Layered Substrate Research Articles

Coherent growth of oxide films on a cleaved layered metal oxide substrate

Understanding oxide interface-induced effects requires controlled epitaxial growth of films on well-defined substrate surfaces. While conventional film growth on ex situ prepared substrates has proven to be a successful route, the choices of appropriate substrates with atomically defined surfaces are limited. Here, by depositing $\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ on $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$ (001), we present an alternative method of growing oxide thin films on in situ cleaved surfaces of layered-structured substrates. Cleaving $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{4}$ at low temperature in ultrahigh vacuum exposes an atomically flat, solely SrO-terminated surface with up to micrometer-scale terraces. The deposition of $\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ spontaneously diminishes the surface $\mathrm{Ru}{\mathrm{O}}_{6}$ in-plane rotational distortion of the substrate and results in a cubic-like perovskite film structure with (La/Sr)-O layer termination. The interface is atomically sharp without obvious deviation of lattice spacing and chemical valence, except in the first unit cell where Ru-Mn intermixing is observed. These results demonstrate that film growth on a cleaved substrate can be an alternative route to obtain well-defined interfaces and in addition increase the availability of substrates for future oxide films.

Sedum root foraging in layered green roof substrates

Layered profiles of designed soils may provide long-term benefits for green roofs, provided the vegetation can exploit resources in the different layers. We aimed to quantify Sedum root foraging for water and nutrients in designed soils of different texture and layering. In a controlled pot experiment we quantified the root foraging ability of the species Sedum album (L.) and S. rupestre (L.) in response to substrate structure (fine, coarse, layered or mixed), vertical fertiliser placement (top or bottom half of pot) and watering (5, 10 or 20 mm week−1). Water availability was the main driver of plant growth, followed by substrate structure, while fertiliser placement only had marginal effects on plant growth. Root foraging ability was low to moderate, as also reflected in the low proportion of biomass allocated to roots (5–13%). Increased watering reduced the proportion of root length and root biomass in deeper layers. Both S. album and S. rupestre had a low ability to exploit water and nutrients by precise root foraging in substrates of different texture and layering. Allocation of biomass to roots was low and showed limited flexibility even under water-deficient conditions.

Mechanosensitivity of Cancer Cells in Contact with Soft Substrates Using AFM

Cancer cells are usually found to be softer than normal cells, but their stiffness changes when they are in contact with different environments because of mechanosensitivity. For example, they adhere to a given substrate by tuning their cytoskeleton, thus affecting their rheological properties. This mechanism could become efficient when cancer cells invade the surrounding tissues, and they have to remodel their cytoskeleton in order to achieve particular deformations. Here we use an atomic force microscope in force modulation mode to study how local rheological properties of cancer cells are affected by a change of the environment. Cancer cells were plated on functionalized polyacrylamide substrates of different stiffnesses as well as on an endothelium substrate. A new correction of the Hertz model was developed because measurements require one to account for the precise properties of the thin, layered viscoelastic substrates. The main results show the influence of local cell rheology (the nucleus, perinuclear region, and edge locations) and the role of invasiveness. A general mechanosensitive trend is found by which the cell elastic modulus and transition frequency increase with substrate elasticity, but this tendency breaks down with a real endothelium substrate. These effects are investigated further during cell transmigration, when the actin cytoskeleton undergoes a rapid reorganization process necessary to push through the endothelial gap, in agreement with the local viscoelastic changes measured by atomic force microscopy. Taken together, these results introduce a paradigm for a new—to our knowledge—possible extravasation mechanism.

On the possibility of predicting some types of earthquake by a mechanical approach

The problem of prediction of the recently established new type of earthquake called “starting” earthquakes is considered. These arise in the earth’s crust at the moment of contact of lithospheric plates. The origin of the “starting” earthquakes is associated with the concentration of contact stresses below them. The problem is considered under the assumption that the lithospheric plates and the below layered substrates are linearly elastic. The layered bases are modeled by three-dimensional bodies, while the lithospheric plates are modeled by Kirchhoff plates. The paper addresses the stress concentration under the plates for different mutual positions when they approach each other with their ends. Both cases of distant plates and contacted plates are considered. The paper demonstrates that this result cannot be obtained by the finite element method and other numerical methods based on the energy integral. The topological method of the block element elaborated in this paper differs from the earlier approaches by the present authors. In the earlier works, local coordinate systems were introduced which complicates understanding the results. The present paper proposes a unified coordinate system which makes the approach applicable to other problems. This approach also reveals a singular concentration of contact stresses which coincides with the previously obtained singularity; however, the present result is more transparent. This result allows us to discuss the approach enabling the prediction of location, time and intensity of an earthquake, as well as the conditions that ensure the realization of prognostication.

