We report the results of an extensive investigation metal-molecule-metal tunnel junctions based on oligophenylene dithiols (OPDs) bound to several types electrodes (M1-S-(C6H4)n-S-M2, with 1 ≤ n 4 and M1,2 = Ag, Au, Pt) examine impact molecular length (n) metal work function (Φ) junction properties. Our includes (1) measurements by scanning Kelvin probe microscopy electrode changes (ΔΦ ΦSAM - Φ) caused chemisorption OPD self-assembled monolayers (SAMs), (2) current-voltage (I-V)...

This work emphasizes that the transition voltages ${V}_{t\ifmmode\pm\else\textpm\fi{}}$ for both bias polarities ($V$ $\ensuremath{\gtrless}$ 0) should be used to properly determine energy offset ${\ensuremath{\varepsilon}}_{0}$ of molecular orbital closest electrodes' Fermi level and asymmetry $\ensuremath{\gamma}$ in junctions. Accurate analytical formulas are deduced estimate solely terms ${V}_{t\ifmmode\pm\else\textpm\fi{}}$. These estimates validated against experiments, by showing full...

We report detailed measurements of transport and electronic properties molecular tunnel junctions based on self-assembled monolayers (SAMs) oligophenylene monothiols (OPT n, n = 1-3) dithiols (OPD Ag, Au, Pt electrodes. The were fabricated with the conducting probe atomic force microscope (CP-AFM) platform. Fitting current-voltage ( I-V) characteristics for OPT OPD to analytical single-level tunneling model allows extraction both HOMO-to-Fermi-level offset (εh) average molecule-electrode...

We report here an extensive study of transport and electronic structure molecular junctions based on alkyl thiols (CnT; n = 7, 8, 9, 10, 12) dithiols (CnDT; 10) with various lengths contacted different metal electrodes (Ag, Au, Pt). The dependence the low-bias resistance (R) contact work function indicates that is HOMO-assisted (p-type transport). Analysis current-voltage (I-V) characteristics for CnT CnDT tunnel analytical single-level model (SLM) provides both HOMO-Fermi energy offset...

The multistate vibronic dynamics in the X̃ 2E1g-Ẽ 2B2u electronic states of benzene radical cation is investigated theoretically by an ab initio quantum-dynamical approach. coupling scheme and values system parameters are adopted from previous Paper I. Vibronic line spectra obtained with Lanczos procedure. Extensive calculations on wave-packet propagation have been performed aid multiconfiguration time-dependent Hartree method. Up to five coupled potential energy surfaces 13 vibrational...

The transport properties of molecular junctions based on alkanedithiols with three different methylene chain lengths were compared similar chains wherein every third −CH2– was replaced O or S, that is, following the general formula HS(CH2CH2X)nCH2CH2SH, where X = CH2, O, S and n 1, 2, 3. Conducting probe atomic force microscopy revealed low bias resistance increased upon substitution in order CH2 < S. This change is ascribed to observed identical trend contact resistance, Rc, whereas...

The Stark effect plays a key role in understanding why, against expectation, alkane thiols are not high-performance molecular rectifiers.

Laws of corresponding states known so far demonstrate that certain macroscopic systems can be described in a universal manner terms reduced quantities, which eliminate specific substance properties. To quantitatively describe real systems, all these laws contain numerical factors adjusted empirically. Here, we report law deduced analytically for charge transport via tunneling molecular junctions, validate against current–voltage measurements conducting probe atomic force microscope junctions...

The accurate determination of the lowest electron attachment (EA) and ionization (IP) energies for molecules embedded in molecular junctions is important correctly estimating, example, magnitude currents (I) or biases (V) where an I-V curve exhibits significant non-Ohmic behavior. Benchmark calculations several typical utilized to fabricate single-molecule characterized by n-type conduction (4,4'-bipyridine, 1,4-dicyanobenzene 4,4'-dicyano-1,1'-biphenyl) p-type (benzenedithiol,...

Experiments on n-type perylene diimide nanojunctions with different contacts at variable temperature allow discrimination between tunneling and hopping mechanisms.

Strong stochastic fluctuations witnessed as very broad resistance (R) histograms with widths comparable to or even larger than the most probable values characterize many measurements in field of molecular electronics, particularly those based on single molecule junctions at room temperature. Here we show that containing 80 oligophenylene dithiol molecules (OPDn, 1 ≤ n 4) connected parallel display small relative statistical deviations—δR/R ≈ 25% after only ∼200 independent measurements—and...

