Photoelectron Spectroscopy Depth Profiling Research Articles

How Relevant Are SEI Studies from Half Cell Samples to Understand Aging Mechanisms in Potassium Batteries? An in-Depth Photoelectron Spectroscopy Study

Owing to a shared common technological basis, monovalent K-ion battery (KIB) systems follow in the footsteps of Li-ion batteries (LIBs) with the aim to develop a broader portfolio of available battery technologies and to put them on a more sustainable material basis. For example, both cations intercalate into a graphite host structure, which can be used in combination with carbonate-based electrolytes as negative electrode. Especially in half cells, the degradation of graphite electrodes in KIBs is significantly accelerated in comparison to LIBs. Previous surface studies demonstrated that the formation of a durable and protective solid electrolyte interphase (SEI), that is paramount for long cycle life in alkali-ion batteries, is a major bottleneck for KIBs because of less benign SEI properties[1][2].Recently reported crosstalk phenomena in half cell configurations due to the highly reactive potassium counter electrode make the analysis of surface layers a particular challenge [2][3]. In this presentation, a detailed characterization of the SEI formation on graphite was performed in both half and full cell configurations by in-house and synchrotron-based photoelectron spectroscopy (PES) in order to demonstrate fundamental differences in surface layer composition under the influence of a reactive counter electrode. While it is generally acknowledged that PES results show differences in SEI composition and thickness between both configurations, our results clearly demonstrate that in case of KIBs the changes become severe. This challenges interpretations of SEI layer properties made in half cells, as they are distinctly different from those in full cells. More importantly, this also affects interpretations on the major electrolyte degradation pathways in these systems. Using PES depth profiling and complementing results with gas chromatography, as well as DFT calculations, delivers new insights on the irreversible processes in KIBs. Reference s : [1] Naylor, et al., ACS Appl. Mater. Interfaces. 11 (2019) 45636–45645.[2] Allgayer et al., ACS Appl. Energy Mater. 5 (2022) 1136–1148.[3] Hosaka et al., ACS Energy Lett. 6 (2021) 3643–3649.

An Evaluation of Nanoparticle Distribution in Solution-Derived YBa2Cu3O7−δ Nanocomposite Thin Films by XPS Depth Profiling in Combination with TEM Analysis

This work discusses the development of an analysis routine for evaluating the nanoparticle distribution in nanocomposite thin films. YBa2Cu3O7−δ (YBCO) nanocomposite films were synthesized via a chemical solution deposition approach starting from colloidal YBCO solutions with preformed nanoparticles. The distribution of the nanoparticles and interlayer diffusion are evaluated with X-ray photoelectron spectroscopy (XPS) depth profiling and compared with cross-sectional transmission electron microscopy (TEM) images. It is shown that the combination of both techniques deliver valuable information on the film properties as nanoparticle distribution, film thickness and interlayer diffusion.

Improvement of Thermal and Environmental Stabilities of Short Channel Coplanar Amorphous InGaZnO Thin‐Film Transistors by Introducing Amorphous ZrAlOx Interlayer

The short channel coplanar amorphous indium gallium zinc oxide (a‐IGZO) thin‐film transistor (TFT) is reported by introducing a ZrAlO x (ZAO) interlayer deposited by spray pyrolysis at the substrate temperature of 350 °C. The atomic ratio (at. %) of In:Ga:Zn:O is 1:2.5:1.2:5.2 in the a‐IGZO film deposited by sputtering. The a‐IGZO TFT with ZAO layer with 0.87 μm channel length exhibits the field‐effect mobility of 6.44 cm2 V−1 s−1, the threshold voltage of −2.16 V, and on/off current ratio of 7.6 × 107. It is found from the X‐ray photoelectron spectroscopy depth profile and high‐resolution transmission electron microscope analysis that some Zr atoms diffuse into the a‐IGZO underlayer. The formation of ZrO bonds on a‐IGZO surface region reduces the carrier concentration in the a‐IGZO TFT offset region, between source/drain contact and the channel, and blocks the carrier diffusion into the channel. This reduces the field‐effect mobility of 10 μm channel length TFT from 21.86 to 14.01 cm2 V−1 s−1, but the ZAO layer protects the a‐IGZO from the diffusion of H2O and O2. As a result, 0.87 μm TFT shows high on/off current ratio and stable under 85 °C and 85% relative humidity test for 2 days.

