Relaxation Of Layers Research Articles

B3LYP and B3PW computations of BaSnO3 and BaZrO3 perovskite (001) surfaces

By means of the B3LYP and B3PW hybrid exchange-correlation functionals, as it is included in the CRYSTAL computer code, we performed ab initio computations for BaSnO3 and BaZrO3 perovskite (001) surfaces. For BaSnO3 and BaZrO3 perovskite (001) surfaces, with a few exceptions, all atoms of the upper surface layer relax inwards, all atoms of the second surface layer relax outwards, and all third layer atoms, again, relax inwards. The relaxation of BaSnO3 and BaZrO3 (001) surface metal atoms for upper two surface layers, for both BaO and BO2-terminations, as a rule, are considerably larger than the relaxation of relevant oxygen atoms. The BaO (1.30 eV) and ZrO2-terminated (1.31 eV) BaZrO3 (001) surface energies are almost equal. The BaZrO3 perovskite BaO (4.82 eV) and ZrO2-terminated (4.48 eV) (001) surface Г-Г band gaps are reduced regarding the respective bulk Г-Г band gap value (4.93 eV). The B–O chemical bond populations in BaSnO3 and BaZrO3 perovskite bulk always are smaller than near their SnO2 and ZrO2-terminated (001) surfaces, respectively.

High Performance CMOS RF Switch Based on Highly Carbon Doped Raised Source/Drain Regions

The demand for high-performance Radio Frequency (RF) CMOS RF SOI (Silicon on Insulator) switches has rapidly increased, driven by the need for advanced wireless technologies (1). In this paper we give new insights on high carbon incorporation, where a Si(1-y)Cy layer with 1% of substitutional carbon (y = Csub) is grown on 40 nm on top on silicon. This layer is used for Raised Source/Drain (RSD) to strain the Si channel, for reducing on-state resistivity (Ron) and which should result in a theoretical 16% gain in current (3), (4). Si(1-y)Cy growth parameters were carefully optimized to increase Csub. Firstly, with the reduction of the temperature. Then, with H2 carrier gas reduction and total pressure increase. These two process modifications have a positive impact on the carbon concentration, thanks to the higher growth rate, without layer relaxation (5).

Mechanical behavior and biological activity performance of Li+/Ca2+@Li+/K+ ion-exchanged lithium disilicate glass-ceramics

Lithium disilicate (LD) glass-ceramics used for bone repair need to have good mechanical properties and biological activity. Ion-exchange can lead a significant surficial strengthening and bioactivity of LD glass-ceramics. In this work, LD glass-ceramics were Li+/Ca2+@Li+/K+ exchanged in a mixed salt bath of 30 % Ca(NO3)2 + 70 % KNO3 (in mol %) at 400 °C for 16 h, 32 h and 64 h respectively. LD glass-ceramics were significantly strengthened after Li+/Ca2+@Li+/K+ exchange. However, due to the shallow depth of the ion-exchange layer and stress relaxation, the strengthening effect deteriorated with the prolongation of the ion-exchange time. The Li+/Ca2+@Li+/K+ exchanged LD glass-ceramics could be conducive to the formation of the hydroxyapatite (HA) after soaking in the simulated body fluid (SBF). Moreover, the protein adsorption, cytotoxicity, cell adhesion, osteoblast proliferation and alkaline phosphatase (ALP) activity expression of Li+/Ca2+@Li+/K+ exchanged LD glass-ceramics were investigated. Ca2+ release might promote the bioactivity of ion-exchanged LD glass-ceramics. Therefore, Li+/Ca2+@Li+/K+ exchange can improve the mechanical properties and bioactivity of LD glass-ceramics, which has important significance for its application in orthopedic reconstruction.

Multifiller-based polymer composites for shielding high energy ionising radiation.

Polydimethyl silicone rubber-based polymer composites filled with molybdenum and bismuth were fabricated using simple open mold cast technique. The physical and chemical structure and gamma shielding parameters like attenuation coefficient, half-value layer (HVL) thickness and relaxation length have been investigated for the said novel materials using X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR) and gamma ray spectrometer. XRD study reveals the crystalline nature of the composites. It is evident from FTIR studies that there is no chemical interaction between the polymer matrix and filler particles. The results of attenuation studies reveal that the linear attenuation coefficient increases with addition of Bi and Mo and is found to be 0.653, 1.341 and 1.017, 1.793 and 0.102, 0.152cm-1 for 1MMB and 2MMB polymer composites at 80, 356 and 662keV gamma rays, respectively. The HVL thickness of the materials is found to be 1.06, 0.51 and 0.68, 0.38 and 6.73, 4.532cm for 1MMB (20Mo+10Bi phr) and 2MMB (40Mo+20Bi phr) at these energies, respectively. The mass attenuation coefficient of the novel composites 1MMB and 2MMB is found to be higher than the conventional materials like lead and barite for 356keV gamma rays. In addition, the material is found to be light weight and flexible enabling to be molded in required forms, thus being a substitute for the material lead that is known to be heavy and toxic by nature.

