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Nondestructive analysis of single crystals of selenide spinels by X-ray spectrometry techniques.

Malicka E, Sitko R, Zawisza B, Heimann J, Kajewski D, Kita A - Anal Bioanal Chem (2010)

Bottom Line: If the measured single crystal is precisely positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel.In case of the XPS analysis, the accuracy of results depends on the proper preparation of the sample surface.The ion etching, commonly used for cleaning the surface, leads to preferential sputtering; therefore, the reliable results cannot be obtained.

View Article: PubMed Central - PubMed

Affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland. ewa.malicka@us.edu.pl

ABSTRACT
The paper presents possibilities and difficulties in nondestructive analysis of small multielement single crystals performed by means of X-ray spectrometry techniques: micro-X-ray fluorescence spectrometry (μ-XRF), energy-dispersive electron probe microanalysis (ED-EPMA), and X-ray photoelectron spectroscopy (XPS). The capability of the X-ray spectroscopy techniques in elemental analysis is demonstrated with the single crystals of selenide spinels of the general formula M(x)N(y)Cr(z)Se(4) (M(+2) and N(+3) are, for example, Zn(+2), V(+3), Ga(+3), Cd(+2), In(+3), and Sb(+3)). The results of the nondestructive analyses (μ-XRF, ED-EPMA, and XPS) are compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) and wavelength-dispersive X-ray spectrometry (WDXRF) following sample digestion. The present study shows satisfactory agreement between the results of μ-XRF analysis performed using the standardless fundamental parameter method and the results obtained with the WDXRF and ICP-OES analyses. If the measured single crystal is precisely positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel. The reliable results of ED-EPMA can be obtained only if the measured area is sufficiently large, i.e., of 200 × 300 μm. Even if this condition is fulfilled, the relative difference between the ED-EPMA and the wet analysis may reach 10% rel. In case of the XPS analysis, the accuracy of results depends on the proper preparation of the sample surface. It should be free of contamination that can be obtained by scraping in situ in ultrahigh vacuum. The ion etching, commonly used for cleaning the surface, leads to preferential sputtering; therefore, the reliable results cannot be obtained.

No MeSH data available.


Chromium 2p core levels for the contamination-free crystal fresh surface obtained by scrapping in ultrahigh vacuum and after sputtering. The surface deterioration by sputtering reveals as a disappearance of the 2p3/2 peak splitting
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Fig6: Chromium 2p core levels for the contamination-free crystal fresh surface obtained by scrapping in ultrahigh vacuum and after sputtering. The surface deterioration by sputtering reveals as a disappearance of the 2p3/2 peak splitting

Mentions: Considering further possibility of the nondestructive characterization of the selenide spinel crystals, the XPS method was also applied. XPS gives information only from the outer surface of the sample (up to approximately 10 nm); therefore, to evaluate the effect of the surface preparation on the results of analysis, two modes of measurements were checked. First, the chemical composition was analyzed based on the spectrum detected from the sample without previous surface cleaning (after about 1 h in vacuum, the first measurement was made and revealed at dirt surface, in atomic percents, 80.1% C, 16.4% O, 2.4% Se, 0.4% Cr, 0.4% Zn, 0.2% N, and 0.1% Cd). Next, the sample with a fresh surface obtained by scraping in situ in 10−10-hPa vacuum was measured (that time the composition was 62.4% Se, 22.1% Cr, 11.4% Zn, and 4.1% Cd, the contamination, i.e., C, O, and N, was less than 0.1%). Table 6 shows the results for Zn0.81Cd0.20Cr1.99Se4 crystal obtained with and without surface scraping; for comparison consistency in calculations for dirt surface, we omit contamination (C, O, and N). For comparison, the results of the μ-XRF, ED-EPMA, and wet analysis are also given. It turned out that the reliable chemical composition can be obtained only if the measurement is made for the fresh surface prepared by scraping in situ in 10−10-hPa vacuum. The accuracy of 10% is typically quoted for atomic concentrations routinely determined from the XPS experiments. However, the quantitative chemical analysis relies on several factors; therefore, standard assumptions may result in enormous errors in quantification [19, 20]. Also, the contamination of the surface is a source of serious errors. The best method in obtaining a free of contamination fresh surface is cleaving or scraping the crystal in situ in ultrahigh vacuum. The ion etching, commonly used for surface cleaning, may cause preferential sputtering in multielemental samples that leads to a change in their chemical composition. Besides, the investigations show that not only the preferential sputtering takes place (Fig. 5) but also some amount of contamination still remains. Moreover, in effect of the etching, the crystal surface may be deteriorated. The case is illustrated in Fig. 6, where the splitting of the 2p3/2 peak disappears after the sputtering. Moreover, a small broadening of the XPS bands is observed. The 2p3/2 peak splitting is typical for Cr3+ and can be observed only in the high-resolution measurements of surface of good-quality single crystals. The nature of the splitting is described in the literature [3].Table 6


Nondestructive analysis of single crystals of selenide spinels by X-ray spectrometry techniques.

