Chemical Depth Profiling Research Articles

Physiological Degradation Mechanisms of PLGA Membrane Films under Oxygen Plasma Treatment

Degradation under simulated physiological conditions of poly(lactic-co-glycolic) (PLGA) copolymer membrane films subjected to an oxygen plasma treatment compared to its “as prepared” state has been studied by gas cluster ion beam assisted X-ray photoelectron spectroscopy for chemical depth profiling analysis. This investigation is complemented with atomic force microscopy, weight loss measurements, and visual inspection of the films at the different stages of the degradation process. The obtained results show that the carbon functional groups of the PLGA membrane films undergo a heterogeneous hydrolytic degradation to different rates depending on the plasma pretreatment. The content of glycolic groups (GA) in untreated PLGA samples immersed for 3 weeks in a phosphate-buffered saline solution decreased at the surface, whereas the ratio between glycolic and lactic units (LA) did not vary in the inner regions (∼400 nm depth) of the degraded membrane films. By contrast, oxygen plasma pretreatment enhances the...

Application of nickel oxide thin films in NiO/Ag multilayer energy-efficient coatings

Energy-efficient coatings based on transparent heat mirrors are reported. These coatings are spectrally selective in that they transmit light and reflect heat in the form of infrared radiation, and thus save energy in buildings. In this work, these coatings were achieved by depositing a two-layer structure consisting of nickel oxide deposited on silver by thermal evaporation. First, the structural, chemical, and optical properties of nickel oxide thin films, that are relevant to their use in transparent heat mirrors, were investigated. This was achieved through x-ray diffraction, atomic force microscopy, x-ray photoelectron spectroscopy, and spectrophotometric characterization. Then, the optical properties of the two-layer structure were determined. Their performance was evaluated through integrated spectral quantities over the solar and visible ranges. Moreover, chemical depth profiling was carried out to investigate the spatial distribution of the elements among the layers. The deposited heat mirrors were found to exhibit the desired behavior of high visible transparency and high infrared reflection.

GD-OES and XPS coupling: A new way for the chemical profiling of photovoltaic absorbers

In this paper, we examine the complementarity of Glow Discharge Optical Emission Spectroscopy (GD-OES) and X Ray Photoelectron Spectroscopy (XPS) for the realization of fine chemical depth profiling of photovoltaic absorbers using Cu(In,Ga)Se2 (CIGS) materials.The possibility to use sequentially these two techniques is discussed in this paper. We have evaluated the chemical modifications of the crater after GD-OES analyses which depend on the manner of finishing the plasma etching sequence; and we propose different ways to limit or eliminate this effect. For the moment, an intermediate step (wet chemical etching or weak sputtering) is required to obtain a CIGS phase in the crater.Finally, we have demonstrated the possibility to restart the GD-OES analyses of the materials after XPS quantification or GD-OES breaking without modifying the profile shape.

Composition of uncontrolled impurities and their chemical states and depth profiles at the Al-Si interface

Auger electron spectroscopy and secondary-ion mass spectrometry are used to study the compositions of uncontrolled impurity atoms, their chemical composition, and the atomic distribution profiles at the Al-Si interface. Low concentrations (<0.1%) of impurity C, O, N, Ti, Fe, and other atoms are detected in Al. An analysis of the chemical shifts of the Auger peaks of metal atoms shows that compounds of the AlO and Al2O3 types form at the Al-Si interface.

Effects of Tungsten Addition on Mechanical and Tribological Properties of Carbon Nitride Prepared by DC Magnetron Sputtering

