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Register a new userPiezoelectric-based uniaxial pressure cell with integrated force and displacement sensors
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We present a design for a piezoelectric-driven uniaxial stress cell suitable for use at ambient and cryogenic temperatures, and that incorporates both a displacement and a force sensor. The cell has a diameter of 46 mm and a height of 13 mm. It can apply a zero-load displacement of up to ~45 $mu$m, and a zero-displacement force of up to ~245 N. With combined knowledge of the displacement and force applied to the sample, it can quickly be determined whether the sample and its mounts remain within their elastic limits. In tests on the oxide metal Sr$_2$RuO$_4$, we found that at room temperature serious plastic deformation of the sample onset at a uniaxial stress of ~0.2 GPa, while at 5 K the sample deformation remained elastic up to almost 2 GPa. This result highlights the usefulness of in situ tuning, in which the force can be applied after cooling samples to cryogenic temperatures.
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We present a piezoelectric-driven uniaxial pressure cell that is optimized for muon spin relaxation and neutron scattering experiments, and that is operable over a wide temperature range including cryogenic temperatures. To accommodate the large samples required for these measurement techniques, the cell is designed to generate forces up to 1000 N, and to minimize the background signal the space around the sample is kept as open as possible. We demonstrate here that by mounting plate-like samples with epoxy, a uniaxial stress exceeding 1 GPa can be achieved in an active volume of 5 mm3. We show that for practical operation it is important to monitor both the force and displacement applied to the sample. Also, because time is critical during facility experiments, samples are mounted in detachable holders that can be rapidly exchanged. The piezoelectric actuators are likewise contained in an exchangeable cartridge.
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The high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature anneals. These sensors are readout using a low cost battery-powered circuit board, with a responsivity of up to 47.8 aF Pa$^{-1}$ mm$^{-2}$, thereby outperforming commercial sensors.
The thin film configuration presents obvious practical advantages over the 1D implementation in energy harvesting systems such as easily manufacturing and processing and long lasting and stable devices. However, most of the ZnO-based piezoelectric nanogenerators (PENGs) reported so far relay in the exploitation of single-crystalline ZnO nanowires because their self-orientation in the c-axis and ability to accommodate long deformations resulting in a high piezoelectric performance. Herein, we show an innovative approach aiming to produce PENGs by combining polycrystalline ZnO layers fabricated at room temperature by plasma assisted deposition with supported small-molecule organic nanowires (ONWs) acting as 1D scaffold. The resulting hybrid nanostructure is formed by a single-crystalline organic nanowire conformally surrounded by a three dimensional (3D) ZnO shell that combines the mechanical properties of the organic core with the piezoelectric response of the ZnO layer. In a loop forward towards the integration of multiple functions within a single wire, we have also developed ONW@Au@ZnO nanowires including a gold shell acting as inner nanoscopic electrode. Thus, we have built and compare thin films and 3D core@shell ONW@ZnO and ONW@Au@ZnO PENGs showing output piezo-voltages up to 170 mV. The synergistic combination of functionalities in the ONW@Au@ZnO devices promotes an enhanced performance generating piezo-currents almost twenty times larger than the ONW@ZnO nanowires and superior to the thin film nanogenerators for equivalent and higher thicknesses.
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