Quantitative Depth Profiling Research Articles

Towards drug quantification in human skin with confocal Raman microscopy

Understanding the penetration behaviour of drugs into human skin is a prerequisite for the rational development and evaluation of effective dermal drug delivery.The general procedure for the acquisition of quantitative drug penetration profiles in human skin is performed by sequential segmentation and extraction. Unfortunately, this technique is destructive, laborious and lacks spatial resolution. Confocal Raman microscopy bares the potential of a chemically selective, label free and nondestructive analysis. However, the acquisition of quantitative drug depth profiles within skin by Raman microscopy is impeded by imponderable signal attenuation inside the tissue.In this study, we present a chemical semi-solid matrix system simulating the optical properties of human skin. This system serves as a skin surrogate for investigation of Raman signal attenuation under controlled conditions. Caffeine was homogeneously incorporated within the skin surrogate, and Raman intensity depth profiles were acquired. A mathematical algorithm describing the Raman signal attenuation within the surrogate was derived from these profiles. Human skin samples were incubated with caffeine, and Raman intensity depth profiles were similarly acquired. The surrogate algorithm was successfully applied to correct the drug profiles in human skin for signal attenuation. For the first time, a mathematical algorithm was established, which allows correction of Raman signal attenuation in human skin, thus facilitating reliable drug quantification in human skin by confocal Raman spectroscopy.

Quantitative and depth-resolved deep level defect distributions in InGaN/GaN light emitting diodes

Deep level defects in the multi-quantum well (MQW) region of InGaN/GaN light emitting diodes (LEDs) were investigated. InGaN quantum well and GaN quantum barrier defect states were distinguished using bias-dependent steady-state photocapacitance and deep level optical spectroscopy, and their possible physical origin and potential impact on LED performance is considered. Lighted capacitance-voltage measurements provided quantitative and nanoscale depth profiling of the deep level concentration within the MQW region. The concentration of every observed deep level varied strongly with depth in the MQW region, which indicates evolving mechanisms for defect incorporation during MQW growth.

Recommended cross-section of the [formula omitted] reaction below 2.5 MeV: A potential tool for quantitative analysis and depth profiling of oxygen

The cross-section of the O16(p,γ)F17 reaction is well studied at low energies. It can be used for analytical purposes to extract the oxygen content of thin samples or surface layers of bulk samples from the measured γ-ray yield. Here we recommend absolute cross-sections for the laboratory proton energy range from 500 to 2500keV, where the cross-sections are non-resonant and thus vary smoothly with energy.

Overcoming Low Ge Ionization and Erosion Rate Variation for Quantitative Ultralow Energy Secondary Ion Mass Spectrometry Depth Profiles of Si1–xGex/Ge Quantum Well Structures

We specify the O(2)(+) probe conditions and subsequent data analysis required to obtain high depth resolution secondary ion mass spectrometry profiles from multiple Ge/Si(1-x)Ge(x) quantum well structures (0.6 ≤ x ≤ 1). Using an O(2)(+) beam at normal incidence and with energies >500 eV, we show that the measured Ge signal is not monotonic with concentration, the net result being an unrepresentative and unquantifiable depth profile. This behavior is attributed to a reduced Ge ionization rate as x approaches 1. At lower beam energies the signal behaves monotonically with Ge fraction, indicating that the Ge atoms are now ionizing more readily for the whole range of x, enabling quantitative profiles to be obtained. To establish the depth scale a point-by-point approach based on previously determined erosion rates as a function of x is shown to produce quantum well thicknesses in excellent agreement with those obtained using transmission electron microscopy. The findings presented here demonstrate that to obtain reliable quantitative depth profiles from Ge containing samples requires O(2)(+) ions below 500 eV and correct account to be taken of the erosion rate variation that exists between layers of different matrix composition.

