Mechanical properties of ZnS nanobelts

Mechanical properties of ZnS nanobelts were measured at room temperature by direct nanoindentation experiments. It was found that the ZnS nanobelts achieve 79% increase in hardness but 52% decrease in elastic modulus compared to bulk ZnS. The nanobelts were found to exhibit creep under indentation. Indentation cracking was preferred along the belt growth direction. Indentation deformation behavior and fracture mechanisms of the ZnS nanobelts are discussed in conjunction with their crystalline structure, size effect, and surface-to-volume ratio.     

Preparation and characterization of single-crystalline gallium oxide nanobelts

Single-crystalline β-Ga₂O₃ nanobelts were synthesized by a simple physical evaporation method in argon atmosphere with the starting materials of Ga. The β-Ga₂O₃ nanobelts have a width of 50-100 nm and width-to-thickness ratios of 5-10, and length of up to a few millimeters, which may have potential applications in nanosize sensors or optoelectronic nanodevices.     

First-principles studies of the electronic and mechanical properties of ZnO nanobelts with different dominant surfaces

The electronic and elastic properties of [0001] ZnO nanobelts with different lateral dimensions have been studied by employing first-principles approaches. We find that the surface effects are dominant for the energetic stability of the nanobelt, while the quantum confinement effect plays an important role in the band gaps of the nanobelts. More importantly, we show that the different dominant surfaces of nanobelts have important influences on the band gaps, but minimal effects on the size dependence of the Young's modulus. The Young's modulus is larger than the bulk value and decreases with the increase of the square root of the cross-sectional area of the nanobelts. Finally, we find that the continuum-based model proposed for the Young's modulus of nanostructures is applicable for ZnO nanowires of 10-200?nm diameter, but not for ultrathin nanowires and nanobelts.     

Evaluation the effect of aspect ratio for Young’s modulus of nanobelt using finite element method

The traditional nanoindentation method provides experimental data for the calibrating mechanical parameters of nanobelt through semi-empirical formulae. In this paper, a technique to identify Young’s modulus of nanobelts with different aspect ratios is introduced combining finite element method (FEM) and nanoindentation test. For the nanobelt on the substrate, the power function relationship is used to describe the loading curve of the nanobelt indentation behavior. The loading curve exponent of the power function which is the fitting parameter can reflect the influence of aspect ratio of nanobelt on Young’s modulus of nanobelts as well as the maximum indentation load. In the forward analysis, considering the substrate effect and the size effect, the numerical loading responses are simulated at the appropriate penetration depth, and then the dimensionless equations between the parameters characterizing the indentation loading curve and the properties of nanobelt/substrate system can be established via extensive FEM simulation. In the reverse analysis, the nanoindentation tests were performed on ZnO and ZnS nanobelts, and the experimental indentation loading curves can be fitted as power function. The maximum indentation loads and the loading curve exponents are extracted from two experimental loading curves, and then they are substituted into the dimensionless equations to solve the Young’s moduli of ZnO and ZnS nanobelts. The results show the Young’s moduli solved are close to previous values, indicating that the Young’s moduli are reasonable. This developed method is effective to identify the Young’s modulus of nanobelt and it can be applied to identify the Young’s modulus of other nanobelts in practice.     

Linear buckling analysis of orthotropic inhomogeneous rectangular plates under uniform in-plane compression

Summary A linear buckling analysis is carried out for orthotropic inhomogeneous rectangular plates under uniform in-plane compression. It is assumed that material inhomogeneities of Young's modulus and shear modulus of elasticity are continuously changed in the thickness direction with the power law of the coordinate variable, while Poisson's ratio is assumed to be constant. The buckling equation can be successfully constructed as the linearized von Kármán plate model by introducing the newly defined position of the reference plane which enables us to easily deal with the problem. The critical buckling loads of the simply supported rectangular plate are presented using the derived fundamental relations. Effects of material inhomogeneity, material orthotropy, aspect ratio, width-to-thickness ratio and load ratio are discussed.     

