Neutron Depth Profiling Technique Research Articles

Measurement of Nanoscale Film Thickness Using Neutron Depth Profiling Technique.

Determination of geometric parameters for thin film materials has always been a critical concern in scientific research. This paper proposes a novel approach for high-resolution and nondestructive measurement of nanoscale film thickness. In this study, the neutron depth profiling (NDP) technique was employed to accurately measure the thickness of nanoscale Cu films, achieving an impressive resolution of up to 1.78 nm/keV. The measurement results exhibited a deviation from the actual thickness of less than 1%, highlighting the accuracy of the proposed method. Additionally, simulations were conducted on graphene samples to demonstrate the applicability of NDP in measuring the thickness of multilayer graphene films. These simulations provide a theoretical foundation for subsequent experimental measurements, further enhancing the validity and practicality of the proposed technique.

Neutrons for Battery Research (in-situ and operando studies): An Overview

The further development of battery materials and cells must go hand in hand with improved in-situ and operando characterization methods. Such techniques provide a better and deeper understanding of the mechanisms to determine even minor changes in cell components and their impact on the overall performance of cells and their capacity or battery life.The last ten years there has been a great deal of interest in scattering techniques for examining battery components and in particular complete cells [1]. Neutrons as a probe or techniques derived from neutrons play a special role in this development because their unique properties and possibilities are very well suited for battery research. On the one hand, neutrons can penetrate deep into materials and on the other hand, they are very sensitive to light elements as Li, H or N. In addition, neutron methods are non-destructive, which makes it possible to measure the inner part of a cell as well as to perform operando measurements. Improvements of neutron instrumentation including coatings of neutron guides, higher counting rates of detector systems and dedicated sample environments. Further the higher neutron flux of modern neutron large scale facilities accelerate the development of neutrons for battery research. In-situ and operando studies while changing external parameters such as charging/discharging or temperature change etc. are carried out to examine cells under real working conditions.Neutron diffraction, small-angle neutron scattering, neutron imaging and neutron depth profiling are considered among the most suitable methods for battery research. This contribution presents typical applications of these different neutron methods, which are used on different length scales. Neutron diffraction and small-angle neutron scattering are suitable to investigate changes from the atomic scale up to the mesoscopic scale (~ 300 nm). Processes such as Li intercalation in graphite anodes during battery charging can be described in detail [2,3]. Neutron imaging is suitable to follow in-situ the electrolyte filling process in hard case cells [4]. The neutron depth profiling technique is applied for studies of the Lithium mobility at the different electrode interfaces to determine the Li concentration profile in approximately the first 50 mm [5], e.g. the SEI layer [6]. Reference s : [1] R. Gilles, Journal of Surface and Investigations: X-ray, Synchrotron and Neutron Techniques (2020), in print.[2] V. Zinth et al., Journal of Power Sources 361 (2017) 54-60.[3] J. Hattendorff et al., J. Appl. Cryst. (2020), 53, 210-221.[4] W. J. Weydanz et al., Journal of Power Sources 380 (2018) 126-134.[5] M. Trunk et al., Materials Characterization (2018), 146, 127-134.[6] S. Whitney et al., Journal of the Electrochemistry Society (2009), 156(11) A886.

Study of Li diffusion in thin film of Re annealed at high temperatures

Depth profiles of 6Li implanted into high-melting point rhenium refractory metal has been measured for as-implanted, as well as thermally annealed samples using a non-destructive Thermal Neutron Depth Profiling technique at the LWR-15 research reactor in Řež. The Gaussian-like shape, typical for as-implanted Li-depth profile, is preserved after the thermal annealing at high temperature demonstrating the activation of the Li atom diffusion process at the Re-target. The diffusion coefficient at 1830̂C has been evaluated by the comparison of the Li profiles before and after the thermal annealing. This study aims to investigate the applicability of Re metal in ISOL related applications.

Lithium encapsulation in etched nuclear pores in polyethylene terephthalate

Encapsulation of lithium in ion-track etched polymer has been studied using both ion and neutron-based techniques. Latent tracks have been formed in Polyethylene terephthalate foils by irradiation with high energy Xe26 + ions. Subsequently, the latent-tracks have been developed, via chemical etching. The resulting pore shapes have been characterized by Ion Transmission Spectroscopy. From the analysis of the energy spectra of the ions transmitted through the membrane, it was possible to estimate pores' inner geometry and its evolution during etching. The etched foils were exposed to a LiCl aqueous solution and the depth distribution of Li incorporated into the pores was examined by implementing the Neutron Depth Profiling technique. The ability of the membrane to encapsulate the lithium in pores, was determined. The present study can be relevant to several applications, e.g., lithium-ion batteries and biosensors, where an in-depth knowledge of the pores' shape/size and of their trapping capability is required.

