Ratio Of HF Research Articles

Fabrication and electrical properties of flexible polymer-based MIM capacitors of high-k nanolaminate dielectrics of HfO2–SnO2–TiO2 with ultrathin Al2O3 insertion layer by plasma-enhanced atomic layer deposition

Abstract Flexible metal–insulator–metal (MIM) capacitors of high-k nanolaminate HfO2–SnO2–TiO2 thin films were fabricated on several polymer substrates of polyethylene terephthalate, polyimide and epoxy resin at 80 °C by plasma-enhanced atomic layer deposition. The electrical properties were optimized by adjusting the sub-cycle ratio of Hf: Sn: Ti to 6: 5: 4. In order to reduce the leakage current density of flexible capacitors, the ultrathin Al2O3 layer varying from 0.5 to 1.5 nm was inserted to form Al2O3/HfO2–SnO2–TiO2/Al2O3 stacking capacitors. The effect of the Al2O3 insertion layer thickness and the super-cycle number of HfO2–SnO2–TiO2 on the capacitance density, leakage, and quadratic voltage linearity was investigated. Under optimal processing, flexible MIM capacitors could stand 40 000 bending cycles at curvature radius of 8.2 mm, indicative of better electrical stability. Moreover, compared with the polymer-based HfO2–SnO2–TiO2 capacitors, the introduction of 1 nm Al2O3 ultrathin layer greatly decreases the leakage current density by 4 orders of magnitude (10−8 A cm−2) with relative lower voltage linearity (350–540 ppm V−2), but the capacitance density also declines (∼3 fF μm−2) simultaneously. Despite this, the method of inserting Al2O3 ultra-thin layer is still an effective method to improve the electrical performances of polymer-based HfO2–SnO2–TiO2 nanolaminate capacitors for flexible electronics.

First-principles calculation, synthesis, and oxidation mechanism of Ta1-xHfxC ultra-high temperature ceramics

According to first-principles calculations, the mechanical properties of Ta1-xHfxC (x = 0.2, 0.4, 0.5) improve as the Ta content increases due to enhanced bonding between Ta and C atoms. The negative mixing enthalpies indicate that all three solid solutions can be prepared as single-phase materials. Single-phase Ta1-xHfxC (x = 0.2,0.4,0.5) were prepared using Spark Plasma Sintering. Studies on oxidation reveal that Ta0.5Hf0.5C demonstrates the most superior oxidation resistance among the three compositions. During oxidation, forming a Ta2O5-Hf6Ta2O17 layer is essential for improving oxidation resistance. The research indicates that balancing the ratio of Ta and Hf is crucial for achieving optimal mechanical properties and oxidation resistance in practical applications.

Fabrication and characterization of HfxAl(1-x)Oy ceramic targets and thin films by RF sputtering

The potential of HfO2 as a memory semiconductor material with ferroelectric properties in thin-film deposition has been recently analyzed. In this study, the preparation, composition, and physical properties of Al-doped hafnium oxides were analyzed. HfxAl(1-x)Oy (HAO) [x = 0.33, 0.5, and 0.67] powders were prepared by controlling the ratio of Hf to Al and using ball milling. The HAO powder was calcined at 1000 °C in a furnace and then sintered in a temperature range of 1000–1600 °C by a solid-state reaction method to fabricate high-quality targets with high densities. The density and crystal size increased with the sintering temperature. The 1600-°C Hf0.67Al0.33Oy target was optimal for thin-film deposition. In addition, the target properties were affected by an increase in the HfO2 content x. The crystal structures and sizes, surface free energies, contact angles, and band gaps of the HAOs were evaluated to analyze their potential as high-k dielectric materials. HAO is a promising high-k dielectric and memory material, valuable for further studies on ferroelectric gate oxide materials. This study contributes to the increasing number of studies on the ferroelectricity of HfO2 thin films and provides a fundamental understanding of this material and its potential for novel device applications.

