Intercalation of hafnium oxide between epitaxially-grown monolayer graphene and Ir(111)substrate

Intercalation of insulating materials between epitaxial graphene and the metal substrates is highly demanded to restore the intrinsic properties of graphene,and thus essential for the graphene-based devices.Here we demonstrate a successful solution for the intercalation of hafnium oxide into the interface between full-layer graphene and Ir(111)substrate.We first intercalate hafnium atoms beneath the epitaxial graphene.The intercalation of the hafnium atoms leads to the variation of the graphene moire superstructure periodicity,which is characterized by low-energy electron diffraction(LEED)and lowtemperature scanning tunneling microscopy(LT-STM).Subsequently,we introduce oxygen into the interface,resulting in oxidization of the intercalated hafnium.STM and Raman's characterizations reveal that the intercalated hafnium oxide layer could effectively decouple the graphene from the metallic substrate,while the graphene maintains its high quality.Our work suggests a high-k dielectric layer has been successfully intercalated between high-quality epitaxial graphene and metal substrate,providing a platform for applications of large-scale,high-quality graphene for electronic devices.

Solvent extraction of hafnium from thiocyanic acid medium in DIBK-TBP mixed system

A novel process for the separation of hafnium from thiocyanic acid medium using the mixture of diisobutyl ketone（DIBK） and tributyl phosphate（TBP） as the extractant was developed.This extraction process was investigated experimentally as a function of the amount of TBP added,acidity,zirconium and hafnium concentrations,salting-out agent,temperature,duration,respectively.The results show that hafnium is enriched in the organic layer and zirconium is in aqueous layer in DIBK-TBP system.Under the optimal technological conditions：TBP addition 20%（v/v）,aqueous phase acidity 3.0 mol/L,ammonium sulfate addition 0.8-1.25 mol/L,room temperature and extraction time 10 min,the separation factor of hafnium from zirconium is 9.3.

Equilibrium and kinetic data of adsorption and separation for zirconium and hafnium onto MIBK extraction resin

The equilibrium and kinetics of methyl isobutyl ketone(MIBK) extraction resin for adsorption and separation of zirconium and hafnium were studied under the different conditions of acidity,initial total concentrations of zirconium and hafnium and temperature.The equilibrium data of both zirconium and hafnium are found to follow the Freundlich adsorption isotherm,and the Freundlich isotherm constants(KF) are 3.53 and 0.64 mg/g,respectively.The equilibrium data of zirconium also fit the Langmuir adsorption isotherm,and the saturation adsorption capacity(Qmax) and the Langmuir isotherm constant(KL)are 75.93 mg/g and-0.012 7 L/g,respectively.The obtained kinetic data of both zirconium and hafnium are found to fit the HO pseudo-second-order kinetic model,and the rate constants of pseudo-second-order equation(k2) are-0.019 and 0.41 g/(mg·min),respectively.Column tests show that the MIBK extraction resin could be used as efficient adsorbent material for separating hafnium from zirconium.

Separation of hafnium from zirconium in hydrochloric acid solution with di(2-ethylhexyl)phosphoric acid by solvent extraction

The preparation of nuclear-grade zirconium and hafnium is very important for nuclear power. The separation of hafnium from zirconium in a hydrochloric acid solution by solvent extraction was investigated with di(2-ethylhexyl)phosphoric acid(D2 EHPA). The effects of hydrochloric acid concentration, extractant concentration,diluents, and temperature on the distribution coefficient of hafnium and zirconium were studied. The species extracted were ZrOA_2·2 HA and HfOA_2-2 HA. In this process, the separation factors varied with different diluents and followed the order octane > hexane > toluene > chloroform.A high separation factor value of 4.16 was obtained under the conditions of a solution containing 0.05 mol/L HCl and0.01 mol/L D2 EHPA for the separation of hafnium from zirconium. The extraction reaction was endothermic.

Corrosion behavior of hafnium in anhydrous isopropanol and acetonitrile solutions containing bromide ions

The corrosion behaviors of hafnium in Et4NBr isopropanol and acetonitrile(ACN)solutions were investigated usingelectrochemical measurements,ICP-AES and SEM techniques.Results revealed that the open circuit potential gets more positive dueto the increased passivity of the surface oxide film with increasing immersion time until it reaches a steady state value.Thepotentiodynamic anodic polarization curves did not exhibit an active dissolution region near corrosion potential due to the presenceof an oxide film on the electrode surface,which was followed by pitting corrosion.SEM images confirmed the existence of pits onthe electrode surface.Cyclic voltammetry and galvanostatic measurements allowed the pitting potential(φpit)and the repassivationpotential(φp)to be determined.φpit increased with increasing potential scanning rate but decreased with increasing temperature,Br-concentration and ACN concentration.The impedance spectra showed that the resistances of the solution and charge transferdecreased with the increase of ACN concentration.

