Structure-property relationships of novel electronic functional materials using contactless probing

This proposal is an attempt to obtain the structure-property relationship of 3 different types of semiconductor materials by using vibrational data using Raman spectroscopy/ scanning near-field optical microscopy (SNOM), electronic responses generated from photoluminescence and transport characteristics using far-field time-resolved millimeter-wave conductivity (TR-mmWC) pump-probe method employing frequencies relevant to near future communication frequencies. Materials are selected with the view of their strong field-effect functionality as apparent from recent publications. We propose to use one inorganic 2D electronic material Hafnium Diselenide, hybrid perovskite methylammonium lead halide (MAL3I), and another fully organic PCBM (and its electron beam irradiated variants) for establishing the structure-property relationships. We propose to evaluate each of these materials and relate to their field-effect property. Transition metal dichalcogenide HfSe2 2D layered semiconductor films will be made using commercially available small crystals. These films will be subjected to TR-mm WC reflection and transmission probing and the charge dynamical properties will be extracted from the high signal-to-noise ratio averaged datasets. Raman and SNOM will be extensively used for evaluating the structural properties using vibrational and electronic responses. Spectroscopy will be performed using ultrafast Fourier Transform Infra-Red (FTIR) available with the SNOM facility. We will deposit HfSe2 on prefabricated FET test chips and use a parametric analyzer for collecting transconductance and transfer characteristics data to find mobility and evaluate impacts using structure-property relationship. Hybrid three-dimensional MAL3I films will be prepared in-house and triple cation, mixed halide perovskite versions of MAL3I. We will study the phase, defects, and thermal properties of these variants of 3D MAL3I using the Raman system and nano-FTIR will be performed for noting phase transitions, and structural disorder of this hybrid material. We will also prepare 3D MAL3I FET test chips and obtain the transfer characteristics to realize the benefits that we might have in different cation engineered samples. Organic PCBM (99.5% pure) is suitable for application as organic FET (OFET) and its electronic band structure is reported as tunable using a 50 keV electron beam, and the HOMO, LUMO levels change with the incident electron fluence. We will produce the pristine PCBM sample and use a standard electron gun at various fluences and obtain the photo-response using TRmmWC and relate it to the structural information. OFET test chips will be produced, and transfer characteristics will also be used for studying the outcomes of electron beam irradiation on its performance as a FET. This project will be of interest because we will be able to obtain datasets on materialÕs structure, property, and performance as an electronic device as well. The 2D HfSe2 exhibits high on/off current modulation. The Raman spectrum of this sample is published, however, the structure and properties in IR, THz, and millimeter-wave are not yet well established. In the light of its high current modulation ability, FET characteristics, and supposedly good photo-response will be an important contribution to the knowledge base. 3D MAL3I has been declared a very good candidate for photovoltaic applications with efficiencies exceeding 25% however, its application in electronics is not so well published. These experiments will enable us to report the structure-property relationships of MAL3I and its cation-engineered versions and how the properties manifest under the different structural constitutions. Low cost organic electronics is an attractive area and PCBM, because of its band-structure tunability using electron beam irradiation will be an interesting area to investigate further considering the structure-property relations and performance as OFET material.