Surface Stress Measurements Research Articles

Surface Stress Measurements of Lead UPD on Electrodeposited Copper Films

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A high sensitivity momentum flux measuring instrument for plasma thruster exhausts and diffusive plasmas

A high sensitivity momentum flux measuring instrument based on a compound pendulum has been developed for use with electric propulsion devices and radio frequency driven plasmas. A laser displacement system, which builds upon techniques used by the materials science community for surface stress measurements, is used to measure with high sensitivity the displacement of a target plate placed in a plasma thruster exhaust. The instrument has been installed inside a vacuum chamber and calibrated via two different methods and is able to measure forces in the range of 0.02-0.5 mN with a resolution of 15 microN. Measurements have been made of the force produced from the cold gas flow and with a discharge ignited using argon propellant. The plasma is generated using a Helicon Double Layer Thruster prototype. The instrument target is placed about 1 mean free path for ion-neutral charge exchange collisions downstream of the thruster exit. At this position, the plasma consists of a low density ion beam (10%) and a much larger downstream component (90%). The results are in good agreement with those determined from the plasma parameters measured with diagnostic probes. Measurements at various flow rates show that variations in ion beam velocity and plasma density and the resulting momentum flux can be measured with this instrument. The instrument target is a simple, low cost device, and since the laser displacement system used is located outside the vacuum chamber, the measurement technique is free from radio frequency interference and thermal effects. It could be used to measure the thrust in the exhaust of other electric propulsion devices and the momentum flux of ion beams formed by expanding plasmas or fusion experiments.

Failure analysis of the draft tube connecting bolts of a Francis-type hydroelectric power plant

In this paper, the failure of the bolts that fasten the draft tube of a 95-MW Francis turbine is presented. The fracture of the bolts is especially frequent when the machine operates at partial load. Fracture surface analysis and stress measurements under several power levels were done. Stress was also measured, while pressure relief in the spiral case was performed. Finally, stress measurements were conducted while pressured air was injected at the stay vanes and the machine was operating at partial load. With the strain measured, stress on the bolts was calculated. The fracture surface analysis showed that fatigue is the failure mechanism. Stress measurements revealed that strong vibration and broad stress variation is present when the machine operates at powers below 80 MW. Air injection effectively decreases vibration and stress fluctuation, but pressure relief in the spiral case did not show any beneficial effect.

Dynamic measurement of the surface stress induced by the attachment and growth of cells on Au electrode with a quartz crystal microbalance

The processes of adhesion, spreading and proliferation of human mammary cancer cells MCF-7 on two Au electrodes with different surface roughness ( R f and R f = 3.2 or 1.1) were monitored and clearly identified with the quartz crystal microbalance (QCM) technique. Analyses of the QCM responses on the resonant frequency shifts (Δ f 0) vs. the motional resistance changes (Δ R 1) revealed a significant surface-stress effect in the involved courses, in addition to a viscodensity effect and a relatively small mass effect (especially at the smooth electrode). Experiments of fluorescence microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were conducted to investigate the cell population on the electrode vs. the electrode-surface roughness. Simplified equations are deduced to quantitatively evaluate the surface stress, and a novel QCM method for dynamically measuring the surface stress on an electrode in cell-culture course is thus described. It was found that the smoother surface ( R f = 1.1) gave a higher surface stress during cell attachment and less cell population on it than the rougher surface ( R f = 3.2). In addition, real-time QCM monitoring showed on the same electrode the surface stress induced by hepatic normal cells being notably higher than that caused by hepatic cancer cells at cell-attachment stage, suggesting that the surface-stress measurement can exhibit the difference of adhesion-performance between the healthy and ill-behaved cells.

Cantilever measurements of surface stress, surface reconstruction, film stress and magnetoelastic stress of monolayers.

We review the application of cantilever-based stress measurements in surface science and magnetism. The application of thin (thickness appr. 0.1 mm) single crystalline substrates as cantilevers has been used successfully to measure adsorbate-induced surface stress changes, lattice misfit induced film stress, and magneto-elastic stress of ferromagnetic monolayers. Surface stress changes as small as 0.01 N/m can be readily measured, and this translates into a sensitivity for adsorbate-coverage well below 0.01 of one layer. Stress as large as several GPa, beyond the elasticity limits of high strength materials, is measured, and it is ascribed to the lattice misfit between film and substrate. Our results point at the intimate relation between surface stress and surface reconstruction, stress-induced structural changes in epitaxially strained films, and strain-induced modifications of the magneto-elastic coupling in ferromagnetic monolayers.

