Combined Rutherford Backscattering Research Articles

Sensitive in-operando observation of Li and O transport in thin-film Li-ion batteries

Thin-film batteries often contain oxides in the anode, cathode, and electrolyte materials. In-operando methods capable of Li and O depth profiling are relevant for battery research to study, e.g. diffusion and trapping of constituents. Here, we demonstrate ion beam–based analytical methods with high depth resolution and sensitivity for depth profiling Li and O in thin-film batteries using 10 MeV Li and He ions. Simultaneous depth profiling of Li and O was performed using combined coincidence elastic recoil detection analysis and Rutherford backscattering spectrometry measurements in the battery with 8 MeV He ions, and the Li and O transport was measured in operando. Reversible Li transport was observed from the LMO anode to the NbO cathode on charging and vice versa during discharging. O transport was observed from the LMO anode to the NbO cathode on first charging with 3.5 V but was not observed on further charging and discharging of the battery. Our in-operando measurements allow direct and quantitative observation of Li and O transport during charge-discharge cycles for thin-film batteries.

Electric field strength-dependent accuracy of TiAlN thin film composition measurements by laser-assisted atom probe tomography

Accurate quantification of absolute concentrations represents a major challenge for atom probe tomography (APT) since the field evaporation process is affected significantly by the measurement parameters. In the present work we investigate systematically the effect of laser pulse parameters on the accuracy of laser-assisted APT for a TiAlN thin film previously quantified by ion beam analysis, combining Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. The electric field strength is estimated from the Al2+/Al+ charge state ratio for all systematically varied measurement parameters. Subsequently, the absolute concentrations from laser-assisted APT are compared to ion beam analysis data. An increase of the electric field strength from approximately 25–28 V nm−1 improves the accuracy of absolute concentrations measured by laser-assisted APT from 11.4 to 4.1 at% for N, from 8.8 to 3.0 at% for Al and from 2.8 to 0.9 at% for Ti. Our data emphasize that the measurement accuracy of laser-assisted APT for TiAlN is governed by the electric field strength. It is shown that the smallest compositional discrepancies between ion beam analysis and APT are obtained for the maximum electric field strength of approximately 28 V nm−1 at 10 pJ laser pulse energy. This can be rationalized by considering the enhanced ionization of neutral fragments caused by the increased electric field strength.

On the chemical composition of TiAlN thin films - Comparison of ion beam analysis and laser-assisted atom probe tomography with varying laser pulse energy

We compare the chemical composition of TiAlN thin films determined by ion beam analysis and laser-assisted atom probe tomography (APT). The laser pulse energy during APT was increased subsequently from 10 to 20, 30, 40, 50, 100 and 200 pJ within a single measurement, covering the range that is typically employed for the analysis of transition metal nitrides. The laser pulse energy-dependent Ti, Al and N concentrations were compared to ion beam analysis data, combining Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) with the total measurement uncertainty of 2.5% relative deviation. It can be learned that the absolute N concentration from APT is underestimated by at least 5.5 at.% (up to 8.2 at.%) and the absolute Al concentration from APT is overestimated by at least 4.5 at.% (up to 6.2 at.%), while absolute Ti concentration values are for both techniques in good agreement with maximum deviations <2 at.%. Hence, the here presented comparative analysis clearly shows that absolute Al and N concentration values obtained by ion beam analysis deviate significantly to the APT data for the laser pulse energy range from 10 to 200 pJ. Possible causes for the compositional discrepancy between Rutherford backscattering spectrometry/elastic recoil detection analysis and APT, such as molecular ions, multiple detection events and preferential evaporation/retention of species with different evaporation fields, are discussed. The presented data emphasize that laser-assisted APT is a precise tool to quantify the chemical composition of TiAlN thin films, that lacks accuracy.

Soft x-ray optical constants of sputtered chromium thin films with improved accuracy in the L and M absorption edge regions

In this study, we determine with improved accuracy the complex index of refraction n = 1 − δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge.

