Effect Of Tip Radius Research Articles

Calibration and data-analysis routines for nanoindentation with spherical tips

Instrumented spherical nanoindentation with a continuous stiffness measurement has gained increased popularity in microphysical investigations of grain boundaries, twins, dislocation densities, ion-induced damage, and more. These studies rely on different methodologies for instrument and tip calibration. Here, we test, integrate, and re-adapt published strategies for tip and machine-stiffness calibration for spherical tips. We propose a routine for independently calibrating the effective tip radius and the machine stiffness using standard reference materials, which requires the parametrization of the effective radius as a function of load. We validate our proposed workflow against key benchmarks and apply the resulting calibrations to data collected in materials with varying ductility to extract indentation stress–strain curves. We also test the impact of the machine stiffness on recently proposed methods for identification of yield stress. Finally, we synthesize these analyses in a single workflow for use in future studies aiming to extract and process data from spherical nanoindentation.Graphic abstract

Effect of tip radius on the nanoscale viscoelastic measurement of polymers using loss tangent method in amplitude modulation AFM

We study the influence of tip radius on the viscoelastic characterization of polymers using a recently developed loss tangent (tan δ) method operated in amplitude modulation atomic force microscopy (AM-AFM) mode. By decreasing the tip radius, we found that AM-AFM tan δ of a homogeneous polystyrene film decreased close to the bulk limit value, which can be ascribed to a reduced effect of the probe/sample adhesive interaction for a smaller tip. Decreasing the tip radius also shifted the tan δ values of nanostructured blocks in a poly(styrene-b-isoprene-b-styrene) triblock copolymer film to their bulk limits, but in different trends for glassy styrene and rubbery isoprene blocks. Besides minimizing the effect of the adhesive interaction, we demonstrate that reducing the tip radius being smaller than the characteristic size of nanostructured domains is critical to obtain their true tan δ image.

Crack Tip Radius Effect on Fatigue Crack Growth and Near Tip Fields in Plastically Compressible Materials

Motivated by the prospective uses of plastically compressible materials such as, metallic and polymeric foams, transformation toughened ceramics, toughened structural polymers etc., the present authors investigate the crack-tip radius effect on fatigue crack growth (FCG) of a mode I crack and near-tip stress-strain fields in such plastically compressible solids. These plastically compressible materials have been characterised by elastic-viscoplastic constitutive equations. Simulations are conducted for plane strain geometry with two different hardness functions: one is bilinear hardening and the other one is hardening-softening-hardening. It has been observed that plastic compressibility as well as strain softening lead to significant deviation in the amount of crack growth. It has further been revealed that the nature of FCG is appreciably affected by initial crack-tip radius. Even though it may look from outside that the increase in tip radius will lead to decrease in FCG, but the nature of FCG variation with respect to tip radius is found to be a combined effect of tip radius, plastic compressibility and work or strain softening etc.

Spherical nanoindentation on tungsten single crystal: The transition from source-controlled plasticity to bulk plasticity

Spherical nanoindentation was performed on tungsten single crystal to investigate the effects of tip radius on the pop-in stress. The results show that the pop-in stress decreases as the tip radius increases. A statistical model with randomly distributed dislocation sources captures experimentally observed source-controlled indentation size effect. The discrepancy between model and experimental data especially for a large tip was corrected by considering the collective activation of multiple dislocation sources. Our results provide a quantitative insight into the understanding of the transition from source-controlled plasticity to bulk plasticity under spherical nanoindentation.

Pseudoelasticity and Shape Memory Effects on Deformation Recovery of Indented Titanium-Nickel Alloy Films

The deformation behavior of shape-memory titanium-nickel (TiNi) alloy films indented by diamond tips of various nominal radius of curvature under different contact loads was investigated by nanoindentation. Pseudoelasticity and shape-memory effect (SME) strongly affected the deformation recovery of the indented films. The effects of tip radius and maximum indentation load on the deformation recovery of austenitic and martensitic TiNi films are interpreted in terms of associated deformation mechanisms controlled by pseudoelasticity, SME, and dislocations. The results reveal the important roles of pseudoelasticity and SME on the capacity of TiNi films to either fully annihilate or partially recover from deformation induced by nanoindentation, illustrating a high potential for applications requiring large reversible deformations.

Dependence of pop-in behavior of a high-entropy alloy FeCoCrMnNi on tip radius

Our previous work has established that the dislocation nucleation during the onset of plasticity, the so-called pop-in, in face-centered cubic single-phased high-entropy alloy FeCoCrMnNi is controlled by vacancy defects. This implies that the tip radius would affect the pop in behavior as the number of vacancy, the available sites for dislocation nucleation, within the stressed volume is proportional to radius. To verify this in current work, a wide range of nanoindenter tips with radius across from 200 to 2013 nm were used. It was found that when tip radius is smaller than 638 nm, the pop-in or displacement burst size increases linearly with it, and that when tip radius is larger than 638 nm, the pop—in size became essentially constant. These experimental findings confirm the effect of tip radius on pop-in behavior. A theoretical model based on image force has been developed to rationalize the above observations.

