ToF-SIMS Measurements Research Articles

Influence of Moisture on the Electrochemical Performance of Prelithiated C/SiOx Composite Anodes for Li-Ion Batteries

Prelithiation of Si containing anodes has commonly been acknowledged as a potential solution to the challenge of the high irreversible lithium losses that still hinder the widespread adoption of this next-generation anode active material. However, upscaling and implementation in the process chain remain major hurdles for most proposed prelithiation processes. A significant part of this comes down to the high reactivity of prelithiation agents and prelithiated electrodes towards moisture. In industrial scale electrode production, dry rooms with dew point controlled atmospheres are already in use, but are a significant cost factor. Therefore, the compatibility of prelithiated electrodes with dry room conditions is a major factor for the implementation of prelithiation into existing production lines.In this work C/SiOx composite anodes are electrochemically prelithiated and subsequently subjected to industry relevant moisture levels. The influence of dew point and exposure time is examined. After exposure, the anodes are assembled into half-cells and their electrochemical performance during the first lithiation/delithiation cycle is analysed using a 3-electrode setup. The evaluation of the specific capacities and the potential curves provides information about the extent of the damage to the electrode. The results indicate a promising stability window for dew points of up to -40° C and realistic exposure times of up to one hour. Additional aging investigations in full cells against NMC622-based cathodes confirm these findings. Furthermore, electrochemical impedance spectroscopy, XPS and ToF-SIMS measurements are performed to elucidate the effect of moisture exposure on the solid electrolyte interface (SEI) composition. The results suggest the development of a double-layered SEI structure, where the first layer forms during prelithiation and is altered by moisture exposure, while the second layer forms on top of the first layer during formation. Figure 1

Electrical Characterization of Ultra-Thin Silicon-on-Insulator Films Doped By Means of Phosphorus End-Terminated Polymers

Starting at the 3 nm node, the microelectronics industry is anticipated to transition toward new stacked device architectures, such as gate-all-around field-effect transistors (GAAFETs). In GAAFETs, the gate completely surrounds a silicon nanosheet that serves as a channel, improving the control of the current and performances. The introduction of ultra-scaled stacked 3D devices posed new technological and fundamental problems. In particular, doping techniques commonly used in the mass production of advanced transistors, such as ion implantation or diffusion, present some limitations when applied to these 3D structures. Perego et al.[1] suggested the use of dopant end-terminated polymers as a mild and simple alternative approach to achieve semiconductor doping. Considering the current trend in ultra-scaled microelectronic devices, exploitation of this doping technology requires the demonstration of the possibility to dope thin silicon membranes, achieving a uniform doping concentration throughout the entire film and optimized electrical properties.In this work, ex-situ doping of silicon-on-insulator (SOI) substrates, with device layer thickness ranging from 6 to 70 nm, is performed by using poly(methylmetachrylate) polymers end-terminated with a P containing moiety (PMMA-P), following a procedure described in our previous works.[1,2] Accordingly, a phosphorus δ-layer is created at the interface between a SiO2 capping layer and the underlying Si device layer. Drive-in of the P atoms is performed by annealing the samples in a RTP system at temperatures ranging from 900 to 1200 °C in N2 atmosphere. Annealing time is selected to inject a constant P dose of ∼ 1 x 1013 cm-2 into the SOI substrate, achieving a uniform dopant concentration, as verified by ToF-SIMS measurements. Sample resistivity (ρ), carrier concentration (ne ) and mobility (μ) are determined through sheet resistance and Hall measurements in van der Pauw configuration.Figure 1 shows the results of the electrical and compositional measurements obtained on SOI samples with 30 nm thick device layer as a function of the drive-in temperature. An average activation rate (ηa) above 95% is observed at room temperature in the samples annealed at 1000 °C, indicating full activation of the injected dopants. In the temperature range considered, the mobility is almost constant and is perfectly compatible with values reported in the literature for bulk Si,[3]as shown in the inset. Moreover, the low temperature (5-300 K) electrical characterization indicates that the evolution of ρ, ne and μ values with temperature is consistent with those reported for a P doped bulk Si.[3]Figure 2 shows the results of the electrical and compositional measurements obtained on SOI samples with device layer thickness ranging from 6 to 70 nm upon drive-in of the P dopants at 1000 °C for 100 s. When decreasing the thickness of the device layer, P concentration progressively increases above 1019 atoms/cm3, suggesting that the capping SiO2 film and the buried oxide act as diffusion barrier for P atoms injected into the device layer. ηa well above 80% are achieved for the SOI substrates with device layer thickness greater than 10 nm. However, ηa drops below 10% when further decreasing the thickness of the device layer. A similar reduction of the activation rates was observed in silicon nanowires by Bj ö rk et al.[4]Interestingly, in extremely-thin SOI samples, donor deactivation is correlated to an increase in electron mobility with computed values even greater than those reported for a bulk Si[3], as shown in the inset of Figure 2. Figure 3 shows the relative electron mobility variation as a function of the ratio between the thickness and the average distance between donors for SOI samples annealed at 900 and 1000 °C. The computed values are perfectly compatible with those reported by Kadotani et al.[5] Their model suggests that the enhanced electron mobility observed in heavily doped extremely-thin SOI is caused by the transition from 3D to almost 2D conduction, which results in the reduction of the Coulomb scattering due to the lower number of neighbor donor ions.In conclusion, an experimental study of the doping of ultra-thin SOI by means of phosphorus end-terminated polymers, demonstrates effective doping of silicon with extremely high activation rates of the dopants. Significant deactivation of P atoms and extremely high electron mobility are observed when decreasing the thickness of the device layer below 20 nm where bulk conducting properties transitioned to confinement related phenomena.[1] M.Perego et al., ACS Nano 12 (2018) 178-186.[2] M.Perego et al., J.Mater.Chem.C 8 (2020) 10229-10237.[3] S.M.Sze, K.K.Ng, Physics of Semiconductor Devices (2006) 5-75.[4] M.T.Björk et al., Nature Nanotechnology 4 (2009) 103-107.[5] N.Kadotani et al., Journal of Applied Physics 110 (2011) 034502. Figure 1