Deviations from Vegard's law in semiconductor thin films measured with X-ray diffraction and Rutherford backscattering: The Ge1-ySny and Ge1-xSix cases

The compositional dependence of the lattice parameter in Ge1-ySny alloys has been determined from combined X-ray diffraction and Rutherford Backscattering (RBS) measurements of a large set of epitaxial films with compositions in the 0 &amp;lt; y &amp;lt; 0.14 range. In view of contradictory prior results, a critical analysis of this method has been carried out, with emphasis on nonlinear elasticity corrections and systematic errors in popular RBS simulation codes. The approach followed is validated by showing that measurements of Ge1-xSix films yield a bowing parameter θGeSi =−0.0253(30) Å, in excellent agreement with the classic work by Dismukes. When the same methodology is applied to Ge1-ySny alloy films, it is found that the bowing parameter θGeSn is zero within experimental error, so that the system follows Vegard's law. This is in qualitative agreement with ab initio theory, but the value of the experimental bowing parameter is significantly smaller than the theoretical prediction. Possible reasons for this discrepancy are discussed in detail.

Study of the distribution profile of iron ions implanted into silicon

Iron ions with energies of 90 and 250 keV and a dose of 1016 cm–2 are implanted into a silicon single crystal with the (110) orientation. The method of Rutherford backscattering in combination with channeling is used to study the distribution profiles of the introduced impurity and also the profiles of the distribution of radiation-induced defects in the crystal lattice. Experimental data are compared with the results of simulation performed using the TRIM software package. It is shown that, at an energy of 4.6 keV/nucleon, the average projected ranges coincide; however, at an energy of 1.6 keV/nucleon, the difference amounts to 35%. In addition, it is shown that the calculation incorrectly takes into account the dose dependence at energies of 1.6–4.6 keV/nucleon.

Lithium Content and Low-Temperature Conductivity of NiO:Li Films Deposited by Spray Pyrolysis

The objective of this work was to quantify the amount of lithium incorporated into nickel oxide thin films and study its effects on the oxidation state of the elements and on the electrical conductivity of the films. A set of films was deposited on alumina substrate by spray pyrolysis. The lithium to nickel ratio in the sprayed solution, 0, 20, 40, and 60 at.%, determined the amount of lithium incorporated into the films. The lithium concentration was obtained by combined energy recoil detection analysis and Rutherford backscattering. The ratios of lithium to nickel atoms incorporated in the films were 0, 12.9, 27.9, and 46.9%, respectively. These results were confirmed by x-ray photoemission spectroscopy, which was also used to analyze the oxidation state of the atomic species in the samples. When the electrical conductivity of selected samples was studied as a function of temperature in the range 50–450 K, kinked–linear behavior was observed; this was attributed to different conducting mechanisms activated by temperature.

New experimental approach to study aqueous alteration of amorphous silicates at low reaction rates

Understanding the kinetics of silicate alteration in aqueous media is central to the study of oceanic hydrothermal systems, nuclear glass durability or carbonaceous asteroids from which chondrites are coming. We present a new experimental approach in combination with an integrated analytical protocol designed to study alteration processes at low temperatures (<200°C) and slow reaction rates. We used pulsed laser deposition (PLD) to produce micrometer thick films of amorphous silicate of controlled chemical composition. After reacting with water in sealed capsules, the films consist of a succession of compositionally different layers. The initial planar geometry of the film allows a complete characterization of the transformed materials at the nanometer scale. By combining Rutherford back-scattering (RBS), nuclear reaction analysis (NRA), transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM), it is possible to constrain the propagation rate of the reaction fronts, the thicknesses of individual layers, spatial variations in composition, the nature of the interface between the layers, the iron redox state, the water content along depth profiles, as well as the porosity and the density.We investigated the serpentinization of amorphous silicate films with stoichiometry close to olivine (~Fe1.1Mg0.9SiO4.15H0.3) at 90°C (2weeks) and 200°C (2h). In both cases, ~500nm of altered material is formed. At the reaction front, a hydrated, amorphous and oxidized Fe-rich layer forms. At the interface with the fluid, a more Mg-rich layer develops. The system evolves towards a biphasic assemblage of Fe-serpentine and Mg-saponite composition. Both layers remain amorphous. It is shown that water propagation is coupled to hydrolysis, iron oxidation (Fe3+/∑Fe ratio>50%) and H2 formation, whose quantifications are crucial to understand terrestrial serpentinization processes. Interfacial precipitation–dissolution seems to be the rate controlling mechanisms. In addition, we investigated a crystallized film reacted at 190°C (2h), which transformation rate is ten times slower than that of the amorphous silicate but is nevertheless readily observable. This approach can be used to understand alteration in terrestrial and extraterrestrial samples. In particular, we reproduced several features observed in carbonaceous chondrites (amorphous and oxidized hydrated silicates) and show that, at 90°C, alteration may be faster than usually considered. It should allow us in the future to constrain the temperatures and timescales of alteration in chondrites.

