Probe Charge Transport Research Articles

(Invited) Probing Charge Carrier-Induced Changes in the Complex Dielectric Function in Carbon Nanotube Dispersions

The injection of charge carriers into pi-conjugated semiconductors, whether by electrochemical injection or chemical charge transfer, is a powerful approach to tune their electrical conductivity. Recently, the concept of dielectric catastrophe, where the charge carrier density is sufficiently large to significantly alter the intrinsic dielectric properties, has been demonstrated at high doping levels in organic semiconductor thin films. The observed increase in the dielectric constant leads to reduced coulombic interactions between charge carriers and the associated counterions, promoting enhanced free carrier generation and transport.Here, we employ a combination of steady state optical spectroscopy, quantitative 19F NMR studies, and microwave dielectric loss spectroscopy to probe charge carrier density and transport in doped single-walled carbon nanotube dispersions. We demonstrate that a similar dielectric catastrophe phenomenon can be observed even in isolated single-walled carbon nanotubes dispersed in a low dielectric constant solvent AND, perhaps more surprisingly, at carrier densities less than one carrier per nanotube. The precise details of the observed changes in complex dielectric function are dependent on the chemical structure of the charge-transfer dopant, with a near-instantaneous increase in the dielectric constant and electrical conductivity observed for low carrier densities using bulky benzyloxy-substituted icosahedral dodecaborane cluster dopants, DDBs. We attribute the observations to weak coulombic interactions between the injected charge carrier and the dopant counterion, along with the large polarizability afforded by the unique physicochemical properties of single-walled carbon nanotubes. If time permits, we will show results from recent studies where we extend this approach to the doping of other nanocarbons.

(Invited) Evaluating Chemical Doping and Charge-Carrier Transport in Carbon Nanotube Dispersions

Chemical charge-transfer, or redox, doping has long been recognized as a powerful approach to tune the charge carrier density in pi-conjugated semiconductors. Despite this, and the extensive effort that has been put into developing novel redox dopants, several challenges remain to understand (i) the doping mechanism/efficiency, (ii) the interactions between the injected charge carrier and the associated counterion, and (iii) the impact that these have on charge carrier transport. This is complicated by the fact that it is very difficult to accurately measure charge carrier densities in pi-conjugated semiconductors and to assess carrier-counterion interactions. Here we employ dispersions of enriched semiconducting single-walled carbon nanotubes (s-SWCNT) as a prototypical pi-conjugated semiconductor, since the rigid structure and strong optical transitions offer some advantages over typically more disordered conjugated polymers. We employ a suite of spectroscopic techniques to probe charge carrier doping and transport in isolated polymer-wrapped s-SWCNT in a low dielectric constant solution-phase environment. We compare solution-phase s-SWCNT samples in toluene that are p-type doped by either 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) or (2,3,4,5,6-pentafluoro)benzyloxy-substituted icosahedral dodecaborane cluster (DDB-F60). We use a combined approach of steady state optical spectroscopy with 19F NMR studies. Optical spectroscopy allows us to track the bleach of the electronic transitions due to excitons and the appearance of signature due to charge carrier-induced trions, which we can correlate to the concentration of dopant counterions extracted from NMR experiments. This combined methodology allows for quantitative determination of a molar extinction coefficient for free carriers for the SWCNT dispersion. We subsequently show that DDB-F60 is a more potent charge-carrier dopant than F4-TCNQ at low concentrations but that the ultimate injected hole charge-carrier density is limited by the large size of the DDB-F60 counteranion, due to saturation of the carbon nanotube surface area that is accessible to the dopant molecules. Using a non-contact spectroscopy technique in the microwave frequency region (ca. 9 GHz), we show that the holes injected by DDB-F60 are more delocalized and mobile, consistent with calculations that suggest a smaller coulombic binding energy between the hole on the carbon nanotube and the electron on the DDB-F60 counteranion. However, samples doped by F4-TCNQ reach a higher peak conductance than is achieved by DDB-F60 doping, where the conductance in the latter case is limited by the maximum achievable hole charge-carrier density and hole scattering processes that reduce the carrier mobility at high hole densities. Our observations point to the need to understand the subtle balance between the carrier-counterion interactions and the injected charge-carrier density to optimize charge-carrier transport in chemically doped s-SWCNT systems.

