A new patent application has been filed by the University of Trento, resulting from a joint research activity with Fondazione Bruno Kessler (FBK). The patent is for a device and a method for determining the mechanical properties of nanomaterials and comes out of a collaboration between the University’s Laboratory of Bio-Inspired & Graphene Nanomechanics and the Centre for Materials and Microsystems at FBK. There are three inventors: ourselves and Giorgio Speranza, a researcher at FBK. The activity of the Laboratory of Bio-Inspired & Graphene Nanomechanics focuses on cutting edge research topics in the field of the nanomechanics of materials and structures, studying phenomena at the nanometre scale (a billionth of a metre).
The invention in this patent is an innovative setup for the tensile testing of nanomaterials such as microfibres and ultrathin films including monoatomic layers such as graphene. The idea behind this new device is very simple: it uses an actuator (to apply forces/displacement) and a sensor (to measure a force), and the sample to be tested is placed between these. Activating the actuator applies a displacement to the extremity of the sample attached to it. This displacement causes a deformation in the sample and a displacement of the sensor, which is connected to the opposite side. By using an optical microscope to monitor the displacement of the extremities of the sample under tension, it is possible to obtain the principal mechanical properties of the sample, such as the maximum load it can withstand and its capacity to elongate before breaking.
The main novelty of this testing configuration is the way in which the specimen is positioned between the actuator and the sensor. The sample, which could be a microfibre or a thin film, is placed on a substrate that has an incision on the lower surface. During the preparation of the test, the substrate is bonded to the actuator on one side and to the sensor on the other. The substrate is incised with a fine point, so that it can break into two parts at the level of the incision, to allow relative movement between the actuator and the sensor. Substrate movements that could compromise the integrity of the sample are avoided by using a special clamp during the incision phase.
Having a sample initially placed on a substrate overcomes the difficulties of handling samples of very small dimensions, such as microfibres (with a diameter of less than 10 micrometres) or ultrathin films (with a thickness of less than a micrometre). On the other hand, for the experiment to be successful, the sample must be attached to the substrate at its two extremities (either side of the incision) but must otherwise be able to move, so that it can deform during the tensile test. A prototype of the device was built and used for the mechanical characterization of aluminium nanofilm (800nm thick) and microfiber (18 μm diameter). Experiments are in progress on ultrathin films with graphene, and may be extended to other innovative nanomaterials in line with scientific and technological progress.
The device is versatile and can be used for the characterization of a range of micro/nanomaterials, which are gaining increasing interest around the world due to the desire to create new materials with extraordinary properties that can be employed in the next generation of multifunctional electronic devices. These materials will include those consisting of a single layer of atoms, of which graphene is just one example. To best use the enormous potential of these nanomaterials we need to have an in-depth knowledge of their mechanical behaviour. So this is the scenario that has led to this invention, which offers a new test setup that meets the specific requirements for the manipulation of components with very small dimensions.
For industrial use, this device offers many advantages. These include the possibility to determine the elastic, and possibly plastic, properties of a nanomaterial of interest through a simple setup that requires no expensive or particularly sophisticated equipment. The dimensions of the testing device are macroscopic, making it easy to operate and compatible with a microscope, which allows the sample to be observed in real time during the mechanical test.