Amorphous hafnium oxide thin films for antireflection optical coatings

Hafnium oxide (HfO₂) thin films were grown on silicon and quartz substrates by radio frequency reactive magnetron sputtering at temperature < 52 °C. X-ray diffraction of the films showed no structure, suggesting that the films grown on the substrates are amorphous. The optical properties of these films have been investigated using spectroscopic ellipsometry with wavelength range 200-1400 nm and ultraviolet-visible spectrophotometer techniques. Also, the effects of annealing temperatures on the structure and optical properties of the amorphous HfO₂ (a-HfO₂) have been investigated. The films appeared to be monoclinic structure upon high temperature (1000 °C) annealing as confirmed by X-ray diffraction. The results show that the annealing temperature has a strong effect on the optical properties of a-HfO₂ films. The optical bandgap energy of the as-deposited films is found to be about 5.8 eV and it increases to 5.99 eV after the annealing in Ar gas at 1000 °C. The further study shows that the measurement of the optical properties of the amorphous films reveals a high transmissivity (82%-99%) and very low reflectivity (< 8%) in the visible and near-infrared regions at any angle of incidence. Thus, the amorphous structure yields HfO₂ film of significantly higher transparency than the polycrystalline (68%-83%) and monoclinic (78%-89%) structures. This means that the a-HfO₂ films could be a good candidate for antireflection (AR) optical coatings.     

Reaction behavior and formation mechanism of ZrC and ZrB2 in the Cu–Zr–B4C system

In this work, the formation mechanism of ZrC and ZrB₂ in the Cu–Zr–B₄C system was studied by differential scanning calorimeter and X-ray diffraction. Moreover, the effect of heating rate on the reaction behavior was also investigated. The results revealed that the heating rate did hardly influence the reaction process and product in the range of 10–30 °C/min. The formation mechanism of ZrC and ZrB₂ in the Cu–Zr–B₄C system could be ascribed to the solid-state reaction between Zr and B₄C particles, and the replacement reactions of B₄C with the Cu–Zr liquid and copper zirconium compounds. The addition of Cu in the Cu–Zr–B₄C reactants can change the phase evolution route via producing various Cu–Zr intermediate phases and promote the formation of ZrC and ZrB₂.     

Experimental determination of intermetallic phases, phase equilibria, and invariant reaction temperatures in the Fe-Zr system

The phase diagram of the binary Fe-Zr system was redetermined by differential thermal analysis (DTA), electron-probe microanalysis (EPMA), x-ray diffraction (XRD), and metallography in the whole range of compositions. The stable intermetallic phases of the binary system are the cubic and the hexagonal polymorphs of the Fe₂Zr Laves phase and the Zr-rich phases FeZr₂ and FeZr₃. While the cubic polymorph of the Laves phase is the stable structure at the stoichiometric Fe₂Zr composition, the hexagonal C36-type polymorph of the Laves phase is a high-temperature phase that is found at Zr concentrations as low as 26.6 at.%. The Zr-rich phases FeZr₂ and FeZr₃ have small homogeneity ranges of about 0.5 at.%. FeZr₂ is a high-temperature phase, stable between 780 and 951 °C. FeZr₃ decomposes peritectoidally at 851 °C. The frequently reported phase Fe₂₃Zr₆ (Fe₃Zr) is found not to be an equilibrium phase of the binary system.     

Experimental determination of intermetallic phases, phase equilibria, and invariant reaction temperatures in the Fe-Zr system

The phase diagram of the binary Fe-Zr system was redetermined by differential thermal analysis (DTA), electron-probe microanalysis (EPMA), x-ray diffraction (XRD), and metallography in the whole range of compositions. The stable intermetallic phases of the binary system are the cubic and the hexagonal polymorphs of the Fe₂Zr Laves phase and the Zr-rich phases FeZr₂ and FeZr₃. While the cubic polymorph of the Laves phase is the stable structure at the stoichiometric Fe₂Zr composition, the hexagonal C36-type polymorph of the Laves phase is a high-temperature phase that is found at Zr concentrations as low as 26.6 at.%. The Zr-rich phases FeZr₂ and FeZr₃ have small homogeneity ranges of about 0.5 at.%. FeZr₂ is a high-temperature phase, stable between 780 and 951 °C. FeZr₃ decomposes peritectoidally at 851 °C. The frequently reported phase Fe₂₃Zr₆ (Fe₃Zr) is found not to be an equilibrium phase of the binary system.     

