Showing papers on "Hafnium published in 2009"

Atomic layer deposition of hafnium lanthanum oxides

Abstract: There is provided an improved method for depositing thin films using precursors to deposit binary oxides by atomic layer deposition (ALD) techniques. Also disclosed is an ALD method for depositing a high-k dielectric such as hafnium lanthanum oxide (HfLaO) on a substrate. Embodiments of the present invention utilize a combination of ALD precursor elements and cycles to deposit a film with desired physical and electrical characteristics. Electronic components and systems that integrate devices fabricated with methods consistent with the present invention are also disclosed.

Hafnium binary alloys from experiments and first principles

Abstract: Despite the increasing importance of hafnium in numerous technological applications, experimental and computational data on its binary alloys is sparse. In particular, data is scant on those binary systems believed to be phase separating. We performed a comprehensive study of 44 hafnium binary systems with alkali metals, alkaline earths, transition metals and metals, using high-throughput first principles calculations. These computations predict novel unsuspected compounds in six binary systems previously believed to be phase separating They also predict a few unreported compounds in additional systems and indicate that some reported compounds may actually be unstable at low temperatures. We report the results for the following systems: AgHf, AlHf, AuHf, BaHf*, BeHf, BiHf, CaHf*, CdHf, CoHf, CrHf, CuHf, FeHf, GaHf, HfHg, HfIn, HfIr, HfK*, HfLa*, HfLi*, HfMg, HfMn, HfMo, HfNa*, HfNb*, HfNi, HfOs, HfPb, HfPd, HfPt, HfRe, HfRh, HfRu, HfSc, HfSn, HfSr*, HfTa*, HfTc, HfTi, HfTl, HfV*, HfW, HfY*, HfZn, and HfZr. (* = systems in which the ab initio method predicts that no compounds are stable).

Electron blocking layers for electronic devices

Abstract: Methods and apparatuses for electronic devices such as non-volatile memory devices are described. The memory devices include a multi-layer control dielectric, such as a double or triple layer. The multi-layer control dielectric includes a combination of high-k dielectric materials such as aluminum oxide, hafnium oxide, and/or hybrid films of hafnium aluminum oxide. The multi-layer control dielectric provides enhanced characteristics, including increased charge retention, enhanced memory program/erase window, improved reliability and stability, with feasibility for single or multi state (e.g., two, three or four bit) operation.

Properties of tungsten-rhenium and tungsten-rhenium with hafnium carbide

Abstract: Historically, tungsten-25wt.% rhenium alloy has been manufactured into wire for the thermocouple market, but recent demands for high-temperature structural components have forced the development of novel processing techniques for tungsten-rhenium and tungsten-rhenium with hafnium carbide. With a melting temperature of 3,050°C, and a recrystallization temperature near 1,900°C, tungsten-rhenium alloys are being used in aerospace, temperature measuring, and friction stir welding applications. The mechanical properties and microstructures of tungsten-25wt.% rhenium and tungsten-25wt.% rhenium with hafnium carbide are reported at ambient temperature, 1,371°C, and 1,926°C, after processing by three methods: hot isostatic pressing, swaging, and extrusion.

A simple method for the precise determination of boron, zirconium, niobium, hafnium and tantalum using ICP-MS and new results for rock reference samples

Abstract: An analytical technique for determining boron, zirconium, niobium, hafnium and tantalum contents in rock samples by inductively coupled plasma mass spectrometry (ICP-MS) is described. The rock samples (<30 mg) were decomposed with mannitol-added HF, and dissolved in a 0.015 M HF/0.12 M HNO3 acid mixture for ICP-MS analysis. Boron, zirconium, niobium, hafnium and tantalum concentrations were measured by the internal calibration curve method using three internal standard elements, beryllium for boron, indium for zirconium and niobium, and rhenium for hafnium and tantalum. Seventeen rock reference samples from the Geological Survey of Japan and the U.S. Geological Survey were analyzed, and the determined concentrations showed good agreement with the reported values obtained by isotope dilution method, as well as with the recommended values. This technique is a simple method for the precise determination of boron, zirconium, niobium, hafnium and tantalum concentrations, and it has wide potential for geochemical application, particularly for the determination of boron.

