Feasibility of in‐line instruments for high‐resolution inelastic X‐ray scattering

Inelastic X‐ray scattering instruments in operation at third‐generation synchrotron radiation facilities are based on backreflections from perfect silicon crystals. This concept reaches back to the very beginnings of high‐energy‐resolution X‐ray spectroscopy and has several advantages but also some inherent drawbacks. In this paper an alternate path is investigated using a different concept, the `M⁴ instrument'. It consists of a combination of two in‐line high‐resolution monochromators, focusing mirrors and collimating mirrors. Design choices and performance estimates in comparison with existing conventional inelastic X‐ray scattering instruments are presented.     

Metamictization in zircon: Raman investigation following a Rietveld approach. Part II: Sampling depth implication and experimental data

Profile line deconvolution following a Rietveld approach is applied to Raman spectra obtained from natural zircon grains from the European Alps. The corrected bandwidths are in perfect agreement with the values obtained from an established correction method (after Irmer) as far as the area of validity of the latter is concerned. For Raman active modes smaller than that, the Rietveld approach also yields accurate values for the true Raman bandwidth. Moreover, changes to instrument parameters are compensated by the correction routine. As for the studied zircon grains, Raman spectroscopy was shown to be a suitable tool for the examination of zoning (i.e. regions which show a variable degree of radiation‐induced damage because of a different amount of incorporated uranium and/or thorium). This is complicated by the fact that the measured Raman signal is not restricted to the depth expected from the axial resolution (several micrometers) but a significant contribution comes from a comparatively large excitation volume (tens of micrometer deep). This sampling volume, however, lies within the same order of magnitude as zoning, which itself is blurred by the range of amorphization‐causing alpha‐particles. Copyright © 2008 John Wiley & Sons, Ltd.     

Correction of optical distortions in dry depth profiling with confocal Raman microspectroscopy

We present a generalized approach to obtain improved Raman intensity profiles from in‐depth studies performed by confocal Raman microspectroscopy (CRM) with dry objectives. The approach is based on regularized deconvolution of the as‐measured confocal profile, through a kernel that simulates optical distortions due to diffraction, refraction and collection efficiency on the depth response. No specific shape or restrictions for the recovered profile are imposed. The strategy was tested by probing, under different instrumental conditions, a series of model planar interfaces, generated by the contact of polymeric films of well‐defined thickness with a substrate. Because of the aforementioned optical distortions, the as‐measured confocal response of the films appeared highly distorted and featureless. The signal computed after deconvolution recovers all the films features, matching very closely with the response expected. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical simulations of confocal Raman spectroscopic depth profiles of materials: a photon scattering approach

We present a simple model that uses a novel photon scattering approach to predict the depth profile response obtained when confocal Raman spectroscopy is applied both to silicon and to a number of related polymeric materials of varying optical clarity. This paper first provides an overview of the models proposed to date to demonstrate the evolution in understanding of the confocal Raman response of semi‐transparent materials, based upon geometrical optics. A new model is then described that is based upon the twin notions of a permanent extended Raman illuminated volume and the degree of extinction of the incident and Raman scattered photons from the whole of the illuminated volume as it is gradually moved further into, or defocused above, the sample. The model's predictions are compared with empirical data from previous studies of a range of semi‐crystalline polymers with different scattering properties and, by means of contrast, with that of a silicon sample. We show that, despite its inherent simplicity, the physics this model utilizes is able successfully to predict the form of the depth profile for each material, something that has not been achieved by any model previously proposed, and that the parameters used in the model scale with independent physical measurements. Finally the model is used to account for the fact that useful Raman spectra can be obtained when the laser is focused as much as 40 µm above the sample surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Confocal Raman microscopy: how to correct depth profiles considering diffraction and refraction effects

A new approach to obtain corrected depth profiles by confocal Raman microscopy, which considers diffraction and refraction effects is presented. The problem of diffraction effects encountered intrinsically in the confocal configuration can be described using a linear Fredholm integral equation of the first kind, which correlates apparent and true Raman intensities with the depth resolution curve of the instrument. Refractive index differences between air and the polymer sample, which cause further errors in the obtained depth profile due to strong aberration effects have been considered. This has been carried out using an empirical variation of the depth resolution function, which is able to simulate the broadening of the depth of focus with depth and also the discrepancy between nominal and measured depth scales. It is shown that considerable differences between apparent and corrected depth profiles exist at the surface and that these depend on the gradient of the profile and the depth resolution of the Raman microscope. Copyright © 2007 John Wiley & Sons, Ltd.     