Operando study of HfO2 atomic layer deposition on partially hydroxylated Si(111)

The introduction of atomic layer deposition (ALD), to the microelectronics industry has introduced a large number of new possible materials able to be deposited in layers with atomic thickness control. One such material is the high-κ oxide HfO2; thermally stable and ultrathin HfO2 films deposited by ALD are a significant contender to replace SiO2 as the gate oxide in capacitor applications. We present a mechanistic study of the first deposition cycle of HfO2 on the Si(111) surface using tetrakis(dimethylamido) hafnium (TDMAHf) and water as precursors using operando ambient pressure x-ray photoelectron spectroscopy. Here, we show that the hydroxylation of the clean Si(111) surface by residual water vapor, resulting in a 0.3 monolayer coverage of hydroxyls, leads to instantaneous full surface coverage of TDMAHf. The change in the atomic ratio of Hf to C/N found during the first deposition half-cycle, however, does not match the assumed immediate ligand loss through reaction with surface hydroxyls. One would expect an immediate loss of ligands, indicated by a Hf:N ratio of approximately 1:3 as TDMAHf deposits onto the surface; however, a Hf:N ratio of 1:3.6 is observed. The partial hydroxylation on the Si(111) surface leads to binding through the TDMAHf ligand N atoms resulting in both N and CH3 being found remaining on the surface post water half-cycle. Although there is evidence of ligand exchange reactions occurring at Si–OH sites, it also seems that N binding can occur on bare Si, highlighting the complexity of the substrate/precursor reaction even when hydroxyls are present. Moreover, the initial low coverage of Si–OH/Si–H appears to severely limit the amount of Hf deposited, which we hypothesize is due to the specific geometry of the initial arrangement of Si–OH/Si–H on the rest- and adatoms.

Composition Design and Tensile Properties of Additive Manufactured Low Density Hf-Nb-Ta-Ti-Zr High Entropy Alloys Based on Atomic Simulations.

High-entropy alloy (HEA) is a new type of multi-principal alloy material and the Hf-Nb-Ta-Ti-Zr HEAs have attracted more and more attention from researchers due to their high melting point, special plasticity, and excellent corrosion resistance. In this paper, in order to reduce the density of the alloy and maintain the strength of the Hf-Nb-Ta-Ti-Zr HEAs, the effects of high-density elements Hf and Ta on the properties of HEAs were explored for the first time based on molecular dynamics simulations. A low-density and high-strength Hf0.25NbTa0.25TiZr HEA suitable for laser melting deposition was designed and formed. Studies have shown that the decrease in the proportion of Ta element reduces the strength of HEA, while the decrease in Hf element increases the strength of HEA. The simultaneous decrease in the ratio of Hf and Ta elements reduces the elastic modulus and strength of HEA and leads to the coarsening of the alloy microstructure. The application of laser melting deposition (LMD) technology refines the grains and effectively solves the coarsening problem. Compared with the as-cast state, the as-deposited Hf0.25NbTa0.25TiZr HEA obtained by LMD forming has obvious grain refinement (from 300 μm to 20-80 μm). At the same time, compared with the as-cast Hf0.25NbTa0.25TiZr HEA (σs = 730 ± 23 MPa), the as-deposited Hf0.25NbTa0.25TiZr HEA has higher strength (σs = 925 ± 9 MPa), which is similar to the as-cast equiatomic ratio HfNbTaTiZr HEA (σs = 970 ± 15 MPa).

Effect of Homogenization on the Transformation Temperatures and Mechanical Properties of Cu15Ni35Hf12.5Ti25Zr12.5 and Cu15Ni35Hf15Ti20Zr15 High-Entropy Shape Memory Alloys.

The major challenge of high-temperature shape memory alloys (SMAs) is the collocation of phase transition temperatures (TTs: Ms, Mf, As, Af) with the mechanical properties required for application. Previous research has shown that the addition of Hf and Zr into NiTi shape memory alloys (SMAs) increases TTs. Modulating the ratio of Hf and Zr can control the phase transformation temperature, and applying thermal treatments can also achieve the same goal. However, the influence of thermal treatments and precipitates on mechanical properties has not been widely discussed in previous studies. In this study, we prepared two different kinds of shape memory alloys and analyzed their phase transformation temperatures after homogenization. Homogenization successfully eliminated dendrites and inter-dendrites in the as-cast states, resulting in a reduction in the phase transformation temperatures. XRD patterns indicated the presence of B2 peaks in the as-homogenized states, demonstrating a decrease in phase transformation temperatures. Mechanical properties, such as elongation and hardness, were improved due to the uniform microstructures achieved after homogenization. Moreover, we discovered that different additions of Hf and Zr resulted in distinct properties. Alloys with lower Hf and Zr had lower phase transformation temperatures, followed by higher fracture stress and elongation.

