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Nondestructive and Nonpreparative Chemical Nanometrology of Internal Material Interfaces at Tunable High Information Depths Beatrix Pollakowski,*,† Peter Hoffmann,*,‡ Marina Kosinova,§ Olaf Baake,‡ Valentina Trunova,§ Rainer Unterumsberger,† Wolfgang Ensinger,‡ and Burkhard Beckhoff† †

Physikalisch-Technische Bundesanstalt, Abbestr. 2-12, 10587 Berlin, Germany Technische Universität Darmstadt, Materials Sciences, Petersenstr. 23, D-64287 Darmstadt, Germany § Nikolaev Institute of Inorganic Chemistry SB RAS, Acad. Lavrentyev Pr. 3, Novosibirsk 630090, Russia ‡

ABSTRACT: Improvement in the performance of functional nanoscaled devices involves novel materials, more complex structures, and advanced technological processes. The transitions to heavier elements and to thicker layers restrict access to the chemical and physical characterization of the internal material interfaces. Conventional nondestructive characterization techniques such as X-ray photoelectron spectroscopy suffer from sensitivity and quantification restrictions whereas destructive techniques such as ion mass spectrometry may modify the chemical properties of internal interfaces. Thus, novel methods providing sufficient sensitivity, reliable quantification, and high information depths to reveal interfacial parameters are needed for R&D challenges on the nanoscale. Measurement strategies adapted to nanoscaled samples enable the combination of Near-Edge X-ray Absorption Fine Structure and Grazing Incidence X-ray Fluorescence to allow for chemical nanometrology of internal material interfaces. Their validation has been performed at nanolayered model structures consisting of a silicon substrate, a physically vapor deposited Ni metal layer, and, on top, a chemically vapor deposited BxCyNz light element layer.

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Destructive analytical techniques may modify the physical or chemical properties of internal interfaces that are often correlated with the material features.4 The formation of chemical bonds between the layers, i.e. at the interfaces, can be revealed, for example, by employing secondary ion mass spectrometry (SIMS, destructive) and X-ray photoelectron spectroscopy (XPS with sputtering: destructive; XPS with angle resolution: nondestructive) for depth profiling. In particular, SIMS and XPS with sputtering have the drawback that the chemical bonds at the interfaces may be modified or destroyed during the sputtering process. Thus, nondestructive and nonpreparative methods for chemical nanometrology providing sufficient sensitivity, reliable quantification, and high information depths to reveal interfacial properties of interest such as the chemical state and related mass deposition are needed to allow for reliable interfacial

he further development of improved characteristics of functional nanoscaled devices involves novel materials, more complex structures, and advanced technological processes, requiring analytical techniques to be well adapted to the nanoscale.1−3 The transitions to heavier elements such as highk materials4 in current nanoelectronics and to several tens of nanometers thick cap layers such as in Si based photovoltaics restrict access to the characterization of the internal material interfaces determining the electronic device properties. With both increasing atomic number of the cap layer constituents and increasing depths of these interfaces from the device surface, established nondestructive characterization methods such as X-ray photoelectron spectroscopy (XPS)5 suffer from severe sensitivity and quantification restrictions due to a limited information depth of about 5 to 8 nm or 30 to 40 nm for conventional and synchrotron radiation based approaches, respectively. Also angle-resolved photoelectron spectroscopy6 features the same limited information depth as XPS due to the mean free path of the electrons. © 2012 American Chemical Society

Received: August 28, 2012 Accepted: November 22, 2012 Published: November 22, 2012 193

dx.doi.org/10.1021/ac3024872 | Anal. Chem. 2013, 85, 193−200

Analytical Chemistry

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Figure 1. Sample (right) and sketch (left) arrangement for the GIXRF-NEXAFS measurements.

measurements at appropriate angles. These angles correspond to mean penetration depths reaching down to the interface as well as to the entire layer system thickness, respectively. The chemical bonds in the interfaces were to be determined by the combined GIXRF-NEXAFS technique. Layered systems of conducting, semiconducting, and isolating nanosized films play a steadily increasing role in the effort to downscale electronic devices. Metals are used as conducting materials, whereas boron carbonitride (BxCyNz, referred to in this paper as BCN for simplicity) is in discussion as a semiconducting partner.10 Furthermore, h-BCN and cBCN have outstanding mechanical, optical, and chemical properties.11 A detailed description of the synthesis and characterization of carbonitrides is provided elsewhere.12