Carbon nitride coatings doped with tungsten were deposited on high speed steel disks by unbalanced DC magnetron sputtering using nitrogen-argon mixture gas. The coatings were deposited on three different types of interlayer (Ti, Ti/TiN and Ti/TiC), and the tungsten target current was varied from 0 to 0.9 A. Surface morphology of the coatings were measured by roughness testing and scanning electron microscopy (SEM). In addition, the chemical composition and depth profile were analyzed by X-ray Diffraction (XRD) analysis, Raman spectroscopy, and glow discharge spectroscopy (GDS). Finally, the hardness (H) and elasticity (E) were measured by nanoindentation and a Rockwell indentation test, while the tribological properties were tested using a pin-on-disk tribometer. After all, the coatings were measured by cutting testing of tuning inserts and micro-drillers. It is found that all of the coatings are amorphous and have a thickness of approximately 1.5 μm. Moreover, the nitrogen content is around 30 at%, while the tungsten content varies in the range of 0-9 at%. In addition, the hardness values are in the range of 15-20 GPa and the elasticity varies from 236 to 274 GPa. A good correlation is observed between the wear resistance and the indentation adhesion level. Furthermore, it is found that the hardness is not significantly correlated to the tungsten content and the coatings deposited on the Ti/TiC interlayer have greater adhesion. Finally, the coatings generally have a very low coefficient of friction (0.01-0.3) and a wear coefficient as low as 10-6 mm3/Nm, and the CN/TiC coating reduced 41% and 43% of flank wear in the cutting testing of turning inserts and micro-drillers respectively.

Energy-saving spectrally-selective coatings based on MoO3/Ag thin films

Transparent heat mirrors are spectrally selective coatings that transmit light and reflect heat in the form of infrared radiation. In this work, these coatings were achieved by depositing a two-layer structure consisting of molybdenum oxide thin films deposited on silver thin films by thermal evaporation. First, the structural, chemical, and optical properties of molybdenum oxide thin films, that are relevant to their use in transparent heat mirrors, were investigated. Then, the optical properties of the two-layer structure were determined. Moreover, chemical depth profiling was carried out to investigate the spatial distribution of the elements among the layers. The deposited heat mirrors were found to exhibit the desired behavior of high visible transparency and high infrared reflection.

Chemical depth profiling and 3D reconstruction of III–V heterostructures selectively grown on non‐planar Si substrates by MOCVD

The chemical characterization of novel 3D architectures with nanometre‐scale dimensions is extremely challenging. The chemical composition of InGaAs/AlAs quantum wells selectively grown in SiO2 trenches, 100–300 nm wide, is studied. Combining high lateral resolution 3D ToF‐SIMS analysis and Auger measurements, the chemical composition of individual trenches was obtained confirming the uniformity of these III–V heterostructures. These results correlate well with an average approach using SIMS depth profiling. The effects of ion beam orientation on the surface topography of confined structures were highlighted. (© 2015 WILEY‐VCH Verlag GmbH &amp;Co. KGaA, Weinheim)

High-resolution chemical depth profiling of solid material using a miniature laser ablation/ionization mass spectrometer.

High-resolution chemical depth profiling measurements of copper films are presented. The 10 μm thick copper test samples were electrodeposited on a Si-supported Cu seed under galvanostatic conditions in the presence of particular plating additives (SPS, Imep, PEI, and PAG) used in the semiconductor industry for the on-chip metallization of interconnects. To probe the trend of these plating additives toward inclusion into the deposit upon growth, quantitative elemental mass spectrometric measurements at trace level concentration were conducted by using a sensitive miniature laser ablation ionization mass spectrometer (LIMS), originally designed and developed for in situ space exploration. An ultrashort pulsed laser system (τ ∼ 190 fs, λ = 775 nm) was used for ablation and ionization of sample material. We show that with our LIMS system, quantitative chemical mass spectrometric analysis with an ablation rate at the subnanometer level per single laser shot can be conducted. The measurement capabilities of our instrument, including the high vertical depth resolution coupled with high detection sensitivity of ∼10 ppb, high dynamic range ≥10(8), measurement accuracy and precision, is of considerable interest in various fields of application, where investigations with high lateral and vertical resolution of the chemical composition of solid materials are required, these include, e.g., wafers from semiconductor industry or studies on space weathered samples in space research.

