Specific Process Knowledge/Characterization/XPS/NexsaOverview: Difference between revisions
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|LMdocAuthor=SR Bare | |LMdocAuthor=SR Bare | ||
|docLink=https://doi.org/10.1016/j.susc.2015.10.048 | |docLink=https://doi.org/10.1016/j.susc.2015.10.048 | ||
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|Sample=Zeolites, Metal oxides | |Sample=Zeolites, Metal oxides | ||
|Abstract=The surface Si/Al ratio in a series of zeolite Y samples has been obtained using laboratory XPS, synchrotron (variable kinetic energy) XPS, and low energy ion scattering (LEIS) spectroscopy. The non-destructive depth profile obtained using variable kinetic energy XPS is compared to that from the destructive argon ion bombardment depth profile from the lab XPS instrument. All of the data indicate that the near surface region of both the ammonium form and steamed Y zeolites is strongly enriched in aluminum. It is shown that when the inelastic mean free path of the photoelectrons is taken into account the laboratory XPS of aluminosilicates zeolites does not provide a true measurement of the surface stoichiometry, while variable kinetic energy XPS results in a more surface sensitive measurement. A comprehensive Si/Al concentration profile as a function of depth is developed by combining the data from the three surface characterization techniques. The LEIS spectroscopy reveals that the topmost atomic layer is further enriched in Al compared to subsequent layers. | |Abstract=The surface Si/Al ratio in a series of zeolite Y samples has been obtained using laboratory XPS, synchrotron (variable kinetic energy) XPS, and low energy ion scattering (LEIS) spectroscopy. The non-destructive depth profile obtained using variable kinetic energy XPS is compared to that from the destructive argon ion bombardment depth profile from the lab XPS instrument. All of the data indicate that the near surface region of both the ammonium form and steamed Y zeolites is strongly enriched in aluminum. It is shown that when the inelastic mean free path of the photoelectrons is taken into account the laboratory XPS of aluminosilicates zeolites does not provide a true measurement of the surface stoichiometry, while variable kinetic energy XPS results in a more surface sensitive measurement. A comprehensive Si/Al concentration profile as a function of depth is developed by combining the data from the three surface characterization techniques. The LEIS spectroscopy reveals that the topmost atomic layer is further enriched in Al compared to subsequent layers. | ||
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|LMdocID=5391 | |||
| | |LMdocTitle=Surface composition analysis by low-energy ion scattering | ||
| | |LMdocType=Publication, background | ||
|LMdocAuthor=H H Brongersma | |||
| | |docLink=https://doi.org/10.1016/j.surfrep.2006.12.002 | ||
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|Abstract=Low-energy ion scattering (LEIS) is an analytical tool that provides information on the atomic composition of the outer surface, when noble gas ions are used as projectiles. In fact, quantitative composition analysis is currently done on a huge variety of materials, including catalysts and organic materials. The information on the surface composition is contained in the signal of backscattered ions (typically 1–3 keV He+, Ne+). In order to translate the LEIS signal to an elemental surface concentration all factors determining the LEIS signal must be known. These are in particular the scattering cross section and the ion fraction of the backscattered particles. The scattering cross section, which is due to the screened electrostatic potential between target atom and projectile, is well-known for the prevailing conditions of LEIS. It is an intriguing fact that, despite the large quantity of successful applications, the charge exchange processes in LEIS are not yet fully understood. It is e.g. not known why in LEIS for a given atomic species on the surface the signal usually does not depend on which other species are present (absence of matrix effects). Significant progress has recently been made in the understanding of the underlying charge exchange processes. Therefore, the aim of this review is twofold: on the one hand, to summarize the present understanding of the factors that determine the ion fraction of the scattered projectiles in LEIS, i.e. charge exchange processes. On the other hand, to summarize how quantitative surface composition analysis can be accomplished. In addition, we critically review publications that deal with surface composition analysis by LEIS, and analyze in which cases and by what means this was achieved and where and why it was successful or failed. After reading this review the reader will be able to deal with the pitfalls encountered in LEIS and to choose preferred experimental conditions for quantitative surface composition analysis. | |||
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|LMdocID=5393 | |||
|LMdocTitle=Diffusion of In<sub>0.53</sub>Ga<sub>0.47</sub>As elements through hafnium oxide during post deposition annealing | |||
|LMdocType=Publication | |||
|LMdocAuthor=W Cabrera | |||
|docLink=https://doi.org/10.1063/1.4860960 | |||
|XPSused=x |UPSused= |ISSused=x |REELSused= |Ramanused= | |||
|AdditionalOption=TEM | |||
|Sample=HfO2, InGaAs, ALD | |||
|Abstract=Diffusion of indium through HfO2 after post deposition annealing in N2 or forming gas environments is observed in HfO2/In0.53Ga0.47As stacks by low energy ion scattering and X-ray photo electron spectroscopy and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, arsenic oxide is detected at the surface of atomic layer deposition-grown HfO2 and is desorbed upon annealing at 350 degree C. Reduction of the interfacial layer thickness and potential densification of HfO2, resulting from indium diffusion upon annealing, is confirmed by an increase in capacitance. | |||
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|LMdocID=5394 | |||
|LMdocTitle=Low energy ion scattering (LEIS). A practical introduction to its theory, instrumentation, and applications | |||
|LMdocType=Publication, review | |||
|LMdocAuthor=C V Cushman | |||
|docLink=https://doi.org/10.1016/j.apsusc.2018.04.127 | |||
