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Transparent, flexible, and chemically stable conducting electrodes are the most important key components for fabricating optoelectronic devices. However, in conventional bulk metal–semiconductor (MS) junctions, Fermi-level pinning is a major concern that limits the charge transport properties of the devices. In this work, we have designed MS junctions using two-dimensional (2D) MXene nanosheets and Al-doped ZnO nanoparticles as a metal and an n-type semiconductor, respectively. The heterojunction was formed by layer-by-layer self-assembly on an indium tin oxide (ITO) substrate and probed by the Pt/Ir scanning tunneling microscopy (STM) tip at room temperature. By recording the tunneling current of the components that in turn yielded the density of states of the materials, we could identify their energy positions to determine the band alignments. We then proceeded to form heterojunctions and characterized their current–voltage characteristics through scanning tunneling spectroscopy. The junctions showed rectification, and the rectification ratio varied with the semiconductor doping concentrations. However, the shift of the Fermi level toward the conduction band edge of the semiconductor reduces the Schottky barrier width and consequently lowers the rectification ratio. Additionally, the MS junction with the poly-allylamine (PAH)-functionalized MXene nanosheets and the ZnO layer show a nonrectifying nature with low contact resistance at the interface. This work shows how a functionalized 2D-metal MXene and doped ZnO nanoparticle can tune the MS junction properties, used for implementing various flexible optoelectronic devices and transistor applications. Post-print / Final draft

A very simple solid-state Diels Alder reaction of bulk boron nitride (BN) with maleic anhydride followed by ultrasonication in an aqueous solution was used to mass production of maleic acid functionalized highly exfoliated water dispersible single and few layers of boron nitride nanosheets (BNNS-MA). We demonstrate that as-synthesized BNNS-MA can be used to reinforce and toughen nano-fibrillated cellulose membranes. publishedVersion

A new and efficient catalytic hydrolysis of aliphatic and aromatic thiolates under ambient conditions is presented. Previously, we have demonstrated (Ganguly et al.

Iron(ii)-α-keto complexes of tridentate ligands immobilized on thiol-protected gold nanoparticles display enhanced reactivity in dioxygen-dependent decarboxylation and substrate oxidation. The geometry of ligands also affects catalytic dioxygen activation.

Cobalt(ii)–carboxylate complexes of the 6-Me3-TPA ligand in combination with hydrogen peroxide perform the oxygenation of aliphatic C–H bonds of alkanes and epoxidation of alkenes with high chemo- and stereo-selectivity. A metal-based oxidant is proposed as the active oxidant.

Multilingual Sentiment analysis plays an important role in a country like India with many languages as the style of expression varies in different languages. The Indian people speak in total 22 different languages and with the help of Google Indic keyboard people can express their sentiments i.e reviews about anything in the social media in their native language from individual smart phones. It has been found that machine learning approach has overcome the limitations of other approaches. In this paper, a detailed study has been carried out based on Natural Language Processing (NLP) using Simple Neural Network (SNN) ,Convolutional Neural Network(CNN), and Long Short Term Memory (LSTM)Neural Network followed by another amalgamated model adding a CNN layer on top of the LSTM without worrying about versatility of multilingualism. Around 4000 samples of reviews in English, Hindi and in Bengali languages are considered to generate outputs for the above models and analyzed. The experimental results on these realistic reviews are found to be effective for further research work.

Chirality switching of self-assembled molecular structures is of potential interest for designing functional materials but is restricted by the strong interaction between the embedded molecules. Here, we report on an unusual approach based on reversible chirality changes of self-assembled oligomers using variable-temperature scanning tunneling microscopy supported by quantum mechanical calculations. Six functionalized diazomethanes each self-assemble into chiral wheel-shaped oligomers on Ag(111). At 130 K, a temperature far lower than expected, the oligomers change their chirality even though the molecules reside in an embedded self-assembled structure. Each chirality change is accompanied by a slight center-of-mass shift. We show how the identical activation energies of the two processes result from the interplay of the chirality change with surface diffusion, findings that open the possibility of implementing various functional materials from self-assembled supramolecular structures.

