PAC investigations of radiation damage annealing in In implanted ZnO

The structural and electronic environment about implanted radioactive ¹¹¹In(→¹¹¹Cd) probe atoms as a function of annealing temperature in a single crystal of ZnO(0 0 0 1) has been monitored on an atomic scale using perturbed angular correlation technique, a nuclear hyperfine method. This technique is based upon the hyperfine interaction of the nuclear electric quadrupole moment or magnetic moment of the probes, respectively, with the electric field gradient or magnetic hyperfine field arising from the extra-nuclear electronic charges and spin distributions. The probe atoms ¹¹¹In were recoil-implanted at room temperature following heavy-ion nuclear reactions. The electric quadrupole interaction was measured at room temperature for as-implanted and annealed samples. The thermal annealing in ambient nitrogen up to 1000 °C showed a progressive reduction of disorder around the probe atom as evidenced via continual decrease in width of the distribution of quadrupole interaction frequencies. Present measurements suggested that annealing at 800 °C for 30 min in flowing nitrogen is enough to produce an optimum recovery of crystallinity. After annealing of radiation damage at 1000 °C we observed an axially symmetric electric field gradient which is characterized by the unique quadrupole interaction frequency of 30.6(3) MHz and a frequency distribution of width nearly zero. The observed electric field gradient was attributed to substitutional incorporation of probe atoms at cation-sites of ZnO. In contrast to annealing in ambient nitrogen at 1000 °C, air annealing of ¹¹¹In implanted ZnO samples revealed change in local stoichiometry about probe atoms which is attributed to the internal oxidation of the indium probes. The measured electric field gradient and asymmetry parameter at cation-sites of ZnO have been compared with theoretical calculations using a simple point charge model.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Enhancement of fatigue endurance and retention characteristic in Bi3.25Eu0.75Ti3O12 thin films

The effects of moderate annealing temperature (600–800 °C) on the microstructure, fatigue endurance, retention characteristic, and remnant polarization (2P_r) of Bi_3.25Eu_0.75Ti₃O₁₂ (BET) thin films prepared by metal-organic decomposition (MOD) were studied in detail. 2P_r (66 µC/cm² under 300 kV/cm), fatigue endurance (3% loss of 2P_r after 1.2 × 10¹⁰ switching cycles), and retention characteristic (no significant polarization loss after 1.8 × 10⁵s) for BET thin film annealed at 700 °C are better than those for thin films annealed at other temperature. The mechanisms concerning the dependence of microstructure and ferroelectric properties on the annealing temperature were discussed.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Solid phase epitaxy on N-type polysilicon films formed by aluminium induced crystallization of amorphous silicon

In this work, undoped amorphous silicon layers were deposited on n-type AIC seed films and then annealed at different temperatures for epitaxial growth. The epitaxy was carried out using halogen lamps (rapid thermal process or RTP) or a tube conventional furnace (CTP). We investigated the morphology of the resulting 2 µm thick epi-layers by means of optical microscopy. An average grain size of about 40 µm is formed after 90 s annealing at 1000 °C in RTP. The stress and degree of crystallinity of the epi-layers were studied by micro-Raman Spectroscopy and UV–visible spectrometer as a function of annealing time. The presence of compressive stress is observed from the peak position which shifts from 520.0 cm^− 1 to 521.0 cm^− 1 and 522.3 cm^− 1 after CTP annealing for 10 min and 90 min, respectively. It is shown that the full width at half maximum (FWHM) varies from 9.8 cm^− 1 to 15.6 cm^− 1, and the magnitude of stress is changing from 325 MPa to 650 MPa. Finally, the highest crystallinity is achieved after annealing at 1000 °C for 90 min in a tube furnace exhibiting a crystalline fraction of 81.5%. X-ray diffraction technique was used to determine the preferential orientation of the poly-Si thin films formed by SPE technique on n⁺ type AIC layer. The preferential orientation is 100 for all annealing times at 1000 °C.     

Effects of electron irradiation on SiGe devices

The degradation and the recovery behavior of the device performance for SiGe diodes and p-MOSFETs irradiated by 2-MeV electrons are reported. For diodes, it is noted that both the reverse and forward current increase by irradiation. An interesting observation is that the forward current decreases after irradiation for a forward voltage larger than ~ 0.7 V. This reduction can be explained by an increased resistivity of the Si substrate. The degradation recovers by thermal annealing after irradiation. For a fluence of 1 × 10¹⁵ e/cm², the diode performance almost recovers to the initial condition after 250 °C annealing. For the transistors, after irradiation, a slight negative shift of the threshold voltage and a decrease of the drain current for input and output characteristics have been observed together with a decrease of hole mobility. This is mainly due to the increase of the threshold voltage induced by positive charge trapping in the gate oxide.     

