Low-temperature vibrational properties of tin nanoparticles in porous glass

The heat capacity has been studied in the temperature range 2.2–40 K and in magnetic fields up to 2 T in tin, which has been embedded in nanometer-size pores in glass having diameter ∼7 nm, in bulk tin and in glass with empty pores. Comparison of the properties of tin nanoparticles and bulk tin has been performed. An increase in the coefficient of electronic heat capacity has been found in nanostructured tin as compared with the bulk tin, and also a considerable deviation of the low-temperature lattice heat capacity from the Debye law in the temperature region T > 3 K has been found. The fact that the density of thermal vibrations in nanocrystalline tin for low energies is higher than in bulk tin has been established using low-temperature heat capacity data.     

Solidification of tin on quasicrystalline surfaces

A two-phase alloy of β-Sn and Al₆₃Cu₂₅Fe₁₂ quasicrystal produced by melt-spinning was annealed and aged to form various microstructures of tin in a quasicrystalline (QC) or microcrystalline (MC) matrix. The morphology and structure of the interfaces was studied by scanning and transmission electron microscopy and was related to melting and solidification behavior of tin studied by differential scanning calorimetry. In a MC matrix the tin phase occurred as nanoparticles and solidified with an undercooling of about 35°C. In a QC matrix, tin formed intergranular layers on faceted matrix grains. Tin showed multiple solidification peaks in undercooling ranging from 8°C to 43°C, indicating several distinct nucleation sites which compete with each other and are selected kinetically. The interfacial energy (depending on the structural state of the matrix) had a more dominating effect on the solidification of tin than the size, shape and the distribution of the tin particles. It was also concluded that solidification of tin is easier on quasicrystalline surfaces than on aluminum.     

Atomic dynamics of tin nanoparticles embedded into porous glass

The method of resonant nuclear inelastic absorption of synchrotron radiation has been used to study the phonon spectrum for tin nanoparticles (with a natural isotope mixture) embedded into a porous glassy (silica) matrix with an average pore diameter of 7 nm in comparison to the analogous spectrum of bulk tin enriched with ¹¹⁹Sn isotope. Differences between the spectra have been observed, which are related to both the dimensional effects and specific structural features of the porous glass-tin nanocomposite. Peculiarities in the dynamics of tin atoms embedded into nanopores of glass are interpreted in terms of a qualitative model of the nanocomposite structure.     

Electron spectroscopic studies of tin surface segregation on iron single crystal surfaces

AES, ELS, LEED and XPS investigations of the surface segregation of tin dissolved in a Fe-4wt%Sn alloy were performed in ultra-high vacuum at elevated temperatures. The three low indexed surface orientations (100), (110) and (111) were studied. In all cases, no dependence of the maximum tin surface coverage on temperature was detected within the temperature range from 450 to 650°C. An order-disorder transition was observed by LEED, AES and XPS for the (100) oriented surface during tin segregation. The binding state for the segregated tin atoms abruptly changes at the order-disorder transition as determined by XPS. Similar results were obtained for the (111) surface. A deviating behaviour was observed for the (110) surface orientation, where two different ordered hexagonal surface structures were detected by LEED during tin surface enrichment. The first structure is similar to the diamond structure of pure tin, and the second one corresponds to the formation of a thin layer of the intermetallic compound FeSn on the (110) surface. The electron binding energies of the segregated tin atoms determined by XPS increase with increasing tin coverage on the (110) oriented surface. ELS studies on (100) and (111) oriented surfaces saturated with segregated tin show in comparison with literature data of pure tin a surface plasmon loss peak but no signal for the corresponding bulk loss. An energy loss signal found only for the (110) surface at Sn saturation coverage seems to be characteristic of an intermetallic FeSn surface phase.     

