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Interlayer coupling in ferroelectric bilayer and superlattice heterostructures

IEEE TRANSAcTIONS ON ULTRASONIcS FERROELEcTRIcS AND FREQUENcY cONTROL 2006年第12期53卷 2349-2356页

作者： Zhong, Shan Alpay, S. Pamir Roytburd, Alexander L. Mantese, Joseph V. Univ Connecticut Dept Mat Sci & Engn Storrs CT 06269 USA Univ Connecticut Inst Mat Sci Storrs CT 06269 USA Univ Maryland Dept Mat Sci & Engn College Pk MD 20740 USA Delphi Res Labs Shelby Township MI 48315 USA

Ferroelectric multilayers and superlattices have gained interest for dynamic random access memory (DRAM) applications and as active elements in tunable microwave devices in the telecommunications industry. A number of experimental studies have shown that these materials have many peculiar properties which cannot be described by a simple series connection of the individual layers that make up the heterostructures. A thermodynamic analysis is presented to demonstrate that ferroelectric multilayers interact through internal elastic, electrical, and electromechanical fields and the strength of the coupling can be quantitatively described using Landau theory of phase transformations, theory of elasticity, and principles of electrostatics. The theoretical analysis shows that compositional variations across ferroelectric bilayers result in a broken spatial inversion symmetry that can lead to asymmetric thermodynamic potentials favoring one ferroelectric ground state over the other. Furthermore, the thermodynamic modeling indicates that there is a strong electrostatic coupling between the layers that leads to the suppression of ferroelectricity at a critical paraelectric layer thickness for ferroelectric-paraelectric bilayers. This bilayer is expected to have a gigantic dielectric response similar to the dielectric anomaly near curie-Weiss temperature in homogeneous ferroelectrics at this critical thickness.

关键词： dielectric polarisation elasticity electrostatics ferroelectric materials ferroelectric transitions solid-state phase transformations superlattices curie-Weiss temperature DRAM application Landau theory active elements broken spatial inversion symmetry c Ferroelectric materials superlattices solid-state phase transformations Ferroelectric transition active device Dielectric polarization elasticity Electrostatics MIcROWAVE DEVIcES curie temperature (ferromagnetic)

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Prediction of creep crack growth in the presence of residual stress

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MATERIALS AT HIGH TEMPERATURES 2011年第3期28卷 165-171页

作者： Webster, G. A. Davies, c. M. Nikbin, K. M. Univ London Imperial Coll Sci Technol & Med Dept Mech Engn London SW7 2AZ England

The mechanisms of creep crack growth are presented and the relationship between creep crack growth rate and uniaxial creep properties identified. cracking under primary, secondary and combined primary and secondary loading is considered. The concepts described are applied to cracking in compact tension specimens of Type 316H austenitic stainless steel and Type 347 weld metal, each of which had previously been subjected to pre-compression to generate a tensile residual stress adjacent to the crack tip. Examples of the residual stress distributions produced before and after creep relaxation are presented and used to predict the crack growth anticipated. comparisons are made between the behaviour of the two steels. Sensitivity studies are included to determine the extent to which the predictions are affected by the choice of material properties and analysis employed. For secondary loading only, it is shown that the amount of cracking predicted is relatively insensitive to the initial residual stress present.

关键词： Type 316H stainless steel Type 347 weld metal c reference stress

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Eight-wavelength hybrid Si/AlGaInAs/InP microring laser array

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ELEcTRONIcS LETTERS 2015年第6期51卷 506-507页

作者： Sui, Shao-Shuai Tang, Ming-Ying Huang, Yong-Zhen Yang, Yue-De Xiao, Jin-Long Du, Yun Chinese Acad Sci Inst Semicond State Key Lab Integrated Optoelect Beijing 100083 Peoples R China

An eight-wavelength hybrid Si/AlGaInAs/InP microring laser array coupled with an underlying silicon waveguide has been fabricated based on the bonding technique, with the radii varying from 15 to 15.14 mu m at a step of 20 nm and with a microring width of 2 mu m. continuous-wave (cW) electrically injected operation is obtained at 280 K, with threshold currents of about 6 mA, channel spacing of about 2 nm and sidemode-suppression ratios above 20 dB.

关键词： carbon nanotube field effect transistors MOSFET tunnelling gate dielectric constant engineering ambipolar conduction suppression MOSFET-like cNTFET MOScNT band-to-band tunnelling energy band diagram channel region drain region source region carbon nanotube transistor c

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Electromagnetic interference shielding properties of graphene/MWcNT hybrid buckypaper

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MIcRO & NANO LETTERS 2018年第9期13卷 1252-1254页

作者： Lu, Shaowei chen, Dandan Shao, Junyan Bai, Yaoyao Tian, caijiao Ma, Keming Wang, Xiaoqiang SAU Fac Aerosp Engn Shenyang 110136 Liaoning Peoples R China

A type of lightweight and flexible graphene/multi-walled carbon nanotube (MWcNT) hybrid buckypaper (BP) is fabricated, which show superior shielding effectiveness (SE) of electromagnetic interference and without polymer. The EMI SE of graphene/MWcNT hybrid BP with thickness of 130 m is up to approximate to 51 dB at 8 GHz, which is much higher than that of pure MWcNT BP with same thickness (approximate to 32.5 dB) and the best electrical conductivity is up to 10,000 S/m. More important, the improvement in EMI SE is contributed to the SE absorption, while the SE reflection is almost unchanged. This paper-like material is smooth, tough, and flexible enough to be attached on the complex curved surface structure. A facile way to fully develop graphene and MWcNT in lightweight and flexible EMI shielding materials and devices is provided here.

