Nanomechanical strain testing of low dimensional materials with micro-electro mechanical system (MEMS) chips

Abstract

This thesis explores nanomechanical strain testing of low-dimensional materials. The limitations of existing experimental environments for testing low-dimensional materials are discussed. To overcome these limitations, the study proposes the use of self-designed Micro-Electro Mechanical Systems (MEMS) chips. The fabrication methods and advantages of MEMS chips are explained. The investigation involves studying few-layer 2H-MoS2 crystals using MEMS chips. Device preparation techniques, such as mechanical exfoliation and all-dry transfer, are outlined. Raman measurements are conducted on MoS2 to analyze its response to strain, specifically focusing on the E12g mode Raman peak. The piezoelectric properties of MoS2 are extensively discussed, including piezo voltage-resistivity and IV mea-surements. An interesting thermoelectric bipolar photocurrent response in MoS2 is explored using scanning photocurrent microscopy (SPCM). Possible contributions of different mechanisms such as the Photothermoelectric Effect (PTE) or Flexo-photovoltaic effect of Bipolar Photocurrent response are discussed. The contribution of stress on the recently shown substrate effect is tested in this work. The growth and transfer optimization of V2O3 crystals which have a strain-dependent phase transition properties is explored, with a focus on adapting growth to a conventional CVD chamber. Polymer-assisted transfer techniques and passivation methods are investigated. Raman spectroscopy results demon-strate a shift in the Raman spectrum, and completed V2O3 MEMS devices are showcased. In addition, some preliminary work upon V2O3 growth in different substrates (Mica) is tested. Finally, some small top-gate modulations of V2O3 exploiting Metal-insulator transition property is shown. Overall, this thesis contributes to the field of nanomechanical strain testing of low-dimensional materials by introducing MEMS chips as an effective experimental platform. The investigations provide valuable insights into the mechanism of the substrate-engineered photocurrent generation analysis of 2H-MoS2. The thesis also provides a device fabrication methodology to study interesting phase transitions in strongly-correlated materials. These findings have implications for understanding the properties and potential applications of low-dimensional materials.