Thermal Annealing Experiments Research Articles

Helical-sampled fiber Bragg grating inscribed by a femtosecond laser in a ring core fiber.

The inscription of a helical-sampled fiber Bragg grating (HSFBG) in a ring core fiber (RCF) using a low repetition rate femtosecond laser point-by-point technique is demonstrated. The reflection spectrum exhibits several peak groups attributed to the helical-sampled structure, with the wavelength interval between different groups determined by the helical pitch. Meanwhile, the number and spacing of the peaks within each group are dictated by the RCF. An investigation into the effects of helical pitch, helical radius, and grating length of the HSFBG on the reflection spectra is conducted. Furthermore, thermal annealing experiments demonstrate that this HSFBG can survive at the temperatures up to 800°C.

Mechanochemical removal of lithium aluminosilicate glass-ceramics

In this study, the material removal behaviors of diamond and SiO2 tips on lithium aluminosilicate (LAS) glass-ceramics surface were investigated in vacuum and deionized water using atomic force microscope. Two types of mechanochemical removal, stress corrosion and tribochemical removal were identified depending on counter-surface chemical activity. Their mechanisms were revealed using Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. In addition, combined with Raman spectra detection and thermal annealing experiments of removal areas, it was confirmed that compared with stress corrosion removal which reduced the removal energy threshold, tribochemcial removal was dominated by mechanochemical interaction without structural damage. The findings enrich the mechanochemical removal theory and furnish theoretical guidance for nano-precision machining of LAS glass-ceramic surface.

Highly Regular Hexagonally-Arranged Nanostructures on Ni-W Alloy Tapes upon Irradiation with Ultrashort UV Laser Pulses.

Nickel tungsten alloy tapes (Ni—5 at% W, 10 mm wide, 80 µm thick, biaxially textured) used in second-generation high temperature superconductor (2G-HTS) technology were laser-processed in air with ultraviolet ps-laser pulses (355 nm wavelength, 300 ps pulse duration, 250–800 kHz pulse repetition frequency). By employing optimized surface scan-processing strategies, various laser-generated periodic surface structures were generated on the tapes. Particularly, distinct surface microstructures and nanostructures were formed. These included sub-wavelength-sized highly-regular hexagonally-arranged nano-protrusions, wavelength-sized line-grating-like laser-induced periodic surface structures (LIPSS, ripples), and larger irregular pyramidal microstructures. The induced surface morphology was characterized in depth by electron-based techniques, including scanning electron microscopy (SEM), electron back scatter diffraction (EBSD), cross-sectional transmission electron microscopy (STEM/TEM) and energy dispersive X-ray spectrometry (EDS). The in-depth EBSD crystallographic analyses indicated a significant impact of the material initial grain orientation on the type of surface nanostructure and microstructure formed upon laser irradiation. Special emphasis was laid on high-resolution material analysis of the hexagonally-arranged nano-protrusions. Their formation mechanism is discussed on the basis of the interplay between electromagnetic scattering effects followed by hydrodynamic matter re-organization after the laser exposure. The temperature stability of the hexagonally-arranged nano-protrusion was explored in post-irradiation thermal annealing experiments, in order to qualify their suitability in 2G-HTS fabrication technology with initial steps deposition temperatures in the range of 773–873 K.

In situ thermal annealing transmission electron microscopy of irradiation induced Fe nanoparticle precipitation in Fe–Si alloy

The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe–15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional–integral–differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms.

Thermal annealing behavior of InP-based HEMT damaged by proton irradiation

In this paper, the effects of thermal annealing on the radiated InP-based high electron mobility transistors (HEMTs) is investigated. Proton irradiation is performed with energy of 2 MeV and fluence of 5 × 1013 cm−2, and subsequently the thermal annealing experiments are carried out at 100 ℃ and 200 ℃. Both drain-source saturation current (Id,sat) and maximum transconductance (gm,max) of the radiated devices demonstrate a certain degree of recovery after annealing at 100 ℃ and 200 ℃. Id,sat and gm,max recover by the maximum values of 17.37 % and 13.66% for 10 min annealing at 100 ℃, and 12.65% and 14.54% for 5 min thermal annealing at 200 ℃. The main reason for the recovery about the DC characteristics are the restore of carrier concentration and mobility. Thermal annealing has enhanced the atoms vibration, which decreases the concentration of defects by recombination and weakens the lattice scattering by rearranging the lattice. In addition, this paper reveals that different annealing temperature and duration will have different effects on irradiated InP-based HEMTs.