Label-free quantification of cell-to-substrate separation by surface plasmon resonance microscopy

We study surface plasmon resonance microscopy (SPRM) for label-free quantification of cell-to-substrate separation. We have established a depth extraction model in which we compare a layered cell substrate model with resonance characteristics obtained by SPRM. We have applied the model to human aortic endothelial cell (HAEC) culture and determined the separation distance to be 40–60 nm. We have also investigated the precision of the SPRM model associated with the deviation in the model parameters, which is estimated to be 15 nm. The results can serve as the basis for more extensive cell-to-surface studies in a massive and automated way.

Modeling of Silicon-Based Substrates of Patch Antennas Operating in the Sub-THz Range

The paper describes a convenient way to numerically model planar antennas dedicated to sub-terahertz (THz) radiation detectors while accounting for multiple oxide layers included in typical silicon-based substrates used in microelectronics. Several approaches are presented, including a solution based on calculations of effective permittivity of the layered substrate. The results suggest that this approach can work at lower frequencies, but will not be effective in the sub-THz range due to different mechanisms of dispersion occurring in transmission lines with either homogeneous or layered substrate. Therefore, an alternative approach based on anisotropic layers has been proposed, which proves to be efficient and easy to adopt in typical numerical models. It also explains well the results of experiments done using a set of patch antennas fabricated on thin membranes and operating at various frequencies from 240 GHz up to 370 GHz.

Precision Cutting of Glass by Laser-assisted Machining

Precision machining of glass has been receiving attention in various applications because of the use of glass interposers in layered semiconductors or glass substrates for microfluidic chips. These applications require complicated and three-dimensional machining for further product functionality. Etching is conventionally used for precision machining of glass. However, applying etching for three-dimensional machining is difficult, and thus, a method which is applicable to three-dimensional machining of glass is needed. Cutting is a method applicable to three-dimensional machining. However, precision cutting of glass is difficult because glass is a hard and brittle material. In this research, we applied laser-assisted machining for cutting of glass. We first conducted laser-assisted milling for plane surface cutting. We then proposed laser-assisted drilling for glass drilling to perform the three-dimensional cutting of glass by laser-assisted machining. Through the experimental analyses, we demonstrated the feasibility of the precision and three-dimensional cutting of glass.

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

Two dimensional atomic crystals, like grapheme (G) and molybdenum disulfide (MoS2), exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress in the understanding of the interfaces of van der Waals (vdW) heterostructures between small organic molecules (pentacene, copper phthalocyanine (CuPc), perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and dioctylbenzothienobenzothiophene (C8-BTBT)) and layered substrates (G, MoS2 and hexagonal boron nitride (h-BN)). The influences of the underlying layered substrates on the molecular arrangement, electronic and vibrational properties will be addressed.

Layered Gold and Titanium Dioxide Substrates for Improved Surface Enhanced Raman Spectroscopic Sensing.

This manuscript describes a simple process for fabricating gold-based, multi-layered, surface-enhanced Raman scattering (SERS) substrates that can be applied to a variety of different nanostructures, while still providing multi-layer enhancement factors comparable to those previously achieved only with optimized silver/silver oxide/silver substrates. In particular, gold multi-layered substrates generated by atomic layer deposition (ALD) have been fabricated and characterized in terms of their optimal performance, revealing multi-layer enhancements of 2.3-fold per spacer layer applied. These substrates were fabricated using TiO2 as the dielectric spacer material between adjacent gold layers, with ALD providing a conformal thin film with high surface coverage and low thickness. By varying the spacer layer thicknesses from sub-monolayer (non-contiguous) films through multiple TiO2 layer thick films, the non-monotonic spacer layer thickness response has been elucidated, revealing the importance of thin, contiguous dielectric spacer layers for optimal enhancement. Furthermore, the extended shelf life of these gold multi-layered substrates was characterized, demonstrating usable lifetimes (i.e. following storage in ambient conditions) of greater than five months, with the further potential for simple limited electrochemical regeneration even after this time.

Clickable Polymeric Coating for Oriented Peptide Immobilization.

A new methodology for the fabrication of an high-performance peptide microarray is reported, combining the higher sensitivity of a layered Si-SiO2 substrate with the oriented immobilization of peptides using a N,N-dimethylacrylamide-based polymeric coating that contains alkyne monomers as functional groups. This clickable polymer allows the oriented attachment of azido-modified peptides via a copper-mediated azide/alkyne cycloaddition. A similar coating that does not contain the alkyne functionality has been used as comparison, to demonstrate the importance of a proper orientation for facilitating the probe recognition and interaction with the target antibody.

