due to generation of a spin current, heterogeneity of a ferromagnetic layer, two-magnon scattering, and eddy current is discussed.

Towards an on-chip optical microsystem for spectroscopic detection of gastrointestinal dysplasia

This paper presents a CMOS optical microsystem with a 4 × 4 photodiodes array and their readout electronics, based on 16 light-to-frequency converters, and 16 high selective optical filters, for spectrophotometric measurement of diffuse reflectance and fluorescence signals, applied to the detection of gastrointestinal dysplasia. The photodiodes array is based on n+/p-epilayer junction silicon photodiodes. Their readout electronics outputs a digital signal, with a frequency proportional to the photodiode current, featuring a sensitivity of 26 Hz/nA at 550 nm, a spectral resolution of 9 MHz and a power consumption of 1 mW. The optical filters are based on 16 thin-film narrow-band Fabry-Perot resonators, in which dielectric mirrors are used. They feature high transmittances and low full-width-half-maximum. Experimental measurements, using phantoms representative of the main absorbing, scattering and fluorescence properties of gastrointestinal tissues, proved the viability of the CMOS optical microsystem with the optical filters to extract those signals, when comparing the obtained results with commercial equipment. The implemented apparatus is ready to be used as a portable system on a surgery room to verify the total removing of gastrointestinal cancer tissue. Moreover, the developed approach is a step forward in the implementation of a gastrointestinal dysplasia detection miniaturized tool.

Near-unity, full-spectrum, nanoscale solar absorbers and near-perfect blackbody emitters

The design of sub-wavelength structure with full-spectrum near-unity solar absorption is a long-sought-after goal of crucial importance for optoelectronic materials and technology. To date, numerous attempts to tackle this problem consisted either of using stronger absorption-but narrowband or the broader spectrum-but moderate light trapping mechanisms. Herein, a novel strategy that achieves perfect absorption for solar energy in the full-spectrum range of the sun's radiance is presented by the thin-film refractory metal resonators. This impressive absorption mainly stems from the cooperative effect of strong plasmonic resonances and the intrinsic broadband spectral responses by the refractory metals, such as Ti, V, W, etc. The full-spectrum weighted solar absorption efficiency is exceeding 98%, showing a near-unity light trapping for the sun's radiation. Moreover, excellent thermal emitting with the spectral averaged efficiency ~ 91% is achieved in the wavelength range (280–4000 nm) by the W-based absorber, suggesting a platform for near-perfect blackbody emitting source. More importantly, the investigations on achieving full-spectrum solar absorbers and thermal emitters provide new insight on the mechanism and philosophy for the design. Just like the proverb, in order to catch bandits, the first thing is to catch the ringleader. As for the purpose of achieving full-spectrum near-unity absorbers or radiators, the key point is to perfectly trap or excite the solar/thermal power in the main distribution ranges for the sunlight or the blackbody radiation. Accordingly, these attractive properties and findings suggest that the investigation and the related full-spectrum solar absorbers and blackbody radiator might have promising applications in the fields related to energy harvesting and conversion.

Ferromagnetic resonance in thin films studied via cross-validation of numerical solutions of the Smit-Beljers equation: Application to (Ga,Mn)As

(Dated: August 3, 2018) The new method of numerical analysis of experimental ferromagnetic resonance (FMR) spectra in thin films is developed and applied to (Ga,Mn)As thin films. Specifically, it starts with the finding of numerical solutions of Smit-Beljers (SB) equation and continues with their subsequent statistical analysis within the cross-validation (CV) approach taken from machine learning techniques. As a result of this treatment, we are able to reinterpret the available FMR experimental results in diluted ferromagnetic semiconductor (Ga,Mn)As thin films with the resulting determination of magnetocrystalline anisotropy constants. The outcome of CV analysis points out that it is necessary to take into account terms describing the bulk cubic anisotropy up to the fourth order to reproduce FMR experimental results for (Ga,Mn)As correctly. This finding contradicts the wide-spread conviction in the literature that only first order cubic anisotropy term is important in this material. We also provide numerical values of these higher order cubic anisotropy constants for (Ga,Mn)As thin films resulting from SB-CV approach.