Experimental Annealing of Zircon: Influence of Inclusions on Stability, Intracrystalline Melt Migration, Common Lead Leaching, and Permeability to Fluids.

Zircon derived from crustal rocks can survive dissolution into hot basalts during magma hybridization and rock assimilation if it is shielded as an inclusion phase in early-formed phenocrysts or in minerals from non-disaggregated xenoliths. Under these conditions, zircon can be thermally shocked, triggering recrystallization of metamict domains and reaction with its hosted mineral inclusions. This work simulates this process by performing thermal annealing experiments on zircon grains with variable degrees of metamictization. These were embedded in cristobalite powder under a N2 atmosphere at 1 bar and 1300 °C. The thermal annealing produces recrystallization of metamict domains, melting of multi-phase mineral inclusions, nanopore formation, and microcrack propagation by thermo-elastic stress. The porosity enhances intracrystalline melt mobility, leaching out trace-element and mineral impurities. Baddeleyite was formed at temperatures below the thermal decomposition of pure zircon by two mechanisms: (i) recrystallization of metamict domains assisted by silica migration from the reaction site and (ii) incongruent zircon dissolution into molten mineral inclusions with a high CaO/SiO2 ratio. Highly metamict zircons with elevated common Pb and radiogenic Pb loss, which were impossible to date with SHRIMP, lost all their common Pb and some radiogenic Pb upon annealing, producing well-fitted discordias with a significant upper intercept age.

Fabrication of SiC Sealing Cavity Structure for All-SiC Piezoresistive Pressure Sensor Applications.

High hardness and corrosion resistance of SiC (silicon carbide) bulk materials have always been a difficult problem in the processing of an all-SiC piezoresistive pressure sensor. In this work, we demonstrated a SiC sealing cavity structure utilizing SiC shallow plasma-etched process (≤20 μm) and SiC–SiC room temperature bonding technology. The SiC bonding interface was closely connected, and its average tensile strength could reach 6.71 MPa. In addition, through a rapid thermal annealing (RTA) experiment of 1 min and 10 mins in N2 atmosphere of 1000 °C, it was found that Si, C and O elements at the bonding interface were diffused, while the width of the intermediate interface layer was narrowed, and the tensile strength could remain stable. This SiC sealing cavity structure has important application value in the realization of an all-SiC piezoresistive pressure sensor.

Optimal design of the annealing furnace and quality improvement for KDP crystals

The optical, physical and mechanical properties of bulk crystalline materials might be improved by thermal annealing experiments. In this paper, we designed and self-manufactured a thermal annealing equipment for bulk crystalline materials. The temperature, stress distributions as well as airflow vectors in the equipment were carefully studied by the Finite Element Method. By using this equipment, we performed various of the thermal annealing experiments for KDP crystals in air, vacuum, N2 and H2, and we firstly found that its optical homogeneity can be greatly increased by annealing in H2, and whereas no obvious effect in air and N2. In addition, the thermal and stress field distributions in the annealing materials were also investigated, which has a guidance to avoid the local stress production and even break for the annealing materials.

The self-repairing of ion irradiation damaged Mo–S–Ti (MoST) lubricant films by thermal annealing

Mo–S–Ti composite films deposited by magnetron sputtering were irradiated by 2 MeV Au2+ with a high fluence of 3.3 × 1015 ion cm−2. Upon intense bombardment by 2 MeV Au2+, the Mo–S–Ti thin film exhibits sensitivity to radiation-induced amorphization at room temperature. Afterwards, thermal annealing experiments on the irradiated thin films were conducted over the temperature range of 200 °C–900 °C. Subsequent annealing experiments found that the effect of heavy ion irradiation on Mo–S–Ti films was a reversible reaction, with the irradiation-damaged MoS2 lattice being completely self-repaired by thermal annealing. In the annealing temperature range of 200 °C–600 °C, no evidence of an amorphous to recrystallized transition was observed. When the temperature was increased to as high as 700 °C, the damaged MoS2 molecules were well recrystallized. HRTEM images of irradiated samples annealed at 700 °C strikingly found that the self-repaired MoS2 crystallites preserving long range ordering were still rearranged in an intrinsic (0 0 2) crystal orientation. MoS2 nanocrystals that survived the ion bombardment step may provide some nucleus for subsequent MoS2 grains growing dominantly in the (0 0 2) direction in thermal annealing. Compared with the difficult recrystallization in thermal annealing, the irradiation-amorphized MoS2 phases were easily self-repaired under friction. The low transition potential barrier from irradiation-induced amorphization to crystallization, achieved by mechanical working, may be an important reason for the quick recrystallization.

