2,087 research outputs found
Probing Wigner correlations in a suspended carbon nanotube
The influence of the electron-vibron coupling on the transport properties of
a strongly interacting quantum dot built in a suspended carbon nanotube is
analyzed. The latter is probed by a charged AFM tip scanned along the axis of
the CNT which induces oscillations of the chemical potential and of the linear
conductance. These oscillations are due to the competition between finite-size
effects and the formation of a Wigner molecule for strong interactions. Such
oscillations are shown to be suppressed by the electron-vibron coupling. The
suppression is more pronounced in the regime of weak Coulomb interactions,
which ensures that probing Wigner correlations in such a system is in principle
possible
Theory of the STM detection of Wigner molecules in spin incoherent CNTs
The linear conductance of a carbon nanotube quantum dot in the Wigner
molecule regime, coupled to two scanning tunnel microscope tips is inspected.
Considering the high temperature regime, the nanotube quantum dot is described
by means of the spin-incoherent Luttinger liquid picture. The linear
conductance exhibits spatial oscillations induced by the presence of the
correlated, molecular electron state. A power-law scaling of the electron
density and of the conductance as a function of the interaction parameter are
found. They confirm local transport as a sensitive tool to investigate the
Wigner molecule. The double-tip setup allows to explore different transport
regimes with different shapes of the spatial modulation, all bringing
information about the Wigner molecule
AFM probe for the signatures of Wigner correlations in the conductance of a one-dimensional quantum dot
The transport properties of an interacting one-dimensional quantum dot
capacitively coupled to an atomic force microscope probe are investigated. The
dot is described within a Luttinger liquid framework which captures both
Friedel and Wigner oscillations. In the linear regime, we demonstrate that both
the conductance peak position and height oscillate as the tip is scanned along
the dot. A pronounced beating pattern in the conductance maximum is observed,
connected to the oscillations of the electron density. Signatures of the
effects induced by a Wigner molecule are clearly identified and their stability
against the strength of Coulomb interactions are analyzed. While the
oscillations of the peak position due to Wigner get enhanced at strong
interactions, the peak height modulations are suppressed as interactions grow.
Oscillations due to Friedel, on the other hand, are robust against interaction.Comment: 9 figure
Temperature-induced emergence of Wigner correlations in a STM-probed one-dimensional quantum dot
The temperature-induced emergence of Wigner correlations over finite-size
effects in a strongly interacting one-dimensional quantum dot are studied in
the framework of the spin coherent Luttinger liquid. We demonstrate that, for
temperatures comparable with the zero mode spin excitations, Friedel
oscillations are suppressed by the thermal fluctuations of higher spin modes.
On the other hand, the Wigner oscillations, sensitive to the charge mode only,
are stable and become more visible. This behavior is proved to be robust both
in the thermal electron density and in the linear conductance in the presence
of an STM tip. This latter probe is not directly proportional to the electron
density and may confirm the above phenomena with complementary and additional
information
Correlation functions for the detection of Wigner molecules in a one-channel Luttinger liquid quantum dot
In one-channel, finite-size Luttinger one-dimensional quantum dots, both
Friedel oscillations and Wigner correlations induce oscillations in the
electron density with the same wavelength, pinned at the same position.
Therefore, observing such a property does not provide any hint about the
formation of a Wigner molecule when electrons interact strongly and other tools
must be employed to assess the formation of such correlated states. We compare
here the behavior of three different correlation functions and demonstrate that
the integrated two point correlation function, which represents the probability
density of finding two particles at a given distance, is the only faithful
estimator for the formation of a correlated Wigner molecule.Comment: 6 pages, 5 figure
Optical sub-diffraction limited focusing for confined heating and lithography
Electronics and nanotechnology is constantly demanding a decrease in size of fabricated nanoscale features. This decrease in size has become much more difficult recently due to the limited resolution of optical systems that are fundamental to many nanofabrication methods. A lot of effort has been made to fabricate devices smaller than the diffraction limit of light. Creating devices that are capable of confining fields by means of interference patterns of propagating wave modes and surface plasmon, has proven successful to confine light into smaller spot sizes.
Zone plate diffraction lenses generate spots with dimensions very close to the diffraction limit. We report the fabrication of zone plates to be used in laser direct writing of silicon nanowires. We show experimentally and with numerical models that a silicon substrate subjected to a focused spot is capable of reaching the necessary temperature for the synthesis of silicon nanowires with widths of 60 nm, which is considerably smaller than the diffraction limit of the processing laser.