Guided wave Generation in Elastic Layered Substrates with Piezoelectric Coatings and Patches

Piezoelectrically generated surface and pseudosurface acoustic waves are simulated and analyzed in the mathematical framework based on the integral representations and guided wave asymptotics. In addition to the abilities of the conventional modal analysis, the integral equation approach explicitly provides the amplitudes of waves generated by a specified source, making it possible to evaluate the wave energy transmitted from the source into the substrate and its distribution among the excited guided waves. Diamond based microdevices and piezoelectric patch actuators are considered as examples.

Surface-plasmon induced polarized emission from Eu(III)--a class of luminescent lanthanide ions.

The intrinsically unpolarized emission from luminescent Eu(III) ions is transformed to wavelength-resolved and sharply directional polarized emission by coupling with plasmonic and photonic modes present in metal-dielectric layered substrates. This nanoscale control over lanthanide luminescence can facilitate the design of novel emissive structures with potential technological applications.

Wave Concept Iterative Procedure Analysis of Patch Antennas on Nanostructured Ceramic Substrates

The wave concept iterative procedure (WCIP) is proposed to analyze rectangular and circular patch antennas on nanostructured ceramic substrates. Principles of WCIP are described and advantages are emphasized. The analysis of microstrip antennas on double layered substrates is performed in space and spectral domains. In addition, Fast Fourier Transformation (FFT) is used to improve the efficiency of the method. WCIP simulated results are compared to HFSS software ones. A good agreement is observed.

Investigation into the suitability of layered silicates as adsorption media for essential oils using FTIR and GC–MS

This study assessed the suitability of layered silicate substrates as adsorption media for an essential oil (EO) blend with antimicrobial properties. It is anticipated that adsorption of the EO blend within the layered silicate will lead to controlled release of the blend. Three montmorillonites (Mt), a natural/synthetic hybrid Mt and two synthetic layered silicates were selected as potential adsorption materials. Gas chromatography (GC) was used to follow static adsorption of the EOs from heptane. The GC adsorption studies enabled the effect of adsorption on the individual molecular components of the oils to be determined, as well as providing a value for the overall level of adsorption of the EO. The Mts were found to degrade some of the important molecules in the EO and were therefore deemed to be unsuitable. The synthetic layered silicates provided the highest levels of adsorption, achieving up to 170mg·g−1 without the degradation effects shown by the natural Mts.

Multi-layer graphene obtained by high temperature carbon implantation into nickel films

We present a study of carbon implantation in a stacked layered substrate made of Ni(200nm)/SiO2(300nm)/Si(100). The carbon atoms have energy of 20keV. Simultaneous or subsequent heat treatment is performed in the 450–600°C range. The carbon dose was set to be 4 equivalent graphene monolayers (EGM). Most of the carbon implanted diffuses directly to the surface, forming multi-layer graphene (MLG). A progressive structuration of these graphitic fragments occurs with the increase of the implantation temperature. However, this structuration is more pronounced if the thermal treatment is performed in situ following the carbon implantation at room temperature. The mean MLG thickness, corresponding to around 4–5 EGM, was measured by angular X-ray Photoemission Spectroscopy. Moreover, the overall carbon concentration inside and at the limits of the nickel films, determined by nuclear reaction analysis (NRA), is in the 7–10 EGM range. This concentration depends on the temperature but it exceeds surprisingly the expected carbon concentration. This discrepancy shows that some carbon is incorporated along the different steps. NRA analyses of the preparation confirm this point. To obtain large film, the presented results stress the interest to better understand the full system carbon–nickel in the preparation of MLG at each step of the process.

New Configurations of Low-Cost Dual-Polarized Printed Antennas for UWB Arrays

A novel class of structures is proposed to realize ultra-wide-band radiating elements for large arrays, providing dual polarization, beam scanning, and compact and inexpensive realization based on suitable rhombic arrangements of dipoles printed on low-cost layered substrates. In a first implementation, four rhombic shapes, orthogonally placed on the same layer, provide two orthogonal polarizations. In a second implementation, the two polarizations are excited by two rhombic shapes printed on two different layers in a stacked-patch-like arrangement. This latter structure leads to a better lateral shielding of the single radiating element, in order to reduce mutual interactions among adjacent elements in array environment. The behavioral features of these antennas have been tested with various parametric analyses. Practical aspects have been addressed such as the choice of appropriate feeding and of commercially available dielectric layers. The resulting antennas are matched at the input ports in an extremely wide range of frequencies (5–25 GHz), covering various microwave applications, such as aircraft surveillance, weather polarimetric radars, and control and communications systems. Good radiating features, in terms of pattern shape and gain, are observed in a large band of frequencies. The basic scanning performance of large and small array configurations is finally investigated.