Surface Stress Measurements during the Adsorption and Electrochemical Oxidation of CO on Pt{111}

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Experimental study on the surface stress measurement with Rayleigh wave detection technique

In this paper, experimental study on the surface stress measurement of a metallic material based on the Rayleigh wave acoustoelastic theory is introduced. A Rayleigh wave acoustoelastic formula deduced by Husson is optimized to estimate the surface stress of the material. Two micro Rayleigh wave transducers with 5 MHz frequency one of which is used for acoustic pulse emitter and another for receiver are used to determine the time of flight of Rayleigh wave propagating in a certain distance along the surface of the material. The difference in time of flight between two ultrasonic signals obtained in stressed and unstressed object surface is identified by the digital correlation method. A specimen made of Q235 steel and applied with tensile load is used for calibration to obtain the acoustoelastic coefficients of Q235 steel. Furthermore, some principal factors which may result in errors in the experiment are discussed and some measurements are proposed to prevent these errors. Finally the surface stress of a cantilever beam is detected by the Rayleigh wave acoustoelastic technique and the experimental result is well compared with the theoretical value.

Fretting Fatigue Behavior of Shot-Peened Ti-6Al-4V and IN100

Abstract Shot-peened titanium alloy Ti-6Al-4V and nickel-based super alloy IN100 were subjected to plain and fretting fatigue under cylinder-on-flat contact condition at room temperature. Measurement of compressive residual surface stress from shot-peening before and after fretting showed relaxation, which was significant in IN100 and near the contact surface. The fretting fatigue life of IN100 did not improve significantly due to shot-peening, while there was considerable improvement for Ti-6Al-4V and relatively less relaxation of the residual surface stress. Further, fretting had a relatively more detrimental effect on the fatigue performance of Ti-6Al-4V than in the case of IN100. A critical plane-based fatigue crack initiation model, a modified shear stress range parameter, was computed from finite element analysis for two levels of residual surface stress relaxation: no relaxation and complete relaxation. This analysis suggested that not only crack initiation but also propagation should be considered to characterize fretting fatigue behavior of shot-peened specimens; however, it showed an appropriate trend with the measured fretting fatigue life and agreement with several other experimental observations.

Absence of surface stress change during pentacene thin film growth on the Si(111)-(7 × 7) surface: a buried reconstruction interface

We use high-resolution surface stress measurements to monitor the surface stress during the growth of pentacene (C22H14) on the (7×7) reconstructed silicon (111) surface. No significant change in the surface stress is observed during the pentacene growth. Compared to the changes in the surface stress observed for Si and Ge deposition on the Si(111)-(7×7) surface, the insignificant change in the surface stress observed for the pentacene growth suggests that the pentacene molecules of the first adsorbate layer, although forming strong covalent bonds with the Si adatoms, do not alter the structure of the (7×7) reconstruction. The (7×7) reconstruction remains intact and, with subsequent deposition of pentacene, eventually becomes buried under the growing film. This failure of the pentacene to affect the structure of the reconstruction may represent a fundamental difference between the growth of organic thin films and that of inorganic thin films on semiconductor surfaces.

Surface Stress Observations during the Adsorption and Electrochemical Oxidation of CO on Pt{111}

The adsorbate-induced surface stress was studied for the system CO/Pt{111}-textured thin films in CO-saturated 0.1 M HClO4 and characterized through the techniques of cyclic voltammetry and chronoamperometry. A compressive stress of −1.1 N/m was measured for a saturation coverage. It is shown that CO blocks the electrode both electrochemically (charge transfer) and physically (surface stress changes). Additionally, it is demonstrated with surface stress measurements that CO does not desorb with the removal of CO from the electrolyte. The adsorption kinetics of CO are shown to be slow, with a saturation coverage taking more than 65 s to acquire. When driven electrochemically, CO oxidation kinetics are fast, occurring in much less than 1 s.