Deconvolution of very low primary energy SIMS depth profiles

In this paper, the deconvolution of SIMS profiles analysed at very low primary energy (0.5 keV/O₂⁺) is addressed. The depth resolution function (DRF) of the SIMS analysis in presence of roughness is established and a deconvolution procedure is implemented without or in presence of roughness on samples containing delta-doped layers of boron in silicon. It is shown that the deconvolution procedure can lead to a great improvement of the full width at half maximum (FWHM) of the measured peaks in the case where no roughness in detected in the crater bottom. In the case where it is present, the conditions required to use a deconvolution procedure are discussed, and the deconvolution is implemented using precise and restrictive assumptions.     

Ultra‐Precision Surface Machining with Reactive Plasma Jets

Atmospheric Plasma Jet Machining (PJM) is a technology for non‐mechanical ultra‐precision surface shape generation, shape error correction and smoothing based on atmospheric plasma jets. PJM is favorably applied to generate optical surfaces like aspheres, acylinders, or free‐forms but also to improve the surface shape accuracy in a very fast and cost‐efficient way. For that purpose a mainly fluorine containing plasma jet is brought into contact with a surface to locally remove material by a chemical reaction forming volatile products. Hence, the technology is limited to materials like silicon, fused silica and similar, or silicon carbide. Furthermore, the etch profile results from a convolution of the radical and the temperature distribution at the surface. Since the temperature distribution is also influenced by the plasma jet this leads to a non‐linear dependence of the removal function of the plasma tool on its velocity. Using the dwell‐time algorithm for deterministic surface machining by superposition of the local removal function of the plasma tool an advanced process simulation is necessary. In a first local approximation the velocity dependence of the removal function, which has to be determined previously, must be incorporated. Second order thermal effects due to inhomogeneous heating caused by the part geometry and the tool path can be managed by a sophisticated calculation of the surface temperature evolution during machining based on the Finite Element Method (FEM). With the help of this procedure the accuracy and convergence of the machining process can be significantly improved. In the article several examples of surface processing using plasma jet machining are presented. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Deconvolution of Raman spectra for the quantification of ternary high‐pressure phase equilibria composed of carbon dioxide,water and organic solvent

The paper reports on a routine to extract the composition of multi‐component mixtures from their Raman spectra at elevated pressures. The strategy is based on fitting weighted Raman spectra of the pure compounds to the measured Raman spectrum of the mixture, also considering the effects of intermolecular interactions onto the Raman spectra by applying Gaussian and Voigt profile deconvolution of the Raman peaks. Thereby, an improved accuracy compared to previous evaluation strategies could be obtained. The more accurate data of the ternary mixtures of carbon dioxide, water and organic solvents are presented. Copyright © 2014 John Wiley & Sons, Ltd.     

A compact optical parametric oscillator Raman microscope for wavelength‐tunable multianalytic microanalysis

