Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 488
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Authors: Duong, Anh Tuan; Nguyen, Thi Thanh Huong; Nguyen, Thi Minh Hai; Pham, Anh Tuan; Dinh, Thi My Hao; Cho, Sunglae (2019) - In this article, we provide a simple method for growth of bulk single crystalline. By the control temperature along a vertical furnace, we can easily fabricate bulk single crystals. This technique is called the temperature gradient method. To create a temperature gradient along the body of the furnace, the density of resistance wire which is coiled along the body of furnace is different. The density increases from the bottom to the top of the furnace. So that, at any time of the growing process, the temperature at the bottom of furnace is the smallest. During could down process, single crystal in the ampoule has been grown up from a seed at the bottom. Using this method, we successful...
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Authors: Pham, Van Huan; Phuong, Dinh Tam; Nguyen, Thi Ha Hanh; Cao, Xuan Thang; Pham, Vuong-Hung (2019) - This paper the role of Cu 2+ concentrations in luminescence quenching of Eu 3+ / Cu 2+ doped ZrO2 nanoparticles synthesized by co-precipitation method. The synthesized Eu 3+ / Cu 2+ doped ZrO2 nanoparticles were observed to have sphere morphology with a diameter of 25 nm. The XRD patterns of the nanoparticles revealed the peaks that were to be crystalline tetragonal ZrO2. The addition of Cu 2+ to the Eu 3+ doped ZrO2 nanoparticles resulted in a significant suppress
luminescence in Eu 3+ / Cu 2+ doped ZrO2 nanoparticles, which was attributed to the spectral overlap occurs between Cu 2+ absorption and Eu 3+ emission (5D0→ 7F2 transition).
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Authors: Nguyen, Quang Hoc; Tran, Dinh Cuong; Nguyen, Duc Hien (2019) - The analytic expressions of the free energy, the mean nearest neighbor distance between two atoms, the elastic moduli such as the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C11, C12, C44 for interstitial alloy AB with BCC structure under pressure are derived from the statistical moment method. The elastic deformations of main metal A
is special case of elastic deformation for interstitial alloy AB. The theoretical results are applied to alloy FeC under pressure. The numerical results for this alloy are compared with the numerical results for main metal Fe and experiments
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Authors: Pham, Thi Nguyet; Nguyen, Thi Minh Phuong; Vu, Thu Hien; Vu, Ngoc Hung (2019) - (Ba0.85Sr0.15)(Ti0.9Zr0.1)O3 (BSZT) lead-free ferroelectric thin films at the vicinity of the morphotropic phase boundary (MPB) were successfully deposited on Pt/Ti/SiO2/Si using a modified spin-coated sol-gel method. Microstructure and electrical properties of the thin film were studied. High resolution synchrotron X–ray powder diffraction (SXRD) combined with Rietveld refinement revealed that the samples were crystalized in tetragonal perovskite structure with in-plane symmetry (c < a). Raman spectra also confirmed a tetragonal perovskite crystalline lattice structure. Polarisation studies demonstrate that BSZT films exhibit a rather high saturation polarisation of 22.25 µC.cm−2. Le...
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Authors: Bui, Thi Hoan; Phuong, Dinh Tam; Pham, Vuong-Hung (2019) - In this article carbon quantum dots (Cdots) were prepared by a facile, green, economical hydrothermal method of the mixed deionized water and lemon juice. Optical and structural properties of the Cdots have been extensively studied by UV–visible and fluorescence spectroscopy, x-ray diffraction (XRD) techniques, and high-resolution TEM (HR-TEM). Surface functionality of Cdots has been illustrated by Fourier transform infrared spectroscopy (FTIR). The fabricated Cdots emit bright green light with a broad spectrum. The Cdots exhibit captivating
sensitivity and selectivity toward Fe 3+ with a linear range from 0 to 80 ppm and a detection limit of 38.08 ppm.
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Authors: Nguyen, Tu Niem; Bach, Thanh Cong (2019) - This work studies on the thermodynamic properties of the ultra-thin magnetic films within the framework of a transverse Ising model. Equations for free energy, entropy and specific heat of spin system are obtained by using the mean field approximation. We also analyze the effect of the next nearest neighbor interaction on critical temperature, layer magnetization and specific heat of the thin films.