High‐Efficiency Photon‐Number‐Resolving Detectors based on Hafnium Transition‐Edge Sensors

Abstract: Generation of nonclassical states of light is at the foundation of numerous quantum optics experiments and optical quantum information processing implementations. One such non‐Gaussian optical quantum state can be obtained by photon subtraction from a squeezed optical state. Photon‐number‐resolving detectors with high efficiency and low dark counts are needed for heralding the subtraction of one, two or more photons. Transition‐edge sensors (TES) optimized for high detection efficiency at 850 nm, seem to be ideal heralding detectors for such quantum optics experiments. In this work, we describe the fabrication and characterization of hafnium TESs embedded in an optical structure for optimal absorption at 850 nm. Accurate measurements of optical constants for all materials and fine control of layer thicknesses in the optical cavity should increase the detector efficiency to values higher than 95%.

X-Ray Photoemission Study of the Oxidation of Hafnium

Abstract: About 20  of hafnium were deposited on silicon substrates using the electron beam evaporation technique. Two types of samples were investigated. In one type, the substrate was kept at the ambient temperature. After the deposition, the substrate temperature was increased to 100, 200, and . In the other type, the substrate temperature was held fixed at some value during the deposition. For this type, the substrate temperatures used were 100, 200, 300, 400, 500, 550, and . The samples were characterized in situ by the technique of X-ray photoelectron spectroscopy. No trace of elemental hafnium is observed in the deposited overlayer. Also, there is no evidence of any chemical reactivity between the overlayer and the silicon substrate over the temperature range used. The hafnium overlayer shows a mixture of the dioxide and the suboxide. The ratio of the suboxide to dioxide is observed to be more in the first type of samples. The spectral data indicate that hafnium has a strong affinity for oxygen. The overlayer gets completely oxidized to form at substrate temperature around for the first type of samples and at substrate temperature greater than for the second type.

The molecular composition of non-modified and acac-modified propoxide and butoxide precursors of zirconium and hafnium dioxides

Abstract: Long-term storage at 0 °C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr4O(OnPr)14(nPrOH)2 in over 20% yield. The structure of this molecule can be described as a triangular Zr3(μ3-O)(OR)10(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)4(ROH) unit attached through a pair of (μ-OR) bridges. Mass spectrometric and 1H NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be ~20% for n-propoxide and ~35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr(OnPr)(OiPr)3(iPrOH)]2, from zirconium n-propoxide. A high yield has been observed (~90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)3(acac)]2 in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)4 through very unstable M(acac)3(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by 1H NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction. Electronic supplementary material The online version of this article (doi:10.1007/s10971-009-1988-0) contains supplementary material, which is available to authorized users.

Breakdown and degradation of ultrathin Hf-based (HfO2)x (SiO2)1-x gate oxide films

Abstract: Ultrathin films of hafnium oxide (HfO2) and hafnium silicate (HfO2)x(SiO2)1−x gate stacks (∼3nm) have been subjected to localized electrical stress with a conductive atomic force microscope (C-AFM) in ultrahigh vacuum. The nanoscale current-voltage (I-V) characteristics, prebreakdown temperature dependent I-V measurements on large area metal-insulator-semiconductor capacitors, postbreakdown (BD) topography, current maps, and AFM tip-surface contact force are used to interpret the progressive degradation of the oxide under electrical stress. For the pre-BD phase, trap-assisted tunneling and Fowler–Nordheim tunneling were found to be dominant current transport mechanisms in Hf-based gate stacks contributing to oxide leakage current. For the post-BD phase, an overall effect of barrier limited tunneling current on the charge propagation is confirmed and related to post-BD conductivity features observed by constant voltage scanning. A critical trap density required to trigger a BD event of the ultrathin (HfO2)...

Atomic Layer Deposition of Hafnium Silicate Thin Films Using Tetrakis(diethylamido)hafnium and Tris(2-methyl-2-butoxy)silanol

Abstract: Hafnium silicate films were grown by atomic layer deposition using the liquid precursors tetrakis(diethylamido)hafnium (TDEAH) and tris(2-methyl-2-butoxy)silanol, [CH 3 CH 2 C(CH 3 ) 2 O] 3 SiOH (TMBS) Using in situ ellipsometry, ex situ high resolution transmission electron microscopy (HRTEM), medium energy ion scattering (MEIS), and X-ray photoelectron spectroscopy (XPS), the details of the film thickness and composition were examined as functions of both the substrate temperature and silanol pulse time Both HRTEM and MEIS measurements revealed that the films comprised two layers, with the surface layer containing more Hf than the layer in contact with the substrate A self-limiting growth with a rate ~ 1ML/cycle was observed only after several initial cycles, a behavior that is ascribed to the chemistry of the initial Si substrate surface Hf 4f XPS confirmed that the films were stoichiometric Hf x Si 1-x O 2 throughout despite the nonconstant Hf concentration with depth A reaction mechanism between TDEAH and TMBS is proposed