Effects of thermal oxidation temperature on vacuum evaporated tin dioxide film

In order to investigate the effect of thermal oxidation temperature on tin dioxide (SnO₂), tin dioxide films were obtained on quartz substrates by vacuum evaporation of tin metal. The films were characterized by X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), temperature dependent electrical resistivity measurement and optical absorption spectroscopy. The SEM images showed that the films are dense, continuous and are composed of nanoparticles and particle sizes are increased after thermal oxidation. From the X-ray measurement results, the films indicated two strong reflection peaks of tetragonal structure in the orientations of (1 0 1) and (2 0 0) at 2θ = 33.89° and 37.95°, respectively. Intensity of the peaks increased with increasing thermal oxidation temperature. We found resistivity values of about 10⁻⁴ Ω-cm. Optical absorption spectra of the films in the UV–Vis spectral range revealed that optical band gap (E_g) value of the films increases with increasing thermal oxidation temperature.     

Temperature dependent structural and optical properties of tin oxide nanoparticles

Nanocrystalline tin oxide (SnO₂) powders were synthesized through wet chemical route using tin metal as precursor. The morphology and optical properties, as well as the effect of sintering on the structural attributes of SnO₂ particles were analyzed using Transmission electron microscopy (TEM), UV–visible spectrophotometry (UV–vis) and X-ray diffraction (XRD), respectively. The data revealed that the lattice strain plays a significant role in determining the structural properties of sintered nanoparticles. The particle size was found to be 5.8 nm, 19.1 nm and 21.7 nm for samples sintered at 300 °C, 500 °C, and 700 °C, respectively. Also, the band gaps were substantially reduced from 4.1 eV to 3.8 eV with increasing sintering temperatures. The results elucidated that the structural and optical properties of the SnO₂ nanoparticles can be easily modulated by altering sintering temperature during de novo synthesis.     

Ab initio calculation and synchrotron X-ray spectroscopy investigations of tin oxides near the Sn <Emphasis Type="Italic">L</Emphasis><Subscript>3</Subscript> absorption edges

The results of theoretical and experimental investigations of the electron-energy structure of the conduction band of tin oxides have been presented. The Sn L ₃ X-ray absorption near-edge fine structure (XANES) has been calculated for the first time for single crystals of metallic tin and tin monoxide, as well as for the orthorhombic and tetragonal phases of tin dioxide, using the linearized augmented plane wave (LAPW) method. The fine structure of the XANES spectra has been compared with the specific features of the energy distribution of the local partial densities of states of the tin compounds under investigation. A joint analysis of the results of the simulation and the experimental X-ray synchrotron Sn L ₃ XANES spectra of commercial bulk samples of metallic tin and tin oxides SnO and SnO₂ has been carried out.     

Effect of doping and annealing on the physical properties of ZnO:Mg nanoparticles

Well-dispersed undoped and Mg-doped ZnO nanoparticles with different doping concentrations at various annealing temperatures are synthesized using basic chemical solution method without any capping agent. To understand the effect of Mg doping and heat treatment on the structure and optical response of the prepared nanoparticles, the samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX), UV–Vis optical absorption, photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The UV–Vis absorbance and PL emission show a blue shift with increasing Mg doping concentration with respect to bulk value. UV–Vis spectroscopy is also used to calculate the band-gap energy of nanoparticles. X-ray diffraction results clearly show that the Mg-doped nanoparticles have hexagonal phase similar to ZnO nanoparticles. TEM image as well as XRD study confirm the estimated average size of the samples to be between 6 and 12 nm. Furthermore, it is seen that there was an increase in the grain size of the particles when the annealing temperature is increased.     

Structural, optical and electrical characterization of antimony-substituted tin oxide nanoparticles

Antimony-doped tin oxide (ATO) nanostructures were prepared using chemical precipitation technique starting from SnCl₂, SbCl₃ as precursor compounds. The antimony composition was varied from 5 to 20 wt%. The lower resistance was observed at composition of Sn:95 and Sb:05, when compared with undoped and higher doping concentration of antimony. The average crystalline size of undoped and doped tin oxide was calculated from the X-ray diffraction (XRD) pattern and found to be in the range of 30-11 nm and it was further confirmed from the transmission electron microscopy (TEM) studies. The scanning electron microscopy (SEM) analysis showed that the nanoparticles agglomerates forming spherical-shaped particles of few hundreds nanometers. The samples were further analyzed by energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and electrical resistance measurements.     