Probing the Recombination Process at the Intermixed Interface of a Solution-Processed Organic Light Emitting Diode By Impedance Spectroscopy

Solution-processed organic light emitting diode (s-OLED) has garnered considerable research interest due to its cost-effectiveness, improved energy efficiency, and material-saving advantages over conventional vacuum deposition methods in OLED production. Recent studies have shown that the thermal annealing process of multilayered s-OLEDs induces intermixing at the interfaces of the layers and enhances the device performance [1,2]. However, the physical origin of the enhanced s-OLED performance by intermixing at the interfaces is poorly understood. To address this issue, we utilized electrical impedance spectroscopy (IS) to investigate the thermal-induced modifications of charge carrier dynamics in a bilayer s-OLED comprising an electron transporting layer (ETL) and an emission layer (EML). We separately assessed the conductance of the ETL and the charge carrier accumulation at the EML/ETL interface by the characteristic relaxation frequency and the plateau at a low frequency regime (20~100 Hz) extracted from the frequency-dependent capacitance spectra, respectively. The IS analysis revealed that improved charge transport in the ETL by thermal annealing process was mainly responsible for the performance enhancement, rather than intermixing at the EML/ETL interface. Notably, we found that annealing the s-OLEDs above the glass transition temperature (Tg) of the ETL, at which significant intermixing occurs, increased the magnitude of negative capacitance, indicating the increased rate of nonradiative trap-assisted recombination [3]. Accordingly, our IS analysis clarified that extended intermixing at the EML/ETL interface is rather detrimental to the performance of s-OLEDs. This study demonstrates that IS can serve as a powerful tool for accurately analyzing charge carrier dynamics in s-OLEDs by simultaneously probing charge transport, interfacial charge accumulation, and recombination processes, thereby providing valuable insights for optimizing s-OLED performance.[1] ACS Appl. Mater. Interfaces 2015, 7 (37), 20779–20785. https://doi.org/10.1021/acsami.5b05818.[2] Advanced Materials Interfaces 2019, 6 (4), 1801627. https://doi.org/10.1002/admi.201801627.[3] Phys. Rev. Lett. 2018, 120 (11), 116602. https://doi.org/10.1103/PhysRevLett.120.116602. Figure caption. The capacitance at 20 Hz and current efficiency at 100 nit are plotted against the ratio of annealing temperature (T) to glass transition temperature (Tg) of ETL. Figure 1

(First Place Poster Award) Probing Charge Transport Mechanisms in 2D Metal Organic Frameworks

