Multi-component molecular assembly involves self-assembly of two or more types of molecules on surfaces. Increased complexity of the inter-molecular interactions amongvarious types of molecules and also with the substrates leads to a rich assembly on surfaces. The co-assembly of two types of molecules of dissimilar symmetries and sizes such as three-fold symmetric trimesic acid (TMA) and two-fold symmetric 4,4′,4′′,4′′′-([1,1′-biphenyl]-4,4′-diylbis(azanetriyl)) tetrabenzoic acid (H4BPTA) molecules on HighlyOriented Pyrolytic Graphite (HOPG) surface at the solid-liquid interface exhibits two kind of phases. At a comparable concentration of TMA with respect to H4BPTA, the assembly results into a phase where one or two TMA molecules occupy a single pore of H4BPTA network. On the other hand, at a relatively higher concentration of TMA molecules, a lateral heterostructure of mono-component assemblies of TMA and H4BPTA with an atomically sharp interface is observed. While the earlier phase may be attributed to small size of TMA molecules compared to the pore size of H4BPTA network, the latter phase may be attributed to compatible lattice type of the TMA and H4BPTA assemblies where the strain due to large lattice mismatch is mitigated by the presence of flexible hydrogen bonding at the interface of the two mono-component self-ssemblies.These results provide insight into two-component self-assembly of molecules with dissimilar symmetries and sizes and may have implications in the development of novel molecular materials.

Abstract Food adulterants due to harmful chemicals refer to a serious global concern for food safety and people’s health, which makes the detection and monitoring of food quality essential nowadays. Optical sensors with high sensitivity, reconfigurability, and stability have played an important role in advancing biochemical sensors for the selective detection of target food adulterants. However, many of these sensors suffer from limited selectivity and are less sensitive to external stimuli. Hence, these limitations are overcome by an efficient approach for developing a compact, highly sensitive biosensing system that can be achieved by combining optical fiber-based interferometry with an artificial recognition element. Here, a biosensor has been developed for detecting toxic food adulterant melamine by functionalizing an inline interferometric transducer with MIP. The sensor has a broad detection range of 10–10 M to 10–3 M concentration of melamine sample solution with a sensitivity of 8.8 × 109 nm/M. The sensor offers a remarkable LOD of 6.4 pM for the melamine sample. The proposed sensor facilitates a significant working potential for several practical applications, including food safety inspections, clinical sectors, and manufacturing industries.

Multi-component molecular assembly involves self-assembly of two or more types of molecules on surfaces. Increased complexity of the inter-molecular interactions among various types of molecules and also with the substrates leads to a rich assembly on surfaces. The co-assembly of two types of molecules of dissimilar symmetries and sizes such as three-fold symmetric trimesic acid (TMA) and two-fold symmetric 4,4 ',4 '' ,4 '''- ([1,1 '-biphenyl]-4,4 '-diylbis(azanetriyl)) tetrabenzoic acid (H4BPTA) molecules on Highly Oriented Pyrolytic Graphite (HOPG) surface at the solid-liquid interface exhibits two kind of phases. At a comparable concentration of TMA with respect to H4BPTA, the assembly results into a phase where one or two TMA molecules occupy a single pore of H4BPTA network. On the other hand, at a relatively higher concentration of TMA molecules, a lateral supramolecular heterojunction of mono-component assemblies of TMA and H4BPTA with an atomically sharp interface is observed. While the earlier phase may be attributed to small size of TMA molecules compared to the pore size of H4BPTA network, the latter phase may be attributed to compatible lattice type of the TMA and H4BPTA assemblies where the strain due to large lattice mismatch is mitigated by the presence of flexible hydrogen bonding at the interface of the two mono-component self-assemblies. These results provide insight into two-component self-assembly of molecules with dissimilar symmetries and sizes and may have implications in the development of novel molecular materials.