Thermal evolution and optical properties of Cu nanoparticles in SiO2 by ion implantation

SiO₂ samples were implanted by 45 keV Cu ions at a dose of 1 × 10¹⁷ /cm², and subjected to furnace annealing at temperatures ranging from 200 to 600 °C in nitrogen atmosphere. The results indicate that the Cu nanoparticles have been synthesized by Cu ion implantation, and subsequent annealing induces the diffusion and nucleation of nanoparticles partially. The results from XPS measurements show that the Cu⁰ is the dominate charge state in the implanted and subsequent annealed samples. With increasing annealing temperature, the size and distribution of Cu nanoparticles have been modified gradually. The surface plasmon resonance (SPR) of Cu nanoparticles at 570 nm has been observed by optical transmission spectroscopy. The strongest SPR signal at 400-600 °C indicates that lots of Cu nanoparticles have grown and show good optical properties. Moreover, the luminescence has been investigated in Cu implanted and subsequent annealed samples. Possible luminescence mechanisms, such as radiation induced defects, Cu (ions or atoms) related luminescence centers, etc., have been discussed.     

Effect of annealing temperature on the pitting corrosion resistance of super duplex stainless steel UNS S32750

The pitting corrosion resistance of commercial super duplex stainless steels SAF2507 (UNS S32750) annealed at seven different temperatures ranging from 1030 °C to 1200 °C for 2 h has been investigated by means of potentiostatic critical pitting temperature. The microstructural evolution and pit morphologies of the specimens were studied through optical/scanning electron microscope.Increasing annealing temperature from 1030 °C to 1080 °C elevates the critical pitting temperature, whereas continuing to increase the annealing temperature to 1200 °C decreases the critical pitting temperature. The specimens annealed at 1080 °C for 2 h exhibit the best pitting corrosion resistance with the highest critical pitting temperature. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The aforementioned results can be explained by the variation of pitting resistance equivalent number of ferrite and austenite phase as the annealing temperature changes.     

Ambipolar microcrystalline silicon thin-film transistors

Hydrogenated microcrystalline silicon (µc-Si:H) has recently received significant attention as a promising material for thin-film transistors (TFTs) in large area electronics due to its high electron and hole charge carrier mobilities. We report on ambipolar TFTs based on microcrystalline silicon prepared by plasma-enhanced chemical vapor deposition at temperature of 160 °C with high electron and hole charge carrier mobilities of 40 cm²/Vs and 10 cm²/Vs, respectively. The ambipolar microcrystalline silicon TFTs provide a simple route in realizing large area integrated circuits at low cost. The electrical characteristics of the ambipolar microcrystalline silicon TFTs will be described and the first results on ambipolar inverters will be presented. The influence of the ambipolar TFT characteristics on the performance of the inverter will be also discussed.     

Photoactivity of anatase–rutile TiO2 nanotubes formed by anodization method

Titania (TiO₂) nanotubes were prepared by anodizing titanium (Ti) foils in an electrochemical bath consisting of 1 M glycerol with 0.5 wt.% NH₄F.The pH of the bath was kept constant at 6 and the anodization voltage was varied from 5 V, 20 V to 30 V. It is found that the morphology of the anodized titanium is a function of anodization voltage with pits-like oxide formed for the sample made at 5 V and samples made at 20 V and 30 V consisted of well-aligned nanotubes growing perpendicularly on the titanium foil. However, the nanotubes formed on the samples made at 30 V were not uniform in terms of the nanotubes' diameter and wall thickness. Regardless of the anodization voltage, as anodised samples were amorphous. The crystal structure evolution was studied as a function of annealing temperatures and was characterised by X-ray diffraction and Raman spectroscopy analyses. Crystallization of the nanotubes to anatase phase occurred at 400 °C while rutile formation occurred at 700 °C. Disintegration of the nanotube arrays was observed at 600 °C and the structure completely vanished at 700 °C. TiO₂ nanotube annealed at 400 °C and containing 100% anatase revealed the highest photocatalytic activity for the degradation of methyl orange. Consequently, these results indicate that diameter, wall thickness, crystal structure and degree of crystallinity of the TiO₂ nanotube arrays are the important factors influencing the efficiency of the photocatalytic activity.     

