基于LFM的类金刚石膜纳米摩擦现象研究

使用原子力显微镜(AFM)中的侧向力(LFM)模式对类金刚石膜纳米尺度的摩擦现象进行了研究,主要考察了载荷、微观形貌、粘附对类金刚石膜纳米摩擦性能的影响.首先结合粘附的影响提出了适用于外加载荷在100 nN以下类金刚石膜纳米摩擦力表征的修正Amonton公式.其次,试验发现摩擦过程中表面接触峰的斜率对薄膜的微观摩擦力的影响较大,微观摩擦系数与倾角θ成正比例关系,最后结合两者给出了综合考虑载荷、表面形貌、粘附且可用于类金刚石膜纳米尺度摩擦力表征的数学方法.     

参激非线性振子不稳定区域的实验研究

对一端固定、一端滑动、受轴向简谐激励的屈曲梁的非线性动力学行为进行了实验研究。对固定的参数激励频率和阻尼，当参数激励幅值较小时梁的运动是周期的，但大幅值激励会使运动通过倍周期分岔变为混沌。实验得到了动态响应在参数平面上的分布，并研究了阻尼对分布区域的影响。实验结果为全面了解系统解的分布及该类结构的动力学设计提供了有价值的资料。     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Chemical Imaging Beyond the Diffraction Limit: Experimental Validation of the PTIR Technique

Photothermal induced resonance (PTIR) has recently attracted great interest for enabling chemical identification and imaging with nanoscale resolution. In this work, electron beam nanopatterned polymer samples are fabricated directly on 3D zinc selenide prisms and used to experimentally evaluate the PTIR lateral resolution, sensitivity and linearity. It is shown that PTIR lateral resolution for chemical imaging is comparable to the lateral resolution obtained in the atomic force microscopy height images, up to the smallest feature measured (100 nm). Spectra and chemical maps are produced from the thinnest sample analyzed (40 nm). More importantly, experiments show for the first time that the PTIR signal increases linearly with thickness for samples up to ≈ 1 μm (linearity limit); a necessary requirement towards the use of the PTIR technique for quantitative chemical analysis at the nanoscale. Finally, the analysis of thicker samples provides the first evidence that the previously developed PTIR signal generation theory is correct. It is believed that the findings of this work will foster nanotechnology development in disparate applications by proving the basis for quantitative chemical analysis with nanoscale resolution.     

Structure and Microtribological Mechanism of Teflon Deposited Film

1.IntroductionPolytetrafluoroethylene(PTFE)iswidelyusedassolidlubricantandthecomponentofcompositeplat-ingormultilayerfilmintheIowfrictionmaterialsde-...signing.Inthecompositeplating[1]andmultilayerfilml2],Teflonisintheformofultrafineparticlesorthinlayer.Becausethepropertiesoftheselowdimen-sionalmaterialsaredifferentfromtheirbulkstates,itisveryurgenttorevealthepropertiesoftheselowdi-mensionalmaterials,andthendevelopnewmaterialswithhighspecificperformance.In1995,thefrictionforcemicroscope(AF…     

Nanoscale periodic modulations on sodium chloride surface revealed by tuning fork atomic force microscopy

The sodium chloride surface is one of the most common platforms for the study of catalysts, thin film growth, and atmospheric aerosols. Here we report a nanoscale periodic modulation pattern on the surface of a cleaved NaCl single crystal, revealed by non-contact atomic force microscopy with a tuning fork sensor. The surface pattern shows two orthogonal domains, extending over the entire cleavage surface. The spatial modulations exhibit a characteristic period of 5.4 nm, along <110> crystallographic directions of the NaCl. The modulations are robust in vacuum, not affected by the tip-induced electric field or gentle annealing (<300?°C); however, they are eliminated after exposure to water and an atomically flat surface can be recovered by subsequent thermal annealing after water exposure. A strong electrostatic charging is revealed on the cleavage surface which may facilitate the formation of the observed metastable surface reconstruction.     

Combined laser interference and photolithography patterning of a hybrid mask mold for nanoimprint lithography

A lithography technique that combines laser interference lithography (LIL) and photolithography, which can be a valuable technique for the low cost production of microscale and nanoscale hybrid mask molds, is proposed. LIL is a maskless process which allows the production of periodic nanoscale structures quickly, uniformly, and over large areas. A 257 nm wavelength Ar-Ion laser is utilized for the LIL process incorporating a Lloyd's mirror one beam inteferometer. By combining LIL with photolithography, the non-selective patterning limitation of LIL are explored and the design and development of a hybrid mask mold for nanoimprint lithography process, with uniform two-dimensional nanoscale patterns are presented. Polydimethylsiloxane is applied on the mold to fabricate a replica of the stamp. Through nanoimprint lithography using the manufactured replica, successful transfer of the patterns is achieved, and selective nanoscale patterning is confirmed with pattern sizes of around 180 nm and pattern aspect ratio of around 1.44:1.     

