Laser shock based platform for controllable forming of nanowires and nanomembranes

Ji Li, Purdue University

Abstract

With the ever-growing development of nanotechnology, nanowires (NWs) and nanomembranes (NMs) have attracted enormous research interest in the past decades as two of the most important nanostructures, due to their unique and novel mechanical, electrical, and optical properties. In order to fully realize their wide applications in nanoelectrical, nanophotonic and nanoelectromechanical devices, more and more research interest have been focused on post-processing of the nanomaterials, such as bending, straining, and cutting. Flexibly changing the shape of NWs and NMs is both challenging and crucial to change their property and open wide functions, such as strain engineering, electronic transport, mechanical properties, band structure, and quantum properties, etc. However, despite the importance of controlling the shape, strain and size of NWs and NMs, there are very limited methods for flexibly and scalably shaping of these nanomaterials. Although forming and machining are common processes to change bulk metallic component into desired shape, it is still a great challenge in nano world, due to the experimental limitations caused by the ultra small size of the work pieces. In this study, a novel approach to shape NWs and NMs into nano/submicro scale features is proposed, in which the laser ablation generated shock pressure is utilized as the force source. In the experiment, the to-be-formed nanomaterial sample is placed on top of a substrate with nano-patterns. When the laser shock pressure is applied on the sample, it is pushed into underneath patterns and took the shapes. There is no tooling limitation of this novel force application technique, thus it can flexibly form NWs and NMs into 3-dimensional nano-shapes. Meanwhile, the laser beam size is quite large (mm scale), thus the processing area is in macro scale and this is a scalable process for shaping nano-features. In this research, shaping and straining of metallic NWs, semiconductor NWs and graphene by the proposed laser shock based forming method are successfully achieved and demonstrated. Different forming results, such as shaping, bending, compression, bulging, and cutting, are obtained on different NWs and graphene. The processing conditions are investigated, including laser intensity, pressure, mold size, mold shape and the layout of the forming unit. The feasible setup and optimal processing conditions are found for different material types. The deformation behaviors of NWs and NMs during the laser shock forming process are also studied. It is found that the metallic NWs exhibit very good ductility in the forming process. And the main deformation mechanism in metallic NWs under dynamic loading is formation of twinning and stacking fault, while dislocation motion and pile-up is less obvious. Semiconductor NWs exhibit good elasticity and maintains uniform and single crystal structure, by adopting appropriate experimental conditions. Graphene can be either nano-shaped or patterned depending on the induced straining level. Molecular dynamic (MD) simulation is also carried out to study the dynamic deforming process of graphene. The presented technique is a fast and effective nanomanufacturing approach to control and change the shape of NWs and NMs.

Degree

Ph.D.

Advisors

Cheng, Purdue University.

Subject Area

Industrial engineering|Nanotechnology|Materials science

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