Transport In Junctions Research Articles

Characterization of Coulomb Interactions in Electron Transport Through a Single Hetero-Helicene Molecular Junction Using Scanning Tunneling Microscopy.

Characterization of the structural and electron transport properties of single chiral molecules provides critical insights into the interplay between their electronic structure and electrochemical environments, providing broader implications given the significance of molecular chirality in chiroptical applications and pharmaceutical sciences. Here, we examined the topographic and electronic features of a recently developed chiral molecule, B,N-embedded double hetero[7]helicene, at the edge of Cu(100)-supported NaCl thin film with scanning tunneling microscopy and spectroscopy. An electron transport energy gap of 3.2 eV is measured, which is significantly larger than the energy difference between the highest occupied and the lowest unoccupied molecular orbitals given by theoretical calculations or optical measurements. Through first-principles calculations, we demonstrated that this energy discrepancy results from the Coulomb interaction between the tunneling electron and the molecule's electrons. This occurs in electron transport processes when the molecule is well decoupled from the electrodes by the insulating decoupling layers, leading to a temporary ionization of the molecule during electron tunneling. Beyond revealing properties concerning a specific molecule, our findings underscore the key role of Coulomb interactions in modulating electron transport in molecular junctions, providing insights into the interpretation of scanning tunneling spectroscopy features of molecules decoupled by insulating layers.

Adipocytes reprogram the proteome of breast cancer cells in organotypic three-dimensional cell cultures.

While epidemiological evidence has long linked obesity with an increased risk of breast cancer, the intricate interactions between adipocytes and cancer cells within the tumor microenvironment remain largely uncharted territory. The use of organotypic three-dimensional (3D) cell cultures that more accurately mimic the spatial architecture of tumors represents an innovative approach to this complex issue. In the present study, we investigated the effects of adipocytes on the proteome of Hs578t breast cancer cells cultured in a 3D microenvironment. Using different treatments, we rigorously optimized the experimental conditions to induce the optimal differentiation of 3T3-L1 fibroblasts into mature adipocytes. Then, we grow the Hs578t cells in a simulated microenvironment using an on-top model for organotypic 3D cultures. Our data showed that cancer cells formed 3D stellate-like architectures when grown over an extracellular matrix proteins-enriched scaffold for 48h. Proteomic profiling using LC-MS/MS mass spectrometry of Hs578t cells grown in 3D conditions with or without the adipocyte-enriched culture discovered 916 unique proteins. Of these, 605 showed no significant changes in abundance, whereas 87 proteins were significantly upregulated and 224 downregulated after interaction with fat cells (p < 0.05, FC > 2.0). Bioinformatic analysis of upregulated proteins indicated that the most enriched GO terms and molecular functions were related to lipids transport, cell differentiation, hypoxia response, and cell junctions. In addition, several modulated proteins have been previously associated with breast cancer progression. Interestingly, lipid transport proteins, including PITPNM2, ATP2C1, ABCA12, HDLBP, and APOB, showed perturbations in their expression, which were also associated with low overall survival in breast cancer patients. Functional studies showed that the knockdown of apolipoprotein B (APOB) expression in Hs578t cells reduced the size of 3D cellular structures. Moreover, APOB-knocked cells cocultured with adipocytes for 48h exhibited a significant decrease of intracellular lipids, whereas an increase in the adipocytes was found. Our results indicate that the 3D microenvironment and the adipocytes crosstalk reprogram the proteome of breast cancer cells. These data help us understand the environmental effects in gene expression and contribute to discovering novel tumor proteins with potential intervention in breast cancer therapy.

Energy conversion and transport in molecular-scale junctions

Molecular-scale junctions (MSJs) have been considered the ideal testbed for probing physical and chemical processes at the molecular scale. Due to nanometric confinement, charge and energy transport in MSJs are governed by quantum mechanically dictated energy profiles, which can be tuned chemically or physically with atomic precision, offering rich possibilities beyond conventional semiconductor devices. While charge transport in MSJs has been extensively studied over the past two decades, understanding energy conversion and transport in MSJs has only become experimentally attainable in recent years. As demonstrated recently, by tuning the quantum interplay between the electrodes, the molecular core, and the contact interfaces, energy processes can be manipulated to achieve desired functionalities, opening new avenues for molecular electronics, energy harvesting, and sensing applications. This Review provides a comprehensive overview and critical analysis of various forms of energy conversion and transport processes in MSJs and their associated applications. We elaborate on energy-related processes mediated by the interaction between the core molecular structure in MSJs and different external stimuli, such as light, heat, electric field, magnetic field, force, and other environmental cues. Key topics covered include photovoltaics, electroluminescence, thermoelectricity, heat conduction, catalysis, spin-mediated phenomena, and vibrational effects. The review concludes with a discussion of existing challenges and future opportunities, aiming to facilitate in-depth future investigation of promising experimental platforms, molecular design principles, control strategies, and new application scenarios.