Metal Organic Frameworks (MOFs) are a class of highly porous crystalline materials that are constructed from zero- or one-dimensional inorganic chains in combination with multitopic organic ligands.1 They have received great attention recently due to their large surface area, tunable porosity, and easy preparation, which lead to their versatile applications including gas storage2 and separation3, sensing4, catalysis5 and drug delivery6. The versatility of MOFs is further entrenched in the vast available design space offered by the enormous number of metal-linker combinations7, 8. However, majority of MOFs are insulators with very few of them showing appreciable electrical conductivity. The insulating nature of MOFs can be traced back to the starting materials used in constructing these hybrid materials9. Although conductive MOFs have been reported, very little information about the mechanism of charge transport is available.10-12 There are mainly two types of charge transport mechanism reported in such materials, hopping and band transport.13 Hopping mechanism is dominated by movement of charges from donor to acceptor moieties due to charge localization which exists at specific sites within the MOF.13 Band transport relies on delocalization of carriers throughout the valence and conduction bands.14 These mechanisms require low energy pathways for charge transport which are not present in MOFs. Recently, researchers have focused on two synthetic approaches from a chemical perspective to achieve such low energy pathways; through bond approach and through space approach.13 Ideally, both pathways can either lead to band or hopping transport. The through space mechanism utilizes non-covalent interactions like π-π stacking between organic linkers, which creates an extended pathway for charge delocalization usually pronounced in 2D MOFs.15, 16 Recent studies which have successfully quantified and identified charge carrier types in MOFs17 show that conductivity increases mainly with chemical oxidation signifying hole formation18, but mobility and directional charge transfer is still limited by geometry.19 Although the field of electrically conductive MOFs has experienced tremendous expansion in the last decade and yielded a variety of MOFs with high mobility and conductivity, majority of these works focus on material design principle and conductivity measurement, leaving the fundamental understanding of CT mechanism underexplored; yet the latter is essential for the further development of this class of materials to be exploited in optoelectronics, solar cells, and photocatalysis. I will present my progress in exploring CT mechanisms in 2D MOFs using advanced spectroscopic techniques.ReferencesC. Janiak and J. K. Vieth, New J. Chem., 2010, 34, 2366-2388.M. Latroche, S. Surble, C. Serre, C. Mellot-Draznieks, P. L. Llewellyn, J. H. Lee, J. S. Chang, S. H. Jhung and G. Ferey, Angewandte Chemie-International Edition, 2006, 45, 8227-8231.Z. J. Zhang, Y. G. Zhao, Q. H. Gong, Z. Li and J. Li, Chem. Commun., 2013, 49, 653-661.E. A. Dolgopolova, A. M. Rice, C. R. Martin and N. B. Shustova, Chem. Soc. Rev., 2018, 47, 4710-4728.Y. X. Zhou, W. H. Hu, S. Z. Yang, Y. B. Zhang, J. Nyakuchena, K. Duisenova, S. Lee, D. H. Fan and J. Huang, Journal of Physical Chemistry C, 2020, 124, 1405-1412.I. A. Lazaro and R. S. Forgan, Coord. Chem. Rev., 2019, 380, 230-259.C. Muschielok and H. Oberhofer, J. Chem. Phys., 2019, 151.L. Sun, M. G. Campbell and M. Dinca, Angewandte Chemie-International Edition, 2016, 55, 3566-3579.P. F. Li and B. Wang, Isr. J. Chem., 2018, 58, 1010-1018.K. W. Nam, S. S. Park, R. dos Reis, V. P. Dravid, H. Kim, C. A. Mirkin and J. F. Stoddart, Nature Communications, 2019, 10, 10.T. Chen, J.-H. Dou, L. Yang, C. Sun, N. J. Libretto, G. Skorupskii, J. T. Miller and M. Dincă, J. Am. Chem. Soc., 2020, 142, 12367-12373.S. S. Park, E. R. Hontz, L. Sun, C. H. Hendon, A. Walsh, T. Van Voorhis and M. Dincă, J. Am. Chem. Soc., 2015, 137, 1774-1777.M. Ko, L. Mendecki and K. A. Mirica, Chem. Commun., 2018, 54, 7873-7891.R. Dong, P. Han, H. Arora, M. Ballabio, M. Karakus, Z. Zhang, C. Shekhar, P. Adler, P. St Petkov, A. Erbe, S. C. B. Mannsfeld, C. Felser, T. Heine, M. Bonn, X. L. Feng and E. Canovas, Nature Materials, 2018, 17, 1027-+.L. Y. Qu, H. Iguchi, S. Takaishi, F. Habib, C. F. Leong, D. M. D'Alessandro, T. Yoshida, H. Abe, E. Nishibori and M. Yamashita, J. Am. Chem. Soc., 2019, 141, 6802-6806.L. S. Xie, E. V. Alexandrov, G. Skorupskii, D. M. Proserpio and M. Dinca, Chemical Science, 2019, 10, 8558-8565.A.C. Hinckley, J. Park, J. Gomes, E. Carlson and Z. Bao, J. Am. Chem. Soc., 2020, 142, 11123-11130. S.

Probing Charge Transport in Sp 3-Functionalized Single-Walled Carbon Nanotubes with Terahertz Spectroscopy

The covalent functionalization of semiconducting single-walled carbon nanotubes (SWCNTs) with luminescent sp 3-hybridized defects gives rise to tunable, narrowband emission in the near-infrared and increases their photoluminescence quantum yields [ACS Nano 2019, 13, 9259]. To enable their application in electrically driven light sources, a detailed understanding of the impact of sp 3 defects on charge transport within individual nanotubes and nanotube networks is required. Here, we investigate the ultrafast carrier dynamics in sp 3-functionalized, polymer-sorted (6,5) SWCNT dispersions and thin films using optical-pump terahertz-probe (OPTP) spectroscopy. OPTP spectroscopy relies on the photo-generation of charge carriers that are subsequently probed by a single-cycle terahertz pulse, rendering it a highly suitable technique for the determination of intrinsic charge transport properties (e.g., carrier mobility) in a quantitative and contact-free fashion. We observe a large transient photoconductivity of pristine and functionalized nanotubes that is dominated by the contribution of free charge carriers. The photoconductivity intensity and lifetime decrease upon functionalization, corroborating the impact of sp 3 defects on intra-nanotube charge transport. Through combination of (temperature-dependent) OPTP measurements of sp 3-functionalized SWCNT dispersions and films with electrical measurements of ambipolar, light-emitting field-effect transistors based on functionalized SWCNT networks [ACS Nano 2021, 15, 10451], we can separate the contributions of sp 3 defects (intra-nanotube) and nanotube junctions (inter-nanotube) to charge transport in such networks and distinguish the short- and long-range transport characteristics. Fig. 1: Ultrafast optical-pump terahertz-probe spectroscopy is a highly suitable technique to study the intrinsic charge transport properties of sp 3-functionalized (6,5) SWCNTs in dispersions and thin films. Figure 1

