Limits...
Nucleation and growth of primary nanostructures in SrTiO3 homoepitaxy.

Phark SH, Chang YJ - Nanoscale Res Lett (2015)

Bottom Line: Second, one-dimensional SrTiO3 islands of a 4 uc width grew along the crystal symmetry directions.These observations suggest that 4 × 4-uc (2) islands act as a minimum nucleation seed, and the addition of SrTiO3 molecular species of the same width is the primary and dominant growth process in SrTiO3 homoepitaxy.A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO3 islands.

View Article: PubMed Central - PubMed

Affiliation: Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul National University, Seoul, 151-747 Republic of Korea ; Department of Physics and Astronomy, Seoul National University, Seoul, 151-747 Republic of Korea.

ABSTRACT
SrTiO3 nanoislands on SrTiO3 (001) in a diffusion-limited growth regime were studied using in situ scanning tunneling microscopy (STM). The STM images revealed two characteristic features of nucleation stages. First, the minimum lateral size of the one-unit-cell (uc)-high SrTiO3 islands was 4 × 4 uc (2). Second, one-dimensional SrTiO3 islands of a 4 uc width grew along the crystal symmetry directions. These observations suggest that 4 × 4-uc (2) islands act as a minimum nucleation seed, and the addition of SrTiO3 molecular species of the same width is the primary and dominant growth process in SrTiO3 homoepitaxy. A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO3 islands.

No MeSH data available.


Related in: MedlinePlus

STM images for defect formations in the initial growth stage. (a) to (c) 20 × 20-nm2 STM images showing the formation of defects in the substrate surfaces of 1-, 2-, and 3-p samples, respectively. All STM images were obtained with VS = 2.0 V and Iset = 50 pA. The inset of (a) shows an STM image of the same area with the same length scale that was obtained using a different tip. The gray arrows indicate large white structures, which are 1-uc-high SrTiO3 islands. The red (blue) curve in (d) shows the STM apparent height profile along the red (blue) line in (a) ((b)). (e) FT power spectrum map of (a). The yellow circles show bright spots in the FT power spectrum at (1/2 0), which are indicative of 2 × 2 RC. (f) FT power spectrum map of (c). The bright spots indicated by the green circles at (1/4 0) correspond to a periodicity of 4 uc along the directions of crystal symmetry.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4385118&req=5

Fig3: STM images for defect formations in the initial growth stage. (a) to (c) 20 × 20-nm2 STM images showing the formation of defects in the substrate surfaces of 1-, 2-, and 3-p samples, respectively. All STM images were obtained with VS = 2.0 V and Iset = 50 pA. The inset of (a) shows an STM image of the same area with the same length scale that was obtained using a different tip. The gray arrows indicate large white structures, which are 1-uc-high SrTiO3 islands. The red (blue) curve in (d) shows the STM apparent height profile along the red (blue) line in (a) ((b)). (e) FT power spectrum map of (a). The yellow circles show bright spots in the FT power spectrum at (1/2 0), which are indicative of 2 × 2 RC. (f) FT power spectrum map of (c). The bright spots indicated by the green circles at (1/4 0) correspond to a periodicity of 4 uc along the directions of crystal symmetry.

Mentions: The STM images shown in Figure 2 also reveal that the changes in the island growth patterns were related to the substrate surface structures. Figure 3a shows STM images of 1-p sample grown at Tsub = 620°C. We can see a 2D connection between the bright contrast of the two aligned along the two equivalent surface crystallographic directions. Similar structures have been reported for the surface of a 10-uc-thick SrTiO3 homoepitaxial film [25]. An STM image obtained with different tip conditions is shown overlaid in the inset of Figure 3a, for the same area with the same length scale, which reveals 2 × 2 periodicity. The apparent difference in the patterns of the STM contrasts measured on the same sample surface with an identical periodicity (i.e., 2 × 2) may be attributed to different contributions of the electronic structures of the tips. This reflects the importance of the local electronic structure of the tip and sample in the STM contrast rather than the sample geometry and emphasizes that care is required in the interpretation of the apparent height in STM images. To identify the symmetry of the local surface electronic structure, we carried out Fourier transform (FT) power spectrum analysis of the image in Figure 3a, as shown in Figure 3e. The bright spots at (1/2 0) in the FT power spectrum are indicative of the existence of a (2 × 2) RC [26] in the substrate surface. Theoretical modeling [14,27,28] and transmission electron microscopy [29] of the SrTiO3 surface suggest that oxygen vacancies form linear clusters in SrTiO3, which may explain the (2 × 2) RC as pairs of oxygen vacancy clusters.Figure 3


Nucleation and growth of primary nanostructures in SrTiO3 homoepitaxy.