Depth resolved band alignments of ultrathin TiN/ZrO2 and TiN/ZrO2-Al2O3-ZrO2 dynamic random access memory capacitors

In this paper, we investigated the interface band alignment of TiN/ZrO2 and TiN/ZrO2-Al2O3-ZrO2 (TiN/ZAZ) structures by analyzing the conduction band offset (CBO) and valence band offset at the electrode/dielectric interface using depth-resolved spectroscopy techniques. At the center of the interface, which is defined by the chemical composition depth profile, CBO values of 2.03 eV and 2.57 eV for ZrO2 and ZAZ were found, respectively. Subcutaneous TiON, which is induced by the process, was identified at this interface, and it played an important role in creating sub-band states. Based on combined analyses on both intrinsic and sub-band structures, a band alignment model is proposed. It was confirmed that the Al2O3 layer in ZAZ leads to a lowering of the Fermi energy or a p-doping effect, thereby increasing both the CBO and the tunneling barrier height in metal-insulator-metal capacitors.

Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air

The high-temperature characteristics (at 600 °C) of Ti/Al/Pt/Au multilayer contacts to gallium nitride (GaN) in air are reported. Microfabricated circular-transfer-line-method test structures were subject to 10 h of thermal storage at 600 °C. Intermittent electrical characterization during thermal storage showed minimal variation in the contact resistance after 2 h and that the specific contact resistivity remained on the order of 10−5 Ω-cm2. In addition, the thermally stored multilayer contacts to GaN showed ohmic I-V characteristics when electrically probed at 600 °C. The microstructural analysis with atomic force microscopy showed minimal changes in surface roughness after thermal storage. Observations of the thermochemical reactions after thermal storage using Auger electron spectroscopy chemical depth profiling showed diffusion of Pt and minimal additional Al oxidation. The results support the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.

High temperature behavior of nanolayered CrAlTiN coating: Thermal stability, oxidation, and tribological properties

Hard protective nitride coatings are often applied to cutting tools operating at high temperature. To further develop and optimize their performance, in-situ investigation of structure, oxidation, mechanical and tribological properties at elevated temperature is required. In this study we focus on the high temperature behavior of a nanolayered CrAlTiN coating deposited on WC substrates by cathodic arc evaporation. The coating's chemical composition and the bonding state were evaluated by electron probe microanalysis and by X-ray photoelectron spectroscopy (XPS). The structure of as-deposited and annealed samples was analyzed using X-ray diffraction. The adhesion was investigated by scratch test and the mechanical properties were studied by depth sensing nanoindentation. The main objective of this work was to have a detailed analysis of friction and wear properties tested by high temperature tribometer (pin-on-disc) with alumina balls as counterparts in the temperature range of 20–800°C. Selected wear track cross-sections were prepared by focused ion beam and analyzed by transmission electron microscopy; the wear track was investigated as well by XPS (chemical depth profile) and by Raman spectroscopy. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500°C and then decreased, whereas the wear rate was negligible up to 600°C and then increased significantly for higher temperatures. Oxidation of the worn surfaces was surprisingly low even at the highest temperature corroborating results of oxidation tests. The main identified wear mechanism was polishing combined with a nanoscale delamination of thin coating layers; nanoscale multilayer proved to be a vital factor blocking vertical crack propagation.

Understanding the signature of rock coatings in laser-induced breakdown spectroscopy data

Surface compositional features on rocks such as coatings and weathering rinds provide important information about past aqueous environments and water–rock interactions. The search for these features represents an important aspect of the Curiosity rover mission. With its unique ability to do fine-scale chemical depth profiling, the ChemCam laser-induced breakdown spectroscopy instrument (LIBS) onboard Curiosity can be used to both identify and analyze rock surface alteration features. In this study we analyze a terrestrial manganese-rich rock varnish coating on a basalt rock in the laboratory with the ChemCam engineering model to determine the LIBS signature of a natural rock coating. Results show that there is a systematic decrease in peak heights for elements such as Mn that are abundant in the coating but not the rock. There is significant spatial variation in the relative abundance of coating elements detected by LIBS depending on where on the rock surface sampled; this is due to the variability in thickness and spatial discontinuities in the coating. Similar trends have been identified in some martian rock targets in ChemCam data, suggesting that these rocks may have coatings or weathering rinds on their surfaces.