INTERACTION OF HAFNIUM(IV) WITH 6,7-DIHYDROXY‑4-CARBOXYL‑2- PHENYLBENZOPYRYLLIUM SALTS IN BINARY SYSTEMS AND IN THE PRESENCE OF CATIONIC SURFACTANTS

In the current study, the peculiarities of the complexation of Hafnium(IV) with 6,7-dihyroxy‑4-carboxyl‑2-phenylbenzopyrylium salts (CDC) in binary systems and in the presence of cationic surfactants (Surf) were studied. The CDC was synthesized by condensation of pyrogallol A with benzoylpyruvic acid in an acetic acid medium in the presence of perchloric acid. To obtain KDC bromide and chloride, the synthesis was carried out in the presence of bromide acid or by sparging of dry hydrogen chloride, respectively. Using classical spectrophotometric methods of molar ratios and Bent-French, it was found that at pH 2.5 in binary system one complex with stoichiometry Hf(IV): CDC1:2 was formed. Molar absorptivity coefficient was calculated for Hf(IV) complex with CDC and it was equal 3,9⸱104. It was shown that in the presence of cetylpyridinium chloride or cetyltrimetrylammonium bromide complexes with a molar ratio of Hf(IV): CDC: Surf = 1:2:2 were formed. It is noted that the complexes were formed within 10–15 minutes, and the absorbance of the solutions remains constant for at least 2 hours. It was established that the nature of the anion, which is part of the reagent, does not significantly affect the characteristics of the analytical form. It is shown that in the presence of cationic surfactants, the optimal pH of complex formation shifts to a more acidic region. In addition, the introduction of cationic surfactants leads to a batachromic shift of the absorption band by 10–15 nm and an increase in the molar absorptivity to 5.8⸱104 and 6.4⸱104 when cetylpyridinium chloride or cetyltrimetrylammonium bromide were used respectively. It is noted that the found analytical forms can be used as a basis for the development of combined spectroscopic methods for determining trace amounts of Hafnium(IV).

Occurrences and patterns of major elements in coal fly ash under multi-acid system during microwave digestion processes

Coal fly ash (CFA) is a typical industrial solid waste generated from coal combustion. Microwave digestion is a common measure to determine the element compositions for complex samples like CFA, of which the reagents of digestion processes largely affect the results. In this work, to explore the behaviors of major elements during the digestion process and the effects of pre-treatments, the digestion patterns of Al, Ca, Fe, K, Mg and Ti in CFA samples were studied. The results showed that hydrofluoric acid greatly enhanced the digestion when the ratio of HF went up from 0 to 0.22, of which the digestion efficiencies increased from 21.79% to 59.55% for Al, from 82.23% to 88.23% for Ca, from 50.86% to 84.93% for Fe, from 16.94% to 76.95% for K, and from 9.94% to 95.90% for Ti. Perchloric acid functioned the same as nitric acid. The most suitable schemes for major elements in CFA was (7 mL HNO3 + 2 mL HCl + 2 mL HF) for 0.25 g of samples (Al: 100.00%, Ca: 93.05%, Fe:97.58%, K: 100.00%, Mg: 81.10%, Ti: 98.30%). According to the experiment of pre-treatments and the structure analysis, it could be concluded that Fe mostly existed in the amorphous phase while K and Ti mostly existed in the crystalline phase, and Ca and Mg were mostly embedded in the Al-related crystalline phase.

Light Trapping of Inclined Si Nanowires for Efficient Inorganic/Organic Hybrid Solar Cells.

