排序方式: 共有34条查询结果,搜索用时 18 毫秒
21.
Mechanics and Friction at the Nanometer Scale 总被引:2,自引:0,他引:2
In this overview, we will give an introduction to experiments in which manipulation is used a means of uncovering the intrinsic response and dynamical behavior of small objects. Experiments done on individual particles reveal new and rich behaviors that are inaccessible to averaging methods. Experiments exploring the stiffness and toughness of carbon nanotubes will be presented showing that nanometer scale engineered materials can far outperform current engineering materials. Through AFM manipulation, imaging and force measurements, the stiffness of this material was found to equal or exceed diamond. Their toughness is also extraordinary. Due to their near crystalline perfection, carbon nanotubes are able to undergo strains exceeding 15% during bending without damage. Through AFM manipulation experiments, these large deformations have been shown to be highly reversible. Experiments in which the lateral force of manipulation of small objects across surfaces is measured show that friction at the nanometer scale occurs without wear processes and is an intrinsic property of the particular interface. Results are also presented showing anisotropic behavior in friction and movement due to commensurate lattice effects. At the nanometer scale, the contacting surfaces can be nearly perfect so that commensurate effects are not partially averaged out by many differently oriented domains. It has been shown that friction can very over an order of magnitude depending on the relative orientation of the contacting surfaces. The relative orientation of object and substrate lattices also can determine the modes of motion. In some cases the particle is confined to move in one direction. In other cases the relative orientation determines whether the particle rolls, rotates in-plane or slides. These effects may have implications on the fundamental mechanisms of friction. They provide a laboratory for testing different geometrical configurations of atoms sliding on atoms. The results may also have implications in the design of nanometer scale electromechanical mechanisms. 相似文献
22.
ZHAO Cun-Yuan ZHANG Yong FANG Wei-Hai YOU Xiao-ZengCoordination Chemistry Institute the State Key Laboratory of Coordination Chemistry Nanjing University Center for Advanced Studies in Science Technology of Microstructures Nanjing Jiangsu China 《中国化学》1996,14(5):393-398
We present here a systematically theoretical study on the nonlinearities and their structure-property relationship of cyanovinyl-substituted donor-acceptor molecules by virtue of semiem-pirical PM3/AM1-FF approach.Good consistency between measured and calculated hyperpolarizabil-ities is obtained.Results show that conformation has a significant effect on hyperpolarizabilities.The torsion angle change between two conjugated parts of the molecular systems can substantially alter the nonlinearities.The total amount of charge transfer difference from donor to acceptor has been introduced to understand the microscopic nature of the nonlinear optical properties for the title molecules.General guidelines may be sought out in the search of molecules with large values of β Some molecules with large molecular hyperpolarizabilities can be predicted by the optimization for the longer π-electron systems with both acceptor and donor groups. 相似文献
23.
WANG CaiLu GAO XiangDong LI XiaoMin JIANG ZhengWu YANG ZhengHong GU ZhengYing & HE Peng State Key Lab of High Performance Ceramics Superfine Microstructures 《中国科学:物理学 力学 天文学(英文版)》2012,(7):1183-1188
ZnO-TiO2 hybrid photoanodes were fabricated via the doctor-blade method by integrating vertically-grown sparse ZnO arrays with hydrothermal TiO2 nanoparticles. A special surface-coating technique was developed to deposit a thin TiO2 layer on the surface of ZnO rods. Microstructure, optical and photoelectrochemical performance of the hybrid photoanodes were investigated. The denser ZnO array exhibited bad filling behavior of nanoparticles in the interspace of ZnO rods, strong scattering and low conversion efficiency (0.27%). The sparser array showed a much better integrated microstructure, improved transmittance and high conversion efficiency (2.68%). The surface modification of ZnO rods by the TiO2 thin layer was found useful in improving the interfacial microstructure between the ZnO rod and the TiO2 bulk film, and the total conversion efficiency of 3.01% was achieved, higher than that of the pure TiO2 nanoparticle cell (2.93%). The increased scattering effects on the incident light, the enhanced electron transportation at TiO2/dye/electrolyte interface, and the inhabited recombination were responsible for this improvement. 相似文献
24.
