Surface Depth Profiling Research Articles

Micro-grooving into thick CVD diamond films via hollow-cathode oxygen plasma etching

Hollow-cathode oxygen plasma etching was proposed as a promising means to make micro-texturing into CVD diamond coatings. Oxygen ions and electrons were confined in the hollow-cathode to have higher ion and electron densities in the order of 1017 to 1018m−3 in the inside of hollow-cathode. Quantitative plasma diagnosis proved that direct reaction of oxygen atom or radicals with carbon in the diamond coating should drive the reactive ion etching (RIE) process. A diamond-coated WC (Co) disc specimen was employed to describe the RIE-behavior with aid of stainless steel mask with the line width of 100μm. Surface depth profile measurement as well as the Raman spectroscopy demonstrated that a micro-groove was precisely etched into the diamond film as a sharp-edged profile.

Dynamic formation of a solid-liquid electrolyte interphase and its consequences for hybrid-battery concepts.

The discharging and charging of batteries require ion transfer across phase boundaries. In conventional lithium-ion batteries, Li(+) ions have to cross the liquid electrolyte and only need to pass the electrode interfaces. Future high-energy batteries may need to work as hybrids, and so serially combine a liquid electrolyte and a solid electrolyte to suppress unwanted redox shuttles. This adds new interfaces that might significantly decrease the cycling-rate capability. Here we show that the interface between a typical fast-ion-conducting solid electrolyte and a conventional liquid electrolyte is chemically unstable and forms a resistive solid-liquid electrolyte interphase (SLEI). Insights into the kinetics of this new type of interphase are obtained by impedance studies of a two-chamber cell. The chemistry of the SLEI, its growth with time and the influence of water impurities are examined by state-of-the-art surface analysis and depth profiling.

Simultaneous detection of positive and negative secondary ions

A secondary ion mass spectrometer (SIMS) instrument is described that is configured with two SIMS detectors that are both low-field extraction, quadrupole-based filters. Secondary ions are generated by sputtering with a liquid-metal ion gallium source and column of the type that is common on two-beam electron microscopes. The gallium ion beam, or focused ion beam achieves sub-100 nm focus with a continuous current of up to 300 pA. Positive secondary ions are detected by one SIMS detector, and simultaneously, negative secondary ions are detected by the second SIMS detector. The SIMS detectors are independently controlled for recording mass spectra, concentration depth profiles, and secondary ion images. Examples of simultaneous positive and negative SIMS are included that demonstrate the advantage of this facility for surface analysis and depth profiling. The SIMS secondary ion collection has been modeled using the ray tracing program simion (“simion”, Scientific Instrument Services, Inc., Ringoes, NJ, 08551-1054, see http://www.simion.com) in order to understand the interaction of the secondary ions of opposite polarities in the extraction volume for the purpose of optimizing secondary ion collection.

First 236U data from the Arctic Ocean and use of 236U/238U and 129I/236U as a new dual tracer

The first dataset of 236U/238U in the water column of the Arctic Ocean (AO) is presented and shows the widest range of ratios reported so far in the open ocean, from (5±5) to (3840±260)×10−12. Surface samples and depth profiles were collected during two GEOTRACES expeditions in 2011–2012 and analyzed for the concentrations of 236U and 129I, with the aim of investigating whether the combination of 236U/238U and 129I/236U can be used as a new oceanographic tool in the AO. Results show that the distributions of the 236U/238U and 129I/236U atomic ratios are consistent with the different water masses in the AO. High 236U/238U and 129I/236U ratios in the upper water column (>2000×10−12 and >200, respectively) illustrate the penetration of Atlantic waters (AW) into the AO. Lower values were found in Pacific waters (PW) and deep waters of the AO. Rivers seem to represent a temporally and spatially-constrained third anthropogenic source of 236U but more data are needed to confirm this. In a simple mixing model, the combination of 236U/238U and 129I/236U reveals a high contribution (>99%) of natural background waters (pre-nuclear era) in the deep and bottom waters of the Amerasian basin, indicating an apparent water mass renewal time of >1000 years. Despite the relatively high apparent age of the Amerasian Basin deep waters, this work shows the potential of using the dual-tracer approach as a new oceanographic tool in the Arctic Ocean.

