Nam nhat Hoang

Nam nhat Hoang
Vietnam National University, Hanoi | VNU · Faculty of Engineering Physics and Nanotechnology

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70
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482
Citations
Citations since 2016
15 Research Items
205 Citations
2016201720182019202020212022010203040
2016201720182019202020212022010203040
2016201720182019202020212022010203040
2016201720182019202020212022010203040

Publications

Publications (70)
Article
Full-text available
The experimental evidence for the contraction of volume of gold implanted with hydrogen at low doses is presented. The contraction of lattice upon the addition of other elements is very rare and extraordinary in the solid-state, not only for gold but also for many other solids. To explain the underlying physics, the pure kinetic theory of absorptio...
Article
A current research trend for nanostructured functional materials and their applications are summarized in this paper, for which a recently published special issue in Materials Transactions, Vol. 59, No. 7, is mainly surveyed here. Among the progresses of the functional materials, several important topics were covered in this special issue, which ar...
Article
This study presents results on crystal structure and phase transition in La1−yCeyFe11.44Si1.56 (y = 0.1 and 0.3) compounds. All the samples were prepared by using arc-melting method in argon atmosphere. The effect of temperature was studied by X-ray diffraction method. As shown, the compounds possess clear NaZn13-type cubic phase with ferromagnetic...
Article
This study discusses the crystal structure and magnetic properties of the rare-earth doped La0.8R0.2(Fe0.88Si0.12)13 (with R = Sm, Tb) compounds. All the samples were prepared by using arc-melting technique in argon atmosphere and the obtained result shows that after heat treatment, the samples exhibited the NaZn13-type cubic phase with a small amo...
Article
Low-field magnetocaloric effect occurred in itinerant metamagnetic materials is at core for magnetic cooling application. This works reports the magnetocaloric responses obtained at 1.35 T for the silicon-doped iron-based binary alloy La(Fe0.88Si0.12)13 in the bulk and ribbon form. Both samples possess a same symmetry but with different crystallite...
Article
An ab initio study on the magnetoelectric coupling at interfaces of ferromagnetic perovskite Sr-doped LaMnO3 (LSMO) and ferroelectric perovskite BaTiO3 (BTO) with (001) and (111) perovskite orientations is presented. It was found that the interfaces with both orientations exhibit significant magnetoelectric couplings. The effects of the orientation...
Article
The La-excess alloys La1+δ(Fe0.85Si0.15)13 (δ = 0.06 and 0.09) exhibit large magnetocaloric effect which has been attributed to the occurrence of itinerant-electron metamagnetic transition near the Curie temperature T C. The maximum entropy change −ΔS m was shown to be from 4.5 to 11.5 J/kg K for the applied field variation ΔH from 20 to 70 kOe, re...
Conference Paper
The thermoelectric properties of La-excess alloys of composition La1+δ(Fe0.85Si0.15)13 (δ = 0.06 and 0.09) were studied. As temperature increased from near 0K to room temperature we observed a corresponding increase of electrical resistivity, as a result of continuous metallic behavior of the alloys. On the other hand, the increase of temperature i...
Article
Cathodoluminescence properties of the colloidal ZnS nanopowders synthesized by using hydrothermal process, a large scale production method, are reported. The cathodoluminescence spectra were obtained for temperature from 5 to 300 K, where an intensive free exciton originated 326 nm emission was observed. This band did not split under the increase o...
Article
Theoretical prediction of magnetism induced by defects or doping in non-metallic colloids has gained a renewed interests recently. In this work, we investigated the possible appearance of magnetism in Cu doped CaO nanocolloids activated by SPAN-80 in the framework of density functional theory (DFT). Despite of strong antiferromagnetic superexchange...