Probing Reaction Heterogeneity in Thick Electrodes: LiFePO4 Versus LiNi0.6Mn0.2Co0.2O2

Introducing thick electrodes is a sound practice for increasing the energy density of lithium-ion batteries by minimizing the ratio of inactive components at device level. However, the inferior rate performance of the thick electrodes, which is believed to be caused by the inhomogeneous reaction, limits their further applications. In this study, we investigate the reaction distribution in LiFePO4 and LiNi0.6Mn0.2Co0.2O2 thick electrodes with combined scanning X-ray fluorescence (XRF) microscopy and X-ray absorption near edge structure (XANES) spectroscopy. 2D XRF-XANES imaging shows discharge reaction is highly non-uniform in the LFP electrode’s depth direction, the degree of which increases with the discharge rate. In contrast, NMC retains a uniform SOC distribution up to 1C (or 1.5C) rate. The XRF-XANES observations are verified by ToF-SIMS measurements. The different reaction distributions observed in LFP and NMC is explained by P2D modeling and has a thermodynamic origin Figure 1

Label-free sub-micrometer 3D imaging of ciprofloxacin in native-state biofilms with cryo-time-of-flight secondary ion mass spectrometry

High spatial resolution mass spectrometry imaging has been identified as a key technology needed to improve understanding of the chemical components that influence antibiotic resistance within biofilms, which are communities of micro-organisms that grow attached to a surface. Time-of-flight secondary ion mass spectrometry (ToF–SIMS) offers the unique ability for label-free 3D imaging of organic molecules with sub-micrometer spatial resolution and high sensitivity. Several studies of biofilms have been done with the help of ToF–SIMS, but none of those studies have shown 3D imaging of antibiotics in native-state hydrated biofilms with cell-level resolution. Because ToF–SIMS measurements must be performed in a high-vacuum environment, cryogenic preparation and analysis are necessary to preserve the native biofilm structure and antibiotic spatial distribution during ToF–SIMS measurements. In this study, we have investigated the penetration of the antibiotic ciprofloxacin into Bacillus subtilis biofilms using sub-micrometer resolution 3D imaging cryo-ToF–SIMS. B. subtilis biofilms were exposed to physiologically relevant levels of ciprofloxacin. The treated biofilms were then plunge-frozen in liquid propane and analyzed with ToF–SIMS under cryogenic conditions. Multivariate analysis techniques, including multivariate curve resolution (MCR) and inverse maximum signal factor (iMSF) denoising, were used to aid analysis of the data and facilitate high spatial resolution 3D imaging of the biofilm, providing individually resolved cells and spatially resolved ciprofloxacin intensity at “real world” concentrations.Graphical

2-((5-Mercapto-1,3,4-thiadiazol-2-yl)thio)acetic acid as a novel chalcopyrite depressant for selective flotation separation of molybdenite from chalcopyrite

In this work, 2-((5-mercapto-1,3,4-thiadiazol-2-yl)thio)acetic acid (MTAA), a stable and eco-friendly organic small-molecule reagent, was introduced as chalcopyrite depressant for selective flotation separation of molybdenite from chalcopyrite. In the flotation experiments of single mineral and artificially mixed mineral, the recovery of chalcopyrite reduces from 90% to 5% in the pH range of 5 to 10 when MTAA (8 mg/L) is added. The results of IR and zeta potential show that there are two tautomers (thione and thiol) in solid MTAA, while in aqueous solution, MTAA is mainly in the form of thiol and reacts with copper ions. The results of XPS and Tof-SIMS measurements indicate that MTAA may react with copper ions to form a quaternary chelate structure via the S and N atoms. The DFT calculation results also show that MTAA is more likely to react with copper ions than iron ions.