Sonochemical Synthesis of Air-Insensitive Carbide-Stabilized Hafnium Subhydride Nanopowder

Abstract: An air-passivated hafnium subhydride subcarbide nanopowder of the formula Hf3.47C1.00H2.40Li0.10O0.12 was prepared via a slurry sonochemical reaction of HfCl4 and LiH, followed by a 900 °C vacuum anneal. HRTEM of the nanopowder revealed crystallites of 10 nm average diameter that are agglomerated into larger porous structures.

Determination of microamounts of hafnium in zirconium using inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry during their separation by ion exchange on Diphonix chelating resin.

Abstract: Inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICPMS) methods were applied to check the possibility of determination of hafnium in zirconium at a level lower than 100 ppm. A zirconium matrix of hafnium content lower than 10 ppm was obtained using a worked-out separation method exploiting ion exchange on Diphonix resin. Both methods give results in good agreement with each other as well as with those for certified reference material BCR-098 (Zircaloy-4). They were utilized in determination of Hf in the samples collected during separation of microamounts of hafnium from zirconium by the mentioned ion exchange. These results proved the earlier described method of separation on Diphonix resin to be effective even when the initial concentration of hafnium in zirconium decreases from 2.4% to 0.0082%.

Hafnium oxide thin films: Effect of growth parameters on oxygen and hafnium vacancies

Abstract: Thin films of hafnium oxide were grown by reactive molecular beam epitaxy. The growth parameters, substrate temperature, and oxidation conditions were varied in a wide range in order to investigate their influence on the thin film characteristics. The oxidation conditions during growth were decisive to hafnium oxide film orientation on c-cut sapphire substrates; it was possible to grow single oriented (00l) or (−111) oriented hafnium oxide films depending upon the oxidation conditions. The authors could successfully grow hafnium oxide thin films with oxygen or hafnium vacancies, depending on the oxidation conditions during growth, evident from optical band gap measurements. All the hafnium oxide thin films investigated in this study, irrespective of oxygen/hafnium vacancies, failed to show any ferromagnetic characteristics.

Composition-structure-dielectric property of yttrium-doped hafnium oxide films deposited by atomic layer deposition

Abstract: Sequential atomic layer deposition was used to deposit yttrium-doped hafnium oxide films with variable yttrium content using tris(ethylcyclopentadienyl) yttrium and tetrakis(diethylamino) hafnium as metal precursors and water vapor as the oxidizer. The structure and electrical properties of the resulting films were analyzed after different postdeposition annealing conditions to assess composition-structure-dielectric property relationships. The 2.5-100% yttrium-doped films annealed above 600°C for 5 min consistently yielded cubic-HfO 2 structures. However, there was a strong compositional effect on the dielectric constant, which maximized at ∼14% yttrium content. The films studied had a leakage current density of 10 -5 A/cm 2 or less at 1 V.

Growth and Material Characterization of Hafnium Titanates Deposited by Atomic Layer Deposition

Abstract: Hafnium titanate (HTO) films were deposited within a large Hf-Ti compositional range by atomic layer deposition using HfCl4/TiCl4/H2O precursors. The Hf content of the layers is well controlled by the precursor pulse ratio, as indicated by Rutherford backscattering. The saturation conditions of ternary HTOs are different compared to those of the binary oxides, First-principles simulation confirmed the enhancement of the Hf precursor reactivity in the presence of Ti-OH. Growth curves of HTOs showed a good linearity with the number of reaction cycles. A linear correlation between density, quantified by X-ray reflectometry, and composition was observed. X-ray diffraction indicated that the as-deposited films are amorphous up to 500-700 degrees C, depending on the Hf/Ti ratio. The orthorhombic HfTiO4 diffraction lines in the samples (30-64% Hf) annealed at 850 degrees C were observed. For a Hf content higher than 82%, a monoclinic HfO2-Iike structure was reported. The dielectric constant and leakage current depend on the Ti content, the film crystallinity, and the anneal atmosphere. The posideposition anneal in O-2, is found to have a drastic effect in leakage Current density reduction and could be a key for further improvements of HTO electrical properties.