The rapid increase in acute myocardial infarction (AMI), which causes sudden heart failure, is a critical concern these days, causing a large number of deaths. Therefore, the rapid and robust detection method holds promise to manage the AMI. In this work, we have fabricated an electrochemical immunosensor for the detection of cardiac troponin T (cTnT), an AMI biomarker, using the nanostructure of molybdenum disulfide nanosheets and tungsten trioxide nanorods (MoS2 NSs-WO3 NRs). The spectroscopic and microscopic analytical characterization techniques are used to investigate the structural and morphological characteristics of the material. XPS results confirm the presence of metallic (1T) and semiconducting (2H) phases of MoS2 in molybdenum disulfide nanosheets and tungsten trioxide nanorods (MoS2 NSs-WO3 NRs) composites, which effectively improved the sensing performance due to excellent electrochemical conductivity and a large number of active sites, which facilitate high antibody immobilization. Notably, in this study, we used a direct physical adsorption technique for the immobilization of antibodies onto the MoS2 NSs-WO3 NRs-modified electrode surface. The fabricated electrochemical immunosensor shows potential for cTnT detection. Under ideal circumstances, the immunosensor has a broad linearity from 10 fg mL-1 to 1 mu g mL-1 with a low detection limit of 4.77 fg mL-1. In addition, fabricated MoS2 NSs-WO3 NRs based immunosensors have shown remarkable selectivity, sensitivity, and repeatability for cTnT. Furthermore, the quantifications of cTnT in human diluted serum samples exhibit that it is practicable and produced findings that were comparable. Hence, the immunosensor demonstrates its effectiveness as a possible tool for point-of-care immunosensing for the diagnosis of AMI.

Zirconium disulphide (ZrS2) homojunction solar cells are proposed as a sustainable top sub-cell for effective perovskite tandem solar cell (TSC) for higher efficiency, and enhanced spectral utilization with a potential for low-cost fabrication. The simulation shows that the two terminal (2T) ZrS2 and CH3NH3SnI3 (Methylammonium tin iodide) based tandem solar cells may provide optimal efficiency up to 37.20%. SCAPS-1D software has been utilized to investigate the dependence of various parameters such as thickness, doping densities, and defect densities on the photovoltaic properties of the standalone sub-cells. Specifically, bandgap of the perovskite layers is varied between 1.18 and 1.36 eV to investigate its effect on the performance of the cell. The current matching criteria to be approximate to 19.33 mA cm-2, at each point of the investigation has been checked, to get the perfectly matched ZrS2/CH3NH3SnI3 tandem solar cell. The quantum efficiency (QE) versus wavelength curve confirms that the top ZrS2 sub-cell absorbs the shorter wavelength whereas the perovskite bottom sub-cell absorbs the longer wavelength photons, promising a better utilization of most of the incident photons. This work provides a numerical justification for the experimental realization of 2T tandem solar cells with ZrS2 as a top sub-cell in perovskite TSCs for higher efficiencies.

Perovskite solar cells have shown power conversion efficiencies (PCE) comparable to cystalline silicon solar cell despite involving low-temperature, solution based synthesis processes outside clean room environment. As the theoretical PCE of a perovskite solar cell with band gap 1.55 eV is capped to 33 % due to Shockley–Queisser limit, tandem configurations are being investigated to go beyond this limit. Here, we propose a two-terminal (2T) tandem solar cell structure consisting of perovskite and multilayer transition metal dichalcogenide as the absorber layers of the top and the bottom subcells, respectively and investigate their performance parameters using Solar Cell Capacitance Simulator-1 Dimension (SCAPS-1D) software package. We demonstrate that the 2T tandem solar cell consisting of CH3NH3PbI3 with band gap 1.55 eV and MoTe2 with bandgap 1.1 eV shows PCE of maximum 35.3 % under AM 1.5 G illumination. This work motivates experimental realization of such solar cells for further

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496-1616 ns), deposition pressure (3.1 x 10(-3)-1.9 x 10(-2) mbar) and sputtering power (25-250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Recent studies on nanostructured MoS2 show promising performance in the detection of reducing gases like ammonia (NH3). However, this material in the pristine form possesses limitations in terms of response, recovery, and repeatability over a long duration of time. Several attempts have been made to overcome these shortcomings by modifying it chemically to make a hybrid form or direct doping with other atoms. In this work, we demonstrate that suitable defect engineering of 3D nanostructured MoS2 induced by a low energy ion beam can lead to a significantly improved performance of sensing NH3 compared to the as-prepared one. Significant decreases in response and recovery times have been demonstrated at room temperature for the modified MoS2 compared to its pristine form, which shows its best response only at a higher temperature of about 200 degrees C. A 3D nanoflower-like structure of MoS2 was synthesized hydrothermally, which was coated on substrates, and then irradiated with 5 keV argon ions at different doses. While the ion beam-induced morphological modifications are observed via electron microscopic study, the surface defects are apparent in X-ray diffraction, Raman scattering, and X-ray spectroscopic studies. The ion beam-modified MoS2 shows a higher electrical conductivity and water-repelling nature compared to the pristine one, which are complementary properties for better sensing performance. While Monte Carlo-based 3D ion-solid interaction simulation was used to support the morphological modifications and defect developments after ion irradiation, the sensing mechanism and change in conductivity were successfully explained using density functional theory-based simulations.