Insights into Fullerene Passivation of SnO2 Electron Transport Layers in Perovskite Solar Cells

AbstractInterfaces between the photoactive and charge transport layers are crucial for the performance of perovskite solar cells. Surface passivation of SnO2 as electron transport layer (ETL) by fullerene derivatives is known to improve the performance of n–i–p devices, yet organic passivation layers are susceptible to removal during perovskite deposition. Understanding the nature of the passivation is important for further optimization of SnO2 ETLs. X‐ray photoelectron spectroscopy depth profiling is a convenient tool to monitor the fullerene concentration in passivation layers at a SnO2 interface. Through a comparative study using [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) and [6,6]‐phenyl‐C61‐butyric acid (PCBA) passivation layers, a direct correlation is established between the formation of interfacial chemical bonds and the retention of passivating fullerene molecules at the SnO2 interface that effectively reduces the number of defects and enhances electron mobility. Devices with only a PCBA‐monolayer‐passivated SnO2 ETL exhibit significantly improved performance and reproducibility, achieving an efficiency of 18.8%. Investigating thick and solvent‐resistant C60 and PCBM‐dimer layers demonstrates that the charge transport in the ETL is only improved by chemisorption of the fullerene at the SnO2 surface.

Origin of Degradation in Si‐Based All‐Solid‐State Li‐Ion Microbatteries

AbstractLike all rechargeable battery systems, conventional Li‐ion batteries (LIB) inevitably suffer from capacity losses during operation. This also holds for all‐solid‐state LIB. In this contribution an in operando neutron depth profiling method is developed to investigate the degradation mechanism of all‐solid‐state, thin film Si–Li3PO4–LiCoO2batteries. Important aspects of the long‐term degradation mechanisms are elucidated. It is found that the capacity losses in these thin film batteries are mainly related to lithium immobilization in the solid‐state electrolyte, starting to grow at the anode/electrolyte interface during initial charging. The Li‐immobilization layer in the electrolyte is induced by silicon penetration from the anode into the solid‐state electrolyte and continues to grow at a lower rate during subsequent cycling. X‐ray photoelectron spectroscopy depth profiling and transmission electron microscopy analyses confirm the formation of such immobilization layer, which favorably functions as an ionic conductor for lithium ions. As a result of the immobilization process, the amount of free moveable lithium ions is reduced, leading to the pronounced storage capacity decay. Insights gained from this research shed interesting light on the degradation mechanisms of thin film, all‐solid‐state LIB and facilitate potential interfacial modifications which finally will lead to substantially improved battery performance.

Printed Nonvolatile Resistive Memories Based on a Hybrid Organic/Inorganic Functional Ink

Organic memories are increasingly being considered as promising candidates for a number of novel consumer applications, such as smart labels and smart packaging devices. Indeed, organic memories can be fabricated on highly flexible substrates at low temperatures from liquid phase, employing for instance printing techniques. In this work, a nonvolatile resistive memory element conceived for large‐area processing and operation in ambient conditions is presented. In particular, a functional ink made out of an air stable organic semiconductor, namely ActivInk N1400, and gold nanoparticles (NPs) is developed and optimized for the fabrication of high performance memories through inkjet printing. The ink formulation is varied in order to explore the influence of Au NPs concentration on the switching behavior. Devices are operated in ambient conditions with reproducible memory behavior, high ON/OFF current ratios, and low programming voltages. In depth material analysis with time‐of‐flight secondary ion mass spectrometry and X‐ray photoelectron spectroscopy depth profiles are carried out on operated devices to shine a light on resistive switching mechanism and to determine the average gold content and its 3D distribution in stable memories.

