Resulting Depth Profiles Research Articles

Bulk ratio method for determining surface enhancement using Auger analysis

The surface analysis techniques of Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are often used to characterize the near surface composition of stainless steel. AES is most often used to determine the oxide thickness and the maximum chromium to iron ratio as this information is used to determine if the material is properly electropolished. XPS is primarily used to determine the near surface chemistry as well as the chromium to iron ratio. Instrument calibration is critical to reliable composition determination. For AES, the use of elemental sensitivity factors is found to be a significant source of error. Proposed is a new method for the determination of Cr∕Fe ratios using AES. The resulting depth profiles show the proper stainless steel composition under the surface enhanced layer.

Three-Dimensional Compositional Analysis of Drug Eluting Stent Coatings Using Cluster Secondary Ion Mass Spectrometry

Cluster secondary ion mass spectrometry (cluster SIMS) employing an SF5+ polyatomic primary ion sputter source in conjunction with a Bi3+ analysis source was used to obtain three-dimensional molecular information in polymeric-based drug-eluting stent coatings. The formulations of the coatings varied from 0% to 50% (w/w) sirolimus drug in poly(lactic-co-glycolic acid) and were prepared on both MP35N metal alloy coupons and bare metal stents. All cluster SIMS depth profiles obtained indicated a drug-enriched surface region, followed by a drug-depletion region, and finally a constant bulk composition region, similar to previous data obtained in polymeric blend systems. The drug overlayer thickness was determined to increase with increasing sirolimus content. Sample temperature was determined to play an important role in the resulting depth profiles, where it was shown that the best profiles were obtained at low temperatures (-100 degrees C). At these temperatures, molecular signals typically remained constant through the entire depth of the film (approximately 6.5 microm) in some cases, as opposed to the typical 1 microm-2 microm depth limit, which is achievable at room temperature. The 3-D imaging capabilities of cluster SIMS were successfully demonstrated and indicated a significant amount of subsurface domain formation in the 25% and 50% sirolimus samples, but not in the 5% sample, which was homogeneous. These results clearly illustrate the utility of cluster SIMS for probing the 3-D structure in polymeric-based drug delivery devices.

Topical Delivery of Retinyl Ascorbate

This influence of skin stretching and hair follicle sealing on the delivery of retinyl ascorbate (RA-AsA) to the epidermis was probed in vitro. Porcine ear skin was subjected to stretching by 2 and 4 mm (3.3 and 6.7%, respectively); the hair follicles of other skin sections were located and painstakingly sealed using adhesive. After mounting in Franz cells the skin was dosed with 100 µl of 2.5 mM RA-AsA in methanol/PBS with water as receptor phase. After 24 h the diffused areas were subjected to tape stripping, and the amount of RA-AsA was determined in 5 groups of 9 strips. Statistical analysis of the resulting depth profiles showed that there was no statistical difference between unstretched skin and the skin that had the follicles sealed across the 5 depth bands. Between 0 and 2 mm stretch there were generally significant differences; between 0 and 4 mm p < 0.001 was obtained at each depth. The data from this limited exercise suggest that in native skin the follicular route does not contribute to dermal absorption, but when disturbed (as when stretched) follicular delivery can substantially increase drug delivery into the skin by up to approximately 20–40%. Skin stretching becomes difficult beyond about 7%.

Formation mechanisms of low-resistance and thermally stable Pd∕Ni∕Pd∕Ru Ohmic contacts to Mg-doped Al0.15Ga0.85N

The authors report on the formation of low-resistance and thermally stable Pd∕Ni∕Pd∕Ru Ohmic contacts to Mg-doped AlGaN. The contacts become Ohmic with a contact resistivity of (1.4±0.3)×10−5Ωcm2 upon annealing at 600°C for 1min in a N2 ambient. The samples do not experience significant degradation of the specific contact resistance and the surface roughness even after annealing at 600°C for 60min. Based on x-ray photoelectron spectroscopy depth profile results, atomic force microscopy, and contact resistivity-temperature data, possible Ohmic formation and carrier transport mechanisms are described and discussed.

