• Korean Journal of Materials Research
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• v.19 no.7
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• pp.356-361
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• 2009

The optical characterization of self-assembled InAs/AlAs Quantum Dots(QD) grown by MBE(Molecular Beam Epitaxy) was investigated by using Photoluminescence(PL) spectroscopy. The influence of thin AlAs barrier on QDs were carried out by utilizing a pumping beam that has lower energy than that of the AlAs barrier. This provides the evidence for the tunneling of carriers from the GaAs layer, which results in a strong QD intensity compared to the GaAs at the 16 K PL spectrum. The presence of two QDs signals were found to be associated with the ground-states transitions from QDs with a bimodal size distribution made by the excitation power-dependent PL. From the temperature-dependent PL, the rapid red shift of the peak emission that was related to the QD2 from the increasing temperature was attributed to the coherence between the QDs of bimodal size distribution. A red shift of the PL peak of QDs emission and the reduction of the FWHM(Full Width at Half Maximum) were observed when the annealing temperatures ranged from 500 $^{\circ}C$ to 750 $^{\circ}C$, which indicates that the interdiffusion between the dots and the capping layer was caused by an improvement in the uniformity size of the QDs.

• Transactions on Electrical and Electronic Materials
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• v.1 no.3
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• pp.23-28
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• 2000

A block-oxide layer was formed on the surface of Cu-based leadframe by chamical oxidation method in order to enhance the adhesion strength between Cu-based leadframe and epoxy molding compound (EMC) Using sandwiched double cantilever beam (SDCB) specimens, the adesion strength was measured in terms of interfacial fracture toughness, G$\sub$IC//Results showed that the black-oxide layer was composed of two kinds of layers: pebble-like Cu$_2$O layer and acicular CuO layer, At the initial stage of oxidation the Cu$_2$O layer was preferentially formed and thickened up to around 200 nm whithin 1 minute of the oxidation time. Then the CuO layer started to from atop of the Cu$_2$O layer and thickened up to around 1300 nm until 20 minutes. As soon as the CuO layer formed, the thickness of Cu$_2$O layer began to reduce and finally reached to around 150 nm. The pre-cleaned and the Cu$_2$O coated leadframes showed almost no adhesion of EMC, however, as the CuO precipitates appeared and became continuous, G$\sub$IC/ increased up to around 80 J/㎡. Further oxidation raised G$\sub$IC/ up. to around 100 J/㎡.

• Advances in nano research
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• v.14 no.4
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• pp.335-353
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• 2023

The possibility of energy harvesting as well as controlled vibration of a three-layered beam consisting of two piezoelectric layer and one core layer made of nonpiezoelectric material is investigated using paradox-free local/nonlocal theory. The three-layered nanobeam is resting on an elastic foundation and subjected to a blast load. Also, the core layer is made of Nano-composites reinforced by CNTs and carbon fibers (MHCD). Governing equations as well as boundary conditions are obtained using Hamilton,s principle. The equations discretized by Generalized Differential Quadrature Method (GDQM) and solved by Newmark beta method. In addition, two differential and integral gains are employed for controlling the forced vibration. The size-dependency of the elastic foundation is considered using two-phase elasticity. The effect of elastic foundation, control gains, nonlocal factor, as well as parameters affecting the core material on the forced vibration and energy harvesting is investigated in detail. The equations as well as solution procedure is validated utilizing some compassion studies. This work can be a basis for future studies on energy harvesting and controlled vibration in small scales.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.713-722
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• 2020

This article aims to illustrate the damped dynamic responses of layered functionally graded (FG) thick 2D beam under dynamic pulse sinusoidal load by using finite element method, for the first time. To investigate the response of thick beam accurately, two-dimensional plane stress problem is assumed to describe the constitutive behavior of thick beam structure. The material is distributed gradually through the thickness of each layer by generalized power law function. The Kelvin-Voigt viscoelastic constitutive model is exploited to include the material internal damping effect. The governing equations are obtained by using Lagrange's equations and solved by using finite element method with twelve -node 2D plane element. The dynamic equation of motion is solved numerically by Newmark implicit time integration procedure. Numerical studies are presented to illustrate stacking sequence and material gradation index on the displacement-time response of cantilever beam structure. It is found that, the number of waves increases by increasing the graduation distribution parameter. The presented mathematical model is useful in analysis and design of nuclear, marine, vehicle and aerospace structures those manufactured from functionally graded materials (FGM).

