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The synthesis of a family of alkanethiol molecules with planar aromatic head groups, designed to anchor molecules effectively to graphene electrodes, is reported. Characterisation of self-assembled monolayers of these molecules on a gold surface via conductive atomic force microscopy shows that when an aromatic head group is present, the conductance Ggraphene obtained using a graphene coated probe is higher than the conductance GPt obtained using a platinum (Pt) probe. For Pt probe and graphene probe junctions, the tunnelling decay constant of benzyl ether derivatives with an alkanethiol molecular backbone is determined as 𝛽 = 5.6 nm-1 and 3.5 nm-1, respectively. The conductance ratio Ggraphene/GPt increases as the number of rings present in the aromatic head unit, n, increases. However, as the number of rings increases, the conductance path length increases because the planar head groups lie at an angle to the plane of the electrodes. This means that overall conductance decreases as n increases. Density functional theory-based charge transport calculations support these experimental findings. This study confirms that planar aromatic head groups can function as effective anchoring units for graphene electrodes in large area molecular junctions. However, the results also indicate that the size and geometry of these head groups must be considered in order to produce effective molecular designs.

Understanding and controlling the orbital alignment of molecules placed between electrodes is essential in the design of practically-applicable molecular and nanoscale electronic devices. The orbital alignment is highly determined by the molecule-electrode interface. Dependence of orbital alignment on the molecular anchor group for single molecular junctions has been intensively studied; however, when scaling-up single molecules to large parallel molecular arrays (like self-assembled monolayers (SAMs)), two challenges need to be addressed: 1. Most desired anchor groups do not form high quality SAMs. 2. It is much harder to tune the frontier molecular orbitals via a gate voltage in SAM junctions than in single molecular junctions. In this work, we studied the effect of the molecule-electrode interface in SAMs with a micro-pore device, using a recently developed tetrapodal anchor to overcome challenge 1, and the combination of a single layered graphene top electrode with an ionic liquid gate to solve challenge 2. The zero-bias orbital alignment of different molecules was signalled by a shift in conductance minimum vs. gate voltage for molecules with different anchoring groups. Molecules with the same backbone, but a different molecule-electrode interface, were shown experimentally to have conductances that differ by a factor of 5 near zero bias. Theoretical calculations using density functional theory support the trends observed in the experimental data. This work sheds light on how to control electron transport within the HOMO-LUMO energy gap in molecular junctions and will be applicable in scaling up molecular electronic systems for future device applications.

The thermoelectric properties of parallel arrays of organic molecules on a surface offer the potential for large-area, flexible, solution processed, energy harvesting thin-films, whose room-temperature transport properties are controlled by quantum interference (QI). Recently, it has been demonstrated that constructive QI (CQI) can be translated from single molecules to self-assembled monolayers (SAMs), boosting both electrical conductivities and Seebeck coefficients. However, these CQI-enhanced systems are limited by rigid coupling of the component molecules to metallic electrodes, preventing the introduction of additional layers which would be advantageous for their further development. These rigid couplings also limit our ability to suppress the transport of phonons through these systems, which could act to boost their thermoelectric output, without comprising on their impressive electronic features. Here, through a combined experimental and theoretical study, we show that cross-plane thermoelectricity in SAMs can be enhanced by incorporating extra molecular layers. We utilize a bottom-up approach to assemble multi-component thin-films that combine a rigid, highly conductive ‘sticky’-linker, formed from alkynyl-functionalised anthracenes, and a ‘slippery’-linker consisting of a functionalized metalloporphyrin. Starting from an anthracene-based SAM, we demonstrate that subsequent addition of either a porphyrin layer or a graphene layer increases the Seebeck coefficient, and addition of both porphyrin and graphene leads to a further boost in their Seebeck coefficients. This demonstration of Seebeck-enhanced multi-component SAMs is the first of its kind and presents a new strategy towards the design of thin-film thermoelectric materials.

