Optical printing is a powerful all-optical method that allows the incorporation of colloidal nanoparticles (NPs) onto substrates with nanometric precision. Here, we present a systematic study of the accuracy of optical printing of Au and Ag NPs, using different laser powers and wavelengths. When using light of wavelength tuned to the localized surface plasmon resonance (LSPR) of the NPs, the accuracy improves as the laser power is reduced, whereas for wavelengths off the LSPR, the accuracy is independent of the laser power. Complementary studies of the printing times of the NPs reveal the roles of Brownian and deterministic motion. Calculated trajectories of the NPs, taking into account the interplay between optical forces, electrostatic forces, and Brownian motion, allowed us to rationalize the experimental results and gain a detailed insight into the mechanism of the printing process. A clear framework is laid out for future optimizations of optical printing and optical manipulation of NPs near substrates.
The realization of materials at the nanometer scale creates new challenges for quantitative characterization and modeling as many physical and chemical properties at the nanoscale are highly size and shape-dependent. In particular, the accurate nanometrological characterization of noble metal nanoparticles (NPs) is crucial for understanding their optical response that is determined by the collective excitation of conduction electrons, known as localized surface plasmons. Its manipulation gives place to a variety of applications in ultrasensitive spectroscopies, photonics, improved photovoltaics, imaging, and cancer therapy. Here we show that by combining electron tomography with electrodynamic simulations an accurate optical model of a highly irregular gold NP synthesized by chemical methods could be achieved. This constitutes a novel and rigorous tool for understanding the plasmonic properties of real three-dimensional nano-objects.
In this paper, we investigate theoretically the electromagnetic field enhancement arising from excitation of silver and gold nanowires (NWs) of finite length, capable of sustaining surface plasmon resonances of different multipole order, using the Discrete Dipole Approximation (DDA). The influence of NW length on the degree of enhancement and confinement of the electromagnetic field for each surface plasmon mode is analyzed by a 3D mapping of the near field for different planes around the NW as well by calculating its variation with distance along two different directions, one parallel to and the other perpendicular to the NW axis, outside of the NW. It was found that the enhancement is still significant at relative large distances from the NW end, its decay being of much longer range than that predicted by a simple dipole approximation, especially at near-infrared wavelengths.
In order to examine the controversial hypothesis put forward to explain the entropy step experimentally observed for the stage II to stage I transition for lithium intercalation in graphite, a transparent statistical mechanical model is developed. The results obtained show that the entropy increase can be explained by the change of configurational entropy occurring at occupation of half of the lattice. Comparison with experimental data shows that attractive interactions between intercalated particles in the same layer must be assumed, in agreement with the ansatz made in the original experimental work. 5,6 and graphite, 7,8 are commonly found in electrodes of commercially lithium-ion cells. In addition to the mentioned intercalation materials, there are many others that are currently being studied or used as electrodes in lithium-ion cells. In particular, graphite is the most common material found in anodes of commercial lithium-ion cells.One of the most important features of the intercalation materials is that they can have ions stored in them with little changes in their crystalline structures. This feature allows a fast ion insertion and extraction and therefore high power density cells can be obtained when used as electrodes. However, a fast ion insertion and extraction generates heat in the cell, which can produce high temperature excursions of the cell and a premature aging.It has been demonstrated that a great portion of the heat that is generated in the intercalation materials comes from the intercalation entropy during a discharge. [9][10][11] In this sense, different methods to measure the intercalation entropy have been developed. [12][13][14][15][16][17] In the case of Li-ion insertion into graphite, the experimental curve for entropy as a function of composition, Reference 12, shows a step in the transition of stage II to stage I that could not be explained in the terms presented there. In a subsequent work, 18 two of the previous authors, state that a possible mechanism of the stage I phase formation may involve a 'dilute lithium layer' (noted dil-Li) that would have an alternating 'normal' Li layer (Li) with a hexagonal structure and a dilute lithium layer following the sequence (Li)-G-(dil-Li)-G. However, in a more recent review, Fultz 19 stated that the vibrational entropy resulting from the insertion dominates the entropy, and also he added that there should be a small change in the configurational entropy when compounds are formed in stage I or II, as they are ordered.In a previous work 20 we have proposed a theoretical approach to determine the intercalation entropy, and we applied this approach to the graphite/lithium compound. In order to clarify the origin of this entropy, in the present work we have used a simplified two-level lattice gas model to analyze the configurational contribution to the intercalation entropy of the graphite/lithium compound. The main features of the intercalation entropy are elucidated. z E-mail: eze_leiva@yahoo.com.ar Model and Statistical Mechanical Backgroun...
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