Intensification of zirconium and hafnium separation through the hollow fiber renewal liquid membrane technique using synergistic mixture of TBP and Cyanex-272 as extractant

The novel synergistic mixture of TBP and Cyanex-272 is used as the extractant in the hollow fiber renewal liquid membrane(HFRLM) technique for Zr/Hf separation.The effects of the chemical and operational parameters such as HNO3 concentration in the donor phase,NH4 F concentration in the acceptor phase,Cyanex-272 and TBP concentration in the liquid membrane phase,the lumen and shell side flow rates,and aqueous/organic volume ratio on the mass transfer and separation performance of HFRLM method were investigated.The obtained results reveal the intensification potential of proposed HFRLM technique for selective extraction of Zr over Hf with separation factor higher than 100.The HFRLM method provides two times higher mass transfer flux in comparison with hollow fiber supported liquid membrane(HFSLM).Also,the HFRLM method shows satisfactory stability for 700 min of continuous operation.The Zr ion transport through the LM phase follows the coupled co-transport mechanism and the diffusion in the renewal layer is recognized as the rate-controlling step in the HFRLM process.Moreover,the Zr mass transfer coefficient and molar flux in the HFRLM method are calculated in the range of 1×10^-8 to 8.4×10^-7 m·s^-1 and 4.9×10^-6 to 20.1×10^-6 mol·m^-2·s^-1,respectively.

Effect of hafnium addition on solidification structure of cast Ti-46Al alloys

To investigate the effect of hafnium addition on the solidification structure, Ti-46AI alloys with nominal compositions of Ti-46AI-xHf （x = 0, 3, 5, 7） （at.%） were arc-melted into small ingots in an argon atmosphere. The characteristics of the macrostructures and microstructures were studied using a linear intercept method, OM, SEM （BSE）, XRD and TEM. The results showed that the ingots with Hf have near lamellar microstructure in columnar and dendrite morphology. The hafnium concentration has a strong effect on the columnar spacing refinement. Increasing Hf from 0 to 7 （at.%）, the columnar spacing can be reduced from - 1000 to-400 μm. Constitute phases of the ingots are a2, a small amount of B2 and 7. Most of the B2 phases, richer in Hf and leaner in AI and Ti, exist on the node of the dendrite core in block shape and a little across the lamellar colonies in stick shape. The 7 phases exist on the boundaries of lamellar colonies in small cellular shape. There also exists a segregation of Hf on the columnar and dendrite core. Particularly, both the a-and ,β-phase form from the melt as prior phases. The possible phase sequencing during solidification and solid-state transformations with Hf is given in this paper.

Low-temperature Rapid Synthesis of Ultrafine Hafnium Carbide Ceramic Powders

Nano hafnium carbide（HfC） powders were synthesized by sol-gel combining hightemperature rapid heat treatment process using citric acid and hafnium tetrachloride as the raw materials. The effects of ball milling treatment on the phase and morphology of pyrolysis products（HfO_2-C） and final HfC product were investigated and the influences of heat treatment temperature and holding time on the structure and properties of the synthesized hafnium carbide powders were also studied. The experimental results showed that the HfO_2-C powders with good uniformity and small particle size were prepared by controlling the milling time. Pure HfC powders with an average particle size of 500 nm were obtained at 1 700 ℃ with a holding time of 3 min, and the oxygen content was about 0.69 wt%, lower than that of the hafnium carbide powders prepared by SPS（0.97%）.

Study of Zirconium and Hafnium Separation by Solvent Extraction Technique from Nitric and Hydrochloric Solutions with Acid, Basic and Neutral Extractants

This paper describes the study of the extraction of Zr and Hf in nitric and hydrochloric media by solvent extraction technique using different types of extractants. The effect of the extractants DEHPA, IONQUEST?801 and CYANEX?272, TBP, CYANEX?923, PRIMENE?JTM, ALAMINE?336 and ALIQUAT?336 was investigated. For acid extractants in both nitric and hydrochloric media, a high degree of extraction was observed, although they had low selectivity in separating the metals. For the acid extractants also, it was not possible to strip the metals from the organic phase through acid solutions. In this case, a stripping solution with very high acidity would be required, and this is not viable. When the basic extractants were used, no metal extraction was observed under the conditions investigated, indicating no extractable anionic species in either media. The optimum zirconium/hafnium separation was achieved using an acidity of 7.0 mol?L?1, nitrate concentration of 9.2 mol?L?1 and 1.5 mol?L?1 of TBP. In these conditions, a separation factor of 12.6 was obtained.