Electrical properties of Sm-doped bismuth titanate thin films prepared on Si (100) by metalorganic decomposition

Samarium-doped bismuth titanate [Bi_4−xSm_xTi₃O₁₂ (BSmT)] thin films have been grown on n-type Si (100) substrates using metalorganic decomposition and subsequent annealing at 700 °C for 1 h. X-ray diffraction analysis showed layered perovskite structures with a single phase in the films. The current-voltage characteristics displayed ohmic conductivity in the lower voltage range and space-charge-limited conductivity in the higher voltage range. The capacitance-voltage characteristics of Au/BSmT/Si (100) exhibited hysteresis loops due to the ferroelectricity and did not show large carrier injections. The fixed charge density and the surface state density of BSmT films on Si substrate were calculated to be in the range of 10¹¹ cm⁻² and 10¹² cm⁻² eV⁻¹, respectively.     

Mechanically activated synthesis of nanocrystalline ternary carbide Fe3Mo3C

In this investigation, Fe₃Mo₃C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe₃Mo₃C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe₂C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C.     

N-type PTCDI–C13H27 thin-film transistors deposited at different substrate temperature

N-type organic thin-film transistors based on N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide have been fabricated by thermal evaporation at different substrate temperatures. The best device was obtained at 120 °C with a field-effect mobility of 0.12 cm²/V·s and threshold voltage around 46 V. In this work, the microstructure of the films is correlated with the device performance. In particular, the dependence of the activation energy for the channel conductance on gate voltages has been related to the properties of the layers.     

Thermal annealing behaviour of Pd Schottky contacts on melt-grown single crystal ZnO studied by IV and CV measurements

Current-voltage (IV) and capacitance-voltage (CV) measurement techniques have successfully been employed to study the effects of annealing highly rectifying Pd/ZnO Schottky contacts. IV results reveal a decrease in the contact quality with increasing annealing temperature as confirmed by a decrease in the zero bias barrier height and an increase in the reverse current measured at −1.5 V. An average barrier height of (0.77 ± 0.02) eV has been calculated by assuming pure thermionic emission for the as-deposited material and as (0.56 ± 0.03) eV after annealing at 550 °C. The reverse current has been measured as (2.10 ± 0.01) × 10⁻¹⁰ A for the as-deposited and increases by 5 orders of magnitude after annealing at 550 °C to (1.56 ± 0.01) × 10⁻⁵ A. The depletion layer width measured at −2.0 V has shown a strong dependence on thermal annealing as it decreases from 1.09 μm after annealing at 200 °C to 0.24 μm after annealing at 500 °C, resulting in the modification of the dopant concentration within the depletion region and hence the current flowing through the interface from pure thermionic emission to thermionic field emission with the donor concentrations increasing from 6.90 × 10¹⁵ cm⁻³ at 200 °C to 6.06 × 10¹⁶ cm⁻³ after annealing at 550 °C. This increase in the volume concentration has been explained as an effect of a conductive channel that shifts closer to the surface after sample annealing. The series resistance has been observed to decrease with increase in annealing temperature. The Pd contacts have shown high stability up to an annealing temperature of 250 °C as revealed by the IV and CV characteristics after which the quality of the contacts deteriorates with increase in annealing temperature.     

Simulated heat affected zone in ASTM A533-B steel plates under low heat inputs

To investigate the weldability of A533-B steel plates, simulations of the coarse grained region of heat affected zone (with heat inputs of 10, 20 and 30 kJ cm⁻¹) followed by inter-pass heating at 300 °C and post-weld heat treatments at 590 °C were carried out. The microstructural evolution, the hardness and the toughness of the simulated heat-affected zone were studied. With heat inputs of 10 and 20 kJ cm⁻¹, both of the simulated microstructures contain mixtures of lower bainite and auto-tempered martensite. With heat input of 30 kJ cm⁻¹, the simulated microstructure is composed mainly of lower bainite. The Charpy impact toughness has also been measured for the simulated heat input specimens, which were treated by inter-pass heating at 300 °C and post-weld treatment at 590 °C.     