Al-rich portion of the Al-Hf phase diagram

Abstract: Electrical resistivity measurements, differential thermal analysis, optical microscopy, and the deposition of hafnium compound particles from a melt are used to study the Al-rich portion of the Al-Hf phase diagram. Prominence is given to the hafnium solubility in solid and liquid aluminum. The studies show a peritectic character of the invariant reaction during the solidification of alloys with sufficiently high hafnium contents and a slight difference between the peritectic and melting temperatures of pure aluminum. The hafnium solubility in solid and liquid aluminum is shown to increase with the temperature. The hafnium solubility in solid aluminum at the peritectic temperature (maximum solubility) is 1.00 wt % (0.153 at %); the hafnium solubility in liquid aluminum at this temperature is 0.43 wt % (0.065 at %).

Internal correction of hafnium oxide spectral interferences and mass bias in the determination of platinum in environmental samples using isotope dilution analysis

Abstract: A method has been developed for the accurate determination of platinum by isotope dilution analysis, using enriched 194Pt, in environmental samples containing comparatively high levels of hafnium without any chemical separation. The method is based on the computation of the contribution of hafnium oxide as an independent factor in the observed isotope pattern of platinum in the spiked sample. Under these conditions, the ratio of molar fractions between natural abundance and isotopically enriched platinum was independent of the amount of hafnium present in the sample. Additionally, mass bias was corrected by an internal procedure in which the regression variance was minimised. This was possible as the mass bias factor for hafnium oxide was very close to that of platinum. The final procedure required the measurement of three platinum isotope ratios (192/194, 195/194 and 196/194) to calculate the concentration of platinum in the sample. The methodology has been validated using the reference material “BCR-723 road dust” and has been applied to different environmental matrices (road dust, air particles, bulk wet deposition and epiphytic lichens) collected in the Aspe Valley (Pyrenees Mountains). A full uncertainty budget, using Kragten’s spreadsheet method, showed that the total uncertainty was limited only by the uncertainty in the measured isotope ratios and not by the uncertainties of the isotopic composition of platinum and hafnium.

Low Temperature Chemical Vapor Deposition of Hafnium Nitride—Boron Nitride Nanocomposite Films

Abstract: Nanocomposite HfNx-BN thin films are deposited by chemical vapor deposition at substrate temperatures of 350−800 °C using the single-source precursor hafnium borohydride, Hf(BH4)4, in combination w...

Excitation functions for proton-induced reactions on natural hafnium: Production of 177Lu for medical use

Abstract: There is an increasing interest in using radioisotopes of rare earth elements for internal radiotherapy and for imaging in nuclear medicine. 177Lu is one of the promising radionuclides. This article reports on the first measurements of the excitation function for the production of 177Lu with proton-beam energies up to 17 MeV on natural hafnium targets. The experimental cross sections for the reaction natHf(p,x)177Lu were obtained by the activation of a stacked-foil target and subsequent gamma spectrometry. Theoretical cross sections were calculated up to 35 MeV with the EMPIRE nuclear reaction model code. The measured and calculated cross sections were used for deriving the thick-target yields and for estimating the production of other nuclides than 177Lu. Measured production cross sections of 175,176,177,178Ta on the same target are also presented.

Hafnium Resonance Parameter Analysis Using Neutron Capture and Transmission Experiments

Abstract: The focus of this work is to determine the resonance parameters for stable hafnium isotopes in the 0.005- to 200-eV region, with special emphasis on the overlapping 176Hf and 178Hf resonances near ...

Method for manufacturing alloy powders based on titanium, zirconium and hafnium, alloyed with the elements ni, cu, ta, w, re, os, and ir

Abstract: A method for manufacturing alloy powders based on titanium, zirconium and hafnium, alloyed with the elements Ni, Cu, Ta, W, Re, Os, and Ir is described in which an oxide of Ti and/or Zr and/or Hf is mixed with a metal powder of the elements named and with a reducing agent, and wherein this mixture is heated in a furnace, optionally under a argonate atmosphere or, optionally under hydrogen atmosphere (forming metal hydrides in the process), until the reducing reaction begins, the reaction product is leached and then washed and dried, wherein the oxide used has an average grain size of 0.5 to 20 μm, a specific surface area according to BET of 0.5 20 m2/g and a minimum content of 94 wt.-%. An easy to produce powder, in particular in relation to the ignition point and burning time, is produced.