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排序方式: 共有182条查询结果,搜索用时 31 毫秒
91.
研究了Ni/HfO2(10 nm)/Pt存储单元的阻变特性和机理.该器件具有forming-free的性质,还表现出与以往HfO2(3 nm)基器件不同的复杂的非极性阻变特性,并且具有较大的存储窗口值(105).存储单元的低阻态阻值不随单元面积改变,符合导电细丝阻变机理的特征.采用X射线光电子能谱仪分析器件处于低阻态时的阻变层HfO2薄膜的化学组分以及元素的化学态,结果表明,Ni/HfO2/Pt阻变存储器件处于低阻态时的导电细丝是由金属Ni导电细丝和氧空位导电细丝共同形成的. 相似文献
92.
Revealing the Unusual Rigid Boron Chain Substructure in Hard and Superconductive Tantalum Monoboride
Dr. Shuailing Ma Prof. Kuo Bao Dr. Qiang Tao Dr. Li Li Dr. Yanping Huang Dr. Xiaoli Huang Dr. Yongsheng Zhao Dr. Chunhong Xu Prof. Pinwen Zhu Prof. Tian Cui 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):5051-5057
Poor electrical conductivity severely limits the diverse applications of high hardness materials in situations where electrical conductivities are highly desired. A “covalent metal” TaB with metallic electrical conductivity and high hardness has been fabricated by a high pressure and high temperature method. The bulk modulus, 302.0(4.9) GPa, and Vickers hardness, 21.3 GPa, approaches and even exceeds that of traditional insulating hard materials. Meanwhile, temperature-dependent electrical resistivity measurements show that TaB possesses metallic conductivity that rivals some widely-used conductors, and it will transform into a superconductor at Tc=7.8 K. Contrary to common understanding, the hardness of TaB is higher than that of TaB2, which indicates that low boron concentration borides could be mechanically better than the higher boron concentration counterparts. Compression behavior and first principles calculations denote that the high hardness is associated with the ultra-rigid covalent boron chain substructure. The hardness of TaB with different topologies of boron substructure shows that besides incorporating higher boron content, manipulating light element backbone configurations is also critical for higher hardness amongst transition metal borides with identical boron content. 相似文献
93.
Leonardo Tensi Dr. Robert D. J. Froese Dr. Roger L. Kuhlman Prof. Dr. Alceo Macchioni Prof. Dr. Cristiano Zuccaccia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3758-3766
Heterobimetallic complexes with inequivalent bridging alkyl chains are very often invoked as key intermediates in many catalytic processes, yet their interception and structural characterization are lacking. Such complexes have been prepared from reactions of the cationic cyclometalated hafnocene [CpPrCp Hf][B(C6F5)4] ( 1 ) with main group metal alkyls to afford the corresponding hetero-bridged cationic products, [CpPrCp Hf(μ-R)E(R)n][B(C6F5)4] (E=Al or Zn; R=Me, Et, or iBu). NMR and DFT studies demonstrate that both bridging alkyls establish agostic interactions with Hf, which are appreciably stronger for ethyl rather than methyl groups. Hf–Al and Hf–Zn distances are surprisingly short and only slightly longer than computed Hf–Al or Hf–Zn single bond lengths (2.80 Å). Finally, a reaction of [CpPrCp Hf(μ-Me)Zn(Me)][B(C6F5)4] with excess ZnMe2 yields an unprecedented heterotrimetallic species, [(CpPr)2Hf(μ-Me)(ZnMe)(μ3-CH2)ZnMe][B(C6F5)4], the detailed structure of which is elucidated by a combination of NMR spectroscopic methods and molecular calculations. 相似文献
94.
95.
基于密度泛函理论平面赝势波法的第一性原理计算,研究过渡金属单硼化物TMB(以3d系列中的TiB、VB和CrB;4d系列中的ZrB、NbB和MoB;5d系列中的HfB、TaB和WB为例)的热力学稳定性、力学性质和微观机制.发现过渡金属单硼化物的热力学稳定与硬度异常的规律.当价电子浓度为8 e·(f.u.)-1时,热力学最稳定,且硬度最高.计算TMB的电子结构,发现TMB的价电子浓度为8 e·(f.u.)-1时,pd共价键合,有效阻碍了金属双层之间的位错滑动,防止剪切变形,致使其具有高硬度. 相似文献
96.