Evidence for π-Shifted Cooper Quartets and Few-Mode Transport in PbTe Nanowire Three-Terminal Josephson Junctions.

Josephson junctions are typically characterized by a single phase difference across two superconductors. This conventional two-terminal Josephson junction can be generalized to a multiterminal device where the Josephson energy contains terms with contributions from multiple independent phase variables. Such multiterminal Josephson junctions (MTJJs) are being considered as platforms for engineering effective Hamiltonians with nontrivial topologies, such as Weyl crossings and higher-order Chern numbers. These prospects rely on the ability to create MTJJs with nonclassical multiterminal couplings in which only a few quantum modes are populated. Here, we demonstrate these requirements in a three-terminal Josephson junction fabricated on selective-area-grown (SAG) PbTe nanowires. We observe signatures of a π-shifted Josephson effect, consistent with interterminal couplings mediated by four-particle quantum states called Cooper quartets. We further observe a supercurrent coexistent with a non-monotonic evolution of the conductance with gate voltage, indicating transport mediated by a few quantum modes in both two- and three-terminal devices.

Boosting thermoelectric performance of molecular junction by utilizing edge branches and weak coupling

In this study, we investigated the thermoelectric properties of molecular junctions, created by trapping naphthacene (C18H12) and rubrene (C42H28) molecules between two graphene electrodes. It is found that the charge transport of naphthacene-based and rubrene-based graphene junctions is not sensitive to the introduction of edge side branches or the increase in molecular length and still maintains resonance transport at the Fermi level. Notably, the presence of pendant branches on the molecular trunk in rubrene-based graphene junctions leads to a suppression of phonon transport, attributed to multiple scattering at the branch attachment points or Fano resonance scattering. The phonon thermal conductance of the rubrene junctions can be reduced by nearly half compared to that of naphthalene junctions. Furthermore, the room-temperature figure of merit (ZT) is significantly enhanced from 0.2 to 1.1 upon constructing weak coupling junctions, representing an almost tenfold increase over covalent junctions. These findings mean that it is highly desirable to find a mechanism that can suppress the phonon thermal conductance of self-assembled molecular films, while preserving their power factor at optimal levels to obtain high-efficiency thermoelectric performance.

Atom layer deposited TiO2 electron transport layer for silicon heterojunction solar cells to achieve high performance

Silicon/compound heterojunction (SCH) solar cells based on p-type and n-type c-Si wafers using atom layer deposition-TiO2 and low work function metal as the electron transport layer and rear electrode are fabricated. Efficiencies of 20.6 % and 21.6 % are achieved on p-type and n-type silicon solar cells, respectively. High Voc exceeding 700 mV have been realized on both kinds of Si wafers. Special attention has been paid to the SCH solar cells based on p-type c-Si wafers in which the TiO2 electron transport layer serves as the emitter. Carrier transport mechanisms and junction characteristics of the SCH solar cells are analyzed based on dark J-V measurement. The formation of a strong inversion layer at the Si surface region is determined, which implies the high Voc potential of the SCH solar cells based on p-type Si. An optical loss analysis is performed along with a possible solution to further improve the Jsc. The feasibility of TiO2 applied as an efficient electron transport layer (emitter) in p-type SCH solar cells with high performance has been showed.

Traffic analysis of different geometries of a junction for optimization of vehicle capacity and traffic safety increase

Abstract Identifying various vehicle movement characteristics inside a network requires a careful assessment and different measurements technics, in regards to road traffic studies. These measures are influenced by a variety of variables, including the direction of traffic, changes in daily transportation demand, junction geometry and location in areal of study, style of road and also the size of the study area. Examining various geometries and arrangements of lanes with different distributions of vehicle platoons of the junction based on traffic-related elements is the goal of this essay. The analysis of the junction in regards to the speed, volume, capacity, pollution and traffic safety can give alternative solution and provide a foundation for the implementation of various political strategies in the area.

