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Investigations of ripple pattern formation on Germanium surfaces using 100-keV Ar(+) ions.

Sulania I, Agarwal D, Husain M, Avasthi DK - Nanoscale Res Lett (2015)

Bottom Line: The formation of nanoripples initiates at an angle of θ ~ 45°.Ripple pattern formation has taken place on the Ge surface in the energy regime of 100 keV as compared to the other reports which had been carried out using very low energy ions.Raman spectra reveal that the near surface of crystalline Ge samples becomes amorphous due to interaction of Ar(+) ions due to creation of defects through collision cascades.

View Article: PubMed Central - PubMed

Affiliation: Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi, 110067 India ; Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025 India.

ABSTRACT
We have investigated the formation of nanoripples on the surface of germanium, Ge(100), due to the effect of 100-keV Ar (+) ion irradiation. The irradiation was carried out at different incidence angles from 0° to 75° in steps of 15° with respect to the surface normal with a fixed ion fluence of approximately 3 × 10(17) ions/cm(2). Atomic force micrographs show an increase in surface roughness from 0.5 to 4.3 nm for the pristine sample and the sample irradiated at 60° incidence angle due to cos(-1)(θ) dependence on sputtering yield. With increase in angle of incidence, there is transition observed from nanodots to aligned nanodots perpendicular to the direction of the beam. There is an increase in size of the nanostructures observed from 44 to 103 nm with angle of incidence. The formation of nanoripples initiates at an angle of θ ~ 45°. Ripple pattern formation has taken place on the Ge surface in the energy regime of 100 keV as compared to the other reports which had been carried out using very low energy ions. Raman spectra reveal that the near surface of crystalline Ge samples becomes amorphous due to interaction of Ar(+) ions due to creation of defects through collision cascades.

No MeSH data available.


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Schematic representation of ion beam falling at different angles with respect to surface normal onto Ge surface. (a) 0°, (b) 30°, and (c) 60°.
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Fig6: Schematic representation of ion beam falling at different angles with respect to surface normal onto Ge surface. (a) 0°, (b) 30°, and (c) 60°.

Mentions: The Raman analysis shows that as the angle of incidences was increased, the thickness of the amorphous layer decreases due to lesser penetration depth of the Ar+ ion inside Ge. The amorphous Ge peak does not shift with change in angle of incidence which indicates that no strain is developed in the samples upon irradiation. Since, the range of 100-keV Ar+ ions inside Ge is approximately 72 nm [30] and the penetration depth of the Ar ion laser with a wavelength of 514 nm is about 20 nm [35,36], the crystalline Ge peak is not observed for the case of irradiated samples. The schematic representation of the ion beam penetrating the Ge sample at three different incidence angles is shown in Figure 6. The incident beam strikes the sample surface at an angle (θ) with respect to the surface normal. In particular, it is shown that three samples are irradiated with the same Ar+ ion fluence or dose but at different incidence angles (0°, 30°, and 60°) with respect to the surface normal. Figure 6 shows the top views of the corresponding schematic and represents the formation of nanostructures on the surface. The thickness of the amorphous layer is higher in the case of normal incidence irradiation as shown in Figure 6a because of the higher projected ion range for 0° as compared to higher angle. At normal ion beam irradiation, the dots are formed in an irregular symmetry due to the random strike of ions on the sample surface, and as the angle of irradiation is increased, the alignment of dots has been observed in the direction perpendicular to the beam direction (Figure 6b) which is more pronounced for the case of higher angle as visible in Figure 6c. As the angle of irradiation is increased, the thickness of the amorphous layer decreases which is scaled with the intensity of the Raman peak in Figure 5. Decrement in relative intensity of the a-Ge peak in Raman clearly indicates the lesser thickness of the amorphous layer at higher angles as represented by the schematic in Figure 6. The Raman analysis qualitatively depicted the reduction in thickness of the amorphous layer with increase in ion beam irradiation angle, as we are only getting the signal from the amorphous or modified layer of the Ge surface due to ion irradiation which becomes lesser for higher incidence angles. The signal from the bulk or unmodified Ge is missing in the irradiated samples due to less penetration of the 514-nm Ar laser used in the Raman characterization.Figure 6


Investigations of ripple pattern formation on Germanium surfaces using 100-keV Ar(+) ions.