Ordered nanoparticle arrays formed on engineered chaperonin protein templates

Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Some proteins, for example, have been used to form ordered two-dimensional arrays. Here, we fabricated nanoscale ordered arrays of metal and semiconductor quantum dots by binding preformed nanoparticles onto crystalline protein templates made from genetically engineered hollow double-ring structures called chaperonins. Using structural information as a guide, a thermostable recombinant chaperonin subunit was modified to assemble into chaperonins with either 3 nm or 9 nm apical pores surrounded by chemically reactive thiols. These engineered chaperonins were crystallized into two-dimensional templates up to 20 microm in diameter. The periodic solvent-exposed thiols within these crystalline templates were used to size-selectively bind and organize either gold (1.4, 5 or 10nm) or CdSe-ZnS semiconductor (4.5 nm) quantum dots into arrays. The order within the arrays was defined by the lattice of the underlying protein crystal. By combining the self-assembling properties of chaperonins with mutations guided by structural modelling, we demonstrate that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.     

Nanofriction behavior of cluster-assembled carbon films

We have characterized the frictional properties of nanostructured carbon films grown by supersonic cluster beam deposition via an atomic force-friction force microscope (AFM-FFM). The experimental data are discussed on the basis of a modified Amonton's law for friction, stating a linear dependence of friction on load plus an adhesive offset accounting for a finite friction force in the limit of null total applied load. Molecular dynamics simulations of the interaction of the AFM tip with the nanostructured carbon confirm the validity of the friction model used for this system. Experimental results show that the friction coefficient is not influenced by the nanostructure of the films nor by the relative humidity. On the other hand the adhesion coefficient depends on these parameters.     

Optical characteristics of femtosecond laser micromachined periodic structures in Si <100>

A frequency doubled Ti:sapphire laser of 400 nm wavelength, 160 fs pulse width, and 1 kHz repetition rate, combined with a high resolution computer-controlled X-Y stage, was used to direct write periodic structures on Si <100>. Laser pulses of approximately 130 nJ energy were focused using an objective lens of 0.65 NA. Laser micromachining yielded lines of 700 nm width and ablation depths of 600 nm. One- and two-dimensional periodic structures of 5 and 5x5 microm spacing were fabricated, and the structures were characterized by using optical and atomic force microscopy. The light diffraction characteristics of the periodic 1D and 2D patterns were examined. The diffraction properties of the 1D structures were highly dependent upon the light polarization orientation with respect to the micromachining direction.     

Fracture of steel beam to box column connections

Abstract

This study is aimed at examining the behavior of the beam to interior box column connection. Cruciform type test setups are selected with the column under constant gravity load while both beams under gradually increased cyclic loading in opposite directions to simulate earthquake load. The tearing strength of the column plate by the transmitted out‐of‐plane load from the beam web is analyzed by yield line theory. A simplified method is proposed to establish the relationship between the thickness of beam web and column plate. A series of experimental studies are also conducted to examine the effect of a diaphragm plate on the transmission of applied force from beam flanges. Based on the results of this study, suggestions are made for the design and construction of beam to box column connections to achieve better strength and ductility.     

Further study on the refined theory of rectangle deep beams

Based on the refined theory for narrow rectangular deep beams, two different displacement boundary conditions of the fixed end of a cantilever beam are used to study the deformation of the beam. One is the conventional simplified displacement boundary condition, and the other is a new boundary condition determined by the least squares method. Three load cases are investigated, which are a transverse shear force at the free end of the beam, a uniformly distributed load at the top surface, and a linearly distributed load at the top surface, respectively. Solutions are given for both the refined theory and the Timoshenko beam theory and are compared with the known solutions from the elastic theory and results by the finite element method. It is shown that the solutions of the refined theory coincide with those of the elastic theory; the solutions from the Timoshenko theory by using the two different displacement boundary conditions are the same; the refined theory by using the new boundary condition provides better results than using the conventional boundary condition and also better than those of the Timoshenko beam theory.     

The formation mechanism of periodic Zn nanocrystal arrays embedded in an amorphous layer by rapid electron beam irradiation

A periodic nano-island array of ～7?nm diameter Zn single crystals embedded in an amorphous Zn(2x)Si(1-x)O(2) layer was created by using rapid electron beam irradiation for 50?s. A sequential process of 900?°C thermal annealing followed by electron beam irradiation induces the formation of an amorphous Zn(2x)Si(1-x)O(2) layer containing periodic Zn nanocrystals. It is shown that the periodic Zn crystal array can be produced with good control of their size and spacing. Possible formation mechanisms for the Zn crystal nano-islands are described on the basis of the experimental results.     

Entropic unfolding of DNA molecules in nanofluidic channels

Single DNA molecules confined to nanoscale fluidic channels extend along the channel axis in order to minimize their conformational free energy. When such molecules are forced into a nanoscale fluidic channel under the application of an external electric field, monomers near the middle of the DNA molecule may enter first, resulting in a folded configuration with less entropy than an unfolded molecule. The increased free energy of a folded molecule results in two effects: an increase in extension factor per unit length for each segment of the molecule, and a spatially localized force that causes the molecule to spontaneously unfold. The ratio of this unfolding force to hydrodynamic friction per DNA contour length is measured in nanochannels with two different diameters.     

