Modification of the etching properties of x-cut Lithium Niobate by ion implantation

In this work x-cut Lithium Niobate crystals were implanted with 0.5 MeV O ions (nuclear stopping regime), 5 MeV O ions (sub-threshold electronic stopping regime) and 12.5 MeV Ti ions (ion track regime) at the fluences required for the formation of a surface fully disordered layer. The damage depth profiles were determined by RBS-channeling. Wet etching was performed at room temperature in 50% HF:H₂O solution. The data indicated an exponential dependence of the etching rate on the damage concentration. Independently of the damage regime, once random level in the RBS-channeling spectra was attained we measured the same etching rate (50-100 nm/s) and the same volume expansion (∼10%) in all samples. These results indicate that the fully disordered layers obtained by electronic damage accumulation have the same chemical properties of those obtained by conventional nuclear damage accumulation and therefore they can be defined “amorphous”. The impressive etching selectivity of ion implanted regions makes this process suitable for sub-micro machining of Lithium Niobate.     

Performance of the new single stage accelerator mass spectrometer at the SUERC

A NEC 250 kV single stage accelerator mass spectrometer (SSAMS) has been installed along-side our five year old 5 MV spectrometer. The new instrument is intended to take over routine radiocarbon measurement, thereby providing more capacity for our rapidly growing cosmogenic nuclide programme. Initial tests show that although flawed the SSAMS sufficiently mimics the good performance of the first machine; high-precision ¹⁴C/¹³C measurement is being achieved with a background limited by sample preparation.     

High temperature oxidation of Fe-9Cr-1Mo steel in stagnant liquid lead-bismuth at several temperatures and for different lead contents in the liquid alloy

This research project deals with the feasibility studies concerning the construction of an hybrid reactor for the transmutation of long-lived radioactive wastes. In this context, the liquid lead-bismuth eutectic (LBE) is considered to be a good candidate for the spallation target material needed for the neutrons production necessary to the transmutation. In this hybrid reactor, the LBE, which is enclosed in a T91 (Fe-9%Cr) steel container, can induce corrosion concerns. If the oxygen content dissolved in Pb-Bi is higher than the needed content for magnetite formation, corrosion proceeds by oxidation of the steel. Previously, specific results were reported, obtained in stagnant liquid LBE at 470 °C. An analytical model taking into account the oxide layer structure has been carried out. It involves iron, oxygen and chromium bulk diffusion and diffusion via preferential paths such as liquid lead-bismuth nano-channels incorporated in the oxide layer structure and grain boundaries. In this paper, experimental results on corrosion kinetics, obtained at different temperatures with different percentages of lead in the lead-bismuth alloy, are presented. The model, adapted to the different experimental conditions, is compared to these kinetics and to experimental points coming from the literature at different temperatures in LBE, in pure lead and in pure bismuth.     

Characterisation of an enamelled metallic object found in Guerrero Negro (Baja California) by PIXE and RBS techniques

The coast of Guerrero Negro (Baja California) has been known for a long time by archaeologists for its shipwrecks. Archaeologists are recovering objects that come from sunken Spanish galleons in the colonial period, and reach the American coast in the frontier of the USA with Mexico.An enamelled metallic object was found next to the beach in Guerrero Negro. We have analysed the piece with proton induced X-ray emission (PIXE) and Rutherford backscattering (RBS) in an attempt to establish whether the object could come from one of the colonial shipwrecks and to valuate its cleaning process.Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) have been also performed in three samples taken from the object in order to observe the heterogeneity of the material.The materials found revealed the presence of typical lead-glass enamels from with pigments such as cuprite (red), or lead-tin yellow used in colonial times. The metallic part consisted of brass. As for the cleaning process, the average efficiency considered as the weight% of chlorine removed, was of 83.4% for brass and 100% for enamels.     

Oxidation behavior of Incoloy 800 under simulated supercritical water conditions

For a correct design of supercritical water-cooled reactor (SCWR) components, data regarding the behavior of candidate materials in supercritical water are necessary. Corrosion has been identified as a critical problem because the high temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics. The goal of this paper is to investigate the oxidation behavior of Incoloy 800 exposed in autoclaves under supercritical water conditions for up to 1440 h. The exposure conditions (thermal deaerated water, temperatures of 723, 773, 823 and 873 K and a pressure of 25 MPa) have been selected as relevant for a supercritical power plant concept. To investigate the structural changes of the oxide films, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and electrochemical impedance spectroscopy (EIS) analyses were used. Results show changes in the oxides chemical composition, microstructure and thickness versus testing conditions (pressure, temperature and time). The oxide films are composed of two layers: an outer layer enriched in Fe oxide and an inner layer enriched in Cr and Ni oxides corresponding to small cavities supposedly due to internal oxidation.     

