High Temperature Annealing Treatment Research Articles

Fiber Bragg gratings with enhanced thermal stability by residual stress relaxation

Fiber Bragg gratings with greatly enhanced thermal stability have been fabricated by the use of femtosecond laser pulse irradiation on optical fibers with relaxed residual stress, through using high temperature annealing treatment. The grating reflectivity and resonant wavelength can be maintained for periods up to 20 hours using isothermal measurements and temperatures up to 1200 degrees C. No hysteresis was observed in the wavelength response when the gratings were annealed and the temperature cycled repeatedly between room temperature and 1200 degrees C.

Recrystallization of twin-roll cast Al–Fe–Si foil stock processed without homogenization

Differential scanning calorimetry, hardness testing, electrical conductivity measurements and microstructural analysis were employed in the present work to investigate the response of twin-roll cast Al–0.8Fe–0.6Si strips to interannealing without prior homogenization. Recrystallization which occurs at 400 °C in sheet samples cold rolled only lightly ( ɛ ∼ 0.2) is gradually displaced to lower temperatures with increasing strain until ɛ ∼ 2.3. Precipitation occurs largely before a measurable recrystallization reaction at low strains, ɛ < 2.3, producing an acceptable grain structure across the section. The interaction of the two reactions at ɛ > 2.3 is believed to be responsible for a decreasing recrystallized fraction and for coarse grains at the surface where the interaction is likely to be most pronounced. Interannealing of the Al–0.8Fe–0.6Si alloy without a homogenization treatment produces acceptable grain structures across the section of the strip for much of the cold rolling strain range. It is thus concluded that Al–0.8Fe–0.6Si foil stock, intended for cosmetic foil applications where formability is not critical, could be processed without a high-temperature annealing treatment.

Size Dependent Allotropic Transition of Co Fine Particles

In order to investigate the size dependent allotropic transition of Co in wide size range, nanometer scaled (9 nm-350 nm) and micrometer sized (1 microm-18 microm) Co particles were prepared by laser induced pyrolysis, reduction as well as high temperature annealing treatment. In wide size range, from 9 nm to 10 microm for example, the crystal structure of the Co particles is dependent on their thermal history in which the particle involved in preparation or in annealing treatment. Only when the particle size is very large, much greater than 10 microm for example, the fcc-hcp transformation could occur during the cooling from high temperautre. According to the effect of surface energy on the martensitic transformation, the size dependent allotropic transformation of Co was discussed.

High temperature annealing treatment on Co doped ZnO bulks

Zn0.95Co0.05O Bulk samples were synthesized by solid state reaction method and annealed by different processes. The Zn treated samples show ferromagnetism，whereas the vacuum annealed samples do not show ferromagnetism. The XRD patterns show that there is Co impurity phase in the sample after Zn treatment at 1100℃，which is the reason of the ferromagnetism observed. At low temperature，both the positive and negative magnetoresistance （MR） effect can be observed for all the samples. We conclude that the s-d exchange_interaction_induced spin-splitting gives rise to positive MR， while the formation of bound magnetic polarons and the magnetic field suppressed spin-disorder scattering are responsible for the negative MR behavior under high field.

Mechanical Sintering Techniques for Printed Electrodes with Various Work-function on a Plastic Substrate