Light/matter interaction of low-dimensional silicon (Si) strongly correlated with its geometrical features, which resulted in being highly critical for the practical development of Si-based photovoltaic applications. Yet, orientation modulation together with apt control over the size and spacing of aligned Si nanowire (SiNW) arrays remained rather challenging. Here, we demonstrated that the transition of formed SiNWs with controlled diameters and spacing from the crystallographically preferred <100> to <110> orientation was realized through the facile adjustment of etchant compositions. The underlying mechanism was found to correlate with the competing reactions between the formation and removal of oxide at Ag/Si interfaces that could be readily tailored through the concentration ratio of HF to H2O2. By employing inclined SiNWs for the construction of hybrid solar cells, the improved cell performances compared with conventional vertical-SiNW-based hybrid cells were demonstrated, showing the conversion efficiency of 12.23%, approximately 1.12 times higher than that of vertical-SiNW-based hybrid solar cells. These were numerically and experimentally interpreted by the involvement of excellent light-trapping effects covering the wide-angle light illuminations of inclined SiNWs, which paved the potential design for next-generation optoelectronic devices.

Investigation of shape memory characteristics and production of HfZrTiFeMnSi high entropy alloy by mechanical alloying method

High entropy alloy (HEA) with shape memory effect (SME) has been the subject of great interest for the past few decades. However, with the increased demands for new materials for high thermal applications, the research activities on the multi elemental high entropy shape memory alloys (HESMA) have been increased by many folds recently. The nano crystalline HEA powder with shape memory effect developed in this study, HfZrTiFeMnSi, was produced by mechanical alloying (MA) for the first time. In this method equiatomic ratio of Hf, Zr, Ti, Fe, Mn, and Si were mixed together and milled by MA process for 100 h. The powder formed was of amorphous in nature. Elemental mapping of the powder from SEM-EDS revealed homogeneity of the alloying elements confirming successful fabrication of HfZrTiFeMnSi HEA powder. The DSC studies from ambient to 500 °C of the annealed alloy powders showed reversible austenitic to martensitic (A↔M) transformations. The A↔M transformation hysteresis seemed to vary with the milling time and annealing temperature. The enthalpy values, ΔH, for the transformation were calculated from the DSC plots using tangent method for peak area calculation. Regardless of the annealing temperature, the thermal analysis revealed that the ΔH, equilibrium temperature (T0), and crystallization temperature values decreased with the increasing milling time.

Effects of ECG Data Length on Heart Rate Variability among Young Healthy Adults.

The relationship between the robustness of HRV derived by linear and nonlinear methods to the required minimum data lengths has yet to be well understood. The normal electrocardiography (ECG) data of 14 healthy volunteers were applied to 34 HRV measures using various data lengths, and compared with the most prolonged (2000 R peaks or 750 s) by using the Mann–Whitney U test, to determine the 0.05 level of significance. We found that SDNN, RMSSD, pNN50, normalized LF, the ratio of LF and HF, and SD1 of the Poincaré plot could be adequately computed by small data size (60–100 R peaks). In addition, parameters of RQA did not show any significant differences among 60 and 750 s. However, longer data length (1000 R peaks) is recommended to calculate most other measures. The DFA and Lyapunov exponent might require an even longer data length to show robust results. Conclusions: Our work suggests the optimal minimum data sizes for different HRV measures which can potentially improve the efficiency and save the time and effort for both patients and medical care providers.

Rigid three-dimensional networks of hafnium diboride for improving mechanical and wear properties of boron carbide

Being one of the hardest materials known in nature, boron carbide (B4C) suffers from severe degradation of mechanical properties when subjected to external pressure or shear stress, which hinders its application in metal forming and machining industries. Herein, based on the phase diagrams, a new strengthening strategy consisting of constructing three-dimensional hafnium diboride (HfB2) networks was proposed to reinforce B4C using the molten-salts method followed by spark plasma sintering (SPS). It was found that the surface amorphization and subsequent decarburization were the main wear regime of pure B4C. Incorporating hard HfB2 networks in B4C resulted in enhanced mechanical properties and reduced wear rates, as the deformation and decarburization of B4C grains were effectively restrained. The excessively high Hf contents, however, made the composites prone to severe adhesive wear following the material transfer from mating materials during the inception of sliding contact, which led to deteriorated wear performances. Thus, the optimal molar ratio of Hf to B4C was determined with the underlying wear mechanisms delineated. The presented results not only show the feasibility of B4C-HfB2 composites as tool materials but also provide a novel designing strategy employing hard networks rather than conventional compliant binders to fabricate wear-resistant composite materials.