Object Recognition in Flight: How Do Bees Distinguish between 3D Shapes?

Honeybees (Apis mellifera) discriminate multiple object features such as colour, pattern and 2D shape, but it remains unknown whether and how bees recover three-dimensional shape. Here we show that bees can recognize objects by their three-dimensional form, whereby they employ an active strategy to uncover the depth profiles. We trained individual, free flying honeybees to collect sugar water from small three-dimensional objects made of styrofoam (sphere, cylinder, cuboids) or folded paper (convex, concave, planar) and found that bees can easily discriminate between these stimuli. We also tested possible strategies employed by the bees to uncover the depth profiles. For the card stimuli, we excluded overall shape and pictorial features (shading, texture gradients) as cues for discrimination. Lacking sufficient stereo vision, bees are known to use speed gradients in optic flow to detect edges; could the bees apply this strategy also to recover the fine details of a surface depth profile? Analysing the bees’ flight tracks in front of the stimuli revealed specific combinations of flight maneuvers (lateral translations in combination with yaw rotations), which are particularly suitable to extract depth cues from motion parallax. We modelled the generated optic flow and found characteristic patterns of angular displacement corresponding to the depth profiles of our stimuli: optic flow patterns from pure translations successfully recovered depth relations from the magnitude of angular displacements, additional rotation provided robust depth information based on the direction of the displacements; thus, the bees flight maneuvers may reflect an optimized visuo-motor strategy to extract depth structure from motion signals. The robustness and simplicity of this strategy offers an efficient solution for 3D-object-recognition without stereo vision, and could be employed by other flying insects, or mobile robots.

Deep-UV Laser Ablation Technology [213 nm] Coupled with Plasma Quadrupole Mass Spectrometry for Rapid Determination of Nickel/ Vanadium Ratios in Asphaltenes

Knowledge of nickel/vanadium (Ni/V) ratios in petroleum fuel is essential to source geochemical information and to limit catalytic poisoning and corrosive effects in chemical refining processes. However, these ratios have been found to vary widely and are affected by various factors, including the sulphur content of the petroleum feedstock. They are normally obtained by digesting and treating the feedstock in suitable acid or organic media followed by numerical analysis. Our research investigated a novel sample introduction technique for obtaining Ni/V ratios by ablating petrified asphaltene samples (following liquid nitrogen pre-treatment) with a 213 nm laser beam coupled to a hyphenated plasma mass spectroscopic system. Laser ablation is ideal for delving beneath the surface of a solid matrix to measure the composition of the substrate. Iterative scanning of the sample surface and subsequent depth-profiling was achieved at pre-determined surface points to depths of 50 μm at selected sub-surface intervals. Characteristic intensities originating from the metals of interest were measured. Laser results were compared with the ‘digested’ results obtained directly by ICP-MS. In the case of the digested crude oil samples, these ratios varied between 0.6 and 0.8. This was higher than corresponding literature values, which occurred within a range of 0.3-0.6. The laser ablation results for typical asphaltene samples showed that Ni/V ratios varied in the interval 0.2-0.8, which were considered to be elevated and in keeping with the elevated crude oil ratios. The digested asphaltenes also reflected higher ratios, suggesting the influence of sample inhomogeneity and nickel impurities. Factors affecting variations in this ratio are presented, and the advantages of a more stable ratio are discussed. The study is of definite interest to petroleum engineers, and has considerable scope for extended research.

Prevention of enamel demineralization with a novel fluoride strip: enamel surface composition and depth profile.