Depth profiling of carbon in silicon using the C(p, p′γ) reaction

An analytical method has been developed for the measurement of a carbon depth profile of the region a few tens of μm from the surface, using a ¹²C(p, p′γ) reaction. Measurements for a SiC sample coated with a silicon layer and a carbon-implanted silicon sample were performed using this method. Two charged particle detectors and two γ-ray detectors were utilized for the coincident detection of scattered protons and γ-rays from the first excited state (E_x = 4.4 MeV) of ¹²C. The measured depth profiles agree well with results obtained using a surface profiler and an Auger microprobe. These results demonstrate that this method is useful for the non-destructive analysis of carbon at depths of a few tens of μm from the surface.     

Oxidation kinetics and oxygen diffusion in low-tin Zircaloy-4 up to 1523 K

This paper deals with the study of oxidation kinetics and the identification of oxygen diffusion coefficients of low-tin Zy-4 alloy at intermediate (973 K ? T ? 1123 K) and high temperatures (T ? 1373 K). Two different cases were considered: dissolution of a pre-existing oxide layer in the temperature range 973 K ? T ? 1123 K and oxidation at T ? 1373 K. The results are the following ones: in the temperature range 973-1123 K, the oxygen diffusion coefficient in α_Zr phase can be expressed as D_α = 6.798 exp(−217.99 kJ/RT) cm²/s. In the temperature range 1373-1523 K, the oxygen diffusion coefficients in α_Zr, β_Zr and ZrO₂, were determined using an ‘inverse identification method’ from experimental high temperature oxidation data (i.e., ZrO₂, and α_Zr(O) layer thickness measurements); they can be expressed as follows: D_α = 1.543 exp(−201.55 kJ/ RT) cm²/s, D_β = 0.0068 exp(−102.62 kJ/ RT) cm²/s and D_ZrO2=0.115exp(−143.64kJ/RT)cm²/s. Finally an oxygen diffusion coefficient in α_Zr in the temperature range 973 K ? T ? 1523 K was determined, by combining the whole set of results: D_α = 4.604exp(−214.44 kJ/RT) cm²/s. In order to check these calculated diffusion coefficients, oxygen concentration profiles were determined by Electron Probe MicroAnalysis (EPMA) in pre-oxidized low-tin Zy4 alloys annealed under vacuum at three different temperatures 973, 1073 and 1123 K for different times, and compared to the calculated profiles. At last, in the framework of this study, it appeared also necessary to reassess the Zr-O binary phase diagram in order to take into account the existence of a composition range in the two zirconia phases, α_ZrO2 and β_ZrO2.     

Analysis of C, N and O in aerosol collected on an organic backing using internal blank measurements and variable beam size

A method with low MDL (minimum detection limit) was developed for analysis of carbon (C), nitrogen (N) and oxygen (O) in aerosol samples collected on an organic backing. An accelerator-produced beam of protons interacting with the sample and the detection of elastically scattered protons (PESA; particle elastic scattering analysis) and emitted X-rays (PIXE; particle-induced X-ray emission) were the basic components of the setup. The method is based on measurement of internal blank concentrations, i.e. measurement of the blank concentration outside the aerosol deposit in each sample, and the use of two sizes of the beam in order to improve the MDL of the analysis. Large beam size covering the entire aerosol deposit was used to obtain quantitative analysis with PIXE. Small beam was used to obtain relative elemental concentrations with PESA and PIXE, which were transformed to absolute values by the aid of large-beam analysis. The small-size-beam served two purposes: to make internal blank measurements feasible and to improve the signal ratio of aerosol-deposit to backing. Compared with the traditional way of analysis, using a beam that is larger than the deposit and specially prepared blank samples, the new method reduced the MDL of C, N and O by a factor of 130, 70 and 90, respectively. The new method was applied to aerosol samples collected in the upper troposphere and the lowermost stratosphere from the CARIBIC platform. As far as the authors know, these measurements are the first quantitative determinations of C, N and O in the aerosol of this part of the atmosphere. The results show that these elements together with sulfur are major components of the aerosol.     

Determination of non-Rutherford cross-sections from simple RBS spectra using Bayesian inference data analysis

Analysis of RBS and ERDA data relies first and foremost on knowledge of the relevant stopping power and scattering cross-sections. Scattering cross-sections in the non-Rutherford region are often used for enhanced sensitivity to light elements, or for instance in 4He-ERDA measurement of hydrogen. Accurate experimental cross-section values in the energy and scattering angle regions of interest to IBA are thus essential to much analysis work. We developed a new method to determine scattering cross-sections experimentally, which consists in collecting many RBS spectra at different energies, and analysing them taking the cross-sections as fitting parameter. High quality simulations of resonances is essential. A Bayesian inference analysis leads not only to the cross-section curve that best fits the data, but also leads to confidence limits on the results obtained. We apply the method to several (p,p) resonances, and compare them to the literature experimental and evaluated values.     