Desorption spectrometry II: coupled desorption of Li marker and degradation of polypyrrole

In this work, different aqueous Lithium salt markers were introduced into polypyrrole, thereafter the system was dried, and finally water was again allowed to enter with the aim to desorb the incorporated Li marker. The Li desorption is closely followed by the Neutron Depth Profiling technique. It turns out that the desorption spectra strongly depend on the solubility of the applied markers, and furthermore, the polymer-water interaction influences the outcome. Finally, there are hints that the Li markers incorporated within the polymeric free volume may undergo chemical bonds with the polymer. Especially the desorption of incorporated LiF from the polymer leads to very peculiar Li depth distributions which closely resemble the well-known Case II diffusion profiles, with steep profile concentration changes emerging at the front of the water penetration from the outside.

Neutron Depth Profiling Technique for Studying Rechargeable Lithium Metal Anodes

Neutron Depth Profiling Technique for Studying Rechargeable Lithium Metal Anodes

NIXE: Neutron Depth Profiling coupled with Particle Induced X-ray Emission

A modification of the Neutron Depth Profiling (NDP) technique is proposed which uses the charged particle-induced X-ray emission generated from the light energetic ions produced in nuclear reactions to provide additional information about the depth profile of elements in the surface of a material. It is demonstrated that the particle-induced X-ray emission (PIXE) spectrum can also be measured with an NDP apparatus with the addition of an X-ray detector. By using coincidence counting methods, it is possible, in principle, to measure the elemental depth profile in the top few microns of a specimen. In this study, theoretical calculations and Monte Carlo radiation transport simulations were performed for 1400 keV alpha particles in a borosilicate glass material with three layers containing differing concentrations of Na2O, P2O5, B2O3 and SiO2. The production of K-shell X-rays for these elements was calculated from the production rate of alpha particles in (n, α) reactions, simulated using the Monte Carlo of N-Particle (MCNP6) radiation transport code. The main constraints on quantification limits and depth resolution for this technique depend on the material composition, detector efficiencies, and the neutron beam flux.

Li Garnet Dopant Stability Against Li Metal: A TOF-SIMS Study

Solid-state lithium batteries (SSLiBs) has been extensively studied in the past five years. The widely studied solid-state electrolytes (SSEs) includes LiSICON [1], NASICON-type Li conductors [2], perovskites [3] and garnets [4]. It is realized that garnet electrolyte is the most promising oxide electrolyte, due to its high Li-ion conductivity, stability with high voltage Li cathodes and Li anode. However, recently there has been reports [5, 6] on metal element reduction in certain garnet composition. Metal element reduction can lead to electronic conductivity, which is detrimental to cell performance. The reduction reaction is mostly likely to occur at grain boundaries. Since grain boundary is very thin and Li element is hard to detect, limited techniques can characterize the reduction reaction. Fudong and co-workers [5] applied neutron depth profiling technique to study Li content variation. Yisi and co-workers [6] conducted advanced XPS technique to study reduction on garnet grain surface. TOF-SIMS is surface sensitive technique with nano scale resolution. Herein, we will present our TOF-SIMS study on garnet dopant stability against Li metal. It is found that Nb dopant is not stable to Li metal. Nb doped garnet changes color upon contacting Li metal. This color change progress through the whole ceramic sample. EIS results show that resistance continues increase while the reaction progress. TOF-SIMS results indicate Nb element segregates to grain boundary and presents a different coordination at grain boundary than in bulk garnet. Reference: [1] Xu, X. et al. Chem. Mater. 23, 3798-3804 (2011). [2] Feng, J. K. et al. Mater. Technol. 28, 276-279 (2013). [3] Ihlefeld, J. F. et al. Adv. Mater. 23, 5663-5667 (2011). [4] Thangadurai, V. et al. Chem. Soc. Rev. 43, 4714-4727 (2014). [5] Han, F. et al. Nature Energy 4, 187-196 (2019). [6] Zhu, Y. et al. Adv. Energy Mater. 9, 1803440 (2019). Figure 1