AbstractA print technique of an electrode on a plastic substrate is one of the most important techniques for developing a printed large area device. Especially, preparation of a metal electrode with low work function by printing is very important to develop printed active devices such as diode and transistors. Work function values of electrodes strongly affect device properties (1,2), because the work function difference between a semiconductor and an electrode is related to charge injection from the electrode to the semiconductor. Recently, many solution-processable n-type semiconductors have been developed (3), because these are required to fabricate printable EL devices, printable CMOS devices, and so on. Low-work function metals are necessary to inject electrons to n-type semiconductor. In spite of this fact, very few printable low-work function metal inks have been developed, because low-work function metals are easily oxidized during print process owing to high temperature annealing treatment and their conductivities are lost.In this study, we have examined to develop a new annealing technique on a printed electrode to reduce the process temperature during metal printing. We have newly developed a mechanical sintering technique in which mechanical forces is applied on a printed metal pattern. Control of the direction balance of applied mechanical force was effective to reduce resistivity of the printed metal without any destruction of plastic substrate. Furthermore, distribution control of metal particle in the metal ink was also effective to reduce resistivity. By using this technique, we have succeeded in the preparation of an aluminum, zinc, copper and tin electrode on a plastic substrate. On the other hand, we have tried to prepare a metal alloy ink to control the work function of printed electrode. Metal alloy ink was composed of two kinds of metal particles. Work function of the electrode was controlled by changing composition of these metal contents in an alloy ink. By applying our developed mechanical sintering technique on the printed alloy pattern, printed electrode with various work functions from 3.5eV to 5eV could be prepared on a plastic substrate. These printed alloys were effective to improve the performance of printed diode and transistors.

Nanoscale (EOT = 5.6 nm) nonvolatile memory characteristics usingn-Si/SiO2/HfAlO nanocrystal/Al2O3/Pt capacitors

The charge storage characteristics of thehigh-κ HfAlO nanocrystal memory capacitors prepared by atomic layer deposition in ann-Si/SiO2/HfAlO/Al2O3/Pt structure have been investigated after high-temperature annealing treatment. Thehigh-resolution transmission electron microscopy image shows that the diameter ofhigh-κ HfAlOnanocrystal is<2 nm. The high-κ HfAlO nanocrystals have been also confirmed by x-rayphotoelectron spectroscopy measurement. Due to the formation ofhigh-κ HfAlO nanocrystals with the high-temperature(∼900 °C) annealing treatment, a large hysteresis memory window of 3.7 V at a sweeping gate voltage<10 V isobserved as compared to that of the as-deposited memory capacitors. A hysteresis memory window of∼1.7 V with a small sweepinggate voltage of ± 5 V is also observed. A small equivalent oxide thickness (EOT) of 5.6 nm is obtained due to thehigh-κ memory structure design. A significant memory window ofΔV≈0.7 V at20 °C andΔV≈0.6 V at85 °C is observedafter 104 s of retention time, due to the charge confinement in thehigh-κ HfAlO nanocrystals.

Iron filled carbon nanostructures from different precursors

Here, we present a study on the synthesis of different nanostructures with one single-step in situ filling (encapsulation) via carbon vapor deposition (CVD). Ferrocene, acetylferrocene and iron (II) nitrate as iron precursors were explored. The application of each of these compounds resulted in different carbon nanomaterials such as: iron filled multiwalled carbon nanotubes with a low filling ratio (Fe-MWCNT), iron filled nanocapsules and unfilled MWCNT. The as-produced samples were purified by high temperature annealing and acid treatment. The purified materials were characterised using transmission electron microscopy (TEM) and Raman spectroscopy.

Near band-edge luminescence and evidence of the weakening of the N-conduction-band coupling for partially relaxed and high nitrogen composition GaAs1−xNx epilayers