knowledge required in R&D processes. When considering photons, in contrast to electrons, in the detection channel,3,7 the information depths can be significantly increased in all kinds of materials allowing for the speciation of deeply buried interfaces, involving cap layers in the 5 to 500 nm range, by means of high energy resolution X-ray absorption spectroscopy (XAFS) or X-ray emission spectroscopy (XES), respectively. While XES provides only moderate absolute detection sensitivities due to rather low detection efficiencies and solid angles of detection, XAFS can take advantage of absolute detection sensitivities allowing for the registration of even a fraction of a species monolayer when operated in totalreflection or grazing-incidence conditions employing an energydispersive solid state detector for the element-specific fluorescence radiation.8 With very flat layered systems, one can benefit from the depth distribution of the X-ray Standing Wave (XSW) field intensity9 depending on the angle of the incident radiation with the sample surface. A variation of this incident angle allows for tuning the mean penetration depth and, as a consequence, the X-ray information depth in a high dynamic range from a few nanometers to several hundreds of nanometers. Depending on both the XSW intensity and sample structures, the depth resolution is in the low nanometer range. Appropriate measurement strategies adapted to a specific nanoscaled stratified sample enable the combined technique of Near-Edge X-ray Absorption Fine Structure (NEXAFS) and Grazing Incidence X-ray Fluorescence (GIXRF) to provide interfacial species information. GIXRF-NEXAFS is a nondestructive and nonpreparative technique which has the significant advantage that the interfacial chemical binding state remains predominantly unchanged by the measurement. It has already been shown that the GIXRF-NEXAFS method allows for a nondestructive chemical speciation of thin deeply buried nanolayers under certain conditions.7 The GIXRFNEXAFS techniques have the potential not only to determine the percentage of the interface species of the entire layer but also to provide information on the absolute values of the atomic or mass deposition involved when employing calibrated instrumentation.8 The performance of the GIXRF-NEXAFS method for interfacial speciation has been evaluated at nanolayered model structures consisting of a silicon substrate, a physically vapor deposited Ni metal layer, and, on top, a chemically vapor deposited BxCyNz light element layer. For this purpose a twostep procedure has been set up that involves variations of the angle of incidence at the model samples and NEXAFS

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EXPERIMENTAL PROCEDURE

Synthesis of Samples. Silicon substrates were first covered by a physical vapor deposition (PVD) technique with a Ni layer of about 5 nm thickness. The BCN layer was synthesized by a chemical vapor deposition (CVD) method described in detail elsewhere.13 This process was conducted by adding trimethylamine borane (TMAB) as the precursor and ammonia as an additional reactant (both at p = 0.7 Pa respectively) at various temperatures such as 200, 400, and 500 °C, respectively. Figure 1 exhibits a sketch of the sequence of the layered structure. Analytical Approach. The photon-in photon-out spectroscopic method GIXRF-NEXAFS in the soft X-ray range leads to reliable results for deeply buried single layers using public domain XSW software and library data of optical constants or complex refraction indexes, respectively.7 When analyzing objects with thicknesses larger than several tens of nanometers, it is necessary to calculate the intensity distribution of the X-ray standing wave field in the depth of interest. The XSW field arises when the incident and reflected beams interfere with each other.14 The result of the XSW calculation is affected by the complex refraction index of the layered system. Furthermore, monitoring of the penetration depth is required, especially when the absorption edge of a main matrix element is to be measured. In that case, the penetration depth strongly varies when the incident photon energy passes the absorption edge. As a consequence, the angle of incidence has to be adapted depending on the photon energy to stabilize the penetration depth. For NEXAFS measurements one has to ensure that the variation of the penetration depth is in the order of only some few nanometers or even in the subnanometer range. For very thin layers, as in the case for interfaces, a constant incident 194