Malicka E, Sitko R, Zawisza B, Heimann J, Kajewski D, Kita A - Anal Bioanal Chem (2010)

Chromium 2p core levels for the contamination-free crystal fresh surface obtained by scrapping in ultrahigh vacuum and after sputtering. The surface deterioration by sputtering reveals as a disappearance of the 2p3/2 peak splitting
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3044239&req=5

Fig6: Chromium 2p core levels for the contamination-free crystal fresh surface obtained by scrapping in ultrahigh vacuum and after sputtering. The surface deterioration by sputtering reveals as a disappearance of the 2p3/2 peak splitting
Mentions: Considering further possibility of the nondestructive characterization of the selenide spinel crystals, the XPS method was also applied. XPS gives information only from the outer surface of the sample (up to approximately 10 nm); therefore, to evaluate the effect of the surface preparation on the results of analysis, two modes of measurements were checked. First, the chemical composition was analyzed based on the spectrum detected from the sample without previous surface cleaning (after about 1 h in vacuum, the first measurement was made and revealed at dirt surface, in atomic percents, 80.1% C, 16.4% O, 2.4% Se, 0.4% Cr, 0.4% Zn, 0.2% N, and 0.1% Cd). Next, the sample with a fresh surface obtained by scraping in situ in 10−10-hPa vacuum was measured (that time the composition was 62.4% Se, 22.1% Cr, 11.4% Zn, and 4.1% Cd, the contamination, i.e., C, O, and N, was less than 0.1%). Table 6 shows the results for Zn0.81Cd0.20Cr1.99Se4 crystal obtained with and without surface scraping; for comparison consistency in calculations for dirt surface, we omit contamination (C, O, and N). For comparison, the results of the μ-XRF, ED-EPMA, and wet analysis are also given. It turned out that the reliable chemical composition can be obtained only if the measurement is made for the fresh surface prepared by scraping in situ in 10−10-hPa vacuum. The accuracy of 10% is typically quoted for atomic concentrations routinely determined from the XPS experiments. However, the quantitative chemical analysis relies on several factors; therefore, standard assumptions may result in enormous errors in quantification [19, 20]. Also, the contamination of the surface is a source of serious errors. The best method in obtaining a free of contamination fresh surface is cleaving or scraping the crystal in situ in ultrahigh vacuum. The ion etching, commonly used for surface cleaning, may cause preferential sputtering in multielemental samples that leads to a change in their chemical composition. Besides, the investigations show that not only the preferential sputtering takes place (Fig. 5) but also some amount of contamination still remains. Moreover, in effect of the etching, the crystal surface may be deteriorated. The case is illustrated in Fig. 6, where the splitting of the 2p3/2 peak disappears after the sputtering. Moreover, a small broadening of the XPS bands is observed. The 2p3/2 peak splitting is typical for Cr3+ and can be observed only in the high-resolution measurements of surface of good-quality single crystals. The nature of the splitting is described in the literature [3].Table 6

Bottom Line: If the measured single crystal is precisely positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel.In case of the XPS analysis, the accuracy of results depends on the proper preparation of the sample surface.The ion etching, commonly used for cleaning the surface, leads to preferential sputtering; therefore, the reliable results cannot be obtained.

View Article: PubMed Central - PubMed

Affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland. ewa.malicka@us.edu.pl

ABSTRACT
The paper presents possibilities and difficulties in nondestructive analysis of small multielement single crystals performed by means of X-ray spectrometry techniques: micro-X-ray fluorescence spectrometry (μ-XRF), energy-dispersive electron probe microanalysis (ED-EPMA), and X-ray photoelectron spectroscopy (XPS). The capability of the X-ray spectroscopy techniques in elemental analysis is demonstrated with the single crystals of selenide spinels of the general formula M(x)N(y)Cr(z)Se(4) (M(+2) and N(+3) are, for example, Zn(+2), V(+3), Ga(+3), Cd(+2), In(+3), and Sb(+3)). The results of the nondestructive analyses (μ-XRF, ED-EPMA, and XPS) are compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) and wavelength-dispersive X-ray spectrometry (WDXRF) following sample digestion. The present study shows satisfactory agreement between the results of μ-XRF analysis performed using the standardless fundamental parameter method and the results obtained with the WDXRF and ICP-OES analyses. If the measured single crystal is precisely positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel. The reliable results of ED-EPMA can be obtained only if the measured area is sufficiently large, i.e., of 200 × 300 μm. Even if this condition is fulfilled, the relative difference between the ED-EPMA and the wet analysis may reach 10% rel. In case of the XPS analysis, the accuracy of results depends on the proper preparation of the sample surface. It should be free of contamination that can be obtained by scraping in situ in ultrahigh vacuum. The ion etching, commonly used for cleaning the surface, leads to preferential sputtering; therefore, the reliable results cannot be obtained.

No MeSH data available.