The production of free-standing large aspect ratio metal nanofilms by femtosecond laser separation
(2009)
We demonstrate a new method for the production of free-standing metal films of thickness down to several tens of nanometres. Films of different metals as well as multilayer structures have been produced by means of femtosecond laser-induced separation of evaporated layers from a plane glass surface. This technology enables the production of large-area films with different properties for optical or nanotechnological applications. We study the properties of the film and demonstrate the possibility of high-pass filtering of electrons with an energy of several keV by means of the free-standing films. The physical mechanisms leading to the film separation under femtosecond laser radiation are discussed.
Silicon microprotrusions with tailored chirality enabled by direct femtosecond laser ablation
(2020)
Here, we report on formation of nanoprotrusions on the surface of a bulk crystalline silicon wafer under femtosecond-laser ablation with a donut-shaped laser beam. By breaking circular symmetry of the irradiating donut-shaped fs-pulse beam, a switch in geometry of the formed surface nanoprotrusions from regular to chiral was demonstrated. The chirality of the obtained Si nanostructures was promoted with an asymmetry degree of the laser beam. An uneven helical flow of laser-melted Si caused by asymmetry of the initial intensity and temperature pattern on the laser-irradiated Si surface explains this phenomenon. Chirality of the formed protrusions was confirmed by visualizing cross-sectional cuts produced by focused ion beam milling as well as Raman activity of these structures probed by circularly polarized light with opposite handedness. Our results open a pathway towards easy-to-implement inexpensive …
The need for portable and on site screening methods for viruses is evident in face of virus infections that can spread lastly in a heavily connected world. A robust and efficient method for detecting viruses is a novel technique called Plasmon Assisted Microscopy of Nanoobjects. It is based on the acquisition of images from a sensor surface exploiting the behavior of surface plasmons in the presence of nanoobjects. In this paper an efficient image analysis approach with respect to the requirements of the sensor is presented and an embedded image processing system for this purpose is introduced. The processing pipeline comprises three steps and starts with restorating the images by removing the background and filtering artifacts. The acquired image series is analyzed pixel by pixel in a second pipeline step in order to detect pixels containing nanoobjects. In a last step pixels are aggregated to nanoobject structures. The paper introduces in the context of this virus detection method a configurable embedded system that was used for rapid prototyping of the image analysis algorithms in a flexible way. (C) 2010 Elsevier B.V. All rights reserved.
Current self-sustained oscillations in a Townsend discharge are studied analytically. The proposed method for solving simple equations is applicable even when the Townsend coefficient of electron reproduction g (the main factor governing the oscillations) cannot be determined theoretically. The coefficient g is related to the discharge current-voltage characteristic, which can be obtained experimentally or from numerical simulations. Self-oscillating solutions (limit cycles) are found under various conditions. The mechanisms governing the excitation and stabilization of the solutions obtained are interpreted. It is shown that the waveform of the undamped oscillations may change significantly (the current peaks are smoothed, and the oscillation period decreases) when a weak constant cathode current, which is presumably related to the emission caused by slowly diffusing metastable molecules, is included in the equations.
Self-sustained current oscillations in a Townsend discharge that is excited in a short plane discharge gap and is uniform along the electrode surface are investigated experimentally. A thin semiconductor plane serves as a discharge cathode, a ballast resistor, and an additional capacitor in the dc power supply circuit. The domain of existence and the frequency and waveform, of oscillations are determined over a wide pressure range.