Ultra Thin SiN<sub>X</sub> on a-Si <i>In Situ</i> Hot-Wire CVD by Decomposing NH<sub>3</sub> Gas

The fabrication of ultra thin silicon nitride (SiNX) layer (< 2 nm) on amorphous silicon (a-Si) in-situ hot-wire CVD by decomposing ammonia (NH3) gas is reported. Approximately 1.5 nm thin SiNX is formed by nitridation of 40 nm thick a-Si for 10 min at substrate temperature of 250 °C. The amorphous phase of SiNX formed on a-Si and a-Si layer deposited on c-Si wafer is identified by Raman spectroscopy. The formation of ultra thin SiNX by nitridation of a-Si at 250 °C is confirmed by X-ray photoelectron spectroscopy (XPS) depth profile measurement of SiNX/a-Si structured film. The report indicates that the HWCVD method can be used for fabricating superlattice structures consisting of ultra thin SiNX layers (< 2 nm).

Proposal and achievement of a relatively Al-rich interlayer for In-rich Al x In1−x N films deposition

Ternary In-rich AlxIn1−xN films were successfully grown on Si (111) and (0001) sapphire substrates by radio-frequency magnetron sputtering on a relatively Al-rich AlxIn1−xN layer after AlN buffer. X-ray diffraction (XRD) patterns of the films indicate highly c axis-oriented wurtzite structure and the indium content of about 0.76 has been evaluated according to the Vegard’s law. An Al-rich AlxIn1−xN transition layer was formed between the ultimate In-rich AlxIn1−xN film and the AlN buffer, which served as a further buffer to alleviate mismatch. X-ray photoelectron spectroscopy (XPS) depth profiling analyses confirm the alternative of indium and aluminum composition and the unavoidable oxygen impurities from surface to bulk. Owing to high indium content, obvious E2H and InN-like A1 (LO) phonon model accompanying with slight AlN-like A1 (LO) phonon model are observed. Hall effect measurements demonstrate n-type electrical conductivity in these alloys with carrier concentrations n=1019 cm−3. The strain in In-rich AlxIn1−xN films can be significantly reduced by introducing an Al-rich interlayer, facilitating the improvement of film quality for diverse device applications.

Quantitative elemental analysis of photovoltaic Cu(In,Ga)Se2 thin films using MCs+ clusters

In the process of optimizing solar cells, a quantitative and depth‐resolved elemental analysis of photovoltaic thin films is strongly required. Regarding Cu(In,Ga)Se2 (CIGS) thin film solar cells, depth‐dependent stoichometric changes of Ga and In are of great interest because the In/Ga ratio has a large effect on solar cell efficiencies. In this paper, we investigate the elemental composition of CIGS thin film solar cells based on secondary ion intensities in time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) depth profiling, providing high sensitivities and high spatial resolution. Quantification of the data is obtained by comparison to X‐ray photoelectron spectroscopy depth profiles. The detection of MCs+ clusters is used for semiquantitative elemental analysis of CIGS thin films. Correlation plots of the intensities of GaCs+ and InCs+ indicate that there is no relevant matrix effect for In and Ga due to changes in stoichiometry in the layer. Additional high‐resolution inductively coupled plasma mass spectrometry measurements show a strong correlation between the ratio of the bulk concentrations of Ga and In and the ratio of integrated ToF‐SIMS intensities of GaCs+ and InCs+ therefore supporting the quantitative interpretation of MCs+ data. Copyright © 2012 John Wiley & Sons, Ltd.

