Papers by Keyword: Nanocluster

Abstract: : In this paper, activation procedures under size effects of some gold nanoparticles (Au₁₀₁, Au_naked and Au_citrate) and nanoclusters (Au₈ and Au₉) immobilized on powder Norit^® activated carbon (abbreviated to AC) and/or Vulcan carbon (abbreviated to VC) on the catalytic activity of gold nanocatalysts were studied. The gold nanostructures were activated through the washing procedure with a base in MilliQ water or hot toluene and then followed by heating in static air (abbreviated to W+S) or under vacuum (abbreviated to W+V) at 100 °C for 3 h. The highest activity of gold nanocatalysts for benzyl alcohol oxidation was obtained for activated (W+V) ‘naked’ gold nanoparticles immobilized on Norit^® activated carbon when the gold nanoparticle diameters was ~4.4 nm.

Abstract: This study investigates the possibility of Bose-Einstein condensation (BEC) in 2D-nanoclusters. A ground state equilibrium structure involves the single phonon exchange approximation. At critical temperature, the specific heat, entropy, and free energy of the system can be determined. The results support the existence of BEC in nanoclusters, and they lead to predictions of the behaviour of 2Dmaterials at low temperatures.

Abstract: This study prepared an SiC thin film by using the ratio frequency magnetron sputtering method, investigated the effects of different sputtering powers on the SiC material and analysed the changes in crystal morphology and photoluminescence characteristics caused by changes in the growth conditions used. It was considered that there was 6H-SiC crystal morphologies in the SiC thin film under the experimental conditions prevailing in this study. The SiC morphologies with small grain sizes intermingled and therefore formed anSiC thin film. The analyses of the photoluminescence spectra and Scanning Electron Microscope indicated that the SiC thin film materials with preferable crystal compositions could be prepared under appropriate power inputs.

Abstract: In this work, the calculation algorithms of cascade and probability functions and vacancy nanoclusters concentration were developed and their calculations for various incident particles in silicon and iron were made.

Abstract: Properties of composite materials irradiated by electrons have been studied. Effects of lavsan and montmorillonite nanocluster fillers on mechanical properties of polyimide-based polymer film materials have been studied. Catastrophic destruction models adequately describing stress-strain relationship curves for all test composites have been suggested.

Abstract: he negative differential capacity has been observed in case of MIS structures with SiO_x and Si_xO_yN_z films containing Si nanoclusters. It has been shown that existence of negative differential capacity depends on charge state of Si nanoclusters or electron traps　in the insulating matrix. In case of Si_xO_yN_z films the two peaks have been revealed in C-V characteristics connected with Si nanoclusters and electron traps. The low-temperature annealing of Si_xO_yN_z films in hydrogen passivates the electron traps caused by Si dangling bonds and as a result the peak in C-V characteristics connected with electron traps disappears. The following low-temperature annealing in vacuum caused the some effusion of hydrogen from the film and appearance of electron traps and connected with them capacity shoulder on C-V characteristics. It has been shown, that the frequency and temperature dependences of the negative differential capacitance in C-V curves can be successfully used for the determination of nanoclusters and traps parameters for the samples with the nanoclusters embedded in SiO₂ or Si_xO_yN_z films.

Abstract: In this paper we have studied the size and number of atom-pairs dependence normalized per atom pair binding (cohesive) energy and melting temperature of the Aluminium nitride () nanoparticle using simple model approach. It is observed that the per-atom-pair binding (cohesive) energy and melting temperature are a quadratic function of the inverse of the particle size fornano-particle. The per atom-pair binding (cohesive) energy and melting temperature comes near that of their bulk value with increasing the particle size and same as the bulk material when the particle size is above than 100 nm.Keywords Semiconductors; Size effect; Binding energy; Melting temperature; nanoparticle; nanocluster.

Abstract: The effects of pre-aging and natural aging on the bake hardening behavior of Al-0.62Mg-0.93Si (mass%) alloy with multi-step aging process were investigated by means of Vickers hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). The characteristics of nanoclusters (nano scale solute atom clusters) formed during pre-aging and natural aging were also investigated using the three dimensional atom probe (3DAP) analysis. The results revealed the occurrence of natural age hardening and that the bake hardening response was decreased after the extended natural aging even though the pre-aging was conducted before natural aging. Since the 3DAP results exhibited the Si-rich clusters were newly formed during extended natural aging, it was assumed that the Si-rich clusters caused the natural age hardening and the reduced bake hardening response corresponding to Cluster(1). The decrease of the bake hardening response was markedly higher in the later stage of bake hardening than in the early stage. The size of the β’’ precipitates were reduced with increasing the natural aging time. Exothermic peaks of Peak 2 and Peak 2’ were observed in the DSC curves for the alloys pre-aged at 363K. Peak 2’ became larger with the natural aging time. This is well understood by the following model. The transition from Cluster(2) to the β’’ phase occurs preferentially at the early stage of the bake hardening. Then the growth of the β’’ phase is inhibited by the presence of Cluster(1) at the later stage of bake hardening. The combined formation of Cluster(1) and Cluster(2) by the multi-step aging essentially affects the bake hardening response and the β’’ precipitates in the Al-Mg-Si alloys.

Abstract: Two types of nanoclusters are formed during low temperature aging and play important roles in age-hardening of Al-Mg-Si alloys. The formation behavior of these nanoclusters depends on the alloy composition and heat-treatment process. In this work, the various alloys with different Mg and Si concentration were used in order to clarify the influence of alloy composition on the nanocluster formation using differential scanning calorimetry (DSC), hardness and electrical resistivity measurements. Based on the DSC results, two overlapped exothermic peaks were clearly detected, showing the formation of Cluster (1) and Cluster (2) in all examined alloys with different alloy composition. These two overlapped peaks are separated by the Gaussian function method to analyze the volume fraction of nanoclusters quantitatively. It is found that the Si and Mg concentration of Al-Mg-Si alloys has a marked effect on the nanocluster formation. The formation of Cluster (1) is more related with the Si concentration, whereas Cluster (2) is correlated with both of the Mg and Si concentration. Furthermore, the important point is that the formation behavior of nanoclusters strongly depends on the Mg/Si ratio of the alloys. The formation of nanoclusters is most enhanced when the Mg/Si ratio is approximately 1.0.

Abstract: The characteristic age-hardening response of Al-3.0Mg-1.0Cu (mass%) alloys with and without Ag addition has been investigated by the hardness measurement, differential scanning calorimetry (DSC) and electrical resistivity measurement. The alloy compositions locating in the (α+S+T) phase field of the Al-Mg-Cu phase diagram are known to be effective to harden in two stages separated by a distinct and often prolonged hardness plateau. The first stage of hardening occurs very rapidly (e.g. within 60 s at 443 K) and contributes to increase hardness as much as 50 % of the total age-hardening. In the Ag-added alloy, the hardness change during the first stage of hardening is larger and the plateau stage is shortened as a result of the fast arrival at the second stage of hardness. Small amount of Ag changes the age hardening response of the Base alloy dramatically. In the low temperature aging, the incubation stage at which no clear hardness and electrical resistivity increase appears for a long period before the first stage of hardening. After the pre-aging at this incubation period, a characteristic two-step aging response is observed. The peak hardness dramatically changes in the Al-3.0Mg-1.0Cu alloy, while no clear change in the Ag-added alloy.