97.
Luis C. Ortiz-Dosal Eleazar S. Kolosovas-Machuca M. Carmen Rodríguez-Aranda Edgar López-Luna Heber Hernández-Arriaga Gustavo Vera-Reveles 《Analytical letters》2017,50(18):2937-2943
Self-assembled monolayers of 3-aminopropyltriethoxysilane (APTES) are commonly used to promote adhesion between substrates and organic or metallic materials with applications ranging from advanced composites to biomolecular lab-on-a-chip devices. In this work, the silanization on hafnium oxide (HfO2) films is reported. The layers of HfO2 were deposited on Si (001) substrates by atomic layer deposition. The grown HfO2 films were modified in accordance with three main steps: oxidation, silanization, and cross-linking of the APTES monolayer using glutaraldehyde as cross-linking agent. Microscopic features were characterized by atomic force microscopy. Further, both bovine serum albumin and antibovine serum albumin agents were deposited on the samples to test their potential use as the immunosensor. 相似文献
98.
Atomic Layer Deposition of Hafnium(IV) Oxide on Graphene Oxide: Probing Interfacial Chemistry and Nucleation by using X‐ray Absorption and Photoelectron Spectroscopies
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Theodore E. G. Alivio Luis R. De Jesus Dr. Robert V. Dennis Ye Jia Dr. Cherno Jaye Dr. Daniel A. Fischer Prof. Uttam Singisetti Prof. Sarbajit Banerjee 《Chemphyschem》2015,16(13):2842-2848
Interfacing graphene with metal oxides is of considerable technological importance for modulating carrier density through electrostatic gating as well as for the design of earth‐abundant electrocatalysts. Herein, we probe the early stages of the atomic layer deposition (ALD) of HfO2 on graphene oxide using a combination of C and O K‐edge near‐edge X‐ray absorption fine structure spectroscopies and X‐ray photoelectron spectroscopy. Dosing with water is observed to promote defunctionalization of graphene oxide as a result of the reaction between water and hydroxyl/epoxide species, which yields carbonyl groups that further react with migratory epoxide species to release CO2. The carboxylates formed by the reaction of carbonyl and epoxide species facilitate binding of Hf precursors to graphene oxide surfaces. The ALD process is accompanied by recovery of the π‐conjugated framework of graphene. The delineation of binding modes provides a means to rationally assemble 2D heterostructures. 相似文献
99.
Boglio C Micoine K Rémy P Hasenknopf B Thorimbert S Lacôte E Malacria M Afonso C Tabet JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(19):5426-5432
Monolacunary polyoxotungstates [alpha(1)-P(2)W(17)O(61)](10-) and [alpha-PW(11)O(39)](7-) react with HfCl(4) to yield [alpha(1)-HfP(2)W(17)O(61)](6-) and [alpha-Hf(OH)PW(11)O(39)](4-), isolated as organo-soluble tetrabutylammonium (TBA) salts. Subsequent analyses, including mass spectrometry, show that they are stronger Lewis acids than (TBA)(5)H(2)[alpha(1)-YbP(2)W(17)O(61)]. The new polyoxotungstates catalyze Lewis acid mediated organic reactions, such as Mukaiyama aldol and Mannich-type additions. In particular, reactions with aldehydes, which were impossible with lanthanide polyoxotungstates, are made possible. Thus these modifications of the polyoxometalate composition allowed fine tuning of the Lewis acidity. The catalysts could be easily recovered and reused. 相似文献
100.
Michael A. Bau Stefan Wiesler Sara L. Younas Dr. Jan Streuff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10531-10545
This minireview provides a survey of the various synthetic approaches to chiral ansa-metallocenes of Ti, Zr, and Hf containing a carbon-based bridge. The individual strategies to install substitution patterns at either the cyclopentadienyl framework or the bridging unit are highlighted with focus on the progress made towards a direct preparation of single complex stereoisomers. The review further includes the discussion of potential problems such as the formation of undesired diastereomers, the threat of racemization of enantiopure material, and synthetic challenges originating from the synthesis, purification, and isolation of the target complexes. The review has been written with the goal in mind to facilitate the design and synthesis of new chiral ansa-metallocene derivatives for emerging research areas in asymmetric catalysis and organometallic chemistry. 相似文献