Effect of nitrogen incorporation on the structural, optical and dielectric properties of reactive sputter grown ITO films

Abstract The changes in the optical, microstructural and electrical properties, following the nitrogen incorporation into indium tin oxide thin films are investigated. The films are formed by r.f. sputtering from an indium-tin-oxide (80% In2O3–20% SnO2) target in a mixture of Ar and N2 plasma (75% N2–25% Ar and 100% N2 respectively) on fused silica glass substrate. The impact of rapid thermal annealing (up to 500 °C, in N2 ambient) on the properties of indium tin oxynitride (ITON) thin films is also reported. The UV–vis–NIR ellipsometry (SE) characterization of ITON films was performed assuming several realistic approaches based on various oscillator models, using a chemical composition gradient depth profiling, in agreement with the X-ray photoelectron spectroscopy measurements. The Hall measurements show that the ITON films prepared by r.f. sputtering in 75% N2 and annealed at 500 °C behave as degenerate semiconductors. X-ray diffraction analysis proved that ITON thin films retain an amorphous structure even after RTA at 500 °C in N2 ambient and atomic force microscopy showed the formation of continuous and smooth ITON thin films, with a morphology consisting in quasispherical nanometric particles.

A Combined Investigation into the Effect of Ni/Mn/Co Ions on Lithium-Ion Battery Anodes Using X-Ray Photoelectron Spectroscopy and Secondary Ion Mass Spectrometry

Nickel Cobalt Manganese (NCM) cathodes utilize the combination of transition metal ions to achieve good specific capacity, voltage, and safety characteristics, and are among the best performing of industrially produced cathode materials. However, Mn is known to escape the cathode via a disproportionation reaction as Mn2+, and has been detected on the anode solid electrolyte interface (SEI). Furthermore, batteries incorporating Mn in the cathode are known to have a reduced cycle life due to increased impedance (1). A recent study of Lithium Manganese Oxide (LMO) cathodes reveals the Mn to stay in the 2+ oxidation state (2), but little is otherwise known about the role of Mn in the SEI layer.To analyze the effect of the SEI on the degradation of NCM full cells, the authors previously analyzed anodes taken from commercial NCM batteries of varying degrees of degradation (3). X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used along with other techniques to analyze the presence of elements in the SEI as a function of depth. However, analysis of chemical species was complicated by the presence of PVDF binder, air exposure of the sample, and ion implantation/chemical decomposition due to exposure to a high energy ion beam.In this study, the effect of temperature, cycling, and the presence of transition metal ions were studied in thin film half cells. Ni2+, Mn2+, and Co2+ion salts were each introduced, as these ions all dissolve into the electrolyte from NCM cathodes and have been detected in the SEI (4,5). A thin film carbon anode was used to obviate the binder, and allow clearer chemical analysis and depth profiling. XPS analysis was used to reveal chemical information about the SEI, while SIMS was used to provide a depth profile.XPS analysis showed an increase in LiF composition with the number of charge/discharge cycles for all cells, but otherwise indicated a chemically different SEI when the salts are added. SIMS analysis showed the presence of Ni/Co/Mn ions and other species through the depth of the SEI layer. By combining these two methods, the character of the SEI with and without the transition metal ions was hypothesized.REFERENCESM. Wohlfahrt-Mehrens, C. Vogler, J. Garche, J. Power Sources 127, 58-64 (2004).C. Zhan, J. Lu, A. Jeremy Kropf, T. Wu, A. N. Jansen, Y.-K. Sun, X. Qiu, K. Amine, Nat. Commun. 4, (2013).J. T. Lee, N. Nitta, J. Benson, A. Magasinski, T. F. Fuller, G. Yushin, Carbon 52, 388-397 (2012).D. P. Abraham, T. Spila, M. M. Furczon, E. Sammann, Electrochem. Solid-State Lett. 11, A226-A228 (2008).H. Zheng, Q. Sun, G. Liu, X. Song, V. S. Battaglia, J. Power Sources 207, 134-140 (2012).

