Bending Module Research Articles

Ferroelectric Control of the Conduction at the LaAlO3/SrTiO3 Heterointerface

Modulation of band bending at a complex oxide heterointerface by a ferroelectric layer is demonstrated. The as-grown polarization (Pup ) leads to charge depletion and consequently low conduction. Switching the polarization direction (Pdown ) results in charge accumulation and enhances the conduction at the interface. The metal-insulator transition at a conducting polar/nonpolar oxide heterointerface can be controlled by ferroelectric doping.

Physical and mechanical properties of wood plastic composites polystyrene-white oak wood flour

This study examines the effect of particle size and wood flour content on the properties of polystyrene filled with white oak flour. Wood-plastic ratios 10:90, 30:70 and 50:50% (wt/wt) and particle size 40, 50, 65 and 100 mesh were used. Tensile, bending and impact bending strength as well as the melt flow index were evaluated. Additionally, composite density and water absorption capacity were also tested. Scanning electronic microscopy revealed good adhesion between wood particles and polystyrene. Results show that mechanical properties are strongly influenced by wood flour content and particle size. A reduction in tensile module, elongation and deflection were observed, however, the bending module was increased. Impact strength increased with particle size and content. Melt flow index values are reduced with the increasing amount of filler content while water absorption increases with the amount of wood particles.

Electromodulation spectroscopy of optical transitions and electric field distribution in GaN/AlGaN/GaN transistor heterostructures with various AlGaN layer thicknesses

AbstractGaN/AlGaN/GaN field effect transistor (FET) heterostructures with various thicknesses of AlGaN layer (10, 20, and 30nm) were investigated by electromodulation spectroscopy [i.e. contactless electroreflectance (CER) and photoreflectance (PR)]. In PR spectra optical transitions in GaN cap, AlGaN and GaN buffer layers were clearly observed whereas in CER spectra the optical transition in GaN buffer layer was not observed due to the screening of band bending modulation in CER spectroscopy by the two dimensional electron gas at the AlGaN/GaN interface. The transition related to GaN‐cap was observed ∼0.1 eV above the energy gap of GaN due to the quantum confinement in the surface GaN quantum well. The built‐in electric field in AlGaN layer was determined from the analysis of AlGaN‐related Franz‐Keldysh oscillation. For the sample with 10, 20, and 30nm thick AlGaN layer the electric field has been determined from CER(PR) measurements to be 0.30(0.27), 0.46(0.39) and 0.78(0.63) MV/cm, respectively. The smaller electric field, which is obtained from PR measurements, results from the photovoltaic effect which is eliminated in CER spectroscopy. The electric field distribution in the full heterostructure (GaN(cap) layer, AlGaN layer, and near the AlGaN/GaN interface in GaN(buffer) layer) has been found comparing theoretical calculations for the full heterostructure with the electric field for AlGaN layer obtained from CER measurements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Long-scale dynamics of crystalline membranes

We investigate effects of long-wavelength dynamic fluctuations in free-standing crystalline membranes by means of the renormalization group method. Thermal fluctuations lead to power dispersion laws for two acoustic in-plane sound modes (longitudinal and transversal) and one out-of-plane bending mode governed by the renormalized static elastic and bending modules. There is no logarithmic contribution to the attenuation of the modes in the marginal membrane dimension $D=4$; therefore, in the dimensionality $D\ensuremath{-}\ensuremath{\epsilon}$, the attenuations are slave, following the same scaling laws as the dispersion laws. We anticipate that our results can be relevant for a better understanding of the graphene (and other crystalline films) dynamics.

Based on the Theory of Thin-Walled Bar Flexure-Torsion Analysis of the Oblique Combined Structure

This paper assumes that a row of the frame, shear wall structure as affected by lateral bending and torsion modules coupling effect of thin-walled members, through the floor to work together to establish a collaborative analysis of structural bias of the Hamiltonian on the dual system, with precise integration method for the numerical solution of high-precision systems, analysis of bias is given a set of construction the structure of collaborative work. The results make the structure more in line with the actual deformation.