The first simultaneous measurements of transition voltage (Vt) spectroscopy (TVS) and conductance (G) histograms (Guo et al., J. Am. Chem. Soc.2011, 133, 19189) form a great case for studying stochastic effects, which are ubiquitous in molecular junctions. Here an interpretation those data is proposed that emphasizes the different physical content Vt G reveals fluctuations orbital alignment have significantly larger impact on than initially claimed. present study demonstrates usefulness...

Results of a seminal study (B. Xu and N. J. Tao, Science, 2003, 301, 1221) on the single-molecule junctions based bipyridine placed in solvent have been challenged recently (S. Y. Quek et al., Nat. Nano, 2009, 4, 230) by implicitly assuming negligible impact molecular transport merely considering low bias conductance data. In this paper we demonstrate that effects are important, to show focus our attention energy offset ε0 dominant orbital (LUMO) relative electrode Fermi level. To estimate...

Extensive studies on thin films indicated a generic cubic current-voltage $I-V$ dependence as salient feature of charge transport by tunneling. A quick glance at data for molecular junctions suggests qualitatively similar behavior. This would render model-based almost irrelevant, since, whatever the model, its parameters can always be adjusted to fit symmetric (asymmetric) curves characterized two (three) expansion coefficients. Here, we systematically examine popular models based tunneling...

In this paper, we report results on the electronic structure and transport properties of molecular junctions fabricated via conducting probe atomic force microscopy (CP-AFM) using self-assembled monolayers (SAMs) n-alkyl chains anchored with acetylene groups (CnA; n = 8, 9, 10, 12) Ag, Au, Pt electrodes. We found that current–voltage (I–V) characteristics CnA CP-AFM can be very accurately reproduced by same off-resonant single-level model (orSLM) successfully utilized previously for many...

Despite numerous prior studies on molecular tunnel junctions, many important questions remain about the nature of metal–molecule contacts. Using conducting probe atomic force microscope (CP-AFM) platform, we report here an investigation electrical contact effects in junctions based oligophenylene and alkyl dithiols (OPDn, n = 1, 2, 3 CnDT, 8, 9, 10) linked via thiol anchoring groups to dissimilar Ag, Au, Pt metal electrodes. Our data reveal a peculiar effect: two interfaces "talk" each...

The Newns-Anderson model is ubiquitous in studies of the molecular transport presence solvent (outer) reorganization. present work demonstrates that intramolecular reorganization can also be significant for through molecules with floppy degrees freedom, which extended. expressions parameters deduced from electronic structure calculations (4, 4')-bipyridine (44BPY) quantitatively differ those characteristic outer due to strong anharmonicities. These utilized as input 44BPY-based junctions...

We report results of quantum chemical calculations for the neutral and anionic species (4,4')-bipyridine (44BPY), a prototypical molecule with floppy degree freedom, placed in vacuo solvents. In addition to equilibrium geometries vibrational frequencies spectra, we present adiabatic energy curves modes significant intramolecular reorganization upon charge transfer. Special attention is paid strongly anharmonic freedom 44BPY, which related most salient structural feature, namely twist angle θ...

In a recent experimental work, results of the first transition voltage spectroscopy (TVS) investigation on azurin have been reported. This forms great case to better understand electron transfer through bacterial redox metalloproteins, process fundamental importance from chemical, physical, and biological perspectives, practical for nano(bio)electronics. present paper we challenge tentative interpretation put forward in aforementioned study propose different theoretical interpretation. To...

The (4,4′)-bipyridine molecule (44bpy) has attracted particular interest in molecular electronics because single-molecule junctions can be directly formed via nitrogen–gold affinity, obviating the need of understanding nontrivial invasive effects due to extra anchoring groups. In a recent study, an apparent conundrum related transport through 44bpy been resolved by emphasizing essential role environment (solvent vs ambient conditions). present paper, we demonstrate robustness conclusion that...

A variety of homologous carbon chains (HCnH, HCnN, CnS, CnO, and OCnO) are found to exhibit an appealing even-odd effect. Chains containing a number atoms certain parity possess singlet ground states, while members opposite have triplet states. From general perspective, it is important that this effect confounds straightforward chemical intuition. Whether the most stable form or neither simply related fact species in question normal (closed-shell, nonradical) molecule nor (di)radical (e.g.,...