无模板剂水热合成Bi12O17Cl2纳米带及其阻燃性能研究

以β-Bi2O3为原料,采用无模板剂水热法制备了Bi_(12)O_(17)Cl_2纳米带,利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和高分辨透射电镜(HRTEM)对其形貌和结构进行了表征并作为阻燃剂添加到聚氯乙烯(PVC)中评价其阻燃性能。结果表明,适宜的Bi/Cl物质的量比对水热合成Bi_(12)O_(17)Cl_2纳米带及其化学计量比影响显著,当Bi/Cl物质的量比为1∶2.5时,可得到分散性好、形貌均匀的Bi_(12)O_(17)Cl_2纳米带;改变Bi/Cl物质的量比,纳米带中Bi/Cl化学计量比从6∶1变成2.4∶1。初步探讨了Bi_(12)O_(17)Cl_2纳米带可能的生长机理,在水热反应过程中,Bi 3+与Cl-发生络合反应形成BiCln3-n络合物,从而合成Bi_(12)O_(17)Cl_2纳米带。     

单侧约束三边支承高强钢板的局部屈曲性能

部分包裹组合柱的翼缘板可归类为三边固支、一边自由,并在面外受混凝土单侧约束的平板。此类板件的局部屈曲可通过限制板件的宽厚比来避免。为了得到此类高强钢板的宽厚比限值,该文以薄板的弹塑性局部屈曲理论为基础,采用Bleich近似计算方法,结合Ramberg-Osgood高强钢材本构模型,推导出了板件在均布压应力作用下的弹塑性屈曲应力,给出了板件宽厚比限值的近似计算公式。采用有限元法进行了高强钢部分包裹组合柱轴压数值试验,有限元结果与已有的试验结果验证了该文提出的宽厚比限值近似计算公式的准确性。与相关规范的对比分析表明:混凝土的单侧约束作用可以使三边支承高强钢板的宽厚比限值提高39%;该文近似计算公式所得的受混凝土单侧约束、三边固支、一边自由高强钢板的宽厚比限值比澳大利亚规范AS/NZS 2327:2017的计算结果小19%,与欧洲规范EN 1994-1-1的计算结果仅相差5%。建议受混凝土单侧约束、三边固支、一边自由高强钢板的宽厚比限值可偏安全地取该文近似计算公式和EN 1994-1-1计算结果的较小值。     

高强度钢焊接方形截面轴心受压构件的局部和整体相关屈曲

钢结构设计规范GB 50017-2003规定箱形截面轴心受压构件板件宽厚比不应超过40√235/f_y,但实际工程中板件宽厚比达到120,远远超过此值。该文采用ANSYS有限元软件建立模型分析了高强度钢(名义屈服强度为460MPa)宽厚比超限的焊接箱形截面轴心受压构件的极限承载力。分析中考虑几何缺陷(整体、局部初弯曲)和残余应力,以及几何非线性和材料非线性的影响。同时,采用曲线a 代替规范GB 50017-2003中规定的曲线b,用直接强度法对这些构件进行计算,并将计算结果和有限元模拟结果相比较。针对误差较大的压杆,提出修正的直接强度法。研究表明:该文有限元模型能够很好地模拟高强度钢焊接箱形截面轴心受压构件非线性屈曲的性能;对板件宽厚比B/T≥45的轴心受压构件,有限元计算结果和直接强度法计算结果吻合较好,而对B/T<45者,二者相差较大;提出的修正直接强度法和试验结果吻合很好。     

Water molecule-induced stiffening in ZnO nanobelts

We report the observation of remarkable water molecule-induced stiffening in ZnO nanobelts using atomic force microscopy three-point bending test. It was found that the elastic modulus of ZnO nanobelts could increase significantly from 40 GPa under ambient condition up to 88 GPa at the relative humidity level of 80%. The physical mechanism for this phenomenon was explained in terms of increasing surface stress induced by water molecule adsorption on ZnO nanobelt surface. Our first-principles density functional theory calculations revealed that the water molecules adsorbed on the ZnO surface would attract surface Zn atoms to move outward and hence increase the value of surface stress of ZnO surface.     