Adhesion forces between a parabolic-shaped AFM tip scanning a grooved gold surface: Comparison of a model and an experiment

Adhesion forces largely depend on the precise geometry of contact between two surfaces; however, this relationship has not yet been systematically studied. In this paper, the adhesion forces between a parabolic-shaped tip and a grooved gold surface were measured on an atomic force microscope (AFM) under ambient conditions. Experimental results show that the fluctuation in mean adhesion force corresponds to the substrate's profile (which is symmetric), yet is asymmetric. A numerical model is proposed based on geometry of the contact zone. Adhesion force was found to be largely dependent on the combined effects of tip radius, profile and tilt angle, and the concavity, principal curvatures and slope of the substrate surface. Moreover, adhesion force is increased by the superposition of the concave upward profile, and vice versa; while its variation in magnitude depends on the principal curvature. The adhesion force increases if the tip's contact point becomes further away from its vertex due to the slope of the curved sample. The slope has an additional effect due to the difference between the contact normal and pull-off directions. The adhesion force distribution is asymmetric for a tilted tip due to the asymmetric distribution of contact points on the tip. The modelled results of the adhesion forces estimated to occur while scanning along the curved surface are in reasonable accordance with the experimental results. The proposed model may allow better quantitative comparisons of adhesion forces measured experimentally and those estimated theoretically.

(Invited) Tip – Surface Electrode Interactions and the Effects of These Interactions on Scanning Electrochemical Microscopy Response

In operando studies of heterogenous active sites using Scanning Electrochemical Microscopy (SECM) can be hindered by non-planar active sites interacting with non-apex portions of the SECM electrode tip. Concentration field distortion can result from surface sites approaching the tip size. We aim to remove these effects via finite-element modeling for a higher-fidelity depiction of surrounding concentration fields. Experimental concentration fields near ~100 nm Pt nanoparticles are compared to a parallel, steady-state model of the identical system at varying tip-surface separations to extract kinetic and transport parameters, the concentration profile surrounding the particle, and the effective tip radius in relation to tip-surface separation. Differences between the model based on the tip presence is used to correct the experimental data for the presence of the tip. This approach increases the measurement quality of SECM and improves understanding of heterogeneous reaction mechanisms.

Characterization of Frictional Properties of Single-Layer Molybdenum-Disulfide Film Based on a Coupling of Tip Radius and Tip⁻Sample Distance by Molecular-Dynamics Simulations.

Lateral-force microscopy is a powerful tool to study the frictional properties of two-dimensional materials. However, few works distinctly reveal the correlation between the tip radius with the tip–sample distance and the frictional properties of the two-dimensional (2D) materials. We performed molecular-dynamics simulations to study the atomic-scale friction of a typical two-dimensional single-layer molybdenum disulfide (SLMoS2). The effects of tip radius and tip–sample distance on the frictional properties were analyzed and discussed. The frictional force–sliding-distance curves show typical stick–slip behaviors, and the periodicity can be used to characterize the lattice constants of SLMoS2. Sub-nanoscale stick-slip movements occur in one-lattice sliding periods along with only the armchair (AC) direction and only when the tip radius is smaller than 3 Å with 1.47 Å tip-sample distance. At the same tip–sample distance, a smaller tip can provide a more detailed characterization and higher-precision frictional properties of SLMoS2. A larger tip is capable of providing comparative frictional properties of SLMoS2 at a proper vertical tip–sample distance, compared with the small tip.

The effects of tip sharpness and coating thickness on nanoindentation measurements in hard coatings on softer substrates by FEM

The FEM modelling combined with the experimental nanoindentation hardness and indentation modulus depth profiles with the indenter tips of different radii on hard W-C coating/softer steel substrate with different coating thicknesses, revealed the strong influence of the tip radius and coating thickness on the shape of hardness and indentation modulus depth profiles, and the subsequent underestimation of coating property values extracted from the profiles. The effects of tip radius and coating thickness on hardness profiles have the same physical reason – faster penetration of the zone of plasticity into substrate at the same relative indentation depths when the indenter tip radius increases and/or coating thickness is reduced. Thus, the validity of the “10% rule” is limited also by the indenter radius. The main parameters critical for proper nanoindentation measurements in the studied W-C coating/steel substrate system include indenter tip radius ≤500nm, coating thickness ≥0.5μm and the ratio of the tip radius to coating thickness ≤0.1.