Thin films comprising synthetically robust, scalable molecules have been shown to have major potential for thermoelectric energy harvesting. Previous studies of molecular thin-films have tended to focus on massively parallel arrays of discrete but identical conjugated molecular wires assembled as a monolayer perpendicular to the electrode surface and anchored via a covalent bond, know as self-assembled monolayers. In these studies, to optimise the thermoelectric properties of the thin-film there has been a trade-off between synthetic complexity of the molecular components and the film performance, limiting the opportunities for materials integration into practical thermoelectric devices. In this work, we demonstrate an alternative strategy for enhancing the thermoelectric performance of molecular thin-films. We have built up a series of films, of controlled thickness, where the basic units—here zinc tetraphenylporphyrin—lie parallel to the electrodes and are linked via π–π stacking. We have compared three commonly used fabrications routes and characterised the resulting films with scanning probe and computational techniques. Using a Langmuir-Blodgett fabrication technique, we successfully enhanced the thermopower perpendicular to the plane of the ZnTPP multilayer film by a factor of 10, relative to the monolayer, achieving a Seebeck coefficient of −65 μV K−1. Furthermore, the electronic transport of the system, perpendicular to the plane of the films, was observed to follow the tunnelling regime for multi-layered films, and the transport efficiency was comparable with most conjugated systems. Furthermore, scanning thermal microscopy characterisation shows a factor of 7 decrease in thermal conductance with increasing film thickness from monolayer to multilayer, indicating enhanced thermoelectric performance in a π–π stacked junction.

Dialkynylferrocenes exhibit attractive electronic and rotational features that make them ideal candidates for use in molecular electronic applications. However previous works have primarily focussed on single-molecule studies, with limited opportunities to translate these features into devices. In this report, we utilise a variety of techniques to examine both the geometric and electronic structure of a range of 1,1'-dialkynylferrocene molecules, as either single-molecules, or as self-assembled monolayers. Previous single molecule studies have shown that similar molecules can adopt an 'open' conformation. However, in this work, DFT calculations, STM-BJ experiments and AFM imaging reveal that these molecules prefer to occupy a 'hairpin' conformation, where both alkynes point towards the metal surface. Interestingly we find that only one of the terminal anchor groups binds to the surface, though both the presence and nature of the second alkyne affect the thermoelectric properties of these systems. First, the secondary alkyne acts to affect the position of the frontier molecular orbitals, leading to increases in the Seebeck coefficient. Secondly, theoretical calculations suggested that rotating the secondary alkyne away from the surface acts to modulate thermoelectric properties. This work represents the first of its kind to examine the assembly of dialkynylferrocenes, providing valuable information about both their structure and electronic properties, as well as unveiling new ways in which both of these properties can be controlled.

The cerebellum is involved in encoding balance, posture, speed, and gravity during locomotion. However, most studies are carried out on flat surfaces, and little is known about cerebellar activity during free ambulation on slopes. Here, it has been imaged the neuronal activity of cerebellar molecular interneurons (MLIs) and Purkinje cells (PCs) using a miniaturized microscope while a mouse is walking on a slope. It has been found that the neuronal activity of vermal MLIs specifically enhanced during uphill and downhill locomotion. In addition, a subset of MLIs is activated during entire uphill or downhill positions on the slope and is modulated by the slope inclines. In contrast, PCs showed counter-balanced neuronal activity to MLIs, which reduced activity at the ramp peak. So, PCs may represent the ramp environment at the population level. In addition, chemogenetic inactivation of lobule V of the vermis impaired uphill locomotion. These results revealed a novel micro-circuit in the vermal cerebellum that regulates ambulatory behavior in 3D terrains.

Dynamic microtubules play a critical role in cell structure and function. In nervous system, microtubules are the major route for cargo protein trafficking and they specially extend into and out of synapses to regulate synaptic development and plasticity. However, the detailed depolymerization mechanism that regulates dynamic microtubules in synapses and dendrites is still unclear. In this study, we find that KIF2C, a dynamic microtubule depolymerization protein without known function in the nervous system, plays a pivotal role in the structural and functional plasticity of synapses and regulates cognitive function in mice. Through its microtubule depolymerization capability, KIF2C regulates microtubule dynamics in dendrites, and regulates microtubule invasion of spines in neurons in a neuronal activity-dependent manner. Using RNAi knockdown and conditional knockout approaches, we showed that KIF2C regulates spine morphology and synaptic membrane expression of AMPA receptors. Moreover, KIF2C deficiency leads to impaired excitatory transmission, long-term potentiation, and altered cognitive behaviors in mice. Collectively, our study explores a novel function of KIF2C in the nervous system and provides an important regulatory mechanism on how activity-dependent microtubule dynamic regulates synaptic plasticity and cognition behaviors.

Nanoscale variations in the structure and composition of an object are an enticing basis for verifying its identity, due to the physical complexity of attempting to reproduce such a system. The biggest practical challenge for nanoscale authentication lies in producing a system that can be assessed with a facile measurement. Here, a system is presented in which InP/ZnS quantum dots (QDs) are randomly distributed on a surface of an aluminium-coated substrate with gold nanoparticles (Au NPs). Variations in the local arrangement of the QDs and NPs is shown to lead to interactions between them, which can suppress or enhance fluorescence from the QDs. This position-dependent interaction can be mapped, allowing intensity, emission dynamics, and/or wavelength variations to be used to uniquely identify a specific sample at the nanoscale with a far-field optical measurement. This demonstration could pave the way to producing robust anti-counterfeiting devices.