There is no topically applicable low concentration fluoride delivery device available for caries prevention. This study was aimed to assess the use of a low concentration (1450 ppm) fluoride strip as an effective fluoride delivery system against enamel demineralization. The enamel surface composition and calcium-deficient hydroxyapatite or toothpaste treatments were investigated using X-ray photoelectron spectroscopy. In vitro enamel demineralization was assayed using a pH cycling model and the dissolution of calcium ions from the treated specimens was quantified using ion chromatography. After 24-hr fluoride-strip treatment, the enamel was covered with a CaF2 layer which showed a granular morphology of 1 μm in size. Below the CaF2 layer was a region of mixed fluorapatite and CaF2. Fluoride infiltrated extensively in enamel to produce highly fluorinated fluorohydroxyapatite. In comparison, low-fluoride-level fluorinated fluorohydroxyapatite was formed on the enamel specimen exposed to toothpaste. The treatments with the fluoride strip as short as 1 hr significantly inhibited enamel demineralization. The fluoride strip was effective for topical fluoride delivery and inhibited in vitro demineralization of enamel by forming CaF2 and fluoride-containing apatites at the enamel surface. It exhibited the potential as an effective fluoride delivery device for general use in prevention of caries.

Utilization of heavy alkali dopants as a beacon to study the cathode electrolyte decomposition layer in lithium-ion batteries

We introduce low levels of CsClO4 and RbClO4 into the electrolyte of LiCoO2 electrochemical half-cells to probe the composition of the passivation film on the surface of the cathode, the electrolyte decomposition layer (EDL). The advantages of these heavy alkali dopants lie in their large ionic radii, which limit intercalation, yet their strong light scattering cross-section creates a beacon that highlights the formation of products near the cathode surface. Detailed surface analysis and depth profiling with X-ray photoelectron spectroscopy, and bulk analysis utilizing X-ray absorption spectroscopy, show evidence for the formation of Cs/Rb compounds, such as carbonates, halides, and perchlorates, similar to those formed by lithium in previous studies, but also reveal the significantly reduced mobility of the Cs/Rb relative to Li in the non-uniform EDL. This unique approach could open several presently untapped techniques to gather new information on the EDL in Li-ion batteries.

Lithium-Titanate Thin Films By Solid State Reaction As Electrode Material for Thin-Film Lithium-Ion Batteries

Lithium titanate (Li4Ti5O12) or LTO continues to attract great interest as anode for lithium ion because of its safety and the potential high power for the nanoparticle form. Its spinel structure allows a reversible three lithium ions intercalation at 1.55V vs Li+/Li which is well above the potential for the reduction of most electrolytes including solid electrolytes. The high voltage of lithium ion insertion/extraction in/from Li4Ti5O12 also prevents the formation of dendritic lithium which can happen due to overcharging for anodes which have low potentials close lithium deposition (0V vs Li+/Li). Such metallic lithium filaments can cause a short circuit between the battery anode and cathode with potential overheating and rupture. Moreover, LTO shows a negligible volume change during battery charging and discharging. Despite all these advantages, LTO has a poor electronic conductivity that leads to a limitation in the rate capability of this electrode. In this talk we will report on a novel and low cost fabrication method of lithium titanate thin film electrodes for thin-film lithium ion batteries. The process is based on a solid state reaction occurring between TiO2 and Li2CO3 stacked-layers upon thermal annealing. The TiO2 layer was prepared by thermal oxidation of a sputtered Ti film and the Li2CO3 layer was deposited by spin-coating. LTO thin films were prepared on both Pt and TiN current collectors. The phase and morphology of the prepared LTO films were investigated using a X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD patterns display intense characteristic diffraction LTO peaks and SEM micrographs show a close and continuous 70 nm thick LTO film. Furthermore, the stoichiometry of the fabricated LTO films was evaluated by X-ray photoelectron spectroscopy (surface spectra and depth profile analyses) and elastic recoil detection (ERD) analyses. Films with composition the spinel Li4Ti5O12 composition were fabricated, proving that the thermal treatment causes elements intermixing leading to the formation of a Li4Ti5O12 material. The electrochemical activity of the films was studied by cyclic voltammetry and galvanostatic charge/discharge experiments. The cyclic voltammogram reveals redox peaks around 1.55V (vs. Li+/Li) corresponding to the Li-ion insertion/extraction in/from the spinel Li4Ti5O12 upon reduction/oxidation of Ti4+/Ti3+. The lithiation and delithiation curves show extremely flat plateaus at 1.55 V (vs. Li+/Li) characteristic of Li4Ti5O12. A 100% of the LTO theoretical capacity was reached at 0.1 C. A difference between the lithiation and delithiation capacities at the same C-rate was detected. This discrepancy will be explained by the difference in Li-ion diffusion kinetics during Li-ion insertion and extraction processes.