Ion Microbeam Studies of Charge Transport in Semiconductor Radiation Detectors With Three-Dimensional Structures: An Example of LGAD

The development of semiconductor detectors with an increased tolerance to high radiation levels often results in devices that deviate significantly from those of the classical design with planar electrodes. Decreasing the charge drift distance and/or introducing localised charge multiplication volumes are two detector development strategies that are often used in an attempt to increase the device radiation hardness. However, such approaches result in a more complex three-dimensional distribution of electrodes and sensitive detector volumes, which presents a challenge for the microscopic characterisation of charge transport properties. IBIC (ion beam-induced charge) is one of the available microscopic characterisation techniques that utilises focused, MeV energy range ions to probe charge transport. Here we used IBIC to probe different detector depths by varying the ion energy and/or angle of incidence and to probe certain detector regions by ions of the same range but with different stopping powers. These investigations are particularly important for studying low gain avalanche diode (LGAD) detectors, where measured interpad distances change with proton energy and where an increased carrier density results in changes in the charge multiplication, which are studied in this work.

Asymmetric charge carrier transfer and transport in planar lead halide perovskite solar cells

Understanding charge carrier extraction from the perovskite photoactive layer is critical to optimizing the design of perovskite solar cells. Herein, we demonstrate a simple time-resolved photoluminescence method to characterize the kinetics of charge transport across the bulk perovskite and charge transfer from the perovskite layer to the interlayers, elucidating the dependence of these dynamics on film thickness, grain boundaries (GBs), and interlayers. Using asymmetric laser excitation, we selectively probe charge transport by generating charges both close to and far from the heterojunction interface and correlate these results with device performance. We observe that both film thickness and GBs affect the asymmetry between electron and hole charge transport across the bulk perovskite and charge transfer from the bulk perovskite to the respective interlayers. • Time-resolved photoluminescence with spatially localized excitation • Asymmetries of charge carrier transfer and transport are quantified • Lateral grain boundaries result in unbalanced charge transport • Aerosol-assisted solvent treatment removes lateral grain boundaries effectively Xu et al. demonstrate a simple time-resolved photoluminescence method to selectively probe charge transfer and charge transport in perovskite films with interlayers. The results show both film thickness and grain boundaries affect the asymmetry between electron and hole charge transfer and charge transport.

Structural Asymmetry of Metallic Single-Atom Contacts Detected by Current-Voltage Characteristics.

The complex behavior of the simplest atomic-scale conductors indicates that the electrode structure itself is significant in the design of future nanoscale devices. In this study, the structural asymmetry of metallic atomic contacts formed between two macroscopic Au electrodes at room temperature was investigated. Characteristic signatures of the structural asymmetries were detected by fast current-voltage (I-V) measurements with a time resolution of approximately 100 μs. Statistical analysis of more than 300,000 I-V curves obtained from more than 1000 contact-stretching processes demonstrates that the current rectification properties are correlated with the conductance of the nanocontacts. A substantial suppression of the variation in current rectification was observed for the atomic contacts with integer multiples of the conductance quantum. Statistical analysis of the time-resolved I-V curves revealed that the current rectification variations increased significantly from 500 μs onward before the breakage of the atomic contacts. Ab initio atomistic simulations of the stretching processes and corresponding I-V characteristics confirmed the magnitude of the rectification and related it to the structural asymmetries in the breakdown process of the junctions. Overall, we provide a better understanding of the interplay between geometric and electronic structures at atomically defined metal-metal interfaces by probing charge transport properties in extremely sensitive nanocontacts.

Ion Microprobe Study of the Polarization Quenching Techniques in Single Crystal Diamond Radiation Detectors.