In-Situ Measurement of Distribution of Lithium Atoms in Li-Ion Batteries and Their Components Using Thermal Neutron Beam

Nowadays, rechargeable Li-ion batteries are widely used in various devices. The further development of these secondary batteries depends on investigation of new materials for electrodes, electrolyte and interphases. The many physical or electrochemical methods, e.g., x-ray diffraction, x-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), can evaluate or investigate various aspects of these materials. Nevertheless, none of these methods can provide experimental spatial distribution of lithium atoms within full cell, half cell or some prospective materials. This very important information can be supplemented by nondestructive nuclear analytical technique, Neutron Depth Profiling (NDP) [1]. This unique technique is based on irradiation of samples by an intense beam of thermal neutrons and analyzing the energy loss of charged particles following the 6Li(n,α)3T reaction. The high nominal resolving power (depth resolution) of this method, about 10 nm, charge neutrality of neutron beam and high cross section of the capture reaction, 940 b, enable various in-situ measurements in various electrochemical conditions. Beside traditional NDP technique the above mentioned reaction can be exploited for high resolution imaging of 2D distribution of lithium in thin samples [2]. The both method capability for investigation of Li-ion battery samples will be discussed and examples of usage will be presented in this contribution.

Measurement of Li diffusion in porous carbon by neutron depth profiling

ABSTRACTDiffusion of Li in porous carbon material has been studied using a nondestructive neutron depth profiling technique. It has been acknowledged that carbon-based materials are good candidates for electrodes in lithium-ion batteries. It is because they exhibit a high ability to effectively release Li ions during charging and discharging processes. The Li diffusion was studied in porous carbon material with several annealing cycles. The produced data were useful for the determination of relative straight porosity level and diffusion coefficient, which result to be between 5.13E-11 cm2/s and 5.56E-11 cm2/s, that agree with the literature but obtained with a technique that does not alter the sample during the analysis.

3D Mapping of Lithium in Rechargeable Batteries

Rechargeable Li-ion batteries (LIBs) are an indispensable technology in modern life for efficient energy storage; they are deployed in large numbers and operate close to their electrochemical stability limits. Detrimental reactions at battery electrodes can cause capacity fade and even catastrophic failures, hindering the widespread use of LIBs, particularly in mobile power energy solutions such as all-electric vehicles. It is valuable to visualize the distribution and flow of the active element, lithium, in electrodes for better diagnosis of battery functioning and failure. Specifically, to address issues of the degradation of electrodes and growth of Li metal dendrites, the neutron depth profiling (NDP) technique was applied with two dimensional (2D) pinhole aperture scans to spatially map lithium in 3D. NDP is a neutron activation analysis method used to quantitatively measure the abundance and depth distribution of several technologically important elements (Li, B, N, He, Na, etc). The technique has been used to measure the Li distribution in modern battery technologies based on the nuclear reaction, 6Li + n → a (2055 keV) + 3H (2727 keV). Charged a and triton (3H) particles lose kinetic energy during transport through the specimen media, which is measured to determine the depth of the activation reaction. The normalized counts of activation events are recorded to determine the abundance of Li at the corresponding depth. The method has been applied to measuring the spatial distribution of Li in two LixFePO4 electrode films. Because NDP is sensitive only to the 6Li isotope of Li, which has a natural isotope abundance of 7.5 at%, isotope enrichment of LFP was used to greatly improve mapping efficiency. Two electrodes were prepared, one with a single charge/discharge cycle and the other with 5532 cycles, denoted as LFP1 and LFP5k, respectively. It was shown that the Li concentration is high and homogeneous in LFP1, with x = 0.65 ± 0.06 and Li concentration variation of 9%, where that in LFP5k much lower and spatial distribution much more heterogeneous, with x = 0.38 ± 0.05 and Li concentration variation of 13%. The significant capacity decay in the LFP5k electrode is discussed in the context of structural changes in electrode materials due to electrochemical processes. The nature of Li dendritic growth in polymeric electrolytes has also been investigated. A symmetric sandwich cell of Li / poly(ethyleneoxide) (PEO) : lithium bis(trifluoromethane)sulfonamide (LiTFSI) / Li was used to as a model system in this study. In situ NDP measurements has been carried out during directional Li pumping from the bottom Li electrode to the top at a constant electric current of 0.1 mA. After a period of steady Li plating, dendrites start to grow, and eventually short-circuit the polymer electrolyte. Li mapping studies reveal rather heterogeneous lateral distribution of Li over length scales from below a millimeter to centimeters. The lateral mobility of Li appears to be large and the deposited Li layer on top electrode partly deform from its original circular shape. Most Li in the electrolyte layer resides in dendrites growing from the top electrode, with overall composition decrease linearly from the electrode interface to the bulk of the electrolyte. It is observed that dendrites also grow from the bottom electrode, where presumably only Li oxidation reaction occurs. The revelation poses new design and engineering challenges in using Li metal electrode in future batteries. Figure 1