大宽厚比H形截面轴压构件极限承载力直接强度法研究

利用ANSYS有限元程序对大宽厚比H形截面轴压构件的极限承载力进行了非线性有限元分析。分析中考虑了材料非线性和初始几何缺陷的影响,通过变化构件尺寸、材料屈服强度等参数,对共计44个构件进行了分析。应用新兴的直接强度法和传统的有效截面法对构件的极限承载力进行了计算。结果显示:有限元计算结果与直接强度法计算结果及有效截面法计算结果比值的平均值分别为1.039和1.098。与直接强度法相比,有效截面法计算过程较繁琐,且结果略显保守。直接强度法起源于单轴对称截面冷弯薄壁型钢结构构件的承载力计算,分析表明用其对大宽厚比H形截面柱的极限承载力进行计算是可行的。     

单晶Bi纳米带的合成与表征

采用溶剂热方法,以苯乙烯为还原剂和配位剂,合成了宽度为40nm-60nm、长度为600nm-1μm铋纳米带,并对其反应机理进行了探讨。在铋纳米带的合成中,α-铋的层状结构是形成铋纳米带的关键因素。配位试剂在各晶面的吸附对产物的形貌具有重要影响。通过改变配位试剂与铋盐的质量比,可以实现对铋纳米结构和形貌的调控。     

Coordination-induced formation of nanobelts of organic-inorganic hybrid materials at room temperature

The unexpected finding that the direct mix of o-phenylenediamine and H₂PdCl₄ aqueous solution at room temperature leads to supramolecular nanobelts of coordination polymers was reported. The morphology of the structures was characterized by scanning electron microscopy (SEM) and the chemical composition was examined by energy-dispersed spectrum (EDS) and X-ray maps analysis. The possible formation process of such supramolecular nanobelts is given and the influence of the molar ratio of reactants on the formation of these nanobelts is also examined. It is also found that the molar ratio of reactants has strong influence on the formation of the supramolecular structures.     

Controlled synthesis of CdS nanobelts and the study of their cathodoluminescence

Cadmium sulfide nanobelts were synthesized on an Au-capped Si substrate via chemical vapor deposition by annealing CdS powder at 860 °C. Two types of nanobelts were found. While both types grew towards [101¯0], only one type had Au particle at its tip. Room-temperature cathodoluminescence (CL) was performed on the nanobelts which were prepared between 840 and 1060 °C. Each CL spectrum exhibited two peaks. The maximum band edge emission (BEE) was found at 510 nm in all spectra while that of the deep level emission (DLE) was located between 706 to 756 nm. The ratio of intensity of BEE to that of DLE increased with increasing annealing temperature. The variation of the DLE intensity in the samples was due to the variation of defect density. A blue shift up to 49 nm was detected for DLE as the annealing temperature was increased by 160 °C. Such a shift is due to the presence of more than one type of defects in these CdS nanobelts.     

Force-deflection spectroscopy: a new method to determine the Young's modulus of nanofilaments

We demonstrate the determination of Young's modulus of nanowires or nanotubes via a new approach, that is, force-deflection spectroscopy (FDS). An atomic force microscope is used to measure force versus deflection (F-D) curves of nanofilaments that bridge a trench patterned in a Si substrate. The FD data are then fit to the Euler-Bernoulli equation to determine Young's modulus. Our approach provides a generic platform from which to study the mechanical and piezoelectric properties of a variety of materials at the nanoscale level. Young's modulus measurements on ZnS (wurtzite) nanowires are presented to demonstrate this technique. We find that the Young's modulus for rectangular cross section ZnS nanobelts is 52 +/- 7.0 GPa, about 30% smaller than that reported for the bulk.     

水热法合成MoO3单晶纳米带及其形成机理

以HCl和Na2MoO4·2H2O为原材料,不用任何模板剂的情况下,用简单的水热法成功地制备了正交相单晶α-MoO3纳米带.用X射线衍射仪、扫描电子显微镜、透射电子显微镜、紫外-可见光分光光度计对产物进行了表征.结果显示,α-MoO3纳米带是由低温条件下形成的亚稳相h-MoO3微米棒通过溶解-重结晶转变而来,其沿着c轴方向生长,加入表面活性剂CTAB可以提高α-MoO3纳米带的长径比.     

