ZrO2 HfO2 Research Articles

Raman spectra and structure of multicomponent oxide planar waveguides prepared by sol-gel

This work was aimed at understanding the structure of SiO2–MO2 (M = Ti, Zr, Hf) and SiO2–HfO2–MO2 (M = Ti, Zr) materials, used as mixed oxide glass hosts for Er3+ ions in the fabrication of optical planar waveguides by sol-gel processing. This structural study was performed by Waveguide Raman Spectroscopy (WRS), complemented with X-ray diffraction (XRD). The admixture of TiO2 to HfO2, SiO2–HfO2 and HfO2–ZrO2 compositions was found to cause precipitation of nanocrystals of tetragonal HfO2 or ZrO2, or the formation of hafnia-titania mixed crystals, depending on the HfO2/TiO2 molar ratio.

Scalability of phononic crystal heterostructures

Phononic (or acoustic) band structure calculations have been performed for a nanoscale HfO2–ZrO2 multilayer stack using first-principles methods at the atomistic level and by solving the acoustic wave equation at the continuum level, as a first step toward determining the length scales when conventional continuum acoustic band-gap treatments become inadequate. Transverse acoustic waves are the focus of this study. The material parameters that continuum acoustic band gap methods require, such as the mass density and transverse wave velocity of the components of the acoustic crystal (i.e., for HfO2 and ZrO2), were determined using separate phonon calculations of the corresponding bulk materials. Comparison of the phononic band structure for a nanoscale HfO2–ZrO2 multilayer stack calculated using first-principles and continuum methods indicates the need for careful treatments of wave propagation properties at these length scales.

Zr and Hf oxoclusters as building blocks for the preparation of nanostructured hybrid materials and binary oxides MO2–SiO2(M = Hf, Zr)

Silica materials embedding ZrO2 or HfO2 were prepared by copolymerisation of organically modified oxozirconium or oxohafnium clusters M4O2(OMc)12 (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane or (methacryloxypropyl)trimethoxysilane. Free radical copolymerisation of the oxoclusters bearing 12 methacrylate groups with the methacrylate-functionalized siloxanes allows stable anchoring of the clusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. This route represents a valuable strategy to yield a very homogeneous dispersion of the MO2 precursors inside the silica matrix. The composition and the microstructural features of the starting hybrid gels were studied by solid state 13C and 29Si NMR spectroscopy and FT IR transmission spectroscopy. Their evolution upon mild heating (up to 180 °C) was followed by FT-IR Attenuated Total Reflectance spectroscopy (ATR), while their thermal behaviour was studied by thermogravimetric analysis (TGA). The covalent incorporation of the clusters into the silica hybrid matrix was studied at several temperatures. Through X-Ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) it is demonstrated that temperatures above 800 °C yield binary oxides MO2–SiO2 (M = Zr, Hf). Delayed crystallisation of HfO2 and tetragonal ZrO2 from 450 °C to at least 800 °C was detected, which is ascribed to the presence of a homogeneous dispersion of the guest oxide in the silica matrix.

Film and interface layer properties of ultraviolet-ozone oxidized hafnia and zirconia gate dielectrics on silicon substrates

We report on the use of ultraviolet-ozone (UVO) oxidation of thin film hafnium and zirconium to fabricate high-dielectric constant (high-k) gate oxides with chemically modified silicon dioxide-based interface layers on silicon (100) substrates. Using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy, the oxidation state and thickness of the interfacial layer are characterized before and after UVO exposure. Reduction of the chemical oxide followed by reoxidation is observed. The reoxidized silicon is found to be substoichiometric. Thickness series fabricated by repeating the UVO process multiple times for the same substrate indicate a constant interface layer thickness. Inverse capacitance density versus physical thickness plots were used to determine that the dielectric constants for the UVO HfO2 and UVO ZrO2 are 17.3 and 24.8, respectively.

Microstructural evolution of ZrO2–HfO2 nanolaminate structures grown by atomic layer deposition

Zirconia–hafnia (ZrO2–HfO2) nanolaminate structures were grown using the atomic layer deposition (ALD) technique with different stacking sequences and layer thickness layer thicknesses. The microstructural evolution and surface roughness were compared with those of single-layer ZrO2 or HfO2 films using transmission electron microscopy and atomic force microscopy. Thin single-layer ALD-ZrO2 films were polycrystalline and composed of the tetragonal ZrO2 phase as-deposited, whereas thicker (>14 nm) films were composed mainly of the monoclinic phase. HfO2 films were amorphous as-deposited and crystallized into primarily monoclinic during subsequent anneals at temperatures over 500 °C. All the nanolaminate structures having individual layer thicknesses greater than approximately 2 nm were crystalline (mixture of tetragonal and monoclinic phases) independent of layer sequence and also exhibited a layer-to-layer epitaxy relationship within each grain. However, the identity of the starting layer determined the final grain size and surface roughness of the nanolaminates. A qualitative model for the observed microstructure evolution of the laminate films is proposed.

