The C 1s signal from ubiquitous carbon contamination on samples forming during air exposure, so called adventitious carbon (AdC) layers, is the most common binding energy (BE) reference in X‐ray ...photoelectron spectroscopy studies. We demonstrate here, by using a series of transition‐metal nitride films with different AdC coverage, that the BE of the C 1s peak EBF
varies by as much as 1.44 eV. This is a factor of 10 more than the typical resolvable difference between two chemical states of the same element, which makes BE referencing against the C 1s peak highly unreliable. Surprisingly, we find that C 1s shifts correlate to changes in sample work function ϕSA
, such that the sum EBF+ϕSA
is constant at 289.50±0.15 eV, irrespective of materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination than offered by the conventional methods. Our findings are not specific to nitrides and likely apply to all systems in which charge transfer at the AdC/substrate interface is negligible.
Zeros matter: The C 1s signal from adventitious carbon (AdC) is the most common binding energy (BE) reference in X‐ray photoelectron spectroscopy. It is shown here that the BE of the C 1s peak EBF
is substrate dependent, which makes BE referencing highly unreliable. Surprisingly, C 1s shifts correlate to changes in the sample work function ϕSA
, such that the sum EBF+ϕSA
is constant irrespective of the materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination.
X‐ray photoelectron spectroscopy (XPS) is an indispensable technique in modern materials science for the determination of chemical bonding as evidenced by more than 10 000 XPS papers published ...annually. A literature survey reveals that in the vast majority of cases an incorrect referencing of the binding energy scale is used, neglecting warnings that have been formulated from the early days of the technique. Consequences for the data reliability are disastrous and decades of XPS work require revisiting. The purpose of this Viewpoint is to highlight the existing problems, review the criticism and suggest ways forward.
X‐ray photoelectron spectroscopy (XPS) is an indispensable technique in modern materials science. A literature survey reveals that in the vast majority of cases an incorrect referencing of the binding energy scale is used, neglecting warnings that have been formulated from the early days of the technique. The purpose of this Viewpoint is to highlight the existing problems and suggest ways forward.
Thin films in the aluminosilicate (AlSiO) system containing up to 31 at. % Al and 23 at. % Si were prepared by reactive RF magnetron co-sputtering in order to investigate the dependence of film ...formation and optical properties on substrate temperature and Si and Al contents. The obtained films were amorphous with smooth microstructure. The growth rate at different substrate temperatures ranged from 1.2 to 3.3 nm/min and increase with increasing the Si target power. The roughness decreases and thickness increases with increasing Si content. The thickness of the films grown at a deposition temperature of 100 °C is found to be higher than the films deposited at 300 and 500 °C. The AlSiO-coated glasses have a higher transmission in the visible region than the uncoated glass. The spectroscopic ellipsometry analysis reveals that the refractive index value decreased with decreasing the Al content, having extinction coefficient values of zero in the measured spectral region and band gap values ≥ 3.4 eV. The obtained thin films have over 90% transmittance in the visible range and no systematic variation of transmittance was observed with substrate temperature. The results suggest that glass substrate coated with AlSiO thin films have improved optical properties.
•AlSiO film (up to 400 nm thick) were synthesized by using RF magnetron sputtering of Al and Si metallic targets.•AlSiO films have x-ray amorphous structure.•The AlSiO films are stoichiometric and are not phase-separated.•The glassy AlSiO films are smooth, having a typical surface roughness dEMA < 2 nm.•AlSiO films exhibit 90% or more average light transmittance over the visible range.
The C1s signal from ubiquitous carbon contamination on samples forming during air exposure, so called adventitious carbon (AdC) layers, is the most common binding energy (BE) reference in X-ray ...photoelectron spectroscopy studies. We demonstrate here, by using a series of transition-metal nitride films with different AdC coverage, that the BE of the C1s peak E B F varies by as much as 1.44eV. This is a factor of 10 more than the typical resolvable difference between two chemical states of the same element, which makes BE referencing against the C1s peak highly unreliable. Surprisingly, we find that C1s shifts correlate to changes in sample work function S A , such that the sum E B F + S A is constant at 289.50±0.15eV, irrespective of materials system and air exposure time, indicating vacuum level alignment. This discovery allows for significantly better accuracy of chemical state determination than offered by the conventional methods. Our findings are not specific to nitrides and likely apply to all systems in which charge transfer at the AdC/substrate interface is negligible.
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•C 1 s peak of adventitious carbon (AdC) is often used for binding energy (BE) referencing in XPS.•We analyze AdC layers on 360 samples comprising different materials systems.•BE of C ...1 s peak EBF varies by 2.89 eV depending on the substrate.•EBF of C 1 s peak correlates to the sample work function ϕSA: EBF+ϕSA = constant.•Electronic levels of the AdC layer align to the vacuum level.•Complementary measurement of ϕSA is necessary for BE referencing based on C 1 s peak.
The correct referencing of the binding energy scale is essential for the accuracy of chemical analysis by X-ray photoelectron spectroscopy. The C 1s C–C/C–H peak from adventitious carbon (AdC), most commonly used for that purpose, was previously shown to shift by several eVs following changes in the sample work function ϕSA, thus indicating that AdC aligns to the sample vacuum level (VL). Here, results from a much larger sample set including 360 specimens comprising metals, nitrides, carbides, borides, oxides, carbonitrides, and oxynitrides are presented. Irrespective of the material system the C 1s peak of AdC is found to follow changes in ϕSA fully confirming previous results. Several observations exclude differential charging as plausible explanation for the C 1s peak shifts. All experimental evidence points instead to the VL alignment at the AdC/sample interface as the main reason. Should the C 1s peak of AdC be used for spectra referencing the measurement of sample work function is necessary, irrespective of whether samples are measured grounded or insulated from the spectrometer.
AlMgB
14
coatings have been deposited by DC magnetron sputtering from elemental targets on Si (001), Al
2
O
3
(0001) and MgO (001) substrates at temperatures in the range of 25–350 °C. The structural ...and mechanical properties of AlMgB
14
films were characterized by X-ray diffraction, scanning electron microscopy, nanoindentation, and analyzed as a function of deposition conditions and substrate materials. The results show that all films are X-ray amorphous, and the mechanical properties of the deposited films depend on the substrate and growth temperature. AlMgB
14
thin films deposited at 350 °C are found to have smoother surfaces and containing more well-formed B
12
icosahedra than the films deposited at lower temperature, which consequently increase the hardness of the deposited films. The maximum hardness and Young’s modulus of the as-deposited films are about 32.3 GPa and 310 GPa, respectively, for films deposited on Al
2
O
3
substrate at 350 °C.
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