Substrate Bilayer Research Articles

Research on the impact performance of polyurethane coating on the steel structure surface

Focusing on the 3060 Goal, China builds a large energy base in Inner Mongolia. The steel structure facilities are subjected to long-term impacts from hard particles in the desert environment. Damage to the surface coatings of the steel structures resulted in reduced durability, and safety. The impact test of polyurethane coating was carried out by using an automatic ball impactor, the strain field of PU coating under impact load was collected by combining with Digital Image Correlation, the damage degree of PU coating was investigated by using Laser Scanning Confocal Microscopy, and elastic-plastic properties of PU coating were also studied. The results show that at the same impact height, the indentation depth of the substrate was Steel substrate > PU coating-steel substrate bilayer system, indicating that the PU coating played a better role in protecting the steel substrate. The compressive strain area at the impact contact point of the PU coating-steel substrate bilayer system increased with the increase of impact height, and the surface of the coating appeared to have different degrees of cracks and spalling. The dynamic hardness increases and then decreases with the increase of impact height, and the dynamic hardness value is the largest when the impact height is 30 cm.

An asymptotic modeling and resolution framework for morphology evolutions of multiple-period post-buckling modes in bilayers

A stiff thin film bonded to a compliant substrate initially buckles into wrinkles, following with some intricate advanced instability modes when the compression exceeds higher thresholds. Here, we present an asymptotic modeling and resolution framework to quantitatively predict and continuously trace secondary bifurcation transitions in the non-linear post-buckling region. An advantage of this framework, besides its applicability to finite-strain deformations, is its asymptotic consistency with the three-dimensional (3D) field equations and interface continuity conditions in a pointwise manner. Based on our model, we reveal intricate post-buckling responses involving successive advanced mode transitions, i.e., period-doubling, period-tripling, period-quadrupling, ridge, and hierarchical wrinkles in film–substrate bilayers upon excess compression. Apart from modulus ratio, pre-stretch and pre-compression of the substrate can alter surface morphology of film–substrate bilayers. With substrate pre-compression, a bilayer may eventually involve into a period-tripling or period-quadrupling mode. We observe hierarchical wrinkles and ridges in films attached on pre-stretched substrates. With high substrate pre-tension and modulus ratio, a novel pattern, namely, periodic ridges, appears at the secondary bifurcation. Fundamental understanding and quantitative prediction of non-linear morphology evolutions of soft bilayers play important roles in rational designs of wrinkle-tunable functional surfaces.

Microtubules' local and global order on membrane-bound motor proteins

As part of the cytoskeleton, microtubules (MTs) are vital components of all Eukaryotic cells, important for cell division and intracellular transport. Converting chemical energy into mechanical energy, kinesin motor proteins “walk” on MTs, transporting cargo throughout the cell. In this project, we investigated MT-kinesin-based transportation. We take advantage of the microtubule gliding assay configuration to probe collective behavior in dense MT swarms. Experiments were performed using kinesin motors coupled to either a glass substrate or lipid bilayer.

Hertzian Indentation Behavior of Electroless Ni-P-Ti Composite Coatings

Ni-P-Ti composite coatings have been prepared by co-depositing Ni-P and nano-Ti particles which were then annealed. Tensile tests were conducted on standalone coatings to acquire the mechanical properties of the coatings without the effect of the steel substrate. The Hertzian indentation tests were performed on coating-steel substrate bilayer systems to investigate the indentation behavior of the coatings. After annealing, Ni3Ti and superelastic NiTi phases are identified in composite coatings by XRD and EDS. Compared to the as-deposited Ni-P coatings, the toughness of the annealed composite coatings improved significantly. The superelastic effect of NiTi particles was observed in the Hertzian indentation behavior of the annealed composite coatings. The strengthening mechanisms as well as toughening mechanisms such as crack bridging, crack deflection, crack arresting, and transformation toughening were discussed. Recovery ratio (η) values as well as Hertzian indentation stress distribution were computed to analyze and explain the indentation behavior of the as-deposited and annealed coatings.

