Subcritical switching dynamics and humidity effects in nanoscale studies of domain growth in ferroelectric thin films

Ferroelectric domain switching in c-axis-oriented epitaxial Pb(Zr$_{0.2}$Ti$_{0.8}$)O$_3$ thin films was studied using biased scanning probe microscopy tips. While linear and logarithmic dependence of domain size on tip bias and writing time, respectively, are well known, we report an additional linear dependence on relative humidity in the 28-65% range. We map out the switched domain size as a function of both the tip bias and the applied pulse time and describe a growth-limited regime for very short pulses and a nucleation-limited regime for very low tip bias. Using "interrupted-switching" measurements, we probe the nucleation regime with subcritical pulses and identify a surprisingly long relaxation time on the order of 100 ms, which we relate to ionic redistribution both on the surface and within the thin film itself.Comment: 11 pages, 4 figure

Understanding polarization vs. charge dynamics effects in ferroelectric-carbon nanotube devices

To optimize the performance of multifunctional carbon nanotube-ferroelectric devices, it is necessary to understand both the polarization and charge dynamics effects on their transconductance. Directly comparing ferroelectric Pb(Zr0.2Ti0.8)O3 and dielectric SrTiO3 field effect transistors, we show that the two effects strongly compete, with transient charge dynamics initially masking up to 40% of the ferroelectric field effect. For applications, it is therefore crucial to maximize the quality of the ferroelectric film and the interface with the carbon nanotube to take full advantage of the switchable polarization.Comment: 5 pages, 4 figure

Evolution of humoral immune response to SARS-CoV-2 mRNA vaccine in liver transplant recipients - a longitudinal study.

BACKGROUND AND AIM Liver transplant recipients show suboptimal vaccine-elicited immune responses to severe acute respiratory coronavirus 2 (SARS-CoV-2) vaccination. This study aimed to assess real-world data on SARS-CoV-2 antibodies after the second and third SARS-CoV-2 vaccination in liver transplant recipients in Switzerland. METHODS We enrolled liver transplant recipients who attended regular follow-up visits between 01/07/2021 and 30/04/2022 at the outpatient clinic of the Department of Visceral Surgery and Medicine at Bern University Hospital, Switzerland. Following the Swiss Federal Office of Public Health recommendations, we measured SARS-CoV-2 anti-spike IgG antibodies in 117 liver transplant recipients ≥4 weeks after the second SARS-CoV-2 mRNA vaccination from 07/2021-04/2022. In case of antibody levels of 100 AU/ml were defined as "responders", those with 12-100 AU/ml as "partial responders" and those with <12 AU/ml as "non-responders". RESULTS After two vaccinations, 36/117 (31%) were responders, 42/117 (36%) were partial responders and 39/117 (33%) were non-responders. The humoral immune response improved significantly after the third vaccination, resulting in 31/55 (56%) responders among the previous partial or non-responders. A total of 26 patients developed COVID-19, of whom two had a moderate or severe course (both non-responders after three doses). DISCUSSION One third of liver transplant recipients showed an optimal response following two vaccinations; a third dose achieved a complete antibody response in more than half of partial and non-responders. We observed only one severe course of COVID-19 and no deaths from COVID-19 in the vaccinated liver transplant recipients

Probing nanoscale limits of polarization switching and controlling electronic properties in devices combining carbon nanotubes and ferroelectrics

La présente thèse est consacrée en grande partie à l'étude des interactions entre les nanotubes de carbone et les couches minces ferroélectriques. D'une part, l'effet de champ ferroélectrique peut moduler de façon réversible et non-volatile la densité de porteurs de charge de nanotubes semi-conducteurs. D'autre part, des nanotubes mis sous tension électrique peuvent être utilisés comme une source de champ électrique extrêmement concentrée pour modifier localement la polarisation d'une couche mince ferroélectrique sous-jacente. Ces effets ont été explorés dans cette thèse dans le cadre de la création de transistors à effet de champ ferroélectrique formés par des nanotubes semi-conducteurs déposés sur une couche mince ferroélectrique de Pb(Zr0.2Ti0.8)O3. De tels transistors sont non-volatils tout en permettant une lecture non-destructive. L'utilisation de nanotubes de carbone comme électrode a permis la création et l'étude de domaines ferroélectriques de dimensions nanométriques avec une durée de vie supérieure à 1,5 an

Minimum domain size and stability in carbon nanotube-ferroelectric devices

Ferroelectric domain switching in c-axis-oriented epitaxial Pb(Zr0.2Ti0.8)O3 thin films was studied using different field geometries and compared to numerical simulations and theoretical predictions. With carbon nanotubes as electrodes, continuous nanodomains as small as 9 nm in radius in a 270 nm thick film could be switched, remaining stable for over 20 months. Defect pinning of domain walls appears to play a key role in stabilizing such domains, below the predicted thermodynamic size limit.Comment: 5 pages, 4 figure

Dynamic response and roughening of ferroelectric domain walls driven at planar electrode edges

AbstractUnderstanding and controlling the motion, stability, and equilibrium configuration of ferroelectric domain walls is key for their integration into potential nanoelectronics applications, such as ferroelectric racetrack memories. Using piezoresponse force microscopy we analyse the growth and roughness of ferroelectric domains in epitaxial thin film Pb(Zr0.2Ti0.8)O3, driven by the electric fields at straight edges of planar electrodes at two different temperatures. This device relevant geometry allows us to confirm that the domain walls are well described as 1-dimensional monoaffine elastic interfaces driven in random-bond disorder. However, we observe a progressive increase of roughness as initially flat domain walls move through the disorder landscape, which could prove a significant limiting factor for racetrack-type memories using ferroelectrics

Good Practice Guide on the calibration procedure for traceable electrical power measurement at the generator, converter and the filter using a reference power measurement system

&lt;p&gt;This report has been produced within the EMPIR project entitled &lt;i&gt;Traceable Mechanical and Electrical Power Measurement for Efficiency Determination of Wind Turbines&lt;/i&gt; or &lt;i&gt;19ENG08 WindEFCY.&lt;/i&gt; More information about this collaborative research project can be found on the project's website &lt;a href="https://www.ptb.de/empir2020/windefcy/home/"&gt;https://www.ptb.de/empir2020/windefcy/home/&lt;/a&gt;. This report is a good practice guide on the calibration procedure for traceable electrical power measurement in nacelle test benches using a reference power measurement system.&lt;/p&gt;&lt;p&gt;The project 19ENG08 – WindEFCY has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme.&lt;/p&gt

Pre-normalisation of grid impedance measurement in the power line communication frequency band

Power line Frequency and Time dependent Grid Impedance (FTdGI) influences the propagation of the Power Line Communication (PLC) signals and impacts the communication with Smart Meters. The precise measurement of the power line impedance is ill-defined and only possible with a limited number of instruments. This paper presents the results of the Z-NET project aiming to establish a metrological traceable grid impedance standard that enables the objective comparison of the proposed measuring techniques. A Static Impedance Reference (SIR) was defined, built, and characterized. Comparative results of measurements with five different impedance analysers are presented