Hafnium Incorporation in InZnO Thin Film Transistors as a Carrier Suppressor.

In this study, we fabricated Hf-doped indium zinc oxide thin-film transistors (HIZO TFTs) using a solution process. Channel layers of the TFTs were optimized by varying the molar ratio of Hf in the channel layers. The electrical properties of the fabricated devices were compared to gallium indium zinc oxide (GIZO). HIZO TFTs showed 0.12 V threshold voltage, 0.45 V/decade subthreshold swing and 1.24 × 106 on-off current ratio, which were excellent compared to that of GIZO. In particular, when a positive gate bias stress of 10 V was applied for 10³ s, the HIZO TFT exhibited a lower threshold voltage shift of 1.11 V than the GIZO TFT (1.88 V). These results originate from the higher oxygen bonding with Hf in IZO compared to Ga atoms. We confirmed that Hf acts as an excellent carrier suppressor whose properties exceed those of Ga.

Structural, mechanical, electronic properties of refractory Hf–Al intermetallics from SCAN meta-GGA density functional calculations

Hf–Al intermetallics are novel promising high-temperature structural materials, which exhibit excellent mechanical properties. In this work, the structural parameters, elastic constants, and mechanical anisotropies of Hf–Al intermetallics are investigated by applying the latest meta-GGA functional SCAN as well as several other widely used density functionals such as LDA, PBE and PBEsol. It is found that HfAl2 is the most thermodynamically stable stoichiometric compound among all Hf–Al binary intermetallics. The elastic moduli like B, G, E, ductility index (B/G ratio) and Poisson's ratio (σ) of Hf–Al intermetallics are predicted based on Voigt–Reuss–Hill approximation, indicating most Hf–Al binary intermetallics are brittle except Hf5Al3 and Hf2Al. Besides, the three-dimensional (3D) contour plots of mechanical moduli are provided to characterize the elastic anisotropy in Hf–Al intermetallics. HfAl shows obvious anisotropy in both Young's and bulk moduli along different crystallographic directions, while very weak anisotropy is revealed for both HfAl2 and Hf4Al3 phases since the 3-D surface contours of mechanical moduli show little deviations from isotropic spherical shapes. The calculated electronic properties indicate that relatively high thermodynamic stability of HfAl2 phase is mainly ascribed to the formation of a pseudo-gap in the electron density of states originating mainly from the Al-2p and Hf-5d states at the Fermi level.

Cardiac Autonomic Modulation during on-Call Duty under Working Hours Restriction.

Background: Medical residency is a time of high stress and long working hours, which increase the risk of cardiovascular disease. This study aimed to investigate the autonomic modulation of resident physicians throughout the on-call duty cycle. Methods: Spectral analysis of heart rate variability (HRV) was used to compute cardiac parasympathetic modulation (high-frequency power, HF) and cardiac sympathetic modulation (normalized low-frequency power, LF%, and the ratio of LF and HF, LF/HF) of 18 residents for a consecutive 4-day cycle. Results: Male residents show reduced cardiac sympathetic modulation (i.e., higher LF/HF and LF%) than the female interns. Medical residents’ cardiac parasympathetic modulation (i.e., HF) significantly increased on the first and the second post-call day compared with the pre-call day. In contrast, LF% was significantly decreased on the first and the second post-call day compared with the pre-call day. Similarly, LF/HF was significantly decreased on the second post-call day compared with the pre-call day. LF/HF significantly decreased on the first post-call day and on the second post-call day from on-call duty. Conclusion: The guideline that limits workweeks to 80 h and shifts to 28 h resulted in reduced sympathetic modulation and increased parasympathetic modulation during the two days following on-call duty.