On the timescale of electrochemical processes

There is an ongoing discussion in the literature if simulations of electrochemical reactions should be performed at constant electrode potential. In this context we examine the timescales at which electrochemical processes take place. We take molecular dynamics simulation of hydrogen desorption from graphene and gold as examples. Charge transfer processes are governed by the accompanying solvent reorganization, and their speed is determined by the solvent dynamics, whose timescale is of the order of picoseconds — the exact value depends on the details of the system. In contrast, double layer relaxation, which controls the electrode potential, requires times of the order of nanoseconds. We suggest that this difference is due to the fact, that solvent reorganization is a local phenomenon, while double layer relaxation involves the whole solvent between working and reference electrodes, which is of macroscopic dimensions. We conclude, that simulations of electrochemical reactions should not be performed at constant potential. In contrast, calculations for thermodynamic properties can be performed at constant potential or at constant charge, since the question of timescales does not arise in this case.

Suppressing dipolar relaxation in thin layers of dysprosium atoms

The dipolar interaction can be attractive or repulsive, depending on the position and orientation of the dipoles. Constraining atoms to a plane with their magnetic moment aligned perpendicularly leads to a largely side-by-side repulsion and generates a dipolar barrier which prevents atoms from approaching each other. We show experimentally and theoretically how this can suppress dipolar relaxation, the dominant loss process in spin mixtures of highly magnetic atoms. Using dysprosium, we observe an order of magnitude reduction in the relaxation rate constant, and another factor of ten is within reach based on the models which we have validated with our experimental study. The loss suppression opens up many new possibilities for quantum simulations with spin mixtures of highly magnetic atoms.

Dissipation estimation for the impedance tube measurement using Bayesian inference

Although air dissipation is usually neglected in the impedance tube measurement, it affects the accuracy of the measurement results. Multiple effects contribute to the sound dissipation in an impedance tube, like the boundary layer effect or relaxation effect. This work formulates a transfer function model incorporating different dissipation. Bayesian inference is applied to estimate the acoustic dissipation in an impedance tube. Critical parameters in dissipation models are estimated based on the transfer function measured from an empty impedance tube. Nested sampling is applied to get an accurate approximation of parameters. The results of the analysis demonstrate that the critical parameters estimated by the Bayesian method are accurate. The accurate estimated dissipation helps improve the accuracy of impedance measurement with the material under test.

The ionic boundary layer relaxation in the problem of proton exchange

The ionic boundary layer relaxation in the problem of proton exchange

(Invited) Suspended 1D/2D Nanomaterials: Progress on a Waferlevel Technology and Applications

The use of 1D and 2D nanomaterials in emerging electronics and sensor technologies is becoming increasingly important due to their unique properties. Here we would like to highlight a scalable process for suspended nanomaterials that provides additional scope for the development of device properties that can be used in advanced concepts ranging from molecular sensing to quantum applications [1]. For example those applications benefit from arrangements as CNT-based nanoresonators with extremely high quality factors [2] usable for quantum bits with long coherence time [3] or suspended sensing nanomaterials for ultra-low power and extremely sensitive gas sensors [4]. Moreover, straining allows to tune intrinsic physical properties of nanomaterials. Thus, the strain-dependence of the band gap (e.g. CNTs <100meV/% [5], MoS2 ~60meV/% [6],) paves the way for integrated-, highly-efficient-, and tunable light sources for on-chip spectrometry in the context of photonic integrated circuits (PICs), as recently reviewed in [7].Our technological solution to manufacture suspended nanomaterials is aligned with established semiconductor processing chains on 200 mm wafer level and is developed to be modular integrable and compatible with MEMS, MEOMS or CMOS technologies [8]. Along the process chain, we demonstrate wafer-validated deposition processes for semiconducting CNT films which properties can be adjusted with respect to density and even alignment. In particular, for straining aligned CNTs as well as any transferable 2D nanomaterial, we implemented a stressed functional SiO2/SiN layer stack arranged on embedded sacrificial Cu-structures on the wafer surface. After contacting of the nanomaterial and release of sacrificial elements, stressed layers relax, strain and suspend the nanomaterial. This surface engineering approach greatly simplifies the introduction of strain into nanomaterials and makes it accessible for arbitrary device numbers on wafers as well as for monolithic 3D electronic concepts. Unique features include in-plane strains that are applicable in multiaxial directions and can be controlled by designing only two lithography planes. We show that devices with CNTs strained up to 1% determined from Raman spectral analysis, have a positive impact on sensor operation. We show application examples such as a mechanical stress sensor with extremely low on-set sensitivity.