Study on the Ion Migration of Silver Ions from Aqueous Solution in Epoxy-Based Molding Compounds by TOF-SIMS Measurements

Epoxy molding compounds are typically used for the encapsulation of modern-day electronic devices. These protect the semiconductor components from environmental influences, such as humidity and oxygen, which could harm the device. However, there is still a risk for corrosion phenomena, when the device is used in harsh conditions (e.g. high humidity and temperature). Electrochemical migration is a mechanism that can occur in the semiconductor device. For instance, silver wires, glues, solders or leadframe-platings used in the package combined with high humidity contact are a huge risk. For this type of corrosion to happen, Ag ions need to migrate through the molding compound. Therefore, measurement of the diffusion coefficient of silver ions in molding compounds can help to better predict the risk of silver migration and corrosion. In this study silver(I)salts were used source for Ag + ions. An Arrhenius correlation was found in the range from 298 K to 393 K. The diffusion coefficient as well as the activation energy of silver ions in four different molding compounds have been evaluated. The investigated activation energies as well as diffusion coefficients are in the range of 0.12 to 0.50 eV.

Solid Electrolyte Interphase for Ca Metal Batteries

New battery technologies have received increased attention in recent years, especially those based on the use of divalent cations such as calcium and magnesium. Their high abundance (calcium and magnesium being, respectively, the 5th and 8th most abundant element in the earth crust) and the possible safe use of metal anodes could result in more sustainable devices with lower cost and higher energy density systems when compared to Li-ion. Feasibility of plating/stripping of calcium metal has been demonstrated recently1 in very few organic electrolyte formulations. In all cases, some degree of electrolyte reduction and formation of passivation layer were reported. In particular, using Ca(BF4)2 in a mixture of carbonate solvents, a fully conformal passivation layer is formed at the surface of the metal anode.2 Yet this layer allows for Ca plating and stripping, thus exhibiting similar behavior as a solid electrolyte interphase (SEI). However, the nature and composition of such layer remain mostly unknown.In this communication, an in-depth analysis of the SEI will be presented. The influence of the electrolyte formulation (salt, solvent and additive) on the formation of the SEI and how it affects Ca plating and stripping kinetics were investigated. Among other technics, XPS, EELS and ToF-SIMS measurements allowed to detail the composition of the SEI. The homogeneity, the morphology and the microstructure were studied by means of TEM and FTIR microspectroscopy. Ponrouch, A. et al. Towards a calcium-based rechargeable battery. Nat. Mater. 15, 169 (2015).Forero-Saboya, J. et al. Understanding the nature of the passivation layer enabling reversible calcium plating. Energy Environ. Sci. 13, 3423–3431 (2020).