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chamber and of the actual measurement arrangement is shown in Figure 1. The main component of the chamber is a 9-axis manipulator allowing for an accurate adjustment and positioning of the samples. Its translational x-y-z stage can be aligned vertically to the radiation taking advantage of s-polarized radiation. Moreover, the x-y-z stage layout ensures that the pivotal point is placed in the middle of the sample surface. The accessible range for the angle of incidence is 0° to 45° so that depth-resolved measurements can be carried out for various kinds of sample configurations. Calibrated photodiodes ensure the measurement of the absolute flux or radiant power at a certain energy. In that case, the samples are moved to an other position so that the undisturbed beam can be recorded. This is of importance for a reference-free quantitative analysis of the mass deposition and of the layer thickness, respectively. Furthermore, a photodiode placed on a 2θ arm of the manipulator enables the monitoring of the reflected beam and, thus, X-ray reflectometry (XRR) measurements. The details of this UHV instrumentation are to be published elsewhere. The three samples in the present study could be mounted on a sample carrier and were measured sequentially. For the determination of the interface positions, elemental depth profiles were determined by means of angular dependent measurements recording the fluorescence intensity of the respective element: for BCN the B−Kα, C−Kα, and N−Kα and for the nickel layer the Lα and Lβ lines. The exciting photon energy is set above the respective absorption edges of these elements. The intensity of each element was measured as a function of the incident angle and normalized to the incident radiant power. From analyzing the run of the curves, the maximum position was observed to exhibit the critical angle of total reflection for thin top layers on a substrate, whereas the maximum position of the curve’s derivative represents the critical angle for the buried layer elements. Based on these findings, the incident angles were determined, at which NEXAFS spectra were to be taken. In the following step, the NEXAFS spectra of boron (energy range: 183.0−209.2 eV; step width 0.2 eV), carbon (274.0− 305.0 eV; 0.2 eV), nitrogen (396.0−415 eV; 0.2 eV), and nickel (845.0−885.0 eV; 0.2 eV) of each sample were measured sequentially for the predetermined angles. The spectra were recorded by means of a windowless silicon drift detector (SDD). Depending on the intensity of the fluorescence radiation the distance between sample and detector could be varied several centimeteres with respect to a tolerable count rate and dead time of the SDD detector.

angle may be sufficient in the case of simple systems whereas more complex systems require the inclusion of the XSW field intensity to reliably control the excitation conditions at the depth of interest. In contrast to complex structures of thicker layers, a basic strategy can be pursued for measurements at different depths of interest. Primarily, an elemental depth profile is measured by analyzing the fluorescence radiation of a certain element depending on the angle of incidence. Here, the sequence of the elements15 from the top to the bottom and, thus, the angle of incidence for the respective X-ray absorption measurements can be deduced. There are several different approaches possible for the chemical speciation of interfaces by means of GIXRF-NEXAFS. In the case of internal material interfaces, the matrix elements of the two adjacent layers are involved. By analyzing the elements of the deeper positioned layer, an identification of the interface species can be carried out using a highly sensitive comparison approach. Two NEXAFS spectra at different angles of incidence are required for this purpose. First, the incidence is below the critical angle of total reflection of the lower layer. The measured X-ray absorption spectrum is mainly influenced by the chemical bond of the interface with only a small fraction originating from the whole lower layer. A complementary measurement carried out at a large incident angle allows for the identification of the species of the entire lower layer. The fine structure of the absorption edge is dominated by the layer species in this case. The contribution from the interface becomes negligible. By comparing both spectra, the chemical species of the interface can be identified. Similar measurements at the absorption edges of the element of the upper layer are required at a very shallow angle of incidence. There are different possibilities for determining the respective shallow and steep incident angles. For example, the calculation of the penetration depth based on the algorithm of de Boer et al.14 can be used for deducing the required incident angle for a preselected depth criterion. This course of action implies that the layered structure is well-known, i.e. the layer thickness, thus including information on the interface depth, the optical properties, and the sequence of layers. Alternatively, the incident angles can be experimentally determined as is done in the current work. For this purpose, the angularly dependent fluorescence lines of the element of interest are analyzed. The energy of the exciting radiation should be set close to above the NEXAFS range. The run of the angular dependent fluorescence radiation of thin layers is characterized by a significant slope to a maximum value, after which a decline is observable.16 In order to derive the shallow angle for the interface measurement, a value is chosen for which the intensity is less than half of the maximum intensity and smaller than the angle for maximum intensity. Staying slightly below the angle of total reflection additionally reduces the risk of any unintentional cross-talk from the bottom layer. For deducing the steep angle, an angle is chosen sufficiently far away from the maximum in a region where the intensity does not change anymore. Measurements. The synthesized samples were inserted into a newly designed and recently installed ultrahigh-vacuum measurement chamber that was placed at the plane grating monochromator beamline (PGM) of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II. The PGM beamline provides monochromatized undulator radiation of well-known flux and high spectral purity in the soft X-ray range. A sketch of the beam geometry in the UHV

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RESULTS Thickness Determination. In total, three samples were prepared with varying temperature during the deposition process on 1 × 2 cm2 Si(100) substrates. The thickness of these samples was determined by ellipsometry in order to monitor the depositions. The respective results are summarized in Table 1. Table 1. Thickness of the Sample Layers Determined by Using Ellipsometry