For a variety of applications in quatum communication and sensing, Nitrogen Vacancy (NV -) centres with negatively charged inside diamonds must be connected to optical systems. An adiabatic photon channeling from a highly effective mode index to a lowered effective mode index, or vice versa is necessary to achieve efficient power transfer from an optical fibre to on-chip photonic devices. To achieve this, there is a major issue in dealing with photonics structures. Here, we report a combined structure of elliptically-faceted (ELFA) diamond nanowire with NV-centres and optical nanofiber, exhibiting tunable bidirectional coupling with improved efficiency. Coupling efficiency oscillation with modulation contrast value shows diabatic to adiabatic transition, corresponding to smaller to longer values of etched length. Our estimates show a coupling efficiency of 85% with directional tunability.

Transfer of strong photomechanical effect from dynamic crystals to hybrid polymer composite is an evolving field of research and holds high potential for actuation and photo-switch development. An organic counter anion (dinitrobenzoate) stabilized nitropentaamminecobalt(III) complex (Co-dnb-1) showing fast photomechanical motions under UV light (365 nm) was synthesized. Detailed experimental and theoretical studies attribute the photomechanical motion to the formation of metastable nitrito-coordinated species (Co-dnb-2) after irradiation. The energy difference between nitro-nitrito complexes was estimated to be 3.54 eV which is close to irradiation energy (3.4 eV). However, in a slow process, by absorbing energy of similar to 0.4 eV/cation through external perturbations such as temperature, Co-dnb-2 recovers to the initial configuration. Three different crystal-polymer composite films (PCF-1-3) were fabricated using photoactive crystals with polyvinylalcohol (PVA), polyvinyldifluride(PVDF) and agarose polymers, respectively by solution casting method. The composite films show quick and excellent photo-actuation though, the extent varies with the polymers used. The actuation of the composite films starts immediately (<2-3 s) and can be deflected up to 90 degrees within a few seconds of the onset of UV light. PCF-3 shows reversible photo-actuation measured up to multiple cycles. Dynamical transfer of photomechanical energy from crystal to composite films leads to successful assembly of a prototype photoswitch. The presented work provides a new dimension towards the development of smart functional composite materials as photo-actuators.

The directional coupling of single photon emission from nitrogen vacancy (NV–) emitters to optical systems for various applications requires a suitable interface between NV– emitters and optical waveguides. Unidirectional coupling of photons may have significant importance in next generation quantum technology such as quantum and complex optical networks, quantum communication, and multi‐scale quantum photonics devices including quantum non‐linearity and quantum metrology. Here, a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg grating (BG) containing negatively charged NV– center for efficient and unidirectional optical coupling to optical nanowire (waveguide) is proposed. The calculations indicate that the structure can provide coupling efficiency of ≈90% toward the elliptically facet direction and ≈1% in the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the ELFA structure. This structure is significantly robust against imperfect placement and rotational alignment of dipole from its intended position.

The demand of single photon coupling to optical systems requires a suitable interface between negatively charged Nitrogen Vacancy (NV-) emitters in diamond to waveguides or optical circuits for applications in quantum network systems and in unidirectional emission with controlled photon states. Here, we propose a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg Grating containing negatively charged NV center for efficient and unidirectional optical coupling to optical nanowire. Our calculations indicate that the structure can provide coupling efficiency of ~90% towards the elliptically facet direction and ~1% towards the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the Bragg Grating assisted ELFA structure. Further, we observe higher chirality constant for ELFA+BG structure -- an indicative of efficient unidirectional photon coupling. By integrating two ELFA diamond nanowire having opposite aligned elliptical facet can be used to design and develop complex optical circuits. Further, this structure can also be used as an inline polarizer filter where it can reflect only one particular mode (e.g. TE mode or TM mode) with higher extinct ratio. The hybrid structure can potentially be used for various applications in quantum photonics, quantum-nonlinear systems.

Negatively charged nitrogen vacancy ( N V − ) centers in diamond are required to be coupled to optical systems for various applications. A slowly varied tapered waveguide displays a near-unity power transfer from an optical fiber to on-chip photonic devices. This physical situation refers to an adiabatic transition of photons from a highly effective confinement mode to a lower effective confinement mode or vice versa. Here, we report tunable bidirectional coupling with enhanced efficiency in a hybrid structure of elliptically faceted (ELFA) diamond nanowire with N V − centers integrated to optical nanowire. Initiating from diabatic transition to adiabatic transition, corresponding to smaller length to longer wire length, respectively, the coupling efficiency oscillates and asymptotically saturates to a maximum value. Our calculations indicate coupling efficiencies of 85% and 84% for azimuthal and radial dipole configurations for the hybrid structure, respectively. The structure with optimum geometry provides similar coupling efficiency of ∼ 81 % for radial and azimuthal dipole configurations. By excitation of one of few dipoles placed strategically at various locations in the cylindrical region of the diamond nanowire will allow one to tune coupling efficiency in the two directions. Tailored size and tunable bidirectional coupling of ELFA diamond nanowire with enhanced efficiency will enable its wide-field applications including multi-scale quantum photonics devices.