Interfacial Oxide Formation during Anodization of Hafnium/Aluminium Superimposed Layers

The anodization behaviour of Hf/Al stacked thin films, sequentially deposited from vapour phase without breaking vacuum, was investigated using scanning droplet cell microscopy. Surface microstructure and crystallographic analysis revealed the formation of highly textured and compact hexagonal Hf films for thicknesses above 7.5nm. Cyclic voltammetry suggested the formation of discrete anodic layers starting with pure HfO2 on the surface, a mixture of HfO2 and Al2O3 as an intermediate layer and pure Al2O3 in depth of the films. Coulometric investigations revealed oxide formation factors of 2.2nmV−1 for HfO2 while for pure Al2O3 a maximum of 1.4nmV−1 was measured. Electrochemical impedance spectroscopy performed for various Hf thicknesses and different final anodization potentials revealed almost ideal dielectrics formed from mixed HfO2/Al2O3, permittivities up to 26 being measured for the anodized Hf/Al films. Surface analytical investigations and depth profiling as well as high resolution transmission electron microscopy confirmed the discrete anodic layer growth and the mixing of both anodic oxides. The significant thickness values found for the mixed oxide layer must redefine the general expectations for the use of anodized superimposed layers in various applications.

Depth profiles and free volume in aircraft primer films

Positron annihilation lifetime spectroscopy (PALS) and associated techniques provide non-destructive methods to study the free volume inside polymeric materials, and to study material characteristics over a depth profile. Cast free films of organic- or aqueous-based, non-chromated aerospace primers, when cured for about one week, had very different water vapour transport (through-plane) behaviour. In addition, both types of primer films showed strong anisotropic behaviour in in-plane versus through-plane water vapour transport rates. We report the differences between the organic- and aqueous-based aircraft primer films samples and their surface depth profiles. In bulk PALS measurements, an aged, organic-based film exhibited typical lifetimes and intensities for a particulate-containing polymer film on both faces. In contrast, aqueous-based films exhibited face oriented-dependent differences. In all aqueous- based samples, the I3 value of the back of the sample was smaller. The primer film samples were also evaluated with mono-energetic positron beam techniques to generate depth profile information. The heterogeneity in the samples was verified by Doppler broadening of energy spectroscopy (DBES). A model for the differences in the faces of the films, and their layered structure is discussed.

Process Optimization of CoSi2 Formation on P-Doped Poly-Si by Hot Wall-Based Rapid Thermal Annealing

Low resistivity junctions and low resistivity contacts are essential for fabricating high performance devices with advanced device modes. Significant effort has been expended to develop low resistivity junctions, industry wide. However, low resistivity contact formation has not received significant attention, other than changing the silicide of choice, depending on required minimum line width or device node. Once the candidate silicide material is chosen for the device node, relatively small improvement in resistivity has been made in recent years, despite silicidation process optimization which include modifications of process steps and integration schemes. In this study, we have investigated the effect of annealing temperature and time on the resulting resistivity of Co2Si contacts with P-doped poly-Si using a single wafer furnace-based (hot wall) rapid thermal annealing (RTA) system. The hot wall RTA resulted in significantly (>20%) lower Rs, down to 19.6 ohm/sq. from equivalent RTA process using conventional tungsten halogen lamp-based (cold wall) RTA systems over a very wide process window (RTA temperature and time). Secondary ion mass spectroscopy (SIMS) dopant (P) depth profiling results revealed that the P atoms in the CoSi2 film and at the CoSi2/P-doped poly-Si interface, redistribute very differently under different RTA conditions. The same Rs value can be realized by different P profiles resulting from different RTA conditions. To enable contact resistance reduction, P pile-up near the CoSi2/P-doped poly-Si interface for and to suppress P depletion from P-doped poly-Si layer for resistivity reduction, lower temperature RTA for longer times in the hot wall RTA system was found to be beneficial. Wafers with almost identical P depth profiles after CoSi2 formation RTA in the cold wall RTA and the hot wall RTA systems, still showed an Rs difference of ~20%. The wafers annealed in the hot wall RTA system always showed lower Rs values indicating higher P dopant activation in the P-doped poly-Si layer. The difference in wafer heating mechanisms between the cold wall (lamp-based) RTA and the hot wall (furnace-based) RTA may have played an important role in the dopant activation and Rs differences. Hot wall RTA is very promising for realizing the low resistivity contacts required in advanced high performance devices. The simple change of annealing technique may extend the life cycle of CoSi2/P-doped poly-Si contacts. The Rs response surface (as a function of RTA temperature and time) and SIMS depth profiles of P atoms will be presented at the meeting. Figure 1