Photoluminescence and absorption spectroscopy experiments are implemented on as-grown and thermally annealed GaAs1−xNx epilayers grown on GaAs(001) having a nitrogen content in the range of 0.4%–7.1%. At low temperature, photoluminescence spectra exhibit two sets of features: (i) a relatively broad peak at low energy in the vicinity of the band gap predicted by the band anticrossing model (BAC) and (ii) sharp excitonic features at higher energy (over 100meV above the band gap for x&amp;gt;4%). An enhancement of the photoluminescence response of excitonic emissions and a notable intensity reduction of the deeper luminescence were systematically observed for samples subjected to high-temperature postgrowth annealing treatments. For pseudomorphically strained low nitrogen-containing epilayers (x&amp;lt;2%), and by taking into account the strain magnitude and the average substitutional nitrogen concentration (as extracted from x-ray analysis), excitonic energies and corresponding band gaps (as determined by absorption spectroscopy) are well described within the framework of the BAC model. The extracted binding energies of split heavy- and light-hole excitons are found to be consistent with the expected increase of electron effective masses. For thick partially relaxed epilayers (1%&amp;lt;x&amp;lt;2%) and relaxed epilayers with high nitrogen content (x&amp;gt;4%), the fundamental band gap of GaAsN is found at significantly higher energies than those predicted by the BAC model using the commonly accepted nitrogen coupling parameter CNM=2.7eV. To account, within the BAC framework, for the apparent deceleration in the band-gap reduction rate requires the use of a smaller coupling constant (CNM=2.0eV), which suggests a weakening of the strength of the interaction between the localized nitrogen state and the conduction band of the host matrix. This observation seems to be associated with the increasing population of N-related defects.

Physical and electrical characteristics of atomic layer deposited TiN nanocrystal memory capacitors

The physical and electrical characteristics of atomic layer deposited TiN nanocrystals embedded in high-k Al2O3 films in a metal/Al2O3∕[TiN∕Al2O3]∕SiO2∕p-Si structure have been investigated. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy show the formation of tiny TiN nanocrystals embedded in Al2O3 films after subsequent annealing treatment. The TiN nanocrystals with a high density of &amp;gt;1×1012∕cm2 and a small size of &amp;lt;3nm have been observed. A large hysteresis memory window of ∼4.3V at small sweeping gate voltage of 3V has been observed as compared with a pure Al2O3 charge trapping layer, due to highly charge confinement in the TiN metal nanocrystals. The hysteresis memory window of 1.4V has also been observed under an extremely small sweeping gate voltage of 1V. A large memory window of ∼3.9V is observed after 10years of retention. A maximum hysteresis memory window is limited by both of the nanocrystal density and leakage current at a high temperature annealing treatment of the TiN nanocrystal memory capacitors.

Charge trapping characteristics of atomic-layer-deposited HfO2 films with Al2O3 as a blocking oxide for high-density non-volatile memory device applications

Charge trapping characteristics of high-relative permittivity (high-κ) HfO2 films with Al2O3 as a blocking oxide in p-Si/SiO2/HfO2/Al2O3/metal memory structures have been investigated. All high-κ films have been grown by atomic layer deposition. A transmission electron microscope image shows that the HfO2 film is polycrystalline, while the Al2O3 film is partially crystalline after a high temperature annealing treatment at 1000 °C for 10 s in N2 ambient. A well-behaved counter-clockwise capacitance–voltage hysteresis has been observed for all memory capacitors. A large memory window of ∼7.4 V and a high charge trapping density of ∼1.1 × 1013 cm−2 have been observed for high-κ HfO2 charge trapping memory capacitors. The memory window and charge trapping density can be increased with increasing thickness of the HfO2 film. The charge loss can be decreased using a thick trapping layer or thick tunnelling oxide. A high work function metal gate electrode shows low charge loss and large memory window after 10 years of retention. High-κ HfO2 memory devices with high-κ Al2O3 as a blocking oxide and a high work function metal gate can be used in future high-density non-volatile memory device applications.

Rapid synthesis of TiC–Fe 3C composite by electric discharge assisted mechanical milling of ilmenite (FeTiO 3) with graphite

Carbo-thermic reduction of ilmenite (FeTiO 3) to TiO 2 and/or TiC is traditionally carried out by a high temperature annealing treatment at ∼1500 °C. In this work, electric discharge assisted mechanical milling (EDAMM) has been used to synthesise TiC + Fe 3C from FeTiO 3 in 5 min. In this study we report of the reduction of FeTiO 3 with C that does not require an additional high temperature annealing treatment.

