Transport Studies of Isolated Molecular Wires in Self-Assembled Monolayer Devices

We have fabricated a variety of novel molecular diodes based on self-assembled-monolayers (SAM) of solid-state mixture of molecular wires (1,4 benzene-dimethane-thiol), and molecular insulator spacers (1-pentanethiol) with different concentration ratios r of wires/spacers, which were sandwiched between two gold (Au) electrodes. We introduce two new methods borrowed from Surface Science to (i) confirm the connectivity between the benzene-dimethane-thiol molecules with the upper Au electrode, and (ii) count the number of isolated molecular wires in the devices. The electrical transport properties of the SAM diodes were studied at different temperatures via the conductance and differential conductance spectra. We found that a potential barrier caused by the spatial connectivity gap between the pentanethiol molecules and the upper Au electrode dominates the transport properties of the pure pentanethiol SAM diode (r = 0). The transport properties of molecular diodes with low r-values are dominated by the conductance of the isolated benzene-dimethane-thiol molecules in the device. We found that the temperature dependence of the molecular diodes is much weaker than that of the pure pentanethiol device indicating the importance of the benzene-dimethane-thiol simultaneous bonding to the two Au electrodes that facilitate electrical transport. From the differential conductance spectra we also found that the energy difference, Delta between the Au electrode Fermi-level and the benzene-dimethane-thiol HOMO (or LUMO) level is ~1.5 eV; whereas it is ~2.5 eV for the pentanethiol molecule. The weak temperature dependent transport that we obtained for the SSM diodes reflects the weak temperature dependence of Delta.Comment: 38 p 8 Fi

Optical and transport studies of single molecule tunnel junctions based on self-assembled monolayers

ManuscriptWe have fabricated a variety of novel molecular tunnel junctions based on self-assembled-monolayers (SAM) of two-component solid-state mixtures of molecular wires (1,4 methane benzene-dithiol; Me-BDT with two thiol anchoring groups), and molecular insulator spacers (1-pentanethiol; PT with one thiol anchoring group) at different concentration ratios, r of wires/spacers, which were sandwiched between two metallic electrodes such as gold and cobalt. FTIR spectroscopy and surface titration were used, respectively to verify the formation of covalent bonds with the electrodes, and obtain the number of active molecular wires in the device. The electrical transport properties of the SAM devices were studied as a function of (i) r-value, (ii) temperatures, and (iii) different electrodes, via the conductance and differential conductance spectra. The measurements were used to analyze the Me-BDT density of states near the electrode Fermi level, and the properties of the interface barriers. We measured the Me-BDT single molecule resistance at low bias and gold electrodes to be 6x109 Ohm. We also determine the energy difference, Δ between the Me-BDT HOMO level and the gold Fermi level to be about 1.8 eV. In addition we also found that the temperature dependence of the SAM devices with r < 10-4 is much weaker than that of the pure PT device (or r = 0), showing a small interface barrier

Electrical and optical studies of gap states in self-assembled molecular aggregates

Journal ArticleWe fabricated a variety of two-terminal devices using self-assembled monolayers (SAM) of solid-state mixtures comprised of molecular "wires" [1,4-methane-benzenedithiol (Me-BDT)] and molecular insulator "spacers" [1-pentanethiol], which were prepared at various molar concentrations ratio, r of wires/spacers, and sandwiched between two gold electrodes. The devices' electrical transport was investigated at several r values using the bias voltage (V) dependencies of the conductance and differential conductance at various temperatures. In parallel, we also studied the UV-visible absorption and photoluminescence (PL) emission spectra of the SAM mixtures grown on silica transparent substrates

Transport studies of isolated molecular wires in self-assembled monolayer devices