Assessment of dye distribution in sensitized solar cells by microprobe techniques

Dye sensitized solar cells (DSCs) have received considerable attention once this technology offers economic and environmental advantages over conventional photovoltaic (PV) devices. The PV performance of a DSC relies on the characteristics of its photoanode, which typically consists of a nanocrystalline porous TiO2 film, enabled with a large adsorptive surface area. Dye molecules that capture photons from light during device operation are attached to the film nanoparticles. The effective loading of the dye in the TiO2 electrode is of paramount relevance for controlling and optimizing solar cell parameters. Relatively few methods are known today for quantitative evaluation of the total dye adsorbed on the film. In this context, microprobe techniques come out as suitable tools to evaluate the dye surface distribution and depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam were used to quantify and to study the distribution of the Ru organometallic dye in TiO2 films, making use of the different penetration depth and beam sizes of each technique. Different 1D nanostructured TiO2 films were prepared, morphologically characterized by SEM, sensitized and analyzed by the referred techniques. Dye load evaluation in different TiO2 films by three different techniques (PIXE, RBS and EPMA/WDS) provided similar results of Ru/Ti mass fraction ratio. Moreover, it was possible to assess dye surface distribution and its depth profile, by means of Ru signal, and to visualize the dye distribution in sample cross-section through X-ray mapping by EPMA/EDS. PIXE maps of Ru and Ti indicated an homogeneous surface distribution. The assessment of Ru depth profile by RBS showed that some films have homogeneous Ru depth distribution while others present different Ru concentration in the top layer (2μm thickness). These results are consistent with the EPMA/EDS maps obtained.

Application of 210Po isotope dating for chronological assessment of organochlorine pesticides in estuarine sediment

In recent years there has been growing concern all over the globe about marine pollution due to persistent organic pollutants. Sediments, which is an important component of marine environment can serve as sorbent or concentrator for these pollutants. In this study, estimation of sedimentation rate using 210Po dating was carried out to study the depth profile of accumulated OCPs in sediments of Thane Creek Mumbai, India. The creek is a triangular mass of brackish water receiving huge municipal and industrial sewage inputs. Spatial distribution of OCPs was assessed in surface grab sediments and depth profiles of HCH and DDT were obtained in different cores. Radiological dating was performed by estimating the 210Po activity by alpha spectrometry, whereas the OCPs determination was carried out using gas chromatography.The total HCH concentration in the surface sediment samples was in the range of 5.6–13.3 ng/g while total DDT concentration in the surface sediment samples was in the range of 3.2–5.5 ng/g. DDT and γ-HCH were the dominant OCPs in sediments from the creek. The sedimentation rate was determined using 210Po activity measurement in different cores of the sediment and was found to be 0.67 cm/y on average. It was observed that the sediments were highly contaminated during the period of 1970–80 just after the green revolution in India. Total DDT was highest in the 1974–1978 layers of the sediments. Total HCH was highest in the 1972–1976 layers at all the locations.