A Time of Flight-Energy spectrometer for stopping power measurements in Heavy Ion-ERD analysis at iThemba LABS

The quantitative analysis of thin layers using Heavy Ion-Elastic Recoil Detection (HI-ERD) can be reliably performed if the stopping powers of the probing ions and recoils in a given target matrix are known accurately. Unfortunately for many projectile/target combinations experimental data is limited and where available, deviations of up to 50% between experiment and theory have been reported. This presentation describes the assembly of a Time of Flight-Energy (ToF-E) detector system developed for HI-ERD analysis and adapted for stopping power measurements at iThemba LABS. First results from energy loss measurements of 0.1-0.5 MeV/nucleon ²⁸Si and ⁸⁴Kr ions in ZrO₂ are presented and compared with predictions of the widely used SRIM2003 (Stopping Range of Ions in Matter).     

Development of a time-of-flight spectrometer at the Ruder Boškovi? Institute in Zagreb

A new TOF telescope has been constructed for thin film and surface analysis. The timing system consists of two electrostatic mirror type detectors of Busch design. The detection efficiency of timing stations for very light ions was significantly improved using DLC (diamond like carbon) foils coated with LiF instead of the conventionally used carbon foils. Ion energy is measured by a 300 mm² ULTRA ion-implanted silicon detector. For the ERDA measurements with heavy and energetic ion beams, a time-of-flight (TOF) spectrometer is positioned at 37.5°. Spectrometer can be easily moved to 120° backward angle for time-of-flight RBS analysis with low energy beam of light ions. Positioning and fine adjustments of sample orientation are performed with a motorized sample stage. The same spectrometer can be also installed at the ion microprobe scattering chamber for 3D elemental imaging.     

Structural characterization of Fe/Ag bilayers by RBS and AFM

Fe/Ag thin films are intensively investigated due to their special magnetic properties. Recently a deposition-order dependent asymmetric interface has been found. When iron is grown on silver, the interface is sharp, while the growth of Ag on Fe results in a long, low-energy tail of the Ag peak in the Rutherford backscattering spectrometry (RBS) spectra. The main purpose of this paper is to show that the low-energy Ag tail is caused by grain boundary diffusion, and that, when elevating the growing temperature of the Ag layer this effect becomes more significant. Two sets of polycrystalline and epitaxial Fe/Ag bilayers were prepared simultaneously onto Si(1 1 1) and MgO(1 0 0), respectively. The iron layers were grown at 250 °C and annealed at 450 °C in both sets, while the Ag layer was grown in the first set at room temperature (RT) and in the second set at 250 °C (HT). The sample composition, the interface sharpness and the quality of the epitaxy were studied by Rutherford backscattering spectrometry (RBS) combined with channeling effect. The surface morphology was determined by atomic force microscopy (AFM). RBS spectra show that in the case of RT samples the epitaxial MgO/Fe/Ag bilayer has sharp, well-defined interface, while for the polycrystalline Si/Fe/Ag sample the silver peak has a low-energy tail. Both the Fe and Ag peaks smeared out in the case of HT samples. AFM-images show that the RT samples have a continuous Ag layer, while the HT samples have fragmented surfaces. The RBS spectra taken on the HT samples were successfully simulated by the RBS-MAST code taking into account their fragmented structures.     

Strain enhancement in Si induced by direct bonding of a LaAlO3 film to a Si substrate

The depth profiles of lattice strain near the interface regions of LaAlO₃/Si and the SiO₂ interfacial layer/Si were investigated by the ion channeling technique using high-resolution Rutherford backscattering spectroscopy (HRBS). In the case of the LaAlO₃/Si stack, horizontal tensile strain in the Si near the interface was clearly observed. However, this strain was relaxed by formation of the interfacial layer through annealing in an oxygen ambient. These results suggest that the strain in Si induced by a dielectric strongly depends on the material in contact with Si.     

Tuning magnetic properties of Co/Pt thin films using energetic ions

In this paper, we present the changes occurring in Co/Pt bi- and multi-layer thin films modified under wide range of ion energy and species and fluence. We have shown the possibility of achieving controlled tuning of magnetic properties of the Co/Pt thin film system. Monte Carlo simulation results for ion-induced atomic displacements were used to explain the observed effects of ion-irradiation interface mixing across the Co/Pt interfaces. Phase formation has been explained in the light of heat of formation rule. On the other hand, we propose that ion induced point defect clustering governs the changes occurring in the structural and the magnetic properties.     