We have developed a high‐throughput microscope for wavelength‐tunable microscopic studies of materials by Raman, surface‐enhanced Raman, fluorescence, and reflectance spectroscopy. Narrow‐band excitation over a broad tuning range (410–2200 nm) is provided by a solid‐state, compact, and relatively inexpensive new class of diode‐pumped Nd:YAG optical parametric oscillator emitting approximately 1‐mJ, 10‐ns pulses at a rate up to 100 Hz. Rayleigh rejection over the tuning range is obtained with an array of angle‐tuned custom dielectric filters. Although high‐power, low duty‐cycle light sources have so far had only very limited use for tunable Raman and surface‐enhanced Raman spectroscopy, we show that undesirable nonlinear effects that arise from the high peak power of the output can be mitigated to produce good results with the proper choice of additional microscope elements. Measurements can be performed across the visible range with 20% sample‐to‐detector throughput and 10 cm⁻¹ resolution. The system is also fitted with a fiber optic imaging system to perform fluorescence and reflectance spectroscopy measurements with a spatial resolution of 5 µm. We demonstrate the instrument's analytical capabilities by recording resonance Raman and surface‐enhanced Raman emissions from a commercial lake pigment and crystal violet, respectively, colorants of interest in cultural heritage studies and forensic science. We also isolate and measure the reflectance spectrum of a commercial lake pigment and the ultraviolet fluorescence spectrum of a single fiber of cochineal‐dyed silk. The tunability, flexibility, compactness, and spatial resolution of the device provide novel capability for multianalytic materials research in fields such as forensic science and cultural heritage studies. Copyright © 2012 John Wiley & Sons, Ltd.     

One-Step Nanosecond-Laser Microstructuring,Sulfur-Hyperdoping,and Annealing of Silicon Surfaces in Liquid Carbon Disulfide

We perform a single-shot IR nanosecond laser processing of commercial silicon wafers in ambient air and under a 2 mm thick carbon disulfide liquid layer. We characterize the surface spots modified in the liquid ambient and the spots ablated under the same conditions in air in terms of its surface topography, chemical composition, band-structure modification, and crystalline structure by means of SEM and EDX microscopy, as well as of FT-IR and Raman spectroscopy. These studies indicate that singlestep microstructuring and deep (up to 2–3% on the surface) hyperdoping of the crystalline silicon in its submicron surface layer, preserving via pulsed laser annealing its crystallinity and providing high (10⁴ cm^?1) spectrally flat near- and mid-IR absorption coefficients, can be obtained in this novel approach, which is very promising for thin-film silicon photovoltaic devices.     

Deconvolution filtering: Temporal smoothing revisited

Inferences made from analysis of BOLD data regarding neural processes are potentially confounded by multiple competing sources: cardiac and respiratory signals, thermal effects, scanner drift, and motion-induced signal intensity changes. To address this problem, we propose deconvolution filtering, a process of systematically deconvolving and reconvolving the BOLD signal via the hemodynamic response function such that the resultant signal is composed of maximally likely neural and neurovascular signals. To test the validity of this approach, we compared the accuracy of BOLD signal variants (i.e., unfiltered, deconvolution filtered, band-pass filtered, and optimized band-pass filtered BOLD signals) in identifying useful properties of highly confounded, simulated BOLD data: (1) reconstructing the true, unconfounded BOLD signal, (2) correlation with the true, unconfounded BOLD signal, and (3) reconstructing the true functional connectivity of a three-node neural system. We also tested this approach by detecting task activation in BOLD data recorded from healthy adolescent girls (control) during an emotion processing task.     

Computing Raman and infrared wavenumbers of nanostructures: application to silicon nanowires

The characterization of nanostructures with spectroscopic methods is a fundamental tool in nanoscience. For novel nanostructures, the interpretation of spectral features is a challenging task. To address this issue, we present the “Symmetry‐Filtered Molecular Dynamics (SFMD)” method to calculate Raman and infrared wavenumbers from molecular dynamics (MD) simulations, employing only the symmetry of the atomic structure. Explicit and expensive calculations of the electric polarizability or the dipole moment are not required. Therefore, our method can be easily used with any standard MD software. On the basis of the density functional tight‐binding method for the MD simulations, we apply our method to bulk silicon and small‐diameter hydrogen‐passivated silicon nanowires. For bulk silicon, we study the wavenumber shift of the Raman peak with temperature and obtain results that are in good agreement with experiments. We further show that thermal lattice expansion is a minor effect (22%) and that temperature‐driven anharmonic effects (78%) are the main contributions to that wavenumber shift. By analyzing the bond lengths of different silicon nanowires, we found that surface stress manifests as a 0.37% shortening of bonds only in the outermost silicon layer. We further analyzed the diameter‐dependent wavenumber shift of a Raman peak in silicon nanowires. We found that the main contribution to the wavenumber shift comes from the phonon confinement effect and surface stress leads to an additional shift of 9–22%. Our results indicate that our method is able to produce quantitative results that can be compared with experiments. We propose our method to be used for the understanding of Raman and infrared spectra of novel bulk and nanostructures. Copyright © 2012 John Wiley & Sons, Ltd.     

