Search query: Structural, mechanical, and electronic properties of P3m1-BCN

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abstract: Abstract The mechanical and electronic properties of P3m1 BCN have been studied by using first principles calculations. The anisotropy studies of Young's modulus, shear modulus and Poisson's ratio show that P3m1 BCN exhibits a large anisotropy. Electronic structure study shows that P3m1 BCN is an indirect semiconductor with band gap of 4.10 eV. Unusually, the band gap of P3m1 BCN increase with increasing pressure.
author_names: Qingyang Fan

Qun Wei

Changchun Chai

Haiyan Yan

Meiguang Zhang

Zheng-Zhe Lin

Zixia Zhang

Junqin Zhang

Dongyun Zhang
title: Structural, mechanical, and electronic properties of P3m1 BCN
year: 2015

abstract: Magnesium and magnesium alloys are used in a wide variety of structural applications including automotive, aerospace, hand tools and electronic industries thanks to their light weight, high specific strength, adequate corrosion resistance and good castability. Al and Zn are the primary alloying elements in commercial Mg alloys and commonly used in automotive industries. AZ91 is one of the most popular Mg alloys containing 9% Al and 1% Zn. Hence, lots of research have been done during last decades on AZ91D. However, the existing data concerning mechanical properties and microstructural features showed large scatter and is even contradictory. This work focused on the correlation between the microstructure and the mechanical properties of as cast AZ91 alloy. An exhaustive characterization of the grain size, secondary dendrite arm spacing (SDAS) distribution, and fraction of Mg17Al12 using optical and electron backscattered diffraction (EBSD) was performed. These microstructural parameters were correlated to offset yield point (Rp0.2) fracture strength and elongation to fracture. It was understood that the intermetallic phase, Mg17Al12, plays an important role in determining the mechanical and physical properties of the alloy at temperature range from room temperature up to 190oC. It was realized that by increasing the Mg17Al12 content above 11% a network of intermetallic may form. During deformation this rigid network should break before any plastic deformation happen. Hence, increase in Mg17Al12 content resulted in an increase in offset yield point. The presence of this network was supported by study of thermal expansion behaviour of the alloy containing different amount of Mg17Al12. A physically based model was adapted and validated in order to predict the flow stress behaviour of as cast AZ91D at room temperature up to 190oC for various microstructures. The model was based on dislocation glide and climb in a single phase (matrix) material containing reinforcing particles. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material.
author_names: Hoda Dini

Nils-Eric Andersson

Anders E W Jarfors
title: Effect of Mg17Al12 content on mechanical properties of AZ91D cast alloy
year: 2015

abstract: Kapton polyimide films are one of the most commonly used flexible and robust substrates for flexible electronic devices due to their excellent thermal, chemical, mechanical, and electrical properties. However, such films feature an inert and highly hydrophobic surface that inhibits the deposition of functional materials with water based fluids (solutions, suspensions, inkjet inks, etc. which raise the need for their surface modification to reduce their inherent surface inertness and/or hydrophobicity in order to allow for the fabrication of electronic devices on the substrates. Traditional Kapton surface modification approaches use harsh conditions that not only cause environmental and safety problems but also compromise the structural integrity and the properties of the substrates. This chapter focuses on two recently developed mild and environmentally friendly wet chemical approaches for surface modification of Kapton HN films. Unlike the traditional methods that target the polyimide matrix of Kapton films, these two methods target the slip additive embedded in the polyimide matrix. The surface modified Kapton films resulted from these two methods allowed for not only great printability of both waterand organic solvent based inks (thus facilitating the full inkjet printing of entire flexible electronic devices) but also strong adhesion between the inkjet printed traces and the substrate films.
author_names: Yunnan Fang and Manos M Tentzeris
title: Surface Modification of Polyimide Films for Inkjet Printing of Flexible Electronic Devices
year: 2018