Fast and reliable pre-approach for scanning probe microscopes based on tip-sample capacitance

Within the last three decades Scanning Probe Microscopy has been developed to a powerful tool for measuring surfaces and their properties on an atomic scale such that users can be found nowadays not only in academia but also in industry. This development is still pushed further by researchers, who continuously exploit new possibilities of this technique, as well as companies that focus mainly on the usability. However, although imaging has become significantly easier, the time required for a safe approach (without unwanted tip-sample contact) can be very time consuming, especially if the microscope is not equipped or suited for the observation of the tip-sample distance with an additional optical microscope. Here we show that the measurement of the absolute tip-sample capacitance provides an ideal solution for a fast and reliable pre-approach. The absolute tip-sample capacitance shows a generic behavior as a function of the distance, even though we measured it on several completely different setups. Insight into this behavior is gained via an analytical and computational analysis, from which two additional advantages arise: the capacitance measurement can be applied for observing, analyzing, and fine-tuning of the approach motor, as well as for the determination of the (effective) tip radius. The latter provides important information about the sharpness of the measured tip and can be used not only to characterize new (freshly etched) tips but also for the determination of the degradation after a tip-sample contact/crash.

A CAD-FEM-QSA integration technique for determining the time-varying meshing stiffness of gear pairs

Estimation of time-varying meshing stiffness (TVMS) is a vital process as it is one of the primary sources of vibration and noise. There are two ways to evaluate the TVMS, the analytical method (AM) and the finite element method (FEM). Owing to the complex geometries and the use of empirical values, analytical model is not precise to perform the exact calculation. The current FEM is inconvenient due to the use of complex programming codes. Therefore, the first aim of this study is to develop a new technique to determine the TVMS based on NX, ANSYS Workbench, and Quasi-static Algorithm (QSA). The second aim is to compare results of the analytical method (AM) and the proposed method. The effects of tip radius and misalignment of gear pair are also analysed using this new method.

Scanning Microwave Microscopy for Electronic Device Analysis on Nanometre Scale

Probing electrical properties of state-of-the-art electronic devices is one of the key features of Scanning Microwave Microscopy. While providing valuable information on charge carrier properties, the combination of an atomic force microscope cantilever with a microwave signal raises the question on the actual spatial resolution of the system. On the example of the highly confined two-dimensional electron gas of an AlGaN/GaN structure, the effective tip radius is demonstrated to be in the range of the theoretical tip radius for sharp tips, while both values differ for unevenly shaped cantilever tips. The presented method demonstrates the role of the microwave excitation region for the spatial resolution of the system as well as the potential of this method to characterise the effective tip radius.

Process modeling and optimization of the staggered backward flow forming process of maraging steel via finite element simulations

Flow forming is used to produce thin-walled high-precision tubular components. A 3D thermo-mechanical finite element model for staggered backward flow forming of a cylindrical workpiece of maraging steel has been developed using Abaqus/Explicit. The effect of tip radius of the rollers and friction between the rollers and the workpiece has been considered. Simulations have been carried out at different process conditions to study the state variables, such as stresses and strains obtained during the deformation. The model has been benchmarked for thickness reduction and roll forces against the experimental results and analytical solutions, respectively. The effect of flow forming process variables, such as feed rate and reduction ratio, on the stress/strain distribution and roll forces have been studied. An increase in feed rate from 1 to 2.33 mm/s leads to an increase of 7 % in effective plastic stress. An increase of 72 % in equivalent plastic strain has been observed when the reduction ratio is increased from 23 to 33 %. In addition, a parametric study has been conducted to study ovality, diametral growth, roll forces, stresses, and strains as a function of process parameters. The circularity of the tube is a very important geometrical feature in the flow forming process. It is imperative to study the key parameters affecting the circularity of the preform. Eight process variables have been considered in a response-surface-based computer design of experiments to minimize the ovality. The feed rate, reduction ratio, and the attack angle of the roller Z are found to be most significant parameters in order to control the circularity of the tube. Among all process variables, the reduction ratio is found to be the most significant parameter. The order of their relative significance is reduction ratio, feed rate, and the attack angle of the roller Z.

