Dynamical bi-stability of single-molecule junctions: A combined experimental/theoretical study of PTCDA on Ag(111)

The dynamics of a molecular junction consisting of a PTCDA molecule between the tip of a scanning tunneling microscope and a Ag(111) surface have been investigated experimentally and theoretically. Repeated switching of a PTCDA molecule between two conductance states is studied by low-temperature scanning tunneling microscopy for the first time, and is found to be dependent on the tip-substrate distance and the applied bias. Using a minimal model Hamiltonian approach combined with density-functional calculations, the switching is shown to be related to the scattering of electrons tunneling through the junction, which progressively excite the relevant chemical bond. Depending on the direction in which the molecule switches, different molecular orbitals are shown to dominate the transport and thus the vibrational heating process. This in turn can dramatically affect the switching rate, leading to non-monotonic behavior with respect to bias under certain conditions. In this work, rather than simply assuming a constant density of states as in previous works, it was modeled by Lorentzians. This allows for the successful description of this non-monotonic behavior of the switching rate, thus demonstrating the importance of modeling the density of states realistically.Comment: 20 pages, 6 figures, 1 tabl

Обоснование параметров усовершенствованного сошника для внесения минеральных и органо-минеральных удобрений

When using the conventional coulters for applying organic-and-mineral fertilizers, reliable technological process cannot be ensured unless a fertilizer funnel is adapted to such fertilizers. (Research purpose) Determination of the parameters of an improved coulter for introducing organic-and-mineral fertilizers. (Materials and methods) The authors conducted theoretical studies using the methods of theoretical and agricultural mechanics, as well as analytic geometry. They also considered the horizontal flow of soil particles under the action of the pointed part of a leg and made diagrams of the progressive speed of a cultivator depending on the cutting-point angle of the coulter leg at friction angles of 25, 30, and 35 degrees. (Results and discussion) An analytical relationship was obtained to determine progressive flowability of organic-and-mineral fertilizers through a coulter funnel. The author also found the cutting-point angle of a coulter leg for introducing fertilizers at a certain depth. In this case they neither stick to the coulter surface nor pack up before entering it. The optimum diameter of the fertilizer funnel was determined as well. (Conclusions) It has been proved that the cutting-point angle of a working tool leg for introducing mineral and organic-and-mineral fertilizers developed according to the research should range from 54 to 66 degrees. The authors have determined that an easy flow of fertilizers can be ensured if the diameter of a fertilizer funnel of a coulter should be not less than 43 millimeters.При использовании существующих сошников для внесения органо-минеральных удобрений не обеспечивается надежное протекание технологического процесса, так как шейка тукопровода не приспособлена к внесению таких удобрений. (Цель исследований) Обосновать параметры усовершенствованного сошника для внесения минеральных и органо-минеральных удобрений. (Материалы и методы) Провели исследования с использованием методов теоретической и земледельческой механики, а также аналитической геометрии. Рассмотрели движение частиц почвы по горизонтальной плоскости под действием заостренной части стойки. Построили графики изменения поступательной скорости культиватора в зависимости от угла заострения стойки сошника при углах трения 25, 30 и 35 градусов. (Результаты и обсуждение) Получили аналитическую зависимость для определения поступательной способности органо-минеральных удобрении через шейку сошника. Определили угол заострения стойки сошника для внесения удобрений на определенную глубину, при котором они не прилипают к его поверхности и не сгруживаются перед ним. Обосновали диаметр шейки тукопровода сошника. (Выводы) Доказали, что угол заострения стойки рабочего органа для внесения минеральных и органо-минеральных удобрений, разработанного по результатам проведенных исследований, должен быть в пределах 54-66 градусов. Рекомендовали для обеспечения свободного прохода удобрений диаметр шейки тукопровода сошника, превышающий 43 миллиметра

Magnetoresistance through a single molecule

The use of single molecules to design electronic devices is an extremely challenging and fundamentally different approach to further downsizing electronic circuits. Two-terminal molecular devices such as diodes were first predicted [1] and, more recently, measured experimentally [2]. The addition of a gate then enabled the study of molecular transistors [3-5]. In general terms, in order to increase data processing capabilities, one may not only consider the electron's charge but also its spin [6,7]. This concept has been pioneered in giant magnetoresistance (GMR) junctions that consist of thin metallic films [8,9]. Spin transport across molecules, i.e. Molecular Spintronics remains, however, a challenging endeavor. As an important first step in this field, we have performed an experimental and theoretical study on spin transport across a molecular GMR junction consisting of two ferromagnetic electrodes bridged by a single hydrogen phthalocyanine (H2Pc) molecule. We observe that even though H2Pc in itself is nonmagnetic, incorporating it into a molecular junction can enhance the magnetoresistance by one order of magnitude to 52%.Comment: To appear in Nature Nanotechnology. Present version is the first submission to Nature Nanotechnology, from May 18th, 201

Metallic, magnetic and molecular nanocontacts

Scanning tunnelling microscopy and break-junction experiments realize metallic and molecular nanocontacts that act as ideal one-dimensional channels between macroscopic electrodes. Emergent nanoscale phenomena typical of these systems encompass structural, mechanical, electronic, transport, and magnetic properties. This Review focuses on the theoretical explanation of some of these properties obtained with the help of first-principles methods. By tracing parallel theoretical and experimental developments from the discovery of nanowire formation and conductance quantization in gold nanowires to recent observations of emergent magnetism and Kondo correlations, we exemplify the main concepts and ingredients needed to bring together ab initio calculations and physical observations. It can be anticipated that diode, sensor, spin-valve and spin-filter functionalities relevant for spintronics and molecular electronics applications will benefit from the physical understanding thus obtained