Article
ZnS:Mn nanoparticles were synthesized by co-precipitation method from the precursors solutions of 0.1M Zn(CH\(_{3}\)COO)\(_{2}\), Na\(_{2}\)S and Mn(CH\(_{3}\)COO)\(_{2}\) then were capped with polyvinyl pyrrolidone. The XRD patterns showed that the ZnS:Mn nanoparticles possessed the \(T_d^2 - F4\bar {3}m\) cubic structure with the average crystall...
Article
Morphology evolution of the active layer in bulk hetero-junction organic photovoltaic is modeled and visualized. The width of the phase domain can be predicted using the relationship of characteristics length and evolution time of the process. The 3D numerical simulation of the PCBM/P3HT blend morphology evolution with respect to time is presented....
Article
In this work, the perovskite-type oxides LaMO3 (M = Mn, Fe, Co, Ni) were utilized for sensing electrodes of the electrochemical gas sensors based on the electrolyte YSZ (ZrO2 + 8%mol Y2O3). The sensors with configuration of Pt/YSZ/LaMO3 were sintered at high temperature of 1200 °C in order to analyze influence of the 3d transition metals (M) on gas...
Article
The exemplars of gold carbide AuC in cubic F-43m structure and cluster form Au6C3 are reported. The characteristics of structures were obtained on basis of Time-Dependent Density Functional Theory (TD-DFT) embedded within the framework of Generalized Gradient Approximation (GGA) and utilized Pardew-Burke-Ernzerhof functional (PBE) and spin-polarize...
Article
Full-text available
Crystal structure and magnetic properties of Cerium-doped La1-yCeyFe11.44Si1.56 (y = 0.0 - 0.3) compounds are reported. The compounds possess the NaZn13-type cubic structure with ferromagnetic arrangement. The substitution of Ce into the host lattice slightly decreased the lattice constant from 1.1477 to 1.1471α, and as the doping content increased...
Article
This paper presents the application of the bond valence method to estimate the valence charge distribution in several perovskite systems: La1-xxPbxMn03 (x=0.1-0.5), La0.6Sr0.4.xTixMnO3 (x=0.0- 0.25) and La1=xSrxCoO3 (x=0.1-0.5). The results showed a failure of elastic bonding mechanism in all compounds and revealed a deficit of valence charge in th...
Article
The structure and electrical properties of the thin gold leaves fabricated by Vietnam traditional laminating technology are introduced. The gold leaves are usually created with the average size of 3x3cm, and 200nm thickness, they can easily be broken when handling carelessly. By the measurements of X-ray Diffraction (XRD), and Electron Scanning Mic...
Article
Low Fe-doped insulating ferromagnets La$_2$CoMnO$_6$ were prepared and studied. The compounds crystallized in orthorhombic space group Pnma with slight changes in the lattice constants. We have observed a significant reduction of resistivity due to doping, together with an increase of magnetization and saturated magnetization as doping level increa...
Article
Full-text available
The Mn-doped ZnS nanoparticles with $T_{d}^{2}-Foverline 43~{rm m}$ cubic structure and an average crystalline size of about 16 nm were synthesized using the hydrothermal method at 220 $^{circ}{rm C}$ for 15 h from ${rm Zn}({rm CH}_{3}{rm COO})_{2}(0.1{rm M})$ , ${rm Mn}({rm CH}_{3}{rm COO})_{2}(0.01{rm M})$ , and ${rm Na}_{2}{rm S}_{2}{rm O}_{3}(0...
Article
This special section contains 38 papers selected from those ones presented at the First International Symposium on Frontiers in Materials Science (IS FMS), held in Hanoi, Vietnam, November 17??19, 2013.
Article
Full-text available
This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of La0.7Ca0.3Mn1-xCoxO3(x = 0.09-0.17) prepared by solid-state reaction. Magnetic measurements versus temperature revealed a gradual decrease of the magnetization (M) and Curie temperature (T-C) with increasing Co concentration (x). The...
Article
We report the optical behaviors of the Fe-doped CaMnO3 family of compounds at low doping concentrations x ≤ 5%. The study aims at assisting the evaluation of the competition between ferroand antiferromagnetic orderings, which is believed to be a cause of many interesting properties of this class of compounds, including the magnetization reversal ef...