Recovery effects due to the interaction between nuclear and electronic energy losses in SiC irradiated with a dual-ion beam

Single and dual-beam ion irradiations of silicon carbide (SiC) were performed to study possible Synergetic effects between Nuclear (Sn) and Electronic (Se) Energy Losses. Results obtained combining Rutherford backscattering in channeling conditions, Raman spectroscopy, and transmission electron microscopy techniques show that dual-beam irradiation of SiC induces a dramatic change in the final sample microstructure with a substantial decrease of radiation damage as compared to single-beam irradiation. Actually, a defective layer containing dislocations is formed upon dual-beam irradiation (Sn&amp;Se), whereas single low-energy irradiation (Sn alone) or even sequential (Sn + Se) irradiations lead to full amorphization. The healing process is ascribed to the electronic excitation arising from the electronic energy loss of swift ions. These results shed new light on the long-standing puzzling problem of the existence of a possible synergy between Sn and Se in ion-irradiation experiments. This work is interesting for both fundamental understanding of the ion-solid interactions and technological applications in the nuclear industry where recovery Sn/Se effects may preserve the integrity of nuclear devices.

Influence of hydrogen content and network connectivity on the coefficient of thermal expansion and thermal stability for a-SiC:H thin films

Thin films of a-SiC:H are of interest for numerous applications in optoelectronic, nanoelectronic, and nanoelectromechanical devices due to a large optical band gap and excellent chemical inertness. In many cases, a low coefficient of thermal expansion (CTE) and high temperature stability are also desired. In this regard, we report an investigation of the influence of hydrogen content and average bond coordination (〈r〉) on the thermal stability and CTE of a-SiC:H thin films deposited by plasma enhanced chemical vapor deposition. The a-SiC:H hydrogen content determined by combined nuclear reaction analysis and Rutherford backscattering measurements (NRA–RBS) was skewed from 25 to 60% resulting in films with 〈r〉 ranging from 2.0 up to 3.2. We show that increased hydrogen content is accompanied by changes in the thermal stability and CTE for the a-SiC:H films. The most dramatic changes were observed to occur for films with hydrogen content >45% where 〈r〉 is near the critical coordination number (〈r〉c) that delineates over and under constrained materials. For a-SiC:H films above 〈r〉c, relatively little change was observed in CTE with 〈r〉. However for films near or below 〈r〉c, CTE was observed to increase with decreasing 〈r〉 and significant hydrogen loss was observed after the annealing measurements.

Investigation of atomic layer deposited beryllium oxide material properties for high-k dielectric applications

Beryllium oxide (BeO) is a wide band gap alkaline earth oxide material that has recently shown significant promise as a high-k dielectric material in Si and III-V metal–oxide–semiconductor field effect transistor devices. However, many of the basic material properties for BeO thin films utilized in these devices have not been reported or remain in question. In this regard, the authors report an investigation of the chemical, physical, electrical, and mechanical properties of BeO thin films formed via atomic layer deposition (ALD). Combined Rutherford backscattering and nuclear reaction analysis measurements show that ALD BeO thin films exhibit a low hydrogen content (&amp;lt;5%) and are nearly stoichiometric (Be/O ≅ 1.1 ± 0.05). Reflection electron energy loss spectroscopy measurements reveal a wide band gap of 8.0 ± 0.14 eV, and nanoindentation measurements show that ALD BeO has a high Young's modulus and hardness of 330 ± 30 and 33 ± 5 GPa, respectively.

Technical Study of a set of Metallic Artifacts from the Maya Site of Lagartero, Chiapas, Mexico

ABSTRACTDuring the excavations made at a burial of the post-Classic Mayan period (1220-1521 A.D.) in the pyramid number 2 of the pre-Hispanic site of Lagartero, Chiapas, Mexico, a set of four small metallic artifacts depicting reptile’s heads, were recovered. The objects were in poor conservation conditions and were taken to the Metal Conservation Laboratory of the National School of Conservation (ENCRyM- INAH) for suitable cleaning and conservation treatments.Analyses allowed identifying important technological features such as gilding remains. The analytical techniques included optical microscopy followed by X-Ray Fluorescence Spectroscopy (XRF), and Scanning Electron Microscope-coupled with Energy Dispersive Spectrometer (MEB-EDS). For the elemental depth profile a combined Particle X-Ray Emission Spectroscopy and Rutherford Backscattering Spectrometry (PIXE–RBS) analysis was carried out.The results indicate that the objects are made of a copper alloy, and then gilded probably using electrochemical replacement gilding (thickness has less than 1 μm). This technology has been observed in other metallic objects recovered from the Chichen-Itza Cenote in Yucatan, but it was not available in Mesoamerican areas so far. So, it could imply that these artifacts might have been imported from South American areas.