Monopole antenna in quantitative near-field microwave microscopy of planar structures

We have developed an analytical model of a near-field microwave microscope based on a coaxial resonator with a sharpened tip probe. The probe interacts with a layered sample that features an arbitrary depth distribution of permittivity. The microscopic tip end with the accumulated charge is regarded as a monopole antenna radiating an electric field in near zone. The impedance of such an antenna is determined within a quasi-static approximation. The proposed model is used for calculating the sample-sensitive parameters of the microscope, specifically, resonance frequency f0 and quality factor Q0, as a function of probe-sample distance h. The theory has been verified experimentally in studies of semiconductor structures, both bulk and thin films. For measurements, we built a ∼2.1 GHz microscope with an effective tip radius of about 100 μm. The theoretical and experimental dependences f0(h) and Q0(h) were found to be in a good agreement. The developed theory underlies the method for determining sheet resistance Rsh of a semiconductor film on a dielectric substrate proposed in this article. Studies were performed on doped n-GaN films on an Al2O3 substrate. The effective radius and height of the probe determined from calibration measurements of etalon samples were used as the model fitting parameters. For etalon samples, we employed homogeneous sapphire and doped silicon plates. We also performed four-probe dc measurements of Rsh. The corresponding values for samples with Rsh > 1 kΩ were found to be 50% to 100% higher than the microwave results, which are attributed to the presence of microdefects in semiconductor films.

Modeling and de-embedding the interferometric scanning microwave microscopy by means of dopant profile calibration

This paper presents the full modeling and a methodology for de-embedding the interferometric scanning microwave microscopy measurements by means of dopant profile calibration. A Si calibration sample with different boron-doping level areas is used to that end. The analysis of the experimentally obtained S11 amplitudes based on the proposed model confirms the validity of the methodology. As a specific finding, changes in the tip radius between new and used tips have been clearly identified, leading to values for the effective tip radius in the range of 45 nm to 85 nm, respectively. Experimental results are also discussed in terms of the effective area concept, taking into consideration details related to the nature of tip-to-sample interaction.

Optimization of end milling parameters and determination of the effects of edge profile for high surface quality of AISI H13 steel by using precise and fast measurements

This work researches end milling process parameters and also various coating effects on surface quality of the machined parts experimentally. It especially focuses on the effects of tip radius of the tools on the machined surface quality with modern and precise measurement techniques and methods. Taguchi, design of experiments method, was used to determine the optimum processing parameters like cutting speed and depth of cut. Additionally the best coating material which combined with different tool radiuses to obtain high surface quality for the end milling process of AISI H13 hot work steel were investigated. The conducted statistical tests were indicated that coating type is the most effective parameter for the surface roughness according to the selected parameters and their levels. The created mathematical model can explain the 0.90 proportion of the total variability in Ra, arithmetical average surface roughness parameter. High precisely captured optical images indicate tip radius wear effects on surface quality clearly.

PS0030-445 円周切欠き丸棒の延性破壊に及ぼすひずみ拘束の影響 : 先端径の違いによる臨界Jとその破断面の考察

PS0030-445 円周切欠き丸棒の延性破壊に及ぼすひずみ拘束の影響 : 先端径の違いによる臨界Jとその破断面の考察

Effective AFM cantilever tip size: methods for in-situ determination

In atomic force microscopy (AFM) investigations, knowledge of the cantilever tip radius R is essential for the quantitative interpretation of experimental observables. Here we propose two techniques to rapidly quantify in-situ the effective tip radius of AFM probes. The first method is based on the strong dependency of the minimum value of the free amplitude required to observe a sharp transition from attractive to repulsive force regimes on the AFM probe radius. Specifically, the sharper the tip, the smaller the value of free amplitude required to observe such a transition. The key trait of the second method is to treat the tip–sample system as a capacitor. Provided with an analytical model that takes into account the geometry of the tip–sample’s capacitance, one can quantify the effective size of the tip apex fitting the experimental capacitance versus distance curve. Flowchart-like algorithms, easily implementable on any hardware, are provided for both methods, giving a guideline to AFM practitioners. The methods’ robustness is assessed over a wide range of probes of different tip radii R (i.e. 4 < R < 50 nm) and geometries. Results obtained from both methods are compared with the nominal values given by manufacturers and verified by acquiring scanning electron microscopy images. Our observations show that while both methods are reliable and robust over the range of tip sizes tested, the critical amplitude method is more accurate for relatively sharp tips (4 nm < R < 10 nm).

Molecular Dynamics Simulation Study of Tool Wear in Vibration Assisted Nano-Impact-Machining by Loose Abrasives

Vibration assisted nano-impact-machining by loose abrasives (VANILA) is a novel target specific nano-abrasive machining process wherein, nano-abrasives, injected in slurry between the workpiece and the vibrating atomic force microscope probe, impact the workpiece causing nanoscale material removal. In this study, a molecular dynamics (MD) based simulation approach is used to investigate the tool wear mechanism. The simulation results reveal that the tool wear is influenced by the impact velocity of the abrasive grains and the effective tool tip radius. It is seen that based on the process conditions, the wear process could happen through distinctive mechanisms such as atom-by-atom loss, plastic deformation, and brittle fracture. Experimental results show evidences of tool wear by aforementioned mechanisms in VANILA process.