Article
Full-text available
We report the errors in the evaluation of the surface plasmon resonance of gold nanorods by three classical approaches: the Gans model, the Discrete Dipole Approximation and the Surface Integral method. Using these methods, which are based on the propagation of an electromagnetic wave through a composite medium with different refractive indices, mi...
Article
Full-text available
The Mn-doped ZnS nanoparticles with Mn content of 0–15 mol% were synthesized by a hydrothermal method from the solutions Zn(CH3COO)2 0.1 M, Mn(CH3COO)2 0.01 M, and Na2S2O3 0.1 M at 220°C for 15 h. These nanoparticles presented the cubic structure with average particle size about 16 nm. The yellow-orange photoluminescence (PL) band at 586 nm was att...
Article
The reaction temperature has essential effect on quality of the product synthesized by hydrothermal method. We report here the variation of the optical characteristics of Mn-doped ZnS nanocrystallites prepared by mean of the stated method from Zn(CH$_{3}$COO)$_{2}$.2H$_{2}$O, Mn(CH$_{3}$COO)$_{2}$.4H$_{2}$O and Na$_{2}$S$_{2}$O$_{3}$.5H$_{2}$O as t...
Conference Paper
Full-text available
The nanofluids containing the surface activated particles have great application potential in modern technology. In this paper, we studied the optical properties of the ceramic particles of forms Ca(FeMn)O 3 and (CaPr)(MnRu)O 3 dispersed in water solution by using SPAN-80 as surface activated agent (called surfactant). The UV-Vis absorption and pho...
Article
Electronic structure of a surface-activated PbS by a bio-active molecule 4-aminothiophenol (4-ATP) was investigated using density functional theory (DFT). The obtained results demonstrated the importance of charge transfer which accounted for the flipping of surface rumpling and the nature of the binding between the activated surface and the cappin...
Article
Quantum surface effects (new emission bands, blueshifts, intensity enhancement) were observed in SPAN-80 activated ZnS nanocolloids and explained in terms of time-dependent density functional theory. The experimental evidences were demonstrated for both undoped and Cu, Mn-doped colloidal phases. The photoluminescence spectra of these materials show...
Article
The magnetic and transport properties of the perovskites La0.67Ca0.33Mn1-xTMxO3 were found to be sufficiently changed with the substitution of Mn-sites by other 3d transition-metal cations (TM=Cu,Zn; x=0.15). The values of TC, TM−I, and TCMR were surveyed when Mn was replaced by Cu and Zn. The magnetic field induced resistivity and magnetic entropy...
Article
Full-text available
The structure and optical properties of artificial opal thin films, which were synthesized from silica spheres by a modified self-assembly protocol, in the absence and under the applied magnetic field were studied. The surface characterization showed a homogeneous well-ordered face centered cubic structure of silica balls at average size 305 ± 5 nm...
Article
Full-text available
The Ca<sub>0.85</sub>Pr<sub>0.15</sub>Mn<sub>1-y</sub>Ru<sub>y</sub>O<sub>3</sub> (y = 0, 0.04, 0.08, 0.12, 0.16, and 0.20) manganate thin films were prepared by pulsed laser deposition (PLD) technique. The X-ray diffraction (XRD) analysis revealed that the samples were single-phased with orthorhombic structure. The scanning electron microscopy (SE...
Article
The electronic structures of bulk, 2D slabs and clusters of CaMnO3 in various magnetic configurations are presented. The obtained results including optimized cell constant, band-gap, Mn magnetic moment, on-site Coulomb repulsion potential and p–d charge separation potential are in good agreement with experiment data. The energetically most preferab...
Article
The crystal lattice and the bond valence structure of perovskite system La1-xSrxCoO3 are reported. The atomic valences for the given perovskites were determined on the basis of bond-valence theory. For the studied compounds the failure of distortion theorem was observed, and the non-stoichiometry of oxygen was estimated. The model for oxygen distri...
