Electrocorticography (ECoG) is a powerful tool for direct mapping of local field potentials from the brain surface. Progress in development of high-fidelity materials such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on thin conformal substrates such as parylene C enabled intimate contact with cortical surfaces and higher quality recordings from small volumes of neurons. Meanwhile, stimulation of neuronal activity is conventionally accomplished with electrical microstimulation and transcranial magnetic stimulation that can be combined with ECoG to form the basis of bidirectional neural interface. However, these stimulation mechanisms are less controlled and primitively understood on the local and cellular levels. With the advent of optogenetics, the localization and specificity of neuronal stimulation and inhibition is possible. Therefore, the development of integrated devices that can merge the sensitivity of ECoG or depth recording with optogenetic tools can lead to newer frontiers in understanding the neuronal activity.
Herein, we introduce a hybrid device comprising flexible inorganic LED arrays integrated PEDOT:PSS/parylene C microelectrode arrays for high resolution bidirectional neuronal interfaces. The flexible inorganic LEDs have been developed by the metal-organic vapor phase epitaxy of position-controlled GaN microLEDs on ZnO nanostructured templates pre-grown at precise locations on a graphene layer. By transferring it onto the microelectrode arrays, it can provides the individual electrical addressability by light stimulation patterns. We will present experimental and simulation results on the optoelectronic characteristics and light activation capability of flexible microLEDs and their evaluation in vivo.
Nanostructures provide novel opportunities of studying epitaxy in nano/mesoscale and on nonplanar substrates. Epitaxial
growth of silicon (Si) on the surfaces of Si nanowires along radial direction is a promising way to prepare radial <i>p-(i)-n</i>
junction in nanoscale for optoelectronic devices. Comprehensive studies of Si radial epitaxy in micro/nanoscale reveal
that morphological evolution and size-dependent radial shell growth rate for undoped and doped Si radial shells. Single
crystalline Si radial <i>p-i-n</i> junction wire arrays were utilized to fabricate photovoltaic (PV) devices. The PV devices
exhibited the photoconversion efficiency of 10%, the short-circuit current density of 39 mA/cm<sup>2</sup>, and the open-circuit
voltage of 0.52 V, respectively.