Nanocomposite Multilayer Binary Nitride Coatings Based on Transition and Refractory Metals: Structure and Properties

One area of constant interest in many fields of industry is development of functional multilayer coatings that possess excellent performance characteristics. That is why in our brief review the results of studies of structure and properties of multilayer structures based on binary nitrides of transition or refractory metals obtained by various physical-vapor deposition (PVD) techniques are presented. The influence of substrate temperature, substrate bias voltage, bilayer thickness and interface boundaries on the structure of coatings and their properties, such as hardness, plasticity, wear and corrosion resistance, are discussed in detail. This review may be useful for students and growing community of researchers interested in the synthesis-structure-properties relationship in multilayer coatings based on metal nitrides.

A General and Robust Strategy for Fabricating Mechanoresponsive Surface Wrinkles with Dynamic Switchable Transmittance

AbstractPreparation of surface wrinkles on a skin layer/elastomer substrate bilayer film has attracted extensive attention because of their unique and broad applications in flexible electronic devices, tunable diffraction gratings, and smart windows. However, it still remains a great challenge to develop a general strategy for fabricating mechanoresponsive surface wrinkles using various skin layer materials with wide tunability of wrinkles' wavelength and amplitude, large optical modulation range, rapid optical switching rate, and high stability. Here, a general, simple, and cost‐effective strategy is reported, through uniaxially stretching and subsequently releasing skin layer/elastomer substrate bilayer films, for producing highly ordered, crack‐free, 1D surface wrinkles on elastomeric polydimethylsiloxane (PDMS) substrates with various skin layer materials, including polyvinyl alcohol (PVA), chitosan (CS), hydroxyethyl cellulose, and the mixtures of PVA and CS. The surface wrinkles on PVA/PDMS bilayer film exhibit excellent mechanoresponsive optical switching properties, such as large transmittance modulation range (transmittance from ≈6% to 91% at visible region), high optical sensitivity with small mechanical strain (less than 20%), and long optical switching cycles (over 2000 times). It is anticipated that this method will enable a new path to the fabrication of mechanoresponsive surface wrinkles with outstanding performance for applications in dynamic optical switching fields and beyond.

Patterning artificial lipid bilayer on nanostructured surfaces.

Artificial lipid bilayer on solid substrate plays an important role as an interface between nanotechnology and biology. In this study, grid structures were patterned on Au-Nb-glass substrate and artificial bilayer was prepared on these structures. The fluidity was checked using fluorescence recovery after photobleaching (FRAP), and neuronal adhesion was monitored on such structure using EphrinA5-tethered lipid bilayer. EphrinA5 is a ligand that binds to the Eph receptors of rat cortical neurons and influences cellular adhesion. Our result elucidated that influence of these nanopatterned protein-tethered lipid bilayer on cellular guidance and signaling can address many underlying mechanisms of cellular functioning and help us to understand and differentiate the signaling procedure in cancer and neurodegenerative diseases.

High quality epitaxial graphene by hydrogen-etching of 3C-SiC(111) thin-film on Si(111)

Etching with atomic hydrogen, as a preparation step before the high-temperature growth process of graphene onto a thin 3C-SiC film grown on Si(111), greatly improves the structural quality of topmost graphene layers. Pit formation and island coalescence, which are typical of graphene growth by SiC graphitization, are quenched and accompanied by widening of the graphene domain sizes to hundreds of nanometers, and by a significant reduction in surface roughness down to a single substrate bilayer. The surface reconstructions expected for graphene and the underlying layer are shown with atomic resolution by scanning tunnelling microscopy. Spectroscopic features typical of graphene are measured by core-level photoemission and Raman spectroscopy.

Praseodymium Doped Ceria Oxygen Surface Exchange Coefficient and Film Stress Measurements Via the Curvature Relaxation Technique

