arXiv subjects

Achim Wixforth

Publications and source records attributed to Achim Wixforth.

23 records · Page 2Linked to original sources

arXiv2010

Dynamics of Fluid Vesicles in Flow through Structured Microchannels

The dynamics of fluid vesicles is studied under flow in microchannels, in which the width varies periodically along the channel. Three types of flow instabilities of prolate vesicles are found. For small quasi-spherical vesicles -- compared to the average channel width -- perturbation theory predicts a transition from a state with orientational oscillations of a fixed prolate shape to a state with shape oscillations of symmetrical ellipsoidal or bullet-like shapes with increasing flow velocity. Experimentally, such orientational oscillations are observed during the slow migration of a vesicle towards the centerline of the channel. For larger vesicles, mesoscale hydrodynamics simulations and experiments show similar symmetric shape oscillation at reduced volumes $V^* \gtrsim 0.9$. However, for non-spherical vesicles with $V^* \lesssim 0.9$, shapes are found with two symmetric or a single asymmetric tail.

cond-mat.soft↗

arXiv2007

Shock Waves in Nanomechanical Resonators

The dream of every surfer is an extremely steep wave propagating at the highest speed possible. The best waves for this would be shock waves, but are very hard to surf. In the nanoscopic world the same is true: the surfers in this case are electrons riding through nanomechanical devices on acoustic waves [1]. Naturally, this has a broad range of applications in sensor technology and for communication electronics for which the combination of an electronic and a mechanical degree of freedom is essential. But this is also of interest for fundamental aspects of nano-electromechanical systems (NEMS), when it comes to quantum limited displacement detection [2] and the control of phonon number states [3]. Here, we study the formation of shock waves in a NEMS resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves we are able to determine the anomalous acoustocurrent. This current is only found in the regime of shock wave formation. We ontain very good agreement with model calculations.

cond-mat.mes-hall↗

arXiv2005

Pulsed Laser Deposition of La0,67Ca0,33MnO3 thin films on LiNbO3

Surface Acoustic Waves on piezoelectric substrates can be used to investigate the dynamic conductivity of thin films in a non-contact and very sensitive way, especially at low conductivities. Here, we report on such surface acoustic wave studies to characterize thin manganite film like La0.67Ca0.33MnO3, exhibiting a Jan Teller effect with a strong electron phonon interaction and a metal insulator transition at high temperatures. We report on the deposition of La0.67Ca0.33MnO3 on piezoelectric substrates (LiNbO3 in different crystal cuts) employing a pulsed laser deposition technique. The structural qualities of the thin films are examined by X-Ray Diffraction, Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy. For the electrical characterization, we employ the surface acoustic wave technique, accompanied by conventional DC-resistance measurements for comparison.

cond-mat.stat-mech↗

arXiv2004

Observation of single defect relaxation in a freely suspended nano resonator

Relaxation of single defects in a nanometer sized resonator is observed by coupling surface acoustic waves to a freely suspended beam. The surface waves act on the resonator as driving forces being able to modify the internal friction in the beam. In analogy to classical experiments on internal friction in macroscopic samples, we perform frequency, amplitude, and temperature dependent experiments on the nano resonator and find a scenario which is consistent with the observation of single defect relaxation.

cond-mat.other↗

arXiv2003

Acoustic "distributed source" mixing of smallest fluid volumes

Acoustically driven mixing of small fluid volumes is reported. Using surface acoustic waves on a mixer chip, conversion of those into bulk waves, and employing wave guiding effects enables us to distribute a set of "virtual sources" for acoustic streaming over large areas. we demonstrate the applicability of our mixing technique to micro array applications, for mixing of individual wells in a micro titer plate, and other state-of-the-art hybridization assays.

physics.flu-dyn↗