(Invited) Photoemission-Based Characterization of Gate Dielectrics and Stack Interfaces

In the development of Metal-Insulator-Semiconductor (MIS) devices, gate dielectric technologies are of great importance and include major scientific and technological issues to be solved for required device performance and reliability. To gain a better understanding of physics of gate dielectric stacks and insights into interface control, characterization of electronic structures of gate dielectrics and quantification of electronic defects in dielectric stacks are imperative. In this work, we have demonstrated how energy dependent dielectric responses of gate dielectrics are evaluated by photoelectron energy loss spectroscopy (PEELS) [1, 2] and how energy distributions of defect states in wide gap materials and their interfaces are quantified by total photoelectron electron yield spectroscopy (PYS) [3-5]. Determination of Complex Dielectric Function The analyses of core-line photoemission spectra have been extensively conducted to characterize chemical bonding features in materials and heterointerfaces of interest. On the other hand, electron energy loss spectroscopy is an effectively used method for study the excitation spectra of atoms, molecules, and solids. Thus, we have measured and analyzed energy loss signals (ELS) incidental to core-line spectra not only to determine energy bandgap values of dielectrics but also to characterize dielectric functions of dielectrics since, inherently, photoexcited electrons passing through dielectrics can suffer inelastic losses due to electronic excitations such as plasmons and band-to-band transitions. As the first step, we examined a complex dielectric function of 50nm-thick SiO2 grown at 1000 ºC in dry O2 from the ELS analyses of both Si2p3/2 and O1s lines. In each analysis, based on photoelectron take-off angle dependence of ELS, the pure bulk component being proportional to the negative imaginary part of inverse dielectric function was extracted carefully, and then the real part of inverse dielectric function can be calculated by Kramers-Kronig transformation of the extracted bulk component. Almost the same results were obtained from the ELS analyses of both Si2p3/2 and O1s photoelectrons, and are very consistent with the dielectric function calculated from reported optical constants of SiO2 glass [6]. Notice that obtained dielectric function enables us to confirm the validity of the energy band gap value determined simply from the onset energy of ELS. We have extended this PEELS to characterization of dielectric functions of CVD SiO2 formed by reaction between SiH4 and remote O2 plasma, Hf- and Al-silicates prepared by plasma-assisted ALD, and confirmed that spectral broadening and tailing become significant with an increase in structural fluctuation and incorporation of Hf and Al atoms. Quantification of Energy Distribution of Defect States Since photoelectron yield is obtained by counting the total number of photoelectrons emitting from the sample as a function of incident photon energy and normalized by the incident photon flux, the spectrum is related to an integral over the occupied density of states involving photoemission near the sample surface. Changes in photoelectron yield spectrum with wet-chemical thinning of 5.2nm SiO2 formed 500ºC by remote plasma enhanced CVD on n-type GaN(0001) show presence of occupied defects in SiO2, near the interface and in GaN but a relatively large number of defects are located within ~1.5nm from the SiO2/GaN interface. From the 1st derivative of the measured yield spectrum with respect to incident photon energy which leads us to the energy distribution of occupied defect state densities in consideration of density of states of the GaN valence band (VB), we found that occupied states are reduced down to ~1x1011cm-2eV-1 at the energy corresponding to the midgap of GaN near the SiO2/GaN interface with N2 anneal at 800ºC. The defect state density near the conduction band edge, which was crudely estimated in consideration of electron occupation probability based on the Fermi-Dirac distribution, are in good agreements with the result obtained from the capacitance-voltage (C-V) analysis using the Terman method. We also found that, for Hf-silicate with a compositional ratio of Hf/(Si+Hf) = ~75% and a relative dielectric constant of ~16 formed on GaN by plasma-assisted ALD and followed by 800ºC anneal in N2 ambience, a similar energy distribution of defect state density to the 800ºC-annealed SiO2/GaN was obtained in the energy range from ~1eV above the GaN valence band edge toward the conduction band edge.

Fast and maskless nanofabrication for high-quality nanochannels

Nanochannels are critical components for the fundamental and applied studies of nanofluids. However, the intrinsic low efficiency and high cost of conventional bulk-/surface-/mold-machining methods severely hinder the wide application of nanochannels. Here, we reported a fast, low-cost and maskless fabrication strategy based on friction-induced selective etching in HF/HNO3 mixtures for controllable preparation of diversified and high-quality Si nanochannels. Owing to its distinct anisotropic etching characteristic to scratched area, this novel integrated fabrication process eliminated the limitation of HF/HNO3 mixtures in nanofabrication. Particularly, the etching efficiency and depth of scratched Si in HF/HNO3 mixtures are 12 and 2 times of those in HF solution, respectively. Furthermore, the effects of the volume ratio of HF and HNO3 as well as scratching parameters on nanochannel fabrication were investigated systematically. Cross-sectional transmission electron microscopy observation indicated that the as-fabricated nanochannels have no structural damage. Finally, the corresponding nanofluidic device was designed, fabricated and verified in sequence. The results demonstrate the feasibility of proposed approach for nanochannel fabrication in the area of nanofluids, particularly in analytical chemistry, biochemistry, liquid transport and metering, and energy conversion.