Introduction Praseodymium doped ceria (PCO) is a mixed ionic electronic conductor (MIEC) that can be used as a cathode material in solid oxide fuel cells (SOFCs). Under SOFC operating conditions, PCO undergoes the following reaction [1]: ½ O2 + 2Pr’ Ce + VӦ à 2PrCe + Oo x The kinetics of this oxygen exchange reaction are represented by the oxygen surface exchange coefficient (kchem ). In this work, simultaneous kchem and stress measurements on PCO thin films atop yttria-stabilized zirconia (YSZ) substrates were performed from 625-725 oC using the curvature relaxation (κR) technique. Experimental Methods Phase pure Pr0.1Ce0.9O1.95 powder was prepared through glycine nitrate combustion and subsequent powder calcination in air. (001) oriented 9.5% YSZ substrates (Crystec, GmbH) were pre-annealed at 1450oC for 20 hours. PCO thin films were sputtered onto YSZ substrates at room temperature and then sintered for 1 hour at 1100oC. The bilayer structures were tested using a multi beam optical stress sensor (MOSS) from 625oC to 725oC with 25oC increments. The κR technique determines kchem by fitting a solution of Fick’s 2nd Law to the curvature response of mechano-chemically active film | inert substrate bilayers reacting to sudden changes in oxygen partial pressure (synthetic air (21% O2 - 79% Ar) and 10% synthetic air - 90% Ar) [2,3]. Film stress values were calculated using Stoney’s equation [2,3]. In order to compare the kchem values with those in the literature, electrically-measured PCO kq values from the literature [4] were turned into kchem values by multiplying them by the corresponding PCO thermodynamic factor from Ref [5]. Results Figure 1 shows how the kchem value measured via the κR technique compares with literature [4,5] values. Conclusions The PCO kchem and activation energies measured here are significantly different than those reported in the literature. Although additional work is needed before these effects can be explained in full, these discrepancies may be caused by the different synthesis techniques (sputtering vs. pulsed laser deposition) used to produce the two films shown in Figure 1. Acknowledgements This material is based upon work supported by the Department of Energy under Award Number DE-FE0023315.

Low temperature annealing effect on photoresponse of the bilayer structures of ZnO nanorod/nanodiamond films based on ultraviolet photodetector

This study presents a low temperature annealing process to improve the photoresponse of the ZnO nanorod (ZnO NR)/nanodiamond film (NDF)/glass substrate bilayer structure of an ultraviolet (UV) photodetector. The wurtzite structure of ZnO NRs with a diameter/length of 160nm/2.7μm was grown by the hydrothermal method on a 700-nm-thick NDF layer synthesized by a microwave plasma chemical vapor deposition system. A photoluminescence spectra showing a near-band-edge emission at 3.28eV with a shoulder peak at 3.20eV for the Zn interstitial was observed for the 200°C annealed sample. The Raman spectra of samples showed an improved 1332cm−1 sp3 diamond quality and reduced the non-diamond components while increasing the annealing temperature. A high photoresponse of 249.6 can be achieved by a 150°C annealing process, which is about 6 times better than the as-grown sample. The low dark current of 1.76×10−5A for the 150°C annealing sample was believed to be due to the improvement of the interface quality between the NDF and ZnO layer. However, the Zn interstitial generated in the 200°C annealed sample disrupted the carrier's trapping process, resulting in a lower photocurrent. In addition, this type of defect also caused the interface quality of the ZnO NR/NDF bilayer structure to degrade and increase the dark current. The experimental results indicated that the annealing temperature plays an important role in improving the photoresponse of ZnO NR/NDF bilayer structured UV photodetector.

Dirac fermions in a Fe ultrathin film

We show the existence of massive Dirac fermions in electronic band structures of a few Fe atomic layers with perpendicular magnetization. Based on a tight binding model fitted to ab-initio band structure, we observe four distinct massive Dirac fermions near the Fermi level, which result from atomic spin-orbit coupling of Fe and a band inversion between Fe $4s$-$3d_{x^2-y^2}$ hybrid orbital band and $3d_{xy}$ orbital band. These lead to a valence band with finite Chern integer (+2) and chiral edge modes near the Fermi level. When the chemical potential is set inside the Dirac gap by carrier doping, the Hall conductivity exhibits a plateau-like structure with quantized value $2\frac{e^2}{h}$, and orbital magnetization shows a prominent increase, latter of which is mostly due to chiral orbital motion of electrons along the edge modes. We discuss the stability of the Dirac fermions in Fe(001) monolayer on MgO(001) substrate and Fe(001) bilayer case.

Specific adhesion of membranes simultaneously supports dual heterogeneities in lipids and proteins.