Article
The Cu–O based spin chain system A2CuO3 (A=Sr, Ca) has attracted considerable attention of scientists during the last decades due to its unique electronic structure. This paper presents a ground state optimization for the periodic structure of Ca2CuO3 using the Density Functional Theory (DFT). The electronic structure analysis was carried out on th...
Article
This paper shows how different lengths, terminations and electronic spin states of one-dimensional chains of Cu–O affected the shieldings in copper nuclear magnetic resonance signals. The calculation was performed for both periodic structure and model clusters of different size and shape. The obtained results showed that there was relatively large...
Article
The spin chain systems with one-dimensional magnetic ordering are promising candidates for quantum optical devices. This paper shows how the optical excitation can induce various phonon modes in an ideal Cu–O chain at various lengths. The calculation was carried out at different level theories including configuration interaction singles for excited...
Article
The bond-valence sum approach to spontaneous valence polarization in perovskite-like nanocrystallites ABO3 is presented. As the bond-valence method allows estimating the amount of valence charge distributed within the given bond according to bond length, the microscopic polarization in the ABO3 structure may be directly derived from the valence dev...
Article
Among the perovskite manganites, a series of La1−xCaxMnO3 has the largest magneto-caloric effect (MCE) (|ΔSm|max=3.2–6.7J/kgK at ΔH=13.5kOe), but the Curie temperatures, TC, are quite low (165–270K). The system of LaSrMnO3 has quite high TC but its MCE is not so large. The manganites La0.7(Ca1−xSrx)0.3MnO3 (x=0, 0.05, 0.10, 0.15, 0.20, 0.25) have b...
Article
The Raman scattering spectra of uranium-doped Ca2CuO3 were investigated. The small doping of uranium (≤5%) in this one-dimensional spin 1/2 chain system induced three new first-order scattering bands and two new multiphonon bands in the structure of forbidden phonons. The first-order bands were found to agree well with the existing theoretical resu...
Article
Full-text available
The authors studied the conduction mechanism in an uranium doped low dimensional magnetic system . This system exhibits the S=1/2 quasi 1D antiferromagnetic chains of -Cu-O- with strong magnetic coupling, and demonstrates continuous semiconductor-like behavior with constant covalent insulator character. This paper identifies the conduction is due t...
Conference Paper
Full-text available
We studied the rate equations of a semiconductor laser operating in a direct modulation mode for the purpose of obtaining the direct dependence of output photon density on modulating current. We show that the system of differential equations may be reduced to a special case when the spontaneous carrier decay rate is equal to the photon decay rate....
Article
Full-text available
The technological settings of a modified sol-gel method for the preparation of highly fine homogeneous powder of Ca2CuO3 doped with uranium 238 (x= 0.0–0.05) is presented. The analysis of structure, purity of phases and the justification for the role of uranium in the given compounds are provided, together with an almost complete classification of...
Article
We present the cluster-model ab initio study of the optical phonons in the one-dimensional antiferromagnet Ca2CuO3 based on the Hartree–Fock self-consistent field calculation with the 3-21G basis set. The obtained results showed very good agreement with the observed data. The Cu–O bands generally showed lower shifts in Ca2CuO3 than in pure CuO and...
Article
In the spin 1/2 antiferromagnetic Ca2CuO3 the optical excitation along 1D a Cu-O chain showed the enrichment of forbidden peaks that could not be explained by the group theory. We present the cluster-model ab initio study of these optical phonons based on the Hartree-Fock SCF calculation with the 3-21G basic set. The obtained results showed very go...
Article
Full-text available
The technological settings of a modified sol-gel method for preparation of highly fine homogeneous powder Ca2CuO3 doped with uranium 238 (x=0-0.05) is presented. The analysis of structure, purity of phases and the justification for the role of uranium in the given compounds are provided together with almost complete classification of observed optic...