Advanced surface analysis using GCIB-C60++-tandem-ToF-SIMS and GCIB-XPS of 2-mercaptobenzimidazole corrosion inhibitor on brass

A gas cluster ion beam (GCIB) sputtering source in association with high-resolution X-ray photoelectron spectroscopy measurements were employed to slowly sputter and analyze a 2-mercaptobenzimidazole (MBIH) corrosion inhibitor surface layer on brass substrate after immersion in chloride solution. Furthermore, ToF-SIMS measurements and imaging were performed to further describe the structure of this surface layer. In addition, the powerful nature of the tandem ToF-SIMS (MS/MS) technique was demonstrated to detect and confirm the organometallic complexes that formed among the brass corrosion products and MBIH. Also, the issue of spectral interferences was considered for the organometallic complexes of 63Cu, 65Cu, 64Zn, and 66Zn in combination with MBIH. Large-area ToF-SIMS imaging (4.8 by 3.2 mm) in positive and negative polarities was performed to show the 2D distribution of the MBIH on the brass surface. Finally, 3D ToF-SIMS imaging using GCIB and C60++ sputtering sources showed the depth distribution of different species at the MBIH/brass interface. This type of analytics is currently state-of-the-art in the surface analysis of corrosion inhibitors.

Flotation separation of molybdenite from chalcopyrite using an environmentally-efficient depressant L-cysteine and its adsoption mechanism

In this work, L-cysteine was introduced as an environmentally-efficient flotation reagent in the selective separation of molybdenite from chalcopyrite. Its flotation performance and adsorption mechanism onto chalcopyrite were also investigated by flotation experiment, zeta potential, FTIR spectra, Raman spectra, TOF-SIMS measurements and DFT calculations. The flotation results indicated that L-cysteine exhibited stronger depressing ability than the conventional chalcopyrite depressants of Na2S, NaHS and sodium thioglycolate, suggesting it could become a promising potential depressant in the selective flotation separation of molybdenite from chalcopyrite. The results of zeta potential, FTIR spectra, TOF-SIMS and Raman spectra measurements demonstrated that L-cysteine might chemisorb on the Cu atoms of chalcopyrite surface via -SH and –NH2 groups to form a stable L-cysteine-Cu chelate compound. The DFT calculations further supported the experimental characterizations; the calculated adsorption reaction energy of L-cysteine with Cu in the (0 0 1) surface of chalcopyrite was much lower than that of L-cysteine with Fe, which implied that L-cysteine would prefer to adsorb onto the Cu site of chalcopyrite surface.

Sample Preparation of Biological Tissues and Cells for the Time-of-Flight Secondary Ion Mass Spectrometry

The review is devoted to the application of time-of-flight secondary ion mass spectrometry (ToF–SIMS) to the analysis of biological tissues and cells. The invention of cluster primary ions significantly improved the sensitivity, especially in the mass range above several hundred of Daltons, which opened up the study of lipids, amino acids, nucleic acids, metabolites, and drugs. As other methods based on the bombardment of sample surface with a particle beam, ToF–SIMS measurements are carried out under ultrahigh vacuum conditions, which makes sample preparation of biological materials a critical stage of the experiment. Several techniques have been developed for preparing single cells, cell cultures, and tissues for the analysis. Most of them are based on conventional techniques used in histology and cytology, including optical, electron, probe microscopy and electron probe microanalysis. However, the analytical features of ToF–SIMS make it necessary to adapt these techniques. A universal solution does not exist, and the main objective of this review was to systematize and compare the developed techniques of the sample preparation for ToF–SIMS. The effect of instrumental factors on the results of the ToF–SIMS analysis of biological samples was also reported.