Journal ArticleWe have fabricated a variety of isolated molecule diodes based on self-assembled monolayers (SAM) of solid-state mixture (SSM) of molecular wires [1,4-methane benzene dithiol (Me-BDT)], and molecular insulator spacers [penthane 1-thiol (PT)] with different concentration ratios r of wires/spacers, which were sandwiched between two gold (Au) electrodes. We introduce two specialized methods borrowed from surface science to (ii) confirm the connectivity between the Me-BDT molecules with the upper Au electrode, and (ii) count the number of isolated molecular wires in the devices. The electrical transport properties of the SSM SAM diodes were studied at different temperatures via the conductance and differential conductance spectra. We found that a potential barrier caused by the spatial connectivity gap between the PT molecules and the upper Au electrode dominates the transport properties of the pure PT SAM diode (r=0). The transport properties of SSM diodes with r values in the range 10−8<r<10−4 are dominated by the conductance of the isolated Me-BDT molecules in the device

Kazakhstan and Tarim microcontinents on the Devonian paleotectonic reconstructions

Devonian latitudes of the Kazakhstan and Tarim microcontinents obtained from paleomagnetic data. Definition based on the results of the study pre-folded high-temperature components of magnetization of rocks. The article uses the results of paleomagnetic studies of Devonian sedimentary and magmatic rocks, which formed on the continental crust. In these studies, conducted by various researchers, the high-temperature pre folded primary component of magnetization detected in Devonian rocks on 19 plots. Based on that data the latitude of 24.6 ± 5.5° determined for the Center of Kazakhstan microcontinent in the Early-Middle Devonian and 22.7 ± 4.6° in the Late Devonian. The Early-Middle Devonian latitude 6.1 ± 4.2° determined for the Сenter of the Tarim microcontinent. A significant number of paleotectonic schemes of Asia with different design and detail were proposed. We reviewed the position of the Kazakhstan and Tarim microcontinents in 19 paleo-tectonic reconstructions published after 2000. There are three groups of paleoreconstructions among them. On many reconstructions, the location of continental terranes and island arcs of Kazakhstan and Central Asia in the Early and Middle Paleozoic resembles the modern structure of the Indonesian region. On other reconstructions, these terranes form an arc that connected two paleocontinents in the Paleozoic - the Baltic and the Siberian ones. In the alternative design of reconstructions, the terranes have a relatively isolated position in the Paleoocean. As a result, а way of for co-ordination of matching paleotectonic reconstructions with paleomagnetic data is proposed

Molecular Photovoltaics in Nanoscale Dimension

This review focuses on the intrinsic charge transport in organic photovoltaic (PVC) devices and field-effect transistors (SAM-OFETs) fabricated by vapor phase molecular self-assembly (VP-SAM) method. The dynamics of charge transport are determined and used to clarify a transport mechanism. The 1,4,5,8-naphthalene-tetracarboxylic diphenylimide (NTCDI) SAM devices provide a useful tool to study the fundamentals of polaronic transport at organic surfaces and to discuss the performance of organic photovoltaic devices in nanoscale. Time-resolved photovoltaic studies allow us to separate the charge annihilation kinetics in the conductive NTCDI channel from the overall charge kinetic in a SAM-OFET device. It has been demonstrated that tuning of the type of conductivity in NTCDI SAM-OFET devices is possible by changing Si substrate doping. Our study of the polaron charge transfer in organic materials proposes that a cation-radical exchange (redox) mechanism is the major transport mechanism in the studied SAM-PVC devices. The role and contribution of the transport through delocalized states of redox active surface molecular aggregates of NTCDI are exposed and investigated. This example of technological development is used to highlight the significance of future technological development of nanotechnologies and to appreciate a structure-property paradigm in organic nanostructures

Optical and Transport Studies of Single Molecule Tunnel junctions based on Self-Assembled Monolayers