First-principles study of static nanoscale friction between MoO3 and MoS2

The motion of a nanoscale MoO3 crystal on an MoS2 substrate is an ideal case for the study of the effects of microstructure on macroscopic phenomena like friction, because both components of this system can be prepared with atomically flat surfaces. We apply a recently developed real-space density functional theory method to investigate the energetics of sliding an MoO3 crystal on an MoS2 substrate. We then link the results to simple models based on continuum elastic theory, in order to study the mechanical behavior of the oxide crystals under loads that correspond to realistic situations. Based on these results, we extract estimates of the force which must be applied with an atomic force microscope in order to move the oxide crystal on the substrate, for different orientations of the two components.     

Impact force measurement of an actuator arm of a hard disk drive

Impact forces of an actuator arm of a hard disk drive (HDD) are measured by means of modifying the levitation mass method (LMM) whose basic concept was proposed by the first author. In the LMM, force is measured as the inertial force of a mass levitated with sufficiently small friction using an aerostatic linear bearing. The Doppler frequency shift of the laser beam reflecting from the mass is accurately calculated from the waveform recorded using a digitizer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. In the experiments, the mechanical response of an actuator arm of a HDD against an impact load and the inertial force of the actuator arm in free oscillation are measured. The importance and the problems concerning the present knowledge on the impact force of an actuator arm of a HDD are also discussed.     

Identifying the Magnitude and Location of a Load on a Slender Beam Using a Strain Gauge Based Force Transducer

A unique strain gauge based method is developed to identify the magnitude and location of a load on a slender beam with variable cross sections, and pinned, firm rest, soft rest, pinned‐fixed, and fixed boundary conditions. Four uniaxial strain gauges are mounted to the bottom surface of the beam, and the bending moment diagram of the beam can be constructed using measured strains on the beam. By combining individually scaled strain gauge outputs, the magnitude and location of the load can be accurately identified. The strain gauge based force transducer methodology is experimentally validated on prismatic beams with firm rest, soft rest, firm rest‐fixed, and fixed boundary conditions, and a continuously tapered beam with rest boundary conditions. The force transducer methodology is independent of the boundary conditions of the beam, and the error from strain gauge drift due to uniform thermal expansion on a prismatic beam can cancel out.     

Nanoscale impedance microscopy-a characterization tool for nanoelectronic devices and circuits

A recently developed conductive atomic force microscopy (cAFM) technique, nanoscale impedance microscopy (NIM), is presented as a characterization strategy for nanoelectronic devices and circuits. NIM concurrently monitors the amplitude and phase response of the current through a cAFM tip in response to a temporally periodic applied bias. By varying the frequency of the driving potential, the resistance and reactance of conductive pathways can be quantitatively determined. Proof-of-principle experiments show 10-nm spatial resolution and ideal frequency-dependent impedance spectroscopy behavior for test circuits connected to electron beam lithographically patterned electrode arrays. Possible applications of NIM include defect detection and failure analysis testing for nanoscale integrated circuits.     

壳板凸肩叶片的非线性振动特性

以凸肩叶片为研究对象,应用Donnell’s简化壳理论建立模型的非线性振动方程,考虑了几何非线性、阻尼、凸肩接触面正压力、摩擦力等因素。采用Galerkin法将振动微分方程离散到模态坐标上,分别应用数值法和近似解析法对方程组求解,得到系统的频率响应曲线,并讨论了系统周期解的稳定性。结果表明,由于凸肩接触面之间摩擦力方向周期性改变,导致系统的振动特性产生不连续性,以摩擦力为正、负方向分别绘制一条频率响应曲线。则随着摩擦力方向T/4周期变换一次,系统的振动也以T/4为周期在两条频率响应曲线上来回跳跃,从而有效抑制叶片的振动响应,提高叶片使用的安全性。     

Mechanical elasticity of vapour-liquid-solid grown GaN nanowires

Mechanical elasticity of hexagonal wurtzite GaN nanowires with hexagonal cross sections grown through a vapour-liquid-solid (VLS) method was investigated using a three-point bending method with a digital-pulsed force mode (DPFM) atomic force microscope (AFM). In a diameter range of 57-135?nm, bending deflection and effective stiffness, or spring constant, profiles were recorded over the entire length of end-supported GaN nanowires and compared to the classic elastic beam models. Profiles reveal that the bending behaviour of the smallest nanowire (57.0?nm in diameter) is as a fixed beam, while larger nanowires (89.3-135.0?nm in diameter) all show simple-beam boundary conditions. Diameter dependence on the stiffness and elastic modulus are observed for these GaN nanowires. The GaN nanowire of 57.0?nm diameter displays the lowest stiffness (0.98?N?m(-1)) and the highest elastic modulus (400 ± 15?GPa). But with increasing diameter, elastic modulus decreases, while stiffness increases. Elastic moduli for most tested nanowires range from 218 to 317?GPa, which approaches or meets the literature values for bulk single crystal and GaN nanowires with triangular cross sections from other investigators. The present results together with further tests on plastic and fracture processes will provide fundamental information for the development of GaN nanowire devices.