Bikas C. Das | Indian Association for the Cultivation of Science (original) (raw)

Papers by Bikas C. Das

Journal of Physics D: Applied Physics

The light-soaking effect is one of the major drawbacks for inverted organic solar cells (OSCs) if... more The light-soaking effect is one of the major drawbacks for inverted organic solar cells (OSCs) if metal oxides are used as the electron transport layer (ETL). The oxide ETL primarily originates the above effect from the energy barrier, deep level defects, and excess carriers tunneling. Here, electron-beam evaporated high-quality pristine and post-treated e-ZnO thin films are utilized to fabricate inverted OSC as the ETL between the transparent cathode and active bulk-heterojunction PBDB-T-2Cl:PC61BM layer to study the influence on device performance. Various experimental techniques, including AFM, XRD, XPS, and UPS, are utilized to identify the surface and semiconducting properties of differently treated interfacial e-ZnO films precisely. XPS results reveal the variation of oxygen vacancies and adsorbed oxygen species on the surface of e-ZnO layers. The semiconducting nature of various e-ZnO thin films for the use of ETL are also probed with the help of UPS results, which accurately...

Applied Physics Letters, 2021

IEEE Transactions on Electron Devices, 2020

Low-voltage, high-performance thin film transistors (TFTs) that use amorphous metal oxide (MO) se... more Low-voltage, high-performance thin film transistors (TFTs) that use amorphous metal oxide (MO) semiconductors as the active layer have been getting tremendous attention due to their essential role in future portable electronic devices and systems. However, reducing the operating voltage of these devices to or below 1 V is a very challenging task because it is very difficult to obtain low threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula>) and small subthreshold swing (SS) MO TFTs. In this article, indium gallium zinc oxide (IGZO) TFTs that use solution-deposited Ta2O5 operating at 1 V are demonstrated. To enhance the dielectric properties of the fabricated ultrathin (<inline-formula> <tex-math notation="LaTeX">${d} \sim {22}$ </tex-math></inline-formula> nm <inline-formula> <tex-math notation="LaTeX">$\pm ~2$ </tex-math></inline-formula> nm) tantalum pentoxide films, <inline-formula> <tex-math notation="LaTeX">${n}$ </tex-math></inline-formula>-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) was used. The morphology and electrical properties of both pristine and OTS-treated Ta2O5 films have been studied. The optimized Ta2O5/OTS IGZO TFTs operate at 1 V with saturation field-effect mobility larger than 2.3 cm2/<inline-formula> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula>, threshold voltage of around 400 mV, SSs below 90 mV/dec, and current ON- OFF ratios well above <inline-formula> <tex-math notation="LaTeX">$10^{{5}}$ </tex-math></inline-formula>. The performance of the presented TFTs is high enough for many commercial applications such as disposable sensors or throwaway, low-end electronics significantly reducing the cost of their production.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2009

We report that an enhancement in electrical bistability in devices based on organic molecules can... more We report that an enhancement in electrical bistability in devices based on organic molecules can be achieved by the introduction of semiconducting nanoparticles. Here, devices based on alternate layers of a dye in the xanthene class and CdSe nanoparticles have been compared with devices based on the individual components. Results from dye/CdSe devices have yielded an appreciable enhancement in electrical bistability compared with those based on the dye or the nanoparticles. The enhancement is due to augmented carrier transport through the nanoparticles to the dye that consequently undergoes a change in its conformation, having a higher conductivity. We have evidenced read-only and random-access memory applications in the dye/nanoparticle hybrid system.

Organic Electronics, 2008

ACS Nano, 2008

We report growth, monolayer formation, and (electrical bistability and memory phenomenon) propert... more We report growth, monolayer formation, and (electrical bistability and memory phenomenon) properties of hybrid core-shell nanoparticles. While inorganic quantum dots, such as CdS or CdSe, act as the core, a monolayer of ionic organic dye molecules, electrostatically bound to the surface of functionalized quantum dots, forms the shell. We form a monolayer of the core-shell hybrid nanoparticles via a layer-by-layer electrostatic assembly process. Growth and monolayer formation of the organic-inorganic hybrid nanoparticles have been substantiated by usual characterization methods, including electronic absorption spectroscopy of dispersed solution and atomic force microscope images of scratched films. Devices based on the hybrid nanoparticles have exhibited electrical bistability and memory phenomena. From the comparison of these properties in core-shell nanoparticles and in its components, we infer that the degree of conductance switching or on/off ratio is substantially higher in the hybrid nanoparticles. Also, they (core-shell particles) provide routes to tune the bistability and memory phenomena by choosing either of the components. A monolayer of hybrid nanoparticles has been characterized by a scanning tunneling microscope tip as the other electrode. We show that a single core-shell hybrid nanoparticle can exhibit bistability with an associated memory phenomenon. Charge confinement, as evidenced by an increase in the density of states, has been found to be the mechanism of electrical bistability.