Ligand-free preparation of polymer/CuInS2 nanocrystal films and the influence of 1,3-benzenedithiol on their photovoltaic performance and charge recombination properties.

Bulk heterojunction solar cells based on conjugated polymer donors and fullerene-derivative acceptors have received much attention in the last decade. Alternative acceptors like organic non-fullerene acceptors or inorganic nanocrystals have been investigated to a lesser extent; however, they also show great potential. In this study, one focus is set on the investigation of the in situ growth of copper indium sulfide nanocrystals in a conjugated polymer matrix. This preparation method allows the fabrication of a hybrid active layer without long-chain ligands, which could hinder charge separation and transport. In contrast, surfactants for the passivation of the nanocrystal surface are missing. To tackle this problem, we modified the absorber layer with 1,3-benzenedithiol and investigated the influence on charge transfer and solar cell performance. Using ToF-SIMS measurements, we could show that 1,3-benzenedithiol is successfully incorporated and homogeneously distributed in the absorber layer, which significantly increases the power conversion efficiency of the corresponding solar cells. This can be correlated to an improved charge transfer between the nanocrystals and the conjugated polymer as revealed by transient absorption spectroscopy as well as prolonged carrier lifetimes as disclosed by transient photovoltage measurements.

Pyrite-based mixtures as composite electrodes for lithium-sulfur batteries

Pyrite-based composite materials (Li/S) were prepared by high-energy ball milling of FeS2 with one or more metal sulfides, Li2S, Cu2S, and CuS, in various molar ratios and under different conditions. Prolonged grinding resulted in the formation of mixed compounds rather than single-phase lithiated chalcopyrite. The composite materials were primarily investigated via XPS, XRD, and TOF-SIMS characterization methods, and performance of the materials as composite cathodes was evaluated via analysis of dQ/dV curves. Evidence of main active phases in the materials was found, including, Cu-doped FeS2 (pyrite) and/or nonstoichiometric chalcopyrite (CuxFeyS2 − z). TOF-SIMS measurements exhibited further evidence of formation of partially lithiated pyrite mixtures. Lithium cells comprising mixed pyrite cathodes demonstrate superior electrochemical performance, namely, 98–100% coulombic efficiency and 300–320 mAh g−1 (per gram of active material) after 150 cycles over a voltage range of 1.2–2.8 V at 0.1 C-rate, whereas pristine FeS2/Li cells exhibit only 220 mAh g−1 at similar operating conditions. Lowering of cut-off discharge voltage from 1.2 to 1.0 V of the FeS2/Li cells with FeS2-rich mixed cathodes is accompanied by about 15% capacity enhancement (350–450 mAh g−1 after 200 cycles). The cells with mixed pyrite composite cathodes exhibit an increase in maximum pulse power capability from 5 to 15 W/g and C-rate from 0.3 to 2.5, which points towards higher electrical conductivity of the active material as compared to the pristine pyrite.

Titania-Silica Catalysts for Lactide Production from Renewable Alkyl Lactates: Structure–Activity Relations

Different Ti-Si catalysts, viz. TiO2 supported on amorphous SiO2 or Si-MCM-41, TiO2-SiO2 xerogels, and Ti zeolites (TS-1 and Ti-beta), were compared in terms of activity and selectivity for the direct conversion of methyl lactate to lactide in the gas phase. Except for Ti-beta, all catalysts exhibit a high lactide selectivity of 88–92% at conversions below 50%. From DR UV–vis spectroscopy, it is evidenced that the catalytic activity of tetrahedral TiO4 sites is higher than those of polymerized TiO5 or the octahedral TiO6 counterparts, irrespective of the catalyst structure, an analysis supported by ToF-SIMS measurements. A kinetic analysis shows that the catalytic activity is proportional to the number of vacant sites on the catalyst surface. Thus, the activity increase observed for tetrahedral TiO4 sites may be attributed to an increased number of vacant sites (e.g., two for TiO4, zero for TiO6). Lactide productivity thus highly benefits from an increased dispersion of Ti sites on the catalyst surface an...