Due to the propagation of graph data, there has been a sharp focus on developing effective methods for classifying the graph object. As most of the proposed graph classification techniques though effective are constrained by high computational overhead, there is a consistent effort to improve upon the existing classification algorithms in terms of higher accuracy and less computational time. In this paper, an attempt has been made to classify graphs by extracting various features and selecting the important features using feature selection algorithms. Since all the extracted graph-based features need not be equally important, only the most important features are selected by using back propagation learning algorithm. The results of the proposed study of feature-based approach using back propagation learning algorithm lead to higher classification accuracy with faster computational time in comparison to other graph kernels. It also appears to be more effective for large unlabeled graphs.

Poly(amidoamine) dendrimers grafted on carbon nanotubes have been appended with iron(II)-α-keto acid (benzoylformate) complex of polypyridyl ligand to design artificial non-heme oxygenase model. This nano-enzyme was applied for selective catalytic oxidation of organic molecules. Although the carbon nanotubes serve as a robust heterogeneous platform, the amine terminals of dendrimers provide catalysts binding sites and the amide bonds provide a necessary second coordination sphere similar to the enzymatic polypeptide chains. Such a hybrid design prevented the deactivation of the primary active sites leading to 8 times faster oxidative decarboxylation rates than those of its homogeneous analogue. An electrophilic iron(IV)-oxo intermediate has been intercepted, which catalyzes the selective oxidation of alcohols to aldehydes and incorporates single oxygen atoms into sulfides and olefins by using aerial oxygen with multiple turnover numbers. The catalyst was consecutively regenerated three times by mild chemical treatment and showed negligible loss of activity.

An iron(II)-benzilate complex [(TPASH)FeII(benzilate)]ClO4@C8Au (2) (TPASH = 11-((6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-yl)methoxy)undecane-1-thiol) immobilized on octanethiol stabilize...

Monolayer protected metal and metal sulfide nanocrystals (NCs) have mainly two constituents; the inorganic metal or metal chalcogenide complex as core and organic molecule as shell. Noticing that m...

A rational synthetic method that produces monodisperse and air-stable metal sulfide colloidal quantum dots (CQDs) in organic nonpolar solvents using octyl dithiocarbamic acid (C8DTCA) as a sulfur source, is reported. The fast decomposition of metal-C8DTCA complexes in presence of primary amines is exploited to achieve this purpose. This novel technique is generic and can be applied to prepare diverse CQDs, like CdS, MnS, ZnS, SnS, and In2S3, including more useful and in-demand PbS CQDs and plasmonic nanocrystals of Cu2S. Based on several control reactions, it is postulated that the reaction involves the in situ formation of a metal–C8DTCA complex, which then reacts in situ with oleylamine at slightly elevated temperature to decompose into metal sulfide CQDs at a controlled rate, leading to the formation of the materials with good optical characteristics. Controlled sulfur precursor’s reactivity and stoichiometric reaction between C8DTCA and metal salts affords high conversion yield and large-scale product...

Pt nanoparticles supported on carbon are an important technological catalyst. A corresponding model catalyst was prepared by physical vapor deposition (PVD) of Pt on sputtered HOPG (highly oriented pyrolytic graphite). The carbon substrate before and after sputtering as well as the Pt/HOPG system before and after Pt deposition and annealing were examined by XPS and STM. This yielded information on the surface density of defects, which serve as nucleation centres for Pt, and on the size distribution (mean size/height) of the Pt nanoparticles. Two different model catalysts were prepared with mean sizes of 2.0 and 3.6 nm, both turned out to be stable upon UHV-annealing to 300 °C. After transfer into a UHV-compatible flow microreactor and subsequent cleaning in UHV and under mbar pressure, the catalytic activity of the Pt/HOPG model system for ethylene hydrogenation was examined under atmospheric pressure flow conditions. This enabled to determine temperature-dependent conversion rates, turnover frequencies (TOFs) and activation energies. The catalytic results obtained are in line with the characteristics of technological Pt/C, demonstrating the validity of the current surface science based model catalyst approach.