Synthetic single crystal diamond grown using the chemical vapor deposition technique constitutes an extraordinary candidate material for monitoring radiation in extreme environments. However, under certain conditions, a progressive creation of space charge regions within the crystal can lead to the deterioration of charge collection efficiency. This phenomenon is called polarization and represents one of the major drawbacks associated with using this type of device. In this study, we explore different techniques to mitigate the degradation of signal due to polarization. For this purpose, two different diamond detectors are characterized by the ion beam-induced charge technique using a nuclear microprobe, which utilizes MeV energy ions of different penetration depths to probe charge transport in the detectors. The effect of polarization is analyzed by turning off the bias applied to the detector during continuous or discontinuous irradiation, and also by alternating bias polarity. In addition, the beneficial influence of temperature for reducing the effect of polarization is also observed. Finally, the effect of illuminating the detector with light is also measured. Our experimental results indicate that heating a detector or turning off the bias, and then applying it during continuous irradiation can be used as satisfactory methods for recovering the CCE value close to that of a prepolarized state. In damaged regions, illumination with white light can be used as a standard method to suppress the strength of polarization induced by holes.

Probing Charge Transport Kinetics in a Plasmonic Environment with Cyclic Voltammetry.

Possible modifications in electrochemical reaction kinetics are explored in a nanostructured plasmonic environment with and without additional light illumination using a cyclic voltammetry (CV) method. In nanostructured gold, the effect of light on anodic and cathodic currents is much pronounced than that in a flat system. The electron-transfer rate shows a 3-fold increase under photoexcitation. The findings indicate a possibility of using plasmonic excitations for controlling electrochemical reactions.

Optical activation and detection of charge transport between individual colour centres in diamond

Charge control of color centers in semiconductors promises opportunities for novel forms of sensing and quantum information processing. Here, we articulate confocal fluorescence microscopy and magnetic resonance protocols to induce and probe charge transport between discrete sets of engineered nitrogen-vacancy (NV) centers in diamond, down to the level of individual defects. In our experiments, a "source" NV undergoes optically-driven cycles of ionization and recombination to produce a stream of photo-generated carriers, one of which we subsequently capture via a "target" NV several micrometers away. We use a spin-to-charge conversion scheme to encode the spin state of the source color center into the charge state of the target, in the process allowing us to set an upper bound to carrier injection from other background defects. We attribute our observations to the action of unscreened Coulomb potentials producing giant carrier capture cross-sections, orders of magnitude greater than those typically attained in ensemble measurements. Besides their fundamental interest, these results open intriguing prospects in the use of free carriers as a quantum bus to mediate effective interactions between paramagnetic defects in a solid-state chip.

(Energy Technology Division Graduate Student Award sponsored by Bio-Logic) Understanding Charge Transport for Current and Future Electrochemical Energy Storage Technologies

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, spatiotemporal x-ray fluorescence mapping was used to quantify elemental composition near the electrode and in the electrolyte of operando cells. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. X-ray diffraction was employed to track phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

Probing charge transport in manganite film through switching parameters

We have investigated the bipolar resistive switching of Y0.95Ca0.05MnO3 (YCMO) thin film on Si substrate using pulsed laser deposition. Simulation of Mn L3,2 near-edge X-ray absorption fine structure has been executed by CTM4XAS to corroborate the presence of a mixed-valence state of Mn ions and oxygen vacancies. The charge transport in the film is described by the space charge limited mechanism. Murgatroyd and space charge limited mechanism relations are used to calculate the mobility and other switching parameters at high resistance state. With a decrease in the switching layer (near to positively biased electrode) thickness, better resistive switching was observed. This work indicates that the localized switching thickness and temperature strongly affect the resistive switching of the YCMO film.

60 Years of physica status solidi

60 Years of <i>physica status solidi</i>

A Chemically Soldered Polyoxometalate Single-Molecule Transistor.

Polyoxometalates have been proposed in the literature as nanoelectronic components, where they could offer key advantages with their structural versatility and rich electrochemistry. Apart from a few studies on their ensemble behaviour (as monolayers or thin films), this potential remains largely unexplored. We synthesised a pyridyl‐capped Anderson–Evans polyoxometalate and used it to fabricate single‐molecule junctions, using the organic termini to chemically “solder” a single cluster to two nanoelectrodes. Operating the device in an electrochemical environment allowed us to probe charge transport through different oxidation states of the polyoxometalate, and we report here an efficient three‐state transistor behaviour. Conductance data fits a quantum tunnelling mechanism with different charge‐transport probabilities through different charge states. Our results show the promise of polyoxometalates in nanoelectronics and give an insight on their single‐entity electrochemical behaviour.

