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In-situ SEM analysis tool for stretchable metal-elastomer-laminate-membranes for flexible sensors
(2023)
The charge response of a force applied to piezoelectric stack actuators was characterized in the range of 0 N – 20 N for application in piezoelectric self-sensing. Results show linear behavior between ap-plied force and collected charge for both actuators tested in this study. One actuator exhibits a 3.55 times higher sensitivity slope than the other related to its larger capacitance. An error analysis reveals a reduction of relative error in charge measurement with rising forces applied to the actuators.
In this work, we characterise a flexural mechanical amplifier, which is used for the realisation of a miniaturised piezoelectric inchworm motor designed for large force (some N) and stroke (tens of mm) operation as it is required e.g., for medical implants. The characterisation is based on high precision optical displacement measurements and a force self-sensing approach. An optically measured displacement of 292 nm in lateral direction and 910 nm in vertical direction of the flexural mechanical amplifier has been obtained, corresponding to a deflection attenuation factor of 3.1. Piezoelectric self-sensing of force was used to determine a force amplification factor of 3.43 from the mechanical oval structure.
Investigations to improve the adhesion between the PECVD coated silicon carbide thin films and monocrystalline (110) silicon wafer substrate is reported. The surface treatment of silicon wafer is realized by roughening the wafer surface by wet etching in 1.8M potassium hydroxide solution at 50°C with ultrasonic agitation. The average surface roughness of the silicon wafer was increased from 2.9 nm for polished wafer to a range between 32 nm to 250 nm by wet etching for a duration of 10 minutes to 55 minutes, respectively. The adhesion between the PECVD coated silicon carbide thin films (ca. 300 nm thickness) and the silicon wafers with varying surface roughness was characterized by means of scanning scratch test. The critical load initially increased from 153 mN to 169 mN on increasing the average surface roughness from 2.9 nm to 33 nm, respectively. While with further increase in average surface roughness adversely in-fluenced the adhesion indicated by a gradual decrement in the critical load to 124 mN for the maximum investigated average surface roughness of 250 nm.
Microfabricated 2D inductive eddy-current transducers operating in a reflection differential transmitter-receiver mode are presented for the micro nondestructive detection of micro grinding burn. 2D spiral circular microcoils are employed as excitation coils, while an innovatively conceptualized “interconnected split-D” type differential microcoil is used as a sensing coil. Finite element modelling using COMSOL revealed the efficacy of proposed concept in non-destructive testing of small grinding burn having a width of 100 µm. The induced sensing coil voltage changed as a function of presence of grinding burn, with successful recording of the signal for the investigated lift-off range of 250 µm - 1000 µm for 100 kHz to 1 MHz driving frequencies of excitation coil. Experimental validation showed a 94% increase in the induced voltage of the sensing coil in presence of grinding burn on increasing the driving frequency of excitation coil from 100 kHz to 1 MHz. Thereby, revealing the superficial nature of the grinding burn defect, and showing the efficacy of the proposed concept for the non-destructive testing of grinding burn.
The influence of bath hydrodynamics on the resultant micromechanical properties of electrodeposited nickel-cobalt alloy system is investigated. The bath hydrodynamics realized by magnetic stirring is simulated using COMSOL Multiphysics and a region of minimum variation in velocity within the electrolytic cell is determined and validated experimentally. Nickel-cobalt alloy and nickel coating samples are deposited galvanostatically (50 mA/cm2) with varying bath velocity (0 to 42 cm/s). The surface morphology of samples gradually changed from granular (fractal dimension 2.97) to more planar (fractal dimension 2.15) growth type, and the according average roughness decreased from 207.5 nm to 11 nm on increasing the electrolyte velocity from 0 to 42 cm/s for nickel-cobalt alloys; a similar trend was also found in the case of nickel coatings. The calculated grain size from the X-ray diffractograms decreased from 31 nm to 12 nm and from 69 nm to 26 nm as function of increasing velocity (up to 42 cm/s) for nickel-cobalt and nickel coatings, respectively. Consecutively, the measured Vickers microhardness values increased by 43% (i.e., from 393 HV0.01 to 692 HV0.01) and by 33% (i.e., from 255 HV0.01 to 381 HV0.01) for nickel-cobalt and nickel coatings, respectively, which fits well with the Hall–Petch relation.
The approach of using current transients to model the nucleation rate as reported in the seminal work of Scharifker and Mostany is limited to electrodeposition system without bath hydrodynamics (BHD). Therefore, in this work in situ electroanalytical approach is proposed to unveil the influence of BHD on the nucleation kinetics of electrochemically deposited Nickel-Cobalt alloy system (eNiCo). Using the Hydrodynamic linear sweep voltammetry (HLSV) technique, the limiting current density as a function of BHD is computed, wherein it increased (for eNiCo alloys) from 186 mA/cm² to 222.6 mA/cm² on increasing BHD from 0 to 42 cm/s, respectively. Consecutively, the diffusion layer thickness is found to decrease from 19 µm to ca. 15.8 µm on increasing BHD from 0 to 42 cm/s, respectively. Additionally, from Nyquist plots recorded using the Galvanostatic Electrochemical Impedance Spectroscopy (GEIS), the charge transfer coefficient (Rct), exchange current density (io) and double layer capacitance (Cdl) as a function of BHD is computed. It is found that Rct decreased and io, Cdl increased as function of BHD. Thereby, indicating the enhancement in the charge transfer on the cathode surface and reduction in the thickness of the diffusion layer. Hence, with the use of BHD, it is possible to control the growth kinetics, therefore enabling the deposition of tailor-made materials possessing specific required properties.