Synthesis and Assembly of Monodisperse High‐Coercivity Silica‐Capped FePt Nanomagnets of Tunable Size, Composition, and Thermal Stability from Microemulsions

The large uniaxial magnetic anisotropy energy (∼ 6.6 MJ m) of Fe–Pt alloys makes their nanostructured forms attractive for potential use as nanoscale magnetic bits in ultrahigh-density information storage devices or as fillers to create new types of magnetocomposites. The high magnetic anisotropy and coercivity arise from the chemically ordered face-centered-tetragonal (fct) L10 phase, which is sensitive to both chemical composition and the size of the nanoparticles. Control over particle size and dispersity 13] is essential to form ordered arrays of nanoparticles, and preserve these features against agglomeration during high-temperature annealing (e.g., 550 °C) treatments used to obtain the L10 phase. Therefore, it is crucial to develop protocols to produce FePt nanoparticles with control over composition, particle size, and dispersity, and thermal stability for exploiting their assemblies for data-storage media applications. The synthesis technique described here is a promising approach to realize all these features simultaneously. Prior works have demonstrated FePt nanoparticles synthesis with either excellent size control or chemical compositional control but not both. Thermal decomposition of Fe(CO)5 vapor, and reduction of Pt(acac)2, produces monodisperse nanoparticles with tunable sizes in the 2–15 nm range. But, the chemical composition of the nanoparticle is different from the initial molar ratio of the metal precursors due to different precursor decomposition rates. Size control is further complicated by the strong influence of parameters such as Ar gas flow rate, heating rate, and temperature. For example, a Fe(CO)5/Pt(acac)2 ratio of two yields Fe-deficient (Fe44Pt56) 9 nm nanoparticles or Fe-rich (Fe53Pt47) 6 nm nanoparticles, depending on the heating rate. In contrast, coreduction of FeCl2 and Pt(acac)2 results in nanoparticles with chemical compositions within 2 % of the initial molar ratio of the metal precursors, but the particle size is constrained to a limited range of approximately 3–5 nm. Neither of these two synthesis routes is easily amenable to coating the nanoparticles with a protective shell of a thermally stable material (e.g., silica or titania) that could prevent particle shape and size changes during postsynthesis annealing for obtaining the L10 phase. Although a Fe3O4 shell can be formed [15] by the thermal decomposition method, the shell degrades at temperatures less than 600 °C and destroys the nanoparticle structure and shape. Techniques to coat a silica shell on clusters of magnetic nanoparticles that have been presynthesized using a separate processing method have been demonstrated, but these techniques are not well suited for creating organized assemblies of well-separated nanoparticles for recording media applications. Here, we report the room-temperature synthesis of monodisperse FePt nanoparticles with tunable particle size over an extended range of 4–20 nm and excellent compositional control using microemulsions. We further use the same microemulsion to enhance the nanoparticle thermal stability by forming a 2 nm thick silica shell, which is also used for functionalization with organosilanes. Organized assemblies formed from the molecularly capped core/shell particles exhibit high coercivity Hc ∼ 850 mT due to L10 ordering in the particles upon annealing to 650 °C, without any observable changes to the overall nanoparticle size and shape. Synthesis and integration of high-coercivity nanomagnets of controlled shape, size, composition, surface chemistry, and stability, with molecularly engineered surfaces and matrices (e.g., polymers and biomaterials) open up new possibilities for realizing novel flexible memory devices and magnetocomposites. K2PtCl4 and FeCl3 were reduced simultaneously with N2H4, in reverse micellar microemulsions composed of nanoscopic water droplets stabilized by nonionic surfactant molecules, brij 56 or brij 52, in iso-octane. Scheme 1 illustrates the partiC O M M U N IC A IO N S

Equilibrium shape of titanium silicide nanocrystals on Si(111)