Single Source Precursors for Calcium Sulfide (CaS) Deposition

Here we describe preliminary studies into the synthesis structural characterisation and thermal properties of a family of calcium xanthate precursors for application in the deposition of CaS thin films. The straightforward, low‐temperature syntheses are detailed along with characterisation of the resulting compounds by 1H and 13C NMR and elemental analysis. Solid state molecular structures of all compounds, obtained from single‐crystal X‐ray diffraction, are presented and discussed in detail. The decomposition behaviour of the precursors has been probed through TGA, TGA‐MS and thermal annealing experiments, indicating that the compounds decompose cleanly into CaS.

Growth of a Surface-Tethered, All-Carbon Backboned Fluoropolymer by Photoactivated Molecular Layer Deposition.

The synthesis of an all-carbon backboned fluoropolymer using photoactivated molecular layer deposition (pMLD) is developed. pMLD is a vapor-phase, layer-by-layer, organic thin film synthesis method utilizing UV light, allowing for the creation of materials previously unavailable via thermal MLD. The carbon backbone is achieved by reacting an iodine-containing fluorocarbon monomer (1,4-diiodooctafluorobutane) and a diene monomer (1,5-hexadiene) under UV irradiation in a step-growth polymerization sequence. The polymerization occurs with a growth rate of 1.3 Å/cycle, forming a copolymer containing hydrocarbon and fluorocarbon segments. X-ray photoelectron spectroscopy (XPS) was used to confirm the formation of new carbon-carbon bonds and quantify the final film composition. In situ XPS thermal annealing experiments confirm the film stability up to 400 °C. The ability to pattern the fluoropolymer on a surface is demonstrated using a photomask, suggesting that these films could be incorporated into photolithographic processes. Together, these results demonstrate that pMLD can be used to synthesize carbon backboned films with photopatterning ability, expanding the available chemistries and potential applications of MLD polymers.

Stability investigations of the thermal insulating performance of aerogel blanket

Nowadays fibre reinforced silica aerogels receive special attention due to their application in the building construction sector. Aerogel, besides the Vacuum Insulation Panels are one of the so-called super/advanced/nano-technological insulation materials due to their low declared thermal conductivity. However, these days their high manufacturing cost goes against their common use. Nonetheless, the investigations of their thermal and material properties are highlighted research topics in the last few years. The testing as well as the development of these insulation materials are very important both for the manufacturers and for the designers. Therefore investigations of the thermal properties (e.g.: thermal conductivity) are extremely important. In order to show the stability of the thermal insulation performance of glass fibre reinforced aerogel blankets, firstly, moisture related investigations will be presented taking special look at the sorption isotherm and the wetting kinetic curves of the samples carried out by climatic chamber method. Then thermal conductivity measurements will be presented after humidity and thermal annealing as climatic ageing and exposures. Two types of measurement series were accomplished for thermal annealing experiments: (a) time kinetic (isothermal) investigations at 70°C for 1–42 days and (b) isochronal (1 day) annealing experiments were done, where the temperature was changed from 70°C to 210°C. After both experiment series the thermal conductivities were registered by Holometrix 2000 apparatus. The measurement results will be presented as graphs, too. Afterwards, images taken with optical microscope for exploring the changes on the surface and in the hydrophobicity of the samples will be also presented. These investigations as well as the results can serve as proof of the good thermal stability and the excellent performance of this insulation.

Ca-, Sr-, and Ba-Coordination polymers based on anthranilic acid via mechanochemistry.

Ca-, Sr-, and Ba-Based coordination polymers (CPs) were prepared mechanochemically by milling metal-hydroxide samples with anthranilic acid (oABAH). {[Ca(oABA)2(H2O)3]}n (1) consists of one-dimensional polymeric chains that are further connected by a hydrogen-bonding network. {[Sr(oABA)2(H2O)2]·H2O}n (2) is a one-dimensional CP in which water molecules bridge Sr2+ ions and increase the dimensionality by building an extended network. {[Ba(oABA)2(H2O)]}n (3) crystallizes as a two-dimensional CP comprising one bridging water molecule. The cation radii influence the inorganic connectivity and dimensionality of the resulting crystal structures. The crystal structures were refined from powder X-ray diffraction data using the Rietveld method. The local coordination environments were studied via extended X-ray absorption fine structure (EXAFS) measurements. The compounds were further characterized using comprehensive analytical methods such as elemental analysis, thermal analysis, MAS NMR, imaging, and dynamic vapor sorption (DVS) measurements. Compounds 1, 2, and 3 exhibit small surface areas which decrease further after thermal annealing experiments. All compounds exhibit a phase transformation upon heating, which is only reversible in 3.