Molecular Depth Profiling with Cluster Ion Beams

Peptide-doped trehalose thin films have been characterized by bombardment with energetic cluster ion beams of C60+ and Aux+ (x = 1, 2, 3). The aim of these studies is to acquire information about the molecular sputtering process of the peptide and trehalose by measurement of secondary ion mass spectra during erosion. This system is important since uniform thin films of approximately 300 nm thickness can be reproducibly prepared on a Si substrate, allowing detailed characterization of the resulting depth profile with different projectiles. The basic form of the molecular ion intensity as a function of ion dose is described by a simple analytical model. The model includes parameters such as the molecular sputtering yield, the damage cross section of the trehalose or the peptide, and the thickness of a surface layer altered by the projectile. The results show that favorable conditions for successful molecular depth profiling are achieved when the total sputtering yield is high and the altered layer thickness is low. Successful molecular depth profiles are achieved with all of the cluster projectiles, although the degree of chemical damage accumulation was slightly lower with C60. With C60 bombardment, the altered layer thickness of about 20 nm and the damage cross section of about 5 nm2 are physically consistent with predictions of molecular dynamics calculations available for similar chemical systems. In general, the model presented should provide guidance in optimizing experimental parameters for maximizing the information content of molecular depth profiling experiments with complex molecular thin film substrates.

Experimental and model study of the Rh/Al system by means of EPES

AbstractThe Rh/Al system has drawn significant attention as a model heterogeneous catalyst due to its unique adsorption properties. In this study, a set of samples consisting of Al substrates made of polished and etched pure metal sheets and deposited in situ with ultrathin Rh overlayers of different thickness was prepared. During the preparation of the samples, in‐depth diffusion of Rh into the surface region of Al substrates obviously took place. To quantify this process, i.e. by non‐destructively ascertaining the resulting depth profile of the samples, elastic peak electron spectroscopy (EPES) was employed. An EPES measurement was performed for energies of 500, 750 and 1000 eV with the initial Rh overlayer thickness in the range 3–20 Å and using pure Rh and Al standards. The measurement was carried out on a precision spherical retarding‐field analyser (RFA). The resulting experimental EPES intensities, as a function of the primary energy and the initial thickness of the Rh overlayer, were compared and fitted with the intensities simulated by the Monte Carlo (MC) method. An MC model of the sample surface consisting of three regions of different inelastic mean free path (IMFP) and Rh concentration were assumed: the first—Rh on the substrate top, the second—Rh/Al with exponential decay of Rh in Al and the third—pure Al. The best fit and best consistency for different primary energies were achieved under the assumption that no Rh was left on Al substrate top, but an exponentially decaying profile of Rh in Al was created at the surface. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Radon‐222 as a Tracer for Nonaqueous Phase Liquid in the Vadose Zone: Experiments and Analytical Model

The potential use of the naturally occurring noble gas 222Rn as a tracer for vadose zone contamination by nonaqueous phase liquids (NAPLs) is studied experimentally and theoretically. n‐Dodecane was chosen as the model NAPL. In batch experiments containing unsaturated alluvial sand, a 2.9‐fold decrease of the steady‐state 222Rn activity in soil gas was measured as a consequence of the increase in the volumetric NAPL content from 0 to 0.074. A one‐dimensional analytical reactive transport model was developed that includes 222Rn production, gas‐phase diffusion, partitioning, and radioactive decay. Radon‐222 soil gas profiles were predicted for homogeneous and heterogeneous sandy profiles where NAPL contamination was restricted to selected depth layers. The resulting depth profiles document that the position of the NAPL has great influence on the 222Rn activity depth profile. An outdoor lysimeter experiment was performed using unsaturated alluvial sand contaminated by NAPL at depths from 1 to 1.2 m. In the lysimeter experiment, a spill of 2 L m−2 NAPL did not alter significantly the 222Rn profile, as predicted also by model calculations. We concluded that 222Rn can be used as a NAPL tracer in the vadose zone only at heavily polluted sites with uniform spatial 222Rn production.

Radon-222 as a Tracer for Nonaqueous Phase Liquid in the Vadose Zone: Experiments and Analytical Model

The potential use of the naturally occurring noble gas 222 Rn as a tracer for vadose zone contamination by nonaqueous phase liquids (NAPLs) is studied experimentally and theoretically. n -Dodecane was chosen as the model NAPL. In batch experiments containing unsaturated alluvial sand, a 2.9-fold decrease of the steady-state 222 Rn activity in soil gas was measured as a consequence of the increase in the volumetric NAPL content from 0 to 0.074. A one-dimensional analytical reactive transport model was developed that includes 222 Rn production, gas-phase diffusion, partitioning, and radioactive decay. Radon-222 soil gas profiles were predicted for homogeneous and heterogeneous sandy profiles where NAPL contamination was restricted to selected depth layers. The resulting depth profiles document that the position of the NAPL has great influence on the 222 Rn activity depth profile. An outdoor lysimeter experiment was performed using unsaturated alluvial sand contaminated by NAPL at depths from 1 to 1.2 m. In the lysimeter experiment, a spill of 2 L m −2 NAPL did not alter significantly the 222 Rn profile, as predicted also by model calculations. We concluded that 222 Rn can be used as a NAPL tracer in the vadose zone only at heavily polluted sites with uniform spatial 222 Rn production.

