In-plane and out-of-plane waves in nanoplates immersed in bidirectional magnetic fields

Keivan Kiani,Saeed Asil Gharebaghi,Bahman Mehri 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.1

Prediction of the characteristics of both in-plane and out-of-plane elastic waves within conducting nanoplates in the presence of bidirectionally in-plane magnetic fields is of interest. Using Lorentz’s formulas and nonlocal continuum theory of Eringen, the nonlocal elastic version of the equations of motion is obtained. The frequencies as well as the corresponding phase and group velocities pertinent to the in-plane and out-of-plane waves are analytically evaluated. The roles of the strength of in-plane magnetic field, wavenumber, wave direction, nanoplate’s thickness, and small-scale parameter on characteristics of waves are discussed. The obtained results show that the in-plane frequencies commonly grow with the in-plane magnetic field. However, the transmissibility of the out-of-plane waves rigorously depends on the magnetic field strength, direction of the propagated transverse waves, small-scale parameter, and thickness of the nanoplate. The criterion for safe transferring of the out-of-plane waves through the conducting nanoplate immersed in a bidirectional magnetic field is also explained and discussed.

Nonlocal discrete and continuous modeling of free vibration of stocky ensembles of vertically aligned single-walled carbon nanotubes

Keivan Kiani 한국물리학회 2014 Current Applied Physics Vol.14 No.8

Free dynamic analysis of transverse motion of vertically aligned stocky ensembles of single-walled carbon nanotubes is of particular interest. A linear model is developed to take into account the van der Waals forces between adjacent SWCNTs because of their bidirectional transverse displacements. Using Hamilton's principle, the discrete equations of motion of free vibration of the nanostructure are obtained based on the nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The application of such discrete models for frequency analysis of highly populated ensembles would be associated with so much computational effort. To overcome such a problem, some useful nonlocal continuous models are established. The obtained results reveal that the newly developed models can successfully capture the predicted fundamental frequencies of the discrete models. Through various numerical studies, the roles of slenderness ratio, radius of the SWCNT, small-scale parameter, population of the ensemble, and intertube distance on the fundamental flexural frequency of the nanostructure are examined and discussed. The capabilities of the proposed nonlocal continuous models in predicting flexural frequencies of the nanostructure are also addressed.

Axial buckling scrutiny of doubly orthogonal slender nanotubes via nonlocal continuum theory

Keivan Kiani 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10

Using nonlocal Euler-Bernoulli beam theory, buckling behavior of elastically embedded Doubly orthogonal single-walled carbonnanotubes (DOSWCNTs) is studied. The nonlocal governing equations are obtained. In fact, these are coupled fourth-order integroordinarydifferential equations which are very difficult to be solved explicitly. As an alternative solution, Galerkin approach in conjunctionwith assumed mode method is employed, and the axial compressive buckling load of the nanosystem is evaluated. For DOSWCNTswith simply supported tubes, the influences of the slenderness ratio, aspect ratio, intertube free space, small-scale parameter, and propertiesof the surrounding elastic matrix on the axial buckling load of the nanosystem are addressed. The proposed model could be consideredas a pivotal step towards better understanding the buckling behavior of more complex nanosystems such as doubly orthogonalmembranes or even jungles of carbon nanotubes.

Application of elastically supported single-walled carbon nanotubes for sensing arbitrarily attached nano-objects

Keivan Kiani,Hamed Ghaffari,Bahman Mehri 한국물리학회 2013 Current Applied Physics Vol.13 No.1

The potential application of SWCNTs as mass nanosensors is examined for a wide range of boundary conditions. The SWCNT is modeled via nonlocal Rayleigh, Timoshenko, and higher-order beam theories. The added nano-objects are considered as rigid solids, which are attached to the SWCNT. The mass weight and rotary inertial effects of such nanoparticles are appropriately incorporated into the nonlocal equations of motion of each model. The discrete governing equation pertinent to each model is obtained using an effective meshless technique. The key factor in design of a mass nanosensor is to determine the amount of frequency shift due to the added nanoparticles. Through an inclusive parametric study, the roles of slenderness ratio of the SWCNT, small-scale parameter, mass weight, number of the attached nanoparticles, and the boundary conditions of the SWCNT on the frequency shift ratio of the first flexural vibration mode of the SWCNT as a mass sensor are also discussed.

Revisiting the free transverse vibration of embedded single-layer graphene sheets acted upon by an in-plane magnetic field

Keivan Kiani 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.9

Murmu et al. [23] recently presented a nonlocal model for the transverse vibration of simply supported graphene sheets in the presenceof a unidirectional in-plane magnetic field. Further studies showed that the majority of Lorentz's force components were improperly providedand led to invalid governing equations. To remove such deficiencies, the most general form of Lorentz's force components is carefullyextracted in the present work. The nonlocal equations of motion of the problem are reconstructed and solved again. The influencesof crucial parameters on the flexural frequencies of magnetically affected graphene sheets and nanoribbons are examined in detail. Furthermore,the crucial discrepancies between the results obtained in this study and those of the abovementioned previous work are rationallydiscussed. Some erroneous results of the latter are rectified.