A study of the structural and magnetic properties of ZnO implanted by Gd ions

The structural and magnetic properties of ZnO (0001) single crystals implanted with 200keV Gd ions up to a fluence of 5×1015cm−2 and subsequently annealed at 800°C in various atmospheres were studied. The chemical composition and concentration depth profiles of ion-implanted layers were characterised by Rutherford Back-Scattering spectrometry (RBS) and compared to SRIM simulations. The as-implanted Gd depth profiles were found to be broader than those simulated by SRIM, but the projected range coincided well with that simulated. After annealing at 800°C, the depth profiles became narrower. The structural changes in the layers modified by ion implantation and subsequent annealing were characterised by RBS channelling. The annealing led to partial recrystallisation and a decrease in the number of Gd atoms situated in substitutional positions. Raman spectroscopy showed that the point defects in Zn and O vacancies had been created by implantation and that these defects are most effectively cured after annealing in oxygen atmosphere. AFM analysis was used to determine the surface-morphology changes after the implantation and annealing procedures. The as-implanted samples exhibited ferromagnetism persisting up to room temperature. The annealing procedure led to paramagnetic behaviour, probably caused by the formation of gadolinium clusters.

Intrinsic reduction of the ordered4fmagnetic moments in semiconducting rare-earth nitride thin films: DyN, ErN, and HoN

Polarized neutron reflectometry and x-ray reflectometry were used to determine the nanoscale magnetic and chemical depth profiles of the heavy rare-earth nitrides HoN, ErN, and DyN in the form of 15- to 40-nm-thick films. The net ferromagnetic components are much lower than the predictions of density-functional theory and Hund's rules for a simple ferromagnetic ground state in these $4f$ ionic materials, which points to the intrinsic contribution of crystal-field effects and noncollinear spin structures. The magnetic moment per rare-earth ion was determined as a function of temperature in the range 5--100 K at fields of 1--4 T. It is demonstrated that the films are stoichiometric within 1--3% and magnetically homogeneous on the nanometer scale.

Characterization of solid electrolyte interphase on lithium electrodes cycled in ether-based electrolytes for lithium batteries

The electrochemical behavior, chemical composition and the topography of the solid electrolyte interphase (SEI) on lithium electrodes cycling in ether-based electrolytes are investigated using X-ray photoelectron spectroscopy (XPS), scanning probe microscopy (SPM) and electrochemical impedance spectroscopy (EIS). Electrolytes with ethers (1,2-Dimethoxyethane (DME), Diethylene glycol dimethyl ether (DG) and Triethylene glycol dimethyl ether (TEGDME)) are employed to understand the effect of ether/alkyl moieties ratio on the formation of the SEI films. The cycling behavior and impedance spectra of the symmetrical cells show that the stability and property of those SEI films depend on the selection of the solvent. The results indicate that DG and TEGDME based electrolytes lead to a higher resistance for lithium ion migration through the SEI film. Combined with XPS spectra and depth profile, different chemical composition and depth profile distribution for those SEI films are observed. This difference could be attributed to the decomposition of the electrolytes with different ethers. The height images and phase images obtained from SPM show that the decomposition of the three solvents on lithium metal is active after the immersion of the lithium electrodes in electrolytes. In contrast, the decomposition of TFSI− from lithium salt is more active during the cycling of the cells.

