Limits...
Low-temperature fabrication of layered self-organized Ge clusters by RF-sputtering.

Pinto SR, Rolo AG, Buljan M, Chahboun A, Bernstorff S, Barradas NP, Alves E, Kashtiban RJ, Bangert U, Gomes MJ - Nanoscale Res Lett (2011)

Bottom Line: In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures.The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution.The crystallization of the clusters was achieved at annealing temperature of 700°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, University of Minho, 4710-057 Braga, Portugal. sarapinto@fisica.uminho.pt.

ABSTRACT
In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.

No MeSH data available.


Related in: MedlinePlus

Raman spectra of as-deposited and annealed multilayers. (a) Raman spectra of the as-deposited and annealed multilayers at temperatures indicated in the figure. The spectra are normalized to the intensity of Si-substrate peak at 520 cm-1. (b) The same spectra after the subtraction of Si substrate contribution. Dashed lines show the positions of peaks of amorphous Ge (a-Ge), crystalline Ge (c-Ge), and Si-Ge vibrational modes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211430&req=5

Figure 5: Raman spectra of as-deposited and annealed multilayers. (a) Raman spectra of the as-deposited and annealed multilayers at temperatures indicated in the figure. The spectra are normalized to the intensity of Si-substrate peak at 520 cm-1. (b) The same spectra after the subtraction of Si substrate contribution. Dashed lines show the positions of peaks of amorphous Ge (a-Ge), crystalline Ge (c-Ge), and Si-Ge vibrational modes.

Mentions: We employed Raman spectroscopy which is a very effective tool to study the crystalline structure and the stoichiometry of the nanoparticles. Figure 5a shows the Raman spectra of the as-deposited, annealed multilayers and Si substrate, and Figure 5b shows the same spectra after the subtraction of Si substrate contribution. The as-grown multilayer shows a broad band near to 270 cm-1, which is characteristic of amorphous Ge [16]. The samples annealed at 700 and 800°C show strong peaks at 292 and 295 cm-1, respectively. These peaks show existence of crystalline Ge (c-Ge) nanoparticles in the film. The peaks are slightly red-shifted and asymmetrically broadened with respect to the Ge bulk peak (300.4 cm-1) because of the phonon confinement in the nano-sized particles [17]. The shifts are in accordance with the results of GISAXS analysis showing formation of Ge clusters with radii of 2.5 and 3.8 nm for the films annealed at 700 and 800°C, respectively. A small peak coming from the Si substrate exists near to 304 cm-1; however, for the annealed samples, this peak is associated to Ge NCs. The samples annealed at 1000°C do not show any Raman peak because of NCs, and only the Raman signal arising from the silicon substrate is observed. This absence of Raman peak can be attributed to the loss of Ge atoms during the annealing. We have already observed a total loss of Ge atoms from the Al2O3 film during thermal treatments, because of the volatilization of Ge mono-oxide (GeO) [18]. In the present case, the loss of Ge is partial, since RBS spectra of the samples reveal the presence of Ge atoms in the layers near the interface film-substrate. The lack of the presence of for any Raman feature can be interpreted as a consequence of the decrease in the amount of material inside the scattering volume. Rodriguez et al. [14] observed a similar behavior, and concluded that, after a certain annealing temperature, the compositional changes due to the out-diffusion of Ge from the crystallized nanoparticles and the associated reduction of the scattering volume cause the NCs to fall below the detection limit of the Raman setup, thus accounting for the disappearance of the Raman signal. The observed absence of Si-Ge and Si-Si Raman peaks for the annealed samples could be explained by the low amount of Si used during the growth and/or a loss of Si atoms during the thermal treatments, which can oxidize and form SiO2.


Low-temperature fabrication of layered self-organized Ge clusters by RF-sputtering.

