9 research outputs found
A physical method for investigating defect chemistry in solid metal oxides
The investigation of the defect chemistry of solid oxides is of central
importance for the understanding of redox processes. This can be performed by
measuring conductivity as a function of the oxygen partial pressure, which is
conventionally established by using buffer gas mixtures or oxygen pumps based
on zirconia. However, this approach has some limitations, such as difficulty
regulating oxygen partial pressure in some intermediate-pressure regions or the
possibility of influencing the redox process by gases that can also be
incorporated into the oxide or react with the surface via heterogeneous
catalysis. Herein, we present an alternative physical method in which the
oxygen partial pressure is controlled by dosing pure oxygen inside an
ultra-high vacuum chamber. To monitor the conductivity of the oxide under
investigation, we employ a dedicated four-probe measurement system that relies
on the application of a very small AC voltage, in combination with lock-in data
acquisition using highly sensitive electrometers, minimizing the
electrochemical polarization or electro-reduction and degradation effects. By
analyzing the model material SrTiO3, we demonstrate that its characteristic
redox behavior can be reproduced in good agreement with the theory when
performing simultaneous electrical conductivity relaxation (ECR) and
high-temperature equilibrium conductivity (HTEC) measurements. We show that the
use of pure oxygen allows for a direct analysis of the characteristic oxygen
dose, which opens up various perspectives for a detailed analysis of the
surface chemistry of redox processes.Comment: 25 page
Misfit strain dependence of ferroelectric and piezoelectric properties of clamped (001) epitaxial Pb(Zr0.52,Ti0.48)O3 thin films \ud
A study on the effects of the residual strain in Pb(Zr0.52Ti0.48)O3 (PZT) thin films on the ferroelectric and piezoelectric properties is presented. Epitaxial (001)-oriented PZT thin film capacitors are sandwiched between SrRuO3 electrodes. The thin film stacks are grown on different substrate-buffer-layer combinations by pulsed laser deposition. Compressive or tensile strain caused by the difference in thermal expansion of the PZT film and substrate influences the ferroelectric and piezoelectric properties. All the PZT stacks show ferroelectric and piezoelectric behavior that is consistent with the theoretical model for strained thin films in the ferroelectric r-phase. We conclude that clamped (001) oriented Pb(Zr0.52Ti0.48)O3 thin films strained by the substrate always show rotation of the polarization vecto
Использование угловых отражателей при ультразвуковом контроле сварных швов пластмассовых трубопроводов
Рассмотрена возможность применения вертикального цилиндрического отверстия вместо зарубки для настройки чувствительности при контроле сварных швов трубопроводов из пластмасс. Обоснована целесообразность применения для расчета эквивалентной площади дефектов в пластмассе формул, полученных эмпирически [4,6] для стали. Проведены расчеты эквивалентной площади дефектов при использовании в качестве опорного отражателя углового цилиндрического отверстия для частот 2,5 и 5 МГц
Non-destructive piezoelectric characterisation of Sc doped aluminium nitride thin films at wafer level
Scandium doped aluminium nitride (ScAlN) gained much attention during last years, since its piezoelectric response is much enlarged as compared to pure AlN films. Above 30% Sc the films are of high interest for piezoMEMS sensing and actuation, ultrasound generation, as well as energy harvesting applications. In this work, piezo-performance uniformity maps are presented for 20% and 33% Sc containing films, sputter deposited on 200-mm wafers. Furthermore, we employ a new method to determine the electro-mechanical coupling k(t)(2). Coupling results for various Sc/(Sc+Al) concentration (0, 6, 20, 26, 33%) are shown. In addition, the dielectric constant epsilon(r) and dielectric loss tan delta, and the transversal and the longitudinal piezoelectric coefficients, e(31,f) and d(33,f,) were measured. The wafers show a high with-in-wafer uniformity (1 sigma uniformity < 2% for Sc20Al80N and < 1% for Sc33Al67N). The highest coupling k(t)(2) = 21.2% was achieved for a 33% Sc film. The presented Al-Sc property-uniformity maps provide a good foundation for ScAlN based MEMS device design and manufacturing
Analysis of transient currents during ultrafast switching of TiO2 nanocrossbar devices
In this letter, bipolar fast-pulse switching in TiO2-based nanocrossbar devices was investigated. A dedicated measurement setup was used to measure the transient currents during 5-ns resistive switching. Transient peak currents for the SET and RESET processes were as high as 200 and 230 mu A, respectively. The currents observed during fast-pulse switching are explained and simulated by Joule heating, which is needed for fast oxygen-vacancy movement. The measured transient currents enable a further optimization of resistive switches based on TiO