Article
Full-text available
Study of the effect of Nd substitution for La on magnetocaloric effect (MCE) of polycrystalline perovskites (La 1-x Nd x) 0.7 Sr 0.3 MnO 3 (x = 0.0, 0.2 , 0.4, 0.6, 0.8, 1.0) is presented. Large MCE is observed in all samples. The presence of Nd affects to both maximum magnetic entropy change, |∆S m | max , and Curie temperature, T C. |∆S m | max s...
Article
The excellent agreement with experimental data has been achieved in fitting the resistivity of doped manganate–ruthenates for whole temperature range. The analysis interpreted the resistivity in terms of percolation of carriers through the system of grain boundaries, having been assumed as the conductive fractal medium. The percolative conduction r...
Article
Full-text available
This paper presents the solution to the De Prony's problem of separation of the overlapping exponents using the binomial coefficient as the weighting factors. The algebraic structure of the signal classes is discussed and the applicability of method is demonstrated.
Article
Full-text available
We studied the rate equations of direct modulation laser and showed that it may be reduced to the special case when spontaneous carrier decay rate is equal to the photon decay rate. The solution in this case is unique. For the general case, we investigated the vector field of the differential system of the rate equations and pointed out the basic s...
Article
Full-text available
The existence of reference levels of signals which determine directly the temperature dependence of emission factor in deep level transient phenomena is discussed. The basic algebraic structure of reference levels in the classical DLTS is studied and various signal forms with derived reference levels are given. We then demonstrate the use of these...
Article
Full-text available
Highly homogeneous finely powdered Ca2CuO3 has been prepared by the sol–gel technique. No evidence for CaO and CuO impure phases was observed. The single-phase purity was observably better than that of samples prepared by the ceramic method and oxalate co-precipitation. On the basis of the structural parameters determined, the bond valence sum appr...
Article
Percolation theory has been involved to explain the temperature dependence of conductivity in the K-doped perovskite ruthenates and to estimate the resistivity of grain boundary in the percolative conduction regime. Using the two-layer simple effective medium model [A. Gupta, G.Q. Gong, G. Xiao, P.R. Duncombe, P. Lecoeur, P. Trouilloud, Y.Y. Wang,...
Article
The Nd0.5Sr0.5Mn1−xCuxO3 (x=0.00; 0.02; 0.10) and Nd0.25Pr0.25Sr0.5MnO3 perovskites have been prepared by solid reaction technology. The manganites are of single phase with orthorhombic structure. The FC and ZFC measurements show an evident existence of charge-ordering effect at low temperatures. At the charge-ordering temperature the magnetic entr...
Article
Full-text available
This paper presents the bond valence calculation for several perovskite systems and describes the evidences for a valence charge transfer process in these compounds. The reviewing of the crystal structures of La1-xPbxMnO3 (x=0.1-0.5), La0.6Sr0.4-xTixMnO3 (x=0.0-0.25) and La1-xSrxCoO3 (x=0.1-0.5) is also presented. On the basis of testing samples, t...
Article
Full-text available
This works presents the theoretical study on several correlation integrals of the capacitance transients of the deep levels. The deconvolution of the transient signals was the major subject of the number of methods referred to under the common name as the Deep Level Transient Spectroscopy methods. In general the separation of the overlapping expone...
Article
Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La0.7Sr0.3Mn0.95Cu0.05O3 (No. 1) and La0.7Sr0.3Mn0.9Cu0.1O3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions...
Article
Full-text available
La1−xPbxMnO3 (x=0.1, 0.2, 0.3, 0.4, and 0.5) perovskites were prepared by a solid-state reaction. Except for x=0.5 (cubic) and x=0.4 (rhombohedral), the structure of the other compositions was pseudo-rhombohedral with P1 symmetry. The particle size of the grains is depending on the Pb content of the samples. The Curie temperature Tc increases from...