The aim of this work was to find the equilibrium shape of titanium silicide nanocrystals, epitaxially grown on Si(111) in ultrahigh vacuum. To attain the state of equilibrium, the so-grown nanocrystals were subjected to a series of prolonged high-temperature annealing treatments, and closely monitored by scanning tunneling microscopy at every annealing stage. It was established, that the equilibrium shape of the equilibrium phase (C54-$\mathrm{Ti}{\mathrm{Si}}_{2}$) nanocrystals grown by solid-phase epitaxy is a flat, hexagonal island with (01 $\overline{3}$) atomic plain parallel to Si(111), achieved after 750 \ifmmode^\circ\else\textdegree\fi{}C anneal. The nanocrystal behavior is well described by generalized Wulf-Kaishew theorem (adjusted for epitaxial nanocrystals), with their vertical aspect ratio decreasing and the top facet area increasing upon introduction of misfit dislocations at the nanocrystal-substrate interface. Screw dislocations were also observed, and seemed to play a role in facilitating the three-dimensional-to-two-dimensional shape transformation.

PRODUCTION AND GRAIN STABILITY OF NANOCRYSTALLINE Fe-Si POWDERS AND THE EFFECTS OF ALUMINIUM ADDITION

The present work studied the production of nanocrystalline Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys via a high-energy ball milling technique and their grain growth responses to high-temperature annealing treatments. The grain sizes of the resulting powders were determined by X-ray diffraction peak broadening and were also confirmed by transmission electron microscopy. A minimum crystallite size of 13-17 nm could be achieved in Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys. The lattice parameters of as-milled Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 attained minimum values of about 0.2860, 0.2842 and 0.2862 nm respectively after 60 h, and thereafter remained constant for prolonged milling times. The grain size of Fe 90 Si 10 increased from approximately 17 nm to about 35 nm after annealing at 873 K. Fe 75 Si 25 exhibited some stability against grain growth at low temperatures but not above 673 K. Fe 75 Si 15 Al 10 grains showed better stability with no significant grain growth until 873 K. For Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys annealing at 773 K, 873 K and 973 K resulted in the formation of ordered DO 3 structure.

The Grain Size and Microstructure of Jet-Electroplated Damascene Copper Films

Electroplated damascene copper is rapidly replacing aluminum-copper alloys for on-chip interconnect metallization in advanced ultralarge scale integrated (ULSI) semiconductor devices. In addition to a high degree of (111) crystallographic texture, large defect-free grains are desired to enhance the performance and reliability of copper interconnects in such devices. The brightening additive level and dc current density of electroplating baths are two parameters that affect the process gap-filling capability and the degree of additive incorporation in these copper films. Additive incorporation can inhibit grain growth during the room-temperature recrystallization process and therefore affect the final grain size in electroplated copper films. This investigation explores the grain size and microstructure of dc jet-electroplated damascene copper films deposited as a function of current density and brightening additive level after first receiving a high-temperature annealing treatment. In 1.3 μm thick blanket films it was found that large, lognormally distributed, low-resistivity, highly twinned grains with an average diameter of 1.7-1.9 μm could consistently be produced over a wide variety of electroplating conditions. These results suggest that any grain growth inhibition factors, such as remnant electroplating impurities incorporated in the blanket film microstructure after the self-annealing process, can be effectively removed from these films with a sufficient thermal budget to create a stable grain size and microstructure. © 2005 The Electrochemical Society. All rights reserved.

Nanometer scale precipitation in ferritic MA/ODS alloy MA957

The microstructure of a commercial mechanically-alloyed oxide dispersion strengthened MA957 alloy has been characterized in the as-received condition and after annealing for up to 24 h at 1300 °C (∼0.85 T m) by atom probe tomography and electron microscopy. Atom probe tomography revealed a high number density of ultrafine 2-nm-diameter Ti-, Y- and O-enriched particles in the ferrite matrix in the as-received condition. The size increased and the number density of these particles decreased during the annealing treatment for 1 and 24 h at 1300 °C. Some coarser (∼10 nm) Ti-, Y- and O-enriched precipitates were also observed at the grain boundaries. No significant grain growth or recrystallization was observed during the high temperature annealing treatment.

