Ion-beam reduction of the surface of tantalum higher oxide

The process of reduction of the surface of higher oxide Ta₂O₅ under irradiation by inert gas (Ar⁺) and chemically active gas (O₂⁺) ions with an energy of 3 keV in high vacuum is investigated by X-ray photoelectron spectroscopy at room temperature. It is found that intermediate oxide TaO₂, lower oxide TaO, and metallic Ta form in the surface layers of Ta₂O₅ under Ar⁺ ion bombardment. An insignificant amount of intermediate oxide TaO₂ forms in the surface layers of Ta₂O₅ under O₂⁺ ion bombardment. Ion-beam-induced reduction of the Ta₂O₅ surface is shown to depend on the type of ion and irradiation dose.     

Effects of packing materials on the sensitivity of RadFET with HfO2 gate dielectric for electron and photon sources

The radiation sensing field effect transistor (RadFET) with SiO₂ gate oxide has been commonly used as a device component or dosimetry system in the radiation applications such as space research, radiotherapy, and high-energy physics experiments. However, alternative gate oxides and more suitable packaging materials are still demanded for these dosimeters. HfO₂ is one of the most attractive gate oxide materials that are currently under investigation by many researchers. In this study, Monte Carlo simulations of the average deposited energy in RadFET dosimetry systems with different package lid materials for point electron and photon sources were performed with the aim of evaluating the effects of package lids on the sensitivity of the RadFET by using HfO₂ as a gate dielectric material. The RadFET geometry was defined in a PENGEOM package and electron–photon transport was simulated by a PENELOPE code. The relatively higher average deposited energies in the sensitive region (HfO₂ layer) for electron energies of 250?keV–20?MeV were obtained from the RadFET with the Al₂O₃ package lid despite of some deviations from the general tendency. For the photon energies of 20–100?keV, the average amount of energy deposited in RadFET with Al₂O₃ package was higher compared with the other capped devices. The average deposited energy in the sensitive region was quite close to each other at 200?keV for both capped and uncapped devices. The difference in the average deposited energy of the RadFET with different package lid materials was not high for photon energies of 200–1200?keV. The increase in the average deposited energy in the HfO₂ layer of the RadFET with Ta package lid was higher compared with the other device configurations above 3?MeV.     

Effect of oxide surface metallization under ion-beam irradiation

Changes in the surface chemical composition of WO₃, Ta₂O₅, MoO₃, and Nb₂O₅ oxides after Ar⁺ ion irradiation and those of the WO₃ surface after He⁺ ion irradiation under high vacuum were investigated by X-ray photoelectron spectroscopy. Upon Ar⁺ ion irradiation with an energy of 3 keV, the pronounced effect of ion-beam metallization was observed on the WO₃ oxide surface; a moderate effect was found for the Ta₂O₅ oxide surface; a weak one for the MoO₃ oxide surface; and no effect was discovered for the Nb₂O₅ oxide surface. At the saturation dose, 44 at % W, 12 at % Ta, and 2 at % Mo form on the oxide surfaces. Irradiation by light He⁺ ions with energies of 1 and 3 keV results in WO₃ surface metallization. At the saturation dose, 2 and 10 at % W (at 1 and 3 keV, respectively) forms on the oxide surface. The nature, mechanisms, and features of the oxide surface metallization effect induced by ion-beam irradiation are discussed.     

Control of the properties of Pb(TixZr1-x )O3 solid solutions by external disturbances

The influence of x-ray irradiation to absorbed radiation doses D = (0.5?12) × 10⁸ rad on the properties of ferroelectric ceramic Pb(Ti_xZr_1?x )O₃ solid solutions with compositions close to the morphotropic phase boundary was studied. The effects of x-ray radiation on the electrical conductivity of ferroelectric ceramics are shown to differ with x ranging from 0.42 to 0.60. Using empirical equations and numerical techniques, quantitative relations are established between the composition, absorbed radiation dose, and electrical conductivity for Pb(Ti_xZr_1?x )O₃.     