Contactless electroreflectance of AlGaN/GaN heterostructures deposited on c-, a-, m-, and (20.1)-plane GaN bulk substrates grown by ammonothermal method

Room temperature contactless electroreflectance (CER) has been applied to study optical transitions and the distribution of the built-in electric field in AlGaN/GaN heterostructures grown on c-, a-, m-, and (20.1)-plane GaN substrates obtained by the ammonothermal method. It has been clearly shown that polarization effects in the AlGaN/GaN heterostructures grown on the c-plane lead to a strong built-in electric field in the AlGaN layer. The aforementioned field was determined to be ∼0.43 MV/cm from the period of Franz–Keldysh oscillations (FKOs). In addition, polarization effects lead to the formation of a two dimensional electron gas at the AlGaN/GaN interface, which screens the band bending modulation in the GaN buffer layer, and, therefore, GaN-related excitonic transitions are not observed for this heterostructure. Such features/effects are also not observed in the AlGaN/GaN heterostructures grown on nonpolar and semipolar GaN substrates because any strong polarization effects are not expected in this case. For these heterostructures, very strong and sharp GaN excitonic resonances are clearly visible in CER spectra. The resonances are very similar to the excitonic transitions observed for the GaN epilayers deposited on nonpolar and semipolar substrates. Moreover, there is a very weak AlGaN-resonance without FKO for nonpolar and semipolar heterostructures instead of the strong AlGaN-related FKO, which is typical of polar AlGaN/GaN heterostructures.

Modulation of Band Bending of Gallium Arsenide with Oriented Helical Peptide Monolayers

We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconductors by the covalent deposition of uniform monolayers of helical peptides. After the optimization of coupling groups and reaction conditions, structures of peptide monolayers on GaAs were characterized by the combination of grazing incidence-X-ray scattering and Fourier transform infrared spectroscopy yielding the thickness, the area occupied by one peptide helix, and the tilt angle of helical axis with respect to the surface normal. The deposition of the same peptides on high electron mobility transistor (HEMT) devices resulted in a clear change in the carrier mobility depending on the length of peptide helices. The obtained results demonstrated that the macrodipole potential of oriented peptide helices can be utilized for flexible tuning of the electronic structure (band bending) of semiconductors, which can offer a unique alternative to the commonly used doping of charge carriers.

Avaliação tecnológica de painéis MDF de madeira de <i>Eucalyptus grandis </i> confeccionados em laboratório e em linha de produção industrial

Chapas MDF de fibras da madeira de Eucalyptus grandis foram confeccionadas em laboratório e em linha de produção industrial e determinadas suas propriedades anatômicas, físicas e mecânicas. O desfibramento da madeira provocou o rompimento transversal da parede das fibras. Os painéis MDF obtidos em linha de produção apresentaram menores valores de inchamento e de absorção e melhores propriedades mecânicas para módulo de ruptura, módulo de elasticidade e resistência à tração superficial. Para os painéis MDF confeccionados em laboratório, verificou-se correlação estatisticamente significativa entre módulo de ruptura e de elasticidade, densidade média e resistência à tração perpendicular e inchamento e absorção. Para os painéis MDF confeccionados em linha de produção industrial, verificaram-se as mesmas tendências, sem significância estatística. A avaliação dos parâmetros de qualidade de painéis MDF de eucalipto confeccionados em laboratório e em linha de produção visa a calibrar as variáveis para a obtenção de chapas MDF em pequena escala e melhorar a precisão das análises de rotina de controle de qualidade bem como nas informações apresentadas em publicações científicas.