Influence of the hydrogen contained in amorphous silicon thin films on a pulsed radiofrequency argon glow discharge coupled to time of flight mass spectrometry. Comparison with the addition of hydrogen as discharge gas

Thin film solar cells technology based on hydrogenated amorphous silicon (a-Si:H) has undergone a great expansion during recent years. Pulsed radiofrequency glow discharge time-of-flight mass spectrometry (rf-PGD-ToFMS) is able to perform depth profiling analysis of coated materials, providing an excellent tool for rapid and high sensitive chemical characterisation of photovoltaic devices. The hydrogen concentration on a-Si:H thin films is around 10%, which represents a challenge for quantitative depth profile analyses by using GD sources due to the so-called “hydrogen effect”. It is well-known that when hydrogen is present in the Ar discharge, even in small quantities, significant changes can occur in the ion signal intensities and sputtering rates measured. Therefore, a critical comparison has been carried out by rf-PGD-ToFMS in terms of pulse profiles, spectral interferences and depth resolution for two modes of hydrogen introduction in the discharge, exogenous hydrogen in molecular gaseous form (using the mixture 0.2% H2 + Ar as discharge gas) or endogenous hydrogen, sputtered as a sample constituent. For this purpose, non-hydrogenated materials (containing B, P and Si) and three types of a-Si:H thin films were investigated. Exogenous hydrogen was found to produce a noteworthy influence on the pulse profiles of the analytes, whereas the effect of the hydrogen sputtered from the samples could be considered less notorious. Moreover, the proper selection of the after-peak region was found to be critical to obtain optimum mass spectra (i.e. high analyte sensitivities free of interferences).

Growth Characteristics of Pulse Electrodeposition Fe-Si Layer

Fe-Si layer was prepared on silicon steel substrate from KCl-NaCl-NaF-SiO2 molten salts by pulse current at different time. The quantitative Si concentration depth profile, surface morphology and phase structure of the layer were studied by glow discharge optical emission spectroscopy, atomic force microscopy and X-ray diffraction. The layer growing process was analyzed from nucleation process, growth pattern and microstructure. It was observed that the Fe-Si alloy nucleated in the way of three dimensional conical shape and initially grew in the orientation of matrix, then gradually adjusted to the lowest energy state. With deposition time going on, the phase structure of the layer changed in the order of -Fe (Si) →α-Fe (Si) ＋Fe3Si →Fe3Si

Accurate depth profiling of dry oxidized SiGeC thin films by extended Full Spectrum ToF-SIMS

The abundance of work on SiGe based devices demonstrates the importance of compositional characterization of such materials. However accurate SIMS depth profiling of SiGe, and especially of SiGe/silicon dioxide interfaces can be difficult due to matrix effects. Therefore, we highlight here the improvements brought by the extended Full Spectrum protocol, presented in previous works and allowing minimization of matrix effects. Previous studies on this protocol showed that it was extremely precise and reproducible for Ge and impurity quantification in non oxidized matrices. In this study we thus investigated its accuracy for simultaneous quantitative depth profiling of both matrix elements (Si, Ge, O) and impurities (C) in Si 0.82Ge 0.16C 0.02 layers annealed in oxidizing atmosphere, by comparing results with more classic protocols. The profiles provided by the extended Full Spectrum protocol were found to be more accurate than the others, especially around interfaces. This results in a better comprehension of the behaviour of SiGeC layers under oxidizing anneal and thus allows the fabrication of very well controlled three dimensional Ge nanowire structures for next generation devices.

Quantitative depth profiling of ultrathin high-k stacks with full spectrum time of flight–secondary ion mass spectrometry

Elemental concentration depth profiles of high-k material stacks for 32 nm node devices and below were acquired by high resolution backscattering spectrometry (HRBS), parallel angle resolved-x-ray photoelectron spectroscopy (pAR-XPS), and time of flight–secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS data were analyzed using an original calibration method which the authors shall refer to as the full spectrum protocol. Three different samples were studied in this work, one ultrathin insulating layer (IL) alone and two nitridized high-k/IL samples with different nitridation conditions for the IL. Although HRBS and AR-XPS already proved their ability in this domain, SIMS or ToF-SIMS characterization of high-k material stacks is still hampered by various matrix effects. Comparison of the elemental profiles obtained by all three techniques allows the accuracy of the full spectrum ToF-SIMS protocol to be assessed, both in terms of chemical composition quantification and depth resolution. This study reveals the feasibility of quantitative and depth resolved ToF-SIMS profiling of ultrathin high-k material stacks.