Origins of low resistivity in Al ion-implanted ZnO bulk single crystals

The origins of low resistivity in Al ion-implanted ZnO bulk single crystals are studied by combining Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), photoluminescence (PL), and Van der Pauw methods. The Al-ion implantation (peak concentration: 2.6 × 1020cm−3) into ZnO is performed using a multiple-step energy. The resistivity decreases from ∼104 Ω cm for un-implanted ZnO to 1.4 × 10−1 Ω cm for as-implanted, and reaches 6.0 × 10−4 Ω cm for samples annealed at 1000 °C. RBS and NRA measurements for as-implanted ZnO suggest the existence of the lattice displacement of Zn (Zni) and O (Oi), respectively. After annealing at 1000 °C, the Zni related defects remain and the Oi related defects disappear. The origin of the low resistivity in the as-implanted sample is attributed to the Zni (∼30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]). In contrast, the origin of the low resistivity in the sample annealed at 1000 °C is assigned to both of the Zni related defects and the electrically activated Al donor. A new PL emission appears at around 3.32 eV after annealing at 1000 °C, suggesting electrically activated Al donors.

Evaluation of zinc interstitial in Si-ion implanted ZnO bulk single crystals by a Rutherford backscattering study: An origin of low resistivity

The relation between low resistivity and Zn interstitial in ZnO single crystals implanted with the peak Si atomic concentration of 2.62 × 1020 cm−3 is studied by combining Rutherford backscattering spectroscopy/channeling, photoluminescence, and Van der Pauw methods. The variation in resistivity from ∼104 Ω cm for un-implanted ZnO to ∼10−3 Ω cm for as-implanted ones is observed. The lattice displacement of Zn atoms of ∼0.10 Å from the 〈0 0 0 1〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-implanted ZnO with a minimum yield (χmin) of ∼11%. The low resistance is maintained by the 1000 °C annealing, accompanied with the lattice displacement of Zn atoms of ∼0.07 Å. These results suggest the existence of the shallow donor consisting of Zn interstitial and/or Zn interstitial-related complex corresponding to a newly appeared 3.33 eV-emission located at ∼40 meV from the bottom of the conduction band.

Electrical and magnetic properties of RE-doped ZnO thin films (RE = Gd, Nd)

Abstract Due to the small magnetic moments observed for 3d transition metals in ZnO [M. Diaconu, H. Schmidt, H. Hochmuth, M. Lorenz, G. Benndorf, J. Lenzner, D. Spemann, A. Setzer, K.W. Nielsen, P. Esquinazi, M. Grundmann, Thin Solid Films 486 (2005) 117], there is still space for optimizing ZnO-based diluted magnetic semiconductors for spintronics applications. Motivated by the observation of magnetic moments as high as 4000μB/Gd atom in GaN:Gd [S. Dhar, O. Brandt, M. Ramsteiner, V.F. Sapega, K.H. Ploog, Phys. Rev. Lett. 96 (2005) 037205], we investigated ZnO films doped with 0.01, 0.1 or 1 at.% rare earth (RE) metals. The films, with thicknesses between 20 nm and 1 μm, have been grown by pulsed laser deposition on a -plane sapphire or fused silica substrates. The homogenous incorporation of the RE ions in ZnO was investigated by combined Rutherford backscattering and particle induced X-ray emission measurements. Hall measurements revealed an unexpected dependence of the electron concentration on film thickness, proving a non-uniform distribution of electrically active defects. Magnetotransport measurements at different temperatures were performed to study the magnetoresistance and the presence of the anomalous Hall effect. Large negative magnetoresistance was obtained at 5 K, while no anomalous Hall effect was observed. These results indicate that there are no exchange interactions between the RE ions.