Origin of Twist-Bend Coupling in Actin Filaments

Actin filaments are semiflexible polymers that display large-scale conformational twisting and bending motions. Modulation of filament bending and twisting dynamics has been linked to regulatory actin-binding protein function, filament assembly and fragmentation, and overall cell motility. The relationship between actin filament bending and twisting dynamics has not been evaluated. The numerical and analytical experiments presented here reveal that actin filaments have a strong intrinsic twist-bend coupling that obligates the reciprocal interconversion of bending energy and twisting stress. We developed a mesoscopic model of actin filaments that captures key documented features, including the subunit dimensions, interaction energies, helicity, and geometrical constraints coming from the double-stranded structure. The filament bending and torsional rigidities predicted by the model are comparable to experimental values, demonstrating the capacity of the model to assess the mechanical properties of actin filaments, including the coupling between twisting and bending motions. The predicted actin filament twist-bend coupling is strong, with a persistence length of 0.15–0.4 μm depending on the actin-bound nucleotide. Twist-bend coupling is an emergent property that introduces local asymmetry to actin filaments and contributes to their overall elasticity. Up to 60% of the filament subunit elastic free energy originates from twist-bend coupling, with the largest contributions resulting under relatively small deformations. A comparison of filaments with different architectures indicates that twist-bend coupling in actin filaments originates from their double protofilament and helical structure.

Noncontact interface trap determination of SiO2–4H–SiC structures

A sequence of noncontact corona-Kelvin metrology is introduced that enables the determination and monitoring of interface properties in dielectric/wide band gap semiconductor structures. The technique involves the incremental application of precise and measured quantities of corona charge, QC, onto the dielectric surface followed by determination of the contact potential difference, VCPD, as the material structure response. The V-Q characteristics obtained are used to extract the surface barrier, VSB, response related to the applied corona charge. The described approach differs from the common noncontact method applied in the case of dielectric/silicon structures where for each quanta of applied charge the value of surface barrier voltage, VSB, is obtained. Materials with wide band gaps and high concentrations of deep levels, as suggested for silicon carbide, do not permit quick determination of VSB by modulation of the band bending in the semiconductor with light. Light exposure in the case of SiC results in a long recovery time required to approach the nominal value of the preillumination VCPD value. The metrology approach presented determines an intersection of the VCPD-QC characteristic obtained in the dark with the Vox-QC characteristic representing the dielectric response. The specific VSB-QC dependence surrounding the reference VFB value is obtained from this approach and enables the noncontact determination of the dielectric interface trap density and its spectrum. Application of the modified metrology method to thermal oxide on n-type 4H-SiC demonstrates the modification of the Dit distribution by Fowler–Nordheim stress. In addition, an ability to quantify and separate trapped charge components is shown.

Contactless and soft contact electroreflectance of AlGaN/GaN and GaN/AlGaN/GaN field effect transistor heterostructures

AbstractAlGaN/GaN field effect transistor (FET) structures with a two dimensional electron gas (2DEG) at the interface were investigated by electromodulation spectroscopy [contactless electroreflectance (CER), and soft contact electroreflectance (SCER)]. It has been clearly shown that in contactless mode of electroreflectance (i.e., CER spectroscopy) the 2DEG screens the band bending modulation in GaN layer from the external electromodulation which is generated by the capacitor‐like system. In a result only the optical transition in AlGaN layer and no signal, which could be associated with the optical transition in GaN buffer layer, is observed in CER spectra. This screening is not present in soft contact mode of electroreflectance (i.e., SCER spectroscopy). It has been clearly shown that the soft contact mode of electrorefletance works very well for AlGaN/GaN FET structures with a 2 nm thick GaN cap layer. In this mode of electroreflectance measurements the signal from GaN buffer layer was clearly observed whereas in CER spectra this signal was not detected. In CER spectra only the AlGaN‐related transition and the GaN cap‐related transition were observed. The last transition was observed at the energy of ∼3.65 eV because of quantum confinement in GaN cap layer, i.e., a surface quantum well in fact. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Bending behavior of Cu-plated Pd–Ni alloys ribbon driven by hydrogenation