Improved near surface characterization of shallow arsenic distribution by SIMS depth profiling

Accurate depth profile analyses of distributions created by ultra low energy (ULE) ion implantation and annealing in Si has been difficult because the implanted element distribution often is mainly within the surface oxide and spans the oxide interface. Although negative ions have the best sensitivity for As in Si, quantification of the negative ion intensities in ULE As distributions near the surface oxide is difficult due to large ion yield changes. The use of an oxidizing ambient and positive ion detection has poor sensitivity. Furthermore, the oxidizing ambient causes profile distortion due to As migration during the depth profile. Therefore, we focused our attention to Cs bombardment analyses. We investigated ULE As ion implanted samples with oxide thicknesses of 1–5 nm. Using the doses calibrated by RBS and oxide thicknesses measured by XPS, we formulated RSF and sputter rate changes across the oxide/Si interface. The resulting depth profiles dramatically improve the dose accuracy and profile shape in samples with oxides thicker than 1 nm, which is especially important in annealed samples for which most of the As is near the surface.

原子プローブ電界イオン顕微鏡による銅シリサイドの解析

Phase formation and diffusion have been investigated in Cu-Si system. Field ion microscope (FIM) and atom-probe field ion microscope (AP-FIM) were used to determine the crystal structures and chemical compositions of the grown phases. From the results of depth profile by AP-FIM, it is proved that the silicide phase take the layer structure of Cu-Si mixture layer and pure Cu layer. The Cu silicide phase estimated was Cu3Si of orthorhombic structure. The orientation relationship of silicide and Si substrate was [111]Cu3Si || [111]Si. The measured value of the diffusion of Cu atoms in Si was four orders in magnitude smaller than the estimated value calculated by the equation of Hall and Racette. Field ion images of Cu atoms in the Cu silicides were dark compared with Si atoms, so that the crystal structures of the Cu silicides have not been determined by FIM.

Ti diffusion in La-doped SrTiO3single crystals

Titanium tracer diffusivities were determined in donor doped SrTiO3 at temperatures between 1573 and 1673 K in synthetic air. La-doped SrTiO3 single crystals cut in the three crystal orientations (100), (110), and (111), were used. After annealing, the well known formation of SrO islands is observed. Their number and size increase with the La content supporting the model that under oxidizing conditions the dopant is compensated by Sr vacancies. Tracer sources of 49Ti or 50Ti were applied by ion implantation. The resulting depth profiles were measured by secondary ion mass spectrometry (SIMS). The bulk Ti tracer diffusivity is found to be several orders of magnitude lower than the O diffusivity and also the La and Nd diffusivities reported recently. In contrast to La, the Ti tracer profile broadening shows largely ideal behaviour. As even long term annealing (several weeks) of weakly doped SrTiO3 does not lead to significant tracer migration, the Ti diffusion seems to be enhanced by the presence of the donor induced Sr vacancies. Although microscopic investigations undertaken on the same samples show strong differences in the surface reconstruction depending on the crystal orientation, no orientation dependence of the Ti diffusivity is observed.

Fabrication of Pb(Zr,Ti)O 3 films on epitaxial γ-Al 2O 3(0 0 1)/Si(0 0 1) substrates

Pb(Zr,Ti)O 3 (PZT) films with (0 0 1) orientation were grown on epitaxial-Al 2O 3(0 0 1)/Si(0 0 1) substrates. The crystalline Al 2O 3 thin film was used as an insulating layer to fabricate metal–ferroelectric–insulator–semiconductor structures. The epitaxial-Al 2O 3(0 0 1) buffer layer was grown on Si(0 0 1) substrates at 1000°C using ultrahigh-vacuum chemical vapor deposition. The PZT films were grown on the Al 2O 3(0 0 1)/Si(0 0 1) substrates using a sol–gel method. Cracks on the surface of the PZT film were not observed with epitaxial-Al 2O 3(0 0 1) films greater than 30 nm thick. X-ray diffraction peaks associated with a perovskite structure were observed, indicating strongly (0 0 1) oriented patterns on the epitaxial-Al 2O 3(0 0 1)/Si(0 0 1) substrate. It was also found from results of Auger electron spectroscopy depth profiles that epitaxial-Al 2O 3(0 0 1) films prevent any reaction between Si and the PZT.