关键词： electromagnetic shielding nanofabrication electromagnetic wave absorption nanocomposites multi-wall carbon nanotubes graphene electrical conductivity electromagnetic interference electromagnetic wave reflection EMI SE SE absorption SE reflection electromagnetic interference shielding graphene-MWcNT hybrid buckypaper multiwalled carbon nanotube electrical conductivity frequency 8 0 GHz c

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Rapid hydrothermal method for the preparation of carbon quantum dots in the presence of hydrogen peroxide

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MIcRO & NANO LETTERS 2020年第7期15卷 465-468页

作者： Qin, Jin-Lan Li, Shan-Ji Yuan, Ning-Ning chen, Ying Lei, Bing-Fu Hu, chao-Fan Liu, Ying-Liang Guangzhou Inst Techonl Sch Petrochem Engn Guangzhou 510075 Peoples R China South China Agr Univ Coll Mat & Energy Guangdong Prov Engn Technol Res Ctr Opt Agr Guangzhou 510642 Peoples R China

carbon quantum dots (cQDs) have been studied for years as one of the most promising fluorescent nanomaterials. Herein, cQDs were prepared rapidly by a simple, eco-friendly one-pot hydrothermal method in the presence of hydrogen peroxide. Different sizes of cQDs are obtained by changing the reaction time. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometry demonstrated the existence of a large number of oxygen-containing groups on the surface of cQDs. The as-prepared cQDs exhibited bright yellow luminescence under UV light, they are applied for bioimaging of HeLa cells, and showed bright luminescence and excellent biocompatibility.

关键词： quantum dots carbon X-ray photoelectron spectra fluorescence cellular biophysics photoluminescence Fourier transform infrared spectra biomedical optical imaging rapid hydrothermal method carbon quantum dots hydrogen peroxide fluorescent nanomaterials reaction time X-ray photoelectron spectroscopy Fourier transform infrared spectrometry oxygen-containing groups bright yellow luminescence UV light bioimaging HeLa cells biocompatibility ecofriendly one-pot hydrothermal method c

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X-ray diffraction analysis on layers in graphene samples obtained by electrolysis in molten salts: a new perspective

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MIcRO & NANO LETTERS 2015年第12期10卷 683-685页

作者： Andonovic, Beti Grozdanov, Anita Paunovic, Perica Dimitrov, Aleksandar T. SS Cyril & Methodius Univ Fac Technol & Met Skopje 1000 Macedonia

There are several accepted methods used for X-ray diffraction analysis on graphene layers and sample's stacking height L-c. The Scherrer equation is avoided since the layers in the graphene samples are non-uniformly distributed and therefore the samples have non-uniform thickness. Instead, a model that includes thickness distribution is used to calculate the average number of layers and then the stacking height. The analysis was performed on 12 graphene samples produced by high-temperature electrolysis in molten salts. Another method that was used to calculate the number of layers and hence the samples' stacking height, was Raman spectra c-peak position method. It served as a control model for the analysed samples, since for four samples the corresponding parts of the Raman spectra were not usable due to the very low-frequency region. However, the obtained results of both methods were in agreement, and indicate that studied graphene samples are few layered.

关键词： X-ray diffraction graphene electrolysis Raman spectra X-ray diffraction electrolysis graphene layers Scherrer equation nonuniform thickness high-temperature electrolysis molten salts Raman spectra c

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ITU-R total attenuation predictions in comparison with slant path measurements in southern England

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ELEcTRONIcS LETTERS 2002年第18期38卷 1058-1059页

作者： Ventouras, S Wrench, cL Rutherford Appleton Lab Radio Commun Res Unit Didcot OX11 0QX Oxon England

A simple method to obtain the total attenuation statistics from the statistics of different attenuation effects (gases, clouds, rain) is proposed and tested against measured data along with the current ITU-R methods. The new method based on a rigorous mathematical foundation and experimental observation gives a good agreement with experimental data and highlights the impact of atmospheric gases. cloud and light rain on earth-space systems operating at higher frequencies (Ka/V band).