Surface stress generation during formation of alkanethiol self-assembled monolayer (SAM)

A high resolution curvature interferometer [Wang, J., Shrotriya, P., Kim, K.S., 2006. Surface residual stress measurement using curvature interferometry. Experimental Mechanics 46 (1), 39–46] is utilized to measure surface stress development associated with formation of self-assembled monolayers (SAM) of octadecanethiols on macroscale domains (25 mm × 25 mm). Atomistic simulations are performed to investigate surface stress generation associated with SAM formation. The results of the molecular simulations are incorporated into the multiscale framework to understand the surface stress generation and curvature change observed during experiments at continuum scale.

On the temperature compensation of parallel piezoresistive microcantilevers in CMOS biosensor

Abstract Microcantilever with embedded piezoresistor has been applied to in situ surface stress measurement of biochemical reaction, where the parallel microcantilever by using an active cantilever for biosensing and another reference cantilever for noise cancellation has previously been proposed. This paper shows that the microcantilever measurement is sensitive to the temperature effect induced by the piezoresistor. The two cantilevers of 125 μm × 60 μm × 0.75 μm may have 40 °C temperature difference, 1.65 mV offset voltage, and 0.01 mV/°C temperature drift in 10 V operation because of their different thermal inertia. A parallel microcantilever design is developed for temperature compensation by using a signal conditioning circuit and the stripe pattern immobilized layer. Analyses and experiments show that the performance of parallel microcantilever sensor can be significantly improved.

Surfactant-Mediated Growth Revisited

The x-ray structure analysis of the oxygen-surfactant-mediated growth of Ni on Cu(001) identifies up to 0.15 monolayers of oxygen in subsurface octahedral sites. This questions the validity of the general view that surfactant oxygen floats on top of the growing Ni film. Rather, the surfactant action is ascribed to an oxygen-enriched zone extending over the two topmost layers. Surface stress measurements support this finding. Our results have important implications for the microscopic understanding of surfactant-mediated growth and the change of the magnetic anisotropy of the Ni films.

A piezoresistive microcantilever array for surface stress measurement: curvature model and fabrication

This paper presents a procedure for the fabrication of a piezoresistive microcantilever array for surface-stress-based chemical and biochemical sensing applications. All existing microcantilever surface stress sensors that are based on single-crystal silicon use p-doped piezoresistors. In this work, the advantages of using n-doped silicon piezoresistors for surface stress sensing have been demonstrated. Further, a new model for surface-stress-sensitive cantilevers, based on classical laminated plate theory, is presented. This model allows for the estimation of the deformation and piezoresistive response of a multilayered microcantilever to surface stresses during analyte measurement and residual stresses in the structural layers due to fabrication processes. Also, the model accounts for bending–stretching coupling in the microcantilever response to the stresses. The utility of the model as a design tool for control of cantilever curvature during the fabrication process has been demonstrated.

Multiwell micromechanical cantilever array reader for biotechnology

We use a multiwell micromechanical cantilever sensor (MCS) device to measure surface stress changes induced by specific adsorption of molecules. A multiplexed assay format facilitates the monitoring of the bending of 16 MCSs in parallel. The 16 MCSs are grouped within four separate wells. Each well can be addressed independently by different analyte liquids. This enables functionalization of MCS separately by flowing different solutions through each well. In addition, each well contains a fixed reference mirror which allows measuring the absolute bending of MCS. In addition, the mirror can be used to follow refractive index changes upon mixing of different solutions. The effect of the flow rate on the MCS bending change was found to be dependent on the absolute bending value of MCS. Experiments and finite element simulations of solution exchange in wells were performed. Both revealed that one solution can be exchanged by another one after 200 microl volume has flown through. Using this device, the adsorption of thiolated DNA molecules and 6-mercapto-1-hexanol on gold surfaces was performed to test the nanomechanical response of MCS.