Controls on lithium concentration and diffusion in zircon

Thermal annealing of zircons prior to uranium-lead dating by laser ablation inductively coupled plasma mass spectrometry is a commonly-implemented procedure which improves data accuracy and precision by partially repairing radiation damage from the decay of uranium and thorium. However, it also leads to significantly higher concentrations of lithium in the zircon lattice, which become positively correlated with trivalent yttrium and rare earth elements. Prior to such treatments, zircons typically contain lithium below detection limits (typically <0.55 μg g−1), unless correlated with lanthanum and aluminum (i.e., melt/mineral inclusion tracer elements). This suggests that lithium in zircon is primarily sequestered within inclusions, and is able to permeate the crystal lattice to couple with yttrium and rare earth elements during the thermal annealing procedure. This process occurs 2–3 orders of magnitude faster than diffusion experiments have previously determined, indicating that another diffusion mechanism may apply. A model is proposed, whereby: (i) charge compensation of stoichiometrically over-abundant trivalent cations under water-rich magmatic conditions is likely accomplished by hydrogen, given the incompatibility of lithium in zircon and the abundance of hydrogen. However, (ii) conditions that are high temperature and low pressure (characteristic of both thermal annealing and the syn-eruptive environment), drive silicate melt inclusions to exsolve water, generating a motive force for both hydrogen and lithium from inclusions to permeate the lattice in order to reestablish electrochemical equilibrium between the interior and exterior of the zircon. To test the pressure dependency of lithium migration in the zircon lattice, thermal annealing experiments were performed at 850 °C and 1 bar, 2 kbar and 6 kbar using zircons from the Fish Canyon Tuff. The experiments demonstrate that thermal annealing at 2 and 6 kbar inhibits lithium mobility, with zircons registering lithium concentrations below detection limits similar to controls. The experimental results suggest that lithium concentrations in zircon are vulnerable to rapid perturbation by decompression (concurrent with high temperatures), which further indicate that lithium-in-zircon diffusion data should be interpreted with caution.

Study of aluminium oxide thin films deposited by plasma-enhanced atomic layer deposition from tri-methyl-aluminium and dioxygen precursors: Investigation of interfacial and structural properties

Aluminium oxide (Al2O3) films were deposited on silicon substrates using plasma-enhanced atomic layer deposition (PE-ALD) technique with tri-methyl-aluminium TMA (Al(CH3)3) and dioxygen (O2) as precursors. PE-ALD experiments were performed in order to (i) investigate the interfacial properties between the silicon substrate and the alumina layer, and (ii) understand the impact of growth and crystallization phenomena on the Al2O3 films properties (structural, optical, mechanical, dielectric and etch). The formation of oxide-based transition layers, either silicon oxide SiO2 and/or aluminosilicate AlxSiyO, was evidenced for the TMA/O2 PE-ALD process. Based on these results, it appears that no substrate-enhanced growth occurs at the early stages of the growth process, as assumed in previous reports. Thus, constant growth rate (0.08 nm per cycle) and refractive index (1.64 at a 450 nm wavelength) were obtained for the Al2O3 layer deposited at 300 °C. Finally, thermal annealing experiments were performed on these films, evidencing the influences of atomic structural rearrangement and crystallization on the Al2O3 film main characteristics: interface steepness, atomic structure, refractive index, residual stress, dielectric constant and etch rate.

Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Super-hydrophobic surfaces are attractive due to self-cleaning and anti-corrosive behaviors in harsh environments. Laser texturing offers a facile method to produce super-hydrophobic surfaces. However, the results indicated that the fresh laser ablated surface was generally super-hydrophilic and then gradually reached super-hydrophobic state when exposed to ambient air for certain time. Investigating wettability changing mechanism could contribute to reducing wettability transition period and improving industrial productivity. To solve this problem, we have studied the bare aluminum surface, fresh laser ablated super-hydrophilic surface, 15-day air exposed surface, and the aged super-hydrophobic surface by time-dependent water contact angle (WCA) and rolling angle (RA), scanning electron microscopy (SEM), 3D profile and X-ray photoelectron spectroscopy (XPS). The origins of super-hydrophilicity of the fresh laser ablated surface are identified as (1) the formation of hierarchical rough structures and (2) the surface chemical modifications (the decrease of nonpolar carbon, the formation of hydrophilic alumina and residual unsaturated atoms). The chemisorbed nonpolar airborne hydrocarbons from air moisture contributed to the gradual super-hydrophobic transition, which can be proved by the thermal annealing experiment. Particularly, to clearly explore the wettability transition mechanism, we extensively discussed why the laser-induced freshly outer layer was super-hydrophilic and how the airborne hydrocarbons were chemisorbed. This work not only provides useful insights into the formation mechanism of laser ablated super-hydrophobic surfaces, but also further guides industry to effectively modify surface chemistry to reduce wettability transition period and rapidly produce stable and durable super-hydrophobic surfaces.