The Photoelectric Properties of Oxygen-deficient Mixed-phase TiO2 Nanotube Arrays

ABSTRACTThe photoelectric properties of oxygen-deficient titanium dioxide (TiO2) nanotube arrays are investigated in this study. The TiO2 nanotube arrays are prepared by anodization, followed by annealing at 450 to 750 °C for 3 h in air to form different crystalline phase mixtures. When the annealing temperature is increased, several phenomena are observed: (1) the ratio of anatase to rutile decreases, (2) the anatase nanotubes are shortened and (3) the thickness of the dense rutile film layer underneath the anatase nanotubes increases. The efficiency of visible light absorption of the nanotube arrays is enhanced with increasing annealing temperature. This is believed to be caused by the ionic defects, especially the oxygen vacancies, generated during the annealing procedure, enabling the absorption of low-energy radiations. The X-ray photoelectron spectroscopy (XPS) depth profile analysis provides the supporting evidence on the chemical nonstoichiometry (i.e., oxygen-deficiency) of the TiO2 nanotube arrays annealed at high temperature. With increasing annealing temperature, a decrease and an increase in the photocurrent density of the nanotube arrays under UV and visible light (wavelength > 500 nm) irradiations, respectively, are detected. The decrease of the photocurrent density under UV irradiation is caused by the reduction in the specific surface area (i.e., anatase nanotubes transform into rutile film with vigorous annealing). In contrast, the increase of the photocurrent density under visible light irradiation is contributed to the oxygen vacancies in the nanostructure, providing extra electron energy levels (locating below the conduction band of TiO2) within the band structure.

Electrochemically synthesised bronze patina: characterisation and application to the cultural heritage

The aim of the present study is to determine the role of tin on the corrosion behaviour of bronzes. For this purpose, different nuances of single phase α-Cu(Sn) are immersed in a 10–2 mol L–1 deaerated sulphate solution, buffered at pH 6·8. Then, the chemical–physical and electrochemical characterisation of an artificial patina, thin layer of corrosion products electrochemically formed at the surface of a 7 wt-% tin bronze are performed. First of all, the synthesised species are cathodically reduced. The successive steps of the potential–time curves, characteristic of the electrochemical reactions occurring at the electrode surface, are successfully calibrated with reference oxides. In order to complete the previous results, X-ray photoelectron spectroscopy (XPS) depth profiles are carried out by abrading progressively the oxidised surface. The deconvoluted XPS and Auger electron spectroscopy (AES) spectra speak in favour of an 'alloy/SnO2/Cu2O' layered structure similar to that reported in the literature. Analyses carried out on the oxidised samples by transmission electron microscopy (TEM) confirm this pattern.

Influence of Liquid Evaporation on the Components of SiC High Emissivity Coating

The process of Electron Beam-Physical Vapor Deposition (EB-PVD) preparing SiC coating with liquid evaporation was firstly discussed from a thermodynamic viewpoint. The results showed that the ratio of SiC in the as-deposited coating gradually increases and tends to reach a stable maximum of 0.73 with the evaporation temperature increase from 2500 K to 3400 K. To verify the thermodynamic analysis, amorphous SiC coating was deposited on Si substrate by EB-PVD at 3100 K. SiC concentration across the cross section of coating was calculated from the area of elements spectrum in X-ray photoelectron spectroscopy (XPS) depth profile analysis. The results showed that the average SiC concentration was about 0.7.

Electronic structure of a laterally graded ZrO2–TiO2 film on Si(100) prepared by metal-organic chemical vapor deposition in ultrahigh vacuum

A TiO2–ZrO2 film with laterally graded stoichiometry has been prepared by metal-organic chemical vapor deposition in ultrahigh vacuum. The film was characterized in situ using synchrotron radiation photoelectron spectroscopy (PES) and x-ray absorption spectroscopy. PES depth profiling clearly shows that Ti ions segregate toward the surface region when mixed with ZrO2. The binding energy of the ZrO2 electronic levels is constant with respect to the local vacuum level. The binding energy of the TiO2 electronic levels is aligned to the Fermi level down to a Ti∕Zr ratio of about 0.5. At a Ti∕Zr ratio between 0.1 and 0.5, the TiO2 related electronic levels become aligned to the local vacuum level. The addition of small amounts of TiO2 to ZrO2 results in a ZrO2 band alignment relative to the Fermi level that is less asymmetric than for pure ZrO2. The band edge positions shift by −0.6eV for a Ti∕Zr ratio of 0.03. This is explained in terms of an increase in the work function when adding TiO2, an effect that becomes emphasized by Ti surface segregation.

