共查询到20条相似文献,搜索用时 0 毫秒
1.
Kyu Won Lee 《Solid State Communications》2004,129(11):697-700
We have studied the finite size effect in the quasi-two-dimensional Ising model by using a Monte Carlo simulation. A marked finite size effect was found with decreasing interlayer interaction. Aside from the well-known three- to two-dimensional crossover, a three- to one-dimensional crossover at a crossover size Lc∼(λ/2)−ν/φ was revealed as an origin of the marked finite size effect, where λ is the interlayer to intralayer interaction ratio, and ν and φ are the critical exponent for the correlation length and the crossover exponent, respectively. While the former crossover is driven by temperature, the latter is driven by size at a fixed λ. 相似文献
2.
Using molecular dynamics simulations with the quantum corrected Sutton-Chen type many-body potential, we investigate the thermal characteristics and structural evolution of Pt nanoparticles with spherical and polyhedral shapes under the heating process. The main focus of this work is the shape effects on the thermal characteristics of Pt nanoparticles. The simulation results show that all types of nanoparticles present the same overall melting temperature in spite of their different shapes. These nanoparticles can hold their initial shapes and structures at low temperature. However, polyhedral nanoparticles undergo a remarkable shape transformation before their overall melting. The critical temperature of shape transformation depends on their shapes and associated Miller index of the surface. Our study indicates that octahedron-truncated nanoparticle displays a better thermal stability than other polyhedral nanoparticles. 相似文献
3.
Andy Wijaya Katherine A. Brown Joshua D. Alper Kimberly Hamad-Schifferli 《Journal of magnetism and magnetic materials》2007
Fe-doped Au nanoparticles are ideal for biological applications over magnetic oxides due to their conjugation chemistry, optical properties, and surface chemistry. We present an AC magnetic field heating study of 8 nm Fe-doped Au nanoparticles which exhibit magnetic behavior. Magnetic heating experiments were performed on stable aqueous solutions of the nanoparticles at room temperature. The nanoparticles exhibit magnetic field heating, with a specific absorption rate (SAR) of 1.84 W/g at 40 MHz and H=100 A/m. The frequency dependence of the heating follows general trends predicted by power loss equations and is similar to traditional materials. 相似文献
4.
G. Ouyang 《Applied Surface Science》2006,252(11):3993-3996
With the aim of understanding the thermal stability of binary immiscible metallic multilayers, we propose a generally size-dependent thermodynamic criterion for determining the interface alloying in multilayers, with respect to the size-dependent interface energy of binary metal systems. Taking the copper/tungsten bilayer as an example, we obtain the interfacial alloying phase diagram based on the proposed thermodynamic model. Our theoretical predictions are consistent with experiments, implying that the size-dependent thermodynamic criterion of the thermal stability could be expected to be applicable to many multilayers. 相似文献
5.
N. Yu. Sdobnyakov S. V. Repchak V. M. Samsonov A. N. Bazulev D. A. Kul’pin D. N. Sokolov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(3):508-511
The correlation between the melting and crystallization temperatures of metal nanoparticles is investigated by means of the thermodynamic approach. Size-dependent variations in the melting temperature of aluminum, tin, and copper nanoparticles are calculated with allowance for the corresponding size dependences of surface tensions in solid and liquid phases and interfacial tension. Size-dependent variations in crystallization temperature are determined under the assumption that a certain effective surface layer (skin-layer) arises before melting. 相似文献
6.
We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q-gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum. 相似文献
7.
Received: 15 April 1997/Accepted: 16 April 1997 相似文献
8.
X. L. Li G. Ouyang G. W. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):295-298
We have investigated the nucleation thermodynamics and kinetics of the Ge
quantum dot (QD) self-assembly on the Au-patterned Si substrates based on
the surface chemical potential theory. It is find that the minimum chemical
potential on the substrate surface is located at the center site of the
square lattice constructed by Au islands, which indicates that the
nucleation of QD is thermodynamically favorable at the center site. The
nucleation probability of QD at the center site is kinetically calculated by
the mechanochemical potential-based approach. The influence of the surface
orientation of Si substrates on the QD shape is addressed by the surface
chemical potential theory. 相似文献
9.