Monodisperse Polypyrrole Nanoparticles Prepared via γ‐Ray Radiolysis of Water: An Efficient Near‐Infrared Photothermal Agent for Cancer Therapy

Biosafe nanoparticles with strong near‐infrared (NIR) light photothermal conversion effect can bring effective hyperthermia as one of the promising approaches in cancer therapy. In this work, a new facile and green preparation method of polypyrrole (PPy) nanoparticles based on ⁶⁰Co γ‐ray radiation on a simple air‐saturated strong acidic aqueous solution of pyrrole (pH ≤ 1) is studied. According to the MCAP‐FACSIMILE simulation on the concentrations of the radiolysis products of water at the presence of H⁺ and O₂, the main strong oxidative radiolysis products · OH and H₂O₂ rapidly induce the polymerization of pyrrole. The size of the prepared PPy nanoparticles is about several tens of nanometers and can be controlled by the pH, the concentration of the stabilizer poly(vinyl alcohol), and the absorbed dose rate (the amount of energy absorbed per unit mass of the irradiated material within per unit of time). The PPy nanoparticles show rapid and remarkable NIR (808 nm) photothermal conversion efficiency up to 40.1% in water. Furthermore, the in vitro and in vivo experiments confirm that the prepared PPy nanoparticles exhibit enough strong NIR photothermal effect in tumor cells (4T1 and HeLa) and show a promising prospect as the NIR photothermal agent for the future cancer therapy.     

Structural and compositional changes in ion-bombarded Ta2O5

A detailed study of the effect of heavy-ion bombardment on Ta₂O₅ has been undertaken using a combination of radioactive tracer techniques, electron microscopy, and Rutherford backscattering. Crystalline Ta₂O₅ is amorphized at ~6 × 10¹³ ions cm^?2, while at a dose of ~5 × 10¹⁶ ions cm^?2 the electron microscopy reveals the development of random grains of a new crystalline phase. By ~1 × 10¹⁷ ions cm^?2 the grains are not yet overlapping but still yield a diffraction pattern consistent with either δ-Ta-O (not to be confused with TaO) or Ta_1?xO₂, thus indicating that Ta₂O₅, like most other transition-metal oxides, is subject to preferential sputtering. Preferential sputtering was confirmed by backscattering analysis of specimens bombarded to high doses, where the average surface composition was found to be Ta_1.8±0.2O₂ or, equivalently, Ta₂O_2.2±0.2. The surface alteration had an average composition independent of the mass and energy of the incident ions.     

Stretching the limits of static SIMS with C60

Pristine and Au-covered molecular films have been analyzed by ToF-SIMS (TRIFT™), using 15 keV Ga⁺ (FEI) and 15 keV C₆₀⁺ (Ionoptika) primary ion sources. The use of C₆₀⁺ leads to an enormous yield enhancement for gold clusters, especially when the amount of gold is low (2 nmol/cm²), i.e. a situation of relatively small nanoparticles well separated in space. It also allows us to extend significantly the traditional mass range of static SIMS. Under 15 keV C₆₀⁺ ion bombardment, a series of clusters up to a mass of about 20,000 Da (Au₁₀₀⁻: 19,700 Da) is detected. This large yield increase is attributed to the hydrocarbon matrix (low-atomic mass), because the yield increase observed for thick metallic films (Ag, Au) is much lower. The additional yield enhancement factors provided by the Au metallization procedure for organic ions (MetA-SIMS) have been measured under C₆₀⁺ bombardment. They reach a factor of 2 for the molecular ion and almost an order of magnitude for Irganox fragments such as C₄H₉⁺, C₁₅H₂₃O⁺ and C₁₆H₂₃O⁻.     

Mineralogical,geochemical and radiological characterisation of Selmo Formation in Batman area,Turkey

This work deals with the mineralogical, geochemical and radiological characterisations of Selmo Formation in Batman neighbourhood. The upper Miocene–Pliocene Selmo Formation is common in the centre of Batman and composed of carbonated sandy claystones and silty–sandy stone lenses. The common whole minerals of the samples are quartz, feldspars, calcite and dolomite. The clay minerals are smectite, illite, chlorite and mixed-layer clay (chlorite–smectite). The geochemical mean values of the samples are 51.7% SiO₂; 12.6% Al₂O₃; 6.2% Fe₂O₃; 3.6% MgO; 6.3% CaO; 1.1% Na₂O; 1.7% K₂O; 0.8% TiO₂; 0.2% P₂O₅; 0.1% MnO; and 0.03% Cr₂O₃. In addition, baseline maps for the concentrations of each radionuclide, the radium equivalent activity and the outdoor gamma dose rate distributions have been plotted for the study area. The mean activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs were determined to be 32, 24, 210 and 9 Bq kg^?1, respectively. The assessments of the radiological hazard indices, such as radium equivalent activity, absorbed dose rate in air, annual effective dose equivalent, excess lifetime cancer risk, external hazard index and internal hazard index, were calculated and compared with the internationally accepted reference values. This study shows that the concentrations of radioactivities in the measured samples were within the recommended safety limits and did not pose to be any significant source of radiation hazard.     