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synthesis temperature / °C

200

400

500

thickness Ni / nm thickness BCN / nm

6±1 6±1

6±1 3±1

6±1 5±1



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Table 2. Thickness of the Sample Layers by Using Reference-Free Quantificationa atomic fraction (%)

a

synthesis temperature / °C

thickness Ni / nm

thickness BCN / nm

B

C

N

200 400 500

5.1 ± 0.8 5.2 ± 0.8 4.8 ± 0.7

6.4 ± 1.0 4.3 ± 0.6 5.6 ± 0.8

31 ± 5 23 ± 3 32 ± 5

44 ± 7 54 ± 8 48 ± 7

25 ± 4 23 ± 3 20 ± 3

The estimated relative uncertainty (k = 1) of the determined layer thickness is 15%.

Figure 2. Angular dependent count rate of the Ni−Lα,β (right) and C−Kα (left) fluorescence lines. For an optimal excitation, the C−Kα fluorescence radiation was recorded at a photon energy of 510 eV and the Ni−Lα,β fluorescence radiation at 1060 eV photon energy of the excitation radiation. From this the angle of incidence for the NEXAFS analysis can be concluded. The count rate can be converted into the emitted intensity by means of the known counting efficiency of the SDD. The second row of pictures exhibits the respective angular dependent count rates normalized to both the effective solid angle of detection and the projected path through the mass deposition per unity area.18

temperatures. Also the stoichiometry of boron, carbon, and nitrogen changes in the layer. It was the production goal that the entire thickness of both layers be about 10 nm, which is reached in all cases. This is of importance because of a significant self-absorption contribution at the extremely low photon energies for the elements of the BCN layer and for the Ni−L radiation for very shallow incident angles. Angular Dependent Fluorescence Radiation. The angular dependence of the fluorescence lines of interest was measured for the determination of the respective angle of incidence for the X-ray absorption spectroscopic analysis. Depending on the energy position of the absorption edge of the respective element, the photon energy is chosen slightly above the absorption edge. Measurements of the BCN layers were performed at 510 eV, and for the Ni layers, the energy was set

The resulting thickness of the Ni layers remains almost constant for the different temperatures. In contrast to that, the BCN thickness changes with increasing temperature during the CVD process. It ranges from 3 to 6 nm. A complementary estimation of the layer thicknesses was carried out by a reference-free XRF quantification approach17 based on the knowledge of all instrumental parameters (ensured by calibrated instrumentation) and of atomic fundamental parameters (provided by databases or by own measurements). The corresponding results are elemental mass depositions per unit area that can be converted into thickness values based on knowledge of the density. All thicknesses and the percentage distributions of the light elements are shown in Table 2. The thickness for all Ni layers can be stated to be about 5 nm. In line with the ellipsometry analysis, the BCN layer thickness varies in the range from 4 to 6 nm for different 196



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Figure 3. Nickel L3,2 NEXAFS spectra for steep incident angle of 15° (a) (offset: 100 for 400 °C and 160 for 500 °C) to analyze the species of the entire layer, and for shallow incident angles (b), e.g. 0.5°/1.0°/1.5° (offset: 90 for 400 °C with a scaling factor of 0.7 and 140 for 500 °C with a scaling factor of 0.7) gaining access to the interface. In particular, the determination of the shallow angles is sensitive to distribution of the Ni atoms in the sample and results from the angular dependent fluorescence radiation. The measurements of (b) need a correction of the excitation conditions varying with the photon energy. This can be done by using the lower energy fluorescence lines of the overlying layer, e.g. the N−Kα of the BCN layer (offset: 10 for 400 °C and 15 for 500 °C with a scaling factor of 2) in the respective energy range as depicted in (c). Thus the corrected Nickel L3,2 NEXAFS spectra (d) measured at shallow incident angles are derived.