Thermal explosion synthesis of ZrC particles and their mechanism of formation from Al–Zr–C elemental powders

ZrC particles were fabricated by thermal explosion (TE) from mixture of Al, Zr and C elemental powders. Without the addition of Al, the synthesized ZrC particles had irregular shape of ~ 4.0 μm in average. Increasing Al content up to 30 wt.%, however, refined significantly them down to < 0.2 μm with regularly square morphology. The Al effect of reaction mechanism promoted the ZrC formation as diluents in the course of TE, which was clarified using differential thermal analysis and X-ray diffraction technique. The melting of Al favored the reaction with Zr to generate ZrAl₃, and then the dissolution of C into the Al–Zr liquid resulted in precipitation of ZrC. Meanwhile, the exothermic effect prompted C atoms dissolving into Zr–Al liquid and eventually led to precipitation of ZrC out of the supersaturated liquid. The Al addition inhibited particle growth, but also promoted the TE reaction.     

Static Recrystallization of Cold Rolled Intermetallic Fe17Al4Cr0.3Zr Alloy

The final microstructure of cold rolled intermetallic disordered alloy Fe17Al4Cr0.3Zr was rebuilt during the annealing at moderate temperatures in the range of 800 to 900?°C. The time necessary to obtain recrystallized structure was determined at several annealing temperatures to optimize the processing technology of the plates. The phases present in the material during this process were identified. The grain growth (grain boundary movement) during static recrystallization (SRX) is connected with the interaction with an array of the Laves phase ??₁(Fe,Al)₂Zr and ZrC particles. The Avrami-based phenomenological model describing kinetics of SRX was developed. The activation energy for recrystallization was estimated.     

Investigation of metal distribution and carbide crystallite formation in metal-doped carbon films (a-C:Me, Me = Ti, V, Zr, W) with low metal content

Metal-doped amorphous carbon films (a-C:Me) were deposited at room temperature by magnetron sputtering using a metal (Me = Ti, V, Zr, W) and a graphite target. The metal distribution and the temperature-induced carbide crystallite formation were analyzed by X-ray diffraction (XRD), electron microscopy (TEM, STEM) and X-ray absorption spectroscopy (EXAFS, XANES), focusing on low metal concentrations between 6.5 and 9.5%. In as-deposited samples, the metal atoms are atomically distributed in the carbon matrix without significant formation of carbide particles. With annealing to 900 K the local atomic environment around the metal atoms becomes similar to the carbide. The carbide crystallites grow with annealing up to 1300 K, their size is dependent on the metal type: V > Ti > Zr≈W. W₂C and WC_1 − x crystallites were identified for W-doped films, whereas the monocarbides are formed for the other metals. It is demonstrated, that EXAFS and high resolution electron microscopy are required to get a correct picture of the structure of the analyzed a-C:W films.     