Characterisation of 32P beta source for external radiation protection

Custom-made design of ³²P patch sources are used in brachytherapy applications. Use of this source requires external radiation protection. This implies measurement of absorbed dose rate to tissue at a depth of 0.07 mm. Towards this goal, 2.75 mCi ³²P patch source was locally developed. Characterization of this source has been carried out by measuring source parameters such as uniformity in the activity distribution and beam uniformity. The characterization also includes output measurements in terms of absorbed dose rate to air using an extrapolation chamber at 11, 20 and 30 cm from the source. Various correction factors which are dependent on the cavity length as well as independent of the cavity length were also determined in this study. The backscatter correction and Bragg–Grapy stopping power ratio were calculated using the Monte Carlo techniques. Using these correction factors and the measured absorbed dose rate to air, absorbed dose rate to tissue at a depth of 0.07 mm was determined. The study also includes measurements of H_p(0.07) and H_p(10) at different source-to-detector distances using an electronic pocket dosimeter.     

Nuclear resonance fluorescence in94Mo,95Mo and96Mo

Using gaseous sources of Tc₂O₇ containing the radioactive isotopes⁹⁴Tc,⁹⁵Tc and⁹⁶Tc, levels at 871.0keV (⁹⁴Mo), 765.8, 820.6, 947.8, 1074.0keV (⁹⁵Mo) and 778.3keV (⁹⁶Mo) have been excited. From the effective cross sections for nuclear resonance scattering and from the lifetimes of the 947.8, 1074.0 and 778.3keV levels known from Coulomb excitation experiments the profiles of theγ-lines have been determined. A broadening of theγ-lines due to Coulomb explosion of the molecules has been observed. Making use of the line profiles, lifetimes ofΤ=(6.4±1.0) ps andΤ=(0.90 ± 0.20) ps have been determined for the 765.8 and 820.6keV levels, respectively. The angular distribution of the resonantly scattered radiation yields an amplitude ratioδ for the mixed M1 E2 765.8keV transition ofδ=0.14 _?0.009 ^+0.08 . TheB(E2) from a Coulomb excitation experiment and the lifetimeΤ from the present experiment yield ¦δ¦=0.07±0.01 for the 820.6keV transition.     

The use of the TL and OSL phenomena for determination of absorbed dose rates of 90Sr + 90Y sources by a postal method

International recommendations establish that ⁹⁰Sr + ⁹⁰Y clinical applicators have to be calibrated in order to determine the absorbed dose rates in the case of the sources that do not have original calibration certificates, or to update the absorbed dose rates presented in the source certificates. Following these recommendations, a postal dosimetric system was developed to calibrate clinical applicators using two luminescent techniques: thermoluminescence (TL) and optically stimulated luminescence (OSL). In this work, Al₂O₃:C commercial detectors were characterized and their TL and OSL responses were analyzed. The results showed the efficiency and the optimal behavior of this material in beta radiation beams. After characterization, the system was sent to the Federal University of Sergipe (UFS), Brazil, for calibration of five ⁹⁰Sr + ⁹⁰Y clinical applicators, where the detectors were irradiated and returned to IPEN, for their evaluation and determination of the absorbed dose rates. A comparison between these absorbed dose rates and those adopted by the UFS as original was made; the differences obtained were within those of other studies, and they demonstrated the usefulness of the system.     

Availability of water glass/Bi2O3 composites in dielectric and gamma-ray screening applications

ABSTRACT

Sodium silicate (Na₂Si₃O₇) also known as water glass is a very low cost material which is used in many industrial applications such as a builder in detergents, as a binder and adhesive etc. But so far the electrical properties of sodium silicate and its ability to screen radiation have never been investigated. In the present study, the frequency dependent electrical properties and gamma-ray shielding performance of water glass based bismuth oxide composites have been studied for the first time. In accordance with this purpose, Na₂Si₃O₇/Bi₂O₃ glassy composites have been prepared for searching their possible applications in electronics and radiation screening. The surface morphology of the samples have been determined by Scanning Electron Microscope (SEM). The frequency dependent electrical properties such as complex impedance, complex dielectric function and conductivity have been analyzed at room temperature between 1 and 40?MHz. As a result of alternative current (ac) electrical analysis, it has been determined that the Na₂Si₃O₇/Bi₂O₃ composites can be utilized as a dielectric layer in capacitors. On the other hand, since bismuth oxide is an anti-radiative material, the gamma-ray screening parameters such as mass attenuation coefficient, half layer and tenth layer values along with mean free path of the composites have been defined experimentally by using NaI(Tl) scintillation detector for the Ba-133 radiation source at 81 and 356?keV. The values of these parameters have also been checked by Monte–Carlo simulation. Since a good agreement has been assigned between experimental and Monte–Carlo simulation results, the related gamma ray shielding parameters have been determined by Monte–Carlo simulation for other gamma photon energies (140?keV, 208?keV, 468?keV, and 661?keV) which are generated from Tc-99, Lu-177, Ir-132, and Cs-137 sources. Ultimately, Na₂Si₃O₇/Bi₂O₃(35%) composite has been suggested as an eco-friendly, lead-free glassy structured material for the gamma radiation shielding in medical applications.     