Development of 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea derivatives as robust corrosion inhibitors for mild steel in 1 M HCl environment: Insight from ,molecular, experimental, and microscopic-scale modelling approaches

Cost-effective, novel urea derivatives, 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea (U-1), 1‐(4‐fluorophenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-2), and 1‐(4‐methylphenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-3) were synthesized to investigate as the corrosion inhibitors for mild steel/1 M HCl interface. Inhibition efficiency increases with the increasing inhibitor’s concentration but decreases with increasing temperature. Thermodynamic adsorption and activation parameters demonstrate that the adsorption of inhibitors follows Langmuir isotherm via physicochemical interactions. Potentiodynamic polarization measurements reveal that the inhibitors are mixed-type, impeding the charge-transfer process. Surface analysis supports a thin inhibitor film formation on the mild steel. The maximum inhibition efficiency of U-1, U-2 and U-3 are 94.97 ± 0.38%, 93.60 ± 0.62% and 97.42 ± 0.48% respectively. The calculated electrochemical impedance spectra (EIS) parameters such as ohmic resistance, double layer capacitance, relaxation time, effective thickness, and conductivity of grain and grain boundary are in-line with the efficiencies of NHUs. The performance of corrosion inhibitors follows a sequence U-3 > U-1 > U-2, emphasizing the influence of the substituent’s inductive effect (-CH3 > -H > -F) in inhibitors. Density functional theory (DFT) was performed to understand the correlation between molecular structure and inhibition efficiency. The Fukui indices confirm the presence of local attacking sites on the metal surface where inhibitors attack. A molecular dynamic (MD) simulation is used to determine the interaction energies between the inhibitors and mild steel. Radial Distribution Function (RDF) measurements confirm the existence of the chemical nature of the interaction. Furthermore, the diffusion coefficient of corrosive particles, self-diffusion coefficient of inhibitors, fractional free volume (FFV), and interaction between inhibitor’s film and corrosive particles are examined. Theoretical studies support experimental results.

Experimental investigation of the tire wear process using camera-assisted observation assessed by numerical modeling

This paper presents a novel experimental method to study the abrasion mechanism of car tires. It is based on the detection of microscopic movements associated with material damage (cracking) on the rubber tread. This is referred to as degrading layer relaxation. It correlates with the wear rate and, interestingly, the direction of the pattern’s movement is opposite to the lateral forces during cornering. To measure and analyze the microscopic movements, a new camera-based method with feature point matching using video stabilization was developed. Besides extensive experimental investigation, the formation and propagation of microcracks are investigated using a simplified numerical model in which a phase field approach coupled with a viscoelastic constitutive behavior is implemented in a finite element framework.

Biaxial, Hybrid Plastic-Elastic Relaxation in Micropatterned Semipolar InGaN Buffer Layers Improves Quality of Templated Quantum Well Emitters

Despite significant progress and multiple creative approaches taken toward the realization of long-wavelength III-nitride based light emitters over the past decade, high double-digit external quantum efficiencies remain elusive for GaN/InGaN based devices for wavelengths longer than 525 nm. This stems from the large mismatch between the GaN and InGaN lattice that manifests in deleterious crystal strain gradients, degrades surface growth morphology, and introduces diverse and potent nonradiative defects.A promising route to mitigation of strain-based effects is templating epitaxial growth on relaxed InGaN epilayers; in particular, a known and controllable platform for uniaxial strain relaxation is the creation of 1-D misfit dislocation arrays at semipolar GaN/InGaN heterointerfaces. Leveraging work by Hardy et al. on achieving >200 nm thick, partially relaxed semipolar InGaN layers [1] and precise determination of InGaN epilayer strain state and composition by Young et al. [2], we explore the potential for 2-D buffer layer relaxation in (11-22) InGaN layers via micron- and sub-micron patterning. Cathodoluminescence microscopy and x-ray diffraction indicated significant increases in biaxial epilayer relaxation with increased pillar aspect ratio; quantum wells deposited atop these relaxed InGaN buffers showed dramatic threading dislocation reduction, luminescence and morphology improvements, and evidence of improved indium incorporation relative to planar samples at nominally identical growth conditions.[1] Hardy, M.T., Young, E.C., Hsu, P.S., Haeger, D.A., Koslow, I.L., Nakamura, S., DenBaars, S.P., Speck, J.S. Suppression of m-plane and c-plane slip through Si and Mg doping in partially relaxed (20-21) InGaN/GaN heterostructures. Appl. Phys. Lett. 101, 132102 (2012).[2] Young, E. C., Romanov, A.E., Speck, J.S., Determination of composition and lattice relaxation in semipolar ternary (In,Al,Ga)N strained layers from symmetric x-ray diffraction measurements. Appl. Phys. Express. 4, 061001 (2011).