Due to the inherent challenges in probing nanoscale properties within bulk heterojunction (BHJ) active layers of organic photovoltaic (OPV) devices, the relationship between morphology and nanoscale electronic structure is not well understood. Here, we employ scanning tunneling microscopy (STM) dI/dV imaging and localized density of states (DOS) spectra to investigate the influence of additives on morphology in a high-performance OPV system. In short, we are able to correlate the use of diiodooctane (DIO) additive with significant changes to the distribution of the localized DOS, most notably a broader distribution of PCE10 polymer HOMO levels and PC70BM fullerene LUMO levels, as well as significantly smaller domain sizes and significantly higher overall device efficiencies. We further correlate this data with a nearly 3-fold increase in charge carrier lifetimes in the active layer when DIO is employed, determined by time-resolved microwave conductivity (TRMC) measurements. The results are consistent with...

We form junctions between two single layers of p-type WSe2 and n-type MoS2 in both sequences. The WSe2|MoS2 and MoS2|WSe2 junctions of ultimate thickness limit exhibit current rectification when characterized vertically with a scanning tunneling microscope (STM) tip. The direction of rectification in the pn-junction is opposite to that of the np-junction, confirming occurrence of the rectification to be due to the junctions themselves. From scanning tunneling spectroscopy (STS) and correspondingly the density of states (DOS), we locate the conduction and valence band edges (CB and VB, respectively) of the materials inferring their single-layer and 2H phase configuration. Band edges of the semiconductors form a type-II band alignment resulting in current rectification. In junctions of WSe2 and MoS2 with single layers having a partial overlap, we map band edges along different points on individual semiconductors and the overlapped region (junction). The results have provided experimental evidence of current...

The band diagram in heterojunction solar cells is of utmost importance when visualizing the possibility of charge separation and carrier transport. The diagram should in principle be drawn from the viewpoint of the charge carriers in the devices. While considering solar cells based on conjugated organics and/or inorganic compound semiconductors, we have shown in this Perspective that scanning tunneling spectroscopy (STS) can draw appropriate band diagrams, which the carriers would encounter during the separation and transport processes. Moreover, differential conductance (dI/dV) images in scanning tunneling microscopy are capable of energy mapping; one can therefore map domains of the materials in a bulk heterojunction (BHJ). Correlation between morphology of the components in BHJs and device performance can therefore be envisaged through STS.

The synergistic effects of foreign ion incorporation into a semiconductor host crystal lattice can produce new functional properties. This concept has been adopted in the design of various energy materials for light harvesting, charge transport, and energy storage applications. Going beyond the traditionally used group II–VI and III–V semiconductor nanostructures, herein, 1D materials involving Bi(III) and Sb(III) sulfides are reported. Upon Sb dilution into the Bi2S3 lattice, exciting new material properties, including induction of localized surface plasmon resonance (LSPR) and a drastic change to the 1D crystal growth pattern, were observed. The presence of the Sb(III) precursor along with Bi(III) led to nanotubes with controlled length as the ultimate product, and their transformation to nanorods via chemical filling emerged as a new fundamental mechanism of crystal growth. Due to its slow thermal decomposition rate, the Sb(III) precursor dominantly filled these tubes, resulting in graded alloy Bi1.09S...

We formed a heterojunction based on a monolayer of nickel phthalocyanine (NiPc) and another layer of cobalt-doped ZnO (Co@ZnO) nanoparticles on an electrode. By tunneling current through a monolayer of the components that in turn yielded density of states (DOS) of the semiconductors, we located energy levels of NiPc, which were electron donating in nature, and also the band edges of the n-type nanoparticles. Energies of the components in a heterojunction showed that there would be a preferential transfer of electrons from Co@ZnO to NiPc in junctions formed in either sequence (NiPc|Co@ZnO and Co@ZnO|NiPc). We then proceeded to form heterojunctions with the magnetization vector of Co@ZnO and the easy magnetization axis of the metalorganic parallel to each other. When such aligned junctions were characterized with spin-polarized scanning tunneling spectroscopy (SP-STS), we observed that the configuration acted as a unique diode applicable to spin-polarized electrons.

