A Grease for Domain Walls Motion in HfO2-based Ferroelectrics

A large coercive field EC of HfO2 based ferroelectric devices poses critical performance issues in their applications as ferroelectric memories and ferroelectric field effect transistors. A new design to reduce EC by fabricating nanolaminate Hf0.5Zr0.5O2 / ZrO2 (HZZ) thin films is used, followed by an ensuing annealing process at a comparatively high temperature 700 °C. High-resolution electron microscopy imaging detects tetragonal-like domain walls between orthorhombic polar regions. These walls decrease the potential barrier of polarization reversal in HfO2 based films compared to the conventional domain walls with a single non-polar spacer, causing about a 40% decrease in EC. Capacitance vs. electric field measurements on HZZ thin film uncovered a substantial increase of dielectric permittivity near the EC compared to the conventional Hf0.5Zr0.5O2 thin film, justifying the higher mobility of domain walls in the developed HZZ film. The tetragonal-like regions served as grease easing the movement of the domain wall and reducing EC

RESEARCH OF AlO и Al NANOPOWDER FORMATION PROCESSES IN PLASMA UNDER THE INFLUENCE OF DEFOCUSED DUAL LASER PULSES ON ALUMINUM IN THE AIR ATMOSPHERE

Изучено влияние величины и типа расфокусировки сдвоенных лазерных импульсов на целенаправленное формирование компонентного и зарядового состава лазерной плазмы при воздействии сдвоенных лазерных импульсов на мишень из алюминиевого сплава АД1 (спектрометр LSS-1). Показано, что при расфокусировке более +1 мм интенсивность линии ионов Al III увеличивается в несколько раз в сравнении с нулевой расфокусировкой, интенсивность линий ионов Al II, N II также более менее монотонно увеличивается. Одновременно с этим интенсивность полос AlO практически становится равным нулю. При значении величины расфокусировки 1 мм проведены исследование процессов образования смешанных нанопорошков AlO и Al при воздействии последовательных серий сдвоенных лазерных импульсов энергией 53 мДж и меж-импульсным интервалом 10 мкс на алюминиевую мишень, помещенную в закрытую стеклянную прямоугольную кювету. Размер первичных частиц AlOоцененный с помощью электронной микроскопии высокого разрешения, преимущественно составил 30 - 40 нм, а Al - 45 - 60 нм. Частицы собраны в агломераты. The influence of the magnitude and type of defocusing of twin laser pulses on the purposeful formation of the component and charge composition of laser plasma under the influence of twin laser pulses on a target made of aluminum alloy AD1 (LSS-1 spectrometer) has been studied. It is shown that when defocusing is more than 1 mm, the intensity of the ion line Al III increases several times in comparison with zero defocusing, the intensity of the ion lines Al II, N II also increases more or less monotonously. At the same time, the intensity of the bands AlO practically becomes zero. At the 1 mm defocusing value, the processes of formation of mixed nanopowders were studied and, under the influence of successive series of double laser pulses with the energy of 53 mJ and the inter-pulse interval of the iss on an aluminum target placed in a closed rectangular glass cuvette, the size of primary Al Oparticles estimated using high-resolution electron microscopy was mainly 30 - 40 nm, and Al -45 - 60 nm. The particles are collected into agglomerates.

Highly ordered N-heterocyclic carbene monolayers on Cu(111)

The benzannulated N-heterocyclic carbene, 1,3-dibenzylbenzimidazolylidene (NHCDBZ) forms large, highly ordered domains when adsorbed on a Cu(111) surface under ultrahigh vacuum conditions. A combination of scanning tunneling microscopy (STM), high resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculations reveals that the overlayer consists of vertical benzannulated NHC moieties coordinating to Cu adatoms. Long range order results from the placement of the two benzyl units from a single NHC on opposite sides of the benzimidazole moiety, with the planes of their aromatic rings approximately parallel to the surface. The organization of three surface-bound benzyl substituents from three different NHCs into a triangular array controls the formation of a highly ordered Kagome-like lattice on the surface. This study illustrates the importance of dispersive interactions to control the binding geometry and self-assembly of the NHC.

Readout of an antiferromagnetic spintronics system by strong exchange coupling of Mn2Au and Permalloy

In antiferromagnetic spintronics, the read-out of the staggered magnetization or Néel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Néel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-established read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are only slightly diminished. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Néel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.

Deep Bayesian local crystallography

The advent of high-resolution electron and scanning probe microscopy imaging has opened the floodgates for acquiring atomically resolved images of bulk materials, 2D materials, and surfaces. This plethora of data contains an immense volume of information on materials structures, structural distortions, and physical functionalities. Harnessing this knowledge regarding local physical phenomena necessitates the development of the mathematical frameworks for extraction of relevant information. However, the analysis of atomically resolved images is often based on the adaptation of concepts from macroscopic physics, notably translational and point group symmetries and symmetry lowering phenomena. Here, we explore the bottom-up definition of structural units and symmetry in atomically resolved data using a Bayesian framework. We demonstrate the need for a Bayesian definition of symmetry using a simple toy model and demonstrate how this definition can be extended to the experimental data using deep learning networks in a Bayesian setting, namely rotationally invariant variational autoencoders.