Bonding, antibonding and tunable optical forces in asymmetric membranes

We demonstrate that tunable attractive (bonding) and repulsive (anti-bonding) forces can arise in highly asymmetric structures coupled to external radiation, a consequence of the bonding/anti-bonding level repulsion of guided-wave resonances that was first predicted in symmetric systems. Our focus is a geometry consisting of a photonic-crystal (holey) membrane suspended above an unpatterned layered substrate, supporting planar waveguide modes that can couple via the periodic modulation of the holey membrane. Asymmetric geometries have a clear advantage in ease of fabrication and experimental characterization compared to symmetric double-membrane structures. We show that the asymmetry can also lead to unusual behavior in the force magnitudes of a bonding/antibonding pair as the membrane separation changes, including nonmonotonic dependences on the separation. We propose a computational method that obtains the entire force spectrum via a single time-domain simulation, by Fourier-transforming the response to a short pulse and thereby obtaining the frequency-dependent stress tensor. We point out that by operating with two, instead of a single frequency, these evanescent forces can be exploited to tune the spring constant of the membrane without changing its equilibrium separation.

Analysis of Microstrip Dipole Antennas on a Layered Metamaterial Substrate

A numerical method is developed to analyze microstrip dipole antennas on a planar layered metamaterial substrate based on periodic "method of moments" (MoM). In the developed numerical method the spectral domain Green function in conjunction with the "array scanning method" (ASM) is applied. The substrate is made of planar periodic metallic patches inserted in a two layer grounded dielectric slab. Effects of metamaterial loading on input impedance of dipole antennas is investigated using the developed numerical method. It is shown that with metamaterial loading antenna miniaturization is achieved.

Numerical Ellipsometry: Ellipsometer analysis in the n– k plane for growing films on unknown homogeneous, isotropic substrates and unknown, layered substrates

Ellipsometry is an optical analytical method based on measuring the change in polarization state of reflected or transmitted polarized light. A major challenge of the method has been the computation of reflecting surface physical parameters of interest from the raw measured data. These methods in common use are plagued by local minima and algorithm performance. The mathematics of the light reflection has long taken advantage of some aspects of Complex Analysis. The authors have used much more of Complex Analysis to treat growing films on homogeneous, isotropic substrates. The work presented here explores this advanced treatment for unknown homogeneous, isotropic substrates and for unknown layered substrates. The results lay the groundwork for a set of solution algorithms which are much more powerful and convenient than existing algorithms. Such algorithms eliminate the multiple solution problems inherent in least squares methods.

이중 기판 결함 접지 구조를 이용한 비대칭 월킨슨 전력 분배기

종래의 DGS를 이용한 초고주파 회로의 메탈 패키징(metal packaging)시 존재했던 DGS의 접지면 접촉 문제를 해결하고자, 본 논문에서는 이중 기판 결함 접지 구조 구조를 제안하고, 이를 1:4 비대칭 전력 분배기에 적용한 응용예를 제시한다. 이중 기판에 구현된 사각형 DGS는 종래와 같이 마이크로스트립 선로의 특성 임피던스를 표준형 선로보다 크게 증가시킨다. 이중 기판 DGS 구조를 형성하기 위하여 제2유전체 기판이 DGS가 구현된 기판면의 바닥 접지면에 접합된다. 따라서 제2유전체 기판이 메탈 패키지 바닥면에 장착되므로, DGS가 직접 패키지 접촉되는 것을 막을 수 있다. 초고주파 회로 응용예를 보이기 위해, 이중 기판 DGS를 이용하여 패키지 접지 문제를 해결한 1:4 비대칭 전력 분배기의 설계 및 측정 결과가 제시되는데, 시뮬레이션과 측정 결과에 있어서 잘 일치하는 특성을 보인다. A novel 1:4 unequal wilkinson power divider using rectangular-shaped defected ground structure(DGS) in double layered substrate is proposed for removing the ground problem of DGS in packaging. Rectangular-shared DGS produces the transmission line having much higher characteristic impedance than standard microstrip line. The proposed unequal divider is composed of DGS and double layered substrate in order to be free from the ground problem of DGS patterns in packaging in metal housings. The second substrate is attached to the first substrate which contains DGS pattern on its ground plane at the bottom side to form the double layered substrate. In order to show the validity of the proposed DGS in the double layered substrate, a 1:4 unequal power divider is designed and measured. The predicted and measured performances are shown with an excellent agreement between them.