Role of gallium diffusion in the formation of a magnetically dead layer at the Y3Fe5O12/Gd3Ga5O12 epitaxial interface

We have clarified the origin of magnetically dead interface layer formed in yttrium iron garnet (YIG) films grown at above 700{\deg}C onto gadolinium gallium garnet (GGG) substrate by means of laser molecular beam epitaxy. The diffusion-assisted formation of a Ga-rich region at the YIG / GGG interface is demonstrated by means of composition depth profiling performed by X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and X-ray and neutron reflectometry. Our finding is in sharp contrast to the earlier expressed assumption that Gd acts as a migrant element in the YIG/GGG system. We further correlate the presence of Ga-rich transition layer with considerable quenching of ferromagnetic resonance and spin wave propagation in thin YIG films. Finally, we clarify the origin of the enigmatic low-density overlayer that is often observed in neutron and X-ray reflectometry studies of the YIG / GGG epitaxial system.

Forced coupling vibration analysis of FBAR based on two-dimensional equations associated with state-vector approach

In our previous work, a system of two-dimensional equations for piezoelectric thin-film acoustic wave resonators (FBAR) has been derived and then successfully applied on the free vibration analysis of a finite FBAR plate. In this paper, we analyzed the forced vibrations of FBAR with alternating voltage applied on its electrodes. The derived two dimensional equations were simplified based on straight-crested wave approximations and were rewritten into matrix formalism by state-vector approach. With the knowledge of matrix function, the state-vector equation was successfully solved. Results of admittance were obtained with the dependence on the driving frequency and the aspect ratio. The obtained figure was compared with the frequency spectra obtained in free vibration analysis. Different aspect ratios and quality factors were taken to study the effects of them on the admittance. It is shown that admittance is highly influenced by mode couplings. Thus the work in this paper will be important for the thorough understanding of the coupling vibration of FBAR and its optimization design.

Mode couplings in high-frequency thickness-extensional vibrations of ZnO thin film resonator based on weak boundary condition

In this paper, the mode coupling vibration of finite ZnO thin film resonator (FBAR) with its c-axis along the thickness direction operating at the thickness-extensional mode is studied. The dispersion curve of unbounded fully-electroded ZnO thin film indicates that the thickness-extensional mode couples to two unwanted spurious modes. Since the displacement solutions consisting of the sum of three mode branches in the dispersion curve have satisfied the differential equations and boundary conditions on the top and bottom surfaces exactly, the substitution of them into Hamilton principle as weak boundary condition (WBC) can give an integral boundary condition across plate thickness at the side edge of ZnO thin film resonator. Two other WBCs are also employed to study the same coupling problem to prove the validity of Hamilton principle. The frequency spectra obtained through all three WBCs indicate that the extent of mode couplings is sensitive to plate length/thickness ratios. The desirable values of plate aspect ratios where thickness-extensional mode weakly couples to two spurious modes are all located at the flat part of the obtained frequency spectra. Besides, the frequency spectra obtained through Hamilton principle include those obtained through other two WBCs because the mathematical expressions of Hamilton principle contain all terms in other two WBCs. The frequency spectra predicted by Hamilton principle have wider flat part than those from other WBCs providing more structural choices for device designers. These obtained results provide a significant guidance to the design and optimization of FBARs.

Surface Plasmon Resonance of Au Thin Films Modified By Pt and Pd Monolayer Catalyst