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Authors: Luong, Duy Thanh (2019) - In this work, the fractal model for the streaming potential coefficient in porous media recently published has been examined by calculating the zeta potential from the measured streaming potential coefficient. Obtained values of the zeta potential are then compared with experimental data. Additionally, the variation of the streaming potential coefficient with fluid electrical conductivity is predicted from the model. The results show that the model predictions are in good agreement with the experimental data available in literature. The comparison between the proposed model and the Helmholtz-Smoluchowski (HS) equation is also carried out. It is seen that the prediction from the propos...
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Authors: Nguyen, Xuan Sang (2019) - This work reports photoluminescence evolution of hydrothermally homogeneous ZnO nanorods under thermal annealing at various temperatures. The crystalline structure and morphology of synthesized samples were characterized by X-ray diffractometry and Scanning Electron Microscopy. The optical properties induced by defect state transitions were investigated
by photoluminescence emission. Besides defect states induced emissions in the visible range, the photocatalytic activity of annealed samples was evaluated which indicated that the higher visible photoluminescence intensity gives the better catalytic activity
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Authors: Pham, Thanh Luan; Vu, Duc Minh; Oksum, Erdinc (2019) - Simple geometry model structures can be useful in quantitative evaluation of selfpotential data. In this paper, we solve local wavenumber equation to estimate the horizontal position, the depth and the type of the causative source geometry by using a linear least-squares approximation. The advantages of the algorithm in determining the horizontal position and depth measure are its independency to shape factor of the sources and also its simple computations. The algorithm is built in Matlab environment. The validity of the algorithm is illustrated on variable noise-free and random noise included synthetic data from two-dimensional (2-D) models where
the achieved parametric quantities ...
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Authors: Quan, Thai Ha; Lai, Tien Minh; Nguyen, Minh Tuan (2019) - This paper presents the convolution for the offset linear canonical transform (OLCT) with the Gaussian weight and its applications. The product theorem is also studied. In applications, some ways to design the filters in the OLCT domain as well as the multiplicative filter and the Gaussian filter are introduced
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Authors: Tran, Ngoc; Phan, Thi Hoai Thương; Hoang, Sy Tai (2019) - Spectroscopic properties of Tb3+ and Sm3+ ions co-doped in alkali aluminoborate glasses (70-x-y)B2O3.28Li2O.2Al2O3.xSm2O3.yTb2O3 (ABL:Tb, Sm) fabricated by melting method have been studied. The emission intensity of Tb3+ or Sm3+ in ABL:Tb or ABL:Sm glasses is influenced by the Tb3+ or Sm3+doping concerning with the 0.75 mol% and 1.0 mol% optimum concentrations, respectively. The concentration quenching effect of Tb3+ or Sm3+ in ABL:Tb, Sm glasses is observed. The mechanism of this phenomenon is attributed to the f-f intersaction for either Tb3+/Sm3 . The ABL:Tb, Sm glasses can produce color emission from green to red by properly tuning the relative ratio between Tb3+ and Sm3+. The emi...
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Authors: Pham, Van Thu (2018) - This paper presents the investigation on the buckling of three-phase orthotropic composite plates used in shipbuilding subjected to mechanical loads by analytical approach. The basic equations are established based on the Classical Plate Theory. The analytical method is used to obtain the expressions of critical loads of the three-phase composite plate. The results in the article are compared to the results obtained by other authors to validate the reliability of the present method. The approach in this direction is for. The effects of fiber and particle volume fraction, material and geometrical parameters on the critical load of three-phase composite plates are discussed in detail.
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Authors: Pham, Thi Linh (2018) - In this paper, the index-1 notion for arbitrarily switched discrete-time linear singular systems (SDLS) has been introduced. Based on the Bohl exponents of SDLS as well as properties of associated positive switched systems, some necessary and sufficient conditions have been established for exponential stability.
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Authors: Nguyen, Thi Yen Mai; Nguyen, Thi Ha (2018) - Copper nanodisks (Cu NDs) of 50 nm were prepared on square-inch anodic aluminum oxide substrates by sputtering method. The samples were annealed at 450oC, then the walls of AAO substrates were lift off in a solution of acid phosphoric. The 2D arrays of Cu NDs were fabricated in high quality. Morphology of the substrates were observed by scanning electron microscopy. Surface plasmon resonance absorption was observed with different peaks in the range of 400-1400nm wavelengths that means the substrate is promising for SERS application. To demonstrate, we observed Raman spectrum of Rhodamine 6G using the enhancement effect of the substrate.