Tin/Indium nanobundle formation from aggregation or growth of nanoparticles

Shape and size controlled gram level synthesis of tin/indium (SnIn) alloy nanoparticles and nanobundles is reported. Poly(N-vinylpyrrolidone) (PVP) was employed as a capping agent, which could control the growth and structure of the alloy particles under varying conditions. Transmission electron microscopy showed that unique SnIn alloy nanobundles could be synthesized from the bulk materials above a certain concentration of PVP and below this concentration, discrete spherical nanoparticles of variable size were evolved. The morphology and the composition of the as-synthesized SnIn alloy nanobundles were investigated by high-resolution transmission electron microscopy (TEM). The possible mechanisms on the formation of these structures were discussed.     

The origin of the redshift in Brillouin spectra of silica films containing tin nanoparticles

The abrupt change of velocity in surface acoustic waves in thin films of amorphous SiO_x containing nanometre scale -Sn crystals is shown to be directly associated with the size-dependent melting of the nanoparticles, confirming preliminary experiments. High resolution thin film powder diffraction using synchrotron radiation shows that the abrupt redshift in the Brillouin spectra satellites occurs at the same temperature as the melting of the nanoparticles, evident for the loss of the Bragg peaks. Effective medium theory is used to explain the origin of the anomaly. A central peak in the Brillouin spectrum, the intensity of which shows a maximum at the melting temperature, can be interpreted in terms of overdamped fluctuations in the dielectric function. The melting temperature as a function of particle size is in agreement with theoretical predictions. No evidence for strain could be found on the X-ray diffraction profiles; the a- and c-axis thermal expansion coefficients are the same as those in bulk tin. Received 30 March 2000 and Received in final form 24 July 2000     

Fabrication and Tribological Properties of Pb Nanoparticles

In this paper, we describe a surfactant-assisted solution dispersion method to obtain metal nanoparticles, which involves dispersing and stabilizing metal droplets in an appropriate solvent. This method has been successfully used to prepare Pb nanoparticles from bulk Pb. The X-ray powder diffraction and transmission electron microscopy investigations show the formation of Pb nanoparticles possessing the same crystal structure as bulk metal and an average particle diameter of 40 nm. Thermal analysis indicates that Pb nanoparticles have organic shell, which is in agreement with the excellent oil-solubility. In addition, the tribological properties of Pb nanoparticles as additive in oil are discussed.     

Influence of the liquid environment on the products formed from the laser ablation of tin

Tin targets immersed in ethanol and distilled water were ablated using a UV pulsed laser. The ablated products were investigated with transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy. For ablation in both liquids, the size distribution of the produced particles was bimodal, with particles having diameters of ～10 nm and ～1 μm. Formation mechanisms that caused the bimodal distribution are suggested. Ablation in ethanol resulted in nanoparticles that were found to be single crystals of tin coated with tin hydroxide (Sn(OH)₂) while ablation in water yielded nanoparticles that were polycrystalline tin dioxide (SnO₂) throughout.     

形貌可控的Fe3O4纳米粒子的水热合成及磁性能研究

Fe3O4是一种重要的磁性材料.由于其独特的光、电、磁、热等性能而备受关注.在本文中,我们采用水热溶剂热法合成了Fe3O4磁性纳米粒子.利用X-射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）和振动样品磁强计（VSM）对产物的结构、形貌及磁性能进行了研究.结果表明,通过前驱物的适当选择,可以实现Fe3O4纳米粒...     

油溶性Ag纳米微粒的制备及表征

以双十八烷氧基二硫代磷酸吡啶盐为修饰剂 ,以单宁酸为还原剂 ,在水醇混合溶剂中合成了表面修饰的Ag纳米微粒 ,采用X射线粉末衍射仪、透射电子显微镜、傅立叶变换红外光谱仪、热分析仪等对其进行了结构表征 ,在四球摩擦试验机上测试了其抗磨性能 .结果表明 ,表面修饰的Ag纳米微粒粒径分布均匀 ,平均粒径约为15nm ,无团聚现象 ,可溶于液体石蜡等有机溶剂 ,作为润滑油添加剂 ,具有良好的抗磨作用 ,可显著提高基础油的承载力 .     