Surface plasmons (SP’s) or surface plasmon polaritons are longitudinal electromagnetic waves which propagate at the interface between a metal and a dielectric. They are localized in the interface and are sensitive to the optical properties of the materials comprising the interfacial region. As such, the SP present a unique probe to study the electrochemical interface and double layer [[1],[2]].Typical plasmonic metals/electrodes are Au and Ag thin films, which have been a subject of studies where the SPs have been used to probe the electrochemical processes such as adsorption and underpotential deposition [1,[3],[4]]. The most recent developments indicate that the SPs can be used to enhance certain electro-catalytic and photocatalytic reactions [[5]]. In this report, we present the results investigating the catalyst monolayer modification effect on plasmon resonance of Au thin films. The experiments are conducted using an attenuated total reflection arrangement in which p-polarized light is incident through a prism onto a thin (-400 A) Au film deposited on the mica substrate. (Kretschmann configuration [[6]]). The angle of incidence on the base of the prism is greater than the critical angle for the prism: electrolyte interface and SPs are excited by the evanescent wave generated under these conditions of total internal reflection. The excitation is manifested by a decrease in the intensity of reflected light. The Pd monolayer on Au were electrodeposited using procedure reported by Kolbe et al [[7],[8]], while the Pt submonolayer/monolayers were deposited on Au using Surface Limited Redox Replacement (SLRR) of Pb UPD monolayer [[9]]. The plasmon resonance frequency of Au(hkl), PdML/Au(hkl) and PtML/Au(hkl) and PtSML/Au(hkl) were investigated as a function of the applied potential in the range between -0.24 V to 0.4 V vs. SCE. The comparative analysis, between Au and catalyst monolayer modified Au(hkl) samples indicate that SP resonant frequency change is induced by both; surface charge and adsorption of H on the catalyst monolayer surface in the UPD region. The latter effect is quantified using subtractive analysis between the Au and catalyst modified Au surface and solutions with different pH. In conclusion, we present a simple model describing the catalyst monolayer effect on plasmon resonance of Au films. [1] J.G. Gordon II and S. Ernst, Surface Science, 101 (1980) 499 [2] R. Kotz et al, Surface Science, 69 (1977) 359 [3] D.M. Kolb, D. Leutloff and M. Prasnyski, Surface Science, 47 (1975) 622 [4] A. Bewick, and B. Thomas, J. Electroanalytical Chem., 65 (1975) 911 [5] S. Linic, U. Aslam, C. Boerigter and M. Morabito, Nature Materials, 14, (2015) 567. [6] E. Kretschmann and H. Raether, Z. Natutforsch. 23a (1968) 2135. [7] L.A. Kibler, M. Kleinert, R. Randler, D.M. Kolb, Surface Science, 443 (1999) 19. [8] J. Tang, M. Petri, L.A. Kibler, D.M. Kolb, Electrochimica Acta, 51, (2005) 125 [9] K. Sasaki et al, Electrochim. Acta, 55, (2010) 2645.

The influence of dielectric environment on the localized surface plasmon resonance of silver-based composite thin films

Ag-based thin films with different topography were prepared by annealing process and laser irradiation, respectively. The tunability of localized surface plasmon resonance (LSPR) was realized by adjusting the cover layer thickness of ITO or TiO2. The effect of dielectric environment of Ag-based composite thin films on structure, surface morphology and optical property was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), UV-VIS-NIR double beam spectrometer and Raman system, respectively. With the thickness of dielectric layer increasing, the topography of as-irradiated Ag-based thin films became smoother while the as-annealed Ag-based thin films had a rougher surface. LSPR absorption of both ITO/Ag and TiO2/Ag bilayers showed red shift with the thickness of dielectric layer increasing. The electromagnetic field coupling between dielectric layers and Ag thin films contributed to increase significantly the sensitivity of surface enhanced Raman scattering (SERS). Additionally, the result of finite-difference time-domain (FDTD) simulation was in good agreement with that of the experiment.

Optoelectronic correlations for gold thin films in different annealing temperature

The manufacturing, characterization, and modification of noble nanomaterials such as gold have recently drawn important attention because of their unique characteristics that make them useful in technological applications. In some cases, we need special bulk properties in small objects or some properties should be eliminated in that scale and we must modify them. The mainstream of this project is to decrease surface resistance at an effective annealing temperature and to provide a comparable correlation between surface resistance and surface plasmon resonance (SPR) in gold thin films. Our experiments clearly explain the well-known dependence of optical and electrical properties of gold thin films on annealing temperature. A relation between absorption spectrum and electrical surface resistance in gold thin films have been found. It is understood that annealing temperature of 300° centigrade is a more reduction of surface resistance due to increasing of island size and participating more electrons in conduction band; In this time, the electrical resistance in nanoscale is tended to bulk resistance and plasmon peak is entirely eliminated. The surface resistance is decreased from 50 MΩ to about 5 KΩ. The plasmon absorption peak showed a significant blueshift with increasing annealing temperature at 500° centigrade in comparison with the early sample (unannealed thin-film).

Trapped-Energy Thickness-Extensional Mode of a Partially Electroded ZnO Thin-Film Resonator.

