Achieving High Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electro-Active Unites

Achieving high rectifying performance of molecular scale diode devices through synthetic chemistry and device construction remain a formidable challenge due to the complexity of the charge transport process and the device structure. We demonstrated here high-performance molecular rectification realized in self-assembled monolayer (SAM) based device by low-cost and fast screening the electroactive units. SAMs of commercial available carboxylate terminated alkane thiols on gold substrate, coordinated with a variety of metal ions, structures denoting as Au-S-(CH2)n-1COO-Mm+ (Cn+Mm+), where n=11, 12, 13, 14, 16, 18 and Mm+=Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, were prepared and junctions were measured using a eutectic indiumgallium alloy top contact (EGaIn). The C18+Ca2+ and C18+Zn2+ junctions were found to afford a record high rectification ratio (RR) of 756 at ±1.5 V. Theoretical analysis based on single level tunneling model shows that optimized combination of the asymmetry voltage division, energy barrier and the coupling of carboxylate-metal complex with electrode. Our method described here represent a general strategy for fast, cheap and effective exploration of the metal complex chemical space for high-performance molecular diodes devices.

Investigation of DC and analog/RF performance of C-shaped pocket TFET (CSP-TFET) with fully overlapping gate

In this paper, a C-shaped pocket tunnel field effect transistor (CSP-TFET) has been designed and optimized based on the traditional double-gate TFETs by introducing a C-shaped pocket region between the source and channel to improve the device performance. A gate-to-pocket overlapping structure is also examined in the proposed CSP-TFET to enhance the gate controllability. The effect of pocket length, pocket doping concentration and gate-to-pocket overlapping structure on the DC and analog/RF characteristics of the CSP-TFET are estimated after calibrating the tunneling model in double-gate TFETs. The DC and analog/RF performance such as on-state current (I on ), on/off current ratio (I on /I off ), subthreshold swing (SS), transconductance (g m ), cut-off frequency (f T ), and gain-bandwidth product (GBP) are investigated. The optimized CSP-TFET device exhibits excellent performance with high I on (9.98×10-4 A/μm), high I on /I off (~1011), as well as low SS (~12 mV/dec). The results reveal that the CSP-TFET device could be a potential alternative for the next generation of semiconductor devices.

Single Level Tunneling Model for Molecular Junctions: Evaluating the Simulation Methods

Single level tunneling model has been the most popular model system in both the experimental and theoretical study of molecular junctions. We performed a detailed simulation study on the performance of the single level tunneling model in analyzing the charge transport mechanism of molecular junctions. Three different modeling methods, including the numerical integration of the Landauer formula and two approximated analytical formulas that are extensively used for extracting key transport parameters from current–voltage (I-V) characteristics, i.e. the energy offset and the coupling between molecule and electrode, were compared and evaluated for their applicability. The simulation of I-V plots shows that the applicability of the two approximated analytical models is energy offset and coupling strength dependent. Model fitting based on the three methods performed on experimental data attained from representative literature papers revealed that the two approximated analytical methods are neither suitable for the situation of small coupling strength and low energy offset, and they also deviated from the exact results at high bias. We finally provided a phase map of the applicability of different modeling methods as a guide for their proper usage in charge transport study in molecular devices.

Single Level Tunneling Model for Molecular Junctions: Evaluating the Simulation Methods

Single level tunneling model has been the most popular model system in both the experimental and theoretical study of molecular junctions. We performed a detailed simulation study on the performance of the single level tunneling model in analyzing the charge transport mechanism of molecular junctions. Three different modeling methods, including the numerical integration of the Landauer formula and two approximated analytical formulas that are extensively used for extracting key transport parameters from current–voltage (I-V) characteristics, i.e. the energy offset and the coupling between molecule and electrode, were compared and evaluated for their applicability. The simulation of I-V plots shows that the applicability of the two approximated analytical models is energy offset and coupling strength dependent. Model fitting based on the three methods performed on experimental data attained from representative literature papers revealed that the two approximated analytical methods are neither suitable for the situation of small coupling strength and low energy offset, and they also deviated from the exact results at high bias. We finally provided a phase map of the applicability of different modeling methods as a guide for their proper usage in charge transport study in molecular devices.