As the field of molecular-scale electronics matures and the prospect of devices incorporating molecular wires becomes more feasible,itisnecessary to progress from the simpleanchorgroupsusedinfundamentalconductancestudies to more elaborate anchors designed with device stability in mind. This study presents aseries of oligo(phenylene-ethynylene) wires with one tetrapodal anchor and aphenyl or pyridyl head group.The new anchors are designed to bind strongly to gold surfaces without disrupting the conductance pathway of the wires.Conductive probe atomic force microscopy(cAFM) was used to determine the conductance of self-assembled monolayers (SAMs) of the wires in Au–SAM–Pt and Au– SAM–graphene junctions,from whicht he conductance per molecule was derived. Fortolane-type wires,mean conductances per molecule of up to 10@4.37 G0 (Pt) and 10@3.78 G0 (graphene) were measured, despite limited electronic coupling to the Au electrode,demonstrating the potential of this approach.Computational studies of the surface binding geometry and transport properties rationalise and support the experimental results. &nbsp

This paper describes tunneling junctions comprising self-assembled monolayers that can be converted between resistor and diode functionality in-place. The rectification ratio is affected by the hydration of densely packed carboxylic acid groups at the interface between the top-contact and the monolayer. We studied this process by treatment with water and a water scavenger using three different top-contacts, eutectic Ga-In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO), demonstrating that the phenomena is molecular in nature and is not platform-speciffc. We propose a mechanism in which the tunneling junctions convert to diode behavior through the lowering of the LUMO, which is suffcient to bring it close to resonance at positive bias, potentially assisted by a Stark shift. This shift in energy is supported by calculations and a change in polarization observed by X-ray photoelectron spectroscopy and Kelvin probe measurements. We demonstrate light-driven modulation using spiropyran as a photoacid, suggesting that any chemical process that is coupled to the release of small molecules that can tightly bind carboxylic acid groups can be used as an external stimulus to modulate rectification. The ability to convert a tunneling junction reversibly between a diode and a resistor via an effect that is intrinsic to the molecules in the junction extends the possible applications of Molecular Electronics to reconfigurable circuits and other new functionalities that do not have direct analogs in conventional semiconductor devices.

Correction for ‘Molecular-scale thermoelectricity: as simple as ‘ABC’’ by Ali Ismael et al., Nanoscale Adv., 2020, 2, 5329–5334, DOI: 10.1039/D0NA00772B.

It is well known that various polysaccharides present anti-tumour effects by inducing cell apoptosis and immunomodulation. However, it is still unclear about the roles of polysaccharides isolated from Artemisia apiacea (HQG) to hepatoma and its underlying mechanism. The objective of the study was to examine the anti-hepatoma effects of HQG and its related mechanism.HQG was prepared in house and the quality and purity were confirmed by infra-red spectrum and gel permeation chromatography (GPC). Tumour-bearing mice induced by injection of mouse hepatoma H22 cells were used to evaluate the tumour growth inhibition by HQG administration. Cell immunostaining, JC1 staining and flow cytometer were performed to examine the cell apoptosis, mitochondrial membrane potential change and immunomodulation in response to HQG treatment.HQG treatment inhibited hepatoma growth in tumour-bearing mice. Cell apoptosis rate of human hepatoma 7402 cells and of the cells from ascites in tumour-bearing mice was increased after HQG treatment. Mitochondrial membrane potential in human hepatoma 7402 cells was decreased after HQG treatment. CD4+ and CD8+ T-lymphocytes subpopulation was increased while the ratio of CD4+/ CD8+ decreased in tumour-bearing mice after HQG administration. IFN-γ and IL-4 secretion was increased in spleen lymphocytes in tumour-bearing mice after HQG administration.The study concluded that polysaccharides isolated from Artemisia apiacea (HQG) can inhibit hepatoma cell growths by facilitating cell apoptosis and immuno-defence.