SU-FF-I-120: Integration of a Pressure Sensing Array Into Ultrasonic Strain Imaging

Purpose: Mechanical in vitro tests have shown differences between fibroadenomas and invasive ductal carcinomas (IDCs) in their non‐linear stress/strain behavior, which could be utilized to differentiate between the two lesion types (and potentially eliminate an unneeded biopsy). Stress and strain measurements are required to quantify this non‐linear behavior in vivo. We are investigating the feasibility of integrating a pressuresensor to obtain a surface stress measurement during ultrasound strain image acquisition. The prototype pressuresensor plate design, methods for calibration and initial results will be presented. Methods/Materials: A custom pressure sensing array was obtained from Pressure Profile Systems, Inc. A variety of tests were performed with the array to gauge its stability, sensitivity and calibration in reference to its application in ultrasoundelastography.Measurements on elastographic phantoms were also performed with comparisons to finite element analysis (FEA) simulations. In addition, data was collected from a small clinical trial at the University of Wisconsin Breast Center. Results: Initial tests show that the pressuresensor array is stable in an ultrasound imaging environment. A reliable calibration technique was also developed. Measurements on phantoms have shown modest agreement with FEA simulations. However, geometric inhomogeneities on the surface of the sensor as well as the variability of the absolute calibration have made an accurate map of the pressure distribution difficult to obtain. From the clinical work the device has been shown to be sensitive enough to detect initial contact with the breast, a crucial objective in quantifying non‐linear stress/strain behavior. Conclusions: The pressuresensor has demonstrated the ability to measure a relative surfacepressure from initial contact to full compression during an ultrasound strain image acquisition, providing a method to quantify the non‐linear stress/strain behavior in breast lesions. However, system limitations may hamper efforts to obtain accurate surfacepressure maps for modulus reconstruction.

Digital processing of multi-mode nano-mechanical cantilever data

Nanomechanical sensors based on cantilever technology allow the measurement of various physical properties. Here we present a software for the comprehensive analysis of such data. An example for the combined measurement of mass and surface stress is presented.

Etching-enhanced surface stress relaxation during initial ozone oxidation

Initial oxidation via ozone on the Si(1 0 0) surface is investigated by measuring surface stress and observing atomic structure via a scanning tunneling microscopy (STM). A similar investigation is also carried out for molecular oxygen and the results are compared. As a result, monotonic increase of the surface stress to the compressive stress side is obtained up to 0.33 N/m for ozone oxidation at room temperature, while molecular oxygen shows only tiny surface stress growth. From the STM observations, it is found that the difference between ozone and molecular oxygen oxidation is the existence of surface etching. As the origin of the surface stress, therefore, the reduction of the intrinsic tensile surface stress due to the reconstructed surface by the etching process is proposed.

OS5-3-2 Raman Spectroscopic Analysis of Surface Stress Distribution on Single Crystal Silicon Microstructures under Uniaxial Tensile Loading

This paper describes an experimental analysis of surface stress distribution on single crystal silicon (SCS) microstructures using laser Raman spectroscope. A handmade tensile tester was employed to apply a uniaxial tensile stress to SCS specimen with a 270 nm-height and 4 μm-square SCS boss in the gauge section. In room temperature, Raman spectroscope measured surface stress, applied by the tensile tester, around the boss. The stress distribution obtained from two-curve fitting of Raman spectrum was in good agreement with that estimated by finite element analysis (FEA).

Electrical, Thermal, and Mechanical Characterization of Silicon Microcantilever Heaters

Silicon atomic force microscope (AFM) cantilevers having integrated solid-state heaters were originally developed for application to data storage, but have since been applied to metrology, thermophysical property measurements, and nanoscale manufacturing. These applications beyond data storage have strict requirements for mechanical characterization and precise temperature calibration of the cantilever. This paper describes detailed mechanical, electrical, and thermal characterization and calibration of AFM cantilevers having integrated solid-state heaters. Analysis of the cantilever response to electrical excitation in both time and frequency domains aids in resolving heat transfer mechanisms in the cantilever. Raman spectroscopy provides local temperature measurement along the cantilever with resolution near 1 mum and 5degC and also provides local surface stress measurements. Observation of the cantilever mechanical thermal noise spectrum at room temperature and while heated provides insight into cantilever mechanical behavior and compares well with finite-element analysis. The characterization and calibration methodology reported here expands the use of heated AFM cantilevers, particularly the uses for nanomanufacturing and sensing