Nanoscale ridge apertures are devices with a great potential to confine light energy. Such apertures have been experimentally proven to create very small lithography features. We believe that these apertures can be further modified in order to achieve a practical smaller confinement in the near field region. In this thesis we discuss several attempts to design and fabricate apertures with sharp edges and implement them in a previously reported parallel lithography setup. In an attempt to use apertures for parallel fabrication of patterns, we developed a system to control the position of the near-field region with respect to a lithography substrate. To do this we use a method of interferometric-spatial- phase-imaging (ISPI). With the implementation of this method we were able to produce an array of 32X32 lines with confined widths as small as 22 nm. Nanoscale ridge apertures were also studied to be used as near field transducers for heat-assisted magnetic recording. They have the capability of transmitting and confining enough energy to increase the temperature of a recording medium without reaching detrimental temperatures themselves. Numerical methods are presented to prove theoretically that a well-designed aperture performs well as a near field transducer. The size of the spot region focused by the aperture could allow us to record data with higher area density than current conventional methods
Carbon nanotube sensor for vibrating molecules
The transport properties of a CNT capacitively coupled to a molecule
vibrating along one of its librational modes are studied and its transport
properties analyzed in the presence of an STM tip. We evaluate the linear
charge and thermal conductances of the system and its thermopower. They are
dominated by position-dependent Franck-Condon factors, governed by a
position-dependent effective coupling constant peaked at the molecule position.
Both conductance and thermopower allow to extract some information on the
position of the molecule along the CNT. Crucially, however, thermopower sheds
also light on the vibrational levelspacing, allowing to obtain a more complete
characterization of the molecule even in the linear regime
Social hotspots life cycle assessment: A case study on social risks of an antimicrobial keyboard cover
This article explores the application of social life cycle assessment (S-LCA) to products or technologies in their earliest developing phase. Indeed, it would be beneficial to have an overview of the social risks generated by novel products and understand what their potential supply chain would be like. To this end, this study presents a S-LCA study for identifying hotspots linked to a novel product: an antimicrobial keyboard cover integrating gold nanoparticles. Firstly, countries which could supply Europe with the input materials required in the system were identified, then by following the S-LCA methodology working hours and working functional hours were estimated. Ultimately, social risks were calculated by combining working functional hours with social risk levels and weights, concerning the relative importance of each category and sub-category.
The analysis helped to determine which countries could supply the materials needed and hence become part of the potential supply chain of antimicrobial keyboard covers integrating gold nanoparticles. Furthermore, it led to the identification of main social hotspots linked to each material used. In general, results show that the stakeholders most at risk of adverse social impacts across different sectors and countries are workers. Indeed, they may be affected on both their rights and work conditions, health and safety. The process of gold mining highlights the difference in terms of social risks between more developed countries, such as Australia and Sweden, and developing countries, such as South Africa. The production of chemicals presents a homogeneity in terms of risk hours associated to the considered European countries
АВТОМАТИЗОВАНА КОМПОЗИЦІЯ СЕМАНТИЧНИХ ВЕБ-СЕРВІСІВ У ВИКОНУВАНІ ПРОЦЕСИ. ПЕРЕКЛАД СТАТТІ «AUTOMATED COMPOSITION OF SEMANTIC WEB SERVICES INTO EXECUTABLE PROCESSES\ud (ПЕРЕКЛАД РЕМАРОВИЧ С.)\ud
Пропонується метод планування для автоматизованої композиції Веб-сервісів, які описані в OWL-S моделях процесу, який може\ud
ефективно боротися з недетермінізмом, частковою спостережністю і складними цілями.\ud
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Abstract\ud
Different planning techniques have been applied to the problem of automated composition of web services. However, in realistic cases, this planning problem is far from trivial: the planner needs to deal with the nondeterministic behavior of web services, the partial observability of their internal status, and with complex goals expressing temporal conditions and preference requirements. We propose a planning technique for the automated composition of web services described in OWL-S process models, which can deal effectively with nondeterminism, partial observability, and complex goals. The technique allows for the synthesis of plans that encode compositions of web services with the usual programming constructs, like conditionals and iterations. The generated plans can thus be translated into executable processes, e.g., BPEL4WS programs. We implement our solution in a planner and do some preliminary experimental evaluations that show the potentialities of our approach, and the gain in performance of automating the composition at the semantic level w.r.t. the automated composition at the level of executable processes
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