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles for strained‐silicon surface enhanced Raman spectroscopy

Poly(vinylpyrrolidone)‐stabilized silver nanoparticles deposited onto strained‐silicon layers grown on graded Si_1−xGe_x virtual substrates are utilized for selective amplification of the Si–Si vibration mode of strained silicon via surface‐enhanced Raman scattering spectroscopy. This solution‐based technique allows rapid, highly sensitive and accurate characterization of strained silicon whose Raman signal would usually be overshadowed by the underlying bulk SiGe Raman spectra. The analysis was performed on strained silicon samples of thickness 9, 17.5 and 42 nm using a 488 nm Ar⁺ micro‐Raman excitation source. The quantitative determination of strained‐silicon enhancement factors was also made. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental study of the vibrational spectra of (CH3)3GeBr supported by DFT calculations

The infrared and Raman spectra of bromotrimethylgermane (BTMG) were recorded afresh to complete the assignment of its vibrational spectra. The vibrational spectrum of BTMG has been predicted from hybrid density functional theory calculations (B3LYP) with several basis sets. The resulting harmonic wavenumbers were scaled by Pulay's scaled quantum mechanical (SQM) and the wavenumber‐linear scaling (WLS) methods to obtain accurate force fields which could aid in the vibrational assignment. Low‐temperature infrared techniques together with Fourier self‐deconvolution (FSD) on the Raman spectrum were used to improve the resolution of the spectra for the modes that could not be observed before. An SQM analysis was carried out to obtain the valence force constants and a set of scale factors that best reproduced the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Measurement Error Correction for Distributed Properties – Filter Cake Thickness Measurements

The measurement of a distributed property is frequently encountered in engineering applications. The impact of a possible measurement error on the measured distribution is described and two methods to account for such an error are detailed: A Fourier transform based deconvolution procedure and a moment based deconvolution approach via kernel estimators are presented. The deconvolution methods can be used in many particle characterization and process applications where particle features or properties are commonly presented in a distributed form. In the current instance, these methods are carefully explored by using artificially generated data and applied to experimental data obtained from filter cake thickness measurements.     

褶积反演中的脉冲压缩准则

通过分析基于脉冲压缩原理的反褶积方法,提出了具有广泛用途的广义L_p模准则,像脉冲反褶积、极小熵反褶积、L₁模反褶积和D模反褶积等都为其特例。根据有限维欧氏空间的L。模性质和高维欧氏空间的几何性质,分析了广义L_p模方法中的参数影响。为了比较不同反褶积方法的脉冲压缩效果,给出了一类判别函数,从理论上证明了,为什么对非小相位信号L₁模法的脉冲压缩效果优于脉冲反褶积;D模反褶积要比常规极小熵法更具有"简单性"。广义L_p模准则为构造、分析新的反褶积方法和进一步研究最优脉冲压缩准则提供了必要的理论基础。     

Low energy boron implantation profiles in silicon from junction depth measurements

Some methods have been recently developed to investigate the distribution of implanted ions in semiconductors, especially into silicon. Generally, these techniques are not valid for boron due to the absence of convenient radioactive isotopes, or to a too small sensitivity when the lower part of the distribution is of interest. This corresponds to our problem, since boron implanted nuclear particle detectors prepared with high resistivity material (up to 50,000 ω.cm) are needed. The properties of these P-N junctions depend in a certain amount on the impurity distribution existing several orders of magnitude below the top of the distribution. Therefore, only the junction location method can be employed. In this method a series of N-type silicon samples, differing each from the other by an increase in resistivity are implanted with boron. The depth of the P-N junction corresponds to the point of the profile where the concentration N_A is equal to that of the substrate N_D (i.e. this latter being well known from the resistivity of the starting material). If the location of the junction can be measured, the profile can then be constructed point by point. The junction location is visualized generally by copper staining. Roosild,⁽¹⁾ Kleinfelder,⁽²⁾ Fairfield⁽³⁾ and D. E. Davies⁽⁴⁾ have used this procedure for boron implantations at energies higher than 50 keV. There is a problem due to the small penetration of the boron ion, and, for high resistivity materials, it is difficult to know the true limits of the zones stained with copper.