Santhi Ani Joseph Misha Hari Gaurav Sharma V.M. Hadiya V.P.N. Nampoori 《Optics Communications》2010,283(2):313-581
Dual beam mode-matched thermal lens method has been employed to measure the heat diffusion in nanofluid of silver with various volumes of rhodamine 6G, both dispersed in water. The important observation is an indication of temperature dependent diffusivity and that the overall heat diffusion is slower in the chemically prepared Ag sol compared to that of water. The experimental results can be explained assuming that Brownian motion is the main mechanism of heat transfer under the present experimental conditions. Light induced aggregation of the nanoparticles can also result in an anomalous diffusion behavior. 相似文献
10.
Sommer JU 《The European physical journal. E, Soft matter》2006,19(4):413-422
The equilibrium state of polymer single crystals is considered by explicitly taking into account the amorphous fraction formed
by loops and tails of the chains using a statistical model introduced by Muthukumar (Philos. Trans. R. Soc. London, Ser. A
361, 539 (2003)). We show that under realistic conditions below the equilibrium melting temperature, tight loops and close re-entries
are favored, and that the amorphous fraction can be mapped into an excess surface free energy. The model is extended to many-chain
crystals where it is shown that the lamellar thickness increases with the number of chains in the crystal and extended-chain
conformations are thermodynamically favored if the number of chains in the crystal is sufficiently large. The number of chains
necessary to form an extended-chain crystal in thermodynamic equilibrium scales with the square of the degree of polymerization
of the chains. We discuss the temperature behavior of the equilibrium crystal thickness in the under-cooled state. 相似文献
11.
Mostafa Mirjalili 《Journal of Physics and Chemistry of Solids》2008,69(8):2116-2123
Many models have been developed to predict size-dependent melting temperature of nanoparticles. A new model based on the cluster mean coordination number (MCN) calculations is developed in this work. Results of the model for Al, Au, Pb, Ag, Cu, In, Sn, and Bi were compared with other models and experiments. The comparison indicated that the MCN model is in good agreement with available experimental values. It is also found that the melting temperature is more dependent on particle size as the atomic radius increased. 相似文献
12.
Jean-François Willart Jacques Lefebvre Serge Comini Marc Descamps 《Solid State Communications》2005,135(8):519-524
In this paper, we study the structural, nanostructural and thermodynamic evolutions of crystalline Γ-sorbitol upon mechanical milling. The investigations have been performed by powder X-ray diffraction and differential scanning calorimetry. The results clearly show that the evolution upon milling can be divided in two stages. The first one only reveals micro and nanostructural modifications of the crystallites appearing through a size reduction, deformations, and changes of shape. On the other hand, the second stage reveals a complete structural transformation of the Γ-form of sorbitol towards the metastable A-form of sorbitol. Special attention has been paid to the nanostructural features derived from the first stage, which trigger the ultimate structural transformation. 相似文献
13.
The process of decomposition of hexagonal copper hydride has been observed in situ in a diamond anvil cell (DAC) using the energy dispersive X-ray diffraction (EDXRD) method. The presence and intensity of diffraction lines of the hexagonal CuH0.8 phase have been taken as a probe for the decomposition process. The intensity of diffraction lines decreases abruptly in the vicinity of 8.4 GPa, indicating complete decomposition of the hydride. The determined value of decomposition pressure is equal to 8.4±0.6 GPa. The standard Gibbs energy of formation of 54.0±1.3 kJ mol−1 (H2) calculated for copper hydride has been compared with the result obtained from calorimetric studies. The large discrepancy between the two values suggests that the decomposition pressure does not describe ‘true’ equilibrium conditions in this system. 相似文献
14.
Based on the thermodynamic and thermophysical properties of bulk materials, Gibbs free energy for nanostructured materials is obtained and used to study the size-dependent melting point depression phenomenon. The effects of volume change due to fusion, the thermal expansion and the temperature dependency of surface free energy of bulk materials on the melting point depression are investigated. Conversely, the solid surface free energy of bulk materials is also researched by means of the size-dependent melting temperature of nanostructured materials. 相似文献
15.