to 1060 eV. The initially measured angular dependent runs for Ni and C are given in the Figure 2. The run of all curves related with the thin surface and buried layers exhibited in Figure 2 are in line with both the expected XSW calculations and the thicknesses as quantified by means of reference-free XRF. The angular dependence of the Ni−L lines exhibits changing behavior with increasing temperature in the chemical reactor. The maximum position shifts toward smaller angles of incidence, and the initial slope increases as well for higher temperatures. That means that Ni atoms are closer to the surface and are partly diffused in the BCN layer. For the NEXAFS analysis of the expected interface between BCN and Ni, the following incident angle can be estimated: 1.5° for T = 200 °C, 1.0° for T = 400 °C, and 0.5° for T = 500 °C. The NEXAFS measurements to probe the species of the entire layer were carried out at an incident angle of 15°. As an example for the BCN layers, the angle dependent C− Kα fluorescence line intensity is shown in Figure 2. The noticeable difference in the run of curves here is mainly affected by the variation in the layer thickness, which is in line with the results of the reference-free XRF quantification within the respective uncertainties of both techniques. Primarily, the increasing slope of the run of C−Kα measurement is not of particular interest as it characterizes the surface and thus the

boundary to the ambient air or vacuum in the present case. An incident angle chosen in the decreasing slope of the angular dependent C−Kα line ensures a penetration depth to record information from both the entire layer and the interface. The contribution of an interface is clearly visible in the respective Xray absorption spectrum in the case of very thin films. For C− K, B−K, and N−K NEXAFS analysis, an angle of incidence of about 12° is chosen. The respective NEXAFS spectra of Ni are exhibited in the Figure 3, and those of B, C, and N are shown in Figure 4. Please note the absolute scale of the fluorescence count rate normalized to the incident radiant power that can be converted into mass depositions taking into account both the angular-dependent effective solid angle of detection and the SDD’s counting efficiency. X-ray Absorption Fine Structure Analysis. The elemental depth profiles of the different samples presented in the previous section enable finding reliable angles of incidence for the near edge X-ray fine structure analysis down to the interface and for the entire layer. With knowledge of the penetration depth at a certain incident angle, Ni−L3,2 NEXAFS spectra at a steep and shallow angle and B−K, C−K, and N−K NEXAFS spectra at a steep angle were measured. Starting with Ni−L3,2 NEXAFS analysis, the following strategy was pursued: Different parts of the Ni layers were analyzed regarding the 197



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Ni. Hence, for a sample produced at 200 °C, the incident angle is 1.5°, for the next temperature, 1.0°, and for the highest one, 0.5°. All NEXAFS measurements for determination of the entire layer Ni chemical species took place at 15°. The Ni−L3,2 NEXAFS spectra recorded at an incident angle of 15° from the sample created at 200 °C (see Figure 3a) show the typical pattern of metallic Ni. The given π* features at about 852 and 870 eV are identical with the position of the peaks in XPS spectra attributed to the Ni2p3/2 and Ni2p1/2 states due to the spin orbit splitting.19 In the same Ni−L3,2 NEXAFS spectra from the samples created at 400 and 500 °C (Figure 3a) the intensities of the features typical for metallic Ni decrease and additional peaks at about 854 and 872 eV are observed. These new peaks can be attributed to Ni−Si bonds. This can be supported by the fact that nickel silicide is formed in layered structures of Ni and Si at about 400 °C.20 The significant contribution of the Ni−Si bonds in the Ni−L3,2 NEXAFS spectrum implies that a significant portion of Ni atoms diffuse into the silicon substrate and bond with Si atoms. The Ni−L3,2 NEXAFS spectra were recorded at shallow incident angles, namely 0.5°,1.0°, and 1.5°, to analyze the interface between BCN and Ni. Actually, if the analyzed structures involve several nanolayers, the spectra measured at shallow angles have to be corrected by the excitation conditions scaling with the XSW field intensity at the interface. These specimens are associated with excitation conditions varying strongly with increasing photon energy due to their different structures. A good approximation for the respective XSW field intensity in the interfacial region can be derived from the appropriate fluorescence lines of the lighter elements of the overlying layer as the interfacial XSW intensity follows the mean XSW value of the top layer apart from a small attenuation. Figure 3c shows the dependence of the N−Kα line intensity on the photon energy in the region of the Ni−L3,2 absorption edges. The run of this curve can be used to derive the corrected fine structure of the Ni−L3,2 absorption edges by normalizing the measured Ni−Lα,β fluorescence intensity with the N−Kα fluorescence intensity as the interfacial XSW is in line with the top layer XSW. If the complex refractive index in the respective energy range for the interface and Ni layer is known by previous experiments to complete the database, accurate depth-dependent XSW intensity calculations are enabled and an angular correction can be concluded ensuring a nearly constant penetration depth for all photon energies of interest. Usage of the approximation of the XSW field intensity enables the interfacial species to be reliably derived, when Figure 3b and Figure 3d are considered together, in comparison to Figure 3a. For the samples synthesized at 400 and 500 °C, the spectra exhibit again the typical pattern for metallic Ni. The situation changes for samples produced at 200 °C: In this Ni− L3,2 NEXAFS spectrum, a peak occurs at about 851 eV and a small shift of the feature occurs in the σ*-region. Probably, at relatively low temperatures a chemical bond is created between Ni and another element which decomposes at elevated temperatures. From the sample geometry such a partner element can be boron, carbon, or nitrogen. From the NEXAFS spectra of these elements (Figure 4 a,b,c) only carbon analog features at about 288 eV are observed. Therefore, a relatively weak bond is present, which is formed up to temperatures of about 300 °C and decomposes between 300 and 400 °C. That is in agreement with data given in the literature for the system Ni−C.21