Free and forced vibration analysis of ZnO thin-film resonator operating with trapped-energy thickness-extensional (TE) mode is performed based on the dispersion curves for both the unbounded fully electroded and unelectroded films. The thickness solutions to the free vibration problem consist of the mode branches of the dispersion curves for the electroded and the unelectroded regions, respectively. The mode branches in the unelectroded region that carry energy away from the vibration zone are neglected because this effective energy loss corresponds to a complex frequency in the frequency spectrum. Since the thickness solutions in each region have satisfied the differential equations and the boundary conditions on the major surfaces exactly, the substitution of the thickness solutions into the modified Hamilton variational principle derived by Tiersten gives an approximate continuity condition in the form of integral over the thickness of the resonator at the interface between the electroded and unelectroded regions. The stationary condition of the integral continuity condition leads to a system of homogeneous linear equations, which determines the frequency spectrum ranging from the first TE cutoff frequency of the fully electroded film to that of the unelectroded film where the conventional trapped-energy vibration occurs. Forced vibration analysis of ZnO thin film driven into TE mode by applying a voltage to the top and bottom electrodes is also performed, which further verifies the validity of the obtained results from the free vibration analysis.

Analysis of Characteristics of Al MKID Resonators

We have prepared two kinds of Al resonators using thin films made by evaporation or sputtering and studied temperature behavior of their quality factors and resonance frequencies with the help of the extended Mattis-Bardeen (M-B) equations and its approximated analytical expressions. We have found that temperature behavior of both the internal quality factor and resonance frequency shift measured in evaporated Al thin-film resonators are well agreed with those calculated by the analytical expressions of the complex conductivity given by the M-B theory. In the Al thin film resonators made by sputtering, the internal quality factor and resonance frequency shift show a peak and a bump near 0.17 K in the respective temperature dependence. It is found that inverse of the internal quality factor is well approximated by a-b*log(T) below 0.15 K, where T is the temperature. This type of temperature dependence strongly indicates the existence of the magnetic impurity scattering of residual quasiparticles due to the Kondo effect. It is shown that temperature dependence of the internal quality factor and resonance frequency shift observed in the sputtered Al resonators can be well fitted by the theory taking the Kondo effect and kinetic inductance of the residual quasiparticles into account.

Surface plasmon resonance and nonlinear optical behavior of pulsed laser-deposited semitransparent nanostructured copper thin films

In this paper, surface plasmon resonance (SPR) and nonlinear optical properties of semitransparent nanostructured copper thin films fabricated on the glass substrate at 400 °C by pulsed laser deposition technique are reported. The thickness, linear absorption coefficient and linear refractive index of the films were measured by spectroscopic ellipsometer. The average particle size as measured via atomic force microscope was in the range of 12.84–26.02 nm for the deposition time ranging from 5 to 10 min, respectively. X-ray diffraction spectra revealed the formation of Cu (111) and Cu (200) planes. All these thin films exhibited broad SPR peak. The third-order optical nonlinearity of all the samples was investigated via modified z-scan technique using cw laser at a wavelength of 632.8 nm. The open aperture z-scan spectra of Cu thin film deposited for 5 min duration exhibited reverse saturation absorption whereas all the other samples displayed saturation absorption behavior. The nonlinear refractive index coefficient of these films showed a positive sign having the magnitude of the order of 10− 4 cm/W. The real and imaginary parts of susceptibilities were also calculated from the z-scan data and found to be of the order of 10− 6 esu.

Excitation of Ferromagnetic Resonance Using Surface Acoustic Waves

SUMMARYMechanical rotation of a crystal lattice in ferromagnetic materials can be energetically coupled with its magnetization via magnetoelastic coupling or spin rotation coupling. Surface acoustic wave (SAW) in piezoelectric materials is one of the promising candidates to realize the mechanical excitation of magnetization dynamics. In order to understand the mechanical rotation induced magnetization dynamics quantitatively, we examined the ferromagnetic resonance in an Ni film using a SAW in a LiNbO3 substrate. By decreasing a period of interdigital transducer as short as 4 μm which is one‐fifth of the previous work by Weiler [M. Weiler and co‐workers, Elastically driven ferromagnetic resonance in Nickel thin films. Phys Rev Lett 106, 117601 (2011)], the fundamental frequency of SAW could be higher than 800 MHz. From the dependence of microwave absorption on the angle between the magnetization and the wave vector of SAW, it was confirmed that the Rayleigh type SAW, which was significant to obtain a large mechanical coupling with the magnetization, was dominantly excited in the 800‐MHz‐SAW device.