Radioactive 129I in surface water of the Celtic Sea

Relatively large amounts of radioactive iodine 129I (T 1/2 = 15.7 Ma) have been documented in seawater such as the English Channel, the Irish Sea and the North Sea. Data on the concentration of the iodine isotopes in waters of the Celtic Sea are missing. Aiming to provide first 129I data in the Celtic Sea and compare them with levels in the other close-by seawater bodies, surface seawater samples were analyzed for the determination of 127I and 129I concentrations. The results revealed a high level of 129I in these waters and suggest strong influence by liquid discharges from La Hague and Sellafield reprocessing facilities. 127I concentrations are rather constant while the 129I/127I ratio reaches up to 2.8 × 10−8 (ranging from 10−10 to 10−8), which is 2–4 orders of magnitude higher than pre-nuclear era natural level. Transport of 129I to the Celtic Sea is difficult to depict accurately since available data are sparse. Most likely, however, that discharges originated from La Hague may have more influence on the Celtic Sea 129I concentrations than the Sellafield. Comprehensive surface water and depth profiles 129I data will be needed in the future for assessment of environmental impact in the region.

Effect of surface composition and microstructure of aluminised steel on the formation of a titanium-based conversion layer

The presented work aims at determining the influence of surface composition and microstructure of hot dip aluminium–silicon coated steel on the formation characteristics and mechanism of a titanium-based conversion layer. Varying the amount of silicon in the molten aluminium bath changes the surface nature which in turn affects the subsequent pre-treatment process. Different phases in the layer formation process were identified in the open circuit potential evolution as a function of immersion time in the conversion solution. The homogeneity and the thickness of the conversion layer in each of these regions were evaluated using secondary electron images, Auger elemental surface maps and depth profiles. While intermetallic precipitates (FeAl3) act as nucleation centres in pure Al coatings, eutectic Si is responsible for the deposition process in a Si-rich coating. A continuous surface conversion layer is formed after 45s of immersion in the conversion bath. Also, the presence of silicon in the coating leads to the deposition of a thicker conversion layer. A model for build-up of the conversion layer is proposed based on these observations.

Rough Surface Depth Profiles for the Characterization of Real World Corrosion and Deposition

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Focus on analytical equipment and diagnostics

Focus on analytical equipment and diagnostics

Effect of Scratch Velocity on Deformation Features of C-plane Sapphire during Nanoscratching

The effects of scratch velocity on plastic and brittle deformation features of (0001) C-plane sapphire were studied in nanoscratch tests. The test was conducted under a ramping loading condition from 40 μN to 200 mN using a nanomechanical test system. A Berkovich nanoindenter was employed in this study. The scratch velocities were set at 2, 4, 8, and 16 μm/s. Plastic and brittle deformation features were observed by scanning electron microscopy. The residual stress features of the deformation zones in the scratch groove were observed by Raman spectroscopy. Comparative studies of surface depth profiles and scratch groove features obtained with different scratch velocities reveal that the scratch velocities have distinct effects on the deformation features of C-plane sapphire.

AES Studies of Heteroepitaxial SiC Films Deposited on Si and on Sapphire Substrates by MOCVD

<p>Auger electron spectroscopy (AES) has been used to investigate the chemical composition of the heteroepitaxial silicon carbide films grown on Si (100) and sapphire (0001) substrates at 900 °C by the MOCVD technique using DEMS precursor. Auger spectra were obtained from the surface and as a function of depth of 2 micron thick SiC films. AES measurements were performed under very high vacuum 10<sup>-9</sup> Torr conditions. Surface cleaning and depth profile studies were carried out by using Ar<sup>+</sup> ion beam sputtering. Auger spectra of the surface indicate Si LVV, C KLL and O KLL peaks. The Si LVV signals on the as prepared’ surfaces for both substrates indicated that the silicon was in the oxide state, which was removed after 15 min Ar+ ion cleaning. Depth profile studies showed, that after 20 min of ion cleaning the SiC films possess near stoichiometric composition. Moreover, the C KLL signal on the ion cleaned films showed the carbon in the carbide state. X-ray diffraction analysis of the SiC films on the sapphire (0001) and Si(100) substrates has shown a high intensity single peaks at 35.7°, which indicates the presence of SiC at orientation (111).</p>