Hafnium oxide (HfO2), particularly at low-dimensional scales, exhibits extensive promising applications in ultrahigh density devices like low-power logic and non-volatile memory devices due to its compatibility with current semiconductor technology1-5. However, achieving ferroelectricity (FE) at ultimate scale especially in undoped HfO2 remains challenging as the non-centrosymmetric FE phase, so-called O-III (space group: Pca21) is metastable and FE has a strong tendency of depolarization with the decrease in thickness6. Up to now, this phase has usually stabilized via doping with other elements7-9. But the minimum film thickness is still limited to 1 nm, about 2-unit-cell, to keep FE8. Thinner and undoped films, conducive to further miniature device size and avoid contamination during deposition process, have been a challenge to fabricate on Si substrates. Herein, we report the robust FE observed in undoped HfO2 ultrathin films directly grown on Si substrate via atomic layer deposition (ALD) and post-heat treat in vacuum. The so-fabricated ferroelectric O-III phase contains about 4.48 at% oxygen vacancy, is robust even monoclinic phase (space group: P21/c) coexists. The spontaneous and switchable polarization is remarkably stable, still surviving even in films down to 0.5 nm (one-unit-cell). Our results show the robust FE O-III phase can be obtained in films down to one-unit-cell in thickness on Si, providing a practical way to fabricating this important material in thickness limit.
Abstract In this paper, pure cubic chromium silicide (Cr 3 Si) hollow particles have been successfully synthesized through the solid-state reaction of chromium sesquioxide, silicon powder and metallic lithium in an autoclave at 600 °C for 10 h. The as-prepared samples were characterized by means of X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, which showed that the as-prepared samples were cubic phase Cr 3 Si hollow particles. Furthermore, the oxidation resistance of the obtained Cr 3 Si sample was also investigated.
In this work, we synthesized single crystal of EuCd$_2$As$_2$, which exhibits A-type antiferromagnetic (AFM) order with in-plane spin orientation below $T_N$ = 9.5~K.Optical spectroscopy and transport measurements suggest its topological insulator (TI) nature with an insulating gap around 0.1eV. Remarkably, a dual topological Hall resistivity that exhibits same magnitude but opposite signs in the positive to negative and negative to positive magnetic field hysteresis branches emerges below 20~K. With magnetic force microscopy (MFM) images and numerical simulations, we attribute the dual topological Hall effect to the N\'{e}el-type skyrmions stabilized by the interactions between topological surface states and magnetism, and the sign reversal in different hysteresis branches indicates potential coexistence of skyrmions and antiskyrmions. Our work uncovers a unique two-dimensional (2D) magnetism on the surface of intrinsic AFM TI, providing a promising platform for novel topological quantum states and AFM spintronic applications.
Abstract Chromium boride (CrB) has been prepared by using the chromium trioxide (CrO 3 ) and sodium borohydride (NaBH 4 ) as starting materials in a stainless‐steel autoclave. The X‐ray powder diffraction pattern indicates that the as‐prepared product is orthorhombic phase CrB. Scanning electron microscopy shows that the product is composed of nanosheets and nanoparticles. In addition, the oxidation resistance of the as‐prepared CrB product has also been investigated.
In catalysts,heavy metal pollution is a serious problem.The XRF method was introduced in this paper for determining Ni,V,Sb in FCC catalysts.By the establishment of analytical method,the cause and effect of content determination has been discussed.The matrix effect can be overcome by using calibration standards with fresh catalyst as matrix.Linearity window is 0.10%～1.20% for Ni,0.05%～0.30% for V,0.02%～0.20% for Sb,the correlative coefficients are larger than 0.999 9 for three metals,and measurement RSDs are less than 2%.Results show that the method is fast,accurate and convenient.The results are generally consistent with those from AAS.
Magnetic skyrmions, the topological states possessing chiral magnetic structure with non-trivial topology, have been widely investigated as a promising candidate for spintronic devices. They can also couple with superconducting vortices to form skyrmion-vortex pairs, hosting Majorana zero mode which is a potential candidate for topological quantum computering. A lot of theoretical proposals have been put forward on constructing skyrmion-vortex pairs in heterostructures of chiral magnet and superconductor. Nevertheless, how to generate skyrmion-vortex pairs in a controllable way experimentally remains a significant challenge. We have designed a heterostructure of chiral magnet and superconductor [CoFeB/Ir/Ta]7/Nb in which zero field N\'eel-type skyrmions can be stabilized and the superconducting vortices can couple with the skyrmions when Nb is in the superconducting state. We have directly observed the formation of skyrmion-superconducting vortex pairs which is dependent on the direction of the applied magnetic field. Our results provide an effective method to manipulate the quantum states of skyrmions with the help of superconducting vortices, which can be used to explore the possible existence of Majorana zero mode for future quantum computation.
In this study, silicon carbide (SiC) nanoplates are prepared from the waste quart tube (main composition: silicon dioxide) and waste autoclave lining (main composition: polytetrafluoroethylene) produced in the laboratory. The reaction is carried in a stainless steel autoclave at 600 °C through a magnesium reduction route. Electron microscopy investigations show that the nanoplate thickness of the SiC sample is about 20 nm, and the edge length is about 200 nm. Furthermore, the photoluminescence property of the obtained SiC nanoplates is investigated.
In this paper, we have successfully prepared porous chromium carbide ceramics by a facile one-step method. The synthesis reaction is carried out in an autoclave using waste polyethylene as a carbon source. Generally, the as-obtained chromium carbide is characterized by X-ray diffraction, scanning electron microscope (SEM) and transmission electron microscope. X-ray diffraction pattern shows that the as-obtained sample is cubic phase chromium carbide (Cr23C6). The SEM results show that the sample is composed of porous particles with an average pore size of 200 nm. In addition, the oxidation resistance of the as-obtained Cr23C6 sample was studied by thermogravimetric analyzer. The resource utilization of waste plastic can solve the problems of energy shortage and environment pollution simultaneously to achieve sustainable development.
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