Figure 4. Complementary to the Ni−L3,2 NEXAFS spectra, B−K (a), C−K (b), and N−K (c) NEXAFS spectra were recorded at an incident angle of 12° to validate the assumed species of Ni. Offsets B−K: 50 for 400 °C and 200 for 500 °C with a scaling factor of 0.7; offsets C−K: 50 for 400 °C and 250 for 500 °C; offsets N−K: 30 for 400 °C and 400 for 500 °C.

species, and from comparison of both spectra, measured at a shallow and steep incident angle, the occurrence of an interface can be validated. The B−K, C−K, and N−K absorption edge is analyzed as well for complementary information and verification. When considering the element distribution of the element nickel, it is noted to be different for higher deposition temperatures, as shown in Figure 2. Due to this finding, different incident angles are needed to analyze a similar fraction of nickel belonging to the interface region between BCN and 198



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Figure 5. Additional C−K (left) and N−K (right) NEXAFS spectra for shallow and steep incident angle (2° and 12°) for the sample deposited by 200 °C. It allows for correlation of the chemical species and depth, e.g. surface, bulk, and interface.

species are available. Thereby the mass deposition or the number of atoms per unit area in the interfacial species can be concluded as well as the interface thickness. In view of the performance outlined here, GIXRF-NEXAFS can be expected to substantially contribute to the chemical and physical characterization of internal material interfaces of technologically relevant materials at a high dynamic range of interfacial depths.

In addition to the X-ray absorption measurements at a steep angle of incidence (12°) further investigations were carried out at a shallow angle of 2° at B−K, C−K, and N−K absorption edges. These investigations exhibit only, for the sample produced by a temperature of about 200 °C, differences for the measurements at shallow and steep angles. In Figure 5 it is shown that the fine structure of the C−K and N−K absorption edge varies significantly and additional structures arise. The respective N−K NEXAFS spectrum measured at 2° shows two additional structures at 398.0 and 399.4 eV which can be associated to the near-surface region because their intensities decrease for the spectrum recorded at 12°. That means clearly there is no contribution from the interface. In contrast to that finding, the C−K NEXAFS measured at 2° shows a BCN-like structure.13 The spectrum recorded at 12° exhibits two further peaks at 286 and 288.8 eV which can be correlated to the occurrence of an interface species of carbon.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support by Deutsche Forschungsgemeinschaft (DFG), Grants EN 207/25-1 and BE 1372/6-1, and by Russian Fond Fundamental Research (RFFI), Grant 10-03-91332.

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CONCLUSION AND PERSPECTIVES A set of nanolayered systems consisting of a silicon substrate deposited with a thin nickel layer and a BCN layer varying in the temperature during the BCN deposition were employed to illustrate the novel measurement procedure developed for the chemical speciation of interfaces with depth-resolving GIXRFNEXAFS. By means of a comparison approach, identification of the interface species could be successfully performed. For this purpose, two NEXAFS spectra providing information originating from different depths are required. Particularly for the BCN−Ni systems, it was shown that Ni forms different bonds depending on the synthesis temperature. For the temperature T = 200 °C, an interface between the BCN and Ni occur and a Ni−C bond was identified. In the cases of T = 400 and 500 °C, the Ni−C bond vanishes and Ni is existent in metallic form. The entire Ni layer exists as a metal for the temperature T = 200 °C. With increasing temperatures up to 500 °C, the nickel atoms react with the silicon atoms of the substrate, and a considerable percentage of Ni−Si bonds become observable. The presented results confirm the potential of this method for interfacial speciation. Furthermore, X-ray absorption spectroscopy in combination with calibrated instrumentation can provide absolute values of species mass depositions with known uncertainties. It opens up the possibility for determination of the respective fractions of the chemical bonds, provided that reference spectra of the involved

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