Quantitative profiling of SiGe/Si superlattices by time‐of‐flight secondary ion mass spectrometry: the advantages of the extended Full Spectrum protocol

The abundance of work on SiGe-based devices demonstrates the importance of the compositional characterization of such materials. However, Secondary Ion Mass Spectrometry (SIMS) characterization of SiGe layers often suffers from matrix effects due to the non-linear variation of ionization yields with Ge content. Several solutions have been proposed in order to overcome this problem, each having its own limitations such as a restricted germanium concentration range, or a weak sensitivity to dopants or impurities. Here, we studied the improvements brought by an alternative protocol: the extended Full Spectrum protocol, which states proportionality between the composition of the secondary ion beam and that of the actual material. Previous studies on this protocol showed that it was extremely precise and reproducible for Ge quantification in a permanent regime, because of minimized matrix effects. In this study we thus investigated its accuracy for the simultaneous quantitative depth profiling of both matrix elements (Si, Ge) and impurities (B, C or P) in strained SiGe/Si superlattices by comparing results with those from more classic protocols. The profiles provided by the extended Full Spectrum protocol were found to be accurate, and to exhibit better properties than classic protocols in terms of signal/noise ratio and signal stability, along with a slight enhancement in depth resolution.

Quantitative depth profiling of SiGe‐multilayers with the Atom Probe

AbstractThe laser‐assisted Atom Probe has been proposed as a metrology tool for semiconductor technology to meet the requirements accompanying the analysis of the ever smaller and more complex structures targeted for fabrication. In order to support its routine application, we carried out a quantitative assessment of the performance of the Atom Probe (AP) on semiconductor compound multilayers. We analyzed a silicon, silicon‐germanium multilayer structure with Atom Probe Tomography (APT), SIMS, Transmission Electron Microscopy (TEM) and high resolution X‐ray diffraction (HRXRD), and studied the impact of the laser power on the accuracy. Under optimized conditions, the AP outperforms SIMS by a factor of 3 in terms of depth resolution providing a decay length of less than 0.4–0.6 nm/dec whereas the compositions and layer thicknesses are in close agreement with the SIMS, HRXRD and TEM results. Copyright © 2010 John Wiley & Sons, Ltd.

Quantitative depth profiling of boron and arsenic ultra low energy implants by pulsed rf-GD-ToFMS

In very recent years particular effort is being devoted to the development of radiofrequency (rf) pulsed glow discharges (GDs) coupled to time of flight mass spectrometry (ToFMS) for depth profile qualitative analysis with nanometre depth resolution of technological materials. As such technique does not require sampling at ultra-high vacuum conditions it facilitates a comparatively high sample throughput, related to the reference technique secondary ion mass spectrometry (SIMS). In this work, pulsed rf-GD-ToFMS is investigated for the fast and sensitive characterization of boron and arsenic ultra low energy (ULE) implants on silicon. The possibility of using a simple multi-matrix calibration procedure is demonstrated for the first time for quantification of this type of samples and the validation of the proposed procedure has been carried out through the successful analysis of a multilayered sample with single and couple 11B delta markers. Results obtained with the proposed methodology for boron and arsenic ULE implants, prepared under different ion doses and ion energy conditions, have proved to be in good agreement with those achieved by using complementary techniques including SIMS and grazing incidence X-ray fluorescence. Thus, although further investigations are necessary for more critical evaluation of depth resolution, the work carried out demonstrates that rf-GD-ToFMS can be an advantageous tool for the analytical characterization of boron and arsenic ULE implants on silicon.