WU Hao ZHENG HouZhi LIU Jian LI GuiRong XU Ping ZHU Hui ZHANG Hao & ZHAO JianHua State Key Laboratory for Superlattices Microstructures 《中国科学:物理学 力学 天文学(英文版)》2010,(4)
A spin-injection/-detection device has been fabricated based on the multiple quantum well light emitting diode (LED) structure. It is found that only a broad electroluminescence (EL) peak of a full width at half maximum of 8.6 nm appears at the wavelength of 801 nm in EL spectra with a circular luminescence polarization degree of 18%, despite PL spectra always show three well resolved peaks. The kinetic energy gained by injected electrons and holes in their drift along opposite directions broadens the EL pe... 相似文献
25.
为观察MgO在MgB2超导样品中的影响和存在形式,通过在MgB2胚体样品之外,增加周围MgO量的实验方法,经过4 h 750℃的烧结,在制备好的MgB2超导样品内得到了壁厚是约4纳米,直径在50~80纳米,长为30~40微米以上的氧化镁(MgO)纳米管.在MgB2样品表面可以看到少量直径是200~300纳米的氧化镁(MgO)亚微米线.经过扫描电镜的能量损失谱和透射电镜EELS分析测量,证明了纳米管中没有硼元素.实验观测也表明这些氧化镁(Mgo)纳米管是由许多氧化镁(MgO)纳米晶片组成. 相似文献
26.
Papadakis SJ Hall AR Williams PA Vicci L Falvo MR Superfine R Washburn S 《Physical review letters》2004,93(14):146101
We report on the characterization of nanometer-scale resonators. Each device incorporates one multiwalled carbon nanotube (MWNT) as a torsional spring. The devices are actuated electrostatically, and their deflections, both low frequency and on resonance, are detected optically. These are some of the smallest electromechanical devices ever created and are a demonstration of practical integrated MWNT-based oscillators. The results also show surprising intershell mechanical coupling behavior in the MWNTs. 相似文献
27.
28.
SHEN Chao WANG LiGuo ZHU Hui & ZHENG HouZhi State Key Laboratory for Superlattices Microstructures 《中国科学:物理学 力学 天文学(英文版)》2011,(6)
Photoluminescence (PL) polarization of a spin ensemble was examined over a wide excitation wavelength range from 520 nm to 700 nm and a temperature range from 3.5 K to 300 K after it transfers from a (AlGa)As barrier layer and eventually quenches irradiatively in a GaAs quantum well (QW).A highest PL circular polarization of 30% can be kept at temperatures up to 120 K,while its room temperature value reaches about 17%.It is found that the main features of the optical spin orientation in bulk Al 0.27 Ga 0.73... 相似文献
29.
PEI Jia TANG YanChun XU Ning LU Wei XIAO ShouJun &LIU JianNing State Key Laboratory of Coordination Chemistry Nanjing National Laboratory for Microstructures School of Chemistry Chemical Engineering Nanjing University Nanjing China State Key Laboratory of Bioelectronics Southeast University Nanjing China Institute of Molecular Medicine China 《中国科学B辑(英文版)》2011,(3)
Porous silicon(PSi)was applied as a supporting substrate for stepwise covalent derivatization of undecylenic acid, N-hydroxysuccinimidyl ester(NHS-ester)and nitrilotriacetic acid(NTA).By taking the advantages of porous silicon as a supporting matrix such as high surface area to volume ratio,infrared transparency,porous semiconductors for laser desorption/ionization mass spectroscopy,and low fluorescence background,a multi-mode detection biochip prototype can be realized. We prepared such a protein microarra... 相似文献
30.
WANG GuanZhong ZHAO MingMing MA JiYang LI GuanYu CHEN Yuan JIANG XiaoShun XIAO Min 《中国科学:物理学 力学 天文学(英文版)》2015,(5):66-69
We demonstrate radiation-pressure-driven mechanical oscillations from high optical quality factor silica microdisk resonators on chip. Mechanical quality factors of 3520 in air and 12540 in vacuum for the fundamental radial breathing modes are obtained from 73 μm-diameter silica microdisks with mechanical frequencies of ~51 MHz. The measured mechanical oscillation threshold powers for the input light are determined to be 62.5 μW in air and down to 26.6 μW in vacuum. 相似文献