First-Principles Calculations of Phonons and Thermodynamic Properties of Zr(Hf)S2-Based Nanotubes

Comparative hybrid density functional calculations on the structure, stability, and phonon frequencies of monolayers and single-walled nanotubes are performed for Zr(Hf)S₂ disulfides. The first-principles calculations of HfS₂-based nanotubes are made for the first time. The symmetry analysis of infrared and Raman active vibrational modes in ZrS₂ and HfS₂ nanotubes is made using the induced representations of the isogonal point groups of line groups. It is shown that the number of infrared and Raman active modes is constant for NTs with the same chirality type. The correlation of the phonon modes of the nanotubes of relatively large diameters with those of monolayer is analyzed. The thermodynamic functions of monolayers and nanotubes with various chirality and diameters are calculated on the basis of the obtained phonon frequencies. It is established that the phonon contribution to the nanotube strain energy is small, but may be important for an accurate estimate of the stability of the nanotubes of small diameters. The calculated results show that the thermal contributions to Helmholtz free energy are positive; thereby they slightly reduce the stability of ZrS₂ and HfS₂ nanotubes at elevated temperatures. © 2019 Wiley Periodicals, Inc.     

High‐temperature monoclinic α‐SrHfF6, and isostructural α‐SrZrF6: associating Hf2F12 bipolyhedra and SrF8 snub disphenoids

The structure of the high‐temperature monoclinic variety α‐SrHfF₆ (strontium hafnium hexafluoride) [and of isostructural α‐SrZrF₆ (strontium zirconium hexafluoride)] associates Hf₂F₁₂ bipolyhedra and SrF₈ snub disphenoids, forming zigzag twisted [SrF₆]_n layers. The distribution of the Hf and Sr polyhedra forms a three‐dimensional framework which can be related to the family of anion‐excess ReO₃‐related superstructures. α‐SrHfF₆ corresponds to a new ABX₆ type and is compared to the other main families already described. A partial amorphization of this structure is observed in samples quenched from the melt.     

缺陷对电荷俘获存储器写速度影响

基于密度泛理论的第一性原理以及VASP软件,研究了电荷俘获存储器(CTM)中俘获层HfO2在不同缺陷下(3价氧空位(VO3)、4价氧空位(VO4)、铪空位(VHf)以及间隙掺杂氧原子(IO))对写速度的影响.对比计算了HfO2在不同缺陷下对电荷的俘获能、能带偏移值以及电荷俘获密度.计算结果表明:VO3,VO4与VHf为单性俘获,IO则是双性俘获,HfO2在VHf时俘获能最大,最有利于俘获电荷;VHf时能带偏移最小,电荷隧穿进入俘获层最容易,即隧穿时间最短;同时对电荷俘获密度进行对比,表明VHf对电荷的俘获密度最大,即电荷被俘获的概率最大.通过对CTM的写操作分析以及计算结果可知,CTM俘获层m-HfO2在VHf时的写速度比其他缺陷时的写速度快.本文的研究将为提高CTM操作速度提供理论指导.     

离子束技术对氧化铪薄膜性能的影响

 在基底清洗、薄膜沉积和薄膜后处理三个阶段均采用离子束技术,制备了氧化铪薄膜,并对薄膜的光学性能、表面特性和激光损伤阈值特性进行测试和研究。结果表明,利用离子束技术清洗基底可以增强表面吸附;离子束辅助沉积在合适离子束能量下可以得到高堆积密度、高损伤阈值的薄膜;离子束后处理氧化铪薄膜可以降低表面粗糙度,改善抗激光损伤阈值。说明在三个薄膜制备阶段同时采用合适的离子束参数可以制备出结构致密、阈值高、表面粗糙度好的氧化铪薄膜。     

First principles study of hafnium intercalation between graphene and Ir(111) substrate

The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials. Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures, showing potential applications in electronic devices. Here we theoretically investigate the hafnium intercalation between graphene and Ir(111). It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius, which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures. Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.     

离子束技术对氧化铪薄膜性能的影响

在基底清洗、薄膜沉积和薄膜后处理三个阶段均采用离子束技术,制备了氧化铪薄膜,并对薄膜的光学性能、表面特性和激光损伤阈值特性进行测试和研究。结果表明,利用离子束技术清洗基底可以增强表面吸附;离子束辅助沉积在合适离子束能量下可以得到高堆积密度、高损伤阈值的薄膜;离子束后处理氧化铪薄膜可以降低表面粗糙度,改善抗激光损伤阈值。说明在三个薄膜制备阶段同时采用合适的离子束参数可以制备出结构致密、阈值高、表面粗糙度好的氧化铪薄膜。     

钛、锆、铪的二茂铁基甲酰丙酮螯合物和二茂铁基二茂钛络合物的质谱

本文研究了钛、锆、铪的二茂铁基β-双酮螯合物(1～6)和取代的二茂铁基钛茂络合物(7～8)的质谱。螯合物1～4的质谱中出现强的分子离子和特征碎片离子,而5～6未出现分子离子峰,7和8络合物出现低强度的分子离子峰。     

Solvent-Activated Hafnium-Containing Zeolites Enable Selective and Continuous Glucose–Fructose Isomerisation

The isomerisation of glucose to fructose is a critical step towards manufacturing petroleum-free chemicals from lignocellulosic biomass. Herein we show that Hf-containing zeolites are unique catalysts for this reaction, enabling true thermodynamic equilibrium to be achieved in a single step during intensified continuous operation, which no chemical or biological catalyst has yet been able to achieve. Unprecedented single-pass yields of 58 % are observed at a fructose selectivity of 94 %, and continuous operation for over 100 hours is demonstrated. The unexpected performance of the catalyst is realised following a period of activation within the reactor, during which time interaction with the solvent generates a state of activity that is absent in the synthesised catalyst. Mechanistic studies by X-ray absorption spectroscopy, chemisorption FTIR, operando UV/Vis and ¹H–¹³C HSQC NMR spectroscopy indicate that activity arises from isolated Hf^IV atoms with monofunctional acidic properties.