Microstructural evolution of ZrO2–HfO2 nanolaminate structures grown by atomic layer deposition

Microstructural evolution of ZrO2–HfO2 nanolaminate structures grown by atomic layer deposition

HfO2–ZrO2 Doped Silica Thin Films by XPS

Silica thin films embedding ZrO2 and HfO2 were prepared by spin-coating on silica glass via a modified sol-gel processing. The novel synthetic route is based on the co-polymerization of two organically modified oxozirconium and oxohafnium clusters (M4O2(OMc)12 with M = Zr, Hf and OMc = OC(O)–C(CH3)=CH2)) with (methacryloxypropyl)trimethoxysilane (MAPTMS). The crystalline clusters, which are the precursors for the corresponding metal oxides (MO2) were prepared via the sol-gel route by reacting zirconium or hafnium butoxide with methacrylic acid. The copolymerization of the cluster with previously prehydrolyzed methacrylate-functionalized siloxane, allows the anchoring of the oxoclusters to the forming silica network. Thin films were prepared starting from a THF (tetrahydrofurane) solution with molar ratios Hf4O2(OMc)12: Zr4O2(OMc)12:MAPTMS of 1:1:88. After deposition, the films were annealed 3 h at 800 °C in air to promote the decomposition of the hafnium and zirconium oxoclusters to give the corresponding HfO2 and ZrO2 oxides. The obtained HfO2–ZrO2–SiO2 films resulted transparent, homogeneous and displayed a very good adhesion to the substrate. The composition of the films was investigated by secondary ionization mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). The depth profiles evidenced a very homogenous distribution of both zirconium or hafnium species within the whole silica films and sharp film-substrate interfaces. As far as XPS analyses are concerned, the main XPS core-levels were analyzed for the annealed sample and the formation of hafnium and zirconium oxides was evidenced.

Introduction to XPS Studies of Metal and Metal-oxide Nanosystems

Metal and metal-oxide based nanosystems are intriguing candidates for a plethora of advanced applications thanks to their diversified chemico-physical properties, that can be further tailored by the use of proper synthesis procedures. Among the different preparation techniques, chemical vapor deposition (CVD), rf sputtering, and sol-gel (SG) display promising features for the design and control of nanosystem characteristics even beyond thermodynamical predictions, thanks to the soft synthetic conditions that enable nucleation to prevail over the subsequent particle agglomeration. In this context, a direct feedback between the nanosystem synthesis and characterization represents a unique tool for the optimization of the process. In particular, XPS spectroscopy plays an outstanding role for the investigation of surface and in-depth chemical composition of thin films as a function of the experimental conditions. In this article, the attention is devoted to the XPS analysis of different kinds of nanosystems, from nanostructured thin films (LaCoO3) to oxide clusters in silica matrices (HfO2 and HfO2–ZrO2 in SiO2) and metal cluster-based composites (Au/graphite, Au/TiO2, Ag/SiO2). This Introduction provides an overview of the data presented in the collected spectral data records, focusing in particular on the interest in these systems and on the most relevant results obtained by XPS investigations.

Nanocrystalline ceramics based on the ZrO2-HfO2-Y2O3 system

The formation of nanopowders of cubic solid solutions in the ZrO2–HfO2–Y2O3 system is investigated using the coprecipitation method. Conducting ceramic materials are prepared from the powders at 1450°C.

Synthesis of Nanopowders in the ZrO2–HfO2–Y2O3 System

Powders with a crystallite size of 3–5 nm are prepared using back coprecipitation. The effect of the precipitation temperature on the size of crystallites and agglomerates is investigated. It is established that, for the chosen compositions, only the cubic phase is formed at a temperature above 550°C.