Majorana-mediated thermoelectric transport in multiterminal junctions

Majorana-mediated thermoelectric transport in multiterminal junctions

Hawthorn-leaf flavonoid alleviate intestinal health and microbial dysbiosis problems induced by glyphosate

Glyphosate is the active ingredient in the herbicide (i.e., Roundup, Touchdown and Erasure), the safety of which has become a social concern. Hawthorn-leaf flavonoid (HF) possesses various biological functions, including antioxidant, regulating lipid metabolism and intestinal microbiota. Whether HF could reduce the health risk of pure glyphosate to birds remain unknown. The experiment aimed to evaluate the effects of pure glyphosate (25 mg/kg added to water) on the intestinal health and microbiota of chicks and the protective roles of HF (60 mg/kg added to the diet). Exposure to glyphosate decreased growth performance, ileal morphology structure, and antioxidant capacity, and increased the serum level of lipid and pro-inflammatory factors. 16S rRNA sequencing indicated that glyphosate decreased bacterial richness and the abundance of Lactobacillus, and increased proportions of pathogens in the ileum. Metabolomic results revealed that glyphosate increased the level of the cholic acid and fatty acids in the ileac digesta. Meanwhile, glyphosate down-regulated the protein expression associated with lipid transport, antioxidant and tight junction in the ileal mucosal tissue, and up-regulated the pro-inflammatory, oxidative stress proteins. However, dietary HF supplementation effectively mitigated the adverse effects of glyphosate and improved intestinal health of chicks. Therefore, dietary HF can ameliorate the harmful effects of glyphosate on birds, which highlights the potential application of HF in reducing the health risks.

Unified diagrammatic approach to quantum transport in few-level junctions for bosonic and fermionic reservoirs: Application to the quantum Rabi model

Unified diagrammatic approach to quantum transport in few-level junctions for bosonic and fermionic reservoirs: Application to the quantum Rabi model

Novel insights into the mechanisms of seasonal cyclicity of testicles by proteomics and transcriptomics analyses in goose breeder lines

Spermatogenesis is a crucial indicator of geese reproduction performance and production. The testis is the main organ responsible for sperm production, and the egg-laying cycle in geese is a complex physiological process that demands precise orchestration of hormonal cues and cellular events within the testes, however, the seasonal changes in the transcriptomic and proteomic profiles of goose testicles remain unclear. To explore various aspects of the mechanisms of the seasonal cyclicity of testicles in different goose breeds, in this study, we used an integrative transcriptomic and proteomic approach to screen the key genes and proteins in the testes of 2 goose males, the Hungarian white goose and the Wanxi white goose, at 3 different periods of the laying cycle: beginning of laying cycle (BLC), peak of laying cycle (PLC), and end of laying cycle (ELC). The results showed that a total of 9,273 differentially expressed genes and 4,543 differentially expressed proteins were identified in the geese testicles among the comparison groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that the DEGs, in the comparison groups, were mainly enrichment in metabolic pathways, neuroactive ligand-receptor interaction, cyctokine-cyctokine receptor interaction, calcium signaling pathway, apelin signaling pathway, ether lipid metabolism, cysteine, and methionine metabolism. While the DEPs, in the 3 comparison groups, were mainly involved in the ribosome, metabolic pathways, carbon metabolism, proteasome, endocytosis, lysosome, regulation of actin cytoskeleton, oxidative phosphorylation, nucleocytoplasmic transport, and tight junction. The protein-protein interaction network analysis (PPI) indicated that selected DEPs, such as CHD1L, RAB18, FANCM, TAF5, TSC1/2, PHLDB2, DNAJA2, NCOA5, DEPTOR, TJP1, and RAPGEF2, were highly associated with male reproductive regulation. Further, the expression trends of 4 identified DEGs were validated by qRT-PCR. In conclusion, this work offers a new perspective on comprehending the molecular mechanisms and pathways involved in the seasonal cyclicity of testicles in the Hungarian white goose and the Wanxi white goose, as well as contributing to improving goose reproductive performance.