We have fabricated a variety of novel molecular tunnel junctions based on self-assembled-monolayers (SAM) of two-component solid-state mixtures of molecular wires (1,4 methane benzene-dithiol; Me-BDT with two thiol anchoring groups), and molecular insulator spacers (1-pentanethiol; PT with one thiol anchoring group) at different concentration ratios, r of wires/spacers, which were sandwiched between two metallic electrodes such as gold and cobalt. FTIR spectroscopy and surface titration were used, respectively to verify the formation of covalent bonds with the electrodes, and obtain the number of active molecular wires in the device. The electrical transport properties of the SAM devices were studied as a function of (i) r-value, (ii) temperatures, and (iii) different electrodes, via the conductance and differential conductance spectra. The measurements were used to analyze the Me-BDT density of states near the electrode Fermi level, and the properties of the interface barriers. We measured the Me-BDT single molecule resistance at low bias and gold electrodes to be 6x10^9 Ohm. We also determine the energy difference, D between the Me-BDT HOMO level and the gold Fermi level to be about 1.8 eV. In addition we also found that the temperature dependence of the SAM devices with r < 10^-4 is much weaker than that of the pure PT device (or r = 0), showing a small interface barrier.Comment: 32 pages 10 fugure

СИСТЕМЫ РАЗЛОМОВ В ВЕРХНЕЙ КОРЕ ФЕННОСКАНДИНАВСКОГО ЩИТА ВОСТОЧНО-ЕВРОПЕЙСКОЙ ПЛАТФОРМЫ

Directions of 683 faults located in the southeastern part of the Fennoscandian (Baltic) shield were statistically analyzed, and three orthogonal associations of fault systems were identified in the study area. According to the dynamic analysis of the fault systems and their associations, the main NW-striking faults belong to the fault network originating mainly from the early Paleoproterozoic. These faults functioned in the Paleoproterozoic during four main deformation stages: D1 – sinistral shear transtension and asymmetric rift genesis (2.1–1.9 Ga); D2 – sinistral shear transpression under oblique accretion and convergence (1.9 Ga); D3 – sinistral shear transpression under oblique collision (1.89–1.80 Ga); D4 – dextral strike-slip displacements at the background of complex escape tectonics of the late collision stage (1.80–1.78 Ga). The regional stress field changed as follows: D1 – northeast- or east-trending extension; D2 – northeast compression; D3 – sub-latitudinal compression; D4 – sub-meridian compression. Changes in dynamic loading conditions led to multiple kinematic inversions of the fault networks. Widespread transtension and transpression settings in the southeastern parts of the Baltic Shield give evidence of asymmetric rifting, oblique accretion and collision in the Paleoproterozoic, which must be taken in to account in geodynamic reconstructions.Статистический анализ направлений 683 разломов юго-восточной части Фенноскандинавского (Балтийского) щита позволил выделить три ортогональные ассоциации систем дизъюнктивных нарушений. Динамический анализ систем разломов и их ассоциаций показал, что главные структурообразующие разломы территории, имеющие северо-западное простирание, принадлежат сети разломов, которая была создана преимущественно в раннем палеопротерозое. В палеопротерозое они функционировали на протяжении четырех главных этапов деформаций: D1 – левосдвиговая транстенсия и асимметричный рифтогенез (2.2–1.9 млрд лет), D2 – левосдвиговая транспрессия в обстановке косой аккреции и конвергенции (1.9 млрд лет), D3 – левосдвиговая транспрессия в условиях косой коллизии (1.89–1.80 млрд лет), D4 – правый сдвиг на фоне сложной коллажной тектоники позднеколлизионного этапа (1.80–1.78 млрд лет). Региональное поле напряжений в процессе эволюции нарушений менялось следующим образом: D1 – растяжение в северо-восточном (или ВСВ) направлении, D2 – сжатие в северо-восточном направлении, D3 – сжатие в субширотном направлении, D4 – сжатие в субмеридиональном направлении. Изменения динамических условий нагрузки обусловили многократную кинематическую инверсию сети разрывных нарушений. Широкое распространение обстановок транстенсии и транспрессии на юго-востоке Балтийского щита свидетельствует о проявлении асимметричного рифтинга, косой аккреции и коллизии в палеопротерозое, что необходимо учитывать при геодинамических реконструкциях