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder.     

Surface modification of indium tin oxide anode with self-assembled monolayer modified Ag film for improved OLED device characteristics

Modification of electrodes has attracted much attention in the study of organic semiconductor devices. A self-assembled monolayer (SAM) of 4-fluorothiophenol is employed to modify the Ag film on the surface of indium tin oxide (ITO) to improve the hole injection and the surface morphology. The modified anode was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and UV–vis transmittance spectra. To investigate the effect of the modification on the device characteristics, typical double layer devices with the structure of anode/-naphthylphenylbiphenyl diamine (NPB, 60 nm)/tris-(8-hydroxyquinoline) aluminum (Alq₃, 60 nm)/LiF(0.7 nm)/Al(100 nm) were fabricated using the modified anode and the bare ITO. The effect of Ag layer thickness on the device performance is also investigated. The results revealed that SAM modified ultra-thin Ag film is an effective buffer layer for organic light emitting diode. The device using the ITO/Ag (5 nm)/SAM as anode show improved device characteristics than that of using bare ITO as anode. The enhancements in luminance and efficiency are attributed to enhanced hole injection and smooth surface between anode and the organic material. The Ag thickness of 5 nm is chosen as an acceptable compromise between substrate transparency and the device performance.     

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应用SolidWorks和ANSYS软件设计了自由液态锡表面流体结构模型,计算了初始流速和热通量不同时液态锡的速度变化和温度变化,得到了流动液态锡的速度分布和温度分布。结果表明,垂直流动方向液态锡流速较为均匀,沿流动方向液态锡流速逐渐增大、液态锡液面厚度逐渐变薄。初始温度为600K的条件下,热通量为1MW·m?2时,液态锡出口温度为623.38K;热通量为5MW·m?2时,液态锡出口温度为720.18K。在相同条件下使用液态锂作为计算流体,结果表明出口处液态锂的温度低于液态锡的温度。     

自由液态锡表面结构的流体模型

应用SolidWorks 和ANSYS 软件设计了自由液态锡表面流体结构模型,计算了初始流速和热通量不同时液态锡的速度变化和温度变化,得到了流动液态锡的速度分布和温度分布。结果表明,垂直流动方向液态锡流速较为均匀,沿流动方向液态锡流速逐渐增大、液态锡液面厚度逐渐变薄。初始温度为600K 的条件下,热通量为1MW·m⁻² 时,液态锡出口温度为623.38K;热通量为5MW·m⁻² 时,液态锡出口温度为720.18K。在相同条件下使用液态锂作为计算流体,结果表明出口处液态锂的温度低于液态锡的温度。     

Fabrication and optical study of Ag@SnO<Subscript>2</Subscript> core-shell structure nanoparticle thin films

Ag@SnO₂ core-shell nanoparticles dispersed in poly-(vinyl) alcohol films were fabricated on glass substrate by employing a dip-coating technique. Synthesis of Ag@SnO₂ nanoparticles with core-shell morphology is carried out by a soft-chemical technique in aqueous phase at 60°C. Formation of core-shell structure is monitored by the red-shift of the surface plasmon band of Ag nanoparticles (from 390 to 410 nm) in the UV-visible spectrum. These nanoparticles are deposited on the glass substrate. The structure and morphology of these films were investigated by X-ray diffraction technique and field-emission transmission electron microscopy, respectively. Optical properties of these pseudo-solids were studied by UV-visible spectroscopy. Surface plasmon spectrum of the core-shell nanoparticles film remained unaltered with increase in the number of layers. However, silver nanoparticles films have shown peak broadening and development of additional peaks with increase in the number of layers. Our investigations showed that the surface plasmon band of the silver nanoparticles could be preserved by controlled deposition of the tin dioxide shell.