abstract: In lightweight construction, integrated piezoelectric sensors and actuators find application for structural health monitoring, vibration control, reduction of noise emission and condition monitoring. In order to create such smart components, we embedded piezofiber composites into thermoplastic structures. Thermal and mechanical loads during the integration process can lead to partial depolarization and thus degradation of the piezoelectric properties. In the present work, we investigate the effect of the integration on the poling condition and polarizability of piezofiber composites. 1 3 piezofiber composites (PFC) consisting of a monolayer of PZT fibers embedded in epoxy resin were used as starting material [1] In the first integration step, they were positioned between two transparent thermoplastic carrier films and consolidated by hot pressing, forming the so called TPM (thermoplastic compatible piezoceramic module) In the second integration step, these TPMs were integrated into a fibre reinforced plastic (FRP) structure [2] The investigated samples were divided into three groups: reference samples, which were poled but not integrated, pre poled samples, which were poled and integrated, re poled samples, which were additionally poled after each processing step. The natural aging without the influence of fabrication processes and re poling was deduced from the capacitance of the reference samples. The poling condition was evaluated by the Laser Intensity Modulation Method (LIMM) and the thermal pulse method. The pyroelectric current was analyzed by heating with an intensity modulated laser beam or laser pulses [3] Hysteresis measurements were performed to determine the effect of the integration on the polarizability. The pyroelectric current spectra of the same sample were compared for the three states PFC, TPM and FRP. Pre poled samples showed a degradation of the remanent polarization after integration. The range of degradation varied widely between 1% and 23% for one integration step. The polarization of the repoled samples was increased or only slightly decreased. Consequently, the results obtained by LIMM were confirmed by the thermal pulse response. The attainable remanent polarization was derived from the hysteresis curves of the PFC and of the repoled samples after each integration step. It was decreased after integration. The remanent polarization of the integrated composites reached 95% of the initial value. In conclusion, the integration of a PFC into a structural component leads to a decrease of the remanent polarization and of the polarizability. However, the observed depolarization is within the variation of the polarization state of the PFC and thus, negligible. Hence, re poling after the integration appears not to be necessary, although possible. REFERENCES [1] K. Hohlfeld, P. Neumeister, S. Gebhardt, A. Michaelis, "Tailored Composite Transducers Based on Piezoceramic Fibres and Pearls" Proc. ACTUATOR 16, Bremen, Germany, June 13 15, 2016, 69 72, www.actuator.de. [2] W. Hufenbach, M. Gude, N. Modler, Th. Heber, A. Winkler and T. Weber, "Process chain modeling and analysis for the high volume production of thermoplastic composites with embedded piezoceramic modules" Smart Mater. Res. Vol. 2013, 201631, (2013) [3] A. Eydam, G. Suchaneck, K. Hohlfeld, S. Gebhardt, A. Michaelis, G. Gerlach, "Evaluation of the polarization state of piezofiber composites" IEEE Joint ISAF PFM 2013, Electronic Proc. 190 193, doi: 10.1109/ISAF.2013.6748683.
author_names: Kai Hohlfeld

Sophia Esslinger

Angelique Eydam

Anders Winkler

Tony Weber

Maria R Gude

Niels Modler

G Gerlach

Gunnar Suchaneck

Alan John Michaelis

Andreas Schonecker

Siegmar Gebhardt

Peter Neumeister
title: Effect of the Integration of Piezoceramic Composites into Structural Components on their Poling Condition and Polarizability
year: 2017

abstract: Electronic, structural, and spectroscopic properties of the ground state neutral and singly ionized mono di tri and tetrafluoropyrroles are studied using ab initio and density functional theory quantum mechanical methods. The effects of the number and position of the substituents on the electrochemical properties of the pyrrole ring have been studied. Using the optimized structures obtained for these molecules and their cations, IR and NMR spectra have been calculated and analyzed. The results of this study, including charge and spin density distribution analyses, show that among all of these compounds 3 fluoropyrrole and 3,4 difluoropyrrole have the most suitable conditions for electropolymerization.
author_names: and Hassan Sabzyan

