Real-time observation of the actual contact area between surface interfaces at the nanoscale enables more precise examination of what happens during friction. We have combined micro electro mechanical system actuators and transmission electron microscopy (TEM) observation, to both apply and measure forces across nanoscale junctions and contacts. This custom-designed experimental system can measure the true surface area of a contact site from a lateral viewpoint, while simultaneously measuring the friction force. We scratched surfaces coated with diamond like carbon, a classical solid lubricant, and observed the formation of wear particles that slipped and rolled between the interface. TEM images showed that the shape of the surface at the nanoscale underwent permanent deformation when acted upon with forces as low as several tens of nano newtons. The results demonstrated the limitations of friction analyses relying on friction force measurements without real-time surface profiling.
Liquid cells are hermetically sealed capsules that make it possible to image through liquids at the nanoscale using Transmission Electron Microscopes (TEM). Liquid cells can be passive vessels or integrate electrodes up to now for electrodeposition experiments. Temperature is a key parameter for chemical kinetics of processes. This paper describes a temperature controlled liquid cell for in-situ TEM studies. The liquid cell integrates a resistive element for both heating and sensing temperature. A capacitively coupled heat feedback technique is implemented to control the temperature of the liquid cell from room temperature to 100°C with accuracy 0.1°C. In-situ TEM experiment illustrate the heating capability of such temperature controlled liquid cell while observing at the nanoscale.
The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay sensitivities that rival or exceed conventional standards, silicon-based microelectromechanical systems remain underutilised for biological and biomedical applications. Although microelectromechanical resonators and actuators do not always exhibit optimal performance in liquid due to electrical double layer formation and high damping, these issues have been solved with some innovative fabrication processes or alternative experimental approaches. This paper focuses on several examples of silicon-based resonating devices with a brief look at their fundamental sensing elements and key fabrication steps, as well as current and potential biological/biomedical applications.
Electrostatic microactuators require external DC biasing in order to achieve the widest possible range of displacements for a given AC input. This report proposes a novel microspeaker structure that utilizes a potassium-ion-electret to reduce the need for such DC voltage application. Electrets exhibiting quasi-permanent charges enable large fixed voltages to be integrated directly within the MEMS structure, acting as an ersatz DC bias. Prototype devices were fabricated and characterized to approximate the effects of electret incorporation on the device performance.
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