关键词： electromagnetic wave absorption rain clouds tropospheric electromagneticwave propagation microwave propagation millimetre wave propagation statistical analysis satellite links ITU-R methods total attenuation statistics atmospheric gases c

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Submerged arc discharge for producing nanoscale graphene in deionised water

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MIcRO & NANO LETTERS 2018年第1期13卷 31-34页

作者： Tseng, Kuo-Hsiung chou, chih-Ju Shih, Sheng-Hao Tien, Der-chi Ku, Hsueh-chien Stobinsk, Leszek Natl Taipei Univ Technol Dept Elect Engn Taipei 10608 Taiwan Warsaw Univ Technol Fac Chem & Proc Engn Warynskiego 1 PL-00645 Warsaw Poland

This work proposed a novel nanomanufacturing approach, in which a submerged arc discharge method was adopted to produce graphene in deionised water. Graphene produced using this approach can be evenly dispersed and suspended in deionised water without the use of a surfactant or stabiliser, and is suitable for storage at room temperature. Ultraviolet-visible spectroscopy was employed to analyse the optical properties of the graphene nanostructure. The Zetasizer system was used to examine the particle size and zeta potential of the graphene nanoparticles, and scanning electron microscopy, energy-dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy were adopted to explore the morphology, size, and dispersion of the particles, using the Raman spectrum, it is observed that there are two characteristic peaks. Without mixing any surfactant or stabiliser in deionised water, the zeta potential of negatively charged graphene nanoparticles was -51.5 mV. The nanoparticles were stably suspended in the deionised water instead of depositing as sediments. The results of this work confirmed that graphene production with submerged arc discharge is a low-cost, fast, and effective manufacturing method.

关键词： graphene nanoparticles nanofabrication arcs (electric) plasma materials processing ultraviolet spectra visible spectra particle size electrokinetic effects scanning electron microscopy X-ray chemical analysis transmission electron microscopy Raman spectra suspensions submerged arc discharge deionised water nanomanufacturing ultraviolet-visible spectroscopy optical properties Zetasizer system particle size zeta potential scanning electron microscopy energy-dispersive X-ray spectroscopy high-resolution transmission electron microscopy particle morphology particle dispersion Raman spectrum negatively charged graphene nanoparticles suspension c

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Synthesis and characterisation of modified carbon nanotubes with potassium salts of the monosubstituted Keggin polyoxometalates

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MIcRO & NANO LETTERS 2014年第7期9卷 482-485页

作者： Bamoharram, Fatemeh F. Poorzaki, Maryam Morsali, Ali Beiramabadi, S. Ahmadpour, Ali Heravi, Majid M. Ayati, Ali Islamic Azad Univ Mashhad Branch Dept Chem Mashhad 91735413 Iran Ferdowsi Univ Mashhad Dept Chem Engn Mashhad Iran Alzahra Univ Dept Chem Tehran *** Iran Lappeenranta Univ Technol Dept Chem Technol Lab Membrane Technol & Tech Polymer Chem Lappeenranta Finland

A novel hybrid of potassium salts of the monosubstituted Keggin polyoxometalates/carbon nanotube nanocomposite is synthesised. Multiwalled carbon nanotubes (MWcNTs) were synthesised by the catalytic chemical vapour deposition method. The characterisation of the materials by Fourier transform infrared spectroscopy, and transmission electron microscopy, shows that the functionalisation of MWcNTs by potassium salts of the monosubstituted Keggin polyoxometalates was successfully achieved via the impregnation method in both endohedral and exohedral forms. Theoretical studies for the covalent conjugation of Keggin polyoxometalates to carbon nanotubes, showed that the functionalisation of MWcNTs by some groups such as cOOH and OH is required.

关键词： polymers carbon nanotubes nanocomposites nanofabrication potassium compounds chemical vapour deposition catalysis Fourier transform spectra infrared spectra transmission electron microscopy modified carbon nanotubes potassium salts monosubstituted Keggin polyoxometalates-carbon nanotube nanocomposite multiwalled carbon nanotubes catalytic chemical vapour deposition method Fourier transform infrared spectroscopy FTIR transmission electron microscopy TEM impregnation method endohedral form exohedral form covalent conjugation c

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Investigation of carbon dioxide adsorption effects on graphene nanoribbon conductance

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ELEcTRONIcS LETTERS 2015年第14期51卷 1092-1093页

作者： Akbari, E. Buntat, Z. Enzevaee, A. Univ Teknol Malaysia Fac Elect Engn Inst High Voltage & High Current Johor Baharu Malaysia

A novel method is employed for the derivation of an analytical model for a carbon-dioxide (cO2) gas sensor based on graphene nanoribbon (GNR) conductance variation. The capacitance gradient created between the channel and the gate of a field effect transistor device is employed as an important property in the interpretation. Gas concentration and its effect on capacitance are incorporated as a modelling platform. In another attempt to model the electrical conductance in GNRs, an intelligent artificial neural network scheme is used in the modelling stage. A satisfactory agreement is presented by comparison between the empirical data extracted from a study conducted by Yoon et al. and the proposed models.

关键词： carbon compounds adsorption graphene nanoribbons capacitance field effect transistors electrical conductivity gas sensors nanosensors carbon dioxide adsorption graphene nanoribbon conductance carbon-di-oxide gas sensor cO2 gas sensor capacitance gradient field effect transistor device FET device gas concentration electrical conductance intelligent artificial neural network ANN c cO2

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