Performance Analysis of Thiocarbonohydrazide as a Novel Selective Depressant for Chalcopyrite in Molybdenite-Chalcopyrite Separation

A novel surfactant, thiocarbonohydrazide (TCH), was synthesized and tested for the first time as a selective chalcopyrite depressant in Cu-Mo separation. Its adsorption mechanisms on chalcopyrite were studied by flotation tests, zeta potential, FTIR, XPS and ToF-SIMS measurements. FTIR and zeta potential analyses suggested that there was a strong chemisorption reaction between TCH and chalcopyrite, resulting in the formation of TCH–copper complexes. XPS and ToF-SIMS measurements further confirmed the chemisorption of TCH onto the chalcopyrite surface and showed that this chemisorption reaction is due to its S and N atoms, which form five-membered chelating rings by releasing H ions.

Interfacial Mechanophore Activation Using Laser-Induced Stress Waves

A new methodology is developed to activate and characterize mechanochemical transformations at a solid interface. Maleimide-anthracene mechanophores covalently anchored at a fused silica-polymer interface are activated using laser-induced stress waves. Spallation-induced mechanophore activation is observed above a threshold activation stress of 149 MPa. The retro [4+2] cycloaddition reaction is confirmed by fluorescence microscopy, XPS, and ToF-SIMS measurements. Control experiments with specimens in which the mechanophore is not covalently attached to the polymer layer exhibit no activation. In contrast to activation in solution or bulk polymers, whereby a proportional increase in mechanophore activity is observed with applied stress, interfacial activation occurs collectively with spallation of the polymer film.

Molybdenum and Tungsten Contamination in MOS Capacitors

In this paper, the impact of molybdenum and tungsten contamination on the properties of MOS capacitors is analyzed, with the aim to investigate whether measurements of MOS capacitors can be used to detect this sort of contaminants. Surface Photovoltage (SPV) measurements of carrier diffusion length and of the oxide charge (obtained from high injection SPV) are compared to the results of MOS capacitor measurements. In agreement with previous DLTS data, both SPV and generation lifetime data show that molybdenum remains in the solid solution in silicon in the studied dose range. As a consequence, molybdenum contamination has limited impact on the interface state density at the oxide-silicon interface. Vice versa, tungsten was shown to deactivate starting from rather low doses (1011 cm−2). Tungsten deactivation is associated with the formation of new peaks in interface state density spectra. However, no tungsten segregation at the oxide-silicon interface could be detected by ToF-SIMS measurements. We suggest that in MOS capacitors tungsten deactivation is associated with segregation in the oxide layer. SPV has limited sensitivity to these impurities. Generation lifetime is a good monitor of tungsten contamination, whereas for molybdenum DLTS is the most sensitive contamination monitor.

Oxygen diffusion at high temperatures within the SnO2/Sst interlayer in sputtered thin films

SnO2 and Stainless Steel 316 (Sst) films are useful materials for the production of interferential decorative coatings because they provide a high sputtering rate and low cost respectively. Multilayers of SnO2 and Stainless Steel 316 were deposited using DC pulsed magnetron sputtering, and oxygen diffusion processes were studied in the interface. Studies were made at selected temperatures between 450°C and 650°C for different exposure times: 0, 15, 30, 60 and 120min. TOF-SIMS depth profiles determined the oxygen penetration in Sst films and evidenced the formation of a chromium oxide film. This method is noted for its simplicity for a full study at different temperatures and exposure times with few TOF-SIMS measurements. Oxidation kinetics can be described by two different contributions: a fast oxide film formation and parabolic growth. Results are useful for predicting the thickness of the chromium oxide film and the degradation of the coating at high temperatures.