Electric Characteristic Enhancement of an AZO/Si Schottky Barrier Diode with Hydrogen Plasma Surface Treatment and AlxOx Guard Ring Structure

In this study, the design and fabrication of AZO/n-Si Schottky barrier diodes (SBDs) with hydrogen plasma treatment on silicon surface and AlxOx guard ring were presented. The Si surface exhibited less interface defects after the cleaning process following with 30 w of H2 plasma treatment that improved the switching properties of the following formed SBDs. The rapid thermal annealing experiment also held at 400 °C to enhance the breakdown voltage of SBDs. The edge effect of the SBDs was also suppressed with the AlxOx guard ring structure deposited by the atomic layer deposition (ALD) at the side of the SBDs. Experimental results show that the reverse leakage current was reduced and the breakdown voltage increased with an addition of the AlxOx guard ring. The diode and fabrication technology developed in the study were applicable to the realization of SBDs with a high breakdown voltage (>200 V), a low reverse leakage current density (≤72 μA/mm2@100 V), and a Schottky barrier height of 1.074 eV.

Thermoluminescence in Lapis Lazuli crystal: Glow peaks and their connection with F-centers estimated by ESR analysis

The mineral Lapis Lazuli exhibits three thermoluminescence (TL) peaks approximately at 140, 260 and 370°C. The TL intensity of the three peaks grows with radiation dose and it saturates only beyond 9 kGy. Electron Spin Resonance (ESR) studies have been carried out to identify the defect centers responsible for the thermoluminescence peaks. The ESR spectrum of the as-received natural sample presented the typical six signals due to Mn2+ ion and a large signal around g=2.030 due to Fe3+ ion. Room temperature ESR spectrum of irradiated Lapis Lazuli shows the formation of a defect center. This center (center I) is identified as an F+-center (singly ionized oxygen vacancy) and seems to correlate with 140 and 250°C TL peaks. An additional defect center is observed during thermal annealing experiments and this center (center II - assigned to F+-center) appears to originate from an F-center (oxygen vacancy with two electrons). This F-center, precursor of center II, may be related to the observed high temperature 360°C TL peak in Lapis Lazuli.

Structural relaxation phenomena in silicate glasses modified by irradiation with femtosecond laser pulses

Structural relaxation phenomena in binary and multicomponent lithium silicate glasses were studied upon irradiation with femtosecond (fs) laser pulses (800 nm central wavelength, 130 fs pulse duration) and subsequent thermal annealing experiments. Depending on the annealing temperature, micro-Raman spectroscopy analyses evidenced different relaxation behaviours, associated to bridging and non-bridging oxygen structures present in the glass network. The results indicate that the mobility of lithium ions is an important factor during the glass modification with fs-laser pulses. Quantitative phase contrast imaging (spatial light interference microscopy) revealed that these fs-laser induced structural modifications are closely related to local changes in the refractive index of the material. The results establish a promising strategy for tailoring fs-laser sensitivity of glasses through structural mobility.

Probing the densification mechanisms during flash sintering of ZnO

Using ZnO as a model system, the densification mechanisms of flash sintering are investigated. Controlled experiments via limiting the maximum current or the effective ramp rate suggest that both the maximum specimen temperature and the high heating rate (on the order of 200 °C/s) are essential for the rapid densification during the flash sintering. Moreover, benchmarking rapid thermal annealing (RTA) experiments, which were conducted to mimic the heating profiles in the flash sintering, achieved similar densification and grain growth rates with comparable heating profiles, attesting that the ultrafast densification is mainly enabled/determined by the T(t) profile. The combination of these experiments suggest that, at least for ZnO, the rapid heating profile is a key factor for the observed rapid densification in flash sintering, while various electric field/current effects could also exist. A clear and consistent correlation between the grain sizes and relative densities is also evident for specimens made by both flash sintering and RTA with different conditions, suggesting the same conventional grain growth mechanism in both cases under the current experimental conditions.