Longitudinal, transverse, and torsional vibrations and stabilities of axially moving single-walled carbon nanotubes

Keivan Kiani 한국물리학회 2013 Current Applied Physics Vol.13 No.8

Thanks to the brilliant mechanical properties of single-walled carbon nanotubes (SWCNTs), they are suggested as high speed nanoscale vehicles. To date, various aspects of vibrations of SWCNTs have been addressed; however, vibrations and instabilities of moving SWCNTs have not been thoroughly assessed. Herein, vibrational properties of an axially moving SWCNT with simply supported ends are studied using nonlocal Rayleigh beam theory. Employing assumed mode and Galerkin methods, the discrete governing equations pertinent to longitudinal, transverse, and torsional motions of the moving SWCNT are obtained. The resulting eigenvalue equations are then numerically solved. The speeds corresponding to the initiation of the instability within the moving nanostructure are calculated. The roles of the speed of the moving SWCNT, small-scale parameter, and aspect ratio on the characteristics of longitudinal, transverse,and torsional vibrations of axially moving SWCNTs are scrutinized. The obtained results show that the appearance of the small-scale parameter would result in the occurrence of both divergence and flutter instabilities at lower levels of the speed.

Nanowires in Thermoelectric Devices

Keivan Davami,이정수,Meyya Meyyappan 한국전기전자재료학회 2011 Transactions on Electrical and Electronic Material Vol.12 No.6

The low efficiency of bulk thermoelectric materials has limited the widespread application of thermoelectric power generation. Theoretical and experimental investigations indicate that materials prepared in the form of nanowires show higher thermoelectric coefficients, thus promising to revolutionize the field. This article reviews the basics of thermoelectric power generation, conventional devices, the role of nanowires and the current status of the field.

Bandgap engineering of Cd(x)Zn(1-x)Te nanowires.

Davami, Keivan,Pohl, Judith,Shaygan, Mehrdad,Kheirabi, Nazli,Faryabi, Hamid,Cuniberti, Gianaurelio,Lee, Jeong-Soo,Meyyappan, M RSC Pub 2013 Nanoscale Vol.5 No.3

<P>Bandgap engineering of single-crystalline alloy Cd(x)Zn(1-x)Te (0 x 1) nanowires is achieved successfully through control of growth temperature and a two zone source system in a vapor-liquid-solid process. Extensive characterization using electron microscopy, Raman spectroscopy and photoluminescence shows highly crystalline alloy nanowires with precise tuning of the bandgap. It is well known that bulk Cd(x)Zn(1-x)Te is popular for construction of radiation detectors and availability of a nanowire form of this material would help to improve detection sensitivity and miniaturization. This is a step forward towards the accomplishment of tunable and predetermined bandgap emissions for various applications.</P>

<i>In situ</i> observation of morphological change in CdTe nano- and submicron wires

Davami, Keivan,Ghassemi, Hessam M,Sun, Xuhui,Yassar, Reza S,Lee, Jeong-Soo,Meyyappan, M IOP Pub 2011 Nanotechnology Vol.22 No.43

<P>We report growth and characterization of CdTe wires 30–400 nm in diameter by the vapor–liquid–solid technique. Individual nanowires were placed on a movable piezotube, which allowed three-dimensional motion toward a scanning tunneling microscope (STM). A bias was applied to the STM tip in contact with the nanowire, and the morphological changes due to Joule heating were observed <I>in situ</I> using a transmission electron microscope (TEM) in real time. For thick CdTe wires (<I>d</I> > ∼ 150 nm), the process results in the growth of superfine nanowires (SFNWs) of 2–4 nm diameter on the surface of the wire. Smaller diameter nanowires, in contrast, disintegrate under the applied bias before the complete evolution of SFNWs on the surface. </P>

Synthesis of ZnTe nanostructures by vapor–liquid–solid technique

Devami, Keivan,Kang, Daegun,Lee, Jeong-Soo,Meyyappan, M. Elsevier 2011 Chemical physics letters Vol.504 No.1

<P><B>Graphical abstract</B></P><P><ce:figure id='f0040'></ce:figure></P><P><B>Research highlights</B></P><P>► ZnTe nanowire growth using VLS technique. ► Morphology largely depends on temperature. ► Reactor modeling to gain understanding and for growth optimization.</P> <P><B>Abstract</B></P><P>We have synthesized nanowires of ZnTe using a vapor–liquid–solid approach and found the morphology to be dependant upon the growth temperature. Widely varying structures ranging from cylindrical and tapered nanowires to nanoribbons are obtained depending on the substrate location, gas flow rate and pressure all of which change the temperature distribution within the reactor. The reactor is also modeled to understand the impact of temperature on growth morphology.</P>