Organic charge-transfer complexes (CTCs) formed by strong electron acceptor and strong electron donor molecules are known to exhibit exotic effects such as superconductivity and charge density waves. We present a low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) study of a two-dimensional (2D) monolayer CTC of tetrathiafulvalene (TTF) and fluorinated tetracyanoquinodimethane (F4TCNQ), self-assembled on the surface of oxygen-intercalated epitaxial graphene on Ir(111) (G/O/Ir(111)). We confirm the formation of the charge-transfer complex by dI/dV spectroscopy and direct imaging of the singly-occupied molecular orbitals. High-resolution spectroscopy reveals a gap at zero bias, suggesting the formation of a correlated ground state at low temperatures. These results point to the possibility to realize and study correlated ground states in charge-transfer complex monolayers on weakly interacting surfaces.

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and φ) and one disordered phase (ε). We have determined the boundary free energies between the disordered and order phases by analyzing the thermally induced meandering of the domain boundaries. On the basis of these results, we are able to accurately predict the two-dimensional phase diagram of the decanethiolate/Au(111) system. The order-disorder phase transition of the χ* phase occurs at 295 K, followed by the order-disorder phase transition of the β phase at 325 K. Above temperatures of 325 K, only the densely packed φ and disordered ε phases remain. Our findings are in good agreement with the phase diagram of the decanethiolate/Au(111) system that was put forward by Poirier et al. [Langmuir 2001, 17 (4), 1176-1183].

Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the strong interaction with the substrate masks the intrinsic electronic properties of the MOF. In addition to electronic decoupling from the underlying metal support, synthesis on weakly interacting substrates (e.g., graphene) would enable direct realization of heterostructures of 2D MOFs with inorganic 2D materials. Here, we demonstrate synthesis of 2D honeycomb MOFs on epitaxial graphene substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by density-functional theory (DFT) calculations, we show the formation of a 2D band structure in the MOF decoupled from the substrate. These results open the experimental path toward MOF-based designer electronic materials with complex, engineered electronic structures.

π-conjugated organic molecules tend to adsorb in a planar configuration on graphene irrespective of their charge state. In contrast, here we demonstrate charging-induced strong structural relaxation of tetrafluorotetracyanoquinodimethane (F4TCNQ) on epitaxial graphene on Ir(111) (G/Ir(111)). The work function modulation over the graphene moiré unit cell causes site-selective charging of F4TCNQ. Upon charging, the molecule anchors to the face-centered cubic sites of the G/Ir(111) moiré through one or two cyano groups. The reaction is reversible and can be triggered on a single molecule by moving it between different adsorption sites. We introduce a model taking into account the trade-off between tilt-induced charging and reduced van der Waals interactions, which provides a general framework for understanding charging-induced structural relaxation on weakly interacting substrates. In addition, we argue that the partial sp3 rehybridization of the underlying graphene and the possible bonding mechanism between the cyano groups and the graphene substrate are also relevant for the complete understanding of the experiments. These results provide insight into molecular charging on graphene, and they are directly relevant for potential device applications where the use of molecules has been suggested for doping and band structure engineering.

Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule–substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from flexible electronics and OLEDs to novel electronic devices and spintronics.

We report on molecular self-assembly employing a host guest architecture to pattern the growth of molecules on graphene model surface. Under suitable conditions, the 1,3,5-benzenetribenzoic acid (BTB) self assembles into an extended honeycomb mesh on graphene on Ir(111), with the molecules in the network being stabilized by linear hydrogen bonds between the carboxylic groups. The nanopores of the mesh are used to host and govern the assembly of cobalt phthalocyanine (CoPC) guest molecules. We characterize the assembled structures structurally and electronically using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a coverage higher than one CoPc per pore, the flexible hydrogen bonds of the host network undergo stretching to accommodate two CoPCs in a single pore. When the pores are uniformly doubly occupied, the guest molecules arrange into a herringbone pattern. This minimizes the energy cost associated with the stretching and twisting of the hydrogen bonds between the BTB molecules. The phenomenon observed here can be used to tailor molecular assemblies on graphene to controllably modify its properties. In addition, it allows the formation of guest monomers and dimers stabilized mechanically on the surface of graphene, an archetypical weakly interacting substrate.