Shreyasi Pal

Low temperature solution processed ZnO/CuO heterojunction photocatalyst for visible light induced photo-degradation of organic pollutants

The possibility of integrating manifold functionalities, coupled with various associated noble interface phenomena in the hierarchical nanoforms, either comprised of geometrical intricacies or achieved via the rational coupling of several components, has made them immensely pertinent from both research and technological aspects. Here, an oxide based nanostructure hybrid has been realized by integrating low bandgap copper oxide nanosheet with high bandgap one dimensional zinc oxide nanowires on a flexible carbon cloth as well as on a flat substrate. These bandgap modulated hybrid nanostructures are generated for the efficient absorption of visible light, targeting their possible use in waste water management. Our work presents a novel ambient condition protocol for morphological tuning in the nanoscale or their organization in a hierarchical structure. Environmental remediation through catalytic activity under the visible light irradiation of the synthesized samples was inspected using both anionic and cationic dyes (methyl orange and Rhodamine B, respectively) as the model contaminants, where the optimized heterostructure exhibits significantly better performance than the mono component oxides. Such enhanced performance could be explained by the formation of favorable staggered gap multiple p–n junctions at ZnO/CuO interface, which in turn retards the photogenerated electron–hole pair recombination within the heterostructure. The signature of successful p–n junction formation at ZnO nanorod/CuO nanosheet interface has been identified via current–voltage measurements with a conducting tip AFM in contact mode. The creative designing of novel heterojunctions adopting this protocol will pave the way for the utilization of the entire visible light range: thus, offering potential in solar energy conversion devices.

Recent advances in low temperature, solution processed morphology tailored ZnO nanoarchitectures for electron emission and photocatalysis applications

Having the benefit of several features such as low cost, straightforward processing, easy fabrication, large area deposition and physical flexibility, low temperature solution processed electronic devices have gained traction in the eyes of the research community as the difficulties associated with conventional higher temperature crystalline semiconductor devices are incrementally rendering them outdated. Over the last decade, amongst metal oxides, ZnO with its rich variety of nanoforms has been documented as the candidate with the highest economic impact by virtue of its diverse use in a plethora of electronic and optoelectronic applications relying on its associated unique functional features such as high mobility, excellent thermal stability and high transparency. To date, most review articles in the literature focused on ZnO nanostructures realized via the vapour phase method whereas a comprehensive study on solution processed nanoforms and their widespread use is still lacking. The current article mainly highlights an overview of recent developments in multi-dimensional ZnO nanoarchitectures processed via low temperature, rational approaches and their functional properties in field emission devices and environmental remediation. In addition to these descriptions of controlled morphology design and the usage perspective, significant issues pertinent to such geometrical evolution and device performance determination and the possible outlook for low temperature research on ZnO are also described.

Controlling the sharpness of ZnO tetrapods by restricted zinc oxidation in the open air: a low turn-on field emitter stabilized by graphene

A simple, novel and economical approach was developed for the synthesis of ZnO tetrapods through the controlled open air oxidation of a commercial zinc foil. Unrestricted by stringent criteria such as the maintenance of a high vacuum level or the usage of catalysts, this protocol yields scalable amounts of high quality tetrapods, thus highlighting its convenience over other reported methods. A thin coating of gold on top of the zinc foil is found to restrict the free open air oxidation and thus plays a pivotal role in this alternative kind of tetrapod formation. Investigations using cathodoluminescence spectroscopy confirmed the high optical quality of the tetrapods. Additionally, these tetrapods are found to exhibit an excellent electron emission performance. Finally, with the expectation of gaining better field enhancement, thermally reduced graphene oxide is attached to the tetrapods. This hybrid system is observed to possess outstanding electron emission activity with very low turn-on and threshold field values, as well as much improved stability, which were not achieved for the separate components. This indicates the potential usability of these materials in field emission nanodevices.

Spontaneous hyper-branching in ZnO nanostructures: morphology dependent electron emission and light detection

Higher dimensional ZnO nanoforms offer unprecedented advantages over their low dimensional counterparts in emerging technologies. This motivated the researchers to design ZnO hierarchical architectures which are expected to offer performances improved to device benchmarks. Starting from 1D ZnO nanospike arrays, hierarchical cactus and tree-like ZnO arrays with increasing branching and complexities have been grown via a simple wet chemical approach in ambient conditions. The zero thermal budget, large area of fabrication and absence of any structure-directing agents are the novel highlights of the current synthesis protocol. Cathodoluminescence spectroscopic investigation reveals a gradual increment in defect constitution in these nanoforms with increasing structural complexity. The synthesized nanostructure arrays display promise in electron field emission owing to their structural uniqueness as indicated by field distribution calculations using ANSYS electromagnetic software. Furthermore, these higher order nanostructures are capable of detecting UV light with photocurrent gains as high as 2.21 × 104.