Measurement of L_Ⅲ Subshell Absorption Jump Parameters of Hafnium

The L_Ⅲ subshell absorption jump ratio and jump factor of hafnium have been measured using two different ways which are X-ray attenuation method and Energy Dispersive X-ray Fluorescence technique.The results obtained both ways have been compared with theoretical values.They are in good agreement with each other.

Simultaneous Determination of Zirconium and Hafnium by Dual System and Dual Wavelength Spectrophotometry

A dual system and dual wavelength spectrophotometry (DSDWS) used to simultaneously determine Zr and Hf were proposed. Zr(Hf)-XO-CIMAB and Zr(Hf)-CAB-CDMAA-Triton X-100 were chosen as a pair of chromophoric systems. The difference of chromophoric behaviours between Zr and Hf is increased by the addition of hydrogen peroxide as masking agent and by adjustment of acidity. The apparent molar absorptivities of Zr and Hf are 2.0×105 and 5.0×104 L&middotmol-1&middotcm-1 respectively. The procedure is simple and rapid.

Optimization of parameters, characterization and thermal property analysis of hafnium ethoxide synthesized by electrochemical method

Hafnium ethoxide was synthesized using electrochemical method.Optimization experiments were used to optimizevarious parameters namely Et4NBr concentration(c):0.01?0.06mol/L,solution temperature(t):30?78°C,polar distance(D):2.0?4.0cm and current density(J):100?400A/m2.The electrolytic products obtained under optimum conditions of c=0.04mol/L,t=78°C,D=2.0cm and J=100A/m2were further isolated by vacuum distillation under5kPa.The product was characterized byFourier transform infrared(FT-IR)spectra,nuclear magnetic resonance(NMR)spectra.The results indicated that the product washafnium ethoxide.ICP analysis suggested that the content of hafnium ethoxide in the final product exceeded99.997%.Thermalproperties of the product were analyzed by TG/DTG.The vaporization enthalpy of hafnium ethoxide was found to be79.1kJ/mol.The result confirmed that hafnium ethoxide was suitable for the preparation of hafnium oxide by atomic layer deposition.

High-pressure elastic anisotropy and superconductivity of hafnium:A first-principles calculation

The elastic anisotropy and superconductivity upon hydrostatic compression ofα,ω,and β Hf are investigated using first-principle methods.The results of elastic anisotropies show that they increase with increasing pressure for α and ω phases,while decrease upon compression forβphase.The calculated superconducting transition temperatures are in excellent agreement with experiments.Electron-phonon coupling constants(λ)are increasing with pressure for α and ω phases,while decreasing for β phase.For β phase,the large values ofλare mainly due to the obvious TA1 soft mode.Under further compression,the TA1 soft vibrational mode will disappear gradually.

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.

Rapid label-free SERS detection of foodborne pathogenic bacteria based on hafnium ditelluride-Au nanocomposites

Two-dimensional(2D)nanomaterials have captured an increasing attention in biophotonics owing to their excellent optical features.Herein,2D hafnium ditelluride(HfTe_(2)),a new member of transition metal tellurides,is exploited to support gold nanoparticles fabricating HfTe_(2)-Au nanocomposites.The nanohybrids can serve as novel 2D surface-enhanced Raman scattering(SERS)substrate for the label-free detection of analyte with high sensitivity and reproducibility.Chemical mechanism originated from HfTe_(2) nanosheets and the electromagnetic enhancement induced by the hot spots on the nano-hybrids may largely contribute to the superior SERS effect of HfTe_(2)-Au nanocomposites.Finally,HfTe_(2)-Au nanocomposites are utilized for the label-free SERS analysis of foodborne pathogenic bac-teria,which realize the rapid and ultrasensitive Raman test of Escherichia coli,Listeria mono-cytogenes,Staphylococcus aureus and Salmonella with the limit of detection of 10 CFU/mL and the maximum Raman enhancement factor up to 1.7×10^(8).Combined with principal component analysis,HfTe_(2)-Au-based SERS analysis also completes the bacterial classification without extra treatment.

Nanometer Thick Diffused Hafnium and Titanium Oxide Light Sensing Film Structures

We examine 10 nm thick film structures containing either Hf or Ti sandwiched between two respective oxide layers. The layers are deposited onto heated substrates to create a diffusion region. We observe a high degree of light sensitivity of the electric current through the film thickness for one polarity of an applied voltage. For the other polarity, the current is not affected by the light. We explain the observed phenomenology using the single-particle model based on the existence of interface states on the metal-oxide interfaces.