Formation and stability of refractory metal diborides in an Fe3Al matrix

The feasibility of forming refractory diboride particles in an Fe₃Al matrix by conventional casting techniques is examined; the microstructural stability of such particles upon subsequent exposure to elevated temperatures is discussed. Four different alloys were cast (Fe–Al–Ti–B, Fe–Al–Zr–B, Fe–Al–Nb–B, and Fe–Al–Ta–B); the nominal composition in each case was intended to yield stoichiometric Fe₃Al with 10 vol% of the stoichiometric refractory diboride. As-cast, annealed and heat treated alloys were examined using optical microscopy, X-ray diffraction, differential thermal analysis and scanning electron microscopy in conjunction with energy dispersive X-ray (EDX) spectroscopy to understand the formation and thermal stability of refractory diborides (TiB₂, ZrB₂, TaB₂, NbB₂) in Fe₃Al. In all four cases, refractory diborides formed; the Fe–Al–Ti–B and Fe–Al–Zr–B alloys yielded a two-phase microstructure of Fe₃Al and the diboride. The Ti and Zr diboride reinforcements were stable and showed minimal coarsening following high temperature exposure. The Nb- and Ta-containing quaternary alloys, in addition to the respective diborides, included a eutectic reaction at temperatures between 1150°C and 1200°C that results in the formation of an Fe-rich phase thought to be Fe₂B.     

Mechanical alloying characteristic and thermal stability of Al<Subscript>78</Subscript>Fe<Subscript>20</Subscript>Zr<Subscript>2</Subscript> amorphous powders

The powders of pure Al, Fe, and Zr for preparing Al₇₈Fe₂₀Zr₂ were subject to a high-energy planetary ball milling. The microstructure evolution of the mixtures at the different intervals of milling was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). It was found that a nearly complete amorphization could be achieved in the mixtures after ball milling for 23 h. Further ball milling led to the crystallization of the amorphous powders. A long time ball milling, e.g., 160 h, led to a complete crystallization of the amorphous powders and the formation of Al₃Zr and Al1₃Fe₄. The crystallization products caused by ball milling are almost the same as that produced by isothermal annealing of the amorphous powders in vacuum at 800 K for 1 h.     

原位合成ZrC颗粒增强锆基非晶复合材料及力学性能

利用zr与TiC粉末之间的原位反应经铜模铸造方法制备了zrC颗粒增强zr41Til4Cul2.5Ni10Be22．5块状非晶复合材料结果表明：原位合成的ZrC颗粒尺寸细小、形状规整并均匀地分布在非晶基体上．与锆非晶合金相比，复合材料的压缩强度得到提高，塑性得到改善．对ZrC颗粒原位合成及强化机理进行了讨论．     

X-ray diffraction study of the effect of annealing temperature on the phase and structural states of Fe79Zr10N11 films produced by magnetron sputtering

Fe₇₉Zr₁₀N₁₁ films 0.7 μm thick deposited on glass substrates have been produced by rf reactive magnetron sputtering. The films are a soft magnetic material, which can exhibit a combination of a high saturation inductance and a low coercive force and, therefore, shows promise as magnetic recording cores for the high-density magnetic recording. The results of X-ray diffraction studies of the phase and structural states of the films and the effect of annealing on these states are considered.     

Effect of magnetron sputtering conditions and subsequent annealing on the structure and magnetic properties of Fe97−x Zr3N x films

X-ray diffraction analysis was used to study the structure of Fe_97?x Zr₃N _x thin films produced under different conditions of rf magnetron sputtering (on rotary and stationary substrates) and subsequent annealing. Either a single-phase structure, namely, a supersaturated bcc α-(FeN) solid solution, or a mixed structure that consists of two crystalline phases, such as a supersaturated bcc α-Fe(N) solid solution and an fcc Fe₄N nitride, and a Fe-based amorphous phase were shown to be formed in films deposited on either stationary or rotating substrate, respectively. As the annealing temperature increases, the content of nitrogen in the bcc phase decreases; the grain size of the bcc phase in the films deposited on rotating and stationary substrates increases from 8 to 14 nm and from 10 to 30 nm, respectively; the amount of the Fe₄N phase increases. The results of the study of the magnetic properties of the films are reported. The maximum saturation induction B _s reached is 1.8–1.9 T; the minimum coercive force H _c is 1 Oe. The optimum combination of the magnetic properties (B _s = 1.8–1.9 T and H _c = 1.5–1.8 Oe) is observed for the films deposited on the rotating substrate and subsequently annealed at 400°C.     