We report introduction of pn -junction nanorods in a polymer matrix to form hybrid bulk-heterojunction (BHJ) solar cells. This is a paradigm shift from conventional hybrid solar cells, where quantum dots or nanorods of an inorganic semiconductor and a conjugated polymer form a BHJ. The pn -junctions were formed in n -type CdS nanorods through a controlled cationic exchange process; here p -type Cu 2 S formed from one end of CdS due to selective reactivity of crystalline planes of the nanorods. Due to an epitaxial attachment between Cu 2 S and CdS semiconductors in the nanorod, a depletion region hence formed in the pn -junction, which is a classical example of type-II band-alignment at the interface. The junction separated charge carriers under illumination through a drift of minority carriers across the depletion region. Hybrid BHJs based on Cu 2 S|CdS pn -junction nanorods in a conventional polymer matrix therefore acted as efficient solar cells as compared to similar BHJ devices with nanorods of individual materials, that is Cu 2 S or CdS. We varied the relative lengths of p - and n -sections of the pn -junctions that in turn controlled charge separation and carrier transport processes to optimize the solar cell performance.

2D molecular materials, namely, metal alkyl thiolates, have been used as a single-source precursor for the synthesis of semiconducting metal sulphide nanocrystals (NCs) by thermal decomposition. These 2D molecular precursors have all the ingredients required for metal sulphide synthesis (metal source, sulphur source and protecting ligand). In this study, we demonstrate a simple and general ‘solvothermal decomposition’ approach for the synthesis of high-quality $$\hbox {Cu}_{2}\hbox {S}$$ , PbS, CdS, MnS and ZnS NCs. The size of the NC can also be controlled by changing the decomposition temperature. Furthermore, the optical properties of the NCs have also been studied.

A 2D form of Bi2Se3 which acts as a topological insulator was grown through colloidal synthesis method. The surface-states and edge-states of the nanoplates were simultaneously probed through scanning tunneling spectroscopy (STS). At the interior, density of states (DOS) revealed the location of conduction and valence band edges. The DOS at the edges, on the other hand, brought out gapless conducting states along with a Dirac point at a non-zero value below the Fermi energy representing the Dirac cone of a 2D topological insulator. In differential tunnel conductance (dI/dV), images are recorded at different voltages and the two sections of the topological insulator can be viewed selectively or simultaneously with a clear contrast in illumination. Upon increasing the 2D-nanoplates thickness, the material turned into a 3D topological insulator with gapless surface states.

We map band-edges across a pn-junction that was formed in a nanorod. We form a single junction between p-type Cu2S and n-type CdS through a controlled cationic exchange process of CdS nanorods. We characterize nanorods of the individual materials and the single junction in a nanorod with an ultrahigh vacuum scanning tunneling microscope (UHV-STM) at 77 K. From scanning tunneling spectroscopy and correspondingly the density of states (DOS) spectra, we determine the conduction and valence band-edges at different points across the junction and the individual nanorods. We could map the band-diagram of nanorod-junctions to bring out the salient features of a diode, such as p- and n-sections, band-bending, depletion region, albeit interestingly in the nanoscale.

We report the synthesis of a gold–carbon dot nanocomposite and its utility as a recyclable catalyst for the reduction of aromatic nitro groups. The presence of carbon dots on gold nanosurfaces enhanced the reduction rate by two-fold.