3D mapping of lithium in battery electrodes using neutron activation

The neutron depth profiling technique based on the neutron activation reaction, 6Li (n, α) 3H, was applied with two dimensional (2D) pinhole aperture scans to spatially map lithium in 3D. The technique was used to study model LiFePO4 electrodes of rechargeable batteries for spatial heterogeneities of lithium in two cathode films that had undergone different electrochemical cycling histories. The method is useful for better understanding the functioning and failure of batteries using lithium as the active element.

A Monte Carlo code to get response spectrum of ions for Neutron Depth Profiling

This paper presents a Monte Carlo code to get response spectrum of ions for the Neutron Depth Profiling (NDP) technique called Monte Carlo NDP (MC-NDP) that simulates the behavior of ions transmitted through a sample matrix and generates the energy spectrum for a specified detector. The MC-NDP model is based on the Ziegler-Bier- sack-Littmark Model, but incorporates the advantages of TRIM and CORTEO. The Impulse Approximation method is used to determine the flight length with the indexical inter- polation method rather than the Magic algorithm for the scattering angle between ions and nucleus. This makes MC- NDP more efficient and convenient to simulate entire ion histories by a Monte Carlo approach. MC-NDP's results agree well with both TRIM results and the experimental data.

Profiling lithium distribution in Sn anode for lithium-ion batteries with neutrons

Measuring the distribution of lithium in high capacity lithium-ion battery (LIB) electrodes is essential to understanding the coulombic losses during the lithiation/delithiation processes that occur while charging and discharging the cell. In this research, two half-cell prototypes were fabricated by electrochemically lithiating Sn foil anodes in 1M LiBF4 in a 1:1 (wt:wt) ethylene carbonate and dimethyl carbonate solutions at a constant potential of 0.50 and 0.67 V (vs. Li/Li+). The neutron depth profiling (NDP) technique was employed to study the Li distributions in the anodes. Li concentration profiles were resolved for the samples lithiated under different conditions for LIB studies. In addition, this paper demonstrated an in situ NDP measurement of an electrochemical cell with a thin window design, which reveals the dynamics of lithium distribution within the Sn anode.

Neutron depth profiling technique for studying aging in Li-ion batteries

During operation of a Li-ion cell, lithium diffuses in and out of the solid phase anode and cathode. Measuring the lithium concentration within the electrodes of the cell over its operational life could provide key information for understanding the loss of active lithium and the associated aging mechanisms. Concentration profiles of lithium in a cell are difficult to measure with traditional spectroscopic techniques. Here, neutron depth profiling was used to measure lithium near-surface concentration profiles along the anode and cathode strips in off-the-shelf cylindrical Li-ion batteries as a function of the aging process. A buildup of the surface concentration of lithium was found in graphite anode as well as a general decrease in the intercalation efficiency in lithium iron phosphate cathode material with aging.

The effect of boron doping and gamma irradiation on the structure and properties of microwave chemical vapor deposited boron-doped diamond films