Flotation separation of copper–molybdenum sulfides using chitosan as a selective depressant

Chitosan, a natural biodegradable polymer, was studied as a selective depressant in copper–molybdenum sulfide separation by flotation. Although chitosan depressed both molybdenite and chalcopyrite in single mineral flotation, selective flotation was achieved during the flotation of molybdenum-bearing copper sulfide concentrate at pH 6; the recovery of molybdenum in the froth product was over 70% while the recovery of copper was less than 24%. Adsorption measurements showed that chitosan had a higher adsorption density on chalcopyrite than on molybdenite. FTIR and ToF-SIMS measurements were carried out to confirm the different degrees of interaction of chitosan with molybdenite and chalcopyrite and the results showed that chitosan mostly adsorbed on chalcopyrite via amide groups when both molybdenite and chalcopyrite were present in the suspension.

Predicting Transport Properties at Electrode/SEI/Electrolyte Interfaces in Li Ion Batteries

The electrode/solid-electrolyte-interphase (SEI)/electrolyte interface is rather complex and critially important in Li-ion battereis. Improving Li transport and preventing electron leakage through the solid electrolyte interphase (SEI) are critical to Li-ion batteries capacity drop and power loss. Identification of the dominant diffusion carriers and their diffusion pathways in main components of SEI is a necessary step to understand the functionality of SEI before tailoring its properties. Therefore, dominant Li diffusion carriers and the ionic conductivity in perfect SEI components (such as Li2CO3 and LiF) were predicted with density functional theory (DFT) over a broad voltage range of the electrode materials that the SEI component covers. It was predicted that the main diffusion carriers in Li2CO3 on anode are excess Li ion interstitials (Li i +), however, above 3.98V, Li ion vacancies (V Li -) become the dominant. In contrast, the main diffusion carriers in LiF was predicted to be Schottky pairs (V Li - and V F +), agreeing with experimental observations. While the V Li - diffuses through direct hopping, the Li i + diffuses by knocking off the Li+ ion from a lattice. Meso-scale Li+ ion diffusion equations were then formulated based on the diffusion mechanisms discovered by DFT and the boundary conditions of isotope exchange experiments in order to make direct comparison with TOF-SIMS measurements. Furthermore, by studying the point defect formation and diffusion, it is proposed that electron or polaron hopping can be facilitated by the diffusion of point defects, such as Li i 0 interstitial, when the SEI is thicker than electron tunneling length. Ab initio molecular dynamics of electrode/SEI/electrolyte interface simulations further demonstrated that when a Li i 0 interstitial transports into the electrolyte, ethylene carbonate (EC) reduction is observed immediately. This is a possible mechanism to explain electron leakage through thick SEI films into the electrolyte.

A comparative analysis of different measurement techniques to monitor metal and organic contamination in silicon device processing

A few key techniques for the analysis of contamination in silicon are compared for their ability to detect different impurities. Both metal and organic contamination is included in this study. In addition, common contaminants and elements recently introduced in the fabrication process are considered. For what concerns metal contamination, it is shown that different approaches are required depending on the in-depth distribution of the contaminant and hence on its diffusivity. Copper, iron, molybdenum, and tellurium are chosen as examples of contaminants with different diffusivity and solubility properties. Total reflection X-ray fluorescence (TXRF), recombination and generation lifetime measurement techniques, deep level transient spectroscopy (DLTS) and capacitance versus voltage measurements are compared. The detection of slow diffusers is found to be very critical, because a very low dose may result in a non-negligible concentration in the device region. As a consequence, the sensitivity per unit area required for these elements is difficult to reach with surface techniques such as TXRF. On the other hand, very fast diffusers such as copper can hardly be revealed in the solid solution in silicon. Copper in silicon can be revealed at the oxide–silicon interface by TOF-SIMS measurements, or by surface generation velocity measurements with the Zerbst method. For what concerns organic contamination, surface recombination velocity and gate oxide integrity tests were compared. The most relevant effects of organic contamination were observed by electrical stress of the oxide. Indeed, the fraction of capacitors with degraded breakdown voltage increased dramatically in wafers with intentional organic contamination.