Interaction of Si Atom with the (001) Surface of TiN, AlN and TaN Compounds

Nowadays, the application of multicomponent coatings with multiphase nanocrystalline structure is the most promising direction in the search for wear-resistant protective coatings with a full set of necessary operational properties. Nanocrystalline multicomponent coatings based on the Ti-Al-Ta-Si-N system have a high hardness combined with thermal stability and oxidation resistance. Silicon atoms are weakly soluble in the TiN, Ti1−xAlxN, and TaN crystalline phases of the Ti-Al-Ta-Si-N system and interact preferentially with N atoms, forming the amorphous Si3N4 phase. In this context, it is important to first study the peculiarities of the interaction of Si atoms with the simplest structural units of the Ti-Al-Ta-Si-N system, such as TiN, AlN, and TaN compounds with the NaCl structure. This work is devoted to the study of the interaction of a Si atom with the (001) surface of AlN, TiN, and TaN compounds with the NaCl structure using ab initio calculations. This provides information for a deep understanding of the initial stages of the formation of different crystallites of the considered composite. It was established that the adsorption of silicon on the (001) surface of AlN, TiN, and TaN significantly increases the relaxation of the surface layers and leads to an increase in the corrugation observed on the clean surfaces. The largest corrugation is observed on the surface of the TaN compound. The most energetically favorable adsorption positions of Si atoms were found to be the position of Si above the N atom on the TiN and TaN surfaces and the quadruple coordinated position on the AlN surface. The valence electron density distribution and the crystal orbital Hamiltonian population were studied to identify the type of Si atom bonding with the (001) surface of AlN, TiN, and TaN compounds. It was found that silicon forms predominantly covalent bonds with the nearest metal and nitrogen atoms, except for the quadruple coordinated position on the surface of TiN and TaN, where there is a high degree of ionic bonding of silicon with surface atoms.

Relationship between Internal Stress Distribution and Microstructure in a Suspension-Sprayed Thermal Barrier Coating with a Columnar Structure

The suspension plasma spray (SPS) method is expected to become a novel coating method because it can achieve various microstructures using a suspension with submicron spray particles. Thermal barrier coatings (TBCs) with a columnar structure, which might achieve high strain tolerance, can be obtained using the SPS technique. This study evaluated the internal stress distribution of the suspension-plasma-sprayed thermal barrier coating (SPS-TBC) with different columnar structures using hybrid measurement using high-energy synchrotron X-ray diffraction analysis and laboratory low-energy X-rays. The relationship between the microstructure and the internal stress distribution of the SPS-TBC was discussed on the basis of the experimental results. In addition, the in-plane internal stress was decreased by decreasing the column diameter. The thin columnar microstructure of the SPS-TBC has superior strain tolerance. The internal stresses in the SPS-TBC are periodic decrements caused by stress relaxation in porous layers in its column.

Polarity Inversion of GaN via AlN Oxidation Interlayer Using Metal–Organic Vapor Phase Epitaxy

The polarity inversion of GaN films grown on vicinal sapphire substrates is demonstrated using the metal–organic vapor phase epitaxy (MOVPE) method via an AlN oxidation interlayer for application in wavelength conversion devices. By annealing the N‐polar AlN surface at 900 °C in air, the pit‐free Ga‐polar GaN layer can be regrown. Anisotropic etching in KOH and transmission electron microscopy confirms the formation of a GaN polarity‐inverted structure. X‐ray diffraction measurements reveal an increase in threading dislocations due to the nucleation island formation by low‐temperature GaN layer and strain relaxation at the regrown interface. The simple fabrication process of the GaN polarity‐inverted structure using an AlN oxidation interlayer will pave the way for applications in new devices that require polarity‐controlled and/or polarity‐inverted stacking structures.