Sol-gel silica coatings for the protection of cultural heritage glass

To slow down the phenomenon of weathering of ancient stained glass, the present work proposes the coating of glass. Several recipes have been tested in the past. The coatings are made of sol-gel silica prepared with different catalysts like H⁺, Pb(II), Sn(IV) and without catalyst. All the investigated samples show a good adhesion of the coating to the glasses used to simulate the behaviour of ancient artefacts and a good resistance to ageing tests.In the present work, some tests on Au and Ti surfaces coated with sol-gel silica were done, in order to investigate the adhesion of a H⁺ sol-gel coating to the surface of metals. In fact, in the case of glassy mosaics called “golden leaf tessera”, the adhesion of the glass to the metal is a critical point, due to the fact that the weathering of such tesserae causes the detaching of the “cartellina” (small glass layer) from the metal leaf. The main techniques adopted to investigate are optical microscopy (OM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Rutherford backscattering spectroscopy (RBS).     

Production and characterization of thin Li targets fabricated by ion implantation

Very high fluence implantation of ⁷Li⁺ ions was used to promote the formation of a thin and high density ⁷Li target in the surface region of Al samples. The implanted volume was characterized by particle induced gamma-ray emission, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and nuclear reaction analysis, revealing that the implanted surface is a combination of Li₂CO₃, metallic lithium, LiOH and C, with almost no Al present. Radiation damage effects by proton beams were studied by observing the evolution of the ⁷Li(p, α)⁴He nuclear reaction yield with the accumulated charge, at different proton energies, revealing high stability of the produced Li target.     

Production and preliminary characterization of DC plasma polymerized allylamine film (PPAA) by NRA, ERD and XPS

Due to its surface properties, especially the presence of amine groups, plasma polymerized allylamine (PPAA) is involved in a large range of applications. Most of them are related to biology and biochemistry. In this work, we demonstrate a quick and simple way to produce PPAA thin films by conventional DC magnetron sputtering. To the best of our knowledge, this is the first method not involving radiofrequency (RF) or microwave discharges. In this paper, we show preliminary characterizations on the produced films (bulk analysis) carried out by ion beam techniques. The Hydrogen content in the whole layers was measured by ERD. The surface composition was probed by XPS on pentafluorobenzaldehyde (PFBA) derivatized films: the maximum concentration of amine groups is 1.6%.     

Silver surface enrichment controlled by simultaneous RBS for reliable PIXE analysis of ancient coins

Evidence of silver surface enrichment of ancient silver-copper coins has been pointed out in the past years. Surface enrichment can be fortuitous or intentional. In this paper, we have investigated the cleaning procedures usually performed after excavation or in museums. We have shown that chemicals or commercial products routinely used dissolve preferentially the copper phase and consequently contribute to the silver surface enrichment. As a result, surface analyses such as PIXE or XRF can be strongly affected by this effect. By using simultaneously RBS and PIXE, it is possible to check through the silver surface enrichment and then select the reliable measurements, characteristic of the bulk composition. Results on coins recently discovered and mechanically or chemically cleaned are presented.     

FTIR and RBS study of ion-beam synthesized buried silicon oxide layers

Single crystal silicon samples were implanted at 140 keV by oxygen (¹⁶O⁺) ion beam to fluence levels of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² to synthesize buried silicon oxide insulating layers by SIMOX (separation by implanted oxygen) process at room temperature and at high temperature (325 °C). The structure and composition of the ion-beam synthesized buried silicon oxide layers were investigated by Fourier transform infrared (FTIR) and Rutherford backscattering spectroscopy (RBS) techniques. The FTIR spectra of implanted samples reveal absorption in the wavenumber range 1250-750 cm⁻¹ corresponding to the stretching vibration of Si-O bonds indicating the formation of silicon oxide. The integrated absorption band intensity is found to increase with increase in the ion fluence. The absorption peak was rather board for 325 °C implanted sample. The FTIR studies show that the structures of ion-beam synthesized buried oxide layers are strongly dependent on total ion fluence. The RBS measurements show that the thickness of the buried oxide layer increases with increase in the oxygen fluence. However, the thickness of the top silicon layer was found to decrease with increase in the ion fluence. The total oxygen fluence estimated from the RBS data is found to be in good agreement with the implanted oxygen fluence. The high temperature implantation leads to increase in the concentration of the oxide formation compared to room temperature implantation.