CVD Boron Carbo-Nitride as Pore Sealant for Ultra Low-K Interlayer Dielectrics

AbstractBlanket porous methyl silsesquioxane (pMSQ) films on a Si substrate were studied with the intent to seal the pores and prevent penetration of a metallic precursor during barrier deposition. The blanket pMSQ films studied were approximately 220 nm thick and had been etched and ashed. When tantalum pentafluoride (TaF5) is exposed to an unsealed pMSQ sample, X-ray photoelectron spectroscopy (XPS) depth profiling and secondary ion mass spectroscopy (SIMS) depth profiling reveal penetration of Ta into the pores all the way to the pMSQ / Si interface. Boron carbo-nitride films were grown by thermal chemical vapor deposition (CVD) using dimethylamine borane (DMAB) precursor with Ar carrier gas and C2H4 coreactant. These films had a stoichiometry of BC0.9N0.07 and have been shown in a previous study to have a k value as low as 3.8. BC0.9N0.07 films ranging from 1.8 to 40.6 nm were deposited on pMSQ and then exposed to TaF5 gas to determine the extent of Ta penetration into the pMSQ. Ta penetration was determined by XPS depth profiling and sometimes SIMS depth profiling. XPS depth profiling of a TaF5 / 6.3 nm BC0.9N0.07 / pMSQ / Si film stack indicates the attenuation of the Ta signal to < 2 at. % throughout the pMSQ. Backside SIMS of this sample suggests that trace amounts of Ta (< 2 at. %) are due to knock-in by Ar ions used for sputtering. An identical film stack containing 3.9 nm BC0.9N0.07 was also successful at inhibiting Ta penetration even with a 370°C post-TaF5 exposure anneal, suggesting the stability of BC0.9N0.07 to thermal diffusion of Ta. All BC0.9N0.07 films thicker than and including 3.9 nm prevented Ta from penetrating into the pMSQ.

SYNTHESIS OF Fe NANOPARTICLES BY REDOX REACTION USING AN ELECTRON BEAM DEPOSITION TECHNIQUE

A new technique for synthesizing Fe nanoparticles based on an electron beam deposition technique from a Fe 2 O 3 source has been developed. We deposited Fe 2 O 3 films directly on Si (001) substrates, Al and Cu buffer layer, and observed the formation of Fe nanoparticles at the Si (001) and Al interfaces respectively. The Al at the interface is oxidized to Al 2 O 3 and Si is oxidized to SiO 2. For films deposited on Cu buffer layer, however, no Fe nanoparticles were formed. We explain our results in terms of the enthalpy of formation of the oxides. The enthalpy of formation of SiO 2 and Al 2 O 3 is much lower than that of Fe 2 O 3, thus promoting the formation of Fe nanoparticles. The enthalpy of formation of CuO is however, greater than that of Fe 2 O 3 thus forbidding the formation of Fe nanoparticles. This is in agreement with both X-ray Photoelectron Spectroscopy (XPS) depth profile analysis and Transmission Electron Microscopy (TEM).