Scientific Reports, 2022

Here, various synaptic functions and neural network simulation based pattern-recognition using no... more Here, various synaptic functions and neural network simulation based pattern-recognition using novel, solution-processed organic memtransistors (memTs) with an unconventional redox-gating mechanism are demonstrated. Our synaptic memT device using conjugated polymer thin-film and redox-active solid electrolyte as the gate dielectric can be routinely operated at gate voltages (VGS) below − 1.5 V, subthreshold-swings (S) smaller than 120 mV/dec, and ON/OFF current ratio larger than 108. Large hysteresis in transfer curves depicts the signature of non-volatile resistive switching (RS) property with ON/OFF ratio as high as 105. In addition, our memT device also shows many synaptic functions, including the availability of many conducting-states (> 500) that are used for efficient pattern recognition using the simplest neural network simulation model with training and test accuracy higher than 90%. Overall, the presented approach opens a new and promising way to fabricate high-performan...

he transport gap of nanoparticle-passivated Si substrates is measuredby scanning tunneling micros... more he transport gap of nanoparticle-passivated Si substrates is measuredby scanning tunneling microscopy. Passivation is achieved using amonolayer of CdSe nanoparticles. It is shown that the transport gap andconduction-band edge of the system change upon passivation. The size ofthenanoparticlesthatpassivatetheSisubstrateisvariedtostudyitseffectonthe transport gap of the system. Plots of the tunneling current versus voltageshowthat the transportgap of the system can be tuned by the bindingof justa monolayer of suitable nanoparticles. From the normalized density ofstates, it is shown that the conduction-band edge of the system responds tothe size of the nanoparticles. Here, a monolayer of the nanoparticles, whichwere capped with suitable functional groups, has been formed viaelectrostatic adsorption with the substrate.1. Introduction

We report the reversible polymorphic phase transition of [Ni6(PET)12] (PET = phenylethanethiol) a... more We report the reversible polymorphic phase transition of [Ni6(PET)12] (PET = phenylethanethiol) and its effect on the conductivity. This cluster's self-assembly leads to two polymorphic structures with distinct conductivity, caused by variation of the non-covalent SS interactions. These results enlighten the effect of non-covalent interactions on conductivity.

ACS Applied Nano Materials

Nanotechnology

Here, we report robust and highly reproducible nonvolatile resistive switching (RS) devices with ... more Here, we report robust and highly reproducible nonvolatile resistive switching (RS) devices with artificial synaptic functionalities utilizing redox-exfoliated few-layered 2H-MoS2 nanoflakes. Advantageous polar solvent compatibility of 2D MoS2 from this method were utilized to fabricate thin film devices very easily and cost-effectively using polystyrene as matrix. Prominent RS property of polystyrene thin film devices with varying MoS2 concentrations strongly favors electroforming-free operation. The conduction band position of 2D MoS2 nanosheet in combination with the work functions of chosen electrodes looks alleviating to switch the current from low to high at a suitable positive bias voltage. We further confirmed the mechanism of charge transport through fitting the results with theoretical models, say injection-dominated Schottky emission model for low-conducting states and space-charge-limited current mechanism for the high-conducting state. Interestingly, a relatively high current On/Off ratio 102 was recorded during the pump-probe testing to show resistive random-access memory (ReRAM) application. Finally, artificial synaptic functionalities- the building blocks of neuromorphic computing architectures is also illustrated by considering the robust RS property and ReRAM application.

Microwave Heating - Electromagnetic Fields Causing Thermal and Non-Thermal Effects

Incorporation of dopants efficiently in semiconductors at the nanoscale is an open challenge and ... more Incorporation of dopants efficiently in semiconductors at the nanoscale is an open challenge and is also essential to tune the conductivity. Typically, heating is a necessary step during nanomaterials’ solution growth either as pristine or doped products. Usually, conventional heating induces the diffusion of dopant atoms into host nanocrystals towards the surface at the time of doped sample growth. However, the dielectric heating by microwave irradiation minimizes this dopant diffusion problem and accelerates precursors’ reaction, which certainly improves the doping yield and reduces processing costs. The microwave radiation provides rapid and homogeneous volumetric heating due to its high penetration depth, which is crucial for the uniform distribution of dopants inside nanometer-scale semiconducting materials. This chapter discusses the effective uses of microwave heating for high-quality nanomaterials synthesis in a solution where doping is necessary to tune the electronic and o...