Background: It is well known that various polysaccharides present anti-tumour effects by inducing cell apoptosis and immunomodulation. However, it is still unclear about the roles of polysaccharides isolated from Artemisia apiacea (HQG) to hepatoma and its underlying mechanism. The objective of the study was to examine the anti-hepatoma effects of HQG and its related mechanism. Materials and Methods: HQG was prepared in house and the quality and purity were confirmed by infra-red spectrum and gel permeation chromatography (GPC). Tumour-bearing mice induced by injection of mouse hepatoma H22 cells were used to evaluate the tumour growth inhibition by HQG administration. Cell immunostaining, JC1 staining and flow cytometer were performed to examine the cell apoptosis, mitochondrial membrane potential change and immunomodulation in response to HQG treatment. Results: HQG treatment inhibited hepatoma growth in tumour-bearing mice. Cell apoptosis rate of human hepatoma 7402 cells and of the cells from ascites in tumour-bearing mice was increased after HQG treatment. Mitochondrial membrane potential in human hepatoma 7402 cells was decreased after HQG treatment. CD4+ and CD8+ T- lymphocytes subpopulation was increased while the ratio of CD4+/ CD8+ decreased in tumour-bearing mice after HQG administration. IFN-γ and IL-4 secretion was increased in spleen lymphocytes in tumour-bearing mice after HQG administration. Conclusion: The study concluded that polysaccharides isolated from Artemisia apiacea (HQG) can inhibit hepatoma cell growths by facilitating cell apoptosis and immuno-defence.

A major potential advantage of creating thermoelectric devices using self-assembled molecular layers is their mechanical flexibility. Previous reports have discussed the advantage of this flexibility from the perspective of facile skin attachment and the ability to avoid mechanical deformation. In this work, we demonstrate that the thermoelectric properties of such molecular devices can be controlled by taking advantage of their mechanical flexibility. The thermoelectric properties of self-assembled monolayers (SAMs) fabricated from thiol terminated molecules were measured with a modified AFM system, and the conformation of the SAMs was controlled by regulating the loading force between the organic thin film and the probe, which changes the tilt angle at the metal-molecule interface. We tracked the thermopower shift vs. the tilt angle of the SAM and showed that changes in both the electrical conductivity and Seebeck coefficient combine to optimize the power factor at a specific angle. This optimization of thermoelectric performance via applied pressure is confirmed through the use of theoretical calculations and is expected to be a general method for optimising the power factor of SAMs., A major potential advantage of creating thermoelectric devices using self-assembled molecular layers is their mechanical flexibility.

The realization of self-assembled molecular-electronic films, whose room-temperature transport properties are controlled by quantum interference (QI), is an essential step in the scale-up of QI effects from single molecules to parallel arrays of molecules. Recently, the effect ofdestructiveQI (DQI) on the electrical conductance of self-assembled monolayers (SAMs) has been investigated. Here, through a combined experimental and theoretical investigation, we demonstrate chemical control of different forms ofconstructiveQI (CQI) in cross-plane transport through SAMs and assess its influence on cross-plane thermoelectricity in SAMs. It is known that the electrical conductance of single molecules can be controlled in a deterministic manner, by chemically varying their connectivity to external electrodes. Here, by employing synthetic methodologies to vary the connectivity of terminal anchor groups around aromatic anthracene cores, and by forming SAMs of the resulting molecules, we clearly demonstrate that this signature of CQI can be translated into SAM-on-gold molecular films. We show that the conductance of vertical molecular junctions formed from anthracene-based molecules with two different connectivities differ by a factor of approximately 16, in agreement with theoretical predictions for their conductance ratio based on CQI effects within the core. We also demonstrate that for molecules with thioether anchor groups, the Seebeck coefficient of such films is connectivity dependent and with an appropriate choice of connectivity can be boosted by ∼50%. This demonstration of QI and its influence on thermoelectricity in SAMs represents a critical step toward functional ultra-thin-film devices for future thermoelectric and molecular-scale electronics applications.

As the field of molecular‐scale electronics matures and the prospect of devices incorporating molecular wires becomes more feasible, it is necessary to progress from the simple anchor groups used in fundamental conductance studies to more elaborate anchors designed with device stability in mind. This study presents a series of oligo(phenylene‐ethynylene) wires with one tetrapodal anchor and a phenyl or pyridyl head group. The new anchors are designed to bind strongly to gold surfaces without disrupting the conductance pathway of the wires. Conductive probe atomic force microscopy (cAFM) was used to determine the conductance of self‐assembled monolayers (SAMs) of the wires in Au–SAM–Pt and Au–SAM–graphene junctions, from which the conductance per molecule was derived. For tolane‐type wires, mean conductances per molecule of up to 10−4.37 G0 (Pt) and 10−3.78 G0 (graphene) were measured, despite limited electronic coupling to the Au electrode, demonstrating the potential of this approach. Computational studies of the surface binding geometry and transport properties rationalise and support the experimental results., Four‐legged friends: Self‐assembled monolayers of molecular wires with new anchoring units containing four thiomethyl groups were formed on gold and their conductance was measured. The tetrapodal anchors provide effective binding but contribute minimally to the conductance pathway of the wires. Surface binding and electronic coupling can therefore be considered independently.