Study of Fe, Mn and Eu doped LiNbO3 by combined Rutherford backscattering and nuclear reaction analysis

Lithium niobate crystals with various dopents, such as Fe (0.3wt%), Mn (0.1wt%) and Eu (1wt%) ions have been successfully grown using the Czochralski technique. The crystals have been cut in suitable sizes and polished. It is essential to know the concentration and location of dopants in the crystal lattice in order to improve the crystal growth parameters to grow large crystals of LiNbO3 with known impurities. Using Li(p,α) nuclear reaction profile the Li in LiNbO3 crystal was located. Using Rutherford backscattering spectrometry (RBS), the dopants and their concentration as a function of depth were measured. Using channeling, both RBS channeling and (p,α) channeling the lattice location of impurities and the location of Li in the doped crystal could be identified. The energy of the incident protons is maintained at 1.0MeV to avoid neutron production.

Smoothing of Si0.7Ge0.3 virtual substrates by gas-cluster-ion beam

The planarization of the SiGe virtual substrate surface is crucial for the fabrication of high-performance strained-Si metal-oxide-semiconductor field-effect transistors. In this letter, we report on the smoothing of the inherently crosshatched rough surfaces of SiGe deposited by molecular beam epitaxy on Si substrates by gas cluster ion beams. Atomic force microscopy measurements show that the average surface roughness (Ra) of the SiGe layer could be reduced considerably from 3.2 to 0.7 nm without any crosshatched pattern. Rutherford backscattering in combination with channeling was used to study the damage produced by cluster bombardment. No visible surface damage was observed for the normal-incidence smoothed SiGe with postsmoothing glancing angle cluster ion beam etching.

Smoothing of ZnO films by gas cluster ion beam

Planarization of wide-band-gap semiconductor ZnO surface is crucial for thin-film device performance. In this study, the rough initial surfaces of ZnO films deposited by r.f. magnetron sputtering on Si substrates were smoothed by gas cluster ion beams. AFM measurements show that the average surface roughness (Ra) of the ZnO films could be reduced considerably from 16.1nm to 0.9nm. Raman spectroscopy was used to monitor the structure of both the as-grown and the smoothed ZnO films. Rutherford back-scattering in combination with channeling effect was used to study the damage production induced by the cluster bombardment.

Structure and hydrogen content of polymorphous silicon thin films studied by spectroscopic ellipsometry and nuclear measurements

The dielectric functions of amorphous and polymorphous silicon films prepared under various plasma conditions have been deduced from UV-visible spectroscopic ellipsometry measurements. The measured spectra have been firstsimulated by the use of the Tauc-Lorentz dispersion model and then the compositions of the films have been obtained by the use of the tetrahedron model combined with the Bruggeman effective medium approximation. This approach allows us to determine the hydrogen content, the crystalline fraction, and the void fraction of the films. This is particularly important in the case of polymorphous films in which the low crystalline fraction (below 10%) can only be detected when an accurate description of the effects of hydrogen on the dielectric function through the tetrahedron model is considered. The hydrogen content and film porosity deduced from the analysis of the spectroscopic ellipsometry measurements are in excellent agreement with the hydrogen content and film density deduced from combined elastic recoil detection analysis and Rutherford backscattering spectroscopy measurements. Moreover, despite their high hydrogen content (∼15%-20%) with respect to hydrogenated amorphous silicon films deposited at the same temperature (8%), polymorphous silicon films have a high density, which is related to their very low void fraction.

Lattice distortions and the transmuted-Ge related luminescence in neutron-transmutation-doped GaN

The lattice distortion and the transmuted-Ge related luminescence in neutron-transmutation-doped (NTD) GaN are studied by combining Rutherford backscattering spectroscopy/channeling, Raman scattering, and photoluminescence methods. The lattice displacement of Ga atoms of ∼0.12 Å from the 〈0001〉 row is estimated from the normalized angular yield profiles, preserving the single crystallinity in as-irradiated GaN with a minimum yield (χmin) of 7%. A 2.84 eV emission band observed in 600 °C annealed NTD-GaN is associated with the Ga interstitial, supporting the lattice distortion. Two emission bands at 2.90 eV and 2.25 eV observed in 1000 °C annealed NTD-GaN are assigned to a negatively charged DX-like center of Ge at Ga site and a complex defect attributed to Ge at Ga site and Ga vacancy, respectively.