In recent years, human-type robots attract much attention in the field of medical welfare and industrial applications under severe environmental conditions, such as in space. For the realization of such robots, the development of an actuator having superior functions as human fingers is required. It is known that hydrogen storage alloys exhibit a significant volume change of 10–30% on hydrogenation, which is several tens times greater than that caused by thermal expansion. Since the driving force of an actuator driven by hydrogenation is based on phase transformation, the actuator can be expected to show high power. In the present work, a bending module having a sheet form of palladium-base hydrogen storage alloy foils bond with a copper foil was prepared and its bending behaviors were investigated.

Elasticity Mapping of Pore‐Suspending Native Cell Membranes

The mechanics of cellular membranes are governed by a non-equilibrium composite framework consisting of the semiflexible filamentous cytoskeleton and extracellular matrix proteins linked to the lipid bilayer. While elasticity information of plasma membranes has mainly been obtained from whole cell analysis, techniques that allow addressing local mechanical properties of cell membranes are desirable to learn how their lipid and protein composition is reflected in the elastic behavior on local length scales. Introduced here is an approach based on basolateral membranes of polar epithelial Madin-Darby canine kidney (MDCK) II cells, prepared on a highly ordered porous substrate that allows elastic mapping on a submicrometer-length scale. A strong correlation between the density of actin filaments and the measured membrane elasticity is found. Spatially resolved indentation experiments carried out with atomic force and fluorescence microscope permit relation of the supramolecular structure to the elasticity of cellular membranes. It is shown that the elastic response of the pore spanning cell membranes is governed by local bending modules rather than lateral tension.

The Caenorhabditis elegans AMP-activated Protein Kinase AAK-2 Is Phosphorylated by LKB1 and Is Required for Resistance to Oxidative Stress and for Normal Motility and Foraging Behavior

AAK-2 is one of two alpha isoforms of the AMP-activated protein kinase in Caenorhabditis elegans and is involved in life span maintenance, stress responses, and germ cell cycle arrest upon dauer entry. We found that AAK-2 was phosphorylated at threonine 243 in response to paraquat treatment and that this phosphorylation depends on PAR-4, the C. elegans LKB1 homologue. Both aak-2 mutation and par-4 knockdown increased the sensitivity of C. elegans worms to paraquat, and the double deficiency did not further increase sensitivity, indicating that aak-2 and par-4 act in a linear pathway. Both mutations also slowed body bending during locomotion and failed to reduce head oscillation in response to anterior touch. Consistent with this abnormal motility and behavioral response, expression of the AAK-2::green fluorescent protein fusion protein was observed in the ventral cord, some neurons, body wall muscle, pharynx, vulva, somatic gonad, and excretory cell. Our study suggests that AMPK can influence the behavior of C. elegans worms in addition to its well known function in metabolic control.

Design of a bending module for assembling reconfigurable endoluminal surgical system

Design of a bending module for assembling reconfigurable endoluminal surgical system

Dynamics of Nearly Spherical Vesicles in an External Flow

Tank-treading, tumbling, and trembling are different types of the vesicle behavior in an external flow. We derive a dynamical equation enabling us to establish a state of nearly spherical vesicles. For a 2D external flow, the character of the vesicle dynamics is determined by two dimensionless parameters, depending on the vesicle excess area, fluid viscosities, membrane viscosity and bending modulus, strength of the flow, and ratio of the elongational and rotational components of the flow. The tank-treading to tumbling transition occurs via a saddle-node bifurcation, whereas the tank-treading to trembling transition occurs via a Hopf bifurcation. A slowdown of vesicle dynamics should be observed in a vicinity of a point separating the transition lines. We show that the slowdown can be described by a power law with two different critical exponents 1/4 and 1/2 corresponding to the slowdown of tumbling and trembling cycles.