Elemental Depth Profiling of Fluoridated Hydroxyapatite: Saving Your Dentition by the Skin of Your Teeth?

Structural and chemical changes that arise from fluoridation of hydroxyapatite (Ca(5)(PO(4))(3)OH or "HAp"), as representing the synthetic counterpart of tooth enamel, are investigated by X-ray photoelectron spectroscopy (XPS). Elemental depth profiles with a depth resolution on the nanometer scale were determined to reveal the effect of fluoridation in neutral (pH = 6.2) and acidic agents (pH = 4.2). With respect to the chemical composition and the crystal structure, XPS depth profiling reveals different effects of the two treatments. In both cases, however, the fluoridation affects the surface only on the nanometer scale, which is in contrast to recent literature with respect to XPS analysis on dental fluoridation, where depth profiles of F extending to several micrometers were reported. In addition to the elemental depth profiles, as published in various other studies, we also present quantitative depth profiles of the compounds CaF(2), Ca(OH)(2), and fluorapatite (FAp) that were recently proposed by a three-layer model concerning the fluoridation of HAp in an acidic agent. The analysis of our experimental data exactly reproduces the structural order of this model, however, on a scale that differs by nearly 2 orders of magnitude from previous predictions. The results also reveal that the amount of Ca(OH)(2) and FAp is small compared to that of CaF(2). Therefore, it has to be asked whether such narrow Ca(OH)(2) and FAp layers really can act as protective layers for the enamel.

Quantitative depth profile analysis of metallic coatings by pulsed radiofrequency glow discharge optical emission spectrometry

In recent years particular effort is being devoted towards the development of pulsed GDs because this powering operation mode could offer important analytical advantages. However, the capabilities of radiofrequency (rf) powered glow discharge (GD) in pulsed mode coupled to optical emission spectrometry (OES) for real depth profile quantification has not been demonstrated yet. Therefore, the first part of this work is focussed on assessing the expected advantages of the pulsed GD mode, in comparison with its continuous mode counterpart, in terms of analytical emission intensities and emission yield parameters. Then, the capability of pulsed rf-GD-OES for determination of thickness and compositional depth profiles is demonstrated by resorting to a simple multi-matrix calibration procedure. A rf forward power of 50 W, a pressure of 600 Pa, 1000 Hz pulse frequency and 50% duty cycle were selected. The quantification procedure used was validated by analysing conductive layers of thicknesses ranging from a few tens of nanometer up to about 20 μm and varied compositions (hot-dipped zinc, galvanneal, back contact of thin film photovoltaic solar cells and tinplates).

Quantitative depth profile analysis of boron implanted silicon by pulsed radiofrequency glow discharge time-of-flight mass spectrometry

The analytical potential of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (pulsed-rf-GD-TOFMS) is investigated for fast quantitative analysis of major and dopant elements in bulk and thin film layers. This technique does not require sampling at ultra-high vacuum conditions and so it facilitates high sample throughput compared to reference techniques as secondary ionization mass spectrometry (SIMS). In this paper, bulk and boron implanted silicon samples are analyzed. Boron concentration in Si samples is calculated from calibration curves obtained using solar grade silicon and B doped silicon wafers as calibrating materials, and using 29Si + ion signal as internal standard. Qualitative depth profiles of 10B implanted silicon are determined in a few seconds using the low-pressure pulsed-rf-GD-TOFMS system. Additionally, quantitative depth profiles are easily determined making use of the calibration curves. A good agreement with the depth profiles measured using SIMS was obtained, demonstrating the analytical potential of the pulsed-GD-TOFMS system for fast, sensitive and high depth resolution analysis of implanted silicon samples.