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|Abstract=Low energy ion scattering (LEIS) probes the elemental composition of the outermost atomic layer of a material and provides static depth profiles of the outer ca. 10 nm of surfaces. Its extreme surface sensitivity and quantitative nature make it a powerful tool for studying the relationships between surface chemistry and surface related phenomena such as wetting, adhesion, contamination, and thin film growth. The high depth resolution obtained in LEIS in its static and sputter depth profile modes are useful for studying the layer structures of thin films. LEIS instrumentation has improved significantly in recent years, showing dramatic increases in its sensitivity and further expanding its potential applications. In this article, we provide a practical introduction to the technique, including a discussion of the basic theory of LEIS, LEIS spectra, LEIS instrumentation, and LEIS applications, including catalysts, solid oxide fuel cells (SOFCs), and thin films in integrated circuits. | |||
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|LMdocID=5397 | |||
|LMdocTitle=HfO<sub>2</sub> on MoS<sub>2</sub> by Atomic Layer Deposition: Adsorption Mechanisms and Thickness Scalability | |||
|LMdocType=Publication | |||
|LMdocAuthor=S McDonnell | |||
|docLink=https://doi.org/10.1016/j.apsusc.2018.04.127 | |||
|XPSused= |UPSused= |ISSused= |REELSused= |Ramanused= | |||
|AdditionalOption=AFM, ALD | |||
|Sample=HfO2, MoS2 | |||
|Abstract=We report our investigation of the atomic layer deposition(ALD) of HfO<sub>2</sub> on the MoS<sub>2</sub> surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO<sub>2</sub> and MoS<sub>2</sub> is detected. We highlight that individual precursors do not permanently adsorb on the clean MoS<sub>2</sub> surface but that organic and solvent residues can dramatically change ALD nucleation behavior. We then posit that prior reports of conformal ALD deposition on MoS<sub>2</sub> flakes that had been exposed to such organics and solvents likely rely on contamination-mediated nucleation. These results highlight that surface functionalization will be required before controllable and low defect density high-κ/MoS<sub>2</sub> interfaces will be realized. The band structure of the HfO<sub>2</sub>/MoS<sub>2</sub> system is experimentally derived with valence and conduction band offsets found to be 2.67 and 2.09 eV, respectively. | |||
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| [[media:Prusa-2015-Highly-sensitive-detection-of-surfa.pdf | Highly Sensitive Detection of Surface and Intercalated Impurities in Graphene by LEIS]]||Publication||S Prusa||[http://apps.webofknowledge.com.proxy.findit.dtu.dk/CitedFullRecord.do?product=WOS&colName=WOS&SID=F6P8vdNQigRKywglhCq&search_mode=CitedFullRecord&isickref=WOS:000361087000013 link]||||||X||||||||graphene||<span title="Low-energy ion scattering (LEIS) is known for its extreme surface sensitivity, as it yields a quantitative analysis of the outermost surface as well as highly resolved in-depth information for ultrathin surface layers. Hence, it could have been generally considered to be a suitable technique for the analysis of graphene samples. However, due to the low scattering cross section for light elements such as carbon, LEIS has not become a common technique for the characterization of graphene. In the present study we use a high-sensitivity LEIS instrument with parallel energy analysis for the characterization of CVD graphene transferred to thermal silica/silicon substrates. Thanks to its high sensitivity and the exceptional depth resolution typical of LEIS, the graphene layer closure was verified, and different kinds of contaminants were detected, quantified, and localized within the graphene structure. Utilizing the extraordinarily strong neutralization of helium by carbon atoms in graphene, LEIS experiments performed at several primary ion energies permit us to distinguish carbon in graphene from that in nongraphitic forms (e.g., the remains of a resist). Furthermore, metal impurities such as Fe, Sn, and Na located at the graphene−silica interface (intercalated) are detected, and the coverages of Fe and Sn are determined. Hence, high-resolution LEIS is capable of both checking the purity of graphene surfaces and detecting impurities incorporated into graphene layers or their interfaces. Thus, it is a suitable method for monitoring the quality of the whole fabrication process of graphene, including its transfer on various substrates."> Abstract</span> | | [[media:Prusa-2015-Highly-sensitive-detection-of-surfa.pdf | Highly Sensitive Detection of Surface and Intercalated Impurities in Graphene by LEIS]]||Publication||S Prusa||[http://apps.webofknowledge.com.proxy.findit.dtu.dk/CitedFullRecord.do?product=WOS&colName=WOS&SID=F6P8vdNQigRKywglhCq&search_mode=CitedFullRecord&isickref=WOS:000361087000013 link]||||||X||||||||graphene||<span title="Low-energy ion scattering (LEIS) is known for its extreme surface sensitivity, as it yields a quantitative analysis of the outermost surface as well as highly resolved in-depth information for ultrathin surface layers. Hence, it could have been generally considered to be a suitable technique for the analysis of graphene samples. However, due to the low scattering cross section for light elements such as carbon, LEIS has not become a common technique for the characterization of graphene. In the present study we use a high-sensitivity LEIS instrument with parallel energy analysis for the characterization of CVD graphene transferred to thermal silica/silicon substrates. Thanks to its high sensitivity and the exceptional depth resolution typical of LEIS, the graphene layer closure was verified, and different kinds of contaminants were detected, quantified, and localized within the graphene structure. Utilizing the extraordinarily strong neutralization of helium by carbon atoms in graphene, LEIS experiments performed at several primary ion energies permit us to distinguish carbon in graphene from that in nongraphitic forms (e.g., the remains of a resist). Furthermore, metal impurities such as Fe, Sn, and Na located at the graphene−silica interface (intercalated) are detected, and the coverages of Fe and Sn are determined. Hence, high-resolution LEIS is capable of both checking the purity of graphene surfaces and detecting impurities incorporated into graphene layers or their interfaces. Thus, it is a suitable method for monitoring the quality of the whole fabrication process of graphene, including its transfer on various substrates."> Abstract</span> | ||
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