Abdollah Omrani
title: Ab Initio and DFT Study of All Mono Di Tri and Tetrafluoropyrroles and Their Cations: Predicting Structural, Spectroscopic, Electropolymerization, and Electrochemical Properties
year: 2003

abstract: CuZSM 5 is the most active catalyst known for the direct decomposition of NOx. We have performed first principles quantum mechanical calculations to evaluate the electronic and structural properties of species adsorbed to Cu sites that might be involved in NOx decomposition. Using statistical mechanics, we have calculated DUdeg, DHdeg, and DGdeg of possible elementary reactions in order to evaluate the stability of adsorbates on Cu sites and the ease of their interconversion. On the basis of these calculations, we propose a reaction pathway for NOx decomposition. This scheme involves only single, isolated copper sites, is internally consistent, and is consistent with experimental observations.
author_names: Bernhardt L Trout

and Arup K Chakraborty

Alexis T Bell
title: Analysis of the Thermochemistry of NOx Decomposition over CuZSM 5 Based on Quantum Chemical and Statistical Mechanical Calculations
year: 1996

abstract: Unusual electronic states arise at ferroelectric domain walls due to the local symmetry reduction, strain gradients and electrostatics. This particularly applies to improper ferroelectrics, where the polarization is induced by a structural or magnetic order parameter. Because of the subordinate nature of the polarization, the rigid mechanical and electrostatic boundary conditions that constrain domain walls in proper ferroics are lifted. Here we show that spin driven ferroelectricity promotes the emergence of charged domain walls. This provides new degrees of flexibility for controlling domain wall charges in a deterministic and reversible process. We create and position a domain wall by an electric field in Mn0.95Co0.05WO4. With a magnetic field we then rotate the polarization and convert neutral into charged domain walls, while its magnetic properties peg the wall to its location. Using atomistic Landau Lifshitz Gilbert simulations we quantify the polarization changes across the two wall types and highlight their general occurrence.
author_names: Naemi Leo

Anders Bergman

Andres Cano

Narayan Poudel

Bernd Lorenz

Manfred Fiebig

Dennis Meier
title: Polarization control at spin driven ferroelectric domain walls.
venue: Nature communications
year: 2015

abstract: In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single walled carbon nanotubes. For the multi walled carbon nanotubes the focus is on inter shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density functional theory (DFT) Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more p stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.
author_names: Anders Hansson

Sven Stafstrom
title: Electronic structure calculations of potassium intercalated single walled carbon nanotubes
year: 2005

abstract: In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single walled carbon nanotubes. For the multi walled carbon nanotubes the focus is on inter shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density functional theory (DFT) Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more p stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.
author_names: Johan Bohlin

Anders Hansson

Sven Stafstrom
title: Electronic structure calculations of a phenalenyl based neutral radical conductor
year: 2006

abstract: Multilayer MoS2 possesses highly anisotropic thermal conductivities along in plane and cross plane directions that could hamper heat dissipation in electronics. With about 9% cross plane compressive strain created by hydrostatic pressure in a diamond anvil cell, we observed about 12 times increase in the cross plane thermal conductivity of multilayer MoS2. Our experimental and theoretical studies reveal that this drastic change arises from the greatly strengthened interlayer interaction and heavily modified phonon dispersions along cross plane direction, with negligible contribution from electronic thermal conductivity, despite its enhancement of 4 orders of magnitude. The anisotropic thermal conductivity in the multilayer MoS2 at ambient environment becomes almost isotropic under highly compressive strain, effectively transitioning from 2D to 3D heat dissipation. This strain tuning approach also makes possible parallel tuning of structural, thermal and electrical properties, and can be extended to the whole family of 2D Van der Waals solids, down to two layer systems.
author_names: Xianghai Meng

Tribhuwan Pandey

Suyu Fu

Jing Yang

Jihoon Jeong

Ke Chen

Akash Singh

Feng He

Xiaochuan Xu

Abhishek Kumar Singh

Jung-Fu Lin

Yaguo Wang Department of Mechanical Engineering

The University of Texas at Austin

Materials Research Centre

India Debye Institute for Nanomaterials Science

John A Katherine G Jackson School of Geosciences

Texas Materials Institute

Omega Optics

Center for Space Science

Technology Advanced Research
title: Giant Thermal Conductivity Enhancement in Multilayer MoS2 under Highly Compressive Strain
year: 2017