Analysis of an uncommon coating defect on industrial galvannealed high strength interstitial free steel

Abstract The surface quality of galvannealed coated steels has improved substantially with the use of integrated process control. However, some defects appear on the surface of these products. In this paper a hitherto unknown and uncommon defect found on the galvannealed coating of a high strength interstitial free steel has been subjected to in-depth study and analysis to determine the root cause of the defect. Scanning electron microscopy along with energy dispersive spectroscopy, quantitative depth profiling using glow discharge optical emission spectroscopy, auger electron spectroscopy and crystallographic texture analysis of the coated layer was employed for characterization purpose. It appears that formation of a sticky oxide layer of Fe2O3 during upstream processing is the root cause of this defect. The defect manifests itself as a mixture of galvanized layer coupled with an under-alloyed delta phase that forms over and above the pickling-resistant oxide layer during the galvannealing process.

Depth profile analysis: coatings and thin layers

Coatings and thin films are present in an amazing number of applications in our daily lives although in many cases we are not conscious of them. The field extends from protective layers for mechanical and corrosion resistance to multilayered materials for electronic, optoelectronic, or magnetic applications, coated glasses for buildings, biomaterials, photovoltaic devices, catalysts, sensors, imitation jewellery, and decorative coatings. Moreover, polymeric coatings are now also used for various technological applications, ranging from poly-LED displays or organic photovoltaic systems to food packaging. The ability to carry out the in-depth profile analysis of a given material, i.e., to determine the changes in the composition of major and trace components from the surface down to the bulk homogeneous solid, provides information about the composition and thickness of the layers, the distribution of doping constituents, possible diffusion processes, and the presence of impurities. The depth-resolved analytical data allow us to better understand the processes occurring at nanometer-length dimensions and to improve the materials, with the aim of achieving the optimum final performance. The rapid progress in materials science constantly poses new challenges for analytical chemistry and prompts the development of improved techniques and methods. The influence is particularly strong for coated materials and thin films, for which applications and demands are increasing at a rapid pace, with thinner films and more complex surface modifications continually being developed both to fit common market needs and also for high-tech applications. This special issue contains 15 papers (four reviews and 11 original research papers) from universities, institutes, and research laboratories working with direct solid analytical techniques such as X-ray photoelectron spectroscopy, grazing incidence X-ray fluorescence, confocal Raman spectroscopy, glow discharges coupled with optical emission or mass spectrometry, and atomic force microscopy. The contributions show the potential for improved analytical techniques and methods to adapt their performance to the new challenges brought by materials science, for example, expanding their capabilities from just elemental to also molecular information, allowing the analysis of thin films of a few nanometers instead of just micrometer-thick coatings, assisting the development of advanced materials of proper quality, allowing for nondestructive depth profile analysis, and providing not just qualitative but also quantitative depth profile information. We specially thank the authors for their contributions and wish them all the best in their professional lives. We are also very thankful to the reviewers for the thorough and ontime reviews of the papers, and, last but not least, to the editorial team of Analytical and Bioanalytical Chemistry for the invitation for us to act as guest editors of this issue and for their support. B. Fernandez :R. Pereiro (*) Department of Physical and Analytical Chemistry, University of Oviedo, 33006 Oviedo, Spain e-mail: mrpereiro@uniovi.es

The hydrogen effect as a function of discharge parameters - investigations of the variation of emission yield in glow discharge plasmas

It is well known that traces of hydrogen in the glow discharge plasma enhance or suppress the intensities of other spectral lines, in this work termed “the hydrogen effect”. In this work, the focus is on the variation of the hydrogen effect as a function of the discharge parameters, for the purpose of developing effective correction methods in quantitative depth profile analysis. A simple, but effective experimental method was employed: The intrinsic contamination of the source leads to an increased amount of hydrogen in the plasma at the beginning of the discharge, which is rapidly reduced with sputtering time. Thus, by recording the intensity depth profiles of multi-element bulk reference materials, the influence of hydrogen on several emission lines can be observed. The decay or increase in intensity, correlated to the intensity of the hydrogen emission line, gives the desired information. Systematic investigations by varying current and voltage in a considerable range provided a good matrix of data to find a model describing these variations. Furthermore, renewed investigations of the variation of emission yields (EY) with discharge parameters have led to a model which has been used to correct the obtained data for the hydrogen intensities, so as to represent the actual content of hydrogen in the plasma. The information extracted from these studies is expected to be of great importance for routine depth profile analysis, as the hydrogen correction is a relevant tool in software quantification algorithms. Existing correction models for the hydrogen effect do not take variations in the discharge parameters into account. This work clearly shows that it is necessary to implement such variations for accurate correction.