Article
The crystal structure of Na2[Co(Hida)2] · 6H2O (Hida = iminodiacetato) contains discrete units [Co(Hida)2]2-, ions Na+, and water molecules. The pseudooctahedral coordination of Co(II) is created by four O atoms (the bond lengths Co - O are 0.202(1), 0.203(1), 0.207(1), and 0.210(1) nm) and two N atoms of two Hida ligands (bond lengths Co - N are 0...
Article
The crystal structure of the title compound contains centrosymmetric trans-[Cu(C7H3ClFO2)(2)(C6H6N2O)(2)] units held together by van der Waals forces. The coordination sphere around the Cu atom is a tetragonally deformed octahedron. Each Cu atom is coordinated by four O atoms [Cu-O 2.019(3) and 3.141(3) Angstrom] and two N atoms [Cu-N 1.936(6) Angs...
Article
The compound Cu(p-OHC 6 H 4 COO) 2 (DENC) 2 (DENC = N,N′-diethylnicotinamide) crystallizes in the orthorhombic system, space group Pbca (No. 61), with unit cell parameters a = 44.966(1) Å, b = 16.267(1) Å, c = 14.0147(3) Å, and Z = 12. The final R value for 5528 independent reflexions is equal to 0.054. Its structure consists of centrosymmetric [Cu...
Article
[Cu2(C2H3O2)4(C6H7NO)2], M(r) = 581.53, triclinic, P1BAR, a = 7.301 (4), b = 8.216 (4), c = 10.709 (5) angstrom, alpha = 91.407 (1), beta = 98.247 (1), gamma = 1 14.242 (3)-degrees, V = 577.27 angstrom3, Z = 1, D(m) = 1.63, D(x) = 1.67 Mg m-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 1.90 mm-1, F(000) = 298, T = 293 K. Final R = 0.042 for 1699 ob...
Article
Dark violet crystals of Cu(C6H4OHCOO)2(NC5H4CONH2)2 crystallize in the orthorhombic system, group Pbca (No. 61), with unit cell parameters a = 14.625(7), b = 9.572(5), c = 18.671(9) angstrom, V = 2613.76 angstrom3. Z = 4. The structure was solved using direct methods, and refined by the least-squares method. Final R = 0.055 for 1361 independent ref...
Article
[CU(C7H5O3)2(C6H7NO)2], M(r) = 556.03, orthorhombic, Pbca, a = 12.947 (1), b = 9.401 (3), c = 20.005 (3) angstrom, V = 2435.16 angstrom3, Z = 4, D(m) = 1. 50, D(x) = 1.52g cm-3, lambda(Cu Kalpha) = 1.54178 angstrom, mu = 16.949 cm-1, F(000) = 1148, T = 293 K, final R = 0.044 for 1 122 observed reflections. The crystal structure consists of molecule...
Article
[Cu(C7H5O3)2(C6H7NO)2], M(r) = 556.03, monoclinic, C2/c, a = 15.786 (1), b = 13.299 (2), c = 12.083 (1) angstrom, beta = 97.22 (1)-degrees, V = 2516.73 angstrom 3, Z = 4, D(m) = 1.45, D(x) = 1.46 g cm-3, lambda(Cu K-alpha) = 1.54178 angstrom, mu = 16.389 cm-1, F(000) = 1148, T = 293 K, final R = 0.046 for 1300 observed reflections. The copper(II) a...
Article
Full-text available
[Cu(CTHsO3)2(C6H7NO)2], Mr = 556.03, monoclinic, C2/c, a = 15.786 (1), b = 13.299 (2), c = 12.083 (1) A, /3 = 97.22 (1) °, V = 2516.73 A 3, Z = 4, Om = 1.45, Dx = 1.46 g cm-3, A(Cu Ka) = 1.54178/~, /z = 16.389 cm-1, F(000) = 1148, T= 293 K, final R = 0.046 for 1300 observed reflections. The copper(II) atom is situated on a centre of sym- met...

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