Plasma immersion ion implantation of TiAl using chlorine containing plasma

In order to apply the protective effect of Cl doping for high-temperature oxidation resistance of TiAl alloys of complex-shaped parts, plasma immersion ion implantation (PI 3) of chlorine into technical TiAl alloys was investigated. A specialized PI 3 apparatus was optimized for the strongly etching electronegative Cl plasma. Plasma diagnostics was performed using a Langmuir probe. In order to sustain a sufficiently dense plasma, different RF antenna configurations are discussed and the resulting densities are compared. The influence of plasma pulsing on the surface interaction of Cl during the process was evaluated. Two different commercial alloys were implanted and tested. The resulting depth profiles of the modified surface layer were investigated using depth profiling with Auger electron spectroscopy (AES). After implantation, the Cl is located close to the surface. Oxidation tests at 900 °C in air for 100 h showed a strong decrease in oxidation, which is comparable to conventional beamline implantation of Cl. The effect is rather independent of the alloy composition.

Metal distribution during diagenesis in the contaminated sediments of Dulas Bay, Anglesey, N. Wales, UK

The Tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from Dulas Bay, Anglesey. Results provide data on the chemical association of heavy metals (Fe, Mn, Cu, Zn, Cd, and As with major) sedimentary phases, and provide information on changes in metal partitioning associated with the changing physico-chemical conditions encountered during burial. Extremely high concentrations of heavy metals were recorded (e.g. Zn 3000 μg g −1, Cu 2000 μg g −1) and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where, with increasing depth, Fe, Mn and Cu become increasingly associated with sulphide phases. Substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions. All metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and O 2 utilisation in thermodynamically favoured sequence, Fe and Mn oxide and oxyhydroxide dissolution act as controlling variables leading to zones of solid phase metal enrichment. Phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation.

Characteristics of NO x adsorption and surface chemistry on impregnated activated carbon

Adsorption characteristics of NO x were studied with granular activated carbon (GAC) impregnated with potassium hydroxide (KOH). To confirm the selective adsorptivity of KOH-impregnated activated carbon (K-IAC) to NO x in a fixed-bed adsorption column, temperature of 303–403K, linear velocity of 10–32 cm/sec, and effect of added oxygen were observed. Using scanning electron microscopy (SEM), time of flight secondary ion mass spectrometry (ToF-SIMS), and SIMS depth profile, surface-reaction phenomena of adsorbent, caused by the KOH impregnation and NO x adsorption, were investigated. NO2 adsorbs by chemical reaction with impregnated KOH, from which NO is generated. When oxygen exists, the NO again adsorbs to NO2 with oxygen chemisorbed on the surface, which increases the adsorptivity. In the results of ToF-SIMS and SIMS depth profile, NO2 − and NO3 − increased at the surface distribution by forming oxide crystals of KNO2 and KNO3 due to bond formation with potassium ions. The SIMS depth profile of KO− ensured that KOH provided the selective adsorption site of NO x . In the mechanism studied, the basic character was led on K-IAC by surface basic OH− ions of KOH, oxidation rate from KNO2 to KNO3 was delayed, and adsorptivity of K-IAC to NO x was improved.

Cation Transport and Surface Reconstruction in Lanthanum Doped Strontium Titanate at High Temperatures

ABSTRACTTracer diffusion experiments were carried out in synthetic air at 1573 K in SrTiO3(100) and (110) single crystals, which were either undoped or doped with up to 1 at.% La, respectively. Tracer sources of 139La and 142Nd were applied by ion implantation. The resulting depth profiles were measured by SIMS. The reconstruction of the surface was monitored ex-situ using microscopic and spectroscopic methods including SEM, EPMA, and AFM. The measured tracer diffusivities show no dependency on orientation. The tracer diffusion takes place via cation vacancies. Under oxidizing conditions the dopant is compensated by Sr vacancies. Hence the diffusion is increasing strongly with La concentration. The observed time dependency of the diffusivities may be related to a space charge layer postulated by the current defect chemistry model for donor doped SrTiO3. At high dopant concentrations annealing leads to segregation of bulk La to the surface. La is not significantly incorporated into the secondary crystallites at the surface which consist almost entirely of Sr and O.