(Invited) Electron Transport in Nanocarbon Networks for Energy Conversion and Storage Applications

Carbon nanostructures have attracted great attention in recent years as novel electrode materials in batteries with increased capacity and conductivity as well as enhanced material stability. In these nanostructures, nanocarbons such as carbon nanotubes and graphene nanoplatelets are interconnected to construct their three-dimensional networks around the host materials for Li deposition. This work focuses on the study of electron transport phenomena in these nanocarbon networks with two model material systems: (1) single-walled carbon nanotube (SWCNT) networks co-embedded with silica microparticles (Fig. (a)), and (2) free-standing three-dimensional graphene (3DG) structures with polymeric surface modifications (Fig. (b)). We characterize the materials for electrical conductivity and thermopower with varying material contents in the composites to reveal several key factors determining their energy-dependent carrier transport characteristics. It is found that in these three-dimensional nanocarbon networks, carrier tunneling at the junctions between nanocarbons along with the network morphology predominantly determines the transport properties. Simultaneous increase in electrical conductivity and thermopower is achieved for SWCNT networks co-embedded with silica microparticles by increasing silica content up to 40 w.t.% at a fixed CNT content. The enhanced electron transport is attributed to the reduced junction distances due to the intimate network formation on the surface of silica particles with a polymer binder. Our transport theory based on the Landauer formalism for junction tunneling reveals that the junction modification with polymer can alter the potential barrier heights for both electrons and holes at the junction to significantly change the transport properties of the composite. Doping of nanocarbons is also investigated for their impacts on the junction transport and the geometric factor of the networks. Finally, we also investigate the use of these carbon nanostructures in solid-state thermoelectric (TE) energy harvesters and ionic TE capacitors to harvest thermal energy from temperature gradients and fluctuations. Figure 1

Evidence of an Off-Resonant Electronic Transport Mechanism in Helicenes.

Helical molecules have been proposed as candidates for producing spin-polarized currents, even at room conditions, due to their chiral asymmetry. However, describing their transport mechanism in single molecular junctions is not straightforward. In this work, we show the synthesis of two novel kinds of dithia[11]helicenes to study their electronic transport in break junctions among a series of three helical molecules: dithia[n]helicenes, with n = 7, 9, and 11 molecular units. Our experimental measurements and clustering-based analysis demonstrate low conductance values that remain similar across different applied voltages and molecules. Additionally, we assess the length dependence of the conductance for each helicene, revealing an exponential decay characteristic of off-resonant transport. This behavior is primarily attributed to the misalignment between the energy levels of the molecule-electrodes system. The length dependence trend described above is supported by ab initio calculations, further confirming an off-resonant transport mechanism.

Optimal tree tensor network operators for tensor network simulations: Applications to open quantum systems.

Tree tensor network states (TTNS) decompose the system wavefunction to the product of low-rank tensors based on the tree topology, serving as the foundation of the multi-layer multi-configuration time-dependent Hartree method. In this work, we present an algorithm that automatically constructs the optimal and exact tree tensor network operators (TTNO) for any sum-of-product symbolic quantum operator. The construction is based on the minimum vertex cover of a bipartite graph. With the optimal TTNO, we simulate open quantum systems, such as spin relaxation dynamics in the spin-boson model and charge transport in molecular junctions. In these simulations, the environment is treated as discrete modes and its wavefunction is evolved on equal footing with the system. We employ the Cole-Davidson spectral density to model the glassy phonon environment and incorporate temperature effects via thermo-field dynamics. Our results show that the computational cost scales linearly with the number of discretized modes, demonstrating the efficiency of our approach.

Spin-correlation transport and multiple resistive states in multiferroic tunnel junctions

Spin-correlation transport and multiple resistive states in multiferroic tunnel junctions

Peptide-Based Electrical Array Sensor for Discriminating Heavy Metal Ions.

Charge transport in molecular junctions provides an excellent way to investigate the response of molecules to intrinsic changes and external stimuli, exhibiting powerful potential for developing sensors. However, achieving multianalyte recognition remains a challenge. Herein, we innovatively developed an electrical array sensor based on peptide self-assembled layers for discriminating various heavy metal ions. Three peptide sequences were designed as sensing units with varying binding affinities for different metal ions. Electrical measurements demonstrated that different metal ions diversely affect the charge transport of peptide junctions. By using principal component analysis, a clear discrimination between the five kinds of heavy metal ions can be achieved. In the analysis of real samples, the array sensor showed a reliable anti-interference capability. The array sensor offers possibilities for large-area molecular junctions to construct functional molecular sensing devices.

