A mechanical system for tensile testing of supported films at the nanoscale

M.F. Pantano, G. Speranza, N. M. Pugno
University of Trento,
Italy

Keywords: nanomaterials, thin films, tension, mechanical properties

Summary:

Standard tensile tests of materials are usually performed on freestanding specimens. However, such requirement is difficult to implement when the materials of interest are of nanoscopic dimensions due to problems related to their manipulation and gripping. In this study, we propose a novel platform for tensile testing of thin nanomaterials, which allows tests to be carried out on specimens initially deposited onto a macroscopic pre-notched substrate, which is connected to an actuator on one side and to a load sensor on the other side. During the test, however, no substrate effects are introduced, allowing the specimen to be freely stretched. Indeed, before the test starts, the Si substrate supporting the specimen is engraved causing the onset of a fracture line running parallel to its groove at the bottom. In order to avoid any undesirable movement, which could cause damage to the specimen, the Si substrate is kept firmly in place by a mechanical clamp that presses it against a fixed surface. After fracture, the clamp is released and the sample results to be connected to two facing Si blocks that can move one with respect to the other. The effectiveness of the mechanical clamp is confirmed by the tiny width of the fracture line (that is in the range of 1-3 micrometers) and the absence of defects induced in specimens during the substrate fracture. The system does not require any complex electronics to operate – feature that simplifies significantly its operation protocol. Then, its macroscopic size offers the distinctive possibility to test large-area (>1 mm2 area) nanofilms with real time optical observation. This latter feature is really unique, as common systems used for the mechanical characterization of nanoscale samples are based on complex Microsystem (MEMS) technology and operate under vacuum on sub-micrometer thick films and few micrometers square area. A wide variety of materials in the shape of both 1D and 2D micro/nanostructures can be tested, such as microwires and ultra-thin films, metals and polymers. Indeed, our device is versatile and can be efficiently customized according to the sample of interest. The results obtained from a variety of thin metal or polymeric films are very promising for the further development of this technique as a standard method for nanomaterial mechanical testing.