Controllable Fabrication of Percolative Metal Nanoparticle Arrays Applied for Quantum Conductance-Based Strain Sensors

A 3D Composited Flexible Sensor Based on Percolative Nanoparticle Arrays to Discriminate Coupled Pressure and Strain

Flexible mechanical sensors based on nanomaterials operate on a deformation-response mechanism, making it challenging to discern different types of mechanical stimuli such as pressure and strain. Therefore, these sensors are susceptible to significant mechanical interference. Here, we introduce a multifunctional flexible sensor capable of discriminating coupled pressure and strain without cross-interference. Our design involves an elastic cantilever fixed on the pillar of the flexible main substrate, creating a three-dimensional (3D) substrate, and two percolative nanoparticle (NP) arrays are deposited on the cantilever and main substrate, respectively, as the sensing materials. The 3D flexible substrate could confine pressure/strain loading exclusively on the cantilever or main substrate, resulting in independent responses of the two nanoparticle arrays with no cross-interference. Benefitting from the quantum transport in nanoparticle arrays, our sensors demonstrate an exceptional sensitivity, enabling discrimination of subtle strains down to 1.34 × 10^-4. Furthermore, the suspended cantilever with one movable end can enhance the pressure perception of the NP array, exhibiting a high sensitivity of -0.223 kPa^-1 and an ultrahigh resolution of 4.24 Pa. This flexible sensor with multifunctional design will provide inspiration for the development of flexible mechanical sensors and the advancement of decoupling strategies.

Gas phase fabrication of morphology-controlled ITO nanoparticles and their assembled conductive films

ITO nanoparticles were generated in the gas phase with a magnetron plasma gas aggregation cluster source. Their morphologies were modified by modulating the discharging power of magnetron sputtering. The shape of the nanoparticles changed from rough spheroid formed with a higher discharging power to multi-branch formed with a lower discharging power. With a discharging power of 25 W, the ITO nanoparticles were enriched with tripod and tetrapod-shaped nanoparticles. The formation mechanism of multi-branch nanoparticles was attributed to the oriented attachment of the initially nucleated smaller nanocrystallites. Transparent conductive ITO nanoparticle films were fabricated by depositing the preformed nanoparticles with controlled thickness. The electron conduction in the film was dominated by electron tunnelling and/or hopping in the percolative channels comprised of closely spaced ITO nanoparticle assemblies and could be tuned from highly resistive nonmetal-like to highly conductive metal-like by changing the deposition thickness. The film also displayed a SPR band in the near-IR region. The conductivity of the multi-branch ITO nanoparticle film was significantly superior to that of the spheroidal nanoparticle film. For a 46 nm thick multi-branch ITO nanoparticle film, a surprisingly low specific resistance of 3.09 × 10^-4 Ω cm, which is comparable to the top-class conductivity of bulk ITO films, was obtained after annealing at a mild temperature of 250 °C, with a transmittance larger than 85%.

Dewetting Process of Silver Thin Films and Its Application on Percolative Pressure Sensors with High Sensitivity

This work reports on an innovative dewetting process of silver thin films to realize percolative nanoparticle arrays (NPAs) and demonstrates its application on highly sensitive pressure sensors. The dewetting process, which is a simple and promising technique, synthesizes NPAs by breaking the as-deposited metal film into randomly distributed islands. The NPA properties, such as the mean particle size and the spacing between adjacent particles, can be easily tailored by controlling the dewetting temperature, as well as the as-deposited metal-film thickness. The fabricated NPAs were employed to develop gauge pressure sensors with high sensitivity. The proposed sensor consists of a sealed reference-pressure cavity, a polyimide (PI) membrane patterned with an interdigital electrode pair (IEP), and a silver NPA deposited on the IEP and the PI membrane. The operational principle of the device is based on the NPA percolation effect with deformation-dependence. The fabricated sensors exhibit rapid responses and excellent linearity at around 1 atm. The maximum sensitivity is about 0.1 kPa-1. The advantages of the proposed devices include ultrahigh sensitivity, a reduced thermal disturbance, and a decreased power consumption. A practical application of this pressure sensor with high resolution was demonstrated by using it to measure the relative floor height of a building.