Sulania I, Agarwal D, Husain M, Avasthi DK - Nanoscale Res Lett (2015)

Schematic representation of ion beam falling at different angles with respect to surface normal onto Ge surface. (a) 0°, (b) 30°, and (c) 60°.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385137&req=5

Fig6: Schematic representation of ion beam falling at different angles with respect to surface normal onto Ge surface. (a) 0°, (b) 30°, and (c) 60°.
Mentions: The Raman analysis shows that as the angle of incidences was increased, the thickness of the amorphous layer decreases due to lesser penetration depth of the Ar+ ion inside Ge. The amorphous Ge peak does not shift with change in angle of incidence which indicates that no strain is developed in the samples upon irradiation. Since, the range of 100-keV Ar+ ions inside Ge is approximately 72 nm [30] and the penetration depth of the Ar ion laser with a wavelength of 514 nm is about 20 nm [35,36], the crystalline Ge peak is not observed for the case of irradiated samples. The schematic representation of the ion beam penetrating the Ge sample at three different incidence angles is shown in Figure 6. The incident beam strikes the sample surface at an angle (θ) with respect to the surface normal. In particular, it is shown that three samples are irradiated with the same Ar+ ion fluence or dose but at different incidence angles (0°, 30°, and 60°) with respect to the surface normal. Figure 6 shows the top views of the corresponding schematic and represents the formation of nanostructures on the surface. The thickness of the amorphous layer is higher in the case of normal incidence irradiation as shown in Figure 6a because of the higher projected ion range for 0° as compared to higher angle. At normal ion beam irradiation, the dots are formed in an irregular symmetry due to the random strike of ions on the sample surface, and as the angle of irradiation is increased, the alignment of dots has been observed in the direction perpendicular to the beam direction (Figure 6b) which is more pronounced for the case of higher angle as visible in Figure 6c. As the angle of irradiation is increased, the thickness of the amorphous layer decreases which is scaled with the intensity of the Raman peak in Figure 5. Decrement in relative intensity of the a-Ge peak in Raman clearly indicates the lesser thickness of the amorphous layer at higher angles as represented by the schematic in Figure 6. The Raman analysis qualitatively depicted the reduction in thickness of the amorphous layer with increase in ion beam irradiation angle, as we are only getting the signal from the amorphous or modified layer of the Ge surface due to ion irradiation which becomes lesser for higher incidence angles. The signal from the bulk or unmodified Ge is missing in the irradiated samples due to less penetration of the 514-nm Ar laser used in the Raman characterization.Figure 6

Bottom Line: The formation of nanoripples initiates at an angle of θ ~ 45°.Ripple pattern formation has taken place on the Ge surface in the energy regime of 100 keV as compared to the other reports which had been carried out using very low energy ions.Raman spectra reveal that the near surface of crystalline Ge samples becomes amorphous due to interaction of Ar(+) ions due to creation of defects through collision cascades.

View Article: PubMed Central - PubMed

Affiliation: Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi, 110067 India ; Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025 India.

ABSTRACT
We have investigated the formation of nanoripples on the surface of germanium, Ge(100), due to the effect of 100-keV Ar (+) ion irradiation. The irradiation was carried out at different incidence angles from 0° to 75° in steps of 15° with respect to the surface normal with a fixed ion fluence of approximately 3 × 10(17) ions/cm(2). Atomic force micrographs show an increase in surface roughness from 0.5 to 4.3 nm for the pristine sample and the sample irradiated at 60° incidence angle due to cos(-1)(θ) dependence on sputtering yield. With increase in angle of incidence, there is transition observed from nanodots to aligned nanodots perpendicular to the direction of the beam. There is an increase in size of the nanostructures observed from 44 to 103 nm with angle of incidence. The formation of nanoripples initiates at an angle of θ ~ 45°. Ripple pattern formation has taken place on the Ge surface in the energy regime of 100 keV as compared to the other reports which had been carried out using very low energy ions. Raman spectra reveal that the near surface of crystalline Ge samples becomes amorphous due to interaction of Ar(+) ions due to creation of defects through collision cascades.

No MeSH data available.


Related in: MedlinePlus