Pinto SR, Rolo AG, Buljan M, Chahboun A, Bernstorff S, Barradas NP, Alves E, Kashtiban RJ, Bangert U, Gomes MJ - Nanoscale Res Lett (2011)

Raman spectra of as-deposited and annealed multilayers. (a) Raman spectra of the as-deposited and annealed multilayers at temperatures indicated in the figure. The spectra are normalized to the intensity of Si-substrate peak at 520 cm-1. (b) The same spectra after the subtraction of Si substrate contribution. Dashed lines show the positions of peaks of amorphous Ge (a-Ge), crystalline Ge (c-Ge), and Si-Ge vibrational modes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211430&req=5

Figure 5: Raman spectra of as-deposited and annealed multilayers. (a) Raman spectra of the as-deposited and annealed multilayers at temperatures indicated in the figure. The spectra are normalized to the intensity of Si-substrate peak at 520 cm-1. (b) The same spectra after the subtraction of Si substrate contribution. Dashed lines show the positions of peaks of amorphous Ge (a-Ge), crystalline Ge (c-Ge), and Si-Ge vibrational modes.
Mentions: We employed Raman spectroscopy which is a very effective tool to study the crystalline structure and the stoichiometry of the nanoparticles. Figure 5a shows the Raman spectra of the as-deposited, annealed multilayers and Si substrate, and Figure 5b shows the same spectra after the subtraction of Si substrate contribution. The as-grown multilayer shows a broad band near to 270 cm-1, which is characteristic of amorphous Ge [16]. The samples annealed at 700 and 800°C show strong peaks at 292 and 295 cm-1, respectively. These peaks show existence of crystalline Ge (c-Ge) nanoparticles in the film. The peaks are slightly red-shifted and asymmetrically broadened with respect to the Ge bulk peak (300.4 cm-1) because of the phonon confinement in the nano-sized particles [17]. The shifts are in accordance with the results of GISAXS analysis showing formation of Ge clusters with radii of 2.5 and 3.8 nm for the films annealed at 700 and 800°C, respectively. A small peak coming from the Si substrate exists near to 304 cm-1; however, for the annealed samples, this peak is associated to Ge NCs. The samples annealed at 1000°C do not show any Raman peak because of NCs, and only the Raman signal arising from the silicon substrate is observed. This absence of Raman peak can be attributed to the loss of Ge atoms during the annealing. We have already observed a total loss of Ge atoms from the Al2O3 film during thermal treatments, because of the volatilization of Ge mono-oxide (GeO) [18]. In the present case, the loss of Ge is partial, since RBS spectra of the samples reveal the presence of Ge atoms in the layers near the interface film-substrate. The lack of the presence of for any Raman feature can be interpreted as a consequence of the decrease in the amount of material inside the scattering volume. Rodriguez et al. [14] observed a similar behavior, and concluded that, after a certain annealing temperature, the compositional changes due to the out-diffusion of Ge from the crystallized nanoparticles and the associated reduction of the scattering volume cause the NCs to fall below the detection limit of the Raman setup, thus accounting for the disappearance of the Raman signal. The observed absence of Si-Ge and Si-Si Raman peaks for the annealed samples could be explained by the low amount of Si used during the growth and/or a loss of Si atoms during the thermal treatments, which can oxidize and form SiO2.

Bottom Line: In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures.The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution.The crystallization of the clusters was achieved at annealing temperature of 700°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physics Department, University of Minho, 4710-057 Braga, Portugal. sarapinto@fisica.uminho.pt.

ABSTRACT
In this article, we present an investigation of (Ge + SiO2)/SiO2 multilayers deposited by magnetron sputtering and subsequently annealed at different temperatures. The structural properties were investigated by transmission electron microscopy, grazing incidence small angles X-ray scattering, Rutherford backscattering spectrometry, Raman, and X-ray photoelectron spectroscopies. We show a formation of self-assembled Ge clusters during the deposition at 250°C. The clusters are ordered in a three-dimensional lattice, and they have very small sizes (about 3 nm) and narrow size distribution. The crystallization of the clusters was achieved at annealing temperature of 700°C.

No MeSH data available.


Related in: MedlinePlus