Electrical and optical properties of tantalum oxide thin films prepared by reactive magnetron sputtering

Tantalum oxide thin films were prepared by using reactive dc magnetron sputtering in the mixed atmosphere of Ar and O₂ with various flow ratios. The structure and O/Ta atom ratio of the thin films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The optical and dielectric properties of the Ta₂O₅ thin films were investigated by using ultraviolet-visible spectra, spectral ellipsometry and dielectric spectra. The results reveal that the structure of the samples changes from the amorphous phase to the β-Ta₂O₅ phase after annealing at 900 °C. The XPS analysis showed that the atomic ratio of O and Ta atom is a stoichiometric ratio of 2.50 for the sample deposited at Ar:O₂ = 4:1. The refractive index of the thin films is 2.11 within the wavelength range 300-1000 nm. The dielectric constants and loss tangents of the Ta₂O₅ thin films decrease with the increase of measurement frequency. The leakage current density of the Ta₂O₅ thin films decreases and the breakdown strength increases with the increase of Ar:O₂ flow ratios during deposition.     

Crystallization of amorphous Zr60Al15Ni25 alloy

The phase formation and crystallization kinetics during the thermal treatment of amorphous Zr₆₀Al₁₅Ni₂₅ alloy were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). By lowering the isothermal annealing temperatures, it is revealed that the crystallization of the amorphous Zr₆₀Al₁₅Ni₂₅ alloy consists of a primary transformation followed by a polymorphic transformation, corresponding to the precipitations of hexagonal Zr₆Al₂Ni and the Zr₅AlNi₄ with a U₃Si₂-typed superstructure. The primary phase being Zr₆Al₂Ni rather than Zr₅AlNi₄ in the crystallization is because the latter has a complex structure and its formation requires the diffusion of Al and Zr atoms on a large scale.     

Effect of γ-(Fe,Ni) crystal-size stabilization in Fe–Ni–B amorphous ribbon

The effect of stabilizing crystal size in a melt-quenched amorphous Fe₅₀Ni₃₃B₁₇ ribbon is described upon crystallization in a temperature range of 360–400°С. The shape, size, volume fraction, and volume density have been investigated by transmission electron microscopy and X-ray diffraction methods. The formation of an amorphous layer of the Fe₅₀Ni₂₉B₂₁ compound was found by means of atomic-probe tomography at the boundary of the crystallite–amorphous phase. The stabilization of crystal sizes during annealing is due to the formation of a barrier amorphous layer that has a crystallization temperature that exceeds the crystallization temperature of the matrix amorphous alloy.     

Decomposition of the supersaturated solid solutions at the stage of coalescence under conditions of passage from dislocation-controlled to volume diffusion

The microstructure and thermal stability of multilayered Co/Zr amorphous films differing in the composition and thickness of individual layers have been studied. The range of the amorphous-phase existence was shown to be determined by both the chemical composition of films and thicknesses of individual layers. The critical thickness of cobalt layers which corresponds to the nucleation of a crystalline phase is 22–24 Å. A model of an island layered structure of multilayered Co/Zr amorphous films is suggested. Changes in the structure and phase composition of multilayered Co/Zr amorphous films caused by isothermal annealing have been studied. The temperature of the onset of crystallization (T _x) is shown to decrease from 460 to 380°C as the thickness of Co layers increases from 12 to 18 Å. The effect of annealing in the course of continuous heating on the specific saturation magnetization of the multilayered Co/Zr amorphous films has been studied. The effect of irreversible increase in the specific saturation magnetization was found for the first time at temperatures below the temperature of the onset of crystallization. A conception of a diffusion character of the structural relaxation and crystallization processes is used to interpret the results obtained.     

