Fidelity study in surface measurements in nanometre metrology

The object of this Ph.D work is to evaluate fidelity in surface measurements in nanometric metrology for both contact and non-contact methods, namely stylus instruments and scanning tunnelling microscopy. Fidelity is defined, in this thesis, as a measure to which an instrument system reproduces the surface features and thus the parameters of interest. High fidelity measurement has two meanings; less distortion in the measured result and less disturbance to the surface being measured. Interaction at the interface between the probe and the surface is the source of failure to achieve high fidelity. No instrument measures surface topography alone: all instruments measure a convolution of topography and the geometrical and physical interaction of the measured probe and the surface. In the case of a mechanical stylus, factors extraneous to the topography include (a) the shape and size of the stylus, (b) mechanical properties of the stylus and the specimen such as elastic moduli and hardness, (c) frictional force of the sliding pair. and (d) dynamic interaction forces during the sliding. For the scanning tunnelling microscope, factors which affect measurement in addition to topography include the geometry of the tip, the electronic properties of the surface and mechanical deformation due to electrostatic forces and contamination. 'These factors have been investigated in great detail, particularly for the stylus instruments. A specially designed electro-magnetic force actuator has been developed to give a better control on loading force during the experiments. Tracking force effects were evaluated by profiling statistical parameters, and scanning electron microscopy. Friction between a stylus and specimen has been measured for different loading force, sliding speed, material and surface finish. Improvement on dynamic characteristics of a stylus system has been achieved by active damping control. An optimal damping ratio for stylus instruments is found to be within 0.5-0.7. Through the study, the tracking force and traversing speed are found to be the crucial factors to be tackled so that high fidelity measurement can be obtained. A similar investigation has been also made on two home-built scanning tunnelling microscopes to explore the potential applications of STM on nanometric metrology

Finite element simulation for the effect of loading rate on visco-hyperelastic characterisation of soft materials by spherical nanoindentation

Nanoindentation test performed by atomic force microscopy is highly recommended for the characterisation of soft materials at nanoscale. The assumption proposed in the characterisation is that the material is pure elastic with no viscosity. However, this assumption does not represent the real characteristics of soft materials such as bio tissues or cells. Therefore, a parametric finite element simulation of nanoindentation by spherical tip was carried out to investigate the response of cells with different constitutive laws (elastic, hyperelastic and visco-hyperelastic). The investigation of the loading rate effect on the characterisation of cell mechanical properties was performed for different size of spherical tips. The selected dimensions of spherical tips cover commercially available products. The viscosity effects are insensitive to the varied dimensions of spherical tip in this study. A limit loading rate was found above which viscous effect has to be considered to correctly determine the mechanical properties. The method in this work can be implemented to propose a criterion for the threshold of loading rate when viscosity effect can be neglected for soft material characterisation

A review of NIST projects in surface and topography metrology for firearm evidence identification in forensic science

This is a review of the National Institute of Standards and Technology’s (NIST) efforts in surface metrology and topography measurements for firearm evidence identifications in forensic science. Based on the research projects in surface metrology and standardization, NIST researchers have developed Standard Reference Material (SRM) Bullets and Cartridge Cases (Certain commercial equipment, instruments, or materials are identified in this paper to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose) and established a 2D/3D Ballistics Topography Measurement System. They formulated a Traceability and Quality System to support nationwide ballistics identifications within the National Integrated Ballistics Information Network (NIBIN) in the United States. They have recently proposed a Congruent Matching Cells (CMC) method for accurate ballistic identification and error rate estimation, which provides a statistical foundation and a practical method to promote firearm evidence identifications from qualitative image comparisons to quantitative topography measurements

Correlation analysis of surface tilt effect on its mechanical properties by nano-indentation

In this study, finite element analysis and nano-indentation experiments were carried out to investigate the effect of surface tilt on the nanoindentation test results. This paper revealed that standard Oliver–Pharr method underestimated the contact area due to the influence of the tilt condition. Consequently, it is necessary to compensate this difference to ensure that the result is reliable. The finding was verified by the nano-indentation experiments on a sinusoidal surface sample, which is used for the study of correlation between surface topography and its mechanical properties. A corrective action was implemented to compensate the errors by finite element analysis. By eliminating such errors, the study of the relationship between surface topography and mechanical properties was performed and discussed

Jurisdiction over E Commerce

Expansion of business onto the Internet crosses national borders and creates uncertainty as to the propriety of jurisdiction by the courts of nations and their internal political units. Analysis of jurisdiction in United States law reveals that traditional rules provide guidance for resolving the question of constitutional jurisdiction in cases that cross geopolitical line

Axisymmetric contact problem for a flattened cell : contributions of substrate effect and cell thickness to the determination of viscoelastic properties by using AFM indentation