Stability of fluorinated parylenes to oxygen reactive-ion etching under aluminum, aluminum oxide, and tantalum nitride overlayers

The fluorine stability of two parylenes, aliphatic-fluorinated AF-4 (α, α, α′, α′ poly(p-tetrafluoroxylylene) and aromatic-fluorinated VT-4 (2, 3, 5, 6 poly(p-tetrafluoroxylylene), were investigated underneath Al, Al2O3, and TaNX overlayers with and without exposure to oxygen reactive-ion etching (RIE). No fluorine diffusion was observed for Al films deposited onto the as-received parylenes. However, after oxygen RIE, x-ray photoelectron spectroscopy (XPS) depth profiling detected fluorine diffusion throughout Al and to a lesser extent Al2O3 but in contrast to Ta2.67N. Metal-fluoride bonding was evident at the metal/parylene interface for all the overlayers after the parylene was exposed to oxygen RIE and annealed.

Correlation between the XPS peak shapes of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ and film quality

X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ thin films were intentionally created of varying quality. The films were deposited on LaAlO/sub 3/ by pulsed laser deposition with J/sub c/ values ranging from poorly conducting up to several MA/cm/sup 2/. Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film quality. A potential correlation may also exist with the Cu(2p)/Ba(3d) ratio indicating an interrelationship to the FWHM of the Y(3d) peak. Film quality was determined by current transport, resistive T/sub c/, and AC magnetic susceptibility measurements.

Study of Zr1?xSnxTiO4 thin films prepared by a polymeric precursor route

Zirconium-stannate titanate Zr 1-x Sn x TiO 4 (ZTS) thin films, undoped and doped with Sb, Ta and Nb, were prepared by a polymeric precursor technique. The ZTS films were deposited on the multilayered substrates (Pt/Ti/SiO 2 /Si) by means of multiple spin-coating. After this deposition, the samples were heated at different temperatures (300-700 °C). The chemical composition of these films and bulk ZTS samples was investigated by using x-ray photoelectron spectroscopy and selected-area XPS depth profiling. A partial surface segregation of Sn IV and the presence of Sn 0 , Ti II and Ti III species in the films were revealed from XPS depth profiles. An optimized ZTS deposition process, where an oxidizing agent (H 2 O 2 ) is added to the gel, is proposed.

EFFECT OF Y ADDITION ON THE CORROSION BEHAVIOR OF MELT-SPUN AMORPHOUS Mg–Cu RIBBONS

Hydrogen evolution testing and anodic potentiodynamic polarization revealed that Y addition has a beneficial effect on the corrosion resistance of melt-spun amorphous Mg–Cu ribbon, which is related to the properties of the surface film of Mg–Cu and the manner in which its properties are modified as a result of Y alloying. X-ray photoelectron spectroscopy (XPS) depth profiling revealed that the breakdown of Mg–Cu was caused by the hydration of surface oxide components and the incorporation of detrimental CO 32– anions into the surface film. Y addition in Mg–Cu improves the corrosion resistance by Y 2 O 3 incorporation into the passive film, thus stabilizing the surface oxide components from hydration and preventing the incorporation of CO 32– into the passive film.

Silicide Formation for Ni and Pd Bilayers on Si(100) Substrates

ABSTRACTThe silicide formation for Ni/Pd and Pd/Ni bilayers on Si(100) substrates was investigated. X-ray diffraction and photoelectron spectroscopy (XPS) depth profiling have been applied to study the phase formation of the silicide. We found that with addition of Pd into Ni/Si, a uniform layer of ternary Ni1−xPdxSi layer formed and kept stable for a wide temperature range. The lattice parameter of Ni1−xPdxSi as a function of Pd addition was calculated. The nucleation temperature of NiSi2 was delayed due to the addition of Pd. The higher the Pd addition, the larger the increase in NiSi2 nucleation temperature. We also studied the effect on the addition of Ni to the Pd/Si reaction. For pure Pd/Si reaction PdSi nucleated from Pd2Si at 750°C or above. For Ni/Pd/Si reaction, Pd2Si changed to Ni1−xPdxSi at temperature lower than 750°C due to the incorporation of Ni. The phenomena were explained by classic nucleation theory taking into account the effect of mixing entropy effect.