• Steel and Composite Structures
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• v.45 no.4
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• pp.591-603
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• 2022

The flexural strengthening of reinforced concrete beams by external bonding of composite materials has proved to be an efficient and practical technique. This paper presents a study on the flexural performance of reinforced concrete continuous beams with three spans (one span and two cantilevered) strengthened by bonding carbon fiber fabric (CFRP). The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened continuous beam, i.e., the continuous concrete beam, the FRP plate and the adhesive layer. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends. Remarkable effect of shear deformations of adherends has been noted in the results. The theoretical predictions are compared with other existing solutions that shows good agreement, and It shows the effectiveness of CFRP strips in enhancing shear capacity of continuous beam. It is shown that both the normal and shear stresses at the interface are influenced by the material and geometry parameters of the composite beam.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1042-1045
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• 2002

We have carried out two-beam interference experiments to form holographic gratings on amorphous $MgF_2$/As-Ge-Se-S multi-layer. In this study, holographic gratings have been formed using He-Ne laser(632.8nm). under different polarization combinations. The diffraction efficiency was obtained by +1st order intensity. The maximum diffraction efficiency of As-Ge-Se-S single layer and $MgF_2$/As-Ge-Se-S multi-layer were 0.8% and 1.4%

• Steel and Composite Structures
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• v.16 no.6
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• pp.559-576
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• 2014

A new mathematical model and its finite element formulation for the non-linear stress-strain analysis of a planar beam strengthened with plates bolted or adhesively bonded to its lateral sides is presented. The connection between the layers is considered to be flexible in both the longitudinal and the transversal direction. The following assumptions are also adopted in the model: for each layer (i.e., the beam and the side plates) the geometrically linear and materially non-linear Bernoulli's beam theory is assumed, all of the layers are made of different homogeneous non-linear materials, the debonding of the beam from the side-plates due to, for example, a local buckling of the side plate, is prevented. The suitability of the theory is verified by the comparison of the present numerical results with experimental and numerical results from literature. The mechanical response arising from the theoretical model and its numerical formulation has been found realistic and the numerical model has been proven to be reliable and computationally effective. Finally, the present formulation is employed in the analysis of the effects of two different realizations of strengthening of a characteristic simply supported flexural beam (plates on the sides of the beam versus the tension-face plates). The analysis reveals that side plates efficiently enhance the bearing capacity of the flexural beam and can, in some cases, outperform the tensile-face plates in a lower loss of ductility, especially, if the connection between the beam and the side plates is sufficiently stiff.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.31-37
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• 1989

The effectiveness of using a composite beam with constrained visco-elastic layer as a dynamic vibration absorber is investigated. The performance of this absorber is evaluated in terms of displacement transmissibility when to a primary beam with built-in ends and compared to that of the uniform beam absorber. The results of analysis and design show that it is possible to suppress simultaneoulsy the peak transmissibilities at two or more resonance frequencies and the optimal parameters are located within the available viscoelastic material properties.

• Smart Structures and Systems
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• v.1 no.3
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• pp.309-324
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• 2005

This paper presents an efficient and accurate coupled beam model for piezoelectric bimorphs based on improved first-order shear deformation theory (FSDT). The model combines the equivalent single layer approach for the mechanical displacements and a layerwise modeling for the electric potential. General electric field function is proposed to reasonably approximate the through-the-thickness distribution of the applied and induced electric potentials. Layerwise defined shear correction factor (k) accounting for nonlinear shear strain distribution is introduced into both the shear stress resultant and the electric displacement integration. Analytical solutions for free vibrations and forced response under electromechanical loads are obtained for the simply supported piezoelectric bimorphs with series or parallel arrangement, and the numerical results for various length-to-thickness ratios are compared with the exact two-dimensional piezoelasticity solution. Excellent predictions with low error estimates of local and global responses as well as the modal frequencies are observed.

• Applied Microscopy
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• v.48 no.4
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• pp.126-127
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• 2018

Carbon has numerous allotropes and various crystalline forms with full dimensionalities such as diamond, graphite, fullerenes, and carbon nanotubes leading a wide range of applications. Since the emerge of graphene consisting of a single atomic layer of carbon atoms, a fabrication of all-carbon-based device with combination of one-, two-, and three-dimensional carbons has become a hot issue. Here, we introduce an ultimate one-dimensional carbon atomic chain. Carbon atomic chains were experimentally created by removing atoms from monolayer graphene sheet under electron beam inside transmission electron microscope (TEM). A series of TEM images demonstrate the dynamics of carbon atomic chains over time from the formation, transformation, and then breakage.