Phark SH, Chang YJ - Nanoscale Res Lett (2015)

STM images for defect formations in the initial growth stage. (a) to (c) 20 × 20-nm2 STM images showing the formation of defects in the substrate surfaces of 1-, 2-, and 3-p samples, respectively. All STM images were obtained with VS = 2.0 V and Iset = 50 pA. The inset of (a) shows an STM image of the same area with the same length scale that was obtained using a different tip. The gray arrows indicate large white structures, which are 1-uc-high SrTiO3 islands. The red (blue) curve in (d) shows the STM apparent height profile along the red (blue) line in (a) ((b)). (e) FT power spectrum map of (a). The yellow circles show bright spots in the FT power spectrum at (1/2 0), which are indicative of 2 × 2 RC. (f) FT power spectrum map of (c). The bright spots indicated by the green circles at (1/4 0) correspond to a periodicity of 4 uc along the directions of crystal symmetry.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385118&req=5

Fig3: STM images for defect formations in the initial growth stage. (a) to (c) 20 × 20-nm2 STM images showing the formation of defects in the substrate surfaces of 1-, 2-, and 3-p samples, respectively. All STM images were obtained with VS = 2.0 V and Iset = 50 pA. The inset of (a) shows an STM image of the same area with the same length scale that was obtained using a different tip. The gray arrows indicate large white structures, which are 1-uc-high SrTiO3 islands. The red (blue) curve in (d) shows the STM apparent height profile along the red (blue) line in (a) ((b)). (e) FT power spectrum map of (a). The yellow circles show bright spots in the FT power spectrum at (1/2 0), which are indicative of 2 × 2 RC. (f) FT power spectrum map of (c). The bright spots indicated by the green circles at (1/4 0) correspond to a periodicity of 4 uc along the directions of crystal symmetry.
Mentions: The STM images shown in Figure 2 also reveal that the changes in the island growth patterns were related to the substrate surface structures. Figure 3a shows STM images of 1-p sample grown at Tsub = 620°C. We can see a 2D connection between the bright contrast of the two aligned along the two equivalent surface crystallographic directions. Similar structures have been reported for the surface of a 10-uc-thick SrTiO3 homoepitaxial film [25]. An STM image obtained with different tip conditions is shown overlaid in the inset of Figure 3a, for the same area with the same length scale, which reveals 2 × 2 periodicity. The apparent difference in the patterns of the STM contrasts measured on the same sample surface with an identical periodicity (i.e., 2 × 2) may be attributed to different contributions of the electronic structures of the tips. This reflects the importance of the local electronic structure of the tip and sample in the STM contrast rather than the sample geometry and emphasizes that care is required in the interpretation of the apparent height in STM images. To identify the symmetry of the local surface electronic structure, we carried out Fourier transform (FT) power spectrum analysis of the image in Figure 3a, as shown in Figure 3e. The bright spots at (1/2 0) in the FT power spectrum are indicative of the existence of a (2 × 2) RC [26] in the substrate surface. Theoretical modeling [14,27,28] and transmission electron microscopy [29] of the SrTiO3 surface suggest that oxygen vacancies form linear clusters in SrTiO3, which may explain the (2 × 2) RC as pairs of oxygen vacancy clusters.Figure 3

Bottom Line: Second, one-dimensional SrTiO3 islands of a 4 uc width grew along the crystal symmetry directions.These observations suggest that 4 × 4-uc (2) islands act as a minimum nucleation seed, and the addition of SrTiO3 molecular species of the same width is the primary and dominant growth process in SrTiO3 homoepitaxy.A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO3 islands.

View Article: PubMed Central - PubMed

Affiliation: Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul National University, Seoul, 151-747 Republic of Korea ; Department of Physics and Astronomy, Seoul National University, Seoul, 151-747 Republic of Korea.

ABSTRACT
SrTiO3 nanoislands on SrTiO3 (001) in a diffusion-limited growth regime were studied using in situ scanning tunneling microscopy (STM). The STM images revealed two characteristic features of nucleation stages. First, the minimum lateral size of the one-unit-cell (uc)-high SrTiO3 islands was 4 × 4 uc (2). Second, one-dimensional SrTiO3 islands of a 4 uc width grew along the crystal symmetry directions. These observations suggest that 4 × 4-uc (2) islands act as a minimum nucleation seed, and the addition of SrTiO3 molecular species of the same width is the primary and dominant growth process in SrTiO3 homoepitaxy. A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO3 islands.

No MeSH data available.


Related in: MedlinePlus