How Tuning Interfaces Impacts the Dynamics and Structure of Polymer Nanocomposites Simultaneously

Fundamental understanding of the macroscopic properties of polymer nanocomposites (PNCs) remains difficult due to the complex interplay of microscopic dynamics and structure, namely interfacial layer relaxations and three-dimensional nanoparticle (NP) arrangements. The effect of surface modification by alkyl methoxysilanes at different grafting densities has been studied in PNCs made of poly(2-vinylpyridine) and spherical 20 nm silica NPs. The segmental dynamics has been probed by broadband dielectric spectroscopy and the filler structure by small-angle X-ray scattering and reverse Monte Carlo simulations. By combining the particle configurations with the interfacial layer properties, it is shown how surface modification tunes the attractive polymer-particle interactions: bare NPs slow down the polymer interfacial layer dynamics over a thickness of ca. 5 nm, while grafting screens these interactions. Our analysis of interparticle spacings and segmental dynamics provides unprecedented insights into the effect of surface modification on the main characteristics of PNCs: particle interactions and polymer interfacial layers.

How does lithospheric viscosity control the temporal patterns of seismicity during an earthquake cycle?

The temporal patterns of regional seismicity, such as acceleration and deceleration patterns of seismic moment release, Benioff strain release, or number of earthquakes over time before a big earthquake or between two big earthquakes, have been observed in various regions. However, the mechanisms or controlling factors to cause these temporal patterns of seismicity have not been fully clarified. In this study, we collect, summarize, and analyze temporal patterns of regional seismicity (acceleration and deceleration patterns) in the world and observe a statistical relation between them and regional lithospheric viscosity values. We also develop and use a three-dimensional viscoelastoplastic finite-element model and an analytical model, to investigate and explain the importance of lithospheric viscosity on temporal patterns of seismicity during an earthquake cycle. We find that viscosity in lower crust and upper mantle can control seismicity acceleration and deceleration patterns during an earthquake cycle: low viscosity tends to cause deceleration pattern because fast postseismic stress accumulation within upper crust due to fast stress relaxation in viscoelastic layers following an earthquake induces frequent occurrence of regional earthquakes at early stage of an earthquake cycle, but on the contrary, high viscosity encourages acceleration pattern with frequent occurrence of regional earthquakes at late stage of an earthquake cycle. Between the low and high viscosity, a transitional viscosity zone roughly ranging from ∼1 × 1019 to ∼1 × 1020 Pa s exists. When average viscosity in lower crust and upper mantle stays in this range, regional seismicity acceleration and deceleration patterns can coexist at similar percentages and it is statistically hard to distinguish which pattern dominates in the region. Regional tectonic loading velocity also has an impact on temporal patterns of seismicity during an earthquake cycle: slow tectonic loading velocity tends to induce seismicity deceleration pattern, but fast tectonic loading velocity encourages seismicity acceleration pattern.

Carbon coated porous iron oxide nanotubes for optimized lithium storage

Iron oxide is intensively explored for its high capacity and abundant reserves. Suffering from poor conductivity and huge volume variation during repeating lithiation/delithiation, the capacity decays quickly. Herein, carbon coated porous iron oxide nanotubes (FeOx@C) is synthesized via hydrothermal method and subsequent annealing to achieve cycling stability. FeOx@C-2 exhibits excellent rate capability and superior cycling life. As anode material for lithium ion batteries, it delivers a high reversible capacity of 948.5 mAh g−1 at 2 A g−1 after 500 cycles. The initial coulombic efficiency is 88.7% and nearly 100% in the following cycles. The superior electrochemical performance belongs to improved electrical conductivity of carbon coating layer and exceptional stress relaxation of porous hollow structure of nanotube.

Stress Relaxation in SGOI Structure Obtained by Condensation

Years of work have been dedicated to the optimization of thickstrain-relaxed buffers. Thanks to the use of graded Ge content layersbeneath the constant composition layers on top, threadingdislocations densities around 105 cm-2 have been obtained. Recentlyan innovative phenomenon has been observed concerning SiGe-On-Insulator (SGOI) layer relaxation. We propose to use this approachto obtain fully relaxed SGOI layers without dislocations in industrialconditions on 300mm wafers. This new approach would enable usto fabricate relaxed SGOI layers which are uniform in composition.Such an innovation would be relevant for several applications suchas, for instance, the re-epitaxy of Si0.5Ge0.5 layers.

Magnetoresistance analysis of intercalated lithium layer relaxation following discharge of primary lithium-manganese elements

Magnetoresistance analysis of intercalated lithium layer relaxation following discharge of primary lithium-manganese elements