X-Ray Photoelectron Spectroscopy
What is XPS ?
XPS is a surface analysis technique used to obtain chemical information about the surfaces of solids. Thanks to XPS, the% distribution of the atomic composition on the surface, the stoichiometric ratios of the atomic composition on the surface, the rate of change in the atomic composition of the surface, and many other surface analyzes are used. In the analysis with XPS, measured binding energy values and chemical shift values are used (Ertan, 2020).
How XPS Works ?
1. On the sample to be characterized, when an accelerated x-ray hits, the electron is thrown from the layer close to the nucleus.
2. The energy of this electron depends on the fast electron or x-ray photon energy that forms it.
3. Sum, the method of surface analysis by determining the energy of this photoelectron is called XPS. It provides scattering of photoelectrons using an x-ray beam that stimulates solid samples (Uslu, 2013).
Result & Discussion
XPS study of the films was done to investigate whether there are different types of thin films. After X-ray photoelectron spectroscopy, detailed high resolution spectra were created for Zn2p, N1 and O1 level regions. In addition, a depth analysis study was carried out on zinc nitride films to question the existence of different species at different levels in the film. The film was moved with low energy Ar ions for about 30 seconds until the substrate interface was reached. After the procedures, high resolution XPS spectra of regions at Zn2p, N1 and O1 levels were observed. Figure 1 shows the screening of the film enlarged to 0.60 in N2 / Ar ratio. The spectrum shows the presence of Zn2p, O1s, N1s and C1s regions. The carbon peak arises because of the hydrocarbon contaminants that accumulate before and after growth of the sample into XPS. The C1s peak at 284.8 eV was used as a binding energy reference.Due to the rotational trajectory, the level of Zn2p is divided into two peaks Zn2p3 / 2 and Zn2p1 / 2.
The high resolution XPS spectrum of the Zn2p3 / 2 level region formed after 30 seconds of mobility is as in Figure 2. It was observed that the N1s peak was located at 395.8 eV, which showed a large chemical shift compared to the N2 peak, at 395.8 eV.
In particular, this showed that Zn — N bonds were formed, but another small peak was observed around 402 eV due to N — N bond formation in the film.It was observed that the N1 peak shifted towards the low binding energy for the deeper spectra in the film.
In Figure 3, an increase in the O1 peak at different etching levels was observed. No chemical shift of the O1 peak was observed for the deeper spectra taken in the film (Haider, 2017).
Finally, XPS only detects electrons escaping from the sample to the vacuum of the instrument and delivers them to the detector. To escape from the sample to vacuum, a photoelectron must pass through the sample. In summary, in the XPS studies, the formation of Zn-N bonds was confirmed and it was determined that the density of the N1s peak decreased in the depth profile and the peak density of O1 increased in the film. This indicates that more nitrogen gaps are formed at the beginning of the film, and atmospheric oxygen eliminated these gaps (Zhang,2017).
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Thanks & REFERENCES
Ertan,Y. (2020). Fotoelektrik olay
Retrieved from https://evrimagaci.org/fotoelektrik-etki-fotoelektrik-olay-nedir-8225
Graham,J. (2018). Notable Applications
Retrieved from https://www.nist.gov/laboratories/tools-instruments/x-ray-photoelectron-spectroscopy
Haider, M. XPS Depth Profile Analysis of Zn3N2 Thin Films Grown at Different N2/Ar Gas Flow Rates by RF Magnetron Sputtering. Nanoscale Res Lett 12, 5 (2017).
Retrieved from https://nanoscalereslett.springeropen.com/articles/10.1186/s11671-016-1769-y
Uslu, M. (2013). X-Işını Fotoelektron Spektrometresi
Retrieved from https://www.slideshare.net/iuslu/xn-fotoelektron-spektroskopisi
Zhang, Y., Lin, N., Li, Y. et al. The isotype ZnO/SiC heterojunction prepared by molecular beam epitaxy — A chemical inert interface with significant band discontinuities. Sci Rep 6, 23106 (2016).
Retrieved from https://www.nature.com/articles/srep23106