Nitrogen plasma-induced HfSiON film growth from Hf nanoscale islands on SiO2/Si

HfSiON films for high-k dielectric applications are synthesized from Hf nanoscale islands on SiO2/Si(100) substrates using the exposure of nitrogen inductively coupled plasma (ICP). The process consists of the novel interfacial reaction of nanoscale islands with the substrate induced by plasma-derived radicals and ions. The Hf metal islands nucleate on an SiO2/Si(100) surface by strain-induced engineering during electron beam evaporation. In vacuo AFM measurement shows that the N2 ICP exposure collapses the islands to form films. XPS analysis shows that the ICP exposure initially nitrides Hf islands in 1 min. Then, it induces the intermixing of the base SiO2 with HfN in the next stage. The rapid nitridation of Hf is the unique feature of the process initiated from nanoscale islands. The chemical composition ratio of Hf:Si:N in the film can be roughly controlled to be 1:1:1 with an ICP exposure time of 20 min. The uniformity of the grown films depends on the initial uniformity of the islands and the surface diffusion of materials. The study is a unique example of the film-growth method based on the nanoscale interaction of the surface of nucleated islands and the substrate material induced by plasmas.

Synthesis of Lithium Fluoride from Spent Lithium Ion Batteries

Lithium (Li) is considered a strategic element whose use has significantly expanded. Its current high demand is due to its use in lithium ion batteries for portable electronic devices, whose manufacture and market are extensively growing every day. These days there is a great concern about the final disposal of these batteries. Therefore, the possibility of developing new methodologies to recycle their components is of great importance, both commercially and environmentally. This paper presents results regarding important operational variables for the dissolution of the lithium and cobalt mixed-oxide (LiCoO2) cathodes from spent lithium ion batteries (LIBs) with hydrofluoric acid. The recovery and synthesis of Co and Li compounds were also investigated. The dissolution parameters studied were: temperature, reaction time, solid-liquid ratio, stirring speed, and concentration of HF. The investigated recovery parameters included: pH, temperature, and time with and without stirring. The final precipitation of lithium fluoride was also examined. The results indicate that an increase in the HF concentration, temperature, and reaction time favors the leaching reaction of the LiCoO2. Dissolutions were close to 60%, at 75 °C and 120 min with a HF concentration of 25% (v/v). The recovery of Co and Li were 98% and 80%, respectively, with purities higher than 94%. Co and Li compounds, such as Co3O4 and LiF, were synthesized. Furthermore, it was possible to almost completely eliminate the F− ions as CaF2.

Concurrent Cationic Vinyl-Addition and Coordination Ring-Opening Copolymerization via Orthogonal Propagation and Transient Merging at the Propagating Chain End.

Controlled cationic vinyl-addition polymerization of an alkyl vinyl ether (VE) and ring-opening polymerization of ε-caprolactone (CL) simultaneously proceeded using HfCl4/Hf(OBu)4 as a dual-role catalyst for both mechanisms, yielding a graft copolymer consisting of a poly(VE) main chain and several poly(CL) side chains. The copolymer of conventionally incompatible monomers was generated via the unprecedented mechanisms consisting of orthogonal propagating reactions and transient merging. Specifically, the poly(CL) chains were incorporated into a poly(VE) chain through an exchange reaction between the VE-derived alkoxy group and the propagating poly(CL) chain at the acetal moiety of the propagating end of the poly(VE) chain. An appropriate ratio of HfCl4 and Hf(OBu)4 was indispensable for both the simultaneous vinyl-addition and ring-opening polymerizations and the alkoxy group exchange reaction.