Membrane adhesion is a vital component of many biological processes. Heterogeneities in lipid and protein composition are often associated with the adhesion site. These heterogeneities are thought to play functional roles in facilitating signalling. Here we experimentally examine this phenomenon using model membranes made of a mixture of lipids that is near a phase boundary at room temperature. Non-adherent model membranes are in a well-mixed, disordered-fluid lipid phase indicated by homogeneous distribution of a fluorescent dye that is a marker for the fluid-disordered (Ld) phase. We specifically adhere membranes to a flat substrate bilayer using biotin-avidin binding. Adhesion produces two types of coexisting heterogeneities: an ordered lipid phase that excludes binding proteins and the fluorescent membrane dye, and a disordered lipid phase that is enriched in both binding proteins and membrane dye compared with the non-adhered portion of the same membrane. Thus, a single type of adhesion interaction (biotin-avidin binding), in an initially-homogeneous system, simultaneously stabilizes both ordered-phase and disordered-phase heterogeneities that are compositionally distinct from the non-adhered portion of the vesicle. These heterogeneities are long-lived and unchanged upon increased temperature.

Self-organized metal-semiconductor epitaxial graphene layer on off-axis 4H-SiC(0001)

The remarkable properties of graphene have shown promise for new perspectives in future electronics, notably for nanometer scale devices. Here we grow graphene epitaxially on an off-axis 4H-SiC(0001) substrate and demonstrate the formation of periodic arrangement of monolayer graphene on planar (0001) terraces and Bernal bilayer graphene on (112 — 0) nanofacets of SiC. We investigate these lateral superlattices using Raman spectroscopy, atomic force microscopy/ electrostatic force microscopy (AFM/EFM) and X-ray and angle resolved photoemission spectroscopy (XPS/ARPES). The correlation of EFM and ARPES reveals the appearance of permanent electronic band gaps in AB-stacked bilayer graphene on (112 — 0) SiC nanofacets of 150 meV. This feature is confirmed by density functional theory (DFT) calculations. The charge transfer between the substrate and graphene bilayer results in an asymmetric charge distribution between the top and the bottom graphene layers opening an energy gap. This surface organization can be thus defined as self-organized metal–semiconductor graphene.

Chemically Resolved Interface Structure of Epitaxial Graphene on SiC(0001)

Atomic-layer 2D crystals have unique properties that can be significantly modified through interaction with an underlying support. For epitaxial graphene on SiC(0001), the interface strongly influences the electronic properties of the overlaying graphene. We demonstrate a novel combination of x-ray scattering and spectroscopy for studying the complexities of such a buried interface structure. This approach employs x-ray standing wave-excited photoelectron spectroscopy in conjunction with x-ray reflectivity to produce a highly resolved chemically sensitive atomic profile for the terminal substrate bilayers, interface, and graphene layers along the SiC[0001] direction.

Low Temperature Lanthanum Strontium Ferrite Thin Film Stress and Oxygen Surface Exchange Coefficient Measurements

Mechano-chemical coupling of La0.6Sr0.4FeO3-δ thin films were observed below 500oC for the first time using a curvature relaxation technique. Chemical oxygen surface exchange coefficients (k’s) were measured by fitting the transient curvature of the thin film|substrate bilayer specimens under controlled temperature and oxygen partial pressure. Reproducible k values and their activation energies were obtained and are consistent with bulk sample k’s extrapolated from the literature.

The mechanism of phase formation in Pt/Co bilayers during ion beam mixing

Ion beam mixing of Pt/Co/Si (Substrate) bilayers were carried out with a 4MeV Si+ ion beam at two different temperatures – room temperature and 300°C. When the mixing is carried out at 300°C, diffusion of Co atoms to the top Pt layer is observed thereby synthesizing CoPt and Co3Pt crystalline phases. When the irradiation is carried out at room temperature, Co and Pt atoms diffuse inwards to the silicon substrate and no new crystalline phase formation is observed. We propose that the direction of movement of the atoms and the resulting concentration profile in the Pt/Co/Si bilayers during ion beam mixing decides the nature of phase synthesized.