Optical properties of multilayer structures

The possibility of using the ellipsometry method for investigation of the optical properties of multilayer films and structures is shown. The optical properties of structures HfO₂/SiO₂/Si, HfO₂/Si, ZrO₂/Si, Ta₂O₅/Si, and Al₂O₃/Si are studied. It is found that a layer of hafnium silicate is formed at the interface between the HfO₂ film and Si. Annealing of the structures in oxygen shows that oxides studied are oxygen-permeable and that the thickness of SiO₂ at the film-substrate interface increases. The growth rate of SiO₂ layers depends on the chemical nature of an oxide. Al₂O₃ films are impermeable for oxygen diffusion. The production of layers of alloys (Al₂O₃) _x (HfO₂)_{1 ? x} is optimized, which allows one to obtain layers with a homogeneous distribution of elements over the thickness.     

Electronic structures and ferroelectric properties of ABi2Ta2O9 (A=Ca, Sr, and Ba)

The electronic structures of ABi₂Ta₂O₉ (A=Ca, Sr, and Ba) were calculated by using first-principles under optimized structure. As the size of A-site cation decreases from that of Ba²⁺ to Ca²⁺, the band-gap between O 2p and Ta 5d increases from 2.0 to 2.9 eV, which responses to the stronger orbital hybridizations between Ta 5d and O 2p orbits favoring improvement of the ferroelectric property, decrease in leakage current, and increase in both spontaneous polarization and Curie temperature by the structural distortion. In contrast to CaBi₂Ta₂O₉ and SrBi₂Ta₂O₉, the hybridization between Ba 5p orbits and O 2p orbits in BaBi₂Ta₂O₉ has better structural stability.     

Surface plasmon resonance in nano-gold antimony glass–ceramic dichroic nanocomposites: One-step synthesis and enhanced fluorescence application

A single-step melt-quench in situ thermochemical reduction technique has been used to synthesize a new series of Au° nanoparticles embedded antimony glass–ceramic (K₂O–B₂O₃–Sb₂O₃–ZnO) dichroic nanocomposites. X-ray and selected area electron diffractions manifest growth of Au° nanoparticles along (2 0 0) planes. The particle sizes obtained from X-ray diffraction patterns are found to vary in the range 4–21 nm. Dichroic behavior is attributed to the elliptical shape gold nanoparticles having aspect ratio 1.2, as observed from the transmission electron microscopy (TEM) images. The Au° nanoparticles exhibit surface plasmon resonance band (SPR) around 600 nm, which experiences red-shifts with increasing Au concentration. These nanocomposites when co-doped with Sm₂O₃ and excited at 949 nm, exhibit 2-fold intensification of 636 nm red emission transition (⁴G_5/2 → ⁶H_9/2) due to SPR induced local field enhancement of Au° nanoparticles and are promising materials for display applications.     

Study of interfacial reactions and phase stabilization of mixed Sc, Dy, Hf high-k oxides by attenuated total reflectance infrared spectroscopy

Grazing angle attenuated total reflectance Fourier transform infrared spectroscopy is applied to study ultrathin film Hf⁴⁺, Sc³⁺ and Dy³⁺oxides, due to its high surface sensitivity. The (multi)metal oxides studied, are of interest as high-k dielectrics. Important properties affecting the permittivity, such as the amorphous or crystalline phase and interfacial reactions, are characterized.Dy₂O₃ is prone to silicate formation on SiO₂/Si substrates, which is expressed in DyScO₃ as well, but suppressed in HfDyO_x. Sc₂O₃, HfScO_x and HfO₂ were found to be stable in contact with SiO₂/Si. Deposition of HfO₂ in between Dy₂O₃ or DyScO₃ and SiO₂, prevents silicate formation, showing a buffer-like behavior for the HfO₂.Doping of HfO₂ with Dy or Sc prevents monoclinic phase crystallization. Instead, a cubic phase is obtained, which allows a higher permittivity of the films. The phase remains stable after anneal at high temperature.     