Nanoindentation technology has proven an effective method to investigate the viscoelastic properties of biological cells. The experimental data obtained by nanoindentation are frequently interpreted by Hertz contact model. However, in order to facilitate the application of Hertz contact model, a mass of studies assume cells have infinite thickness which does not necessarily represent the real situation. In this study, a rigorous contact model based upon linear elasticity is developed for the interpretation of indentation tests of flattened cells which represent a factual morphology. The cell, normally bonded to the petri dish, is initially treated as an elastic layer of finite thickness perfectly fixed to a rigid substrate, and the conic indenter is assumed to be frictionless. The theory of linear elasticity is utilized to solve this contact issue and then the solutions are extended to viscoelastic situation which is regarded as a good indicator for mechanical properties of biological cells. To test the present model, an AFM-based creep test has been conducted on living human hepatocellular carcinoma cell (SMMC-7721 cell) and its fullerenol-treated counterpart. The results indicate that the present model could not only describe very well the creep behavior of SMMC-7721 cells, but can also curb overestimation of the mechanical properties due to substrate effect. Moreover, the present model could identify the difference between the control and treated SMMC-7721 cells in terms of the extracted viscoelastic parameters, suggesting its potential in revealing the biomechanical effects of fullerenol-like drug treatment on cancerous cells

Fabrication of super-hydrophobic nickel film on copper substrate with improved corrosion inhibition by electrodeposition process

Inspired by the famous “lotus effect”, we have fabricated the super-hydrophobic surfaces with nickel film on copper substrates using a one-step electrodeposition method. By adjusting processing time, water contact angle of as-prepared surfaces can reach as high as 160.3 ± 1.5° with small rolling angle of 3.0 ± 0.5°, showing excellent super-hydrophobicity. After the deposition of nickel coating, the pristine copper surfaces became much rough with packed cauliflower-/thorn-like clusters. This unique surface texture contributed to trapping large amount of air and forming the air cushion underneath the water droplet, which can prevent the liquids contacting the copper substrate. The examination of surface chemical compositions implied that the deposited super-hydrophobic coating consisted of nickel crystals and nickel myristate. In this research, the formation mechanism of the electrodeposited super-hydrophobicity was extensively explained based on the analyses of surface texture and surface chemistry. Moreover, the corrosion resistance of the as-fabricated super-hydrophobic surface was estimated by the potentiodynamic polarization tests as well as the electrochemical impedance spectroscopy (EIS) measurements. The results demonstrate that the super-hydrophobic nickel coating showed excellent corrosion inhibition in simulated seawater solution. The existence of the super-hydrophobic coating could be regarded as a barrier and thus provide a perfect air-liquid interface that inhibits the penetration of the corrosive ions. This facile and effective method of electrodeposition process offers a promising approach for mass production of super-hydrophobic surfaces on various metals

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Super-hydrophobic surfaces are attractive due to self-cleaning and anti-corrosive behaviors in harsh environments. Laser texturing offers a facile method to produce super-hydrophobic surfaces. However, the results indicated that the fresh laser ablated surface was generally super-hydrophilic and then gradually reached super-hydrophobic state when exposed to ambient air for certain time. Investigating wettability changing mechanism could contribute to reducing wettability transition period and improving industrial productivity. To solve this problem, we have studied the bare aluminum surface, fresh laser ablated super-hydrophilic surface, 15-day air exposed surface, and the aged super-hydrophobic surface by time-dependent water contact angle (WCA) and rolling angle (RA), scanning electron microscopy (SEM), 3D profile and X-ray photoelectron spectroscopy (XPS). The origins of super-hydrophilicity of the fresh laser ablated surface are identified as (1) the formation of hierarchical rough structures and (2) the surface chemical modifications (the decrease of nonpolar carbon, the formation of hydrophilic alumina and residual unsaturated atoms). The chemisorbed nonpolar airborne hydrocarbons from air moisture contributed to the gradual super-hydrophobic transition, which can be proved by the thermal annealing experiment. Particularly, to clearly explore the wettability transition mechanism, we extensively discussed why the laser-induced freshly outer layer was super-hydrophilic and how the airborne hydrocarbons were chemisorbed. This work not only provides useful insights into the formation mechanism of laser ablated super-hydrophobic surfaces, but also further guides industry to effectively modify surface chemistry to reduce wettability transition period and rapidly produce stable and durable super-hydrophobic surfaces. [Abstract copyright: Copyright © 2018. Published by Elsevier Inc.

Investigation of effect of fullerenol on viscoelasticity properties of human hepatocellular carcinoma by AFM-Based creep tests

Cellular elasticity is frequently measured to investigate the biomechanical effects of drug treatment, diseases and aging. In light of cellular viscosity property exhibited by filament actin networks, this study investigates the viscoelasticity alterations of human hepatocellular carcinoma (SMMC-7721) cell subjected to fullerenol treatment by means of creep tests realized by AFM indentation. An SMMC-7721 cell was first modeled as a sphere and then a flattened layer with finite thickness. Both Sneddon’s solutions and Dimitriadis model have been modified to adapt for viscoelastic situation, which are used to fit the same indentation depth – time curves obtained by creep tests. We find that the SMMC-7721 cell’s creep behavior is well described by the two modified models, and the divergence of parameters determined by the two models is justified. By fullerenol treatment, the SMMC-7721 cell exhibits a significant decrease of elastic modulus and viscosity, which is presumably due to the disruption of actin filaments. This work represents a new attempt to understand the alternation of the viscoelastic properties of cancerous cells under the treatment of fullerenol, which has the significance of comprehensively elucidating the biomechanical effects of anticancer agents (such as fullerenol) on cancer cells