Sunil Kumar Samji

Bio: Sunil Kumar Samji is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Thin film & CZTS. The author has an hindex of 4, co-authored 6 publications receiving 50 citations. Previous affiliations of Sunil Kumar Samji include Indian Institute of Technology Bombay.

Integration of perovskite PZT thin films on diamond substrate without buffer layer

Abstract: Integration of lead zirconate titanate (PZT) thin film on diamond substrate offers a great deal of potential for the application of multifunctional devices under extreme conditions. However, fabrication of perovskite PZT thin films on diamond substrate without a buffer layer has not been realized to date. We report for the first time on the successful deposition of PZT thin film directly on a diamond substrate without any buffer layer using the pulsed-laser deposition technique. The perovskite phase was realized only under specific growth conditions. X-ray diffraction and Raman studies confirmed the perovskite phase. The ferroelectric behaviour of the deposited PZT thin film was confirmed using piezo response microscope phase image and ferroelectric hysteresis loop.

A Spectroscopy and Microscopy Study of Parylene-C OFETs for Explosive Sensing

Abstract: In this paper, we have explored Parylene-C (PC) as a sensing material for its unique signature and selectivity for explosive sensing. We have used a bi-layer deposition process to fabricate bottom-gate-top-contact organic field effect transistor (OFET) structures. Opening of dangling bonds on subjecting PC to plasma oxidation (POPC) renders these molecules to be employed as a receptor material in sensing vapors of both explosives and non-explosives, such as Trinitrotoulene (TNT), 1,3,5 trinitro-1,3,5-triazacyclohexane(RDX), PETN, Dinitrobenzene (DNB), Nitrobenzene (NB), Benzoquinone (BQ), and Benzophenone (BP). The change in: 1) the vibrational modes of the molecule by infrared spectroscopy; 2) surface potential of POPC by Kelvin probe force microscopy (KPFM); and 3) electrical characterization by I-V measurements of PC-based OFET on exposing to vapors have been systematically studied. Different signatures for all the analytes have been observed while exact and perfect selectivity for TNT, RDX were found from I-V studies and for PETN by KPFM studies. Thus, the OFET device-based chemical sensors demonstrated here with improved sensitivity and excellent selectivity, stand as promising candidates for explosives detection.

Light induced phase change in Cu2−xZn1.3SnS4 thin films

Abstract: Cu2ZnSnS4 and its alloy based thin film solar cells have shown better photovoltaic performance under Cu-poor and Zn-rich conditions However, the effect of Cu-stoichiometry on the coexistence of kesterite (KS), stannite and/or partially disordered kesterite (PD-KS) phases and their influence on photovoltaic performance is not clearly understood Raman studies were carried out on Cu2−xZn13SnS4 (x = 0, 03, and 05) thin films by changing the intensity of the incident laser beam It was observed that both Cu-stoichiometry and incident laser beam intensity induce a disorder in the system Disorder induced transformation of KS (I4¯) to PD-KS (I4¯2m) is explained by Raman studies

Organic field-effect transistor-based flexible sensors

Abstract: Flexible electronic devices have attracted a great deal of attention in recent years due to their flexibility, reduced complexity and lightweight. Such devices can conformably attach themselves to any bendable surface and can possess diverse transduction mechanisms. Consequently, with continued emphasis on innovation and development, major technological breakthroughs have been achieved in this area. This review focuses on the advancements of using organic field-effect transistors (OFETs) in flexible electronic applications in the past 10 years. In addition, to the above mentioned features, OFETs have multiple advantages such as low-cost, readout integration, large-area coverage, and power efficiency, which yield synergy. To begin with, we have introduced organic semiconductors (OSCs), followed by their applications in various device configurations and their mechanisms. Later, the use of OFETs in flexible sensor applications is detailed with multiple examples. Special attention is paid to discussing the effects induced on physical parameters of OFETs with respect to variations in external stimuli. The final section provides an outlook on the mechanical aspects of OSCs, activation and revival processes of sensory layers, small area analysis, and pattern recognition techniques for electronic devices.

Methanol and Humidity Capacitive Sensors Based on Thin Films of MOF Nanoparticles.

Abstract: The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal-organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96(Al) MOF thin films via the Langmuir-Blodgett (LB) method on the IDE chips, which allowed the study of their gas/vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness ∼250-300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities.

Green and low-cost synthesis of zinc oxide nanoparticles and their application in transistor-based carbon monoxide sensing

Abstract: There has been steady progress in developing reliable and cost-effective strategies for the clean production of zinc oxide (ZnO) nanoparticles (NPs) owing to their unique structural and wide functional characteristics. While the green synthesis of such NPs from plant extracts has emerged as a sustainable and eco-friendly protocol, it is greatly restricted owing to the scarcity of potential natural precursors necessitating comprehensive investigations in this direction. Herein, we report a facile, low-cost green synthesis and characterization of ZnO NPs along with the demonstration of their usage as an active media in organic field-effect transistor (OFET) devices for sensing carbon monoxide (CO) gas. The ZnO NPs obtained from Nelumbo nucifera (lotus) leaf extract-mediated solution combustion synthesis at a much lower initiation temperature, the first of its kind, were characterized by various techniques such as UV-vis spectroscopy, XRD, EDX analysis, TEM and FESEM. The data derived from these experiments clearly evidence the formation of very pure and crystalline ZnO NPs possessing nearly spherical-shape with a size of 3–4 nm. The p-type organic field-effect transistor (OFET) device, fabricated using poly(3-hexylthiophene-2,5-diyl) (P3HT) and ZnO NPs, showed a field-effect mobility of 10−2 cm2 V−1 sec−1 with a slightly enhanced response of detecting CO gas at room temperature (RT). The phenomenon was further confirmed by the variation in electrical parameters of the OFET such as field-effect mobility (μ), on-current (Ion), and off-current (Ioff). The selectivity and sensitivity of the fabricated device in CO gas detection was found to be more prominent than the other reducing gases (hydrogen sulphide, H2S and ammonia, NH3) and methanol vapours tested.

Zinc oxide as a defect-dominated material in thin films for photovoltaic applications – experimental determination of defect levels, quantification of composition, and construction of band diagram

Abstract: In the present work, thin ZnO layers were synthesized by the sol–gel method with subsequent spin-coating on Si(100). We show that the detailed analysis of lab-recorded photoemission spectra in combination with Kelvin probe data yielded the work function, ionization energy, and valence band – Fermi level separation – and hence enabled the construction of band diagrams of the examined layers. With small modifications in preparation, very different films can be obtained. One set shows a homogeneous depth-dependent n carrier distribution, and another a significant carrier concentration gradient from n-type conductivity to almost metal-like n+ character. Likewise, the surface morphology can be tuned from a uniform, compact surface with spherical single-nm sized grain-like features to a structured surface with 5–10 nm tall crystallites with (002) dominating crystal orientation. Based on the band-bending and the energy levels observed, defects of contradictory nature, i.e. acceptor–donor–trap (ADT) properties, were identified. These defects may be groups of point defects, with opposite character. The ADT states affect the energy levels of the oxide layers and due to their nature cannot be considered in the photoemission experiment as mutually independent. The versatile nature of the synthesis provides us with the opportunity to tune the properties with a high degree of freedom, at low processing costs, yielding layers with an exotic electronic structure. Such layers are interesting candidates for applications in photovoltaic and nanoelectronic devices.