Quantum transport through STM-lifted single PTCDA molecules

Using a scanning tunneling microscope we have measured the quantum conductance through a PTCDA molecule for different configurations of the tip-molecule-surface junction. A peculiar conductance resonance arises at the Fermi level for certain tip to surface distances. We have relaxed the molecular junction coordinates and calculated transport by means of the Landauer/Keldysh approach. The zero bias transmission calculated for fixed tip positions in lateral dimensions but different tip substrate distances show a clear shift and sharpening of the molecular chemisorption level on increasing the STM-surface distance, in agreement with experiment.Comment: accepted for publication in Applied Physics

Investigation of a metal-organic interface - realization and understanding of a molecular switch

The field of molecular organic electronics is an emerging and very dynamic area. The continued trend to miniaturisation, combined with increasing complexity and cost of production in conventional semiconductor electronics, forces companies to turn their attention to alternatives that promise the next levels of scale at significantly lower cost. After consumer electronic devices based on organic transistors, such as TVs and book readers, have already been presented, molecular electronics is expected to offer the next breakthrough in feature size. Unfortunately, most of the organic/metal interfaces contain intrinsic defects that break the homogeneity of the interface properties. In this thesis, the electronic and structural properties of such defects were examined in order to understand the influence of the inhomogeneities on the quality of the interface layer. However, the main focus of this work was the investigation of the local properties of a single molecule. Taking advantage of the Scanning Tunnelling Microscope's (STM's) ability to act as a local probe, a single molecular switch was realized and studied. Moreover, in close collaboration with theory groups, the underlying mechanism driving the switching process was identified and described. Besides the investigation of the switching process, the ability of the STM to build nanostructures of different shapes from large organic molecules was shown. Knowing the parameters for realization and control of the switching process and for building the molecular corrals, the results of this investigation enable the reconstruction of the studied molecular ensemble and its deployment in electric molecular circuits, constituting a next step towards further miniaturization of electronic devices

Si(100):H and Ge(100):H dimer rows contrast inversion in low-temperature scanning tunneling microscope images

Detailed low-temperature scanning tunneling microscope images of the Si(100)-2$\times$ 1-H and the Ge(100)-2$\times$ 1-H surfaces show a remarkable contrast inversion between filled- and empty-state images where the hydrogen dimer rows appear bright for filled-state images and dark for empty-state images. This contrast inversion originates from the change in the dominant surface states and their coupling to the tip apex and the bulk channels as a function of the bias voltage

Mathematical modeling and research methods of horizontal wells hydrodynamic cleaning

Актуальность исследования определяется потребностью: уяснения современных достижений в вопросах моделирования процессов транспорта шламов в реальных условиях выполнения буровых операций, способствующих увеличению скорости бурения, повышающих эффективность очистки скважин; установления преимуществ/недостатков существующих подходов, современных моделей и комплексных методов описания динамики систем с частицами для эффективного воздействия на реологические свойства промывочных жидкостей; устранения причин потери оборудования. Цель: уяснение современного опыта моделирования процессов очистки скважин со сложной образующей ее ствола, преимущественно лежащего в горизонтальной плоскости; изучение особенностей течения смесей в межтрубном пространстве с круглым ядром; выдача рекомендаций в практику моделирования и расчета гидродинамических процессов, интенсифицирующих очистку. Методы. Теоретические и практические методы исследования из смежных областей гидродинамики и тепломассопереноса в реофизически сложных системах; методы численного моделирования ламинарного и турбулентного потоков в условиях прямоточного и закрученного течений способом вращающейся стенки вокруг своей продольной оси и орбитального вращения эксцентричного ядра (внутренней трубы с подвижной/неподвижной стенкой) относительно продольной оси буровой колонны, влияющих на формирование слоя шламов и динамику частиц дисперсной смеси. Результаты. Представлены результаты современных численных исследований процессов очистки скважин с горизонтальными участками. Приведены сведения об аспектах детального гидродинамического и диффузионного моделирования сложных течений в скважинах с криволинейной образующей. Сформулированы популярные в практике приложений модели и методы, привлекаемые для изучения характеристик течения и тепломассопереноса гомогенных и гетерогенных сред во внутренних системах. Обсуждаются аспекты моделирования процессов транспорта шламов в рамках эйлерова/лагранжева подходов с учетом особенностей, вносимых эффектами межфазного взаимодействия/вращения и способов закрутки. Представлены данные о деталях прогноза дисперсных систем с характеристикой влияния изменений реологических свойств (модели степенной жидкости, Гершеля-Балкли), формы/размеров частиц, режимов течения смесей, инерционных сил на интенсивность образования шламов. Проанализированы проблемы повышения точности моделирования транспорта шламов, возможности новых технологий, оригинальных моделей турбулентности и их опорных двухпараметрических динамических баз, привлекаемых для интенсификации и эффективности процессов очистки. Даны рекомендации по их решению в рассматриваемых гидродинамических и геометрических конфигурациях. Представлены результаты и отмечены проблемы, имеющие фундаментально-прикладное значение, составляющие самостоятельный предмет перспективных исследований.Relevance of the research is determined by the need to understand modern achievements in modeling the processes of sludge transport in real conditions of drilling operations that increase drilling speed and the efficiency of well cleaning; to establish the advantages/disadvantages of existing approaches, modern models and complex methods for describing the dynamics of systems with particles in order to effectively choose the rheological properties of drilling fluids and eliminate the reasons of equipment loss. The aim of this work is to understand the modern experience of modeling the processes of cleaning wells with complex geometries, mainly lying in the horizontal plane; to study the features of the flow of mixtures in the annular space with a circular core; providing recommendations for the practice of modeling and calculating hydrodynamic processes that increase hole cleaning efficiency. Methodology. Theoretical and practical research methods from related fields of hydrodynamics and heat and mass transfer in rheologically and physically complex systems; methods for numerical modeling of laminar and turbulent flows under conditions of direct-flow and swirling flows created by a co-axially or orbitally rotating wall, which affect the formation of a layer of cuttings and the dynamics of particles of a dispersed mixture. Results. The paper introduces the results of modern numerical studies of cleaning wells with horizontal sections and the information on aspects of detailed hydrodynamic and diffusion modeling of complex flows in inclined wells. The applied models and methods used to study the characteristics of flow and heat and mass transfer in homogeneous and heterogeneous media in internal systems are formulated. Aspects of modeling the processes of cuttings transport in the framework of Euler/Lagrangian approaches are discussed, taking into account the features introduced by the effects of interfacial interaction/rotation. The paper introduces the changes in cuttings concentration based on rheological properties (power-law or Herschel-Bulkley), different shapes/sizes of particles, flow regimes and inertial forces. The problems of improving the accuracy of cuttings transport modeling, the possibilities of new technologies, original turbulence models and their two-parameter dynamic bases used for increasing the intensification and efficiency of cleaning processes are analyzed. The authors have given the recommendations for their solution in the considered hydrodynamic and geometric configurations. The results and problems that are of fundamental and applied significance and constitute an independent subject of prospective research are indicated