Current Research Projects

We acknowledge the National Science Foundation (Grant nos. DMR-1807263, ECCS-1827846, ECCS-1707588, 1305642, 0823563, 0523656, IIA-1339011, DMR-0413601), Research Corporation, ACS-Petroleum Research Fund, Dept. of Army, and the University of Missouri Research Board for funding our research.

Organic and Hybrid Electronics

A major focus of our research in the past few years has been on improving the performance of organic field-effect transistors (FETs) by controlling the polymer-dielectric interface and understanding the mechanism of carrier transport. Our current work focuses on understanding charge transport mechanisms in FETs using polymer ferroelectric dielectrics. Ferroelectric dielectrics, where the dielectric constant can be tuned by an order of magnitude with temperature, are ideal for extracting information on polaron hopping lengths and barrier heights.

We use vibrational spectroscopy from organic FETs and light-emitting diodes under applied electric fields. These studies elucidate the role of conformational changes in the molecules/polymers along with insights into the role of polarons/bipolarons in charge-transport. We have developed a novel technique of generating Raman maps across the polymer-Au interface in FETs, providing a powerful visualization tool for correlating the device performance under bias stress to the structural changes of the molecule/polymer.

Hybrid interfaces using nanopatterned ZnO and donor-acceptor conjugated polymers are being developed for near-IR photodetectors and solar cells. These architectures pave the way for non-fullerene based hybrid photodetectors.

ACS Appl. Mater. Interfaces 2020,12, 26757

Phys .Rev. Appl. 2018, 10, 014011

ACS Appl. Mater. Interfaces 2018, 10, 19844

Tuning Metal Halide Perovskites

Lead halide perovskites have a rich landscape of structural and optical properties, which can be explored and controlled by applying high pressure. With the recent discovery of Ruddlesden-Popper (RP) faults in 3D CsPbBr3 perovskite nanocrystals which result in their exceptional emission stability, there is a quest for tuning these faults to improve the overall optical properties in lead halide perovskite materials.

By combined photoluminescence, synchrotron-based x-ray diffraction, and Raman-scattering studies as a function of pressure from methylammonium lead bromide (MAPbBr3), we shed light on an isostructural phase transition due to the coupling of the MA cation and the PbBr6 lattice through hydrogen bonding.

Chem. Mater. 2020, 32, 785

ACS Appl. Energy Mater. 2020 3, 2350

Phys Rev. Mater. 2020, 4, 105403

J. Mater. Research 2021

Peptide and Other Nanomaterials

The performance of molecular electronics as biomimetic devices is mainly determined by the supramolecular organization of functionalized nanoscale biocompatible materials. The nanostructures obtained from biomolecules are attractive due to their biocompatibility, ability for molecular recognition, and ease of chemical modification. Peptide-based nanostructures (PNS) derived from natural amino acids are superior building blocks for biocompatible devices as they can be used in a bottom-up process without any need for expensive lithography. Based on self-assembly and mimicking the strategies occurring in nature, peptide materials play a unique role in a new generation of hybrid materials.

We are developing charge modulated FETs using PNS and silk fibroin for biosensing applications. Here a floating gate transistor is biased through a control capacitor. The sensing area, separate from the FET, is obtained by exposing a portion of the floating gate. The control voltage is modulated by an expression that is proportional to the net electric charge immobilized on the active sensing area. A modulation of the charge will change the floating gate voltage, and thus the drain current. Since the sensing area is separate from the actual FET, they can be re-used for sensing and detection.

ACS Appl. Electron. Mater. 2019 1, 2086

ACS Appl. Nano Mater, 2018, 1, 1175

Adv. Mater. Interfaces, 2015, 2, 1500265

ACS Appl. Mater. Interfaces, 2014, 6, 21408

Ultrafast Laser Spectroscopy and Nonlinear Optics

We have recently setup an ultrafast laser laboratory as part of an NSF funded MRI award. Please check the ultrafast laser laboratory. We are currently working on several projects related to nonlinear optical properties such as second/higher harmonic generation from halide perovskites and devices, time-resolved PL, and pump-probe optical spectroscopy.

J. Phys. Chem. Lett. 2021, 12, 4092

AIP Advances 2019, 9, 115202