We formed magnetic moment assisted layer-by-layer (LbL) films of a Prussian Blue analogue (PB). We applied an external magnetic field to each monolayer of PB to orient the magnetic moment of the compound perpendicular to the substrate. Aligned moments or orientation of the magnetic compounds themselves were immobilized in each monolayer, so that the moments could augment formation of the subsequent monolayers of LbL adsorption process. We hence could form multilayered LbL films of PB molecules with their magnetic moments oriented perpendicular to the substrate. We also formed LbL films of the compound with their moments oriented parallel to the substrate and facing one particular direction. We have measured conductivity and dielectric constant of the two types of films and compared the parameters with that of conventional LbL films deposited without orienting magnetic moments of the molecules.

We report controlled formation of heterodimers and their charge separation properties. CdS|CdTe heterodimers were formed through an anionic exchange process of CdS nanostructures. With control over the duration of the anionic exchange process, bulk|dot, bulk|bulk, and then dot|bulk phases of the semiconductors could be observed to have formed. A mapping of density of states as derived from scanning tunneling spectroscopy (STS) brought out conduction and valence band-edges along the nanostructures and heterodimers. The CdS|CdTe heterodimers evidenced a type-II band-alignment between the semiconductors along with the formation of a depletion region at the interface. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors. We report that the width that is instrumental for photoinduced charge separation in the heterodimers has a direct correlation with the performance of hybrid bulk-heterojunction solar cells based on the nanostructures in a polymer matrix.

We introduce dopants in lead sulfide (PbS) quantum dots (QDs) in forming hybrid bulk-heterojunction (BHJ) solar cells. Because an increase in the content of bismuth as dopants in PbS QDs transforms the intrinsic p-type semiconductor into an n-type one, the band alignment between a conjugated polymer and the doped QDs changes upon doping affecting performance of BHJ solar cells. From scanning tunneling spectroscopy (STS) of the doped QDs, we observe a shift in their Fermi energy leading to formation of a type II band alignment in the polymer:doped-QD interface. We also show that the dopants improve electron-conduction process through the QDs. With the dopants controlling both band alignments at the interface and the conduction process, we show that the dopant concentration in QDs influences open-circuit voltage unfavorably and short-circuit current in a beneficial manner. The device performance of hybrid BHJ solar cells is hence maximized at an optimum concentration of bismuth in PbS QDs.

We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials.

We form pn- and np-junctions between monolayers of p- and n-type nanocrystals that exhibit current rectification in the nanodiodes when characterized with a scanning tunneling microscope (STM) tip. With the use of ferromagnetic nanocrystals, we study the effect of mutual alignment of magnetization vectors on current rectification in the junction between the two nanocrystals. We show that when the magnetization vectors of the p- and of the n-type nanocrystals are parallel to each other (and both facing toward the apex of the STM tip) tunneling current in both bias modes increases with correspondingly a higher rectification ratio. This is in contrast to the parameters of the nanodiodes in which magnetization vectors of the components are unaligned or randomized. To analyze the results, we record scanning tunneling spectroscopy of the monolayer of the components having magnetization vectors aligned or unaligned to locate their valence and conduction band edges and to determine the effect of the alignment on the band edges. Upon alignment of the magnetization vectors of the nanocrystals in a monolayer, the conduction band edge of the p-type and valence band edge of the n-type semiconductor shift towards the Fermi energy leading to a change in energy levels of the pn-junctions and accounting for the improved parameters of the nanodiodes.

In forming donor/acceptor assemblies that act as molecular rectifiers, we have introduced magnetic organic molecules as electron-donating and electron-accepting moieties. We have oriented the magnetic moment of the donor and acceptor components separately and immobilized them (and their moments) so that the molecular assemblies that act as rectifiers could be formed with moments mutually parallel or anti-parallel to each other. We have characterized the molecular assemblies formed on an electrode with a scanning tunneling microscope tip. Such donor/acceptor assemblies with a control over the orientation of moments of the components provided unique systems to study the effect of the nature of alignment on molecular rectifiers. We have observed that the rectification ratio increased in junctions with moments of the components being parallel to each other. The improvement in the rectification ratio has been explained in terms of an efficient electron-transfer process in a moment-aligned junction between the donor and acceptor moieties.