High resolution medium energy ion scattering analysis for the quantitative depth profiling of ultrathin high-k layers

Ultrathin high-k layers such as hafnium oxide (HfO2) in combination with a subnanometer SiO2 or Hf silicate have emerged as Si compatible gate dielectric materials. Medium energy ion scattering (MEIS) analysis has been carried out on a range of such metal oxide chemical vapor deposition grown HfO2∕SiO2 and HfSiOx(60%Hf)∕SiO2 gate oxide films of thickness between 1 and 2nm on Si(100), before and after decoupled plasma nitridation (DPN). The ability of MEIS in combination with energy spectrum simulation to provide quantitative layer information with subnanometer resolution is illustrated and the effect of the DPN process is shown. Excellent agreement on the deduced layer structures and atomic composition with the as grown layer parameters, as well as with those obtained from cross section electron microscopy and other studies, is demonstrated. MEIS analysis of a high-k, metal gate TiN∕Al2O3∕HfO2∕SiO2∕Si stack shows the interdiffusion, after thermal treatment, of Hf and Al from the caplayer, inserted to modify the metal gate workfunction.

Phototermal Spectra of Inhomogeneous Coatings

of inhomogeneous thermal properties in photothermal amplitude and phase spectra of coatings. Finally, a method for quantitative depth profiling that makes use of prior knowledge about the type of profile existing in a sample to reduce the instabilities associated with the mathematically ill conditioned task is demonstrated. Photothermal (PT) measurement techniques are being intensively developed and applied with increased success in the measurement of thermal, optical and other related physical properties, as well as for the investigation of subsurface structure and macroscopic defects of various samples. Photothermal methods are based on direct or indirect measurements of temperature variations, which occur because of generation and transfer of the heat produced by excitation of a testing structure by an external source of energy. Hence, a correct description of thermal transport processes is necessary for the analysis of the measured signals and for their application in the determination of the physical sample properties. All the existing models of photothermal signals are based on the solutions of the classical heat conduction equation that neglects the thermal memory eects. However, a large group of ver

Crater effects on H and D emission from laser induced low-pressure helium plasma

An experimental study has been performed on the effects of crater depth on the hydrogen and deuterium emission intensities measured from laser plasmas generated in low-pressure helium ambient gas from zircaloy-4 samples doped with different H and D impurity concentrations as well as a standard brass sample for comparison. The results show that aside from emission of the host atom, the emission intensities of other ablated atoms of significantly smaller masses as well as that of the He atom generally exhibit relatively rapid initial decline with increasing crater depth. This trend was found to have its origin in the decreasing laser power density arriving at the crater bottom and thereby weakened the shock wave generated in the crater. As the crater deepened, the declining trend of the intensity appeared to level off as a result of compensation of the decreasing laser power density by the enhanced plasma confinement at increasing crater depth. Meanwhile, the result also reveals the significant contribution of the He-assisted excitation process to the doped hydrogen and deuterium emission intensities, leading to similar crater-depth dependent variation patterns in contrast to that associated with the surface water, with growing dominance of this common feature at the later stage of the plasma expansion. Therefore, a carefully chosen set of gate delay and gate width which are properly adapted to the crater-depth dependent behavior of the emission intensity may produce the desired intrinsic emission data for quantitative depth profiling of H impurity trapped inside the zircaloy wall.