Spectroscopy of the gamma and X ray leakage radiation from the built-in sources of a Risø TL/OSL reader

In this work we evaluate the intensity and the spectral shape of the leakage radiation from the built-in beta and alpha sources of a Risø TL/OSL reader. LiF (TLD-100), fluorite-based pellets and Al₂O₃:C detectors were used in order to determine the dose rate delivered to the dosimeters when the sources are closed. The leakage spectra under both alpha and beta sources were registered with a CdTe semiconductor detector. The spectrum measured under the beta source shows the X-ray beam generated by the interaction of the beta particles with the lead used to shield the source. Besides, the 59.4 keV gamma ray from ²⁴¹Am was registered under the alpha source. Dose rates from 50 to 100 μGy/h were obtained for the dosimeter positions in the turntable under the beta and the alpha sources with the luminescent dosimeters.     

Microstructure and thermal stability of Fe,Ti, and Ag implanted yttria-stabilized zirconia

Yttria-stabilized zirconia (YSZ) was implanted with 15 keV Fe or Ti ions up to a dose of 8×10¹⁶ at cm^–2. The resulting dopant concentrations exceeded the concentrations corresponding to the equilibrium solid solubility of Fe₂O₃ or TiO₂ in YSZ. During oxidation in air at 400° C, the Fe and Ti concentration in the outermost surface layer increased even further until a surface layer was formed of mainly Fe₂O₃ and TiO₂, as shown by XPS and ISS measurements. From the time dependence of the Fe and Ti depth profiles during anneal treatments, diffusion coefficients were calculated. From those values it was estimated that the maximum temperature at which the Fe- and Ti-implanted layers can be operated without changes in the dopant concentration profiles was 700 and 800° C, respectively. The high-dose implanted layer was completely amorphous even after annealing up to 1100° C, as shown by scanning transmission electron microscopy. Preliminary measurements on 50 keV Ag implanted YSZ indicate that in this case the amorphous layer recrystallizes into fine grained cubic YSZ at a temperature of about 1000° C. The average grain diameter was estimated at 20 nm, whereas the original grain size of YSZ before implantation was 400 nm. This result implies that the grain size in the surface of a ceramic material can be decreased by ion beam amorphisation and subsequent recrystallisation at elevated temperatures.     

Qβ measurements of 158, 159Pm , 159, 161Sm , 160-165Eu , 163Gd and 166Tb using a total absorption BGO detector

Q _β values of the neutron-rich isotopes of ^160-165Eu and ¹⁶³Gd were measured for the first time using a total absorption bismuth germanate (BGO) detector, and previously obtained data on ^{158, 159}Pm , ^{159, 161}Sm and ¹⁶⁶Tb were re-analyzed. These radioactive sources were prepared by an on-line mass separator (Tokai-ISOL) following the ²³⁸U (p,f reaction. The deduced Q _β values are the following: 6085(80)keV for ¹⁵⁸Pm , 3805(65)keV for ¹⁵⁹Sm , 5460(140)keV for ¹⁵⁹Pm , 4705(60)keV for ¹⁶⁰Eu , 5065(130)keV for ¹⁶¹Sm , 3705(60)keV for ¹⁶¹Eu , 5575(60)keV for ¹⁶²Eu , 4690(70)keV for ¹⁶³Eu , 3170(70)keV for ¹⁶³Gd , 6430(70)keV for ¹⁶⁴Eu , 5800(120)keV for ¹⁶⁵Eu , and 4695(70)keV for ¹⁶⁶Tb . Moreover, the deduced mass excesses and two-neutron separation energies ( S _2n values) were compared with those of the atomic mass evaluations and theoretical predictions.     

Combined SIMS,AES, and XPS investigations of tantalum oxide layers

Thick layers of tantalum oxide prepared by thermal and anodic oxidation have been studied by combined SIMS, AES, and XPS during depth profiling by 3keV Ar⁺ ion sputtering. The chemical composition of these films is revealed by the OKLL and O 1s signals and by the “lattice valence” parameter determined from the TaO _n ^± intensities. Thus the anodic film consists of a contamination layer, an oxygen-rich reactive interface and a thick homogeneous oxide layer followed by an interface to the Ta metal. The thermal oxide shows an oxygen concentration decreasing with depth and a broad oxide-metal interface. In both cases, carbon contamination (carbide) prevents the application of the valence model to the clean Ta substrate. The sputtering yield of the oxides was found to be 0.6 Ta₂O₅/ion.