Structure and optical properties of (0 0 1)GaAs surfaces nitrided in plasma-assisted NH3 gas

Structural and optical studies were made on the (001)GaAs surfaces nitrided at 700°C for 15min in the pressure between 0.01 and 0.5Torr, plasma-assisted NH3 gas atmosphere. Reflection high-energy electron diffraction (RHEED) and PLS results indicated that the surface nitrided in 0.01Torr NH3 gas consisted of cubic gallium nitride (c-GaN) with epitaxial orientation: (001), [110]c-GaN//(001), [110]GaAs, showing PL spectrum with sharp, blue emission of λ=440nm and a broad peak approximately 470nm at room temperature. The surface nitrided in 0.05Torr NH3 gas was composed of a mixture of cubic and hexagonal GaN, showing blue photoluminescence (PL) emission with wavelength, approximately 440nm at room temperature. The surface nitrided in 0.5Torr NH3 gas consisted of polycrystalline hexagonal GaN, showing blue PL emission with wavelength, approximately 440nm at room temperature. Results of depth profile of the nitrided surface, by AES with sputtering technique using argon gas, indicated that the nitrided layers varies approximately 50–1000Å in thickness, depending on the NH3 gas pressure, as a GaNAs alloy layer. These results are in reasonable agreement with theoretical prediction on the band-gap energies in GaN–GaAs alloy system.

Crack Path Selection in Adhesively-Bonded Joints: The Role of Material Properties

This paper investigates the role of material properties on crack path selection in adhesively bonded joints. First, a parametric study of directionally unstable crack propagation in adhesively-bonded double cantilever beam specimens (DCB) is presented. The results indicate that the characteristic length of directionally unstable cracks varies with the Dundurs' parameters characterizing the material mismatch. Second, the effect of interface properties on crack path selection is investigated. DCB specimens with substrates treated using various surface preparation methods are tested under mixed mode fracture loading to determine the effect of interface properties on the locus of failure. As indicated by the post-failure analyses, debonding tends to be more interfacial as the mode II fracture component in the loading increases. On the other hand, failures in specimens prepared with more advanced surface preparation techniques appear more cohesive for given loading conditions. Using a high-speed camera to monitor the fracture sequence, DCB specimens are tested quasi-statically and the XPS analyses conducted on the failure surfaces indicate that the effect of crack propagation rate on the locus of failure is less significant when more advanced surface preparation techniques are used. The effect of asymmetric interface property on the behavior of directionally unstable crack propagation in adhesive bonds is also investigated. Geometrically-symmetric DCB specimens with asymmetric surface pretreatments are prepared and tested under low-speed impact. As indicated by Auger depth profile results, the centerline of the crack trajectory shifts slightly toward the interface with poor adhesion due to the asymmetric interface properties. Third, through varying the rubber content in the adhesive, DCB specimens with various fracture toughnesses are prepared and tested. An examination of the failure surfaces reveals that directionally unstable crack propagation is more unlikely to occur as the toughness of the adhesive increases, which is consistent with the analytical predictions that were discussed using an energy balance model.

A focusing multilayer analyser for local diffraction studies

A novel X-ray diffraction technique for the local structural characterization of thick specimens is presented. Broad energy-band focusing elements are used both on the incoming and exit (diffracted) side of the sample. The geometry allows imaging, and magnification, of a line through the thickness of the sample. In comparison with conventional methods of defining three-dimensional gauge volumes the new technique provides superior depth resolution, higher flux, and a remedy for some systematic errors occurring in strain measurements due to, for example, grain size effects. The technique is validated by a synchrotron test experiment using a bent and meridionally graded multilayer as the focusing analyser element. The incoming beam is monochromated, at 30 keV, and focused to a 15 µm spot size by means of a bent Laue crystal. The resulting depth profile from the (222) reflection of a 21 µm-thick rolled Au foil has a width of 44 µm. The depth resolution, magnification and reflectivity as a function of the energy bandwidth are found to be well matched by theory. The prospect of the technique and the associated aberrations are discussed.

Synchrotron radiation-excited glancing incidence xrf for depth profile and thin-film analysis of light elements

First results of depth profile and thin-film analysis by glancing incidence x-ray fluorescence analysis of low-Z elements (carbon to aluminum), usually not detectable by conventional instruments, were obtained by synchrotron radiation excitation (SSRL, Beamline III-4) and by a special energy-dispersive spectrometer with high efficiency for low-energy fluorescence radiation [Ge(HP) detector with an ultra-thin 300 nm entrance window]. The results of calculations taking into account several sample parameters of interest agree with the measurements. Results are presented for the determination of depth profiles of Na, Mg and Al implanted in Si wafers and for thin films of Al and a C bulk sample. Copyright © 1999 John Wiley & Sons, Ltd.