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Authors: Pham, Quoc Trieu; Hoang, Nam Nhat (2018) - The year 2019 marks 45 years in the development of Deep Level Transient Spectroscopy (DLTS) - the signal processing method for determination of overalpping deep levels in semiconductors. From its introduction in 1974 by David Lang (D.V. Lang, J. Appl. Phys. 45, 1974, p.3023) to this date the DLTS method has undergone many changes and modifications: some were purely theoretical speculations, some were to also include new experimental arrangement and technique. This paper provides almost complete review on DLTS, focusing on the main three approaches widely used today. We also summarize the development of this method in the Faculty of Physics, VNU-Hanoi University of Sciences
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Authors: Bui, Thi Hang (2018) - Fe2O3@C material was prepared by one-step hydrothermal method for use as a negative electrode in an iron-air battery. The structure of Fe2O3@C was determined by X-ray diffraction (XRD) measurement while their morphology was observed by scanning electron microscopy (SEM). The electrochemical properties of the Fe2O3@C electrode in alkaline solution were investigated using cyclic voltammetry (CV) measurement. The results showed that Fe2O3@C material with α-Fe2O3 structure and amorphous carbon were successfully synthesized by one-step hydrothermal method. CV measurements indicate that the redox reaction rate of the Fe2O3@C electrode is higher than that of the Fe2O3@AB electrode using comm...
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Authors: Tran, Manh Cuong; Ta, Cong Son; Le, Thi Oanh (2018) - In this paper, we study the convergence for martingale sequences of random bounded operators. The condition for the existence of such a infinite product is established
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Authors: Mai, Thi Lan; Tran, Thu Thuy; Le, Thi Hong Lien; Le, Van Vinh (2018) - We have studied structure of silica glass at different pressures and temperature of 300K by using Molecular Dynamics simulation (MD) method. The model consists of 6000 atoms (2000 Si, 4000 O atoms) with the periodic boundary condition. We applied the Morse-Stretch potentials which describe the pairwise interactions between ions for SiO2 system. There is structural phase transformation from tetrahedra (SiO4) to octahedra (SiO6) network structure. There is splitting in the Si-Si pair radial distribution function (PRDF) at high pressure (100 GPa). The original of this splitting relates to the edge- and face-sharing bonds. The new second peak of the O-O PRDF at the high pressure originate...
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Authors: Vu, Thi Hoai Huong; Dao, Thi Thuy Nguyet; Nguyen, Phuc Duong (2018) - This study examines the effect of substituted concentration on the structure and magnetic properties of Y3Fe5-xInxO12 (x = 0.1 ÷ 0.7) powder samples prepared using the sol-gel method. The morphological properties of the samples were analysed using XRD, SEM. The single phase of garnet was obtained in x = 0.1 ÷ 0.6 samples. The lattice parameters of the samples exhibit a linear increase with the increasing In3+ content, which can be explained by a substitution of In3+ ions for Fe3+ ions, considering the larger ionic radius of In3+ compared with that of Fe3+. Crystallite sizes were determined via the XRD data which are of 38 – 49 nm while the particle sizes were estimated from SEM images...
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Authors: Dinh, Khac Huy; Nguyen, Phuc Duong; To, Thanh Loan; Hoang, Manh Chung; Nguyen, Kim Thanh; Vu, Van Khai (2018) - NiFe2O4/ZnO core-shell nanocomposites were prepared by two-step methodology. First, NiFe2O4 nanoparticles as the cores were synthesized by using hydrothermal method, and then modified by sodium citrate. After that ZnO as the shell was coated on modified NiFe2O4 nanoparticles by two different chemical methods including hydrothermal and co-precipitation. The formation, crystal structure, morphology and magnetic properties of the uncoated and coated samples were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and vibrating sample magnetometer. It was shown that the core nanoparticles are single phase of NiFe2O4 with cubic spi...
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Collection's Items (Sorted by Submit Date in Descending order): 1 to 20 of 488