Затухание спиновой прецессии в гетероструктурах манганит/нормальный металл

Abstract —Temperature dependence of attenuation of magnetic spin precession in two-layer structures with a Pt top layer based on a La_0.7Sr_0.3MnO_3 (LSMO) epitaxial manganite film is studied by measuring the width of a ferromagnetic resonance (FMR) line. Ferromagnetic resonance in thin ferromagnetic manganite films is used for the creation of a spin current at the interface between the metallic and ferromagnetic layers. A significant increase in a width of a line in FMR spectrum in two-layer structures due to generation of a spin current, heterogeneity of a ferromagnetic layer, two-magnon scattering, and eddy current is discussed.

Modeling and eigenfrequency analysis of high Q-factor Baw resonators

The technology is growing very rapidly, and the micro scale devices are playing a very important role in the electronic, mechanical and other application areas due to their integrability with CMOS IC technology, low power consumption, low cost fabrication and large frequency-Quality factor product. As there is a much demand for small and portable devices the applications of micro devices like MEMS based Bulk Acoustic Wave (BAW) resonators are rapidly increasing. In this paper we will present the analysis of thin-film BAW resonator designed in 2D using eigenfrequency, by using the Aluminium Nitrid (AIN) and Lithium Niobate (LiNbO3) materials and try to achieve a high quality ( Q) factor compared with bibliography. The Q-factor is the most important characteristics of a resonator because it describes the frequency selectivity of the device. The high Q-factor greatly helps to implement extremely selective IF and RF filters with small percent bandwidth and low insertion loss.

Chemical solution synthesis and ferromagnetic resonance of epitaxial thin films of yttrium iron garnet

Cubic Yttrium Iron Garnet (YIG) is a technologically important material due to its excellent magneto-optical properties, high electrical resistivity, and a very narrow ferromagnetic resonance, which makes it particularly suitable for applications in filters and resonators at microwave frequencies. These properties depend on the precise stoichiometry and distribution of Fe${}^{3+}$ ions among the octahedral/tetrahedral sites of a complex structure, which required the use of high-vacuum deposition methods for the fabrication of high-quality YIG thin films. In this paper the authors report the synthesis of nanometer-thick epitaxial films of YIG by a simple water-based chemical method. The films show a long spin relaxation time, comparable to that obtained from high-vacuum physical deposition methods. These results demonstrate that chemical methods can compete to develop nanometer-thick YIG films with the quality required for spintronic devices and other high-frequency applications.

Transient processes in thin film bulk acoustic wave piezoelectric resonators

ABSTRACTWe studied electrically forced, transient thickness-extensional vibration of piezoelectric plates of crystals of class 6 mm as thin film bulk acoustic wave resonators. A generalized Fourier series solution was obtained and verified by comparison with finite element numerical analysis. The transient processes of the startup or shutting down of a resonator was examined. It was found that for a typical thin film resonator of ZnO or AlN with a 2 µm thickness, a fundamental thickness-extensional frequency of 1–2 GHz, and a damping described by a material quality factor of 105, the characteristic startup time from rest to time-harmonic motion is about 0.1 millisecond.

Quantum dot emission modulation using piezoelectric photonic crystal MEMS resonators.

Quantum dots (QDs) integration into photonic devices requires varied approaches to control and modulate their emission. We demonstrate voltage-tunable PC structures with integrated QDs over suspended piezoelectric aluminum nitride thin film resonators that modulate PC enhancement at MHz frequencies. When the piezoelectric device is actuated at its resonant mechanical frequency, the extracted QD emission direction is likewise modulated via the optical resonant frequency of the PC. Modulation uses nanometer-scale mechanical displacements, offering the potential for greater switching speed and improved mechanical robustness that is not subject to the effects of stiction with a scalable fabrication approach.

Incorporation of surface plasmon resonance with novel valinomycin doped chitosan-graphene oxide thin film for sensing potassium ion

In this study, the combination of novel valinomycin doped chitosan-graphene oxide (C–GO–V) thin film and surface plasmon resonance (SPR) system for potassium ion (K+) detection has been developed. The novel C–GO–V thin film was deposited on the gold surface using spin coating technique. The system was used to monitor SPR signal for K+ in solution with and without C–GO–V thin film. The K+ can be detected by measuring the SPR signal when C–GO–V thin film is exposed to K+ in solution. The sensor produces a linear response for K+ ion up to 100ppm with sensitivity and detection limit of 0.00948°ppm−1 and 0.001ppm, respectively. These results indicate that the C–GO–V film is high potential as a sensor element for K+ that has been proved by the SPR measurement.