Exact solutions for thermally induced electromechanical fields of PN junctions in centrosymmetric semiconductors

PN junctions play important roles in semiconductor devices. Flexoelectricity, an electromechanical coupling between strain gradient and electric polarization, has non-negligible contributions in nano-devices. The thermoflexoelectric effect is a phenomenon in which temperature gradients generate inhomogeneous strains and further induce flexoelectric polarizations. Therefore, temperature gradients can affect carrier transport in PN junctions through the thermoflexoelectric effect. In this paper, a one-dimensional model of the PN junction under a uniform temperature change is established. Exact solutions for the electromechanical fields in the PN junction are obtained for the first time. The effects of the temperature gradient, doping level, and flexoelectric coefficient on the electromechanical behaviors of the PN junction are numerically analyzed. The results indicate that carrier concentrations in the p and n regions are sensitive to temperature gradients because of the screening effect of the mobile charge on the flexoelectric polarization induced by the temperature gradient. Meanwhile, the flexoelectric field and the initial built-in electric field in the depletion region jointly determine the magnitude of the potential barrier, and thus, the temperature-gradient-induced flexoelectric field can tune the switching characteristics of the PN junction. This study provides a theoretical basis for the tuning of the electromechanical behavior of the PN junction by thermally induced flexoelectric fields.

Cluster Formation of Self-Assembled Triarylbismuthanes and Charge Transport Characterizations of Gold-Triarylbismuthane-Gold Junctions.

Organometallic molecules are promising for molecular electronic devices due to their potential to improve electrical conductance through access to complex orbital covalency that is not available to light-element organic molecules. However, studies of the formation of organometallic monolayers and their charge transport properties are scarce. Here, we report the cluster formation and charge transport properties of gold-triarylbismuthane-gold molecular junctions. We found that triarylbismuthane molecules with -CN anchoring groups form clusters during the creation of self-assembled submonolayers. This clustering is attributed to strong interactions between the bismuth (Bi) center and the nitrogen atom in the -CN group of adjacent molecules. Examination of the influence of -NH2 and -CN anchoring groups on junction conductance revealed that, despite a stronger binding energy between the -NH2 group and gold, the conductance per molecular unit (i.e., molecule for the -NH2 group and cluster for the -CN group) is higher with the -CN anchoring group. Further analysis showed that an increase in the number of -CN groups from one to three within the junctions leads to a decrease in conductance while increasing the size of the cluster. This demonstrates the significant effects of different anchoring groups and the impact of varying the number of -CN groups on both the charge transport and cluster formation. This study highlights the importance of selecting the appropriate anchoring group in the design of molecular junctions. Additionally, controlling the size and formation of clusters can be a strategic approach to engineering charge transport in molecular junctions.

Marcus Theory and Long-Range Activationless Transport in Molecular Junctions.

Intrachain transport in molecular junctions (MJs) longer than 5 nm has been modeled within the theoretical framework of Marcus theory. We show that in oligo(bisthienylbenzene)-based MJs, electronic transport involves polarons, localized on three monomers that are close to 4 nm in length. They hop and tunnel between adjacent localized sites with reorganization energies λ close to 400-600 meV and electronic coupling parameters Hab close to λ/2. As a consequence, the activation energy for intrachain transport, given by the equation ΔG* = (λ/4)(1 - 2Hab/λ)2, is close to zero, and transport along the chain is activationless, in agreement with experimental observation. On the contrary, similar calculations on conjugated oligonaphthalenefluoreneimine wires show that Hab is much less than λ/2 and predict that the activation energies for intrachain hopping between adjacent sites, close to λ/4, are ∼115 meV. This work proposes a new perspective for understanding long-range activationless transport in MJs beyond the tunneling regime.

A Systematic Study of Methyl Carbodithioate Esters as Effective Gold Contact Groups for Single-Molecule Electronics.

There are several binding groups used within molecular electronics for anchoring molecules to metal electrodes (e.g., R-SMe, R-NH2, R-CS2 -, R-S-). However, some anchoring groups that bind strongly to electrodes have poor/unknown stability, some have weak electrode coupling, while for some their binding motifs are not well defined. Further binding groups are required to aid molecular design and to achieve a suitable balance in performance across a range of properties. We present an in-depth investigation into the use of carbodithioate esters as contact groups for single-molecule conductance measurements, using scanning tunnelling microscopy break junction measurements (STM-BJ) and detailed surface spectroscopic analysis. We demonstrate that the methyl carbodithioate ester acts as an effective contact for gold electrodes in STM-BJ measurements. Surface enhanced Raman measurements demonstrate that the C=S functionality remains intact when adsorbed on to gold nanoparticles. A gold(I) complex was also synthesised showing a stable C=S→AuI interaction from the ester. Comparison with a benzyl thiomethyl ether demonstrates that the C=S moiety significantly contributes to charge transport in single-molecule junctions. The overall performance of the CS2Me group demonstrates it should be used more extensively and has strong potential for the fabrication of larger area devices with long-term stability.