Thermally Robust HfN Metal as a Promising Gate Electrode for Advanced MOS Device Applications

A systematic study of thermally robust HfN metal gate on conventional SiO/sub 2/ and HfO/sub 2/ high-/spl kappa/ dielectrics for advanced CMOS applications is presented. Both HfN-SiO/sub 2/ and HfN-HfO/sub 2/ gate stacks demonstrates robust resistance against high-temperature rapid thermal annealing (RTA) treatments (up to 1000/spl deg/C), in terms of thermal stability of equivalent oxide thickness (EOT), work function, and leakage current. This excellent property is attributed to the superior oxygen diffusion barrier of HfN as well as the chemical stability of HfN-HfO/sub 2/ and HfN-SiO/sub 2/ interfaces. For both gate dielectrics, HfN metal shows an effective mid-gap work function. Furthermore, the EOT of HfN-HfO/sub 2/ gate stack has been successfully scaled down to less than 10 /spl Aring/ with excellent leakage, boron penetration immunity, and long-term reliability even after 1000/spl deg/C annealing, without using surface nitridation prior to HfO/sub 2/ deposition. As a result, the mobility is improved significantly in MOSFETs with HfN-HfO/sub 2/ gate stack. These results suggest that HfN metal electrode is an ideal candidate for ultrathin body fully depleted silicon-on-insulator (SOI) and symmetric double-gate MOS devices.

Indium distribution in epitaxially grown InGaN layers analyzed by transmission electron microscopy

An overview is given about microstructure and composition analyses of InGaN quantum wells embedded in Ga(Al)N barriers to study the mechanisms which determine the In distribution in epitaxially grown InGaN layers. The applied technique is transmission electron microscopy (TEM). The main prerequisite for this work was the development of a technique based on high-resolution lattice fringe images that allows quantitative chemical analyses of InGaN on an atomic scale. A large variety of samples was investigated that were produced by molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE). The effect of the deposition temperature, growth rate, strain and high-temperature annealing treatments on the average In concentration and In distribution was studied to assess the influence of phase separation, In surface segregation and In desorption. Composition fluctuations in InGaN are always observed on two different lateral scales independent of the growth technique and particular set of growth parameters but the strength of the composition fluctuations can be influenced by the details of the growth. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrafast directional nickel-silicide-induced crystallization of amorphous silicon under high-density current stressing

Ultrafast directional crystallization that combined the electric current stressing with metal-induced crystallization has been achieved for BF2+-implanted amorphous Si (a-Si) at room temperature. Polycrystalline Si was observed to grow from anode towards cathode and the channels of a-Si strips with a length of 140 μm and a width of 10 μm can be fully crystallized with a stressing time less than 0.2 s. The directional growth of crystalline Si nanowires, 50 nm in width and as long as 3 μm in length, with an extraordinarily high aspect ratio of 60, indicates a strong electric-field-induced effect on the growth. The growth method provides a promising scheme to solve the problems caused by high-temperature and long-term annealing treatment for the applications of optoelectronic devices.

Observations related to healing of interface damage and cavity nucleation during superplastic flow

Two critical observations related to the nucleation of superplastic cavities are reported. Cavities preexisting in a fine grain Al–Mg alloy prior to superplastic deformation have been minimized, but not completely eliminated by a high temperature annealing treatment. This has reduced the density of emerging cavities during subsequent deformation, however nucleation of cavities occur continuously with superplastic strain, starting possibly from partially healed defects of imperceptible (nanoscale) size. The observations raise doubts about the often-used cavity nucleation criterion based on a thermodynamically stable void size. Diffusional cavity growth model, used in conjunction with this assumed “stable” size artificially enlarges its perceived contribution, but still predicts less growth than the observed cavitation levels in superplastic metals. Alternate growth mechanism for submicron size cavities is suggested.