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- ItemPolarization manipulation of surface acoustic waves by metallization patterns on a piezoelectric substrate(Melville, NY : AIP Publishing, 2020) Weser, R.; Darinskii, A.N.; Schmidt, H.Surface acoustic waves (SAWs) with large normal (vertical) surface displacement at the surface are commonly utilized in microfluidic actuators in order to provide the desired momentum transfer to the fluid. We present an alternative concept using a SAW with comparatively small vertical displacement. Such a SAW passes underneath the microfluidic vessel walls with minimum losses but it needs to be converted inside the vessel into surface vibrations with large vertical displacements. The principal operability of the above idea is illustrated by experimental and numerical studies of the polarization conversion of a leaky SAW on 64° rotated Y-cut of lithium niobate owing to the partial metallization of the substrate surface. In particular, it is found that vertical displacements on the metallized surface can be up to 3.5 times higher as compared to their values on the free surface. Results of computations agree reasonably well with measurements carried out with a laser Doppler vibrometer and allow the clarification of some specific features of this polarization conversion by means of spatial frequency analysis. © 2020 Author(s).
- ItemEffect of post-metallization anneal on (100) Ga2O3/Ti–Au ohmic contact performance and interfacial degradation(Melville, NY : AIP Publ., 2022) Lee, Ming-Hsun; Chou, Ta-Shun; Bin Anooz, Saud; Galazka, Zbigniew; Popp, Andreas; Peterson, Rebecca L.Here, we investigate the effect of post-metallization anneal temperature on Ti/Au ohmic contact performance for (100)-oriented Ga2O3. A low contact resistance of ∼2.49 × 10−5 Ω·cm2 is achieved at an optimal anneal temperature of ∼420 °C for (100) Ga2O3. This is lower than the widely-used temperature of 470 °C for (010)-oriented Ga2O3. However, drastic degradation of the (100)-oriented contact resistance to ∼1.36 × 10−3 Ω·cm2 is observed when the anneal temperature was increased to 520 °C. Microscopy at the degraded ohmic contact revealed that the reacted Ti–TiOx interfacial layer has greatly expanded to 25–30 nm thickness and GaAu2 inclusions have formed between (310)-Ga2O3 planes and the Ti–TiOx layer. This degraded interface, which corresponds to the deterioration of ohmic contact properties, likely results from excess in-diffusion of Au and out-diffusion of Ga, concurrent with the expansion of the Ti–TiOx layer. These results demonstrate the critical influence of Ga2O3 anisotropy on the optimal post-metallization anneal temperature. Moreover, the observed Ti/Au contact degradation occurs for relatively moderate anneal conditions (520 °C for 1 min in N2), pointing to the urgent necessity of developing alternative metallization schemes for gallium oxide, including the use of Au-free electrodes
- ItemFeasibility of electrostatic microparticle propulsion(College Park, MD : Institute of Physics Publishing, 2008) Trottenberg, T.; Kersten, H.; Neumann, H.This paper discusses the feasibility of electrostatic space propulsion which uses microparticles as propellant. It is shown that particle charging in a plasma is not sufficient for electrostatic acceleration. Moreover, it appears technically difficult to extract charged particles out of a plasma for subsequent acceleration without them being discharged. Two novel thruster concepts are proposed. In the first one, particles with low secondary electron emission are charged using energetic electrons in the order of magnitude of 100eV. The second concept charges the particles by contact with needle electrodes at high electrostatic potential (∼20kV). Both methods allow the maximum possible charges on microparticles. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.