Double Proton Tautomerism via Intra- or Intermolecular Pathways? The Case of Tetramethyl Reductic Acid Studied by Dynamic NMR: Hydrogen Bond Association, Solvent and Kinetic H/D Isotope Effects

Using dynamic liquid-state NMR spectroscopy a degenerate double proton tautomerism was detected in tetramethyl reductic acid (TMRA) dissolved in toluene-d8 and in CD2Cl2. Similar to vitamin C, TMRA belongs to the class of reductones of biologically important compounds. The tautomerism involves an intramolecular HH transfer that interconverts the peripheric and the central positions of the two OH groups. It is slow in the NMR time scale around 200 K and fast at room temperature. Pseudo-first-order rate constants of the HH transfer and of the HD transfer after suitable deuteration were obtained by line shape analyses. Interestingly, the chemical shifts were found to be temperature dependent carrying information about an equilibrium between a hydrogen bonded dimer and a monomer forming two weak intramolecular hydrogen bonds. The structures of the monomer and the dimer are discussed. The latter may consist of several rapidly interconverting hydrogen-bonded associates. A way was found to obtain the enthalpies and entropies of dissociation, which allowed us to convert the pseudo-first-order rate constants of the reaction mixture into first-order rate constants of the tautomerization of the monomer. Surprisingly, these intrinsic rate constants were the same for toluene-d8 and CD2Cl2, but in the latter solvent more monomer is formed. This finding is attributed to the dipole moment of the TMRA monomer, compensated in the dimer, and to the larger dielectric constant of CD2Cl2. Within the margin of error, the kinetic HH/HD isotope effects were found to be of the order of 3 but independent of temperature. That finding indicates a stepwise HH transfer involving a tunnel mechanism along a double barrier pathway. The Arrhenius curves were described in terms of the Bell–Limbach tunneling model.

FTIR and dielectric relaxation analysis for PVC-Pb3O4 polymer nanocomposites

This work studies the FTIR as well as dielectric characteristics of the PVC-Pb3O4 nanocomposite films. FTIR analysis shows the small shift in 650, 845 and 1732 cm− 1 band positions as a confirmation of interaction between Pb3O4 nanoparticles with PVC polymer matrix. The real permittivity (ε1) decreases with increasing frequency for all samples with the appearance of a relaxation peak at high temperatures. The dielectric loss data (ε2) of the PVC-Pb3O4 nanocomposite revealed a shift of the dielectric absorption peak towards high frequency with increasing the temperature. The activation energy values for both α and β relaxations almost decreased with increasing the Pb3O4 concentration. The energy density of samples containing Pb3O4 has a lower energy density than the pure PVC polymer film. The exponent s often increased with increasing the temperature, and this behavior is consistent with overlapping large-polaron tunneling model. The DC activation energy decreased when the percentage of Pb3O4 increased to 3.0 wt% and then increased at 4.0 wt%. Additionally, a convergence between these values and the activation energies of α and β relaxations observed, which is indicates that the same type of charge carriers participate in the processes.

No light at the end of the tunnel

The tunneling model for laser-induced processes implies the replacement of the propagating field of a laser by an oscillatory electric field. The view of the electric field as the primary influence in charged particle interactions fails for laser processes where the propagation property is important. Electric fields lack several quintessential laser-field properties that become dominant at high intensities and/or low frequencies. Quantum tunneling is not a concept generally suited to laser light. Conversely, laser criteria do not apply to electric-field phenomena like Sauter–Schwinger pair production in the vacuum, contrary to a widespread assumption. Graphic abstract