Scalable approach for the realization of garland shaped 3D assembly of CuTCNQ nanorods: an efficient electron emitter

Going beyond the conventional presentation of CuTCNQ nanostructures over 2-dimensional Cu/Cu coated substrate, in the current work, the 3-dimensional backbone of metallic Cu nanowires was used to materialize garland shaped hierarchical nanoforms. Simplicity and a scalable amount of high quality product yield are the hallmarks of the current synthesis procedure, which offers a brilliant contrast to the existing severe lack of adequate protocols for synthesizing CuTCNQ nanostructures in bulk. In the present approach, gradual consumption of Cu in an acetonitrile solution during prolonged intervals is found to be responsible for triggering structural variances. A possible growth mechanism substantiated by FESEM and XRD analysis and based on temporal morphology evolution is also proposed. The optimized hierarchy, armed with the benefit of numerous emitters and appreciable inter-tip separation, is found to exhibit high field emission performance with low turn-on and threshold field values (2.69 and 6.11 V μm−1 respectively). Moreover, the experimental electron emission result is verified through electrostatic field distribution calculation using ANSYS electromagnetic software. This facile strategy may pave the way for the practical realization of other charge transfer complex nanostructures, and on its own warrant their potential usage as humidity sensors, photo-detectors, photocatalysts etc.

ZnO-(Cu/Ag)TCNQ heterostructure network over flexible platform for enhanced cold cathode application

Multistage field emitters consisting of organic/inorganic hybrid nanostructures with branched geometry are designed via a two-step protocol: a simple wet chemical method followed by a vapor-solid-phase technique. (Cu/Ag)TCNQ (copper/silver-7,7,8,8-tetracyanoquinodimethane) nanowires (NWs) were grown hierarchically on zinc oxide (ZnO) nanorods (NRs) to form ZnO-(Cu/Ag)TCNQ heterostructure assemblies. By monitoring the metallic Cu and Ag coating thickness on ZnO NRs, precise control over the morphology and orientations of the secondary organic NWs is achieved. In-depth analysis of electron field emission (FE) behavior of the ZnO-(Cu/Ag)TCNQ-based hierarchy suggests highest emission performance with low turn-on as well as threshold fields of 1.15 and 3.75 V μm(-1) respectively from the morphology-optimized hierarchy. Beneficial orientation of the branched organic NWs ensures sequential electric field enhancement in the consecutive stem and branches whereas its low work function eases electron emission; these aspects combined together render an overall enhancement in the emission behavior of the hybrid system. As compared to individual building units, the heterostructures show improved field electron emission. Additionally, successful construction of this novel hybrid over a fabric platform displays great potential in opening up new pathways in the highly-anticipated field of flexible electronics.

Geometrically Intricate Oxide-Based Heterostructure Over Flexible Platform: Morphology-Induced Catalytic Performance Enhancement Under UV Light

Tailor-made heterostructural nanoform based on multiple low-dimensional frameworks not only offers manifold functionalities also bestows several novel interface phenomena. From the broad usage window of heterostructures, photocatalysis is very significant nowadays. In this work, we have realized oxide-based hybrid comprising 1D TiO2–ZnO nanoform on flexible carbon cloth via facile chemical approach. Successful presentation of the hybrid over foldable platform was established via FESEM which discloses its typical morphology. To attain a clear insight of the elemental composition EDX analysis and elemental mapping of the hybrid was also carried out. Catalytic activity of the synthesized samples under UV light illumination was inspected taking Rhodamine B as the model contaminant where the heterostructure exhibited much-improved performance as compared to the individual structural building block. Prolonged separation time of the photogenerated charge carriers in heterostructure ensures enhanced photocatalytic activity. Such work on morphology-induced catalytic performance enhancement will inspire the researchers toward creative designing of different photocatalyst comprising other multifunctional oxides.

Structural origination of charge transfer complex nanostructures: Excellent candidate for field emission

Worldwide strategies for amalgamating rationally controlled one-dimensional organic nanowires are of fundamental importance for their applications in flexible, cheaper and lighter electronics. In this work we have fabricated large-area, ordered CuTCNQ (copper-7,7,8,8-tetracyanoquinodimethane) nano architecture arrays over flexible conducting substrate and discussed the rational growth and integration of nanostructures. Here we adopted the organic solid phase reaction (VLS) technique for the growth of organic hierarchies and investigated how field emission properties changes by tuning the nanostructures morphology i.e., by varying length, diameter, alignment and orientation over flexible substrate. The CuTCNQ nanowires with optimized geometry exhibit excellent high field emission performance with low turn-on and threshold field values. The result strongly indicate that CuTCNQ nanowires on flexible carbon cloth substrate are promising candidates for constructing cold cathode based emission display devices, ...