Optimization of ferroelectricity and endurance of hafnium zirconium oxide thin films by controlling element inhomogeneity

Ferroelectric thin films based on HfO_(2) have garnered increasing attention worldwide,primarily due to their remarkable compatibility with silicon and scalability,in contrast to traditional perovskite-structured ferroelectric materials.Nonetheless,significant challenges remain in their widespread commercial utilization,particularly concerning their notable wake-up effect and limited endurance.To address these challenges,we propose a novel strategy involving the inhomogeneous distribution of Hf/Zr elements within thin films and explore its effects on the ferroelectricity and endurance of Hf_(0.5)Zr_(0.5)O_(2) thin films.Through techniques such as grazing incidence X-ray diffraction,transmission electron microscopy,and piezoresponse force microscopy,we investigated the structural characteristics and domain switching behaviors of these materials.The experimental results indicate that the inhomogeneous distribution of Hf/Zr contributes to improving the frequency stability and endurance while maintaining a large remnant polarization in Hf_(0.5)Zr_(0.5)O_(2) ferroelectric thin films.By adjusting the distribution of Zr/Hf within the Hf_(0.5)Zr_(0.5)O_(2) thin films,significant enhancements in the remnant polarization(2P_(r)>35μC/cm2)and endurance(>109)along with a reduced coercive voltage can be achieved.Additionally,the fabricated ferroelectric thin films also exhibit high dielectric tunability(≥26%)under a low operating voltage of 2.5 V,whether in the wake-up state or not.This study offers a promising approach to optimize both the ferroelectricity and endurance of HfO_(2)-based thin films.

Durable Ru Nanocrystal with HfO_(2)Modification for Acidic Overall Water Splitting

Durable and efficient bi-functional catalyst,that is capable of both oxygen evolution reaction and hydrogen evolution reaction under acidic condition,are highly desired for the commercialization of proton exchange membrane water electrolysis.Herein,we report a robust L-Ru/HfO_(2)heterostructure constructed via confining crystalline Ru nanodomains by HfO_(2)matrix.When assembled with a proton exchange membrane,the bi-functional L-Ru/HfO_(2)catalyst-based electrolyzer presents a voltage of 1.57 and 1.67 V to reach 100 and 300 mA cm^(-2)current density,prevailing most of previously reported Ru-based materials as well as commercial Pt/C||RuO_(2)electrolyzer.It is revealed that the synergistic effect of HfO_(2)modification and small crystalline domain formation significantly alleviates the over-oxidation of Ru.More importantly,this synergistic effect facilitates a dual-site oxide path during the oxygen evolution procedure via optimization of the binding configurations of oxygenated adsorbates.As a result,the Ru active sites maintain the metallic state along with reduced energy barrier for the rate-determining step(^(*)O→^(*)OOH).Both of water adsorption and dissociation(Volmer step)are strengthened,while a moderate hydrogen binding is achieved to accelerate the hydrogen desorption procedure(Tafel step).Consequently,the activity and stability of acidic overall water splitting are simultaneously enhanced.

熔盐辅助合成硼化铪工艺研究

这是一篇冶金工程领域的论文。以氧化铪和碳化硼为原料,采用氯化钠为熔盐介质,通过硼/碳热还原法合成了纯度较高的硼化铪粉体。研究了反应温度、保温时间等合成工艺参数以及原料配比对材料晶相组成和显微结构的影响。结果表明,以氯化钠为熔盐介质时,氧化铪在1300℃的合成温度下开始转化为硼化铪,其温度远低于传统的硼化铪合成所需温度。在硼过量20%,反应温度和保温时间分别为1400℃和2 h所制备的硼化铪粉体纯度较高,X射线衍射中可以明显观察到硼化铪结晶峰,且在扫描电镜中可以观察到紧密团聚形貌的硼化铪。

化学气相沉积HfO_(2)涂层的制备及性能

采用化学气相沉积(CVD)法在难熔金属Mo表面制备厚约8μm的HfO_(2)涂层。通过HSC Chemistry软件从热力学角度探究CVD HfO_(2)的反应过程,分析HfO_(2)涂层的微观形貌、择优生长情况和纳米力学性能,测试涂层与基体的结合力及抗热震性。结果表明:HfO_(2)涂层与基体结合良好,在经历25~2000℃,100次循环热震后涂层表面未出现宏观剥落;划痕法测定的涂层附着力约23 N;在2.5~5μm波段,涂层表面平均发射率为0.48,将Mo在该波段的平均发射率提高了近5倍。