Synthesis and photoelectric properties of V3O7 x H2O and V3O7, nanobelts

V3O7 x H2O nanobelts have been synthesized via a hydrothermal route. Monoclinic V3O7, nanobelts could be obtained by thermal decomposition of V3O7 x H2O nanobelts at 400 degrees C. The synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It was found that the V3O7 x H2O is of orthorhombic phase and single crystalline nanobelts with width of 100-500 nm and length up to 100 microm. The formation mechanism of the V3O7 x H2O nanobelts was discussed. Light sensitivity in exposure to a simulated sunlight in different intensity and biases have been investigated on the electrode made from the V3O7 x H2O and V3O7, nanobelts. The results show that the photocurrent intensity of the V3O7 nanobelts is much larger than that of the V3O7 x H2O nanobelts. The fast current response has been observed under alternative control of light on and off at 2 s interval.     

A simple method for the growth of high-quality GaN nanobelts

A simple method using two-step growth technology to successfully synthesize the high-quality single crystalline GaN nanobelts was employed in this paper. The as-prepared products are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results of XRD and the selective area electron diffraction (SAED) patterns indicate that the reflections of the samples can be indexed to the hexagonal GaN phase with single-crystal structure. From the SEM morphology, we can see that the width of the nanobelts is about 800 nm, and the ratio of thickness to width is about 1/10. The maximum length is up to several tens of micrometers. In the HRTEM image, the clear lattice fringes indicate the growth of good-quality hexagonal single-crystal GaN nanobelts. Finally, the growth mechanism is also briefly discussed.     

Preparation of Manganese Oxide Nanobelts

Oriented nanobelts of manganese oxide have been firstly and successfully prepared by a microemulsion technique under controlled circumstances. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). Influences of sodium chloride and annealed temperature on the synthesis of Mn3O4 nanobelts were investigated. It was found that NaCl is the key factor to synthesize oriented Mn3O4 nanobelts and 827 K is optimum temperature to produce fine nanobelts. Oriented growth mechanism of Mn3O4 nanobelts was discussed.     

Temperature effect on electrospinning of nanobelts: the case of hafnium oxide

Electrospinning is a convenient and versatile method for fabricating different kinds of one-dimensional nanostructures such as nanofibres, nanotubes and nanobelts. Environmental parameters have a great influence on the electrospinning nanostructure. Here we report a new method to fabricate hafnium oxide (HfO(2)) nanobelts. HfO(2) nanobelts were prepared by electrospinning a sol-gel solution with the implementation of heating and subsequent calcination treatment. We investigate the temperature dependence of the products by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy-dispersive x-ray (EDX) spectroscopy. The heating temperature of spinning ambient is found to be crucial to the formation of HfO(2) nanobelts. By tuning the temperature, the morphological transformation of HfO(2) from nanowires to nanobelts was achieved. It was found that the rapid evaporation of solvent played an important role in the formation process of HfO(2) nanobelts. It is shown that nanobelts can only be obtained with the temperature higher than 50?°C and they are in the high quality monoclinic phase. A possible growth mechanism of the nanobelts based on phase separation is proposed. The enhanced photoluminescence (PL) of HfO(2):Eu(3+) nanobelts is also illustrated.     

Synthesis of B4C nanobelts in porous SiC bodies

B4C nanobelts were synthesized in porous SiC bodies, which had a sponge structure. The interconnected pore size of the SiC bodies was around 600 microm. The raw materials used for the B4C nanobelts were B2O3 for boron and phenolic resin and carbon black for carbon. The nanobelts grew fully inside the porous SiC when heat treated at 1400 degrees C for 1 h using LiCl as a volatilizing agent and cobalt as a catalyst. The thickness of the rhombohedral B4C nanobelts ranged from 0.1 to 1 microm, and their width was 0.5 to 10 microm. The length of the grown B4C belts was up to several hundreds of micrometers, and their growth direction was [110]. These single crystal nanobelts did not show any structural defects such as stacking faults, steps and twins. The low temperature synthesis in this study is attributed for the clean surface. It is suggested that the nanobelts were nucleated by the VLS mechanism, and then grew by the VS mechanism.