Tin-doped In2O3 layers were prepared by the spray technique with doping concentrationsc
Sn between 1 and 20 at. % and annealed at 500 °C in gas atmospheres of varying oxygen partial pressures. The room-temperature electrical properties were measured. Maximum carrier concentrationsN=1.5×1021cm–3 and minimum resistivities =1.3×10–4 cm are obtained if the layers are doped withc
Sn9 at. % and annealed in an atmosphere of oxygen partial pressurep
O2 10–20 bar. At fixed doping concentration, the carrier mobility increases with decreasing oxygen pressure. The maximum obtainable mobility can be described in terms of electron scattering by ionized impurities. From an analysis of the carrier concentration and additional precision measurements of the lattice constants and film thicknesses, a defect model for In2O3:Sn is developed. This comprises two kinds of interstitial oxygen, one of which is loosely bound to tin, the other forming a strongly bound Sn2O4 complex. At low doping concentrationc
Sn4 at. % the carrier concentration is governed by the loosely bound tin-oxygen defects which decompose if the oxygen partial pressure is low. The carrier concentration follows from a relationN=K
1 ·p
O2
–1/8 ·(3 ×1010 × cSn –N)1/4 with an equilibrium constantK
1=1.4×1015 cm–9/4bar1/8, determined from our measurements. 相似文献
16.
Under the pumping of violet lighting emitting diode, quantum yields for multichannel transition emissions have been determined in Sm3+-doped heavy metal tellurite glass for the first time. For the derivation, the necessary fluorescence spectra were measured and calibrated in an integrating sphere connected to a CCD detector with a 400 μm-core optical fiber. The spectral power distribution of the sample was derived from the measured spectra first, and then the quantum yields of the visible emissions of Sm3+ were calculated based on the distribution. The total quantum yield for four emission transitions of Sm3+ in visible region is 4.07%. Integrating sphere with a CCD detector is proven to be a reliable and reproducible method to characterize luminescence and laser materials. 相似文献
17.
Electrodeposition of SiC particles with cobalt matrix in the presence of cesium ions was studied. The influence of Cs+ concentration (0-37.6 mM) on the cathodic polarization curves was determined in galvanostatic and potentiodynamic measurements. It was found that the presence of Cs+ in the solution enhanced adsorption of Co2+ ions on SiC, but preferential cesium adsorption occurred simultaneously. The last phenomena resulted in cesium incorporation in the composite coating. Surface charge of SiC powder and amounts of functional groups on SiC surface were determined. The particles incorporation into deposits was only little dependent on cesium concentration in the bath. Structure of the composite coatings was studied by microscopic observations. Microhardness of the deposits was also determined. 相似文献
18.
Haitao Yang Tomoyuki Ogawa Daiji Hasegawa C.N. Chinnasamy Migaku Takahashi 《Journal of magnetism and magnetic materials》2006
Monodisperse bimetallic Pd–Co nanoparticles were prepared via a thermal decomposition of cobalt carbonyl using palladium seeds at the Pd/Co molar ratios 0.5%, 1%, and 5%. The heterogeneously nucleated nanoparticles without any size-selective precipitation are sufficiently uniform to self-assemble into ordered arrays. The as-synthesized nanoparticles are each a single crystal with a complex cubic structure called ε-Co. The presence of Pd seeds seems to improve the stability of Co nanoparticles against oxidation based on the results from time-dependent magnetization measurement. 相似文献
19.
The size dependence of the nanocrystal melting temperature has been investigated based on a nonequilibrium thermodynamics
approach. An expression has been derived for the melting temperature that, contrary to the classical Tomson formula, takes
into account the metastable character of the crystal nucleus-melt shell equilibrium. Quantitative estimations have been carried
out for small spherical particles of aluminum, tin, and lead. 相似文献
20.
Cooling rate effects on structure and thermodynamics of amorphous nanoparticles were studied in a spherical model using Molecular Dynamics (MD) method. The good equilibrium melts are cooling down by three different cooling rates in order to observe the cooling rate effects. We find that cooling rate effects on thermodynamic quantities such as potential energy and surface energy are more pronounced than those for static quantities. Microstructure of amorphous nanoparticles is analyzed via radial distribution function (RDF) and coordination number distributions. Relatively weak cooling rate effects on such quantities are found. Microstructure of surface and core of amorphous nanoparticles are analyzed. 相似文献