We investigated the effects of gamma irradiation doses of 50, 100, and 103 kGy on boron-doped diamond (BDD) thin films synthesized using microwave plasma-assisted chemical vapor deposition with varying boron concentrations of [B]/[C]gas = 100, 1000, 2000, and 4000 ppm. The diamond thin films were characterized prior to and post-irradiation and the influence was assessed in terms of morphology, structure, and physical properties using scanning electron microscopy, atomic force microscopy, x-ray diffraction, vibrational spectroscopy (Raman and IR), x-ray photoelectron spectroscopy, and electrical measurement techniques. The results clearly showed that the response of gamma irradiation on BDD films was distinctive compared to those of undoped diamond films with changes in electronic behavior from metallic (>1019 to 1020 cm–3) to semiconducting (≤1019 cm–3), especially in the case of heavily boron-doped diamond films demonstrated by micro-Raman spectroscopy and electrical property characteristics. In fact, this modification in electrical property behavior induced by “gamma conditioning” can be effectively used to fine control boron doping in chemically vapor deposited diamond much needed for various electronic devices. The “gamma conditioning” refers to material processing by radiation which helps to passivate electrically active boron and defects with hydrogen migration thus fine tunes the boron acceptor concentration albeit that this is difficult to achieve during BDD film deposition. In addition, the results also indicate that almost all of the BDD films studied hereby tend to reach a state of damage saturation when submitted to gamma irradiation of 103 kGy. We discuss our novel findings in terms of the interplay of boron-hydrogen in diamond with possible multiple scenarios: (i) the generation of point/Frenkel defects due to Compton scattered electrons, (ii) the formation of a nonmetallic boron-rich borocarbide (e.g., B13C2) phase, (iii) the passivation of electrically active acceptor (B) sites due to the invariable presence of H in the grains and at the grain boundaries, (iv) the desorption of H from the diamond surface, and (v) the “priming or pumping” effect, which improves the electronic properties by compensating for the shallow boron acceptors to produce semiconducting/insulating material, verified by the cold neutron depth profiling technique.

Dielectric constant and surface morphology of the elemental diffused polyimide

Polyimide (C22H10N2O5, PMDA-ODA, Kapton-H) samples were doped with phosphorous or boron and fluorine using the radiation assisted diffusion technique, with Co-60 gamma-rays over the dose range ∼64–384 kGy, at room temperature. The diffusion of phosphorus and fluorine was confirmed by the RBS technique and that of boron by the neutron depth profiling technique. The elemental concentration on the surface was studied by the XPS technique. The relative concentration of phosphorus, fluorine and boron increased with increasing dose of gamma-rays. The dielectric constant, ε′, of the polyimide increased by ∼43% after phosphorus doping but decreased by ∼33% after boron and fluorine doping. The increase in ε′ is attributed to the radiation induced chemical coupling of the phosphorus atoms across the intra-molecular polyimide chains. The down shift in ε′ is attributed to the decrease in the degree of electronic polarization and to the increase in the free volume due to the diffused boron or fluorine atoms. For all the doped samples the dielectric constant, ε′, decreased very slowly with increasing frequency, over the range 100 Hz–7 MHz. AFM results reveal that the surface morphology and the roughness of the doped polyimide are appreciably different than that of virgin polyimide.

Diffusion of 6Li in Ta and W

The objective of this work was the study of 6Li diffusion in the Ta and W refractory metals. The samples were prepared by ion implantation of 380keV 6Li+ ions into W and Ta thin foils (up to the fluence of 1016ions/cm2) and annealed up to the temperature 1940°C. The depth profiles of 6Li were determined using the Thermal Neutron Depth Profiling (TNDP) technique. The results showed that diffusion of 6Li in both W and Ta foils is very complex and cannot be described by simple Fick’s laws. Trapping centers (in the subsurface layers of both W and Ta metals) were supposed in a trial to explain the 6Li diffusion behaviour. However, the 6Li depth profiles were only partly explained. Other aspects are necessary to take into account for more proper quantification; such as spatially dependent diffusion coefficients, etc.

100 keV 10-B + implantation into poly-(di-n-hexyl silane), (PDHSi)

100 keV10B+ ions were implanted into poly-(di-n-hexyl silane) in different directions at a fluence of 1×1014 cm-2, and their depth distribution was determined by means of the neutron depth profiling technique. In no case were the projectile ions found to come to rest according to their predicted range profiles. Instead, they are always found to undergo considerable long-range migration. During the irradiation process this motion appears to be radiation-enhanced, and during the subsequent annealing steps one appears to deal with regular thermal diffusion. The implant redistribution is always found to be governed strongly by the self-created damage, insofar as both electronic and nuclear defects in the polymer act as trapping centers. Their population ratio is modified by thermal annealing.

Diffusion of <sup>6</sup>Li in Tantalum and Tungsten Studied by the Neutron Depth Profiling Technique

Diffusion of 6Li in the refractory metals Ta and W has been studied using the nondestructive neutron depth profiling technique. The preliminary results point out the complex behavior of 6Li atoms in W and Ta. The experiment showed that the Fickian diffusion is affected by the presence of traps and radiation defects in the sample surface layer. Further experiments and computer simulations of the diffusion process are in progress.