Determination of components in refractories containing zirconia by x‐ray fluorescence spectrometry

For the purpose of proposing the use of a series of reference materials (SeRMs) for x-ray fluorescence spectrometry (XRFS) of refractories containing zirconia, we examined several methods of chemical analysis, and completed two Japanese Industrial Standard (JIS) methods of analysis for zircon and/or zirconia (ZS) and alumina, zirconia and silica (AZS) and two SeRMs of Japanese Refractory Reference Materials (JRRM) (10 samples per series). Inductively coupled plasma atomic emission spectrometry and XRFS were employed for the determination of HfO2. For XRFS analysis especially, a ZrO2 HfO2 binary calibration curve is employed using synthetic standard samples (with Hf Mα as an analysis line). The compositions of both series, 3–92 mass% for ZrO2 and 0.2–46 mass% for SiO2, cover a wide range of values. A high-precision calibration curve could be produced from these SeRMs. The content of HfO2, which has rarely undergone analysis to date, was 1.6 mass% for zirconia and 1.3–1.4 mass% for zircon. These SeRMs are also registered in the Code d'Indexation des Materiaux de Reference (COMAR). Copyright © 2000 John Wiley & Sons, Ltd.

High permittivity thin film nanolaminates

Thin (∼10 nm) films comprising of Ta2O5–HfO2, Ta2O5–ZrO2, and ZrO2–HfO2 nanolaminates were deposited and characterized for possible gate dielectric applications. These films were deposited on silicon substrates using atomic layer deposition. The dielectric constants of these films were in 12–14 range and the leakage currents in 2.6×10−8–4.2×10−7 A/cm2 range at 1 MV/cm electric field. It was found that as these films were made thinner, the value of their dielectric constant dropped compared to their bulk values. The dominant leakage current mechanism at low electric fields was determined to be Schottky emission, whereas Poole–Frenkel emission dominated at higher fields.

Determination of components in refractories containing zirconia by x-ray fluorescence spectrometry

For the purpose of proposing the use of a series of reference materials (SeRMs) for x-ray fluorescence spectrometry (XRFS) of refractories containing zirconia, we examined several methods of chemical analysis, and completed two Japanese Industrial Standard (JIS) methods of analysis for zircon and/or zirconia (ZS) and alumina, zirconia and silica (AZS) and two SeRMs of Japanese Refractory Reference Materials (JRRM) (10 samples per series). Inductively coupled plasma atomic emission spectrometry and XRFS were employed for the determination of HfO2. For XRFS analysis especially, a ZrO2 HfO2 binary calibration curve is employed using synthetic standard samples (with Hf Mα as an analysis line). The compositions of both series, 3–92 mass% for ZrO2 and 0.2–46 mass% for SiO2, cover a wide range of values. A high-precision calibration curve could be produced from these SeRMs. The content of HfO2, which has rarely undergone analysis to date, was 1.6 mass% for zirconia and 1.3–1.4 mass% for zircon. These SeRMs are also registered in the Code d'Indexation des Materiaux de Reference (COMAR). Copyright © 2000 John Wiley & Sons, Ltd.

Sintering of new oxide ceramics using a high power cw CO2 laser

The sintering of ceramic oxide powders has been investigated using a high power CO2 laser as the heat source. The laser sintering method is very useful for the densification of oxides such as ZrO2, HfO2, and Y2O3 which have high melting points above 2000 °C. The new ceramic in the ternary system of (ZrO2-Y2O3-HfO2) processed by the laser method has a high melting point (2850 °C) and a hardness of about 1800 kg/mm2. The new oxide ceramic is composed of the crystalline phase of tetragonal ZrO2 and ZrO2 HfO2 Y2O3 solid solution, and does not show any phase transitions at high temperatures.

Quantitative determination of hafnium in mixtures of zirconium–hafnium hexachloro alkali compounds by neutron activation analysis and X-ray fluorescence

A procedure for the determination of Hf in both mixtures of HfCl4–ZrCl4 and A2HfCl6–A2ZrCl6, where A = Li, Na, K, Rb, or Cs, is described. The method involves conversion of the chlorocompounds into HfO2–ZrO2 mixtures and subsequent analysis by either X-ray fluorescence or neutron activation analysis. The two analytical techniques are compared with regard to accuracy and simplicity.

Vibrational Spectra of HfO2–ZrO2 Solid Solutions

Vibrational spectra were measured and analyzed for HfO2–ZrO2 solid solutions. Some Raman bands in the high–wave–number region shift almost linearly with changes in ZrO2 concentration between the pure end–members; their band locations can be used to determine ZrO2 concentrations in annealed solid solutions. The Raman bands of pure ZrO2 and HfO2 can be correlated using the band shifts of the solid solutions. Induced stress causes band shifts for the solid solutions.