Influence of Ammoniacal Copper Quaternary treatments on mechanical properties of blue-stained Lodgepole pine wood

Three concentrations (2.8%, 2.0%, 1.2%) of Ammoniacal Copper Quaternary (ACQ) was selected to treat Lodgepole pine wood for evaluating ACQ treatment on mechanical properties of blue-stained wood. The bending modules of elasticity (MOE), modules of rupture (MOR), toughness and shearing strength parallel to grain on tangential surface, are tested according to the criteria GB1927∼1943–91. Non-treated sample were also tested according to the same procedure. The results showed that the three groups specimen impregnated by different concentrations of ACQ solution met the AWPA standard 2003 of America (UC4A 6.4g/cm3). There were significant difference of toughness between treated wood and non-treated wood (p=0.01), but there were no statistically significant differences among three concentrations in terms of toughness, and toughness of treated wood was approximately 20% lower than non-treated. MOR, MOE as well as shearing strength parallel to grain were found to be not significantly different between treated wood and non-treated one, and there were no statistically significant difference among three concentrations of ACQ too. Toughness, MOR, MOE and shearing strength parallel to grain increased with decrease of concentration of ACQ, but they were hardly affected by ACQ preservatives.

β型リン酸三カルシウム粒子分散ポリＬ乳酸複合材料の力学的挙動の実験的評価及び損傷力学解析

Bioactive ceramics/PLLA composites have been expected as a material for the fracture fixations which have more biocompatibility than monolithic PLLA. In this study, β-TCP/PLLA composites containing three different β-TCP contents (4.8, 9.5, 14.3 wt%) were prepared by injection molding. The bending strength of composites decreased and the bending modules of those increased with increasing β-TCP contents. The effect of β-TCP content on the tensile strength and modulus also to does the same tendency of that on bending properties. Nevertheless, the tensile strength was half of bending strength. The results of fracture surface observation showed that the fracture of the composites was initiated by debonding between β-TCP agglomeration and PLLA. In addition, predictions of he tensile stress-strain curves based on the damage mechanics considering the sift of neutral plane were in good agreement with the experimental results.

Photo- and contactless electro-reflectance spectroscopies of step-like GaInNAs/Ga(In)NAs/GaAs quantum wells

Step-like GaInNAs/Ga(In)NAs/GaAs double quantum well (DQW) structures tailored at 1.3μm have been studied in photoreflectance (PR) and contactless electroreflectance (CER) spectroscopies. Spectral features related to absorption in the active part of the step-like DQW structure, i.e. GaInNAs/Ga(In)NAs QW, as well as features related to absorption between states confined above the step-like barrier (SLB) and in GaAs barriers have been observed. It has been shown that these two techniques give information about the same optical transitions. However, due to some differences in the mechanism of band bending modulation, PR and CER spectra are not exactly the same especially for the layer which is under significant internal electric field. It has been shown that Franz–Keldysh oscillations related to GaAs cap layer are clearly observed in CER and disappear in PR at strong modulation conditions due to an effective flattering of the surface band bending during PR measurements.

Photoreflectance study of p-type GaN layers

Layers of GaN:Mg ∼1.5 μm thick with different concentrations of Mg dopant have been investigated by room temperature photoreflectance (PR) spectroscopy. We have compared the results obtained by the PR technique with the results obtained by standard photoluminescence (PL) and reflectance (R) techniques. We have demonstrated that PR spectroscopy is an experimental technique which is sensitive to both optical and electrical properties of investigated samples, in contrast to PL and R spectroscopies, which are only sensitive to optical properties. This feature of PR spectroscopy is very useful for investigations of GaN:Mg layers, where we have to control both optical and electrical properties. In this paper we have shown that with the increase in the number of defect states in GaN:Mg layers, associated with the increase in Mg concentration, the PR signal decreases due to the weakening of the band bending modulation. This indicates that the electrical quality of the GaN:Mg layer deteriorates with the increase in the concentration of Mg atoms.