Void formation in silica glass induced by thermal oxidation after Zn ion implantation

Thermal annealing effects on Zn⁺ ion-implanted silica glass (a-SiO₂) have been studied in order to control void formation. Void formation in a-SiO₂ with Zn⁺ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn⁺ ions of 60 keV were implanted into a-SiO₂ to a fluence of 1.0 × 10¹⁷ ions/cm². After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10-15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO₂ substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10-25 nm in diameter inside the a-SiO₂. These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.     

Evaluation of the film formation and the charge transport mechanism of indium tin oxide nanoparticle films

The structure formation and charge transfer of thin nanoparticulate indium tin oxide (ITO) films prepared by dip-coating was studied as a function of stabilizer before and after annealing at different temperatures. The analysis of the film structure by optical methods revealed that it is a function of the stability. Suspensions containing an optimum stabilizer concentration of 0.1 mol/l resulted in densely packed films with a peak specific conductivity of 8.3 S cm^− 1 after annealing at 550 °C for 1 h in air and 121 S cm^− 1 after annealing in forming gas at 250 °C for 1 h, respectively. Furthermore, for the densely packed films fluctuation-induced tunnelling was found to be the dominant charge transport mechanism, whereas for the low density films a thermally activated charge transport was observed. That the films of maximum density showed a metallic charge transport behaviour at temperatures above 300 K indicated the optimal contact between ITO particles had been achieved.     

Transient liquid phase bonding of titanium to aluminium nitride

Titanium has been successfully joined to aluminium nitride AlN at a temperature as low as 795 °C, using Ag–Cu Cusil^® commercial braze alloy. While reactive wetting and spreading proceeds at the AlN/braze alloy interface, chemical interactions develop at the titanium side rendering possible isothermal solidification of the joint. The determining factor in the solidification process is the fast formation of TiCu₄ crystals by heterogeneous nucleation and growth in the liquid phase. As a consequence, the braze alloy is depleted in Cu and solid Ag precipitates. After annealing, the re-melting temperature of the resulting joint can be increased up to about 910 °C which is nearly 130 °C higher than the melting point of the starting braze alloy.     

Comparative measurements of highly irradiated n-in-p and p-in-n 3D silicon strip detectors

Silicon detectors in 3D technology are a candidate for applications in environments requiring an extreme radiation hardness, as in the innermost layers of the detectors at the proposed High-Luminosity LHC. In 3D detectors, the electrodes are made of columns etched into the silicon perpendicular to the surface. This leads to higher electric fields, a smaller depletion voltage and a reduced trapping probability of the charge carriers compared to standard planar detectors. In this article, the signal and the noise of irradiated n-in-p and p-in-n 3D silicon strip detectors are compared. The devices under test have been irradiated up to a fluence of 2×10¹⁶ 1 MeV neutron equivalent particles per square centimetre (n_eq/cm²), which corresponds to the fluence expected for the inner pixel detector layers at the High-Luminosity LHC. A relative charge collection efficiency of approximately 70% was obtained even after the highest irradiation fluence with both detector types. The influence of different temperatures on the signal and the noise is investigated and results of annealing measurements are reported.     

Structural, electrochemical and optical comparisons of tungsten oxide coatings derived from tungsten powder-based sols

Tungsten trioxide (WO₃) electrochromic coatings have been formed on indium tin oxide-coated glass substrates by aqueous routes. Coating sols are obtained by dissolving tungsten powder in acetylated (APTA) or plain peroxotungstic acid (PTA) solutions. The structural evolution and electrochromic performance of the coatings as a function of calcination temperature (250 °C and 400 °C) have been reported. Differential scanning calorimetry and X-ray diffraction have shown that amorphous WO₃ films are formed after calcination at 250 °C for both processing routes; however, the coatings that calcined at 400 °C were crystalline in both cases. The calcination temperature-dependent crystallinity of the coatings results in differences in optical properties of the coatings. Higher coloration efficiencies can be achieved with amorphous coatings than could be seen in the crystalline coatings. The transmittance values (at 800 nm) in the colored state are 35% and 56% for 250 °C and 400 °C-calcined coatings, respectively. The electrochemical properties are more significantly influenced by the method of sol preparation. The ion storage capacities designating the electrochemical properties are found in the range of 1.62–2.74 × 10^− 3 (mC cm^− 2) for APTA coatings; and 0.35–1.62 × 10^− 3 (mC cm^− 2) for PTA coatings. As a result, a correlation between the microstructure and the electrochromic performance has been established.