Measurements of residual stresses in the Parylene C film/silicon substrate using a microcantilever beam

A series of Parylene C film/silicon substrate bilayer microcantilever beams were fabricated by microelectromechanical processes for the study of residual stresses. The Parylene C films of 2 µm thickness were deposited on the Si substrates with various thicknesses. After deposition at room temperature, deflection of the beam was observed with deposited Parylene C on the concave side. While Parylene C has a higher coefficient of thermal expansion than Si, this deflection is believed to result from the thermal mismatch between Parylene C and Si, and the temperature of monomer gas (which is formed at 690 °C) flowing across the sample could be higher than 25 °C. It is estimated to be 73 °C based on the fitting of the curvature versus substrate thickness relation between the measurements and analytical solutions. In this case, Parylene C films are subjected to tension. In addition, the residual stress in the Parlyene C film decreases with decreasing substrate thickness.

Size-Dependent Thermomechanical Responses of Nano-Sized Multilayers

AbstractThe mechanical behavior of materials/structures at nanoscales has been shown, either experimentally or numerically, to be size-dependent. An accurate analysis of a nano-sized multilayer film/substrate structure subject to temperature variation is developed in the present paper. The size-dependent character is captured by adopting the modified couple stress theory. In addition, the effect of bonding imperfection between any two consecutive layers in the structure is considered by using a linear slip-type weak interface model. In the analysis, each layer is modeled as a non-classical Euler-Bernoulli beam incorporating the couple stress. An efficient state-space formulation for the multilayer structure is presented. Comparisons of the axial force, deflection and interfacial shear stress predicted by the present model with those by the classical beam model are made in cases of a Ni film/Epoxy substrate bilayer and of a Ni film/Ni film/Epoxy substrate trilayer. The results show that a nano-sized struct...

Ytterbium Intercalation of Epitaxial Graphene Grown on Si-Face SiC

The rare-earth metal, ytterbium (Yb), was deposited on graphene grown on Si-face SiC, kept at room temperature. Yb was not found to intercalate, destroy or dope the graphene layer before subsequent heating, unlike alkali metals such as Li and Na. Our photoemission results reveal that heating to 300?C promotes Yb intercalation into the graphene-substrate interface. Real-time low energy electron microscopy (LEEM) measurements indicated intercalation to start at a sample temperature of around 220oC. In the intercalation process, Yb penetrates through the graphene and buffer layer and forms bonds to the silicon in the topmost SiC substrate bilayer, as indicated by the shifted components observed in the C 1s, Si 2p, and Yb 4f spectra. The Yb intercalation decouples the buffer layer from the substrate and transforms it into another graphene layer as manifested by the absence of buffer layer spots in the μ-LEED pattern and the appearance of an additional π band in the ARPES spectra, respectively. Moreover, the observed shift of the Dirac point down from the Fermi level by 1.9 eV indicates electron doping of the graphene layer upon Yb intercalation. The Yb intercalated graphene sample was found to be thermodynamically stable up to temperatures around 700oC.

Effect of characteristics of (Sm,Ce)O 2 powder on the fabrication and performance of anode-supported solid oxide fuel cells

Effect of characteristics of Sm 0.2Ce 0.8O 1.9 (SDC) powder as a function of calcination temperature on the fabrication of dense and flat anode-supported SDC thin electrolyte cells has been studied. The results show that the calcination temperature has a significant effect on the particle size, degree of agglomeration, and sintering profiles of the SDC powder. The characteristics of SDC powders have a significant effect on the structure integrity and flatness of the SDC electrolyte film/anode substrate bilayer cells. The SDC electrolyte layer delaminates from the anode substrate for the SDC powder calcined at 600 °C and the bilayer cell concaves towards the SDC electrolyte layer for the SDC powder calcined at 800 °C. When the calcinations temperature increased to 1000 °C, strongly bonded SDC electrolyte film/anode substrate bilayer structures were achieved. An open-circuit voltage (OCV) of 0.82–0.84 V and maximum power density of ∼1 W cm −2 were obtained at 600 °C using hydrogen as fuel and stationary air as the oxidant. The results indicate that the matching of the onset sintering temperature and maximum sintering rate temperature is most critical for the development of a dense and flat Ni/SDC supported SDC thin electrolyte cells for intermediate temperature solid oxide fuel cells.