In our problem, when heavy particle detectors are desired, it is necessary to implant at lower energies than those indicated previously (< 20 keV). We have developed a new technique derived from the junction depth method, which is useful even at very low implant energy (≈ 10 keV). It consists in measuring the energy loss by 100 keV protons when crossing the entrance window of the P-N junctions used as detectors.

In the first part of this paper the method is described and the possible errors are analyzed and evaluated. In the second part, the distribution of 15 keV boron ions implanted under several experimental conditions is studied. Emphasis is given to the defects resulting from the silicon bombardment.     

Polarization behaviors of twisted carbon nanotube fibers

Polarization behaviors of carbon nanotube (CNT) fibers with different twisting were reported. Scanning electron microscope and polarized Raman spectroscopy were used to investigate the prepared samples. Results indicate that surface twisting angle affects greatly the polarization angle and I_///I_⊥ ratio of twisted CNT fibers. Raman depth profile measurements imply that the twisted fibers consist of non‐uniform CNT alignments. A simplified two‐CNT‐alignment geometric model was proposed to illuminate the experimental observations. The results suggest that polarized Raman depth profile measurement would be a very useful approach for determining the distribution of CNT alignments in CNT fibers. Copyright © 2012 John Wiley & Sons, Ltd.     

An original approach for Raman spectroscopy analysis of radioactive materials and its application to americium‐containing samples

An approach for Raman measurements of highly radioactive samples is presented here. The innovative part of this approach lies in the fact that no single part of the Raman equipment is in direct contact with the radioactive sample, as the sample is sealed in an alpha‐tight capsule. Raman analysis is effectively performed through the optical‐grade quartz window closing the capsule. This allows performing micro‐Raman measurements on radioactive samples with no limitations on the laser source wavelength, polarisation mode, spectrometer mode and microscope mode (provided the focal length of the microscope objective is greater than the thickness of the quartz window and with sub mg samples). Some example results are shown and discussed. In particular, some spectral features of americium‐containing oxide nuclear fuel specimens are presented. Raman spectra clearly reveal in these specimens the presence of abundant oxygen defects induced in the fcc fluorite lattice by trivalent americium. In order to complete the analysis the Raman spectrum of pure americium dioxide was also measured with a lower energy excitation source compared with previous research. The current results seem to be consistent with the possible occurrence of a photolysis process induced by the Raman laser, resulting in the formation of hyperstoichiometric americium sesquioxide Am₂O_{3 + z}. Such a photolytic process is deemed to be unavoidable when visible lasers are used as excitation sources for the Raman analysis of americium dioxide. © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons, Ltd.     

Raman spectroscopy: a tool for biomechanical characterization of Stratum Corneum

The mechanical properties of the Stratum Corneum (SC) have been studied by different authors at the macroscopic level, but the modification of its ultra structure during mechanical extension remains unknown. Moreover, little is described about the effect of the mechanical stress on SC barrier function. In this study, we have examined the SC structure changes, at the molecular level, during uniaxial tensile experiments. This was performed on isolated SC samples using Raman spectroscopy. We could identify the strain status of the analyzed samples by using combination of Raman spectra and Partial Least Squares processing. In addition, this approach provided information about lipids and proteins behavior during the sample extension. The structure of the intercellular lipids bilayer became less organized up to ~9% deformation. For higher strains, a plateau corresponding to the minimum organization is observed till the complete failure of the sample. In the same time, protein structures including desmosomes, were characterized by monotonic secondary structure modifications for deformations up to ~9% followed by a plateau. These observations are relevantly demonstrating the effect of extension on the skin barrier state. Such an approach could be objectively used for clinical applications to evaluate skin discomfort degree and skin elastic behavior. This could therefore help with proof of efficacy for cosmetic and dermatologic products. Copyright © 2013 John Wiley & Sons, Ltd.