Role of amorphous Pb(Zr,Ti)O3 (PZT) in determining the ferroelectric properties of PZT-blended poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) thin films

Precursor films based on poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and P(VDF-TrFE) blended with Pb(Zr,Ti)O₃ were deposited on Si (100) substrates by spin-coating, and subsequently annealed at 443 K for 0.5 h. These films were then characterized using X-ray diffraction, atomic force microscopy and capacitance-voltage curves. Blending the precursor films of Pb(Zr,Ti)O₃ with P(VDF-TrFE) led to the formation of an amorphous oxide whose concentration was proportional to the Pb(Zr,Ti)O₃ content. This resulted in extension of the memory-window width with a large voltage difference ranging from 0.07 V to 4.5 V for metal-ferroelectric-silicon capacitors. Moreover, the formation of the amorphous oxide resulted in parallel shifts toward positive or negative voltages in the capacitance-voltage curves because of the fixed negative or positive charge of the oxide at the ferroelectric/Si-substrate interface. These tunable ferroelectric properties open up possibilities for diverse applications and are essential for functional devices, as well as for the commercialization of nonvolatile high-density FeRAM devices.     

Thickness dependence of crystalline state in FeZrNbCuB thin films obtained by sputter deposition

Differential scanning calorimetry, hysteresis measurements, X-ray diffraction, Mössbauer spectroscopy and transversal Kerr effect have been used to study the thickness and temperature dependence of magnetic properties and crystalline state of Fe₈₄Zr_3.5Nb_3.5B₈Cu₁ (at.%) thin films. Results indicate that a decrease of the saturation magnetization with increasing film thickness can be ascribed to the presence of a crystalline α-Fe phase at the early stages of film growth, followed by the deposition of the amorphous alloy. Thinner films, which have a significant crystalline phase in the as-prepared state, display less prominent crystallization features, whereas thicker films, with a significant amorphous phase in the as-prepared state, are characterized by much more pronounced crystallization effects, that are confirmed by Mössbauer and Transversal Kerr Effect measurements. Progressive thinning of a film by means of sputter etching allows to reduce the amorphous component, leading to the expected increase of saturation magnetization as the thickness decreases.     

Corrosion behaviour of stoichiometric Fe3Si alloy in liquid zinc

The corrosion behaviour of stoichiometric Fe₃Si alloy in a liquid zinc bath for 3 and 62 h at 500°C was examined. The corrosion products at the Fe₃Si/liquid zinc interface were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The corrosion process was controlled by the diffusion of iron and zinc atoms. There were scarcely any silicon atoms diffusing at Fe₃Si/liquid zinc interface from the matrix to liquid zinc. The phase transition process of the stoichiometric Fe₃Si alloy in liquid zinc was Fe₃Si, α, α+ FeSi+δ, FeSi+δ, and the main corrosion products were periodic array of FeSi and δ phase.     

Thermally induced crystallization of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy

Thermally induced crystallization of Fe_73.5Cu₁Nb₃Si_15.5B₇ amorphous alloy occurs in two well-separated stages: the first, around 475 °C, corresponds to formation of α-Fe(Si)/Fe₃Si and Fe₂B phases from the amorphous matrix, while the second, around 625 °C, corresponds to formation of Fe₁₆Nb₆Si₇ and Fe₂Si phases out of the already formed α-Fe(Si)/Fe₃Si phase. Mössbauer spectroscopy suggests that the initial crystallization occurs through formation of several intermediate phases leading to the formation of stable α-Fe(Si)/Fe₃Si and Fe₂B phases, as well as formation of smaller amounts of Fe₁₆Nb₆Si₇ phase. X-ray diffraction (XRD) and electron microscopy suggest that the presence of Cu and Nb, as well as relatively high Si content in the as-prepared alloy causes inhibition of crystal growth at annealing temperatures below 625 °C, meaning that coalescence of smaller crystalline grains is the principal mechanism of crystal growth at higher annealing temperatures. The second stage of crystallization, at higher temperatures, is characterized by appearance of Fe₂Si phase and a significant increase in phase content of Fe₁₆Nb₆Si₇ phase. Kinetic and thermodynamic parameters for individual steps of crystallization suggest that the steps which occur in the same temperature region share some similarities in mechanism. This is further supported by investigation of dimensionality of crystal growth of individual phases, using both Matusita–Sakka method of analysis of DSC data and texture analysis using XRD data.