Electrodeposition of Zn-TiO2 Dispersion Coatings: Study of Particle Incorporation in Chloride and Sulfate Baths

Zn and Zn-TiO2 coatings were galvanostatically electrodeposited on steel substrates from chloride- and sulfate-plating baths. The influence of the electrolyte type on the dispersion behavior of TiO2 nano-particles as well as on the amount of TiO2 incorporation was studied. The electrokinetic behavior of titania in diluted electrolytes is strongly influenced by the specific adsorption of SO42− anions. Chemical depth profile analysis using glow discharge optical emission spectroscopy confirmed the incorporation of particles throughout the layers (up to 0.53 wt% and 0.78 wt% from chloride- and sulfate-bath respectively). Focused-ion-beam assisted cross-sectional analysis showed that TiO2 was incorporated in zinc as small agglomerates (up to ∼200 nm). The TiO2 incorporation was favorable at slightly acid pH values (below pH 5.5) for both baths. The pH zone for maximum incorporation of particles is related with the adsorption of ions at the particle surface. The chloride electrolyte led to a higher co-deposition of TiO2 over a broader pH range (2–5.5) as well as a wider range of current density (2–20 A/dm2) in contrast to sulfate electrolytes. A common feature is that the (102), (103) and (112) preferred orientations were promoted as a result of particle incorporation.

Quantitative X-ray photoelectron spectroscopy-based depth profiling of bioleached arsenopyrite surface by Acidithiobacillus ferrooxidans

In supergene environments, microbial activities significantly enhance sulfide oxidation and result in the release of heavy metals, causing serious contamination of soils and waters. As the most commonly encountered arsenic mineral in nature, arsenopyrite (FeAsS) accounts for arsenic contaminants in various environments. In order to investigate the geochemical behavior of arsenic during microbial oxidation of arsenopyrite, (230) surfaces of arsenopyrite slices were characterized after acidic (pH 2.00) and oxidative decomposition with or without an acidophilic microorganism Acidithiobacillus ferrooxidans. The morphology as well as chemical and elemental depth profiles of the oxidized arsenopyrite surface were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. With the mediation of bacteria, cell-shaped and acicular pits were observed on the reacted arsenopyrite surface, and the concentration of released arsenic species in solution was 50 times as high as that of the abiotic reaction after 10days reaction. Fine-scale XPS depth profiles of the reacted arsenopyrite surfaces after both microbial and abiotic oxidation provided insights into the changes in chemical states of the elements in arsenopyrite surface layers. Within the 450nm surface layer of abiotically oxidized arsenopyrite, Fe(III)-oxides appeared and gradually increased towards the surface, and detectable sulfite and monovalent arsenic appeared above 50nm. In comparison, higher contents of ferric sulfate, sulfite, and arsenite were found in the surface layer of approximately 3μm of the microbially oxidized arsenopyrite. Intermediates, such as Fe(III)-AsS and S0, were detectable in the presence of bacteria. Changes of oxidative species derived from XPS depth profiles show the oxidation sequence is Fe>As=S in abiotic oxidation, and Fe>S>As in microbial oxidation. Based on these results, a possible reaction path of microbial oxidation was proposed in a concept model.

Hydrogen storage in Ti–TiO2 multilayers**Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2012, 30 October – 2 November, 2012, Ha Long, Vietnam.

Multilayered thin films of Ti–TiO2 system have been investigated, focusing on all of the important parameters in both photocatalysis and H storage. Numerous Ti–TiO2 thin films with a single-, bi- and tri-layered structure have been deposited on different substrates by means of dc pulsed magnetron sputtering from a metallic Ti target in an inert Ar or reactive Ar + O2 atmosphere. The film chemical composition, depth profile, layer thickness and structure were determined by combined analysis of x-ray diffraction, x-ray reflectometry, Rutherford back- scattering and optical reflectivity spectra. The results show that the Ti films deposited on Si(111) exhibit a strong preferred orientation with the (00.1) plane parallel to the substrate, while a columnar structure was developed for TiO2 films. H charging at 1 bar and at 300 °C revealed that, in the case of the tri-layered structure of Ti/TiO2/Ti/Si(111), H diffused through the TiO2 layer without any accumulation in it. Pd acts as a catalyst for gathering H in Ti layers and up to 50% of H is stored in the topmost and bottom Ti layers. The preferential orientation in the Ti films was found to be destroyed upon hydrogenation at 100 bar. The hydride TiHx phase (x < 0.66) was formed under such a high H pressure.