A Chemically Soldered Polyoxometalate Single‐Molecule Transistor

AbstractPolyoxometalates have been proposed in the literature as nanoelectronic components, where they could offer key advantages with their structural versatility and rich electrochemistry. Apart from a few studies on their ensemble behaviour (as monolayers or thin films), this potential remains largely unexplored. We synthesised a pyridyl‐capped Anderson–Evans polyoxometalate and used it to fabricate single‐molecule junctions, using the organic termini to chemically “solder” a single cluster to two nanoelectrodes. Operating the device in an electrochemical environment allowed us to probe charge transport through different oxidation states of the polyoxometalate, and we report here an efficient three‐state transistor behaviour. Conductance data fits a quantum tunnelling mechanism with different charge‐transport probabilities through different charge states. Our results show the promise of polyoxometalates in nanoelectronics and give an insight on their single‐entity electrochemical behaviour.

(Energy Technology Division Graduate Student Award Address sponsored by Bio-Logic) Understanding Charge Transport for Current and Future Electrochemical Energy Storage Technologies

Advances in electrochemical energy storage are key for the integration of intermittent wind and solar energy sources into the grid, widespread adoption of electric vehicles, and development of new safe and reliable consumer devices. For grid, transportation, and electronic energy storage markets, each application has distinct needs. Therefore, developing battery technology for emerging and wide-spread applications demands greater understanding of the complex chemical and electrochemical processes that occur within rechargeable batteries. Electron transfer and ion transport are the foundation of battery function where the capacity, loaded voltage and current define the practical energy and power delivery of the system. During operation, repetitive addition and removal of electrons and ions can lead to structural change within the electrode and interfacial formation that can dramatically impact electrochemical outcomes. Thus, structural, chemical, and electrochemical characterization during operation is critically important for next generation electrochemical energy storage technologies. The research efforts highlighted in this talk use multiple advanced characterization techniques, including operando based methods, to probe charge transport properties, structural changes, and interfacial evolution in multiple rechargeable battery systems. Specifically, X-ray absorption spectroscopy enabled structure and oxidation state elucidation in the absence of long-range order. Isothermal microcalorimetry was used to determine heat evolution due to parasitic or decomposition reactions operando. X-ray diffraction was employed to track temperature-induced and lithiation-induced phase changes of distinct electroactive materials. Using advanced characterization, these research efforts provide insight into electron transfer and ion transport properties and their impact on application relevant outcomes (resistance, cycle life, delivered capacity) of electrochemical energy storage technologies.

Coenzyme Coupling Boosts Charge Transport through Single Bioactive Enzyme Junctions.

SummaryOxidation of formate to CO2 is catalyzed via the donation of electrons from formate dehydrogenase (FDH) to nicotinamide adenine dinucleotide (NAD+), and thus the charge transport characteristics of FDH become essential but remain unexplored. Here, we investigated the charge transport through single-enzyme junctions of FDH using the scanning tunneling microscope break junction technique (STM-BJ). We found that the coupling of NAD+ with FDH boosts the charge transport by ∼2,100%, and the single-enzyme conductance highly correlates with the enzyme activity. The combined flicker noise analysis demonstrated the switching of the coenzyme-mediated charge transport pathway and supported by the significantly reduced HOMO-LUMO gap from calculations. Site-specific mutagenesis analysis demonstrated that FDH-NAD+ stably combined own higher bioactivity and boosts charge transport, and the coupling has been optimized via the natural selection. Our work provides evidence of hydrogen bond coupling in bioactivity but also bridges the charge transport through single-enzyme junctions and enzyme activities.

Observation of Quantum Interference at Room Temperature in a Single Perovskite Quantum Dot

Break junction technique allows researchers to probe charge transport properties in a single Perovskite quantum dot(QD) with an Angstrom scale resolution, and observe signatures of quantum interference effects at room temperature.

Probing Charge Transport Difference in Parallel and Vertical Layered Electronics with Thin Graphite Source/Drain Contacts

In the present study, we aim to help improve the design of van der Waals stacking, i.e., vertical 2D electronics, by probing charge transport differences in both parallel and vertical conducting channels of layered molybdenum disulfide (MoS2), with thin graphite acting as source and drain electrodes. To avoid systematic errors and variable contact contributions to the MoS2 channel, parallel and vertical electronics are all fabricated and measured on the same conducting material. Large differences in the on/off current ratio, mobility, and charge fluctuations, between parallel and vertical electronics are evident in electrical performance as well as in charge transport mechanisms. Further insights are drawn from a well-constrained analysis of both temperature-dependent current-voltage characteristics and low-frequency (LF) current fluctuations. This work offers significant insight into the fundamental understanding of charge transport and the development of future layered-materials-based integration technology.